Yes: round in the front and sharp in the back. In this case, I'm using "front" generally to mean any point where the flow hits the wing, and "back" means any point where the flow leaves the wing. So in planview the wing tip starts out blunt (flow is hitting it head on), and then it goes to sharp (flow is leaving it, rolling out the side). What this does is make the trailing vortex roll up at a point further out than if the wing tip were completely rounded. The result is an increase in the effective span, and this reduces the induced drag when pulling g's, which is most of the time in pylon racing.

Michael

Thanks Michael,
I am now building a Sig Something Extra and will be using this method to modify the wing tips. I wanted to be sure that I had the right idea about the drag reduction methods that worked best.

Michael thanks for answering on my post.
The all red wing tip #3 is the one that I designed using Hoerner and adding concave curve to the tip. Saw a picture of a Reno Mustang # 69 using this method.
The though behind this shape is, air flow is diverted for less educed drag in high speed turns, helps hold a knife edge from pylon one to two and from pylon three back to one, also acts as wash out to help in slow speed landings.
Also thanks for listing my R140 Quickee 500 airfoil on UIUC airfoil data site. I try to read every thing you publish.
Pictures are top front bottom and back of wing tip.

Hoerner wing tips provide the largest effective span for a given geometric span or a given wing weight.

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Randy,
Nice work on your wingtips!
I think your on the right track, at your level of competition even the smallest enhancement will help your overall performance. While I do not know the rules involved in your competition, I enjoy the exchange of ideas regarding aerodynamics, as well as trying to maximize the planes performance.

Except that the above is wrong. Constant chord and 1 3/16" thick for 47 1/2". Yeh, it's a small point, but that extra 1/4" does help when shaping a tip.

Was that printed on the back cover of Hoerner's book? Because I'm not buying it.

Edited for spelling error.

just use the P51 tip - --1/2 the airfoil-- good as any for a low AOA wing.

See Hoerner, Drag, p 7-5, Fig 10. It shows lower drag for sharp tips.

Michael

I agree that the sharp edge helps, but just don't think the spoon shaped Hoerner is the best shape.

You know ... we tested your R140. I did not know who designed it, so it's just called the R140. It's in Vol 1 of our airfoil data:
http://www.ae.uiuc.edu/m-selig/uiuc_...ilsTested.html
Bill Friedlander made the wind tunnel model.

My favorite approach to carving tips is the taper the sharp edge to the camber line of the tip airfoil. There's really no proof that this kind of sharp tip is any better than another type of sharp tip. However, I do think the merits of THE Hoerner tip (drooped down) are iffy relative to any other (I agree w/ what HighPlains wrote above). I've not seen any specific data on Hoerner tips. I had one plane that had interchangeable tips - sharp, round, and squared off. What I found was that the squared off and sharp tips produced more max lift (I could pull tighter). This is pretty consistent w/ what Hoerner shows in his Fig 10 - more max lift. The lower drag part was not something I could confirm by flying feel. So I think your "sort-of" sqaured-off tips are going to behave pretty much like squared-off tips proper and also a sharp edge tip.

Michael

The tip thing ---
on our models -just like a good joke - when you reach the end --end it.
the old P51 tip -just round it off is as good as any except ---the slashed tip--undercut 45 degrees (whatever ) does add effective dihedral - I have proven this one on a scale Dalotel I once used for IMAC competition.
actually more effective than I thought it would be .

Michael,

I have used on quickie designs for a number of years a quarter section of an ellipse (in the plan view) with the major axis the wing’s chord, and the minor axis at 2 ¼” to reach the full 52” span with 47 ½” constant chord. I carve to a zero camber line, with an elliptic cross-section. This provides a good approximation of the airfoil that decreases in chord and percentage thickness. It also is well rounded at the leading edge and sharply tapered at the trailing edge.

Around 1995 one of my quickie designs was measured by radar at 172 mph while flying the long course at about 15 feet altitude. This was on a perfectly calm evening at a contest in Medford Oregon with the radar operated by Fred Burgdorf (of APC Props). At the time, the next fastest quickie was in the low to mid-160’s, while most were slightly under 160. All were powered by Nelson engines, which at the time had an output power of around 2.8 hp. With a prop efficiency around 80 to 85%, my nomograph of power/speed/drag gives me a rough estimate of equivalent flat plate drag area of 10.4 sq. in.

Back then I had concluded that fuselage design was far more important to achieving top speeds and widely ignored in racing circles. This is assuming that the wing is well built with very low amplitude surface waves on the front 30-50% of the wing chord. Since quickie rules preclude the use of wing fillets, airflow separation at the wing/fuselage junction often occurred with traditional fuselage designs where the widest part of the fuselage was somewhat aligned with the maximum thickness of the wing. I found that moving the maximum width point to the trailing edge could add as much as 5 mph to top-end speed. I’ve experimented with several contours of how this fuselage width profile is implemented and believe that some do work better than others.

The original premise of this thread was which tip design was best for 180 mph. While I have heard reports that perhaps one of the newest generation of quickie motors has enough power to achieve this goal, I have not witness it personally. With my 12-year-old Thumper design, it would take 14.6% more power or an output of 3.2 hp. Or a better aircraft design, which is why quickie development is interesting under very restrictive design format.

HighPlains,

What you mention above about the fuselage tweak is a really smart
thing to do. I've seen that same kind of tweak used twice before
(different type of problem, same aero effect), and it works. I never
thought of applying this kind of thing to quickie designs. Now the
"whole world" knows. That should give you more competition!

Michael

I first did the “expanding width” fuselage back around 1993-94, and it just made it too easy. Set the national record in quickie around ’95, and later wrote an article for Model Aviation in the April 1998 in the pylon column. There I described the basic idea, so the cat’s been out of the bag for some time. Along with putting the fuel tank on the CG, and why wingspan is important in racing.

I also did the first high aspect ratio wing in pylon back in 1987, which allowed me to gain 50-60 feet on the short winged airplanes in Formula One on each turn. It was good enough to lap everything on the course. Oddly enough, it took two years for everyone in the States to adapt long wings. The rest of the world got the word when our FAI team went 1,2,3,4 around 1990.