Rudder trim surface moves wrong way in GFX

[BitMaster]

Hey Devs,

 

you might have noticed yourself by now but just to make sure it is noted:

 

The trim surface on the P-51's rudder moves the wrong way in graphics.

 

It is working the correct way but optically, GFX-wise, it moves wrong !

 

Checked the ailerons, they are correct but havent checked the elevator.

 

Gonna check them on next opportunity and will post it if it also moves wrong way.

 

 

 

This should be a quick fix, +/- typo kinda thing :)

 

 

Bit

[BitMaster]

OK, I was wrong on the AILERON !!

 

De facto ALL trim surfaces work the WRONG way ! rudder, aileron ( only the left one moves but the wrong direction, right one doesnt move at all ) and the elevator also moves the wrong way.

 

Bit

[Merlin-27]

I just checked. All seem to work properly on mine. The tab moves in the opposite direction of the desired movement of the control surface.

[cichlidfan]

I didn't search but I seem to recall this being brought up once or twice before.

[BitMaster]

I just checked. All seem to work properly on mine. The tab moves in the opposite direction of the desired movement of the control surface.

 

I think I know what you mean but you can't gain more than you put in and in your theory I think the forces would equal out and the effect would be zero, actually you would loose kinetic energy and force the AC into a slip kinda thing, like split flaps on gliders for the ailerons, rudder and elevator would just slow down the AC. Pushing the small one left to push the big one right won't work, physics tell me what u put in is what u get out.

 

I might be wrong on this but from those AC I know of the small control surfaces move the same way the actual full control surface would be set to to trim the AC.

 

Still, the right aileron trim surface won't move at all, that's out of question from this theory bashing ;)

 

Bit

[Merlin-27]

I think I know what you mean but you can't gain more than you put in and in your theory I think the forces would equal out and the effect would be zero, actually you would loose kinetic energy and force the AC into a slip kinda thing, like split flaps on gliders for the ailerons, rudder and elevator would just slow down the AC. Pushing the small one left to push the big one right won't work, physics tell me what u put in is what u get out.

 

I might be wrong on this but from those AC I know of the small control surfaces move the same way the actual full control surface would be set to to trim the AC.

 

Still, the right aileron trim surface won't move at all, that's out of question from this theory bashing ;)

 

Bit

 

Trim Tabs: A trim tab is a small, adjustable hinged surface on the trailing edge of the aileron, rudder, or elevator control surfaces. Trim tabs are labor saving devices that enable the pilot to release manual pressure on the primary controls.

 

Some airplanes have trim tabs on all three control surfaces that are adjustable from the cockpit; others have them only on the elevator and rudder; and some have them only on the elevator. Some trim tabs are the ground-adjustable type only.

 

The tab is moved in the direction opposite that of the primary control surface, to relieve pressure on the control wheel or rudder control. For example, consider the situation in which we wish to adjust the elevator trim for level flight. Level flight is the attitude of the airplane that will maintain a constant altitude. Assume that back pressure is required on the control wheel to maintain level flight and that we wish to adjust the elevator trim tab to relieve this pressure. Since we are holding back pressure, the elevator will be in the up position. The trim tab must then be adjusted downward so that the airflow striking the tab will hold the elevators in the desired position. Conversely, if forward pressure is being held, the elevators will be in the down position, so the tab must be moved upward to relieve this pressure. In this example, we are talking about the tab itself and not the cockpit control.

 

Rudder and aileron trim tabs operate on the same principle as the elevator trim tab to relieve pressure on the rudder pedals and sideward pressure on the control wheel, respectively.

 

EDIT: Not sure about the behavior of the P-51D aileron trim tabs. I would naturally think the left and right trim tabs would have a different behavior as to the torque effect movement of the airframe but I do not know for sure how they should appear.

 

Edited March 8, 2014 by Merlin-27

[BitMaster]

Trim Tabs: A trim tab is a small, adjustable hinged surface on the trailing edge of the aileron, rudder, or elevator control surfaces. Trim tabs are labor saving devices that enable the pilot to release manual pressure on the primary controls.

 

Some airplanes have trim tabs on all three control surfaces that are adjustable from the cockpit; others have them only on the elevator and rudder; and some have them only on the elevator. Some trim tabs are the ground-adjustable type only.

 

The tab is moved in the direction opposite that of the primary control surface, to relieve pressure on the control wheel or rudder control. For example, consider the situation in which we wish to adjust the elevator trim for level flight. Level flight is the attitude of the airplane that will maintain a constant altitude. Assume that back pressure is required on the control wheel to maintain level flight and that we wish to adjust the elevator trim tab to relieve this pressure. Since we are holding back pressure, the elevator will be in the up position. The trim tab must then be adjusted downward so that the airflow striking the tab will hold the elevators in the desired position. Conversely, if forward pressure is being held, the elevators will be in the down position, so the tab must be moved upward to relieve this pressure. In this example, we are talking about the tab itself and not the cockpit control.

 

Rudder and aileron trim tabs operate on the same principle as the elevator trim tab to relieve pressure on the rudder pedals and sideward pressure on the control wheel, respectively.

 

 

 

 

I understand what you say and I try to make myself believe it, for the sake of it but Isaac Newton comes to my mind... How do you want to gain more momentum from 1 tab to the other ? Where is the miracle producing more air resistance/force on the large surface given that it can only set itself off that far as the small surface induces ? It would make far more sense to set the small one in the same direction and thus keep the larger control surfaces level to their respective main surface to keep the whole thing stream lined, more energy efficient I guess and less wear & tear on the hinges and sheeting as well.

 

Look at the A-10C's air brake for example, in theory this is the same despite that both surfaces are equal in size. One cannot push itself harder into the wind than the other, resulting in a neutral behavior of the AC when you hit the brakes.

 

Convince me that Newton is wrong and you gain more than you put in :smartass:

 

Any aeronautical engineer around that can shed some light on this and how Newton is overcome in this equation ?

 

..just comes to my mind. If what you say is correct. As soon as the actual surface was pushed opposite to the smaller one, the smaller ones force would lessen due to its position relative to the air stream, resulting in an overpower on the larger one pushing back--> resulting in the the same again and again, we call this "Ruder Flattern" in german and it won't take long until your surface, the hinges and the rest of the airplane dissolves in small pieces, seen that a few times in RL. You would let them oscillate or whatever that is called cause they would always try to rival against each other.

 

Still, I might be wrong, I just try to explain to myself as an avid R/C model builder what would happen if those 2 surfaces work against each other in a dynamic environment.

 

 

Bit

Edited March 8, 2014 by BitMaster

[Echo38]

Here's a little illustration I made a long time ago which depicts how trim works on real aircraft; sizes are not to scale. (Where it says "no drag," that isn't entirely accurate; there's always going to be some drag on an aerofoil in an airflow. The point is that there isn't a deflection there to cause extra drag.) Do note that not all aircraft throughout history had trim tabs; IIRC, the Me-109 used a trimmable stabilizer instead, which works a bit differently.

[BitMaster]

Here's a little illustration I made a long time ago which depicts how trim works on real aircraft; sizes are not to scale. (Where it says "no drag," that isn't entirely accurate; there's always going to be some drag on an aerofoil in an airflow. The point is that there isn't a deflection there to cause extra drag.) Do note that not all aircraft throughout history had trim tabs; IIRC, the Me-109 used a trimmable stabilizer instead, which works a bit differently.

 

makes sense Echo38, no doubt. from what you say I extract that the trim tab would not move the control surface to not produce more drag induced by the larger surface !?

 

which theory from above applies to trim tabs ?

 

Bit

[Merlin-27]

A google search will give you hours of reading on the subject....

 

Try this:

 

Trim Tabs - Pilot's Handbook of Aeronautical Knowledge

[9.JG27 DavidRed]

yeah google "flettner",...its working correctly in dcs, at least i assume, never looked at it actually, but i know Yo-Yo explaining it a couple of times to a couple of wrong bug reports, so im confident its working correctly.

[ARM505]

The trim tab 'flies' the control surface - it's correct. It's not that you get more than you put in, it's like a kind of aerodynamic boosting, the same as control surfaces where part of the movable surface is placed ahead of the hinge line to reduce stick force.

[Echo38]

the trim tab would not move the control surface to not produce more drag induced by the larger surface !?

 

I'm having a difficult time parsing this question--too many inversions ("double negative").

 

The least draggy situation for the trim tabs--all else equal--is to have the trim tab on the same plane as the elevator (trim tab "centered," or "level" with the elevator). However, that is not generally going to result in a desirable attitude for the aircraft if you take your hands off the stick. Even level flight isn't usually as simple as having the elevator and trim tab level with the wing. Power settings, CoG, airfoil type, etc. all determine what the aircraft is actually going to do in that situation.

 

An example: say you want to execute a steep sustained climb. The best situation from the perspective of drag alone would be to keep the trim tab level with the elevator, and simply move the elevator back to maintain the best pitch & speed, and, once they are achieved, hold the elevator in place to maintain them. However, that would be quite tiring on the arms, and letting go of the stick would result in an abrupt departure from your desired flight path. This is why we trim during our climb, accepting a minor additional "bend" in the airflow (and thus an increase in drag) in order to prevent our arm muscles from becoming overworked.

 

The point of trimming a real aircraft is not to reduce drag; it is to reduce arm muscle workload, to get the airplane to stay at a more or less constant attitude without constant force being applied to the controls. In a flight sim, trimming the aircraft may effectively reduce drag, but this will be a side-effect of the user no longer making as many micro-errors which increase drag. These micro-errors are mostly due to differences in translation of trim from an analogue to a digital medium (e.g. twitchy plastic gaming joysticks). Not a problem in a real aircraft (stick & cable ones, anyway), if you have a steady hand (and assuming we aren't talking about such high stick-forces that your muscles are near their limits); the problem in the real aircraft is simply the aforementioned muscle workload.

 

I really don't how I can fully explain it to someone who's only used flight sim-games. I kinda feel that you pretty much have to have felt it for yourself by flying & trimming a real airplane, as well as having visually observed the effects of moving the wheel on the trim tabs. P.C. flight sim-games, by their inherent nature, portray trim poorly. Even DCS. This is not the fault of Eagle Dynamics. It is the fault of the P.C. medium: we are not feeling the strain of the real airflow on our real arms as we hold the real stick, and feeling that force diminish as we move the real trim wheel toward a trimmed setting. No amount of simulation can replicate that feeling. It's similar to attempting to simulate pain: no simulation can do that. This is why trimming is one of the most misunderstood aerodynamic phenomena in the flight sim community.

 

(I suppose that commercial force-feedback gaming joysticks can replicate some of this feel, but only for low stick forces. Their mechanisms are incapable of handling high stick forces; they'd promptly break from your pull, or else unrealistically give way to avoid breakage. They're shoddy & ill-constructed, and aren't designed for realistic stick forces such as those experienced during untrimmed high-G turns.)

 

Better phrasing of these points is welcome, as are corrections by the more knowledgable to any errors I've made.

Edited March 8, 2014 by Echo38

[PLP]

Although I initially also believed it was wrong, this makes sense, and I am mad at myself for not having thought it through.

 

but in my game only the port aileron fletner is moving, is that correct?

 

and this is why trim does not move your stick when you are stationary, but then moves it when you are at speed *sudden clarity*.

[BitMaster]

I'm having a difficult time parsing this question--too many inversions ("double negative").

 

The least draggy situation for the trim tabs--all else equal--is to have the trim tab on the same plane as the elevator (trim tab "centered," or "level" with the elevator). However, that is not generally going to result in a desirable attitude for the aircraft if you take your hands off the stick. Even level flight isn't usually as simple as having the elevator and trim tab level with the wing. Power settings, CoG, airfoil type, etc. all determine what the aircraft is actually going to do in that situation.

 

An example: say you want to execute a steep sustained climb. The best situation from the perspective of drag alone would be to keep the trim tab level with the elevator, and simply move the elevator back to maintain the best pitch & speed, and, once they are achieved, hold the elevator in place to maintain them. However, that would be quite tiring on the arms, and letting go of the stick would result in an abrupt departure from your desired flight path. This is why we trim during our climb, accepting a minor additional "bend" in the airflow (and thus an increase in drag) in order to prevent our arm muscles from becoming overworked.

 

The point of trimming a real aircraft is not to reduce drag; it is to reduce arm muscle workload, to get the airplane to stay at a more or less constant attitude without constant force being applied to the controls. In a flight sim, trimming the aircraft may effectively reduce drag, but this will be a side-effect of the user no longer making as many micro-errors which increase drag. These micro-errors are mostly due to differences in translation of trim from an analogue to a digital medium (e.g. twitchy plastic gaming joysticks). Not a problem in a real aircraft (stick & cable ones, anyway), if you have a steady hand (and assuming we aren't talking about such high stick-forces that your muscles are near their limits); the problem in the real aircraft is simply the aforementioned muscle workload.

 

I really don't how I can fully explain it to someone who's only used flight sim-games. I kinda feel that you pretty much have to have felt it for yourself by flying & trimming a real airplane, as well as having visually observed the effects of moving the wheel on the trim tabs. P.C. flight sim-games, by their inherent nature, portray trim poorly. Even DCS. This is not the fault of Eagle Dynamics. It is the fault of the P.C. medium: we are not feeling the strain of the real airflow on our real arms as we hold the real stick, and feeling that force diminish as we move the real trim wheel toward a trimmed setting. No amount of simulation can replicate that feeling. It's similar to attempting to simulate pain: no simulation can do that. This is why trimming is one of the most misunderstood aerodynamic phenomena in the flight sim community.

 

(I suppose that commercial force-feedback gaming joysticks can replicate some of this feel, but only for low stick forces. Their mechanisms are incapable of handling high stick forces; they'd promptly break from your pull, or else unrealistically give way to avoid breakage. They're shoddy & ill-constructed, and aren't designed for realistic stick forces such as those experienced during untrimmed high-G turns.)

 

Better phrasing of these points is welcome, as are corrections by the more knowledgable to any errors I've made.

 

 

No problems there, I don't have any problem in understanding why an aircraft needs to be trimmed.

You somehow missed the point of my initial post. All I asked for was to state if the trim surfaces on the P-51 move the wrong way... or the correct way and not why do they move at all.

 

I operate almost any kind of R/C craft there is in small to large size, some larger than some military drones are and I wasn't able to understand from Merlin's explanation alone why he thinks they move into the correct direction. Well, someone else made it physically clear to me as I know Newton inside out but I am no aerodynamics engineer, which is far more complex than any of Isaac's laws. Based on the law of energy conservation I find it hard to believe trim tabs work this way but it is like it is and I have to rethink or find somebody who explains this to me with quotations ;)

 

 

Anyway, thanks for putting this clear and all the explanations and ARM505's comparison with the counter-weights and aerodynamic boosting made me believe it ;)

 

 

Still... right aileron trim tab not working.

 

 

Bit

[ZaltysZ]

Convince me that Newton is wrong and you gain more than you put in :smartass:

 

Let's say your aircraft has tendency to dip right wing and you want means to fly level with hands off. You might implement trim in 2 ways: a) put trim tab on aileron b) put trim tab somewhere on non movable part of wing.

 

Trim tab will have to move up in case (a), and it will have to move down in case (b) to cancel right wing dip. The difference arises because of trim tab location.

 

Case (b) is straight forward: trim tab creates force which directly affects the wing, or in other words: trim tab is like mini aileron.

 

Case (a) is a bit more complicated, because trim tab is like mini elevator of aileron in it. Small trim tab creates lesser force than a force required to deflect aileron, however trim tab does that at distance from the rotation axis of aileron, and so that small force is amplified by lever effect.

 

P-51 trim tabs fall into the case (a).

[BitMaster]

Wikipedia about Anton Flettner's invention:

 

it is "also" used for trimming but the main purpose was not to trim the aircraft but steer it through the Flettner surface while accepting the many downsides of that method aka wear & tear of the hinges and surface and reduced efficiency of the control surface and oscillating surfaces ( thus the wear and tear ). Not being used in modern AC anymore where hydraulics replaced human muscles as Wiki states ( german Wiki ).

 

So I somehow thought correct and the only way it works is by aerodynamically having more gain / efficiency out of the air stream from the actual control surface than from the Flettner surface.

[FunktasticLucky]

KC-135 Crew Chief here. We have only 1 hydraulically controlled control surface on our aircraft. It's the rudder. Everything else is manually controlled through pulleys and cables to the control surface. You can only image how hard it would be to move elevators or the rudder in manual mode while flying at 600mph. So to cut down the effort we have control tabs. Which is probably exactly what is going on here on the P-51. It's like a small control surface for the control surface. You aren't moving the entire surface (except on the ground when there isn't airflow) you are moving the tab and the tab moves the control surface for you. So the tabs are correct in this game.

[effte]

Still... right aileron trim tab not working.

 

That's the one maintenance set on the ground, as part of rigging the aircraft for balanced flight. It can't be controlled from the cockpit.

 

With the aileron trim control, you move the left one.

[Echo38]

You aren't moving the entire surface (except on the ground when there isn't airflow)

With the Cessnas I flew, trimming had no effect on the position of the control surface when the aircraft was stationary on the ground. Only the trim tab moves, in that situation. Only airflow or yoke input could cause the elevator to move on the ground. (Or moving it by hand, as in the hinge check.) In the Me-109, on the other hand, I believe that spinning the trim wheel does result in the entire horizontal stabilizer (not just the elevator) moving, even at zero airspeed, because of the trimmable stabilizer system. Not entirely sure how the trim works in the 109; I got to sit in a functional Buchon on the ground, once, but I was too excited to think of examining the trim system. Edited March 11, 2014 by Echo38

[effte]

Not entirely sure how the trim works in the 109;

 

Wires from the trim wheel operate a jackscrew connected to the leading edge of the fixed part of the stabilizer.

 

That's the way they generally operate, albeit the wires may be replaced by electrical or hydraulic trim motors.

 

Cheers,

/Fred