Gas Engine FAQ

[Azalin]

No, i just copied and pasted it from the first post.. I have not installed any governor yet.

The clutch liner idea is possible.

So, the butterfly looks good to you?

Thanks BTW.

[Doozer]

Hi Guys,
This is what I have:
Helibug HB6-RCT7
Stock G230rc Engine
17T Pinion (6.76 gear ratio)
600 mm blades
Normal Pitch curve: -3 to +11 Aileron Pitch +7 ... mid stick is zero pitch.
Carb: Walbro 603
H needle: 1 1/2 turns open
L needle: 1 3/8 turns open
Normal Throttle curve as of right now: 0, 5, 10, 12.5, 15, 17.5, 45 (lift off at point 4)
Fuel mix: 25:1 Lawnboy Ashless and 87 octane gas (about 3/4 of a gallon through)
Temp at three fins back from the crankshaft (the head faces the rear): 220 ish degrees F

My throttle curve numbers seem a little low compared to the numbers from the first page of the FAQ. I tached with a Hangar 9 tach but that was all over the place. But I did get a spike reading of 203 (2030) at one point. I'm not so sure of the accuracy of that tach, because it was jumping back and forth between 1150 and 1850 with no noticeable change in the sound of the engine. Because I got the 2030 reading I reduced my throttle curve numbers to what you see above. I'm getting a rev lock, I'm over sweating the temps and head speed. Also I noticed that rkeith, from the first page of the FAQ, takes temps 3 flanges back from the plug. When I take temps, I'm at the other end 3 flanges back from the crankshaft. I'm unsure if this matters.

The engine sounds better/cleaner with the needle settings @ High 1 5/8 and Low 1 1/4, but I got that high temp reading, got scared and backed the needle settings to the ones above. Maybe I should just quit taking temps and trust my ear.... I'm not even sure I'm taking the temps right

[Azalin]

@Doozer
I quit taking temps. It makes me a maniac. Now i look to the color of the plug.

For the tach i recommend TTO Tach. It reads perfect. I have checked many times both with GV-1 and TTO Tach. They gives the same reading.

http://www.davesmotors.com/s.nl/c.88...t.A/id.7484/.f

[Doozer]

Thanks Suat! I'm going to pick one of those up for sure. Where are you mounting yours? I think I'm going to check for an airleak though. I've been doing a lot of reading and some of the symptoms I'm having seem to have that characteristic. I've checked and re-checked my needle settings and they are now both @ 1 3/8. My curve numbers keep dropping, but my Head Speed is increasing. I can see it and hear it.

I fouled another plug (2 total):




The engine sounds rich, the needles are right where they're supposed to be, and with those throttle curve numbers I would assume that my head speed/ rpms would decrease. That's not what happens though. My piston looks good from the exhaust port. So, I'm just going to start ruling out problems. An air leak seems like a good place to start.

[Peter]

Have you got the carb butterfly approx 1/3 open at your hover throttle position ??


These carbs aren't like nitro where 1/2 open = 1/2 throttle..

[Doozer]

Understood.. hopefully. Low stick fully closed. I need 4 clicks of throttle trim so it will idle. High stick is fully open when point 7 in my curve is 100%.

Here's my curve, 0, 5, 10, 12.5, 15, 17.5, 45 Hovering between position 5 and 6. Starts to lift off the skids @ 15%

Throttle end points are @ 100% each.

[Greatsteaks]

If your fouling plugs your too rich. An air leak will make you run lean. If your running rich your needle settings are not right where they are suppose to be, your needle settings will be right when the engine runs right. As your engine breaks in you will need to richen it up as it breaks in.
You shouldn't set your carb idle with the trim, set the idle by adjusting the linkage. As your engine breaks in you will need to adjust your idle linkage.

[FRGY28]

Thank you that has posted Q&As...
As I will also be converting one of my Trex 600n into a Helibug, all this info on this thread is really helpful. I wanna read all I can find on how to's for Gassers, so it would be less of a headache once I start my conversion.

On regards to the throttle curve settings, is the settings above towards to top of the Q&A section, more or less the norm on which I should start ? Will I use this same curve to break-in the engine ?

Also, I don't do much 3D... Can I start of by using the Coleman fuels with 25:1 mix ? Or just use 87 pump gas ?

One last Q... I will be using the gv-1 w/ SG on an RC engine. I would tune with the gv-1 Off as I would normally do with my nitros... Correct ?

Thank You all in Advance for the help.

-Juan-

[AtTheCross]

the weather has been kinda crazy here in Southern CA lately, I had my g260rc tuned to my satisfaction in about 75°-80° weather. Then went to fly in 95° weather and my HS was too high and my idle was too high.

Now in trying to find my answer to hot weather tuning, i can across a nitro tuning thread that said that in hot weather you should lean out the motor to cool it down, even in the thread they noted that it was counter-intuitive and the consensus was that yes, you do lean out the settings on a nitro engine in hot weather.

I usually fly in the morning so there's no wind and it's anywhere from 68°-73°, but sometimes, not very often I get to fly in the afternoon and it's 90°-98°.

So is that what i do for my gasser when it's hotter outside then when i normally fly lean it out?

[cbergen]

The reason for leaning the needles has less to do with the temperature of the engine and more to do with maintaining the proper fuel/air ratio going into the engine.

When the outside temperature rises the density of the air decreases. IOW the air is thinner with the affect of less oxygen per given unit.

Similarly, a rise in altitude has the same affect, and requires the same adjustment.

With less air, in order to maintain the proper air/fuel ratio, you must reduce the amount of fuel. You do this by leaning the needles (screwing them IN).

In winter time of course the opposite is true, cooler air is more dense (more oxygen per given unit) requiring more fuel to maintain the fuel/air ratio, therefore richening of the needles is necessary.

[AtTheCross]

@Chris, wow that was the cleanest explaination yet, thanks! I was getting i guess the same info but a lot less clear on another forum. thanks for keeping it simple and understanable

[cbergen]

Glad to help. What forum was that? Maybe I should visit there to look around.

[AtTheCross]

it was RR and would appreciate it if you would post your answer there too, found it very useful

[James Kovach]

The same situation can happen with changes in humidity as well.

When the humidity increases, there is more moisture and less oxygen per given unit. So you would need to lean your needles to compensate for that. The opposite holds true when the humidity decreases.

This is why I mentioned in the other thread that just because the air temperature went up, does not mean you have to lean your needles. If you start the day at 70F with 75% humidity and then fly to the afternoon where it goes to 85F with 30% humidity, you may not have to do any adjustments to your needles.

The main "weather factors" you need to consider are.... Temperature, Humidity, Barometric pressure

Here is a good excerpt from a website explaining it..... Same things hold true for nitro or gas engines........

It's a simple fact: for optimum performance, you must retune your nitro engine every time you run it. Anyone who assumes that the needles can be left alone once they have been set is sadly mistaken. An overnight change in weather conditions may prevent an engine from running or may put it at risk of some damage if adjustments aren't made to the fuel-mixture settings. Ignoring an engine's tuning needs compromises its ability to make horsepower. In response to certain changes in weather, equipment and other variables, nitro engines must be regularly retuned.

Temperature. Hot weather requires a leaner mixture setting; cold weather requires a richer setting. Most people assume the opposite because they treat the mixture needle like a thermostat. It is wrong to assume that colder weather requires a leaner setting to keep heat in the engine and vice versa. Cold air is denser than hot air. The denser, colder air packs more oxygen into the engine, so going from hot weather to cold needs a commensurate increase of fuel to balance ratio of fuel-burning oxygen and the fuel itself. The opposite is true in hotter weather. Going from cold to hot weather requires a leaner mixture setting.

Humidity. Humidity is the amount of moisture (water vapor) in the air. Moisture in the air takes up volume that would otherwise be occupied by fuel-burning oxygen. Less oxygen means less fuel is required to maintain a proper ratio of air and fuel. High humidity requires a leaner mixture setting than dry conditions.

Barometric pressure. A barometer measures the atmospheric pressure (generally listed in the local newspaper or on the local weather forecast on TV). Higher barometric pressure readings mean more air is getting into the engine, requiring a richer mixture setting to balance the air/fuel ratio.

Altitude. Altitude is an important factor that most of us ignore, yet it affects the engine's performance possibly more than any other element. The general formula for power loss with increases in altitude is 3 percent for every 1,000 feet above sea level. If you race in Colorado at 5,000 feet instead of in California at sea level, you can expect to lose about 15 percent of the engine's potential power output, if the engine is tuned properly.
Air is thinner at higher altitudes, which means there's less fuel-burning oxygen than at sea level. You might sense a common theme here: less air (oxygen) means less fuel to maintain the proper air/fuel ratio. So, running at higher altitudes requires a leaner mixture setting than running at sea level.

TUNING FOR THE WEATHER:
This chart indicates the direction in which you should adjust the fuel mixture when faced with changing weather and other conditions. It assumes the engine is currently well tuned. You could face any combination of conditions listed in the chart; knowing which way to go with the mixture adjustments is half the battle.

Here's a chart to go by:

Higher air temperature: Lean
Lower air temperature: Rich
Higher humidity: Lean
Lower humidity: Rich
Higher barometric pressure: Rich
Lower barometric pressure: Lean
Higher altitude: Lean
Lower altitude: Rich

http://www.squidoo.com/nitro-engine-tuning

This is why it is a good idea to become intimately acquainted with your engines because there is not weather reading that is going to tell you for sure what you need to do with your engine. A change in one condition could be equalized by the change in another. Two conditions could feed off each other. They will tell you what they need by how they sound and perform.

[AtTheCross]

thanks, this post was in my opinion, more definitive than what was posted in the other site, even though the information conveyed is similar. I think people are a little gun shy on the other site and instead of stating things clearly and concisely it is communicated in a round about way because someone (no one in particular seems like 'everyone' gets into the fray), will end up bashing the response.

i also think that this post should be copy pasted in the other thread as the thread title is a little more suitable for a google search

btw, i'm in southern ca way inland from the coast closer to palm spings and unless we get 'june gloom' then the only thing that changes much is temp and WIND

[cbergen]

Feel free to post it up yourself over there. Unless there is something absolutely incorrect posted over there that requires my attention (having to do with Bergen), I try to stay out of the fray.

Lately though it seems that a lot of those same players have moved over here, causing similar issues, so I tend to just do more reading here in the HF gasser forum than posting.

[Pinecone]

One thing that may help your understanding of leaning is that the engine burns air and fuel by WEIGHT. But we meter by VOLUME.

So the engine pulls in X cubic units of air, and the carb supplied Y cubic units of fuel.

As the air density goes down (due to temp increase, humidity increase, or pressure decrease) you get less WEIGHT of air into the engine. And the air density varies more with temperature than the fuel denstiy does. So you have to also decrease the weight of fuel being supplied, so you decrease the volume by leaning the needles.

And the converse when the air density increases (temperature decrease, humidity decrease, pressure increase).

And humidity and pressure do not change fuel density, but do change air density.

[ngin]

Originally Posted by cbergen

Feel free to post it up yourself over there. Unless there is something absolutely incorrect posted over there that requires my attention (having to do with Bergen), I try to stay out of the fray.

Lately though it seems that a lot of those same players have moved over here, causing similar issues, so I tend to just do more reading here in the HF gasser forum than posting.

+1 Well said.

Why bother to post it there. If anyone there wants the info, post a link to here. Maybe then more of teh RR people will see how superior HF is. They will soon discover that the info here is much better as the people are much more open minded.

[pnchurch]

Hi this is very helpful.

I having been running the G270RC for a little over a year and everything seems to be going ok at the moment.

Not enough flying means I am still breaking in - nearly 10 litres through at fully synthetic mix of 25:1. I was not aware of the non-linear throttle nature. Just checked my settings and I am running:
N: 0 INH 40 46 100
S1: 70 46 41 46 100
S2: unused at present

I have stock manual needle settings. These seem to work well. When I measured the headspeed last time I had about 2000.

To date I have run without a governor and am just installing the GV-1 with the stator gator. 1 am hoping to run with headspeed of 1800-1850 when finished.

Question is, how do you guys kill the engine?! To date I have done this using the kill switch, now this option is gone, I can't figure out what to adjust to turn the engine off from the remote.

Comments on this and the above very welcome.

[Doug Darby]

I have the throttle Trim set so that if I lower it much below center it kills the engine. So after using throttle hold and autoing down, I simply switch out of TH and lower the trim on the throttle!