posted 01-07- 05:33 AM               

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Hi, this is copied from my response to another post on this newsgroup and should be of some interest to anyone flying or wanting to buy BOB.

This is from a WW2 British handling and performance test: RAE Report No BA 1640.

" Even in a very tight turn (BF 109E) the stall was quite gentle, with no tendency for the aircraft to suddenly flick over on to its back and spin"-Reports and Memoranda No 2361 RAE Report No B.A. 1640

"The aircraft (BF 109E) stalled if the turn was tightened to give more than 4g at speeds below about 200 m.p.h."-ibid

"If the stick was then pulled back a little more, the aircraft (BF 109E) suddenly shuddered and either tended to come out of the turn or dropped its wing further, oscillating meanwhile in pitch and roll and rapidly losing height; the aircraft immediatiely unstalled if the stick was eased forward" -ibid

"If the stick is pulled back too far on the Spitfire in a tight turn , the aircraft may stall rather violently, flick over on to its back, and spin....knowlege of this undoubtedly deters the pilot (Spitfire) from tightening his turn when being chased..." -ibid

"The gentle stall and good control under g (BF 109E) are of some importance as they enable the pilot to get the most out of the aircraft in a circling dog-fight by flying very near the stall."-ibid

"A mentioned in section 5.1, the Me. 109 pilot succeeded in keeping on the tail of the Spitfire in many cases despite the latter aircrafts's superior turning performance, because a number of the Spitfire pilots failed to tighten up the turn sufficiently."-ibid

And here is why the BF 109E is spin resistant...

This is from one of my previous posts on this NG a year or so ago:


Colonel Barkhorn (WW2 ace) was interviewed as to the BF 109 handling characteristics in 1969 in Air Progress Magazine, August, 1969. He stated:

"There is no actual stall break... there is no tendency to spin" So, it looks like the BF 109 needs to "have no tendency to spin" in stalls.

The question was whether the 109 spins as it stalls as many other WW2 fighters do...
in EAW and Warbirds the 109s spin if accelerated stalled (ie. when pulling more than 1 g as in tight turns or going over the top of a loop)... or if the real BF 109 just mushes, porpoises, bobs etc. instead of trying to spin at the stall.

A RAE flight test taken with instruments in 1940 states that the 109 DOES NOT spin and DOES NOT HAVE a tendency to spin either because of the leading edge slats.

This is because the 109 has "slats" on the front of the wings which pop out at the stall which other World War 2 (WW2) fighters don't have.
So someone in this NG said we need to talk to a live 109 pilot...I did! I called up Mark Hanna today ( I first contacted him three years ago) of the Old Flying Machine Company in England which flies 109s in films like the Memphis Belle and test flies newly refurbished 109s with original engines and original fuselages. . (Tragically, he recently passed away from a BF 109 engine-failure accident)

Mark is a former F4 phantom pilot who is permanently flying warbirds as a business. He has flown aircraft such as the Spitfire, Hurricane, BF 109, Mustang, etc....and he stalls them and does aerobatics in them (especially when flight testing newly refurbished ones for air worthiness)...and has written several articles on their handling charastics (even on the 109) in magazines such as Air progress of fall 1991.
Anyway this is what he said when I asked him specific questions...

1. First, he has flown many 109 models some with the original engine and most with the Spanish engine...and stalled several types.

2. Mark said that the BF 109 has leading edge slats near the wing tips and that they do the same thing as "washout" (twist) in modern planes...ie. making the wing tip stall after the wing root so that you have aileron control during the stall.

Otherwise you are prone to have an efficient WW2 tapered wing that will drop suddenly with little warning and often has a tendency to roll and enter a spin.

The "twist" near the wing tips in modern planes give the wing tips a lower angle of attack with a lower angle of incidence.(.usually 2-3 degrees difference in modern planes) during the approach to a stall than the wing root has at the stall and so the wing tips stall last. This gives lateral control at the stall with much more warning before a wing drops.

Slats are not only a high lift device but also a lateral control device that dampens any rolling tendency at the stall... This means that lateral control (roll) can be maintained throughout the stall and tends to dampen any rolling tendency..

Slats are put near the wing tips (as the BF 109 has) so the wing tips will stall after the wing root thereby giving better roll control, the wing won't drop suddenly without warning and will have a much decreased rolling tendency th many other WW21 fighters have.

2. Anyway, Mark said that the 109 would not roll more than 10 degrees in an acceerated stall (in a tight turn or going over a tight loop) and certainly did NOT have a tendency to spin as the Hurricane or Spitfire did if they accelerated stalled and weren't immediately given attention to.

3. The 109 he said would mush, oscilate or porpoise (nose goes up and down)...but would not flip or try to flip over on its back especially like the Hurricane or Mustang would.

4. Conversely, Mark stated, the Spitfire gave more warning in terms of stall buffetting, noises etc. that it was finally going to accelerated stall on you than the BF 109..
.but then the Spitfire had a sharper stall with more of a tendency to spin on you than the 109..ie. the Spits stall is much sharper than the 109 without lateral control during the actual stall...
Well, Mark's findings agree with the RAE flight test... so that makes two sources that state that the 109 will occilate in an accelerated stall and not try to spin...whereas the Spitfire, Hurricane and Mustang have little or no lateral control during the stall and have a tendency to "snap" on you.

Hmmm, lets look at the "bible" and see what it says... The Spitfire Mk. 1 manual (ISBN NO 0-87994-028x) states:

"A high speed stall...tends to flick over laterally the aeroplane and and unless the control column is put forward instantly, a rapid roll and spin WILL result."
hmmm, no slats there!

In conclusion...this means that EAW and Warbirds are wrong when they model the Bf 109 snapping out of a stall.
It hurts gameplay by meaning that if a 109 stalls out in a sim...then you lose altitude, situational awareness (as you snap), and position...whereas historically in a 109, you might occilate or mush...but you would not spin out of the fight as the Spitfire, Hurricane, Mustang etc. would.




Richard Ordway

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posted 01-07- 11:48 AM               

my condolences go out to the hanna famaly.

to change to a lighter note
1.The spit had washout built into the wings you can see it if you stand at the tip and look down the wing.
2.Acording to my dad(who has flow most if not all of the marks of spit still flying from the 1a to the pr19(photo reconasens))
"you have to be a fool to stall a spit, it gives you so mutch warning in the heavy buffet befour the stall that have the time to release the presure on the stick and come out of the buffet, in total contrast the p51( with its high speed laminer flow wing ) would give you know warning what execept the stick would git very light in the push and pull axis, if you noticed this in time you cound push the stick forward and regain control of the aircraft. that is the reason why lots of novices were lost on the p51(they did not react in thime to the suttle warning of the stall and then the aircraft wpuld spin in)".
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WHATCH YOU TAIL

[This message has been edited by Biggles3 (edited 01-07-2001).]

[This message has been edited by Biggles3 (edited 01-07-2001).]

posted 01-08- 11:13 PM               

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Originally posted by bolillo_loco:
I heard the same of the 109 at low speed tight turns, but during a high speed stall it flicked and spun just like any other. it was explained to me that the slats would not work during a high speed (accellerated stall) because air pressure kept the slats retracted and thus they would not work.

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I won't claim this is wrong, but it does sound suspect... the stall is caused by the airflow on the wing, and it's the same airflow on the wing that causes the slats to open. High or low speed shouldn't make much of a difference.

To give you an example I've done accelerated stalls in a number of GA airplanes, and in all of them the stall warning went off - and it works in the same way as a slat. Even more interestingly I've flown a plane with slats - the Rallie - and the slats came out on them in shart turns.

Lastly let us not forget that the 109 was considered to be a bad gunnery platform because in tracking turns the slats would pop out at random times (ie, left before right or vice versa) and spoil the shot.

So I'm skeptical, although I can't say for sure.

posted 01-09- 03:37 AM               

As I understand it, angle of attack causes separation of upper boundary layer and therefore the stall. The low speed stall is caused by the pilot having to increase the angle of attack in order to counter the decreased amount of lift force generated by the airfoil at lower speeds. The accelerated stall would be caused by the pilot yanking back on the stick at high speeds... the inertia of the aircraft would keep it flying forward but the wings have been "angled upward"... thereby increasing angle of attack.

At low angles of attack, the high pressure, "stagnation", region would be essentially on the front of the airfoil...pushing on the slats and keeping them in.

When the angle of attack is sufficiently increased, the stagnation region shifts towards the bottom of the airfoil. Thus, the front of the airfoil (where the slats are) is now in the higher velocity, and therefore lower pressure, "region".... the lower pressure would not be enough to push the slats in and they would pop out.

I think the basic stall warning works on close to the same principle. The "stagnation point" is where the airflow divides to go either over or under the airfoil. When the stagnation point is above a strategically placed switch, the airflow pushes down on it keeping it in the "off" position. Once the angle of attack has been increased, to where the stagnation point has moved below the switch, the airflow pushes up on the switch, turning the switch "on" and activating the stall warning.

posted 01-09- 02:44 PM               

while I have never heard that the slats would affect gunnery, I would imagine that they would because I have heard they would pop open and cause the plane to yaw and nibble at your ailerons. I have also heard that they sometimes popped open and jammed there or jammed shut while the one on the other wing worked fine.

the spitfire is the one I am curious about. seems two parties have found two different types of data for the spitfire. One group says stall was very predictable and controllable, while the other says it wasnt.

I dont know which crowd to believe. the eliptical wing was a great wing that provided good lift and maneouverablity over the other types, but it came at a cost, poor stall warning and wing tended to stall all at once or at the wingtips, vs other types like constant taper which stalled at the roots first and gave ample warning. I have read this in quite a few books and magazines.

posted 01-10- 04:19 AM               

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Originally posted by bolillo_loco:
[B]even at a high IAS would this still permit the slats to open?
[B]

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I am very rapidly getting out of my realm of knowledge here but I think the answer is yes.

OK... I'm trying to remember stuff from my dynamics course (many years ago) so I am in no way claiming that my answer is right.

The key is in how the angle of attack on the airfoil changes the distribution of the pressure around the airfoil (ie the direction of the velocity vector and not the magnitude). Yanking back on the stick would change the orientation of the airfoil to the airstream which would change the pressure distribution around the airfoil. The way the pressure distribution changes with angle of attack should remain fairly consistent with velocity... at least up until trans-sonic compressibility type stuff kicks in.

Please xcuse the following, it doesn't really have much to do with slats, I am just trying to think out loud (Do you smell smoke???):
Now, the rotationial acceleration of the plane about the center of gravity (uhh... how fast the angle of attack would change) is a function of torque (about the COG) and the inertial properties of the plane. The torque is created by the elevator which at higher velocity would create more torque. However, the counter-torque created by the wing would also increase at higher velocities. So I figure that the time it takes to change the orientation of the wing airfoil shouldn't change much with velocity. This means that at higher IAS you could "point" the plane in a different direction quickly by rotating it but it would take longer for the thrust to restore the airflow over the wing to a zero angle of attack (ie this is why at higher IAS you "skid" easier)

Sorry for blabbing on, I know that this isn't really what you are really interested in for this discussion thread, I was just trying to figure it out and typing while I do it makes it a little easier.

posted 01-15- 01:50 PM               

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Originally posted by Bishop:
The Lysander also had the automatic slats. I have also heard a rumor that the Lyzzie designers stole the idea from the Fiessler Storch.

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Actually it's a British invention, they're technically termed "automatic Handley-Page slats". The non-automatic type is what's on the Me 163, ie, fixed open.