Bf 109 elevator trim

This may excessively limit pitch rates as the elevator becomes biased either to far forward or aft. Or the position needed to establish stick free neutral position is beyond the capabilities of the trim system. Lastly, trimming the stabilizer forward may result in an uncomfortable stick position for the pilot.

 

The solution here being to add trim tabs, as the stick free natural point can remain in the centered position within the given range of motion of the controls. However the trim tabs increase the area of the elevator, which also increase it’s effectiveness. So with trim tabs installed the pitch rate for a given elevator deflection increase. To limit these pitch rates you limit the elevator deflection.

:thumbup:

After having given up on asking for it, starting 2 yrs ago, I was tempted to believe it's actually some limitation in the DCS flight dynamics for these combination of elevator + stabilator + elevator trim tabs....

 

In another ww2 sim I use they're set, for nose heavy, and we can see the elevator deflect down just from propwash when we apply takeoff power... The aircraft also handles more plausibly / harmoniously IMO.

oh yeah i did notice it too wow :) elevator is pushed down when power coming in

Oh, come on.. See, thats the problem. Even though you guys know its wrong, the answer always is nothing to see here, please move on.

 

 

 

Yes, I do also trust the sources. Thats why all my arguments are built around them. (Btw the same sources as Yo-Yo) And I trust YoYo in general, he seems to be a good & knowledgable engineer. Yet I know nobody is infallible. Even YoYo corrected several areas of the K-4 FM alone based on discussion/ documentation in the forums in the past

 

 

 

Well, maybe you dont... I addressed it in one of my posts. Take the DCS K-4 to 4000m, MAC 23%, set the stab to 0°, turn the engine to idle, hit Ctrl + Z twice, observe. Finally compare to soviet test.

 

 

 

Aaah, the famous hearsay. Does it even make sense to ask you for sources here? Someone in this forum said feel, opinions and hearsay dont count a penny, or something like that.

 

 

 

Actually I did in all detail, you even quoted the post.

 

Honestly, why are we even still discussing this? Everybody makes mistakes and thats not a problem as long as you dont act like it never happened and everybody else is stupid. The mistakes in drag, roll rate, level speed all were corrected eventuelly and everybody was grateful to ED afterwards. Why is this matter such a religion?

What's your answer to that question again?

...and in my opinion it is a valid question.

I know you guys will not stop to dispute the FM anyway, if ED adds the trim someone will chime in with why it's different/wrong etc. but that can't be helped. I really should try to stay away from these discussions. ;)

https://forums.eagle.ru/showthread.php?p=3908355

What's your answer to that question again?

...and in my opinion it is a valid question.

I know you guys will not stop to dispute the FM anyway, if ED adds the trim someone will chime in with why it's different/wrong etc. but that can't be helped. I really should try to stay away from these discussions. ;)

And I believe I gave a very valid answer, even detailed it into 3 seperate parts. I attached it again below for your enjoyment.

I think by now three people tried to explain that stab trim and trim tabs act differently. You clearly have no engineering background whatsoever and yet you somehow have an opinion that is supposedly more correct & relevant than any proof presented. Then again you demand hard proof from everybody else. So me and others posted proof in form of documents, explained context, answered questions and you simply deny it based on:

Flying for prolonged times at 1.35 AtA requires pushing the stick, as far as I heard from pilot interviews and hearsay it was like that in the real plane.

God, how could the laws of physics be so wrong!? Have they not heard the hearsay yet!? Mind blown.

...and...

Anyway I trust his knowledge and sources more than the usual "could, should, would have" arguments...

I could agree on your last post, that you should stay away of these discussion, that would have probably been better. Ok, I am just pulling your finger here. But please, just calm the nerves and have a think about what we are really saying.

So lets get to the answer why we would want trim tabs in addition to stab trim.

 

First and most bluntly, because its historical. Thats simply how the 109 was constructed and used operationally. In the late models they were doubled in size because they were important features of longitudinal stability. Could they have redesigned the elevator mechanism to be more reasonable? Surely, but changing the production lines most likely wasnt feasable, so they improved on what they could work with. I mean, what are we simulating here, our own personal opinion how the 109 should have been designed & operated, or the real deal?

 

Second, the effects of stab and trim tabs are not the same and I have already emphasized on this. I dont want to repeat myself, just take the fact that elevator reversal can occur at stab incidence of +1,45° with double trim tabs but not at stab +1,45° with single trim tabs, where even +2° is ok. Maybe the sim doesnt model these effects, but in real life the effects are not the same! To that you are suggesting that instead of trimming nose down by tabs, we should actually just use the stab at higher positive values for some unknown safety reason. This is the very setting that causes elevator reversal and makes the plane unsafe!

 

Third, the maximum trim range clearly increases and it would be possible to trim the aircraft at combat cruise. In german manuals combat cruise (in contested airspace) was considered to be maximum permissible continous rating (1,35 ata for K-4) and not maximum fuel efficiency. In air combat patrols you would want to go as fast as your motor possibly allows, since at any moment a P-51 or Yak could jump you. And I am sure pilots would not have liked their aircraft to pitch up constantly because the lazy mechanic has not set the trim tabs to anything but neutral.

Sure, why not? First of all Mach effects. Above critical Mach subersonic flow at the front of the airfoil causes normal shock which leads to boundary layer seperation in the trailing region. This may cause trim tabs and the whole elevator to become useless while stab adjustment still works. In the transsonic region it becomes actually very different as you must know.

Drag is different, you will not be able to reach the same trim at the same thrust. So different equilibrium speed.

I could think of another thing due to different pressure distribution but we touched on that earlier.

Also I kindly refer to what Curly said:

This may excessively limit pitch rates as the elevator becomes biased either to far forward or aft. Or the position needed to establish stick free neutral position is beyond the capabilities of the trim system. Lastly, trimming the stabilizer forward may result in an uncomfortable stick position for the pilot.

 

The solution here being to add trim tabs, as the stick free natural point can remain in the centered position within the given range of motion of the controls. However the trim tabs increase the area of the elevator, which also increase it’s effectiveness. So with trim tabs installed the pitch rate for a given elevator deflection increase. To limit these pitch rates you limit the elevator deflection.

Ok, but it is general information, but we are interesting in 109 IN DIVE and in (as far as I can see) full power trim in level flight.

So, your point, probably is that keeping 1.25 degrees to prevent a plane form unrecovered dive (the report gives us the direct proof of this reason) the trim tab magically put elevator down at lower speed, lower altitude and would never affect high speed/Mach diving... Hate doing it but I have to disappoint you - it's impossible, because the same report stated that trim tabs were used to make high speed power-on diving possible AT HIGH-SPEED/HIGH Mach. And, by the way, it was not mentioned if the trim wheel was used to recover after bending the trim tabs to nose-down.. I think, using the simple logic - yes.

 

So, my question is still actual.

 

And by the way, have you seen mentioned CRUISE seting as +1 degree?

I read a translation of Report. Nr. 109 05 E43 and it outlines why the changes the trim tab size was changed and set for nose down and why it’s not possible to use the trim system to good effect.

1. Due to the type of grease used in the trim system, the trim system would not function beyond the temperatures found above 9km in a dive.

2. Because the trim system could not function while in a dive, the force on the elevator was to great for the pilot push the craft into a dive beyond 30 degrees.

3. As a result of this a second series of test was conducted with the trim tabs at the elevator enlarged by 100%, doubling the trim tabs.

4. A first series of test was conducted with the enlarged trim tabs and it was found that it took to long to initiate a dive and that it was not possible to hold the angle of the dive when the engine was running at full power, due to torque effects of the motor.

5. If the trim setting was increased by just .5 degrees more nose heavy, than the craft became unrecoverable from a dive with the stick alone. This was problematic because the trim system was “just jerkily moveable” in a high speed dive.

6. The solution was to deflect the enlarged trim tabs to a nose heavy position. This resulted in forces that where similar to those found in the powered off dives. I.e. recoverable without the use of the trim system. Which wouldn’t have been operable.

The limits to movement of the stab angle where done as part of the testing protocols. To limit the effects of trimming on the results. As the trim system lacked the resolution to be reliable set to the same position throughout the testing. So they put a stopper in at the desired testing position. However it was found at this test position there was not sufficient elevator force to reach a dive angle of greater than 60 degrees at 100% power. Therefore the trim tab area was doubled, then deflected nose down to ensure adequate handling characteristics.

It seems that second series of test conducted with the enlarged trim tabs was done to find a way to make the craft recoverable without the use of the trim system. As it was considered non functional due to air loads and the grease in the jackscrew becoming frozen.

Question for Yo-Yo...

- Why would then, the German engineers, have chosen to install those trim tabs in the K-4, actually a pair of trim tabs easily seen ?

- Why would the reports mentioned by Curly refer the reasons for it's use ?

DCS is trying to simulate as close as possible the 109 K-4. You find that it doesn't make sense to have that solution, and it is counter-intuitive, so the decision is to simply truncate it by creating a fixed ( at zero deflection ) elevator trim tabs, because you think ( ? ) that's how the ww2 engineers, ground crew and pilots should have chosen to use it ?

I would accept a justification based on complexity of implementing this feature now, that the module is final, due to the fact that you are 1 ( one ) and there is a LOT of work to do because we all want more ww2 modules, and heck, as much as I am critical here, I also am here because DCS is second to none in details, interaction with modeled systems, precision - it's an Air Combat Study Sim, it's THE AIr Combat Study Sim, and pretty much the only one we have at that level and you should be "blamed" for that :-)

I just don't think that questioning the evident is of any use here in this thread. Both rel4y and Curly have done a REMARKABLE job in providing well founded justifications for the importance of modeling those elevator trim tabs.

Ok, but it is general information, but we are interesting in 109 IN DIVE and in (as far as I can see) full power trim in level flight.

So, your point, probably is that keeping 1.25 degrees to prevent a plane form unrecovered dive (the report gives us the direct proof of this reason) the trim tab magically put elevator down at lower speed, lower altitude and would never affect high speed/Mach diving... Hate doing it but I have to disappoint you - it's impossible, because the same report stated that trim tabs were used to make high speed power-on diving possible AT HIGH-SPEED/HIGH Mach. And, by the way, it was not mentioned if the trim wheel was used to recover after bending the trim tabs to nose-down.. I think, using the simple logic - yes.

 

So, my question is still actual.

 

And by the way, have you seen mentioned CRUISE seting as +1 degree?

Yo-Yo please.. lets stop this nonsense. You asked me to name an engineering difference in effect between trim tab and stab. I gave you several. The question was are stab and tab effects the same, because that is what was said earlier in this thread. NO, they are not. Do you disagree?

Then I gave two other pressing reasons why we need trim tabs on the 109. Did I not adress your question here? Do you honestly not see a reason to add trim tabs? My point is not what you put in my mouth but this! The second one is already addressed.

First and most bluntly, because its historical. Thats simply how the 109 was constructed and used operationally. In the late models they were doubled in size because they were important features of longitudinal stability. Could they have redesigned the elevator mechanism to be more reasonable? Surely, but changing the production lines most likely wasnt feasable, so they improved on what they could work with. I mean, what are we simulating here, our own personal opinion how the 109 should have been designed & operated, or the real deal?

 

Second, ...

 

Third, the maximum trim range clearly increases and it would be possible to trim the aircraft at combat cruise. In german manuals combat cruise (in contested airspace) was considered to be maximum permissible continous rating (1,35 ata for K-4) and not maximum fuel efficiency. In air combat patrols you would want to go as fast as your motor possibly allows, since at any moment a P-51 or Yak could jump you. And I am sure pilots would not have liked their aircraft to pitch up constantly because the lazy mechanic has not set the trim tabs to anything but neutral.

And, by the way, it was not mentioned if the trim wheel was used to recover after bending the trim tabs to nose-down.. I think, using the simple logic - yes.

The modelling must not be counter of fundamental laws. Any exceptions, that sometimes are possible to seem agains the laws must have concrete-hard documental proofs.

Sometimes, some speculations based on unproven facts or "I think it must be so" approach are deeply wrong (remember, please, X-wind propwash effect on the wing with flaps ).

Can you tell me how trimming the stab at lets say + 1° and setting the tabs to deflect the elevator ~3° downwards is violating that? Because that would set cruise trim to around combat cruise and is actually what was done in real life. The only thing deeply wrong is your argumentation here.

And, by the way, if we increase these limits the percentage of broken wings will be significantly higher.

109G wings were designed to withstand 10G + margin. I can show you a report where 10.5 Gs were reached. If the pilots violates that, its his own demise/death. I also remember earlier in this thread you said that it would have pretty much no effect at all. Why the sudden change of mind?

I am really sorry how the tone of discussion changed, because Id like to get things done in a civilized matter. But I also wasnt the one to call others stupid in the first place. Now it is just a pi**ing match. Yo-Yo, Id like to ask you again very politely to think about what we are saying and I would be happy for a week straight if youd give us elevator trim tabs. I think this will be my last post in this topic.

Btw, I saved this thread on the wayback machine, just in case somebody chooses to delete it for unknown reasons.

so did the german pilots flying this airframe in WW2 have these elevator trim tabs? If so i would think to be historically accurate they should be on the airframe in this sim? If not then...not. Kind of simple.?

The real question is did the pilots tweak them to their own desires, or were they set by the factory/mechanics to be in a specific criteria.

Pilots messing around with things like that on the ground without the ability to change it once in the air could have disastrous consequences.

The real question is did the pilots tweak them to their own desires, or were they set by the factory/mechanics to be in a specific criteria.

 

Pilots messing around with things like that on the ground without the ability to change it once in the air could have disastrous consequences.

There is a set of FLIR controls in the F-14B, yet it does not have a FLIR, as it was replaced by the TCS. The difference is, we have a good documentation for this change. For the BF.109 K4 there seems not much documentation on late war trim tab use to be around, so we can guess how they "must have been" used, if at all.

I could see some irony in putting the trim tabs in and maybe let people do what they want and complain about the issues deriving from tweaking the trim tabs next?

For a given fuel / amno load reference, say 60% fuel in the DCS 109 settings, ISA atmospheric conditions, and a given altitude, what will be the lowest power setting above which full nose heavy stabilator trim will not be sufficient to overcome the pitching up moment ?

Is it within continuous and combat power settings ? Is it emmergency ?

Whatever it is, the pilot will then have to exert a force, constant, pushing on the stick to maintain altitude.

If the trim tabs are then used / set on ground to a given deflection angle, this force will probably be eliminated for those same flight conditions, so, just as rudder and aileron trim tabs are adjusted to save the pilot from the need for constant rudder and / or aileron deflection at cruise why wouldn't it make sense to give him the very same chance regarding the use of down elevator ?

(...)Whatever it is, the pilot will then have to exert a force, constant, pushing on the stick to maintain altitude.

 

If the trim tabs are then used / set on ground to a given deflection angle, this force will probably be eliminated for those same flight conditions, (...)

...and all other flight conditions, as well, as you cannot climb out the cockpit and "reset" the trim tabs. If the alteration to the nose down trim now puts you in a position where you can accidentally get into a dive with no chance to recover, when you "forget" to adjust for your little trim tweak, or worst case can't trim for a safe landing anymore, you die. In real life most pilots I heard from died only once, and that encouraged most of them to be very careful to adjust, tweak and modify an airplane, unless not checked and double checked by an engineer who knows what he is doing...

So sure you can adjust the elevator with the trim tabs, maybe they did... once. May be they considered to limit the trim before or after they tested the trim tabs, so many "if", "could", "maybe", but no "Pilot XY usually adjusted his elevator trim tabs to XYZ, regularly to ease cruise flights above 1.3 AtA" or "the trim tabs were tested with desastrous results when adjusted in the field, so never used, after initial adjustment for neutral trim" or any other statement, other than their existance. Personally, I could live with the addition of the trim tabs and see what happens if people mess with them... just saying.

I do not see any logic here - because trim tabs and stab does the same job regarding stick forces. And this report shows that there is no magic separation of effects. From the science point of view, withinlinear area of incidence angles (few degrees, that is sufficient to get necessary G-load) hinge moments due to stab incidence or elevator deflection, stab CL changes caused by stab incidence or elevator deflection - they all presented in LINEAR partial derivatives (depending on Mach for sure).

 

Anyway, starting and maintaining dive (where this magic tab helps to nose-down elevator deflection) and recovering (where, as somebody wants, the trim tab must do NOTHING to prevent nose-down shift) are both performed at relatively high Mach region. I mean that nothing can be dramatically changed within this region (significant changes start from 0.85 M for typical stab with elevator).

Additionally somebody wants that this magic tab works again at low M for nose-down help... It's too much, isn't it?

 

And, I think , if Germans have found something magic they would emphasize this effect in the report.

 

By the way - they DID use stab trim to recover dive (see the left diagram).

That's correct in first test they pulled out of the dive with the trim system. In the second test they did not use the trim system and pulled out of the dive with the stick alone. The purpose of the tests conducted on Feburaruy 15 to March 12 1943, is explicitly stated in the notes.

"This trials started with idle dives to estimate an horizontal stabilizer trim setting that makes it possible to recover a dive with the stick. This setting was +1 degree 15 minutes and was blocked in the direction nose heavy by a stop to assure the same settings at every flight." "... After this the plane was pulled out of the dive just using the stick." As indicated by the chart on the right with the trim setting of +1 degree 15 minutes.

The reason why they wanted to know the trim position was because they considered pulling out of a dive with the trim alone unreliable.

"pulling out with the horizontal stabilizer trim is a potential danger (high g acceleration increase in the pull-out) so dive recover should be achieved without changing the position of the horizontal stabilizer."

"If you trim the elevator just .5 degrees more nose heavy the force in the direction push is less but it is not possible to recover just by using the stick, it is necessary to use the horizontal stabilizer trim. At high speed the horizontal stabilizer trim is heavy and just jerkily moveable." The reason these test were conducted was to "investigate insufficient elevator controls at high mach numbers". They were trying to make the craft safer by making it possible to recover from a dive with the stick alone.

They also ran into problems with this trim setting when testing powered on dives. The pilot could not maintain the necessary amount of push force needed to keep the aircraft in a dive with the power on.

“In a full throttle dive despite previous trim to +1.7° just 30° angle and IAS Va = 650 km/h at 6 km altitude was reached because the elevator trim was frozen, and the stick force was too high to push it farther forward”

"unlike idle dives it was not possible to hold the angle of dives at full throttle with the same trim setting, because the upward torque of the engine. Trim tabs were set to nose heavy to reach a similar force like in idle dives." Thus, a powered on dive with the trim set to +1 degree 15 seconds is only recoverable with the stick, if the trim tabs are set to a nose heavy position.

So why use the trim tabs to adjust the stick forces on the elevator during the powered on dive tests? It's the easiest way to change to hinge moment coefficient. So that desired elevator trim position can be achieved with same amount of force. As the hinge moment depends linearly on the tail angle of attack, the elevator deflection and the deflection of the trim tab angle.

Also, the notes indicate that there is a stopper on the trim system. So maybe it was quicker to just adjust the tabs then to adjust the stopper. Also we know from the report that the trim gauge "has an insufficient resolution" to make the small adjustments needed here.

Again, the purpose of these tests was to determine a trim position that allowed the pilot to recover from a high speed dive using only the stick. Since the differences between a successful and unsuccessful result is less than .5 degrees of trim; Adjusting the trim tabs seems like the easiest and most reliable to be able to achieve the desired test results.

The trim tabs are needed in the dive because nose down trim is limited by the stopper. During the dive elevator wants to return to the return hinge moment to zero, as the controls are reversible. The stick is pushing back against the pilot during the dive. Due to the high speed and increasing mach effects, the pilot cannot exert enough force on the stick to maintain a powered on dive at desired angle, <60, with the trim tabs set to neutral and the elevator trim limited to +1, 15'.

By decreasing the hinge moment via the trim tabs it is possible to deflect the elevator sufficiently to make the craft maintain the dive and be recoverable with the stick alone. As the pilot was incapable of pushing or keeping the elevator at the correct postion to maintain a dive angle greater than 60 degrees.

"During first flights the position of the stop unit was at +1°45'. The elevator forces at this stabilizer position were not sufficient to reach a dive angle greater than 60° at 100% power. Therefore, the surface area of the static trim tab was doubled."

No, the bundle of facts you quoted is not relevant to this case and I explained, why.

the derivative dmh/dsigma (hinge moment vs elevator deflection) remains the same regardless of what way you shifted zero moment and you have to apply the same force to get the same g at the same speed.

Changing the trim tab position changes the hinge moment, thus also changing the derivative dhm/disma.

The hinge moment of the elevator is Che = Che0 + dChe/d Alpha with respect to Alpha ht + d CHe / d sigma with respect to sigma e + dChe / dSigma Trim tabs with respect to Sigma of the trim tabs.

So by altering the trim tabs trailing edge down you change the hinge moment.

Curly,

I really can't think of anything clearer than your explanation above! :thumbup: :thumbup: :thumbup:

P.S.: But probably the developers of this module did have access to the report of the first test above, regarding the idle dives, where the risks of setting the trim tabs are described,

but not to the 2nd part where powered / full throttle dives are referred, and the reverse applies, making the setting of the trim tabs into nose-heavy positions understandable / advantageous.

In the end I honestly believe that all of the arguments presented so far are clearly in favor of an update to the current module, even if with low priority given that other modules should

by now be in development and probably taking a lot of time already from the dev team ( ? )

That's correct in first test they pulled out of the dive with the trim system. In the second test they did not use the trim system and pulled out of the dive with the stick alone. The purpose of the tests conducted on Feburaruy 15 to March 12 1943, is explicitly stated in the notes.

 

"This trials started with idle dives to estimate an horizontal stabilizer trim setting that makes it possible to recover a dive with the stick. This setting was +1 degree 15 minutes and was blocked in the direction nose heavy by a stop to assure the same settings at every flight." "... After this the plane was pulled out of the dive just using the stick." As indicated by the chart on the right with the trim setting of +1 degree 15 minutes.

 

The reason why they wanted to know the trim position was because they considered pulling out of a dive with the trim alone unreliable.

 

"pulling out with the horizontal stabilizer trim is a potential danger (high g acceleration increase in the pull-out) so dive recover should be achieved without changing the position of the horizontal stabilizer."

 

"If you trim the elevator just .5 degrees more nose heavy the force in the direction push is less but it is not possible to recover just by using the stick, it is necessary to use the horizontal stabilizer trim. At high speed the horizontal stabilizer trim is heavy and just jerkily moveable." The reason these test were conducted was to "investigate insufficient elevator controls at high mach numbers". They were trying to make the craft safer by making it possible to recover from a dive with the stick alone.

 

They also ran into problems with this trim setting when testing powered on dives. The pilot could not maintain the necessary amount of push force needed to keep the aircraft in a dive with the power on.

 

 

“In a full throttle dive despite previous trim to +1.7° just 30° angle and IAS Va = 650 km/h at 6 km altitude was reached because the elevator trim was frozen, and the stick force was too high to push it farther forward”

 

"unlike idle dives it was not possible to hold the angle of dives at full throttle with the same trim setting, because the upward torque of the engine. Trim tabs were set to nose heavy to reach a similar force like in idle dives." Thus, a powered on dive with the trim set to +1 degree 15 seconds is only recoverable with the stick, if the trim tabs are set to a nose heavy position.

 

So why use the trim tabs to adjust the stick forces on the elevator during the powered on dive tests? It's the easiest way to change to hinge moment coefficient. So that desired elevator trim position can be achieved with same amount of force. As the hinge moment depends linearly on the tail angle of attack, the elevator deflection and the deflection of the trim tab angle.

 

Also, the notes indicate that there is a stopper on the trim system. So maybe it was quicker to just adjust the tabs then to adjust the stopper. Also we know from the report that the trim gauge "has an insufficient resolution" to make the small adjustments needed here.

 

Again, the purpose of these tests was to determine a trim position that allowed the pilot to recover from a high speed dive using only the stick. Since the differences between a successful and unsuccessful result is less than .5 degrees of trim; Adjusting the trim tabs seems like the easiest and most reliable to be able to achieve the desired test results.

 

The trim tabs are needed in the dive because nose down trim is limited by the stopper. During the dive elevator wants to return to the return hinge moment to zero, as the controls are reversible. The stick is pushing back against the pilot during the dive. Due to the high speed and increasing mach effects, the pilot cannot exert enough force on the stick to maintain a powered on dive at desired angle, <60, with the trim tabs set to neutral and the elevator trim limited to +1, 15'.

 

By decreasing the hinge moment via the trim tabs it is possible to deflect the elevator sufficiently to make the craft maintain the dive and be recoverable with the stick alone. As the pilot was incapable of pushing or keeping the elevator at the correct postion to maintain a dive angle greater than 60 degrees.

 

"During first flights the position of the stop unit was at +1°45'. The elevator forces at this stabilizer position were not sufficient to reach a dive angle greater than 60° at 100% power. Therefore, the surface area of the static trim tab was doubled."

 

 

 

Changing the trim tab position changes the hinge moment, thus also changing the derivative dhm/disma.

 

The hinge moment of the elevator is Che = Che0 + dChe/d Alpha with respect to Alpha ht + d CHe / d sigma with respect to sigma e + dChe / dSigma Trim tabs with respect to Sigma of the trim tabs.

So by altering the trim tabs trailing edge down you change the hinge moment.

q.e.d. Bravo!!:thumbup:

Because trim tab and stab do the same thing regarding the hinge moment. Because the derivative dmh/dsigma (hinge moment vs elevator deflection) remains the same regardless of what way you shifted zero moment and you have to apply the same force to get the same g at the same speed.

No they dont, in school academics you are free to use it as approximation for small angles. In the real world you get kicked in the ass.

I cited the german report which speaks of Kraftumkehr im Höhenruder, that translates to elevator reversal.

Thanks Curly. I have honestly lost patience by now.

P.S.: But probably the developers of this module did have access to the report of the first test above, regarding the idle dives, where the risks of setting the trim tabs are described,

but not to the 2nd part where powered / full throttle dives are referred, and the reverse applies, making the setting of the trim tabs into nose-heavy positions understandable / advantageous.

It is the same test and in the abstract both cases are summarized.

Ok Yo-Yo,

I believe I'll try a different, much more practical / pragmatic approach!

Implement the adjustable elevator trim tabs, visit Portugal and I'll pay you a dinner with some excellent Portuguese wine !!!

What about that ? Can you refute it ?

Hey Yo-Yo,

There is so much smoke screen up I dont even know what we are disagreeing on anymore. So from human to human, would you please give us (your customers, critics and fans) an honest answer? Where exactly do you disagree with us?

We agree that the K gear ratio has changed, correct?

Can we also agree that trim tabs and stab trim in real life are accompanied by slightly different effects, but the approximation you are using is perfectly valid for small deflections?

The trim tabs were doubled in size on the K-4, correct?

For doubling the trim tabs the high speed trial report gives insufficient dive angle at 100% power as a reason, agreed?

After adding double trim tabs to get rid of elevator force reversal, the stab was limited to +1,15°. In that case the dive could be recovered with stab at constant +1,15° with elevator only, correct?

In this test the engineers set the trim tabs nose heavy and the stab to +1,15° to gain nose down authority, yes? (Not sure if this was posted yet, but here is the section of the test report stating that.)