A Focke Wulf 190D Dora had a real ram air scoop for its
Jumo 2000 HP 212E V12 engine. It also used ring radiators
inside the cowl with nice cowl flaps.

Paul Lamar

What do you think of the efficiency of the annular inlet (around

the spinner - as FW-190)

as compared to a conventional scoop?  It seems to me it would have

higher drag than a

conventional scoop of the same effective area - more drag area...

Same thing for anular

exhaust on a pusher config.  I find it interesting the FW got that

inlet.  On a radial engine,

it makes sense, however.

Regards,

Matt-

Not according to Hoerner. Those are low drag numbers.
The big problem is making the ring  radiators and the starter

interference.

Another problem is ground taxi cooling and climbing out at low

speeds. You will get more benefit from the prop slip stream if the
intake is further out from the hub.

Paul Lamar

-Matt Prather wrote:

I'll have to think about this..  Does Hoerner discuss the
aspect ratio of a scoop opening (ie a round opening as
compared to a slot)?  I think of the annular inlet as a
slot that's been bent to wrap around a circle.  Does he
get into Reynolds numbers?  I would think that for small
openings, the aspect ratio is more critical than for large
openings.  I suppose the cooling inlet for a 2000hp engine
qualifies as a large opening, so the aspect ratio of the
opening is probably less critical.

Mike Arnold also found that using a spinner on his cowl
didn't improve its performance.  I suspect this is so
because it caused excess acceleration of the air as it
went through the narrow opening - not smoothing of flow
or pressure recovery.  I'm probably smoking crack, however...

:)

Regards,

Matt--

yes yes and yes but you will have to get the book :)

Paul Lamar

"Arnold tried a large-diameter spinner with the inlet air entering through
the circumferential entry, but he found no change in top speed."

Considering his already small cowl, the "large" spinner might have been too
large. He doesn't mention anywhere if he ever tried a smaller one.
Also his engine has the intake inthe cowl. If the spinner covered a good
part of the intake area he probably got less pressure in the cowl and the
engine produced less power. Probably the differences are small, but enough
to not gain any speed, the better aerodynamics cancelled by less power from
the engine.....

I believe withsome experimenting on spinner size and form he could gain some
speed, just the size of it will be very critical......

Thomas J.

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