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503 running staic rpm and props.


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Finally got my 503 150 hr overhaul complete, and she fired up almost immediately! :big_grin: gave it time to warm up, and did a static test, 6050 RPM! with 3 blade 50inch 18deg pitch prop, the prop is a brolga. is this good for a static test of this engine???


before the overhaul all i could get from it was 4500 rpm!! 049_sad.gif.af5e5c0993af131d9c5bfe880fbbc2a0.gif


though, sadly during the full power static run, the aircraft moved the chocks forward slightly, uncovering some loose gravel, and i now have a good 10cent size chunk missing from the leading edge of 1 blade!!!088_censored.gif.2b71e8da9d295ba8f94b998d0f2420b4.gif088_censored.gif.03b4fab6f26a58d5cdf75ba85c450225.gif oh well


the blades were not the best condition anyway, so whats the damage these days to the wallet for a new set of blades, or would it be better to get a new assy from narromine?



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Guest Teenie2

You can buy single blades from brolga . The 6050 rpm sounds allright, in flight that should go up a wee bit ,maybe 6200. For a reasonable fee you can purchase the manuals for the 503 from Bert Flood with heaps of good info like RPM s , the run in method ,now you have o/h the engine this should be followed.



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If you only got4500rpm before the overhaul it was badly needed. By my reckoning it would have been giving about 30 h.p.


Recommended top revs is 6800 according to my CPS book.



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You can download all the rotax manuals from the rotax web site. All information is in there. Those CPS books are like gold and if you do not have one I would suggest getting one. Far more detail about RPM, Cooling, EGT and fault finding.





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I have the rotax manuals that came with the aircraft the repair manual, and operators manual, but strangely there is no reference to static RPM figures with any type of prop fitted, just run in at MAX rpm for so many minutes refer to page 32, page 32 has no reference to rpm, only the tecnical specs state MAX rpm is 6800


, but the CPS books you are talking about sound good! where can i get one?



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Usually manufacturers can't quote a static RPM as this will change depending on the aircraft.


I've never looked into if there's a formula to calculate what a good static RPM should be, but it would be based on something like a percentage of the aircrafts cruise speed, the power available at max RPM and the tip speed of the proppeller at cruise?


If you have an engine with a max RPM of say 6800, to be used in a slow aircraft, say 50 kt cruise, you would be looking at a static RPM of around 6300.


If your aircraft is faster, like 80 kt cruise, a static of around 6000 may be right.


I see no reason why we shouldn't be able to get speeds of over 120 kts from aircraft powered by 503's like mine hopefully! at which point I would assume a static RPM of around 5200 would be about right!


Just need to hope I'm developping enough power to get off the ground?


If you know your engine is capable of developping full power, you then control the static RPM with prop pitch.


If you can't get enough reduction of static RPM with pitch, you need to look at larger prop diameter, or more blades.


Also remember that at WOT (wide open throttle) with a high pitch prop/low static value, two stokes will run rich.


Be ready for this and be careful about rejetting or dropping needles to correct this as you could end up going lean in cruise.





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Thanks Arthur, thats exactly the info i was looking for, so as my vampire cruises at 93 Kts, then 6050 RPM static is a good figure to achieve! though full power take off in the manual is stated at 6300, im certain it will achieve this on the ground roll as the airspeed increases!


thanks again.



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