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goodings(at)yorku.ca
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 Posted: Sat Apr 29, 2006 6:32 am Post subject: RotaxEngines-List Digest: rpm-prop-pitch-vne |
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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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davidjoyce(at)doctors.org
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| Posted: Sat Apr 29, 2006 11:49 am Post subject: RotaxEngines-List Digest: rpm-prop-pitch-vne |
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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
---
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icrashrc
Joined: 16 Mar 2006
Posts: 247
Location: Mishawaka, In
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| Posted: Sun Apr 30, 2006 2:50 am Post subject: RotaxEngines-List Digest: rpm-prop-pitch-vne |
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I think what you're missing is the RPM specs from Rotax. As I recall 5500rpm is max continuous rpm. I think 5800 rpm is time limited to 5 minutes. Most people seem to set prop pitch for max of 5500 to avoid the short time rating.
___________________________________________________________________________
--> RotaxEngines-List message posted by: "John M. Goodings" <goodings(at)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
| | - The Matronics RotaxEngines-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?RotaxEngines-List |
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_________________
Scott
www.ill-EagleAviation.com
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Horizonspace(at)aol.com
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| Posted: Sun Apr 30, 2006 9:42 pm Post subject: RotaxEngines-List Digest: rpm-prop-pitch-vne |
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I would suggest that you also calibrate your RPM gauge. The Rotax gauges have been known to be off by as much as 20 percent. Use a handheld gauge set for the appropriate number of prop blades and adjust for gear box ratio.
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jkuehn(at)mountaintime.my
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| Posted: Mon May 01, 2006 5:01 am Post subject: RotaxEngines-List Digest: rpm-prop-pitch-vne |
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Yes this is true! My tachometer is off by 10 % or more at LOW RPM, up
to about 3000 or so it reads low. That is 2000 is really 2200. But,
thankfully, above 4000 the error becomes insignificant, and at 5000 and
above it is dead accurate.
Jack
912 UL in a Sky Ranger, 46 hours and counting!
Horizonspace(at)aol.com wrote:
| Quote: | I would suggest that you also calibrate your RPM gauge. The Rotax
gauges have been known to be off by as much as 20 percent. Use a
handheld gauge set for the appropriate number of prop blades and
adjust for gear box ratio.
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