Use of the trim wheel
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Use of the trim wheel
I know we were taught to trim out forces and not to "fly on the trim wheel". However, I've noticed myself doing the following to make adjustments to speed when on base or final:
I'll glance at the ASI and notice that my average speed is, say, 5 knots faster than it should be. Since I know from experience that a quarter turn back on the trim wheel gives me that 5 knot reduction, I go ahead and dial it in. I then continue controlling descent with throttle and glance back at the ASI to confirm the speed change. To me, this is far easier than using the "correct" method of pitching for the correct speed and then trimming out the force when I'm busy in the circuit already.
Does this behaviour cause people to clasp their hands to their ears and cry "Unnatural", or is it acceptable practice?
MQ.
I'll glance at the ASI and notice that my average speed is, say, 5 knots faster than it should be. Since I know from experience that a quarter turn back on the trim wheel gives me that 5 knot reduction, I go ahead and dial it in. I then continue controlling descent with throttle and glance back at the ASI to confirm the speed change. To me, this is far easier than using the "correct" method of pitching for the correct speed and then trimming out the force when I'm busy in the circuit already.
Does this behaviour cause people to clasp their hands to their ears and cry "Unnatural", or is it acceptable practice?
MQ.
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For small corrections, don't worry about it, as long as you don't try to 'fly' the a/c using the trim for larger changes I can't see the problem. (I do it myself, but my students aren't allowed until they have demonstrated competance the 'proper' way.)
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Dewdrop wrote:
Uh?
You're not putting it out of trim, surely you're just changing its trim.
I think an a/c is out of trim if I have to sustain a push or a pull to keep the machine at the speed/attitude I require.
Pulling back to slow down gets it out of trim, taking the stick forces out with trim gets it back in - but it's two separate actions at a 'critical time' when a simple tweak of the wheel is a single action achieving the same desired effect.
Seems fine to me.
Steve R
The only comment I would make is that by using the trim wheel in this way you are effectively putting the aircraft out of trim in what is the most critical time of the flight.
You're not putting it out of trim, surely you're just changing its trim.
I think an a/c is out of trim if I have to sustain a push or a pull to keep the machine at the speed/attitude I require.
Pulling back to slow down gets it out of trim, taking the stick forces out with trim gets it back in - but it's two separate actions at a 'critical time' when a simple tweak of the wheel is a single action achieving the same desired effect.
Seems fine to me.
Steve R
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I imagine the the drawback is that you probably need to make several adjustments as using the trim wheel like that is, in other words, trial and error. Do the standard thing of setting your attitude and then removing the control force - one adjustment and possibly another tweak should be sufficient.
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Dewdrop
It can't be out of trim if you are merely turning the trim wheel.
The elevator trim is a control system which maintains airspeed; ie it sets the speed at which the aircraft will fly. (I think it actually controls the AOA but that is equal to airspeed, for a given configuration)
An aircraft is out of trim if you are pushing/pulling the yoke.
It is frowned upon by instructors but I can't see anything wrong with making small altitude adjustments with the trim wheel, and airspeed adjustments SHOULD be done with the trim wheel, otherwise if you lose concentration the IAS will drift back to whatever the trim as set to, and if it was miles out that value could be too low...
It can't be out of trim if you are merely turning the trim wheel.
The elevator trim is a control system which maintains airspeed; ie it sets the speed at which the aircraft will fly. (I think it actually controls the AOA but that is equal to airspeed, for a given configuration)
An aircraft is out of trim if you are pushing/pulling the yoke.
It is frowned upon by instructors but I can't see anything wrong with making small altitude adjustments with the trim wheel, and airspeed adjustments SHOULD be done with the trim wheel, otherwise if you lose concentration the IAS will drift back to whatever the trim as set to, and if it was miles out that value could be too low...
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I regard myself as too inexperienced to answer your question but the following tale may have some relevance, I'd be interested to hear what others think.
I had a rather interesting experience during my training for the night rating. During the climb out from a touch and go (pitch dark, on instruments) the instructor announced a circuit emergency where the control wheel had fallen off (not a very likely one
), he asked me to continue to fly the circuit using just trim and rudder.
So off we went, continued climb to circuit height, turn onto downwind using secondary effects, complete downwind checks, turn base and then final. Never done that before and it was interesting to see just how much control you can have with just the trim tab and rudder.
Didn't manage to complete the full circuit tho, I chickened out on the turn onto final as I was beginning to oscillate in pitch rather more than I cared for
I had a rather interesting experience during my training for the night rating. During the climb out from a touch and go (pitch dark, on instruments) the instructor announced a circuit emergency where the control wheel had fallen off (not a very likely one
), he asked me to continue to fly the circuit using just trim and rudder. So off we went, continued climb to circuit height, turn onto downwind using secondary effects, complete downwind checks, turn base and then final. Never done that before and it was interesting to see just how much control you can have with just the trim tab and rudder.
Didn't manage to complete the full circuit tho, I chickened out on the turn onto final as I was beginning to oscillate in pitch rather more than I cared for
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I flew a C172 for 30 minutes, and landed withough using the yoke at all (no elevator or aeileron) just to practice in the even of a control wire failure 
One example of where flying using the trim doesn't work is say leveling off from a climb. You need to push the nose forward and hold it there until the speed increases, other wise you'll be trimming till the cows come home....Some POH's recommend "three twists of the nose up trim on final" to help in the flare, so now you're flying the final stages of an approach out of trim anyway, having to keep nose down pressure on the yoke. Still makes life easier. What you do sounds fine to me, whatever's easiest really...
EA
One example of where flying using the trim doesn't work is say leveling off from a climb. You need to push the nose forward and hold it there until the speed increases, other wise you'll be trimming till the cows come home....Some POH's recommend "three twists of the nose up trim on final" to help in the flare, so now you're flying the final stages of an approach out of trim anyway, having to keep nose down pressure on the yoke. Still makes life easier. What you do sounds fine to me, whatever's easiest really...
EA
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It's a good exercise to try and fly the a/c without it's primary controls. I woudn't try it for the first time in the circuit though!
The scenario could be quite real, what if you had a control restriction? A mixture of power, rudder and trim is quite an effective way of controlling an a/c, but you do need to be very careful and make all inputs gradually and smoothly.
Don't try this on your own for the first time, but on your next flight with an FI get them to demonstrate it and have a good go.
The scenario could be quite real, what if you had a control restriction? A mixture of power, rudder and trim is quite an effective way of controlling an a/c, but you do need to be very careful and make all inputs gradually and smoothly.
Don't try this on your own for the first time, but on your next flight with an FI get them to demonstrate it and have a good go.
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I'll probably get flamed for this but anyway....
When learned many years ago in the 150 I was taught to wind in 4 turns of trim when reducing power on base leg. Much trim re-correction followed and I continued to fly like that until one day on a check ride in the US an instructor said "Why are you doing all that? You don't need to touch the the trim! Look".
He proceeded to show that for each power adjustment and flap setting the aircraft would settle out at close the correct speed anyway. It's designed that way. All the trim adjustments just caused hunting.
Maybe students aren't taught that way now, maybe it was done to make sure they slowed down before putting in flaps, and maybe I unconciously operate trim anyway, but I'm not aware of making many adjustments or having control forces during the approach nowadays and the PA-28-161 settles nicely at the POH 63Kts full flap from what is close to the cruise trim setting. Of course other aircraft may well have different characteristics.
David
When learned many years ago in the 150 I was taught to wind in 4 turns of trim when reducing power on base leg. Much trim re-correction followed and I continued to fly like that until one day on a check ride in the US an instructor said "Why are you doing all that? You don't need to touch the the trim! Look".
He proceeded to show that for each power adjustment and flap setting the aircraft would settle out at close the correct speed anyway. It's designed that way. All the trim adjustments just caused hunting.
Maybe students aren't taught that way now, maybe it was done to make sure they slowed down before putting in flaps, and maybe I unconciously operate trim anyway, but I'm not aware of making many adjustments or having control forces during the approach nowadays and the PA-28-161 settles nicely at the POH 63Kts full flap from what is close to the cruise trim setting. Of course other aircraft may well have different characteristics.
David
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When I did my aeros instruction many years ago in our Chippy we often used to fly to and from the aeros area without using the stick - just trim, rudder, and power settings. I never attempted a landing and suspect it would be more of a semi-controlled crash in a taildragger, especially if the wind was anything but dead calm. Good practice, though.
And don't forget, if your elevator is physically jammed, the trim tab will work as a small elevator - but in reverse sense. I heard of a guy taking off in a DC3 in WW2 with the elevator control locks in - he managed to fly a cicuit and land back using reverse trim as an elevator control.
SSD
And don't forget, if your elevator is physically jammed, the trim tab will work as a small elevator - but in reverse sense. I heard of a guy taking off in a DC3 in WW2 with the elevator control locks in - he managed to fly a cicuit and land back using reverse trim as an elevator control.
SSD
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And don't forget, if your elevator is physically jammed, the trim tab will work as a small elevator - but in reverse sense
How often have you heard of the elevator becoming jammed? If it did happen at low level, I don't think you'd stand a chance. And at altitude, you'd have time to try various things, and you'd work out which sense the trim wheel works in by trial and error.
(This subject seemed to form a disproportionately large portion of the ATPL syllabus. It's interesting, and helps understand how each of the trim systems works, but doesn't seem to have very much practical use as far as I could tell.)
FFF
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One of my instructors always taught me to set the trimmer nose hight (not excessivly) for take off so as to make the climb out less tiring and slightly nose down for approach for the same reason.
As part of a PFL (and probably a real one), we were also taught to trim for best glide speed.
As part of a PFL (and probably a real one), we were also taught to trim for best glide speed.
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FFF
I'm talking about your standard elevator trim tab a la Cessna 172, 150, Chippy etc. A seperately hinged cut out in the elevator's trailing edge controlled by the trim wheel. What's a V1 tailplane BTW?
As for the anti-servo type used on the PA28 all flying tail - I've no idea. It probably wouldn't work at all as an elevator in the event of the all flying tail becoming jammed.
It did happen - to that DC3 - on take off (you can't get much lower than that) and the technique saved them. Don't give up so readily!
For the same reason, if you run out of elevator effectiveness (say a badly shifted CG) then full forward stick with full back trim will give max elevator 'down' effect, vice versa for max elevator up effect (assuming you have the physical strength to hold the out of trim condition with the stick - OK on the Chippy but not on heavier types). Why? Think about it; You are holding full forward stick and need more down elevator. What is the trim tab but a small elevator? If you want it to add to the total 'down elevator' force you want it to hinge 'down', just like the main elevator of which it is part. To acheive this require winding on full 'up' trim.
SSD
I'm talking about your standard elevator trim tab a la Cessna 172, 150, Chippy etc. A seperately hinged cut out in the elevator's trailing edge controlled by the trim wheel. What's a V1 tailplane BTW?
As for the anti-servo type used on the PA28 all flying tail - I've no idea. It probably wouldn't work at all as an elevator in the event of the all flying tail becoming jammed.
It did happen - to that DC3 - on take off (you can't get much lower than that) and the technique saved them. Don't give up so readily!
For the same reason, if you run out of elevator effectiveness (say a badly shifted CG) then full forward stick with full back trim will give max elevator 'down' effect, vice versa for max elevator up effect (assuming you have the physical strength to hold the out of trim condition with the stick - OK on the Chippy but not on heavier types). Why? Think about it; You are holding full forward stick and need more down elevator. What is the trim tab but a small elevator? If you want it to add to the total 'down elevator' force you want it to hinge 'down', just like the main elevator of which it is part. To acheive this require winding on full 'up' trim.
SSD
Why do it if it's not fun?
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What's a V1 tailplane BTW
There is no separate trim tab. Instead, the trim wheel changes the angle of incidence of the whole of the tailplane. The advantage of this type of trim system is that the elevator should, with no stick force being applied, line up with the forward part of the horizontal stabiliser, thus giving you less drag than the C172 design (where the elevator will have a very large angle of attack in some attitudes) or even the PA28 design (where the trim tab will have a large angle of attack).
As for the anti-servo type used on the PA28 all flying tail - I've no idea. It probably wouldn't work at all as an elevator in the event of the all flying tail becoming jammed
FFF
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Twiddling the trim wheel to make glide path corrections may work okay on a C150 or PA28, but remember that that techniques that you are taught are generic and are devised to work for all aircraft types. Try it on a much heavier aircraft, such as a Cessna 210, which has much greater inertia and responds much slower to trim changes, and you'll find yourself oscillating above and below the correct glide path as you try to get the trim right.
Remember the technique: select attitude - hold and wait for the aircraft to respond - trim. If you do this, you'll be able to fly a stable approach in virtually any aircraft type.
Re the method of deliberately setting the trim nose-up for takeoff, I think that this is a rather bad idea. As soon as the aircraft leaves the runway, it will be in ground effect and will start to climb steeply. Once out of ground effect, the rate of descent and the speed will drop sharply - not a very good position to be in! Set the trim to the recommended takeoff position and use pressure against the trim for transient pitch changes where necessary.
Some aircraft types that I have flown actually need forward pressure on the stick against the trim when you leave the ground to allow you to pick up speed before climbing out of ground effect. If you fly a tailwheel type, you'll need to hold the stick quite a long way forward at the start of the takeoff run in order to raise the tail. You then start to apply gentle back pressure to hold the attitude and gently increase the angle of attack. You couldn't do this in a controlled fashion with the trim wound back - generic techniques again!
Remember the technique: select attitude - hold and wait for the aircraft to respond - trim. If you do this, you'll be able to fly a stable approach in virtually any aircraft type.
Re the method of deliberately setting the trim nose-up for takeoff, I think that this is a rather bad idea. As soon as the aircraft leaves the runway, it will be in ground effect and will start to climb steeply. Once out of ground effect, the rate of descent and the speed will drop sharply - not a very good position to be in! Set the trim to the recommended takeoff position and use pressure against the trim for transient pitch changes where necessary.
Some aircraft types that I have flown actually need forward pressure on the stick against the trim when you leave the ground to allow you to pick up speed before climbing out of ground effect. If you fly a tailwheel type, you'll need to hold the stick quite a long way forward at the start of the takeoff run in order to raise the tail. You then start to apply gentle back pressure to hold the attitude and gently increase the angle of attack. You couldn't do this in a controlled fashion with the trim wound back - generic techniques again!