<snip>
Dave Arbogast wrote:
I think there is a bias in the debate... Try this paradigm -
Look at the engine as a black box... ignore what is inside
and how it works. Measure the volume the box takes in for
one revolution of the output shaft. In the end, nothing else
matters. Right? End of discussion...-dave>
--
-dave
mailto:dave@arb.net
http://arb.net
I totally and unequivocally agree.
Paul Lamar
Now wait a minute! With a 4 stroke piston engine you are only
measuring 1/2 the pistons in one revolution. With a 2-stroke,
one revolution does it. In other words, I can't make the
measurement without knowing what's in the box.
Bob White
--
http://www.bobwhite-abq.com
N93BD - Rotary Powered BD-4
Sure you can. If x amount of air and fuel goes in in a given time
period x amount of HP comes out in the same time period. Actually
the last statement is redundant as HP is work done in a given time
period. Time period is implied when HP is discussed.
That makes a one cylinder two cycle equivalent to an inefficient
two cylinder four cycle and a one rotor. The only way to tell the
difference is there would be more oil in the exhaust of the two
cycle and the one rotor :) Of course there are efficiency
differences in a narrow range between .45 BSFC and .65 BSFC.
It could be a turbo prop engine in there. In that case it would be
really inefficient at a BSFC of over one for a small turbo prop.
Paul Lamar
Dave's statement is refering to measuring displacement, not HP.
"Measure the volume the box takes in for one revolution of the
output shaft."
No HP, no time period, just volume.
Again, intake volume in one revolution won't measure displacement of
a 4-stroke.
Bob White
--
http://www.bobwhite-abq.com
N93BD - Rotary Powered BD-4
OK I missed your point. You are strictly correct but I was referring
to the HP out as I think Dave was implying. Also Dave statement was
strictly correct if you consider the Wankel as a two stroke.
Vance contention was the displacement of the rotary
was somehow more than Mazda claimed so it therefore generated more
power. In fact he claimed it had much more than double the actual two
stroke displacement of the 80 cubic inch rotary and 160 cubic inches
when thought of as a four cycle.
Bill Jepson mentioned that a two stroke actually had another cylinder
in the crankcase so the displacement of the two stroke was double the
number usually attributed to two strokes just like the rotary is
consider a 2.6 L four stroke engine instead of a 1.3 L two stroke
engine.
We might want to call it effective displacement.
Paul Lamar
I have followed the displacement arguments for quit a while. I really
had no intention of making any contribution, but the statement made was
clearly wrong and strictly correct is exactly what I was aiming for. No
assumptions about anything, just facts. It does lead to the following
thought process.
1. The displacement of a 4-cycle or a 2-cycle engine is clearly
defined. How much volume does the piston displace while moving from BDC
to TDC X the number of pistons.
The 4 cycle uses that volume to generate power every other stroke, the
2-cycle every stroke. If there is a discussion about a 1.3L 2-cycle
being equilivent to some other volume 4-cycle, the comparison dosen't
attempt to say the 1.3L isn't 1.3L, just that it compares to something
else.
2. I can measure the displacement as Dave suggested, only by letting
either engine run through a complet cycle. Two revolutions for the
4-stroke, and one for the 2-stroke. At that time all of the parts,
pistons, crank, cam, are back to their original starting point. I only
have to account for the ineffeciencies such as leakage to get the
calculated value of displacement.
I haven't mentioned the Wankel, or horsepower, or time. This seems to
be where the problems arise.
3. Using the above examples as a basis, I come to the conclusion
that to measure displacement, I want to let the engine run through one
complete cycle so that all the parts start and end at the exact same
point. That's how it works for the 2-cycle and the 4-cycle, and it seems
right. Who's number is that? Vance's, everyone else's, something in
between? I don't know but that's what I would call the displacement. If
the German government, you or Vance use a different definition, I won't
argue about it. I've got my number and I'm happy with it.
The only thing I would emphasize is that displacement is just
displacement. It isn't power produced or volume/time. Different
designs use their displacement differently and I'm looking forward to
using mine to create lift.
Bob White
--
http://www.bobwhite-abq.com
N93BD - Rotary Powered BD-4
The AirCraft Rotary Engine NewsLetter. Powered by Linux.
ACRE NL web site. http://home.earthlink.net/~rotaryeng/
Copyright 1998-2003 All world wide rights reserved.