29
votes
How high does the ground effect last?
There is no height at which ground effect is switched off. It just becomes less and less effective. There are two factors which determine how strong ground effect is.:
Height relative to wingspan: ...
- 237k
26
votes
Accepted
Why do helicopters experience a brief dip in altitude during IGE marginal power takeoffs?
There is a discussion of this phenomenon in Raymond Prouty's book Helicopter Performance, Stability and Control. Chapter 3 describes momentum methods for the physics in forward flight, including the ...
- 63k
17
votes
Accepted
How do ground effect vehicles perform turns?
It turns like an airplane by tilting the lift vector. Watch carefully in this video, especially about 50 seconds in, and you can see the craft is turning by banking.
It just can't bank very hard ...
- 136k
16
votes
Accepted
Why did America not build its own ekranoplan?
Best answer: the United States had no need for one. These kinds of large wing-in-ground-effect craft, while impressive, really serve no military purpose and provide no major military advantage for ...
- 75.1k
16
votes
How high does the ground effect last?
I remember studying that ground effect happens within one wingspan. Although it reduces when you gain altitude.
As mentioned in FAA’s Pilot’s Handbook of Aeronautical Knowledge:
When the wing is ...
- 29.5k
14
votes
Accepted
How high does the ground effect last?
Ground effect height is primarily a function of the airfoil, and the "ground" surface. Smooth desert lakebeds have "better" ground effect than forest tree tops. Calm water is better than open water ...
- 17.8k
14
votes
Accepted
Can we borrow Formula One's ground effect for airplanes?
The reduced pressure on the car not only exerts a downward force on the car, but an equal upward force on the ground. Mythbusters did an episode where they drove an Indy car over a manhole to show ...
- 28.7k
13
votes
Can a low flying jet fighter lift water?
And this video gives quite the explanation on how this happens...
The way it works:
condensation effects:
the air speed increases as the air flows around the aircraft
this can mean, that the air ...
- 2,180
11
votes
Can airspeed in ground effect be used to estimate climb performance?
Not really. You don't really know until you work out the numbers, there being so many variables. Although experience and instinct gets you most of the way there if you have the experience.
He was out ...
- 136k
10
votes
Why did America not build its own ekranoplan?
One reason the US never pursued this design is that it can't operate effectively in rough seas. It needs a relatively calm surface, which limits where and when it can be employed. A potential opponent ...
- 8,817
10
votes
Can we borrow Formula One's ground effect for airplanes?
The issue here is that ground effect requires there to be another body in which the airfoil is in close reference to (i.e. the ground).
The wiki article sums it up nicely
A substantial amount of ...
- 102k
9
votes
Accepted
Were stub wings on early flying boats designed or able to exploit ground-effect lift?
In the early 1920s ground effect was not as well studied as today, so it was not considered during development. These stub wings, mostly called sponsons, were meant for roll stabilization on the water,...
- 237k
9
votes
When leaving ground effect, why is there a nose-up change in moment?
Koyovis' explanation is correct and deserves to be the accepted answer. However, as always, much depends on the details of the specific configuration - generalizations like those in your question ...
- 237k
9
votes
Why is ground effect greater over smooth hard surfaces?
From a conservation of energy perspective, the rotor is transferring energy to the air, which then moves down and is deflected by the ground. A soft or drag-inducing surface will absorb more of that ...
- 2,238
7
votes
Accepted
When leaving ground effect, why is there a nose-up change in moment?
The aerodynamic centre of a wing shifts when it is in ground effect. Out of ground effect, the wing produces lift by accelerating air downwards. In ground effect the ground prevents the air from being ...
- 63k
7
votes
Accepted
Is flying in ground effect dangerous?
The decrease in stall AOA is more than offset by a decrease in the AOA required to achieve the same total lift and the result is indicated stall speed actually drops a little bit. And pilots ...
- 136k
7
votes
Would ground effect and FOD ingestion be factors at high speeds close to the ground?
The amount of time a plane in a dive spends close enough to the ground to ingest foreign objects and thereby damage its engines is of order ~fractions of a second.
For a plane that is about to ...
- 22.2k
7
votes
Accepted
Does ground effect scale 1:1 with wingpsan?
It's most definitely not urban legend. However, it also does not scale 1-1 with wingspan. Rather, it scales nonlinearly with above ground height to span ratio ($h/b$). The simplest analytical ...
- 11.1k
7
votes
What about a Plane-Train?
The first issue with airplanes is they are stupendously, freakishly light. Any random American freight diesel locomotive weighs more than a 747-400. Trains rely on this mass to provide the downforce ...
6
votes
What is the difference between ground effect for an infinite wing and for a finite wing?
Ground-effect analysis is generally completed using the method of images, where we imagine an opposite geometry providing a flow that interacts with the original geometry.
The 2D case
Katz and ...
- 3,347
6
votes
Is it practical to use ground effect to extend range in an emergency?
When flying close to the ground, there is an important reduction of induced drag, the larger the closer to the ground one flies, so the airplane needs less engine thrust to keep a given airspeed. ...
- 11.2k
6
votes
Does a wing produce an appreciable amount of lift during the takeoff roll prior to rotation?
Back to the basics: with credit to @jamesqf for the comment about soft/rough field takeoff ... "get weight off the wheels as soon as possible".
With a cross-wind take off, we leave weight on ...
- 21.4k
5
votes
Is it practical to use ground effect to extend range in an emergency?
During glider training, I was taught to use ground effect to my advantage if I was going to come up short on final. It's been a long time, but my recollection is that I was taught to get to ground ...
- 2,377
5
votes
Would ground effect and FOD ingestion be factors at high speeds close to the ground?
How could flight 77 into the pentagon overcome the compression lift of the ground effect at 460 KIAS that close to the ground?
Pitch. If an airplane's nose is low enough, it will descend and ...
- 5,801
5
votes
Can we borrow Formula One's ground effect for airplanes?
No, this doesn't work: it's directly analogous to trying to fly by grabbing your shoelaces and pulling upwards.
Ground effect works for the car because it increases the force between the car and the ...
- 12k
5
votes
What is the indicated airspeed necessary to exit ground effect on takeoff?
The idea that the plane was unable to leave ground effect is not quite right, in fact it's the opposite.
Ground effect results in the plane having slightly more lift (and less drag) at very low ...
- 119
5
votes
Accepted
How does pressure distribution change when a wing enters ground effect?
Ground effect is the increase of lift coefficient than can be seen when an airfoil or a wing is at a distance from the ground less than its chord or span. Generally it can be seen that $C_L$ increases ...
- 16k
4
votes
Why don't helicopters always takeoff from a hover out of ground-effect?
A helicopter takeoff profile is governed by having enough margin to autorotate to a safe landing in event of engine failure, not by more efficient flight due to ground effect. Margin consists of both ...
- 21k
4
votes
Accepted
Human-powered flight in vs. out of ground effect?
Ground effect plays a role when the aircraft is within one wingspan of the ground, so the aerocycle is getting the benefit of lowered induced drag. It looks to be flying about a quarter of a span ...
- 21k
Only top scored, non community-wiki answers of a minimum length are eligible