New nose, what about doublers??

[Curare]

Hey guys, I need a bit of advice. Over the course of the weekend I decked my chipmunk. I'd just done an electric conversion and due to something the motor shut off at the wrong point and it fell in on the lines, and straight down.

The front is mangled.

My question is, how do you go about adding a new nose to a crunched fuselage? How do you rebuild doublers so they're strong enough? finger splice or just a straight line splice? SHould I add a tripler to the join?

Any help will be, er.. helpful.

[Chris McMillin]

Got a picture, Greg?
Chris...

[Curare]

Indeed I do...


Brace yourselves.

[Randy Cuberly]

Cut the old fuselage off just forward of the canopy line on top and a liittle further back on the bottom (maybe about two inches).  Build a completly new front fuselage and fit it to the old wing and rear part of the fuselage.  Use triplers at the fuselage joint.  Having a different splice line at the top and bottom of the fuselage reduces the stress at a single lateral line.

This should work fine, especially with electric where the vibrational stress is greatly reduced.  Be very careful on the alignment of the new fuselage nose to get the thrust line angular deflection the same as it was before.  I would use angular measuring devices on the motor shaft and the wing to accomplish this.

Randy Cuberly

[Motorman]

Another option would be to cut away only enough damage so you can glue on new wood. You would have to ensure all the cracks going back to the wing joint were glued. Depends on what it looks like underneath I guess.

MM

[Randy Ryan]

Cut the old fuselage off just forward of the canopy line on top and a liittle further back on the bottom (maybe about two inches).  Build a completly new front fuselage and fit it to the old wing and rear part of the fuselage.  Use triplers at the fuselage joint.  Having a different splice line at the top and bottom of the fuselage reduces the stress at a single lateral line.

This should work fine, especially with electric where the vibrational stress is greatly reduced.  Be very careful on the alignment of the new fuselage nose to get the thrust line angular deflection the same as it was before.  I would use angular measuring devices on the motor shaft and the wing to accomplish this.

Randy Cuberly

A scarf or angled splice, staggered top and bottom will further relieve the stress Randy refers to.

[Brett Buck]

Cut the old fuselage off just forward of the canopy line on top and a liittle further back on the bottom (maybe about two inches).  Build a completly new front fuselage and fit it to the old wing and rear part of the fuselage.  Use triplers at the fuselage joint.  Having a different splice line at the top and bottom of the fuselage reduces the stress at a single lateral line.

This should work fine, especially with electric where the vibrational stress is greatly reduced.  Be very careful on the alignment of the new fuselage nose to get the thrust line angular deflection the same as it was before.  I would use angular measuring devices on the motor shaft and the wing to accomplish this.

Randy Cuberly

   That's what Jim "20 Point" Aron did when he pancaked his 20-Pointer at the NATs (due to a control failure). Cut off the nose above and below the wing at a 60 degree angle or so, back to undamaged wood, build a new nose with a corresponding angle, put plywood couplers across the joint, and glue on a new nose. He did it with a PA65, no problems. On Jim;'s airplane you can barely tell anything happened, and only if you know exactly where to look and what to look for.

  We have pictures of it somewhere, and it is almost certainly shown on his Concentric Behavior site.

    I have done it several times with Nobler and Fox 35s, also no problem.

   Brett

p.s. Here are some examples from Jim's website. Note that this was a 20-point airplane, one of I think 6 in history. The black mark is good old Central Indiana-quality blacktop sealer from the East side of Circle 2.  Saw it off at an angle, make new nose, fit it up, glue couplers on the inside of one part or the other, glue everything, fiberglass, finish.

[Randy Cuberly]

   That's what Jim "20 Point" Aron did when he pancaked his 20-Pointer at the NATs (due to a control failure). Cut off the nose above and below the wing at a 60 degree angle or so, back to undamaged wood, build a new nose with a corresponding angle, put plywood couplers across the joint, and glue on a new nose. He did it with a PA65, no problems. On Jim;'s airplane you can barely tell anything happened, and only if you know exactly where to look and what to look for.

  We have pictures of it somewhere, and it is almost certainly shown on his Concentric Behavior site.

    I have done it several times with Nobler and Fox 35s, also no problem.

   Brett

Yes I agree with Brett of course, and should ahave mentioned it in my post.  By all means use an angular cut for the splice.  It increases the surface area of the joint and makes it much stronger.

I have done this sort of thing a couple of times in the past (not recently), also with smaller classic airplanes.  One was a Nobler and the other a Ares.  It worked very well on both, and with care can become invisible!

Thanks for mentioning this guys!

Randy Cuberly

[Randy Ryan]

"A scarf or angled splice, staggered top and bottom will further relieve the stress Randy refers to."

"Yes I agree with Brett of course, and should ahave mentioned it in my post.  By all means use an angular cut for the splice.  It increases the surface area of the joint and makes it much stronger."

Guess it only counts when Brett says it. Oh well, what the heck would I know about it?

[Curare]

Thanks guys, all input was absorbed, so don't like you weren't listened to.

Now for the next question. I'm going to lose the stock style removable cowl, but I'm struggling to think as to how I can do the typical chippy cowl as part of an integrated nose, AND have a top loader.

like this for those who don't remember:

[Allan Perret]

  That's what Jim "20 Point" Aron did when he pancaked his 20-Pointer at the NATs (due to a control failure). Cut off the nose above and below the wing at a 60 degree angle or so, back to undamaged wood, build a new nose with a corresponding angle, put plywood couplers across the joint, and glue on a new nose. He did it with a PA65, no problems. On Jim;'s airplane you can barely tell anything happened, and only if you know exactly where to look and what to look for.

  We have pictures of it somewhere, and it is almost certainly shown on his Concentric Behavior site.

    I have done it several times with Nobler and Fox 35s, also no problem.

   Brett

p.s. Here are some examples from Jim's website. Note that this was a 20-point airplane, one of I think 6 in history. The black mark is good old Central Indiana-quality blacktop sealer from the East side of Circle 2.  Saw it off at an angle, make new nose, fit it up, glue couplers on the inside of one part or the other, glue everything, fiberglass, finish.

Amazing repair.  On the maple mounts, do you know if he was able to remove the entire original beams or did the repair involve some sort of splice joint with part of original beam that left in tack aft of the surface splice ?

[Avaiojet]

There's a Chipmunk on ebay.

You might get it for low cost, you'll have a model to copy parts from for your repair and another model to build. 

Sorry I didn't save a link.

Good luck.

[Curare]

Charles, I doubt it would be much interest to me, as I found the original a bit lacking, and I still have the original ABS cowling that I didnt use, I made my own carbon one. Add to the fact that it's probably in the US, and the shipping would kill me.

In this instance, seeing as the plane has the majority of the glow relevant parts crunched off it, I can start a fresh as a pure electric nose.

[Brett Buck]

Amazing repair.  On the maple mounts, do you know if he was able to remove the entire original beams or did the repair involve some sort of splice joint with part of original beam that left in tack aft of the surface splice ?

    It's actually a pretty easy way to go. We briefly considered doing it *at the NATs*, because as I recall, this was Monday evening to we had about 36 hours. We actually did do it at the NATs with Paul Ferrell's Vector in 2007 or 8, I think we got the nose from an ARF and grafted that on. It's about a 5 hour job, if you have all the materials in hand, and don't count the glue-drying time (mostly just the epoxy used to seal it up - you can do everything else with medium Hot Stuff).

   You just have to have the courage of your convictions, particularly when you had a 20-point airplane 10 minutes ago!

No original mounts. The fuselage was left with balsa sides, parts of the doubler, and some cracks around the top block. I was not present, but get the remaining fuse solid, clean it down to bare wood inside, apply plywood triplers inside and now you have keyed system with support across the joint. Then just build the front end of a fuselage, complete with crutch, etc, just without the back half. The trickiest part is making it fit together properly and straight, but that's where the obsessive-compulsive Uncle Jimby perfectionism comes in. He also re-used the cowl, which if you understand how his cowl system works, is a feat in and of itself.

    Then just glue it on. The glue joints, properly made, are better than the balsa and plywood, anyway. The joiner keeps the surfaces stable and in line. You need to sand everything flush, then fiberglass it, but from then on it's a finishing problem. In Jim's case, he also made some other changes (like extending the flaps to full width all the way to the tip) and there were other repairs required, but his wing loading went down after the repair.

   The most amazing this is that the airplane was easily as good as it was before, both in appearance and in performance. It would still be a 20-point candidate. It has since been converted to electric, which increased the performance further - and in fact it was briefly considered to build ANOTHER new front end, and cut the replacement IC engine off. Briefly.

  There's a bunch of pictures on his website under "Current projects" gallery. Including the B-36 with 6 .061s.

http://www.concentricbehavior.com/project.html

   Brett