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ACRO E-mail Archive Thread: [IAC] two-blade vs 3-blade prop

Thread: [IAC] two-blade vs 3-blade prop

Message: [IAC] two-blade vs 3-blade prop

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From: Andrew Boyd <aboyd at host.ott.igs.net>

Date: Wed, 08 Nov 2000 23:23:20 UTC

Message:

  
I normally fly my 2-blade S2B up in Canada, but I'm in San Jose this
week, so I thought I'd get checked out in the S2B's at livermore (KLVK).

Both N117PS (now down for engine overhaul) and N846 (ugly green & red)
now have 3-blade MT props.  N846 used to have a two-blade, but it
just had it's engine overhauled, and they went to the 3-blade MT.

Despite the fresh engine overhaul, N846 surprised me how slowly it
accelerated down the runway.  It's not just the weight of the
extra guy up front - I fly pax in my S2B all the time.  And, the
density altitude is *exactly* the same - both airports are at 400 ASL.

The only difference I can figure is the 2-blade vs the 3-blade.  I
recall in the S2B AFM the numbers for takeoff performance are 
noticeably worse with the expensive 3-blade MT which must be
shipped to europe (takes 3 -> 6 months, I am told) for overhaul.

Plus, the MT blades are oh-so-delicate compared to my aluminum
blades on the hartzell.

I know the crankshaft is more likely to crack with the heavy
2-blade due to gyroscopic precession, and the 3-blade is a
tad easier to fly acro in (not much fwd stick in hammerhead,
for example).

But as long as the crankshaft doesn't crack so badly it departs
the airframe before overhaul, it's much cheaper to plan to
replace the crankshaft during overhaul, than to buy the $30K
hartzell 3-blade "claw" alternative used on the S2C.

The MT 3-blade due to it's poor performance and overhaul
hassles isn't even a serious contender.  And the whirlwind
isn't certified, so it's out.

Is anybody else sticking by their 2-blade (B suffix hub, yes 
I know) instead of going to the so-called superior 3-blade props?

tia,

--
aboyd at igs.net  ATP

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