PatMc Posted March 12, 2013 Share Posted March 12, 2013 David, I'm assuming that the model flying at a cruise throttle setting initialy & is to be flown with the same trim settings at both weights. In which case the power would have to be increased to achieve the higher speed. I didn't say by how much the speed would increase & I don't think anyone else did but it would be roughly the sq root of 1.34 x original speed = 16%. If the model was flying at WOT to start with then the speed would go down but it would need to be re-trimmed to a higher AoA. Quote Link to comment Share on other sites More sharing options...
Bearair Posted March 12, 2013 Share Posted March 12, 2013 Posted by John Privett on 12/03/2013 00:16:56: Posted by Bearair on 11/03/2013 23:24:52: There is NOT A HUGE DIFFERENCE between a model of 0.5 kg and a model of 200000kg if the aerodynamics and wing loading are the same(ok reynolds numbers may make a bit of difference but if anything I would of thought it would favour the larger craft) Weight has got nothing to do with it. Sorry, I have to disagree totally with that. The wing loading will be higher on a larger plane compared to a small plane of similar "behaviour". Wing area goes up with the square of the linear dimensions whereas the weight goes up with the cube. A very quick "back of an envelope" calculation gives a wing loading for my .90 powered 1.6m span Extra 300 at something around 5kg/m^2. So should I expect a rather bigger one - say the full-size aircraft - to have the same wing loading? Well a Cessna 152 has a wing loading of 51kg/m^2 - TEN times that of my model. I wouldn't expect the full-size Extra to be dramatically different. (From figures I can quickly find, the wing loading of the f/size Extra must be something over 60kg/m^2.) Continuing to look at bigger planes, a 747 or A380 has a wing loading of around 700kg/m^2. That's over 100 times the wing loading of the model Extra and about 10 times the loading of the f/size Extra. So you can't simply ignore weight and say that the wing loading gives you the whole picture. You need to take the weight as well as the wing loading. The 1kg. limit for the A and B test is perhaps a bit simplistic, but it's a realistic check to expect the examiner to make. The alternative would need the examiner to measure the model, calculate the wing loading and check both the weight and loading against a chart. On balance I think the 1kg. limit is a sensible choice. My example above is of an aeroplane WITH THE SAME WING LOADING Your Extra and the fullsize Extra display completely different flying characteristics. The holly grail for fulsize aerobatics would be to produce an Extra with the same wing loading as your model Extra. because it would display the same flying characteristics. The 1kg rule was introduced to stop people flying very lightly loaded models but is has failed because the performance can now be obtained from heavier models with the same wing loading. In even simpler terms the handling of a old sub 1kg Ikarus Shockflyer can be reproduced and even bettered by an over 1kg Topmodel Sputnik. You can make a educated guess how a aeroplane(that you no nothing else about) with a wing loading of 5oz per Sqfoot will fly in comparison to an aircraft of 50oz per SqFoot will fly. No one can infer how an aeroplane of 1kg will fly compared to an aeroplane of 5kg. Roger Edited By Bearair on 12/03/2013 11:17:26 Edited By Bearair on 12/03/2013 11:22:34 Quote Link to comment Share on other sites More sharing options...
PatMc Posted March 12, 2013 Share Posted March 12, 2013 Posted by Bearair on 12/03/2013 11:03:59: You can make a educated guess how a aeroplane(that you no nothing else about) with a wing loading of 5oz per Sqfoot will fly in comparison to an aircraft of 50oz per SqFoot will fly. No one can infer how an aeroplane of 1kg will fly compared to an aeroplane of 5kg. Roger If all that's known in the first instance are the wing loadings & all that's known in the second are the weights then you have no more information in the first than in the second. Since your statements come to different conclusions either one of them must be incorrect or both are incorrect. IMO you scored 50%. Quote Link to comment Share on other sites More sharing options...
Bearair Posted March 12, 2013 Share Posted March 12, 2013 Posted by PatMc on 12/03/2013 20:06:39: Posted by Bearair on 12/03/2013 11:03:59: You can make a educated guess how a aeroplane(that you no nothing else about) with a wing loading of 5oz per Sqfoot will fly in comparison to an aircraft of 50oz per SqFoot will fly. No one can infer how an aeroplane of 1kg will fly compared to an aeroplane of 5kg. Roger If all that's known in the first instance are the wing loadings & all that's known in the second are the weights then you have no more information in the first than in the second. Since your statements come to different conclusions either one of them must be incorrect or both are incorrect. IMO you scored 50%. Well I could make an educated guess that the aircraft with the 5oz wing loading is likely to have a lower stalling speed than one with a 50oz wing loading. If you cant so be it. Thanks for the score! Roger Edited By Bearair on 12/03/2013 20:47:24 Quote Link to comment Share on other sites More sharing options...
PatMc Posted March 12, 2013 Share Posted March 12, 2013 Stalling speed is only one of many characteristics that determine how an aeroplane flies. Quote Link to comment Share on other sites More sharing options...
Bearair Posted March 12, 2013 Share Posted March 12, 2013 Posted by PatMc on 12/03/2013 21:18:01: Stalling speed is only one of many characteristics that determine how an aeroplane flies. So are you accepting my first statement above does give you more information about how an aircraft flies than weight alone. I admit it might only be an idea of stalling speed but that is a quite useful piece of information to have, dont you agree? Having an idea of when the model might fall out the sky has always helped me! Quote Link to comment Share on other sites More sharing options...
Glyn R Posted March 12, 2013 Share Posted March 12, 2013 We seem to have lost sight of the safety reasons behind the A test. Quote Link to comment Share on other sites More sharing options...
Bearair Posted March 12, 2013 Share Posted March 12, 2013 Posted by Glyn R on 12/03/2013 22:30:23: We seem to have lost sight of the safety reasons behind the A test. In what respect? Quote Link to comment Share on other sites More sharing options...
Glyn R Posted March 12, 2013 Share Posted March 12, 2013 Posted by Bearair on 12/03/2013 22:35:34: Posted by Glyn R on 12/03/2013 22:30:23: We seem to have lost sight of the safety reasons behind the A test. In what respect? This thread is all about the technical aspects of flying not about the safety message we need, Basic rules of safety do not feature in this discussion. Quote Link to comment Share on other sites More sharing options...
PatMc Posted March 12, 2013 Share Posted March 12, 2013 Posted by Bearair on 12/03/2013 21:38:39: So are you accepting my first statement above does give you more information about how an aircraft flies than weight alone. Nope. Quote Link to comment Share on other sites More sharing options...
Bearair Posted March 12, 2013 Share Posted March 12, 2013 Posted by PatMc on 10/07/2011 19:59:45: The BMFA achievement scheme is just that - a record of personal achievment in the form of a certificate. It's not a safety scheme or a licence to fly any particular type or weight of model. I see no reason that the A cert has to have a lower weight limit but anyone taking the test that had to wait on suitable low wind conditions might not feel they had achieved all that much if they were honest with them-self. Oh well at least we agree absolutly that the Achievement scheme is for and that we see no reason for the weight limit. So I think its pointless our discussing aerodynamics. After all the 1kg weight limit is what the threads about! Quote Link to comment Share on other sites More sharing options...
Max50 Posted March 13, 2013 Share Posted March 13, 2013 I'm with PatMc on this one , from 10/07/2011; " anyone taking the test that had to wait on suitable low wind conditions might not feel they had achieved all that much if they were honest with themselves". As a beginer who didn't fly much, i used to pick my days of no or light wind, with a WOT trainer. My figure of eights were perfect and take off and landing were good gliding in and touching down on all three wheels.no problems.People were saying i should put in for my test. Then i started flying more and in windier conditions. What was once perfect turned to useless and i said to myself that i was no-where near ready , simply because i'd not flown in all types of weather conditions. What's nice and easy on calm days, turns out to be a struggle on windier days, and needs a different kind of practice and flying, and there's not too many calm days in the UK. Still practicing for m A. Quote Link to comment Share on other sites More sharing options...
Bearair Posted March 13, 2013 Share Posted March 13, 2013 As an examiner If someone wanted to attempt an A cert then you booked a day to take your test and took pot luck on the weather. If you cancelled because it was to windy then I would not take you again until a similar day came around! If you just turned up at the field on a nice ,hot day with no wind and asked me to take your test, you would be politely told that as we only ever get days like this very occasionally I was flying my models not yours. Might sound harsh but people soon got the message Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted March 15, 2013 Share Posted March 15, 2013 Is there a minimum weather condition requirement for the 'A' cert? Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted March 15, 2013 Share Posted March 15, 2013 I was thinking that as well Simon - if there is its very well hidden in the small print! So well in fact I've never seen it! BEB Quote Link to comment Share on other sites More sharing options...
Bearair Posted March 15, 2013 Share Posted March 15, 2013 Posted by Biggles' Elder Brother - Moderator on 15/03/2013 08:41:11: I was thinking that as well Simon - if there is its very well hidden in the small print! So well in fact I've never seen it! BEB You could just read my post!. As it says a candidate takes pot luck with the weather.You really shouldnt take the A test so seriously its not a licence to fly, some of the examiners have not "brushed" up on it since Noah launched the ark., there are hugly different standards even across clubs let alone areas. Some examiners have quite wrongly added bits to it, ive heard of one club that actually has a written exam!. Last year I watched a candidate fly right through the pits at zero altitude on his first attempt and pass on his second!. The BMFA is working very hard to make it better across the country and I applaud them for that but for the forseable future it aint gonna change. I would still like to know how anyone passed their A test with a Vapour though, or is it just an Urban myth put out by the "lets have more regulation so I can feel important" brigade Roger Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted March 15, 2013 Share Posted March 15, 2013 I think you have miss understood the point of my post Bearair, but never mind. BEB Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted March 15, 2013 Share Posted March 15, 2013 BEB Simon Quote Link to comment Share on other sites More sharing options...
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