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Elevator horn

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fly boy312/02/2019 17:48:46
3503 forum posts
18 photos

Hi all, just noticed on plan, that the elevator horn must be raked forward. This means I will have to make one ( ply or plastic ?), also what is the reasoning behind this ? Cheers

Nigel R12/02/2019 18:08:22
2985 forum posts
471 photos

Differential movement.

If horn is underneath, result is, more down than up.

If horn is on top, result is more up than down.

Or it could be a mistake in the plan.

What plan is it?

jrman12/02/2019 18:11:51
346 forum posts
3 photos

Isn't it the other way round Nigel?

Denis Watkins12/02/2019 18:20:17
3814 forum posts
54 photos

If this is a lightweight model, then cut the horn from plywood

But for heavyweights, make one from PCB, or paxolin,

Printed Circuit Board

Don Fry12/02/2019 18:27:55
3841 forum posts
42 photos

Hi Boy, is it raked forward, so the horns hole is above the elevator, tailplane join. If so, it's to get equal up/ down movement off the push rod.

fly boy312/02/2019 18:51:11
3503 forum posts
18 photos

Thanks all for quick replies. The plan is for Flying Aces

Sportster, from Outerzone. The horn is raked forward, and model will be less than 4 lbs auw. Also the horn is underneath. Cheers. ps sorry cannot send pic. of plan from iPad.

Edited By fly boy3 on 12/02/2019 19:05:53

jrman12/02/2019 18:59:04
346 forum posts
3 photos

FB3, If the hole for the clevis is in front of the hinge line you will get more up than down for the same degree of servo rotation.

John Duncker12/02/2019 19:06:44
79 forum posts
7 photos

More up than down

fly boy312/02/2019 19:09:27
3503 forum posts
18 photos

Thanks jrman, and yes the hole is well in front of hinge line if drawing is correct.

Bruce Collinson12/02/2019 20:34:00
384 forum posts

There are commercially available plastic horns with a long sweep forward and if the Mancave wasn’t so untidy I’d find one and tell you what to look for. Might well be Multiplex. Modelshop Leeds has them.


Nigel R12/02/2019 21:16:39
2985 forum posts
471 photos
No it works the other way around chaps. Try it and see.

On this plan, it is raked forward so that you can use an internal horn inside fuselage which is soldered to the elevator joiner. The rake is purely to avoid bashing the tailpost when you move elevator upwards.

Edited By Nigel R on 12/02/2019 21:17:51

Frank Skilbeck12/02/2019 22:39:18
4430 forum posts
101 photos

If you offset the servo arm by the same amount, i.e. if the elevator horn is 15 deg in front of the elevator hinge line then move the servo horn round on the splines by a similar amount, should minimise any differential movement.

BTW I make horns where required out of epoxy glass sheet.

Edited By Frank Skilbeck on 12/02/2019 22:39:44

Engine Doctor12/02/2019 22:52:19
2272 forum posts
25 photos

For linear movement the hole in the horn or pivot point should be in line with the control surface neutral .

fly boy313/02/2019 20:56:16
3503 forum posts
18 photos

Hi all, thanks for the replies, I think Nigel R could well be right for the reason for the rake. Due to the rake I will still have some differential during operation. Frank and Engine doctor have also provided useful info together with others. Cheers.

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