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12-17-2011, 09:46 AM
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Join Date: May 2005
Location: Central Florida - Orlando Area
Posts: 58
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Wing tips
Almost complete with the empenage and dreaming about doing the wings has prompted me to post this question. Has anyone thought about droop wing tips for the -10? Or how about winglets like on the Boeing 737?
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12-17-2011, 10:26 AM
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Join Date: Feb 2007
Location: Mpumalanga, South Africa
Posts: 1,065
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Winglets are not effective on straight wing aeroplanes. Swept wings induce a span-wise flow which creates vortices (and therefore drag) at the tips. The winglets are there to reduce that drag.
Of course, there is always the "cool" factor...... 
__________________
Paul
Mercy Air, White River FAWV
RV-10 ZU-IIZ - "Zeus"
Building Bearhawk Bravo - RV-18 not available
2019 Donation Made
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12-17-2011, 11:44 AM
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Join Date: Sep 2006
Location: Douglas Flat, CA
Posts: 589
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Quote:
Originally Posted by paul330
Winglets are not effective on straight wing aeroplanes. Swept wings induce a span-wise flow which creates vortices (and therefore drag) at the tips. The winglets are there to reduce that drag.
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Well, no. You are correct that winglets wouldn't do much for an RV-type airplane.
However, there is still plenty of spanwise flow on straight-wing airplanes. Think of it as if the higher pressure air under the wing is trying to sneak around the wingtip to get to the lower-pressure area over the wing. As a result, there are substantial wingtip vortices on straight wing aircraft, and even on aircraft with forward swept wings.
Consider that sailplanes often if not usually have winglets, and their wings tend to be about as unswept as wings get. Sailplane winglets improve the lift to drag ratio in certain flight regimes, and in some cases yield improved handling while circling.
Note that a winglet is never as effective at increasing the lift to drag ratio as would a span extension equivalent to the winglet height. However, the winglet does not increase the span (which is good for span-limited situations such as racing classes and facilities constraints), and also adds less root bending moment, which is good if wing stiffness or strength are constraining factors.
Maybe Steve Smith will chip in on this. I know that he has designed several winglet installations, including the set on my sailplane project. Steve also designed the wing profile on your RV-10
Thanks, Bob K.
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Bob Kuykendall
HP-24 kit sailplane
EAA Technical Counselor
Last edited by Bob Kuykendall : 12-17-2011 at 11:46 AM.
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12-17-2011, 11:55 AM
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Join Date: Dec 2009
Location: Bismarck, ND
Posts: 212
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Has anyone tried droopy winglets on RVs?
They used to use them on agricultural aircraft and others as well. I was wondering if anyone had experience with them before and after installation.
It would seem that the droopy winglets would contain the spanwise flow and convert it to lift.
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Larry Buller
RV7A slow build, Tip up, IO360 200hp, Catto 3 blade, Dynon Skyview, arinc 429, ems, SV transponder, Garmin GNS430w, Aera 560, Dynon D6.
FLYING!
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12-17-2011, 12:51 PM
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Join Date: Feb 2010
Location: Vancouver, BC, Canada
Posts: 860
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wing tips
There are lots of wing tip shapes that "contain the flow" or reduce the vortex creating tendency of the higher pressure air underneath the wing and the lower pressure above the wing. One way is to have a sharp edge at the intersection. Mooney tips do this, actually they have two sharp edges, on on the top intersection and one on the bottom intersection. Hoerner tips as used on earlier RVs do this as well as the "sheared" tips on later RVs. The latter, although they have a rounded profile, have a tapered planform that helps "contain the flow".
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Terry Edwards
RV-9A (Fuselage)
2020/2021 VAF Contribution Sent
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12-17-2011, 01:17 PM
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Join Date: Aug 2006
Location: Lake Ridge Aero Park - Durham NC
Posts: 199
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Fashion statement
I have a limited understanding of the aerodynamics, but it's interesting to note how drooped, Hoerner inspired wing tips were in style back in the 70s, along with STOL capabilities in general, but seem to have fell out of favor since. That may suggest that the desired benefits weren't there even if they were attractive at some level.
At least that's what I'm thinking each time I watch a local 'STOL' C172 with drooped tips and a run-out engine depart... standing still it looks dowdy, in flight it looks tired, but that's just me.
Given how well the basic design works it would be a waste to do it without committing to some testing. Like putting together a drooped set and a standard set for comparision tests.
Bill
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12-17-2011, 01:20 PM
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Join Date: Oct 2007
Location: Belvidere, IL
Posts: 169
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Bob pretty much covered everything. The stock raked wingtip isn't too bad and there really isn't much performance to be gained from a winglet on an RV-10. In fact, if the design isn't perfectly optimized, there will likely be a net performance loss.
Performance aside, there are still a couple reasons to consider a winglet: 1) They look cool. 2) They often improve the low-speed aileron authority.
I used to fly an ASW-15b that had been modified with ASW-20 winglets. I didn't notice any measurable performance gain but I generally liked the aileron feel for thermal flights. For ridge running, I always removed them because they likely hurt performance at higher speeds.
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David Shelton, Aerospace Engineer and Soaring Nut.
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12-17-2011, 01:22 PM
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Join Date: Dec 2011
Location: Livermore, CA
Posts: 6,797
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The vortex up and over the wing tip tends to reduce the lift, by increasing the pressure on top, so the plane flies at a higher angle of attack to compensate; so the vortex contributes to induced drag.
You'll notice that sailplanes and 737's tend to operate in regions where induced drag is an important consideration. (Sailplanes near best L/D, 737's at high altitudes and hence relatively low indicated airspeeds).
RV-10's tend to operate at altitudes where parasitic drag is much greater than induced drag. So in principle winglets help, but in practice their design has to be "just right" or else they cause more parasitic drag than the gain from reducing the induced drag.
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12-17-2011, 01:37 PM
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Join Date: Oct 2007
Location: Belvidere, IL
Posts: 169
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Quote:
Originally Posted by MauleDriver
... Hoerner inspired wing tips were in style back in the 70s, along with STOL capabilities in general, but seem to have fell out of favor since. That may suggest that the desired benefits weren't there even if they were attractive at some level.
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To be honest, wingtips, swept tails and other features are often selected for aesthetic reasons. These things fall in and out of style like clothing and car bodies. In the most high performance aircraft (sailplanes, airliners, fighters, record setters), they actually invest in trade studies and testing to optimize the tip. In most other cases, they simply select any reasonable tip that looks sexy.
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David Shelton, Aerospace Engineer and Soaring Nut.
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12-17-2011, 03:45 PM
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Join Date: Aug 2006
Location: Lake Ridge Aero Park - Durham NC
Posts: 199
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Fashion statement
True enough about esthetics... but I haven't seen a low aspect ratio 'hersey bar' wing with sexy looking winglets yet.
Nothing more beautiful or functional than a high performance sailplane though.
Bill "always a glider guider in my heart" Watson
PIK20b, LS6b
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