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von_Michelstamm

Should the 109 stabilizer be affected by compressibility?

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Seems odd that a pilot in a dive  at great speed would have to fight the stick to pull up, but could spin the stabilizer wheel to regain lift, as is presently implemented in game. Did it really work like this?

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I'm sure the stabilator and elevator were used in tandem. I think because it is changing the angle of incidence of the entire stabilizer by pushing or pulling on its trailing edge, there is no hinge moment as there is from a hinged control surface that is constantly trying to align itself with the airfoil in front of it.

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45 minutes ago, von_Michelstamm said:

Seems odd that a pilot in a dive  at great speed would have to fight the stick to pull up, but could spin the stabilizer wheel to regain lift, as is presently implemented in game. Did it really work like this?

 

You're meant to hold a 109 in the dive by pushing the stick forward exactly because it was working like this. It takes a pilot several minutes to operate the trim wheel while on the ground and not preoccupied with the earth rushing up at him.

 

And why would an airframe conceived at a time where compressibility wasn't very well understood (or even, y'know, known) not be affected by it?

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55 minutes ago, von_Michelstamm said:

Did it really work like this?

 

Depends on the linkage and hinge-moments (well, jackscrew-moments actually - see the current issues with the 737Max and their "hand-cranking the stabilizer" procedure).

Unless the required moment exceeds the moment a pilot could provide through the wheel (or the electric actuator in the 190), usuing the stab is very effective.

 

In fact, it's so effective that using the stab to trim out of the dive was a big no-no, as the return to normal subsonic flow comes along with a greatly increased stabilizer-effictiveness, leading to a very pronounced dig-in with a possible over-g.

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If you put a bar under a car with a fulcrum and use it as a lever, its highly unlikely you will lift the car. But if you put a jackscrew lift under it, you can almost lift the car by rotating the screw with your bare hand; it just takes a lot longer.

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One question I have is should the stabilizer decrease in effectiveness (speed) the faster you go? Could you really move the stabilizer at the same speed like in game even when hitting compressability?

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The ability to change the bf109's stabiliser's position at speeds of 700km and above has long been a point of frustration as it is unrealistic and allows the bf109 to perform combat maneuvers that are unrealistic.

 

This allows the bf109 to use a -75 (%) trim for the high speed dive and when at speeds of 750km to then set the trim to +75 (or insert any other number here) to pull out without hitting the ground or on the 6 of a low flying Russian plane.

 

This is compounded by the fact that the stabiliser can used at the same time as the throttle which are on the same hand and not only that the speed in which one can trim up and down while pulling 2-3g's and inverted is a tad ridiculous.

 

There is also the contentious implementation of the bf109 trim being linked to the forward/back axis of the joystick.

 

This allows for unrealistic use and advantages for the bf109... and I suspect ever the 190.

 

 

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15 hours ago, Bremspropeller said:

 

Depends on the linkage and hinge-moments (well, jackscrew-moments actually - see the current issues with the 737Max and their "hand-cranking the stabilizer" procedure).

Unless the required moment exceeds the moment a pilot could provide through the wheel (or the electric actuator in the 190), usuing the stab is very effective.

 

In fact, it's so effective that using the stab to trim out of the dive was a big no-no, as the return to normal subsonic flow comes along with a greatly increased stabilizer-effictiveness, leading to a very pronounced dig-in with a possible over-g.

 

Interesting.

What is the source for this? LW pilot handbooks?

 

and using the stab wouldn’t feel drastically different even at really high speeds?

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17 hours ago, von_Michelstamm said:

Seems odd that a pilot in a dive  at great speed would have to fight the stick to pull up, but could spin the stabilizer wheel to regain lift, as is presently implemented in game. Did it really work like this?

 

"Regain lift"?  What makes you think it has lost lift?

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Posted (edited)

Flying tails (all moving tail surfaces) have much higher controll effectiveness at high mach speeds hence why early korean war jets were fitted with them. For the 109 compressebility was known but the wrong use of trim lead to accidents (if trimed all the way forward the aircraft was hard to pull out, if trim was adjusted at high airspeeds it could lead to overcorrection and structual failure). To minimise the accident rate the forward trim range has been limited on the Bf 109 G series onward so that the aircraft always became slightly tailheavy at high airspeeds and recoverable by stick.

 

If you ever get to fly an aircraft with a flying tail you'll sure notice the great difference it makes across the speedrange.

 

Edited by 6./ZG26_5tuka
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3 minutes ago, 6./ZG26_5tuka said:

To minimise the accident rate the forward trim range has been limited on the Bf 109 G series onward so that the aircraft always became slightly tailheavy at high airspeeds and recoverable by stick.

 

If you ever get to fly an aircraft with a flying tail you'll sure notice the great difference it makes across the speedrange.

 

 

Sorry for this potentially silly question- but does that mean that the G model machines have better pitch maneuverability/control authority with this change?

 

Regards

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9 hours ago, Fangthane said:

and I suspect ever the 190.

You can't use the 190 stabilizer on an axis, which makes sense as IRL the stabilizer trim was set with buttons, too.

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2 hours ago, 6./ZG26_5tuka said:

Flying tails (all moving tail surfaces) have much higher controll effectiveness at high mach speeds hence why early korean war jets were fitted with them. For the 109 compressebility was known but the wrong use of trim lead to accidents (if trimed all the way forward the aircraft was hard to pull out, if trim was adjusted at high airspeeds it could lead to overcorrection and structual failure). To minimise the accident rate the forward trim range has been limited on the Bf 109 G series onward so that the aircraft always became slightly tailheavy at high airspeeds and recoverable by stick.

 

If you ever get to fly an aircraft with a flying tail you'll sure notice the great difference it makes across the speedrange.

 

So in other words, a pilot in a n f4 diving at 700km would have the ability to spin the wheel using their arm strength, but there was a good chance that the stabilizer or something else would break, which currently isn’t modeled?

was the stabilator geared at all? Seems with out different gears, like a bike, it would be a lot harder to spin the wheel at high speed vs low speed, due to air resistance. Sort of like pedaling up a steep hill in first gear on a bicycle...

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Posted (edited)
6 hours ago, von_Michelstamm said:

So in other words, a pilot in a n f4 diving at 700km would have the ability to spin the wheel using their arm strength, but there was a good chance that the stabilizer or something else would break, which currently isn’t modeled?

That is not the issue. The problem is that when you‘re getting close to critical Mach, you center of lift moves aft rather quickly. This results in the „Mach tuck“. You suddenly need to pull more to keep the nose level at a flight speed where it is getting difficult to give control inputs. On the other hand, the faster you go, the more effective trim will be. Little trim input at hight speed will cause more control input than you could give on the stick  with all your might. At low speed you might be able to deflect controls sufficiently to counteract trim. At high speeds, this will be impossible. Stab trim is even more effective than Flettner trim, making it the trim mechanism of choice for planes traveling near critical Mach as you can readily counter even drastic changes in center of lift without much interference to you stick controls.

 

In neither case the trim wheel will be hard to move. But if you are experiencing the Mach tuck (this is not exactly at „critical Mach“) and you use trim to make you control centered again, just a slight deceleration can cause your center of lift jumping back to a regular place, resulting in an immediate and drastic nose up trim. You are still traveling fast enough to potentially exceed the structural limits of the aircraft with strong stick inputs.

 

This is what likely happens in a dive using trim. Stab trim makes it just worse as it is easier to give even stronger inputs. You are diving full bore and you notice that suddenly your aircraft plunges more forward, you hardly being able to hold it in the dive. Turning the elevator trim backward to ease stick pressure will initially do just that, but as soon as you are starting to pull out, you aircraft will slow down. Together with reaching a denser atmosphere (increasing Mach speed), you center of lift suddenly jumps forward again making your aircraft pitch up at once. Depending on your settings, this pitch up can be hard enough to black out the pilot or even do structural damage.

 

The stabilizer will only break when you crash. This is why you should have your aircraft trimmed such that you strongly have to push it into the dive. As soon as you experience Mach tuck, the stick forces will ease off. When you pull out on the stick, all you end up with is an aircraft with a controllable trim.

 

6 hours ago, von_Michelstamm said:

was the stabilator geared at all? 

It is a worm gear. Yes. Easy to turn at any speed. 

5-23.gif

Edited by ZachariasX
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Posted (edited)

I see, so the game isn’t wrong, just simplistic, and if anything the stab effect at speed (or rather when recovery starts) isn’t drastic enough (rather than giving the pilot gamey superhuman arm strength.)

Edited by von_Michelstamm

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46 minutes ago, von_Michelstamm said:

I see, so the game isn’t wrong, just simplistic, and if anything the stab effect at speed (or rather when recovery starts) isn’t drastic enough (rather than giving the pilot gamey superhuman arm strength.)

I wouldn‘t know if the trim is not efficient enough. But what‘s for sure, you cannot keep trimming when you‘re at high g‘s. But the devs are considering pilot work loads. So this ability to trim might be subject to change.

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4 hours ago, von_Michelstamm said:

I see, so the game isn’t wrong, just simplistic, and if anything the stab effect at speed (or rather when recovery starts) isn’t drastic enough (rather than giving the pilot gamey superhuman arm strength.)

The ability to change the bf109's stabiliser's position at speeds over 560km (350mph) I.A.S. are wrong and they are giving the pilot 'super' human strength as per the allied testing of a 109 G-2.

 

Source: M.E. 109 G-2. Tactical Trails

  • The rudder is fairly heavy but not uncomfortably so. As there is no rudder trimming device, it is necessary to apply right rudder for take-off and left rudder at high speeds. The ailerons become increasingly stiff with the increase in speed especially at speeds in excess of 350 I.A.S. At speed below 180 I.A.S. the ailerons are not positive and as the stall is approached they are almost non-effective. The elevators also become increasingly difficult to operate as the speed increases. Above 350 I.A.S. this unpleasantness is accentuated as the elevator trim is practically impossible to operate.

Source: M.E. 109 G-2. Summary of Technical Trials carried out in Middle East

  • The Elevators harden up at high speeds and retrimming is necessary, which is difficult as the twin wheel hardens up and becomes almost solid in a dive. Some force is needed on the stick, but accelerations as high as the pilot can stand can be put on.

 

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3 minutes ago, Fangthane said:

The ability to change the bf109's stabiliser's position at speeds over 560km (350mph) I.A.S. are wrong and they are giving the pilot 'super' human strength as per the allied testing of a 109 G-2.

 

Source: M.E. 109 G-2. Tactical Trails

  • The rudder is fairly heavy but not uncomfortably so. As there is no rudder trimming device, it is necessary to apply right rudder for take-off and left rudder at high speeds. The ailerons become increasingly stiff with the increase in speed especially at speeds in excess of 350 I.A.S. At speed below 180 I.A.S. the ailerons are not positive and as the stall is approached they are almost non-effective. The elevators also become increasingly difficult to operate as the speed increases. Above 350 I.A.S. this unpleasantness is accentuated as the elevator trim is practically impossible to operate.

Source: M.E. 109 G-2. Summary of Technical Trials carried out in Middle East

  • The Elevators harden up at high speeds and retrimming is necessary, which is difficult as the twin wheel hardens up and becomes almost solid in a dive. Some force is needed on the stick, but accelerations as high as the pilot can stand can be put on.

 

 

Considering the 262 has had its hydraulics limitation implemented (either you operate the flaps or the gear, not both at the same time), I think it would be trivial for the devs to implement something similar for the 109s at high airspeed.

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9 hours ago, Fangthane said:

The ability to change the bf109's stabiliser's position at speeds over 560km (350mph) I.A.S. are wrong and they are giving the pilot 'super' human strength as per the allied testing of a 109 G-2.

. Above 350 I.A.S. this unpleasantness is accentuated as the elevator trim is practically impossible to operate.

Source: M.E. 109 G-2. Summary of Technical Trials carried out in Middle East

  • The Elevators harden up at high speeds and retrimming is necessary, which is difficult as the twin wheel hardens up and becomes almost solid in a dive. Some force is needed on the stick, but accelerations as high as the pilot can stand can be put on.

 

 

Yet there is lots of pilot memoirs where they recover from steep +700km/h dives by using trim wheel. While it stiffen probably quite lot at extreme speeds, it definitely was not impossible to operate.

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It wasn't once they changed the grease to a kind that didn't freeze at high altitude. Unless of course the whole system was in poor shape or poorly maintained. But even if things were imperfect, it only was "almost solid" and "practically impossible", not solid or impossible to operate.

 

It should be mentioned that "light" operation of the Bf109's trim at high speed would be undesired, because it could easily lead to accidents, given that it was extremely effective. So the desired condition would require a meaningful but exertible force.

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The stab traim on the 109 is relatively lightly geared. You need very few turns to make it travel acrosse the whole range. This means you need to tighten up the wheel a bit for not making coarse movements. At low speeds it is desirable that you can readily give a lot of stab inputs, especially to quickly offset severe flap and gear related lift changes. But at high speeds, this is an open invitation for breaking up your airframe. At high speeds, the trim wheel becomes VERY sensitive. But in order to make it stuck, it had to have issues with the worm gear, as JtD says. either frozen and/or bad lubrication. A worm gear is a very powerful gearing. Also, moving the stab takes very little force. It is so light that for instance the Piper Cherokee (etc.) use an anti-servo tab to make the elevator stiffen up. Besides, the stab would want to travel to any angle other then 0° AoA (unless you counteract with the stick against your trim input), meaning it would want to go in the direction of a pull-up.

 

Airliners have a much higher gearing. Here, you can see how much it actually takes to move the stab over only part of the whole travel:

Spoiler

 

If you have a trim motor working against you and you're not immedialely slowing down such that you can override trim effect with your stick (and then have your help wind that wheel), you're in serious trouble. As it has been demonstrated repeatedly.

 

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"Me 109 G:
"The maximum speed not to be exceeded was 750kmh. Once I was flying above Helsinki as I received a report of Russkies in the South. There was a big Cumulus cloud on my way there but I decided to fly right through. I centered the controls and then something extraordinary happened. I must have involuntarily entered into half-roll and dive. The planes had individual handling characteristics; even though I held the turning indicator in the middle, the plane kept going faster and faster, I pulled the stick, yet the plane went into an ever steeper dive. 
In the same time she started rotating, and I came out of the cloud with less than one kilometer of altitude. I started pulling the stick, nothing happened, I checked the speed, it was about 850kmh. I tried to recover the plane but the stick was as if locked and nothing happened. I broke into a sweat of agony: now I am going into the sea and cannot help it. I pulled with both hands, groaning and by and by she started recovering, she recovered more, I pulled and pulled, but the surface of the sea approached, I thought I was going to crash. I kept pulling until I saw that I had survived. The distance between me and the sea may have been five meters. I pulled up and found myself on the coast of Estonia. 
If I in that situation had used the vertical trim the wings would have been broken off. A minimal trim movement has a strong effect on wings when the speed limit has been exceded. I had 100kmh overspeed! It was out of all limits.
The Messerschmitt's wings were fastened with two bolts. When I saw the construction I had thought that they are strong enough but in this case I was thinking, when are they going to break 
- What about the phenomenon called "buffeting" or vibration, was there any? 
No, I did not encounter it even in the 850kmh speed."
- Kyösti Karhila, Finnish fighter ace. 32 victories. Source: Interview by Finnish Virtual Pilots Association."
 

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8 hours ago, Dark_P said:

The planes had individual handling characteristics;

If you want to pi** off the FAA, present them with production series aircraft that have just that.

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10 hours ago, Dark_P said:

"Me 109 G:
"The maximum speed not to be exceeded was 750kmh. Once I was flying above Helsinki as I received a report of Russkies in the South. There was a big Cumulus cloud on my way there but I decided to fly right through. I centered the controls and then something extraordinary happened. I must have involuntarily entered into half-roll and dive. The planes had individual handling characteristics; even though I held the turning indicator in the middle, the plane kept going faster and faster, I pulled the stick, yet the plane went into an ever steeper dive. 
In the same time she started rotating, and I came out of the cloud with less than one kilometer of altitude. I started pulling the stick, nothing happened, I checked the speed, it was about 850kmh. I tried to recover the plane but the stick was as if locked and nothing happened. I broke into a sweat of agony: now I am going into the sea and cannot help it. I pulled with both hands, groaning and by and by she started recovering, she recovered more, I pulled and pulled, but the surface of the sea approached, I thought I was going to crash. I kept pulling until I saw that I had survived. The distance between me and the sea may have been five meters. I pulled up and found myself on the coast of Estonia. 
If I in that situation had used the vertical trim the wings would have been broken off. A minimal trim movement has a strong effect on wings when the speed limit has been exceded. I had 100kmh overspeed! It was out of all limits.
The Messerschmitt's wings were fastened with two bolts. When I saw the construction I had thought that they are strong enough but in this case I was thinking, when are they going to break 
- What about the phenomenon called "buffeting" or vibration, was there any? 
No, I did not encounter it even in the 850kmh speed."
- Kyösti Karhila, Finnish fighter ace. 32 victories. Source: Interview by Finnish Virtual Pilots Association."
 

Also:

http://www.virtualpilots.fi/hist/WW2History-TaniHuotariEnglish.html#vertical1

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My understanding about compressibility is that this make all controlls non workable due to aerodynamic effect. Recovery from such endeavor have happened by applying all muzzles on the stick until you get to denser air at lower altitude.   

I read a lot about this conserning p39, Vougt corsair and some other types i cant remember. 

I never really read anything about such condition on lw plabes so it is very interesting read. I guess they had pretty much sane issues. 

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