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Oct 23, 2018, 06:34 PM
AndyKunz's Avatar
Build Log

133% Comet Aeronca Chief - A Restoration


Back around 2003 my father Phil translated the 54" Comet Aeronca Chief plans to CAD and then scaled them up to 133% (about 72" span).

He built it per the plans, and we flew it first time one evening at the New Jersey Jumbo Flyers' old field in Belvidere 2004-05-13. There are a few pictures below. The next year we took it to NEAT but I don't recall having much success. This was before 2.4gHz and the flight line was forever long to get your pin and a flight station. I'm glad those days are behind us!

Anyway, we only got a few flights on it when Murphy paid us a visit. I was literally cruising along at low throttle when the right wing folded and the plane came down flat-spinning like a maple seed. I had plenty of time to cut the throttle, and surprisingly very little damage occurred. We gathered the pieces and put it away in Dad's basement, waiting for it to be restored.

About two years ago I was visiting NJ with my son Caleb and saw the Aeronca sitting there, looking forlorn. I asked and was allowed to bring it home to IL with me. It's finally time to bring it back to life.
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Oct 23, 2018, 06:45 PM
AndyKunz's Avatar
A couple days ago I pulled it out of my to-do pile and examined it closely.

The wing spar failure was caused by several factors.

a) The 1/4" SQ spar wood was softer than it should have been,
b) The spar was laminated to form 1/2", but they were CA'd together in spots rather than glued continuously,
c) The inside edge of the ailerons created a stress riser that was not carried well into the inner wing panel, and
d) The strut was truly functional, creating a lever arm that the outer wing panel could fulcrum against.

By itself each would have probably been benign, but taken together it was a ticking time bomb. 20/20 hindsight, of course.

The rear fuselage had a cracked longeron which probably occurred as the outer wing panel smacked into it, most likely as it hit the ground.

The wood that forms the window outline and top of the cockpit where the wing attached split along the grain, separately wing and fuselage except for covering.

A mouse in my shop apparently liked to nibble on balsa on the rudder. That'll be an easy fix and recovering.

A little covering on the elevator was torn, likely hangar rash from 10+ years of storage.

Tomorrow I'll go into my ideas for how I'll be fixing this up. One of my goals is to re-use as much of the original structure and wood as I can. This is a restoration, not a reconstruction or new airplane project.

Andy
Oct 23, 2018, 10:18 PM
Pro Hoarder
turbonut's Avatar
Nice Andy,
Its always a bit rewarding to revive a dead plane rather than trash it...I have a buddy with a full scale Chief..great airplane. His has 31 in tires
Latest blog entry: In flight
Oct 24, 2018, 03:09 PM
AndyKunz's Avatar
This one could have used bigger tires, or smaller grass. We had to hand launch it as I recall because the field hadn't been mowed in a week.

Andy
Oct 25, 2018, 09:21 PM
AndyKunz's Avatar
All I've done so far is remove the covering and glue a few parts back together, then evaluate in more detail exactly what work will be needed.

Fixing the fuselage is going to be rather quick, and I'll be doing it in parallel with the wing. I plan to glue the longeron parts back in their correct place, and use a splint of CF rod to strengthen the area. I should be able to keep the covering on the bottom and left side, as these are intact. Yellow SoLite isn't available any more, and I have a very limited supply on hand. I need to save every little bit and then scrounge the web for more. If you know of somebody with 1 or 2 rolls, please put me in contact with them.

The wing root/cabin top area needs additional strength, but all the parts are fine and fit nicely together. I will glue them back, and then reinforce on the inside with ply and CF to get the strength that is needed. It will be ugly until I paint it - fortunately I have a can of the yellow spray that was used to finish it the first time. Should make for an excellent color match!

The wings are going to be some real effort. I will be replacing most of the spar in both wings with spruce, keeping the outermost spar portion balsa as there is little need for load bearing out there and the spar is tapered at the tip. I also plan to add spars and web at the aileron hinge line to bring it down to the root.

The LE of the right wing will be get a splint like the longeron. I'll also need to replace the top sheeting at the LE, but I have yet to determine if I need to remove it all, or if I can insert the two rib bays that are broken out.

All the rest of the wing parts should be reused. Getting the old spar out will be done with a knife and Dremel.

Andy
Oct 26, 2018, 02:46 PM
Veni Vidi Volavi
Brian Allen's Avatar
Andy

Looks like a fairly easy repair/rebuild. I might have some yellow Solite, will have to check. Needs some trim color though!!

Brian

Veni Vidi Volavi

I came I saw I flew
Oct 26, 2018, 03:51 PM
AndyKunz's Avatar
Quote:
Originally Posted by Brian Allen
Andy

Looks like a fairly easy repair/rebuild. I might have some yellow Solite, will have to check. Needs some trim color though!!
Yeah, it is, which is why it has taken only 13 years to get started on the fixing

It'll be getting black trim per the plans. Not too fancy, just a little more than the plain yellow that it wore when it crashed.

Andy
Oct 26, 2018, 03:53 PM
AndyKunz's Avatar
Thanks for the pictures! That one with the funky cowling looks like Bob Hope is piloting.

Andy
Oct 26, 2018, 08:58 PM
AndyKunz's Avatar
Last night I glued the top of the left side of the fuselage together, then tonight I put the right side back on. Then I moved farther back and fixed the top stringer that was broken, using some hard 1/16" balsa to splint it together. Several of the cross-braces had broken glue joints, so I will be going back and checking each of them.

All the electronics are still with the model with one exception - the crystal! I found one on eBay tonight and bought it immediately. The transmitter (a Hitec Eclipse 7) still has the model in memory. I'll be the only one at our field with a plane on 72. Just for nostalgia - no way am I going back!

After that I turned my attention to the wing. I removed the spar by cutting around each rib joint, then cleaned up the slots. I'll probably have to go through then again with a nail file so the new spars fit.

I didn't remove the spar for the entire span - I left the last rib bay and tip. It would be easier to replace the whole thing, but this is a "labor of love" so I'm allowed to do things the hard way.

Andy
Oct 27, 2018, 07:35 AM
Registered User
slow_flier's Avatar
Looks nice Andy.

I did a laser cut version of the original kit about 6-7 years ago. It was a nice flyer, but fragile by normal RC standards. At a flying weight of 12 ounces it was affair weather flyer.

Tom K
Oct 27, 2018, 08:05 AM
AndyKunz's Avatar
This is definitely a delicate plane, Tom. I'll be posting photos later showing some of the hidden damage and repairs.

I'm OK with it being a dawn & dusk flyer. I've got "real" planes for the rest of the day, and the only other light flyer I have is an ancient GWS Stick (the small one).

Andy
Oct 27, 2018, 12:52 PM
AndyKunz's Avatar
The receiver isn't the only piece of history in this plane. The power comes from a Magnetic Mayhem motor on a gearbox. These were a pretty popular setup for warbirds in the day, something for which I credit Mark Rittinger with his popular plans in MAN and MA.

Back to the fixin'.

As I mentioned earlier, in the process of peeling off covering I found more damage. Several more stringers were damaged, on both sides. I splinted them back together.

This afternoon Ian and I are working on getting his Saito 125 gas engine going. It has an OS gasoline glow plug in it.

Andy
Oct 27, 2018, 02:01 PM
B for Bruce
BMatthews's Avatar
Quote:
Originally Posted by AndyKunz
Yeah, it is, which is why it has taken only 13 years to get started on the fixing
These things need to be done in their own time.... like a fine wine... or a fine whine....

Good analysis for the failure. I note that the wood snapped very cleanly with little or no continuous fibers at each of the breaks. Yeah, a ticking time bomb for sure.

If you have some way of making a saw kerf along that balsa spar you could insert a vertical blade of spruce quite easily without the need to remove the old spar. A table saw set to cut a 1/8" kerf up through the 1/2" of blasa and then slide in a piece of 1/8x1/2 spruce or even good high growth ring count pine? Or even a vertical blade of 1/8 very hard balsa? If you went with balsa perhaps cut up a bit more a little into the ribs above so you could use 1/8 x 5/8". With the struts being functional you don't really need a whole lot of beefing up. The saw kerf, if you have the saw or a buddy with one, would avoid the need to bust out the old spar.

EDIT- I'm too late to the party! I didn't see the pictures of the wing work.

Any chance that the CAD plan is still available? I wouldn't be surprised if a person or three would like to have a go at their own version of this design.
Last edited by BMatthews; Oct 27, 2018 at 02:06 PM.


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