From: doug@alliant.com (Doug Bloomberg)
Newsgroups: sci.aeronautics
Subject: Re: Augmenting cooling by exaust pipe placement
Date: 17 Apr 92 16:31:28 GMT
Article-I.D.: alliant.1992Apr17.163128.5971
Organization: Alliant Computer Systems

>geoffm@purplehaze.Corp.Sun.COM (Geoff Miller) writes:
>
>
>>This idea was used on the Convair 240/340/440 series of airliners back
>>in the Fifties.  The exhaust pipes terminated inside the cowling, just
>>in front of a pair of trumpet-shaped devices called augmentors; there
>>were two per engine.  This setup obviated the need for cowl flaps.  If
>>you've ever seen a Convair-Liner that hasn't been converted to turboprop
>>engines (540/580/600), you might've noticed how smooth the cowlings are
>>compared to those on contemporary machines like the DC-6 (which uses the
>>same engine, incidentally, the P&W R-2800).

AUGMENTORS:
Getting closer to home (small planes) Look at some old Navions, many have
augmentors. They work well getting extra cooling air thru the cowl, but
all good things have a drawback. The augmentors have two drawbacks.
1) Extra weight   2) Noise, they make a rumbleing sound.

The original message asked about increasing speed thru exhaust thrust 
and/or heat from a water cooled engine.

EXHAUST THRUST:
As to the use of exhaust for thrust, a fellow EAA Chapter member, Kent
Paser, Chapter 301, Denver (Aeronautical Engineer) has over the years
modified his Homebuilt Mustang II. Using as an old NACA report as a
starting point he experimented with reducing the outlet of his planes 
exhaust to accelerate the exhaust gas flow and obtain jet thrust from 
these gasses.  It now cruises at 220+ mph at 5.5gph using a Lyc O-320 
and fixed pitch prop. A Mustang II is a low wing, aluminum, conventional
non-retracting, 2 place SBS, experimental aircraft. Kent has flown this
plane for 21+ years. The exhaust nozzles are not the only change he has
made.

THE EXHAUST NOZZLES:

Basically he forms the nozzle at the end of each pipe using reducers and
4130 steel tubing. He started going from the standard 1 3/4" pipes  to
a 1 1/2" outlet. Then in small increaments (thickness of the tubing) he
reduced the outlet to 1".

Now Kent is a lover of statistics and record keeping. This project took
him more than a year to complete. He would make a change, go fly the 
plane. Setting the altimeter to 29.92" for each altitude flown. He 
would fly a two way course and use timing and his loran to figure the
speed.

Kent found for his airplane a nozzle outlet size of 1 1/4" gave him the 
best over-all speed increase.  He flies from Centennial airport near
Denver 5860' MSL and his testing was done at 7000', and 11000'. With
trips to the thicker air in Texas to see what the nozzles did to 
performance near sealevel .

RESULTS:

Kent found that with a 1 1/4" outlet size that he gained 8mph at full
throttle at 7000', his airspeed was over 220 mph.  At 11000' a 1 3/16"
gave slightly better performance. At sealevel performance was decreased.
(We figure this has to do with higher outside airpressure reducing
effectiveness of the jet.)  Also, by further reducing the nozzle size,
>1 1/4"@7000' speed (power) was reduced below a system with no thrust
nozzles. ie a 1" nozzle reduced speed 14mph BELOW a standard exhaust.

Kent did not notice any difference in added speed using 4 single pipe
exhaust or a crossover system.


WATER COOLING, THRUST INCREASE:

It is possible to gain thrust from the heat in a radiator. In fact a
P-51 Mustang does exactly this.  Basically air, at a high velocity,
is directed thru a radiator. Heat is transfered to the air warming 
and expanding it. thru the use of a constricted exit a Jet Effect takes
place and thrust is gained. Usually there is a cowl flap arrangement aft
of the radiator to increase airflow at slow speed and ground ops.

A Bede-4 was at Oshkosh last year. It had a V-8 for power and a radiator
system simular to the P-51's. I talked to the owner and he said that
he had gotten a speed increase after going to this type of radiator
system. He did not give me the figures though.


Doug Bloomberg   doug@alliant.com
Littleton, Colorado
RV-6 Builder  EAA Member