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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
Ed Anderson
Rv-6A N494BW Rotary Powered
Matthews, NC
eanderson@carolina.rr.com
http://www.andersonee.com
http://www.dmack.net/mazda/index.html
http://www.flyrotary.com/
http://members.cox.net/rogersda/rotary/configs.htm#N494BW
http://www.rotaryaviation.com/Rotorhead%20Truth.htm
-----Original Message-----
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On
Behalf Of Mike Wills
Sent: Sunday, February 07, 2010 12:51 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: N.A. Renesis to turbo
Don,
I'm at about 23 hours and am seeing roughly the same performance on my RV-4
with a Bruce T built gen 2 13B. My temps are a little cooler. I'm pretty
happy with the performance, but like you say, its not possible to have too
much power. But I don't have room for a turbo and intercooler.
I think there's more power in my NA engine. I'm still a little mystified by
the fact that at about 1/2 - 2/3 throttle the engine stops making any more
power. But I decided to take several people's advice and just fly it for a
while. I also think there's more speed in it via some drag reduction. A
turbo would be nice to tame the noise though.
I'll be interested in seeing how the Burns muffler works out for you. I'm
not willing to dive into any more muffler experiments for the moment since
my failed trial with the DNA muffler. But sooner or later, and one way or
another I have to quiet this thing down.
Mike Wills
RV-4 N144MW
--------------------------------------------------
From: "Don Wallker" <drwalker@gbis.com>
Sent: Saturday, February 06, 2010 6:21 PM
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Subject: [FlyRotary] N.A. Renesis to turbo
> Dear list, Turbo flyers and especially David Leonard,
> I've 16 flying hours on my RV-8 with a Renesis and all of Tracy's stuff
> and a Catto 76/88. The airplane flys great, just like an RV, no gliding
> time, and about 36 hours on the ground. SPECS
> Full throttle 8,000' 174 mph indicated, 2450 on the prop, water 185, oil
> 205,
> Climb out 110 mph, rate of climb, 1250'/min. Field elevation 5046.
>
> These are not bad numbers, but I would like better. I've been influenced
> by some of the the local jet jocks who say that there is no such thing as
> too much horsepower and they are right! N113BR seems to be performing
> about like a 160-170 HP RV. So I am investigating turboing it! The idea
> is to have a little better than sea level performance on take off
> (designed for 210HP N.A.) and turbo normalizing at cruise. Up to 12000'
> would be nice.
> During the air races this year, Dave Leonard showed up and I was very
> impressed by his airplane. He was able to turbo and inter cool it and
> have it all inside an RV cowl, so I'll likely base my installation on
> his. Plus, he has been through the learning curve of 3 or so turbos so he
> knows what to do, what not to do and what would be better if he were to do
> it all over again.
>
> I've spent the afternoon looking through the archives, reading as much as
> I can find about turbos, and downloading all the photos I can. Here is
> what I am tentatively planning on doing.
> Get one of Techwelding's Renesis exhaust flanges made from 304 SS and have
> my local waterjet guy copy it and make one out of 321SS. I'll weld 321 SS
> and manifold it together and run it into the bottom of the turbo that
> will sit right in front of the exhaust. The turbo will have additional
> support. Run the turbo outlet air from it through a stock RX-7 inter
> cooler sitting in front of the left cheek opening and then out to the
> right side of the engine, probably routing it under the PSRU and then up
> to a throttle body and manifold. Then four al tubes over the top of the
> engine into a cut down and welded up stock RX-8 intake manifold. The
> exhaust out of the turbo will run down and out in the usual center of the
> back of the cowl opening. I am thinking of trying one of Burns Stainless
> all SS mufflers. It is basically a glass pack, but instead of glass, they
> are using stainless steel wool and they say it is holding up for the
> rotary racers. They make it any length you want and is about 4 lbs with
> their SS vs 9 lbs with the hushpower 2 I'm using now. The combustion air
> intake to the turbo will be on the aft left side of the cowl via an NACA
> duct opening as Dave's is.
> The oil cooler will have to be moved to under the engine. I will build up
> a fiberglass scoop, probably based on Van's scoop and modify it to have a
> bigger opening and be farther forward, closer to the prop. I will
> probably have the oil cooler made a little larger (Techwelding) than the
> one I have now.
>
> That's the basic idea at this point. I'll finalize my plan, prebuild as
> much as possible before tearing the airplane apart and try for as little
> down time as possible. I'm looking for the list's critique here, plus
> questions that I will have missed. The following are a list of questions
> that I have.
> 1. Which turbo should I use, which orientation and who should I use to do
> the work, plus what is the approximate price? TO4 hybrid? Dave and
> Steve Brooks mention BNR turbo as a modifier. Who manufactures the turbo?
> 2. What is the ideal situation with a waste gate? Full open or not, or,
> or?
> 3. I read about a N.O.oil line solenoid to the turbo bearings. I assume
> that if the Turbo fails, you turn it on to the N.C. position to prevent
> oil from being pumped down your exhaust? I assume the oil that is used is
> routed back to the sump.
> 4. What size exhaust is optimum? It seems Dave is running 2.5 inch.
> 5. What size throttle body should I use and what would be a good one? One
> throttle body or two? 4. What size injectors should I use, and where
> should the secondaries be placed? Dave is using 480cc and staging is at
> 32 inches. Are you using the same for the primaries and is there an idle
> problem with the larger injectors?
> 5. Anyone out there turboing a Renesis? Anyone flying one?
> 6. My compression is 9.7 to 1. Any problems with this higher
> compression ratio as long as I use an inter cooler and keep the boost no
> higher than 35"?
> And lot more questions, but that's all I can think of now.
> So If any of you can add any thought, let me know.
>
> Don Walker
>
> --
> Homepage: http://www.flyrotary.com/
> Archive and UnSub:
> http://mail.lancaironline.net:81/lists/flyrotary/List.html
>
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