electric trim tab actuator

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Re: electric trim tab actuator

Postby stede52 » Tue Apr 03, 2012 9:06 am

Just FYI, the Highwing cover is not deep enough for the way the servo is mounted on the Highlander elevator. On the kit fox the servo fits deeper in the elevator. I've tried it. I made my own cover.
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Re: electric trim tab actuator

Postby gkremers » Tue Apr 03, 2012 5:48 pm

Steve,
Another part you can sell to the group!!

Gary
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Re: electric trim tab actuator

Postby stede52 » Tue Apr 03, 2012 11:45 pm

Sorry, this one is a one off. I used a lost foam technique to build the part so I don't have a mold.
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Re: electric trim tab actuator

Postby Dave Krall CFII SEL SES » Wed Apr 04, 2012 1:03 am

I guess we'll split a plastic soda bottle open. Could get fancy and even use it for a mold....
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Re: electric trim tab actuator

Postby SheepdogRD » Wed Apr 04, 2012 4:09 am

Dave Krall CFII SEL SES wrote:I guess we'll split a plastic soda bottle open...

The fairing Gil used -- from Sky Raider -- looks an awful lot like a blister pack from some retail product -- the closest I can imagine is a heel sander, or some such thing:
Trim Servo Fairing 1.jpg

Blister packs and soda bottles are often PETG (Poly Ethylene Terephtalate, Glycol-modified); they're tough and light. The model aircraft canopies I mentioned are the same material. But PETG is not polyethylene. It's hard to glue, and it doesn't edge-bond. Epoxy seems to work if the surface is roughened. Mechanical fastening works with washers to spread the load.

I think a blister pack might be a workable solution; it may be worth buying a product and giving it away just to get the blister pack. I'll look around . . .
Richard Holtz
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If just enough is really good, then too much ought to be perfect.
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Re: electric trim tab actuator

Postby Dave Krall CFII SEL SES » Sat Apr 21, 2012 2:22 am

stede52 wrote:I've always used the T3-12a because you want a very slow moving servo since you need very little movement.


Steve, did you do any shimming with the T3-12A or alter the trim tab bell crank? Thanks
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Re: electric trim tab actuator

Postby stede52 » Sun Apr 22, 2012 1:31 am

If you look closs at my setup, I drilled a new hole in the trim control horn because the original hole was too big for the control rod clevis pin. There is no need to shim the servo itself.
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Re: electric trim tab actuator

Postby Dave Krall CFII SEL SES » Sun Apr 22, 2012 1:50 am

stede52 wrote:If you look closs at my setup, I drilled a new hole in the trim control horn because the original hole was too big for the control rod clevis pin. There is no need to shim the servo itself.


Thanks, yeah, I saw the hole you have there. We thought about doing that type of hole but, thought it would be a dangerous comprimise of the bellcrank's strength at that critical attach point. Possibly leading to failure and nasty trim tab flutter in flight -maybe not.

We have more angle in the line of force formed by the actuator arm and the attach assembly going to the bellcrank than I would like to see, so I thought shimming the aft end of the actuator box about 3/4" down from the surface might help.

Or, we could rivet on an additional, exterior mounting plate onto the one already inside the elevator from the outside, to put the whole assembly farther forward so the angle of force is less acute.
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Re: electric trim tab actuator

Postby stede52 » Sun Apr 22, 2012 10:49 am

Dave,
you will not compromise the integrety of the bellcrank as long as the distance between the edge of the hole to the edge of the bellcrank is no less the diameter of the drilled hole. You also will not have an issue with the angle, used electric trim on both airplanes and you have more then enought strenght and throw to trim with, in fact you will never use all the trim except for landing assuming your plane is CG'd correctly. I have never used more then 1/4" of elevator trim to maintain level flight.
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Re: electric trim tab actuator

Postby Gil T » Sun Apr 22, 2012 12:19 pm

IMG_1975.JPG
IMG_1974.JPG
IMG_1219.JPG
Its been a while since I installed my trim motor but the only tweaking I can remember is the filing I did on the forward part of the tab arm which you can see in these pictures. And as you can see there is a whole bunch more trim movement than you will ever need. The pictures show the full throw of the shaft from the trim motor.

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Re: electric trim tab actuator

Postby stede52 » Sun Apr 22, 2012 7:59 pm

If you haven't flown with one of these before, you be surprise at how fast it will change the aircraft attitude. You only need to momentarily hit the trim button otherwise it will overtrim. so the further out you go on the bellcrank the slower it will react.
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Re: electric trim tab actuator

Postby gkremers » Sun Apr 22, 2012 9:03 pm

Steve,
My RV7A reacts the same way. You don't really hold the rocker switch down for trim. Just a tap or two is all it takes.

Should start fitting mine in another week or two. The fabric plates and filler to help with the transition of the trailing edge and fiberglass leading edge took longer than anticipated. I'm using Super Fill 2 part epoxy (same stuff I used on the Pulsar XP) and it takes 18 hours or so to cure enough for sanding.

Gary
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Re: electric trim tab actuator

Postby Dave Krall CFII SEL SES » Mon Apr 23, 2012 5:08 pm

stede52 wrote:Dave,
you will not compromise the integrety of the bellcrank as long as the distance between the edge of the hole to the edge of the bellcrank is no less the diameter of the drilled hole. You also will not have an issue with the angle, used electric trim on both airplanes and you have more then enought strenght and throw to trim with, in fact you will never use all the trim except for landing assuming your plane is CG'd correctly. I have never used more then 1/4" of elevator trim to maintain level flight.


Shouldn't that really be 1 1/2 or 2 diameters for safety, especially in a critical component such as this? We're going to fill in the existing hole with steel and redrill a new bellcrank hole, giving a better margin of strength and safety....
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Re: electric trim tab actuator

Postby stede52 » Mon Apr 23, 2012 10:06 pm

I'm just telling you what will work for that thickness of steel, you can do whatever you wish.
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Re: electric trim tab actuator

Postby Dave Krall CFII SEL SES » Tue Apr 24, 2012 2:15 am

Useful info on hole, form radii and stock thickness:

http://www.resmfg.com/design.html
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