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<< Lancair Builders' Mail List >>
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Eric,
You obviously know your aero but you need to take another look at Bernie's
work over the last few years. He has made major fuel burn improvements with
his blended GII winglet over the factory Gulfstream winglets. As is with
everything in engineering the proper answer to any of this is, " it
depends", on the conditions flown, span loading, flutter margins, structural
margins, etc.... As I stated in my previous post, the cruise lift
coefficients of the Lancair IV are below that which are necessary to make a
winglet very effective for cruise. However, they do have other benefits for
the Lancair IV that make them worth investigating.
I have also done trade studies of simple span extensions with raked tips and
winglets and the only reason for opting for the winglets over the span
increase was to buy back some of the parasite drag that you can not get with
tip extensions alone. You do carry a structural weight penalty but it is
minor and there is sufficient structural and flutter margins in the Lancair
IV wing to allow the change. We did both an FEA and flutter analysis on the
wing with winglets on and winglets off. With the addition of winglets,
Lancair's or AELLC's, the limit flight loads are reduced to 3.8g. Reducing
limit loads is standard procedure for this type of modification.
Obviously if one could start over you would change things in the wing design
and use a different tip. Yes, winglets are band aids just like other after
the fact modifications. Before I quantify the improvements of the new
winglet design I would like to have my numbers backed up by real world
flight data. I am perhaps a bit more skeptical than you concerning academic
experts. I have known many a professor to be proven incorrect after real
world flight data is taken and analyzed. They seem to forget things like
Reynolds number scaling and manufacturing tolerances. I understand your
reservations and would appreciate your patience until I have some initial
flight test data. At that point we could talk in more detail with real
numbers.
Curtis M. Longo
EMail: avi@uia.net
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Please send your photos and drawings to marvkaye@olsusa.com.
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