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Bf 109 elevator trim


grafspee

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K-4 manual

1800767262_109Kstick.thumb.png.74e518a817a19c4bbaf88fc9b9c8def6.png

Ніщо так сильно не ранить мозок, як уламки скла від розбитих рожевих окулярів

There is nothing so hurtful for the brain as splinters of broken rose-coloured spectacles.

Ничто так сильно не ранит мозг, как осколки стекла от разбитых розовых очков (С) Me

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Yeah, that's from the front YoYo. Do you recognize the aileron axis to which the coat hanger bell crank is attached? Also the grip is rotated to the left for more comfort. You marked the sideways throw YoYo, the elevator is 38° and was never changed. I am in bed already, but I can provide you the pictures tomorrow.

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Yes, my fault :) was confused with asymmetric stick shape, By the way, was a bit surprised why these angles are at aileron control drawing. There are no stick angles at the elevator train drawing.


Edited by Yo-Yo

Ніщо так сильно не ранить мозок, як уламки скла від розбитих рожевих окулярів

There is nothing so hurtful for the brain as splinters of broken rose-coloured spectacles.

Ничто так сильно не ранит мозг, как осколки стекла от разбитых розовых очков (С) Me

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So if elevator transversal angle decreased that would mean that low speed turning capabilities would decrease and high speed would increase am i right ??

But this improved elevator trim tabs could be like late k-4 improvemenst ??


Edited by grafspee

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So if elevator transversal angle decreased that would mean that low speed turning capabilities would decrease and high speed would increase am i right ??

But this improved elevator trim tabs could be like late k-4 improvemenst ??

 

No, I do not think so. WWII fighters generally had oversized elevator authority, so the full travel never used to rich CL or g margins. This discussion has only scientific sense. Trim curves for K in respect of flight range of elevator deflection are generally the same as for G.

Ніщо так сильно не ранить мозок, як уламки скла від розбитих рожевих окулярів

There is nothing so hurtful for the brain as splinters of broken rose-coloured spectacles.

Ничто так сильно не ранит мозг, как осколки стекла от разбитых розовых очков (С) Me

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No, I do not think so. WWII fighters generally had oversized elevator authority, so the full travel never used to rich CL or g margins. This discussion has only scientific sense. Trim curves for K in respect of flight range of elevator deflection are generally the same as for G.

 

im not worried about elevator authority i am thinking if elevator transversal range changed and stick movment didnt it has to change something ??


Edited by grafspee

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So if elevator transversal angle decreased that would mean that low speed turning capabilities would decrease and high speed would increase am i right ??

But this improved elevator trim tabs could be like late k-4 improvemenst ??

 

Yes, in principal it does mean exactly that. But although the elevator forces are decreased by about 25-30%, the aerodynamic effect on them is not linear. Dynamic pressure increases with velocity squared.

 

No, I do not think so. WWII fighters generally had oversized elevator authority, so the full travel never used to rich CL or g margins. This discussion has only scientific sense. Trim curves for K in respect of flight range of elevator deflection are generally the same as for G.

 

Actually, there has to be a significant difference, let me explain why. But first I will post the elevator components. Between F and G-2 models the supply number did not change, which means that the parts were the same. The whole elevator transmission chain is basically unchanged except for two parts on the K-4.

 

Bf109-F-Ersatzteil-Liste-Elevator-mech4.jpgBf109-F-Ersatzteil-Liste-Elevator-mech5.jpg Bf109-F-Ersatzteil-Liste-Elevator-mech1.jpg Bf109-F-Ersatzteil-Liste-Elevator-mech2.jpg Bf109-F-Ersatzteil-Liste-Elevator-mech3.jpg

 

Inspecting these parts closely we will find that page 68 part 2 (=Kp2) and page 68 part 14 (=Kp3) were changed. The change in Kp2 will cause the difference in maximum deflection angle since the lever increased, while Kp3 will change the elevator zero incidence downwards at any given horizontal stab angle.

 

Bf-109-K-4-H-henruder-Mechanik.jpg H-henruder-Mechanismus.jpg

 

Now one of the more interesting parts is page 70 part 1, the counterweight. Considering that the elevator horns balance it aerodynamically and weight in these horns mass balance the elevator in respect to the hinge, this is an interesting part. What is it for then?

 

Well I tried to model the transmission chain in Solidworks and the effect is that it moves the stick forward in its neutral position with a higher mechanical lever than the elvator itself can. Considering that the stick is designed with more backwards travel than forward travel, it is pushing the stick in its upright neutral position at about 42% of stick travel.

 

In effect and together with the double trim tabs this will cause an aerodynamic as well mechanical downforce of the elevator and will depress its neutral position in respect to the horizontal stabilizer.

 

I am glad that finally people are listening, now it actually makes sense to calculate the stuff and correct it once and for all.


Edited by rel4y
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Yes, in principal it does mean exactly that. But although the elevator forces are decreased by about 25-30%, the aerodynamic effect on them is not linear. Dynamic pressure increases with velocity squared.

 

 

 

Actually, there has to be a significant difference, let me explain why. But first I will post the elevator components. Between F and G-2 models the supply number did not change, which means that the parts were the same. The whole elevator transmission chain is basically unchanged except for two parts on the K-4.

 

Bf109-F-Ersatzteil-Liste-Elevator-mech4.jpgBf109-F-Ersatzteil-Liste-Elevator-mech5.jpg Bf109-F-Ersatzteil-Liste-Elevator-mech1.jpg Bf109-F-Ersatzteil-Liste-Elevator-mech2.jpg Bf109-F-Ersatzteil-Liste-Elevator-mech3.jpg

 

Inspecting these parts closely we will find that page 68 part 2 (=Kp2) and page 68 part 14 (=Kp3) were changed. The change in part 2 will cause the difference in maximum deflection angle since the lever increased, while part 14 will change the elevator zero incidence downwards at any given horizontal stab angle.

 

Bf-109-K-4-H-henruder-Mechanik.jpg H-henruder-Mechanismus.jpg

 

Now one of the more interesting parts is page 70 part 1, the counterweight. Considering that the elevator horns balance it aerodynamically and weight in these horns mass balance the elevator in respect to the hinge, this is an interesting part. What is it for then?

 

Well I tried to model the transmission chain in Solidworks and the effect is that it moves the stick forward in its neutral position with a higher mechanical lever than the elvator itself can. Considering that the stick is designed with more backwards travel than forward travel, it is pushing the stick in its upright neutral position at about 42% of stick travel.

 

In effect and together with the double trim tabs this will cause an aerodynamic as well mechanical downforce of the elevator and will depress its neutral position in respect to the horizontal stabilizer.

 

I am glad that finally people are listening, now it actually makes sense to calculate the stuff and correct it once and for all.

 

Thanks for taking the time to investigate! We really appreciate the time and effort spent all these years! :thumbup:

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Yes, in principal it does mean exactly that. But although the elevator forces are decreased by about 25-30%, the aerodynamic effect on them is not linear. Dynamic pressure increases with velocity squared.

 

 

 

Actually, there has to be a significant difference, let me explain why. But first I will post the elevator components. Between F and G-2 models the supply number did not change, which means that the parts were the same. The whole elevator transmission chain is basically unchanged except for two parts on the K-4.

 

Bf109-F-Ersatzteil-Liste-Elevator-mech4.jpgBf109-F-Ersatzteil-Liste-Elevator-mech5.jpg Bf109-F-Ersatzteil-Liste-Elevator-mech1.jpg Bf109-F-Ersatzteil-Liste-Elevator-mech2.jpg Bf109-F-Ersatzteil-Liste-Elevator-mech3.jpg

 

Inspecting these parts closely we will find that page 68 part 2 (=Kp2) and page 68 part 14 (=Kp3) were changed. The change in Kp2 will cause the difference in maximum deflection angle since the lever increased, while Kp3 will change the elevator zero incidence downwards at any given horizontal stab angle.

 

Bf-109-K-4-H-henruder-Mechanik.jpg H-henruder-Mechanismus.jpg

 

Now one of the more interesting parts is page 70 part 1, the counterweight. Considering that the elevator horns balance it aerodynamically and weight in these horns mass balance the elevator in respect to the hinge, this is an interesting part. What is it for then?

 

Well I tried to model the transmission chain in Solidworks and the effect is that it moves the stick forward in its neutral position with a higher mechanical lever than the elvator itself can. Considering that the stick is designed with more backwards travel than forward travel, it is pushing the stick in its upright neutral position at about 42% of stick travel.

 

In effect and together with the double trim tabs this will cause an aerodynamic as well mechanical downforce of the elevator and will depress its neutral position in respect to the horizontal stabilizer.

 

I am glad that finally people are listening, now it actually makes sense to calculate the stuff and correct it once and for all.

Nice to see constructive feedback, based on precise evidence.

Shagrat

 

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Nice to see constructive feedback, based on precise evidence.

 

Yeah, that's the way to get stuff done and changed. Thanks Rel4y, good work and easily understandable :thumbup:

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Now one of the more interesting parts is page 70 part 1, the counterweight. Considering that the elevator horns balance it aerodynamically and weight in these horns mass balance the elevator in respect to the hinge, this is an interesting part. What is it for then?

 

 

It is a mean to move free control neutral point aft or to increase free stick stability. It works like an automatic feedback. For example, if you have CoG at the neutral point without this bobweight, the plane can change g-load as it wants regarding small air fluctuation, Moon gravity, etc. So, the pilot have to control the plane to maintain 1g for level flight. This bobweight is a g-load sensor as well as a servo deflecting the elevator to counteract g-load fluctuations.

Ніщо так сильно не ранить мозок, як уламки скла від розбитих рожевих окулярів

There is nothing so hurtful for the brain as splinters of broken rose-coloured spectacles.

Ничто так сильно не ранит мозг, как осколки стекла от разбитых розовых очков (С) Me

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Bf109-F-Ersatzteil-Liste-Elevator-mech4.jpgBf109-F-Ersatzteil-Liste-Elevator-mech5.jpg Bf109-F-Ersatzteil-Liste-Elevator-mech1.jpg Bf109-F-Ersatzteil-Liste-Elevator-mech2.jpg Bf109-F-Ersatzteil-Liste-Elevator-mech3.jpg

 

Inspecting these parts closely we will find that page 68 part 2 (=Kp2) and page 68 part 14 (=Kp3) were changed. The change in Kp2 will cause the difference in maximum deflection angle since the lever increased, while Kp3 will change the elevator zero incidence downwards at any given horizontal stab angle.

 

 

What significant differences you can see for Kp3? Another form? But the arms seems to be very close if not equal... Kp2 isometry and a plane view... Possibly the angle changes a bit. But very hard to say how much. Of course, this element is convenient to change the equivalent arm and, thus, gear ratio to the elevator. The last bellcrank can do this job too...

Ніщо так сильно не ранить мозок, як уламки скла від розбитих рожевих окулярів

There is nothing so hurtful for the brain as splinters of broken rose-coloured spectacles.

Ничто так сильно не ранит мозг, как осколки стекла от разбитых розовых очков (С) Me

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What significant differences you can see for Kp3? Another form? But the arms seems to be very close if not equal... Kp2 isometry and a plane view... Possibly the angle changes a bit. But very hard to say how much. Of course, this element is convenient to change the equivalent arm and, thus, gear ratio to the elevator. The last bellcrank can do this job too...

 

we would need executive drawings to determine how much how high anyway

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we would need executive drawings to determine how much how high anyway

 

I am more than confident, that this 30% changes in gear ratio can not be someting critical IN MODELLING, because the limiting forces used in the simulation is something average regardless of different pilots ability, physical conditions, etc. So, this discussion has mostly historical sense.

K model in simulation has real elevator angle limits though the derivatives got from G docs, that is correct regarding the charachteristics.

Ніщо так сильно не ранить мозок, як уламки скла від розбитих рожевих окулярів

There is nothing so hurtful for the brain as splinters of broken rose-coloured spectacles.

Ничто так сильно не ранит мозг, как осколки стекла от разбитых розовых очков (С) Me

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What significant differences you can see for Kp3? Another form? But the arms seems to be very close if not equal... Kp2 isometry and a plane view... Possibly the angle changes a bit. But very hard to say how much. Of course, this element is convenient to change the equivalent arm and, thus, gear ratio to the elevator. The last bellcrank can do this job too...

 

I am not at home currently, but if you don't believe me just check the replacement part list. The part number changes if the part is changed. I don't believe I have an isometric blueprint of 109 G Kp2 equivalent. I have prepared a picture about the Kp3 changes, I will post it tomorrow. It shifts the elevator travel range to a more nosedown range.

 

Makes sense to me, that the counterweight reacts to G forces. That's what I suspected. However, there is no way the bobweight stabilizes the stick aft at positive G, just check the force flow and you must realize it pushes the stick forward and the elevator downwards aka moves the control neutral point forward.


Edited by rel4y

Cougar, CH and Saitek PnP hall sensor kits + shift registers: https://forums.eagle.ru/showthread.php?t=220916

 

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I am not at home currently, but if you don't believe me just check the replacement part list. The part number changes if the part is changed. I don't believe I have an isometric blueprint of 109 G Kp2 equivalent. I have prepared a picture about the Kp3 changes, I will post it tomorrow. It shifts the elevator travel range to a more nosedown range.

 

Makes sense to me, that the counterweight reacts to G forces. That's what I suspected. However, there is no way the bobweight stabilizes the stick aft at positive G, just check the force flow and you must realize it pushes the stick forward and the elevator downwards aka moves the control neutral point forward.

 

No, you do not understand what neutral point is. Neutral point in stability theory is a point (generally along X axis, vertical shift is neglected) where increment of lift is applied. Generally it is fugured in %% of MAC, sometimes - as absolute distance from a datum point. So, if you place CoG in this point, the plane will be statically neutral, i.e. it will have equilibrum at any AoA it has. In practice for the certain aircraft this value is not constant for the whole range of AoA/CL, but for our educational purposes we can presume it constant.

There are two kinds of NP - fixed stick and free stick. The first one refers to the elevator position, the second one - to elevator moment or stick force.

Generally the first one is greater (more aft) than the second, but there can be exceptions (Spitfire V, for example).

 

As I mentioned above, the neutral plane will tend to increase g-load, even if you slightly pull the stick and return it back, due to inertia (a stable plane will stabilise the certain g proprtional to the stick force). This behavior is not desirable. So, the bobweight working as a feedback and mimics natural stick forces at the stick like for the stable plane. To be accurate, this bobweigt does not change 1 g trim force, so, the trimmed position of the stick will be constant along the speed range, but it helps to control the plane during maneuvers and makes flight in turbulence conditions more comfortable.

Ніщо так сильно не ранить мозок, як уламки скла від розбитих рожевих окулярів

There is nothing so hurtful for the brain as splinters of broken rose-coloured spectacles.

Ничто так сильно не ранит мозг, как осколки стекла от разбитых розовых очков (С) Me

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I completely misread what you said, to my defence I was in a shaky train writing on my phone. While I am familiar with AC, CP, CG, MAC etc, I honestly don’t quite grasp the difference of the two neutral points. Isnt the NP basically the AC of the whole aircraft? So at a fixed tailplane incidence wouldn’t the elevator angle (fixed stick) and stick forces needed for deflection (free stick) and therefore the NPs coincide?

 

If I put the elevator at a positive angle, the elevator chord shortens thus its AC moves forward. This would shift the aircraft neutral point forward as well, wouldn’t it? I understand in contrast to asymmetric airfoils AC for symmetric airfoils is constant with AoA, but as soon as I move the elevator out of its 0 incidence I automatically change the AC forward regardless of AoA or Cl, right? Now I know this will be pretty much negligible, but it should be determinable.

 

Well anyway, here is the plane view comparison of the Kp3 bellcrank.

 

Kp3-K4vs-F.jpg Bf-109-K-4-Kp3-Effekt.jpg

 

My understanding is as follows: The rods and cables are unchanged in length as the supply numbers are unchanged. The attachment point of the rod on Kp3 however is offset to the right by 10°. Since the cable mechanism functions in a parallel fashion the whole parellelogram is skewed to the left. This in turn pushes the elevator rod upwards and rotates the elevato. This shifts the elevator range to the nose heavier region.

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I completely misread what you said, to my defence I was in a shaky train writing on my phone. While I am familiar with AC, CP, CG, MAC etc, I honestly don’t quite grasp the difference of the two neutral points. Isnt the NP basically the AC of the whole aircraft? So at a fixed tailplane incidence wouldn’t the elevator angle (fixed stick) and stick forces needed for deflection (free stick) and therefore the NPs coincide?

 

If I put the elevator at a positive angle, the elevator chord shortens thus its AC moves forward. This would shift the aircraft neutral point forward as well, wouldn’t it? I understand in contrast to asymmetric airfoils AC for symmetric airfoils is constant with AoA, but as soon as I move the elevator out of its 0 incidence I automatically change the AC forward regardless of AoA or Cl, right? Now I know this will be pretty much negligible, but it should be determinable.

 

Well anyway, here is the plane view comparison of the Kp3 bellcrank.

 

Kp3-K4vs-F.jpg Bf-109-K-4-Kp3-Effekt.jpg

 

My understanding is as follows: The rods and cables are unchanged in length as the supply numbers are unchanged. The attachment point of the rod on Kp3 however is offset to the right by 10°. Since the cable mechanism functions in a parallel fashion the whole parellelogram is skewed to the left. This in turn pushes the elevator rod upwards and rotates the elevato. This shifts the elevator range to the nose heavier region.

 

No, you are very far from the scientific point of view regarding AC stability: elevator deflection does not affect NP at least in linear range of AoAs. It does not change mz (AoA) slope, just shift it up and down.

Please read my previous post if you need to clarify the bobweight effect.

Ніщо так сильно не ранить мозок, як уламки скла від розбитих рожевих окулярів

There is nothing so hurtful for the brain as splinters of broken rose-coloured spectacles.

Ничто так сильно не ранит мозг, как осколки стекла от разбитых розовых очков (С) Me

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No, you are very far from the scientific point of view regarding AC stability: elevator deflection does not affect NP at least in linear range of AoAs. It does not change mz (AoA) slope, just shift it up and down.

Please read my previous post if you need to clarify the bobweight effect.

 

Well at least in theory it must, because it shortens the aerodynamic chord of the horizontal stabilizer and thus moves AC forward. If you assume AC at 25% of chord, then if the chord shortens the AC will move forward in respect to CG of the aircraft.


Edited by rel4y

Cougar, CH and Saitek PnP hall sensor kits + shift registers: https://forums.eagle.ru/showthread.php?t=220916

 

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Well at least in theory it must, because it shortens the aerodynamic chord of the horizontal stabilizer and thus moves AC forward. If you assume AC at 25% of chord, then if the chord shortens the AC will move forward in respect to CG of the aircraft.

 

No, that is your wrong opinion... I will try again from the very beginning. If you have a plane and begin to move its CoG aft, the plane initially is stable. It means that if you fix the stick in the position for level flight or trim it for level flight, the plane will return to the level flight after a sudden kick. If you shift CoG far aft the plane will not return to the initial AoA and will depart to high AoA or negative AoA, so it becomes unstable. Between these to areas there is a certain CoG position where the equilibrum is neither stable nor unstable. THIS POINT is aircraft NEUTRAL POINT. By the way, in the Soviet report this neutral point was derived based on flight tests.

 

Then. please return to my posts about the bobweight and how it mimics STABILITY for free control as the plane is NEUTRAL or even unstable a bit.


Edited by Yo-Yo

Ніщо так сильно не ранить мозок, як уламки скла від розбитих рожевих окулярів

There is nothing so hurtful for the brain as splinters of broken rose-coloured spectacles.

Ничто так сильно не ранит мозг, как осколки стекла от разбитых розовых очков (С) Me

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No, that is your wrong opinion... I will try again from the very beginning. If you have a plane and begin to move its CoG aft, the plane initially is stable. It means that if you fix the stick in the position for level flight or trim it for level flight, the plane will return to the level flight after a sudden kick. If you shift CoG far aft the plane will not return to the initial AoA and will depart to high AoA or negative AoA, so it becomes unstable. Between these to areas there is a certain CoG position where the equilibrum is neither stable nor unstable. THIS POINT is aircraft NEUTRAL POINT. By the way, in the Soviet report this neutral point was derived based on flight tests.

 

Then. please return to my posts about the bobweight and how it mimics STABILITY for free control as the plane is NEUTRAL or even unstable a bit.

 

Probably typo, but, if you move the CoG forward then the stability increases and when moving aft then the stability decreases. Right between them is the neutral point, where the center of gravity of the aircraft is neutrally stable.

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Probably typo, but, if you move the CoG forward then the stability increases and when moving aft then the stability decreases. Right between them is the neutral point, where the center of gravity of the aircraft is neutrally stable.

 

It's not a typo. It was presumed that initial position is FORE than a NP. So, the consequent description is right.

Ніщо так сильно не ранить мозок, як уламки скла від розбитих рожевих окулярів

There is nothing so hurtful for the brain as splinters of broken rose-coloured spectacles.

Ничто так сильно не ранит мозг, как осколки стекла от разбитых розовых очков (С) Me

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With your explanations the relevance of defining two neutral points at first didn’t quite occur to me, since at some elevator deflection the free stick NP must coincide with the fixed stick one anyway. After reading up in the literature I realized the free stick NP simply has the hinge moments defined as zero and is important in stability theory for response to perturbation. Well, perturbation response is not what I am interested in currently, I care about stick forces and trim.

 

I think no one disputed your basics, but you seem to be placing them out of context. I am saying the tree is green and you are answering, no you dweeb, the sky is blue. “My wrong opinion” is actually a thing in Torenbeeks “Synthesis of subsonic aircraft design” in the context of plain flaps and how linear airfoil theory underpredicts pitching moments in comparison to empiric data. Now what is an elevator, but a plain flap located on the symmetric airfoil horizontal stab? With these deviation in pitching moments (dM/dalpha =/= 0), horizontal stab AC also moves around. You yourself said earlier that in praxis AC is not constant at quarter chord. This in turn would change the fixed stick NP from the calculated position as soon as the elevator incidence is different from 0. It was more of a thought experiment and like I said earlier will be marginal, but I don’t need to be called an idiot for it.

 

Now lets get back to the real problematic:

 

I do not use the manual just a Soviet report about 109G trim with all CoG positions, recorded elevator angle, etc, etc, for different stab position. I think it's more than enough to judge about the trim of the plane. Then we have special 109K weight and balance chart.

 

What is the magic gear effect? You really have THE SAME GEAR RATIO from the stick to the elevator. So, you will have the same force.

 

I think we all have realized by now, that the gear ratio indeed did change and the stickforces must with it.

 

stick-forces.jpg

 

Looking at the formula we see that stick forces are proportional to hinge moment coefficient and gearing factor amongst other things. Since all we would like to change is gear ratio in the plot, we can for now consider everything but G and Fs as a constant. In the plot we can also see that the stickforces stay pretty much linear over the whole Mach range. At Mach 0,73 the Stickforce amounts to 32,5 kg for an elevator deflection of 2,8°. Corrected for the new gearing factor (x0.76) it amounts to 24,7 kg. That is less than I do one armed rows with. ;)

 

Handkraft-neu.jpg

 

I probably will get into more detail on the stickforces, elevator deflection and CoG in the future.

 

Furthermore, the elevator deflection range in respect to 0° has changed a bit, lets look at stab +1,1°. In G models it was 31,3° upwards of 67° total, so 46,7% of total range. For K models it is 26° upwards out of 51° total, so 51% of total range. Upwards meaning pulling the stick.

 

Ok, so far we have not addressed trimmed cruise flight.

 

Above we have looked at the Stickforce Fs which is proportional to hinge moment coefficient. To get the stickforce to be zero, we must get the hinge moment coefficient to be zero. Let’s look how the hinge moment coefficient is defined. (b0 will be 0 for symmetric tailplanes)

 

hinge-moments.jpg

 

I think we will agree that elevator trim tabs will influence free stick neutral trim. Depending on how I bend/ deflect these trim tabs I can set the elevator angle with zero hinge moment at a specific stab incidence. By bending the trim tab aerodynamic forces exert a moment on the free floating elevator and deflect it.

 

In the soviet tests the elevator deflection is 0° when the stick forces are zero. That means trim tabs are set to neutral and do absolutely nothing at all. If trim tabs were actually set to cruise trim, they would deflect the elevator by some degrees and for that elevator deflection the stick forces would be 0. Even if they were set to cruise speed of a G-2, G-2 optimum cruise is 595 kph at 1,0 ata and K-4 is 645 kph at 1,15 ata. That is a 50 kph difference.

 

According to the soviet G-2 report it would only need 2° of elevator deflection to trim the aircraft at even 30% MAC with 1.3 ata, 2600 rpm, stab +1.5. So lets be generous and say about 3° for stab +1,1. From my experiences it is perfectly possible to deflect the elevator by about 3° with trim tabs.

 

Now, for a second lets assume the Germans didn’t have too much material laying around and were totally bored at the aircraft factories in the final days of war. Why would they possibly add another workstep/ extra material to double the area of trim tabs? I wonder, could it possibly be because the single trim tab config did not create enough moment on the elevator to provide the necessary free stick elevator trim and nose down authority? Well the German test I quoted earlier says exactly that.

 

The conclusion of this test was a completely different one, namely that you couldnt put enough force on the elevator in the first place to reach any dangerous dive angle above 60°.... Then double sized trim tabs were introduced which could yield elevator force reversal at high Mach numbers, so in turn the stab angle was limited to +1,15°, where elevator force reversal did not happen anymore.

 

This test resulted in a production line change of later models to double elevator trim tabs and limiting the stab angle to +1,15° / +1,10°.


Edited by rel4y

Cougar, CH and Saitek PnP hall sensor kits + shift registers: https://forums.eagle.ru/showthread.php?t=220916

 

Shapeways store for DIY flight simming equipment and repair: https://www.shapeways.com/shops/rel4y-diy-joystick-flight-simming

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