Marc Wiese wrote:
Paul,
I found this very interesting. Since you are getting ready to set up a
dyno, it might be a consideration. There are so many variables to
account for!
-----------------------
From: "Darren Tilman" <darren@powerflowsystems.com>
Subject: PowerFlow and Dyno
Paul,
I don't know who Mr. Valenti spoke to, but chances are those people
aren't here anymore (Stu possibly? - he handled the original sale and
contact).
We didn't dyno an 0-360 at Lycon because it wasn't available when we
were doing the testing - and our product was for an 0-320 (at the time).
We have subsequently worked with the XP-360 engine at GAMI - but that
testing data was marred by a myriad of "variables" - not the least of
which included us testing the tired and ragged-out certification engine
at the end of its certification run. That engine was supposed to be
making 180 HP or more, flat out with neutral stacks. It wasn't doing
that. What we learned from Dyno testing is quite simply this: The
numbers produced are "interesting" but only valid for that engine in the
given condition at that temperature and at that altitude. Most Dynos are
not conducted with the same flight prop or accessories - thus the
numbers produced already have a built-in error. In the end the most
meaningful thing to do is to go fly the aircraft on the same profile 3-4
times. Fly it again changing one variable and you have more interesting
and pertinent data as to how the aircraft is performing. Yes, you don't
have a thrust number, but who cares in the end?
Interestingly enough several of our customers have had Lycon or others
do Dyno tests. They have been more than happy, however the numbers
aren't very meaningful. For example, one Cherokee customer gleefully
announced that he had dyno'd his engine and that Power flow produced
more power than even neutral stacks - at 2770 rpm! This is 70 rpm above
red line and for sure this customer takes off at around 2400 rpm.
We know from experience that something as simple as the positioning of
the muffler/exhaust outlet can skew the results by as much as 10%. The
reason? Some Dynos measure the resultant torque applied by the engine -
more twist computed more power. The problem is that the stock exhausts
typically exit to the bottom forward right, causing a torque reaction in
the favor of the engine. PFS exhausts exit to the rear - essentially not
helping or hurting the push from the exhaust outlet. The result, the
same Dyno test done without the thrust of the exhaust output taken into
effect can show that the engine develops more rpm with the power flow
exhaust (fixed pitch club) but has less torque. How is that possible if
wide open throttle produces maximum power? The problem lies in how the
torque number is derived. A thrust measurement would be more of an
accurate measurement, but I am sure it would have its own set of
limitations.
[Well that's a nifty insight.]
As a percentage, our fixed pitch 180 HP C172 owners don't get as large
of a percentage improvement as their 0-320 brothers. In the end, I'm not
sure as to exactly why. Maybe we have reached the peak/optimum
efficiency for this exhaust design - so a different design is needed for
higher HP 4 cylinders? (This is what we are doing for the 200 HP
engines, BTW).
Constant speed owners (180 HP) report different increases than their
fixed pitch '68 buddies. The fact of the matter is a constant speed prop
does behave differently from a fixed pitch, where a constant speed prop
appears to translate additional torque into increased blade pitch so as
to regulate the engine RPM. If someone wanted to purely race an aircraft
at 2700 rpm, we would have to change the fundamental tube length (and
possibly diameter depending on altitude) to optimize more closely for
2700 rpm peak benefit. Our product for the Cardinal is optimized for
2450 RPM. By our flight testing data, 10% either side of that does have
a slight peak performance decline, but it is still way ahead of the
traditional engine exhaust. Maybe by operating at a higher RPM for
takeoff and climb (2700 rpm for the constant speed folks) we haven't
quite optimized the maximum out of the engine, but how many more drops
of juice can you get from that squeezed lemon?
[Oh, the dynamically variable PowerFlow resonator, I can see it now!
With FADEC connection... no limit to complexity, eh? :-)
We'd be mildly interested in the testing Mr. Valenti wants to do and can
offer some suggestions (see above) so as to maximize his quest for data.
But, in the end, you just get lots of data with very little meaning,
IMHO.
[Or meaning that's difficult to discern.]
I hope this helps. I saw the discussion brewing on the Dyno and thought
I might contribute my .02.
Darren Tilman General Manager Power Flow Systems, Inc. 386.253.8833
[Thanks very much, Darren! Your availability and responsiveness is yet
another positive for PowerFlow shoppers.
Marc Wiese
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