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Thread: [IAC] two-blade vs 3-blade prop
Message: Re: [IAC] two-blade vs 3-blade prop
Follow-Up To: ACRO Email list (for List Members only)
From: "Terry Ridgway" <terry at dekt.com>
Date: Thu, 09 Nov 2000 22:11:54 UTC
HI Andrew, I've flown both of the S2B's at Attitude and I've found 846 to be noticeably slower than 7PS, even though it's got a recently overhauled engine. Hopefully 7PS won't come back the same way. The advantage that I see with the 3 blade composite prop is the reduced load on the crank shaft. I know that before 846 had it's prop strike and subsequent overhaul, that Attitude prohibited Snap Rolls in it for this very reason. A few years ago, Sean Tucker had a 2 blade metal prop depart the aircraft in flight due to stress on the crankshaft from repeated high load aerobatics. The crank snapped inside the crank case, so the fracture wasn't something that could be inspected for. I've also flown the S2C from Sean Tucker's school and there's a definite difference between the performance of this plane and those at Attitude. It could be the prop, but I suppose it could be something else. I'm not a mechanic, so the reasons are not obvious to me. Another reason I heard from Attitude as to their selecting the 3 blade prop is that it has a smaller diameter. The larger diameter of the 2 blade metal prop was another factor they attributed to the prop strike, since it only just caught the ground. Had it been equipped with the smaller diameter 3 blade prop it might not have happend. However, this is just hangar talk and could be total BS. I'd certainly be interested to hear what others have to say on this point, though. All the best, Terry Ridgway IAC 26643 ----- Original Message ----- From: "Andrew Boyd" <aboyd at host.ott.igs.net> To: <iac at gatekeeper.handmadesw.com> Sent: Wednesday, November 08, 2000 15:23 Subject: [IAC] two-blade vs 3-blade prop > > 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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