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Old Sep 27, 2010, 08:08 AM
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9-15 Report: another wing tip panel design

Back on 9-12 & 13, I was posting about experimenting with various wing tip shapes :

" I'll likely change the up-swept wingtips to curve a bit more gradually, and to extend farther above the wing's upper surface - (more like those on the earlier DANCER series wings.) This should result in more 'virtual dihedral' affect on the wing, and result in a wing which is more self-stabilizing, and which does not have to be flown so attentively."

As this stage of the experiment, I exaggerated the size of the wing tips, using 7" of Bluecor material , and having them curving up to extend 3-1/4" above the wing's lower surface. I added in some contoured longitudinal ribs to tie the curved panel into the main wing tip structure, ending up with a fairly stiff wing tip panel. I then applied some clear laminating film over the ribs in an effort to smooth the airflow over that area. Resulting wingspan is 58". (In retrospect, this may be where the excess drag is being generated... it needs a better smooth surfacing in this area. Sweeping back the leading edge of the wing tip, similar to the Multiplex Easy Glider's shape, may also help.)

I haven't had good air to fly the wing in since then- mostly late day cold winds without much in the way of warming rising air , but I've been able to confirm that the higher extended wing tips do add 'virtual polyhedral' stability to the wing. From what I've observed, I'm also beginning to think that these particular wing tips are adding more drag than I'd like.

The previously tested shorter sharply curved wing tips on which the outer upper ends did not extend as far flew with less drag, but did not add quite as much of the possible 'virtual polyhedral' stabilizing affect to the wing as might be desirable.

So I think I may have managed to get a better feel for what is "too much", and what is "too little" through these experiments.

After a bit more test flying in better air, I may start carving and reshaping these wing tips. I may also do a smooth overlay panel over the ribs with 1mm Depron to get a smooth airflow surface in this area too as another test. (Hey, it's only foam!)

If I don't end up with what I'm looking for, I'll simply cut away the wing tips & build another set. (The Komet's wing tips work so well, so I may need to revisit that design and adapt something similar on this wing.)

[UPDATE: having the wing tips fully curved into the vertical position seems to form a 'pressure pocket' which adds drag; later, some of the curvature was relaxed out of these wing tips with the heat gun, and the drag was noticably reduced.]

VIKING
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Old Sep 27, 2010, 08:17 AM
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9-15: DANCER III: Fine-tuning the elliptical upswept wing tips

Friends,

I did two modifications to the exaggeratedly large wing tip panels which worked out very well, as far as the improvement in flight performance:

1: I took the heat gun to the wing tips to remove some of the excess curvature. Before this, the last ~1-1/4" of the tall up-swept wing tips was almost vertical. I'm now suspecting, however, that having this steeply upturned wing tip produces a pressure area there which results in excess drag. By bringing the curvature back down to that shown in these latest photos, this pressure buildup may be substantially reduced or eliminated. The test flight observations do definitely find a lot less drag, and smoother handling of the wing now.

2: The second thing I did was to carve away some of the leading edge foam at the front corner of the up-swept wing tips, ending with a more swept-back contour to the leading edge in this area. It worked on the earlier Dancer series wings, & was used on the Komet, and the Multiplex Easy Glider also uses a somewhat similar contour.

I had also reinstalled the 2mm filler panels behind the primary step, but this time without the 4mm spacers under their leading edges. This results in a 4mm primary stepped discontinuity at 50% of chord, and an angled 2mm thick panel extending back to within 3/8" in front of the aileron hinge line, where there then is a 2mm stepped discontinuity. Maximum airfoil thickness is 8.3% of chord.

Wingspan is now 59"

THE FLIGHT TEST

Winds were gusty and irregular, and what thermals were moving through the flying site were quick & dirty, with turbulent air prevalent and gusts running up to ~18-20 MPH. But the recent modifications to the wing tips, and having the new rear 2mm filler panels installed as they are has resulted in an aircraft which ignores the rough air and is now flying very nicely! After launch, I can now pull it up into a full vertical climb and hold it there easily as it climbs smoothly like the proverbial 'homesick angel'. Rolls are smooth & axial, inside & outside loops are equally easy, and inverted flight is very manageable. So some mild 'hot-liner hot-dogging' is also well within the reporitoir of DANCER III. This one is Definitely a KEEPER!!

~~~~~~~~~~~~

[ Question Originally Posted by A Useless Geek: ]

"Are you saying that the up-swept wingtips alone accounted for the vast improvement in stability you experienced on your latest wing test?"

Yes, that's exactly what I was trying to get across. This otherwise flat-built aileron wing with the up-swept wing tips coming up to 2-3/4" from the lower wing surface may be rather similar, stability-wise, to a dihedral wing where each wing tip has roughly the same amount of total rise at it's wing tips.

The advantages are that the wing is easy to build flat, and it responds very well to aileron control, and can roll fairly axially. I fly both rudder and ailerons when I'm hunting / chasing thermals, and I often use cross-control input, where the rudder produces yaw in one direction while opposite aileron is used to keep the sailplane in only a very shallow bank while coming around in a circle. This helps hold altitude in light lift.

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Old Sep 27, 2010, 08:24 AM
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[ Originally Posted by A Useless Geek:]
" I kinda like your heat shaping technique with the covering iron, but that really takes a deft hand and quite some bit of experience to get right, doesn't it?"

IF a builder happens to have a heat iron and a heat gun, they can do some experimenting and practicing on scrap material. Getting the right heat setting, not using too much heat with the iron OR the heat gun is the main thing each has to get comfortable with. From there, if someone discovers that they have ten thumbs & no inclination to invest a bit of extra time, that's OK too... this is supposed to be fun, after all.

The builders of the foamie 'ten minute wonders' may have no time or reason to use these techniques, and that's OK too. K.I.S.S. certainly has it's place- it's all fun!

But demonstrating these very workable techniques for others to possibly try certainly has value. Knowing that inexpensive foam can be very effectively heat formed and heat-tempered is a good thing- it opens up possibilities.

(Applied Aerodynamics is the practice of fine-tuning controlled air movement in practical ways- theory into form, very closely inter-related.) It's nice to know that we are not limited by the fact that foam is typically sold in flat sheets or blocks!

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Old Sep 27, 2010, 08:33 AM
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9-19 summary report on DANCER 3 development

I've tested various step configurations and wing tip designs; I've ended up with the primary step at 48% of chord, with max airfoil thickness at 38% of chord. I test-flew the wing without wing tip plates, then tested three different types of outer ends on the wing, ending up with some extended smoothly up-curved wing tips which both stabilize the wing and minimize drag in the wing tip area. Wingspan is now at 59", average chord at 9". I also did some shaping of the leading edge of the wing to improve it's glide efficiency & wind penetration capability

And I experimented with adding in a 2mm thick depron overlay panel which is taped in place behind the primary step and which extends back to just 3/8" in front of the aileron hinge line. This results in a ~3mm deep primary step at 48% of chord, and a 2mm deep step just in front of the aileron hinge line. This wing is now penetrating winds very well, and gliding very efficiently, with very good stability and very clean response to both ailerons and rudder.

I had also designed a sleek fuselage with a folding prop on the nose to minimize drag during power-off flight. This wing mounts with rubber bands on re-positionable pegs on top of the fuselage, so that other wings might also be test-flown on it.

A couple of days ago I took it out to one of the slope flying sites here in South Park. Winds were peaking to 29 MPH on my wind speed meter, and although 'DANCER III' is light on the wing loading for high wind slope flying- (only about 5.7 ounces per square foot)- I launched it into those winds without turning on the motor, and it flew great. It's penetrating winds well and handling very well, so the latest setup of step location & height has resulted in a low-drag wing that really is flying great, with both good stability, and clean response to control input. (More of the flight report is on the other thread.)

So this has developed into a very fine performing wing! It could likely be mounted to Russ40's fine fuselage design - you just need peg spacing for mounting a 9-3/4" chord wing.

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Old Sep 27, 2010, 08:40 AM
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Dancer III slope flying report
Friends,

With due west winds forecast for this afternoon, I took some time away from work to take Dancer III out to the KING Slope Flying Site. When I arrived, I checked the wind speed with my wind meter, and saw one peak at 29 MPH. Time to fly!!

Dancer III is flying with a Rhino3S 1050 battery now, for a total weight of 19-1/4 ounces. That comes out to a wing loading of only 5.7 ounces per square foot. Most slope fliers would consider this a bit on the light side for penetrating winds up to around 30 MPH, but after the flying I had been doing out on the flats, I wasn't too worried. I waited for the winds to drop off a bit, and launched without turning on the motor at all.

Wow- this sailplane LOVES slope flying conditions! it penetrated well & climbed out & up in front of the slope nicely. The stability added by the up-swept wing tips was apparent right away, and while it handled as if lightly loaded, it dealt with the cycles of building and dieing slope winds very comfortably. (Flying with a heavier battery pack for an increase in wing loading is always an option; I did not try that today, as I wanted to evaluate this wing / aircraft's ability to penetrate the strong slope winds without ever turning on the motor. And Dancer III was easily able to do that!

Turbulent thermal-generated winds were cycling into the face of the slope; between high wind cycles, the wind speeds would die down & the air would go cool, with a noticeable lack of lift, so that I needed to fly a bit more conservatively until the next wave of warmer air & stronger slope winds would cycle in. No problem- it handles light air & soft lift conditions very nicely, too.

When flying back & forth across a ~400 yard section of this slope, I played with turning just with the rudder at times (with a bit of elevator as needed) and then turning just with the ailerons. I was happy to find that it responded well in the slope winds to either the ailerons or the rudder. And while loops just in front of the slope can be a dangerous maneuver for some lightly loaded slope fliers, the Dancer III would come through an inside loop quickly and cleanly without loosing control responsiveness... how well it came through the loops surprised me and impressed me too. At this light of a wing loading, however, inverted flight in slope winds is not it's strong suit... no need to keep it inverted too long- that's best left for a slope ship with a higher wing loading or a load of ballast on-board.

I did have to turn on the motor one time during ~45 minutes of flight for a few seconds. It wasn't because I was loosing altitude, or because I was being carried back behind the ridge- those were never issues during today's flying. No, the reason I had to kick on the power was because one of the local hawks came over to check out the new fancy looking flier on HIS slope. After looking my plane over from several angles, it moved in close behind the tail- within 4 or 5 feet. That's when I gave it full throttle and climbed vertically a hundred feet in a couple of seconds, then cut the motor again. The hawk immediately lost interest after that quick maneuver, and moved back out of the area.

I only made two landings during this flying session, landing on the shelf where the first photo below was taken so that I could grab my camera out of the car. I then launched again, sat on the slope, and started to take some photos of Dancer III cruising in the slope winds. (It's a fairly stable slope flier that will let you fool around with your camera while still flying it as much as necessary in slope winds like I enjoyed today...) I'm REALLY getting to like this aircraft!!

And what a beautiful early fall day it was to be out flying on the slope!

It really IS all fun!

VIKING
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Old Sep 27, 2010, 08:43 AM
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On 9-16, DICKEROO commented: " Bruce... thanks for a great report. It almost makes one feel like you're there. You have designed a wonderful aircraft. What a thrill it must be for you. Congratulations on a great job!"

Dick

Dick,

Thanks so much for the kind words!

This test aircraft has allowed me to explore aspects of using KF stepped discontinuities in ways which I had not previously tested, and I'm impressed and intrigued with the results... "Flying is Believing"! But through all that we've observed so far, I strongly suspect there are still many things to observe, learn, and pass along, and subtleties to understand and employ. And it's great to be able to share the observations and experiences with you and everyone else here on the discussion forums.

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Old Sep 27, 2010, 08:46 AM
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9-17 posting

Quote:
Originally Posted by tolladay View Post
Viking,

I notice you kept the depron filler panels on the wing, reducing the size of the KF steps. Did you decide to keep the wing like this, or are you planing more flights? I'd thought you might take them off half way through to evaluate the difference, but maybe you were having too much fun.
Tolladay,

Utilizing KF stepped discontinuities in ways which minimize or reduce drag (rather than increasing drag) is one of the central themes behind the tests I've been doing with this wing.

I had been wanting to develop a build approach (using simple foamie building techniques) to reduce the depth of the primary step, and possibly of any secondary step, and to shape the structure behind the primary step. I wondered if doing this would result in reduced drag compared to a more 'classic' KFm3 (deeper step) approach, since so many have had less than great results on some KFm3 builds, and some builders have commented that they find KFm2 builds working better for them.

(Tony had commented back in the summer of 2007 that my 'Hot Dog' KFm3 wing on the Slim Beagle was the first KFm3 wing in the air that he was aware of- he hadn't completed one himself at that time. I've continued brainstorming and designing new ways of implementing the stepped discontinuities since then.)

The overlay / filler panel approach is simple to use for testing purposes, and very effective. These 2mm Depron panels simply tape in place quickly, and come back out even quicker. I've had them in, out, and then back in as I've done my test flying over the last few days.

Yesterday I was flying on a slope with a knife-edge top with winds peaking at around 30 MPH & up, and I know what kind of rotors form on the back side... (been there, done that, went home & repaired the damage...) I had no interest in being carried back there.

At Dancer III's light wind loading, I could fly the front side decently, and with the filler panels in place I had enough wind penetration capability (minimal drag) to stay flying out in front of the slope in the strongest of the wind gust cycles. The wing was handling very well - the 4mm primary step was doing it's thing.

And - even more interesting: I found that having the 2mm step just 3/8 of an inch in front of the aileron hinge line resulted in the aileron response being clean and precise during high speed as well as low speed flight.... Yet many have reported that having a 6mm deep step too close to the aileron / elevon hinge line has been known to trash aileron function badly.... This is definitely something to remember on future designs!

Removing the overlay panels might have resulted in just enough increase in drag to reduce the DANCER III's ability to penetrate the high slope winds.... I wasn't ready to try that without adding ballast to increase wing loading to keep the aircraft safe, and I wasn't set up to do that ballasting yesterday.

And yes, as you guessed- mostly, I was just having too much fun, enjoying how well it was handling in the winds!!

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Old Sep 27, 2010, 08:48 AM
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9-17:
Quote:
Originally Posted by Freddie B
Viking,

The filler panels are way cool. I thought about that when I had trouble on the KFm3 wing I did, but haven't because I'm still trying everything to the 'as designed' way, first.

I was thinking that this would mimic a conventional airfoil in that the air would follow the top surface so that my ailerons would become more effective. Also thought this was taking away from KFm 'concept', but I shouldn't have. After all KFm begs to be experimented with. Besides you left a step, only smaller. Opens up some further thinking on the subject for sure.

BTW, very nice looking ship you have made. Also the flight report sounds great. I can't slope soar local here in this part of Nebraska, but sure do remember my days in So. California! I'd love to toss something like that off the slope and fly until my biceps hurt from holding my radio so long without taking a break!

Keep up the great work, but most of all keep having fun!

Fred
Fred,

thanks for the kind words! The nice thing about working in foam is that we can cut, carve, sand, & morph from one shape to another, and we can add & modify as we are inclined. Adding in the 2mm Depron filler panel seems like a relatively straight-forward morph that can be done to any KFm wing build that's not quite performing as well as someone might like. If the old secondary step gets in the way or isn't quite working where it's at- then just "carve away and overlay"!

The sleek low-drag fuselage with the folding prop certainly helps in allowing this wing to show what it can do; a boxy fuselage would be a bit of a handicap in those stronger slope winds when flying at a light wing loading.

And you're right- KFm implementations beg to be experimented with- there's no 'sacred dogma' that restricts us as to how we might implement stepped discontinuities... just a growing database of 'what works' to draw upon as inspiration for further prototyping and testing!

SLOPE FLYING- GOTTA LOVE IT!

Slope flying is one of the things that builds a grin for me that doesn't go away for days- it's the interplay of air and gravity on something which I've crafted with my own hands, and then have been bold enough to toss it out there to fly in an ever-changing environment. When you fly on a slope at eyeball level, the aircraft's response to your every control input is far more visible and obvious that when flying an aircraft 'three mistakes high' over your head out in the flats. Everything happens fast, and you are intimately connected to the river of air that your aircraft is flying within. You feel the wind on your face, and you can feel the subtle shifts in temperature and direction, the build and ebb of the wind strength, and immediately see it's affects on your aircraft. When the winds are up, things happen fast on the slope, and you're intimately a part of all of it.

VIKING
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Old Sep 27, 2010, 08:51 AM
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9-18: Technical Thoughts

Tolladay,

you wrote: "If I'm reading you right, there is a proportional relationship between parasitic drag, and step height. Your post makes me wonder what the minimum step height would be to get the effects of a KF airfoil?"

While this relationship of step height height to drag might be simply characterized that way, we probably need to keep in mind that it's not an isolated dynamic; the step can only act upon the airflow which is delivered to it at the ~50% of chord point, and affect that airflow from that point on back to & past the trailing edge. But we all need to keep in mind that the airflow which is getting to the stepped discontinuity is profoundly affected by the shaping of every aspect of the front half of the wing: - the shaping and positioning of the entry point of the wing structure, the effective camber line of the forward structure, the surface's smoothness or texture, the presence or absence of any surface 'turbulating' features, The total thickness and rates of curvature, etc... And the dynamics are observed to vary as the chord length (~Reynolds Number) changes, and also to some degree as the aspect ratio varies.

How a stepped discontinuity functions is relative simultaneously to so many other structural aspects and factors; from my perspective, this is a very complex subject. So I try not to oversimplify.

My current experiments and observations are focused on minimizing drag and optimizing power-off glide performance and wind penetration capabilities, and are relative to the deeper chord glider-style DANCER III wing which I'm currently testing; this is a flat-built wing at 59" span with a chord tapering from 10" at the wing's center to <8" at the up-swept wing tips. The leading edge shaping is fairly extensive, but probably not optimized, but I'm testing how the KF structures added to the aft half of this wing (in the limited area from 50% of chord to just in front of the ailerons) affect the handling and performance of this particular wing.

Resulting observations will apply to similar wing structures... but may not be universally applicable to all other types of 'Foamies' which are discussed here, and may have less relevance to flat plate wings or wings with bottom stepped discontinuities. This is simply where I'm focusing my testing now, because I'm thinking that power-off glide performance can show us the most about the KF dynamics. Others can test other aspects to check for correlations.

WHAT'S WORKING ?

With all of those cumbersome qualifications out of the way , I'll simplify by saying this;

1: This wing flies better (handles with more stability and predictability) with the Primary step exposed than with it covered;

2: This wing performs better (as far as wind penetration and glide efficiency) with a ~3mm step, and with the overlay panel providing a secondary 2mm deep step just 3/8" in front of the aileron hinge line. Handling in heavy winds and during high speed powered flight is also subjectively better (smooth precise response to aileron control input) with these overlay panels in place.

There's another key concept to keep in mind; adding a KF step may not have to be a trade for stability with a drag penalty... if it's properly implemented. A trapped circulating vortex behind a stepped discontinuity has the potential to actually reduce drag while minimizing surface bubble air separations over the aft portion of the airfoil.

More later- this is a great area for lots of further discussion- and Tolladay always asks the nicely loaded pertinent questions!!!

VIKING
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Old Sep 27, 2010, 08:58 AM
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9-18: More Tech stuff: 'Turbulators'

Quote:
Originally Posted by A Useless Geek :

"Hmm. I'll bring this up in the other thread, but it seems that we're experimenting with step heights that are getting closer to surface turbulators than actual steps. Other people have talked about research into turbulators. The Rooskies did some of this stuff accidentally when they discovered that some of their fighters actually flew better when the top wing skin was stressed rippled after hard usage. "

Geek,

I've played with turbulator structures a lot on sailplane & built up balsa wing structures. I leave ~1/2 of the 1mm CF rod spar caps exposed on the wing surface of some of my foamie wing designs as surface air turbulators.

On the recent DANCER III project, one stage of the testing involved adding an overlay panel with a spacer beneath the leading edge, so that the primary step was reduced to being only a ~.5mm deep turbulator notch. Short analysis: it did not provide the ('circulating vortex-trapping') stabilizing affects which a 3mm deep step is observed to produce. [At the same time, from my subjective evaluation of the flight testing, a 6mm deep step followed by another 6mm secondary step half way back to the aileron hinge line results in the wing being a bit less 'clean- of the wing not gliding quite as efficiently.]

From my flight experience perspective, I'll theorize that the 2mm step just 3/8" in front of the aileron hinge line is a stepped discontinuity which keeps the air running over the aileron's upper surface turbulated / attached. The aileron control response is crisp and precise across the entire speed range.... something's working right here. A 1mm step here might be very appropriate and adequate; I'll test that before long. Yet we also know from many previous reports that a 6mm step that close to the aileron hinge line reduces the aileron effectiveness dramaticly.

(Working in 6mm increments just because that's the way FFF is made & sold is a poor trap to get sucked into; fortunately, Depron is available in many thicknesses- I have 1mm, 2mm, 4mm, 6mm, and 9mm on hand to work with in doing the ongoing testing.)

Discontinuities - of whatever form- can be employed to influence boundary area air flow. But at some point, as the stepped structure gets deeper, a step on a given wing at a given relative location will begin to generate more drag.

Phil Alvirez's blog has his writings on the topic of turbulator devices; you may enjoy reading his thoughts on the subject.

More later!

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Old Sep 27, 2010, 09:00 AM
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9-18:
Quote:
Originally Posted by davereap
Interesting about the low step at the hinge line, cause I am one of those who had normal depth step hinge line problems. All the talk of low steps makes me wonder whether a larger number of small/low, steps might be a worth while trial on any wing..Its an easy enough trial to do..
Dave,

I've been wondering too... but I'm also wondering if we need to leave the primary step 'room to do it's work'. I'm trying to visualize the trapped circulating vortex which keeps the boundary layer air from separating behind the primary step; seems like, on a higher aspect ratio KFm2 wing, this is really doing a pretty good job of influencing the airflow all the way to the trailing edge. If this is the case, adding more steps might possibly interfere with what's already working. (This could be the case of being "too much of a good thing".... I'm going to have to keep this concept in mind & mull it over for a while.)

The 2mm step just in front of the aileron hinge line on the DANCER III wing seems to be working well. It certainly deserves further close scrutiny.

In the case of a <1:1 aspect ratio foamie fun flier or delta, etc, other aerodynamic factors may come into play. We look forward to reading the reports of your experiments!

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Old Sep 27, 2010, 09:02 AM
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9-19:
Quote:
Originally Posted by gpw
V60 , wondering how the air density affects our testing , your air is much thinner than the soup down here at sea level .. So many variables , the only real way ,as you say , is the actual flying ... that's all that matters anyway huh?

Have FUN on vacation ... !!!
GPW,

Flying in the less-dense air up here may show the affects, (as far as in-flight performance, stability, and control responsiveness) of minor changes to wing structures / aircraft design aspects more obviously than when flying in higher density air at sea level. That may then allow us to more critically evaluate the results of some of these test configurations. From there, the aging but very experienced thumbs and eyeballs come into play.

Rich Thompson wrote it well in his article- something to this effect: 'an experienced pilot's observation and evaluation of the 'feel' of an aircraft's performance and handling response when they are flying that aircraft through a variety of maneuvers in a variety of 'real world' air conditions can be very valuable. Simple test equipment does not have that background experience as reference, or the hands-on perspective that the pilot has.' ...(or something like that...)

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Old Sep 27, 2010, 09:06 AM
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9-19:
Quote:
Originally Posted by Russ40

Viking..That is great stuff on the KFm3 wing. I really like the looks of the tips. I may have to build a slope plane with that wing. Thanks for sharing all of your hard work with us.
Russ,

In building this test bed glider wing, I had started with the .210 CF spar tube & primary step at 38% of chord, but I was not as happy with how it flew with the step at that position; so I added in a 1" wide section of Bluecor just behind the first primary step position, effectively moving the primary step back to 48% of chord.

BUT - the airfoil's maximum thickness remained at the point just over the tubular wing spar at 38% of chord. And this may help this wing glide better than if the maximum thickness were back at the primary step at 48% of chord.

On my next prototype of this wing build, I'll place the tubular CF wing spar at about 30% of chord , and build the tapered chord wing with tapering vertical foam strips to support the upper surface. (I'm going to try to more closely follow the MH32 airfoil profile this time, since it has worked so well on the Me163-e Komet.) I want the airfoil's maximum thickness of ~8.7% at the ~30% of chord point, with the wing well-shaped forward of that. I'll set the primary step at 48% of chord. By tapering the span-wise foam airfoil support strips lower as they approach the wing tips, I'll keep the wing's airfoil from getting too thick out where the chord is less. This should also help to minimize drag in the wing tip area. And I'll be incorporating that top rear 2mm Depron overlay/ filler panel, as it's working so well!

[UPDATE - Drawing now added]

I've now added a drawing of the wing structure so everyone has a better idea of what I'm talking about. It'll again be a simple flat build, using hot melt glue for the majority of the center 48" portion of the wing, with the up-swept wing tip sections added to the core wing structure - simple to keep aligned, fairly quick to put together, and very effective in the air.

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Old Sep 27, 2010, 09:14 AM
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9-24 updated: New glider wing build info:

Friends,

I'm actually starting with a 10" chord at center, 8" at the outer ends of the 48" span center section. (I then cut off the wing center section trailing edge so that a 9" long straight piece of 2mm solid CF can be mounted there to reinforce it where the rubber bands hold the wing to the fuselage.) The ailerons are included in the total wing chord. The drawing illustrates the structure at mid-span, where the chord is 9".

I re-sized the drawing to print at 10" chord for the center, and also re-sized it to print at 8" chord for the wing tip. I could then pull the dimensions for the internal support foam strips' inner and outer end heights directly off those printouts. Just measure total height of the airfoil at a point on the drawing where a tapered filler strip will go in place, subtract the thickness of the top & bottom foam layers, and you have the dimensions to cut the internal tapered support strips.

(I actually moved the front internal support strip forward from where it was shown on the drawing; it's center is about 1-9/16" back from the leading edge of the wing. I wanted a good support of the final airfoil shape at this particular point of the curvature.)

[If you want, you can also make a set of upper airfoil surface contour templates from these three size prints to guide you in doing the finish-shaping of the forward section of the wing's airfoil. Or you may be able to eyeball it just fine. I do use a heat iron to do my final forwards section shaping & tempering of the foam For wind penetration and glide efficiency, the shaping in that area really can make a difference.]

My wing's leading edge is a straight line on both DANCER III wings- the trailing edge is what shows the taper. I am using the straight leading edge again, using the fold of the Bluecor at the L.E.; that's the simplest approach to this wing build. On the second wing build, I have now installed the 48" long straight one piece tubular CF spar at 2.7" back from the L.E.

My top surface primary step runs from ~48% of chord in the center of the wing to 39% 0f chord at the outer wing tip ends of this 48" structure.

Wing max thickness at the outer ends of the 48" main wing structure will be 80% of what it is at the center of the wing (since the chord is 80%)- that's why internal vertical support pieces of foam are tapered narrower / lower as they progress from the center of the wing towards the wing tips.

This drawing, and the photos below show the fairly simple build approach for the second generation build of a efficient glider wing which should fly well on Russ40's trainer fuselage.

I am shooting a new series of photos of this wing build; here are three of them for now which show the first phase of the build. Photos always help clarify what may sound a bit complex in text... this really is a fairly simple build approach to end up with a high performance glider wing that will handle high winds very well.

VIKING
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Old Sep 27, 2010, 09:20 AM
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9-25: New Wing Build Complete

I completed the new wing & flew it this afternoon. It's gliding very cleanly, thermaling in light lift VERY efficiently, and has excellent stability in the air. With the up-swept wingtips reaching 2-3/4" above the wing's lower surface, the 'virtual polyhedral' affect allows this wing to turn very nicely in response to rudder control, as well as having good aileron control response too. It was finished out with slightly longer wing tip panels, for a span of 62", 3.7 square feet of wing area.

I'm looking forward to getting this wing out in slope wind conditions before long. It should have very low drag, and therefore be able to penetrate high winds very easily. I'm really liking how this KF3P wing building approach, using the rear overlay panel, is working out! If you get a chance to build one of these, I'm sure you'll like it.

I did shoot a lot more photos of the 2nd wing build process, and especially of these latest generation wing tips. It's flying with the balance at 30% of chord now (=2.7" back from the leading edge), riding light thermal lift easily.


~~~~~~~~~~~~

Next generation DANCER III KF3P wing flying great!

I completed the new 'KF3P' glider wing build for the DANCER III series and flew it this afternoon. It's gliding very cleanly, thermaling in light lift VERY efficiently, and has excellent stability in the air. With the up-swept wingtips reaching 2-3/4" above the wing's lower surface, the 'virtual polyhedral' affect allows this wing to turn very nicely in response to rudder control, as well as having good aileron control response too. Roll rate is a bit slower on this 62" span wing with the extended up-swept wing tips, since there is only ; that's the nature of this style of wing design.

It was finished out with slightly longer wing tip panels, for 3.7 square feet of wing area. This wing build ended up lighter than the previous prototype, so the overall wing loading has decreased from when flying the previous wing build. I focused more attention on this wing design on the shaping of the forward section of the airfoil with the span-wise foam support strips, so that only minimal heat shaping was needed on the wing's leading edge. I still use the heat iron to tighten up the surface of the foam some, and to remove the normal creases that are on the fold between panels of Bluecor FFF, but minimal heat-compressing on the foam in the leading edge area was done. The wing's trailing edges and wing tips are thinned extensively by first carving away excess foam, then heat treating to end up with very thin trailing edges. .

It's was flying this latest test wing with the balance set at 31% of chord yesterday, but I'm thinking that it may may handle a touch smoother in high wind conditions if the balance is shifted forward a bit more, to between 29% and 30% of chord.

Using the 2mm Depron overlay panel [the P in the KF3P designation] aft of the primary step is working very well; this results in only a 4mm deep primary step, with the lower 2mm deep secondary step located just 3/8" in front of the aileron hinge line. There are no deep stepped discontinuities- just these shallower ones. This latest prototype glider-style wing, with it's more careful shaping and it's lower profile stepped structures has better lift and less drag, resulting in a wing which has an even cleaner and somewhat more efficient glide than previous test prototypes. (The sleek fuselage with it's folding prop has to help too.)

I'm looking forward to getting this wing out in slope wind conditions before long; that's where the wing's minimal drag should really show. It certainly seems to have very low drag whild doing the climb-and-glide thermal hunting, and should therefore also be able to penetrate high winds very easily.

Bottom Line: I'm really liking how this KF3P wing building approach, using the rear overlay panel, is working out! Using the aft overlay panel to test the wing's performance with and without the deeper steps exposed has been an interesting process, with rewarding results. This glider wing is a definite performer!

VIKING
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Last edited by viking60; Sep 27, 2010 at 09:26 AM.
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