Ground effect / hot day

[fourierman2]

On final, is there a noticeable increase in ground
speed compared to cold days?

Also, is the "feeling" of ground-effect more or less
noticeable/effective?

I would think with the less dense air, one might see
an increase in Ground Speed, not sure how much though.


I'm not so sure about how ground-effect changes with
increased temps and whether the heat radiated upwards
from the runway plays a part in any of this.

 

[tgrayson]

On final, is there a noticeable increase in ground speed compared to cold days?

Also, is the "feeling" of ground-effect more or less noticeable/effective?

I would think with the less dense air, one might see an increase in Ground Speed, not sure how much though.

I'm not so sure about how ground-effect changes with increased temps and whether the heat radiated upwards from the runway plays a part in any of this.

Your TAS is going to be higher on a hot day, for a given IAS. That will produce a higher groundspeed. You'll certainly cover more territory during your flare and touchdown, but that's not due to ground effect, per se.

Any heat or rising air off the surface shouldn't be a factor; remember, your distance to touchdown is affected by horizontal forces (thrust-drag), not by any vertical forces.

 

[nosehair]

Any heat or rising air off the surface shouldn't be a factor; remember, your distance to touchdown is affected by horizontal forces (thrust-drag), not by any vertical forces.

??...hmmm,...?? not sure about that one, tgray.

The charts don't use any vertical forces in the calculations, but...how can it be that you don't think that vertical forces can extend the float???

 

[tgrayson]

Because vertical forces are in equilibrium, just they are as in any non-accelerated motion.

The landing distance is determined by how much territory the aircraft covers as it decelerates to a landing attitude.

 

[jrh]

Because vertical forces are in equilibrium, just they are as in any non-accelerated motion.

How can gliders stay aloft by riding thermals then?

 

[Cessnaflyer]

How can gliders stay aloft by riding thermals then?

That is because the earth is repelling them!

tgray I think you have some of that information a little misconstrued

 

[tgrayson]

How can gliders stay aloft by riding thermals then?

Gliders descend in an airmass that rises faster than the gliders descend. Vertical forces are (usually) in equilibrium here too, although there are periods of acceleration and deceleration.

This obviously isn't what happens when you flying along the runway in ground effect, because the aircraft isn't rising, so not only are the forces in equilibrium, but the vertical velocity is about zero.

Even if there were a rising current of air from the ground, you'd stop any ballooning effects with your elevators. From then on out, you'd be using your elevators to hold a constant altitude above the runway until the a/c slowed enough to touch down.

Still, any vertical velocity of the air near the ground has got to be pretty low. Drop a piece of lint onto the runway and it will fall.

 

[meritflyer]

??...hmmm,...?? not sure about that one, tgray.

The charts don't use any vertical forces in the calculations, but...how can it be that you don't think that vertical forces can extend the float???

I have to go with tgrayson on this. There is no net vertical force gained due to high heat off the runway that could increase float and even if there is a rising convective rise occuring on the runway, it's effect on floating would be negligible when all things considered. This would only happen, as TG already mentioned, as a result of a higher TAS for a given IAS. As the warm airmass decreases in viscosity, the aircraft will have the potential to "float" for a longer period.