KR> Wind milling
I had a bubble in my fuel line while bouncing through turbulence once and the engine stumbled briefly. The thing that kept it going was the wind blowing through the prop plus lowering the nose to keep the airspeed up. My compression ratio is about 6.6 to 1. That helps a lot. -Joe >Is it possible to restart a VW engine by diving (I mean, make a steep dive >in order to increase airflow and possibly force the prop to windmill), or >is it a lost case?
KR>Wind-milling - Mac UK
>Hi Stephen, Off subject -do you know if Clive Puzzi ?(Harare last I heard) is still around? Don't know the guy Mac but I have put out feelers with some of the kin in Zims - things are really bad for a paleface on that side of the Zambezi. I will let you know if anything crops up. Did you spend any time in Africa? Steve J jayq...@microlink.zm
KR> Wind-milling
Steve, why do you want the dead engine to windmill ? Didn't the CAFE folks find that a =stopped= prop was better for glide range than one wind milling? Hi Art - thanks for the input. You are addressing the topic of what's best after the engine quits and I think you are right, a wind milling propeller creates more drag. I am concerned about the things that make the engine go quiet in the first place. There are various causes of a temporary fuel supply interruption and we are inventing new ones all the time. Some (not many) are genuinely not our fault, most are - we are only human. The ultimate sin is forgetting to change tanks - but it happens. It happened to me in a bird just like yours, the day before I got to solo. My instructor was fascinated by some whales in Blue Water Bay (George coast, South Africa) and made me circle at 500'. As you know, the AA1 uses the tubular spars as fuel tanks and we were probably using the inside (low side) tank. This was 1976 so I don't remember if we ran the tank dry or the turn was just badly coordinated - but I do remember the sudden silence at 500', 400' 300' . It was a lesson in emergency procedures to see my instructor react - like lightening he changed tanks and flipped the fuel pump switch - 200'; 100' and the silence was gone. If the motor had not been wind-milling and patiently waiting for the fuel to arrive - we would have really surprised the whales that day. I can tell another one about the same idiot after going solo, getting his ticket and clocking up a few hundred hours, but I think you see why I prefer to live with the over priced, inefficient and technically outdated airplane engine. It keeps turning, NO OTHER REASON. On that topic - look into ice warning gizmo's for the carby. I have seen a few really good low cost units on the web (not for certified birds). Important not to be caught napping, particularly with a motor that does not wind-mill - the motor must still be rotating if we hope to suck in some warm air and melt the offending ice - yanking the carb heat after the motor stops turning will achieve nothing. Two lessons learnt about carb ice: = when initially applied, the motor may get really unhappy while it is drinking melted ice for a few seconds - don't think you have done something wrong and shut off the carb heat, stay with it. = Icing generally starts close to where the butterfly is. If you feel any resistance or roughness in the action of the throttle control, hit the carb ice. = If the go lever is already frozen solid, don't panic (yet). If you can live with the power setting while the ice melts - OK. Maybe you pulled it right back in a rush descent and it froze there - why would I know all about that? The weather circumstances that promote getting down fast may also be the conditions that promote icing (and keep you busy enough to forget to pull the knob). If this happens, rap the control with the palm of your hand (friction nut off) with increasingly more force. Get onto it fast and the ice will probably be light (weak) enough for the butterfly to break loose when you rap it just right. Again, the motor will get really unhappy with a mouth full broken ice - stay with it. If it stops wind-milling, hit the starter and start looking for a place to set down. Don't worry about rapping it hard enough to break something if a forced landing is on the cards anyway. Think about this when designing and fitting the engine controls, fortunately Piper did and I am here to talk about it. Have a great week Steve J
KR> Wind-milling
-Original Message- From: krnet-boun...@mylist.net [mailto:krnet-boun...@mylist.net] On Behalf Of Stephen Jacobs Sent: Monday, February 23, 2004 3:48 AM To: 'KRnet' Subject: RE: KR> Wind-milling >>>>Steve, why do you want the dead engine to windmill ? Didn't the CAFE folks find that a =stopped= prop was better for glide range than one wind milling? One more guy who likes wind milling props- Had some of the same experiences. Idiot runs tank dry. Quick switch of tanks, hit fuel boost, engine sounds much better, wife didn't even realize it happened, asked why I moved so fast all of a sudden. Why doesn't the auto conversion windmill? Is it engine compression ratio? Or blade area of the prop? Russ Breckenridge,MN KR2/KR1 asir...@702com.net
KR>Wind-milling
Many years ago Burt Rutan mentioned when trying to save weight in the VW powered vari-eze that you couldn't dive fast enough to air start the engine. (High compression - small prop) The fix for this is to put on a starter and electrical system. Lynn N37LH
KR>Wind-milling - Compression ratio
Steve Jacobs wrote: > 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). Good point, and I'm sure you're exactly right that prop diameter also has a lot to do with it. I guess I was assuming all things remained the same. You can make a VW or Corvair turn a prop slowly too. William Wynne's Pietpol ran a Corvair at about 3000 rpm WOT and he claims an output of about 90 hp, and turned a 68" Warp Drive prop on it. See http://www.flycorvair.com/corvair.html#Engine%20Specs for more details. Mark Langford, Huntsville, AL N56ML at hiwaay.net see KR2S project N56ML at http://home.hiwaay.net/~langford
KR>Wind-milling - Compression ratio
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! RegardsMac UK > - Original Message - From: "Stephen Jacobs" <ask...@microlink.zm> To: "'KRnet'" <kr...@mylist.net> 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 krnet-le...@mylist.net > please see other KRnet info at http://www.krnet.org/info.html
