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Thanks for a very helpful post, it really confirms a lot of my internal thoughts that I was uncertain about. You bring up one very important thought and that is the seemingly key "facts" don't pass basic logical thinking - such as the flaps having a neutral pitching effect. Because this format is limited, I'm posting my full response to you on my Patreon site. It will be available to the Public and I will shortly post a link to that writeup here. And, anyone who visits there can sign up for free - just click the three dots to the right. www.patreon.com/klingbergwing

BTW, would it be possible for you to do a complete and reasonably accurate translation of the original document into English? It would help a me a lot and I'm sure others would be very interested. Let me know, Rol

​@@KlingbergWingMkIICertainly! It will be a good chance to cross check the translation and I know of some German guys that can help. Just send me (how?) the original text. Thank you.

Thanks for offering to help translate. Now all we have to do is get the original text - I do not have a copy. I'll check with a couple of my potential sources.

Glad to help.

Thanks for the offer, but it is a really hard drive for me and cost too much in terms of both time and money. I'm very busy building new outer wing panels and preparing for more testing at Marina Bch and El Mirage. I hope everyone in your group follows my progress on my YT channel. Please pass the link to the group. Fly Safe!

Hi Eric: Hope all is well with you, your family and aviation projects - they are unparalleled. What you have written is the results of analysis that was done shortly after the crash. I've never seen any math to back it up, but it might be out there somewhere. Apparently the LBA analyzed the crash over a 6 year period and I'm trying to find that report. I'm currently in contact with Gunther's son to see if I can get a copy of the report and a set of airfoil coordinates. Currently, Steve Morris and I have both done some CFD on the design (different codes) and have seen results that do not align with the reported flight characteristics. It is documented that the pitch trim was neutral with flap deflection, but Steve and I don't get that result. Steve is uncertain why. I'm trying to find out more about the crash because I think I've had similar or related issues with my current glider. So, stay tuned and keep posting your work and flights, they are really great.

I would tend to agree, however, they are technically correct and therefore should be retained for reference. The key question is, "Why would you make this post here?" I am looking for airfoil coordinated for the Flair 30 and your comment is not helping in that regard. Post here only if you can help.

You don't know what you are talking about. There was no tumble involved.

Where did you get your aero eng degree?

You have asked the wrong question. The center of lift does not move with changes in speed. The correct question is, What happens to the pitching moment when the controls are deflected - especially the flap? I and another aero eng are still in the process of analyzing the design to answer this critical question.

@@KlingbergWingMkII Yes...control deflection. One model of that pitch behavior is C-150 full flap deflection forcing a strong down pitch adjustment when still well above stall.

You seem confused over this concept. From the Aviation Stack Exchange, "The aerodynamic center does not move when plain or camber flaps are used." The change in pitching moment is due to the increase in camber and hence the amount of circulation around the airfoil. This is standard aerodynamic theory. I only post this correction so my viewers do not become mis-informed.

Thanks Steve. Don't know if you/ve seen the following video, but my xflr analysis of an airfoil similar to the Swift (BTW, do you have the coords for the Swift airfoil and may I have a copy?) shows exactly what you are talking about. It is clear that at low Re it is important to keep the control hinge line outside of the adverse pressure gradient. I discuss the topic in detail in the video. I mention this as I bet most folks have not seen the video or don't really understand my pts. I suspect that the hinge line of the Flair flap at 40% is the root cause of flow separation and hence a full-on stall (at AoA less than normal stall) and caused the Flair to pitch down rapidly with no room for recovery. I will be posting a full analysis of this issue in the near future. Fly Safe, Rol. Video on the topic: ruclips.net/video/2mh8szvuD40/видео.html

Having the airfoil coordinates would be a huge help. Let me know if you get them or can give me a lead on where to get them - thanks!

Do you happen to know whether or not Gunter was a licensed engineer? If yes, what type of degree did he have?

@@KlingbergWingMkII First of all Günther was a visionary and manager. He was well known in germany for his many airplanes . A team of engineers did the structural and aerodynamic calculations for his projekts so he was well based from a scintific point of view.The real problem was how to finance? He him self was professor for industiedesign in Hamburg- where I met him.

@@KlingbergWingMkII I will try to get, but I can not promise,

@@KlingbergWingMkII I had a call with Holger Rochelt , son of Günther Rochelt ,5 min. ago. He flew the Flair30. I may send you his telephone number so you could get in contact with him. But not here in public. Do have a E-mail adress or something where I could send you the number privatly?

Thanks for the input. I have read the original accident report (poorly translated) and your comments align with that report. However, regarding classic aerodynamics, that analysis appears to be flawed. Having a CG forward of the limit will not cause an aircraft to dive into the ground, especially after 45 minutes of flying time on the fatal flight. A forward CG would require a lot of up elevon to take off or not take off at all depending on how far out of range it is. This would be apparent at the start of flight. A good pilot (seems the accident pilot was very good) would not continue a flight with this issue. But, if the CG were at or near the aft limit, then a good pilot might be able to fly the aircraft for an extended period of time and then either a gust, or different flap setting causes the aircraft to diverge from it's stable config and either pitch up rapidly or dive into the ground. An unstable aircraft can go either way. What most people seem to be missing is that this was, of course, a dynamic event and most of the analysis I've seen is from a static point of view. This approach can lead to incorrect conclusions.

Thank you very, very much for your generous donation. That will cover the cost of some gas so I can get out for more testing!

Yes, one of a kind so difficult to reach conclusions without specific design data.

The crash was indeed filmed/recorded, which was new info for me. The location of that recording is currently unknown, but I'm in contact with a fellow in AU who knows some of the folks involved, but generally does not speak of the event. He may be a possible source. Stay tuned.

I've recently had some surgery and typing is really difficult. My experience may not be very valuable or interesting to you as it's all based on self gained knowledge designing my own rc models over the last 40+ years. I know that aeronautical properties change a lot at scale. With that said, it is true, especially with wings, that there are things done within the designs in any scale that will create huge swings in performance and especially stability. In my humble opinion, these large light "rigid" wings aren't very rigid because of weight concerns. Two things. COG of course is everything. Nose heavy gets away with a lack of correct position. But tail heavy on an aircraft with no tail is a HUGE catastrophic problem. Put a pin in that for the moment. Wing twist is used in nearly every design I've ever seen. Especially in rc models without a fly by wire controller using 10 dof IMU's.... Basically your wing design isn't perfect so we are going to pretwist the wing, to give the wing a little extra up elevon to correct any bad handling tendencies. I know this is basic stuff and very abbreviated I'm trying to demonstrate a basic understanding not trying to tell you anything you don't know. Bare with me, I'm getting there. Other things I've had to work through... Wing sweep. Winglets. Size and locations of control surfaces. All these things I've have added to my early designs because they were bad and I had to according to everyone I didn't ask for advice from... You may be experiencing yourself currently. But as my designs got more complicated I went from an aircraft that wouldn't fly to something that could but not great but then would become a better flyer but began to start eroding the performance to the point of becoming unfliable. And programmable flight controllers became necessary to stay in the air like modern fighters. That's when I changed the goal to making an efficient wing that tracked and steered correctly WITHOUT winglets. That remained stable WITHOUT twist or washout. I reduced the size of the flight surfaces and increased the sweep to bring everything back to a more stable platform and a wider chord at the wing tips. What I found was that the combination of all these things were flexing and twisting the wing to the point where the center of gravity was shifting aft. And in a really strange still not quite understood phenomenon was resulting in a nose down condition. If I'm right, you have a worse problem than I did because you have a PILOT. A pilot moves around. A pilot wants to be comfortable and we all fly full scale aircraft with at least some body English. My wife drives with her tongue hanging out of her mouth. Literally. What I noticed one time was when the car did something unexpected her tongue English was going the wrong way. That got me thinking about the battery in my wing. It was not only moving but it too wanted to be comfortable and was moving in the wrong direction under these weird loads because I used a rubber band (old school) to help secure it. It was pulling on the heavy side by using the wires as a fulcrum. I still don't understand everything that was going wrong there. But what I did was secure the battery, dialed in the correct cog and removed washout. Took advantage of adverse yaw in the elections and flattened the wing. I had good results with 2° anhedral for more aerobatic maneuvers. Thin longer and stronger control surfaces at the root of the wing instead of thick large but short length surfaces at the tip. I'm also blending two airfoils. I have the root airfoil and the tip airfoil and through the magic of CNC hotwire foam cutting I get a PERFECT blended wing with 50/50 throughout the length of the wing. Taking advantage of two airfoils at different areas of the wing means less compromise in choosing one for two very different parts of a wing plan. Just don't get them backwards and spend a year trying to fly something that is literally fighting the air and itself and literally negating every single benefit you thought you were taking advantage of.

Good idea. Do you have any contact info for those still living?

Jim Marske also recently died. Contact info for Matt Kollman, who worked with Jim, can be found over at KollmanWings. Jim's website is still up and still nice to look over. There may be clues about the Flair 30 in Marske's stuff (which Matt Kollman may have insights on).

Only partially true. Models have much lower Re numbers so they do not always behave the same. Just ask the Wright Bros. The Flair had extensive model testing which did not show any problems. I make these comments so that viewers do not get mis-directed by incorrect technical comments.

Yes, tow position was part of the problem. I know have it towing through the vertical CG position. However, even with the tow position off somewhat, there should have been enough elevator control to overcome the moments and there was not. The root cause was separated flow on the elevons. This is due to a Re issue and is discussed at length in other videos. To the best of knowledge, I have since solved that Re issue. Finally, the most recent results and data are available only to members of my channel. You can access them by clicking the join button - only $0.99 per month. Hope to see you there!

I'm not asking for help in analyzing the problem. I'm asking folks if they have any info/source for the airfoil coordinates..

Thanks! I had totally forgotten about that. The info in the book will not solve the whole problem, but will be very helpful. For one item, it confirmed my analysis that the flaps were set up to be neutral in pitch trim when deflected. The pic are not sufficient for getting good coordinates, but they give me some clues that will be useful in future analysis.

Günther Rochelt died from cancer. RIP

An interesting note about the aeroelasticity, but probably not something where there is enough info available on the construction methods to be useful.

If you look at my old videos, can will see that I believe I have solved the stall/spin problem (inboard winglets, control that do not run out to the tip, and special elevon shapes). I believe the Flair crash did not involve a spin as turning or rotation was not reported in any of the 1st person reports.

@@KlingbergWingMkII what’s your conclusion; summing it up in one concise sentence if possible, serious mistakes can be avoided. Thanks for sharing.

I don't have one yet because I don't have all the data I need to do a proper analysis. I have info coming in from multiple sources that will help, but I really need the airfoil coordinates.

We will never know for sure what caused the Flair crash, but it is looking like it was a flow separation and very rapid stall onset that is the root cause.

Testing any new aircraft at altitude with out a parachute is unthinkable! I'm looking at having two of them.

Thanks for the reference. Several folks have pointed it out and it will help my analysis.

Thanks! See my full reply in the other comments.

@@KlingbergWingMkII Lots of interesting info..... good to see this getting plenty of interest!

Yes, the speed that the pilot was flying at the time will be important. At higher speeds, Re would not be an issue as you stated. My current guessing is that the pilot felt he was going to overshoot the landing site and dumped a bunch of flap and unknowingly, and unexpectedly stalled the entire wing, even though he probably had plenty of speed (well above stall speed).

That's an excellent point that I had not considered as I didn't not know he was involved with the HPA world. Now that you mention it, I see some similarities with the Gossamer Condor and Albatross airfoils - low speed stuff. From Nickel's book it also appears the airfoil as similar to was on the early Swift designs. You are right, extracting coordinates from the available pics and drawings would be useless for engineering analysis. However, more info will help guide my speculations.

Fences are for boundary layer problems. Spanwise flow is a potential flow field problem - something completely different

That prototype was the Odyssey - not related to the Flair in any way.

SWIFT is still made by Aériane in Belgium.

The project is to the point where I'm providing highly technical information and education. All the new knowledge is hard won and at significant cost. Access to that knowledge should entail at least a token payment.

D-tube construction has been around since the '30's

Thanks, I'm glad to hear how you have found so much value in the work that I do. I look forward to seeing you as a new member on my Patreon site. Given all the value you have received, I'm sure your pledge will be most generous. Pledge at: www.patreon.com/klingbergwing

@@KlingbergWingMkII Not right now - simply because I can't see my way clear to getting any project of my own started, for financial reasons among others. If my financial situation in particular improves sufficiently, then I'll have no difficulty joining your Patreon site. Meanwhile, best wishes!

Thank you very much!

Well those are terms I know, but what you are trying to say with me I haven't a clue.

It was a great spot! I wish it was up to us today, it would be the best spot for me to do my testing. But hey, we're still kickin; and flyin

Nope, it's a tad difficult to get a sponsor for an aircraft whose flight qualities are still open to question.

Many thanks

Been there, done that: ruclips.net/video/eH4HDLJVp4E/видео.html Fences are for boundary layer problems. This is a Reynold's Number problem. You may wish to review: ruclips.net/video/2mh8szvuD40/видео.html

Thank you. I have a better idea of what you mean. I’ll be honest, I barely have a hobbyist understanding of aerodynamics. I’m a towboat captain on the Lower Mississippi River. I guess I could brag about practical experience in flow dynamics but honestly I have no formal training. After watching several of your videos I keep thinking about the morphing wing profiles that several universities are studying. The problem there is obviously weight. But in that vein, would a two piece control surface be feasible? Shipbuilders had a similar issue with low speed maneuverability and came up with a two piece rudder that increased handling capability and improved fuel efficiency while having a very simple mechanism. The Becker is interesting nonetheless. ruclips.net/video/UDBeCqzYO5k/видео.htmlsi=T2oV7V1xDziQWore

Morphing wing - really cool concept. However one would have to solve the weight/complexity issue to make them effective on a ultralight glider. What one might gain in aero efficiency would most likely be lost in weight gain, not to mention the big increase in build cost. I can't comment on the multi-part boat rudder concept as I've never seen one and I'd have to study it carefully. I can safely say that boats are not airplanes and water is not air - not all concepts transfer well between the two worlds. Overall, I'd say that designing aircraft is like making a fine wine - it is all about compromise across many, many factors and it takes about 50 years to learn how to make a good one....and then you die. (Old wine makers joke!)

Yes, flutter can be a big issue with flat plates and has to be studiously avoided. Spanwise flutter is not an issue because they are directly attached to the wing TE. However, torsion can be a big issue. Most of the "flat plate" controls I've used or seen are actually thin wedges so they form a torsion box to make them stiffer. One also has to be careful of what impact the placement of the control connection point might have. All that said, there are many powered ultralights that use flat, fabric covered, controls and I have not heard of any flutter problems. However, those controls are usually much shorter in terms of span.

From what I can see in the online photos, the answer to your question is, "Yes" It is nearly identical to what I used on my original Klingberg Wing back in the '80s. I should mention that the Phantom appears to have a much larger wing chord than my wing at the elevon. Maybe as much as 30% larger. This means they would not have had the same Re problems I'm dealing with.

Oh, BTW, have you flown a Phantom? I'd love to get first hand comments about its handling. If you don't do you know of someone who has flown one? Please let me know.

I found the original owners manual for the Phantom online! It states that the pilot must stay aware for spins. It says the glider will enter a full-blown spin in just a 1/4 turn! I'm not surprised to read this as the glider has strip ailerons which can really aggravate spanwise flow and promote spins. So, flat plate good, strip ailerons bad. In my early videos I explain why an elevon with "reverse" taper (smaller chord at the root and bigger at the tip) prevents this problem. In fact, I have a spreadsheet for calculating the planform of the elevon required to prevent spins. The results are based on the taper and washout parameters of the main wing.

@@KlingbergWingMkII Some of my glider-club-buddies flew the Phantom. Newer heared anything about spinning. Most of them went back to traditional gliders because the thing was mutch to heavy and quite difficult to land. In alpin CX-competions it is a big disadvantage, if you have to care too much about finding a siutable landing field with the perfect wind. After rought landings the pilots were traped under the havy glider some times in a position that did not allow them to free themselfes from glider or harness.

Of course as that would be lower drag. However, this is an initial experiment and before I spend a lot of time do a bunch of fancy building, let's see if it even works.

Yep, that would be standard design procedure. You can see me test that option in my earlier videos. It proved ineffective, probably because of the low Re. Near stall speed my wing operates at an Re range that is largely unexplored. See this vid for my CFD analysis of the issue: ruclips.net/video/2mh8szvuD40/видео.html

All good pts. There are many aircraft that have employed leading edge slats. I think the most interesting is the Tiger Moth (or was it the Gypsy?) which had LE slats that deployed automatically when it hit a predetermined AoA. If you check out my earlier videos you will see I've tried dozens of different VG options. Problem is, at 20 mph and a very low Re (under 500K) it is very difficult to energize the flow. VGs bring high energy flow from the freestream into the boundary layer but if there isn't much energy in the freestream, then they are useless. What I'm doing here is a simple first rough cut (my common approach to problem solving). Optimizing the solution comes later if the method proves to be effective.

No, the cover on the upper surface could still act as a trip strip even if the bottom slot is closed. Good engineering dictates that the configuration for the upper cover be as close to identical as possible.

Interesting thoughts. Given the format we are working in, I'm not sure I'm correctly visualizing what you describe. That said, the best I can do is to note that I'm not doing this test to use on my flaps. I use the word "flap" as a generic term for a control surface. The elevons for my wing are flaps that must travel up and down, so I'm not sure what you are describing would work. The test I'm going to do is set up for down only to represent what happens on my wing. On my wing I'm having problems with the flow over the elevons only when they are deflected down. Does this make sense?

Be sure to sign up at my Patreon site to get the results

Will they let me test my wing there?

@@KlingbergWingMkII I'll check. in the past we demoed the Carbon Dragon on auto tow after the sailplanes were down. We'll call it demo flights not test flights due to fatal at airport with powered homebuilt. There are hang glider sites near by. Airport runway is about 5000'.