Gnarly Gnu Posted February 12, 2011 Share Posted February 12, 2011 Just wondering if any folk knowledgeable in aerodynamics could comment on wingtip geometry. I recently purchased a GA kit aircraft which includes optional 'drooped' wingtips as opposed to the perhaps more common upturned ones. I might be quite wrong but I suspect the drooped tips may assist in lowering the stall speed but I wonder if they will create more vortex drag during cruise? I'm more interested in lowering the overall airframe drag than STOL performance. Link to comment Share on other sites More sharing options...
Vev Posted February 12, 2011 Share Posted February 12, 2011 Hi GG, I'm sure there will be much more knowledgeable people out there on this subject. However, I attended a seminar at Oshkosh last year on aerodynamic drag and this discussion game up. It was said by the experts, that both the winglet and turned down wing tip do basically the same thing and both reduce drag. They went on to explain a sharp wing tip is the key to lowering drag by reducing wing tip vortex ... how wing tip is positioned is about meeting other design functions and nothing to do with drag reduction. Hopefully some one else can build on this to give you more detail about the theory. Cheers Jack Link to comment Share on other sites More sharing options...
sfGnome Posted February 12, 2011 Share Posted February 12, 2011 Could the difference be just that a droop down is more likely to suffer tip drag during landing, but provides a slightly better view either side the rest of the time? Link to comment Share on other sites More sharing options...
Guest Maj Millard Posted February 12, 2011 Share Posted February 12, 2011 Up or down turned tips can effect the way the wing operates throught it's range. If you are looking for a low-drag tip for efficency at cruise then the "Hoener tip' as used by the Reno Mustang racers is one of the best. The tip on the Cheetah appears to work very well also.................................Maj... Link to comment Share on other sites More sharing options...
djpacro Posted February 12, 2011 Share Posted February 12, 2011 A brief summary of different wingtips and their benefits is shown at Fig 4.27 here. Did a bit deeper on that website and you should find all of the quantitative effects. Hoerner's own book, Fluid Dynamic Drag, is excellent if you can get hold of a copy. Aha, just found the entire book on the net. With its companion, Fluid Dynamic Lift, all you ever wanted to know about lift and drag of almost anything. Well, up to 50 years ago anyway. Wish I could answer more fully and correctly off the cuff about drooped wingtips but it has been 30+ years. Drooped wingtips often bigger so extra wing area. Droop for improved lateral stability at low speeds near the stall. Not more vortex drag in the cruise - more profile drag because I'd expect them to be bigger than the standard tips. Vev - a sharp wing tip - you mean sharp in front view? Link to comment Share on other sites More sharing options...
Vev Posted February 12, 2011 Share Posted February 12, 2011 Hi DJP Vev - a sharp wing tip - you mean sharp in front view? As it was explained to me (but i could have it wrong) in terms of drag reduction .. the taper on the end of the wing tip needs to come to sharp point. It doesn't matter if it points up, down or continues on as an extension of the wing... they all reduce the wing tip vortex. The angle of the winglet (up, down or out) has more to do with lift, wing span and structural issues. I'm a bit out of my comfort zone DJP as I'm just repeating what I heard in the lecture at Oshkosh ... I'm sure if anyone can put some meat on this you can. Cheers Vev Link to comment Share on other sites More sharing options...
Gnarly Gnu Posted February 13, 2011 Author Share Posted February 13, 2011 Thanks folks, appreciate the info. I'll talk to the manufacturer in Canada about it also of course. I bought the kit S/H but untouched so the previous owner had already purchased these tips. Chris Link to comment Share on other sites More sharing options...
Guernsey Posted February 13, 2011 Share Posted February 13, 2011 Wingtip Style. Several years ago I owned a used Cessna 150 which had been imported from America and it came with the downturned wing tips. They were new into Australia at the time but not approved for use here so we had to remove them pending approval. This gave us the opportunity to compare the differences when they were put back on. As far as I could tell there did not appear to be any noticeable improvements in performance however handling at slow speeds was a marked improvement. On approach in particular with flaps down Cessnas tend to 'wallow' around somewhat however mine became much more stable and had no tendency to yaw. It felt like you had fins on the wing tips with no need for much rudder input. They looked pretty cool also. See attached photo with the pretty cool pilot. Alan.:thumb_up: Link to comment Share on other sites More sharing options...
dazza 38 Posted February 13, 2011 Share Posted February 13, 2011 HI Gurensey, was that the "Wren" modification? Link to comment Share on other sites More sharing options...
Guernsey Posted February 13, 2011 Share Posted February 13, 2011 Hi Dazza, I have no idea. Southern Aircraft Maintenance ( Colin Harrison ) based at Parafield was importing used aircraft from the USA at the time and refurbishing them, this one just happened to turn up with a couple of other aircraft. Whilst the tips did improve stability in the air they could cause dramatic instability for the pilot during pre flight if he failed to notice them and walked into them.LOL. Link to comment Share on other sites More sharing options...
dazza 38 Posted February 13, 2011 Share Posted February 13, 2011 HI mate the reason I ask is that the tips look very familar to the WREN mod , but you aircraft dosent seem to have the little canards on it on the nose in front of the doors.Either way it probably doesnt matter, they seem to work from what i have read. Link to comment Share on other sites More sharing options...
eightyknots Posted February 14, 2011 Share Posted February 14, 2011 Whilst the tips did improve stability in the air they could cause dramatic instability for the pilot during pre flight if he failedto notice them and walked into them.LOL. Yes, I can imagine that this could become quite a headache for pilots! Link to comment Share on other sites More sharing options...
PapaFox Posted February 14, 2011 Share Posted February 14, 2011 AFAIK the Wren mod was only performed on 182. A lot more work than just replacing a few stock parts... double slotted flaps and ailerons, which also extend with flap movement, come to mind first. Link to comment Share on other sites More sharing options...
facthunter Posted February 14, 2011 Share Posted February 14, 2011 Leading edge shape is changed also. Sharper leading edge disposed a bit lower. Nev Link to comment Share on other sites More sharing options...
Guernsey Posted February 15, 2011 Share Posted February 15, 2011 Well Eightyknots you are correct but I didn't want to show myself up on this forum. There were several occasions when I was not paying attention during a pre-flight so the aircraft would retaliate and give me a good wing around the ear-hole. Link to comment Share on other sites More sharing options...
dazza 38 Posted February 15, 2011 Share Posted February 15, 2011 In post # 8.Do you guys think that the tips could be Demer also known as Madras Droop Tips.They where installed on some 150/152 and 172 aircraft under a STC. Link to comment Share on other sites More sharing options...
Spin Posted February 15, 2011 Share Posted February 15, 2011 That's the name I was looking for - Demer tips! Yeah Dazza those look like them - flew a Cherokee 140 many moons ago that had them fitted, I don't think they did much for the cruise speed but it certainly didn't want to stop flying either when you were trying to land. On a more positive note, I once watched a Pacer pirouette around on a wing tip and one wheel, the Demer tips certainly prevented it from leaning as far over as it might otherwise have done... Link to comment Share on other sites More sharing options...
dazza 38 Posted February 15, 2011 Share Posted February 15, 2011 Thanks Spin, hopefully we are on the right track.There seems to be a fair few different companies around who produce droop tips.I did a bit of research on the net, a fair few dont exist anymore. Link to comment Share on other sites More sharing options...
Yenn Posted February 15, 2011 Share Posted February 15, 2011 When Cessna introduced the droopy wing tips I flew a demo model and the improvement in low speed handling was apparent. The Spitfire wingtip has a low drag, being an elliptical wing and it has no droop or raise. Link to comment Share on other sites More sharing options...
Guernsey Posted February 15, 2011 Share Posted February 15, 2011 Here's another photo showing the drooped tips a little better. It may help to identify them. Alan. Link to comment Share on other sites More sharing options...
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