Message-ID: <3F613747.300CCCDA@frontiernet.net>
Date: Thu, 11 Sep 2003 23:02:31 -0400
From: Jim Sower <canarder@frontiernet.net>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: turbo wastegate requirements
References: <list-2576627@logan.com>
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<... That's true provided you don't have a problem with the potential 40" MAP you
could get on a std sea level day ...>
True (_could_ being a key word here).  My scheme is to have two "Throttle" levers
- a long one to the throttle and a shorter one to the wastegate.  The wastegate
would remain "OFF" or all the way back for ground and pattern operations.  Take
Off and initial climb would be with wastegate OPEN and throttle adjusted so as to
not exceed 30" MAP even with the "residual" boost that we would have even with
wastegate open.  Climb to altitude (after MAP dropped below 30" at WOT) and cruise
would generally be at WOT and gradually increasing boost (closing the wastegate -
advancing the Boost lever).  The first step for descent would be "Boost - OFF".  I
still have more power available than any NA engine and even if I get excited and
two-block the throttle, I only have a couple of inches of boost - not enough to
damage anything, even at SL.  Easy to develop and ingrain a habit of ... Boost -
last thing on going up, first thing off coming down ...

<... If you're willing to live with a little more workload and the responsibility
of maintaining MAP ...>
I am.

<... through diligent piloting ...>
May I suggest that "diligent" is a bit of a stretch ... anything short of
unconscious would work my scheme quite reliably IMO

<... you could probably do away with the wastegate and popoff entirely.  Run all
the exhaust through the turbo, be gentle with the throttle, pay attention during
descents to maintain your chosen MAP ...>

If I did away with the waste gate, I would have full boost all the time, which
would, as well as excessive care and attention, involve a great deal more
intercooling (and other heat rejection) than I am prepared to accept.
Additionally, I would be pumping full boost through partial throttle which I
presume to be quite inefficient.  It would involve taking off at a little more
than half throttle.  With my scheme, I could two-block the throttle in a T/O (or
more to the point, a rejected landing/go around situation) with virtually no
danger of damage to anything.  All I'd have is an inch or two of boost.

For all the talk, it's STILL ... just a theory .... Jim S.

Marvin Kaye wrote:

> Jim Sower <canarder@frontiernet.net> wrote:
>
> >>><... That ambient pressure outside certainly needs to be accounted for ...>
> OTOH, the back-and-forth between Rusty and I and others seems to indicate that
> 5 or
> 6 psi (or 10-12 in Hg) is all the boost anyone will reasonably need.  So a
> popoff
> valve set for 5 psi and forgotten would allow us to take off with 35" (in the
> unlikely event we needed that much power) and turbo normalize to 15 k ft so it
> would seem that a really dumb popoff valve would work OK.<<<
>
> That's true provided you don't have a problem with the potential 40" MAP you
> could get on a std sea level day... the popoff's whole purpose is to limit MAP
> to some reasonable MAP redline.  If the possibility of hitting 40" is
> acceptable to you I suppose it would be ok.  Alternatively, I also like the
> idea of using a simple pressure switch to sense MAP, set to go off an inch or
> two MAP less than your redline... hooked to big red light on the panel when
> you see it you ease back on the throttle.  The set-and-forget throttles we
> have on the big Continentals and Lycomings incur all the expense and
> complication of a slope controller and an oil-pressure-driven wastegate
> actuator.  If you're willing to live with a little more workload and the
> responsibility of maintaining MAP below redline through diligent piloting, you
> could probably do away with the wastegate and popoff entirely.  Run all the
> exhaust through the turbo, be gentle with the throttle, pay attention during
> descents to maintain your chosen MAP and you would be just fine.  Just another
> thought.
>
>       <Marv>
>
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