Talk:Ground effect in aircraft

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Contents 1 Bad effect explanation 2 WINGSPAN 3 Centripetal Force 4 Confusing tag rational 5 Gilles Villeneuve 6 From a (Now retired) Pilot 7 Common misconception 8 From an amateur power and sailplane pilot 9 Vortex ring / Ground effect in fixed-wing VTOL aircraft 10 Pigeons 11 New article for vehicles 12 Metal Gear Solid Reference 13 Whoa, bad article name 14 Rotary Wing Stuff

[edit] Bad effect explanation

The explanation of the ground effect, specially what it says about vortices, is erroneus: "Wingtip vortices destroy massive amounts of the lift generated by the wing by increasing downwash behind the wing and therefore decreasing the aircraft's theoretical angle of attack". First off, vortices do not destroy lift by increasing downwash; downwash is inherent to lift: more downwash, more lift. The "theoretical angle of attack" is a misleading concept too. As far as I have read, and I understand, ground effect improves efficiency because the upwash (which is what the air flows like before the wing) is reduced, and because wingtip vortices are decreased. For some info visit: explanation for lift If you know about this it would be nice if you change it. I'd do it, but I prefer to wait until I know more. Keta 14:03, 16 October 2005 (UTC)

I agree the current text is poorly worded. I think I see what the author is trying to say, but as it is it's inconsistent with other wikipedia articles that touch on this topic. If you can see a better way please go ahead and have a stab! Graham 06:41, 17 October 2005 (UTC)

The subject is still not completly clear to be but aside from fixing the lift description so that it at least matches the one on the lift (force) page, shouldn't we divide ground effect into span dominated ground effect (reducing induced drag by cancling vortexes), and cord dominated ground effect (increasing lift)[1]? that difference is causing a lot of confusion here. --Sukisuki 04:00, 30 October 2006 (UTC)

I think the introduction could do with a revamp as well. I don't normally like to complain like this without just going ahead and fixing the article, but this is a subject I really don't know enough about to meddle with! But the phrase I find particularly convoluted is: "as it approaches within roughly twice the length of a wingspan's length". What nuances are we supposed to take from "approaches within roughly"? It'd be great if somebody who knows precisely what is being said there, could tidy it up a little. – Kieran T ^(talk) 15:16, 21 March 2007 (UTC)

I echo Kieran T's comments (and his reason for not attempting an improvement!). There is also an apparent contradiction between this article's description of a helicopter hovering 'in ground effect' and the Vortex ring article's explanation of helicopters suffering a loss of lift due to recirculation of air. We need an expert to improve these articles! TraceyR 10:08, 22 March 2007 (UTC)

[edit] WINGSPAN

When I was in ground school, they taught me ground effect comes into play when the aircraft is about 1/4 of the wingspan above ground. This might be useful information to put in this article. This was about airplanes, I do not know about helicopters.

Yes, ground effect depends critically on wingspan. Here's one way to visualize it: an everyday aircraft flying at high altitudes is a reaction engine which must perform work upon the oncoming air, flinging it downwards as a pair of down-moving vortices. Helicopters do something similar. A hovering rocket ship does the same, but the rocket supplies its own reaction mass exhaust, while an aircraft uses the surrounding air to generate the downward "exhaust stream." This "reaction exhaust" process requires energy, uses extra fuel, and it causes lift-induced drag.

But if a wing had infinite span, or if the wingtips extended to the walls of a wind tunnel, in that case the wing resembles a venturi. There are venturi-like pressure patterns, but there is no downward "exhaust". A venturi-wing is connected to a bound vortex and a starting vortex, but it does not create a stream of downward-moving air, so it neither experiences lift-induced drag, nor does it use fuel to perform work upon the air. Simple? No downward exhaust stream, so in theory no fuel needed for flight! In practice, if an aircraft flys at an altitude much less than one wingspan, it acts like an infinite-span wing: it is lifted by the pressure pattern of its bound vortex and does not leave an "exhaust stream" of downward-deflected air. But if the wing should fly higher, then this "ground effect mode" will vanish, and the aircraft will instead behave as a reaction engine which encounters still air and leaves a trail of downward-moving air.--Wjbeaty 04:31, 28 June 2006 (UTC)

[edit] Centripetal Force

Centripetal Force is the force that keeps an object moving in the circle. For example: A weight on string that is being spun in a circle, moves in a circle because of centripetal force. The pivot point and string provide the centripetal force required to keep the weight moving in a circle. The sudden loss of this force, say by the breaking of the string, would fling the weight off at a tangent to the circular motion. It is not centipital force that will fling the car off the track, but rather the basic momentum of the vehicle and the sudden loss of centipital force caused by catastrophic traction loss due to a major loss of downforce.

[edit] Confusing tag rational

The opening sentence/paragraph needs to clearly define the cause and result of the ground effect. For someone with almost zero knowledge of aerodynamics, I got lost looking for it in the text - Jack (talk) 00:44, 11 August 2006 (UTC)

That comment needs a confusing tag BonniePrinceCharlie 03:02, 14 December 2006 (UTC)

[edit] Gilles Villeneuve

While the ground effects may have made his car faster than it otherwise would have been, given that his accident was caused more by a tragic misunderstanding about where he was going to pass the slower car, is the mention of his accident really relevant here? Angmering 06:58, 15 August 2006 (UTC)

[edit] From a (Now retired) Pilot

THIS ARTICLE IS RUBBISH !!!! 87.64.195.155 20:41, 27 August 2006 (UTC)

• The whole point of Wikipedia is that anyone can improve articles; so if you think this article is deficient in some way, you can correct it. There's absolutely no point denigrating it without saying why you think it is rubbish, and what bits need to be improved. User:Jaganath 19:58, 02 September 2006 (UTC)

[edit] Common misconception

"while the air which passes over the curved upper surface must move farther and faster to rejoin the air below at the trailing edge of the wing"

This is definitly wrong and a common misconception. There is no physical law that requires the air above to "hurry up" and rejoin with the air under the wing. It is true that the air above the wing moves faster, but it even reaches the trailing edge earlier than the air on the lower side. So there is no rejoining and this argument can't be used to explain lift! (See the article about lift). —The preceding unsigned comment was added by 81.223.147.216 (talk) 20:34, 10 December 2006 (UTC).

[edit] From an amateur power and sailplane pilot

I have edited the article substantially today (21 December 2006). From my understanding ground effect is the beneficial absence of wingtip vortices, due to the ground preventing their formation. This is what I was always taught. It does not have to do with "downwash", which is an effective component of lift, as pointed out above, so I removed that sentence. I hope the article is more accurate now. The bit on penetration approaches might be better suited in its own article, but I though it was worthwhile to include.

--User: dmhaglund, 1150 UTC, 21 December 2006

On further reflection I am still quite unhappy with the article. My understanding was that wingtip vortices tended to be increased with the wing loading and angle of attack of a wing - and that a high-weight, high-lift attitude (as in takeoff or landing of a large aircraft) would produce a high degree of wingtip vortices, and thus a high degree of induced drag (and hence ground effect could substantially affect such aircraft). So, the fighter plane example given in the article seems wrong: if the plane really is landing with high wing loading and high angle of attack, shouldn't it experience the benefit of ground effect to a greater extent than otherwise?

I didn't want to simply delete the "cushion" theories, but they didn't fit with my explanation, so I moved them to the end of the article. These paragraphs mostly describe what ground effect ISN'T, anyway.

--dmhaglund, 1210 UTC, 21 December 2006

[edit] Vortex ring / Ground effect in fixed-wing VTOL aircraft

Hi,

While looking into flight test data on an early fixed-wing VTOL aircraft Short SC.1, I came across a research memorandum which refers to the losses in vertical thrust due to what is referred to there as "ground effect". This seemed fine, since this is how I would have described it, so I added a link to the article ground effect. When I checked it, however, I discovered that this refers to a net gain in lift experienced by some conventional fixed-wing aircraft wing types when flying close to the ground, so I had to remove the link.

There is a potential confusion here, which I would like to sort out.

• Is "vortex ring" specific to rotary wing aircraft?
• Is "vortex ring" perhaps the U.S. term, "ground effect" the British term for the same thing?
• I have also heard the loss of thrust effect described as "recirculation", but this appears to be more commonly used in the context of optimising effects within internal combustion engines.

Here is the reference: Discussion of ground effect w.r.t. the Short SC.1

I would still like to link the SC.1 article to a description of this effect. Is "Vortex ring" the right one? —The preceding unsigned comment was added by TraceyR (talk • contribs) 12:19, 14 January 2007 (UTC).

[edit] Pigeons

I've observed pigeons "hovering" long distances over the ground with no wing-flaps, and often wondered how exactly they were doing that... I guess this must explain it.

[edit] New article for vehicles

I think the section on vehicle ground effect is so completely unrelated to aircraft ground effect that it would be best to create a new article, perhaps "Ground Effect in Vehicles". The two phenomena have no similarity beyond their name.

Also, the opening description of ground effect perpetuates a common myth. Ground effect is not an increase in lift - an increase in lift would cause the aircraft to accelerate upwards. Ground effect is no more than a decrease in induced drag, due to the inhibition of downwash. This means that less power is required to maintain level flight. KiwiBiggles 21:17, 26 January 2007 (UTC)

If the induced drag is reduced, would this not lead to an increase in speed and therefore an increase in lift? It certainly feels like an increase in lift! Just a thought.

No, the lift doesn't increase. Remember, in level flight, steady climb or steady dive, lift is exactly equal to weight. If lift increases, as when you open the throttle and accelerate, the aircraft accelerates upwards until it reaches a steady climb when once again lift is exactly equal to weight. The reason that it feels like an increase in lift is that the aircraft is (presumably) descending steadily and so is balanced to a spcific lift/drag ratio. Upon reaching ground effect the induced drag is markedly reduced, so the lift/ratio increases and thus the descent angle is reduced, often to zero. KiwiBiggles 02:40, 28 January 2007 (UTC)

I agree whole-heartedly with creating a separate article on ground effect in cars. I also think that the aircraft article should cover conventional fixed-wing, rotary wing and VTOL aircraft separately, incorporating (or certainly referencing) the vortex ring / recirculation information; unfortunately I haven't got the background to attempt that change. TraceyR 08:44, 27 January 2007 (UTC)

I have started this process, it'll take me a while to sort out the pages which link to it.Ground Effect is a disambiguation page now. Spute 11:27, 27 January 2007 (UTC)

[edit] Metal Gear Solid Reference

Wasn't there a ground-effect vehicle featured in Metal Gear Solid: Snake Eater? Perhaps an In Fiction category could be added to facilitate this reference. —The preceding unsigned comment was added by Justin Herbert (talk • contribs) 03:20, 31 January 2007 (UTC).

[edit] Whoa, bad article name

I have literally dozens of books on aircraft, flying, pilotage etc. that all say "ground effect". Googling "ground effect aircraft" turns up lots of hits both with an without WIG mentions. I believe this article has been moved to the wrong title, only the moreso because it's been capitalized. I will accept a compromise position of "ground effects in aircraft". Maury 20:46, 2 February 2007 (UTC)

Wholly agree. -Ravedave ^{(Adopt a State)} 22:26, 2 February 2007 (UTC)

Sounds good, especially in the plural TraceyR 23:17, 2 February 2007 (UTC)

Yes, i wouldn't object. It was me that moved the article, i really just wanted to disambiguate the effects in cars, i chose Wing In Ground becuase this was the section title, bold in the intro, etc. "ground effects in aircraft" sounds good to me, but i'll leave it to those who know more about aircraft.Spute 14:19, 4 February 2007 (UTC)

Ok guys, moved successfully (I'll do some link checking). Thanks for the quick replies! Maury 21:53, 5 February 2007 (UTC)

Could you all take a sec or two and check for links? There's a lot of them! Maury 22:04, 5 February 2007 (UTC)

I know, i changed them all last week!Spute 20:07, 6 February 2007 (UTC)

If Ground effect in aircraft is to be the new article name, then it should be bold in the intro - so i've had a go at re-writing it, hope this is suitable. Oh and is it supposed to be "ground effects (plural) in aircraft" , as above? Hope someone doesn't have to change all the links again... Spute 20:07, 6 February 2007 (UTC)

Oh boy, I forgot entirely about the S. I did it this way because it's the same as cars, which also lacks the S. Definitely NOT worth another move! Good edits BTW. Maury 23:43, 6 February 2007 (UTC)

The article is still lacking any real discussion of other ground effects and continues to use the term when "wing in ground" effect is meant. Perhaps defining the abbreviation "WiG effect" and using it in the article where appropriate would remove the confusion (and start a new trend?). TraceyR 23:37, 1 March 2007 (UTC)

[edit] Rotary Wing Stuff

Ok, throwing this out there in the article to see what comes back. I'll try to add some vector diagrams later. Cheers MickycOZ 10:27, 27 February 2007 (UTC)