I don’t think that is ‘thrust’ from the exhausts per se, rather the positive effect on gas flow through the cylinder heads of having the exhaust stacks exit into an air flow that’s going in the right direction and thus adding a suction effect rather than (if you point them forwards) the exhaust gases having to push against a 300mph+ airflow trying to push them back into the engine!
Active exhaust scavenging, I think the motor racing lot call it. The numbers sound sensible, as in automotive tuning you can easily put 10% on peak power by optimising an exhaust system for performance when compared to a compromise system that is mainly concerned with noise reduction as well as cost and ease of engineering.
I’ve just watched a video about the Rolls Royce Merlin engine from WW2 and they got the equivalent of 150HP extra thrust by pointing the exhausts backwards!
here you have some reading about exhaust gases and some possible use (not only for aviation)
http://www.formula1-dictionary.net/coanda_effect.html
https://en.wikipedia.org/wiki/Coand%C4%83_effect
No intention to shorten the exhaust – quite the opposite. Augmenters typically extend the total length
Additional noise is a factor i had not considered !!! The Germans will eat me alive with their noise level based landing fees.
There must be some reason for setting the exhaust pipe at a sharp angle to the fuselage. If the only intent is to keep the soot away then it is a failure. Turbulence caused by the exhaust tube sticking out sticks the soot back all over the place…
My Commander 520 had augmenter tubes. It’s what made it sound like a pack of Harley’s when one flew by.
All too often, engine exhaust tubes stick out at an odd angle with the gases directed somewhat down and backwards but typically not aligned with local flow on the fuselage.
There have been fatalities in the U.S. where people died of CO because they shortened the exhaust pipes of their planes and CO got into the boundary layer, which moves very slow in comparison to the airspeed, creeping even “forward” (in flight direction) and entering the aircraft cabin …
Exhaust tubes should be long enough or otherwise constructed to prevent the a.m. – do it yourself shortening is a bad idea.
Yes the P51 is a textbook example of using the energy of COOLING to produce thrust. Exhaust is a similar but different discussion. Basically you use the speed of the outgoing gases to suck more gases out around it. Somme googling found this. It is a turboprop but very interesting read on the matter of exhaust gas augmentation
Augmentors were often used on US-built production twins like the Twin Bonanza and Cessna 310.
The P-51 utilized heated radiator exhaust air for propulsion.
There were a lot of these ideas around in the pre-jet era!
Didn’t the P51 Mustang have a specially designed outlet for the exhaust gasses, effectively creating a jet-like boost? Running at 75" MP it must have been worth something…
