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Well, Mike, just for comparison, when I had a 2.17:1 and a 68 x72
Performance prop, 5200 -5400 rpm on a nominal 70deg day was what I got for
static.
While I don't claim my set up was the best in the land, I think it was a
pretty fair set up. So I would say you are doing just fine.
It does not matter how large a throttle body you have when the manifold air
density hits ambient or as close as it can given any losses in the induction
system - that's it. You can continue to open the throttle body, but you
will not get any more power. However, there is a way!
Looking at some of the variables in the power equation we have:
Power(HP) = Torque * rpm/ 5250, swapping some variables around we get:
RPM = Power/torque. So this indicates the rpm can increase if either the
power is increased or the torque is decreased. Well, it's difficult to
increase the power by itself(unless you go to forced induction or nitrous
oxide)
But one way to get more rpm (and ultimately more power) is to lower the
Torque load on the engine. Decreasing the Torque permits more engine rpm
even if power did not increase. However we know that more rpm = more air =
more power. The torque load on the engine caused by the prop decreases as
your gear ratio increases.
By going to a 2.85:1 gear ratio that would reduce the load on the engine by
approx 25% (assuming the same prop at the same static rpm). Now the rpm
power relationship were linear (which it is not with a prop as the load)
then I should have gotten around 6650 rpm with the new gear box - well not
really - due to the cube root relationship between prop rpm and power, it
will be much less of an increase and due to the fact I put on a larger
diameter prop.
But in any case, all this theory aside, with the 2.85 and 74 x88 prop I now
get engine 6000 - 6200 rpm static or about an 13% increase in rpm. So
that's using use the same intake, throttle body and engine for both. But
now because the engine can turn faster (lesser prop load at any specific
rpm).
Now the fact the engine is turning faster means it takes more airflow to
maintain the same (ambient) air density in the manifold. This is because the
higher engine rpm can "suck" that manifold volume (which didn't change) down
faster than it did before. This in turn means that the throttle position
has to be more open to let a sufficient increase in air flow need to achieve
and maintain that (hopefully) ambient air density in the manifold.
So from what you are reporting, I really don't see anything poor about your
performance with your set up. In fact, it's pretty good.
The new set up gave a noticeable benefit in take off performance (and I do
mean noticeable). However, the top end was relatively unaffected - although
I did measure an approx 4 mph increase in top aircraft speed.
In any case, that is my experience.
FWIW
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: Monday, February 08, 2010 10:36 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Throttle limits was Re: N.A. Renesis to turbo
Thanks Ed. Mentioned this a few months ago and was convinced at least for
the moment, to just fly the plane as is. So that's what I have been doing.
To recap, my engine is an NA 13B built by Bruce Turrentine. It is a second
gen engine with Turbo rotor housings (no exhaust splitter) and high
compression NA rotors. The exhaust uses 1 3/4" x 32" primaries into a Burns
merge collector, 2 1/2" outlet directly into my "muffler". My "muffler" is
essentially a 4 1/2" x 30" tube with some spiral baffles and 2 1/2"
inlet/outlet. The intake uses a modified 87 lower manifold casting port
matched to the engine. The upper manifold uses 4 tubes (1 1/2" and 1 1/4"
dia) over the top of the engine to a small dynamic chamber/plenum directly
over the oil filler port in the center iron housing. The throttle body
copies Tracy's original - a stock second gen 3 throat TB cut down to just 2
ports.
The gearbox is Tracy's first RD-1 with 2.17 gears. Prop is a Warnke 68 x 80
(not sure the pitch number is meaningful - everyone seems to measure it
differently). On the ground static RPM is about 5350 and is reached at about
2/3 throttle opening. In flight max RPM I've seen is about 5750.
The Warnke prop is unique due to the shape. The appearance gets a lot of
comments. I'm really hesitant to mess with it and screw it up unless/until I
can say with certainty that there isnt something else I can do with tweaking
(I'm thinking on the intake side) to improve airflow through the engine.
Hard to believe that there isnt more HP to be had when a hacked 2 barrel TB
is only 2/3 open and I've hit the limit. But like you say there are a lot of
variables.
Mike
--------------------------------------------------
From: "Ed Anderson" <eanderson@carolina.rr.com>
Sent: Monday, February 08, 2010 5:06 AM
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Subject: [FlyRotary] Throttle limits was Re: N.A. Renesis to turbo
> 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/
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>> http://mail.lancaironline.net:81/lists/flyrotary/List.html
>>
>
>
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