single element rear wing vs multi element rear wing

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hpi_matrix
0
Joined: 27 Aug 2012, 22:33

single element rear wing vs multi element rear wing

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Hi all

Just want some brief info on the advantages and disadvantages of replacing a single element rear wing with a multi element wing?

Thanks

stez90
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Joined: 10 Jul 2012, 23:31

Re: single element rear wing vs multi element rear wing

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The slots between the elements help the flow stay attached, allowing more aggressive angle of attack and design than a single-element wing. So they can obtain more downforce.

hpi_matrix
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Joined: 27 Aug 2012, 22:33

Re: single element rear wing vs multi element rear wing

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Can anyone add more to this? What happens with drag? Is there an ideal number of elements?

PNSD
3
Joined: 03 Apr 2006, 18:10

Re: single element rear wing vs multi element rear wing

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The slot gaps basically change the effective angle of attack as well adding energy to the BL.

hpi_matrix
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Joined: 27 Aug 2012, 22:33

Re: single element rear wing vs multi element rear wing

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So would there be an increase in drag?

hardingfv32
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Joined: 03 Apr 2011, 19:42

Re: single element rear wing vs multi element rear wing

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hpi_matrix wrote:Can anyone add more to this? What happens with drag? Is there an ideal number of elements?
Not sure what to say about net drag gain.

The most elements I have seen are on SCCA solo/autocross A-Mod cars, four elements. Serious A/A low speed wings...

http://www.tunersgroup.com/Products/wings.html

Brian

Just_a_fan
591
Joined: 31 Jan 2010, 20:37

Re: single element rear wing vs multi element rear wing

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hpi_matrix wrote:So would there be an increase in drag?
Yes. Generally, adding elements adds downforce but also adds drag. Whether it gives an increased or reduced L/D is a different question though.
If you are more fortunate than others, build a larger table not a taller fence.

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andylaurence
123
Joined: 19 Jul 2011, 15:35
Contact:

Re: single element rear wing vs multi element rear wing

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I'd be interested to see data on whether the L/D ratio improves. I've added a second element to my rear wing, but whilst I'm sure it improves downforce, I don't know how much I've added to the drag.

Greg Locock
230
Joined: 30 Jun 2012, 00:48

Re: single element rear wing vs multi element rear wing

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If multiple elements added lift without increasing L/D then gliders would use them all the time. They don't. There's a hundred papers out there on performance of multi element wings, including a whole book by Katz which ANYBODY who pretends to be discussing racecar aerodynamics should own, read and understand.

n_anirudh
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Joined: 25 Jul 2008, 02:43

Re: single element rear wing vs multi element rear wing

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Of course, depending on the aspect ratio of the wing, there would definitely be an increase in the overall drag due to higher induced drag.

Gliders have high aspect ratio, where the main purpose is increased flying time or range, rather than increased lift for a particular combinnation.

NoDivergence
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Joined: 02 Feb 2011, 01:52

Re: single element rear wing vs multi element rear wing

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Correct answer, aspect ratio is the all important factor for a glider. L/D for aircraft is typically extremely high, nevertheless. There are also significant structural/weight implications to running a glider with such long multi element wings that also affect it's glide path performance. A glider isn't lifting huge loads, it has no need for so much lift, it only really needs to decrease drag once the lift generated gets close to the weight. On another note, multi element wings are WIDELY used in aircraft design competitions for carrying loads (bricks, weights, whatever). There, range is not so much the issue

Robbobnob
33
Joined: 21 May 2010, 04:03
Location: Auckland, New Zealand

Re: single element rear wing vs multi element rear wing

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As it has been stated with the glider case, the ideal number of elements / the require Cl and L/D ratio and the Aspect ratio all depend on the given implementation.

For cars the L/D ratio changes with respect to the track design. Monaco with its short straights and low grip puts a premium on downforce to enable the power transmission to the road, therefore a wing with a high angle of attack, more camber and consequently higher CL is chosen and drag is negligible as they are not power limited but traction limited.
For Spa, the balance of downforce to drag is changed. As the straights are very long and the speeds extremely high, a reduction in drag will result in a higher top speed for a given power output from the engine, so the angle of attack and camber of the wing is reduced to provide a more efficient wing section in terms of Lift to drag ratio. Downforce is still important for the 2nd and 3rd sectors, but there is a greater drag penalty.

Therefore in motorsports where the usage of wings is to provide better contact with the track surface more drag is acceptable if it allows more power to be converted into speed and it is that crossover point to which Adrian Newey will optimise his car for at every race track.
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Tommy Cookers
616
Joined: 17 Feb 2012, 16:55

Re: single element rear wing vs multi element rear wing

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wings work by having camber and angle of attack, beyond some limit of either/both they stop working (well)

a single element has lower limits than the 2 element (aka slotted flap)

within those limits the single element will work better than the 2 (thats what defines the limits)

beyond those (single element) limits the 2 element will work better (thats what they are for, the slot flow does this)

car designers don't choose the wing span, but choose the wing type according to the downforce benefit relative to cost in drag
(a low powered car can be served better by a single element, others not)

unless they want to vary the (otherwise natural) flow in a race, eg by changing the slot/gap flow

the aviator varies the wing type, area, camber and/or AoA throughout flight, but flight is basically single element
(2nd etc elements (flaps) are always retracted for most of the flight, 99.9% of planes use natural slot flow only)

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siskue2005
70
Joined: 11 May 2007, 21:50

Re: single element rear wing vs multi element rear wing

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Wont adding more elements decrease the cross section of the aero device and in effect reduce the darg relative to one big element? isnt that basic aero law? smaller cross section decreased drag?

Tommy Cookers
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Joined: 17 Feb 2012, 16:55

Re: single element rear wing vs multi element rear wing

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I don't think that applies if the wings are set (in camber and AoA) to give useful (and equal) DF ?

usually any post of mine on aero attracts many other posts that disagree with mine (and each other), but not this time ?