From: Marc J. Zeitlin Subject: Jack's tips #3 Date: Wed, 4 Oct 95 15:08:14 EDT Jack W. writes: > 3. On my trip to OSH this year I had a engine failure caused > by fuel starvation with 20 gal in the tanks. We (my wife > is my copilot) landed the airplane on a farm road with no > damage. The Technical facts of this incident are as > follows: 1. Altitude: 3500 feet. 2. Weather: Scattered > clouds at 5000 ft.Temp. 75 F. 3. Time: About 12 noon. 4. > Exhaust gas temps began to rise rapidly and then fell.(lean > condition) 5. RPM dropped to 2300 for 10 SEC. 6. BOOST pump > on. Fuel pressure 7 psi. 7. Switch TANKS. 8. RPM dropped to > 1800 for 10 sec. 9. No power. 10. After landing and approx. > 30 min time. We tried to start the engine and it would not > start. The engine was primed manually and it then started > and ran normally. The Ellison was removed and sent back for > analysis and overhaul. Ellison found no problems other > than normal 400 hr wear. The unit was replaced and the > airplane flown for 4 hrs no problem. > Solution: Eliminate single source of failure (Ellison) by > developing a primer system that can be used to run the > engine in a emergency. This has been done but not tested. > Testing begins during the next month. EMAIL me if interested > in hearing more about this solution. -- Marc J. Zeitlin Email: marcz@an.hp.com From: Ken Reiter Date: Mon, 23 Oct 95 09:16:10 CDT Subject: Exhaust System - ? Hello Guys, I hope the days of sanding are nearing an end for me. I am requesting input of exhaust systems. It appears that a 4in4out is the perfered way at present. What about external exit point (per plans) vs. the internal exit point (inside the cooling air exit near the hub)? All input is VERY much welcomed. Ken Reiter (5.67a/IDA-1.5 for ken@qcktrn.com); Mon, 23 Oct 1995 11:24:04 -0400 From: "Dewey Davis" Date: Mon, 23 Oct 1995 11:24:46 -0400 "Exhaust System - ?" (Oct 23, 9:16) Subject: Re: Exhaust System - ? On Oct 23, 9:16, Ken Reiter wrote: > Subject: Exhaust System - ? > Hello Guys, > > I hope the days of sanding are nearing an end for me. > > I am requesting input of exhaust systems. > > It appears that a 4in4out is the perfered way at present. > What about external exit point (per plans) vs. the internal > exit point (inside the cooling air exit near the hub)? > > All input is VERY much welcomed. > Ken Reiter > =01=01=01=01 >-- End of excerpt from Ken Reiter I talked to Charlie Airesman, who tried out this idea first (exit inside the cowling), as far as I can tell. He was going for more speed in his perpetual goal to beat Klaus Savier, Gary Hertzler, et al. He did gain a micronaut or two, but the biggest improvement came in reduced engine temperatures. He claims that the cylinder head temps dropped at least thirty degrees with the exhaust pipes tucked in nearer the prop hub. He thinks this was due to the effects of exhaust augmentation drawing more cooling air from the cowling. It also runs quieter. Since then, another local flyer, John Stuart tried it on his Long EZ and also is very pleased with the reduced temps. John convinced Hal Hunt to modify a set of his pipes for inside the cowl exit. I see that Hal Hunt is now offering that as option for all his new customers. If I were buying a new exhaust system, I would definitely go that way. I did buy the stainless pipe about a year ago to do it myself but never got around to welding it all together. Now that Hal Hunt is offering this as an option, I may just buy a new set from him. Dewey Davis From: Ken Reiter Date: Tue, 24 Oct 95 08:11:46 CDT Subject: Damage to Prop Hub due to Exhaust System Exit - ? Hello Again, I would like to thank those who responded to my exit location; but, a new question has been surfaced. - Is there a Problem/Issue with damage to the prop hub or close to the hub due to the increased temperature of the exhaust? - Thanks Again, Ken (5.67a/IDA-1.5 for ken@qcktrn.com); Tue, 24 Oct 1995 10:32:04 -0400 From: "Dewey Davis" Date: Tue, 24 Oct 1995 10:32:45 -0400 "Damage to Prop Hub due to Exhaust System Exit - ?" (Oct 24, 8:11) Subject: Re: Damage to Prop Hub due to Exhaust System Exit - ? boundary="PART-BOUNDARY=.29510241032.ZM6407.ucserv" On Oct 24, 8:11, Ken Reiter wrote: > Subject: Damage to Prop Hub due to Exhaust System Exit - ? > Hello Again, > > I would like to thank those who responded to my exit location; > but, a new question has been surfaced. > > - Is there a Problem/Issue with damage to the prop hub or close to > the hub due to the increased temperature of the exhaust? - > > Thanks Again, > Ken >-- End of excerpt from Ken Reiter Good question. I can tell you my opinion, for what its worth. I don't thin k there is any problem whatsoever. I base that on the fact that my prop is always at ambient temperature after I fly at all parts of the blade, even that part that is exposed to the exhaust. The exhaust residue will discolor the blade but it doesn't even get the slightest bit warm there, at least as far as I can tell by feeling the blade immediately after flight. The discoloration can be wiped off and the blade finish doesn't seem to be affected at all. If you have ever flown behind another EZ at night you would be amazed to see the foot long plume of fire exiting each exhaust pipe. But it doesn't seem to damage the prop in any way. With the exhaust exiting nearer the hub inside the cowl, it is still a considerable distance from the prop hub, only a few inches closer so I wouldn't expect the temperature to be any different there. Charlie and John also say they don't see problems with the inside the cowl exit. Actually, the biggest temp problem with your prop is not caused by the exhaust gas. It is caused by the prop extension. Most people don't think about this, but your prop extension is essentially running at something near your oil temperature, so your prop hub could get to about 200 degrees F at the point where it mates with your prop extension. Feel the prop extension after flight and you can certainly see that it has been warm. I have heard of some prop hubs actually becoming permanently discolored due to the temperature of the prop extension . Mine doesn't show any signs of discoloration, but Terry Shubert says his prop hub has almost turned dark brown at the prop extension as if a permanent shadow is on the prop hub. Anyway, I don't think the exhaust gas is going to damage the blades at all and moving the exit a few inches inboard to get inside the cowl shouldn't make any significant difference. Dewey Davis Date: Thu, 26 Oct 1995 22:07:09 -0400 From: NBalog@aol.com Subject: NO Damage to Prop from Exhaust - why not? In a message dated 95-10-24 10:53:17 EDT, you write: > I base that on the fact that my prop is always at ambient temperature after I fly at all parts of the blade, even that part that is exposed to the exhaust. The exhaust residue will discolor the blade... >I can tell by feeling the blade immediately after flight. The discoloration can be wiped >off and the blade finish doesn't seem to be affected at all. If you have ever flown behind >another EZ at night you would be amazed to see the foot long plume of fire exiting >each exhaust pipe. But it doesn't seem to damage the prop in any way. Sounds like magic to me Dewey. I gave this some thought the first time someone told me the exhaust wouldn't affect the prop and what I came up with was this: have you ever passed your finger through a candle flame, picked up a charcoal briquette (sp?) with your fingers or poked your hand into your fireplace to reposition a log all or any of which left no permanent injury or even a sensation of fire or heat but may have left some soot on your fingers or hand? Same principle. The prop surface pass in front of the exhaust pipes hundreds of times a minute (2400 RPM/ N blades x # Exhaust outlets) which may or may NOT be during an exhaust phase; this is how, after synchronizing firing mechanisms, the old Vickers and Lewis guns mounted on WWI aircraft could shoot through the prop without destroying it. Maybe with some playing around you could adjust the prop position so NO blade is behind a pipe on the exhaust phase. It probably doesn't matter though, even if there IS heat and flame coming out a pipe there are laminar airflow considerations at the blade: pressure generated by the airfoil probably helps to deflect some of the heat and force. I'm sure Burt Rutan thought of this - or at least intuited it - while he was designing the variviggen/varieze planes. My point? There isn't one, i just felt like taking some of the "wow" factor out of the discussion. It's all in my forthcoming book :The Mysterious Made Mundane, using what you should have learned in high school if you hadn't been partying and getting lucky. -Norm From: "Dewey Davis" Date: Mon, 6 Nov 1995 11:21:50 -0500 Subject: Terry Shubert/Exhaust/Props I saw Terry Shubert yesterday. He flew into Cumberland airport, Charlie Airesman's home field, and I flew up there to meet them. Charlie is welding a set of four-pipe exhausts that exit inside the cowling for Terry's airplane. Since this was a recent topic on the net, I thought I would pass along an update. As you may have read in Central States, Terry has been conducting lots of experiments with his airplane to improve cooling and lower drag. The new exhaust system has been working well for the few builders that have tried it, so Terry asked Charlie to work up a set for his airplane. Terry got there at 11 am and the pipes were all cut, fit, and tack welded by dark. Charlie is an amazing craftsman, excellent work and very fast. (He says his Honda engine conversion will be ready for static tests next month, but thats another topic). Terry is hoping to see increased power, less drag, and quieter exhaust...all good things. This is one of those rare changes where there doesn't appear to be any negative tradeoffs. However, the last time I mentioned this on the net, there were a few questions about how the exhaust temperature might have a detrimental effect on the prop since the exhaust pulses are moved a few inches inboard toward the hub. I said I didn't know, scientifically, but that my own gut opinion is that there would be no effect whatsoever, just based on my observations of how little effect there is on the prop from the exhaust in its current location. I also said that the prop extension is a bigger contributor to heat on the prop than anything else. But Terry had a little incident in the race at Jackpot that you may remember from the newsletter. His prop failed. A controversy ensued over the design of the Performance two-bladed prop that he was using. If you read the story in Central States you know that he sent the prop to a 'forest products laboratory' for failure analysis. He has just received the report and I read it yesterday. The bottom-line conclusion is that there was heat damage on the prop! Now the question is, why is there heat damage? Terry's prop had a dark brown discoloration at the hub. Basically everything inside the spinner envelope was heat damaged. I have never seen a wood prop with that kind of severe heat damage except when the prop has not been properly torqued and the hub works against the prop extension. Unfortunately, that will lead to prop failure very quickly and the prop will depart the airplane. The hub of the prop will be found to be charred black from the friction against the prop extension. But that doesn't appear to be the problem in Terry's case because the entire hub seems to be uniformly heat damaged, not just the hub face. It is also unclear why any heat damage at the hub would result in a blade failure two thirds the way up the blade. The prop isn't a good enough conductor of heat to cause damage that far out if the heat source is at the hub. Terry has decided to conduct a survey of prop temperature. He has ordered a batch of thermal strips to send to volunteers so that we can all find out what the prop temperature really is in flight. So you flyers out there can expect to receive a survey questionnaire and kit from Terry sometime soon. I don't understand all I know about this. I still believe that there is no way the exhaust can be causing this problem but I could be convinced otherwise, if we can get some real data. I think Terry has the right approach and I will be making some measurements myself. I also find it interesting that despite his obvious problem with prop heat damage, he is going ahead with the inside the cowling exhaust that Charlie made yesterday. I'm sure we will get some before and after temperature data so that we can finally settle the prop temperature question. Dewey Davis From: Lee Devlin Subject: Re: Terry Shubert/Exhaust/Props Date: Mon, 6 Nov 95 13:31:08 MST Dewey wrote: > The bottom-line conclusion is that there was heat damage on the > prop! Now the question is, why is there heat damage? You don't have to char the wood to heat damage the prop. The adhesive that holds the lamintated wood together has problems with heat just like epoxy. Charred wood in the case of a loose prop indicates a high degree of localized heating (from friction) which can then have a run-away effect as it begins to consume the prop as fuel. The exhaust temperature of the stack is in the 1300-1500F range. The prop is only exposed to it for a portion of its rotation but will begin to take on the average temperature of the environment that it is exposed to. Therefore, if it is in 1400F air 10% of the time and ambient air 90% of the time, the prop's temperature rise _above_ ambient will approach 140F. It doesn't take much of a percentage exposure to hot exhaust gases to dramatically increase the average temperature of the wood. Also, like you mentioned, there will be an automatic temperature increase due to the hub extension conduction of the crankshaft. When the glue that holds the prop together becomes ineffective near the hub, the loads will be transmitted from laminate to laminate further outward on the prop. That's my opinion on how the prop could fail 2/3 outward from the hub from heat damage that occurs around the portion of the prop that is near the exhaust stack. Lee Devlin From: "Dewey Davis" Date: Tue, 7 Nov 1995 09:28:05 -0500 "Re: Terry Shubert/Exhaust/Props" (Nov 6, 13:31) Subject: Re: Terry Shubert/Exhaust/Props On Nov 6, 13:31, Lee Devlin wrote: > Subject: Re: Terry Shubert/Exhaust/Props > Dewey wrote: > > > The bottom-line conclusion is that there was heat damage on the > > prop! Now the question is, why is there heat damage? > > You don't have to char the wood to heat damage the prop. The adhesive > that holds the lamintated wood together has problems with heat just like > epoxy. Charred wood in the case of a loose prop indicates a high degree > of localized heating (from friction) which can then have a run-away > effect as it begins to consume the prop as fuel. > Agreed. Since we don't see real charring and a run-away effect, I suspect the damage is originating somewhere else. > The exhaust temperature of the stack is in the 1300-1500F range. The > prop is only exposed to it for a portion of its rotation but will begin > to take on the average temperature of the environment that it is exposed > to. Therefore, if it is in 1400F air 10% of the time and ambient air > 90% of the time, the prop's temperature rise _above_ ambient will > approach 140F. It doesn't take much of a percentage exposure to hot > exhaust gases to dramatically increase the average temperature of the > wood. Also, like you mentioned, there will be an automatic temperature > increase due to the hub extension conduction of the crankshaft. > Sounds reasonable to me. Although I believe there is a dramatic decrease in exhaust temperature as it flows through the pipes and exits the pipe. From something well over 1500 F at the exhaust valve to hundreds of degrees less as it travels down the pipe. I don't remember the numbers but I remember that this temperature reduction is a significant contribution to exhaust back pressure. I would guess that it is further reduced in the 8 inches of free air before it hits the prop. So there is quite a bit of uncertainty in the temp before it gets to the prop. Also, I think the exhaust area is probably a bit less than 10% of the prop circumference at that point, but I agree this is the right order of magnitude. > When the glue that holds the prop together becomes ineffective near the > hub, the loads will be transmitted from laminate to laminate further > outward on the prop. That's my opinion on how the prop could fail 2/3 > outward from the hub from heat damage that occurs around the portion of > the prop that is near the exhaust stack. Interesting theory. You might be right. Dewey Reply-To: Nigel.Field@HQPSB.SSC.ssc-asc.x400.gc.ca Date: Wed, 08 Nov 1995 15:40:16 GMT From: Nigel.Field@HQPSB.SSC.ssc-asc.x400.gc.ca (Field, Nigel (1416)) Subject: Re: Terry Shubert/Exhaust/Props >The exhaust temperature of the stack is in the 1300-1500F range. The prop is only exposed to it for a portion of its rotation but will begin to take on the average temperature of the environment that it is exposed to. Therefore, if it is in 1400F air 10% of the time and ambient air 90% of the time, the prop's temperature rise _above_ ambient will approach 140F. Lee Devlin> Only about 1/3 of the fuel burned in a piston engine shows up as HP at the crank The other 2/3 is about evenly split between exhaust heat and cooling system heat. The engine exhaust therefore only provides half the heat coming out the back, the other half comes from cooling exhaust which is spread over a much larger area and focused at the inner part of the prop. This would account for a much greater delta T than 140F. Thermal breakdown of the glue joints at the inner part of the prop could occur if it reached 200F or so where most epoxy starts to loose its strength, if they used epoxy. I believe Terry was in a race so he was probably using full power thus high cooling air temps plus exhaust heat. The blade flex loads are higher toward the tip so this could account for the failure location. On my subaru VE (I call her SUZE) the exhaust flame just touched the spinner as evidenced by some mild soot. I discovered that it acted like an oven and baked my hub to the point where the bolts got real loose. Fortunately I picked this up on an inspection before the prop came off in flight. I flew it from then on without the spinner which did nothing any way except add weight and make inspection a real pain. I never had problems with a darkened hub or glue failure but I did get small blisters in the finish on both blades L/E right where the exhaust was concentrated so it was hot. I think Terry has the right approach to instrument some props to find out just what the temps really are. Nigel Field From: Lee Devlin Subject: Re: Terry Shubert/Exhaust/Props Date: Wed, 8 Nov 95 11:09:25 MST Nigel wrote: > Only about 1/3 of the fuel burned in a piston engine shows up as HP at the > crank The other 2/3 is about evenly split between exhaust heat and cooling > system heat. This is an excellent point. The majority of the engine's heat exits the cowl at the back end and in the case of a LongEZ which burns around 6 gallons per hour, you're looking at about 500,000 BTU/hr which flows around the prop. That's about 5-6 times the amount heat that a typical house furnace puts out running at 100%. I think applying the waxes to the prop (on both the front and back) will give a pretty good indication of the average value of the inside. Should be interesting. Lee Devlin