How to check for twisted RV-6 fuselage?

mperrytrucking · #1 07-06-2013, 07:13 PM

I am buying a RV6 that has been wrecked. I suspect the fuselage may be twisted. Where is a good place to get a measurement? There will be no jig available. Please help

Kyle Boatright · #2 07-06-2013, 07:35 PM

I would place a level on the main spar carry through and compare it to the levelness of the horizontal stabilizer, or the two fuselage longerons right in front of the empennage.

The reality is that virtually all of these airplanes have a little twist somewhere. (Except mine, of course.) ;-)

mperrytrucking · #3 07-08-2013, 09:31 AM

Thank you kyle

Bob Axsom · #4 07-08-2013, 09:49 AM

I would level the canopy deck (fwd & aft and side to side) and go from there to check the rigging. If you don't have the builder's manual you may have to ask questions and get answers here or through Van's. My quick build fuselage was not perfectly square but that reference plane and the mutually perpendicular axis is what everything is rigged to. That may not be the implemented truth in every RV ever built - it takes a lot of measuring and rechecking to get the rigging right in spite of variations in a specific airframe.

Bob Axsom

az_gila · #5 07-08-2013, 10:22 AM

A slightly better location for determining the horizontal reference point for the entire aircraft might be the top surface of the F-604A bulkhead.

This bulkhead is about the only pre-drilled item on the -6x kits as it is individually matched by the factory to the wing spars.

The top of the fuselage longerons in the cockpit area should match the bulkhead, but since the holes between the F-604 and the longerons were builder drilled I would start with the F-604 as an initial reference.

Bob A. had a QB kit, but if yours was a SB, then the alignment of the cockpit rails and the F-604 is dependent on the accuracy and stability of the builders jig.

Steve Barnes · #6 07-08-2013, 06:02 PM

If there are no ripples anywhere on the exterior skins then is it doubtful that you have a twisted fuselage.

Steve "The Builders Coach"

az_gila · #7 07-08-2013, 07:12 PM

Quote:

Originally Posted by Steve Barnes

If there are no ripples anywhere on the exterior skins then is it doubtful that you have a twisted fuselage.

Steve "The Builders Coach"

Unless it was built twisted in the first place....

If it was, now is the time to fix it.

IIRC just riveting on the flat decking under the horizontal stiffened up the entire fuselage. It was quite floppy up to that time. If this step was done poorly, it would be easy to get a twisted fuselage.

The OP hasn't stated if it was originally a QB or a SB kit.

mperrytrucking · #8 07-08-2013, 07:57 PM

yes, it has ripples in the side near the center of the cockpit.

rvbuilder2002 · #9 07-08-2013, 10:11 PM

Quote:

Originally Posted by mperrytrucking

yes, it has ripples in the side near the center of the cockpit.

If that is the case, then the reality is, that it doesn't really matter if it is twisted.

The only way to repair it right is to replace any damaged skins.

I don't say that casually, I have repaired a number of RV's and fully rebuilt a wrecked RV-6A which is my daily driver... replaced every single skin except the two on the top of the turtle deck (including the firewall).
BTW, prepuched RV's are soooo much easier to repair....

Steve Barnes · #10 07-08-2013, 10:41 PM

If the skin has some permanent wrinkles, drill the skin off, use it as a template and carefully drill new skin. That may not work if other parts of the fuselage are bent. If the original skin naturally flattens out when you take it off, then the twist could be elsewhere in the fuselage. Without actually seeing the fuselage, it is only speculation.

Good Luck Steve