Flow Separation Primer - Klingberg Wing MkII Development

[@aekurier3442]

Danke! Hello and greetings to you! Great videos, especially the ones about airflow dynamics over aerofoil- and control-surfaces. Maybe, you could include some more information in separate videos, if possible and if you have time, about GA wing design and development, including the theory and technical challenges in wing design, too, as you have done with your 'Klingberg Wing'. I do not fly myself, but have a big passion for aviation, am looking to learn more about aircraft design theory, practices and conversion into aircraft, full scale or model. Carry on with your great videos; have learnt a great deal about airflow characteristics over and under aerofoil sections just from your videos alone. Keep up the great work! With best greetings from UK Andy

[@KlingbergWingMkII]

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!

[@matthewallen3375]

Great video

[@KlingbergWingMkII]

Thanks!

[@christheother9088]

Wonder what the challenges are to a flat component like that - making it stiff enough, flutter issues, etc.

[@KlingbergWingMkII]

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.

[@CaptCreekmore]

Out of curiosity, what effect would small stall fences mounted to the control surfaces have?

[@KlingbergWingMkII]

Been there, done that: kzbin.info/www/bejne/m3mXeXeCf7ujaqc Fences are for boundary layer problems. This is a Reynold's Number problem. You may wish to review: kzbin.info/www/bejne/aJ7Laaawq9p3apI

[@CaptCreekmore]

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. kzbin.info/www/bejne/i3Wllnanr76Ca80si=T2oV7V1xDziQWore

[@KlingbergWingMkII]

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!)

[@in4merATP]

So you're increasing the AOA of roughly 100% of your MAC-aft chordline in order to .. lower the AOA? Doesn't that mean there's an inevitable bottom portion of the speed envelope where you're guaranteed to tip-stall and consequently experience an uncontrollable nose-up moment, as your center-of-lift moves forward?

[@KlingbergWingMkII]

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

[@wolkenbummler]

Didn´t the Aeros Phanton use the flat plane?

[@KlingbergWingMkII]

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.

[@KlingbergWingMkII]

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.

[@KlingbergWingMkII]

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.

[@wolkenbummler]

@@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.

[@pylon500]

OK, so I'm watching these in somewhat random order, but feel I should comment here. Right from the beginning here, you are chasing a problem (obvious in the video), but I feel chasing it from the wrong direction. You are having to pitch forward to stabilise your towing climb, and running into problems with the elevon airflow separating. The problem is not the elevon, but your tow position. Move your tow hooks further up. As for the aerodynamic/Reynolds numbers/flow separation problems, to start with, these won't be a problem in gliding flight (or if the tow hooks are moved), except in stall recovery, and more pointedly, rolling out of steep turns (when the elevon is in aileron mode). The flat plate, hung off the trailing edge, will work, but for three different reasons. Yes, the upper (or lower) surface flow discontinuity can be cured by using a flat plate (which [#1] in effect means you've created a reflexed surface), but you have also [#2] increased your wing area, and thus lowered your wing loading, and you have [#3] extended your elevon moment arm aft, giving it better leverage and thus less requirement for deflection. A possible cure I see (as well as the tow hook), is to go to a bi-convex section at the elevon, or in other words, make the elevon thicker (2~3%?) than the section of wing it is attached to, have a look at the P51 Mustang elevators. You could also try extending the chord of the elevon (gaining #2 and #3 benefit), and utilising a reflexed surface (Mustang ailerons), but I'm not sure of how these changes work at the Re you are using...? Keep at it.

[@KlingbergWingMkII]

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!