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Maximum Continuous RPM for a Rotax 503

 
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lgold(at)quantum-associat
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PostPosted: Thu Apr 26, 2007 9:51 pm    Post subject: Maximum Continuous RPM for a Rotax 503 Reply with quote

Hi,
I am planning to join a group of dedicated (i.e., crazy) UL/LSA flyers who want to fly over 8000 foot mountains going from California to Arizona in planes with 503 and 582 engines. Since I will need to climb as fast as possible for 20-30 minutes at a time, I would like to know the maximum sustained RPM that my 503 will tolerate.

I know that the Rotax manual states that you can run at 6500 all day but should not run at the maximum allowed RPM of 6800 for over 5-minutes. My problem is that the maximum RPM on my my Challenger II long-wing aircraft is only 6200 due to its prop pitch. Does this mean that the maximum sustained RPM also goes down? If so, is this decrease in sustained RPM in proportion to the max speed (e.g., 6200/6800x6200 resulting in a max sustained RPM of 5926)?

Thanks for the help,
Les
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Thom Riddle



Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

PostPosted: Fri Apr 27, 2007 3:59 am    Post subject: Maximum Continuous RPM for a Rotax 503 Reply with quote

Lee,

No. The RPM limitations that Rotax put on their engines do not care
what prop you use and they do not change based on what prop you are
using. They are absolute numbers that refer to limits that the engine
components are designed for.

It means your engine can develop only 6200 rpm (assuming this is at
wide open throttle in straight and level flight) because there is a bit
too much load on it from the high pitch propellor. This is good for
economical low density altitude cruise flight as long as your EGTs are
in normal range. But not good for high altitude operation or for
extended climb perhormance. At 6200 RPM your engine is not developing
its full power and the power it does produce will drop as you climb
into thinner air and you will probably see the max rpm drop even
further as you climb. If your engine is turning 6200 rpm at best climb
speed that is another story and the pitch is probably about right. For
high altitude flight, if you have a ground adjustable prop, it would be
good to set the pitch to get close to 6700-6800(max) rpm in straight
and level flight at low altitudes.

Thom in Buffalo


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Thom Riddle
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