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<< Lancair Builders' Mail List >>
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> Would appreciate some feedback on whether to purchase a hydraulic two or
three
> blade MT prop to hang on my IO360B1F and also whether to choose a 65" or
69"
> diameter.
Hi Angier,
The best prop for you depends on where you want it's strong point to be.
The part of the prop that is LEAST EFFECIENT at producing thrust is the tip.
Since a 3 blade has 50% more tip than a two, it tends to be slightly less
efficient especially in cruise. More blade area will produce slightly MORE
THRUST, especially static or at low speed, so a three blade prop will give
you slightly better take off performance and low speed climb. If you're
operating out of a short strip, you'll probably be more limited by landing
distance than by take off performance though.
The two blade (all else being equal) is a little lighter than a three blade.
When you add weight at the nose, the wings have to carry that weight PLUS
the weight of the increased tail down force that the elevator now has to
produce to balance the whole arrangement (trim drag). This is one reason
that although the 360's certainly climb better than the 320's, they aren't
much faster in cruise even though they're burning more fuel. (sorry Hollis,
and Grease, I couldn't help it)
The three blade will be a little shorter than the two blade so you'll have a
bit more ground clearance. I've been operating my two blade on grass strips
and haven't had any problem with clearance though.
The two blade (all else being equal) is a little less expensive to buy and
maintain than a three blade. With the extra money you'll have, you'll buy
more radios which will probably weigh more than the increased tail-down
force required by the three blade. :-) Sooo, it all boils down to
which one you think would look cooler when you're parked on the grass at
Oshkosh.
I wanted ZQ to be an efficient long range cruiser so I opted for the 2 blade
MT and I've been very happy with it.
Bill
harrelson@erols.com
N5ZQ (11 months since first flight...230 hours!)
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