Gene,

 

You have done the SB on the tubing right?

 

The sucking force of the engine drawing fuel is much stronger than the blowing force of the NACA.  The NACA can't blow our wings up like a balloon, but the engine driven pump can create enough vacuum to buckle the wing skins.

 

I think I'm doing the math right, with 1/4" ID tubing, and 15 GPH the air would move about 20" a second through the tube.  With 3/8" tubing it's more like 9" a second.

 

Mike