Trim Wheel
Thread Starter
Joined: Feb 2009
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From: England
Trim Wheel
the trim wheel does not control altitude, rate of climb, or whatever else. It controls your airspeed.
Do a Hover - it avoids G
Joined: Oct 1999
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From: Chichester West Sussex UK
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.
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.
Joined: Dec 2007
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From: France
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?
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?
Thread Starter
Joined: Feb 2009
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From: England
Joined: Oct 2010
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From: France
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.
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.
Joined: Dec 2011
Posts: 8
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From: France
Hello,
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.
chti guillaume
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.
chti guillaume
Joined: Oct 2003
Posts: 1,300
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From: Canberra Australia
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.
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.
