Some interesting info:

On 7/19/04, Gary Koester wrote:

>Can you tell me about a Balsa USA enforcer with the Byron unit which is
>just sitting on top with no ducting.

Well, Byron is a bit of a special case.. the fan has to eat the garbage air off the back of the engine, and that hurts.

The key thing in that is to get some kind of a good inlet lip radius.
The byron fan has a bit of one, but bigger is better.

>Does an OS 77 and the Byron unit get close to 13 Lbs static thrust?

I have no idea. The 77 is less power, but the larger diameter of the Byron fan can increase thrust compared to the smaller Ramtec. (note, bigger diameter and more static thrust does NOT mean a better performing airplane.. the Viojett is the smallest of the .91 class fans, and gives the best performing airplanes)

>The duct has a slight taper toward the exhaust. Does this help thrust?

For a given engine and fan, set the exit diameter to properly load the engine with whatever pipe you have. It should be on the low end of the pipe range at static so it doesnt overspeed in flight.

On a .91, the Byron normally overloads the engine a bit, so I would not taper the pipe very much. On the 77, I am not sure where it puts out best power.

For a nacelle like that, one option is to make a tapered pipe, and then trim it back to larger diameters and see what happens.

bob