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#81
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what every boy needs - yeah seriously
Peter Dohm wrote:
I really had decided to let this whole matter slide; since, in the end, everything that I might actually want to build would require 80 to 120 horsepower--and more if I really want the aircraft to have utility for transportation. So this mostly an intellectual exercise. However, since you phrase your response in the above manner: 1) To get from a thermal limitation of 45 horsepower to 60 horsepower looks like a 33% increase. If you dissagree, please respond to Hewlett-Packard--since I have been using their calculators for the past 25 years or so. As I understand it, it doesn't actually work that way. As the power goes up, an increasing proportion of the heat goes out the exhaust, but it is probably close enough. According to various reports and Mackerle, the proportion of heat going into the head goes up though, and the proportion going into the cylinder goes down, so if you are trying to maintain the head temp it is likely to be more than 33% difference. 2) Doubling the velocity of airflow should require 400% (not 300'%) of the energy, according to the old engineering texts that I can no longer find. If you could find those texts, they would tell you that when driving a fan, the power required actually goes up as the cube of the difference in RPM and the CFM at subsonic speeds scales with the rpm, so doubling the CFM results in 800% increase in power required. For ram air it is slightly more complicated, but it essentially rises as a cube of the airflow as well. NACA did some tests on fan cooled radials and the Japanese actually deployed some (Kawanishi N1K is one) so there is research out there. As for the 300% I picked it up off of where I had actually started to calculate the power difference required for a 33% increase in HP and a diminished heat transfer coefficient and then left off unfinished. My mistake, but it understates not overstates the problem of improving cooling by just increasing the airflow. As in all things, it depends on just where on the curve you are. The bottom almost looks like a straight line, the top like a brick wall. 3) By the combining the above calculations, and using the latest trusty Hewlett-Packard calculator, the 33% increase in cooling should require 177% of the energy. See above.... 4) The basic point was that: if you climb at 60 (kph, mph, kts, or whatever) and you would need to be climbing at 90 to adiquately cool the engine; then the difference could be made up by the addition of a cooling fan. You would have to figure out how to connect the fan. I think the stock VW fan moves about 1000CFM at 3000rpm and about 1500CFM at 4000rpm (when I have been told the belt starts slipping). Veeduber I am sure has the proper numbers. I don't think it would be a minor thing hooking it up mechanically and not losing everything you gained in additional weight, additional drag and HP losses to the fan. If your design speed is slow enough, I guess you can drop the drag. The Japanese did it with a geared coaxial fan on a radial, so they had a simpler task. They ended up with a smaller nose that was almost completely filled with the spinner and a really small air intake ringing that. 5) As to the real engineering textbooks: BRING 'EM ON. Peter |
#82
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what every boy needs - yeah seriously
On Jan 16, 4:39*pm, Charles Vincent wrote:
You would have to figure out how to connect the fan. *I think the stock VW fan moves about 1000CFM at 3000rpm and about 1500CFM at 4000rpm (when I have been told the belt starts slipping). *Veeduber I am sure has the proper numbers. -------------------------------------------------------------------------------------------------------- The numbers,, proper or not, are 1300cfm, according to the VW Factory Service Manual... or whatever... (black covers w/embossed silver printing). But I think it's a giant LEAP backwards. Somebody out there is sand-casting VW crankcases in aluminum. Torture them with lotsnlotsa money and get them to shuffle things around a bit, allowing a BORE of about 4.625" and a stroke of 88mm, then cast a LONG #1 main bearing and throw away the tranny flange... might even get them to cast a Dyna-Focal mount on the other end... and make some entirely NEW 1-cylinder per head headz, and we can stop calling it a VW (although we'd still be using a lot of VW parts) and start calling it a DIY Homebuilder Engine... with about 100bhp @ 2700 rpm (or whatever... use the C-90 cam timing; get someone like Dick (sp?) Schneider to grind us some wiggle sticks. 40A. coaxial alternator. Itty-bitty geared starter. Electronic ignition. Holes for two plugs. SIX head-stays. Juice valves outta the little Chevy. Absolutely NOTHING certified...although EVERYTHING has done a million miles or more in other engines. That is to say, there ain't nothing new in such a design. Kinda heavy, though... about 181 bare, mostly because of the crank. -Bluesky Bob |
#83
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what every boy needs - yeah seriously
wrote in message ... On Jan 16, 4:39 pm, Charles Vincent wrote: You would have to figure out how to connect the fan. I think the stock VW fan moves about 1000CFM at 3000rpm and about 1500CFM at 4000rpm (when I have been told the belt starts slipping). Veeduber I am sure has the proper numbers. -------------------------------------------------------------------------------------------------------- The numbers,, proper or not, are 1300cfm, according to the VW Factory Service Manual... or whatever... (black covers w/embossed silver printing). But I think it's a giant LEAP backwards. Somebody out there is sand-casting VW crankcases in aluminum. Torture them with lotsnlotsa money and get them to shuffle things around a bit, allowing a BORE of about 4.625" and a stroke of 88mm, then cast a LONG #1 main bearing and throw away the tranny flange... might even get them to cast a Dyna-Focal mount on the other end... and make some entirely NEW 1-cylinder per head headz, and we can stop calling it a VW (although we'd still be using a lot of VW parts) and start calling it a DIY Homebuilder Engine... with about 100bhp @ 2700 rpm (or whatever... use the C-90 cam timing; get someone like Dick (sp?) Schneider to grind us some wiggle sticks. 40A. coaxial alternator. Itty-bitty geared starter. Electronic ignition. Holes for two plugs. SIX head-stays. Juice valves outta the little Chevy. Absolutely NOTHING certified...although EVERYTHING has done a million miles or more in other engines. That is to say, there ain't nothing new in such a design. Kinda heavy, though... about 181 bare, mostly because of the crank. -Bluesky Bob ------------------------------------------------------------------- Well, those weight and power numbers look mighty close to the numbers that Continental is just bringing to market and Lycoming is working on. So, if you feel the need to swing a 70 or 72 inch prop and ALSO prefer a direct drive engine that can idle on approach, they are still good numbers. I could very well be a customer in the easily foreseeable future. Peter |
#84
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what every boy needs - yeah seriously
On Jan 17, 6:43*am, "Peter Dohm" wrote:
. *So, if you feel the need to swing a 70 or 72 inch prop and ALSO prefer a direct drive engine that can idle on approach, they are still good numbers. I could very well be a customer in the easily foreseeable future. --------------------------------------------------------------------------------------------- The fact you CAN swing that biga prop doesn't mean you HAVE to. I was think more along the lines of a crankcase machined to accept a crankshaft machined to accept a connecting rod that was laying there on the shelf, along with the bearing-shells to fit it. We STILL gotta come up with four barrels an' four slugs an' four heads an' four rods... and I've no idea in the blue-eyed world where those would come from. Grab 'Speedway' or 'Jegs' and they got all kinds of neat stuff but if you want four BIG finned cast-iron jugs you're still looking at something around 4" diameter (ie, about 101mm) But they DO got some beeeutiful rods. Old Ford style. Got enough bearing area to use in a steam engine. (See, it has to do with the Specific Impulse and converting Torque into Thrust an' neat **** like that... an' I show up with a VW engine in my pocket and they just LOOK at me... -Bob |
#85
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what every boy needs - yeah seriously
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#86
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what every boy needs - yeah seriously
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