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Jan 17, 2012, 07:57 AM
What could possibly go wrong?
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Build Log

DH 115 Vampire Foam EDF Moved to Scratch build Foam forum!


De Havilland planes - don't you just love them!



Using with one of these little integrated EDF units, I plan to build a scale-ish model using 6mm depron foam.

The fan is 64mm, 220watts. If I start with the 3-view, below, and put one of those fans in it, I get a wingspan of 900mm. Using KFm4 airfoil and taking a little bit of licence for the sake of structure and convenience, I reckon I can make a versatile, small, fast plane, hopefully weighing about 1lb.

Did you know...? The first prototype flew in 1943. One of these was the first jet to fly across the Atlantic and the first jet to land and take-off from a carrier and the first RAF plane to exceed 500mph. Over 3,000 were built and exported all over the world.

Here we go...
Last edited by nickchud; Jan 18, 2012 at 06:02 AM.
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Jan 17, 2012, 08:13 AM
What could possibly go wrong?
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Starting with the fuselage


I will supply drawings when I get Mark I up and ready.

Getting the geometry right for the outlet pipe involved a lot of head scratching and some pi * R squared and some 2 * pi * R stuff.

Basically, the swept area of the fan in the EDF comes by taking account of its radius and the radius of the hub. We want the area of the outlet to be 90% of this swept area.

If anyone spots howlers or wants to suggest improvements to my approach, I would be very glad to hear your views and corrections.

Last edited by nickchud; Jan 17, 2012 at 08:41 AM.
Jan 17, 2012, 11:04 AM
Watt Waster
Tsavah's Avatar

Vampire in Foam


Quote:
Originally Posted by nickchud
KFm4 calls for a sandwich. A picture speaks a thousand words:
Good start and hope to see more soon. I have a few EDF looking for a project.
Latest blog entry: Center of Gravity - Airplanes
Jan 17, 2012, 11:35 AM
Jack
jackerbes's Avatar
The spar placement and configuration of the center panel (the "meat" in the sandwich if you will) as shown in that Nov '07 figure accurately represent the KFm4 concept but not the best way to build KFm4 wings.

In most cases it is better to bring the center panel forward, to or close to the leading edge, and put the spar or spars on the top and/or bottom of the center panel as the edges of the KFm4 strips. With FFF and it's nominal 1/4" thickness, a piece of 1/4" square (balsa, pine, basswood, etc.) was a natural choice for a combination spar and step.

That long elegant taper shown there was most often translated to three layers there were flat and parallel and the taper at the nose was more of a simple rounding that was more abrupt.

On some of the lighter builds, like the Divinity 42, just the three layers of foam with a piece of filament taped beneath one of the KFm4 strips would form a stiff enough wing.

In most cases, the good strength and light build was a combined effect of the filament tape and the layers of foam being glued into 100% full area contact by the foaming action of the PU glues. A PU that foams up, when the foam is wetted with water, like Gorilla and Gorilla Quick, seems to get into the foam better and really bond the layers together.

Jack
Jan 18, 2012, 12:58 AM
ExPat
Aero Andy's Avatar
Subbed

Looking forward to the build Nick.
Andy
Jan 18, 2012, 03:22 AM
What could possibly go wrong?
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Here's a bit more detail.

The thickness at the step is 18mm, all the way along. I figured that 8% close to the middle and thicker towards the tip would not be a bad thing.

It seems pretty rigid. If I need to stiffen it I'll add 6mm strips of bass wood along the back of the steps, top and bottom as Jack suggests. I've been using UHU Por for gluing. Gorilla Glue might have also been a good idea, wish I'd thought of that.

Jan 18, 2012, 06:01 AM
What could possibly go wrong?
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I've moved this thread to the Scratch build foam forum. Sorry! I couldn't find out how to do this when I started it.

Please go here.


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