cornishe 0 #1 October 21, 2004 http://www.hiperusa.com/Blade_Technology.pdf Are the winglets marketing bullshit or is this something that makes for a more effecient airfoil? I found that paragliders have these, and hanggliders also have a type of winglet. move this to gear/rigging? -abbieAbbie Mashaal Skydive Idaho Snake River Skydiving TandemBASE Quote Share this post Link to post Share on other sites
Peej 0 #2 October 21, 2004 I think this definatley needs to be moved to gear and rigging - unless of course you're asking whether winglets would somehow benefit a BASE canopy? With my whopping four BASE jumps and 200 skydives i am no where near experienced enough to address that. However, Precision Aerodynamics use the same kind of winglet on the top of their Nitron canopy. When i asked Chris (GroundZero) about them he said they function much the same way as the stabilizers on aircraft and if i remember correctly are supposed to help the canopy in turns. (Chris, if you see this, maybe you wanna jump in here and explain further?) Just my newbie 2 cents. Advertisio Rodriguez / Sky Quote Share this post Link to post Share on other sites
beezyshaw 0 #3 October 21, 2004 The Nitron isn't Precision's canopy design. It is a copy of Klaus Schenk's NITRO, and unfortunately he is no longer with us. But I can tell you a bit of what I've learned about winglets: Lift is created by the pressure difference of airflow over the upper surface vs. the lower surface of a wing. When air flows over the upper surface of any wing, it begins to rotate in a circular pattern as it moves towards the tips. This of course disrupts the pressure differential and the tip of the wing stalls (or quits generating lift). The winglet acts like a knife-edge and as the rotating air hits the winglet it breaks up the rotation (voritices) and forces the air to resume its path over the surface. This, in turn, allows the entire wing to continue generating lift. I could go on and on with other additional benefits of the winglet, but this is the primary function. Quote Share this post Link to post Share on other sites
TomAiello 26 #4 October 21, 2004 Quotemove this to gear/rigging? Yep.-- Tom Aiello Tom@SnakeRiverBASE.com SnakeRiverBASE.com Quote Share this post Link to post Share on other sites
TomAiello 26 #5 October 21, 2004 Do you think there would be additional benefits to using multiple winglets at intervals across the topskin?-- Tom Aiello Tom@SnakeRiverBASE.com SnakeRiverBASE.com Quote Share this post Link to post Share on other sites
Peej 0 #6 October 21, 2004 Nothing better than info straight from the horse's mouth. I stand corrected, thanks Beezy. Advertisio Rodriguez / Sky Quote Share this post Link to post Share on other sites
beezyshaw 0 #7 October 21, 2004 QuoteDo you think there would be additional benefits to using multiple winglets at intervals across the topskin? *** No, the vortices are only formed as the air flows toward the wingtips. At the center of the canopy the flow is laminar and winglets there would only be a source of additional parasite drag. Quote Share this post Link to post Share on other sites Ron 10 #8 October 21, 2004 Winglets when they disrupt the vorticies also have the benefit of reducing drag... The theory is sound, I have not jumped a canopy like that (Nitron, Jallapino..ect) but some swear by them."No free man shall ever be debarred the use of arms." -- Thomas Jefferson, Thomas Jefferson Papers, 334 Quote Share this post Link to post Share on other sites beezyshaw 0 #9 October 21, 2004 Yes, Ron, that is correct. But to clarify, they reduce "induced" drag (the type of drag that is a by-product of lift itself); winglets do not reduce "parisite" drag, which is what one normally thinks of when referring to "drag" Quote Share this post Link to post Share on other sites TomAiello 26 #10 October 21, 2004 Does anyone know why the winglets are placed a tad inboard, rather than right at the outside edge? Stiffness of canopy? Or is there an aerodynamic reason you'd do that on a stiff wing as well?-- Tom Aiello Tom@SnakeRiverBASE.com SnakeRiverBASE.com Quote Share this post Link to post Share on other sites cornishe 0 #11 October 21, 2004 I was about to ask that as well. On airplanes and on the hang-gliders i've see the winglets are on the tips. Only on non-rigid wings do i see the winglets inboard a bit. Has any manufacturer tested this out with a BASE canopy? what were the findings? -abbieAbbie Mashaal Skydive Idaho Snake River Skydiving TandemBASE Quote Share this post Link to post Share on other sites Ron 10 #12 October 21, 2004 QuoteYes, Ron, that is correct. But to clarify, they reduce "induced" drag (the type of drag that is a by-product of lift itself); winglets do not reduce "parisite" drag, which is what one normally thinks of when referring to "drag" Yeah the only way to reduce parasitic drag is to reduce area that is exposed. What do you think of them?"No free man shall ever be debarred the use of arms." -- Thomas Jefferson, Thomas Jefferson Papers, 334 Quote Share this post Link to post Share on other sites beezyshaw 0 #13 October 21, 2004 QuoteDoes anyone know why the winglets are placed a tad inboard, rather than right at the outside edge? ***We can't ask Klaus that question, unfortunately, but I would say it's for construction considerations. Quote Share this post Link to post Share on other sites TomAiello 26 #14 October 21, 2004 QuoteHas any manufacturer tested this out with a BASE canopy? Not that I know of. A BASE canopy actually doesn't need to be a particularly efficient airfoil. The important characteristics there are openings and landings. In terms of flight profile it's actually generally more desirable to have a high drag and high lift wing, so that it flies slowly, but doesn't eat much altitude. At least, so goes the conventional wisdom.-- Tom Aiello Tom@SnakeRiverBASE.com SnakeRiverBASE.com Quote Share this post Link to post Share on other sites cornishe 0 #15 October 21, 2004 Doesn't a more efficient airfoil exactly mean relatively more lift and slower stall speed? Wouldn't that allow a jumper to sink in easier without stalling, etc?Abbie Mashaal Skydive Idaho Snake River Skydiving TandemBASE Quote Share this post Link to post Share on other sites TomAiello 26 #16 October 21, 2004 I've got no formal education on this topic. But what I understand is that "more efficient" can mean two things: higher lift _or_ lower drag. In general, a BASE flight would be better with higher lift (i.e. loses less altitude) and more drag (i.e. moves forward slower). Or so goes the conventional wisdom. Personally, I don't see why you can't have a high lift _and_ low drag airfoil that just has properly set deep brakes, so you can choose when to use each characteristic of the wing (by deciding when to pop the toggles). As I said, I have no formal education on this topic, so I could be way off the mark.-- Tom Aiello Tom@SnakeRiverBASE.com SnakeRiverBASE.com Quote Share this post Link to post Share on other sites billvon 3,107 #17 October 21, 2004 >The winglet acts like a knife-edge and as the rotating air hits the winglet >it breaks up the rotation (voritices) and forces the air to resume its path > over the surface. However, the air very close to the surface of a wing isn't moving very fast; putting features close to the surface of the wing has a correspondingly small effect on overall performance. In addition, the vortex effect is greatest at the very edge of the wing, where the air begins to 'curl' up from below. That's why aircraft that use winglets put them on the end of the wing and make them long and narrow. I think the winglets on the Nitro may be acting more like vortex generators than true winglets. Many aircraft have vortex generators; they disrupt smooth airflow near the wing and prevent airflow separation at high angles of attack, such as one sees in a flare. On aircraft, this results in better control authority at low speeds and lower stall speeds; I've noticed both characteristics on the Nitro. Quote Share this post Link to post Share on other sites alan 1 #18 October 21, 2004 QuoteNo, the vortices are only formed as the air flows toward the wingtips. At the center of the canopy the flow is laminar and winglets there would only be a source of additional parasite drag. Maybe what the question about having winglets inboard was getting at is the concept of turbulators. Many crop dusting aircraft, for example, have little tabs along the top of the wing just back from the leading edge. The idea is to induce a little turbulance into the boundary layer of the airflow, that has the effect of delaying separation until a higher angle of attack is reached than would occur without them. I've even seen them added to a Piper Cub under an STC. Simply stated, turbulators allow a higher critical aoa before a wing stalls. They may not be pratical or effective on our parachutes, but I don't know if anyone has ever tested them on parachutes. Maybe if they were added to the VX 39 it could be landed at a slower speed.alan Quote Share this post Link to post Share on other sites pilotdave 0 #19 October 21, 2004 I don't care what the marketing says... I don't believe for one second that those are true winglets. Winglets are complex aerodynamic devices. They don't so much disrupt wingtip vortices... rather, they use them to produce thrust. Thrust? With no engine? What?? Yeah, thrust. Winglets are airfoils, set at just the right angle (and maybe even with some twist) to produce a little bit of lift inward and slightly forward, not upward. The forward component of their lift is thrust... or you might call it negative drag I guess. But those things on the canopy are not winglets! As someone else pointed out, they might work as vortex generators...but probably not very effective ones. I think they are most like stall fences. You can see those on planes like the MiG 15. Now I'm not sure what they do on the canopy, but they probably have a straightening effect on the airflow. Planes use them to keep the air flowing straight at high angles of attack. Especially on swept wings. Air flow near stall tends to want to move outward, toward the wingtips. Stall fences sort of force the airflow to keep going straight. You can see the same thing with notched leading edges, which set up a vortex at high angles of attack, which acts like a fence to keep the air flowing straight. Those things might create vortices which can sometimes have a stabilizing effect. But they don't appear to be the type of vortex generators used to energize the turbulent boundary layer on planes. Those would be small, angled to the wind, and probably spread along the upper surface, not just near the wing tips. I seriously doubt those things decrease induced drag at all. But then again, maybe I'm wrong. Dave Quote Share this post Link to post Share on other sites tfelber 0 #20 October 21, 2004 I jump a Nitro 135 loaded at 1.75, thanks Beezy, and I don't know if this is the only reason, but it has a lot of lift on the bottom end. I can get a full flare at about shoulder level. And, flaring to my hips does not induce a stall... I should try some very aggressive stalls up high to see what I have to do to get it to stall because I've been asked this question more than once. Quote Share this post Link to post Share on other sites billvon 3,107 #21 October 21, 2004 > vortex generators...but probably not very effective ones. I think they are > most like stall fences. Stall fences/vortex generators/turbulators are essentially the same things - they are small protrusions into the boundary layer on the tops of airfoils. They have different effects depending on the flight regime, though. (i.e. transsonic, low speed, stall.) I have a feeling we don't have to worry about the effects of the Nitro's winglets on transsonic canopy flight - unless Luigi gets a Nitro 7 or something. Quote Share this post Link to post Share on other sites tfelber 0 #22 October 21, 2004 From Boeing's web page: Quote Winglets affect the part of drag called induced drag. As air is deflected by the lift of the wing, the total lift vector tilts back. The aft component of this lift vector is the induced drag (fig. 1). The magnitude of the induced drag is determined by the spanwise distribution of vortices shed downstream of the wing trailing edge (TE), which is related in turn to the spanwise lift distribution. Induced drag can be reduced by increasing the horizontal span or the vertical height of the lifting system (i.e., increasing the length of the TE that sheds the vortices). The winglets increase the spread of the vortices along the TE, creating more lift at the wingtips (figs. 2 and 3). The result is a reduction in induced drag (fig. 4). The maximum benefit of the induced drag reduction depends on the spanwise lift distribution on the wing. Theoretically, for a planar wing, induced drag is optimized with an elliptical lift distribution that minimizes the change in vorticity along the span. For the same amount of structural material, nonplanar wingtip devices can achieve a similar induced drag benefit as a planar span increase; however, new Boeing airplane designs focus on minimizing induced drag with wingspan influenced by additional design benefits. An important consideration when designing the wingtip device for the BBJ was that it could be retrofitted on BBJs already in service. A blended winglet configuration (patented and designed by Dr. L. B. Gratzer of Aviation Partners, Inc., Seattle, Washington) was selected because it required fewer changes to the wing structure. The aerodynamic advantage of a blended winglet is in the transition from the existing wingtip to the vertical winglet. The blended winglet allows for the chord distribution to change smoothly from the wingtip to the winglet, which optimizes the distribution of the span load lift and minimizes any aerodynamic interference or airflow separation. So it sounds like the reason for the winglets being at the tip on fixed-wing aircraft is not because of optimal flight characteristics, but more because of the need to keep the cost of retrofitting down. And for fixed-wing aircraft the winglets are used to decrease induced drag and thereby decrease fuel consumption, increasing profitability or range. I haven't seen any fixed-wing aircraft with the winglets further in on the wing span. Quote Share this post Link to post Share on other sites tfelber 0 #23 October 21, 2004 QuoteI think they are most like stall fences. Actually that theory sounds very plausible. And that effect would be more useful on a parachute than reducing induced drag. Increasing the speed of a canopy can easily be accomplished by increasing wingloading. However, reducing stall speed is very desirable. Quote Share this post Link to post Share on other sites beezyshaw 0 #24 October 21, 2004 There has been some very good discussion in this thread today about our winglets. To try to comment any further from a purely technological standpoint is way over my head. Although I've been a pilot for 34 years and a skydiver for almost that long, an aeronautical engineer I certainly am not. I'd do well to teach a private pilot ground school class. So I won't try to throw out any fancy terminology. I will say this; in many, many test jumps the winglets proved that they accomplish several things: 1) They allow the parachute to fly to a slower touchdown speed, reducing the necessity to run out landings on no-wind days. 2) They improve the track holding ability of the canopy when landing in a crosswind condition. 3) Winglets give the canopy improved recovery from steep turns. 4) They seem to reduce the diving effect of openings with line twists. Quote Share this post Link to post Share on other sites pilotdave 0 #25 October 22, 2004 When you say they accomplished those things, do you mean the canopy was tested with and without them, and they made a big difference, or are those just characteristics of the canopy? Dave Quote Share this post Link to post Share on other sites Prev 1 2 Next Page 1 of 2 Join the conversation You can post now and register later. If you have an account, sign in now to post with your account. 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Ron 10 #8 October 21, 2004 Winglets when they disrupt the vorticies also have the benefit of reducing drag... The theory is sound, I have not jumped a canopy like that (Nitron, Jallapino..ect) but some swear by them."No free man shall ever be debarred the use of arms." -- Thomas Jefferson, Thomas Jefferson Papers, 334 Quote Share this post Link to post Share on other sites
beezyshaw 0 #9 October 21, 2004 Yes, Ron, that is correct. But to clarify, they reduce "induced" drag (the type of drag that is a by-product of lift itself); winglets do not reduce "parisite" drag, which is what one normally thinks of when referring to "drag" Quote Share this post Link to post Share on other sites
TomAiello 26 #10 October 21, 2004 Does anyone know why the winglets are placed a tad inboard, rather than right at the outside edge? Stiffness of canopy? Or is there an aerodynamic reason you'd do that on a stiff wing as well?-- Tom Aiello Tom@SnakeRiverBASE.com SnakeRiverBASE.com Quote Share this post Link to post Share on other sites
cornishe 0 #11 October 21, 2004 I was about to ask that as well. On airplanes and on the hang-gliders i've see the winglets are on the tips. Only on non-rigid wings do i see the winglets inboard a bit. Has any manufacturer tested this out with a BASE canopy? what were the findings? -abbieAbbie Mashaal Skydive Idaho Snake River Skydiving TandemBASE Quote Share this post Link to post Share on other sites
Ron 10 #12 October 21, 2004 QuoteYes, Ron, that is correct. But to clarify, they reduce "induced" drag (the type of drag that is a by-product of lift itself); winglets do not reduce "parisite" drag, which is what one normally thinks of when referring to "drag" Yeah the only way to reduce parasitic drag is to reduce area that is exposed. What do you think of them?"No free man shall ever be debarred the use of arms." -- Thomas Jefferson, Thomas Jefferson Papers, 334 Quote Share this post Link to post Share on other sites
beezyshaw 0 #13 October 21, 2004 QuoteDoes anyone know why the winglets are placed a tad inboard, rather than right at the outside edge? ***We can't ask Klaus that question, unfortunately, but I would say it's for construction considerations. Quote Share this post Link to post Share on other sites TomAiello 26 #14 October 21, 2004 QuoteHas any manufacturer tested this out with a BASE canopy? Not that I know of. A BASE canopy actually doesn't need to be a particularly efficient airfoil. The important characteristics there are openings and landings. In terms of flight profile it's actually generally more desirable to have a high drag and high lift wing, so that it flies slowly, but doesn't eat much altitude. At least, so goes the conventional wisdom.-- Tom Aiello Tom@SnakeRiverBASE.com SnakeRiverBASE.com Quote Share this post Link to post Share on other sites cornishe 0 #15 October 21, 2004 Doesn't a more efficient airfoil exactly mean relatively more lift and slower stall speed? Wouldn't that allow a jumper to sink in easier without stalling, etc?Abbie Mashaal Skydive Idaho Snake River Skydiving TandemBASE Quote Share this post Link to post Share on other sites TomAiello 26 #16 October 21, 2004 I've got no formal education on this topic. But what I understand is that "more efficient" can mean two things: higher lift _or_ lower drag. In general, a BASE flight would be better with higher lift (i.e. loses less altitude) and more drag (i.e. moves forward slower). Or so goes the conventional wisdom. Personally, I don't see why you can't have a high lift _and_ low drag airfoil that just has properly set deep brakes, so you can choose when to use each characteristic of the wing (by deciding when to pop the toggles). As I said, I have no formal education on this topic, so I could be way off the mark.-- Tom Aiello Tom@SnakeRiverBASE.com SnakeRiverBASE.com Quote Share this post Link to post Share on other sites billvon 3,107 #17 October 21, 2004 >The winglet acts like a knife-edge and as the rotating air hits the winglet >it breaks up the rotation (voritices) and forces the air to resume its path > over the surface. However, the air very close to the surface of a wing isn't moving very fast; putting features close to the surface of the wing has a correspondingly small effect on overall performance. In addition, the vortex effect is greatest at the very edge of the wing, where the air begins to 'curl' up from below. That's why aircraft that use winglets put them on the end of the wing and make them long and narrow. I think the winglets on the Nitro may be acting more like vortex generators than true winglets. Many aircraft have vortex generators; they disrupt smooth airflow near the wing and prevent airflow separation at high angles of attack, such as one sees in a flare. On aircraft, this results in better control authority at low speeds and lower stall speeds; I've noticed both characteristics on the Nitro. Quote Share this post Link to post Share on other sites alan 1 #18 October 21, 2004 QuoteNo, the vortices are only formed as the air flows toward the wingtips. At the center of the canopy the flow is laminar and winglets there would only be a source of additional parasite drag. Maybe what the question about having winglets inboard was getting at is the concept of turbulators. Many crop dusting aircraft, for example, have little tabs along the top of the wing just back from the leading edge. The idea is to induce a little turbulance into the boundary layer of the airflow, that has the effect of delaying separation until a higher angle of attack is reached than would occur without them. I've even seen them added to a Piper Cub under an STC. Simply stated, turbulators allow a higher critical aoa before a wing stalls. They may not be pratical or effective on our parachutes, but I don't know if anyone has ever tested them on parachutes. Maybe if they were added to the VX 39 it could be landed at a slower speed.alan Quote Share this post Link to post Share on other sites pilotdave 0 #19 October 21, 2004 I don't care what the marketing says... I don't believe for one second that those are true winglets. Winglets are complex aerodynamic devices. They don't so much disrupt wingtip vortices... rather, they use them to produce thrust. Thrust? With no engine? What?? Yeah, thrust. Winglets are airfoils, set at just the right angle (and maybe even with some twist) to produce a little bit of lift inward and slightly forward, not upward. The forward component of their lift is thrust... or you might call it negative drag I guess. But those things on the canopy are not winglets! As someone else pointed out, they might work as vortex generators...but probably not very effective ones. I think they are most like stall fences. You can see those on planes like the MiG 15. Now I'm not sure what they do on the canopy, but they probably have a straightening effect on the airflow. Planes use them to keep the air flowing straight at high angles of attack. Especially on swept wings. Air flow near stall tends to want to move outward, toward the wingtips. Stall fences sort of force the airflow to keep going straight. You can see the same thing with notched leading edges, which set up a vortex at high angles of attack, which acts like a fence to keep the air flowing straight. Those things might create vortices which can sometimes have a stabilizing effect. But they don't appear to be the type of vortex generators used to energize the turbulent boundary layer on planes. Those would be small, angled to the wind, and probably spread along the upper surface, not just near the wing tips. I seriously doubt those things decrease induced drag at all. But then again, maybe I'm wrong. Dave Quote Share this post Link to post Share on other sites tfelber 0 #20 October 21, 2004 I jump a Nitro 135 loaded at 1.75, thanks Beezy, and I don't know if this is the only reason, but it has a lot of lift on the bottom end. I can get a full flare at about shoulder level. And, flaring to my hips does not induce a stall... I should try some very aggressive stalls up high to see what I have to do to get it to stall because I've been asked this question more than once. Quote Share this post Link to post Share on other sites billvon 3,107 #21 October 21, 2004 > vortex generators...but probably not very effective ones. I think they are > most like stall fences. Stall fences/vortex generators/turbulators are essentially the same things - they are small protrusions into the boundary layer on the tops of airfoils. They have different effects depending on the flight regime, though. (i.e. transsonic, low speed, stall.) I have a feeling we don't have to worry about the effects of the Nitro's winglets on transsonic canopy flight - unless Luigi gets a Nitro 7 or something. Quote Share this post Link to post Share on other sites tfelber 0 #22 October 21, 2004 From Boeing's web page: Quote Winglets affect the part of drag called induced drag. As air is deflected by the lift of the wing, the total lift vector tilts back. The aft component of this lift vector is the induced drag (fig. 1). The magnitude of the induced drag is determined by the spanwise distribution of vortices shed downstream of the wing trailing edge (TE), which is related in turn to the spanwise lift distribution. Induced drag can be reduced by increasing the horizontal span or the vertical height of the lifting system (i.e., increasing the length of the TE that sheds the vortices). The winglets increase the spread of the vortices along the TE, creating more lift at the wingtips (figs. 2 and 3). The result is a reduction in induced drag (fig. 4). The maximum benefit of the induced drag reduction depends on the spanwise lift distribution on the wing. Theoretically, for a planar wing, induced drag is optimized with an elliptical lift distribution that minimizes the change in vorticity along the span. For the same amount of structural material, nonplanar wingtip devices can achieve a similar induced drag benefit as a planar span increase; however, new Boeing airplane designs focus on minimizing induced drag with wingspan influenced by additional design benefits. An important consideration when designing the wingtip device for the BBJ was that it could be retrofitted on BBJs already in service. A blended winglet configuration (patented and designed by Dr. L. B. Gratzer of Aviation Partners, Inc., Seattle, Washington) was selected because it required fewer changes to the wing structure. The aerodynamic advantage of a blended winglet is in the transition from the existing wingtip to the vertical winglet. The blended winglet allows for the chord distribution to change smoothly from the wingtip to the winglet, which optimizes the distribution of the span load lift and minimizes any aerodynamic interference or airflow separation. So it sounds like the reason for the winglets being at the tip on fixed-wing aircraft is not because of optimal flight characteristics, but more because of the need to keep the cost of retrofitting down. And for fixed-wing aircraft the winglets are used to decrease induced drag and thereby decrease fuel consumption, increasing profitability or range. I haven't seen any fixed-wing aircraft with the winglets further in on the wing span. Quote Share this post Link to post Share on other sites tfelber 0 #23 October 21, 2004 QuoteI think they are most like stall fences. Actually that theory sounds very plausible. And that effect would be more useful on a parachute than reducing induced drag. Increasing the speed of a canopy can easily be accomplished by increasing wingloading. However, reducing stall speed is very desirable. Quote Share this post Link to post Share on other sites beezyshaw 0 #24 October 21, 2004 There has been some very good discussion in this thread today about our winglets. To try to comment any further from a purely technological standpoint is way over my head. Although I've been a pilot for 34 years and a skydiver for almost that long, an aeronautical engineer I certainly am not. I'd do well to teach a private pilot ground school class. So I won't try to throw out any fancy terminology. I will say this; in many, many test jumps the winglets proved that they accomplish several things: 1) They allow the parachute to fly to a slower touchdown speed, reducing the necessity to run out landings on no-wind days. 2) They improve the track holding ability of the canopy when landing in a crosswind condition. 3) Winglets give the canopy improved recovery from steep turns. 4) They seem to reduce the diving effect of openings with line twists. Quote Share this post Link to post Share on other sites pilotdave 0 #25 October 22, 2004 When you say they accomplished those things, do you mean the canopy was tested with and without them, and they made a big difference, or are those just characteristics of the canopy? Dave Quote Share this post Link to post Share on other sites Prev 1 2 Next Page 1 of 2 Join the conversation You can post now and register later. If you have an account, sign in now to post with your account. Note: Your post will require moderator approval before it will be visible. Reply to this topic... × Pasted as rich text. Paste as plain text instead Only 75 emoji are allowed. × Your link has been automatically embedded. Display as a link instead × Your previous content has been restored. Clear editor × You cannot paste images directly. Upload or insert images from URL. Insert image from URL × Desktop Tablet Phone Submit Reply 0
TomAiello 26 #14 October 21, 2004 QuoteHas any manufacturer tested this out with a BASE canopy? Not that I know of. A BASE canopy actually doesn't need to be a particularly efficient airfoil. The important characteristics there are openings and landings. In terms of flight profile it's actually generally more desirable to have a high drag and high lift wing, so that it flies slowly, but doesn't eat much altitude. At least, so goes the conventional wisdom.-- Tom Aiello Tom@SnakeRiverBASE.com SnakeRiverBASE.com Quote Share this post Link to post Share on other sites
cornishe 0 #15 October 21, 2004 Doesn't a more efficient airfoil exactly mean relatively more lift and slower stall speed? Wouldn't that allow a jumper to sink in easier without stalling, etc?Abbie Mashaal Skydive Idaho Snake River Skydiving TandemBASE Quote Share this post Link to post Share on other sites
TomAiello 26 #16 October 21, 2004 I've got no formal education on this topic. But what I understand is that "more efficient" can mean two things: higher lift _or_ lower drag. In general, a BASE flight would be better with higher lift (i.e. loses less altitude) and more drag (i.e. moves forward slower). Or so goes the conventional wisdom. Personally, I don't see why you can't have a high lift _and_ low drag airfoil that just has properly set deep brakes, so you can choose when to use each characteristic of the wing (by deciding when to pop the toggles). As I said, I have no formal education on this topic, so I could be way off the mark.-- Tom Aiello Tom@SnakeRiverBASE.com SnakeRiverBASE.com Quote Share this post Link to post Share on other sites
billvon 3,107 #17 October 21, 2004 >The winglet acts like a knife-edge and as the rotating air hits the winglet >it breaks up the rotation (voritices) and forces the air to resume its path > over the surface. However, the air very close to the surface of a wing isn't moving very fast; putting features close to the surface of the wing has a correspondingly small effect on overall performance. In addition, the vortex effect is greatest at the very edge of the wing, where the air begins to 'curl' up from below. That's why aircraft that use winglets put them on the end of the wing and make them long and narrow. I think the winglets on the Nitro may be acting more like vortex generators than true winglets. Many aircraft have vortex generators; they disrupt smooth airflow near the wing and prevent airflow separation at high angles of attack, such as one sees in a flare. On aircraft, this results in better control authority at low speeds and lower stall speeds; I've noticed both characteristics on the Nitro. Quote Share this post Link to post Share on other sites
alan 1 #18 October 21, 2004 QuoteNo, the vortices are only formed as the air flows toward the wingtips. At the center of the canopy the flow is laminar and winglets there would only be a source of additional parasite drag. Maybe what the question about having winglets inboard was getting at is the concept of turbulators. Many crop dusting aircraft, for example, have little tabs along the top of the wing just back from the leading edge. The idea is to induce a little turbulance into the boundary layer of the airflow, that has the effect of delaying separation until a higher angle of attack is reached than would occur without them. I've even seen them added to a Piper Cub under an STC. Simply stated, turbulators allow a higher critical aoa before a wing stalls. They may not be pratical or effective on our parachutes, but I don't know if anyone has ever tested them on parachutes. Maybe if they were added to the VX 39 it could be landed at a slower speed.alan Quote Share this post Link to post Share on other sites
pilotdave 0 #19 October 21, 2004 I don't care what the marketing says... I don't believe for one second that those are true winglets. Winglets are complex aerodynamic devices. They don't so much disrupt wingtip vortices... rather, they use them to produce thrust. Thrust? With no engine? What?? Yeah, thrust. Winglets are airfoils, set at just the right angle (and maybe even with some twist) to produce a little bit of lift inward and slightly forward, not upward. The forward component of their lift is thrust... or you might call it negative drag I guess. But those things on the canopy are not winglets! As someone else pointed out, they might work as vortex generators...but probably not very effective ones. I think they are most like stall fences. You can see those on planes like the MiG 15. Now I'm not sure what they do on the canopy, but they probably have a straightening effect on the airflow. Planes use them to keep the air flowing straight at high angles of attack. Especially on swept wings. Air flow near stall tends to want to move outward, toward the wingtips. Stall fences sort of force the airflow to keep going straight. You can see the same thing with notched leading edges, which set up a vortex at high angles of attack, which acts like a fence to keep the air flowing straight. Those things might create vortices which can sometimes have a stabilizing effect. But they don't appear to be the type of vortex generators used to energize the turbulent boundary layer on planes. Those would be small, angled to the wind, and probably spread along the upper surface, not just near the wing tips. I seriously doubt those things decrease induced drag at all. But then again, maybe I'm wrong. Dave Quote Share this post Link to post Share on other sites
tfelber 0 #20 October 21, 2004 I jump a Nitro 135 loaded at 1.75, thanks Beezy, and I don't know if this is the only reason, but it has a lot of lift on the bottom end. I can get a full flare at about shoulder level. And, flaring to my hips does not induce a stall... I should try some very aggressive stalls up high to see what I have to do to get it to stall because I've been asked this question more than once. Quote Share this post Link to post Share on other sites
billvon 3,107 #21 October 21, 2004 > vortex generators...but probably not very effective ones. I think they are > most like stall fences. Stall fences/vortex generators/turbulators are essentially the same things - they are small protrusions into the boundary layer on the tops of airfoils. They have different effects depending on the flight regime, though. (i.e. transsonic, low speed, stall.) I have a feeling we don't have to worry about the effects of the Nitro's winglets on transsonic canopy flight - unless Luigi gets a Nitro 7 or something. Quote Share this post Link to post Share on other sites
tfelber 0 #22 October 21, 2004 From Boeing's web page: Quote Winglets affect the part of drag called induced drag. As air is deflected by the lift of the wing, the total lift vector tilts back. The aft component of this lift vector is the induced drag (fig. 1). The magnitude of the induced drag is determined by the spanwise distribution of vortices shed downstream of the wing trailing edge (TE), which is related in turn to the spanwise lift distribution. Induced drag can be reduced by increasing the horizontal span or the vertical height of the lifting system (i.e., increasing the length of the TE that sheds the vortices). The winglets increase the spread of the vortices along the TE, creating more lift at the wingtips (figs. 2 and 3). The result is a reduction in induced drag (fig. 4). The maximum benefit of the induced drag reduction depends on the spanwise lift distribution on the wing. Theoretically, for a planar wing, induced drag is optimized with an elliptical lift distribution that minimizes the change in vorticity along the span. For the same amount of structural material, nonplanar wingtip devices can achieve a similar induced drag benefit as a planar span increase; however, new Boeing airplane designs focus on minimizing induced drag with wingspan influenced by additional design benefits. An important consideration when designing the wingtip device for the BBJ was that it could be retrofitted on BBJs already in service. A blended winglet configuration (patented and designed by Dr. L. B. Gratzer of Aviation Partners, Inc., Seattle, Washington) was selected because it required fewer changes to the wing structure. The aerodynamic advantage of a blended winglet is in the transition from the existing wingtip to the vertical winglet. The blended winglet allows for the chord distribution to change smoothly from the wingtip to the winglet, which optimizes the distribution of the span load lift and minimizes any aerodynamic interference or airflow separation. So it sounds like the reason for the winglets being at the tip on fixed-wing aircraft is not because of optimal flight characteristics, but more because of the need to keep the cost of retrofitting down. And for fixed-wing aircraft the winglets are used to decrease induced drag and thereby decrease fuel consumption, increasing profitability or range. I haven't seen any fixed-wing aircraft with the winglets further in on the wing span. Quote Share this post Link to post Share on other sites
tfelber 0 #23 October 21, 2004 QuoteI think they are most like stall fences. Actually that theory sounds very plausible. And that effect would be more useful on a parachute than reducing induced drag. Increasing the speed of a canopy can easily be accomplished by increasing wingloading. However, reducing stall speed is very desirable. Quote Share this post Link to post Share on other sites
beezyshaw 0 #24 October 21, 2004 There has been some very good discussion in this thread today about our winglets. To try to comment any further from a purely technological standpoint is way over my head. Although I've been a pilot for 34 years and a skydiver for almost that long, an aeronautical engineer I certainly am not. I'd do well to teach a private pilot ground school class. So I won't try to throw out any fancy terminology. I will say this; in many, many test jumps the winglets proved that they accomplish several things: 1) They allow the parachute to fly to a slower touchdown speed, reducing the necessity to run out landings on no-wind days. 2) They improve the track holding ability of the canopy when landing in a crosswind condition. 3) Winglets give the canopy improved recovery from steep turns. 4) They seem to reduce the diving effect of openings with line twists. Quote Share this post Link to post Share on other sites
pilotdave 0 #25 October 22, 2004 When you say they accomplished those things, do you mean the canopy was tested with and without them, and they made a big difference, or are those just characteristics of the canopy? Dave Quote Share this post Link to post Share on other sites
