cpayne(at)joimail.com
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 Posted: Fri Mar 26, 2010 2:03 pm Post subject: Running WFO |
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That's Wide F****** Open. On my current engine I have run it at full rated power (but NOT over) for over 20 minutes at a time. However I did not just jump into this. The Sukhoi guys do this all the time but I don't. There are ways to prep for this kind of operation:
1st: Set valve clearance to the outside limit (about .016"). Make sure that each of the 4 cams on the Int/Exh reads nearly the same. Do this by recording the difference on any given cylinder by pulling through at least 4 TDC and checking clearance. Average the difference for a setting.
Next: "tweek" the governor and prop to achieve no more than 2900 rpm at WFO (M-14P) in level flight. I set the prop blade angle to as much as the governor will allow about at 2985 RPM. I use a digital tach for accuracy.
Don't forget that prop unbalance stresses the engine unnecessarily. Do static and dynamic balance first.
Next: Change oil before test runs and include a generous amount of MMO. I use it in BOTH fuel and oil during test runs.
Also: Whilst testing at 80%, "tweek" the oil cooler outlet opening for the sweet spot where oil temps minimize and speed maximizes. Hint: it isn't wide open nor almost closed. Same goes for the shutters.
Of course, be sure that plugs are clean, torqued, mags timed to upper end of advance limits. Extended runs 80% power is a safe way to clean out the carbon before WFO runs.
Don't forget to use 93 octane Mogas, W/O ethanol if possible.
I'm not concentrating on the airspeed or GPS speed when running, I'm scanning those temps, first sign of trouble of hickup and it's KIO with a pull towards the Blue. If something doesn't feel right, back it off.
Craig Payne
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