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Bob Griffin
Joined: 22 Jan 2006
Posts: 34
Location: Slingerlands,NY
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 Posted: Fri Apr 28, 2006 2:55 am Post subject: rpm-prop pitch- vne |
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Hi gang, we have been running our Allegro 2000 LSA at around 4800 rpm in cruise with our 100 hp 912. We see 4750 climbing out. Yesterday the winds calmed a bit so I opened it up (straight & level) and got 5280. By rights we should bump 5500 at that point ,I beleive. I'm thinking of reducing the pitch to bring up the rpm but here is the dilemma. Where it is set now gives us a cruise of 125 mph which is very easy to see the vne of 138 at times. If I repitch, I'm afraid we will end up running at lower rpm's in cruise to avoid the high speeds. So if I adjust the pitch to see 5500 WO S&L I dont want to run all day at 4500 or so to keep the speed under vne ? Mabey the solution is to leave it where it is ? What do you think ?
Fly Safe
Bob Griffin
Albany NY
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Fly Safe
Bob Griffin
Slingerlands, NY |
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ami(at)MCFADYEAN.FREESERV
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| Posted: Fri Apr 28, 2006 11:48 am Post subject: rpm-prop pitch- vne |
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Interesting.
What prop are you using and at what setting?
With a 912S I see the same rpm on climb out (90mph), but get just under (165mph)Vne at 5500 rpm. Europa + Warp Drive wide chord 64" set at 20.5 degrees (at the tip).
What's wrong with 4500rpm? I rarely run above that! (although there seems to be a rough patch at 4200 to 4400 on mine, so I avoid that).
Duncan McF.
[quote] ---
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bjohnson(at)satx.rr.com
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| Posted: Fri Apr 28, 2006 1:02 pm Post subject: rpm-prop pitch- vne |
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What is the VNE for the experimental Allegro??????
-Bruce Johnson
Building an LSA Sonex, fly w/ a good friend in a 912s powered StingSport.
From: owner-rotaxengines-list-server(at)matronics.com [mailto:owner-rotaxengines-list-server(at)matronics.com] On Behalf Of Duncan McFadyean
Sent: Friday, April 28, 2006 2:48 PM
To: rotaxengines-list(at)matronics.com
Subject: Re: RotaxEngines-List: rpm-prop pitch- vne
Interesting.
What prop are you using and at what setting?
With a 912S I see the same rpm on climb out (90mph), but get just under (165mph)Vne at 5500 rpm. Europa + Warp Drive wide chord 64" set at 20.5 degrees (at the tip).
What's wrong with 4500rpm? I rarely run above that! (although there seems to be a rough patch at 4200 to 4400 on mine, so I avoid that).
Duncan McF.
[quote]
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Thom Riddle
Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)
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| Posted: Sat Apr 29, 2006 3:09 am Post subject: rpm-prop pitch- vne |
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Bob,
Our Allegro (80 hp) is pitched so that it just makes 5,500 rpm at wide
open throttle at low altitudes (less than 5000' DA) and gets 4700-4800
rpm during climb at Vy. If your ASI is like mine it reads a good bit
high on the order of 10% at cruise speeds, which means when I am
indicating 120 mph at 1,000' DA I'm really doing only about 109 mph
TAS. This is at 4,900 rpm and 75% power on the 912UL. I cruise at low
DA anywhere from 4100 rpm to 4900 rpm. At higher density altitudes I
cruise at 4500 to 5200 rpm depending how big a hurry I'm in. There is
nothing wrong with low rpm cruising and you will get much lower fuel
consumption. I would check my ASI accuracy before making any
assumptions about breaking Vne. The % error will probably be different
at different IAS ranges.
If you can't get 5,500 rpm at WOT at low altitudes you could stand to
decrease your pitch just a bit. Best cruise pitch is when your engine
reaches max continuous rpm at wide open throttle. Of course this pitch
depends upon what altitude you wish to cruise at. Mine is set for best
cruise at low altitudes. If I regularly cruised at 7500'-8500' I'd
reduce the pitch slightly because I can't quite get 5,500 rpm at WOT at
these altitudes, only about 5200 rpm which leave some power on the
table, so to speak.
Thom in Buffalo
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Thom Riddle
Buffalo, NY (9G0)
Don't worry about old age... it doesn't last very long.
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