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Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Andy wrote ...
Ash you missed the point about to arrive at , the veolicty is to the power, ether reuqires more power input or generators more thrust
Post edited.
Maybe I missed your point.
Looking at this again, the velocity bit is where all the losses originate. The larger the 'disc area', the lower the velocity for the same 'lift'.
I think this is why the 'v to the power' term disappears.
Is this the point you were making?
EDIT: It also states that "the "efficiency" of an otherwise-perfect thruster, is proportional to the area of the cross section of the propelled volume of fluid"
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Sorry about the double post, but new information:
Ok, 102g requires 1N (1kG/9.81) and 1kG requires 9.81N
9.81^3 = 944
944/(4.9x0.5m^2) = 385
square root 385 = 19W
With 1m^2 disc area, power required is 13.9W
With 2m^2 disc area power required is (Curiously) 9.81W
These figures don't take into account any other losses in the system, but they do demonstrate the point. They are all based on total 'copter mass of 1kg, with a single rotor.
So, in this case, quadrupling the disc area halves the power required, which doubles the flight time.
31.5 inch dia rotor gives 0.5m^2 disc area
and 63 inch diameter rotor gives 2m^2 disc area
We just need to calculate for some more realistic figures.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
I cant figure out how to use this software,(SU^2) its a .tgz , which i un-compressed, but i dont know which file to use? there appears to be know .exe , so do i have to compile this ?
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
im wondering how to use these, or how to choose one.
i may just use this one.
i cant get this to work on my computer : its got all kinds of instructions and possibilities scattered on his pages. i just need one java method that will work.
EDIT: i may have it working...
im not sure what the Vx and Vt numbers mean, but the graph and gradient are amazing.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
im thinking of buying one of these 18 inch props then utting it in pieces. one piece form the tip and so on to the hub. while measuring the critical dimensions. however scaling with fluids always worries me. but going from a 18 to a 26 incher wouldnt be as sketchy as scaling from 10 to 26.
its tempting to make a mold using my 3D printer, and lay up props out of CF. those 26 - 29 inch props are just to expensive to be putting into a tree.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
The other option would be to put a series of 'theoretical' dimensions into a 3D CAD package, and then produce a 'net'. From this you could program a 3D printer to produce a mold.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Ash Small wrote ...
The other option would be to put a series of 'theoretical' dimensions into a 3D CAD package, and then produce a 'net'. From this you could program a 3D printer to produce a mold.
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Propeller Physics and VABs Program.
