Initial CG check
Landing Gear mount
Mounting the Fin
Dec 12 2003
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Building a Hybrid
Pattern Plane
Planes I've Known
Finally back at work on the plane after a busy flying season...
Initial CG Check
I needed an initial CG check in order to figure out whether the
rudder / elevator servo location would be critical.
First I assembled the plane w/ everything - engine (a parts-only YS 120 that will fill in for the 140 (L, I think) that the owner will actually use in it) prop, spinner, (no tank- that'll go on the wing tube anyway), control surfaces, elevator push rod, belly pan, landing gear, wheels - all that - and the CG showed well forward of the wing tube.
With all servos where they'll go - and the rudder / elev servos (used 8231's for the weight check) toward the rear of the canopy opening , the CG still showed well forward of the wing tube. So that tells me that the rudder / elev servs can go all the way at the rear of the opening. Onward...
Landing Gear mount
After some head scratching (and some thoughts from Dean Pappas and
others as to the mechanics of it all) here we go.
I wanted the wheels to come out slightly ahead of the wing leading edge - should be fine for a pattern plane there. So the landing gear got spot-glued to the fuse bottom where it'll mount, and I made up a 1/4"" aircraft ply mounting plate for inside the fuse.
The concept was to put light ply doublers inside the fuse that would
Tie the firewall and wing tube together
Provide mounting point for the internal landing gear mounting plate.
Cause all flight loads -- engine load/ vibration, wing loads, landing loads -- to be shared with each other throughout the bulk of the fuse.
So with that, out came the 1/16 balsa and I made a pattern for
the for the light ply internal doublers
- then used that pattern to shape the ply doubler outlines
- then since it's a pattern plane there HAD to be lightening holes in the
doublers...
- then out comes the HobbyPoxy II and cabosil, and in it all went.
The gear's actually two-piece, from a Piedmont Focus. Each leg will mount with two bolts (probably 6-32), and (a la Ron Lockhart) I'll overlay them with a lightened aluminum strap to distribute landing and ...arrival loads (A similar strap on my Focus landing gear (I think) prevented the gear from separating and totally destroying the airframe during an elevator-out arrival on its fifth flight... a story for another time...)
Next step here will be to put triangle stock around the landing gear support, the wing tube area, and the firewall to give more gluing surface.
Fin mounting
The fin was the next assembly step. Interesting since it's a flat plate (non-air-foiled) balsa / foam assembly that will go into a cuff-like opening in the fuse rear. The thought processes / decisions here were how to cover / finish the fin for max lightness and appearance.
Turns out the fin is somewhat loose in the fuse opening, and
there were ... interesting ... alignment challenges here.
-- Seems to be a bit of twist in the fuse back there..
- Guiding thought - the plane arrived with the stab
permanently set in the fuse, so that's the reference - the wing's aligned to it
- so the fin must also match it.
- When the rudder post is aligned w/ the end of the rear of
the fuse, the fin's not perpendicular to the stab
- When the fin is centered in the fuse opening it's angled to
the right
- When the rudder post is mated to the rear of the fuse,
there's a gap between the top of the fuse opening and the bottom of the chaped
part of the fin.
With all this going on the decision on finishing technique was made for me -- mount / fill/ finish the fin, and then glass it w/ resin and 3/4 ounce cloth, then paint it w/ the fuse.
so after about two nights of fitting and aligning and looking and thinking here we went --
The twist in the fuse / rudder post area seems less fairly small so I added some light balsa to the fuse as filler material.
Aligned the front edge of the rudder post flush to the rear end the fuse.
Squared the fin vertically with the stab - pinned in place with triangulating strips of spruce
Aligned the fin left/ right using fin and fuse centerlines and eyeball.
Got out the HobbyPoxy II and cabosil again - this time /w a bit of microballons as a small nod to the Gods of Weight and Balance
Stuck it all together, aligned it one more time, and left. Checked it a few times over the hours as the glue set - still well-aligned.
After it all set, started adding filler balsa and sanding it to smooth it to the fuse and keep things as symmetrical as possible. Here's what it looks like with the initial filler material and first sanding done - still some hours of finer and much finer work needed before it's ready for glass.
