Jim:

I've noticed and have flown C-15x with the exagerated wing tip (folded
down) and I've not really noticed any improvement at low speed (which
is what I think it is for, better handling at low speed for approach).

What I am interested in is increased lift, and better performance (in
terms of fuel usage) which is what the winglets do for the B-747
(something like 30% improvement in fuel economy! if memory serves me
correctly).

So if we could obtain the equivalent above 6000' MSL without wrecking
the approach speed performance, I was wondering if it would be worth
it. Particularly when looking at US$3/gal for 100LL.

In my case, with speed mods for wheel pants, wing tips, rudder and flap
gap seals, I get 1 Gal/hr better than the POH calls for with a fully
run out engine (I've just had it overhauled and don't have current
figures). What that means is, at 70% power, POH calls for 9.3 GPH at
6000' MSL (STD day). I get 8-8.3 GPH and 4-7 Knots better speed and a
lower actual stall speed. This was rather expensive to do (all the STCs
cost more than I would get back even flying 100+ hours/yr -- thankfully
the plane already had them when I bought it). And I do not do aggresive
leaning (I only lean until I start to get an engine drop of any RPM and
then enrich 1.5 turns).

But if a single mod could take advantage of the vortice energy to
recover 30% at cruise, that might make it worth doing. Particularly if
it added to climb rates (which I also see with all the STCs I currently
have).

Regards,
Steve.T
PP ASEL/Instrument