Trim Tabs and How They Work

[indian]

Trim Tabs are of two type fixed and pilot adjustable. The fixed are just that they are set on the ground by maintenance and cant be moved by the pilot, they are set to deflect the control surface that they are attached to to compensate for and correct that bad attitude of the plane in flight.

The trim tabs that are pilot adjustable also have the fixed tabs on them th correct minor flight carectoristics of the plane. The pilot can then move a trim wheel lever or what ever he uses to move the trim tab to make the plane fly to what he sees as straight and level. Trim tabs move in the opposite direction that you want the airplane to move so that they deflect the control surface towards the direction you want it to go. The only thing trim tabs do is relieve control pressure from the pilots body (arms and legs) you can still fly the plane without touching the trim tabs if its set for a good straight and level flight. Where you can run into problems with trim is where you have alot of down trim for instance and want to pull up the trim tab will fight against you adding only control surface force, again wearing down the pilot.

We do not feel control pressure in a online sim and wont with present day joysticks. If we had real life stick movement at full speed you would only move the stick about a quarter of the total stick deflection and it would be stiff to the feel. If you had full hydraulic control of a WWII plane and yank the stick full back at full speed not only would you put your head in your lap but the wings would unass your airframe in a hart beat, you wouldnt just black out it would probably kill you. If you have any doubt go take a ride with a CFI and see for your self.

Heres another way go out on the highway get up to your legal speed limt and change lanes see how much you move the wheel to get there then do it at much slower speeds much more wheel movement. All trim does is ease pilot work load on his muscle thats it nothing else.

I work on avionics of some of the largest planes around and its all to ease pilot work load.

One thing that could work is to buffet the cockpit of the planes as they get up to speed and and near compression so that you cant get a good sight picture to shoot at, this could also be done at stall speed most planes shake pretty good at stall speeds.

I use auto trim to set level flight at the speed I want to fly at and thats it. I dont touch it again I use the controls to fly the plane becuase the trim tabs are only moveing the same flight control that my stick does.

What HT said by adding trim and the stick movement probably gave you extra control surface movement by using them together you cant go beoyund what the control can actually move.

I hope some of this makes sence I reread it in the morning and correct it if I dont like it.

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Tommy (INDIAN) Toon
Indians Home page were links to help pages can be found.
Indian's Homepage

[Creamo]

I work on avionics of some of the largest planes around and its all to ease pilot work load.

Cool, so this saves me the space for comparison.

Explain how a MD80 Aileron trim works.



[This message has been edited by Creamo (edited 09-05-2000).]

[funked]

I understand what Indian said except this part:

 

What HT said by adding trim and the stick movement probably gave you extra control surface movement by using them together you cant go beoyund what the control can actually move.

Are you talking about what HT said or are you talking about how it works in AH or how it's going to work in AH or how it works in real life?

[indian]

Funked was talking about what HT said I tried to bring it to the debate over CT, but was real tired last night.

Creamo MD80 have cable actuated trim tabs and the elevators are flown almost entirely by the trim tabs the other fight controls are cable with the rudder having hydrualic boost. I can get the Boeing get the Boeing disdription if you want out of the maintenance manual, I know you picked this one because of the elevators right.

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Tommy (INDIAN) Toon
Indians Home page were links to help pages can be found.
Indian's Homepage

[Minotaur]

Funked;

One of the things that I understood HT to say is something that I kind of figured out on my own.  My knowledge about actual A/C is embarrassingly limited.  I take the game as it is presented and try to put that into what I understand to be facts in the real world.  

Keep in mind that I am no great genius (As you well know   ).  It happened by accident during trial and error.  I noticed an effect on the FM, when using trim.

While learning manuvers in AH (beta), I would watch how the trim operated in AutoMode(s).  One thing that really stuck on me, was the incredible amount of control that trim provided.  

I learned that trim controls had more control than normal controls.  Although in "Manual Mode" trim moved very very (irratatingly) slowly, but that its control had a greater range.  Thus; trim had a larger overall effect on control surface deflection than normal controls.  I also noticed that trim control movement was not as restricted at high speeds, as normal controls are.

Say for example:

• A full elevator up control provided less deflection than a full elevator up control plus a full elevator up trim up control.  More importantly, with a full elevator up trim control, the normal control added no more or very little more up elevator control and that down elevator control was clipped or restricted.

I realized that trim control in AH seemed false compared to what I would expect for real life.  It did not modify trim as it would in a real A/C.  AH trim directly effected the control surface under the fasad of using "trim" and in a major way.  Basically overiding or modifying normal control.

I am not alone in this realization, of that I am pretty sure.  Many players probably also know this and take advantage, perhaps giving them an un-intented edge.  Although never a big deal for me, I am also pretty sure it was one of those nagging things that bothered the guys and gals at HTC.  

Good Luck!    

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Mino
The Wrecking Crew

"hehehe...I like this thread squealing Bastids!"
SOB

[This message has been edited by Minotaur (edited 09-05-2000).]

[funked]

Technically I think those are called Servo Tabs Indian (elevator tabs that are linked to the pilot's yoke).

[funked]

Mino I think you got it, bud.  We had the same system in WarBirds but you couldn't see the control surfaces there.  So not that many people realized you could change the max surface deflection by altering trim.

[indian]

Funded you may be right technically but they are still called trim tabs in the maintenance manual. There is no trim control for the elevator we must move the stablizer to trim the plane, thats same on most large planes I believe.

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Tommy (INDIAN) Toon
Indians Home page were links to help pages can be found.
Indian's Homepage

[funked]

That's right Indian, as far as I know all the big ones move the h-stab for pitch trim.  

Servo tabs was a Boeing term I think.

[This message has been edited by funked (edited 09-06-2000).]

[Andy Bush]

Creamo

The DC-9/MD-80 series aircraft use cable actuated tabs on the ailerons to provide roll control and aileron trim.

When the pilot turns the yoke, a control tab located on the trailing edge of the aileron is moved away from the 'faired' or neutral position. This provides an aerodynamic force (lift) that then moves the entire aileron. The aileron movement then rolls the aircraft.

Aileron trim is actuated by the pilot using a wheel knob located on the console between the two cockpit seats. Rotating this knob moves a cable that then moves a trim tab that is located on the trailing edge of the aileron next to the control tab previously described. When this trim tab is displaced from the faired position, it moves the aileron up or down slightly and thus inputs a small roll command.

The pilot uses aileron trim to maintain wings level flight at a particular speed. Depending on the individual aircraft, it is not unusual to change aileron trim settings as the airspeed changes (such as when the aircraft is slowing down for landing).

Andy