brianwallis

brianwallis

VAF moderator
I saw winglets on N357DL on photos of the Vans BBQ... anybody have details?!!!! It's registered to a Leigh Daniel 2007 rv-6.
Best
Brian
 
Antennas

He said he added them because they looked cool and he hid two of his eight antennas in them. He said that he had no idea about performance effects and he generally seemed uninterested in effects. He had also added a spine, with vent, to the vertical stab from a kit for Moonies. Definately the most innovative mods that I saw Saturday.

http://img113.imageshack.us/img113/3679/img3044ql6.jpg

http://img515.imageshack.us/img515/8660/img3046nt2.jpg

http://img515.imageshack.us/img515/4024/img3070es9.jpg

Kerry Stevens
 
I've heard that winglets are only effective at decreasing drag above 350-400 kts. Anything below that and your just adding drag.

Karl
 
ok

well then... lets get a bigger engine!!! 350kts here we come!
If anybody knows what he cruises at... and his config... that would be great... I'd love to see a flight and then a second w stock tips...
"sometimes you just gotta feed a little speed to your ride"
Best
Brian
ps.. thanks for the great pics!
 
If you've noticed, the new jets from Boeing no longer use these little up-turned winglets. Now they are adding long, tapered, wing extensions. The slashed tips, on the RV shown in the picture, have an Oswald efficiency factor of about 0.82 which is really hard to improve on. However, if you use your RV on lots of trips at high density altitudes, you may consider putting on crescent-shaped wing extensions, something like the NXT wing, to reduce your induced drag by increasing the aspect ratio. They, too, have a very high OEF and will increase your TAS and lower your stall speed.
 
Sailplanes

RV8N said:
I've heard that winglets are only effective at decreasing drag above 350-400 kts. Anything below that and your just adding drag.

Karl
Click to expand...

If that is true then why do some of the most efficient and competitive sailplanes have them?

There are many good reasons for winglets but I'm not sure RV's have best wing planform for them.
 
RV8N said:
I've heard that winglets are only effective at decreasing drag above 350-400 kts. Anything below that and your just adding drag.

Karl
Click to expand...

Not true. Winglets materially improve the takeoff performance of Boeings. Also, an airliner indicates about 250 kts at cruise altitudes, so this theory doesn't really fly. 400 kts KIAS would be supersonic.
 
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Heavy clean and slow

It is my understanding that vorticies are the worst (biggest diameter) when an aircraft is heavy clean and slow.. so I'm thinking that they may do wonders for takeoff and ldg... dunno.. besides... looking fast is some of the battle (sex appeal) .... right? Anybody else want to chime in on aerodynamics? I'm sure somebody could cash in big time if they put out a complete mod fiberglass kit for rv's... Should we hire the Team Nemisis guys from Skunkworks? I love the Sam James work... maybe there is something faster out there fairing wise.. ps.. LOVE that strake to the tail... does it have any other bennies than just more rudder area?
Best
Brian
 
Ag airplanes too

Brian,
They're made for Cessna Agwagons/Trucks and Air Tractors as well. The vortices are tighter and a smaller "cone" if you will, as results from actual spray entrapment in the vortices show. In our case, we're interested in less chemical drift as a result of sheared droplets becoming much smaller and more prone to drift.

The downside is reduced wing life. Leland Snow, owner and designer of the Air Tractor series of ag airplanes warned buyers of the winglets to subtract 40% off the spar life if the winglets are installed on any of his airplanes. So my 8000 hour wings become 4800 hour wings :eek: He claims a lot of torsional twist to the wings as a result of the arm the winglets have. BTW, I just replaced my wings last December with 7900 hours on them with a "used" pair that had 3500 hours on them. That's because a new set go for $38,000!!

No winglets here.

Pierre
 
Winglets increase wing efficiency (read aspect ratio improvement) without increasing wing bending moment. You can get the same aero effect by laying down the winglet and therefore increasing the aspect ratio of the wing. The same can be accomplished with the wing tip shape as on the 787 and NXT.
The majority of the winglets out there are to look good and actually do not do a lot of aero improvement. Just adding a winglet with out some testing may hurt your perfomance. Winglets usually have very narrow areas of improvements and may help only 1-2 count of drag. You are reducing CDi (efficiency) but increasing CDo (wetted area). It can pay off only with lots of hours of cruise flying (airliner or biz jet) in fuel economy.
 
what i remember about winglets

is that they prevent the spanwise flow of laminar air to reduce wingtip vortices. but im with the mod man, in that he needed somewhere to put more antennas, so why not make em look cool. they may be induced drag but not as much drag as an antenna. or so it would seem
 
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cytoxin said:
is that they prevent the spanwise flow of laminar air to reduce wingtip vortices. but im with the mod man, in that he needed somewhere to put more antennas, so why not make em look cool. they may be induced drag but not as much drag as an antenna. or so it would seem
Click to expand...
I think he is talking about the dorsal fin, not the winglets.
 
Ying & Yang

N941WR said:
I would like to know more about his fin
http://img515.imageshack.us/img515/4024/img3070es9.jpg

How well does that stop the fishtailing?
Click to expand...
One down side of the dorsal fin is more surface area aft of the CG. That means landing in a cross wind you will weather vane more. Its OK, just the good old ying-N-yang of airplane design, trade-offs and no free lunch rule. It does make it more yaw stable.

Talking about ventral fins, winglets and more fins, the Beech 1900 has 8 of them I can see in this pic: http://www.al-airliners.be/a/air france/afb-1900.jpg Ventral fins are the two long fins at angles at rear bottom of fuselage. They add directional stability. The horz fins on the fuselage must increase pitch stability. The ones hanging straight down from the end of the horz stab? I guess it adds more yaw stability during engine out since they are in the prop wash? Strakes, VG's, Winglet's, Guide vanes........all little aerodynamic helpers, but the goal is to design so you don't need little fixes. I suspect they where trying to use existing parts. When they increased the fuselage hight they needed more stability. Winglet's are the same thing, fixing a wing that just needs to be longer.


I don't want to get into winglets but I did take an engineering grad class on aerodynamics at UW from a Boeing engineer who was involved in the Boeing 747-400 winglets. Short story, like the fin above there are many trade-offs and no free lunch......... Even this aerodynamicist Prof felt the winglet was better at making a place for the airline logo than an aero improvement.

The B747-400 was a derivative airplane with an existing wing. They not only added winglets they added 12 feet span on each wing. They just could not add any more span because it wouldn't fit at some airports. Clearly the winglets do good things for some missions, but if starting with a scratch wing design you going in plan would be to meet the mission with no winglet, which adds cost and weight. The B-777 has no winglets.

JAL took their B747-400 winglets off because the way they fly, like a bus short distance, lower altitudes, up and down Japan. Winglet's help and hurt, just depends (100's of factors).


However with retro fits to old bizz jets or old airliners like the B-727/737, it may help for a new mission. These planes and wings where originally made for short haul, but many operators now use them for long haul. So it "fixes" the wing for a different mission. The BBJ (Boeing Biz Jet) comes with winglets out of the Boeing factory (which is from Aviation Partners, the company that makes the retro fit winglets). Even the variants of the B767 have seen span extensions and winglets (due to increased weight and range missions): http://www.aerospaceweb.org/question/aerodynamics/q0148.shtml (you noticed the sheared tip....that is a winglet laying flat, which is what many aero guys prefer, if you can deal with the span for ground ops.)

Most aero guys I've talked to would rather expand wing span first than add winglets second, if there's a choice.

The little RV winglet pics are small and not real blended winglets, but if you include reducing the drag from two whip antennas its probably a gain (if you must have two more antennas). Overall no winglets (or antennas) would be a net gain and weigh less.

If you do make a real winglet that gains lift, you may have to beef up the wing or lower the load factor, which may cancel the gains (because of the extra weight). The Glasair III has a removable wing extensions. Of course Aerobatics is a no go with the span extender.

Gate space is an issue for airliners and longer wings might not fit. The B-777 was conceived with fordable wing tips! Like a Navy fighter, the idea would be the airliner would fold it's wing tips to park at tighter gates. They gave up even though a big airline was pushing it. Cost, weight and drag where too great. They Aero guys no doubt wanted even longer wings. Of course the fold idea would have to be totally fail safe and foolproof. The last goal is almost impossible to do, because fools are so smart. :rolleyes: "Gear Up....no no not wing tip up....."
 
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NACA duct in dorsel fin area???

http://img515.imageshack.us/img515/4024/img3070es9.jpg

Does anyone know what the NACA duct is doing in the dorsal fin in front of the rudder? Click on link above and look at the picture. I know some certified airplanes have them located in this area for vents that duct forward into the cockpit. Just wondering if this is the case if anyone knew.
 
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Some people put their cabin air inlet back at the tail. But putting a small (1") diameter duct, with a drain for rain, right at the base of the windshield will give LOTS of air! I get plenty when the rpm is over 1000!
 
What do winglets do?

I've got a little experience flying an airplane without winglets, then adding them. I flew a Hawker 800A for 5 years without winglets. We then added the Aviation Partners Blended winglets and flew it for two more. My impression is that the performance gains are outstanding.

Field length improvement. In jets, the runway requirements are based on worst case scenario. The deciding number for the Hawker is usually the Net Second Segment Climb requirement. The winglets add .7% (7/10ths of one percent) to the Net Second Segment gradient. Doesn't sound like much until you consider that the certification requirement is only 1.6%...almost a 50% improvement in climb after losing an engine above V1. In the real world how did that affect ops...basically we could carry 1500 pounds more gas off of a given runway. Huge improvement.

Climbing through the Flight Levels. The Hawker isn't the greatest climber in stock form. At typical weights and temps, the climb in the mid 30's was 700 to 800 fpm. After the winglets, it was doubled. We could steam right on up to FL410, without stopping in the low 30's to burn off gas.

Most noticably, the easiest thing to point to and make the boss smile? The first hour fuel burn was down 10% or more. We went from 2200pph to 1950 pph. Saving 30 or more gallons every flight adds up when fuel cost are skyrocketing. I wished I could pocket the difference.

Cruise speed at altitude was impressively increase. Before winglets, we could count on .74M and a half. After winglets, .77M early and having to pull power late in the flight to maintail .78M. Doesn't sound like much, but when combined with the increased climb, we weren't getting kicked off route to clear faster traffic behind near as much.

The increase in ramp appeal was phenominal. It went from being a nice looking, if somewhat dated design to WOW.

The two downsides?

All that sail area, so far from the CG made a monsterous change in the crosswind handling. In the past, crosswind were fun. The airplane has a max demonstrated crosswind of 35 knots...not a limitation, just a max demonstrated. I've flown lots of landings well above the max demonstated, and they were no big deal...truly an easy airplane to land XWind. 45 knots direct cross...hohum. With the winglets, not on my best day. I don't know that I'm skilled enough to handle more than 25-28. It's definately not your uncles Hawker in XWind.

Oh, that other downside? $425,000.00 installed, and no, they will not dicker price. $420K won't buy them.
 
Timothy, thanks for the report on the Hawker winglets. I used to fly a lot of 800's for EJM, and know exactly what you mean about "Kindly move aside, please". Also, having to wait another hour for a climb to higher altitude. The XP finally put some 'omph' in the 800 line. With your permission, I am going to forward your report to a friend who flies an 800. His boss may be interested in a better performing plane. I have wondered for some time whether these met the manufacturers claims. I probably wouldn't have considered x-wind landing problems, though.
 
by all means

by all means, forward away. If the pilot would like to chat, pass along my phone...(559)352-6145
 
Why winglets?

I think you have to consider why a designer would add winglets. A glider designer, with limited span (3 international classes - Standard, 15 meter & 18 meter - limit the span), does not have too many options, winglets almost give some thing for nothing in improved climb & glide performance. The downside is increased drag and so slightly degraded glide performance at higher speeds.

As a retrofit winglets generally offer improved climb & high altitude performance (I know thats a huge generalisation and is not true in all cases), with little of no increase in wing bending so having little impact structurally.

With a low aspect wing flying (relatively) slowly - such as RVs - the benefits are not so pronounced, especially as the wing works at a reasonably low angle of attack in the cruise (thereby minimising tip vortices and not giving the wing lets much to work on). If you have a turbo & fly at 14K'+ all the time there may be some benefit?

If you wanna look cool, the go right ahead, as noted in the original post they can also hide antennas.

I'm told you have to be quite careful to shape the winglet correctly for your application to get most benefit, otherwise all you get is increased parasite drag.

Pete
 
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