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HP Aircraft now offering low-drag wingtips

scsmith

Well Known Member
Showing on today's front page is Bob Kuykendall's announcement that HP Aircraft is now offering short wingtips for RV 4,6,7,8 (and will fit Harmon Rockets too). These tips reduce wing wetted area by about 14 sq ft compared to the standard modern Van's tips, and by about 12 sq ft compared to the earlier Hoerner tips. The wing span is reduced 28" compared to Vans standard tips, and 16" compared to the older Hoerner tips.

I'm usually the last person on earth to want to reduce wing span, but to make our RVs faster at low/middle altitudes, it is about the only way to reduce wetted area. These tips have the least wetted area for a smooth shape that minimizes flow separation.

Shown here are the tips on Bob Mills' Rocket 6 at Reno, and trial-fitted to my RV-8.
sport49 small tips 2.jpg

short tips rv8.jpg

You will see that these tips do not have provision for lights. That is in the works and will be available soon.

I did an informal market survey a few months ago that demonstrated a lot of interest. We have now shown that these tips are definitely faster on the Sport course at Reno. There was some discussion that they may not be faster on the Medallion course where the g loading is higher. Well, Skylor Piper, Sport 80 has tips very similar to these that he made and won the Sport Medallion race. Two others have essentially flat cut-off tips and are also running well on the Medallion course - but we hope to give those two an extra 2--3 mph with our tips very soon.

The remaining question is at what altitude does the performance trade-off between wetted area and span cross over so that the standard Vans tips would be better for cruise? My guess has been somewhere around 9,000 ft, but we will soon do the actual testing to answer that question. I will post the results here as soon as I have them.

You can order your set of wingtips from Bob Kuykendall at HP Aircraft, LLC by clicking at this link:
https://hpaircraftblog.wordpress.com/short-wingtips-for-rv-4-through-rv-8/

You can also always click on the small ad along the margin of "Previous Day's News"
 
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I'll throw in a big plug for the HP tips, after our experience in Reno this year. First a little background info...

Steve, Bob and I have worked together on a few projects, including our composite wings (we're getting there!). Both fellas are not only brilliant, but fabricators extraordinaire, and committed to quality...and are totally straight shooters. Can't possibly enumerate all of the things I have learned from them!

We first collaborated on wingtips (taking a short break from the wing project) for an L-39 that I raced in Reno. Those tips provided a solid 7-10 knot increase in on-course speed. HP has delivered a number of pairs of these tips to L-39 racers and operators, and along with extra race speed, they have provided better X-C performance. The build is robust and clean.

This year, in trying to squeeze out a little more speed from my Super Six (while the tapered wing project is still in work), Steve and Bob offered to build these tips that are being advertised now. At Reno, I've previously tested both my stock tips and a pair of 3/4" flat tips (I built those for straight-line SARL X-C racing). I've found the flat tips are faster than stock in low altitude straight and level flight, by about 3-5 knots. However, those same tips on the turning course in Reno, especially given the hi DA (7-8K'), bled speed in the turns, and also lost speed in bumpy conditions (common in Reno).

These new RV tips from HP seemed to provide the best of all worlds in this year's testing and racing experience: increased speed, both straight line and turning, less airspeed bleed in the turns on course than the flat tips, and less loss in the bumps. In fact, my fastest laps this year came on the bumpiest day we raced at Reno (that flight was a workout!). Flying the course with the new HP tips "felt" no different than flying with my stock tips...nice and solid...except I was faster (3+ knots, maybe more).

I flew home to TX with my stock tips, while a friend is transporting my HP tips to my place in her motor home. When I have them, I'll do some X-C testing with them, and get a side-by-side comparison with the stock tips at various altitudes. Interestingly, Skylor Piper told me his small tips outperformed his stock tips on some recent X-Cs (around 9,500' I believe). This supports Steve's comments about these HP tips being a great design for medium altitude performance. The HP tips have a different trailing edge design than Skylor's, which fair back to a point, while HP's tips finish with a slight flat portion that matches the aileron. Both are clean, and the fit and fair to the aileron is quite nice in Steve and Bob's HP design.

In the world of speed mods, where knots are sometimes measured in the thousands of dollars per knot, these tips are a huge value, IMHO.

Thanks to Steve and Bob for the work to deliver them in time for Reno, and good luck in this venture!!

Cheers,
Bob
 
Very cool!

What's the impact on stall, landing, slow flight, etc? I'd expect a penalty of some kind there, but it would be interesting to see the numbers.
 
Very cool!

What's the impact on stall, landing, slow flight, etc? I'd expect a penalty of some kind there, but it would be interesting to see the numbers.

No doubt the stall speed is increased slightly, but it would be very hard to measure, given the (at least on my RV-8) mushy nature of the stall. Also, no doubt the climb rate will suffer slightly. That might be measurable with a time-to-climb test to 10,000 ft. The higher cruise speed would quickly make up for that, even on fairly short missions.
 
stall speed

There have been quite a few people with questions about the change in stall speed. Comparing the short tips to the Hoerner tips, the change in wing area is 6%, so the change in stall speed will be 3%. For a 55 kt stall speed, it would increase to 56.6 kts.

You would never notice.
 
It is less wing area, less drag. Is a flat plate wing tip better? I don't know. Anyone do a before and after.
 
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Very cool!

What's the impact on stall, landing, slow flight, etc? I'd expect a penalty of some kind there, but it would be interesting to see the numbers.

There have been quite a few people with questions about the change in stall speed. Comparing the short tips to the Hoerner tips, the change in wing area is 6%, so the change in stall speed will be 3%. For a 55 kt stall speed, it would increase to 56.6 kts.

You would never notice.

******************

Steve, your calcs, as usual, are spot on. I did stall testing on the flat tips that I built several years ago for SARL X-C racing. The tests back then showed top-end speed gain was 3-ish knots, while stall speed went up 2 knots (by my measurements...52-54 knots clean, 57-59 knots full flaps...before and after numbers). Will do more tests on all three tips.

******************

It is less wing area, less drag. Is a flat plate wing tip better? I don't know. Anyone do a before and after.

******************

George,

Lots of discussion on this topic at Reno this year. Dave Anders feels a basic flat plate, with fences near the trailing edge (in the aileron area), will prove to be fastest. Steve feels the HP design is fastest.

I have data (some numbers from flight test, some numbers from racing), and some gut feel/how it flew "pseudo-data".

I flew both the full tips and the flat tips during PRS, and flew the full tips and HP tips during NCAR (the races). Comparative analysis is complicated by conditions in Reno. Cool, calm mornings fly very differently than hot, windy afternoons. Therefore true apples to apples comparisons are sometimes difficult.

Caveats out of the way ;), during PRS I felt the flat tips were a draw with the full tips on the race course. With mostly windy/bumpy conditions, speeds were slower than average on both tips (240's with no nitrous, no tape, and perhaps leaving 100 RPM on the table). The flat tips seemed to bleed a bit more in turns and bumps. Flat tips accelerated well in the chute, but once on the course, I could feel (and see) the speed loss in the turns, especially at Sport 4-5. I was really focusing on turning technique, and working to not bleed in the turns, but the bleed rate was obvious. Flat tips were fast on the straights though. The tradeoffs between these two tips seemed to balance.

During NCAR, the HP tips felt similar to the full tips in and out of the turns. I didn't feel that I had to alter my technique to prevent airspeed bleed. Interestingly, on Saturday, with wind gusting to 28 (and during what I would call one of my bumpiest, most physical races ever) with the HP tips I ran my fastest lap of the week, at 267 mph, with speeds in The Valley of Speed hitting 280. I was honestly shocked by the lap speeds Steve clocked for us that day. The HP tips handled the bumps and turns well.

Now granted, we were pushing an additional 50HP of N2O into my Lycon IO-540 and Whirlwind 330-3B/73 combo, something we felt would help us maximize the benefit of the HP tips. Our premise was the faster we could go, the less bleed rate issues we'd encounter. G on the larger Sport Course is lower than on the smaller Medallion Course, which was a benefit as well. Skylor does well on the Medallion Course with his tips, but it would be very interesting to see he and Chris swap tips back and forth and race each other for comparison testing. Skylor's N20 and Chris's IO-540 made for some fun racing, as shown in another thread!

So how does this translate to everyday performance on these tips? I'll run some more testing (Hi speed, low speed, cruising speed, etc), and see how all three tips compare. Steve will too (full tips vs HP tips), and his testing may be the most valid data with respect to performance expectations for the RV fleet. A flat plate with fences may be in my future too...to give Dave's theory a test.

All this is to support the great work by Steve and Bob, and hopefully get some happy HP Aircraft customers flying some cool low-drag tips! Here's a couple photos from today of the 3 tips (all my X's don't live in Texas, but all my wingtips now do! :p).

I know there is a lot of interest in these tips, and lighting is a universal request. Spoiler alert is that Steve took splashes off his set of HP tips while we were working on our new tapered wings this past week, and Bob is working that lighting issue. Pic 4 is a quick sneak peek of the tapered wing with freshly sealed fuel tanks...while wearing our "HP aircraft uniform". (Apologies...sort of...for the various sponsor promotional sneaks into this post!) :D

Cheers,
Bob

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A0tQxjBge6y-7P3O3rWQnLsHpaPvaaUe5cyinNyvkYETKIJPSA3UXQQNsPAun_qXA0TaFmfQ0piUPmvfLg=w642-h440


mt_k320G7ax08sR4nEc4HLg5R5r_wOK7zIdYWzwdFmBAn1_iAlHDnKjQfOcJwjPL-gXysR1YX685dWVBWg=w650-h440


lm6T3XKkfqF3HSlbWEnHS7g0eKyyLtvRxs_QeiMGe9J9FJ-uIaMXTC7MU6wN2ZTGHSxIuVYQDrQ-fCuedw=w586-h440
 
******************
George,

Lots of discussion on this topic at Reno this year. Dave Anders feels a basic flat plate, with fences near the trailing edge (in the aileron area), will prove to be fastest. Steve feels the HP design is fastest.

I have data (some numbers from flight test, some numbers from racing), and some gut feel/how it flew "pseudo-data".

SNIP Excellent post and info - See above

Cheers,
Bob
Thanks Bob.... this shows how hard it is to quantify changes in speed changes for one modification on an already fast plane. Even 1 kt. or two is hard to measure and may very over different flight conditions. Faster you go, drag increases to 2nd power. You really have to make big changes in drag reduction or HP to see obvious differences. However every little micro knot counts. Ha ha.
 
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Lights!

I know a lot of you have asked for these wingtips with provisions for lights, so we're hard at work on it.

Here is a photo of the first set of tips with the light enclosure. One of them has a fiberglass mockup of the clear plastic lens that is included with the tips. The enclosure is large enough for many common position/strobe light combos, and I have asked my friends at FlyLEDs to develop an LED installation specifically for these tips.

20211114_061029-1.jpg


Here's a pic of the fixture I'm working on to vacuum-form the clear plastic lenses in pairs.

20211114_110043-1.jpg
 
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Thanks, I was unaware Bob had clipped the wings but should have realized that as he calls it a Rocket 6 not a Super 6. I look forward to hearing his cross country results!
 
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