This should be interesting information. I'd certainly be interested in knowing
the answers myself. I recently had my prop pitch flattened by 4 degrees. Before
doing so, the Coupe was a real dog. It would barely ever see 100 MPH, and the
climb was never more than 350 FPM on a good day, fuel burn was also in the high
6.? GPH. Since the re-pitch, I'm seeing 108 MPH at 2550 RPMs. I was concerned
about what 2550 RPMs might do to fuel burn and oil blow by. So I took it on a 4
hour flight, topping off after 2 hours. To my amazement, the fuel burn dropped
from an average of 6.5 GPH, to only 4.69. The oil consumption was only 25% of a
quart, which translates into 16 hour per quart. Which again translates into
adding only 1 quart between 25 hour oil changes. Sounds fine to me. But I'd
like to hear what other think about running higher RPMs.
Richard
Ed Burkhead <[EMAIL PROTECTED]> wrote:
Frank,
John Cooper said it beautifully.
I'm inclined to agree with him on all his points.
Check your prop stamp and see if you have the prop's history. Call some
prop shops recommended by these guys and your FBO/A&P/AI and get estimates.
The prices he mentioned match my memory from casually watching the
reconditioning/repitching correspondence. Or, maybe, the price might have
risen to what Bill said. You can find out tomorrow.
The only downside to repitching to flatter is that it cuts down on your
cruise speed at a given rpm. With my prop repitched to 7146, my climb was
increased to tolerable and my Coupe's airspeed at 2400 rpm was almost
exactly 100 mph.
Being a timid and insecure type (as anyone can tell you), I continued to
cruise at 2400 rpm (except for just a very few instances).
Mind you, with a flat pitched prop, 2400 rpm isn't working the engine very
hard at 100 mph. Several people including mechanics told me to go ahead and
"let it spin" and run at higher rpms.
Engine experts!
* Is it bad to run the C-85 engine at more than 2400 rpm in cruise when you
have a flat, climb prop?
* If the plane cruises at 108 mph with the 7150 prop, is it OK to turn high
rpm to cruise the same airspeed?
* Would that cause lower or higher stress on the engine than flying 108 mph
with the 7140 prop?
Inquiring minds want to know!
Ed Burkhead
http://edburkhead.com East Peoria, Illinois
ed -at- edburkhead???.com (change -at- to @ and remove "???")
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