I'm going to take my duct off soon, to re-finish it.
I'm thinking about trying to fly it without the duct, I'm concerned about take-off distance, climb-rate, and cooling. I'll make some high-speed taxi runs first, to see how it feels.
Perry

Good idea Perry. I forgot how we measured the acceleration the last time.Use a stop watch and see how long it currently takes you to get to 50 MPH. Also with the duct off see what the static RPM is.


Paul Lamar

Vance W Jaqua wrote:

Good for you Perry! I will go out on a limb and predict that the take off run will be a bit longer but do able, and the inflight performance will be measurably better. If you have not checked my web page on prop design, you will find some curves that give relative perf at various disc loading based on momentum laws which set the 100 percent limits, and above 150 mph the loss due to small props is not great


Vance

When you look at that dinky 38" prop on the back of a Long-EZ with the
duct removed, you think "that couldn't possibly work"!

Perry

I ran a 38 in dia prop in my prop model, and the predicted output seems to
say that it is far from hopeless, If you can drive your static rpm up to
the equiv of about 130 bhp you should have in the range about 300lbf
thrust, and I think you are entitled to at least 180mph where the
little prop should be about 70 percent eff. As I recall the direct
drive Suber exceeds these numbers - Take data, as Paul says.
and keep us informed - Vance

That's interesting. The fan is 38" pitch, assuming it can get to 5000
RPM in cruise that works out to 263.9 fps, or 179.92 mph - the same
number you came up with. Unfortunately I predict RPM will also be down
at rotation speed and climb which will hurt. Maybe ductless will require
a shallower pitch to compensate.
With the duct in place it will do 5500 RPM and 160 mph, the approx.
airspeed inside the duct is around 160 * 1.3 = 208 mph. 38" pitch * 5500
RPM gives 290 fps or 197.9 mph, pretty close.
So now I have to re-enter test pilot mode, and if it works, hope ground
cooling issues aren't insurmountable.

Perry

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