On Apr 26, 9:13*am, Justin Craig wrote:
I am sure there is a point where the polar falls off a cliff, however I
doubt you would ever get enough water in!!

When I ran the numbers for what later became the Concrete Glider
episode on Mythbusters, that point was where you get transonic flow
and start hemorrhaging energy into shock waves. I worked the numbers
back through L=1/2*rho*v^2*Cl*A and figured that the upper limit was
on the order of 60000 lbs. I thought it was really cool that you could
cast a 15m sailplane in concrete and rebar, ballast it with tungsten
to get the CG right, and it would smash right along at about 40:1 at a
few hundred knots. Of course, launching it would be a real bear, but
that would be somebody else's problem.

But, no, they wanted a concrete glider that could do a roll-off launch
from a hilltop with Jamie or Adam at the controls. That was a non-
starter, because a Part 103 aircraft was not in the cards. They might
have done so if they'd allowed themselves the kind of fiberglass
reinforcing mesh that Rob Wheen used in the University of Sydney's
concrete hang glider, but the Beyond Productions researcher I was
working with said they wanted it all or at least mostly concrete, with
perhaps some pieces of rebar.

Of course, they ended up scaling the episode way back, and made hand-
launch model gliders instead. I think even that could have been a cool
demonstration of how the rho*v^2 works; they could have taken a
styrofoam toy glider, copied it in cement, and then launched it from
an airplane or fast moving car to show that it would achieve the same
glide ratio as its polystyrene cousin, just at a greater speed.

Thanks, Bob K.