single element rear wing vs multi element rear wing 1

[hpimatrix]

Hi can anyone tell me the difference between a single element rear wing vs a multi element rear wing.

Just want some brief info on the advantages and disadvantages. What happens with drag? Is there an ideal number of elements?

 

[rb1957]

a rear wing is intended to create down force, yes?

consider the aeroforce on the wing as the resultant of the lift and drag forces. so if you orient the aeroforce straight down you have zero drag, yes? note that the aeroforce is dependent on the AoA of the wing which'll change with speed (since the wing is fixed) so in reality ther'll be drag at some speeds (and thrust at others).

a multi-segment wing should generate more aeroforce than a single element. it is tricky to set up, you need the gap between the wings to be just right, the camber, etc need to be carefully designed.

 

[hpimatrix]

So a multi element wing can create the same downforce as a single element with less drag?

 

[rb1957]

i'd say so

 

[patprimmer]

I would have thought if multi element wings had a better down force to drag ratio, then they would make modern aircraft would be bi or tri planes.

The reasons early aircraft had multi element wings was to reduce span due to the limited strength of construction materials.

Gliders are all very wide wingspan narrow section wings for a reason. Same applies to birds that live on the wing like an Albatross. Heck it even applies to sailing boats. A high aspect sail is more efficient and gives a better lift to drag ratio.

Regards
Pat
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[berkshire]

All true,
But you are ignoring the fact that Race cars using multi element foils have end plates that reduce the tip losses.
Think Boxkite.
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

 

[patprimmer]

BE, they certainly do have fences on the end and it is an essential part of their design. Also they are restricted in width by rules, so multi element is the only way to get a longer leading edge without increasing the width of the package.

The idea of a fence on a wing was controversially exploited by the design of the keel on the Aussie yacht, Australia 11 which won the Americas cup of the Americans after being held by them for something like 180 years.

http://en.wikipedia.org/wiki/Australia_II

I believe the advantage of the design was more lift per unit length of the keel. Draft was one of the measurements that was involved in the 12 metre formula, so more lift for depth gave a significant advantage under the 12 metre rule.

Also some model Boeing 747s had an upturned fence on the end of the wing so they could get more lift with a wingspan that still fitted within existing hangars I believe.



Regards
Pat
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[KENAT]

Pat, winglets etc. are more about reducing drag than increasing lift best I recall.

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[GregLocock]

The huge advantage of multi element arrays is that they can operate at very high AoA without stalling, as each airfoil only see the local AoA, not the effective total. As such they can create a lot of lift for a given wing area. They also generate a lot of drag. I'm pretty sure Katz has some graphs of this.

Failing that

http://ntrs.nasa.gov/search.jsp?R=2...tchall&Ntk=All&N=0&Ntt=multiple+element+flaps

and other papers go into more detail than anyone could need.



Cheers

Greg Locock


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[berkshire]

Pat,
I am very familiar with the winged keel design. In 1995 I was fabricating different sized wing cores for the New Zealand team so that they could change the size of the wings on their keel, based on what they thought the weather was doing.

With the multi element wing versus the glider/seagull wing ,you have two opposing ideals. With the glider/ seagull wing you are trying to produce within the limitations of the structure, an infinite wing span to reduce the tip losses and keep induced drag to a minimum thereby improving the lift to drag ratio. The max LD may not be the maximum coefficient of lift the wing can produce, but in a sailplane it does give you the most forward distance for the least loss of height .
The multi element short wing on a race car is striving for max CL( or downforce ) and does not care that much about lift drag ratio so is prepared to accept more drag in order to keep the wheels on the ground.
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

 

[patprimmer]

BE

I am sure F1 would still rather have more down force for the same drag or the same down force for less drag or somewhere in between.



Regards
Pat
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[rb1957]

pat, have you noticed the flaps on airliners, particularly the triple slotted ones on the B747 and B737 ... that's an exmaple of a multi-element wing. a bi-plane is more an example of a multi-wing plane (IMHO).

yes, end-plates are another design element that affect the aeroforce resultant from a wing (as Kenat says, by reducing the tip vortex), but the OP wasn't asking about them.

 

[GregLocock]

Pat -depends on the circuit. Typically they prepare three configurations, Monaco, Monza and a medium speed setup. The change in overall L/D for the car with those setups, is substantial, as is Cl. When I get back to my books I can tell you roughly how much.

Cheers

Greg Locock


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[patprimmer]

Greg

I realise they adjust the wings for different circuits depending on if they want less drag or more down force.

My verbose fuddled comment above meant to say that they still want the best down force to drag ratio they can get while still delivering the required down force.

Regards
Pat
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[GregLocock]

Sure. Roughly speaking the L/D of the body is about 10, the wings are say 4 at the front and 5 at the rear. Then there's the wheels... which give lift and cause a lot of drag. This simple model ignores all the subtleties of the aero, but does 90% of the job.

Cheers

Greg Locock


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[byronagetz]

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