lml@lancaironline.net Mailing List Archive

Yes Bill, that figure was up to 7 kn lower indicated airspeed with winglets. The test was done on N5SV. It had a set of winglets that had been installed per factory and the builder was very particular about details. We flew the winglets first--and then when we removed thge winglets and added the standard wingtips. We duplicated the cruise powers exactly and at the same altitudes up to 22,000. The average was about a negative five knot indicated airspeed.

Actually what we discovered is that the deck angle increased--causing even more drag . This is due to the fact that the winglets area is introduced at the position of the wing where the greatest washout. If you sight down the leading edge of the wing you can see the twist. And adding the winglets just put more area that is twisted down.

The popular belief that adding winglets will cause the lower deck angle and reduce drag at high altitude is not correct. Just the opposite.

The deck angle the situation was a big surprise --but shouldn't have been.

My son is a program director at Gulfstream and I spoke with one of their winglets engineers one time and he said that I would need a cruise .55 mach to see any appreciable gain from adding winglets.

While we're at it-- the latest greatest winglets are circular in shape and join back on the wing. Anybody familiar with them?

Charlie K.

See me on the web at

www.Lancair-IV.com

From: Bill <n5zq@verizon.net>
To: lml@lancaironline.net
Sent: Thursday, June 4, 2009 12:02:11 PM
Subject: [LML] Re: L360 winglets

Hi Rob,

I seem to recall that Charlie K. gathered data on a IV both with and without winglets. Charlie, was the number 7 knots? That is, 7 knots faster WITHOUT the winglets.

Several knowledgeable folks have responded that winglets are mostly an advantage at very high altitudes, and this is true. I would add that my conversations several years ago with some Boeing engineers indicated that the exact shape and placement of winglets was ultra critical. Probably not something that any of us could design and install in our shop and have any hope of improving performance. Extensive wind tunnel testing would be required to get it right. My wind tunnel (powered by hot air) is out of service. To be successful, the winglets would need to reduce drag by more than the increase in drag that they would necessarily cause by increasing wetted area and weight. Imperfectly done, they have the likely outcome of slowing you down. Keep it simple, leave 'em off.

Rob, do you fly out of YPPH or YPJT?

Bill Harrelson

N5ZQ 320 1,650 hrs

N6ZQ IV under construction

I am building a L360 in Australia, and will soon have to make the decision about what wing tips to use. The kit comes with the standard tips. However, I have seen some Lancairs with winglets, and am wondering whether they are worth the investment in time and money. Has anyone out there in LML land done any research into the benefits of winglets? I am interested particularly in before and after comparisons, both in terms of speed and general handling.

Any info would be greatly appreciated.

Rob Stevens

Perth, Western Australia.