bearhawkproject.com Matt Kunkel's Bearhawk Build Log

Counterbalances, Tube Plugs, Trim Tab Hinges

I finished trimming the elevator counterbalances so they are fully recessed within the tubes (won't create bulges in the fabric).  Most of this had been done previously, a little touch up today.

The elevator halves were hung with the requisite 1lb weight at 7.5" from the hinge line (as calculated by Russ Erb and verified by other builders).  I drilled the weight until it is just slightly heavy.   An inspection cover over the weight will allow for final balance after covering/finish if necessary (I could add weight too by filling one of the drilled holes with epoxy/shot slurry).  According to the manufacturer and other users, Stewart Systems tends to come out light, so I will likely have to trim the weight further.

I also trimmed the epoxy/microballoon tube plugs around the trim tabs and added a little in places where the epoxy ran.  Lastlly, I finished reaming the trim tab hinge tubes to accept a 3/16 hinge pin.  There was quite a bit of welding flash in the hinges and some were mishapen or mis aligned..  I used a drill bit brazed onto a rod for some of the work.  I used a reamer for other parts where the drill bit wasn't making a nice round hole.  To finish things off I assembled the hinge tabs with a 3/16 reamer in place of the hinge pin and rotated them a few times.  This made for a nice snug fit on the hinge pins.

Elevator Counterbalance Trimming – 2

Worked on trimming counterbalance on port elevator half.  Short on time again today but some progress was made.

Elevator counterbalance trimming – 1

Today  I started trimming the counterbalances previously poured.  Not much time to work today, so this will be split among several sessions.

Cast Elevator Counterbalances

Today I cast the lead counterbalances into the elevator.  I used a steel plate on the bottom of the ribs to create sort of a bowl to pour the lead into.  I used some high temp rtv to create a gap seal and clamped the plate in place.  It's amazing how thin lead is when melted.  Is about the same viscosity of water with a much much greater mass, a-lot like mercury.  I still had some leakage but learned to pour a little in the bottom, let it set up, pour a little more, etc until I had a nice base to pour the rest onto (with no leaks).

I made a smelting pot from on old metal coffee can, and used a white gas camp stove as a heat source.  The lead shot melted surprisingly fast, I used a blow torch to help speed things up and to help flow the lead back under the flanges on the elevator.  Unfortunately I didn't get pictures of the melting/pouring process since I did it alone and had to work very fast.

Prepped and Primed Elevator Counterbalance Areas

Finished additional T25′s, welded them in place

Plugged trim tab tubes, profiled additional T25′s

The open tubing ends were plugged with a t-88 epoxy and micro-balloon slurry.  I profiled the counterbalance retaining ribs to fit the tubing and other rib in preparation for welding.

Trim Tabs, Counterbalance Prep

I finished cleaning up the areas on the elevator around the trim tab cutouts to get everything flush and smooth.  I also got the hinges working and removed the primer around the counterbalance area to prep for welding in the additional T25 retaining ribs.

Mounted Rudder

Today we mounted the rudder.  One tip I have is to be sure and attach it with correct hardware so the hinge lines up in the exact spot before marking the area for primer removal.  Stacey sanded primer off of  for the top hinge and we bolted it in place.  We also raised the fuselage up onto some sawhorses so the next tasks will be easier.

Cut Trim Tab, Started on push/pull rods

I cut out the right elevator trim tab and started on it's actuating link. I spent most of my time researching a deviation from the plans on the kit and ended up asking the yahoo group. The plans show mm-3 rod ends on both ends but the kit has a forked end and I wasn't sure which way it goes.

I'm going to pass on the elevator trim for now since I have a Bob approved mod coming that might affect things (stay tuned)... I'll go ahead and mount the rudder and start on the control systems.