I've got two different propellers I'm looking at and I'm trying to figure out which
one to buy. I'm soliciting your educated opinions as to which would be better ..
which would provide more thrust in the airspeed range 30 mph to 90 mph.
1.) 68" Warp Drive 5 or 6-blade ground adjustable propeller. Approximately 2" chord
for each blade. (Originally designed for the ultralight/microlight market.) About
$800.
2.) 68" Sensenich 2-blade composite ground adjustable propeller. Approximately 8"
chord for each blade. (Designed for the airboat market.) Manufacturer reports it
is most efficient between 2500 rpm and 3000 rpm. About $1500.
Remember my aircraft is different than most of yours ... it's a two-seat tandem
gyroplane, not an airplane. Think "slow flight". This thing is only going to fly
between 30 mph and 90 mph. I have a '91 Mazda 13B turbo, and a 2.85:1 gear reduction
drive. Gyroplanes need more thrust to fly than do airplanes of comparable weight. I
need at least 600 lbs of static thrust. 800 lbs would be better. I cannot go bigger
than a 68" diameter, otherwise I would be sawing into my vertical fins on either side
of the prop.
I've posted this question to "the rotorcraft conference", at www.rotorcraft.com, and
received mixed reports. Some say they had better performance from a Warp Drive
multi-blade, others a large chord 2-blade. None of them had all the
details/parameters I was looking for ... engine make and model, engine and prop rpm
for max static thrust, engine and prop rpm at cruise, propeller diameter, propeller
chord, number of propellers, propeller make.
The responses I received were as follows:
1. Machine with Subaru Legacy EJ-22 having a 4-blade 68" Warp Drive puts out more
than 600 lbs static thrust easily. Ross 17:1, 12 degrees pitch, 5200 rpm on climb
out, 5000 static.
2."A friend was running a five blade warp drive on a 150 hp Lycoming. It had the
most thrust of any prop he tried, but the noise was too much so he went back to a
Sensenich."
3. Used both a 72" 2-blade Sensenich and a 72" 4-blade Warp Drive on a 180 HP
Lycoming, in a McCullough J-2. The Warp Drive produced more static thrust, more
thrust in-flight and had less vibration.
4. Used both a 68" 2-bladed Prince prop and a 68" 3-bladed Warp Drive on an RAF 2000
gyroplane, having an EJ22 Subaru. User estimated the engine put out 90-110 hp.
Prince prop chord about 5". The Prince prop produced more static thrust and less
vibration. Much preferred. The RAF 2000 has a belt reduction drive. (The reduction
ratio was not reported.) Max engine rpm with the Prince was 5000 rpm, and 5150 rpm
with the Warp Drive. (The Prince is also ground adjustable, I think.)
I bought a copy of "Airplane Aerodynamics and Performance", by Roskam and Chuan-Tau.
They have a chapter on propeller performance estimation. Downloaded a copy of NACA
TN 1338, "Propeller Efficiency Charts for Light Airplanes", July, 1947. This
technical note provides some insight, but is not tailored to slow flying aircraft.
It does give data for engines of 50, 100, 150 and 225 HP, at airspeeds of 50, 100 and
150 mph, and with different number of prop blades with 6 and 8-foot diameter. That's
the low end charts. It goes on to 300 and 400 HP engines, and 10 and 12-foot props,
and 300 and 400 mph. It is interesting how it shows the trends for increasing the
number of blades ... the resultant blade system is efficient over a wider rpm range
at a particular airspeed, and all other parameters fixed.
Most of the charts assume a solidity per blade of 0.0345. A rough estimate for the
solidity per blade of the Warp Drive would be 0.019, and the Sensenich, 0.075. The
charts just don't address either of these solidities. I don't think one can
interpolate the data here for these.
So ... what are your educated opinions?
Thanks,
Scott