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Message-ID: <2e24f88d0706020749v6bf53c4cia178387cc600e72c@mail.gmail.com>
Date: Sat, 2 Jun 2007 08:49:13 -0600
From: "Hans Conser" <hansconser@gmail.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Lynn's Tuning Summation was: [FlyRotary] Re: PP Ve??? was Re: Intake CFM air flow
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References: <list-2080085@logan.com>

I'm glad my little VE comment generated so much discussion, as intended!


On 6/2/07, Ed Anderson <eanderson@carolina.rr.com> wrote:
>
>
>  Great tuning summation!  Lynn.
>
> While not a racer, my experience in experimenting with intake manifolds on
> the rotary for aircraft use tracks with your comments.  I initially tried
> big, short tubes with my first intake and while it would have probably given
> great HP at 8000+ rpm, the prop load prevented the engine from ever getting
> to the magic land.  When I went to smaller diameter and longer tubes for the
> intake - performance at 6400 and below improved considerably.
>
> About the only thing I might add a different perspective to is the rpm
> regime for the HP tuning goal.  Since I personally can't stand to see the $$
> flow at high cruise power settings , I seldom ever hit top HP in flight for
> longer than a few minutes (just to see how it does).
>
>   Most of the time I throttle back to 7.5-8.5 gph for economic cruise.  On
> the other hand, my personal priority is to accelerate rapidly on take off
> and get a good initial climb rate to get my butt over and as high above the
> trees as I can as quickly as I can.  My  (tongue in cheek) viewpoint is that
> I don't care if you can hit 400 mph, if you don't clear the trees, it
> doesn't matter {:>).
>
> So for my priorities, I concentrated on trying to achieve best power at take
> off rpm - around 6000 rpm.  The longer length and smaller diameter tubes
> give the engine lots of oomph in that rpm regime.  Clearly if you wanted an
> all-out air racer you would more likely choose shorter bigger tubes.
>
>
> Thanks again for the great summation.
>
> Ed
>
>
>
>
> In a message dated 6/1/2007 8:20:04 P.M. Eastern Daylight Time,
> daval@iprimus.com.au writes:
> Hi Lynn,
> since the Pport has a 'near lack of reversions' which are the source of
> "organ pipe" tuning theory; would you say that Pport engine is a lot
> less sensitive to "tuned length" than a side port engine?
>
> Or does the Pport overlap between exhaust and inlet also cause a
> pulsation which enhances 'organ pipe' tuned length.
>
> I think this is what I wanted to ask :)
>
>
> As you can in see in pictures of the Le mans engine, great care was taken to
> have the correct length of inlet tract for each RPM. The engine was not used
> even close to its maximum RPM or HP. And it had 700 HP.  Having poor
> performance in the tuned area is not  no performance, and they went to great
> lengths to get as much as was possible.
>
> Larger diameter tubes gets a poor peak tuned effect but flows better from
> less drag. A smaller diameter tube gives a more profound tuned effect but
> flows less outside of the tuned RPM because of drag.  And they had big
> tubes. But the Pport flows like a turbine and power is limited by the
> strength of the pieces. The multi piece crank may have been the limiting
> factor. They could have made a few changes and had 800 HP with good
> reliability. But they wanted perfect reliability. The Lemans cars are forced
> to have broad power bands because there is a low RPM 1st gear corner and a
> 230 MPH straight, so they went for the wider power band that all competitors
> must have.
>
> In a fixed length situation, you can only tune for one RPM, and that must be
> for cruise and still have enough mid range to get the prop and plane into
> the cruise speed range. Up on the cam, or on the pipe. It is not impossible
> to have a killer motor that will not pull hard enough to get a dyno reading
> without going up to RPM (Minimum used for racing) with no load on the dyno,
> because the lightest load cannot be pulled by the engine. It might even be
> that you cruise at or near peak torque and never get to peak HP.  The other
> choice would be to cruise just above peak HP.
>
> I gear the car to pass through peak power well before the end of the longest
> straight.  So we are above best power RPM for much of the distance. The
> driver could not get around that one. Once the drag is equal to the
> available power the car goes no faster in any case.
>
> It is the first car to its top speed that beats you to the other end, and
> seldom the car with the highest top speed. Notice that dragsters that are
> going for a top speed records use a taller gear than the normal get there
> first gear (lower).
>
> The highest HP is not the answer unless there is a variable prop system to
> keep the engine near its best power. Not fun if it takes constant attention
> on clime out to keep things going the right direction. The other end of the
> scale is a broad power band that allows clime with no thought of engine RPM
> and on a fixed pitch prop.
>
> It is possible to stall a prop with a bit of extra power while sitting still
> or while the plane is moving slowly in a takeoff attempt. Most people never
> get to feel that one because at lower RPM there is not enough power being
> produced. But the prop blade stalls the same as a wing stalls. Angle of
> attack is the answer. The speed of the air passing through the prop disc
> alters the effective angle of attack, on any prop fixed or adjustable pitch.
> Of course it is more likely on a high pitched fixed pitch prop. It is also
> counterintuitive to pull off a bit of throttle to stop the stall on a take
> off roll.
>
> So the tuning is not for the max HP but a broad band of power, mostly to the
> south or lower than the maximum HP. A bit lower HP at the bottom of the
> range is fine, and helps avoid the slipping prop (like spinning the wheels)
> and as the speed comes up and more power can be absorbed by the prop the RPM
> brings on more power.
>
> So, straight tubes over curved tubes. Worse if fuel is injected before the
> curve or with a carb at the very end. Longer tubes give a broader band
> than shorter tubes. Smaller diameter tubes give a better effect over a
> smaller range. A peaky cam effect. Long tubes work better at lower RPM.
> Short tubes work better at higher RPM. Probably a tapered tube of medium
> length would be fantastic, but difficult to manufacture. No inter connection
> of the inlet tracts is used on Pport engines.
> A smaller higher velocity port gives a wider band than a huge slower flowing
> port.
>
> A bigger port moves the peak power up the RPM band and is peaky. A smaller
> port works over a wider range, and is less sensitive to tuned length. I had
> a factory Pport housing and it had small "D" shaped ports with the flat part
> on the bottom. So it opened quickly and closed slowly. Later aftermarket
> Pports (Modified factory) had huge rectangular ports you could stick your
> hands in. Those made the power between 9,000 and 10,700.
>
> Lynn E. Hanover
>
>
>
>
>  ________________________________
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