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Author Topic: Inset profile tank - +/-?  (Read 1868 times)

Offline Dennis Toth

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Inset profile tank - +/-?
« on: September 19, 2013, 08:56:52 PM »
Guys,
I'm working on a new Midwest Magician for a Fox 35. I plan on using 1/2" x 3/8" maple mounts with the top mount running back about 1 1/2" over the leading edge and the bottom on ending at the bottom of the wing leading edge. I intend to drill lighting holes through the 1/2" side and use 1/16" plywood doubles with 1/2 oz. glass cloth over the whole thing.

One thing I'm considering is to inset the tank between the mounts to reduce the amount of tank hanging out. I think it looks a little better, but is there any engine run related advantages/disadvantages? This would require thinning out the top mount to allow the tank to be offset up about 1/8" to 3/16". So what's your thoughts?

Best,        DennisT
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Offline Brett Buck

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Re: Inset profile tank - +/-?
« Reply #1 on: September 20, 2013, 12:47:16 AM »
Quote from: Dennis Toth on September 19, 2013, 08:56:52 PM
Guys,
I'm working on a new Midwest Magician for a Fox 35. I plan on using 1/2" x 3/8" maple mounts with the top mount running back about 1 1/2" over the leading edge and the bottom on ending at the bottom of the wing leading edge. I intend to drill lighting holes through the 1/2" side and use 1/16" plywood doubles with 1/2 oz. glass cloth over the whole thing.

One thing I'm considering is to inset the tank between the mounts to reduce the amount of tank hanging out. I think it looks a little better, but is there any engine run related advantages/disadvantages? This would require thinning out the top mount to allow the tank to be offset up about 1/8" to 3/16". So what's your thoughts?

Best,        DennisT


   I think this covered the pros and cons pretty well:

http://stunthanger.com/smf/index.php?topic=26385.0


I probably wouldn't do it myself, I would make a narrower tank.

    Brett
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Offline Jim Thomerson

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Re: Inset profile tank - +/-?
« Reply #2 on: October 11, 2013, 03:58:04 PM »
I have built and flown profile airplanes with the tank on the outside side of the fuselage, inset into the fueselage, and sticking out on both sides of the fuselage.  I didn't see any problems with any of them. 
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Offline Avaiojet

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Re: Inset profile tank - +/-?
« Reply #3 on: October 11, 2013, 04:32:17 PM »
Quote from: Dennis Toth on September 19, 2013, 08:56:52 PM
Guys,
I'm working on a new Midwest Magician for a Fox 35. I plan on using 1/2" x 3/8" maple mounts with the top mount running back about 1 1/2" over the leading edge and the bottom on ending at the bottom of the wing leading edge. I intend to drill lighting holes through the 1/2" side and use 1/16" plywood doubles with 1/2 oz. glass cloth over the whole thing.

One thing I'm considering is to inset the tank between the mounts to reduce the amount of tank hanging out. I think it looks a little better, but is there any engine run related advantages/disadvantages? This would require thinning out the top mount to allow the tank to be offset up about 1/8" to 3/16". So what's your thoughts?

Best,        DennisT

Dennis,

Holes to make the model lighter. Where have I heard that before?  ;D

With your ply doublers covering the holes, I don't think the glass cloth is really necessary. Just MHO.

As far as the looks of the tank, "Profiles" they are known to have the tanks on the side. Part of the beauty. Just MHO.

Charles
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Offline Serge_Krauss

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Re: Inset profile tank - +/-?
« Reply #4 on: October 12, 2013, 01:54:46 AM »
I've built three profile fuselages with inset tanks. The only one I have flown so far had a nice even run with an LA-.25. The nose seemed plenty stiff, and with a cheek tripler on the left, it was very stable. Here are some pictures to show the general arrangement and construction technique as applied to two similar fuselages. I had to move the tank overflow outboard some to clear the fuselage. I didn't go full depth, hoping that a slight "sandwich structure" thickness behind (on left side of) the tank would enhance stiffness. I thought that a 1/64 ply bottom (left side) of the recess would help. However, these seem so stiff with the tripler that I'll probably just leave the tank recess out of the fuselage blank next time, rather than waiting and "milling" most of the way through with the 3/8" boring bit. Neither takes much time though.

The fuselage has a 1/2" thick balsa center and 1/16" laminated doublers on each side, the nose doublers being plywood, while the aft are balsa, with a trussed aft fuselage core. 45-degree biased .56-oz glass and epoxy, with no excess are applied over the skin. These fuselages are very stiff and torsionally resistant.

Anyway, I was satisfied with the engine run and stiffness this technique provided.
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Offline dave siegler

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Re: Inset profile tank - +/-?
« Reply #5 on: October 12, 2013, 04:27:34 AM »
The nose on the magician is long isn't all that tall so getting the enough material to make it stiff would be an issue for me.
This is especially true if you hang a fox out at the end.

A purpose build profile may be a better place to try an inset tank.

I would make a longer skinny tank mount it outboard and fly it.

Also I think this is a second order effect. 
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Offline Dennis Toth

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Re: Inset profile tank - +/-?
« Reply #6 on: October 17, 2013, 02:24:11 PM »
Looking at the layout it seems the material between the mounts on a profile is not adding much additional strength to the nose nor is it doing much to prevent movement of the fuse to wing joint. Most of the stiffness you need comes from the maple motor mounts. I like to run them back over the wing (drill lighting holes if you like), then use 1/32" plywood doubles to finish the job. That gives you stiffness in the fuse.

One thing I do with the mounts is to make up a crutch with cross grain balsa in the front and back (ala ST60 style, Windy mount) of the mounts with the center open for the tank.

Now the fuse/wind joint is another story. The one thing that I have seen work is good fillets to spread the loads. I like to use carved balsa for this. Basically, you cut out two 1/2" or 3/8" oversize center ribs, cutout the center to fit the actual wing size, split it down the middle, then carve/sand a smooth radius fillet into each half. Glue them in place with epoxy and final sand to the fuse and wing. I like to put 1/2 oz glass over them and finish. I also like to do the same on the stab joint.

Best,       DennisT

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Offline Brett Buck

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Re: Inset profile tank - +/-?
« Reply #7 on: October 17, 2013, 03:38:39 PM »
Quote from: Dennis Toth on October 17, 2013, 02:24:11 PM
Looking at the layout it seems the material between the mounts on a profile is not adding much additional strength to the nose nor is it doing much to prevent movement of the fuse to wing joint. Most of the stiffness you need comes from the maple motor mounts.


  I agree that the filler material does not add much. However, the doubler you have to cut away to make the depression definitely does add substantial stiffness. That was the essence of the previous thread.

    Brett
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