pinnedup

I broke the upper and lower spars on my 4 Star, very near the root of the wing. The leading edge was also broken and the ribs were pulled from the trailing edge. My main concern is the main spruce sparse, can these be repaired? Recommendations?

Thanks,
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da Rock

If the broken ends of the spars and leading edge fit back together everything will work out fairly easy. Use some 30min epoxy and you'll not only have time to adjust everything back together but you'll get the best glue penetration. The joints will be stronger than they were as plain wood before.

If you're worried about your epoxying skills, the spars can be backed with additional, short pieces that backup the new joints. You'll need to notch the ribs for them.

dbacque

My Feedback: (3)

Butt joints are notoriously weak, especially in flex. Use of a doubler will make a very strong joint and maintain the spar and LE bending strength.

You can use either a ply plate or a piece of spar. I usually use a strip of ply the same width as the spar. If the breaks are between the ribs you can just put the doubler between the ribs. If the break is at a rib or close to one, notch the rib as Rock said.

Dave

pinnedup

So here is my fix for the broken spars on my 4 Star; for each turbulator and the leading edge I epoxied a 3/16 thick spruce spline between the inboard and outboard ribs from the break, epoxied a 3/16x3/8 spruce spline edgewise to the shear blocks and the lower spar between the inboard and outboard ribs, epoxied a 3/16x3/8 spruce spline along side the upper and lower spar spanning from inboard bay towards the wing joint to two outboard bays past the break, I then covered the breaks in the LE, TE and the portion of the spar that extended into the sheeting with fiberglass.

Test flight is tomorrow, hopefully no pilot errors this time, I sure hate beating up my 4 Star.

KitBuilder

I had the exact same issue when mine took dirt bath.. If you have access to CF tape... lay some on the top of the spars (top and bottom of wing... ) you can adhere it with CA and using wax paper over your finger spread it wth some pressure. CF should be approx 2-3 inches each side of the break. You can thin down the spar the hieght of the tape which is only 1/16 of an inch or so
Mike

SeamusG

Hey pinnedup - your 3rd pic shows a doubler below the broken spar. It appears that only about 20% of the doubler is actually glued to the spar above it.

Good luck with the fix! My crashes / hanger damage usually results in a "repair? who you kiddin'?" comment ...