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Fuselage Types - Box vs Keel (Read 143 times)
Reply #6 - Jan 1st, 2020 at 1:55am

bigrip74   Offline
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Austin, Texas

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I agree that the keel is easier to construct than the box. I am prejudiced since I used the keel construction first and for years, but it is harder to keep the fuselage true.

Ive found the two types lend themselves to different fuselage shapes.

Bob
 

IF IT AINT BROKE DONT FIX IT!
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Reply #5 - Dec 30th, 2019 at 4:30pm

MKelly   Offline
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Helotes, TX

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I think the keel-and-former style is simpler to build, but based on the Skyrocket and T-28 the box frame can come out lighter, stronger and straighter.   When the box frame is a bit smaller than the outer stringers (like on the T-28 pictured below) you get a very strong and rigid fuselage that is very crush- and buckle-resistant.  Being able to run the former grain parallel to the horizontal and vertical box crossmembers adds a lot to the strength of the assembly.

I'd agree with Tom that somewhere around peanut size the box frame loses its advantages unless modeling a slab-sided aircraft.

Mike
 

0529_Bones.JPG (247 KB | 1 )
0529_Bones.JPG
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Reply #4 - Dec 30th, 2019 at 1:02pm

Sky9pilot   Offline
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I hear you AK but lots of the real weight conscious modelers would use the top formers on the box fuselage construction made like the circle of your keel construction for that much less wood in the construction.  It's amazing how much strength the stringers add to a fuselage.  Even with 1/32" formers.  If you've seen the Japanese peanut builders from the Shonai Peanut Club, what they do with thin balsa blows me away!  Click Here
 

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If God is your Co-pilot...switch seats...
Your attitude will determine your altitude!- John Maxwell
And ye shall know the truth, and the truth shall set you free. Jn 8:32
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Reply #3 - Dec 29th, 2019 at 4:34pm

alfakilo   Online
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St Louis, MO

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Tom, in your link, the author believes the keel method to be slightly heavier, and I suppose that's true, all things being equal.

The one point I think might be uncontested is that as the model size decreases, the negative effect of sizing errors in the box construction increases considerably. For that reason, I lean towards the keel method for Peanut size models.

But, all said and done, it may all come down to individual taste.

In this drawing, I'm trying to illustrate a fuselage cross section using the two construction methods. Wood quality and size, # of stringers, type of glue, etc are the same. I tend to glue bracing on the formers, especially when using 1/32" sheet. Result probably is extra weight. Would that be significant? Don't know.

My opinion only, but I think the keel method is more effective at reducing the possibility of a "banana" fuselage, particularly when using one of the jigs.
 

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Reply #2 - Dec 29th, 2019 at 8:33am

New Builder   Offline
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Amherstburg, Ontario, Canada

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My thinking was, when building my assembly frame, was to not use the box type fuselage because I was having trouble making it come out square and finish correctly at the tail. The frame was a complex set of cross members that sandwiched the formers until the majority of the stringers were installed. This frame method reduced the part count by about half or maybe more and this type works for the round or oval fuselages, P47, etc. but need a horizontal reference for alignment and was a bit fussy to set up, probably could have built a frame fuselage in the amount of time needed to put it all together. For square or rectangular types, Piper Cubs, etc. the box frame is nearly the only choice. I searched the archives for a picture of my fixture and only found the writeup but shortly after that several other fixtures started turning up and the are worth looking at.
Click here:
https://www.stickandtissue.com/cgi-bin/yabb2/YaBB.pl?num=1501438185
Mike
 

"Vision is the art of seeing things unseen." James Joyce
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Reply #1 - Dec 28th, 2019 at 11:39pm

Sky9pilot   Offline
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That's a great question AK!  I don't know of any answer I've heard of over the years.  It might be the thought that the box style can be built lighter with the thinner sq balsa stringers and longerons instead of the wider keel type construction.  But that really depends more on wood selection than style of building.  I think the dorsal and ventral keel style might be an easier style for beginners  to pick up and build with. You are almost guaranteed a successful side view shape anyway! 

How about it my fellow modelers, and those of you engineer types, do you know of an advantage one way or the other?
 
EDIT: 12/28/2019 9:52 p.m.
I did find this article on Model Aviation Construction Series: Click Here
 

If God is your Co-pilot...switch seats...
Your attitude will determine your altitude!- John Maxwell
And ye shall know the truth, and the truth shall set you free. Jn 8:32
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Dec 28th, 2019 at 7:24pm

alfakilo   Online
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Retired USAF and TWA.
St Louis, MO

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Is there an argument for one vs the other? It seems that most plans from the 30s and 40s favored the box construction over the keel method.

I suspect from a level of difficulty perspective, the keel is the better choice. But is there another parameter ( strength, weight, etc) that would point to the box technique?
 
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