Del Johnso wrote:

Jake Crause wrote:

Hello everyone,

I've heard references to augmenters but don't have a good understanding
of what they are or how they work.  I was hoping someone could explain
them or point me to where I can find some info.  Are any being used in
light aircraft or are they still in the theoretical stage?   Thanks in
advance.

Jake

There are a bunch of NACA papers on the subject.
You can download them for free from the NASA web site.
http://naca.larc.nasa.gov/

snip<

In addition to the NACA papers there are a number of articles in Contact
(#39, #40, #47 and #66).  Also, there is an article in Sport Aviation, March
2002 issue on Charlie Airesman's VariEze Subaru installation.

Exhaust augmentation discharges exhaust gases into a larger duct that
conducts cooling air and exhaust gases out of the cowling.  The high
velocity exhaust pulses act as a jet pump to expel the cooling air.  Charles
Airesman, in his article "Drag Reduction Through Water Cooling and Exhaust
Augmentation", Contact issue 39, documented ground runup vacuum pressures at
the augmentor as follows:

RPM                      Water Column Height in inches
3,000                             -0.6
4,000                             -0.9
5,000                             -1.6
6,000                             -2.9

He then blocked the airflow through the radiator and measured vacuum at the
augmentor.  At idle he measured a 1 inch drop in the manometer, at 4,000 RPM
he pegged 5 inches!

One of the points that Daniel Nicoson makes in his "Cooling Systems with
Exhaust
Augmenters" article in Contact issue #66 is that Cooling airflow and Cooling
Demand are both a function engine power (when using exhaust augmentation).
You therefore increase cooling capacity when you need it most.

Paul,  If I recall, in past emails on this subject you have suggested that
exhaust augmentation may affect high speed performance (hopefully I'm not
putting words in your mouth).  Can you explain that further.  Both
Airesman's and Nicoson's articles suggest that one of the major benefits
with augmentation is that it can reduce cooling drag which, according to
Nicoson, can be 20-35 percent of the total drag (depending on the aircraft).
Most airplane cooling systems are designed for the worst case situation
(full power climb-outs at moderate airspeeds).  As a result air intake ports
are larger then they are required for cruise.  Because, with augmentation,
you achieve maximum augmentation with maximum power you can probably get by
with smaller intake ducts.
Your comments would be appreciated.

Exhaust augmentors work best at zero airspeed full power. As the airspeed increases
the effectiveness diminishes. At some speed they do nothing. At real
high cruise speeds they could be allowing too much air to flow through
the rad overcooling it and causing more drag than necessary.
The opposite possibility is too little opening at such a speed were
the augmentor effect is inadequate. Some sort of augmentor
system combined with a cowl flap is probably optimum.
I think the British Seafury had a system like that but I can't find
a picture. I think I have one.

The points where all this happens depends on the exact design.
I highly recommend getting the NACA papers.

Paul Lamar
 
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