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By soarback
#405345
which material did you choose for each panel of the sail? You still satisfied for which materials you chose?
Does this glider have the tip extenders on it?....are they worth it
Thanks
User avatar
By NMERider
#405348
soarback wrote:
Fri Oct 12, 2018 11:24 pm
which material did you choose for each panel of the sail? You still satisfied for which materials you chose?
Does this glider have the tip extenders on it?....are they worth it
Thanks
P1 UVPXW10 White
P3 UVPX05 Clear
P4 UVPXW10 White
P5 Magenta 3958
P6A Black 2100
P6R Magenta 3958
I also got the factory raked tips which I believe are a desirable add-on feature.
I make my own raked tips that are a different design and plan to test on my S3155 soon.
I previously flew the demo S3-155 Race with my own raked tips and preferred that setup.
User avatar
By NMERider
#405359
Odakyu-sen wrote:
Sun Oct 14, 2018 2:38 am
What are the objective advantages of the raked tips? (I realize that there just might be a placebo effect component...)
Yes, there is always 'confirmation bias' with anything where there is a desired result. But when there is only curiosity and the desire to experiment and learn fresh then the 'confirmation bias' is manageable and can be filtered out. In the case of raked tips, I have used over a dozen different sets on many different gliders and have also used different installation methods or have tuned the tips based on the way I installed them. I have gotten dozens of different patterns of results and not all of these were favorable. There are a multitude of different design factors from size and shape through material selection and construction technique. I challenge anything to prove that they actually know how they work. You can forget about the NASA crescent wing shape research from the 1980's. Why that worked on a rigid general aviation aircraft wing or on a turboprop propeller may have little of nothing to do with why they work or don't work on a flex-wing hang glider. What matters most to me is that the tips can be installed in a consistent manner and yield a consistent effect on handling. What also matters is whether the tips can be fine tuned to suit the flying conditions and the pilot's personal preferences. Now what this short video and maybe you'll get a sense of what I'm talking about. Maybe not.

User avatar
By TjW
#405362
Odakyu-sen wrote:
Sun Oct 14, 2018 2:38 am
What are the objective advantages of the raked tips? (I realize that there just might be a placebo effect component...)
Objectively, they increase the span, as well as the Reynolds number and aeroelasticity of the tip.
Additional span and Reynolds number usually decrease drag slightly.

But people aren't claiming huge glide increases. The perceived effects seem to be related to the additional flexibility.
It seems plausible to me that a tip being able to twist and conform to the airflow at high AoA, so it stalls later, while not greatly affecting the twist in the middle of the half-span, could affect the low-speed handling.
So it doesn't seem to me like anyone's claiming a magic solution.

But I could be entirely wrong. Flexwings are weird.
User avatar
By jj colorado
#405364
In addition to the additional span, winglets or tip extensions can reduce the tip vortices that occur with any wing. Given the wingtip shape on a S2 or 3 I would anticipate they create a significant vortice. Any reduction like that will improve performance somewhat, especially if the wing is at a higher angle of attack (AoA). The way to tell how much measureable effect this has is to rent a wind tunnel and do some videos with some smoke near the wingtips. Perhaps someone can encourage some grad student in Aeronautical Engineering to do that as part of their research studies. Otherwise, just try them and see if you feel they are worth it.
User avatar
By NMERider
#405365
Sorry folks but the only measurable effect of raked tips is in yaw damping, tracking, handling, pitch pressure and tip stall resistance. All of these can be measured. There is no measurable effect on performance in non-dynamic flight. There are as many different raked tips as there are designs and materials and they all work different. There are reports of raked tips having detrimental effects. Do it carelessly and you might pay.

In short, it's all able the handling. Handling can be measured even though it's mainly qualitative.

Very few pilots and dealers even know how to tune a glider without throwing raked tips into the mix. Then the tips may need to be tuned as my video points out. Good luck and beware of speculators and theorists.

The stock Sport 3 with factory raked tips works just dandy. I can assure you of this. Why it works or how is unknown. What matters is that it does work.

I want more and I have learned how to get it.
YMMV
User avatar
By DMarley
#405366
Take a look at Steve's (aeroexperiments) older vids when he was experimenting with small drag 'chutes near his wingtips. You can see the effects of the tip vorticies generated at high and lower lift coefficients. At high Cl's (slow airspeeds) the drogues are rotating the way you'd initially think they would, rotation from the bottom to the top surfaces, indicating upward tip-lift. But at a certain Cl (lower), they would stop their rotations, then at still-lower Cl's (higher airspeeds), they would rotate the opposite direction (rotation from top to bottom surfaces), indicating downward tip-lift.

Because a flexy has a bunch of aeroelasticity, I figure that the extensions are reducing tip vorticies, not merely by their shape and span-extension to the wing alone, but also because they add more moment behind the local neutral moment of the wing at the tip, thus deflecting the tip more, increasing the wash-out twist, and modifying the lift distribution about the whole wing to more of an exaggerated bell-curve (more lift at the root, less lift nearer the tips) at high Cl's (much to Prandtl's supposed second theory), theoretically further reducing tip drag and overall induced drag. However, I don't completely subscribe to Bower's ideas. By modifying the lift curves, the root now has a greater portion of the lift distribution, thus there is more leading and trailing, vertical flow deflection (action/reaction) near the root, creating more induced drag, whereas the mid wing and tips are doing less work, and almost merely along for the ride (not really, but closer to that condition than without the tips).

At lower Cl's, again the tip extensions are creating a larger local aerodynamic pitch moment to the aeroelastic wing, and possibly help to reduce geometric wash-out (reducing the negative lift dist at the tips and flattening the whole lift-dist curve), allowing less overall induced drag due to the inefficiencies of the typical, highly-twisted (washed-out) wing platform at low Cl's. I would guess there is a limit to that reduced twisting at low Cl's.... too much local pitch-moment-induced deflection from the original design goal and it would hinder the nice, humane, airspeed-limiting characteristics of the glider (more prone to tucking?).

At least this is my theory at this point in time. I'm sure Steve will set me straight. :wink:
User avatar
By DMarley
#405367
Merely theorizing here, again... (beware of speculators and theorists), if indeed the tip extensions do modify the lift distribution curve so that more of the lift is nearer the roots, therefore the span-wise lift moment is closer in towards the lever-arm system that controls sail-shape, it could be thought that this mechanism would make roll inputs easier?
Also, because the center of lift is then a bit further forward at higher Cl's, the center of the pilot's CG would be further forward compared to that of the glider's CG and the aerodynamic center of lateral resistance, it also could be thought to make the glider more directionally stable.
I would wonder if the tip extensions would make flaring a bit less positive, though, due to the (theorized) extra wash-out at very high Cl's?
Anyway, just some thoughts.
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