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Old Jun 16, 2012, 09:41 PM
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Joined Nov 2007
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Well folks, I have some good news.

I scaled the 3 view so that the fuselage length would be 144 inches i.e. 1/4 scale.

Take a look at the attached cutouts from the 3 view.

Notice that on the full scale plane, the opening of the intake is cut at a slant, both in the vertical and horizontal plane. This effectively increases the intake opening area of the duct. Looking at the drawing in 2D gives us the wrong conclusion. But if we account for the slanted cuts and look at it in 3D, the intake opening is actually 12 sq in vs 8 sq in required by a 100 mm EDF.

From the opening towards the fan, the duct dimension in top view remains the same, but in the side view, it gradually increases. I verified that this keeps the area over 12 sq. in. till we reach the fan.

In other words, we don't have a problem of choking the fan if we build it to scale.

The other point is that for a jet this size, we really do need to have smooth intake ducts. Cheater holes create a lot of turbulence on entry to the fan and should be avoided where possible. For an EDF the intake turbulence is actually more harmful than the exhaust. By the time we get to the exhaust, the fan has already done its job.

So how the heck do I make the intake ducts, you may ask? Fear not, I plan on providing foam plugs for the intake ducts as part of the kit. You can wrap FG cloth around these plugs and dissolve the foam plug with gasoline once the epoxy has cured. Pretty simple way to make ducts. Of course there is some sanding and smoothing of the plugs that you will have to do.

So in summary, it looks like the T38 is a go for now. Next I have to look at the aeronautical / aerodynamic aspects to see how it will perform. Stay tuned.

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Last edited by awrightbrother; Jun 16, 2012 at 09:59 PM.
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