Are there any guidelines / rules of thumb for the entrance area of inlet scoops.  I am referring to the leading edge of the scoop.  Is a narrow (1/8") frontal area OK or should it be larger and radiused?  If larger, how large?

 

Joe

Good question, Joe.  I would like further information on that as well. I can tell you what I think I know.  It depends somewhat on the function of the scoop.

 

An induction air scoop that is sized for good ram pressure recovery at speed, and minimal drag, should have a fairly large radius edge.  At low speed and high engine rpm that scoop is pulling air in around that corner, and will be less restrictive with a larger radius. How large? I don’t know exactly how that should be determined.  Mine has about ¼ - 5/16” radius – seems to work fine.

 

Air inlets for cooling, etc. should also have a radius, and somewhat of an airfoil shape on the outside. A radius should give a bit of local external diffusion, and give smoother, attached flow over the surface.  I used a fairly small radius, about 3/32 – 1/8” on the main coolant rad scoop which seems to work very well.

 

I’m thinking my underwing inlet for the oil cooler could benefit from a larger radius, but there are other problems there.

 

Al