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Hot and humid weather affecting edf performance

Old 08-22-2011, 09:02 PM
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Default Hot and humid weather affecting edf performance

Any else experience a large drop off in performance with hot and humid weather? I know the air is less dense and you get less lift when its hot and humid but I must say i was astonished at the drop in performance of my edf converted airhogs titan plane.

I use the 70mm multiplex fan/motor unit sold for the multiplex twister in this plane, it might be a tad underpowered for the AUW but the maiden flight went very well but it was a 70ish degree dry day. Next time I flew her it was prob about 86 hazy hot and humid as anything and The entire flight I was struggling to gain altitude and fighting a stall, did two circuits around and decided i was one little mistake or bump of wind away from it crashing so I landed it...though maybe battery was getting old and needed a fresher one tried that and nope still got a very very sluggish plane in the air and had to bring her down quickly again...
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Old 08-23-2011, 03:17 AM
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heat could effect air density.. but not that much. even denver flyers love edf as only the fan is effected not the motor/power like in IDF.

you may have a motor losing power, fan blades flexing.
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Old 08-23-2011, 07:38 AM
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Increases in temperature and humidity both do lower air density which will have the double effect of requiring the model to fly faster, and the fan to produce less thrust.

I agree that the changes will be small for the sort of temperature difference you talk about here, and for normal humidity ranges.. but if the model was quite marginal on power in the first place then a small difference could have a big effect.

Sounds like you need to increase thrust and/or reduce weight.


Last edited by JetPlaneFlyer; 08-23-2011 at 03:26 PM.
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Old 08-23-2011, 02:40 PM
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The fan unit and the batteries are both fine can't see anything wrong with them. The plane was not really all that under powered as you can see in these two videos of the maiden flight, it could climb ok at a 30 degree angle, def not vertical but not bad.


Today is going to be a lot cooler and drier out than the other day so i will report on how it does after flying tonight.
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Old 09-04-2011, 06:45 PM
Eddie P
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Heat does effect density altitude. Density altitude is pressure altitude corrected for non standard temperature. Standart temperature at sea level is 15C / 59 degrees. It does down 2C for each 1000 feet of rise. If you are at sea level and it's 75 degree your density altitude is about 1250 feet at "standard pressure" of 29.92 "hg. Yes, humidity mathematically does effect density altitude as well but not as much as temperature. It is more of a measure of air burning engine efficiencies than lifting surfaces but it does effect the wing/prop too, so though it's a side bar issue it's there. For example, if you are fully saturated and moist at 75 degrees sea level, your density altitude is over 1400 feet. Same day but now at 97 degrees and saturated, density altitude is 3150 feet.

Have a play yourselves and get a feel for what can do what:

Guys flying at sea level are typically used to relatively "thick" air that allows the models to fly well. Electric guys get a false sense of security in the idea that the batteries and motors could care less about how much pressure there is in the atmosphere. But they can sometimes forget that well over half of the equation in how an airplane flies is actually dependent on how the wing, and also the propelling structure (fan or prop) is "feeling" about the air density Not only that, but sometimes it's easy to forget that the motor efficiency can be effected by heat saturation in the components. Some heat may be good, too much heat can kill efficiency and the loss of performance is also heat related, not just density altitude related, especially on marginal systems with brushed motors. But event the best brushless systems get a whack in high heat.

So yes, you have observed a very real and relevant effect that temperature plays on the performance or an electric powered model airplane.

Go up into the mountains, say at 5000 feet, and a nice 92 degree summer day, and you'll really "feel" the difference density altitude can make. That type of environment is where I fly all the time and over time RC pilots have become very aware of it's effects on model airplanes that are subject to the same laws of physics that the larger airplanes are.

Have fun out there
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