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From: "DaveLeonard" <daveleonard@cox.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Subject: RE: [FlyRotary] Re: Back pressure test results
Date: Mon, 21 Mar 2005 21:05:09 -0800
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Ed, of course I did not expect a turbo to reduce the back pressure, this was
just a chance to quantify some of it.  You are right that adding the turbine
wheel will increase the back pressure somewhat.  But the majority of the
backpressure is caused by the housing itself.  The housing forces the gasses
through a slit-like aperture right before the blades.  This acts like a
nozzle accelerating the gas onto the blades.  This is where the majority of
the backpressure from a turbo comes.

I verified this when I removed the wheel from my housing - no measurable
change in performance at a given MAP.  It didn't even seem to make much of a
difference when I remove the frozen wheel that had broken off.

I also do not believe that the stock turbo manifold creates much back
pressure as Rusty suggests.  It is pretty wide open, although too short for
good tuning.

What I gleaned out of this experiment is that the turbine housing is not
much of a hindrance, so I have little to loose by installing a turbo.

Still to come is a similar trial with the TO4B turbo installed and see what
kind of static RPM I get at various MAP setting.

Dave Leonard


>
> Actually, Dave that is not a good indication of back pressure due to a
> turbo.  Without the turbine in the housing, the results just really don't
> mean much.  All turbo's produce considerably more back pressure
> than a open
> exhaust.  The good installations produce less and the not so good ones can
> produce so much back pressure it significantly reduces the benefit of the
> turbo and increases the heat load on the engine considerably.  So
> all for a
> turbo - POWER and more POWER!  but reduced back-pressure is not one of the
> benefits.
>
> Ed A
>
>
> ----- Original Message -----
> From: "Dave Leonard" <daveleonard@cox.net>
> To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
> Sent: Monday, March 21, 2005 10:44 PM
> Subject: [FlyRotary] Back pressure test results
>
>
> > I did an experiment today to see what effect back pressure from
> a turbine
> > housing has on performance.  My engine is currently set up
> using an empty
> > stock turbine housing as my manifold/muffler.  First I ran the
> engine with
> > the housing and exhaust pipe in place, then I removed the
> housing and ran
> it
> > with just the manifold in place.  Here are the results given in static
> RPM:
> >
> >                           MAP 20     MAP 25   MAP 28.5 (WOT)
> > With Turbine Housing      2700        3350      4700
> > With Manifold only        2790        3450      4790
> >
> >
> > The sound was notably louder without the housing (neighbor came
> out to see
> > what was going on), but not as much of a difference as I was expecting.
> >
> > These results have convinced me to stick with a turbo (not as much
> detriment
> > from back pressure as I thought), still working on the installing the
> TO4B,
> > but it probably won't be done until the Fall (working too hard, and I
> don't
> > want to interrupt my IFR training schedule).
> >
> > Dave Leonard
> >
> >
> > >>  Homepage:  http://www.flyrotary.com/
> > >>  Archive:   http://lancaironline.net/lists/flyrotary/List.html
> >
>
>
>
> >>  Homepage:  http://www.flyrotary.com/
> >>  Archive:   http://lancaironline.net/lists/flyrotary/List.html