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Normal Topic Fuselage Types - Box vs Keel (Read 517 times)
Kaintuck
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Re: Fuselage Types - Box vs Keel
Reply #7 - Jan 23rd, 2020 at 5:41am
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Sky9pilot wrote on Dec 30th, 2019 at 12:02pm:
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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bigrip74
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Re: Fuselage Types - Box vs Keel
Reply #6 - Jan 1st, 2020 at 12:55am
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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
  

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Re: Fuselage Types - Box vs Keel
Reply #5 - Dec 30th, 2019 at 3:30pm
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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
  

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Sky9pilot
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Re: Fuselage Types - Box vs Keel
Reply #4 - Dec 30th, 2019 at 12:02pm
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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
  

( 157 KB | 8 Downloads )
01_003.jpg
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falcon_2.jpg

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alfakilo
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Re: Fuselage Types - Box vs Keel
Reply #3 - Dec 29th, 2019 at 3:34pm
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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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Re: Fuselage Types - Box vs Keel
Reply #2 - Dec 29th, 2019 at 7:33am
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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
  

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Re: Fuselage Types - Box vs Keel
Reply #1 - Dec 28th, 2019 at 10:39pm
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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
  

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Fuselage Types - Box vs Keel
Dec 28th, 2019 at 6:24pm
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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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