Hoerner wing tips

[Mrbill]

I was thinking about adding/building a hoerner wing tip.  Any thoughts about making the straight tip into a hoerner?  Would it increase performance any?

[Dan_]

I was thinking about adding/building a hoerner wing tip.  Any thoughts about making the straight tip into a hoerner?  Would it increase performance any?

I am not encouraging any modifications, but will attach the original Hoerner study and Steve Wittman wing tip article.   I would never extend the wing beyond what Leonard said could be done to the L.E. which was one bay (15") and that was to be added to the inboard end of the wing.  This moves the lift strut attach outboard to counteract the extra leverage a longer span would put on the attach point.  I don't think he has ever said anything about extending the XL.

Hoerner claims a 1 foot per second increase in climb and a 1 or 2 percent increase in range.  (60 ft/min is not insignificant...)

Wittman always said "Hoerner never built anything".  I take that to mean his theory was never verified.

Wittman claimed a 25 percent decrease in sink  (1200 ft/min before his tips and 900 ft/min after) with no decrease in top speed and verified it himself.

Wittman's plane has a 48" chord.

Read it for yourself...

[scottiniowa]

OK-   I got to step in a just a bit,

When did Wittman design a plane that was as slow as the EAGLE,  thus when did a wing tip get tested on something like this (again as slow)  One can read thoughts and theories all day, but unless your “somewhat” comparing apples to apples, it really doesn’t matter what your comparing too.

Kinda like comparing a RV-8 to a X-cub… or the wings for that matter, simply not the same.

Are we (or this thread) asking, about a slow flying wing tip design and what it can do for a STOL type plane, vs a wittman tip on a relative fast flying plane?  

I don’t mean to kick the can over, but taking an idea and then comparing it to two totally different plans, can’t really be used as a answer.  Can it?  I am just asking.  I don’t mind being wrong, as long as I can be shown why and what the right way is.

ok, back to your tuned in radio...

[Dan_]

The information I sent in is about making a wing more efficient no matter how fast or slow it flies. 


Better lift to drag ratio is more efficient. 


Less induced drag is more efficient.  


Wittman did his glide tests to prove better l/d ratio @ 73 mph anyway which is in our wheelhouse.

[okdonn]

Clearly, someone needs to build sets of wings both ways and determine how they work empirically, like Wittman did.

[Tom H]

I did build and install a set of Hoerner tips on LEU Treehugger.  Made them from a core of sandwiched 2" pink builders foam sheet, hot wired to shape, and covered with one layer of FG cloth.  The finish was rough, but we just wanted to see if they would help the climb rate.  We just put them on the ends of the wings.  They were supposed to have a similar effect as having more wingspan, thus more lift, as I recall.  Based on what Dan said above, maybe not a good idea.

Unfortunately, we did not get too many flights with the tips.  One note I found said it lifted off at the 2nd set of tires on the runway (which was apparently an improvement), and had a good climb.  This was in early March 2010, and Treehugger met its demise in early May.  No other notes related to tips, other than to observe that Treehugger failed to climb over the trees at the far side of the runway, but other variables such as wind, temperature etc. probably were significant influences.

I am left with the impression that the tips did not hurt the climb, and maybe helped some.

I've attached some pics to show what they looked like.

On the subject of wing tips, I believe that the flat plates, per plans, that cap the tips may have more drag than a smaller plate that matches the airfoil on the top, but only extends down below the wing profile.  We made that mod on DE Stubby, and I do think that improved top speed, and may have helped the climb, too, and they do look better.  With these airplanes, the result from changes are usually small, and its hard to quantify with all the other variables happening.

Yeah, somebody should make some and do some more thorough testing.

[scottiniowa]

Clearly, someone needs to build sets of wings both ways and determine how they work empirically, like Wittman did.

Yes, that would be my thoughts as well.  If nothing else, the designs applied to  L/D analytical software Which of course also takes a great amount of time.

cheers!