Stability and Control characteristics of the Early Mark Spitfires
 

The early mark Spitfire was a excellent fighter.

It was not without its issues like many aircraft. Raw performance numbers for speed and climb do not tell the whole story about any design. The pilots ability to precisely maneuver and use a fighter to the edge of its envelope as an effective gun platform is just as important to the fighting ability of the design as any other performance parameter.

Amoung the Western Front warring powers during World War II, only two nations had measurable and definable stability and control standards. Stability and control was a young science. Airplanes had simply been two slow and light previously. The forces were small enough such that there was little need. The two nation were the United States and Germany.

At the beginning of World War I, the United States found its aviation industry in a dismal state of affairs. Despite being the nation credited with the first manned, powered, controllable, and heavier than air flight, the US aviation industry had only 8 airplanes and 14 trained pilots in 1914. France on the other hand, had 260 aircraft and 171 trained pilots in 1914. This prompted a flurry of US Government action to bolster the aviation industry included the creation of the NACA in 1915. By wars end, the United States produced 7,000 airplanes and 20,000 engines. The surplus was such that post war, for ~$500 dollars cost for the pilot's license a successful solo resulted in the award of a JN-4 Jenny airplane to the new pilot. The emphasis on the aviation industry continued throughout the 1920's and 1930's.

Everyone is familiar I believe with the Nazi parties emphasis on aviation. Like the events in Russia, unfortunate circumstances would align to bolster the introduction of fresh ideas and innovation in the aviation sector.

Let's not be obtuse. None of this is to claim other nations did not progress in aviation or contribute. It is only to lay the historical foundation as to why these were the only Western Nations to adopt stability and control standards.

This thread is going to cover the definable and measure stability and control characteristics of the Spitfire. It is not going to cover opinion outside of stability and control engineers.

What this thread is not going to do:

1. Get into a debate about "easy to fly". It is not definable and has no bearing on the measured facts.

2. It is not going to discuss the sustained level turning ability of the aircraft. That is also measurable and definable. For Example, anyone who is capable of doing the math will see that the Spitfire outturns the Bf-109 is steady state constant altitude turns at low velocity.

Stability and control is the measurable science of flying qualities as they appear to the pilot. This means it is the science of creating a control system that the pilot can safely extract maximum performance of the aircraft. While there are some subjective areas because historical data is incomplete, It is not pilot opinion and while it is branch of aerodynamics, it does not tell us specific performance numbers of a solid body outside of the control system moments.

Moderators, I ask you to keep a close eye on this thread.

Let's lay some of the ground work for the discussion by first looking at what is acceptable and what is not acceptable for longitudinal stability.

The first condition we will discuss is the Longitudinal stability characteristics in an abrupt pull up and release of the stick.

The NACA found the Spitfire to be acceptable in this area. Why discuss it? It is harbringer of things to come in the Spitfires Longitudinal stability and I think the light bulb will come on for most readers as to the importance of stability and control. It will lay the foundation for more informed discussions of other designs included in the game and in the future as the game grows.

These first charts come from the USAAF and USN stability and control standards as adopted during World War II.

Acceptable Longitudinal stability characteristics in an abrupt pull out:

http://img694.imageshack.us/img694/6...ontrolabru.jpg

Things to notice....

1. The amount of force required is larger than one would think. A separate NACA study determined that the average pilot can easily apply 80lbs of pull force on the controls. In roughly .5 seconds the pilot is able to apply ~80lbs of force to precisely produce an acceleration of ~3.5 G's. Upon release of the stick, which is the top of the stick force curve at ~80lbs, the acceleration curve is nicely sloped without any wild fluctuations.

So even though the stick is moving around and we see the force move from push to pull, there is no change in the airframes acceleration. The controls are floating after release. The control system friction is sufficiently dampened by the inherent stability of the design.

In other words, the pilot can quickly and precise apply a specific amount of acceleration to the airframe and control it.

The high stick forces act as a solid foundation to resist pilot induced oscillations under aceleration. The pilot does not need to brace himself but can precisely control the aircraft from normal seating.

Now let's look at what is unacceptable longitudinal stability in abrupt pull outs:

http://img824.imageshack.us/img824/9...yabruptpul.jpg

First thing to notice is the small amount of stick force that produces a large acceleration. This means the pilot must brace himself if he is going to control the accelerations. It also means it is very easy to apply more accelerations than the airframe can handle. The pilot does not have a solid foundation to resist pilot induced oscillation.

The next thing is the slope of the curve of stick force application to release and the accelerations do not match. This means the acceleration increase is not proportional to the amount of stick travel. As the accelerations increase, less stick travel is required to increase them.

After the stick is released, accelerations continue to increase.

The controls do not float. Instead, they released control continues to produce accelerations as the inherent stability of the design cannot overcome the control system friction. Now that does not mean the control force friction is excessive. It could be that but it can also be the design does not have sufficient dampening on the longitudinal axis.

Our aircraft begins to porpoise and begins another acceleration cycle.

Now let's look at the Spitfire in an abrupt pull out as measured by the NACA.

http://img98.imageshack.us/img98/320...ruptpullup.jpg

First thing to notice is the stick forces. There are light but acceptable in abrupt pull outs. While very steep, the slope of the curve matches our acceleration curve and the controls float without overcoming the inherent stability of the design. The steepness of the curve tells us the pilot is able to very rapidly load the airframe. In fact, the NACA had to make allowance in their stick fixed measurements to prevent damage to the aircraft from acceleration because of the rapid onset the controls allowed.

However, if we look at the acceleration curve we see an abrupt change and not the desirable smooth curve. This points to the stability characteristics contributing to the rapid fluctuations in acceleration that the aircraft exhibits under other conditions.

The harbinger's of things to come:

1. The steepness of the curve tells us the pilot is able to very rapidly load the airframe.

2. The light stick forces does not provide a solid foundation for the pilot to resist oscillation.

Next we will get into the unacceptable longitudinal stability characteristics of the design.

to be Con't.......

Resist oscillation is not the pilot controlling the oscillation with control input. That is the wrong thing to do in most cases and can get you into real trouble.

Instead the high forces mean the stick is not moving and it takes a deliberate effort to control the plane so the chance of over control is reduced.

The light stick forces make it easier to inadvertently over control or apply control pressure when it is not required.

A lot of the NACA stuff can be found here:

http://ntrs.nasa.gov/?method=aboutntrs

It was actually addressed in the Spitfire Mk V but the longitudinal instability existed from the beginning.

The RAE did not have stability and control standards. However, the RAE did agree with the NACA even if they did not know it.

They published all the warnings and characteristics of the Longitudinal instability in the Operating Notes. We will get to that.

As for the CG position theory, again, the RAE was in complete agreement with the NACA. They published all the warnings and characteristics of the Longitudinal instability in the Operating Notes.

It is kind of hard to argue that the NACA was incapable of performing a simple weight and balance when the RAE fixed the same issue and published warnings in the Operating Notes. The truth is they just did not know what the NACA was talking about as the stability and control criteria was classified at the time and Gates had not completed his visit.

Gates was well versed in stability and control, however. When presented with the facts and his own testing, he came to the same conclusions as the NACA. That is why the longitudinal instability was addressed with the bob-weights.

I attached the bob-weights which were added to the Spitfire Mk V to correct the longitudinal instability. I also attached an exerpt from Perkins and Hage.

Some of Gates testing results on the early Mark Spitfires.....

http://www.avialogs.com/list/item/34...in-xii-engines

hve a look p7, 8 & 16 (repect. rpm vs speed as indicated by the manual, handling characteristics and boost). Doc is AP1565B Spit IIA&B flight manual, edited in June 40 and published in July40.

Here is the RAE stuff...

http://aerade.cranfield.ac.uk/listarcrm.php

Nice. Thanks for the links guys.

Good post. The RAE was very much aware of the longitudinal instability and the Operating Notes is full of warnings that are the result.

I will post the relevant graphs, stability and control engineer opinion, and the highlights from the Operating Notes in my continuation.

What is funny is the next aircraft I was going to discuss is the Hawker Hurricane. Sir Sydney Camm may not have understood swept wing theoy during the war but he was a master of stability and control design. The Hurricane was a wonderful gun platform and had near perfect longitudinal stability. His other major designs, the Typhoon and Tempest also exhibited the same characteristics.

http://www.telegraph.co.uk/history/b...been-lost.html

Thank you for your post, Crumpp

Defined like that, any argument is rather moot. If it is defined that the only stability and control engineers at that time were in the US (specifically associated with NACA), and they formulated standards which the Spitfire failed, then the Spitfire failed...as defined in this rather narrow question.

I believe that the work of the pioneering stability and control engineers was interesting and valuable for the future of aviation. But the Spitfire seems to be a bad example to demonstrate that value.

As opposed to the objectively derived flight stability data, the standards that NACA set were subjective (e.g. X inches in control deflection to perform Y). Defensible, intuitively correct, but subjective.

Despite failing these subjective standards, many records exists describing the Spitfire handling as (subjectively) good. Many descriptions exist of Spitfire first flights by novice pilots. Some note the Spitfire pitch issues (e.g "found it easy to black myself out"), but express relief at finding the aircraft benign to fly and push hard.

I realise that you want to exclude all these considerations as being mere anecdotes. But then what it is the argument? I think we all agree that NACA failed the Spitfire on certain aspects of it's flight stability. To determine what that meant, we have to go further.

I think the Spitfire is not a good example of the value of the advances in stability and control. Despite it's rather alarming characteristics in the NACA reports, the young humans sitting inside RAF Spitfires were capable of rapidly adapting to them and making the Spitfire what it was intended to be ..a superlative short range military interceptor.

camber

Gates was not NACA and neither was the RAE when they published the Operating Notes.

It is not meant to be a good example of advances in stability and control. The thread is meant to point out the measureable and definable characteristics so that they can be modeled for the game.

I read the notes. Do you consider that the warnings against misuse are exceptional for the period, or exceptional compared to later WWII aircraft with better stability characteristics?

That is a good idea and worth pursuing, but there is an unfortunate snag. Not only are people using different control hardware to control the same virtual aircraft, they have the option to tune the response between the physical control deflection and the virtual control surface deflection with nonlinear curves. This ability is not under the umbrella of the flight sim software itself. Some people have simulated control surface loading (FFB), some do not, and again the user can quietly do their own stability modifications to make their plane handle differently to what the devs attempt to program.

camber

Yes and no. The user can dampen their inputs to the aircraft (e.g. very flat curve around the center), but the user cannot affect the aircraft's response to said inputs. If the aircraft has a tendency to diverge from equilibrium, then it will still do so regardless of what the user's stick curve looks like. A high-wing monoplane like the Storch will still be very stable in the roll axis due to the keel effect. An aircraft with a lot of anhedral is still going to be largely unstable about the roll axis.

Keeping in mind of course that real control columns have a much greater throw than your average consumer-level HOTAS.

The longitudinal instability existed only if the CoG was in the aft positions as pointed out in the A&AEE report:

Note that early CoG limits are 5.8" to 8.6" aft the datum point. The revised limits are 5.4" to 7.9" for DeHavilland prop without bob weight (7.5" for Rotol prop).

These warning can be found only from the operating notes of the Spitfire II with Rotol prop (most CoG sensitive combination) before the revised CoG limits and bob weights (which were needed only if CoG was too far aft as was case in the NACA tested Spitfire V).


1. RAE criticized NACA static longitudinal stability test and for a good reason. Tests were done only at one position of CoG and that position was aft the revised limits.

2. Operational testing and handbooks of the aircraft were made by A&AEE, not by RAE.

Here is the direct link to the document by Gates:

http://aerade.cranfield.ac.uk/ara/dl...rc/rm/2677.pdf

See the page 9. The Spitfire K.9796 was tested at CoG 7" aft the datum point and that is still quite aft given that the range was from 5.4" to 7.9" (revised limits without bobweight and with DeHavilland prop).

Interesting comparison can be made to the Mohawk AX.882 which was tested at CoG 21" behind datum point, rather nose heavy given the range being 19" to 26". And despite forward CoG, the stick force for pull out was about the same as in the case K.9796.

Thx for the link.

The comparison with the Hurri values is more interesting IMOHO

Here is the NACA Report on Control Characteristics of Spitfire VA specifically stating that the CG of the Spitfire was estimated:

http://i91.photobucket.com/albums/k3...-page-007a.jpg

Crumpp can argue black and blue that NACA accurately calculated the cg properly - the report specifically states this was not the case:

and a Spitfire I CG diagram:
http://i91.photobucket.com/albums/k3...cg-diagram.jpg
Datum point 19.5 in aft of wing leading edge
Maximum aft location of cg was 7.6 in (MiG-3U 7.9 to 8.6 in) aft of datum point, 19.5 in aft of the wing leading edge = 27.1 in aft of leading edge (up to 28.1 in) - NACA calculations = 31.1 in aft of leading edge, enough to make a difference in the longitudinal stability (slightly tail heavy).

You are using the wrong variant weight and balance as well as being an actual W/B for a specific aircraft.

There is not any need though to go into any kind of depth in researching this....

The Operating Notes for the type clearly warn the operator of the characteristics the NACA discovered.

No they exist in the Spitfire Mk I as well.

Really? Then please show us your definitive cg drawings for all Spitfire Mk Is.

In your opinion - IMO this thread is based on a flawed premise which requires detailed research to point out where it is flawed.

Please explain why the NACA report specifically states that their calculations may be in error.

Clarify how an aircraft tested with the cg further aft than specifications can possibly emulate the control characteristics properly.

All the evidence for the Spitfire Longitundinal instability will be posted in this thread, that includes the Operating Notes, Gates conclusions, the NACA results, stability and control engineering opinion, and the steps the RAE took to fix the longitudinal stability in later Marks.

The weight and balance is a sideline that the RAE did not even believe.

You don't need comprehensive drawings to do a weight and balance. I will explain the process and how it works both for a type AND the individual aircraft later in detail with documents.

In short, like anything that comes off an assembly line has variation. CG limits is no different and there is a range of acceptable limits for the empty weight CG for the type.

A weight and balance is done when the aircraft is complete and the empty weight CG is estabilished. It must be within that tolerance range for the type but the empty weight CG will be specific to the individual aircraft.

That empty weight CG for that specific aircraft then has its specific range for foward and aft limits based on its authorized configurations. That is why the weight and balance is part of the Pilot's Handbook for that aircraft. It is required documentation and just like the Handbook, propeller logs, engine logs, and airframe logbooks follows the aircraft throughout its life.

The minimum equipment you need to do an accurate weight and balance on any aircraft is a tape measure, plumb bob, string, scales, chaulk, and pen/paper.

The NACA used percentage MAC. Once you know the percentage MAC range, you get all the data from the tape measure and scales for the individual aircraft.

The basic airframe dimensions of the Spitfires were unchanged up to the Spitfire IX except the nose section and radiator configuration. The loading table is attached, some parts rewritten for clarity. It's for the Spitfire Ia and Ib but the CoG locations are exactly the same for the Spitfire V (as refered in the right corner of the table).

The exact values of the CoG location are following at accuracy of two decimals (verified from drawings and RM 2525), these are values by RAE and slightly different as given by NZtyphoon because mean aerodynamic chord is at different position, datum line being the same:

The lenght of the mean aerodynamical chord is 78.54"
The datum line is 18.65" behind the leading edge of the mean aerodynamical chord
The datum line is 23.60" behind the leading at the wing root
The CoG of the NACA tested Spitfire V was 31.40" behind the leading edge at the wing root and 7.80" behind the datum line.

Please prove that the RAE had no belief in weight and balance, and explain how the RAE took steps to fix so-called longitudinal instability when they had no belief in weight and balance.

NACA did not have any drawings for the Spitfire and specifically state that their measurements might have been in error - without a weight and loading diagram of the specific aircraft tested there is no way to know whether the aircraft was teetering on instability because it was loaded beyond the usual tolerances.

To claim that this report proves all early Spitfires were unstable is a stretch, particularly when the Supermarine chief test pilot Jeffrey Quill, states in his book that the longitudinal stability of the Spitfire I was okay.

Here is the revised CoG part of the loading table attached to make clear how the CoG and use of the bob weight (inertia device) were connected in the case of the original standard elevator:

With DeHavilland propeller:
CoG range 5.4"-7.9" aft of datum point, no inertia device needed
CoG up to 8.2" aft of datum point, 3.5 lbs inertia device
CoG up to 8.6" aft of datum point, 6.5 lbs inertia device

With Rotol propeller:
CoG range 5.4"-7.5" aft of datum point, no inertia device needed
CoG up to 7.8" aft of datum point, 3.5 lbs inertia device
CoG up to 8.2" aft of datum point, 6.5 lbs inertia device

Regarding if the currently flying Spitfires have the bob weighs installed, here is link to a picture of the elevator linkage of the Spitfire Vb BL628 (from spitfiresite.com):

http://spitfiresite.com/2010/07/anat.../07ar_fuse_001

Edit: Attached also the quote from Perkins and Hage to show how the use of bob weigh and CoG at aft center of gravity are connected :)

And as we all love quotes, here is Quill in Spitfire, Portrait of a legend by Leo McKinstry:

"Convex elevator" ? Does anyone have more details on this ?

Why are you regurgitating the same stuff I just posted. Puzzling...

Anyway, yes, the bob weight artificially increases the stick forces so that the pilot can have more control.

That is band-aid to fix the longitudinal instability the NACA reported!!!

The fact Supermarine recognized that longitudinal instability and took measures to fix it invalidates any pointy tin foil hat theory the instability did not exist.

Now let's get back to the NACA report so there is a better understanding of the issue.

We will look at a condition of flight essential to a dogfighter. The ability to make abrupt turns.

The pilot must be able to precisely control the amount of acceleration he loads on the aircraft. All aircraft performance depends on velocity. In order to get maximum performance out of the aircraft above maneuvering speed, Va, he needs to be able to make a 6 G turn and not exceed that load factor to prevent damage to the airframe. Below Va, the pilot needs to control the acceleration so that he does not stall the aircraft making the abrupt maneuver as well being able to maintain a maximum performance turn.

Doing that in an early Mark Spitfire was difficult and something only a skillful pilot could perform.

First the NACA report. Abrupt 180 degree turns were conducted at various entry speeds to gauge the level of control the pilot had in maintaining steady accelerations. The turns were also done to the stall point in order to gauge the behavior and amount of control.

"In turns at speeds high enough to prevent reaching maximum lift co-efficient" means turns above Va.

http://img404.imageshack.us/img404/2525/rapidturns.jpg

http://img513.imageshack.us/img513/6480/rapidturns2.jpg

"By careful flying" a pilot can hold a steady acceleration. That agrees with the Operating Notes warning for the pilot to brace himself against the cockpit to get better control when making turns.

Now lets look at the measured results.

http://img843.imageshack.us/img843/6...dturnfig15.jpg

Here we see in a rapid left turn performed at 223 mph the test pilot is unable to hold constant acceleration on the airframe. Very small variations in stick movement and stick force changes of 1-3lbs results in large fluctuations in acceleration.

Next let's look at the pilots ability to control the accelerations in the pre-stall buffet.

http://img600.imageshack.us/img600/4313/stallbuffet.jpg

Here we see the pilot was able to load the airframe to 5G's in 1 second to reach the pre-stall buffet 3 times. The smooth positive sloped portion of the curve represents the aircraft flying while accelerations are increasing. The top of the acceleration curve represents the pre-stall buffet. The bottom of the curve represents the stall point.

The take away is:

1. The large accelerations change for very little elevator movement.
2. The very rapid rate at which the pilot was able to load the airframe to 5G's.
3. The equally rapid rate at which the airframe unloaded down to 2G's when the pre-stall buffet was encountered. In 1 second, the aircraft went from 5G's to 2G's due to buffet losses. This means a rapid decay in turn rate resulted.
4. The violence of the pre-stall buffet combined with the longitudinal stability and control caused large fluctuations in the accelerations on the aircraft.


Last part of the NACA we will cover for today is the stick force travel. The amount of stick travel as measured by the NACA was not acceptable.

http://img94.imageshack.us/img94/2621/sticktravel.jpg


Next let's look at the opinion of Stability and Control Engineers on the Early Mark Spitfires.

http://img832.imageshack.us/img832/3...sairplanes.jpg

http://img855.imageshack.us/img855/7...airplanes2.jpg

http://img825.imageshack.us/img825/4...airplanes3.jpg

http://img404.imageshack.us/img404/6...shspitfire.jpg

Tomorrow I will post some of the plethora of references to this same issue of longitudinal instability as found in the Spitfire Mk I Operating Notes from July 1940. You will see the same references or similar to the same issue the NACA measured in the Spitfire Mk II Operating Notes.

There is no doubt that the Air Ministry was aware of the longitudinal instability of the early mark Spitfires.

Correct, the NACA did their own weight and balance analysis so their numbers might not agree with the RAF's. That has nothing to do with flying the airplane outside of the CG limits.

You don't need a thing from the manufacturer to do a weight and balance analysis. Your leap of logic requires some pretty hefty suspension of belief. One would have to assume the NACA was incapable of doing a simply weight and balance analysis and constructing a potato chart. That is something every homebuilder in the United States does in his garage. A weight and balance analysis and constructing a potato chart is also something every FBO is capable of doing. It is a routine process in aviation.

You need a few simple tools and the knowledge to run the math is all. It is obvious you don't know what you are talking about but are only trying to muddy the waters in defense of a gameshape.

You do not understand the process and do not realize the datum point is just a random point picked to begin measurements.

So what if the NACA picked a line of rivets that is ~5 inches away from the one Supermarine chose on the back of the firewall instead of the front.....

The reference datum point can be anywhere the person doing the weight and balance analysis decide's to put it.

MAC as measured by RAE:

19.5+8.4 = 27.9/84 = 33.2%

NACA CG as flown = 31.4% MAC

The NACA flew the Spitfire with the CG 1.8% MAC FORWARD of the aft CG limit as defined by Supermarine.

Don't loose your time commenting "comments", Crumpp. Hold the line.

Ended already my long reading for tonight. Enjoyed it as much as any other good entertainment as it shld be from any interested reader in aviation. Sad you don't sell any popcorn. ;)

So now I am waiting for the interludes played by our looney toons :rolleyes:

~S

PS: that story about the NACA not having any drawing is true... but they neither had any for the 109 they tested ;)

Yep, it is not like switching aviation fuel. Weight and balance analysis is simple and easy to do.

Nothing puzzling there, you just forgot to underline the most relevant part for this thread and I fixed it for you; the bob weigh was added because the CoG had slipped too far aft causing londitudinal instability just like Quill notes.

Yep, when the CoG slips too far back, instability exist in pretty much every airplane, including Spitfire and Mustang. Bob weighs were used in some models of both fighters exactly for the same reason: CoG shift. Both aircraft were also stable when the CoG was forward enough.

Here is again A&AEE on stability of the early mark Spitfire:

http://www.spitfireperformance.com/k9787-fuel.html

CoG was at 5.8" aft datum line when the airplane was found to be longitudinally stable, that is 2" more forward than Naca tested. Note that Spitfire IX had CoG around 5" aft datum line at service load, no need for bob weigh.

Slow down and tell me where you get the 78.54 MAC on that sheet.

Do you know what percentage MAC is??

The reason the NACA used percentage MAC is because they did their own weight and balance analysis.

The ONLY number that is comparible...is the percentage MAC!!!

MAC as measured by RAE:

19.5+8.4 = 27.9/84 = 33.2%

NACA CG as flown = 31.4% MAC

The NACA flew the Spitfire with the CG 1.8% MAC FORWARD of the aft CG limit as defined by Supermarine.

If you want to use your 78.54 in MAC with our most narrow aft CG limit...

(19.5 + 5.4) / 78.54 = 31.7% MAC

NACA CG as flown = 31.4% MAC

The NACA flew the Spitfire with the CG .3% MAC FORWARD of the aft CG limit as defined by Supermarine.

http://www.spitfireperformance.com/k9787-fuel.html

Check it out...That is what the NACA said.....

:rolleyes:

Ok let's not go down the rabbit hole again.

You are using a weight and balance sheet that incorporates the longitudinal stability fix and is from February 1944 to prove the NACA conclusion was not correct.

Yes, the RAE addressed the issue of the longitudinal instability in the Spitfire around 1942. However, the Spitfires used in the Battle of Britain did not benefit from the fix.


This is Spitfire K-9787 and was tested in June, 1939.

http://www.spitfireperformance.com/k9787-fuel.html

If you click on the center of gravity link at the bottom of the page...

The weight and balance diagram is K-9788, the very next Spitfire off the production line.

http://www.spitfireperformance.com/k...cg-diagram.jpg

We can eliminate the February 1944 document from the thread as not applicable and conclude it is the result of the NACA findings.

Which brings us back too:

MAC as measured by RAE:

19.5+8.4 = 27.9/84 = 33.2%

NACA CG as flown = 31.4% MAC

The NACA flew the Spitfire with the CG 1.8% MAC FORWARD of the aft CG limit as defined by Supermarine.

You still have the question that has yet to be addressed. If in theory the Spitfire was so poor in its stability, why did all the pilots who flew it of every nation, sing its praises?

I should make clear that I do not doubt the calculations, but its a basic difference

Report RM2535

http://aerade.cranfield.ac.uk/ara/dl...rc/rm/2535.pdf

and (wing and datum point are the same on the Spitfire IX)

http://www.spitfireperformance.com/ab197datum.gif

They gave exact reference point, wing leading edge at the root and they (NACA) admited that their measurements for MAC maybe somewhat in error.

Well, just like in the other discussion, you ignore the data (USAF handbook) which does not support you and post some irrelevant stuff or accusations.

I don't play that game, let the people see the data and decide themselves.

The only thing that changed was the revised CoG limits for the aircraft with Rotol propeller and bob weighs if the CoG went beyond the normal limits, as often happened in the case of the Spitfire V.

As Quill noted, slight unstability was built in for purpose and prefered by pilots. However, stability margins were narrow and improper loading could easily cause problems.

Which has what to do with the MAC on the weight and balance sheet? You can be they did their own weight and balance analysis too!!!


Negative.

Spitfire K-9788 shows an aft CG that is 33.2%.

The most aft MAC with the Feb 1944 revision is 31.7%.

They closed up the CG limits to address the longitudinal instability.

You have presented the solution to the problem in an effort to claim the problem never existed.

Please start another thread if you feel the need to continue down this rabbit hole claiming the NACA could not perform a weight and balance analysis.

Now let's get back to the NACA report so there is a better understanding of the issue.

We will look at a condition of flight essential to a dogfighter. The ability to make abrupt turns.

The pilot must be able to precisely control the amount of acceleration he loads on the aircraft. All aircraft performance depends on velocity. In order to get maximum performance out of the aircraft above maneuvering speed, Va, he needs to be able to make a 6 G turn and not exceed that load factor to prevent damage to the airframe. Below Va, the pilot needs to control the acceleration so that he does not stall the aircraft making the abrupt maneuver as well being able to maintain a maximum performance turn.

Doing that in an early Mark Spitfire was difficult and something only a skillful pilot could perform.

First the NACA report. Abrupt 180 degree turns were conducted at various entry speeds to gauge the level of control the pilot had in maintaining steady accelerations. The turns were also done to the stall point in order to gauge the behavior and amount of control.

"In turns at speeds high enough to prevent reaching maximum lift co-efficient" means turns above Va.

http://img404.imageshack.us/img404/2525/rapidturns.jpg

http://img513.imageshack.us/img513/6480/rapidturns2.jpg

"By careful flying" a pilot can hold a steady acceleration. That agrees with the Operating Notes warning for the pilot to brace himself against the cockpit to get better control when making turns.

Now lets look at the measured results.

http://img843.imageshack.us/img843/6...dturnfig15.jpg

Here we see in a rapid left turn performed at 223 mph the test pilot is unable to hold constant acceleration on the airframe. Very small variations in stick movement and stick force changes of 1-3lbs results in large fluctuations in acceleration.

Next let's look at the pilots ability to control the accelerations in the pre-stall buffet.

http://img600.imageshack.us/img600/4313/stallbuffet.jpg

Here we see the pilot was able to load the airframe to 5G's in 1 second to reach the pre-stall buffet 3 times. The smooth positive sloped portion of the curve represents the aircraft flying while accelerations are increasing. The top of the acceleration curve represents the pre-stall buffet. The bottom of the curve represents the stall point.

The take away is:

1. The large accelerations change for very little elevator movement.
2. The very rapid rate at which the pilot was able to load the airframe to 5G's.
3. The equally rapid rate at which the airframe unloaded down to 2G's when the pre-stall buffet was encountered. In 1 second, the aircraft went from 5G's to 2G's due to buffet losses. This means a rapid decay in turn rate resulted.
4. The violence of the pre-stall buffet combined with the longitudinal stability and control caused large fluctuations in the accelerations on the aircraft.


Last part of the NACA we will cover for today is the stick force travel. The amount of stick travel as measured by the NACA was not acceptable.

http://img94.imageshack.us/img94/2621/sticktravel.jpg


Next let's look at the opinion of Stability and Control Engineers on the Early Mark Spitfires.

http://img832.imageshack.us/img832/3...sairplanes.jpg

http://img855.imageshack.us/img855/7...airplanes2.jpg

http://img825.imageshack.us/img825/4...airplanes3.jpg

http://img404.imageshack.us/img404/6...shspitfire.jpg

Tomorrow I will post some of the plethora of references to this same issue of longitudinal instability as found in the Spitfire Mk I Operating Notes from July 1940. You will see the same references or similar to the same issue the NACA measured in the Spitfire Mk II Operating Notes.

There is no doubt that the Air Ministry was aware of the longitudinal instability of the early mark Spitfires.

It gives exact location of the leading edge needed for calculation (p.7).

I claimed normal service load:

7.7" at normal service load 1939
7.9" aft limit for DeHavilland without inertia device
7.5" aft limit for Rotol without inertia device

This means that on normal combat load there was only change in the case of the Rotol prop assuming that aircraft was properly loaded.

Besides, the revised limits were originally issued sometime around 41/42.

Otherwise you seem to have chosen same tactics as in the FTH discussion so my part end here now.

Cpt Doggles, you see my point now.

You present this like it's some revelation Crummp.

If you have done *any* research you'll have read Quill's book, which you should have done considering you're talking about the Spitfire and it's flying characterisics as it's practically source point one - he test flew the aeroplane in all it's marks over 10 years and countless hours - this makes him somewhat more credible than you, so you'll forgive me if I take his word over your clearly subjective posts.

The point is addressed fully and sufficiently in there to make all your posting here as redundant it is cherry picked.

I'm not going to bother posting it here, if you're serious about research, and truly objective you'll read it and come back here and retract some of this frankly irksome Spitfire smear campaign.

What "tactic" is that? :confused:

You mean showing you the question on an A&P exam?

http://quizlet.com/2496371/print/


Start another thread on the weight and balance or send me a PM. I would be happy to walk you through the steps in determining percentage MAC.

It is not that hard to do. You will understand it and see how ridiculus the theory the NACA could not do one really is!!

In presenting a February 1944 weight and balance document and for the purposes of this discussion on 1940 Spitfires:

You have presented the solution to the problem in an effort to claim the problem never existed.

Completely wrong, neither individual CG drawings, nor weight and balance sheets were issued with the Pilot's Notes - fighter pilots especially were rarely allocated their own aircraft and had to take what was made available. Pilot's Notes General, Section 7:
http://i91.photobucket.com/albums/k3...G-page-001.jpg

Each and every aircraft type used by the RAF and FAA had generic cg/w&b sheets printed, which had fixed fore and aft limits, beyond which the flight qualities started to suffer: Lancaster cg drawings:

http://i91.photobucket.com/albums/k3...2-page-001.jpg

Loading diagram up to L7532...
http://i91.photobucket.com/albums/k3...1-page-002.jpg

L7533 on...
http://i91.photobucket.com/albums/k3...2-page-002.jpg

Careful study shows the cg limits fore and aft were identical, despite different equipment and loadings - the airframe was the same, so the limits stayed the same - those fore and aft limits for ALL early Marks of Merlin engined Spitfires were identical, Mk I to Mk V and were not changed until the modified elevators with larger mass balances were introduced.

It was the responsibility of the groundcrew to ensure that the cg limits were adhered to. The only crews that needed to know the position of the cg were bomber crews with their large disposable loads and multiple crew positions

This is how the cg was calculated:

http://i91.photobucket.com/albums/k3...1-page-001.jpg

http://i91.photobucket.com/albums/k3...2-page-001.jpg

http://i91.photobucket.com/albums/k3...3-page-001.jpg

Relatively small changes in equipment weight and equipment position could still make a big difference to the final cg - a few kg a few inches aft of the rearmost cg position could upset the handling of an aircraft;

NACA made it quite clear that their calculations for the Spitfire may well have been in error - until Crumpp can prove that NACA had calculated the cg position correctly, according to early Spitfire cg data charts, the report needs to be viewed with some suspicion.

http://i91.photobucket.com/albums/k3...-page-007a.jpg

Where did you get this nonsense? Show me accounts of even trainee pilots who found manoeuvring the early marks of Spitfire difficult - I repeat Supermarine's Chief Test Pilot Jeffrey Quill stated categorically that there was no problem with the longitudinal stability of early Mk I & II Spitfires.

A lot of words and a lot of effort into defend a position or a view but nothing to address the basic question:

You still have the question that has yet to be addressed. If in theory the Spitfire was so poor in its stability, why did all the pilots who flew it of every nation, sing its praises?

There is of course another inconvenient point that should be considered and that is have you done these calculations on the Me109E?

I say this because if you believe that the Spitfire to be dangerous and the German pilots considered the Spitfire to be much easier to fly than the Me109E, How dangerous do you think the Me109 was?

there's a difference between "singing praises" and having a stable aircraft. Data is not subjective, data is data. I'm sure once you got how to know the spitit was a wonderful aircraft...but as far as I know it's not an aircraft you can just "fly" and get maximum performance out of

I have some questions. @ Crumpp
We're other contemporary aircraft also tested in this way?
It's all good and well saying the Spit did this, this and this but, how did other aircraft stack up?

Also, how exactly do you intend to model this phenomenon in CLOD?

It seems to depend on stick forces and stick forces aren't calculated in CLOD? Or are they? We all know that the controls on these aircraft stiffend significantly at high speeds, that's not accounted for either.

So really the most important point, considering where we are is, what would you expect to be done to the FM to replicate this?

Yes, many other aircraft were tested. My plan is to do threads on the stability and control of all the main fighters involved in the game.

I am sure I will be hated by both "red and blue".

I don't want to de-rail my own thread so if you want an in-depth discussion we will start another one.

Well, subsonic incompressible flow theory for symmetrical airfoils will give a one dimensional picture of an aircraft. The stability and control characteristics help to complete the picture.

Stability and control was a new science during WWII. Many of the aircraft have issues and those issues should be modeled.

For example, a symmetrical airfoil analysis of the Spitfire and Hurricane would give the impression the Hurricane was the 2nd rate fighter. In fact, the Hurricane was the real workhorse and an airplane the Bf-109 pilot should respect. Why?

The Hurricane was a very stable and maneuverable aircraft. Air combat is not about fancy flying on a warm sunny day. It is about getting bullets on a target. The Hurricane did not have the convergence issues and was an airplane the average pilot could quickly get guns on target as well as accurately shoot from to destroy his opponent.

I am sure there is nothing you can teach a Spitfire ace about finessing an airplane or over controlling.

Well that is up to the devs as I don't know the game engine. If they are using the standard Cm calcs, then it should be rather straight forward.

Air combat is often about speed and climb rate. The Hurricane was effective against bombers but less so against the Bf-109 simply because it was significantly slower and had a poorer rate of climb than the German aircraft. I hope you aren't trying to argue that the pitch sensitivity of the early Spitfire actually made it less effective against fighters than the Hurricane. That would be a very odd thing to be claiming.

At most combat altitude, the Spit had the same prob.

Yes, but by a lesser margin, making that particular problem therefore less of an issue than in the Hurricane.

+1

but we are OT now ;)

The RAF did not have a Pilot's Handbook either, they had Pilot Operating Notes. Your post is nitpicky and irrelevant.

Sometime in the 80's by convention, everybody got on the same page as far as airworthiness documentation formats. Until then, the required information was in each nations own format but still required.

Read the first paragraph of the very first document you posted. The specific weight and balance for that serial numbered aircraft is found in the RAF with the Aircraft handbook.

By convention, it is part of the airworthiness of that specific aircraft and part of the aircraft's maintenance documents. There will also be seperate engine, airframe, and propeller logs.

It is proven. The math has been done several times in this thread. It is not my fault you don't understand it and continue to argue in ignorance.

If you start another thread, I will be glad to go over MAC calculations with you.

The only important information is the NACA's report is their percentage MAC.

What you are taking as evidence of an error is the NACA explaining how they did the weight and balance (percentage MAC) and their numbers might not match.

Percentage MAC does not require the specific numbers to match as long as the margin of error is the same throughout. It is a non-dimensional proportion!!!!

Look at your RAF documents!!! The RAF has the MAC as both 84" and 78.54"!!

Do you really think the RAF did not know what the wing chord was on their own airplane???

Because of the stations chosen for LEMAC and TEMAC, the NACA choose 85" as the MAC.

The fact that has to be explained over and over to folks who pass themselves off as "Gods of Aviation" is puzzling at best. :confused:

OK, let me put it another way, what behaviour would you expect to see?

In layman's terms. What do you expect the Spitfire to do that it isn't already doing in game? Without going into the game engine.

Something like 'if you do xyz then this happens', please.

Just so everyone understands what it is you're asking for, not just the brainiacs..

First there is a Pilot's Handbook and then there is no Pilot's Handbook. :eek:

You shld open another thread on Crumpp.

But it might be that an edito in the next Cosmopolitan issue will be more suited to your prose.

It is truly hilarious that he says his own post is nitpicky and irrelevant. :(

I await with interest his thread on the 109.

Indeed, that's the one I'm really looking forward to aswell.

Holy out of context, Batman!!!

:rolleyes:

I am hoping the Mods will just clean it up. Delete all the pointy-tin foil hat "NACA can't do weight and balance" and sour grapes comments from "lurkers with an agenda".

Winny, I have a few more post's to put out before we get into the nuts and bolts for the game. Let's not put the cart before the horse. I would like to get somewhat of a consense and some input from people who know more about the limits of the game.

I hope that after defining the stability and control behaviors that represent the early mark spitfire, we should be able to produce a list that is reproduceable in the game.

well personally I would expect a much lower Roll rate at speed, and a very sensitive Unbalanced Elevator (unbalanced meaning it needs much more roll input than pitch).

Put the horse before the cart? You're on the CLOD forum so I just want to know, even in a ballpark kinda way what all this means to a Spitfire in CLOD.

I can look at this thread all day and I'm never gonna be able to relate all this info and graphs and whatever else to what is actually supposed to be happening to the Spitfire?

Treat me like the idiot you normally do and spell it out for me!

Are we talking a small amount of movement, wobble, or whatever it is that this instability creates, in RL?

You keep saying that it's unstable but I still don't know What you actually mean.

What exactly is wrong with the Spitfire in game regarding control and stability?

In a nutshell Winny, the Spit was neutrally stable longitudinally, this is an undisputed fact, in very basic terms this means it was very light on the controls in pitch, this basically means the pilot needed very little (only 2 fingers) effort to pitch the aircraft, the other benefit of this is it means the aircraft is very manouverable in the pitch plane too, hence why the Spit was so good at turning, the down side to highly sensitive pitch is the aircraft can be overstressed if used harshly at high speeds and may also mean the aircraft can be stalled very easily too, what this doesn't account for is the fact that despite how the Spit looks on paper all the potentially negative issues never really manifested and the Spit ended up with a reputation of being a 'delight' by the people whose oppinions 'really' count i.e. the pilots, who it turns out were largely not so 'ham fisted' and were able to use sensory feedback to allow the airframe to 'talk' to them and use the effect to it's limits, what Crumpp would like to see is the Spit being 'unforgiving' and basically discourage all of us to use this effect because NACA said it was a problem therefore he canno't accept the truth (we have all seen how resistant he is to hard evidence), it's purely coincidental that this would further pork the Spitfire :rolleyes:

Hey Win, here's the laymans

I'm flying staright and level, trimmed for cruise and hands off in an aeroplane and I hit a pocket of rough air. The right wing drops a fraction:

Stable: aircraft will settle back to it's trimmed state automatically thanks to inherent clever design - basically it's to do with differing lift vectors and their strength and direction. This is great for trainers, light aircraft and commercial machines as it means a minimum of pilot effort to fly the plane in straight lines. However it also means that the plane will resist slightly manouevres initiated by the pilot, cos it just wants to fly straight and level! Not great for fighter aircraft.

Neutrally stable: The plane will stay at that angle of bank and unless controls are manipulated will not return to it's original attitude. More workload for the pilot but generally not hard to fly, just requires more attention.

Unstable - the aircraft continues or even accelerates the wing drop to the right. Without pilot interaction/correction the manoevre would continue or even amplify till 'bad things' happen. Aircraft of this nature are tiring to fly because you're constantly fighting the plane - like being balanced on a pin and in asituation where even your control inputs are being amplified. Not fun. A good example of this is the P-51B/D with the rear fuselage tank full; it pushed it's CoG back far enough that it took it to the limit of acceptable controllability - there is a quote by Bud Anderson where engaged before he could empty this fuel tank he ended up in a turning fight with the nose still pitching up and round but he had nearly full forward stick input to try and keep it from throwing itself into a spin.

Now Crummps agenda is based on one report of a Mk. V with which he wishes to tarnish the handling of all Spitfires, despite reams of evidence to the contrary.

In truth there were some issues with Mk Vs being not correctly loaded (they carried quite a bit more kit in them than the earlier Mks) and a short term measure of intoducing bobweights into the elevator control circuit ('g' acting on the bob weight during pitching manoevres actuallly weighted the control column to provide a resistance to up elevator input). As this problem was investigated, and it's catalysts understood, better and more careful loading instructions, and ultimately a redesigned elevator mass blance made the bob weights obsolete.

Was the Spitfire's CoG range small? Yes. And it didn't take much to put it close to or beyond them. However, if you've done your reading nearly every one who's flown the thing, in whatever Mk, speaks glowingly of it's handling. Sure there were lemons and I suspect the NACA variant was an old war weary machine not in best of trim, but it seems foolish to take the evidence of one report against a veritable sea of contrary opinion.

The RAE had the same conclusion. (Re-)read the report.

But they might hve been also unlucky and get a war weary machine ? Hummm ... might hve been the 5th German column

A SPit Va in 1943 in the USA is going to be a tired machine

However we still have the basic questions

If in theory the Spitfire was so poor in its stability, why did all the pilots who flew it of every nation, sing its praises?

There is of course another inconvenient point that should be considered and that is have you done these calculations on the Me109E?

I say this because if you believe that the Spitfire to be dangerous and the German pilots considered the Spitfire to be much easier to fly than the Me109E, How dangerous do you think the Me109 was?

Any comments

OT. Deleted

Here's a quote from another interesting sticky. Start another thread if you want to keep going.

Thank you for taking the time to explain it.. My head has stopped hurting!


I'm no aerodynamics expert, but I am a very keen amateur historian, BoB being my area of expertise. I'm inclined to agree with you. I've read many, many combat reports, memoirs, interviews written by the people who were there and it's hard to believe that this issue was widespread, or severe. I've never read of anyone complaining about it. Quill and Henshaw both mention problems they encountered whilst testing and this wasn't one of them.

I think the fact that you have to return the stick almost to neutral after entering a high g turn (>3 g) to prevent oversteering in a Spitfire should be in game, also the very sensible elevator with large reaction for small inputs and the roll rate as documented.
This will be a problem for ham-handed pilots, but a delight for the virtuosos, as it was in RL.
I don't see that as "porking" the Spit further, but to give it the characteristics that made it famous.
Every aircraft in CoD should reflect its pro's and con's as they where documented then.

+1

Sorry bongo,
but your posts can be more readily interpreted as
first: a attack on the person, not the post
and second: as the endeavour to keep the status quo of the spit controls.
You seem to be too much emotional influenced, imo.
But thanks anyway, for supporting my position.

Ok, one more as I've been asked how to do the CoG calculation.

The dimensions can be found from the AB197 graph:

http://www.spitfireperformance.com/ab197datum.gif

and from page seven of the RM2535:

http://aerade.cranfield.ac.uk/ara/dl...rc/rm/2535.pdf

Lenght of aerodynamical mean chord (MAC): 78.54"
Location of datum line: 18.65" behind leading edge at MAC
Aft limit at MAC: 34% 26.7036" behind leading edge
Aft limit at wing root: 2.638' = 31.656" behind leading edge
CoG used by NACA: 31.4" behind leading edge at wing root

The rest is simple math:
Aft limit behind datum line at MAC: 26.7036" - 18.65" = 8.05"
Datum line behind leading edge at wing root: 31.656" - 8.05" = 23.6024"
NACA CoG behind datum line: 31.4" - 23.6024" = 7.7976"
NACA CoG location at MAC behind leading edge: 18.65" + 7.7976" = 26.4476"
NACA CoG % at MAC: 26.4476" / 78.54 * 100 = 33.6741%

Over and out.

Crumpp, are you aware you are quoting, and disagreeing with yourself? And I agree, your post is nitpicky and irrelevant.

NACA reports on the spitfire can be found here for anyone who would like to read the whole thing.

Downloadable PDF.

Edit: here's a very interesting document on Spitfire stalling characteristics. NACA again.

These characteristics you describe are NOT representative of all Spitfires. Therefore they should NOT be in game. Read again my post on stability. It affected *some* - and it seems I need to remind some people here that does not mean all - Mk V aircraft. A Mk V is NOT a Mk I, or Mk II.

All I can suggest is that you guys go away and read the books I've read, go further make even more research and come back and make an informed opinion then. Please for pity's sake do not take the one single example of an agenda driven poster as gospel.

The NACA test discovered what they discovered - I can't argue with their findings, FOR ONE PARTICULAR AIRCRAFT. However I cannot agree that these are representative of the breed. And as for relevance, well, I've said it already. A Mk V is not a Mk I.

What is it about the tested aircraft that makes it not a representative sample of the other aircraft?

Did RAE and NACA test the same aircraft ? Because so far we can see they draw the same conclusions.

And oh nasty they are, they even gave some recommendations in the handbook. I guess that they wanted to wage a war 70 years latter on a dark corner of the internet ;)

The "agenda driven" shoe fits some feet here, i believe.

There are some awkward little phrases in the NACA test viz:

http://i91.photobucket.com/albums/k3...-page-007a.jpg

Now, until Crumpp, or anyone else, can prove beyond reasonable doubt that NACA got their cg calculations right there is a question mark over the longitudinal stability of this Spitfire VA as tested.

You know Crumpp's right about expressing CG as a percentage of MAC. The Datum point doesn't have to be in the same spot for the results to be valid. That's why it's called a datum point.

Can you direct me to the RAE test please? I've not read it.

Tomcat, I'm not interested in getting into a slanging match, but I'm finding your tone a little condescending. Can we both agree to keep our future posts a little less aggressive? I'm just trying to present the whole picture as I understand it, without fixating on one source.

Likewise Robtek - I have an agenda, true; I'd like to see every aircraft represented as accurately as possible with the widest possible references to minimise the possibility of error. I just happen to know a great deal about a few aeroplanes (P-38 and P-51 amongst them) with the Spitfire being high on the list. My reference library is not exactly small though by no means complete, and it has been thoroughly absorbed over 20 years. So, you'll exuse me for calling someone out if I think they are presenting data that is either unrepresentative, of poor relevance or inaccurate, on a subject i know a great deal - but not all, admittedly - about.

I'm not after a super plane in game; I simply want both sides to have the pros & cons that the prototypical aircraft had. No more, no less.

Hi Fenrir,

Here's some of what I've found that might be of interest:

NACA A.C.R., Sept 1942: Measurments of the Flying Qualities of a Supermarine Spitfire VA Airplane
NACA A.C.R., Sept 1942: Stalling Characteristics of the Supermarine Spitfire VA Airplane


http://www.wwiiaircraftperformance.o...106_Page_1.jpg
http://www.wwiiaircraftperformance.o...106_Page_2.jpg

Perhaps also of interest: R & M No. 2535 High-speed Wind-tunnel Tests on Models of Four Single-engined Fighters (Spitfire, Spiteful, Attacker and Mustang)

Fwiw from A. & A.E.E. Spitfire I report 15 June 1939:

http://www.spitfireperformance.com/k9788-stability.jpg

Crumpp wasted countless hours nitpicking the 100 Octane threads with minute, forensic examination of every single little detail - his contention, that the early marks of Spitfire had longitudinal stability problems which needs to be replicated by this game, needs to be proven to the same level that he demanded for 100 Octane fuel; nothing less should do.

That 100-octane thread was monumentally stupid on all sides. It just does not matter, even remotely, what percentage of Spitfires were on 100 vs how many were on 87. Both should appear in the game, and both now do appear in the game (performance problems notwithstanding).

Vendettas aside, the sheet that Lane posted looks interesting.

I'm not 100% clear on what those graphs are supposed to be representing, but if we look at #4 for example, it shows the airspeed diverging wildly from equilibrium, which I would assume is due to the aircraft doing the rollercoaster "porpoise" motion.

A stable aircraft should return to equilibrium, not diverge from it.

Just some of the many references to the Longitudinal instability found in all of the early Mark Spitfires.

Spitfire Mk I Operatings Notes, July 1940:

http://img109.imageshack.us/img109/7976/page10jv.jpg

http://img26.imageshack.us/img26/2599/page12dh.jpg

http://img542.imageshack.us/img542/9202/page13o.jpg

http://img607.imageshack.us/img607/2471/page15j.jpg

http://img651.imageshack.us/img651/2456/page16lu.jpg

Tommorrow I think we can discuss game behaviors to ask for in the bugtracker.

:rolleyes:

There is only one accurate reference point for the CoG in the NACA report, the distance of the CoG from the leading edge at the wing root and that is given as 31.4". NACA admits that their measurements for MAC maybe in error and we can easily see that there is error because in the RM2535 the 34% CoG location at the RAE measured MAC is also given same way as distance from the leading edge at the wing root and the value is 2.638' which is 31.656". Even with these values only we can estimate that the real CoG location was about 33.7% at the MAC given by RAE instead 31.4% claimed by NACA (and NACA admited that their value might be wrong).

As we know accurate reference point at the wing root and dimensions for MAC used by RAE and A&AEE and datum line, we can also easily calculate these.

Lenght of the MAC measured by RAE and A&AEE is 78.54" (or 6,54') and position 31.4" behind leading edge at root is 26.4476" at MAC and that means that CoG was at position 33.6741% in the NACA tests using RAE and A&AEE dimensions.

However, British documentation gives CoG values usually as distance from the datum line so we need to make NACA CoG location comparable with these. And that is easy because we know that the datum line is 18.65" behind leading edge at the MAC:

26.4476" - 18.65" = 7.7976"

And this value, 7.8" aft datum line, is comparable with the other sources like A&AEE and RAE tests and loading instructions.

Over and out.

I wonder how exactly would you like to model jaming pilots elbow against his body. :o

My opinion is (flying all available fighter airplane in the game) that it's the Hurricane and Bf 109 elevator is too light even at higher speeds rather than Spitfire elevator being not light enough. Generally I like how game calculates forces on the stick and how they increase with the increasing airspeed, it just needs some fine tuning and obviously structural G limits modelled.

I believe there already is a bugtracker issue raised regarding structural G limits somewhere, will confirm.

The only problem I see at the moment (1.07) is that they have changed something on the Spitfire FM and it is nearly impossible to get the plane into a high speed stall. Before that, iirc, it was a plane matching the description much better - you had to be careful not to bring it too close to the stall, you had to be more careful with the the elevator than now in 1.07. Have you noticed the same thing Crumpp?

Looking at the bugtracker, I can't seem to find the 'structural G limits' issue, but I am sure it has been discussed. This would be a most welcome feature, but very difficult to model reasonably - the virtual pilot is not getting the kind of feedback like the real pilot did. This is already a problem in old Il-2, but the new features enhanced the gameplay in a great way already.

Reading through the other bugtracker issue (re: Merlin incorrect power settings)

http://www.il2bugtracker.com/issues/370#change-1216

I found Crumpp posted following comment:

interpreting the hard data in most extraordinary way. I believe you've made a mistake in there and I suggest you're more careful with your bugtracker activities, because devs seem to actually read that from time to time and your views are often wrong and misleading. Thank you.

Here are some good examples of pages designed to be used by trainee pilots and which are conservative in their assessments: for example the "violent pre-stall buffet" is a feature commented upon favourably by most Spitfire pilots who cite this feature as being a good warning device announcing that a stall was imminent, and it is something which was deliberately designed into the Spitfire by Mitchell.

How many aircraft need to be treated with care in bumpy conditions and high-g? All aircraft, except those that are particularly stable, need care when experiencing bumpy conditions under high-g loading, so there's nothing different about having such a warning in a Pilot's Notes. The "Pilot's Notes General" are specific about flying in bumpy conditions:

In a high speed fighter pilots need to be careful in bumpy air - so what? Jeffrey Quill's comments about the elevators are interesting (to be posted later).

NZTyphoon,
bumpy conditions, where a pilot is moved around in the cockpit despite harness, are not so difficult to master if the pilot has to use some force to move the elevator.
The problem arises when minimal stick forces AND minimal stick movements are resulting in major changes.

To get an actual idea, it's juts like having the joystick on a slippy surface. Each time you pull or push the stick, the base move. Obviously there the phenomena is reversed but roughly it's the same.

The notes specifically talk about the pilot jerking the stick while manoeuvring with high-g in bumpy conditions - that does not sound like minimal stick movement or forces.

Crumpp is putting a worst-case scenario on the "buffeting", a feature which many pilots have praised as a pre-stall warning, and on comments about the pilot accidentally jerking at the stick in adverse conditions; in other threads he has gone as far as to claim that early Spitfires were longitudinally unstable and dangerous to fly - as I have said before, he needs to back up such claims with solid evidence, in the same way he demanded that others provide 100% evidence for 100 Octane use. Why should we expect anything else?

The necessary Stick movement (elevator) to induce a 3 g load at cruise speed was three quarters of an inch in the Spitfire, afaik, very easy to get unintended reactions there if your arm isn't completely fixated.

To be fair, there are loads of references by pilot's to having to either wedge their elbows into the side walls or into their own stomachs to steady themselves.
Quite a few mention going 2 handed. They adapted.

As in most cases in WW2, the pilot's coped with the quirks of their machines and got the best out of them ( the good ones at least ).

Exactly, one of the quirks of the Spit was the extreme easy elevator, great for experts, more difficult for beginners; The difference to planes with "normal" handling should be in the game.
Same for the very heavy elevator at very high speeds (>600 km/h) in the 109, i.e.