Ch 11.6: Elevator Mass Balance - Canard Fab Complete

It's All Gotta Balance

The last part of the canard/elevator build is to install the mass balance weights.  Control surfaces have to balance properly to avoid flutter.  Airplane...and especially pilots, don't like flutter!  Here's how we prevent it.

Lead mass balance glued to H100
PVC foam glued to the elevator.

The first task was to build the outboard mass balance which consist mainly of fabricating the small foam piece that acts as an interface to attach the lead weight to each elevator.  Plans call for H100 PVC foam, 6lbs/ft3.  Don't use any less dense foam here.  It needs to be sturdy.  This is all glued together with 5 min epoxy and then a strip of UNI to bind it to the elevator.  Based on some archives I read, I went ahead and also finished off the sides with 1 ply of BID.


After glassing and cleaning up the mass balance it was time to check the balance of the elevators.  This is done for each elevator separately with the hinge pin installed and the inboard mass balance attached.  I had to tape the inboard pieces of lead to the arm because I didn't have the correct size bolts to install them at the time.  The requirement is that they balance trailing edge up after primer and paint.  You can see in the pics that mine balance with what looks to me like plenty of margin for the weight of primer and paint.  (PS. you can't see the inboard balance in the pic but its there.  It's hanging below the elevator at the other end.)

Port side elevator balance

Starboard side elevator balance

Now I had to modify the canard to accept the outboard mass balances.  To do this, I used a Dremel tool to dig out the cove in the canard for the mass balances to swing into and then applied 1 ply of BID to close it out.

Port side balance cove dug out

Glassing the starboard side cove

And the canard fabrication is finally complete!...except for the finish work of course.  Now I get to mount it to the fuselage.  Finished weight, after installing the alignment tabs in the next chapter, was 33lbs, before finishing and without the counterbalances installed.

Onward!