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Date: Mon, 8 Feb 2010 11:24:19 -0500
Message-ID: <1ab24f411002080824n5dd35fe8p9cd156132d74edb0@mail.gmail.com>
Subject: More throttle now Scotty, we need it now.............
From: Lynn Hanover <lehanover@gmail.com>
To: flyrotary@lancaironline.net
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Hi Mike,

Several things could be causing the situation you see in advancing your
throttle but getting no increased engine rpm.  This is not an uncommon
situation. Ok assuming we are talking naturally aspired engine (no forced
induction), fixed pitch prop and assuming your engine is basically OK (not
weak on compression, etc),

then the most  likely cause is you have simply reach the point at which
where the engine is producing all the power it can - given the prop load it
sees at that moment.  Once that point is reached, then advancing the
throttle more does not result in more air flow through the engine and
therefore no increase in power nor rpm.  In fact, it can cause the engine to
run leaner and actually produce less power than a partial closed throttle.

It's sort of the chicken and the egg in that you need more power to produce
more rpm, but power is dependent on air flow - which is dependent on rpm
which dependent on power produced, etc. {:>).  But to try to be a bit more
helpful, look at it this way.


Basically for every throttle position (at a constant altitude, temp, air
density, etc) there is one associated manifold pressure(air density).  This
manifold pressure is a product of a number of variables, but the most
dominating ones involving the engine are volumetric efficiency,  throttle
position and engine rpm.  Now your volumetric efficiency is more or less
fixed by the intake/exhaust design so we'll eliminate that for the moment.
That leaves throttle position and rpm as controllable variables and your
ambient air density as a fixed (for this discussion).


We know the engine is a positive displacement pump which displaces the same
volume once each engine cycle. The power the engine produces in that cycle
is limited by the density of the air in the combustion chamber as the volume
is always a constant (fixed by size of your combustion chamber).  The air
density into the combustion chamber is dependent on the air density in the
intake manifold.

So that leaves us with:  More throttle = higher manifold air density =
  = more oxygen + More fuel(permits more fuel to be burnt) = more power =
more rpm.  That is until you hit the limit - what limit you say?

The limit is that once you have opened the throttle plate sufficiently that
the air density in the intake manifold is equal to ambient air density (or
as close as its going to get- given intake losses) - then it will not make
any difference (in power) to advance the throttle further.  Once you have
reached that limit, then advancing the throttle further does not further
increase the air density in the manifold and therefore limits the amount of
fuel you can burn/power you can make.

Clearly if you have a large throttle body you can reach that point with a
smaller opening of the throttle plate than if you have a small throttle
body.

As I said - there can be other causes, but this is the one I think most
folks run into. You can find the same situation even on the ground, where
again once the manifold air density = ambient air density (or as close as
your engine Ve will permit) you stop producing power increase even if you
have throttle travel left.

Therefore if your throttle body is sized so you get max power at 100%
throttle opening a sea level, then with every increase in altitude, you will
find you have additional throttle travel that produces no increase in power.
The higher you go in altitude the more throttle travel will be available
that results in no power increase.  This is because the ultimate limit is
based on the ambient air density.

Hope this helped.

Ed

Nobody does technical talk like Ed.

Another example would be a 12A (2292CCs) vice the 13B (2606CCs) race engine
that can do 245 HP with two 36MM chokes. 270 HP with two 38MM chokes and 310
HP with two 44MM chokes.
Those outputs are with a tuned and very long exhaust system, and lots of
overlap.This where the intake and exhaust are connected and help pull in
more than 100% of the displacement on each cycle.

The Renesis has zero overlap. So, you can get no good effect from the
exhaust system. But you can manufature some bad effect with a poor exhaust
system that produces back pressure, and that causes some spent gasses to
stay in the engine this (in effect) reduces the displacement of the
engine.

The zero overlap idea has to do with polution control so the cars could be
sold in California. In order to get back some amount of power the intake
system (in the car) was a complex pipe organ looking thing that changed
tuned length based on engine load and RPM.

And there is your clue. The stock intake runners are not very big. Not big
means higher velocity. (Bernoulli) And what would produce the best power in
any engine? The highest possible velocity at the port opening.  Or, the
highest volume per unit of time.

In airplane applications I suggest that the usual build has two tubes
feeding each rotor, and that is much more than enough. Either tube has
enough cross section to produce the HP requested, but there are two
used anyway. It seems right because there are two ports to feed. In the race
engine there is one 36MM tube to feed one rotor. It is split just after the
carb to form two runners, one for each port.

That 12A race engine, though tuned for 9,500 RPM produces 173HP at 6,500
RPM. The runners are too short, it has tons of overlap, and the exhaust
headers are too short.

So, for most intallations, the runners are too big and the throttle body
diameter is bigger than is needed for the flow required. Once the engine is
consuming whatever amount of air it can for any RPM additional TB size, or
throttle opening adds nothing.

The port timing on the Renesis appears to be quite timid. I would like to
see a bit of a developement program for an aircraft specific engine with
earlier opening and later closing of the intake port. Maintaining zero
overlap is of no value in an airplane, and a big improvement can be had with
just a die grinder.

The other problem is the muffling. One method I would not attempt would be
the homoginizing muffler next to the engine. I cannor imagine this thing not
producing lots of back pressure, and killing off HP.

A short primary on the end ports and a double length primary on the center
ports with two smooth collectors then whatever muffler you want to try is my
opinion.

Alternatively, early rotors and counterweights and a turbo with a huge
compressor wheel and no waste gate to produce just a few pounds of boost
maximum would solve both problems.

And. All that stuff Ed said too.

Lynn E. Hanover

--0015174c3860b577be047f193bb0
Content-Type: text/html; charset=ISO-8859-1
Content-Transfer-Encoding: quoted-printable

<div>Hi Mike,<br><br>Several things could be causing the situation you see =
in advancing your<br>throttle but getting no increased engine rpm.=A0 This =
is not an uncommon<br>situation. Ok assuming we are talking naturally aspir=
ed engine (no forced<br>
induction), fixed pitch prop and assuming your engine is basically OK (not<=
br>weak on compression, etc),<br><br>then the most=A0 likely cause is you h=
ave simply reach the point at which<br>where the engine is producing all th=
e power it can - given the prop load it<br>
sees at that moment.=A0 Once that point is reached, then advancing the<br>t=
hrottle more does not result in more air flow through the engine and<br>the=
refore no increase in power nor rpm.=A0 In fact, it can cause the engine to=
<br>
run leaner and actually produce less power than a partial closed throttle.<=
br><br>It&#39;s sort of the chicken and the egg in that you need more power=
 to produce<br>more rpm, but power is dependent on air flow - which is depe=
ndent on rpm<br>
which dependent on power produced, etc. {:&gt;).=A0 But to try to be a bit =
more<br>helpful, look at it this way.<br><br><br>Basically for every thrott=
le position (at a constant altitude, temp, air<br>density, etc) there is on=
e associated manifold pressure(air density).=A0 This<br>
manifold pressure is a product of a number of variables, but the most<br>do=
minating ones involving the engine are volumetric efficiency,=A0 throttle<b=
r>position and engine rpm.=A0 Now your volumetric efficiency is more or les=
s<br>
fixed by the intake/exhaust design so we&#39;ll eliminate that for the mome=
nt.<br>That leaves throttle position and rpm as controllable variables and =
your<br>ambient air density as a fixed (for this discussion).<br><br><br>
We know the engine is a positive displacement pump which displaces the same=
<br>volume once each engine cycle. The power the engine produces in that cy=
cle<br>is limited by the density of the air in the combustion chamber as th=
e volume<br>
is always a constant (fixed by size of your combustion chamber).=A0 The air=
<br>density into the combustion chamber is dependent on the air density in =
the<br>intake manifold.<br><br>So that leaves us with:=A0 More throttle =3D=
 higher manifold air density =3D<br>
=A0 =3D more oxygen + More fuel(permits more fuel to be burnt) =3D more pow=
er =3D<br>more rpm.=A0 That is until you hit the limit - what limit you say=
?<br><br>The limit is that once you have opened the throttle plate sufficie=
ntly that<br>
the air density in the intake manifold is equal to ambient air density (or<=
br>as close as its going to get- given intake losses) - then it will not ma=
ke<br>any difference (in power) to advance the throttle further.=A0 Once yo=
u have<br>
reached that limit, then advancing the throttle further does not further<br=
>increase the air density in the manifold and therefore limits the amount o=
f<br>fuel you can burn/power you can make. <br><br>Clearly if you have a la=
rge throttle body you can reach that point with a<br>
smaller opening of the throttle plate than if you have a small throttle<br>=
body.<br><br>As I said - there can be other causes, but this is the one I t=
hink most<br>folks run into. You can find the same situation even on the gr=
ound, where<br>
again once the manifold air density =3D ambient air density (or as close as=
<br>your engine Ve will permit) you stop producing power increase even if y=
ou<br>have throttle travel left.<br><br>Therefore if your throttle body is =
sized so you get max power at 100%<br>
throttle opening a sea level, then with every increase in altitude, you wil=
l<br>find you have additional throttle travel that produces no increase in =
power.<br>The higher you go in altitude the more throttle travel will be av=
ailable<br>
that results in no power increase.=A0 This is because the ultimate limit is=
<br>based on the ambient air density.<br><br>Hope this helped.<br><br>Ed<br=
><br>Nobody does technical talk like Ed.</div>
<div>=A0</div>
<div>Another example would be a 12A (2292CCs) vice the 13B (2606CCs) race e=
ngine that can do 245 HP with two 36MM chokes. 270 HP with two 38MM chokes =
and 310 HP with two 44MM chokes.</div>
<div>Those outputs are with a tuned and very long exhaust system, and lots =
of overlap.This where the intake and exhaust are connected and help pull in=
 more than 100% of the displacement on each cycle.=A0</div>
<div>=A0</div>
<div>The Renesis has zero overlap. So, you=A0can get no good effect from th=
e exhaust system. But you can manufature some bad effect with a poor exhaus=
t system that produces back pressure, and that causes some spent gasses to =
stay in the engine this (in effect) reduces the displacement of the engine.=
=A0=A0</div>

<div>=A0</div>
<div>The zero overlap idea has to do with polution control so the cars coul=
d be sold in California. In order to get back some amount of power the inta=
ke system (in the car) was a complex pipe organ looking thing that changed =
tuned length based on engine load and RPM. </div>

<div>=A0</div>
<div>And there is your clue. The stock intake runners are not very big. Not=
 big means higher velocity. (Bernoulli) And what would produce the best pow=
er in any engine? The highest possible velocity at the port opening.=A0 Or,=
 the highest volume per unit of time. </div>

<div>=A0</div>
<div>In airplane applications I suggest that the usual build has two tubes =
feeding each rotor, and that is much more than enough. Either tube has enou=
gh cross section to produce the HP requested, but there are two </div>

<div>used anyway. It seems right because there are two ports to feed. In th=
e race engine there is one 36MM tube to feed one rotor. It is split just af=
ter the carb to form two runners, one for each port.</div>
<div>=A0</div>
<div>That 12A race engine, though tuned for 9,500 RPM produces 173HP at 6,5=
00 RPM. The runners are too short, it has tons of overlap, and the exhaust =
headers are too short. </div>
<div>=A0</div>
<div>So, for most intallations, the runners are too big and the throttle bo=
dy diameter is bigger than is needed for the flow required. Once the engine=
 is consuming whatever amount of air it can for any RPM additional TB size,=
 or throttle opening adds nothing. </div>

<div>=A0</div>
<div>The port timing on the Renesis appears to be quite timid. I would like=
 to see a bit of a developement program for an aircraft specific engine wit=
h earlier opening and later closing of the intake port. Maintaining zero ov=
erlap is of no value in an airplane, and a big improvement can be had with =
just a die grinder.</div>

<div>=A0</div>
<div>The other problem is the muffling. One method I would not attempt woul=
d be the homoginizing muffler next to the engine. I cannor imagine this thi=
ng not producing lots of back pressure, and killing off HP. </div>
<div>=A0</div>
<div>A short primary on the end ports and a double length primary on the ce=
nter ports with two smooth collectors then whatever muffler you want to try=
 is my opinion.=A0</div>
<div>=A0</div>
<div>Alternatively, early rotors and counterweights and a turbo with a huge=
 compressor wheel and no waste gate to produce just a few pounds of boost m=
aximum would solve both problems.=A0</div>
<div>=A0</div>
<div>And. All that stuff Ed said too.</div>
<div>=A0</div>
<div>Lynn E. Hanover=A0=A0</div>
<div>=A0</div>

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