Paul Yaw wrote:

This may top the silly question list, but a bit of embarrasment before
the new year will be OK since I will forget all about it when I open my
gifts on Saturday.  There were two Ivo props shown in a previous
message. One of them was rated at 100 to 700 horsepower.  The 100 to 700
hp version was used on an airplane which had a 260 hp 13B that I built.
74" diameter I think.  With the engine at full throttle, (43" mp) the
rpm never dropped below 6,200 rpm no matter how the prop was set.  If a
260hp engine can spin it 2850 rpm (2.17 reduction ratio.) what is going
to happen with 700 hp on tap?  What am I missing? Before anyone answers
please consider that I know nothing about props (Or airplanes for that
matter.) so make it easy to understand.

Paul, I think this has to do with the strength of the prop itself rather than
whether in a particular application it could effectively convert 700 hp. As I
understand it, one of IVO's biggest markets is airboats (incl swamp buggies?)
which use mostly a pre adjusted fixed pitch prop powered by a big V8. At 700 hp,
each blade must be able to absorb 233 hp (700/3) without failing. Also, there
may be different, or no, reduction ratios. IVO composite props can accept
supersonic tip speeds although it isn't very efficient.

I think the reason that the engine would not change rpm no matter what pitch you
set was because the blade was cavitating similarly to a boat prop, or spinning
the tires. I've got the same problem with my plane in that when I first apply
t/o power, the prop can be set at a pretty deep pitch and the engine rpm will
not be held down. Essentially, the power of the engine overcomes the "traction"
capability of the prop. After the plane has accelerated to a speed that matches
the theoretical prop speed, the blade may no longer be cavitating, IF you have
sufficient blade area (width, length, strength). I wanted high altitude, high
spd cruise capability, but I'm concerned that the IVO blades do not have
sufficient size to accomplish this, but I'll need to test to find out. I don't
know whether you were using the deep pitch prop that can go up to 105" of pitch.
If you were using the normal pitch (up to 90"), you might want to try the deep
pitch.

When we raced dragboats, we had an 11.5" diameter SS prop that had a 17" pitch
that had to absorb 1,400 hp (526" blown alcohol hemi). Surprisingly, at launch
the engine rpms would only come up about 7K (low gear-30% under) and climb to
7.6K in high gear (13K rpm@ prop(70% overdrive)) at 180+ mph. Just changing to a
1/2" larger diameter made the boat uncontrollable. The other interesting aspect
was that only half the prop was in the water transmitting power. We always were
searching for a more effective prop, and at the same time x-raying the prop
after every race.

The point I'm trying to make is that there is a lot more to props than just the
specs, and one of the important aspects is the ability to absorb the hp without
failing. That is what I think IVO is saying about the 700 hp Magnum prop.

 
The Aircraft Rotary Engine Newsletter.              Powered by Linux.

http://home.earthlink.net/~rotaryeng/            http://www.linux.org