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FM/DM threads Everything about FM/DM in CoD

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  #111  
Old 12-08-2012, 07:55 PM
taildraggernut taildraggernut is offline
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Quote:
Originally Posted by Crumpp View Post


That is my airplane and I am at controls in the film.

if you say so, hardly evidence though is it, a medium level turn pumping the elevator to make slats deploy.

Quote:
Originally Posted by Crumpp View Post
Now your trying to morph the discussion into something else.

You keep confusing "anti-spin" device with a spin resistant airplane.
I'm pretty sure I'm not the confused one in this discussion.....anyway...carry on.

Quote:
Originally Posted by Crumpp View Post
Spin resistant airplanes employ anti-spin devices such as wing cuffs, LE slats, and slots to build spin resistance.
Can I stop you here again....sorry but anti-spin would mean spin proof, resistance implies it's not proof, you know like waterproof vs water resistant, none of those devices can be considered a proof against spinning.

Quote:
Originally Posted by Crumpp View Post
What you are missing is the ability to put it all together. If we were talking about the entire wing being able to stall at once, then the airplane will enter a spin.

It takes a lot of work to do that in a Bf-109 by design.

............


The last feature in the Bf-109 is the elevator control is set up so that with the wing root stalled, the pilot cannot continue to raise the nose. The Socata Rallye is designed that way as are many aircraft.

The designer uses control design to keep the pilot safe by limiting the moment the elevator can produce about the CG. This way, the wing tips remain effective throughout the stall. Cessna does this in a C-172 as well. Again, it is a common feature in a properly designed aircraft.
Now, Mtt did have to demonstrate spin entry and normal recovery in the Bf-109. They did this by adversely loading the aircraft to its rearward CG limit and modifying the slats to be pilot controlled. In other words, the airplane was at its rear most CG limit and the pilot could lock the slats so they did not deploy.
and here finally (in bold) is the first bit of credible understanding you show, but subsequently you have exposed the real protection in this case to come from blanking the elevator, you do realise you have just excluded the slats completely from the equation, given that you could design an aircraft without slats that puts the elevator into the turbulent flow and it would have exactly the same pitch limiting effects, the side effect of that is you seriously limit the manouverability......is this starting to make sense or what?

wait a minute...MTT had to lock the slats but still had to put the CoG back too? why bother with the CoG? sounds to me like there was some crazy black magic going on with that aircraft and spin resistance had nothing to do with slats.....more and more NZTyphoons recently deleted comedy poster is making sense.
  #112  
Old 12-08-2012, 09:58 PM
Glider Glider is offline
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Quote:
Originally Posted by Crumpp View Post
I think you are just trolling.

Honestly, slats are an anti spin device.

So what do you think an airplane equipped with an anti-spin device would require good flying to prevent a spin?

Or do you think the training wheels would work to keep the bicycle upright so it does not tip over and fall?

The logical result of your position is that aircraft with slats cannot spin as they are anti spin devices. Are you really sure that is what you are saying?

As a CFI you cannot seriously say that is a fact. The slats are a device that delay the stall, but pushed too far will stall. It doesn't stop a spin.

The Glider I flew that cannot be spun is a K21, it doesn't have slats, but it certainly could be stalled. If anyone is interested we used K13's for spin training.
  #113  
Old 12-08-2012, 11:51 PM
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from my paragliding lessons i learnt an stall is not an spin but falling like a rock due to lose of dynamic sustentation by going to slow

in the past someone would say that with stalls off the game is more realistic(il246) which is an interesting point
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  #114  
Old 12-09-2012, 12:05 AM
*Buzzsaw* *Buzzsaw* is offline
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Salute

For whatever reason, this is a pattern which we see again and again on these boards.

With the same protagonist on one side.

I believe Crrump has some valid points, however the insistence on an 'all or nothing' argument is not useful.

For the record, I understand the following. Feel free to correct me.

1) The low wing area, hence high wing loading on the 109 was an attempt by the designer to reduce weight and drag to increase overall speed and climb. This fit with the most important goal listed by the RLM, ie. an interceptor which was light enough to climb to altitude quickly, and fast enough to catch the modern stressed skin monoplane bombers which were beginning to arrive in the early '30's. Turn capability was very much of secondary importance. At the time of the competition, newer bombers were faster than the existing generation of biplane fighters which were common at the time. A secondary preferred requirement of the competition was a fighter which could be easily transported by rail. The removable wings on the 109 were a design feature intended to satisfy this requirement. At the same time, these removable wings created another issue, that being the requirement to attach the undercarriage to the fuselage, with the result being the off camber wheels, with their inherent instability in landing. This instability would be exacerbated in high speed landings.

2) As a result of the small wing area the aircraft, if equipped with standard slat-less wings, and without the modern flaps which were an innovative part of the 109, would have had a very high stall speed. The stall speed for a 109 without slats and flaps can be estimated as roughly the speed at which the slats on the historical aircraft open without the flaps down. In the case of the 109E3, the RAE test showed with flaps up, the slats opening at 120.5 mph, 25 mph higher speed than the 95.5 mph actual stall speed. With flaps down, slats opened at 100.5, 18.5 mph faster than the 88.5 mph stall speed with flaps down. A landing at 120.5 mph would by the standards of 1934, be unacceptably high. Especially with the wheel instability issue. Messerschmidt obviously understood the issues of high speed stall brought with his high wingloading, hence the installation of the slats and modern design flaps, with their improvements to low speed stall performance.



The primary goal of the slats and the flaps was to reduce stall speed to a manageable low speed, and thus allow safe controllable landings on the off camber undercarriage.

A secondary benefit was the improved low speed maneuverability, and lowered stall speed the slats gave with landing flaps up. This was not the primary goal of the devices, it was welcome additional benefit.

To suggest the primary design goal of the slats was a 'spinless' aircraft is stretching the point considerably, and is not supported by the historical documentation.

At the same time, there is no doubt the slats did give much more benign stall characteristics to the 109 than many other aircraft. Under the control of a pilot who reacted appropriately to a stall, there was very little chance of a spin occurring. Under the control of a pilot who ignored the requirements for stall recovery, the aircraft was undoubtably capable of entering a spin. Spinless?? I don't think so. Easy to recover from a stall? Yes.

Finally, this entire thread has gone so far off track in order to satisfy the viewpoints of posters that it is missing the original point.

Does the game 109 replicate the characteristics of the historical aircraft?

No, it clearly doesn't. Among other mismodelled characteristics, the tendency of the 109 to easily enter, and be difficult to recover from, spins, is clearly wrong.

Last edited by *Buzzsaw*; 12-09-2012 at 12:11 AM.
  #115  
Old 12-09-2012, 12:59 AM
NZtyphoon NZtyphoon is offline
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First is an abridged lecture given by Frederick Handley Page describing the operation of what are, in fact, called automatic slots - the slats are simply the moving airfoil sections.





and, from 1939:




Operative words "the slot could be made to open at a pre-determined angle of incidence....make the wing stable at a large angles of incidence and so ensuring that, although the aircraft would stall, it would not "drop a wing" and go into a spin."

Therefore, automatic slots are not fully effective at all AOAs at low speeds, let alone combat speeds - which, BTW, have not been mentioned - until the wing has reached a certain, pre-set angle of incidence. What was the pre-determined angle of incidence for the 109? And at what speeds did the slots open?

Effectiveness v basic airfoil:


Last edited by NZtyphoon; 12-09-2012 at 07:23 AM.
  #116  
Old 12-09-2012, 08:21 AM
*Buzzsaw* *Buzzsaw* is offline
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Quote:
Originally Posted by NZtyphoon View Post
First is an abridged lecture given by Frederick Handley Page describing the operation of what are, in fact, called automatic slots - the slats are simply the moving airfoil sections.





and, from 1939:




Operative words "the slot could be made to open at a pre-determined angle of incidence....make the wing stable at a large angles of incidence and so ensuring that, although the aircraft would stall, it would not "drop a wing" and go into a spin."

Therefore, automatic slots are not fully effective at all AOAs at low speeds, let alone combat speeds - which, BTW, have not been mentioned - until the wing has reached a certain, pre-set angle of incidence. What was the pre-determined angle of incidence for the 109? And at what speeds did the slots open?

Effectiveness v basic airfoil:

Most of the questions you are asking have been answered by the chart in the post above yours.

The chart you have provided showing effectiveness vs basic aerofoil is quite dated, and I am not sure it can be taken as effective.

NACA did a later, more comprehensive study of wing lift devices, including leading edge slats, I have a copy somewhere in my files, and there should be a link at the NACA site.
  #117  
Old 12-09-2012, 09:52 AM
NZtyphoon NZtyphoon is offline
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Quote:
Originally Posted by *Buzzsaw* View Post
The chart you have provided showing effectiveness vs basic aerofoil is quite dated, and I am not sure it can be taken as effective.
The intention is to show some of the literature that was around at the time the H-P slot was invented. The table dates back to 1933 so, of course it predates the NACA data, but it was the type of material that would have been available at around the time that the Bf 108 and 109 were under development.

What I should have asked is at what combat speeds were slots effective? The data shows they opened at speeds ranging between 90-120.5 mph, but I doubt that a 109 in combat slowed to those speeds.
  #118  
Old 12-09-2012, 11:24 AM
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Afaik the deployment of the slats is dependent on the aoa, not the speed, so the slats might very well deploy in a tight turn at combat speed.
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  #119  
Old 12-09-2012, 11:35 AM
taildraggernut taildraggernut is offline
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Quote:
Originally Posted by robtek View Post
Afaik the deployment of the slats is dependent on the aoa, not the speed, so the slats might very well deploy in a tight turn at combat speed.
Yes robtek is correct here, slats operate as a function of AoA and that remains a fixed quantity but there is means of calculating what speeds slats would open under certain loads.
  #120  
Old 12-09-2012, 01:54 PM
TomcatViP TomcatViP is offline
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At any time Lift(L) equate Weight (mg)

Hence during a turn at X nbr of g the total lift of the plane is L=Xmg

Let's assume the simple flows theo of thin wing with no camber (flat wing) where CL=2Pi()Alpha where CL is the coef of Lift (L/0.5roV²) with V the speed of the air and ro the volumic mass of the air

Then Alpha=Xmg/(2Pi()*0.5roV²) and V(alpha)== SQRT(2Xmg/Pi()roAlpha)

hence for a given alpha at (let's say) 1.5 stall speed and 1g, the speed at witch slats will deploy is augmented as the square of the G ratio.

hence at 4G the speed is the double. AT 8g, teh speed is three time more.

Etc.. etc..

Regarding the 109:

-Slats are deployed in front of the ailerons in order to keep ctrl at stall conditions. No wing drop (and full airflow around the pouter portion of teh wing), no asymmetric stall . Hence no spin. This is why Crumpp refer it as an anti-spin device. So Crumpp was right (again...)

-The 109 undercarriage was not build that way to facilitate it's shipping via train (at least not only - but this is the first time I think that I have to read it). It was made to make assembly easier with the wing being plugged onto the fuselage. Remind that Bf (and not Mtt at the time ) did not have the production facilities that would be needed for such a big order by the RLM. Many parts were subcontracted (heinkel etc...) and had to be moved from one facility to another. Having the fuselage "crated" by its own undercarriage as soon as possible facilitate the production and made the wing stronger for a given weight (and Mr Messer was addicted to weight reduction as any good eng shld be!).

- Providing early 1930's document is a bit risky to prove a given argument in aero term. As I hve alrdy said many time there was a revolution in 1935. And this flow slowly ard the globe from Germany then USA and all obver the globe after 1945.
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