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What are these lower winglets?


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I see these lower 'mini' winglets on older Vari/Longeze.  

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I'm sure there is a long history of discussion about them. Can someone point me where I can read more?

At the moment I have only upper winglet/rudders (Berkut/SQ2000/ERacer style) and wondering about the tradeoffs the between nothing, 'mini'  winglets and full size lower winglets Cozy/Velocity style.  

 

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4 hours ago, lelievre12 said:

I see these lower 'mini' winglets on older Vari/Longeze.  

I'm sure there is a long history of discussion about them. Can someone point me where I can read more?

At the moment I have only upper winglet/rudders (Berkut/SQ2000/ERacer style) and wondering about the tradeoffs the between nothing, 'mini'  winglets and full size lower winglets Cozy/Velocity style.  

 

Those are the first implementation of the original "Whitcomb Winglet" design, invented by Dr. Richard Whitcomb. Look that up. Burt was the first to use Whitcomb's theories on an airplane winglet. The idea was increased efficiency / lower induced drag.

The standard LE/COZY/Velocity/etc. slab winglet is there because it assists in extending the rear CG limit for deep stall protection. They also assist in aileron effectivity at low speeds. Some people remove them because they don't like the aesthetics or believe it will reduce drag (which it will, but not by anything you could measure at our normal cruise speeds). On a Long-EZ, where you don't have to worry much about deep stall because it's relatively easy to keep the CG fwd of the 103" rear limit since there isn't a lot of variation in front seat weight, removing the lower winglets isn't a really big deal (Berkut has the same argument). But in a COZY, where there is a LARGE CG motion with front seat loading and it's easy to get too far aft if you forget to put in enough ballast when flying solo, the lower winglets are more important. Extra margin... On a four seat SQ2000, I'd DEFINITELY have lower winglets, for all the same reasons as the COZYs.

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Marc, thanks for the reply. I hadn't read of Whitcomb but have now.

Winglet-geometry-used-by-Richard-T-Whitcomb-1976.png.51f41fd25c32199b9b4f40f7956f090a.png

Its interesting to note that the 'Typical' winglet sections have outward incidence "i.deg". In Whitcomb's work, this is quite pronounced (7 degree) at the root of the winglet and still 4 degree at the top.  I haven't seen this measure of  either twist or incidence in any canard wings to date, unless I missed something?  Its also interesting to note that the winglet is canted 15 degrees, which again you don't see in canards.

Finally, I see that the lower winglet incidence is set to 11 degrees and 36 degrees cant. This seems a lot but makes sense when you think about trying to 'untwist' the vortex before it happens. 

Your text about full chord lower 'slab' winglets is exactly as I thought. I did read Nat Puffers explanation of them adding "at least 1/2" of aft CG" and I was planning to add them.  It seems  another example of how the early Velocity SE and SQ2000 designs didn't make the leap from 2 seats to 4 seats very well (like Nat did).  

However, despite what Nat did, I'm wondering to what extent the Whitcomb 'mini' lower winglets are as effective as full chord. I haven't yet found any data or flight reports but will keep looking. I wonder if Nat tested them?  It would seem that an 11 degree incidence lower 'Whitcomb' winglet is attempting to be as effective as full slab (and probably will have the same drag!). 

 

 

Edited by lelievre12
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Note that canting the winglet out will result in a nose-down moment when the rudders are deployed together.

Aerocanard (modified) SN:ACPB-0226 (Chapter 8)

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Flight simulator (X-plane) flight model master: X-Aerodynamics

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7 hours ago, lelievre12 said:

... I'm wondering to what extent the Whitcomb 'mini' lower winglets are as effective as full chord.

They're there for different reasons - one for reducing spanwise flow (large lower winglet) the other (small lower winglet) for reducing drag. So, apples and oranges.

7 hours ago, lelievre12 said:

I wonder if Nat tested them?

No - he just copied the large lower winglet that Burt designed for the Long-EZ. The COZY/etc. wings are all identical to the Long-EZ wings, aerodynamically. Only the strakes and spar cap structures are different.

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