Heat and Humidity on Engine Performance
 

Does high heat and humidity(95+F 100% H) have a negative impact on 2 cycle engine performance? Yesterday my engine seemed to be loading up on fuel after setting the throttle for relaxed cruise and then going to full power. The transition was not smooth. Leaning out the low speed needle improved things a bit but still did not get rid of the problem.

RE: Heat and Humidity on Engine Performance
 

I wouldn't say it has a negative impact on them, but temperature and humidity changes can change the way the motor runs. Usually readjusting the mixture a couple of clicks will take care of the problem.

Ken

RE: Heat and Humidity on Engine Performance
 

Being a density altitude issue, it can reduce engine power somewhat.

RE: Heat and Humidity on Engine Performance
 

Brit,
Since we're in Oklahoma it's usually more of a humidity change here and not so much temperature. Here in Oklahoma we have 4 distinct seasons every year - hot, hotter, still hot, and christmas!!! :D:D

Ken

RE: Heat and Humidity on Engine Performance
 

Sounds like Atlanta to me.

RE: Heat and Humidity on Engine Performance
 

Where I live now we actually have 4 normal seasons.

Cold as a witches !@%@$,
I wish it would make up it's mind if it will be cold or hot
Hot as heck with humidity to match
I wish it would make up it's mind if it will be cold or hot

In Orlando we had 2

11 months of hotter than he$$ with humidity to match
1 month of thinking I moved south to get away from the cold

In about 6 of those 11 months you could darn near set your watch using the time the daily thunderstorms would show up

RE: Heat and Humidity on Engine Performance
 

Anything that effects the weight of air that goes into the cylinder every cycle will effect the output.

If the air is cold, then it's more dense and therefore more weight of air enters the cylinder per induction stroke. More air to expand when it combusts, therefore more power. That's what the intercooler in a turbocharged engine does. There's a heat exchanger (radiator) between the turbocharger compressor and the inlet manifold so that the compressed (and therefore hot) air is cooled to increase its density.

Humidity is a bit more difficult as water dissolved in the air does not expand when it gets hot in the same way as the air itself and the burn temperature is different (hence the problems you had in setting the mixtures).

So, low pressure from altitude and high temperature will reduce the output, but a variation in humidity is more difficult to predict!

-David C.

RE: Heat and Humidity on Engine Performance
 

Hmmm. I like medium, medium, medium & medium. You can keep the hot, & I don't like our cold winters. I'm a spring & fall kind of guy. The planes fly better as well. ;)

RE: Heat and Humidity on Engine Performance
 

David Thanks

In NC the weather is unpredictable in every month but June through September. Then the humidity is what the weather men might say is "Juicy". To me it gets more oppresive the older I get. I do recall when I was learning to fly full scale planes that density altitude did effect engine performance thusly takeoff roll and max takeoff weight.

Jay

RE: Heat and Humidity on Engine Performance
 

On really hot days here in LA, there is a noticable drop in engine output which can be rather alarming if you aren't expecting it as it completely changes the responses of the plane if you have become very used to how it reacts.

At least, that's my excuse!

-David C.

RE: Heat and Humidity on Engine Performance
 

Britbrat,
I definately prefer the hot over the cold. I'll take the heat because it means that we're still flying in January. We never reallly shut down for winter here. We still get flying days throughout the winter months.

Ken

RE: Heat and Humidity on Engine Performance
 

Given a choice of two evils, I'll take the hot. We fly in January as well -- but I suspect that it is quite different from your January flying. Flight duration is limited by MTBF (Mean Time Between Frostbites)

RE: Heat and Humidity on Engine Performance
 

:):)

Yes, I image it is quite different. You have to remember that 2" of snow will close schools here. 25° is too damn cold to go outside!!! :D

Ken

RE: Heat and Humidity on Engine Performance
 

'snow'? wassat?

;)

-David C.

RE: Heat and Humidity on Engine Performance
 

Tough guys eh? ;) Our New Years Day Funfly often takes place at MINUS 25 [X(], with a refreshing breeze to add spice. We often use seaplanes instead of bothering with skiis. My Seamaster is a killer snowbird, but I also have a purpose-built "snow goose" aerobat for those refreshing occasions when visibility rises to half a mile & I just can't stay away from the fun.:eek:

RE: Heat and Humidity on Engine Performance
 

Since everyone is talking about the weather, I will chime in. In Houston, Texas, we have three seasons:

1. Nice crisp fall weather - 2 weeks
2. Hot and humid - 25 weeks
3. Humid and hot - 25 weeks

RE: Heat and Humidity on Engine Performance
 

Nashville also has 2 seasons...

Winter (15 days in January)
Road Construction

RE: Heat and Humidity on Engine Performance
 

I wish we had 4 season here in Michigan. Now we only have two, Winter and Road Construction.

RE: Heat and Humidity on Engine Performance
 

Up here in the extreme northwest (alaska) we have:

Lots of snow in winter (great for snowmobiling), wet springs, long summer days (great for flying), and about a week of fall. Tonight the sun will set at 11:38pm (doesn't get dark until 12;30) and rise at 4:30.

So we have a short season, but I'll be flying my plane as late as I want.

RE: Heat and Humidity on Engine Performance
 

Relatively warmer air restricts the number of air molecules entering the engine via a given carb throat. For a given needle setting the engine will be richer. The lower amount of O/2 will require less fuel (leaner needle) thus reducing the power output. A leaner needle will help the running, however the overall power output is still reduced.
By the same token, in relatively cooler air the reverse happens. With proper needle valve setting, cold dry air will produce more power output than warm dry air. Add humidity and additional problems do occur. Thankfully in our modeling world they are not really significant. Humidity does NOT act like water/alcohol injection for additional mass. It simply reduces the combustible oxygen.

Sometimes modelers confuse the observed changes in model performance due to the increased True Air Speed ( TAS )/ Ground Speed (GS) relationship in hot or high altitude flights with engine performance. While in either hot or high alt. the engine performance is less (albeit very small in most cases at a given location) the increase in TAS on those hot days can invite the model pilot to misjudge the approach-to-stall condition of an airplane that he has been flying in much cooler weather.
The warmer air with farther spaced air molecules produces a slightly faster TAS, for a given number of air molecule flow (Indicated Air Speed [ IAS ]) which actually controls the stall characteristics of the flying machine.
In other words, one will try to match that previously observed cool-air speed relative to the ground and stall the model.


edit: format

RE: Heat and Humidity on Engine Performance
 

I guess you could say that. I just knew it was different.

RE: Heat and Humidity on Engine Performance
 

Up here in winter at around 10-15 degrees F, Lipo electric batts will only run about 5 mins. doesn't matter what capacity they are. I made a foam sock for them and they will generate enough heat to keep themselfs warm. A 2100 ma. batt will run for 20 mins to 1/2 hr. with the sock. Of course the fingers only last for 5 mins before they go numb anyway. Bummer. Clubhouse has a woodstove in winter. Moose hoofprints are a bummer on skis too.:D

RE: Heat and Humidity on Engine Performance
 

Yesterday was the hottest, and most humid, day I've flown so far this year. I did have to lean the engine a bit before flying. I didn't really notice a lack of power, but that's possibly due to the extra power this plane has.

RE: Heat and Humidity on Engine Performance
 

Here is a calculator I found online to see about what the power loss is at altitude and humid conditions.

http://wahiduddin.net/calc/calc_hp_dp.htm

To find the values to plug in go to www.weather.com and type in your zip code.

At two of the flying sites that I fly at my engine outputs for today are 74.9% to 84.2% rated power at standard conditions. Now that's why a lot of us high altitude fliers go a little bigger on the engine size, even voiding the product warranty to get a plane to fly like it would at lower altitudes.

I love the variable seasons here, but you need a variety of toys to enjoy it all. Boat, snowmobile, 4 wheeler, golf supplies, skis, SUV, model planes......on some days you could use any one of them and not have to drive more than an hour or two from home. I'll never move because there is never a boring weekend around here.

RE: Heat and Humidity on Engine Performance
 

The main thing I have found is that when it is really hot I need to richen my engines a fair bit to stop them overheating. My TT61 pro in my ultimate can't really be flown above about 38 degrees as the engine will overheat regardless of how rich it is.