Paul,

I am trying to get more information about this, but in the meantime I had to wonder why the exhaust was such a problem, since there are other 20b's flying, to say nothing of 13's, that have evidently tamed their exhausts. Would it just have been because he was trying to fit it into a slender Mustang cowl?

Peter G

We have at least two RV4 tandem airplanes that have flown. I own one and the other was built by Brian Trubee.
Brian's has an aluminum cowl. Mine has SS sheet between the exhaust and the fiber glass cowl.
There is also a scale spitfire running in Texas.

We have a bit of evidence that a too restrictive muffler will raise the EGT's above the normal 1600 to 1700 F.
The secrete is to use thicker wall (.090") bends on the ports. Or even thicker .125".

The mixture ratio enters into it of course.

Here is  our latest muffler recommendations.
Feel free to pass this on to you contacts in ZA.

Paul Lamar ....In Parkes NSW

Forwarded message ----------------------------------------------------

Hi Peter



AS happy New Year to you.

A beautifully built 7 year labour of love ¾  P51 Mustang with a three core 20B Mazda Rotary (Wankel) engine crashed on its third flight.

I learned something new – that exhaust temperatures can be a problem with these rotary installations.

Here is an extract from a discussion on our local forum www.avcom.co.za <http://www.avcom.co.za> – which I believe you have lost your password to!



G


The engine is a 20B with a Tracy Crook PSRU and a local engine management system. The powerplant is popular in the US especially with the Canard guys.


We spent a lot of time with Rob and his conversion as we are installing a 20B into a S208, we have 68 hours of ground testing and are still not entirely happy.


The thing with the 20B is exhaust gas temps - 1850 deg F is not unusual on t/o. During our testing, we noted that nothing inside any type of standard muffler can withstand that heat - we even tried stainless steel wire....it ignited and dripped out the exhaust...the only way to quieten these engines is by separating gas pulses from sound waves and making the sound waves work against each other, that is done through a big ugly exhaust system - and yes, they need to be muffled, the exhaust note is horrific without some form of muffler (much of the combustion is still happening when the rotor passes the exhaust port)

They are fantastic power plants and Rob did a fantastic job but I never liked the exhaust system.


Temps is surely extremely high.


Just a question. Have you consulted with the guys that race with rotary engines. I know that this is/was one of their biggest problems. But a company in the USA came to the rescue with systems that can easily handle 2000 f with ease,and still keep weight and size down.


Just to add to this.Way back ,when the rotary started to show up, On racing tracks and drag strips,many strips banned unmuffled rotary powerplants due to the noise. Lots of research was then done to counter this. And as many also say,The very first thing you need to pay attention to, if you ever want to go the rotary way, is the exhaust system. Forget anything else that might be a obstacle. And for some non sponsered racers, the solution was homebuilt mufflers ,filled with lavarock.



And being limited with space in a aircaft, i gues this must be sort of the nightmare to solve.



We tried everything - the problem is weight - one can put a cast iron exhaust on (as per the automotive arrangement) but these things weigh a lot. We then started researching the subject and started following Paul Lamar's writings on the subject. The lightest way to do it is to use Inconel and separate gas pulses and sound waves through a measured system (using nothing but space as a muffler) The idea we went with uses a 75mm down pipe (has to be long and so exits the cowl underside the aircraft and enter's a round chamber which increases the diameter to 3X the input pipe, this chamber slow's the sound wave frequency and 'confuses' them but still allows the gases to pass without restriction.



The system works, the engine is still loud but nothing inside the exhaust can ignite. It is ugly as sin though and certainly was not a solution for Rob.



Still, this may have nothing to do with Rob's problem and is only speculation at the moment......this accident really hits home, it was such a perfect build project.





A turbocharger quietens the exhaust down quite a bit!



Rotary exhaust temps are also high because it is effectively 3 "cylinders" that share an exhaust port. Racers get the most performance by using equal-length pipes for the manifold, but at the expense of losing a little power, a large diameter "log" type manifold would probably quieten things down a bit.


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