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#1
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effect of changed thrust line.
How does a person determine what the proper height of an engine should be when building an airplane? If a particular engine design mandates the prop is 4 inches, say, lower than where it would be with the engine originally installed, what effect will it have on handling, and what changes in downthrust might be advised? We are building a Pegazair, and my Corvair engine would need to have the cowl higher than ideal to keep the crank centerline at the same hight as say, an O200. Weight wize, the engines are just about identical as equipped Have not determined the center of gravity of the engine yet, to determine the overall length of the mount. For those unfamiliar with the plane it is a highwing STOL 2 placer roughly the same size as a Cessna 150 (150 sq ft wing,33 ft wingspan, ) |
#2
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effect of changed thrust line.
wrote How does a person determine what the proper height of an engine should be when building an airplane? If a particular engine design mandates the prop is 4 inches, say, lower than where it would be with the engine originally installed, what effect will it have on handling, and what changes in downthrust might be advised? We are building a Pegazair, and my Corvair engine would need to have the cowl higher than ideal to keep the crank centerline at the same hight as say, an O200. Weight wize, the engines are just about identical as equipped Have not determined the center of gravity of the engine yet, to determine the overall length of the mount. For those unfamiliar with the plane it is a highwing STOL 2 placer roughly the same size as a Cessna 150 (150 sq ft wing,33 ft wingspan, Doubtful that you would ever notice a difference in a 4" change, but if it originally has downthrust, and you move the prop lower, you would take downthrust out, but not much. 1/2 degree, perhaps? Hardly enough to be able to change, I would think. Also, don't forget the use of washers. (shims) With it being experimental, that is one of the fun things to "have to" figure out. Dang, hours flying around, doing tests! What a way to spend your time, right? g Tough life, but someone's got to do it! g -- Jim in NC |
#3
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effect of changed thrust line.
"Morgans" wrote Doubtful that you would ever notice a difference in a 4" change, but if it originally has downthrust, and you move the prop lower, you would take downthrust out, but not much. 1/2 degree, perhaps? Hardly enough to be able to change, I would think. Dang, it, I got it backwards. It would theoretically need downthrust _added_. Think about it. A seaplane with an engine up on a pylon has up thrust, so when you add power, that the nose does not go down as much. Wit the center of drag higher than the engine, you have down thrust so added power does not lift the nose as much, so going higher, take down out; lower, add down. -- Jim in NC |
#4
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effect of changed thrust line.
wrote For those unfamiliar with the plane it is a highwing STOL 2 placer roughly the same size as a Cessna 150 (150 sq ft wing,33 ft wingspan, Good to see you around, again. :-) Howz the project going? Did you have a web page or blog with your project on it? I lost everything with a total computer melt-down a while back. -- Jim in NC |
#5
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effect of changed thrust line.
In article ,
"Morgans" wrote: "Morgans" wrote Doubtful that you would ever notice a difference in a 4" change, but if it originally has downthrust, and you move the prop lower, you would take downthrust out, but not much. 1/2 degree, perhaps? Hardly enough to be able to change, I would think. Dang, it, I got it backwards. It would theoretically need downthrust _added_. Think about it. A seaplane with an engine up on a pylon has up thrust, so when you add power, that the nose does not go down as much. Wit the center of drag higher than the engine, you have down thrust so added power does not lift the nose as much, so going higher, take down out; lower, add down. Read this. Read it again and again until you get it: Don't take moments about anything other than the centre of mass. -- Alan Baker Vancouver, British Columbia http://gallery.me.com/alangbaker/100008/DSCF0162/web.jpg |
#6
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effect of changed thrust line.
Alan Baker wrote:
In article , "Morgans" wrote: "Morgans" wrote Doubtful that you would ever notice a difference in a 4" change, but if it originally has downthrust, and you move the prop lower, you would take downthrust out, but not much. 1/2 degree, perhaps? Hardly enough to be able to change, I would think. Dang, it, I got it backwards. It would theoretically need downthrust _added_. Think about it. A seaplane with an engine up on a pylon has up thrust, so when you add power, that the nose does not go down as much. Wit the center of drag higher than the engine, you have down thrust so added power does not lift the nose as much, so going higher, take down out; lower, add down. Read this. Read it again and again until you get it: Don't take moments about anything other than the centre of mass. Why? I mean specifically, how else would you even FIND the center of mass? What difference does it make whether it's center of mass or center of the axles? Or leading edge of the wing? Or a point 1" in front of the tip of the spinner??? The numbers for the moments will certaintly look different, but they all relate to the same spot on the aircraft... -- Richard (remove the X to email) |
#7
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effect of changed thrust line.
In article ,
cavelamb himself wrote: Alan Baker wrote: In article , "Morgans" wrote: "Morgans" wrote Doubtful that you would ever notice a difference in a 4" change, but if it originally has downthrust, and you move the prop lower, you would take downthrust out, but not much. 1/2 degree, perhaps? Hardly enough to be able to change, I would think. Dang, it, I got it backwards. It would theoretically need downthrust _added_. Think about it. A seaplane with an engine up on a pylon has up thrust, so when you add power, that the nose does not go down as much. Wit the center of drag higher than the engine, you have down thrust so added power does not lift the nose as much, so going higher, take down out; lower, add down. Read this. Read it again and again until you get it: Don't take moments about anything other than the centre of mass. Why? I mean specifically, how else would you even FIND the center of mass? What difference does it make whether it's center of mass or center of the axles? Or leading edge of the wing? Or a point 1" in front of the tip of the spinner??? The numbers for the moments will certaintly look different, but they all relate to the same spot on the aircraft... First: yes, any *fixed* point will do, which the centre of drag is not. Second, the math is easiest when you pick the point that is actually the one about which the body will rotate. -- Alan Baker Vancouver, British Columbia http://gallery.me.com/alangbaker/100008/DSCF0162/web.jpg |
#8
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effect of changed thrust line.
Alan Baker wrote:
In article , cavelamb himself wrote: Alan Baker wrote: In article , "Morgans" wrote: "Morgans" wrote Doubtful that you would ever notice a difference in a 4" change, but if it originally has downthrust, and you move the prop lower, you would take downthrust out, but not much. 1/2 degree, perhaps? Hardly enough to be able to change, I would think. Dang, it, I got it backwards. It would theoretically need downthrust _added_. Think about it. A seaplane with an engine up on a pylon has up thrust, so when you add power, that the nose does not go down as much. Wit the center of drag higher than the engine, you have down thrust so added power does not lift the nose as much, so going higher, take down out; lower, add down. Read this. Read it again and again until you get it: Don't take moments about anything other than the centre of mass. Why? I mean specifically, how else would you even FIND the center of mass? What difference does it make whether it's center of mass or center of the axles? Or leading edge of the wing? Or a point 1" in front of the tip of the spinner??? The numbers for the moments will certaintly look different, but they all relate to the same spot on the aircraft... First: yes, any *fixed* point will do, which the centre of drag is not. Second, the math is easiest when you pick the point that is actually the one about which the body will rotate. Some people find it "easiest" to avoid the negative numners and use the tip of the spinner -- Richard (remove the X to email) |
#9
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effect of changed thrust line.
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