Video

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: czcams.com/video/eH4HDLJVp4E/video.html Fences are for boundary layer problems. This is a Reynold's Number problem. You may wish to review: czcams.com/video/2mh8szvuD40/video.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. czcams.com/video/UDBeCqzYO5k/video.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: czcams.com/video/2mh8szvuD40/video.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'.

Yes, the slots will add drag but probably a small amount compared to a low Re airfoil. The low Re airfoils have their high drag at AoAs of 1 degree or less. At those low AoAs the slots will be parallel to the flow so the added drag should be minimal because the pressure differential between the lower and upper surfaces is close to zero. There will be added drag only when the flap is deflected downward when turning. Most high speed runs involving minimal turning, so a limited negative impact. However, I still think the best answer will be the flat plate elevons attached to the TE of the wing. That currently looks like the lowest drag option. This upcoming test is an interesting side quest while I wait for good flying weather to test the flat plate elevons. Plus, it could be a good option for the flaps on my wing to make them more effective for pitch trim and landings.

@@KlingbergWingMkII Thank you

Yes, that would be quite easy. However, there is a price to pay. Low Re airfoils are inherently low speed. When taken to higher speeds (low AoA) the drag goes way up. In one of my vids I describe the drag polar for the low Re airfoils and why they get draggy. Gliders such as the Swift were not designed to go fast. I think they had a Vne of about 70 mph. I want a Vne around 100 mph, so this requires a different airfoil. This is all a very sticky problem because we have never really strived for an aircraft that has high performance over such a wide speed range - a vexing problem that requires airfoils that can change shape for different speed ranges (doable but very heavy) or a unique solution the will appear to be "like magic" if I ever find it.

@@KlingbergWingMkII Oh! I hadn't realized that. I'll go watch that video now. Thanks

Best of luck on you impending test flight.

Thanks!

Thank you so much 😀

And who is Mr. Calhoun?

Calhoun is not an engineer, but somehow he leads Boeing. It did not work that well.

I was an engineer on the 757 and 767 development programs. It was a great company back in the day. Never let finance lead an aerospace company.

Glad you liked it. I hope you watch the entire series about stalls and spins. Enjoy!

The honeycomb core is 2 lbs/cu Ft, the best one would do with balsa is around 6 lbs/cu ft and it would take a lot of work to find enough blocks of that density to do just one aircraft. However, end gran balsa does have very good compressive strength and I suppose that is why it is used in some boats and windmill blade. But, too heavy for my purposes.

Sorry I was not clear in the video. My goal is to get the outer skin of foam at the same level of the honeycomb so that both the foam and the honeycomb are bonded to the composite skin. In that way one could gain the advantage of high compression strength of the honeycomb and the added bonding area of the foam. Recent tests have show that it is nearly impossible to press the honeycomb into the PVC foam, so, nothing gained so far. However, my experiments continue. BTW, compressive strength and shear strength are not the same. The are generally 90 degrees out of phase to each other. It is the compressive strength of the core material that prevents local buckling when the sandwich panel is undergoing compressive and/or bending loads. I am making this clear so that my viewers do not get confused.

Resin infusion is way, way too heavy for this type of aircraft. I spread epoxy in the fabric by hand and vacuum bag to the core. You can see this process in many of my early videos. One exception is DOW XPS styrofoam as it is too weak in compression for vacuum bagging. See the spar layup videos for a demo of that material.

@@KlingbergWingMkII Can you provide the video name? I didn't see XPS mentioned in the "Spar Cap Layup" one and I've watched all your videos, so can't remember either 😄

I use xps as the core foam for the spar: czcams.com/video/5mAtcGb2NUs/video.html

routing which material?

@@KlingbergWingMkIIThe foam, carving thin channels for the honeycomb pattern to embed fully while keeping it low tech enough to be feasible at home.

Based on my recent experiments it looks like routing the foam might be essential. I have found that the honeycomb cannot cut into the foam using pressures available to a home builder. The routing would have to leave a very small layer of foam so the various pieces stay together.

You have "special powers". I ordered rubber rollers earlier this evening for just what you suggest, except using urethane glue. I'm also going to try pouring a thin layer of glue in a tray and dipping the honeycomb core in it. I'll be doing videos on the results. Foaming epoxy could also be an interesting experiment.

@KlingbergWingMkII nice! I tried dipping but for the small pitch of the cells I had and the viscosity of the resin used, it didn't work out due to resin membranes bridging the cell gaps. Maybe less viscous infusion resin would have worked though.

Yep, that's a common method for "potting" the core where bolts and other fasteners will pass through. Too heavy for large areas. I experimented with it in the very early stages of my project for the LE of my D-tubes - they were bulletproof but too heavy.

Composites have so many applications beyond aviation, so every video you share is full of fascinating possibilities!!

Your welcome!

You are so welcome!

Yes and no. The local stalls are being caused by flow conditions over the elevons that are the result of the low Reynolds number. To fully understand, you need to watch the following two videos: czcams.com/video/3PqZurAydNw/video.html and czcams.com/video/2mh8szvuD40/video.html

Yep, and we thought all was OK, just a few adjustments to more flare authority. However, 3 years later I'm still working the problem of having enough control authority for this type of wing. Recent analysis has provided some insight and I have mods I believe will work. If you look at my most recent videos, you'll see what I think is the root cause of problems. Hopefully I will have it fixed soon!

Klingberg Wing MkII

A rough set of plans are available for the 1/4 scale version R/C model - it flies great! You get a copy of the plans (and lots of other goodies) in the Welcome Package when you become a Patron at: www.patreon.com/klingbergwing

www.r-g.de/en/list/Sandwich-material--Honeycombs--Foam-/PVC-foam--Airex-Mycell-

I'm curious, why?

Yes, because the rudders are not active controls, just stablizers.

Man, you are dating yourself with that one! You must be at least as old as I am - that pub goes way, way back~

Too complex and heavy, mechanically.

Thanks, we should find out in a couple of weeks, weather permitting.

Always an option and I speak to them in an upcoming video. Spoiler Alert! - VGs only added about 2 degrees of available elevon travel - not enough to solve the problem. You all will be surprised to see the final solution so stay tuned!

Thank you very much for all the kind words. I love all the support. Funny thing, the LE cuff was the preferred solution (Peter's idea) for several days. Then I realized that I had some data that showed there was more at play here than Reynold's number. I think I will be able to stay away from the low Re airfoil choices and thus retain the high speed end performance. Please stay tuned for the entire series, I'm sure you'll be surprised at the final solution!

Thanks for the words of support and encouragement. I won't be going to a constant chord wing because that would require designing and building and entirely new aircraft and I probably don't have enough "healthy" years left in me for that long-term project. However, I will be making progress with the current design until it is fully flyable (I hope). Others can "pick up the stick" and go forward with what we learn from my current efforts.

Thanks! Everyone on this end has been quite surprised about the results. My wife and I had a little celebration because I've been beating on the problem for nearly 2 years now. Hopefully, next time out with the Wing will be much more satisfying and I thank you and all my Patrons for your continued support!

Yep, it's an excellent tool. Great value for the price!

Yes and no. Future video will explain.

How about retractable VGs? 🙃 yeah I’m a lot of help lol

Yep, that has been discussed at length, but the impact to the D-tube would be extensive and would need a series of load rings. However, there is another potential solution, which I will post in a week or so after the next round of tests tomorrow. Stay tuned!