Hot v Cold

[Malc]

Please excuse my lack of scientific knowledge but why do models climb better on warm days?
I know hot air rises and creates thermals but is this the only reason?
Malc

[Rodney]

They do not climb faster on warm days unless you get in a therminal. In fact, if you are using an internal combustion motor, you get better performance on a cold day as the engine puts out slightly more power.

[Ollie]

Aircraft depend on air density. The higher the air density the better the aircraft flies. The air changes with pressure and higher the pressure the higher the density. The air changes with temperature and the higher the temperature the lower the air density.

"Please excuse my lack of scientific knowledge but why do models climb better on warm days?"

In a thermal there is warm, less density air and around cool air that is more density. So the warm air floats on cold air. As the altitude increases the air pressure the air pressure decreasses. Normally during the day, the air temperture lowers with altitude. Thermals form when the lapse of altitude with temperture.

The sailplanes always glide down in the air mass with a sinking speed. If the air mass has a vertical speed compared to the earth and the vertical air speed is more than the sailplane sinking speed then the sailplane gains altitude.

To understand you must have the facts and details of the system not myth.

[Malc]

I'm using a low powwer electric in my GWS Tiger Moth and it seems a lot more reluctant to climb on cold mornings

[Ollie]

To understand you must have the facts and details of the system.

Measure the the battery volts x amperes = watts into the motor. I think you will find that the main problem with the battery power and low temperture.

[vintage1]

I agree. Low battery temp is most likely the key.

[slipstick]

The easiest way to confirm it is with a tacho. You'll find the prop turning a fair bit slower when everything's cold.

Steve