Hi Stephen, Off subject -do you know if Clive Puzzi ?(Harare last I heard) is still around? He gave me some good advice when I was building the KR but lost touch when the guy I lent his notes to promptly lost them. Your comments re windmilling made a lot of sense-I reckon the average homebuild pilot is fully occupied finding somewhere forgiving to flop into rather than losing valuable height trying to windmill a dead donk! Regards Mac UK > ----- Original Message ----- From: "Stephen Jacobs" <[email protected]> To: "'KRnet'" <[email protected]> Sent: Monday, February 23, 2004 3:59 PM Subject: KR>Wind-milling - Compression ratio
> >>>>If you just want to make a VW or Corvair windmill, just lower the > compression ratio > > Thanks for the input Mark > > I have often thought about this, particularly when I hear what you guys > pay for Corvair spares over there. The Corvair is already a good motor, > so de-rating it by 10% will make it bullet proof. > > Your comment is encouraging and I would be delighted if this can work > out - this is however how I see it. > > The tendency (ability) to wind-mill at cruising speeds is influenced by > how much resistance the engine presents to being turned over (CR), as > well as the force that is trying to turn it - and that is very much a > function of propeller diameter and blade area. Smaller props have less > leverage (and inertia). > > To achieve fair grunt out of any motor, we need to let it get a > respectable way up the power curve. In the case of the Corvair I > suspect that this will be well over 3000 rpm, restricting the propeller > diameters to something like 65" on a direct drive. (not that there is > room for much more). > > My instinct has always been that - by the time you drop the CR to the > point that 80mph (approach) will keep a 65" prop turning a 3L engine > (approx)- the CR will be such that maybe 30% of the potential power is > lost. > > If the CR reduction required to allow a typical KR prop to wind-mill is > such that the power loss is 10% /12%) - this would change things for me. > > Take care > Steve > > I visited your engine CC'ing site - excellent piece of work, written in > a way that that makes me want to do one. > > > > _______________________________________ > to UNsubscribe from KRnet, send a message to [email protected] > please see other KRnet info at http://www.krnet.org/info.html
