Horizontal Stab vs Compressibility

[II/JG17_HerrMurf]

I was messing around and put my f4 into a near vertical dive on the US Normal server to escape a rapidly closing Yak. I stopped paying attention to the horizon and focused on him (bad idea). I recognized the wind noise as being excessive but by the time I looked down I was over 680 kph. Tried to pull out at medium altitude but continued to accelerate. Realized I was out of control, chopped the throttle at 728 kph and pulled all the way back with no effect. I had an epiphany and cranked the stabilizer trim way back. Holy cow, IT WORKED!! The nose came up, I recovered and re-trimmed for level flight. I wasn't a lawn dart and survived the mission.

 

Just an idea for you guys. If you get into compressibility problems and have enough time/altitude use the horizontal stab as a stabilator. It saved my bacon tonight.

[AbortedMan]

I was meaning to create a thread on this, as it seems it's somewhat of an exploit in its current implementation to completely negate the effects of control stiffening.

 

If a pilot is unable to pull on the stick because the stiffening is too strong, even with a long control column leverage, wouldn't the stiffening forces against the trim wheel be even greater at the point of control?

 

A lever (flight stick) would afford the most leverage/pressure per unit of "arm strength" in this situation, and a wheel you needed to pull would offer exponentially less leverage vs the same pressure...how is it possible you're easily able to push through the stiffening with the lesser device?

[TX-Zigrat]

If the stab was aerodynamically balanced it wouldn't take much force anyone have a drawing of the pivot location?

 

Conventional elevators lose effectiveness at high Mach due to shock induced separation, stabs don't have same problem

[SR-F_Winger]

If the stab was aerodynamically balanced it wouldn't take much force anyone have a drawing of the pivot location?

 

Conventional elevators lose effectiveness at high Mach due to shock induced separation, stabs don't have same problem

+1

[Panzerlang]

There are plenty of RL accounts of 109 pilots using the 'trim' to get out of a dive. I have no NACA docs to back up their experiences but I reckon ya'll can guess how many hoots I don't give about that.

[AbortedMan]

I'm not saying you're wrong but, with the correct gearing, it could be possible to acheive enough 'strength' by turning a trim wheel.

I have no idea if the current behaviour is accurate, just wanted to point out that it might be.

Yeah I knew that as I was typing, but I can't imagine a trim wheel being designed to have more leverage than a control column...but then again I don't know anything about their design.

[SR-F_Winger]

Yeah I knew that as I was typing, but I can't imagine a trim wheel being designed to have more leverage than a control column...but then again I don't know anything about their design.

I am neither a physician nor do i have big clues about aerodynamics. But i do have decent education and so my common sense tells me it works something like this:

Edited May 14, 2014 by VSG1_Winger

[wastel]

The horizontal stab of the 109 was driven by a spindle/spindel nut combination, which was itself rotaded by the hand wheel with help of an transmission.

 

So you did not need the force you would need by using the stick.

[Tab]

Only problems with the stabilizer were that the control could freeze at higher altitudes (6-8 km) - it was the case during the high speed trials of the G2 in 1943 - the Pilot could not move it beyond 1.7 or 1.5 nose down.

[AbortedMan]

Welp, those explanations work for me! Thanks fellas...now to discuss whether trim should be adjustable while in-game blacked out as it is now.

Edited May 14, 2014 by AbortedMan

[II/JG17_HerrMurf]

Only problems with the stabilizer were that the control could freeze at higher altitudes (6-8 km) - it was the case during the high speed trials of the G2 in 1943 - the Pilot could not move it beyond 1.7 or 1.5 nose down.

Was this common or a one off during a flight test?

 

It never crossed my mind to attmept this in the original Il2 because you could "trim" the 109. Although I did use the infamous trim on a slider to clean up badly damaged aircraft for the limp home. Didn't realize, at the time, this was something of a cheat.

 

Now I have experimented with the adjustable stabilizer quite a bit and will use it during very highspeed flight. It seems reasonable and not really a cheat to me. The greater force is one of the reasons all modern fighters have stabilators now.

[Nil]

Neutral (untouched) stab should make it almost impossible to go into comp, before the plane starts to pull up by itself. if it's pointing a little downward, it's more or less luck that gets you out of the comp. haven't tried the game for almost a week now, been busy. So I haven't even set up the stab control.

[AbortedMan]

Are we talking about compressibility or are we talking about control stiffening?

 

I'm understanding compressibility as allowing control surfaces to move but not doing anything because the air is so disrupted at the leading edge of the wing it making it essentially useless, while control stiffening is just higher air pressure over the control surface which overpowers the leverage available to a pilot using cockpit controls.

 

I feel like people mix them up, or think they're the same thing and that's incorrect...or they are the same thing and I'm incorrect.

[II/JG17_HerrMurf]

I thought it was the same thing. Is it just controls stiffening due to overall pressure or is the boundary layer moved back so it's disrupting at the point of the elevator?

[AbortedMan]

Can't find my usual go-to source right now since I'm at work, and I'm not one to cite pilot accounts as 100% fact...but this guy's recollection of compressibility alludes to the control column being movable but ineffective..."you could do whatever you want"

 

 

Also here's a visual of the compressibility effect. Notice near Mach 1 there is no air near where the control surface would be as it's all being pushed by the high pressure of the leading edge to the outer reaches of the foil (as my humble understanding goes). I don't think we're achieving these speeds to garner the effect of actual compressibility.

 

https://www.youtube.com/watch?v=BsIabrtezIQ

 

This raises a question...were the 109F4's and 109G2's control surfaces in any way hydraulically/pneumatically assisted? I would think that could push through, unless it was just a failed design that even hydraulic/pneumatic assistance couldn't even overcome.

[OBT-Psycho]

I think the very first aircraft using assisted controls was the P-38 (not sure which version though, but I would say J)

[II/JG17_HerrMurf]

This is a 109 E1. The tail surfaces appear to be wire and the main wing controls appear to be push tube. I have also heard, in the past, the P-38 was the first with assisted controls - but only anecdotally.

[AX2]

The FM in Dive is wrong for all planes.

In old IL2 1946 you loose parts and surface controls at 650 km in a Lagg 3 or any in russian plane practically... 

 

In BoS I Can dive a Lagg 3 up to 800+ kph  , without losing parts of the plane. 

Pull up is different .

 

The La 5 FN has 600 - 650 kpm maximun speed in dive allowed in pilot manuals. I don´t remember exactly now.

Maybe someone can correct me.. 

The FM in Dive is wrong for all planes. or uncompleted

Edited May 14, 2014 by Mustang

[AbortedMan]

The FM in Dive is wrong for all planes.

In old IL2 1946 you loose parts and surface controls at 650 km in a Lagg 3 or any in russian plane practically... 

 

In BoS I Can dive a Lagg 3 up to 800+ kph  , without losing parts of the plane. 

Pull up is different .

 

The La 5 FN has 600 - 650 kpm maximun speed in dive allowed in pilot manuals. I don´t remember exactly now.

Maybe someone can correct me.. 

The FM in Dive is wrong for all planes. or uncompleted

They are incomplete...the Yak1 loses ailerons around just below ~700kph, but the LaGG-3 does not lose them at all. I'm sure they will be revised at some point.

[AbortedMan]

So how does everyone feel about the trim wheel negating the effects of control stiffening during a dive? Given that the pivot points provided earlier are legit and points of leverage were strong enough to do so...is trim pulling a valid tactic or "gaming the game"?

[AX2]

@ Extreme_one

 

You can't use a comparison with another game/sim when complaining about the FM of BoS.

The developers are using factual recorded data to model the planes in their sim.

Thankfully they're not listening to speculation, guesswork or hearsay.
How do you, or anyone, know if the FM/DM of the other game/sim is correct?

 

 

 

IL2  1946 +/-  mods = thousands of people + 10 years of research in forums

IL2 1946 +/-  mods = many MANY fights in forums for years about FM/DM,

IL2 1946 +/-  mods = thousands of pages of information, posted in forums

 

I can use a comparison .

Edited May 14, 2014 by Mustang

[Tab]

They are incomplete...the Yak1 loses ailerons around just below ~700kph, but the LaGG-3 does not lose them at all. I'm sure they will be revised at some point.

Lagg loses them too around 800 700 kph (800 was TAS, sorry) and not only ailerons, but also elevator and rudder surfaces

 

@ Extreme_one

 

 

 

IL2  1946 +/-  mods = thousands of people + 10 years of research in forums

IL2 1946 +/-  mods = many MANY fights in forums for years about FM/DM,

IL2 1946 +/-  mods = thousands of pages of information, posted in forums

 

I can use a comparison .

you still bring a computer game as a reference...

Edited May 14, 2014 by Tab

[AX2]

 

 

If you believe something is incorrect then you need to post factual information with verifiable sources.

 

 

Yes LA5 FN pilots manuals say 

Diving is permitted up to speed of 650 kph

 

@ Extreme_one

Need a screen shot ?

 

Ofcourse a La 5 can´t open fire at full power or the bullets hit the propeller, maybe need a screenshot of the pilots manual ? 

 

 

 

[AbortedMan]

Ofcourse a La 5 can´t open fire at full power or the bullets hit the propeller, maybe need a screenshot of the pilots manual ? 

 

 

 

Has anyone tested that in-game?

[AX2]

@ TAB

 

you still bring a computer game as a reference...

 

Sorry I forget... the BoS is a computer game ... or not ??

[AbortedMan]

@ TAB

 

Sorry I forget... the BoS is a computer game ... or not ??

Any computer game is not a representation of official and/or credible data in which to base another historically accurate game on. 

[Sokol1]

In red the (Bf 109) horizontal stabilizer mechanism adjust.

 

http://i42.tinypic.com/sl2ts6.png

 

Sokol1

[BlitzPig_EL]

Trim on a slider, FTW.

 

Everything old is new again...

 

[AbortedMan]

In red the (Bf 109) horizontal stabilizer mechanism adjust.

 

http://i42.tinypic.com/sl2ts6.png

 

Sokol1

I'm no engineer, but by that schematic it seems the trim wheel should be extremely hard to turn under high pressure conditions.

[216th_Jordan]

I'm no engineer, but by that schematic it seems the trim wheel should be extremely hard to turn under high pressure conditions.

 

I guess it would not really matter since the Stabilizertrim works with a screw and you trade force for way of movement and you don't have to apply constant force because the screw just stays in its position. 

 

Also compressability is not about the strength you need for control, it's about that whatever strenght you use it will have no effect on control, because the control surface is effectively in a vacuum.

[AX2]

Sorry for the offtopic.

I want to answer to AbortedMan    

 

 

1 ) La 5  FN  pilots manuals quotes :

 

A) Diving is permitted up to speed of 650 kph

B) For flights at altitude of 1500-2000m use the boost and to do that push throttle and propeller pich controls as far forward as they will go such that revolutions per minute is 2500 and manifold pressure is 1180mm Hg. Boost cannot be used for longer than 5 minutes.

C) Synchronous firing can be made under various conditions of engine speed from 1300 - 2400 revs/min

D) Diving do not allow propeller to turn at spees greater than 2600 RPM for longer than 30 Seconds

Has anyone tested that in-game?

 

( We have only a  La 5 Not La 5 FN, BUT  Magically in BOS, La 5  at Diving the RPMs remain sharply 2420 - 2450 revs/min,  the problem  of the plane in real life,  was artificially fixed  in game,  for over revs in dive, and Synchronous fire through the propeller, also in real life a La 5 FN can not do Synchronous fire at 2500 revs / min  = Boost condition)

Edited May 15, 2014 by Mustang

[JtD]

Because of strong nose down tendencies in a dive, it was dangerous to use the trim in the 109 to get it out of it. When losing speed upon pulling out, thereby getting rid of the nose down tendency, it was easy to overload the airframe if you weren't careful. It was better to permanently fly the 109 with a slight nose up trim, so in the dive it would not get so nose heavy to make it impossible to pull it out with stick alone, and avoid touching the trim wheel in the dive. Some pilots also recommended a little nose up trim for added manoeuvrability in other situations, so overall it seems to be a good recommendation. The downside is you'll need a hand on the stick to push forward all the time, in real life certainly more tiresome than on a desk.

[AbortedMan]

Sorry for the offtopic.

I want to answer to AbortedMan    

 

 

1 ) La 5  FN  pilots manuals quotes :

 

A) Diving is permitted up to speed of 650 kph

B) For flights at altitude of 1500-2000m use the boost and to do that push throttle and propeller pich controls as far forward as they will go such that revolutions per minute is 2500 and manifold pressure is 1180mm Hg. Boost cannot be used for longer than 5 minutes.

C) Synchronous firing can be made under various conditions of engine speed from 1300 - 2400 revs/min

D) Diving do not allow propeller to turn at spees greater than 2600 RPM for longer than 30 Seconds

 

 

( We have only a  La 5 Not La 5 FN, BUT  Magically in BOS, La 5  at Diving the RPMs remain sharply 2420 - 2450 revs/min,  the problem  of the plane in real life,  was artificially fixed  in game,  for over revs in dive, and Synchronous fire through the propeller, also in real life a La 5 FN can not do Synchronous fire at 2500 revs / min  = Boost condition)

Thanks for this...it would help greatly if you could make a photo copy of that page in the manual and post it in a separate thread. I feel that would be a great feature of realism in BoS.

[6./ZG26_5tuka]

This stabilizer isn't bugged ingame, it's just working as it should (maybe even too less effective at high arispeeds).

 

Using the stabilizer to pull up form a fast dive was a common practise among Bf109 pilots, there is even a document describing the procedure of using it to pull a Bf 109 out of 750-800km/h dive (it is clearly mentioned that the pilot had to pay much attention in not movng the trim wheel too far as it could have caused an instant and airframe overstressing pull up otherwise).

 

In BoS the trim wheel doesn't seem to cause such rapid reactions but still it's key feauture is implemented correctly.

 

Moving stabilizers were infact a vital in avoiding loss of elevator authority during high speed flight with compressebility effect as their effective area of attack is much larger than on common elevators, which means pilto has still some little controllebility while compressebility occurs (that's the reason why Sabres, Mig-15s and other after war jets got moving stabilizers as well).

[Crump]

This stabilizer isn't bugged ingame, it's just working as it should (maybe even too less effective at high arispeeds).

 

Using the stabilizer to pull up form a fast dive was a common practise among Bf109 pilots, there is even a document describing the procedure of using it to pull a Bf 109 out of 750-800km/h dive (it is clearly mentioned that the pilot had to pay much attention in not movng the trim wheel too far as it could have caused an instant and airframe overstressing pull up otherwise).

 

In BoS the trim wheel doesn't seem to cause such rapid reactions but still it's key feauture is implemented correctly.

 

Moving stabilizers were infact a vital in avoiding loss of elevator authority during high speed flight with compressebility effect as their effective area of attack is much larger than on common elevators, which means pilto has still some little controllebility while compressebility occurs (that's the reason why Sabres, Mig-15s and other after war jets got moving stabilizers as well).

 

[BlackDevil]

Because of strong nose down tendencies in a dive, it was dangerous to use the trim in the 109 to get it out of it. .

No, it. was even recommended.

 

 

It was better to permanently fly the 109 with a slight nose up trim,...

Where did. you get this nonsense from ?

[Panzerlang]

No, it. was even recommended.

 

 

 

Where did. you get this nonsense from ?

 

It's how most of the real guys flew them.

[DD_bongodriver]

We also have historical accounts of 109's not being able to pull out of dives and evidence that MTT made tests on this specific issue.

[Crump]

 

Here is the high speed flight investigation of the Bf-109.  It has been discussed before.....

 

Diving_Test_109F_W.Nr.9228_ger_eng.pdf

 

http://forum.il2sturmovik.com/topic/4948-fw-190-and-bf-109-longitudinal-stability-and-control/?p=103779

 

http://forum.il2sturmovik.com/topic/4948-fw-190-and-bf-109-longitudinal-stability-and-control/

 

http://forum.il2sturmovik.com/topic/5790-109-elevator-effectiveness/

[DD_bongodriver]

Yes, as discussed before it was noted MTT considered the 109 elevator authority insufficient, it lacked directional stability and had to have tests conducted using a modified airframe, the result of the test called for a fleet wide imposition of a reduced speed limit until such time the required modifications were implemented, these came with the late G models, these are all facts taken directly from the provided sources and the provided links to previous threads all proved this conclusively.

 

Stability and control standards become redundant once an aircraft produced under them displays characteristics of chronic directional instability that lead to documented cases catastrophic failure.