CarpetFlyer

4th Feb 2010, 12:16

Any technically minded pilots out there who can help me with this?

I've been playing around with Airfoil diagrams trying to understand lift, drag, stall speeds etc.

Using the lift equation, I can plug in the CL and the weight of the aircraft and come up with the stall speed. This works out pretty close to actuals on a couple of sample aircraft.

However, when I shift to glide speeds it all goes pear shaped.

Best glide is for max L/D (so I was taught). If I take the corresponding CL from the airfoil curve, plug that into the lift equation for a known weight, I get ridiculous numbers. eg a Cessna 172 with best glide of 94 knots. Or a Piper Cub with best glide of 85 knots.

Can anyone tell me what I am missing? Gotta be something obvious that is staring me in the face, but I just can't see it.

I've been playing around with Airfoil diagrams trying to understand lift, drag, stall speeds etc.

Using the lift equation, I can plug in the CL and the weight of the aircraft and come up with the stall speed. This works out pretty close to actuals on a couple of sample aircraft.

However, when I shift to glide speeds it all goes pear shaped.

Best glide is for max L/D (so I was taught). If I take the corresponding CL from the airfoil curve, plug that into the lift equation for a known weight, I get ridiculous numbers. eg a Cessna 172 with best glide of 94 knots. Or a Piper Cub with best glide of 85 knots.

Can anyone tell me what I am missing? Gotta be something obvious that is staring me in the face, but I just can't see it.