Talk:Ground effect (aerodynamics)

Untitled

Hey I was wondering if someone could put in some calculations or graphs (so that a regression can be done to find calculations) Thanks!

Orbital Class Rocket remains in Ground Effect for about 10 seconds.

On August 28, Astra Space attempted to launch a test load to orbit. One of five engines immediately failed reducing its unassisted lift-to-weight ratio below 1.00 for about 10 seconds before it burned off enough fuel to begin its ascent.

It is described in this YouTube video:

What is not mentioned in this video is how this rocket managed to avoid colliding with the ground for that first 10 seconds. Unless you suspect that the engine was throttled to keep it in that low hover, it's ground effect. And given the spectacular performance of the guidance system, it's safe to assume that it was not hovering by design.

This article should be updated to include this. There are several ways of describing ground effect. The one chosen in this article is "reduced drag". For this rocket, the "assisted lift" explanation would be a better fit.

Scott Bowden (talk) 03:20, 30 August 2021 (UTC)

References

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)

I would really like to see Bernoulis principal removed from here. It's really incorrect, as any Aerospace person can tell you. The basic theory of lift boils down to F=MA. A wing displaces air downwards, this creates an equal and opposite reaction, creating lift. In short, if a plane weighs 800 pounds, the wing must displace 800 pounds of air (+ drag losses etc) to maintain level flight. To climb, it must create more than that. This high and low pressure business is really confusing to laymen. Since the flow is more efficient in ground effect, the wing displaces more air with less speed. This is sensible. —Preceding unsigned comment added by 130.13.155.62 (talk) 06:20, 2 November 2007 (UTC)

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)

I'm no specialist and only dream of flying (have all my life) but there is a slight contradiciton the way this is phrased:

"The effect increases as the wing descends closer to the ground, with the most significant effects occurring at a height of one half the wingspan length above the ground."

"Up to about the height of one half the wingspan length above the ground the effect increases as the wing descends closer to the ground, but then diminishes."

I don't know if the proportion is correct or not but the way it's phrased it's contradictory.

I would like to know the correct proportions though. I stumbled on this entry because of the Spruce Goose. It only got as high as 70 feet and its wingspan is 319 feet 11 inches.

Does this mean that the above figures are incorrect?

Gatorinvancouver 23:31, 15 November 2007 (UTC)

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.

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)

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)

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)

I updated the Principle of ground effect section because the old one was almost dangerous, yes, rubbish but Jaganath is correct; anyone can improve articles. (Without waiting 5 years for it to happen.)V7-sport (talk) 05:38, 30 June 2011 (UTC)

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).

As a physicist I agree with the above statement. This is NOT how lift works. This can easily be proven by generating an airfoil which has a top surface of equal length as the lower surface (effectively a curve with zero thickness). Lift is generated through the process of vortex shedding (See boundary layer theory). — Preceding unsigned comment added by 71.23.205.127 (talk) 02:00, 17 November 2012 (UTC)

Agreed that Bernoulli isn't the primary cause of lift, but the current edit on this is badly done. The author needs to look up how to cite a reference, and either generalize the statement by removing "deflection", or include all 3 contributions to a wing's lift, IMHO. I don't want to revert it because it's SLIGHTLY more accurate, but still not correct nor well-formed. --Sam (talk) 00:20, 27 June 2016 (UTC)

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

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).

Hi I checked out the Shorts SC1 reference and think that the ground effect in relation to jet eflux for virtical takeoff is not the same as ground effect in relation to the close proximity of the ground during light aircraft landing. Not having the wherewithall to conduct my own experiments I have to research other people's work and there is, even after 100 years of aviation history, still controversy over how lift is produced. I am studying aerodynamics. A vortex ring is not specific to rotary wing aircraft. A rotor blade should be considerd the same as a fixed wing in most respects. Ground effect is a universal term, though sometimes misused, which I guesss is the case with the Shorts Paper. Of all the sciences I guess aviation is the least likely to have idiosyncracies between countries in terms of how things are described, especially between the UK and US.Percussim (talk) 09:44, 22 September 2009 (UTC)

SC1 and vortex ring are more similar to the helicopter ground effects, not the WIG / ekranoplan effects. One of the older Harrier history books has some good coverage on this (there's a tendency for a Pegasus to ingest its jet efflux, which limits hover time before overheating) Andy Dingley (talk) 09:55, 22 September 2009 (UTC)

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. (Unsigned comment)

REPLY: You'll note that the "ground effect" occurs mostly within the wingspan of the flying object. Thus, a pigeon hovering "a long distance" above the ground is unlikely to be experiencing ground effect. I suggest what you are seeing is them taking advantage of the wind, which increases in energy as you gain altitude (ever been on top of a good sized building?). While a pigeon, or hawk, or albatross may appear to be hovering relative to the ground, because of the wind, it is the same as if they were flying at a fixed speed through the air, thus lift is generated without need for flapping wings to generate forward velocity. Make sense? Gliders can "hover" the same way in a high enough wind; indeed, if it is very strong, both gliders and birds can appear to be flying BACKWARDS in relation to the ground. This is the important distinction in aeronautics between airspeed and speed over ground. They are rarely the same thing..45Colt 01:47, 18 August 2014 (UTC)

I think you misunderstood his wording: he said "'hovering' long distances over the ground", not "'hovering' at a long distance above the ground". In other words, he was watching pigeons "float" just above the ground, covering a long distance before finally touching down. This would count as ground effect at work. --Colin Douglas Howell (talk) 09:52, 25 January 2019 (UTC)

I've observed hawks (c. 3lbs.) carrying prey of c. 1.5 lbs, flying 3-5 ft. off the ground for 1-200 ft. until close (20 ft?) to a perchable tree, at which point they climb and slow down to perching speed (~ 0 mph!). Are they taking advantage of ground effects in choosing this flight profile? DCDuring (talk) 00:26, 5 October 2022 (UTC)

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)

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).

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)

Not Really related but I don't know how to post my own separate complaint, I think the tone of the article is a little strange. Specifically, how the explanation of the physics at work is broken up into a "basic", "intermediate", and "advanced" section. I've never seen that on a wikipedia page, and it looks sort of silly. —Preceding unsigned comment added by 72.187.35.82 (talk) 21:55, 31 December 2008 (UTC)

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)

Wing In Ground

I gather at one point the article was entitled "Wing In Ground Effect", and there was some complaint over this. I don't see why this should have entailed removing any use of the term from the article at all. Shouldn't it mention somewhere that ground effects are "also known as the 'wing in ground effect' due to its relation to the wingspan of the aircraft"? I know there are certain articles that link to this page with the term "wing in ground effect", because I recall clicking it out of curiosity once upon a time..45Colt 01:53, 18 August 2014 (UTC)

Just fixed or also rotary wings?

The article begins “In fixed-wing aircraft...”, but it later talks about helicopters' rotors and has even an animation involving a helicopter. Which is the best way to fix this? Goochelaar (talk) 18:29, 27 December 2015 (UTC)

They're really two quite different effects (a third if we include VTOL aircraft like the Harrier). These could be separate articles. They certainly need clearly separate sections. Andy Dingley (talk) 20:08, 27 December 2015 (UTC)

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Ground effect in small-scale gliding objects

I have sometimes seen a sheet of paper fall off a table, approach the ground at an angle then level out and skim horizontally for what can be a surprising distance, apparently supported by a narrow cushion of air. Would this meet the definition of ground effect? Beorhtwulf (talk) 11:53, 1 January 2020 (UTC)

Good question. My view is that the observation you describe can reasonably be called ground effect, but it isn’t ground effect (aerodynamics) as described in this article. This article is talking about the beneficial reduction in lift-induced drag when a 3-dimensional airfoil is generating lift in proximity to a broad ground or water surface. A sheet of paper will fall slowly to the ground but that isn’t because it is generating aerodynamic lift; it is mostly because it is experiencing drag that is almost equal to its weight. Dolphin (t) 13:30, 1 January 2020 (UTC)

Thanks, that's a helpful reply. I wondered whether this more generalised ground effect could be incorporated into Wikipedia in some way that didn't confuse this article or any others (I note we have a separate article on ground effect (cars) that's about increased force towards the ground). Can a falling sheet of paper, which twists into different shapes as it falls, not be considered an airfoil at least transiently? Our article on aerodynamic lift has provisos about even flat surfaces producing lift, i.e. not needing to have the flat-underside-convex-top typical wing cross-section.

What I am unsure about is whether what I see with paper falling and then 'hovering' close to the ground is a result simply of it levelling out and therefore having a reduced vertical speed, which gives plenty of time for horizontal motion as it slowly loses its last bit of altitude, such that the same could conceivably be observed if the paper lay horizontal as it approached an arbitrary altitude well above the ground, OR whether there is something specifically helpful in reducing its vertical speed that applies close to the ground. The way I imagine it, the cushion of air under the paper that is a few mm thick but many times wider, could be compressed by the paper on top of it, as it takes time to escape from under the sides. This compression would result in higher pressure under the sheet and hold it up against gravity for a little while. But no such compression would occur well above the ground, as up there is a large volume under the sheet for air to move into. Hence this being a kind of ground effect in which the paper gets additional lift at altitudes <2cm or so.

This is a ramble rather than a clear question or suggestion for an edit, but it seems to me that these are somewhat overlapping topics which are a little tricky to understand, at least for me, so I wanted to ask about the concept here in case it came in useful for article improvement. Beorhtwulf (talk) 14:38, 1 January 2020 (UTC)

@Beorhtwulf: You are right that a body doesn't need the flat-underside-convex-top to experience lift; and even a flat plate will experience lift. However, the conventional definition of two-dimensional airfoil shapes, and three-dimensional airfoils, includes the consideration that airfoils have a high lift-to-drag ratio and adequate thickness that makes them suitable for use as wings, propellers, turbine blades etc. Pieces of paper and flat plates in general can experience lift but they are not suitable for use in practical applications that demand a very high lift-to-drag ratio, so they are not considered to be airfoils. This is why flat plates have never been used as wings on practical airplanes.

There is another consideration that might explain why your example of the piece of paper is not attractive for inclusion in this article. Most of what is written about lift and drag is related to steady flow of the fluid past the airfoil. The opposite of steady flow is unsteady flow and it is more complex, less well understood and less useful than steady flow. The phenomenon you have described, involving a piece of paper or similar, fluttering downwards and changing shape as it goes, before reacting to the approach of a solid surface is definitely unsteady flow. Dolphin (t) 13:40, 6 January 2020 (UTC)