This is interesting. They got a bit less thrust out of
the exhaust stacks with ejectors installed.
I always thought these were supposed to improve the thrust
from the exhaust gasses.
This is a rather comprehensive full scale test of exhaust
ejectors. The ejectors did not help the cooling all that much more than
a good set of cowl flaps. Note the long length of the straight
and diffuser sections. I guess they were deemed not worth the
weight, cost and trouble. Of course radial engines used ram air
type scoops and not NACA scoops.
********************************************************************
2715. Acker, Loren W Kleinknecht, Kenneth S , ***Flight comparison of
performance and cooling characteristics of exhaust-ejector
installation with exhaust-collector-ring installation ,
<http://naca.larc.nasa.gov/reports/1947/naca-rm-e6l13a/>* NACA
RM-E6L13a , February 14, 1947 , pp. 37 .
***********************************************************************
Paul Lamar
I have added a couple of numbers to the bottom of the results chart
to relate the dynamic pressure to the air speed. I was only able to
capture the top two charts. The lower, 15,000 foot chart had the
dynamic pressure labeled.
The left vertical axis is the pressure ratio of what you will get
relative to dynamic pressure. Let's say the dynamic pressure is
10 " H2O and the chart reads 1 at 10,000 feet and 750 HP.
That means the pressure drop across engine cylinders is the
same as dynamic pressure. About what you would get with a
good set of cowl flaps less scoop losses. Above about .8
you are doing pretty good. 1.2 is excellent. Probably around
2 inches below atmospheric or static pressure behinds the cylinders
when dynamic pressure is 10 inches. The total drop across the engine is
then 12 inches at 5,000 feet and 144 MPH.
Unfortunately I have found no such data so far on liquid cooled
aircraft engines with ejectors. The increase in pressure drops
through heat exchangers are significant.
Note the strong reduction in effectiveness as the engine HP drops
off. This happens regardless of the HP level the ejector is optimized for.
There is just not enough energy in the exhaust at idle to work
very well. Ejectors work fine at takeoff power but will help little
at idle. You are much better off with an electric fan.
