Perry Mick wrote:
Well, not exactly. After 5 years and 500 hours of direct-drive,
ducted-fan rotary flying, I did a short first-flight around the pattern
today with a new configuration: RD1B and a prop.
I am used to getting pushed back in my seat when I apply full throttle
for takeoff. The open prop seems very sluggish while taxiing, and at the
start of takeoff roll. I can feel the blades "unstall" after building up
some speed. This is something I never experienced with the ducted fan. I
saw 5400 RPM on climbout, higher than before (5100). 5400 was max. level
flight RPM with the ducted fan, so I expect it will go up to 6000 with
the PSRU. I shed 36 lbs. in the propulsion system doing the changeover,
and had to remove the weather radar indicator from the panel and the wx
antenna from the nose (additional 16 lbs. combined) to get the cg back
(radar needs repair anyway, it's just been balast for a long time).
Climb rate is definitely better (higher revving engine, less weight).
I'm hoping to get at least 180 mph in cruise, 155 was about the best I
could do with the ducted fan.
Perry
Hey Perry finally tried a PSRU. Got some pictures of the prop? Pitch? diameter?
RD1B is 2.85:1 right?
Paul Lamar
I had considered a 2.85 that Peter Cowan had for sale awhile back, but I just couldn't make that ratio work on a pusher (on paper), with my "low" rpm engine (7000 redline).
RD1B is 2.17 six-planet. I actually was not even thinking about putting on a PSRU at this time, but with the big fad of going to 2.85 among the RV crowd, a low-time RD1B went on sale by a guy doing
a conversion to 2.85.
For prop I just looked at what the O-235 LongEZ guys were using and started with that. The average seems to be around 62" in diameter and 68" pitch, so that's what I analyzed and built. I was going
to make it two-blade, but I had some prop bolts laying around I wanted to use, that limited prop hub thickness to 3.5". So I hit on the idea of making it 3-blade with narrow blade chord. I wanted to
keep the diameter small as I have the thrustline lower 2-3 inches from stock. I have about 11 inches of ground clearance.
I have some vibration that only showed up after bolting on the prop, so I assume it's a small imbalance in the prop. But I can't get the dynamic balancing equipment to converge on a solution. That's
why I kept the flight short. I'm going to try again today at a higher RPM.
I'll try to take some photos with my cheap digital camera.
I still like the ducted fan, someday I'll build this LSA Solitaire, where the speed limit is 120 knots.
Perry
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