View Full Version : Trim Wheel
16th Nov 2011, 15:29
the trim wheel does not control altitude, rate of climb, or whatever else. It controls your airspeed.Just saw this on another thread (also stating it controls Aof A)-Ive never heard of this before anyone else care to comment.
16th Nov 2011, 19:13
In an aircraft with manual controls the trim wheel controls the angle of a hinged tab on a control surface.
The elevator trim tab is used to vary the force you are having to exert to hold the elevator where you want it to be. Similarly the aileron and the rudder trim wheels (where these are fitted) are used to control the force you are having to apply to those control surfaces.
Any other suggestion is incorrect.
16th Nov 2011, 19:22
Not always a tab on aircraft with manual controls. Some aircraft have adjustable tailplanes, such as the J-3 or DR400.
16th Nov 2011, 19:29
Seem to rember it was a spring on a Tiger Moth
16th Nov 2011, 19:30
You're right! Also a spring on a K-6E.
16th Nov 2011, 19:35
I clearly should have said a trim wheel is used to control the force a pilot is exerting and left it at that.
16th Nov 2011, 19:52
Dont worry John we know what you meant. They are also trying to work out why you hold the control surface first and then trim!
16th Nov 2011, 19:52
I've no idea what the question is doing here! Your kind nature got the better of you!
16th Nov 2011, 19:54
Let me explain for you.
I thought those with some genuine professional experience mind like to lend some advice
16th Nov 2011, 20:05
Well, some time ago a very experienced FTE showed me, with data, that I was flying an old-ish (not FBW, 60-ish tonne class) medium jet, more or less exclusively on the trim... Consequence of too many years and too many thousand hours on the type, on which I kept my currency in an airline while doing other things. I had learnt not to bother with the pitch inputs and was simply nudging the control column in the right direction and applying an accurate trim correction. I was NOT doing the same thing in testing...
You also remind me of flying trim and rudder circuits, to touchdown, in another time and place. Useful the day a colleague lost the elevator control (maintenance error) and knew what to do.
Is that what you were after?
Pull what - perhaps you could tell us which site that initial quote was on so we can avoid it?
PS Do not post a link - G will nuke it:)
20th Nov 2011, 16:49
Thanks, PW - I'm avoiding it:cool:
11th Dec 2011, 21:44
If you fly with a well trimmed aircraft, and you change the power setting without moving the controls, the new speed you will end at will be the same on a theoretical aircraft.
The theoretical aircraft I'm talking about keeps the same angle of attack whatever the power is (this is very simplified).
That is why a theoretical instructor might say that trim controls the speed.
On a real aircraft, things are different.
For instance, on a 172, speed will increase a bit if you reduce the power, and decrease in you increase the power. That is why when you go around on a 172, you must, if you start from a well trimmed descend at almost idle, push on the control when you apply full power, and retrim.
15th Dec 2011, 08:30
I do not totally agree with John Farley post.
A trim tab in a given position produces a hinge moment, which changes the position of the elevator (without any pilot force, and that also depends on the geared tab law).
For a given center of gravity position, and a given thrust effect (pitch torque, increase of dynamic pressure on the HTP, and change in downwash), this elevator position equilibrates in pitch the aircraft for a given lift coefficient (Cm=0). This lift coefficient, for a given weight, gives a speed.
Of course, in practical, you want to cancel the pilot effort for a given speed and attitude, and you trim the aircraft. whenever you change power or speed, you have to trim again.
Comet 2C Elevator Trimming
The Comet 2C as used by the RAF had a large elevator trim wheel handily beside the centre power lever quadrant. The break-out force for elevator using the spring feel powered flying controls was measured at 5 pounds. There was a tiny amount of friction on the trim wheel. Consequently I found that nearly all manoeuvres in pitch could be best achieved by resting the left hand on the yoke and making all pitch inputs with the right hand using the trim wheel.
It was a bitch of a thing to fly otherwise having breakout forces for ailerons of 11 pnds and 35 pnds for rudder. Spring feel gave absolutely no feel of indicated airspeed.
We TPs at Boscombe Down recommended a change from spring feel to Q feel.