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Maximum Continuous RPM for a Rotax 503

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

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 

   [quote][b]

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Thom Riddle

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

Posted: Fri Apr 27, 2007 3:59 am Post subject: Maximum Continuous RPM for a Rotax 503

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
Buffalo, NY (9G0)

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