Muliplex Alpha Junior Radio Instalation - RC Groups
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Apr 08, 2004, 11:19 PM
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Muliplex Alpha Junior Radio Instalation

I need advise on how to install my radio Hitec 555 & standard or HS 81 servos into my Alpha Junior.

I have never fitted out a fibreglass fuz , always been a trad balsa builder to date. I do not have the instructions as I bought the plane at a recent club swap meet in Calgary.

Can anyone help with tips, instructions, even pics ?

Will HS81s be man enough for rudder & elevator or do I need Std servos ?

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Apr 09, 2004, 01:21 AM
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The HS81 servos will be fine for the Alpha Junior.

Wrap the battery in foam padding and push it as far forward in the fuselage as you can. Wrap the receiver in foam padding and put it in the fuselage just behind the battery. Mount the servos on a tray behind the receiver as far forward as the pushrods permit without crowding the receiver. Do a trial balance with the radio gear loosely in place to make sure that it will require at least a little lead in the nose to balance but will be a bit tail heavy without the lead in the nose.

Make a servo mounting tray from 6MM (1/4") poplar plywood or 4mm (3/16") birch plywood. The tray has to be as long or a bit longer than the overall length of the servos including the mounting lugs. The width of the tray has to fit between the fuselage sides without causing the fuselage sides to bulge at all. An easy sliding fit is what is desired. Make a rectangular cut out in the center of the tray that is as wide or wider than the width of two servos. The length of the cut out should be the length of the servo body plus about one or one and a half MM. The length of the cut out should be just enough to allow the servo to be inserted into the tray by cocking the servo and inserting the cable first. Loosely assemble the servos in the tray so that the mounting lugs lie on the top of the tray and insert the tray in the fuselage. Position the tray so that the output arms of the servos line up with the pushrods and mark the inside of the fuselage for the tray position. Widen the cut out in the tray if necessary to get the servo arms to line up with the pushrods. Remove the servos and epoxy the tray to the sides of the fuselage and epoxy the tray to the fuselage sides using the markings to accurately position the tray. Reinstall the servos loosely into the tray and hook up the pushrods at both ends. Using the eyelets in the servo mounting lugs as drill guides, drill for the servo tray for servo mounting screws and screw the servos to the tray.
Last edited by Ollie; Apr 09, 2004 at 01:38 AM.
Apr 09, 2004, 02:28 AM
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Thanks again Ollie
Apr 09, 2004, 02:37 AM
Registered User
My test balances show significant additional wieght is required in the nose to balance at the spar CG.

Is this the CG as usual ? I do not have the benefit of plans or instructions.