Design question
#6
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Your right it is not that likely , but remotely possible. Thanks for taking the time to reply. I just want to build the model with that particular consideration in mind. The way the german speed guys have their rules setup you only have 50 meters to enter the 100 meter course for the speed run. While pylon planes and gliders can handle it with out burning off too much speed, a plane that is designed for real speed will have problems with small radius turns like that. 513 feet/sec may be possible with the right design given enough power, but that turn will scrub off a lot of speed.
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It's just a design limit at this point, worse case type of thing.
Right now the number to beat is 304 set by the German speed cup guys and the FAI, and they are calling a measurement at the end of a dive straight and level powered fight.
Some say real straight and level would be more like 260-270 MPH.
Anyhow right now I am in the process of developing a design that will have pretty high performance, perhaps even close to that 300 figure I just want to be sure it's not going to fold or explode from the stress. I was afraid it was going to be around that high just as a guess.
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The German speed cup guys do a pull up from a dive as an entry into the timed run that is limited to 50 meter's, last year their high AR planes were doing 304 MPH with that type of a maneuver. A high AR plane will pretty much bleed all of its speed off trying to maneuver in something that tight. I was just curious as to just how high the G's were within that tight of a radius. I don't think the li-pol battery would survive that type of maneuver.
Last edited by iron eagel; 03-01-2014 at 06:42 AM.
#11
During those moments. all those components will hang from the wings, which will need to generate a lifting force of more than 164 lbf (164 lb of dynamic "weight" + negative lift exerted by tail to compensate stability margin) before reaching the critical AOA.
That centrifugal force equals the product of the mass of the model times its centripetal acceleration.
The mass of the model = 3 lbm / 32.17 ft/s-s = 0.093 slugs
The centripetal acceleration = V * V / r = (513 ft/s * 513 ft/s) / 150 = 1754 ft/s-s
The centrifugal or g-force = 0.093 slugs * 1754 ft/s-s = 164 lbf
It's just a design limit at this point, worse case type of thing.
Right now the number to beat is 304 set by the German speed cup guys and the FAI, and they are calling a measurement at the end of a dive straight and level powered fight.
Some say real straight and level would be more like 260-270 MPH.
Anyhow right now I am in the process of developing a design that will have pretty high performance, perhaps even close to that 300 figure I just want to be sure it's not going to fold or explode from the stress. I was afraid it was going to be around that high just as a guess.
Right now the number to beat is 304 set by the German speed cup guys and the FAI, and they are calling a measurement at the end of a dive straight and level powered fight.
Some say real straight and level would be more like 260-270 MPH.
Anyhow right now I am in the process of developing a design that will have pretty high performance, perhaps even close to that 300 figure I just want to be sure it's not going to fold or explode from the stress. I was afraid it was going to be around that high just as a guess.
Last edited by Lnewqban; 03-02-2014 at 10:58 AM.
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It just reinforced the fact that the plane I am building will not be capable of flying that type of a course it doesn't have a tail.
The Germans are doing this with high aspect ratio wings, I know a low aspect plane is able to do this tight of a radius, it could be engineered to withstand the G forces but it would have to trade a lot of it speed for lift which would sort of defeat the purpose. I think their rules are aimed more for DS type of planes which will limit the actual speed they can produce.
Bottom line is this is not really a competition which gives you the real performance limit for straight an level flight, just the speed out of a dive.
The Germans are doing this with high aspect ratio wings, I know a low aspect plane is able to do this tight of a radius, it could be engineered to withstand the G forces but it would have to trade a lot of it speed for lift which would sort of defeat the purpose. I think their rules are aimed more for DS type of planes which will limit the actual speed they can produce.
Bottom line is this is not really a competition which gives you the real performance limit for straight an level flight, just the speed out of a dive.