Date
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Prop Questions
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Chris McAtee <Subcanis@...>
Hey everyone, could you fill me in?
With the diameter of the prop limited on our Q's, should one spin the prop as fast as the engine can handle? For example: at 3600 RPM, the tip of a 60 inch prop (@18 degrees F) is just at the bottom of the recommended tip speed range (as specified by http://www.pponk.com/HTML%20PAGES/propcalc.html). So does this mean that if my motor can handle 3600 continuous RPM's I should, or should I up the pitch and turn it slower? Chris McAtee Tri-Q200 (in progress) Email: subcanis@... subcanis@... Home: 2917 Pheasant Dr. Casper, WY 82604 (307)265-5375 School: University of Wyoming 614 White Hall Laramie, WY 82071 (307)766-8670 _________________________________________________________________ Chat with friends online, try MSN Messenger: http://messenger.msn.com |
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jtenhave@mets.mq.edu.au <jtenhave@...>
Chris,
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this is an easy question to ask but a hard one to answer. One way to consider the problem is to imagine that you were faced with having to select a single gear for your car to be used at all times. Clearly, you would want to choose a gear / prop which is optimised for the use that you will apply it to most frequently, but be prepared to compromise the absolute peak of efficiency so that certain minimum requirements can be met i.e. take off run, rate of climb, hot and high performance etc. Tip speed is important but equally important is to try and match the power requirements of the prop to the available power from the engine for as much of the rpm range as possible. Several factors affect the prop power requirements including pitch, blade area, number of blades, air density etc. That is why ground adjustable propellers such as Warp have so much to offer. There are several excellent propeller design programs around, but it not an exercise for the faint hearted. As with all iterative processes, a good first guess will save a lot of time, money and effort - There are several contributors to the list who have been down this road - may I suggest that you shamelessly imitate the most successful with respect to pitch, diameter and manufacturer. If you are going to err, the most conservative approach is to err on the side of finer pitch. Final thought - Tri Q 200 usually means an 0-200 does it not? It is a bold fellow who would want to run his 0-200 at 3600 rpm for any extended period of time... John -----Original Message-----
From: Chris McAtee [SMTP:Subcanis@...] Sent: Sunday, December 30, 2001 5:50 PM To: Q-LIST@... Subject: [Q-LIST] Prop Questions Hey everyone, could you fill me in? With the diameter of the prop limited on our Q's, should one spin the prop as fast as the engine can handle? For example: at 3600 RPM, the tip of a 60 inch prop (@18 degrees F) is just at the bottom of the recommended tip speed range (as specified by http://www.pponk.com/HTML%20PAGES/propcalc.html). So does this mean that if my motor can handle 3600 continuous RPM's I should, or should I up the pitch and turn it slower? Chris McAtee Tri-Q200 (in progress) Email: subcanis@... subcanis@... Home: 2917 Pheasant Dr. Casper, WY 82604 (307)265-5375 School: University of Wyoming 614 White Hall Laramie, WY 82071 (307)766-8670 _________________________________________________________________ Chat with friends online, try MSN Messenger: http://messenger.msn.com To unsubscribe from this group, send an email to: Q-LIST-unsubscribe@... Quickie Builders Association WEB site http://www.quickiebuilders.org Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/ |
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Justin Mace <n764jm@...>
Chris,
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FWIW! I flew behind a 52" dia prop turning at 2250 rpm max for about 500 hrs. Normal cruise was at 1950 rpm. I heard all the prop experts say that more rpm is way better! I changed props and turned the new prop to 4500 rpm. This was all on my Dragonfly. The top speeds were very close to the same with the climb a little less at 4500 rpm. I was happier with the slow turning prop. {a lot less noise} With that said, I will admit with the slow prop speeds of 2250 rpm the engine was turning at 4400 rpm, like running in second gear in a car. The additional torque available through a PSRU made the difference. It took five (5) blades to absorb the torque at 2250 rpm while the 4500 rpm was with three blades. It seems clear to me that prop speed is not all there is to the equation other factors come into play. My O-200 is currently turning a three bladed 52" prop and I am very happy with it. It will turn about 2900 wide open at altitude with the top speed very close to the Dragonflys' 180 mph Vne. There are a few Q-200s that will fly about 20 to 25 mph faster than my DF at the same rpms, you could contact these guys that have the fast planes and learn from the "Pros". All other comments you get will be opinions or hearsay! As a friend of mine is fond of saying " It's hard to argue with sucess" I have meet these guys and they are willing to help. What a good group. Justin Mace Dragonfly MKII O-200 At 11:49 PM 12/29/2001 -0700, you wrote:
Hey everyone, could you fill me in? |
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RICHARD EDDINGER <mrsrb1@...>
A 0-200 will run fine at 3600 and over if set up correctly balancing is the main consideration. Ask any one of the racers at Reno they are running them well over 3600.
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In fact about the only thing they can do except for balancing is polish about everything internally. The compression ratio, pistons, cam and all eternal parts must meet factory spec.. All engines are given a very extensive test before they can be certified to race. ----- Original Message -----
From: jtenhave@... Sent: Sunday, December 30, 2001 12:00 AM To: 'Q-LIST@...' Subject: RE: [Q-LIST] Prop Questions Chris, this is an easy question to ask but a hard one to answer. One way to consider the problem is to imagine that you were faced with having to select a single gear for your car to be used at all times. Clearly, you would want to choose a gear / prop which is optimised for the use that you will apply it to most frequently, but be prepared to compromise the absolute peak of efficiency so that certain minimum requirements can be met i.e. take off run, rate of climb, hot and high performance etc. Tip speed is important but equally important is to try and match the power requirements of the prop to the available power from the engine for as much of the rpm range as possible. Several factors affect the prop power requirements including pitch, blade area, number of blades, air density etc. That is why ground adjustable propellers such as Warp have so much to offer. There are several excellent propeller design programs around, but it not an exercise for the faint hearted. As with all iterative processes, a good first guess will save a lot of time, money and effort - There are several contributors to the list who have been down this road - may I suggest that you shamelessly imitate the most successful with respect to pitch, diameter and manufacturer. If you are going to err, the most conservative approach is to err on the side of finer pitch. Final thought - Tri Q 200 usually means an 0-200 does it not? It is a bold fellow who would want to run his 0-200 at 3600 rpm for any extended period of time... John -----Original Message----- From: Chris McAtee [SMTP:Subcanis@...] Sent: Sunday, December 30, 2001 5:50 PM To: Q-LIST@... Subject: [Q-LIST] Prop Questions Hey everyone, could you fill me in? With the diameter of the prop limited on our Q's, should one spin the prop as fast as the engine can handle? For example: at 3600 RPM, the tip of a 60 inch prop (@18 degrees F) is just at the bottom of the recommended tip speed range (as specified by http://www.pponk.com/HTML%20PAGES/propcalc.html). So does this mean that if my motor can handle 3600 continuous RPM's I should, or should I up the pitch and turn it slower? Chris McAtee Tri-Q200 (in progress) Email: subcanis@... subcanis@... Home: 2917 Pheasant Dr. Casper, WY 82604 (307)265-5375 School: University of Wyoming 614 White Hall Laramie, WY 82071 (307)766-8670 _________________________________________________________________ Chat with friends online, try MSN Messenger: http://messenger.msn.com To unsubscribe from this group, send an email to: Q-LIST-unsubscribe@... Quickie Builders Association WEB site http://www.quickiebuilders.org Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/ Yahoo! Groups Sponsor ADVERTISEMENT To unsubscribe from this group, send an email to: Q-LIST-unsubscribe@... Quickie Builders Association WEB site http://www.quickiebuilders.org Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service. |
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Pat Panzera <panzera@...>
Chris McAtee wrote:
Loaded question. :) Handle? ...or run at it's best? As an example, the Corvair engine's torque peaks at about 2800, where hp is only about 78. :http://fly.hiwaay.net/~langford/corvair/110curve.jpg At about 3400, horsepower is a solid 100, with little drop in torque, but at about 4400 rpm, where the horsepower reaches it's advertised 110, the torque has dropped almost 15 ft-lbs. These numbers are probably the main reason the Corvair didn't catch on back in the day. In stock trim, as usually installed in a Pietenpol, the engine weight approaches or possibly exceeds 300lbs if memory serves. So 300lbs or better for a 78hp engine don't sound all that sweet. However, through some serious R&D, experimenting, actual flying, a sweet combination of parts has remedied this. Here's an estimated performance graph for a .030 over 110hp engine, with the recommended and tested cam: http://fly.hiwaay.net/~langford/corvair/2700_030_OT10.jpg Although this is a computer graph, the actual dyno'd engine was able to produce the same. It pretty much shows 110hp @ about 3400rpm, at the beginning of the flat torque curve. At about 4500 rpm, the torque begins to drop off, but HP is still on the rise. HP peaks at about 5500 RPM (the car's redline as I understand it). So with all this in mind, and with essentially the airframe's design allowing for almost infinite rpm with the "small" prop, I chose to utilize max torque as my engine range. Therefore I'll set redline at 4000 rpm where I can get 120-130 hp for climb, and probably normally cruse at 3400 where I'll see an honest 100. So does this mean that if my motor can handle 3600 continuous RPM's IIn my opinion, it's all about engine efficiency. You want to run the engine at it's most efficient, not to be confused with most economic. Check the performance charts of just about any piston engine aircraft. Best climb performance?... max. RPM. Best forward speed?... max. RPM. Highest HP?... Max. RPM. Max. fuel consumption?... Max. RPM. Shortest TBO?... Max. RPM. :) As a superstition of mine, I believe an engine should be limited by torque, therefore my decision to not run the engine at speeds in which the torque begins to drop off... even if it means more HP. Pat |
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Chris McAtee <Subcanis@...>
Pat-
Thanks everybody! Pat, especially to you as were doing the about same thing with the same motor (except Im seriously thinking about the Delta cam). Lots of confusion on this end cleared up. Have a happy new year everybody! Chris McAtee Chris McAtee wrote: prop as fast as the engine can handle?Loaded question. :) Handle? ...or run at it's best? As an example, the Corvair engine's torque peaks at about 2800, where hp is only about 78. :http://fly.hiwaay.net/~langford/corvair/110curve.jpg At about 3400, horsepower is a solid 100, with little drop in torque, but at about 4400 rpm, where the horsepower reaches it's advertised 110, the torque has dropped almost 15 ft-lbs. These numbers are probably the main reason the Corvair didn't catch on back in the day. In stock trim, as usually installed in a Pietenpol, the engine weight approaches or possibly exceeds 300lbs if memory serves. So 300lbs or better for a 78hp engine don't sound all that sweet. However, through some serious R&D, experimenting, actual flying, a sweet combination of parts has remedied this. Here's an estimated performance graph for a .030 over 110hp engine, with the recommended and tested cam: http://fly.hiwaay.net/~langford/corvair/2700_030_OT10.jpg Although this is a computer graph, the actual dyno'd engine was able to produce the same. It pretty much shows 110hp @ about 3400rpm, at the beginning of the flat torque curve. At about 4500 rpm, the torque begins to drop off, but HP is still on the rise. HP peaks at about 5500 RPM (the car's redline as I understand it). So with all this in mind, and with essentially the airframe's design allowing for almost infinite rpm with the "small" prop, I chose to utilize max torque as my engine range. Therefore I'll set redline at 4000 rpm where I can get 120-130 hp for climb, and probably normally cruse at 3400 where I'll see an honest 100. So does this mean that if my motor can handle 3600 continuous RPM's IIn my opinion, it's all about engine efficiency. You want to run the engine at it's most efficient, not to be confused with most economic. Check the performance charts of just about any piston engine aircraft. Best climb performance?... max. RPM. Best forward speed?... max. RPM. Highest HP?... Max. RPM. Max. fuel consumption?... Max. RPM. Shortest TBO?... Max. RPM. :) As a superstition of mine, I believe an engine should be limited by torque, therefore my decision to not run the engine at speeds in which the torque begins to drop off... even if it means more HP. Pat Chris McAtee Tri-Q200 (in progress) Email: subcanis@... subcanis@... Home: 2917 Pheasant Dr. Casper, WY 82604 (307)265-5375 School: University of Wyoming 614 White Hall Laramie, WY 82071 (307)766-8670 _________________________________________________________________ Chat with friends online, try MSN Messenger: http://messenger.msn.com |
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jtenhave@mets.mq.edu.au <jtenhave@...>
Richard,
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and the TBO is......? Sure you can over rev anything, but it is misleading to advise anyone to blindly go ahead and run an engine so far beyond design specs and expect durability and reliability. To get the full picture it might be as wise to ask how many engine failures/ stoppages./forced landings the Reno guys have had in the course of their careers. A few hundred revs might not seem like much, but if it takes some of the rotating or oscillating components into resonance ( which is sometimes deliberately avoided by engine designers specifying the rpm range, rotational inertia of the prop etc) the results can be "ahem" unexpected. You might want to examine the case history of the Rolls Royce Viper 680-43 which is fitted the Aermacchi 339 CB, and in particular ask some intelligent questions regarding the resonant frequency of the zero stage compressor blades. From memory 6% change in RPM was all that was required to take the parts out of the resonant range. Sometimes something so innocuous as a 6% change in RPM can ( and did) make the difference between benign behaviour and catastrophic failure. John -----Original Message-----
From: RICHARD EDDINGER [SMTP:mrsrb1@...] Sent: Monday, December 31, 2001 3:29 AM To: Q-list Subject: Re: [Q-LIST] Prop Questions A 0-200 will run fine at 3600 and over if set up correctly balancing is the main consideration. Ask any one of the racers at Reno they are running them well over 3600. In fact about the only thing they can do except for balancing is polish about everything internally. The compression ratio, pistons, cam and all eternal parts must meet factory spec.. All engines are given a very extensive test before they can be certified to race. |
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RICHARD EDDINGER <mrsrb1@...>
I know of a lot of different engines that are so called over reved. You and I both know that commercial built engines especially A/C engines have a large safety margin when rev. spec. are given. I still maintain that properly built up engine and most important proper balance of all moving components will enable you to run an engine at much higher than published specs.. I have helped in the pits at Reno a few times and have yet to see a 0-200 blow up. No doubt there has been some however I haven't seen them.
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Dick ----- Original Message -----
From: jtenhave@... Sent: Sunday, December 30, 2001 5:14 PM To: 'Q-LIST@...' Subject: RE: [Q-LIST] Prop Questions Richard, and the TBO is......? Sure you can over rev anything, but it is misleading to advise anyone to blindly go ahead and run an engine so far beyond design specs and expect durability and reliability. To get the full picture it might be as wise to ask how many engine failures/ stoppages./forced landings the Reno guys have had in the course of their careers. A few hundred revs might not seem like much, but if it takes some of the rotating or oscillating components into resonance ( which is sometimes deliberately avoided by engine designers specifying the rpm range, rotational inertia of the prop etc) the results can be "ahem" unexpected. You might want to examine the case history of the Rolls Royce Viper 680-43 which is fitted the Aermacchi 339 CB, and in particular ask some intelligent questions regarding the resonant frequency of the zero stage compressor blades. From memory 6% change in RPM was all that was required to take the parts out of the resonant range. Sometimes something so innocuous as a 6% change in RPM can ( and did) make the difference between benign behaviour and catastrophic failure. John -----Original Message----- From: RICHARD EDDINGER [SMTP:mrsrb1@...] Sent: Monday, December 31, 2001 3:29 AM To: Q-list Subject: Re: [Q-LIST] Prop Questions A 0-200 will run fine at 3600 and over if set up correctly balancing is the main consideration. Ask any one of the racers at Reno they are running them well over 3600. In fact about the only thing they can do except for balancing is polish about everything internally. The compression ratio, pistons, cam and all eternal parts must meet factory spec.. All engines are given a very extensive test before they can be certified to race. Yahoo! Groups Sponsor ADVERTISEMENT To unsubscribe from this group, send an email to: Q-LIST-unsubscribe@... Quickie Builders Association WEB site http://www.quickiebuilders.org Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service. |
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David J. Gall
John,
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You, of course, meant to say, "take the parts INTO the resonant range." David J. Gall -----Original Message-----
From: jtenhave@... [mailto:jtenhave@...] Sent: Sunday, December 30, 2001 8:07 PM To: 'Q-LIST@...' Subject: RE: [Q-LIST] Prop Questions Richard, and the TBO is......?< snip, snip... > From memory 6% change in RPM was all that was required to take the partsout of the resonant range. |
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David J. Gall
Chris (and Pat),
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I don't think that the pponk prop calculator is an appropriate tool for the kind of work you're asking of it. It seems to be targeted specifically at the C-180 with only certain props. Also, the recommendations made on the pponk page are targeted at static thrust measurements, which are a notoriously bad indicator of propeller performance at speed. In his book "Aircraft Propeller Design," Fred Weick says to pick the prop so as to allow the engine to turn up to full rated RPM at full throttle. (At 8000 ft, that'll give about 75% power, which is what most spam-cans are rated at for cruise.) If you are running an auto conversion or a hot-rodded Continental, then you are the one to decide what is full rated RPM and power. Pat makes a good argument for the Corvair at around 120 hp at 4000 rpm. The engine is rated for 180 hp, so "de-rating" it to 67% makes good sense for longevity. At 100 hp, as William Wynne had run his, it was de-rated to 55% and lived for at least 800 hrs. But the analogy with the engine in auto trim at 3400 rpm at 70 mph is not valid. The engine may test at 100 hp on the dyno at 3400 rpm, but that's at full throttle. There's no assurance that the car would require full throttle to maintain 70 mph, therefore any attempt to say that the engine is "used to this (pulling 100hp)" in auto use is wrong. (Pulling a large boat on a trailer is not considered "normal" for a Corvair.) Likewise, declaring a normal cruise at 3400 rpm is no guarantee that the engine will have to produce 100 hp to maintain that rpm. In fact, there is little chance that the engine will be making 100 hp at that rpm in flight, since it'll have to be throttled back to get the rpm down to that value. The actual horsepower produced will depend on the amount of power absorbed by the propeller and, ultimately, by the airplane's drag. Of course, if the propeller is in-flight adjustable, the engine could be made to run at full throttle at that rpm and then it would be making 100 hp (if done at sea level). You might want to consider buying a ground-adjustable prop if yours is a first-time combination of airframe and engine. If not, then just copy what the fast, successful guys are using. David J. Gall -----Original Message-----
From: Chris McAtee [mailto:Subcanis@...] Sent: Sunday, December 30, 2001 1:50 AM To: Q-LIST@... Subject: [Q-LIST] Prop Questions Hey everyone, could you fill me in? With the diameter of the prop limited on our Q's, should one spin the prop as fast as the engine can handle? For example: at 3600 RPM, the tip of a 60 inch prop (@18 degrees F) is just at the bottom of the recommended tip speed range (as specified by http://www.pponk.com/HTML%20PAGES/propcalc.html). So does this mean that if my motor can handle 3600 continuous RPM's I should, or should I up the pitch and turn it slower? Chris McAtee Tri-Q200 (in progress) Email: subcanis@... subcanis@... Home: 2917 Pheasant Dr. Casper, WY 82604 (307)265-5375 School: University of Wyoming 614 White Hall Laramie, WY 82071 (307)766-8670 _________________________________________________________________ Chat with friends online, try MSN Messenger: http://messenger.msn.com Yahoo! Groups Sponsor ADVERTISEMENT To unsubscribe from this group, send an email to: Q-LIST-unsubscribe@... Quickie Builders Association WEB site http://www.quickiebuilders.org Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service. |
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jtenhave@mets.mq.edu.au <jtenhave@...>
Hi David,
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You and I are both right, but I should have been a bit more concise. I was referring to the remedial derating of the engine (i.e. reducing the RPM range out of resonance). This reduction enabled the jets to remain flying whilst the Rolls Royce engine designers stood in a circle taking turns to kick each others bums for overlooking the "not so obvious" and trying to explain to the bean counters why this "whoopsie" was going to cost several million dollars to fix. happy New Year to you all John -----Original Message-----
From: David J. Gall [SMTP:David@...] Sent: Monday, December 31, 2001 1:44 PM To: Q-LIST@... Subject: RE: [Q-LIST] Prop Questions John, You, of course, meant to say, "take the parts INTO the resonant range." David J. Gall -----Original Message----- From: jtenhave@... [mailto:jtenhave@...] Sent: Sunday, December 30, 2001 8:07 PM To: 'Q-LIST@...' Subject: RE: [Q-LIST] Prop Questions Richard, and the TBO is......?< snip, snip... > From memory 6% change in RPM was all that was required to take theparts out of the resonant range. To unsubscribe from this group, send an email to: Q-LIST-unsubscribe@... Quickie Builders Association WEB site http://www.quickiebuilders.org Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/ |
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John Loram <johnl@...>
As a reference point; a '60s style big American car required about 20
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horsepower to maintain 60 mph on a level straightaway, no wind. This is first hand information. I made the measurements myself. As an side considering thermal efficiency: Assuming 115000 BTU per gallon of gasoline, and 18 miles per gallon, you would produce 383,333 BTUs (404.4MJ / 112.3 Kilowatt hours) of energy in an hour of operation. this is equivalent to 150 horsepower hours, which would suggest that the engine is running at about 14% efficiency. Pretty close to what we expected in the '60s. regards, -john- -----Original Message-----
From: David J. Gall [mailto:David@...] Sent: Sunday, December 30, 2001 7:32 PM To: Q-LIST@... Subject: RE: [Q-LIST] Prop Questions Chris (and Pat), ....... There's no assurance that the car would require full throttle to maintain 70 mph, therefore any attempt to say that the engine is "used to this (pulling 100hp)" in auto use is wrong. (Pulling a large boat on a trailer is not considered "normal" for a Corvair.)...... |
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kittleson1@...
Dear John,
I don't think that a turbine engine hitting some resonant frequency and coming apart has anything to do with revving the O200 over 2750 rpm. I would bet that the redline was set more by them as that's where they achieved the HP they had set out to deliver. Using your empirical wisdom would DICtate that the similarly sized Lycoming would come apart a hundred or so RPM sooner, as it has a lower redline. Happy New Year Al On Mon, 31 Dec 2001 17:54:16 +1100 "jtenhave@..." <jtenhave@...> writes: Hi David,________________________________________________________________ GET INTERNET ACCESS FROM JUNO! Juno offers FREE or PREMIUM Internet access for less! Join Juno today! For your FREE software, visit: http://dl.www.juno.com/get/web/. |
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Michael D. Callahan <micallahan@...>
The PPonk calculator is for seaplanes where static thrust is critical above
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all else (it's not going to go anything near fast with a set of those hanging off of it). Mike C. ----- Original Message -----
From: David J. Gall <David@...> To: <Q-LIST@...> Sent: Sunday, December 30, 2001 9:31 PM Subject: RE: [Q-LIST] Prop Questions Chris (and Pat),the kind of work you're asking of it. It seems to be targeted specifically atso as to allow the engine to turn up to full rated RPM at full throttle. (Athot-rodded Continental, then you are the one to decide what is full rated RPM andThe engine is rated for 180 hp, so "de-rating" it to 67% makes good sense forat full throttle. There's no assurance that the car would require fullthrottle to maintain 70 mph, therefore any attempt to say that the engine is "usedto this (pulling 100hp)" in auto use is wrong. (Pulling a large boat on aThe actual horsepower produced will depend on the amount of power absorbed by60 inch prop (@18 degrees F) is just at the bottom of the recommended tipspeed range (as specified by http://www.pponk.com/HTML%20PAGES/propcalc.html). |
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