Today's Message Index:
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1. 04:09 AM - Re: rpm-prop pitch- vne (Thom Riddle)
2. 07:32 AM - Re: RotaxEngines-List Digest: rpm-prop-pitch-vne (John M. Goodings)
3. 12:49 PM - Re: Re: RotaxEngines-List Digest: rpm-prop-pitch-vne (David Joyce)
4. 05:30 PM - Re: rpm-prop pitch- vnerpm-prop pitch- vnerpm-prop pitch- vne (Airgriff2@aol.com)
Message 1
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| Subject: | Re: rpm-prop pitch- vne |
--> RotaxEngines-List message posted by: Thom Riddle <jtriddle@adelphia.net>
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
Message 2
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| Subject: | Re: RotaxEngines-List Digest: rpm-prop-pitch-vne |
--> RotaxEngines-List message posted by: "John M. Goodings" <goodings@yorku.ca>
Gentlemen: I don't understand your numbers for the Rotax 912S, 100 HP,
gear reduction 2.43:1. I am fairly new to this game, so I go by the book.
My Rotax manual says maximum rpm = 5800 on climb-out at full power (80
mph, 1700 ft/min on a cool day); cruise at 5200 rpm. I had the blade
pitch set at 19.75 degrees; at full power, the engine reached nearly 6000
rpm when hot; cruise at 5200 rpm was about 105 mph; this amateur-built
aircraft has a slow cruise because of its thick airfoil. So I increased
the pitch to 19.5 degrees; it now reaches only 5600 rpm at full power;
cruise at 5200 rpm is about 110 mph. Presumably, I should decrease the
pitch a tad to achieve 5800 rpm at full power when the engine is hot. My
point is, it is my understanding that blade pitch should be adjusted to
achieve full power at 5800 rpm, and cruise power should be 5200 rpm; it is
not good for the engine to run too cool. And yes - avoid the rough spot
near 4200 rpm on these engines; it is hard on the gear reduction drive.
Some of what I am doing does not seem to be in line with what others are
reporting on this Rotax Engines List. Please enlighten me.
John Goodings, C-FGPJ, CH601HD Zodiac with R912S, GSC 68" 3-blade prop,
Toronto/Waterloo
Message 3
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| Subject: | Re: RotaxEngines-List Digest: rpm-prop-pitch-vne |
--> RotaxEngines-List message posted by: "David Joyce" <davidjoyce@doctors.org.uk>
John, The PFA in the shape of Frances Donaldson suggest you set the pitch of
the prop so that fully fine you only get 5600 rpm static with the engine
warmed up properly. The logic seems to be that exceeding 5800 can seriously
damage your engine (& your day), and that a max static of 5600 ensures that
you are unlikely to exceed 5800 in a go around situation where you firewall
the throttle and are much too occupied to look at rev counters. I am a bit
confused about your numbers as 19.75 to 19.5 seems more like a decrease in
pitch which should have increased the rpm!
Regards, David Joyce, G-XSDJ
----- Original Message -----
From: "John M. Goodings" <goodings@yorku.ca>
Sent: Saturday, April 29, 2006 3:30 PM
Subject: RotaxEngines-List: Re: RotaxEngines-List Digest: rpm-prop-pitch-vne
> --> RotaxEngines-List message posted by: "John M. Goodings"
<goodings@yorku.ca>
>
> Gentlemen: I don't understand your numbers for the Rotax 912S, 100 HP,
> gear reduction 2.43:1. I am fairly new to this game, so I go by the book.
> My Rotax manual says maximum rpm = 5800 on climb-out at full power (80
> mph, 1700 ft/min on a cool day); cruise at 5200 rpm. I had the blade
> pitch set at 19.75 degrees; at full power, the engine reached nearly 6000
> rpm when hot; cruise at 5200 rpm was about 105 mph; this amateur-built
> aircraft has a slow cruise because of its thick airfoil. So I increased
> the pitch to 19.5 degrees; it now reaches only 5600 rpm at full power;
> cruise at 5200 rpm is about 110 mph. Presumably, I should decrease the
> pitch a tad to achieve 5800 rpm at full power when the engine is hot. My
> point is, it is my understanding that blade pitch should be adjusted to
> achieve full power at 5800 rpm, and cruise power should be 5200 rpm; it is
> not good for the engine to run too cool. And yes - avoid the rough spot
> near 4200 rpm on these engines; it is hard on the gear reduction drive.
> Some of what I am doing does not seem to be in line with what others are
> reporting on this Rotax Engines List. Please enlighten me.
>
> John Goodings, C-FGPJ, CH601HD Zodiac with R912S, GSC 68" 3-blade prop,
> Toronto/Waterloo
>
>
> ________________________________________________________________________
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>
Message 4
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| Subject: | Re: rpm-prop pitch- vnerpm-prop pitch- vnerpm-prop |
pitch- vne
Hi Bruce, The Allegro , whether factory built or from a kit, has a VNE of
138 mph in the US. Our Allegro has a Compwood prop (composite) 3 blade set at
around 20.5*
Bob Griffin
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