bearhawkproject.com Matt Kunkel's Bearhawk Build Log

Tail Struts, Re-Installed Elevator

Tail struts were installed today to help hold the tail stable while mounting the elevator and trim components.  AN665-34R clevis ends go on the fuselage end of the strut.  This is different from the welded ends in the plans and the only call-out in the manual is via a picture where it says to use a washer as a spacer to not smash the clevis.  The part number isn't mentioned anywhere in the manual (not even the hardware list) but is in the Wicks list on their site.  I searched the yahoo bearhawkqbkit group to confirm the answer.

I ended up adjusting the tail strut fuselage tabs a bit with my hand seamer.  There's a fine line between getting a good enough alignment and bending it so far that you can't get a bolt past the longeron/weld cluster.  You have to settle for something in-between and call it good enough.  I leveled the fuselage and then screwed and unscrewed the clevis to level the tail.  It's actually easiest to leave the clevis end attached and spin the strut in and out to level.  I'm considering using a drilled bolt,  castle nut, and  cotter pin to safety the tail struts given how critical the component is.

Lastly, Stacey and I sanded the primer off of the elevator tubing where the outboard hinges will be.  We installed the elevator, marked the hinge location, and used masking tape prevent sanding outside the hinge area.   The hinges were oiled and elevator installed.  With the elevator installation, I also mounted the little tabs that the flying wires will attach to.  There are 6 tabs with 3 different bend angles.   I found where each tab belongs by running string between the mount locations and comparing the string angle to the tab bend angle.

Tail Re-Assembly (corrected), Cleaned Torque Tube Bushings

Today started with the discovery that things were not 100% correct on my previous tail assembly attempts.  The holes lined up laterally, but there was some twist to the alignment around the tube (bolts wouldn't drop though even after removing the primer).  The holes looked like cat eyes or (). I ended up rotating the carry-through tube about the long axis (keeping left=left, right=right) and the holes lined up perfectly.  I had the stab halves on the correct sides, only the mount tube orientation was amiss.  Correcting this made it even harder to get the left stab half on, but removing a little primer build up made it possible.  The right side slips on pretty easily now and I fastened it in place with correct hardware.

I was asked for more info and provided it in the comments but decided to update the post also:

As mentioned in previous posts the stabilizer halves are supposed to be marked left and right.  I cannot find those markings and according to Mark Goldberg they may have been on the inside of the tubes where I  have sanded to remove primer.  The best way to ensure proper stabilizer component orientation is to lay it out on the floor or a flat bench.  The holes will line up and don't just accept horizontal alignment.  Go ahead and drop in the correct hardware.  Also, don't ream out a "cat eye" hole as it will just elongate and enlarge match drilled hole (this is bad).  I ran a reamer through each part individually to get the primer out of the bolt holes.  Even after going through this exercise things were close,  but re-work was still in order because I only looked at the lateral hole alignment and pinned it together with punches instead of real hardware.

Stacey and I finished the day by cleaning primer out of the torque tube bushings (a Dremel tool made quick work of it).  We greased the torque tubes and slid them in place with the bell-cranks bolted on.

Mounting the Horizontal Stab, Stab primer

Today Stacey helped out on the project.  We worked on mounting the horizontal stab so I was glad to have the help.  On our kit, the fuselage and carry-though tube are marked right/left but I couldn't find any markings on the stab halves so we had to figure it out.  The first way we mounted it, the left side slid on buttery smooth and lined up (figured it was too good to be true), however the right side would bind about halfway on.  I tried removing primer buildup from inside the tube but it didn't help and it became obvious it was a slight misalignment of the tubes that caused the binding, not primer.  We ended up flipping the carry-through tube over along it's long axis (keeping left=left/right=right) nothing fit at first, but then we swapped stab halves.  It went on but not without some name calling; in fact the only way to get the left side on is to make fun of it's mother.  Anyway the holes line up.  I ended up calling Mark at Avipro for re-assurance and he said to mount the elevators and see if they match since there's an oblivious left/right.   Well the elevators line up either way (with trim horn up and down left=right and left-left).  I'm still not 100% convinced it's right because the stab isn't square on the fuse (right side is lower) even though I re-checked both mount tubes and they're level.  The squareness may be something fixed with flying wires.

You can see in the pictures where I'm having to drill through the holes a bit.  I didn't re-drill, just removing primer from inside the holes.  A fractional bit was used (same size as the bolt) to keep a snug (light press) fit.  It's my intention to keep holes to the exact fractional size at first and only drill to the next numbered size larger (per AC43.13) if necessary.  I have some reamers coming next week that will help with this.

On a side note I must be being really particular about bolt length.  The lengths I'm ending up using don't match what's in cross reference at the back of the Avipro Manual at all.  Also, there are some sizes I don't have and need like AN4-22 for the fuselage->stab incidence spacer->carry-though bolt.  This isn't on the hardware list,  figure a -24 is intended but it needs 4 washers.  A shorter -20 bolt was used for now to keep progress going, but have it noted to order.  Others don't match up either.  Where possible I intend to keep things to 1 washer to keep weight down.  I can usually find bolts where the last thread just peeks through, add a washer, and it's good.

Finally, I found some places where the stab rubbed through the primer in shipping so I hit those with a bit of the Rustoleum.

More Cleaning, Little Progress, Afraid to Start Drilling

I spent time in the hangar this evening mostly looking things over, trying to wrap my head around the next steps.  I didn't make much building progress but I'm starting slow on purpose.  I began to clean the fuselage since it must have been outside a little while before being wrapped.  It's probably not really necessary, but I like things clean.  I started rounding up the hardware to mount the tail and trim components.  This process lead to the discovery that the plans lack a few call-outs, the Avipro manual is pretty generic, and there are a few differences between the plans and kit already.  An example is that you have to infer the bolts going from the fuselage to the stab carry through are AN4 because the hole drilled is 1/4" per drawing 19.  Also, the plans show the trim torque tube horns welded on.  It's somewhat logical to drill and bolt them for the kit...  However the manual has no specifics on the discrepancy.  You have to infer that since the bellcrank uses AN3, the end horns get AN3's also.  Searching past yahoo group BearhawkQBkit posts confirmed this.  I knew going into this build that it's not " insert tab A into slot B" like some other kits.  For a first timer it slows you down and requires research to learn the hows and why's instead of being spoon fed.  I don't think it's a bad thing and I'll probably gain and retain a better knowledge of AC43.13 for building this kit.

Lastly, regarding hardware, I "get" the AN bolt sizing parameters (diameter in 16ths and grip length in 8ths).  It will be awhile before I can look at a part and grab the correct bolt.  I'm going to start using a caliper to measure components and then fetch hardware.