Q-500 Racing Discuss AMA 428, AMA 424, and any other variants of Quickie 500 racing

Viper Repair

Old 05-26-2009, 09:19 PM
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Default Viper Repair

Hi All,

Had a little mishap at out last race. I broke the firewall out of my Viper and would like to make the repairs properly, can I just cut up some fiberglass cloth to use with epoxy to put a fillet on the inside of the firewall & tank compartment. When I flew this plane it needed about 3/32 of up trim in the elevator to fly level. I understand that this is a common occurance with this plane. Just to be sure, to take this trim out I need to shim the trailing edge of the stablelizer UP. Any suggestions about how much i should start with when I shim this up?? I will glue it on after I get it shimmed to fly with no elevator trim. Maybe, I don't need the epoxy/glass or carbon fillet on the inside if I use triangle stock on the inside and glass cloth on the outside. Any suggestions would be greatly appreciated.


Old 05-26-2009, 10:38 PM
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Default RE: Viper Repair

Hi Ken,

If you're going to repair the firewall, its pretty much secure you will need to clean it up of dirty and gas.  Use your dremmel to lift all the glue and the outmost layer of skin (fiber, paint, everything).  align the firewall and glue it using glass in the outside.  In the inside you can use a mix of chopped glas and epoxy or chopped carbon fiber is better.

About the stab,  the common problem with these planes is a positive incidence in the stab.  Place your plane making secure its 0° of incidence the wing and the firewall with 0° of thrust. Then put your stab and adjust the fuse until the stab its at 0° of incidence.  Then glue it in place.  You shouldn't have any further problem.

Let me know how it comes.

good luck,


Old 05-27-2009, 12:43 AM
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Default RE: Viper Repair

Ken, also when you,ve glued back the firewall bulkhead you should also make up a new top front lid out of 1/8 th ply and glue this on instead of using the stock balsa lid, then pin all 4 sides of the fuse with 3/4 inch lengths of cane skewers [ 8 pieces ] epoxy these into pre drilled holes. as for your rear tail trim, you said you had to add 3/32 of trim. this means you have to add 3/32 of packing under the rear end of tail. just make sure you get the main front bulkhead aligned as it was originally otherwise this tail trim and other trims will be out more. another thing is when you get the tail incidence correct , dont glue the tail on to the fuse as if you should have a bingle the repair job will be alot harder, as in removing the damaged tail from the fuse.
Old 05-27-2009, 07:18 AM
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Default RE: Viper Repair

Rather than adjust the tail.... especially if it is already glued on... leave the tail at "0" degrees and just raise the front edge of the wing until it flys with no up elevator trim.... I like to add 1/4"balsa doubler to the inside top edge of the wingsaddle and then pot the wing at it's properincidence to the saddle using micro-ballons and a good slow epoxy(wax the wing first).

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