Extreme Speed Prop Planes Discuss the need for speed with fast prop planes (Screamin Demon, Diamond Dust, Shrikes or any REAL sound breakin'''' plane)

No more lean runs?

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Old 10-02-2008, 06:51 AM
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vasek
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Default No more lean runs?

Has anyone tried the CSM CarbSmart automatic carb adjuster to prevent lean runs?

They use them in helis to max the power without the engine overheating.

Myself, I'm thinking of a D/F application but first would like to try on a regular "speed" engine.

Looks like a neat product:
http://www.rcmodels.org/csm/carbsmart.htm

what do you guys think?
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Old 10-02-2008, 07:57 AM
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daven
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Default RE: No more lean runs?

There are several mechanical ones that I've heard work, but I haven't tried them since they are not allowed in the racing I do.

http://www3.towerhobbies.com/cgi-bin...?&I=LXDG65&P=7

http://www.bvmjets.com/Pages/mixcont.htm

and for some reason I thought Sonic Tronics had one also, but I can't seem to find it on there website. The BVM one looks nice, but I haven't tried it.
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Old 10-02-2008, 09:47 AM
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Default RE: No more lean runs?

takes all the fun out if it though .....

You really want to measure exhaust gas temperature if anything is to be measured... not head temp. Head temp means pretty much nothing, since it can vary by 50-100 deg depending on where you measure it and will vary even further with relative airflow and outside air temperature.

Plus, the other limitation i see here, is that you have to have a matrix or chart, and relate the temperature/mixture to the throttle position as well.

In flight mixture control.... yep, used those back in the pattern days quite often. OS, Rossi had good devices. My CMB 60 came standard with mixture control. These were all integrated with the main mixture needle valve and had a range that went from pig rich to shut-off lean. You set the mixture control on center, adjusted the main needle valve for proper mixture... and then adjustements could be made from that point. Very useful, and although its a broad range, a good servo linkage made them as accurate as main needle was moving it by hand.

In flight mixture was sometimes the only way to get the "tweeked" rossi off the ground, and then to get it on the pipe in flight. [&:]

But more than anything else, it was a convenient way of making a mixture adjustment without touching the airplane.

"external" mixture controls can work very well, but you have to use caution so you understand how the carb works. For engines/carbs designed for remote needle valves.... no problem. Some carbs have a relationship (geometry) between the high speed and low speed mixture needles - so just setting the needle rich and then adjusting the inline mixture - may result in a crappy midrange or weird transition.

The BVM device is outstanding. The Conley/perry control should work well too - have not tried one myself.

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Old 10-02-2008, 09:57 AM
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mk1spitfire
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Default RE: No more lean runs?

I have thought of this too and have not tried it. Infact my mate suggests that I use the spare rudder channel to operate a servo which in turn connects to the high speed needle. Then to use the rudder trim to finely adjust in flight.

Sometimes I'm not happy the engine is not quite peaking right, so land and readjust which is a pain in ass and wastes fuel.

Since I fly full throttle ALL the time, the left hand pretty just much helps hold the transmitter so I don't think I would give rudder stick input and detune it by accident.
Also You could run the tank right out and richen to the end. This might help plugs blowing. Plugs are nearly 1/4 price of a gallon of fuel.

Interesting Bob you say exhaust temp more accurate. Though will it cool in the pipe?

I say go for it.

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Old 10-02-2008, 11:02 AM
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Default RE: No more lean runs?

For the German Speedcup often these two R/C in-flight mixture controls are used (pics below):
[ul][*] BVM #6027 ( http://www.bvmjets.com/Pages/mixcont.htm )[*] JMP ( Jet Model Products http://www.jetmodelproducts.com/dynamax.htm )
[/ul]
Both control units do work like a charm.

Such mixture controls are a must for all 6.5 to 15 cc speed engines, especially if operated with speed venturi carb. Successful speed runs (i.e. engine perfoms at its HP and torque peak) through the 200 m speed trap are much more probable if the pilot is able to R/C adjust the mixture...

As for the cylinder head heat triggered automatic mixture adjustment using this CSM CarbSmart unit I suspect that the speed freaks over here
[ul][*] don’t have enough space left over for this unit in their speed machines[*] rather rely on personal experience (ground rpm adjustment, needle and R/C mixture control setting, smoke trail, engine sound) than on electronics[*] will doubt the effectiveness of that CSM unit. As Bob already pointed out this unit should only work properly if there’s no airflow around the cylinderhead (e.g. in cowled cars and helicopters). For the speed plane pilots the exhaust gas temperature would be the right one to measure + calibrate (that is made for dyno runs of R/C engines for example)[/ul]
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Old 10-02-2008, 11:56 AM
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Default RE: No more lean runs?

You all have good points, but I think most of you missed the point!

I do have the BVM mixture control as pictured above BUT it has to be adjusted manually via extra channel.

This product CONTROLS the servo input by itself, richens or leans the engine depending on the head temperature.

Yes Bob, the head temperature is affected by the airflow around it but so is the engine head. Cooler air means the engine can be run leaner without overheating.And you can program the temperature wanted of your head.

Just look at the TEMP graph WITH & WITHOUT the gadgetbottom of the page)

http://www.trextuning.com/carbsmart.php
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Old 10-02-2008, 12:56 PM
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Default RE: No more lean runs?

ORIGINAL: vasek

I do have the BVM mixture control as pictured above BUT it has to be adjusted manually via extra channel.
Exactly this manual control by extra servo is what the speed freaks are looking for... [8D]
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Old 10-02-2008, 02:04 PM
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Default RE: No more lean runs?

ORIGINAL: vasek


Yes Bob, the head temperature is affected by the airflow around it but so is the engine head. Cooler air means the engine can be run leaner without overheating.And you can program the temperature wanted of your head.

That is not entirely accurate. Cooling will not overcome or accomodate a lean combustion mixture. You can not always run the engine leaner simply because it is cold outside. Fuel and air burn at a given temperature for a give mixture and set of conditions. What is inside the cylinder is what dictates the show. And usually when its cold, the trick is keeping heat IN the system to sustatain combustion.

The exhaust gas temperature tells you the internal gas temperatures as a result of the combustion mixture. The head can and will not change temp rapidly enough to sense and correct for a lean condition.

Its not impossible to auto-mixture. Turbines control temps and fuel flow and power - and gain, based on turbine outlet temperature (gas temperature) not the surface temperature of a conducting element.

A sensor like this is not a new idea. It has been done before for auto-mixture and also just for diagnostics.

A number of years ago when 4-c engines were becoming main-stream in pattern, there was a gaget on the market that was quite useful in determining when a YS120 was running right. It had a tach, exh gas temp sensor, head temp sensor, and a few other bells and whistles. Was ground based only - plug it in, set the engine... and go from there. But the key to watching the engine was the exhaust temp.

Yes, head temp will rise when the engine goes lean. And under steady state conditions you could use that for a control loop. But head temp will lag seconds behind the gas/combustion temperature within the cylinder. By the time a sensor sees the head temp rise, the lean condition has existed for a while. If the fuel tank were near empty, and air bubbles entered the fuel, the temperature spike the engine sees is immediate and it will sag. The head temp will

On a helicopter the cooling air is somewhat constant speed, so in practice, this probably will work pretty well. On an passive-air cooled setup like a car, it might not be as effective. On an airplane, flight velocity and thus cooling air changes greatly depending on flight attitude and air speed.... so in that application head temp sensing would be quite a bit less useful.
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Old 10-02-2008, 02:23 PM
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Default RE: No more lean runs?

Maybe you're thinking of this Foremost unit. I used them in my boats up to 15cc. Some of the boat motors don't even have a needle anymore, you have to use a third channel unit.

[link]http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXG868&P=7[/link]


ORIGINAL: daven

There are several mechanical ones that I've heard work, but I haven't tried them since they are not allowed in the racing I do.

http://www3.towerhobbies.com/cgi-bin...?&I=LXDG65&P=7

http://www.bvmjets.com/Pages/mixcont.htm

and for some reason I thought Sonic Tronics had one also, but I can't seem to find it on there website. The BVM one looks nice, but I haven't tried it.
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Old 10-02-2008, 02:36 PM
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Default RE: No more lean runs?

I think you should use your hearing and adjust the mixture in flight like I previously mentioned or time when you need to richen.

The beauty is if its too rich in flight and the engine and pipe are not on song then a few click of trim will put it back on track.



Roll on a replaceable sensor inbuilt into the exhaust that can open and close the high speed needle for you.
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Old 10-02-2008, 03:00 PM
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vasek
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Default RE: No more lean runs?

Bob, of course you're right! I wouldn't dare to argue about engine stuff with en expert like yourself.

I'm just thinking like a kid in toy store

My thought process was based on the fact that in a normal situation, due to the "less glow in the tank" progressive condition that affects the carb setting is slow thus the engine goes lean slowly and the head temperature would "follow" fast enough for the gadget to correct the condition progressively. I know it's based on a hunch more than on empirical data. But hey if it works for the helis it just might work for a D/F[8D]

Since i'm not near any D/F expert (where i'm located) to help me get through my fist flight, I'm just trying to minimize my tasks while flying the plane by the seat of my pants....when the time comes[>:]

Cheers,
Vasek
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Old 10-03-2008, 10:37 AM
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Default RE: No more lean runs?

I forgot about that Formost unit. ....... those are kinda nice ....... its just a tub squisher. No leaks, unless the tube breaks. But its not extraordinarly precise. I used one on a smoke system to control flow rate.
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Old 10-03-2008, 10:39 AM
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Default RE: No more lean runs?

Thats the unit I was thinking about, have one hanging on the pegboard...
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