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G"day Brian,My suspicion is that the prop won"t change much, the engine will just rev higher. You would go to the higher ratio if you wanted to access more horses (thats if the max hp of the engine is above where you currently run it.)CheersFred Yeah, I hadnt thought about it that way Fred, I could see the prop turing slower allowing a bit more pitch to keep engine revs about the same but that in turn could result
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Tony,Ye goode olde stalled prop...A prop is no different to any aircraft airfoil, it flies through the air and provides lift while its angle of attack is not too high for the speed it it doing. [Speed relative to its incoming air flow - not the gyro"s]If you over pitch a prop it will cavitate, the air separates off the back edge of the prop at about 20 ~ 30% of the chord length and the result is a dreadful turbulence from that point on, which means the prop relative to the air is sucking a huge hole through it, not at all efficient and a huge loss of thrust results as the engine"s power is taken up in generating this turbulence, as opposed to generating thrust. If you"ve seen the MiG Sukhoi flight demo with the pilot deliberately stalling the aircraft as a means of providing air brakes this will give you and idea of the effect - the jet is not flying at the time, it is totally stalled and unless the pilot resumes the flow of air to the top suface of the wing he is history.. so too your prop if overpitched.If you are tuning a prop you should start with it in a stalled configuration [to protect the engine from over-reving] and slowly depitch it to the point where it absorbs all the power from the engine, you might consider allowing the prop to be able to let the motor run to revs of max power + 10% but stay well clear of the red line - things have a horrible habit of coming undone at high revs. Never forget that you can have full power on while on descent - gravity will allow the gyro to travel at a speed where the prop can rev more freely and allow your engine to go over the red line, unless you are quick on the throttle, but usually never quick enough. So loading it up to take full power revs is usually a good bench mark to start from.Hope this helps.Nic.
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thanks nic, i would of got close to that. so can it just be called caviting ??????? i ve realised the pitch has been high but with the 2.62 ratio and my engine thats where its ended up. i have ordered a auto flight 2.47 ratio apparently this will max the tip speed out and bring the pitch back to more respectable angle around 13 to 14 degrees . i will you know how it goes , could be a while thou!
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Nick, most props can be made stall, just bleed all or most of thle airspeed off, then give it full throttle. If the stall comes on too soon [with airspeed] then you are in trouble and this is what Birdy was commenting on.
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