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Dec 08, 2009, 09:59 AM
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flyboy320's Avatar

Rounding off a square wood fuse nose?

I have a Skybench Big Bird that I built as a pure glider. I decided this winter to change it to E power. The fuse was 95% finished as a pure glider, and as a result, the nose is quite narrow (about 30mm). I have a motor that will fit, and it has about 2mm on either side for clearance (see attached pictures).

The problem I'm trying to grasp in my head, is how I will transition the square/rectangle shaped nose to a round one where the spinner will fit on. The problem I see is that the width of the fuse is only a few mm wider than the motor itself, so very little room to attach a firewall to --- if I make the firewall round. If I make the firewall the same cross section as the fuse, ie., rectangle/square, then how to I change this (in the short distance I have from the firewall to the end of the gearbox shaft) to transition to a round shape?

I've seen pictures where the motor is much smaller in diameter than the width of the fuse nose, and that gives room to put in triangle stock and sand it to a round shape, but in my case I don't have that room to play with.
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Dec 08, 2009, 10:32 AM
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flyboy320's Avatar
I've sort of built a mock up of what the nose might be like. The square black paper represents the front of the firewall, and the white round paper represents the most rear part of a spinner. The distance from the front of the firewall to the rear of the spinner is 5-6mm, that's all the length of the gearbox shaft will allow. So I guess I have this distance at the most to use balsa blocks to shape the nose
Dec 08, 2009, 10:39 AM
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flyboy320's Avatar
If you look at Bob Cook's nose on his Lil Bird, you'll see what the nose looks like without any rounding.
Dec 08, 2009, 01:34 PM
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Skycruiser's Avatar
I think I'd be inclined to increase the width of the nose by sawcutting vertically through the former behind the motor, then adding a new 1/16 ply crossgrain former to the front of the cut former to spread the sides. Then add a capping strip along the top of the sides all the way back to the wing to make the nose deeper. Those would combine to give a bigger cross section at the spinner back, so you could use the tri stock and still have a bit of meat left.

Another option would be to use a saddle clamp to hold the motor/box and replace everything forward of that with a slip on fibreglass nose made by the lost foam method.

Dec 08, 2009, 03:32 PM
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flyboy320's Avatar
I guess so it looks something like this one posted by Cebola?

In effect making the nose a larger diameter so the round firewall for the motor has, as you said, some meat to bit into?
Dec 08, 2009, 04:29 PM
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Leadchucker's Avatar
Did a similar addition on my friends Oly II. We run the nose through the bandsaw back to the firewall mount location, then blocked it out to fit the spinner. If you have all your hub and spinner parts you can get an idea how far you have to block it out. There is gone to be about 1/2 " of space from the firewall to the back of the spinner allowing for a transiton from square to round. It will be a bit quick of a transition,but should work. Make a new top hatch if you have to fill out the top and forward of the firewall. Just an idea,good luck! See photo.
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Dec 09, 2009, 06:06 AM
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Andy W's Avatar
Fill the corners with triangle stock. You can build it up with narrow strips too. Use adhesive that sands, i.e. wood glue. Once *really* dry, you can sand it to shape.
Dec 09, 2009, 07:55 PM
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Have you determined if you can achieve the correct CG with the components positioned as in the photos? Most electric conversions require reducing the length of the nose to achieve that. The shorter nose will give you more depth and width of fuselage to work with.
Dec 10, 2009, 01:40 AM
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AndreyT's Avatar
These two pictures show what I did with my Spirit 100, which also had a square-shaped front. On the bottom I cut the corners at an angle and closed the triangular gaps with two wedge-shaped pieces of thin ply, so the bottom half is more "polygonal" than round. On top I built a true round cowl (two bent thin ply pieces on the sides and a thick "beam" along the top centerline)
Last edited by AndreyT; Dec 10, 2009 at 02:10 AM.
Dec 10, 2009, 05:37 AM
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flyboy320's Avatar
Originally Posted by DT56
Have you determined if you can achieve the correct CG with the components positioned as in the photos? Most electric conversions require reducing the length of the nose to achieve that. The shorter nose will give you more depth and width of fuselage to work with.
It "test" balances fine with everything installed, and the battery under the wing (although the plane is not covered, but there is a fair amount of room to move the battery (at least 2") fore or aft depending on the final CofG.

Thanks for the pictures AndreyT, sometimes a picture is worth a thousand words!

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