Scubajon Posted September 18, 2009 Share Posted September 18, 2009 We all know that a wing has a longer surface area on top than on the underside to create lift. But,why, when the model is inverted does it not have the opposite effect? Quote Link to comment Share on other sites More sharing options...
Ross Clarkson Posted September 18, 2009 Share Posted September 18, 2009 I think it depends on the shape of the wing Scubajon. If it is a symetrical wing then i think it does have the same effect whether inverted or not. If it is a non-symetrical wing then i assume there would be complications with flying inverted and further control inputs would be needed. My trainer with a flat bottomed wing will fly inverted but it needs alot of down elevator and speed to keep it inverted!! A typical aerobatic aircraft with a symetrical wing can happily fly slow and inverted and may not need too much further control inputs. Also, a big engine providing a lot of power at the front end helps. Very good question though and cant wait for someone to give an aerodynamic answer. Edited By Ross Clarkson on 18/09/2009 18:59:13Edited By Ross Clarkson on 18/09/2009 19:13:49 Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted September 18, 2009 Share Posted September 18, 2009 Not an aerodynamics answer...but my reockoning is that with a non symmetrical wing section, to maintain inverted flight, the angle of attack has to be raised in order to maintain lift....IE as Ross discovered...lots of forward pressure on the stick ( down elevator but now "up" elevator as the model is inverted ) Quote Link to comment Share on other sites More sharing options...
Scubajon Posted September 18, 2009 Author Share Posted September 18, 2009 I can follow that argument if the wing is symetrical, but in the current model I'm building, a Lancaster with 96" wigspan, the wing cofiguration is of the "normal" shape. Not sure I would want to try and fly that upside down!! lol And it would certainly require a lot of "up" elevator to maintain the inversion! Quote Link to comment Share on other sites More sharing options...
Ross Clarkson Posted September 18, 2009 Share Posted September 18, 2009 Ha Ha, brilliant. A Lancaster was not designed to go upside down so that probably dictates why it is of a normal shape wing. You are not planning on trying are you??? Quote Link to comment Share on other sites More sharing options...
Scubajon Posted September 18, 2009 Author Share Posted September 18, 2009 lol not a chance! it was just a joke! I've seen lots of models inverted and now I think of it, most of them were stunt planes or similair so they would most probably have symetrical wings, they would need them perform as they do, but I'm sure not all I've seen are like that so that was what prompted the question. cheers Quote Link to comment Share on other sites More sharing options...
Ross Clarkson Posted September 18, 2009 Share Posted September 18, 2009 Ha Ha, cool. Phew!!! Quote Link to comment Share on other sites More sharing options...
Myron Beaumont Posted September 18, 2009 Share Posted September 18, 2009 Bear in mind that the aeroplane doesn't know whether it's the "right way up "or not - We might get a little confused but can't alter natural forces. Especially with a symmetrical wing section (which birds don't have by the way) Quote Link to comment Share on other sites More sharing options...
Scubajon Posted September 18, 2009 Author Share Posted September 18, 2009 no, and you don't see birds upside down very often! lol but it's a novel thought! Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted September 19, 2009 Share Posted September 19, 2009 There are 2 schools of thought regarding the production of lift and I subscribe to both! The classic explanation involves Bernoulli's principle where a reduction in pressure is caused by the air being "forced" to travel faster over the top wing. Lately, it has become fashionable to discard this in favour of the "Newtonian" theory of lift being an opposite and equal force to the airflow being deflected downwardsby the wing. Having said that I recently read just this explanation in a book from before the First World War! Empirically, my opinion is that both contribute. You can sometimes "see" the reduction in pressure when a wing is pulled to high angles of attack and a cloud of water vapour forms over the top of it as a consequence of the pressure reduction. Equally, a flat plate wing can be made to produce lift by holding it at a positive angle of attack. We know that you can fly a Clark Y flat bottomed profile wing upside down and to do this we need a greater angle of attack to overcome the "inbuilt" angle of attack of the profile and the inefficiency of the airflow round the inverted profile. There is still a longer path for the air to flow over the top (originally the bottom of course) of the wing but it's not such a smooth journey and is much less efficient and prone to turbulence and breakaway. The reason why a symetrical wing needs down elevator is that if it's trimmed to fly level the right way up, it needs elevator to overcome the formerly positive angle of attack trimmed in when turned upside down. To return to the original question, the answer is that if you allowed the wing to maintain the same angle of attack relative to a horizontal line, but inverted, the lift produced would be downwards and the model would descend. We don't, as we add down elevator to increase the angle of attack so that the model maintains a horizontal path. This will, in the case of an asymetric profile, put the wing at a higher angle of attack when inverted to produce the same lift, requiring much more down elevator than a symetrical section due to its aerodynamic inefficiencies.Edited By Martin Harris on 19/09/2009 10:26:37 Quote Link to comment Share on other sites More sharing options...
Scubajon Posted September 19, 2009 Author Share Posted September 19, 2009 Right, don't think I will get a fuller explanation than that. At least I hope not cos I had to read that through twice to take it all in. Thanks. j Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted September 19, 2009 Share Posted September 19, 2009 Barry Beech of Mainly Models in Hitchin, flies his 1/12 scale Lancaster inverted, although it's sacrilege to the purist, on a regular basis at model shows. I don't know what wing section he uses but it still performs rather well in "Australian" mode! Quote Link to comment Share on other sites More sharing options...
Scubajon Posted September 19, 2009 Author Share Posted September 19, 2009 "Australian "mode 1st time I've seen it called that, but I am new (again) to this field of hobby and have seen many new modern abbreviations and sayings that were not around in my day when I last built model aircaraft In the 1950's. I'm gwetting quite confused at times! lol But, a Lanc inverted, that really is sacrilege! There's no way I am going tio deliberatly fly mine like that Normally will be a renewal experience for me as it's a very long time since I flew. My idea is to trim it myself and then get a more experienced flyer to take it up the first time. My turn will come later! lol Quote Link to comment Share on other sites More sharing options...
Vic. P. Posted September 19, 2009 Share Posted September 19, 2009 Hi Scubajon. Well i'd confirm what Bomber Harris, sorry, Martin Harris has to say, particulary as regards symetrical wing sections. I fly a Seb Art Sukhoi 29s 30E which has a symetrical wing section and handles extremely well in inverted flight and in fact needs no elevator input to maintain level flight with the throttle at the right level. I'm not quite sure why or how this is possible as i expected to need to use elevator to keep the nose up (or down in down under mode ) Must be in the overall design of the airframe i guess! Regards Vic. Quote Link to comment Share on other sites More sharing options...
Kelly Posted September 19, 2009 Share Posted September 19, 2009 The full size Lancaster could perform a loop, so maybe it could fly inverted . Quote Link to comment Share on other sites More sharing options...
Scubajon Posted September 19, 2009 Author Share Posted September 19, 2009 Well, if I read right, a symetrical wing works the same both ways adn it's the same profile on the underside as the topside so if the aircraft is trimmed correctly it would need the same setting for elevators as in normal flight. Of course, I could be wrong and I'm sure i will hear about it if I am wrong! lol Bomber Harris eh! I remember him from my childhood. He was still arond when I was little. Damn, now I've let on just how ancient I am! I read somewhere on this web site that being older makes for a better flyer...............but I had better not say any more on that! lol Quote Link to comment Share on other sites More sharing options...
Scubajon Posted September 19, 2009 Author Share Posted September 19, 2009 Performing a loop is a little different from the "Australian" position! The aircraft is in a manouvre where it only inverted for a very short time so i would think it'#s quite a different kettle of fish from inversion. how it got up enough speed to perfoma loop I don't know as it's Max. speed was only 280mph and for an aircraft of it's weight and size i would not have thought that was possible. Well, we live and learn something new each day! lol Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted September 20, 2009 Share Posted September 20, 2009 ScubajonDon't forget that a lightly loaded Lancaster (no bombs, ammo and limited fuel) is a powerful beast. The problem with looping such a plane is more likely to be keeping within limits on the way down rather than getting it up and over. I understand the Vulcan (B2 prototype?) has been unofficially looped straight off the runway and it was certainly rolled. (there is video of it on U tube) Quote Link to comment Share on other sites More sharing options...
Kelly Posted September 20, 2009 Share Posted September 20, 2009 "Test pilot Alex Henshaw is the only known pilot to have barrel rolled a Lancaster bomber, a feat considered almost impossible because of the slow speed of the aircraft." Quote Link to comment Share on other sites More sharing options...
BB Posted September 20, 2009 Share Posted September 20, 2009 BB Quote Link to comment Share on other sites More sharing options...
Scubajon Posted September 20, 2009 Author Share Posted September 20, 2009 Yes, you probably right, with almost no load it would be possible and as you say a problem to pull it out of it. Anyway not going to try it with mine! That video of the roll is amazing. Must have took an enormous amount of courqge and a lot of skill! Would not have liked to be in it at the time! lol My original question has certainly sparked off a lot of discussion. lol Quote Link to comment Share on other sites More sharing options...
Bob S Posted September 20, 2009 Share Posted September 20, 2009 Hi All I have a question, not really regarding the aerodynamics of a lanc downside up. What happens if you are in that position and the bomber crys "Bombs Away" Now you really understand what praying is all about and that adrenalin really is brown ...Edited By Bob S on 20/09/2009 19:09:32 Quote Link to comment Share on other sites More sharing options...
Scubajon Posted September 20, 2009 Author Share Posted September 20, 2009 No, what you do is abandon ship "tout suite" and leave him to his own stupid fate!! lol Interesting scenario though! Especially if you know just how large the bomb bay is on a Lanc. It's about one third the length of the aircraft! and that's an awful lot of munitions!! lol Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted September 20, 2009 Share Posted September 20, 2009 Just to be a little boring and get back on thread a little, a correctly flown loop and a barrel roll are positive G manoeuvres. The likelihood is that a Lancaster wouldn't be stressed for negative G so sustained inverted flight would be a no-no. It wouldn't surprise me if both have been tried with a Lanc at some time! Look at this video for an illustration of maintaining positive G throughout a barrel roll by one of the finest pilots ever to grasp a control column - Bob Hoover: Edited By Martin Harris on 20/09/2009 20:54:26 Quote Link to comment Share on other sites More sharing options...
BB Posted September 20, 2009 Share Posted September 20, 2009 Brilliant vid Martin. Haven't seen that one. There is another out there involving a co-pilot pouring and drinking a glass of orange juice whilst the pilot rolls the plane. If I find it i'll post it. BB Quote Link to comment Share on other sites More sharing options...
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