old man emu Posted February 15, 2021 Share Posted February 15, 2021 What an excellent explanation! Link to comment Share on other sites More sharing options...
Garfly Posted February 15, 2021 Author Share Posted February 15, 2021 Spoiler alert ... 1 1 1 1 Link to comment Share on other sites More sharing options...
facthunter Posted February 16, 2021 Share Posted February 16, 2021 Great invention. Nev Link to comment Share on other sites More sharing options...
skippydiesel Posted February 16, 2021 Share Posted February 16, 2021 Great videos! Link to comment Share on other sites More sharing options...
Garfly Posted February 19, 2021 Author Share Posted February 19, 2021 It's fascinating how aerodynamicists spend countless months and loads of computer power to build very short - if very pretty - visual models of fluid flow which apparently tell them very many, very deep things. Yet, to the humble pilot, these 13 seconds can demonstrate the ordinary fact that wings will fly as well, or not, at any deck-angle. They show that the air couldn't care less about your earthly attitude when you're attacking it. It's going to push back - or not - just the same. Simple! And complicated. BTW, an explanatory note from YT poster, Paul Nathan: "Now it's time to make the computer work hard ;-D! I added 50,000 passive tracer particles that are advected by the local flow field and also indicate the instantaneous velocity vector. This took half a day to compute on one core of a 3.5GHz AMD Phenom X2 550 (overclocked by 0.45GHz, of course. On the edge of stability ;-D ). The computation per frame increases with time since more and more wake vortex panels are shed and these are consequently included in the loop that calculates the wake-induced velocities and also their own self-advection." Link to comment Share on other sites More sharing options...
Garfly Posted February 21, 2021 Author Share Posted February 21, 2021 WTF!! PULL BRS NOW!! Link to comment Share on other sites More sharing options...
old man emu Posted February 21, 2021 Share Posted February 21, 2021 It would be nice to have the link to the full story that video comes from. Without an explanation, it's just an animation. Link to comment Share on other sites More sharing options...
Garfly Posted February 21, 2021 Author Share Posted February 21, 2021 (edited) It still served as dad-joke material, Joyce! But for all you physicists out there ... here ya go! "Using single mode sinusoidal oscillations for pitch heave and surge superimposed on a uniform forward motion I found by trial and error a particular combination of relative amplitudes and phases that give a net lifting force. The motion is small to keep the instantaneous angle of attack less than 15 degrees (no stall please! Not modelled.... yet.... ;-D ). Again, notice how all the wake vortex dipoles have their axes pointing downwards and that they advect themselves downwards." (You can always click through to YT to see the poster's info and the comments.) Edited February 21, 2021 by Garfly Link to comment Share on other sites More sharing options...
old man emu Posted February 21, 2021 Share Posted February 21, 2021 What we tend to miss in all this Lift stuff is the actual difference in pressure that has to be generated per square centimetre of wing to keep an aircraft in the air. It's no much. A Jabiru 160 has a wing area of 8.04 square metres. Its MTOW is 540 kg, giving a wing loading of 67.2 kg/m^2. That's 6.72 grams per square centimetre. 6.72 gms is the weight of one and two thirds teaspoons of sugar. While I was trying to work out the units that you would use to report the amount of lift a wing produces, I think I found something interesting. Here's our old friend, the Lift formula. To make things a bit clearer the formula can be rearranged as Writing this out to show the units each component is measured in, we get If we consolidate the equation we get which is which means that Lift is a combination of the Coefficient of Lift and a Force. Link to comment Share on other sites More sharing options...
kgwilson Posted February 21, 2021 Share Posted February 21, 2021 Then there are those who just don't care They just know that when the stick is pulled back the houses get smaller and when it is pushed forwards they get bigger and when it is pulled all the way back they get smaller quickly but then get bigger really fast and that is the end. 1 Link to comment Share on other sites More sharing options...
old man emu Posted February 22, 2021 Share Posted February 22, 2021 11 hours ago, kgwilson said: Then there are those who just don't care I have no objection to that opinion. I'm not pointing a gun at them telling them to follow or participate in the discussion. Sometimes I feel like this Anyway, getting back to Lift. We are used to equations in Physics being relatively simple: F = ma; Work = mad. Some equations contain a Coefficient. A number used to multiply a variable. Example: 6z means 6 times z, and "z" is a variable, so 6 is a coefficient. In most equations, the Coefficient is always the same - a constant value. However, aerodynamics isn't a game that is played by the usual rules. The Lift equation contains a coefficient, CL But unlike a some coefficients, such as the coefficient of friction in the frictional force equation ( F = CofF x ma), the Coefficient of Lift varies with the Angle of Attack. You can deduce that for the same airspeed and the same air density, a simple wing will start to produce enough Lift to raise the aircraft from just above 4 degrees AoA, and up to maximum about 16 - 17 degrees AoA. We know that the wing will stall around 16 degrees AoA, but various devices seem to be able to allow operation above that angle. Link to comment Share on other sites More sharing options...
Garfly Posted February 22, 2021 Author Share Posted February 22, 2021 No one's interested in proper AoA theory anymore. ;- ) Link to comment Share on other sites More sharing options...
old man emu Posted February 22, 2021 Share Posted February 22, 2021 1 Link to comment Share on other sites More sharing options...
Garfly Posted February 23, 2021 Author Share Posted February 23, 2021 Link to comment Share on other sites More sharing options...
facthunter Posted February 23, 2021 Share Posted February 23, 2021 Can't believe that L/D of about 6 for a conventional wing. Hardly any plane flying is that bad and that's total drag including form (non lift producing) drag Maybe on small models where Reynolds number helps Nev 1 Link to comment Share on other sites More sharing options...
kgwilson Posted February 23, 2021 Share Posted February 23, 2021 Where did the numbers come from? No explanation there. Most light aircraft are 10 to 12 to 1 L/D. No mention of chord or aspect ratio which is how gliders get their 40 to 50 or even 60 to 1 L/Ds (combined with a low drag airframe). 1 Link to comment Share on other sites More sharing options...
Thruster88 Posted February 23, 2021 Share Posted February 23, 2021 That is not a wind tunnel. A flawed computer model perhaps. Wings need a certain amount of thickness just for structural reasons. 1 Link to comment Share on other sites More sharing options...
aro Posted February 23, 2021 Share Posted February 23, 2021 14 hours ago, facthunter said: Can't believe that L/D of about 6 for a conventional wing. I don't think that was the best L/D, also I'm not sure that 2d numbers are comparable to real numbers for a 3d wing. It's not very surprising that a very thin wing works well at high speed with less drag than a thick wing. It would have been more interesting to increase AOA to recover the lift and see what happens, rather than increase speed. Link to comment Share on other sites More sharing options...
IBob Posted February 23, 2021 Share Posted February 23, 2021 I'm just pi**ed off that I could have made do with a couple of barn doors, instead of 7,000 rivets and aluminium origami.........( 2 Link to comment Share on other sites More sharing options...
Garfly Posted February 23, 2021 Author Share Posted February 23, 2021 (edited) The video is a bit of a stir but still, boffins do seem genuinely fascinated by their flat plates and some of the RC crowd do use 'em precisely to save time in the build /re-build. In any case, I suppose the vid serves as a reminder that our favourite NACA profile is basically a refined barn-door and not the magical sine qua non of flight that our aeronautical upbringing suggested it was. (Did someone say Bernoulli?) http://brennen.caltech.edu/fluidbook/externalflows/lift/flatplateairfoil.pdf https://aviation.stackexchange.com/questions/21391/what-is-the-performance-of-a-flat-plate-wing#:~:text=The stall speed of an,attack range will stay similar. Edited February 23, 2021 by Garfly Link to comment Share on other sites More sharing options...
old man emu Posted February 24, 2021 Share Posted February 24, 2021 There's lots of illustrations of various wing designs like this one, But I recently saw one illustration where there was what seemed to be a vented space in the top surface of the wing near the separation point. The vent opened into the inside of the wing, but I can't find the illustration now, but I believe that the effect of the vent was to keep the boundary layer from separating from the surface of the aerofoil, thus increasing the AoA before separation. Here is the precis of a paper on the subject AERODYNAMIC DESIGN AND COMPUTATIONAL ANALYSIS OF VENTED NACA2412 AIRFOIL-A COMPARATIVE STUDY In the field of aerodynamics over the past decades, numerous studies have been dedicated to develop airfoils that produce higher amount of lift over a wide range of angle of attack. The flow over the suction surface of the airfoil must remain attached in order to generate lift otherwise the aircraft is bound to stall. This paper aims to introduce a novel technique on passive blowing flow control, namely, 'vented airfoil'. In the vented airfoil, the high momentum fluid from pressure surface is injected into suction surface just upstream of the flow separation point. https://www.researchgate.net/publication/338388317_AERODYNAMIC_DESIGN_AND_COMPUTATIONAL_ANALYSIS_OF_VENTED_NACA2412_AIRFOIL-A_COMPARATIVE_STUDY Also US Patent B64C21/025) https://patents.google.com/?q=(B64C21%2f025)&oq=(B64C21%2f025) 1 Link to comment Share on other sites More sharing options...
Garfly Posted February 24, 2021 Author Share Posted February 24, 2021 But are they as good as barn-doors? Link to comment Share on other sites More sharing options...
Garfly Posted February 24, 2021 Author Share Posted February 24, 2021 Link to comment Share on other sites More sharing options...
kgwilson Posted February 24, 2021 Share Posted February 24, 2021 Thin swept wings work better the faster you go. Look at the original 1958 English Electric Lightning. Wings as thin as structural integrity would allow and swept back at 60 degrees so much so that the ailerons are on the squared off wing tips. Performance of Mach 2 was astonishing even by todays standards. If they could have fitted barn doors to it that were strong enough it probably would have had the same performance. Link to comment Share on other sites More sharing options...
Jabiru7252 Posted February 24, 2021 Share Posted February 24, 2021 (edited) 9 hours ago, aro said: I don't think that was the best L/D, also I'm not sure that 2d numbers are comparable to real numbers for a 3d wing. It's not very surprising that a very thin wing works well at high speed with less drag than a thick wing. It would have been more interesting to increase AOA to recover the lift and see what happens, rather than increase speed. Edited February 24, 2021 by Jabiru7252 Ignore this post, I have the wrong person but can't seem to delete, only edit. Crap software. Link to comment Share on other sites More sharing options...
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