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Author Topic: Crooked Barnstormer Fuselage  (Read 960 times)

Offline Joe Ed Pederson

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Crooked Barnstormer Fuselage
« on: May 20, 2023, 08:22:27 AM »
Advice, please.

I built a Brodak Barnstormer's fuselage on a board over the top view from the plans with the Tom Morris "L" shaped jigs to hold the fuselage sides in place and the sides vertical.   Now that I've gotten to the point of putting in the wing a problem developed when I cut out the bottom of the fuselage below the wing: the fuselage went crooked.   Quite a bit crooked.  The top blocks are in place and I didn't cut a hole in the top sheeting for the canopy area.

My thoughts are to put the fuselage back in the jig and put in cross pieces of balsa to try to hold the fuselage straight when it comes out of the jig this time.     Any chance of this working?     Or should I just build another fuselage from scratch?

Thanks in advance,

Joe Ed Pederson
Cuba, MO

Offline Tim Wescott

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Re: Crooked Barnstormer Fuselage
« Reply #1 on: May 20, 2023, 09:35:38 AM »
Bent like a banana crooked, or twisted so the wings wouldn't be level with the tail?  I know it's severe in your estimation, but my "severe" may be your "oh, I can barely see that", or visa versa -- can you give us numbers somehow?  Like is it twisted 5 degrees from nose to tail, or is the centerline bowed by 1/8", etc.

Is the fuselage floppy where you've cut it for wing access, or did it go "sproing!" and now it takes a lot of force to make it go straight?

There's different in-between answers for each possible problem, but every single one starts with "if the fuselage is rigid but bent, and if the wings, engine and tail all line up correctly it'll fly right but look odd".  They all end with "yes, it's hopeless, stomp it and start over again".  And note that "hopeless" depends both on your taste, and on how soon you want to get done.

If it's floppy because you've cut out a lot of structure, but you can hold it straight in your hands, then your problem is just one of work-holding while you get the wing in.  As soon as you glue it back up again it'll be a rigid assembly again.  In this case I'd say figure out the work-holding part (maybe figure out how to get it back into the jig, with shims beneath that top block) and get on with the work.

If it when "sproing" when you cut the last fiber of wood that was holding it straight and it really resists being bent back into shape, then either you forced it into shape in the jig and glued in a lot of stress, or the wood had a lot of internal stress that you relieved when you cut it.  Either way, you're either going to need to make more cuts and glue it back together straight, or you're going to have to assemble a straight engine, wings and tail onto a crooked fuselage, or you're going to need to stomp it and start over -- and hope that you don't do exactly the same thing again*.

If the above hasn't made your decision for you, tell us how it's bent and if you can figure out a sensible way, tell us how much.  Maybe include a photo if you can figure out the process.

---------------

* Tangentially related story: My dad built custom cars and restored antique cars.  Someone brought in a boat-tailed model T roadster that had been originally built back in the early thirties or late twenties.  They wanted it restored.

The thing had a persistent warp in the boat tail -- he could chase it around, but he couldn't make it go away.  After a lot of frustration he grabbed some flat sheet, cut out pieces exactly where the original builder had cut their pieces, beat out a new boat tail and welded it up.  When he was done, it had the same warp.

Which is a really long way of saying that rebuilding a warped-up thing doesn't always save your day.
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Online Ken Culbertson

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Re: Crooked Barnstormer Fuselage
« Reply #2 on: May 20, 2023, 02:18:08 PM »
Balsa is very pliable when wet.  A lot of fuselages have a bunch of internal stress from bending two different grained pieces of wood to the same curve.  Tim is correct that the only thing that matters for performance is the relative alignment of the wing, stab and thrust line.  All of those work fine with a warped fuselage.  Personally, I don't put any blocks on or join the rear of the fuselage till I have the wing at least tack glued in.  That is when you want it in the jig.  In the jig I put in all kinds of "X" cross braces using CA glue, then when all of the braces are in I wet the aft portion and let it dry.  This releases all of the tension in the wood.  Now you can join it at the tail and put on the blocks.  On my designs, I use a 1/4" sheet for the bottom.  My 'JIG' is that 1/4" sheet and a 12" triangle to square the sides.  I build the fuselage with that "block" on the bench PRE CUT and marked.  That way the sides stay straight.  Everything else is molded.  Blocks are just too expensive now days.  I guess I was spoiled by building so many I-Beams in my youth that I learned to build around the fuselage as the jig.

If you have full size bulkheads/formers and the sides are warped, consider slicing them in half vertically and regluing them or better yet, replace them with strips.  My fuselages only have formers where there are curves.  Everything else is cross braces made from medium straight grained 1/8" square.

Ken

Something like this. 
« Last Edit: May 20, 2023, 06:01:46 PM by Ken Culbertson »
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Offline Tim Wescott

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Re: Crooked Barnstormer Fuselage
« Reply #3 on: May 20, 2023, 05:39:36 PM »
Because I'm both fussy and a tightwad, I build my fuselages without a jig.  As an incidental part of the process, if the fuselage is tending to being warped before the top & bottom go on, I notice it -- then I curse, and either correct it or at least know going into final assembly that I have to work around it.
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Offline FLOYD CARTER

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Re: Crooked Barnstormer Fuselage
« Reply #4 on: May 20, 2023, 06:46:03 PM »
I would be happy to offer good advice, if the OP would answer the questions posed by others.  Not enough info was given to properly address the problem.
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Offline Joe Ed Pederson

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Re: Crooked Barnstormer Fuselage
« Reply #5 on: May 20, 2023, 07:09:21 PM »
Tim and Ken,

Thanks for the sage advice on building and dealing with a warped fuselage. 

Looking down from above the fuselage at the tail post had to curved to the left, 1/4" I would say.  The sides were still vertical.  I put the fuselage back in the jig a couple of days before posting my request for help.  It took quite a bit of force to get it to go into the jig because the fuselage was curved to the left at the tail post.  When I went to pull it out of the jig today at 7:00 p.m. Saturday, May 20th, the fuselage was straight.   The fuselage would just slip effortlessly into and out of the jig.

It was out in my shop which is separate from our house.  The shop doesn't have central air conditioning.  It has a window unit I turn on when I work out there and it's too hot or too humid.   Over the last few days we've had high humidity and yesterday we had a lot of rain to boot.  Perhaps the high humidity was enough to dampen the wood and relieve the stresses and mold the fuselage back into alignment.

In any event, I'm leaving the fuselage in the jig until the next time I have enough time to attempt mounting the wing again.  I may also see about moving one of the jig uprights behind the wing slot so I can mount the wing while the fuselage remains in the jig.

I use the Walter Umland tools and method of aligning wing and tail and fuselage.   

Walter Umland's tools and method require the fuselage to be straight since everything is measured from the tailpost.  So, if I couldn't have straightened the fuselage, I would have been stuck using a right angle against the short nose and the leading edge of the wing.  But I don't think that that is as accurate a measurement for aligning the wing to the fuselage.   And I'm not sure I would trust that I could get the tail on accurately to compensate for the tail post being 1/4" (or whatever) off from the centerline of the fuselage.  So, if I couldn't have straightened the fuselage from nose to tail, I would have just started over.

Anyway thanks for all the tips on building a straight fuselage and all the tips on how to straighten a fuselage that didn't come out straight.

Joe Ed Pederson


Offline john e. holliday

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Re: Crooked Barnstormer Fuselage
« Reply #6 on: May 20, 2023, 08:09:18 PM »
I too have had fuselages go a little crooked or twisted when wing cut out was made, but once i put the wing in place using pins, tape and what ever else i had it would be straight.  then i spot glue in several places to see if it will hold.  Usually it it works so wing and stab will be in alignment.  If not I make adjustments on the stab location. D>K
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