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| Subject: C-CHEX Prop | |
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Author: Bob P |
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Date Posted: Wed, Dec 05 2012, 13:13:09 GMT In reply to: Dave Piercy 's message, "G-CHEX has flown!" on Sun, Dec 02 2012, 16:45:54 GMT Congratulations :-) I'm not expert in these things but prop selection/pitch is a bit of a compromise with Rotax 582 powered Pulsars. COARSE PROP / OVER-PROPPED On the one hand the plane is very slippery and needs a coarse prop to allow it to fly fast without over-revving the engine (it likes to be driven in 5th gear). Also the engine does not like high rpms at low-mid power settings (EGTs can go into the red) - a coarse prop helps to avoid this condition. On the other hand the 582 (2 stroke) engine has a narrow power band. As the rpm falls, the amount of power falls off rapidly. This can result in long ground runs, or even worse "getting bogged down". My warp prop is prone to this when set too coarse. Max rpm on a ground power check look good because the prop is stalled and not pulling the air efficiently. But as airspeed increases, suddenly the prop digs in; the load increases; the rpm drops off. This results in engine rpm falling right out of the power band so there is not enough power to take-off/climb. FINE PROP / UNDER-PROPPED Good takeoff/climb performance but engine easily over-revved - limiting max speed (like driving around in 2nd gear). Also possible EGT problem. Alan's idea to trim your prop seems a good way to prevent over-propping your engine. But I guess your engine will generate a bit more power as it breaks in, and you can't stick bits back on to your prop so I'd tend to go very carefully (err on the side of being too coarse). Just make sure its fine enough to allow you to take off from any airfield you are likely to land at - in nil wind, mtow etc. Or perhaps you could borrow a finer prop whilst your engine it being broken in? That would also allow you to compare performance. Finally I'd definitely (and carefully)calibrate your taco before chopping bits off your prop - your climb performance looks pretty good (to me) so I wonder if your taco might be under-reading. Just my thoughts. Best to get the consensus of several opinions. Cheers Bob PS LAA have some good info on measuring climb rates, and a spreadsheet that allows you to "normalise" the results. I used a garmin etrex (walking) gps to log my climb performance. [ Next Thread | Previous Thread | Next Message | Previous Message ] |
| Subject | Author | Date |
| Prop | Dave Piercy | Wed, Dec 05 2012, 17:35:12 GMT |