Is hot weather good or bad for gliders?

[Pi1otguy]

I get that hot temperature and the high density altitudes they produce sap performance out of powered aircraft. Spectacularly so at times. But what about gliders?

Are the thermals stronger? Do they offset other performance hits?

 

[Hang 4]

Heat alone neither hurts nor helps. Less drag, but less "lift" (in still air). One of the best hang gliding competitions is held in West Texas in August. Was well over 100 degrees last year, but regularly getting climbs of over 1000fpm. Lift topping out at 12,000 msl. Towing was a bear as the tug engines (Rotax) were not making close to full power. In Florida, slightly less heat, but in the summer, tons of popup thunderstorms make for lousy soaring conditions. Spring/Fall tend to be really good as the air dries out a bit. The key to lift is the stability/instability of the airmass and how high the inversion is. Less stable, high inversion is good. Too good, and you get overdevelopment and thunderstorms.

Lot of words, but absolute heat is basically a neutral.

 

[George Mohr]

Hot days impact the performance of the glider pilot more than the glider

 

[Juliet Hotel]

Hot air rises and rising air (thermals) is generally a good thing in gliders. But creating strong thermals depends on more than just air temperature. Terrain and winds will also be factors that could either help you or hurt you.

 

[AA5Bman]

It's typically hot when the thermals are booming. But the thermals aren't booming because it's hot, per se. Heating and instability/lapse rate have more to do with thermal creation than the raw temperature.

...At least, that's what I remember from my glider license 100 years ago.

 

[George Mohr]

Ok serious contribution then Thermals require instability, which is to say colder air on top than normal or warmer air below. The absolute air temp at ground level doesn't tell you much about this change, known as lapse rate, so you can't say too much about how 'good' the day is.

Having said that, the highest temp days are often in the middle of a higher pressure system, and those airmasses are usually quite stable.

 

[3393RP]

When flying from the Sandias in Albuquerque back in the day, we couldn't launch our kites before 4:30 PM or thereabouts because the thermals were dangerously strong. Even as the lapse rate declined during the late afternoon, one still had to be alert at all times. There was always a chance of flying into a big one. It would try to rip the control bar out of my hands, and dump me out on the backside at what seemed to be a 90 degree nose down attitude.