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Landing; trim set

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Spice Cat23/02/2011 20:58:06
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A member of my club has recommended putting in two clicks of down trim on the final approach before landing. In theory, this seems like a good idea and when the weather improves (groan), I will be trying it out.
Anyone else do this?????
Doug Ireland23/02/2011 21:08:08
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Down trim?
fly boy323/02/2011 21:09:29
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Hi spice cat, yes, an exellent flier in our club always does this,with superb landings. The idea being on final approach, with speed and height ok, the model will now be in a downward attitude,so more or less only the elevator needs to be controlled down to the flair. I suppose the one must remember to give 2 clicks up trim for the next flight. Cheers FB3
Danny Fenton23/02/2011 21:09:39
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Hi, I have a few models where its not really necesary, perhaps we instinctively keep the nose down slightly from experience. However my Hurricane suffers a fair trim shift when the gear and flaps come down. In the past I have compensated by flying the model with a bit of down stick, sort of letting my thumb find a new centre point. This is all very well until you flare. If you have a bit of expo (which I do) then what you will find is a little up will result in very little up elevator, but the same amount of stick movement down results in much greater elevator deflection, and it can cause the model to oscillate, worst case you could stall the model by over compensating.
I have now set flight modes up on my Tx, though i haven't tried it yet, the idea is that you trim the model for the various stages of flight. Takeoff, normal flight, and landing.
 
Cheers
Danny
fly boy323/02/2011 21:15:54
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Hi, another member of my club is learning to fly full size (cessna) and he has spoken of landing trim, but as yet I have not asked him about it. Cheers
Tim Morton23/02/2011 22:50:58
188 forum posts
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could one not programme a modern Tx to do that? Wheels down and the trim is added, wheels up and the trim is removed/changed?
Gary Binnie23/02/2011 23:05:19
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Tim, yes, I'm sure you can.
 
I add two clicks of nose down trim at the 'low key' point (opposite me on the downwind leg of the circuit) but only for gliders.
 
It's a safeguard against wind gradient effects (slow moving air near the ground robs airspeed). Gliders are flown very much on the pitch trim.
 
The brief for full-size gliders is to increase speed to the approach speed at the 'low key' point (typically 50-55 knots against a normal gliding speed of 45 knots) and trim for it, although any seasoned pilot should automatically retrim for the new attitude/speed.
 
For full size powered aircraft you are often slowing down for the landing approach so you would do the opposite, trimming nose up!!
 
Never been advised to do it with powered models but the only harm I can see is a long landing, better that than a short landing with no airspeed!
 
Cheers
 
GB
 
 
 

Martin Harris23/02/2011 23:08:29
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I'd second Doug's question mark...
 
You would normally need to slow down on the circuit and approach from "cruise" speed trim which means trimming nose up a little. Watch a full size approach and you'll see a relatively nose high attitude - ideally you want to establish a steady glide path with a little power so that adjustments can be made either way in case you run through rising or sinking air - increasing the speed by dropping the nose will lead to an increased float and landing distance.
 
I have experimented with programming the right hand slider on my FF10 as an elevator trim which is easier to operate than the normal trim control.
Tim Morton23/02/2011 23:08:53
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Cheers gary - I'll try that once I get something sorted with a warbird
Gary Binnie23/02/2011 23:20:09
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To expand slightly on the full-size 'landing trim', there isn't one. There will be a recommended approach speed though, usually a minimum of 1.4 times the stalling speed.
 
Pilots are taught to retrim whenever they feel a force on the stick that wants to take the aeroplane away from the attitude/new speed that they put it in. Think of it as cruise control.
 
Lowering/raising the flaps does have a big pitching effect in some aircraft, the Piper Cub needs loads of turns on the trim handle when the flaps are lowered but strangely the Piper Pawnee (which uses the Cub wing and flaps) needs no trim adjustments at all!
 
Spoilers on model gliders pitch the nose down (as they do on the full size), I cheat and mix this out with the elevator, automatic trim!!
 
Flaps pitch the nose up when deployed, the opposite effect. Tricky in a model because you have no direct attitude/airspeed feedback.
 
 
 
 
 

Biggles' Elder Brother - Moderator23/02/2011 23:27:31
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I agree with Martin, and by implication Doug. With a powered model the "ideal" landing - if such a thing exists! - would involve controlling your speed with the elevator and your rate of decent with the throttle. This maybe slightly easier to do with a little up elevator trim - it can relieve you of the task of holding back the stick so much on the glide path during finals while you control the speed during decent. I usually aim for the model to be level, or very slightly nose up, on the final stages of approach. In the case of a heavy biplane like my Pitts I find this type of approach under power is the only safe way to do it - otherwise it simply comes in either too fast or dangerously slow.
 
TBH I don't usually actually dial in the up-trim, as holding the stick back is no great harship for us - in the full size it can be slightly more work expecially in a large aircraft with purely manual controls.
 
BEB
Gary Binnie23/02/2011 23:32:53
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Some of the high-end computer trannies can be programmed to lower the flaps and gear, retrim, slide the canopy open and light the pilot's pipe just by lowering the throttle!
 
It's working out how to do it that is the hard bit!!
 
To drop a name for a second I was flying in a competition with Chris Foss last year, I noted that the glider I was flying (one of his designs) pitched markedly nose down when using the spoilers. He said 'just pull the stick back a bit then'.
 
I couldn't because it goes against my full size 'primacy' experience to do it.
 
He also said that I shouldn't be launching my wooden creation on an F3J monster winch per the note on the plan that says 'no winch launching'.
 
There is no note but, as always, he was right!! A wise owl if ever there was one.
 
Digressing but an almost on topic anecdote!!
 
Cheers
 
Gary
 
 

Edited By Gary Binnie on 23/02/2011 23:36:18

Danny Fenton24/02/2011 08:46:10
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Hi Gary, this is what I was referring to in my first post. thats flight modes on my JR,
Takeoff mode- gear down flaps up and trims/expo as reqd.
Flight - gear up flaps up and trims/expo as reqd.
Landing mode - gear down flaps down and trims/expo as required.
 
Its fairly easy on the PCM9XII to set up just enable flight modes then whatever you do is stored for each position of the switch.
 
Cheers
Danny
 
 
Lee Smalley24/02/2011 09:03:09
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well we are not flying full size and i would suspect that they only put down trim in to compensate for the effect of flap deployment, no you should in my opinion use your elevator and throttle to manage your approach altitude
Danny Fenton24/02/2011 09:16:23
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I would agree but full size don't use expo the way some of us do.
 
If you hold in up and use the throttle to position your model on the approach, because of expo - relaxing the up elevator will give very little elevator deflection, increasing the up elevator on the stick by the same amount can give two or three times the deflection on the elevator because the stick is not centred. You really need to trim the model so the stick is closer to centre on your approach or the Expo or will work against you. If you don't use large expo it wont be an issue.
As I say it is only an issue on my warbirds, no issue on any sports models or Chipmunk.
They don't tend to have airflow unsettling dangly bits
Cheers
Danny
Doug Ireland24/02/2011 09:38:18
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Posted by fly boy3 on 23/02/2011 21:15:54:
Hi, another member of my club is learning to fly full size (cessna) and he has spoken of landing trim, but as yet I have not asked him about it. Cheers

FB3. When I was learning to fly (in a Cessna 150 back in the '70s) one thing the instructor kept hammering on about when getting set up on Base Leg was "elevator controls airspeed and throttle controls rate of descent". When slowing from cruising speed of 80Kts to the safe flap deploymrnt speed of 60Kts, a fair amount of up elevator trim had to be used to maintain the speed. Re-trimming needed after each flap setting. If you were doing a "touch-and-go" it needed a good shove forward on the stick to keep the nose down while spinning the trim wheel frantically before your left arm went numb!

Tim Mackey24/02/2011 09:54:34
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I never alter the trims at all after its all been set up to fly straight and level - I do however use a lot of expo on almost all my models, so find "trimming" the attitude of the model in various flight phases is easy enough by gentle application of the required controls. With retracts and flaps etc, I have either mixed in compo using the tx mixing, or again, adjust pitch with elevator stick, following test flights "up high" to assess the effect of said functions.
Ultymate24/02/2011 10:09:04
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With my power models I fly what I've got ie don't want to be fiddling with trims and switches unless absolutely unavoidable. It's a different story with gliders though with variable crow/butterfly and elevator trim etc are all part of the game, that said there's no throttle to worry about.
Spice Cat24/02/2011 22:03:59
1304 forum posts
129 photos
Thanks for this. I'll give it a go and see if it makes any difference. As it is, I cannot tell you what exactly I do during landing as I am suffering with palpitations and tunnel vision.....

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