modesto2
Topic Author
Posts: 2694
Joined: Sun Jul 16, 2000 3:44 am

### Ground Effect In High Density Altitude

How does ground effect change at a high altitude and hot temperature situation compared to standard conditions at sea level? At a high density altitude, will the ground effect be more or less pronounced and why?

lehpron
Posts: 6846
Joined: Tue Jul 10, 2001 3:42 am

### RE: Ground Effect In High Density Altitude

Hmm, subsonic ground effect theory relates the wingspan (or width) of a plane and the height above ground level. The factor calculated multiplies into the induced drag, which is produced by lift as some velocity.

I would suppose that if the air was thicker, the velocity to maintain lift would be less and if it were also in ground effect, the overall velocity would go down a bit more due to a decrease in drag. Likewise if the density was thin, the ground effected velocity would be higher.

Since temperature varies density and viscosity, hot air would make density thin if the air pressure was constant, etc.

[Edited 2005-12-08 00:32:39]
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Pihero
Posts: 4318
Joined: Mon Jan 31, 2005 5:11 am

### RE: Ground Effect In High Density Altitude

It will be the same, as we are talking about equivalent airspeed.
Upon landing, the aircraft wing will be generating the same amount of lift, at grossly the same indicated airspeed. What changes will be the true airspeed of our model.
for more on this,
Ground effect

Regards
Contrail designer

KELPkid
Posts: 5247
Joined: Wed Nov 02, 2005 5:33 am

### RE: Ground Effect In High Density Altitude

 Quoting Modesto2 (Thread starter):How does ground effect change at a high altitude and hot temperature situation compared to standard conditions at sea level? At a high density altitude, will the ground effect be more or less pronounced and why?

You won't notice a difference, trust me...I learned to fly "Hot 'n High" (desert southwest of the USA, the LOWEST field I practiced at was 4100' MSL!).

Indicated airspeed is what performance charts are written for, and for good reason: It doen't change MUCH (I know, it does change some...and there are corrections that can be applied for calibrated or true airspeed) relative to the aircraft's performance (for typical airfield elevations, anyways...).

If you carry 5-10 extra knots on final on a 100 degree (Farenheit) day at, say, LRU, you will float just as far down the runway bleeding off the extra airspeed before the 172 finally decides to land   Actually, maybe even a bit longer, since your groundspeed will be much higher in this instance, than say if the day were more like 60 degrees farenheit.

If you attempt a soft-field takeoff, you will take much longer to get airborne into ground effect (due to the less-dense air effecting both lift and engine performance), however your indicated airspeed will still be more or less the same when you are able to go airborne into ground effect. Once again, if you are hot and high, your actual groundspeed will be pretty high in relation to a much cooler day.
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Stoicescu
Posts: 80
Joined: Sun Sep 11, 2005 2:39 pm

### RE: Ground Effect In High Density Altitude

There will be no difference. The loss of induced drag will be the same (also the downwash)

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