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Author Topic: Filling profile wing opening to fit wing  (Read 625 times)

Offline Joe Ed Pederson

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Filling profile wing opening to fit wing
« on: February 05, 2019, 11:55:53 AM »
I finished the wing for my Sig Akromaster and when I slid it into the wing opening in the fuselage there was 1/16" gap all around the wing.  My kit was made in October 2018. I know this because Sig was out of kits when I called and asked if I wanted to wait a week while they made up a new batch of kits.  In this batch of kits (don't know about previous batches) the fuselage and ply doublers are lazer cut (remainder of kit still die-cut).

Question: a) Is it safe to glue some balsa into the wing opening in the fuselage and sand down to a tight fit?
    or b) should I just cut out a new fuselage?

Thanks,

Joe Ed Pederson
Cuba, Missouri


 


Offline Glenn (Gravitywell) Reach

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Re: Filling profile wing opening to fit wing
« Reply #1 on: February 05, 2019, 12:18:00 PM »
It is absolutely safe to glue the balsa filler in.  Certainly no need to cut a new fuse.  I routinely have to fill a wing opening, cause I'm a terrible builder! H^^
Glenn Reach
Westlock, Alberta
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Offline Tim Wescott

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Re: Filling profile wing opening to fit wing
« Reply #2 on: February 05, 2019, 12:43:13 PM »
You can hold the wing into the fuselage with three or four dots of epoxy + microballoons each on top & bottom (six or eight in all), or with the same number of wood shims epoxied in place.  That will be plenty strong to hold the plane together in flight, and easier to saw through if you ever need to do a major rebuild.  Then put a fillet on to cover all your sins.
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The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Online Dave Hull

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Re: Filling profile wing opening to fit wing
« Reply #3 on: February 05, 2019, 01:41:11 PM »
Having a little clearance is preferred since it allows you to align the wing, engine and tail. You can take up any errors that may have crept in elsewhere, like the engine bearers after they were epoxied in. So 1/16" all around sounds about perfect.

Something people can be bit by, is that a really tight fit--which sounds good at first--puts strain energy into a clamp-up for gluing. So when you take the assembly off the bench, you find out it is crooked. Alignment is the number one issue. The joint is fine when anchored with epoxy-coated balsa shims. Sand the shims until they are thin enough that you do not have to force them in.

I guess I should say that my preferred method of gluing up this joint is to clean off the bench. clamp the nose of the fuse to an angle that will hold it 90 degrees to the bench surface, but lets you tilt the tail up and down. Tilt until you get the engine mount parallel to the bench. Put a wedge block under the tail to stabilize it there. Measure carefully. Slide the wing into the slot. Double check the fuse alignment. Put equal shim blocks under each wingtip to get the wing parallel to the bench and square to the fuse. Use a drafting square or the like to get the wing square in the top view. Measure both sides to make sure the wing has equal (or the intended offset) panel lengths. Finally, measure the center of the LE and center of the TE height above the bench. Get these absolutely equal if you can. Some people like to use a Robart incidence meter. If you have one, Great! Insert epoxy coated shims at front and back. Use 30 minute epoxy, not anything quicker. Check all of the alignments again. Let it set up. This is like tack-gluing. If you are happy with the alignment, then sand, trim and epoxy coat the rest of the shims and insert. Once it is tacked well, you should be able to take it off the bench to fill in the rest of the spots. Don't force fit anything.

You should not need any weights to hold the parts down or try to hold something straight. If you do use weights this way, the structure will spring back when you take them off and it will be misaligned.

The same applies to installing the tail. Get the alignment straight on the bench. Use equal height blocks. Fake credit cards work good for shims. They come in a wide variety of thicknesses, and are free for the opening of your junk mail. Use the ones without the embossed numbers. If the wood is in contact, great! If you have to add weights or in any way force it, take off some material on the fuselage to get it both straight and free. Then epoxy. The epoxy is stronger than the wood, so don't worry about filling a gap. Don't fill huge gaps with epoxy because it is heavier.

Sometimes a bit of masking tape is helpful to control where the epoxy goes. Usually not needed.

I used to glue and fill a wing joint at the same time using SIG's Epoxolite. I wouldn't try it with the blue Super Fil. It doesn't seem to have the right properties. So fill with balsa where you can, because filling with epoxy is heavier. Be sure you get a solid balsa shim right over (and under) each wing spar, and at the LE and TE.

Good luck with your Akromaster. It should be fun.

Dave
« Last Edit: February 05, 2019, 07:17:38 PM by Dave Hull »

Offline Joe Ed Pederson

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Re: Filling profile wing opening to fit wing
« Reply #4 on: February 05, 2019, 05:48:55 PM »
Thanks Glenn, and Tim, and Dave,  H^^

You guys corrected a misconception I had about mounting the wing of a profile.  As you can tell I thought that Sig had made a mistake when it set up the laser cutting program. 

I'm glad to hear that mounting the wing isn't nearly the daunting task I thought it might be.   I'm intending to build some models from plans and one of the tasks I feared was cutting the slot for the wing because I thought it had to be a near perfect fit.  I've got a pretty good scroll saw for cutting the wing slot, but cutting a perfectly smooth arc still isn't easy.  Knowing a 1/16 inch gap is good also takes the fear out of a major rebuild.

I never use 5 min epoxy, sometimes 30 minute epoxy, but mostly I use T-88 structural epoxy which is available from Aircraft Spruce, and most woodworker supply catalogs.

Thanks, Dave, for all the additional details. 

Now for the hard part: cleaning off the workbench. ~^

Joe Ed




Offline Tim Wescott

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Re: Filling profile wing opening to fit wing
« Reply #5 on: February 05, 2019, 06:08:41 PM »
The important part is getting everything square and straight.  I'd write out the whole song and dance but it's been written out before (at least once by me).  Aaaand -- I can't find a thread to point you to.  But I'm still not going to write it all down again, unless you're really lost about how to get the wing square to the fuselage (in both possible directions), and how to get the stab to align with the wing (which is more important than getting it square to the fuselage, because the fuselage might be bent).
AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Joe Ed Pederson

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Re: Filling profile wing opening to fit wing
« Reply #6 on: February 05, 2019, 07:37:24 PM »
The important part is getting everything square and straight.  I'd write out the whole song and dance but it's been written out before (at least once by me).  Aaaand -- I can't find a thread to point you to.  But I'm still not going to write it all down again, unless you're really lost about how to get the wing square to the fuselage (in both possible directions), and how to get the stab to align with the wing (which is more important than getting it square to the fuselage, because the fuselage might be bent).

Tim,

Thanks, but it isn't really necessary.  I've got multiple sources on aligning everything as you put it together (engine thrust line, wing, and tail).  One of them is page 17 of Tom Morris's booklet Tom's Building Tips.  Page 17 is a reprint of Tom's article in the March/April 1999 issue of Stunt News.  There's a ton of building tips in that 66 page booklet.  Tom's booklet is a very good investment for the price ($19.95).


Joe Ed

Online Brent Williams

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Re: Filling profile wing opening to fit wing
« Reply #7 on: February 05, 2019, 07:48:47 PM »
1/32 balsa strips, and shim shimminy shim shim, shim shim sher-ooo is how the song goes.
Laser-cut, "Ted Fancher Precision-Pro" Hard Point Handle Kits are available again.  PM for info.
https://stunthanger.com/smf/brent-williams'-fancher-handles-and-cl-parts/ted-fancher's-precision-pro-handle-kit-by-brent-williams-information/

Offline Joe Ed Pederson

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Re: Filling profile wing opening to fit wing
« Reply #8 on: February 05, 2019, 07:52:11 PM »
I found this thread on aligning a profile model's engine, wing, stab:
https://stunthanger.com/smf/building-techniques/video-that-shows-how-to-align-a-profile-airplane/

As I often do, I'm going to copy and paste that thread and save it in my file folder "Control Line Models."   I've got a lot of copy and paste articles from Stunthanger and Stunt News in that file.

Joe Ed

Offline Joe Ed Pederson

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Re: Filling profile wing opening to fit wing
« Reply #9 on: February 06, 2019, 05:30:52 AM »
And here's the link to a thread on making your own incidence meter.
https://stunthanger.com/smf/open-forum/my-cheap-is-showing/msg542053/#msg542053

About 14 messages down the link above Mark Mc gives a link to a Model Aviation article by Derek Moran on building the Killer Incidence Meter that uses a plumb bob instead of the little water bubbles from a carpenters level.

Joe Ed
« Last Edit: February 06, 2019, 06:06:07 AM by Joe Ed Pederson »

Offline Paul Smith

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Re: Filling profile wing opening to fit wing
« Reply #10 on: February 06, 2019, 11:34:16 AM »
I finished the wing for my Sig Akromaster and when I slid it into the wing opening in the fuselage there was 1/16" gap all around the wing.  My kit was made in October 2018. I know this because Sig was out of kits when I called and asked if I wanted to wait a week while they made up a new batch of kits.  In this batch of kits (don't know about previous batches) the fuselage and ply doublers are lazer cut (remainder of kit still die-cut).

Question: a) Is it safe to glue some balsa into the wing opening in the fuselage and sand down to a tight fit?
    or b) should I just cut out a new fuselage?

Thanks,

Joe Ed Pederson
Cuba, Missouri

If the fuse aperture was die or laser cut, you just built the airfoil undersize.   The kit-maker can't account for the assembly tolerance of the builder.  I can't remember a kit where I didn't either enlarge the hole or fill the gap.  Start out with balsa scrap and finish the job with warm epoxy mixed the micro balloons.
Paul Smith

Offline Joe Ed Pederson

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Re: Filling profile wing opening to fit wing
« Reply #11 on: February 06, 2019, 07:13:28 PM »
If the fuse aperture was die or laser cut, you just built the airfoil undersize.   The kit-maker can't account for the assembly tolerance of the builder.  I can't remember a kit where I didn't either enlarge the hole or fill the gap.  Start out with balsa scrap and finish the job with warm epoxy mixed the micro balloons.


The fuselage and ply doublers were laser cut.  I used the die cut ribs right out of the kit and covered the center section with the same thickness balsa as came in the kit.  The 1/4 inch spars seated properly in the die cut rib nothches (neither sticking out above the rib or sitting below the top of the ribs).
In any event, I will plug in balsa scrap and finish with micro ballons after I buy or make an incidence meter to line wing, tail and motor 0-0-0.

Joe Ed




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