Cl help needed

[Craig Toutolmin]

I need to figure out the Cl of my wing during a DS run in roughly a circle shaped pattern.

Here is the data.

Plane weight = 6.94 kg (248 oz)
Wing Area = .662 m^2 (1026 in^2)
Aspect Ratio = 15:1
Speed = 84.94 m/s (190 mph)
Seconds/cir = 4.16 sec

Could you please show me how it is done? Martin Simon's book shows calcs for the entire plane. I ended up with .003 but don't believe could be that low.

Thanks!

[Sparky Paul]

I presume your "circle shaped pattern" is a loop.
Figure the load on the plane for a loop of the size of you're flying.
It will be high, and consequently the Cl will be high.
.
But don't use this wing area... :)
Wing Area = .662 m^2 (1026 ft^2)

[Craig Toutolmin]

Yes, assume a loop that round. ooops! 1026 in^2 for the area. I'll edit the original post .

I need to know the Cl of the wing so I can calculate how close I'm getting to the max spar bending moment.

[markdrela]

Originally posted by Craig Toutolmin
I need to figure out the Cl of my wing during a DS run in roughly a circle shaped pattern.

Here is the data.

Plane weight = 6.94 kg (248 oz)
Wing Area = .662 m^2 (1026 ft^2)
Aspect Ratio = 15:1
Speed = 84.94 m/s (190 mph)
Seconds/cir = 4.16 sec

Could you please show me how it is done? Martin Simon's book shows calcs for the entire plane. I ended up with .003 but don't believe could be that low.


circle radius:
r = V*time / 2 pi = 84.94*4.16/(2*3.14) = 56.2 m

lift coefficient:
CL = 2 m / (rho S r) = 2*6.94 / (1.23*0.662*56.2) = 0.303


Other related info...

G's pulled:
N = V^2 / (g r) = 84.94^2/(9.8*56.2) = 13.1

lift:
L = N m g = 13.1*6.94*9.8 = 891.1 N = 200 lb

Reynolds number for 10" (0.254m) chord:
Re = V c / nu = 84.94*0.254/1.45e-5 = 1.5 million

[Craig Toutolmin]

Outstanding. I guess now is a good time to thank you for X-Foil too.

Thanks Mark!

[Sparky Paul]

Ummm,... there's one more g to account for... the one at the bottom of the loop.... :)

[markdrela]

Originally posted by Sparky Paul
Ummm,... there's one more g to account for... the one at the bottom of the loop.... :)

Yeah, but I was ignoring gravity, since it's kinda in the noise here. The load variation from a non-circular flight path is surely more than 1 G.

[SkyPyro]

Originally posted by markdrela
Yeah, but I was ignoring gravity, since it's kinda in the noise here. The load variation from a non-circular flight path is surely more than 1 G. Hehehe I was thinking ground, I guess thats just the way I think.:D