Marc de Piolenc wrote:

2. Most people, as already pointed out, don't read the original papers,
so they are not aware of  the fact that the scoop shape is much more
complex than in the usual modern implementation. In particular, there is
a lip that is intended to "fold" the local boundary layer to reduce the
effect of "approach loss" due to boundary layer growth. I have literally
never seen a lip on a NACA inlet in the field.

Best,
Marc de Piolenc

You can see it on this one.

Paul Lamar

Marc de Piolenc wrote:

That one's better than most, but the side lip is still missing.

Just about everything has been tried to get them to work with heat exchangers.
I have seen them with side lips. NACA scoops barely work with low pressure drop air
cooled engines. My next door neighbor with a Long EZ tells me cooling is
marginal. Climb compromises are common.

I wasn't defending it for that application - only pointing out that it
wasn't a true NACA inlet. As I recall, the original application was as a
flush inlet for turbojet installations, and the main purpose was to
"fold" the fuselage boundary layer so that free air could be aspirated
by the turbine, thus reducing approach loss. They were also used
successfully for such low-static-pressure-drop applications as carb. air
intakes and the like.

By the way, the pressure drop in air-cooled engines is not all that low.
In fact, it accounts for the huge gap between the cooling loss that is
theoretically achievable - on the order of 3% of installed power - and
the actual loss, which in most 'planes is five to ten times that.

If the lip was effective I am sure Boeing would use it instead of that high
drag, high angle of attack delta wing.

I'm not sure why they're using it at all. Would love to see the writeup
on that variant.

Marc

Ironically the inventors did not think it good for ICE combustion air intake
either which I found rather strange. If good for jet why not ICE? I at first 
assumed ICE's used more air than could be rammed in. On the other hand the 
Moony ram air intake is worth 1/2 an inch of Hg MAP. Most of the fast race 
planes use ram air intake sans air cleaner. Tracy Crook included.

BTW the orginal NACA scoop paper can be downloaded from
http://naca.larc.nasa.gov/ in pdf form.

Paul Lamar
 
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