Soft-field takeoffs

[CowboyPilot]

JOOC:
I've never found ground effect in any plane, high or low wing to be anywhere near the "one wing span" distance from the surface that I've heard of since day one flying. Where does that old "rule" come from?

Beats the hell outa me.

Down here, ground effect can be the wingspan of a B-52 on a 100F+ day. And down at the runway on the coast by our weekend home, we've flown in on cold, damp days with a northern wind blowing and not felt ANY ground effect no matter what.

Go figure.

Personally, I think the whole thing about ground effect was first written by Wilbur after he watched Orville execute a perfect two-point-skid landing out on the beach of Kill Devil Hills. When Wilbur tried it, he bounced a couple of times. During the bicycle ride back to the home tent, Orville was dissing Wilbur about his landing (which is also when the logbook was invented--so Wilbur could record TWO landings on that one attempt, and thus be ahead of his brother) and Wilbur just shrugged it off and said, "The ground moved.

Orville called bull you-know-what and said, quote, "What the hell effect would THAT have?"

And thus, the rule of Ground Effect was established.

I'm pretty sure this is documented in the very first FAR/AIM that's in the Smithsonian somewhere.

Regards.

-JD

 

[gismo]

JOOC:
I've never found ground effect in any plane, high or low wing to be anywhere near the "one wing span" distance from the surface that I've heard of since day one flying. Where does that old "rule" come from?

The "one wingspan" height (or was it 1/2 wingspan?) is the height AGL above which there is virtually no ground effect. The increase from there to touchdown isn't linear and it increases at a faster rate the closer your wings get to the ground. IME ground effect is far more noticeable in a glider than in an airplane, and pretty much non-existent in a Skyhawk when more than a couple feet above the runway.

 

[Henning]

JOOC:
I've never found ground effect in any plane, high or low wing to be anywhere near the "one wing span" distance from the surface that I've heard of since day one flying. Where does that old "rule" come from?

The effect is there, but to a lesser extent. It's not an ON/OFF siuation.

 

[Dave Krall CFII]

The "one wingspan" height (or was it 1/2 wingspan?) is the height AGL above which there is virtually no ground effect. The increase from there to touchdown isn't linear and it increases at a faster rate the closer your wings get to the ground. IME ground effect is far more noticeable in a glider than in an airplane, and pretty much non-existent in a Skyhawk when more than a couple feet above the runway.

The effect is there, but to a lesser extent. It's not an ON/OFF siuation.

I know the theory but at the upper limits, say the top of 1/2 total wingspan, has any effect ever been actually measured and if so, how, or just logarythmicly extrapolated?

 

[gismo]

I know the theory but at the upper limits, say the top of 1/2 total wingspan, has any effect ever been actually measured and if so, how, or just logarythmicly extrapolated?

Here's a graph of the spanwise ground effect. The X axis is height/span, the Y axis is induced drag divided by the induced drag in free air at the same speed. BTW this is only half of the story, there's a corresponding increase in lift at the same AOA although IIRC this starts to become noticeable even closer to the ground.

 

[nosehair]

Ground Effect is at three feet. Three feet off the runway for all light airplanes and helicopters.
heck. I thought ev'rybody knew that.

 

[MauleSkinner]

Ground Effect is at three feet. Three feet off the runway for all light airplanes and helicopters.
heck. I thought ev'rybody knew that.

There you go oversimplifying again...it's 3 feet, 4.237 inches!

Fly safe!

David

 

[Dwight B. Van Zanen]

I seem to remember that for Mooney guys they mostly retract as soon as they are off the pavement. The Mooney retract mechanism has some trouble working at above 80, so it is a little tight getting off and getting the retraction before you are above that speed.