What is "aircraft stability" - IN VIDEO

[TomcatViP]

Hi all,

since a few months, it has been fashionable on this forum to discuss here and there around the concept of Aircraft Stability.

So, in order to help the reader to understand what does this concept means and makes all understand it easily (as it does not look like that all of those arguing really understand the basis), here is an extract of an interesting video on the Su-27 design story that deals graphically with aircraft stability.

You will be delighted to watch it even more, if you pay attention to who explains it.

Scroll down video to point 29min26 secs for the quick lesson to start

http://www.youtube.com/watch?v=pVZbHYDX6ZY&feature=relmfu

~S!

[Crumpp]

Good film....

[macro]

i could learn to fly with that, if my stick didnt have a center spring :(

[Crumpp]

Pilots learn to fly with such airplanes since the beginning of heavier than air flight.

The more unstable the aircraft, the higher the work load to get it do a given maneuver. It takes more controlling on the part of the pilot.

[6S.Manu]

Very interesting! Thanks Tomcat!

[Kurfürst]

Excellent find, and simply understand!

Thanks! :)

[Crumpp]

i could learn to fly with that, if my stick didnt have a center spring

Relaxed stability aircraft have artificial means to impart feel for the pilot like a center spring.

Would not be any different with your desktop joystick dealing with the instability of the early mark Spitfires.

You would have an advantage the real pilots did not have but it would much more realistic than having a FM that is static and dynamically stable.

[macro]

Dont think thid will be done tbh crump. They cant even get the speed and engine boosts (i.e the simple stuff) right in the model let alone more complex stuff like this. Will have to wait for sdk when you can do it yourself mate

[Crumpp]

They cant even get the speed and engine boosts

Sure they can get it right. They already have the relative performance correct and it is the best simulation of WWII combat piloting to date.

What makes you think they can't get this right too?

In fact, I think they have been looking like most of us, for the characteristics that made these aircraft equal dogfighters.

You won't find it just looking at raw performance numbers.

[Igo kyu]

Dogfights mostly didn't result in a victory.

In a dogfight, most of the time, both pilots escape with their aircraft.

Which is why most victories come from surprise.

Which is why it didn't really matter that the bf109 was a useless dogfighter.

[Crumpp]

What are you fishing??

:rolleyes:

[CaptainDoggles]

Which is why it didn't really matter that the bf109 was a useless dogfighter.

I think the truth of this statement depends greatly on which aircraft you're comparing it to, and the precise definition of "dogfighter".

[JtD]

I don't think it depends on anything, it's just wrong.

[Igo kyu]

I think the truth of this statement depends greatly on which aircraft you're comparing it to, and the precise definition of "dogfighter".
Of course it's relative, all warplane performance is relative to other concurrent warplanes.

The German for "fighter" in WW2 was "Jager", but if you translate that back, it comes out "hunter". For the Germans at the time, hunting was stalking big game with a rifle, not the British style of hunting which involved chasing foxes with hounds.

It's a different attitude, and a different style, and the bf 109 fitted the style.

[macro]

Of course it's relative, all warplane performance is relative to other concurrent warplanes.

The German for "fighter" in WW2 was "Jager", but if you translate that back, it comes out "hunter". For the Germans at the time, hunting was stalking big game with a rifle, not the British style of hunting which involved chasing foxes with hounds.

It's a different attitude, and a different style, and the bf 109 fitted the style.

with a completly different objective at the time. if i was defending against a bomber attack i would rather fly the hurri, but attacking (or hunting as they did) i would definitly choose a 109.

[macro]

Sure they can get it right. They already have the relative performance correct and it is the best simulation of WWII combat piloting to date.

What makes you think they can't get this right too?

In fact, I think they have been looking like most of us, for the characteristics that made these aircraft equal dogfighters.

You won't find it just looking at raw performance numbers.

sorry mate relative performance is not correct, there are other threads that explain this.

[Crumpp]

sorry mate relative performance is not correct


The fighters can all dogfight on equal terms.

How is that not correct relative performance???? :confused:

Some people are pushing for a unrealistic rendition of their favorite gameshape that has the speed, climb, and turn ability but with a stability that did not exist in reality.

In my book that is an overmodeled fantasy that will alter the correct relative performance found in the game now.

[macro]

Im not pushing for performance on any plane. I want realism same as you. I like flying the 109. I dont want "fantasy" fms on any plane. Just because i disagree with you doesnt mean i want this

If you think they are equal then you are either a really good spit pilot or a poor 109 one, check out threads on main page theres a few. If you take away porked temp effects then they are about equal. At present i only blow up a 109 engine if i want to. I can fly full throttle on auto prop pitch until fuel runs out.

Do you play online maybe under a different name? As i wonder how you come to this conclusion

[Crumpp]

If you take away porked temp effects then they are about equal

That is the issue and the NOT the FM performance numbers at this point.
It has been shown there is a problem with the temperature effects. Flying the Spitfire IAW the Operating Notes should reward the pilot with the same performance as found with temperature effects disabled.

It is a much more realistic combat simulator if the FM numbers are off slightly if they cannot reproduce the stability characteristics.

If they can model the stability characteristics of these aircraft then the dogfights will be on equal terms regardless of raw performance numbers. Game players really put an inordinate amount of emphasis on raw performance numbers anyway.

The differences in performance have to be surprisingly large for most parameters for it to be even noticeable in the air.

It is the ability to put the gunsite on a target and kill it in World War II aerial combat that determined the dogfight ability of the airplane.

For example, here we have a much more maneuverable opponent but it is the ability to land the punch that wins the day.

http://www.youtube.com/watch?v=zLRvUhyh2ok

[JtD]

Capoeira has poor longitudinal static stability? Taken from the "Never back down" documentary, it must be true. :confused:

[ACE-OF-ACES]

I want realism same as you. I like flying the 109. I don't want "fantasy" fms on any plane.
Bingo!

The problem with accepting 'relative performance' is it can change the sim in un-expected ways such that it is no longer a representation of reality

For example

Take a WWII P-51 and Fw190 and scale up (multiply) the Top Speed, ROC, and Roll Rates of both planes by say 1.5

In doing so you have maintained the 'relative performance' of both planes..

But now the accuracy of the performance of both planes is off by that amount..

For example the tops speed of the P51 goes from around 426mph to around 639mph..

Due to the inaccuracy of the planes 'performance' it can change the style of dog fighting..

In short you have made this WWII 'prop' flight sim act like a KOREAN 'jet' sim..

Where the sim users will more than likely adjust their style of flying accordingly..

Which in turn will more than likely change the tactics from WWII prop style to KOREAN jet style..

All because of something as simple as an inaccurately simulated top speed..

Same is true if the speeds are scale down..

Only in this case, you have made this WWII 'prop' flight sim act like a WWI 'prop' sim..

In short we should not set the bar so low that we accept 'relative performance'..

In that it is just an excuse for not taking the time to do right..

But if that is all that you require..

Than there are plenty of Xbox WWII shoot-em-up flight sims out there for you to choose from..

But for us hard core simmers..

I think we can all agree that we 'require' a bit more 'realism' than that! ;)

As i wonder how you come to this conclusion
That is just it..

With regards to flight modeling performance accuracy let alone relative performance..

The only thing we know for sure is that no one has provided proof to say one way or another..

All we have thus far are a few tests of a few things done by a few people that hint at some errors in accuracy of flight modeling..

But nothing that anyone would or could say is conclusive let alone complete..

Heck even 1C has stated the flight models have issues that they are working to resolve..

In summary, the user testing thus far and the fact that 1C admits there are issues should be enough to cause all to take pause before making any statements of FACT on how accurate the flight model is simulating performance let alone relative performance!

[macro]

seen that vid before, brilliant.

I seen the question in the community communication thread asking if fm's would change but not seen an answer to say they had been worked on.

hope they have

[Crumpp]

WWII 'prop' flight sim act like a KOREAN 'jet' sim..

Not at all, power producers and thrust producers have completely different aerodynamics as well separate methodology for determining most performance parameters.

The whole premise is completely ludicris regarding a computer game.

Who cares how fast or slow a virtual gameshape is going as long as the it acts in relation to the other objects in the game in a reasonable facsimile of what it is trying to simulate.

In otherwords, it must behave somewhat like the real thing.

[ACE-OF-ACES]

Not at all
That is your opinion and your welcome to it..

But the point your missing is this..

The only thing we know for sure is that no one has provided proof to say one way or another..

All we have thus far are a few tests of a few things done by a few people that hint at some errors in accuracy of flight modeling..

But nothing that anyone would or could say is conclusive let alone complete..

In summary, the user testing thus far and the fact that 1C admits there are issues should be enough to cause all to take pause before making any statements of FACT on how accurate the flight model is simulating performance let alone relative performance!

Hope that helps! S!

[Crumpp]

That is your opinion and your welcome to it..


:confused:

It is not my opinion that power producers and thrust producers use completely different formulation to determine performance and have completely different aerodynamic properties.

It is just a fact.

[ACE-OF-ACES]

It is not my opinion
No, it is your opinion

And again, your welcome to it!

I and others just don't agree with it

that power producers and thrust producers use completely different formulation to determine performance and have completely different aerodynamic properties.

It is just a fact.
Ah, now I see where you are confused..

Note I said nothing about the 'powers'..

That was your tangent topic to take the focus off what I was talking about..

That being the 'speed'

Referring back to my post, note that I was talking about the relative speed, and how scaling it up or down can change the way the game is played

Which is why the attitude that accuracy does not mater as long as everything is relative is in error

Hope that helps

[Crumpp]

:grin:

Wow.....

[macro]

i see what you mean ace, but its not relative anyway.

wondered how long it would be before he bumped this thread. :rolleyes:

[ACE-OF-ACES]

i see what you mean ace,
S!

but its not relative anyway.
Maybe.. maybe not.. All I know for sure is no one has provided any proof to say for sure one way or another.. The few test done by a few people of a few things is just too few to say eitherway! ;)

wondered how long it would be before he bumped this thread. :rolleyes:
Oh that is easy.. When ever he makes an error in a thread, he simply bummps a bunch of 'other/old' threads, like this one, to take the focus off the error he made in another current thread.. In short muddy the water to take the focus off the error.. SOP for him.

[Crumpp]

When ever he makes an error in a thread,

:rolleyes:

OMG, what error? Please point it out so it can be addressed.

Otherwise, it has nothing to do with this conversation.

My reply is based on the fact you don't have a clue about thrust producer aerodynamics and are not someone who can be shown anything different.

[ACE-OF-ACES]

:rolleyes:

OMG, what error?
case in point ^^

[Osprey]

His error was to totally miss the point of what you were saying, probably in yet another herculean effort to show us how clever he is and how thick we all are.

[Al Schlageter]

:rolleyes:

OMG, what error? Please point it out so it can be addressed.

There was only 16 squadrons of Spitfires that used 12lb boost and 100 octane fuel during the BoB.

[Crumpp]

His error was to totally miss the point of what you were saying, probably in yet another herculean effort to show us how clever he is and how thick we all are.

Because I think we should model the aircraft accurately in all aspects and this is not what Tagert wants, I missed his point?

No, I disagree with it. Disagreement is not the same thing as not understanding nor has any mistake been made.

If you are going to simulate an airplane, then do it accurately. What is wrong with my statement?

[bongodriver]

If you are going to simulate an airplane, then do it accurately. What is wrong with my statement?


Nothing is wrong with that statement, the problem lies with your interpretation of accurate, which in essence translates to what Crumpp wants.

[Crumpp]

Baloney.

I am not making any outlandish claims and everything I have ever said is backed up by the science, documents, and the facts.

Prove your accusation, bongodriver.

You are just pissed because I called you out a couple of times on some really basic information.

[bongodriver]

Baloney.

I am not making any outlandish claims and everything I have ever said is backed up by the science, documents, and the facts.

Prove your accusation, bongodriver.

You are just pissed because I called you out a couple of times on some really basic information.

I don't need to prove anything, inevitably as these threads draw out it becomes quite evident what I claim is true, and you have called me out on nothing but one error of grammar, everything you claim is backed up by your own interpretation of documents science and facts, which time and time again have been shown to be agenda led.

[JtD]

I am not making any outlandish claims and everything I have ever said is backed up by the science, documents, and the facts.You've made the outlandish claim that the Hurricane was a hands off aircraft and not backed this up with anything. Your list in fact contained a whole lot of aircraft and you have not shown any evidence for even one. We're in a stability topic here, feel free to provide your evidence here. You can limit yourself to evidence of stability in phugoid and spiral modes, I'd be more than interested. After all, your contradicting NACA's leading WW2 aerodynamics test engineer.

[Crumpp]

You've made the outlandish claim that the Hurricane was a hands off aircraft

Point that out.

I said the Hurricane was stable gun platform with near perfect stability and control. That is a true statement. Sir Sydney Camm did a great job at giving England the right aircraft at the right time. One built with estabilished technology and easy to fly. He designed a workhorse that got the job done.

I have not bothered to continue any discussion's on stability and control because there is no point to it. Why have a discussion on it when the facts will just be subverted by a small vocal part of the community.

After all, your contradicting NACA's leading WW2 aerodynamics test engineer.

Good lord, guy....he makes general statements with nothing specific to the Spitfire. I never contradicted him, I contradicted members of the forum who use those generalities as specifics.

Read the documents NzTyphoon keeps posting in all the stability and control threads. They have nothing to do with the Spitfire and are not in anyway associated with any of the claims he presents. The members of the community do not understand the subject, see the picture of the Spitfire, and read what NzTyphoon writes. CLASSIC!!!! :cool:

:rolleyes:

Every airplane has it fans and it is not my job to convince fanatics there might be flaws in there favorite.

[Crumpp]

I don't need to prove anything,

Of course not, you just make unfounded accusations and then scurry to the dark corners when asked to prove it.

:rolleyes:

[bongodriver]

Of course not, you just make unfounded accusations and then scurry to the dark corners when asked to prove it.

:rolleyes:


Soooo....... gonna show us a copy o that ol' pilot's licence of yours?

[Crumpp]

You Dad pay for an intro flight?

[bongodriver]

You Dad pay for an intro flight?

Actually can you try and not bring family insults into this? my father passed away in 2007 and the circumstances of which are still a fairly painfull memory, I don't seek to bring any of your family into our personal differences here.

But thanks for confirming the hipocrisy of your own scurrying away into dark corners when asked to prove something, you are incapable of providing any evidence of a pilots licence and just resort to the insults.

[Crumpp]

Honestly, Don't dish it if you can't take it.

I am sorry to hear about your Dad.

[bongodriver]

Honestly, Don't dish it if you can't take it.

I am sorry to hear about your Dad.


WTF are you talking about? I can take you making stupid personal insults any day of the week, I'm very comfortable with the reality of our situations, what I don't appreciate are insults to my family.

[TomcatViP]

This thread is another candidate for a lock.

[bongodriver]

Let me ask your pilot advice then on an issue.

Mode C stopped reporting yesterday. What do you think of the trans-cal over the Ack?

Do you have any experience?

shouldn't you ask an avionics engineer? do you need mode C desparately? whats wrong with mode A? are you regularily flying in controlled airspace? it's not mandatory to have mode C outside of controlled airspace here.

[Crumpp]

My homebase is Class C.

[bongodriver]

My homebase is Class C.

OK, I'd still ask an avionics engineer, not entirely sure where you thought a lack of knowlege about the internal workings of a transponder quantifies as proof of not being a pilot, all I'm requred to know about them is when where and how to use them, and I mostly use ones with mode S in order to function with the TCAS II.

[Crumpp]

what I don't appreciate are insults to my family.


You had no problems insulting my family in PM.

internal workings of a transponder quantifies as proof of not being a pilot

It is not proof, but it sure isn't something most non-pilots know about. The internal workings of an altitude encoder are definately not something someone who has not owned an airplane know much about.

The trans-cal is on order. Only 60 bucks more for a 42 month warrenty combined with smaller, lighter, and uses the same tray as the ACK.

[bongodriver]

You had no problems insulting my family in PM.



It is not proof, but it sure isn't something most non-pilots know about. The internal workings of an altitude encoder are definately not something someone who has not owned an airplane know much about.

The trans-cal is on order. Only 60 bucks more for a 42 month warrenty combined with smaller, lighter, and uses the same tray as the ACK.

I insulted your family in PM?.....you mean when I got a bizarre picture of some guy in fatigues holding a baby from you, and I said 'the baby looks beautifull but I don't want your life story just a picture of your license'?

The aircraft I owned never had a transponder as it was classed as an Ultralight, and there is no requirement to have one because ultralights are excluded from operating in controlled airpace full stop.

p.s. in the same series of PM's you were given the benefit of knowing about my father, you were not so sorry to hear the news then and managed to make another reference today....way to go Einstein.

[JtD]

Point that out.Here you go. (http://forum.1cpublishing.eu/showpost.php?p=448364&postcount=539) I'm not really expecting to see any evidence, in particular now where this topic has clearly gone down the drain. :(

[ACE-OF-ACES]

This thread is another candidate for a lock.
Which is Crumpps goal.. When caught in a msitake.. Do something to get it locked.. SOP for him

[bongodriver]

Which is Crumpps goal.. When caught in a msitake.. Do something to get it locked.. SOP for him

Yep, all I asked for was some proof he had a pilots license just like I did, all I got was hostility and evasion, if I was Crumpp I'd try to get the thread locked PDQ.

[Crumpp]

F6F, Hurricane Mk I and Mk II, F4F, Bf-109, FW-190, A6M, and the list goes on...

Glider,

Most aircraft are not positive statically stable and negative dynamically stable stick free. It is an unacceptable characteristic.


Those aircraft all have acceptable stability and control characteristics. What is the issue or what is it you think I am claiming?

You do understand that every aircraft with an issue meant a solution was implemented.

When something is broken, it gets fixed. The Spitfire was fixed by the addition of an inertial elevator. That did not happen though until after the Battle of Britain!!

[JtD]

You were asked to name an aircraft that could be flown hands off (after you were (correctly) stating the Spitfire wasn't one), and you came up with that list. It's not about "acceptable stability", it's about hands off qualities. I'm suggesting you provide evidence for your statement, in particular stability in the phugoid and spiral mode.

[Crumpp]

It's not about "acceptable stability", it's about hands off qualities.

Well that post is about acceptable stability and control characteristics.

The post you quote is a reply to Glider when he made a claim that the norm for fighters in WWII was to have unacceptable stability and control characteristics.

That is not true.

[JtD]

The post you quote is a reply to Glider when he made a claim that the norm for fighters in WWII was to have unacceptable stability and control characteristics.No, that is not true.Can you name any aircraft, of any type, in any airforce, that was hands free during WW2, ie wouldn't eventually destroy itself without pilot input in conditions it was divergent?andIf the Spit is an unusual example, then he should be able to nominate one that was hands free.Your answer was the linked list. It is not possible to determine that a reply to a quoted question is actually just a list with random planes that in no way relate to the question as asked, which is what you are claiming now.

So to be clear - are you now saying that none of the planes on that list were hands off aircraft and this is a misunderstanding? Or are you going to provide evidence as you claim to provide for all your statements?

[Crumpp]

JtD,

There is no such thing as a "hands off aircraft". There is such a thing as a speed stable aircraft.

All of the aircraft in that list were speed stable.

That means they all moved to trim speed and stayed there unless acted upon by an outside force. The airplane does not care about its relationship to the horizon, altitude, or where the pilots hands are at. It cares about the relative wind and the dynamic pressure. A speed stable aircraft will maintain its orientation to the relative wind and keep the dynamic pressure constant.

This is not something the early Mark Spitfires did. If you look at the stability characteristics as measured by the RAE and the NACA, the Spitfire INCREASED speed away from trim.

Each oscillation, the speed would increase or stay the same where neutral stability existed.

That is a fact. There is no putting on rose colored glasses or claims of "it was normal for an aircraft".

The Spitfire was outstanding in its early instability. That is why they fixed it with the addition of an inertial elevator.

It was not because it was normal, or good, or super maneuverable. It was because it had some dangerous characteristics and made the aircraft more difficult to precisely control for the average pilot.

End of story.

[bongodriver]

JtD,

It was not because it was normal, or good, or super maneuverable. It was because it had some dangerous characteristics and made the aircraft more difficult to precisely control for the average pilot.

End of story.

It was not dangerous, most of fighter command at the time were average to below average in terms of skills, thankfully the Spit was eay to fly in combat due to its high manouverability and controllability.....end of story

[TomcatViP]

Well... end of ea new story. Never heard that on the BoB era Spits.

Instead I hve read plenty of desciption of frightened young pilot force to go to batthle with under 10 hours on the type.

Never read such thing on the hurri.

[Crumpp]

“Last Witness” Bob Doe explains: “An average pilot could get more from a Hurricane than from a Spitfire. But if you were good you could get more from a Spitfire. A Hurricane was like a brick-built s---house. It was sturdy and reliable, and it did not leap about when the guns were fired.

Whereas the Spitfire was a musician’s aeroplane, a dream, the Hurricane was a very efficient workman’s tool.

http://www.telegraph.co.uk/history/battle-of-britain/7851030/Battle-of-Britain-without-the-hurricane-the-battle-would-have-been-lost.html

http://imageshack.us/a/img571/3024/hurricanevsspitfire.jpg (http://imageshack.us/photo/my-images/571/hurricanevsspitfire.jpg/)

http://imageshack.us/a/img209/4739/hurricanevsspitfire2.jpg (http://imageshack.us/photo/my-images/209/hurricanevsspitfire2.jpg/)

You can see how precisely the pilot is able to hold a given acceleration and how smoothly the airspeed drops in the rapid turn measurements from the NACA.

http://imageshack.us/a/img855/7204/hurricanerapidturn.jpg (http://imageshack.us/photo/my-images/855/hurricanerapidturn.jpg/)

It is little wonder why the Hurricane accounted for the loin's share of German fighters.

[JtD]

The Hurricane would not move to trim speed and stay there, it would drop a wing and dive into the ground, at an ever increasing speed. It was unstable in the spiral and phugoid modes and much worse at that than the Spitfire, which did at least a few oscillations before departing for good.
The static stability chart you posted is not at all related to phugoid or spiral modes.

[Crumpp]

Hurricane would not move to trim speed and stay there

Yes, a stable airplane will move to trim speed.

If it is statically stable it will move towards trim speed when disturbed.

If it is dynamically stable it will reduce the amount of speed it overshoots trim speed with every oscillation.

The oscillations will grow smaller with each cycle until they are dampened and disappear.

Just like what happens with the Spitfire's stability in Cliff's of Dover....

http://imageshack.us/a/img692/4551/spitfiremkiaoctlongstab.th.jpg (http://imageshack.us/photo/my-images/692/spitfiremkiaoctlongstab.jpg/)

[Crumpp]

The static stability chart you posted is not at all related to phugoid or spiral modes.
]

:confused:

It is also not related to quantum physics. I am sure we can all think of things it has no relation too.

What it is related too is the longitudinal stability and control in an abrupt turn.

[JtD]

I was asking specifically about phugoid and spiral mode. Not my fault you feel a need to bring in all sorts of unrelated things to avoid an answer.

Anyway, I know now that when you said that the Hurricane, F6F and whatnotelse were hands off aircraft you didn't mean they were hands off aircraft. So we can forget about all this before it escalates into yet another 100 pages of outlandish claims without any backup by science, documents and facts.

[Crumpp]

documents and facts.


:rolleyes:

[Crumpp]

phugoid

The NACA did not test long period oscillation in any aircraft. All of the data on Spitfire and Hurricane is for short period only.

[bongodriver]

The NACA did not test long period oscillation in any aircraft. All of the data on Spitfire and Hurricane is for short period only.

Exactly....and the conclusion in that very NACA report you use like a bible is that the short period oscilations in the Spitfire are 'satisfactorily damped in all conditions tested'.....page 18.

[Crumpp]

http://imageshack.us/a/img254/5619/spitfirestability.jpg (http://imageshack.us/photo/my-images/254/spitfirestability.jpg/)

[bongodriver]

http://imageshack.us/a/img254/5619/spitfirestability.jpg (http://imageshack.us/photo/my-images/254/spitfirestability.jpg/)


Really?....youre really going to ignore item 1 in that same page?....the one that states 'CLEARLY' that the 'short-period longitudinal oscillations were satisfactorily heavily damped in all conditions tested'
:rolleyes:

[Crumpp]

Are you really going to ignore the second part, the stick fixed longitudinal instability was unsatisfactory in all conditions?

Are you going to ignore the fact the game characteristics are exactly the opposite of the real thing???

The game results....


http://imageshack.us/a/img692/4551/spitfiremkiaoctlongstab.th.jpg (http://imageshack.us/photo/my-images/692/spitfiremkiaoctlongstab.jpg/)

The RAE results for the same test.....


http://imageshack.us/a/img705/4388/k9788stabilityexplained.th.jpg (http://imageshack.us/photo/my-images/705/k9788stabilityexplained.jpg/)

[bongodriver]

Are you really going to ignore the second part, the stick fixed longitudinal instability was unsatisfactory in all conditions?

Are you going to ignore the fact the game characteristics are exactly the opposite of the real thing???

The game results....


http://imageshack.us/a/img692/4551/spitfiremkiaoctlongstab.th.jpg (http://imageshack.us/photo/my-images/692/spitfiremkiaoctlongstab.jpg/)

The RAE results for the same test.....


http://imageshack.us/a/img705/4388/k9788stabilityexplained.th.jpg (http://imageshack.us/photo/my-images/705/k9788stabilityexplained.jpg/)

Yes I am going to ignore it because you are highlighting stick-free behaviour in game and highlighting stick-fixed in the NACA report and your in game results don't point out what configuration the aircraft was in, you may notice that not all of the stick-free oscillations in the second graph are divergent.

[ACE-OF-ACES]

That and I am pretty sure that klem, the guy that did that ingame stick test, told Crumpp that it was not something he (klem) would consider a full fledged test.. Let alone one that relates to the topic.. Yet Crumpp still keeps posting references to that ingrame graph as if it was some 1C approved 'golden' test.. Also note how Crummp fails to give klem any credit as the one who actully did the test.. Which may falsely lead some to belive that Crumpp is actully doing his own ingame testing

[bongodriver]

That and the fact that both graphs illustrate long period oscillations which even Crumpp can't argue we're not tested by NACA and he also can't argue the fact that long period oscillations matter squat.

Note:

Long period oscillations are measured over minutes

Short period oscillations are measured over seconds

[Christop55her]

It takes more controlling on the part of the pilot.

http://www.gqth.info/0.jpghttp://www.gqth.info/7.jpghttp://www.gqth.info/8.jpghttp://www.gqth.info/9.jpghttp://www.ymeu.info/test5.jpg

[Crumpp]

Yes I am going to ignore it because you are highlighting stick-free behaviour in game

Wow,

Nobody has compared anything in the game regarding the NACA measurements yet.

The test for the game is stick free, just like the RAE measurements!!!!!

They do not match. The RAE found the Spitfire to be longitudinal neutral or unstable Stick Free.

Take a second and digest the data in both test's before frothing at the mouth I am wrong.

[bongodriver]

Wow,

Nobody has compared anything in the game regarding the NACA measurements yet..

Then what the hell are you even contributing here?

The test for the game is stick free, just like the RAE measurements!!!!!

it is for both, fixed values are on the left column and free on the right, and in both cases some stability was recorded, you said it yourself, long period oscillations are irrelevant, if you can't sort out a bit of divergence after 4 minutes then youre either dead or paralysed.

They do not match. The RAE found the Spitfire to be longitudinal neutral or unstable Stick Free..

not in all conditions tested, you took the time to put it in red yourself, both columns show some element of stability, engine off with flap and gear up is stable in bot fixed and free.

Take a second and digest the data in both test's before frothing at the mouth I am wrong.

Look pal, take a second yourself and read from post 68, you are the one that mentioned long period oscillations were not measured, all I did was say 'exactly' and pointed out that NACA concluded short period longitudinal oscillations were satisfactorily heavily damped. you are the one 'frothing' at the mouth in a desparate attempt to give no quarter, you really should just give in because you 'are' wrong.

[bongodriver]

We went down this road on the last Crumpp crusade against the Spit and a point was raised on just exactly how do we simulate stick-free in a computer game given the constraints of current game controllers, how exactly will a computer determine you don't have your hand on the stick? all it will do is sense no input from the controller and assume the stick is being held in place....in essence it will always be stick-fixed.

[SlipBall]

Some interesting thoughts from a man who flew these aircraft in modern times...maybe off topic a bit, but an enjoyable read.
Flying Old Aeroplanes in the 21st Century;
The Handling Qualities of World War II Fighters

by Dave Southwood

A lecture given to the Flight Test Group of the Royal Aeronautical Society
18 March 2004, 4 Hamilton Place, London W1

Introduction
One hundred years after mans' first powered flight, there is still a great fascination for the aviation history of the century of unparalleled technological advances that has just past. For pilots, it is fortuitous that this interest extends to maintaining flying examples of aircraft types from throughout the whole period. The willingness to build flying replicas of the earliest machines has been another indication of the commitment to preserve our aviation heritage for posterity. However, the skills required to fly these early machines, and indeed aircraft from all but the last one or two decades, are considerably different from those needed to fly the modern glass cockpit, fly-by-wire, highly automated airliners and combat aircraft of the early twenty-first century. Flying training has evolved such that only the skills needed to fly the current generation of aircraft are taught. Teaching skills that are required in order to fly older types of aircraft, such as those with a tailwheel or powerful piston engines, when these skills will be redundant after completing training is a luxury that the military, commercial employers and indeed most private pilots cannot afford.

Therefore at the start of the 21st century it must be appreciated that the scope of the training and experience of many of the current generation of pilots, both military and civilian, almost certainly will not have prepared them to fly such aircraft. Their flying ability will be as high as that of previous generations of pilots, but ability only gives an individual the potential to learn the skills required to fly. It does not automatically install those skills; they have to be specifically learnt. In this article I aim to discuss some of the handling qualities from one specific group of vintage aircraft, WWII single piston-engined tailwheel fighters. Hopefully this will provide an appreciation of some of the skills that have to be learnt in order to fly such aircraft safely, competently, and to enjoy the experience. I freely acknowledge that this is only a brief summary of the flying qualities of a few types of aircraft from one generic class that I have been fortunate enough to fly over the last 15 years. Every other class and type of vintage aircraft will have its own individual, and often unique, qualities of which I have little or no experience.

Scope
This article draws on my experiences flying the following aircraft types: Spitfire (Marks V, VIII, IX and XVI - all Merlin-engined), Hurricane Mk XII, Bf109G-2, HA 1112 (Merlin-engined Me109), P-51D Mustang, P-40M Kittyhawk, Corsair (FG-1D and F4U-5) and F6F-5 Hellcat. The flight envelope considered is that pertaining to display flying i.e. up to maximum continuous power, altitudes below 10,000 ft, normal accelerations from +5g to 0g, standard level looping and rolling aerobatics, close formation flying and tailchasing. Aspects covered will be those where the greatest differences from modern aircraft occur; ground handling, take-off, general up-and-away handling qualities, accelerated power-on stalling, high power low speed controllability, engine handling and landing.

But first, it is worth discussing some of the basic characteristics relating to the configuration of this class of aircraft that have a profound effect upon the handling qualities that will be discussed.

Powerful Piston-Engined and Tailwheel Characteristics
The power produced by a piston engine is transmitted to the propeller via torque on the propeller shaft. The propeller then transfers the power to the air flowing through it, resulting in both thrust and, due to the drag on the propeller blades and friction, energy loss. However, if the propeller is not able to transfer to the air all of the power produced by the engine, the torque on the propeller shaft produces a rolling moment on the engine in the opposite direction to the rotation of the propeller. If and when this situation occurs, it is at a combination of high power and low forward airspeed. Note that in piston-engined light aircraft torque effects are not usually seen except in aerobatic aircraft during prolonged upward vertical manoeuvres. At full power our subject aircraft can produce typically 1500 to 2300 horsepower and even though maximum continuous power is somewhat less, torque effects are still seen and will be discussed later.

The nature of the airflow behind the propeller, normally referred to as "propwash", is a helical flow whose velocity and helix angle are largely a function of engine power setting and of the forward airspeed of the aircraft. Obviously, the airflow within the propwash over the left and right sides of the aircraft is not symmetrical, in particular over the fin and rudder. In single-engined propeller driven aircraft this is the main cause of the directional trim changes with variations in airspeed and power. Aircraft with a high-powered engine and a large operating speed range (VNE of the Mustang is 505 mph) potentially will be affected by these trim changes much more than low powered, low speed light aircraft. In addition, any sideslip will displace the propwash laterally, varying the downwash angle experienced by each tailplane and possibly resulting in the blanking of one tailplane by the fin and rudder. Thus, sideslip may give rise to significant pitching moments.

The centre of gravity (c.g.) position of tailwheel aircraft is behind the mainwheels. This situation is inherently directionally unstable on the ground. One way to visualise the mechanism for this instability is to imagine an aircraft landing with right drift applied (i.e. tracking down the runway with the nose pointing to the left of the centreline). The friction on the mainwheels will have a lateral component to the left, but inertia will keep the c.g. travelling along the runway, leading to a yawing moment to the left. The left lateral frictional force on the mainwheels will also result in a right rolling moment of the c.g. about the right mainwheel due to inertia. This will increase the loading on the right mainwheel thus exacerbating the left yawing tendency. This uncommanded directional divergence is commonly referred to as a "groundloop". The tailwheel opposes such a yawing motion, with a locked tailwheel reducing groundloop tendencies considerably compared to a castoring tailwheel.

Ground Handling
The aircraft being considered have some markedly different ground handling characteristics, largely due to the longitudinal distance of the c.g from the mainwheels and the design of the tailwheel.

Probably the greatest vice of the Spitfire is that it is very "tail light" due to a short longitudinal moment arm of the c.g. from the mainwheels. Except when a tail wind prevails, the stick must be kept fully aft and any brake applications must be made very smoothly and progressively. Sharp brake inputs, or large power increases without full aft stick, inevitably cause the tail to leave the ground. Unfortunately, the Spitfire has very little clearance between the propeller tips and the ground, and very expensive ground strikes by the propeller are not unknown! A particular problem can occur during the pre take-off engine checks at high power. The thrust line is above the mainwheels and produces a powerful nose down pitching moment that is opposed by the moment of the c.g. about the mainwheels and the aerodynamic down force on the tailplane and elevator due to propwash and any headwind component. If the tail should rise, closing the throttle will reduce the problematical nose down moment due to the thrust. However, it will also reduce the propwash over the tailplane and elevators, thus reducing the aerodynamic tail down moment, and often making the tail rise even further. Unfortunately, once the tail has started to rise in this situation there is often no recovery. If the stick is held fully back in tailwind conditions, the wind may overcome the propwash resulting in reverse flow over the tail. This causes an aerodynamic upforce on the tail and thus a nose down pitching moment that could cause the tail to rise. Therefore, the elevators are held neutral when taxying in a tailwind. Because the Spitfire is so tail light, taxying in more than 25 kts of wind is performed with a person sitting on the tailplane. During WWII a pilot actually took off with a WAAF still sitting on the tail! He thought that the aircraft was handling somewhat strangely so landed immediately - still with a somewhat shaken young lady adversely affecting his c.g. position.

The Messerscmitt 109, conversely, is very tail heavy and this causes a different problem. Even when the tailwheel is unlocked, it is still held in a fore-and-aft position by a spring. To make a tight turn on the ground, the tailwheel must be made to castor by braking it out from the spring. Due to the narrow undercarriage track, the yawing moment generated by differential braking is small, and it is difficult to break out the tailwheel due to the high weight upon it. The required technique is, whilst applying differential braking, to apply full forward stick and increase power in order to generate upward lift on the tailplane and thus unload the tailwheel - anathema to a Spitfire pilot! Such a manoeuvre on wet grass is still ineffective as any brake application locks the wheel and the aircraft just slides forward in a straight line. Ground handlers have to hold the wingtip on the inside of the turn in order to generate sufficient yawing moment to break out the tailwheel, after which normal taxying is possible.

Take-off
It is worth considering why it is preferable for aircraft with difficult directional control characteristics to take-off and land on grass rather than asphalt or tarmac runways. When an aircraft is drifting during take-off or landing, the magnitude of the lateral force on the mainwheels, and thus the tendency for the aircraft to yaw, is a function of the coefficient of friction of the runway surface. Grass has a lower friction coefficient than hard runways and thus for a given amount of drift, grass surfaces produce less yawing moment. In simple terms, take-offs and landings from grass result in fewer directional control problems.

The power response to throttle inputs is essentially instantaneous with these engines. Therefore, very rapid large power increases at the start of the take-off roll will produce a large yawing moment due to propwash. Note that all of the aircraft being discussed have propellers that rotate clockwise from behind and thus will yaw to the left. The Mustang and Corsair in particular have very little rudder power at the start of the take-off roll, and even full right rudder is insufficient to stop the left yaw if the throttle is opened too rapidly. The only recovery is then to throttle back until the rudder becomes effective and corrects the swing. This problem is exacerbated by crosswinds from the left, and if a significant crosswind exists it is preferable to take-off such that it is from the right whenever possible (tailwind component and runway permitting). Note that all of these aircraft except for the Bf109 have a rudder trim tab. The setting of this tab theoretically has no effect on the rudder authority available at the very start of the take-off roll. However, if it is mis-set, as speed increases the rudder forces may become too great to achieve full rudder, effectively reducing rudder authority and potentially causing a loss of directional control.

The Spitfire needs about half right aileron at the start of the take-off roll to counteract the torque of the Merlin engine at low speed and high power. The torque effect reduces as speed increases, and aileron power increase with speed also. Therefore, the ailerons are effectively back to neutral when unstick occurs. It is easy and quite natural to make this aileron input although somewhat unusual. Sometimes the left undercarriage leg oleo is charged to a greater pressure than the right one to help reduce this phenomenon.

I will now describe the complete take-off technique for the Messerschmitt 109, the worst case aircraft of this selection for take-off and landing. Allegedly, approximately one third of the 33,000 Bf109s built were badly damaged or destroyed in take-off and landing accidents. A prudent pilot tries whenever possible only to operate from grass surfaces and with no more than a 10 kt crosswind component, certainly never with a tailwind. The aircraft is lined up pointing down the runway and the tailwheel lock, which gives the major positive contribution to directional stability during take-off and landing, is engaged. The power is slowly increased to approximately 1.15 atm (34" Hg) manifold pressure (1.3 atm being the maximum setting for the engine) and the aircraft kept straight using about one third to one half right rudder. Once running straight with the power set, the tail is raised very slowly until just clear of the ground. The elevators are effective at very low speeds with take-off power set, but if the tail is raised at an excessively high rate the gyroscopic moment from the propeller generates a very rapid left yaw. Once stabilised on just the mainwheels, the 109 is directionally unstable but luckily the rudder is very powerful. However, any yaw that occurs must be stopped very rapidly or a roll will develop in the opposite sense to the yaw and a catastrophic groundloop becomes a distinctive possibility. Also, once the yaw has been contained it is best to just maintain the heading that the aircraft is on. Any attempt to correct back to the runway bearing may cause a groundloop in the other direction unless the correction is made very slowly. Unfortunately, the field of view from the cockpit on the ground is very poor and thus it is hard to detect when the aircraft yaws off the desired heading. The ability to sense and detect any yaw and then to make the required correction very rapidly are the skills that must be mastered in order to take-off safely in this difficult aircraft.

General Handling Qualities
All of these aircraft have reversible (manual, unpowered) elevators, ailerons and rudders that, over the relatively large speed range available, give some markedly differing flying qualities. The Bf109's flight control system is slightly different from the others in that it has a variable incidence tailplane for pitch trimming and only a fixed tab for rudder trimming. It also has independent free-floating leading edge slats. All of the other aircraft have at least cockpit adjustable elevator and rudder trim tabs.

One of the most striking characteristics for a pilot who is familiar with modern fighters is the relatively poor roll performance. The P-40 has the best roll performance of this group, although qualitatively it is similar to that of a clipped wing Spitfire. A 1g 360¢ª full stick roll in a clipped wing Spitfire IX at 250 KIAS and 5000 ft takes 3 seconds. However, the same manoeuvre in the Hurricane at 200 KIAS takes 6 seconds. The other aircraft lie between these two extremes. Any aileron rolls flown at low level must be entered on a positive climbing line in order to complete the manoeuvre at a height that is not below that of entry, and all require rudder co-ordination.

The next interesting characteristic is apparent manoeuvre stability (stick force per g). The Mustang, Bf109 and P-40 are all very heavy in pitch, requiring approximately 20 lbf/g at around 250 KIAS albeit with gradients that appear to be linear. Thus, two hands are required on the stick for manoeuvres above approximately 3g. For singleton displays this is not a problem as a constant power setting is used. However, close formation manoeuvres, particularly loops and level turns, are a great strain on the forearm and it helps to be trimmed slightly nose up when running in for a loop such that you are holding a push force. Also, a coarse handful of nose up trim during a level hard turn helps to reduce the excessive force, especially when speed has reduced from that at trim. At the other end of the spectrum are the Spitfire and Hurricane, both of which are manoeuvre unstable at aft c.g. positions. The degree of instability increases as a function of g or AoA in that a slight pull is required for low g manoeuvres, changing to zero stick force and then a push as g increases. However, at a more normal mid c.g. position, a clipped wing Spitfire IX with 2650 RPM and +6 lbs boost set, at 250 KIAS and 5000 ft in a steady left turn requires a 9 lbf pull at 2g and a 22 lbf pull at 5g (26 lbf in a right turn). This shows a marked reduction in apparent manoeuvre stability as g increases. However, these overall light forces make the Spitfire delightful to fly in pitch and all required manoeuvres can be flown with one hand. Even at aft c.g. when it is manoeuvre unstable it is still possible to fly aerobatics in the Spitfire although it takes care to avoid excessive g.

The Hurricane has unusual apparent longitudinal static stability characteristics (pitch trim change with speed). Depending on the c.g. position and the type of propeller fitted it varies from slightly stable to slightly unstable. However, at higher power settings (2400 RPM, +4 lbs boost), left sideslip (which occurs as you accelerate) generates a strong nose down pitching moment and right sideslip (seen on deceleration) a moderate nose up pitching moment. Combine this with essentially neutral lateral static stability (rolling moment due to sideslip) and very low sideforce characteristics (lateral acceleration due to sideslip), and it is easy for the sideslip that occurs during speed changes to appear as longitudinal static instability.

To complete the picture, control force harmony varies considerably amongst these aircraft. The P-40 is very heavy in pitch and light in roll. The Spitfire is light in pitch and very heavy in roll. The Mustang and Bf109 have well matched aileron and elevator forces but are very heavy overall. The most pleasant aircraft to fly in terms of elevator and aileron harmonisation and overall control forces are the Corsair and, in particular, the Hellcat.

High Power Accelerated Stalling
I shall just discuss the high power accelerated stall characteristics of the Mustang, as it is indicative of what may occur in this class of aircraft. Note that it has a laminar flow wing. With a typical display power setting of 2700 RPM and 45" Hg MAP, decelerating turns at 3g in either direction eventually, at approximately 125 KIAS, result in a very rapid flick to the right accompanied by a harsh snatch of the stick, also to the right. The word departure is very apt for this manoeuvre! There is essentially no warning of approaching the stall under these conditions, although a very slight burble may just be felt through the elevators. Checking the stick forward breaks the stall quickly, although the ailerons then have to be returned to neutral and inertia continues the roll. Bank angle excursions of around 180¢ª are normal during the stall and can be more. If such a stall occurred at low level, or in combat, the outcome could be disastrous. In a display I always fly the Mustang with sufficient speed that I keep well clear of the stall. Perhaps the very high stick force per g is beneficial in helping to prevent inadvertent stalls. Basically, the Mustang has the most vicious high power accelerated stall characteristics of any of the aircraft that we are discussing.

Low Speed, High Power Handling
At the top of looping manoeuvres, a significant right rudder deflection is needed in all of the aircraft in order to counter the yawing moment due to propwash and thus to keep straight. If the manoeuvre entry speed has been correct, then speed at the top of the loop is high enough that rudder authority is sufficient and the pedal force is easy to apply. However, if a looping manoeuvre has been entered too slowly, the first indication of this error to the pilot is that an excessive right rudder deflection is needed, with a much higher than normal pedal force. It is even possible to reach full rudder and still be unable to control the yaw if the speed is very low, and right aileron may be needed simultaneously to counter the torque. Achieving such a low speed manoeuvre is possible due to the high power of the engine compensating for the lack of kinetic energy at the start of the loop and the reduction in stall speed due to the high-energy propwash over the wing roots. It is a potentially hazardous situation as, if the aircraft experiences either a positive or negative angle of attack (AoA) stall, a very rapid departure may occur due to the sideslip present and the rudder and aileron deflections; this may culminate in a spin. The Mustang and Corsair are probably the worst of these aircraft for encountering this situation. Recovery must be effected by smoothly reducing power whilst maintaining a low AoA, attempting to keep straight with rudder and gently rolling back to wings level. If this occurs during a display, the aircraft's height will be around 2500 ft agl, and great care must be taken to try to avoid getting into an irrecoverable low speed, steep nose low attitude. The moral is do not enter looping manoeuvres too slowly.

Engine Handling
This could be the subject of a complete lecture on its own. Large, powerful piston engines require a great deal of management by the pilot in order to get the best performance from them, and perhaps more significantly when flying them today, conserve engine life and prevent damage which could lead to an engine failure. Oil and coolant/cylinder head temperatures need to be maintained within limits, usually by manual operation of some type of flap or gill. It is very important on the ground not to exceed around 1000 to 1200 RPM, depending on the type of engine, until an oil temperature of 40ºC is reached. This invariably means that you cannot taxy on grass until the oil has warmed up. Conversely, some of the liquid cooled engines, especially in the Spitfire V and Bf109, will overheat and boil quickly on the ground (about 10 minutes from a cold start on a cool day, 5 minutes if the aircraft has been flown previously and a quick turnaround performed). Modern ATC does not understand the need for these aircraft to get airborne expeditiously after engine start!

It is easily possible to overboost all of these engines (exceed the maximum MAP/boost for a given RPM), causing a significant reduction in engine life and increasing the chances of a mechanical failure. On take-off, only two-thirds to three-quarters throttle will be needed to give maximum permitted MAP. Also, the large radial engines have no altitude boost compensation, and neither do some of the in-line ones. Therefore, if the MAP is set at, say, 2000 ft running in for a display, it will increase significantly when diving to display height, possibly resulting in overboosting.

Underboosting is a major concern with the large radial engines such as the PW R2800 in the Corsair and Hellcat. If the MAP is reduced to the point where the propeller is no longer producing thrust and the airflow is driving the propeller, the reverse loading on the crankshaft results in great stress and potential mechanical failure. These engines must not be throttled back below "square power" i.e. 24" MAP at 2400 RPM, 20" at 2000 RPM etc. This makes it difficult to drop back in formation and to decelerate during the circuit to land, particularly in the Hellcat, which does not have much drag from the flaps and little drag in sideslip. Formation flying requires a careful choice of RPM to allow a good operating range of MAP without over- or underboosting the engine.

Fortunately, with these engines no pilot selection of carburettor or other engine anti-icing or de-icing controls is required within today's operating envelope. Mixture control is also simple, with typically just AUTO LEAN, AUTO RICH and EMERGENCY RICH positions.

One big issue with handling these engines is the rate of throttle movement, especially when increasing power. A large and rapid forward throttle movement gives an almost instantaneous increase of power and, at low speeds, this can lead to yaw and/or roll which may not be controllable. Late go-arounds must be handled with great care and with careful throttle handling.

Thermal shock is another potential source of damaging an engine and reducing its life, especially with the radial engines. If a sudden power reduction is made after operating at a high power setting and high cylinder head and oil temperatures, this will result in differential cooling rates for different engine components and thus inconsistent contraction of adjacent components. To prevent this, we aim not to go directly from display power to a very low power setting for a circuit to land. We try to have a few minutes at an intermediate cruise power setting between these two extremes. Also, it is important to let the engine temperatures stabilise by setting a low RPM for a minute before shutdown.

Landing
The relative merits of "3-point" and "wheeled" landings in a given aircraft type are determined by several different flying qualities. To show this, we will examine some of the aircraft that are easiest to land in a 3-point attitude, and some that are best wheeled onto the runway.

The Merlin-engined Spitfire has a threshold speed of 70 KIAS, with a landing configuration idle power stalling speed of 50 KIAS, and controls that are all effective down to almost taxy speed. If a wheeled landing is attempted, the slightest bump on the runway causes the aircraft to become airborne again as the wing is still generating significant lift. Likewise, any attempt to lower the tail prematurely results in a further lift-off. Therefore, a 3-point landing is easier than a "wheeler". But after touchdown, even from a good "3-pointer", full back stick and only very gentle braking must be employed to prevent the tail from lifting and the propeller striking the ground.

The Bf109 has a threshold speed of 175 kph (95 KIAS). The float after flaring is quite prolonged prior to touchdown in a 3-point attitude. However, using a lower threshold speed to shorten the float sometimes results in no reduction in the rate of descent when flaring and a heavy landing. Also, aileron and rudder effectiveness appear to be lost at about touchdown speed. Unfortunately, at idle power the aircraft is markedly directionally unstable on the mainwheels alone and this, combined with an almost ineffective rudder, can easily lead to severe directional control problems if a wheeled landing is attempted. However, by touching down in a 3-point attitude the lockable tailwheel gives a significant contribution to directional stability and a much straighter rollout occurs. If ever I touch down on the mainwheels in the Bf109 I gently ease back on the stick to get airborne and continue the flare for a subsequent 3-point touchdown. The fairly weak brakes on the narrow track main landing gear make directional control after touchdown poor, and the excessive use of the brakes will lead to them becoming less effective as the rollout progresses. The Bf109 is not an easy aeroplane to land, but an understanding of its characteristics does enable it to be flown safely.

Both the P-40 and Hurricane can, on a bumpy grass runway, develop a longitudinal porpoising motion if the stick is not held fully back after touchdown. A "3-pointer" is easier for achieving full back stick quickly although a wheeled landing followed by a gentle lowering of the tail is feasible on smooth runways.

For heavier aircraft such as the Mustang and Corsair, most of the above mentioned difficulties such as bouncing airborne do not occur. However, they both have very little aileron power after a 3-point touchdown and any lateral disturbance can be difficult to control. The higher touchdown speed of a wheeled landing gives greater aileron control power to counter such upsets, and there is sufficient elevator power to maintain the touchdown attitude until well below touchdown speed. Maintaining this flatter attitude also helps maintain the weathercock stability and rudder power as the fin and rudder are not blanked by the fuselage. Note that, particularly in the Corsair, some swing often occurs when the tail is lowered, possibly due to the fin blanking or to gyroscopic moments from the propeller.

Crosswind landing limits for these aircraft are low by modern standards, 10 kts for the Bf109 and 15 kts for the others being sensible. Remember that they were designed in the days of circular grass airfields (or for aircraft carriers) so crosswinds were less important than they are with single runway airfields. It is interesting that the RAF Pilots' Notes for most WWII aircraft advocated a crabbed approach with the drift removed by using rudder just before touchdown. The problem with this technique is that the aircraft may start to drift away from the runway track during the flare, and touching down with drift present will excite the directional instability discussed earlier. The preferred technique of most pilots who fly these aircraft nowadays is to approach wing low, pointing straight down the runway. If the crosswind is not too strong the wings may be levelled using aileron just before touchdown. However, it is often better to touch down with the bank still applied on the into-wind mainwheel (and simultaneously on the tailwheel if a "3-pointer" is essential). Directional control power is the limiting factor of the Bf109, but for many of the aircraft the crosswind limit is determined by available roll control to prevent the into-wind wing lifting due to lateral stability. For this reason, the Mustang needs to be wheeled on in a flat attitude in a strong crosswind to give increased aileron power at the higher touchdown speed. In the Corsair it is advisable to land using only a half flap setting and then to raise the flaps before lowering the tail.

Conclusions
This lecture has given only a very brief overview of some of the more significant flying qualities of a few types of WWII fighter. My intention was to try to show that many of the flying skills needed to fly these aircraft safely are not required in modern aircraft and so have not been learnt by today's pilots. However, flying ability has not changed over the years so modern pilots have the same potential as earlier generations to learn these skills. I hope that I have not made these aircraft sound daunting to fly; they are not. But they are different and require different skills. So saying, they obey the same equations of motion as any other aircraft with reversible (unpowered) flying controls.

As well as handling qualities, there will always be perhaps an even greater interest in the relative effectiveness of these aircraft as fighting machines, a quality that is determined largely by performance. The handling qualities had only to be good enough to realise this performance. However, in the interests of conserving both engine and airframe life today we do not explore the limits of a vintage aircraft's performance. There is a significant amount of documentary evidence on performance from wartime trials and there are books available containing such data to satisfy modern curiosity and thus negate the need for such flying.

As a final thought, please note that it is easy to concentrate on the deficiencies of an aircraft and gloss over its other possibly excellent characteristics. The fact that the Spitfire has poor control force harmonisation and is easy to tip on its nose does not detract from its outstanding turn performance, superb low IAS and high Mach number controllability, and benign stall characteristics. It is a very charismatic and pleasant aircraft to fly overall. And the challenge of trying to master the Bf109 on take-off and landing makes it a very satisfying machine to fly once you have gained some confidence in it.
In my opinion, the nicest pure flying machine of all of those discussed in this lecture is the one that, perhaps, I have mentioned the least - the Hellcat. But then military test pilots never talk much about the good characteristics of an aircraft.

[IvanK]

Here is a similar lecture by Dave Southwood on Youtube as linked by Richie a while ago.

http://forum.1cpublishing.eu/showpost.php?p=430782&postcount=1

[ATAG_Snapper]

A great read, Slipball!

[SlipBall]

Thank you Snapper, please read aloud to Riley so that he remains up to snuff with the rest of us.:)

[Crumpp]

Christop55her says:
It takes more controlling on the part of the pilot.


Exactly. It must be controlled at all times and the pilot must watch his accelerations as he can overload the airframe much easier than other aircraft.

You can see the RAE measurements do not match the game in the most basic of stability characteristics.

The RAE measurements where chosen to be reproduced because of there can be no argument.

A small group of players felt like constantly attacking the NACA data as it was not gathered by the RAE. It was decided to concentrate on reproducing the RAE measurements.

The RAE measured the stability characteristics stick free by recording the oscillation over several minutes.

If you break it down into smaller time elements, you can see the Spitfire is rapidly changing speeds over just a few seconds.

Those oscillations must be controlled by pilot input and as the airplane is not stable, they must be constantly managed.

It is not a stick setting issue but one of the basic flying qualities of the aircraft. Joystick parameters have no effect on it.

Here is what the RAE measured:

http://imageshack.us/a/img145/9152/stickfreerae.jpg (http://imageshack.us/photo/my-images/145/stickfreerae.jpg/)

Here is the results, the aircraft is neutral or unstable dynamically stick free.

http://imageshack.us/a/img40/4388/k9788stabilityexplained.jpg (http://imageshack.us/photo/my-images/40/k9788stabilityexplained.jpg/)

Here is the result of the ingame testing. The conditions are the same. The stability is recorded stick free at 5.46 minutes. At that point the airplane is both static and dynamically stable, something the real aircraft was not during the Battle of Britain.

http://imageshack.us/a/img823/4551/spitfiremkiaoctlongstab.jpg (http://imageshack.us/photo/my-images/823/spitfiremkiaoctlongstab.jpg/)



Dave Southwood


Never flew a Spitfire without an inertial elevator. In otherwords, he describes the aircraft AFTER the longitudinal instability was fixed.

[ATAG_Snapper]

Thank you Snapper, please read aloud to Riley so that he remains up to snuff with the rest of us.:)

Absolutely! Will have to make a new movie, "Dogs of Dover" is so 2011! LOL

[Crumpp]

he also can't argue the fact that long period oscillations matter squat.


You seem to be confused about the ability to control something and it having no effect.

The pilot can control them. He has too or the aircraft will destroy itself left on its own. The oscillations increase in velocity and the airplane will reach its structural limits given enough time.

This is not a characteristics of a joystick setting, it is how the aircraft moves AFTER control input.

The NACA results were not tested in the game.

What was tested was the RAE conclusions to see if the game matched in the basic stability characteristics.

It does not. None of the RAE diagrams show the Spitfire statically and dynamically stable, dampening the oscillation in ~2minutes.

The RAE measurements show the aircraft neutral to unstable in normal and aft CG.

The Spitfire in CoD, is statically and dynamically stable stick free.


That means the player does not have to make double control inputs nor does he have to control the oscillation.

In CoD, a Spitfire can quickly achieve and hold a precise amount of acceleration without any careful flying or additional control inputs.

That is unrealistic and not representative of the early mark Spitfires.

That is something the real Spitfire could not do without careful flying and double control inputs from the pilot.

This is not an attack on the Spitfire, most people want realism and fun gameplay. In order to realistically model the Spitfire as used during the Battle of Britain, it must be neutral or unstable at normal and aft CG. The Operating Notes are filled with warnings and cautions as a result of the flying qualities.

The real aircraft were equal dogfighter. The flying qualities is one of the reason's why they were equals.

[Crumpp]

The Hurricane has unusual apparent longitudinal static stability characteristics (pitch trim change with speed). Depending on the c.g. position and the type of propeller fitted it varies from slightly stable to slightly unstable.

I have no idea what variant or set up of the Hurricane Dave Southwood is refering too here.

It is a fact, the Hurricane Mk I as it was used in service of the RAF during the Battle of Britain, was stable and near perfect in its longitudinal stability and control.

I love this part:

As a final thought, please note that it is easy to concentrate on the deficiencies of an aircraft and gloss over its other possibly excellent characteristics. The fact that the Spitfire has poor control force harmonisation and is easy to tip on its nose does not detract from its outstanding turn performance, superb low IAS and high Mach number controllability, and benign stall characteristics. It is a very charismatic and pleasant aircraft to fly overall. And the challenge of trying to master the Bf109 on take-off and landing makes it a very satisfying machine to fly once you have gained some confidence in it.


All the pilots loved the machine that took them home.

Myopically, some see modeling flying qualities as an attack or effort to "pork" their gameshape.

[klem]

Exactly. It must be controlled at all times and the pilot must watch his accelerations as he can overload the airframe much easier than other aircraft.

You can see the RAE measurements do not match the game in the most basic of stability characteristics.

The RAE measurements where chosen to be reproduced because of there can be no argument.

A small group of players felt like constantly attacking the NACA data as it was not gathered by the RAE. It was decided to concentrate on reproducing the RAE measurements.

The RAE measured the stability characteristics stick free by recording the oscillation over several minutes.

If you break it down into smaller time elements, you can see the Spitfire is rapidly changing speeds over just a few seconds.

Those oscillations must be controlled by pilot input and as the airplane is not stable, they must be constantly managed.

It is not a stick setting issue but one of the basic flying qualities of the aircraft. Joystick parameters have no effect on it.

Here is what the RAE measured:

http://imageshack.us/a/img145/9152/stickfreerae.jpg (http://imageshack.us/photo/my-images/145/stickfreerae.jpg/)

Here is the results, the aircraft is neutral or unstable dynamically stick free.

http://imageshack.us/a/img40/4388/k9788stabilityexplained.jpg (http://imageshack.us/photo/my-images/40/k9788stabilityexplained.jpg/)

Here is the result of the ingame testing. The conditions are the same. The stability is recorded stick free at 5.46 minutes. At that point the airplane is both static and dynamically stable, something the real aircraft was not during the Battle of Britain.

http://imageshack.us/a/img823/4551/spitfiremkiaoctlongstab.jpg (http://imageshack.us/photo/my-images/823/spitfiremkiaoctlongstab.jpg/)





Never flew a Spitfire without an inertial elevator. In otherwords, he describes the aircraft AFTER the longitudinal instability was fixed.

I don't want to get dragged into this but as its my chart that's being used, two things to observe:

1. It was a quick test which I would like to see others repeat although I did go to great lengths to ensure I was trimmed as stable as possible hands-off.
2. It isn't really stick-free as my stick is held central by the springs, so a 'light hand' on the stick if you like. We can't represent stick-free unless someone has FFB (I know nothing about how FFB sticks would be affected by this). That might do it.

[ACE-OF-ACES]

2. It isn't really stick-free as my stick is held central by the springs,
Agreed 100%

so a 'light hand' on the stick if you like.
Depends of the JS.. Some have very stiff spring, some don't. Just too many variations to say one way or another.

We can't represent stick-free unless someone has FFB (I know nothing about how FFB sticks would be affected by this). That might do it.
Maybe.. But there are variations even in FFB stick.. For example, the Microsoft FFB2, when you take your hand off the stick, the FFB is disabled, where as others will simulate springs and pull the stick back towards center.

In summary, apparently Crumpp has not thought this one through all the way.. There is limitations in the PC simulating a plane.. Flying qualities and seat of the pants types of feedback are something we may never obtain with a $1,000 PC and a $50 game. Long story short, no flight simulation ever was, is, or will be real, hence the name 'simulation'. Once Crumpp comes to grips with that simple truth, than and only than will he realize how silly most of his Spitfire simulation arguments are.

[bongodriver]

Even with a FFB stick the game will not recognise the user has taken their hands off the stick and therefore it will still assume it is just being held in whatever position the stick ends up, try it, move a FFB stick without covering the sensor to activate FFB and you can still make inputs, the game will just not simulate stick-free.

[Crumpp]

How about this has already been simulated in one FM and works very well.

It is not that hard to do.


It was a quick test which I would like to see others repeat although I did go to great lengths to ensure I was trimmed as stable as possible hands-off.


I would like to see others repeat it too. It does not take any elaborate set up.

From level flight, pull back and let go. The FM will return to trim speed.....

It is that simple.

Just like the Spitfire in the game is immune to overstress damage, it is statically and dynamically stable.

[ACE-OF-ACES]

Even with a FFB stick the game will not recognise the user has taken their hands off the stick and therefore it will still assume it is just being held in whatever position the stick ends up, try it, move a FFB stick without covering the sensor to activate FFB and you can still make inputs, the game will just not simulate stick-free.
Agreed.. Sadly, Crumpp is so vested in this 'story', that he will ignore these facts and simply double down on the 'story' and ignore all these facts as if they were never mentioned.

[JtD]

I see Crumpp's posting the phugoids and spirals on the Spitfire again (35th time?). So I'll just repeat what NACA leading WW2 aerodynamics test engineer - all fighter aircraft of the era which were tested displayed instability in the phugoid and spiral mode. Put the R.A.E. chart from the Hurricane testing next to the Spitfires and you'll appreciate the Spitfires stability in these modes.

And Crumpp, before you post it a perceived 36th time, can you please remove your wrong labels? A plane going into stall in the first cycle is not stable.

[Crumpp]

Hurricane testing next to the Spitfires

Absolutely, by careful flying, a skilled Spitfire pilot can match the precision found in a stable aircraft.

That is not the issue.

The issue is the Hurricane does not require such attention to achieve and hold a precise acceleration. The Hurricane is stable.

[JtD]

Absolutely, by careful flying, a skilled Spitfire pilot can match the precision found in a stable aircraft.It's stick free behaviour.

[Crumpp]

It's stick free behaviour.

What are you talking about???

The Hurricane abrupt turn as recorded by the NACA is stick fixed. The Spitfire abrupt turn as recorded by the NACA is stick fixed.

The RAE stability measurements for general stability characteristics are stick free.

In both the RAE and NACA measurements, the Spitfire was longitudinally unstable with unacceptable characteristics.

That is why they added the inertial elevator to fix the longitudinal instability.

What is the issue? Why is blatent fact so hard to understand?

All the smoke, mirrors, and baloney put out about "it is normal" and "all fighters of the day" acted like that is pure fantasy.

If there was not a problem, then they would not have fixed anything!!!

:rolleyes:

[Crumpp]

Answer the question JtD:

Why did they modify the aircraft with an inertial elevator?

[fruitbat]

Answer the question JtD:

Why did they modify the aircraft with an inertial elevator?

Heres a question.

If they realised that they needed it for the MkV which no one disputes, why did they not come to the same conclusion for the Mk I in 1939?

It wasn't new tech.

And it has SFA to do with NACA, since they added Bob weigths to the MkV before NACA ever got there Spit V to test.

[Crumpp]

why did they not come to the same conclusion for the Mk I

The Mk I recieved an inertial elevator in July of 1941.

[fruitbat]

The Mk I recieved an inertial elevator in July of 1941.

Did it, what Mk I's were those then.

Mk I was out of service and MKII's and Mk V's in service then.

I know what your desperately using as your source for that claim, and its one of the hundreds of modifications listed in Morgan and Shacklady, which coincidentally were all the modifications that were applied to the MKV, which led to need of Bob weights due to CoG being changed, AFTER BoB.

Again i ask you, if it took the RAE 2 months do decide that they needed bob weights on the Vb, why 3 years for the Mk1 in your world?

[JtD]

What are you talking about???You should know, you even highlighted it on the previous page, but in case you really can't figure it out - I am referring to phugoid and spiral modes, I've only said it about 5 times, so maybe it was lost on you. Phugoid, spiral. That's all I'm talking about. I do this because you keep bringing up an A.&A.E.E. chart supposedly illustrating how poor the Spitfire's stability was, where it shows nothing but long period oscillations, i.e. phugoid and spiral mode. This chart shows nothing out of the ordinary for a high speed fighter of that day and the characteristics shown are way better than that of the Hurricane. It appears to me that up to this minute, you don't even know what you're talking about, and yet you've made 100+ posts on the issue trying to convince innocent bystanders of something that's plainly wrong.

It is really getting on my nerves, and here it is in short form, so I can simply quote me every time you bring that chart up again out of context:

The A.&A.E.E. stability records for Spitfire K.9788 show stick free, long period dynamic stability characteristics, also known as phugoid and spiral mode. The records show typical behaviour for world war 2 fighter aircraft, and the characteristics are clearly better than those of other contemporary aircraft, in particular better than the characteristics of the Hurricane, which was also tested by the A.&A.E.E. at the same time.

[TomcatViP]

JTD the pitching moment decrease with the thickness of an airfoil. Tht's how simple it is.

The great challenge in the 50's with the thin wing design and their lack of stability came with that. The video show how the lift center is moving frwd. This move is faster when the thickness ratio decrease. This is why most of the designer during WWII did stick to the 15% ratio.

Supermarine did not have all the viscous flows knowledge as other did and ran straightforward in the thin wing solution (just like the Brits did in WWI). Hence the long dev process. of the Spitfire. That's simple.

Other planes had flaws inherent to their design and did take as long to be fully flaw free.

[JtD]

OK and thanks for the information as such.

It changes nothing about what I wrote, though, if you meant to refer to that.

[TomcatViP]

Another short video explaining the main diff. btw relaxed stability aircraft and stable aircraft:

http://www.youtube.com/watch?v=VImEvFg3smQ

I think it complete well the first one and was needed here.

[JG14_Josf]

Hi,

From the first video it seems clear enough that an unstable airplane (center of lift in front of the center of gravity) is like pushing a shopping cart and trying to keep the castor wheels facing the wrong way - impossible.

Castor wheels have center of axis ahead of the contact patch where the wheel meets the road.