Greg said:

The Pop Off Valve is a really good idea to keep from breaking things if

you

close the throttle suddenly.  That's the traditional purpose for 'em, and

I

like the thought.

I'm using mine in lieu of a wastegate, to save weight and noise.

John Slade wrote:

Forgive me for jumping in, but there's a point here that I be interested to
hear opinions on.
As I understand it (not much) the wastegate is there to vent exhaust not
needed by the turbo. When the engine is not demanding power this could be
all the exhaust, and a lot of noise. I have no idea how the wastegate is
controlled. Anyway, Greg's wastegate is sealed shut. This means that there
is never any vented exhaust (and associated noise) so his turbo is working
all the time and serves as an effective muffler. Excess (quiet) gas after
the turbo is vented via the pop off. I have no idea how this is controlled
either. Impact on the turbo is that it has to be beefed up some - hence the
T-04 with inconel wheel and ceramic bearings. This seems like a nice
solution to the noise / muffler problem, but it comes at a cost. I believe
that the Turbonetics unit he has cost around $3k.

Greg is busy proving this installation by flying it. In the meantime, does
anyone see any "theoretical" problems with the arrangement? Is there a
reasonably priced alternative to the Turbonetics unit? I understand that the
stock turbo is inadequate for the job.

BTW - I visited Greg last week. If anyone would like to read a novice's
comments, my write-up of the visit is at http://kgarden.com/cozy/chap23c.htm
Pictures will be added soon.

Regards,
John Slade
Cozy IV #757.  Wiring my EC2 and starting the engine this weekend.....

I am not sure the stock 89-92 turbo is inadequate for the job. Mecanair,
I think, and others on here agree. I and others using it will find out.

Hugh MacInnes talks about this subject of POV's in his book "Turbochargers"
starting on page 71. As I read it the main drawback is; it does not
limit turbine RPM. Now since Greg is using a TO4 that may not be a 
problem for him as the turbine housing can be made large enough
to limit turbine RPM. I on the other hand am worried about turbine RPM
because of the small size of the stock unit.

BTW the stock unit has a built in waste gate the passage of which are rather
convoluted so I don't expect a lot of noise when the gate is open.
Also the bearings are water cooled.

Another trick that either Paul Yaw or Jeff Spitzer came up with, I think,
is to merely drill a small hole in the turbine housing to permanently dump
a  percentage of exhaust gas directly into the tail pipe to limit RPM
and boost with a small turbine. This is a lighter weight solution than using
a larger diameter turbine.

Paul Lamar
 
The AirCraft Rotary Engine NewsLetter.              Powered by Linux.
ACRE NL web site.
http://home.earthlink.net/~rotaryeng/            http://www.linux.org