I've read somewhere that the diameter of my tailpipe should be 90% of the fan's swept area. I'm doing a glow conversion and the existing fuselage tapers to slightly more than 50% of the (90mm) swept area of the fan. Do I need to reduce or completely omit the existing fuse' taper for fan efficiency?.
Thanks, Thom

50% is too much. A good rule of thumb is about 80-85% of the fan area for the exhaust. This gives a good combination of static thrust and efflux. The more you choke down the exhaust, the less static thrust you generate, but the faster the air exists the duct. But at 50% it may choke the fan to the point where you may back pressure the fan. You will deffinitely greatly lose your static thrust. What is the size of the airplane? It may be worthwhile to look at a smaller fan...or open up the exhaust.


Chris

The model is a conversion of Jim Newman's "Strikemaster" design from the '70's. It was originally meant to have a glow 40 in the nose. My WeMoTec Midi fan fits very nicely into the fuselage at the trailing edge. Adding inlets to the flat sides of the fuse is no problem. I can also easily widen the rear end as needed, but didn't want to alter the original design any more than necessary (ie; end up with a flying stovepipe). The 80% to 85% you suggest is easily done, just not quite a sexy. It''s gotta fly well tho', so I'll sharpen my pencil open her up a bit. Now, if I could only remember the formula for computing the area of a circle....
Thom