Rear Wing Aero Winglets Discussion

[euro911sc]

After reading Jack Olsen's research on his rear wings ( Poor Man's Aerodynamics Thread ) I was reminded of something I had read long ago in my aero book:


Source: McCormick, Aerodynamics, Aeronautics, And Flight Mechanics. Wiley, 1979. ISBN: 0-471-03032-5

The following pages of the section I chose to leave off since they delve into formulary and math Wouldn't want you all sleeping!

After reviewing several wings while watching the 24 hours of Daytona, none of the wing ends looked like the pic above... They were all flat plates. The wings are all straight accross vs. swept as well so that is also interesting to me as an arm chair aero enthusiast. It seems this would be well suited to wings with no aspect ratios...

I know lots of things have changed since 1979, but I still see lots of current aircraft with winglets like this so it cant be that this information is out of date.

Why do you all think, if winglets can reduce drag, more teams are not using them (or similar thing) on the ends of their wings?

Caveat: If race rules deny their use well... there's my answer.

Best regards,

Michael

[Jack Olsen]

That's interesting. I would guess that rules are the biggest reason that simple end caps are used. Height restrictions explain why end caps rarely go much higher than the highest point on the wing.

Also, end caps in racing are probably valued more for their ability to (effectively) lengthen the airfoil than they are for their ability to reduce drag. Drag isn't as big an issue in racing, given the power to weight ratios of Formula 1 cars.

Flipping this for an automotive application, you'd have a small plate up above the wing, on the leading edge, and a larger plate below, favoring the trailing edge of the wing. It's be easy to duplicate those angles and shapes with flat aluminum. I might try it.

[chancecasey]

I think the better question is how would you detect such a relatively small decrease in drag without exotic tools like a wind tunnel - e.g. - at the track?

[euro911sc]

I'm pretty much assuming that it would only be important for tracks with long high speed section (Daytona and that unknown French race... what was it??).

It probably is not that practical to measure in application, but may be interesting. I guess if you are faster at the end of the straight or get a higher top speed its working

-Michael

[Mahler9th]

I haven't studied the topic in great detail, but it is pretty clear to me that rules dictate what most folks do. You can usually find current rules on line with a given sanctioning body.

At more grassroots levels, there are sometimes more degrees of freedom, but it is difficult to experiment in any meaningful way without spending a lot of money. A lot.

What I like to do is ask some of my very experienced friends about things that have been tried in the past that may be effective , but are not illegal for the type of racing I do. I have a lot of ideas, but even in aggregate they won't add to a second a lap.

[Jack Olsen]

I think that describes it well. Since meaningful research is expensive, and since rules often run (deliberately) in the face of big leaps forward in efficiency (and spending), I think there's a kind of 'natural selection' that takes place in club racing -- you emulate the guys who are doing well within your same rule book, and borrow ideas both from them and also from guys who are making jumps forward in other series, so long as their improvements don't go against the rules of your own group. Everyone moves forward slowly, mostly copying the winners.

In my poor man's aero thread, I was able to do a tiny bit of research for a small amount of money (and a lot of time). But Willow Springs is my home track, so aero research makes sense for me. There are very few other club tracks where aero has as much of an impact as at Willow, where the difference between no aero and a big wing and splitter combo can easily be 1-1.5 seconds per lap. I don't think even half of that gain would be felt at any other track in the state, and maybe then only at Thunderhill (where it would help in 1, 2, 6 and 8).

Since wings are often limited to a set width as well as height, end caps that project out at an angle like these would probably mean sacrificing some surface area of the wing in exchange for the improvement in drag. I suspect the trade-off wouldn't be worth it in terms of overall effectiveness of the aero package. Fortunately for me, I race with ARC, where there are no rules governing aero.

At Willow Springs, the difference in drag between running with my big wing and splitter versus running with no aero is barely noticeable. I doubt anything as subtle as an endcap change would produce a measurable difference in lap times. However, my current end caps look kind of lame. This new type might produce a small improvement in drag, but -- maybe just as important -- might also look better.

[euro911sc]

I agree with you guys on the amount of effect they might have. Also on the rules preventing meaning full movement forward.

Still, if you could get .1 s out of it per lap I'd be impressed Measurement at that level would be virtually impossible. But, if you are running a 20 lap sprint... that's 2 s at the end of the race For enduros even better

Of course, for me, just driving on the track will improve my lap times because I suck But for you more experienced and skill full types, might be an interesting experiment...

best regards,

Michael

[Rough_Rider]

End plates in auto racing circles are kept flat for two reasons.

1, its an extremly efficient vortex generator. If you view a wing aero study you'll notice two large vortex's on the inner plane.
Note: view a modern WRC car's rear wing they've multiple vortex generator's.
As someone else said on a race car your not trying to minimise drag, more generate negative lift without trading off your top speed.

2, any endplate that juts out to the side limits the wing's span. & remember the spanned area is strictly limited.

[cstreit]

If I had the track time and tires, I'd love to pop the end-plates off my wing and see if i noticed the difference.

[chrisp]

do they offer any lateral stability? Meaning, do they keep they car from sliding sideways?

[Joe Ricard]

The 200 sq. inch side plates seem to give my car a much different feel. sort of what I would expect a rudder on an airplane would feel.

we did a test and tune this weekend and one of the elements was a skid pad. Significantly easier to control the rear end as it began to slip.

[Jack Olsen]

When drag is not a big concern, the benefits of larger end plates (anywhere except ahead of the wing) have been proven. The optimal size would look very strange, to our eyes. Height restrictions are the reason we don't see them that way. But it's no surprise that they go from the wing all the way down to the bodywork of many prototypes.

[JasonDTM]

http://www.mulsannescorner.com/wingendplates.html

Should be a good read. Its a bit more biased towards Deep Endplates found on LMP Proto-types.

[URY914]

End plates also keep the air on the wing. Without them air would "spill" off the sides.

This forum has the most info I can find in one place...

http://p081.ezboard.com/Aerodynamics/fdsrforumfrm20?page=4

Here is an end plate thread...

http://p081.ezboard.com/Wing-Endplate-Depth/fdsrforumfrm20.showMessage?topicID=81.topic

[euro911sc]

Joe: Interesting skid pad results!

Great links guys! If I read it right, for a 15cm deep endplate you can increase your theoretical wing length by 17.2%. If you used a design like the one in the book scan, you would end up loosing ~.27 * Cord off of each end to keep the width with in the length limit (assuming your wing was at the limit already).

so... is that more or less then the 17.2% length increase benefit? I do not know...

Height losses not included. I'm assuming on that one, the winglet would be reversed, long tip on the bottom as we want to go down and wings want to go up

Interesting.

best regards,

Michael