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Hi Doug,
A three bladed prop would certainly remove any questions about
sufficient ground clearance.
I flew with a 76 " prop on my RV-6A for about 1 year and you
are correct it does not leave but approx 4-5" in my case between tip and
ground. Taking one inch off makes it 6.
I have been in and out of many grass strips, but always
make it a soft field landing keeping the hose gear out of gopher holes as long a
possible. Flying off of hard surface didn't present any
problem
I once (and that's more than enough) dropped it in from
approx 14-16 feet one time right after installing the new prop 76x88
- hard enough to bend the main gear and drag the tail on the bounce (Did I
mention I had the stick sucked to my backbone) -- a direct result of
failing to go up to altitude with my new 76 " prop and do stall testing and low
speed flight with various power variations.
It turns out, that having only previously flown
with a 68x72 with my 2.17:1 gear box, I was totally unprepared for the airbrake
action of the much larger prop when I pulled it completely back lower than 2200
engine rpm. I must have lost 20 mph in about 2-3 seconds and way too high
before touch down. Due to the much higher "roll" forces with the larger
prop I had encountered on take off, I hesitated to apply full emergency power -
worried about it rolling the aircraft that near stall speed - until the matter
was taken out of my hands.
I suspect I took the correct action (stick full back) not due
to any savy piloting skills, but because I had my brand new $1500 prop on the
nose {:>)
I later replaced the gear and both had been bent by the impact
and replaced the rudder eyebolts where the impact of the bottom of the rudder
with the runway caused the bearing races to jam - but the prop was
undamaged. It was cheaper to replace the main gear than it would have been
to replace the prop, but not by much.
Perhaps needless to say (but, I will) , when you put a new
prop on your bird - go up to altitude and make certain you know what it does
near stall speed.
Ed
Sent: Monday, October 04, 2010 11:57 PM
Subject: [FlyRotary] Sam Hodges Prop area
comparison
Ed Wrote:
"When He put my 74x88 Performance Prop on he got as high as 6100 rpm
one time but each time got at least 6000 rpm...".
Sam's prop actually measured 76 inches long (if I remember right)
which is quite a bit longer than I would want to run on a nose gear equipped
RV. A 76" prop leaves very little clearance off the
ground and will undoubtedly result in a considerable amount of
blade tip erosion over time.
If my IVO prop doesn't really work out I think I will give
the CATO 3 blade version a try since there are quite a few RVers
flying it and it will get the tips off the ground a bit more...at a cost of
a couple knots of top end of course!
Doug Lomheim
RV-9A, FWF / Canopy
OK City
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