kiwi g Posted January 18, 2011 Share Posted January 18, 2011 Posted by David perry 1 on 17/01/2011 20:08:04: Posted by Ernie on 17/01/2011 17:32:10: Here we go again....Surely you launch with the wind directly behind so that the mopdel goes faster, and the lifting molecule things are more efficient ernie I always launch mine with the wind from one side. That way the models tendancy to go sideways counteracts the earths spin and the plane goes straight. Never fails. D You think youve got it bad. try launching you planes when your upside down on this planet. took me years to relise why my takeoffs didnt look like the ones in RCME Quote Link to comment Share on other sites More sharing options...
Steve Houghton 1 Posted January 18, 2011 Share Posted January 18, 2011 I know only one thing, whatever the science involved I will still give the throttle a little upward tweak when turning from the downwind leg into wind as I too have succumbed to the dreaded loss of lift with ensueing stall. Better to be safe than sorry and go home with my pride and joy intact. Quote Link to comment Share on other sites More sharing options...
Ernie Posted January 18, 2011 Share Posted January 18, 2011 Hi kiwi g I think if your upside down, you could try launching into the wind ernie Quote Link to comment Share on other sites More sharing options...
Eck Posted January 18, 2011 Share Posted January 18, 2011 I can find trees and crash my models with no help at all from aerodynamics, thank you! Quote Link to comment Share on other sites More sharing options...
kiwi g Posted January 18, 2011 Share Posted January 18, 2011 Ernie launching into the wind made no difference when launching upside down . I pull up and still hit the ground Quote Link to comment Share on other sites More sharing options...
Peter Miller Posted January 18, 2011 Share Posted January 18, 2011 If anyone is having trouble with all this, just change over to helicopters. They don't fly...They just beat the air into submission. Quote Link to comment Share on other sites More sharing options...
Steve W-O Posted January 18, 2011 Share Posted January 18, 2011 Posted by kiwi g on 18/01/2011 06:12:54: Posted by David perry 1 on 17/01/2011 20:08:04: Posted by Ernie on 17/01/2011 17:32:10: Here we go again....Surely you launch with the wind directly behind so that the mopdel goes faster, and the lifting molecule things are more efficient ernie I always launch mine with the wind from one side. That way the models tendancy to go sideways counteracts the earths spin and the plane goes straight. Never fails. D You think youve got it bad. try launching you planes when your upside down on this planet. took me years to relise why my takeoffs didnt look like the ones in RCME Do cricket balls suffer from the same problem? Quote Link to comment Share on other sites More sharing options...
Dan Hedges Posted January 18, 2011 Share Posted January 18, 2011 Noooooooooooooooooooo... not this again! I have decided that planes fly by magic anyway (works for carpets so why not planes!). The windier it is the more magic you need! Quote Link to comment Share on other sites More sharing options...
Ernie Posted January 18, 2011 Share Posted January 18, 2011 come on Myron, we're waiting ernie Quote Link to comment Share on other sites More sharing options...
Erfolg Posted January 18, 2011 Share Posted January 18, 2011 I am surprised that modeller are that concerned about this issue. To me if a model has a stall speed of say 10mph. In a 10 mph wind a model could just about hover (relative to the ground) into a 10 mph head wind. With the wind directly behind it would need to fly at 20 mph relative to the ground, to remain at the stall. Going cross wind the relative velocity to the ground would need to be at least 10mph, although would probably need to be higher, as I would argue to side wind would not provide zero velocity, effective wind speed, mucking up the airflow over the wing. At 45 degrees i would suspect all should be well, in being at the stall. For me the real situation is that in turning the aircraft, it does not stay level, due to things such as changing drag and lift forces etc on the model. In doing so the model flyer does what is necessary to place the model where he wants it. His principal concern is to place the model where he wants it, at a speed relative to him that keeps him happy without stalling etc. In doing so the model may climb or sink I guess full size pilots have similar issues when landing, a need to keep an aircraft on track, relative to the ground, compensating for wind, which will often change dramatically relative to both ground and aircraft. Although many seem wedded to the idea of pure vectors for addressing the situation, they seem to loose track that there are more issues, related to physics and fluidics than just velocity vectors. These are more than a trivial, affecting on the models flight pattern. Also very seldom is wind velocity constant, speed varying with height, gusting, and changing direction, and so on. So who really cares if it is found necessary to feed in up or down elevator, dependant on what the model is doing relative to the model flyer. It is needs or wants that dictate actions. Observing FF models is also not a pure vector issue either, physics, fluidics and the models inherent flight characteristics all have an influenence on determining what will happen. Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted January 18, 2011 Share Posted January 18, 2011 Posted by Erfolg on 18/01/2011 13:51:34: Going cross wind the relative velocity to the ground would need to be at least 10mph, although would probably need to be higher, as I would argue to side wind would not provide zero velocity, effective wind speed, mucking up the airflow over the wing. At 45 degrees i would suspect all should be well, in being at the stall. Beg pardon Erfolg? Where's this "side wind" coming from? The model has simply turned through 90 degrees (or a bit more if you're offsetting drift correctly) in the air mass that it's flying in. If you were flying in balance at 90 degrees to the wind and could see a tuft of wool attached to the canopy it would be straight back even if the model was slipping merrily across the ground downwind. Steve, your extra throttle in the turn is necessary to counter the additional G loading caused by turning tighter than the same turn in nil wind in order to (probably subconsciously) make it look right. Quote Link to comment Share on other sites More sharing options...
Erfolg Posted January 18, 2011 Share Posted January 18, 2011 Martin my reference point is the ground. Therefore all the discussion is relative to this point. In many ways it is the mathematics of satellite vectors, which are 3 dimensional (xyz axis). The model discussion seems always to be in terms of 2 dimensions (x,y). All other effects are conveniently ignored, such as inertia, fluidics and crucially the wants of the model pilot. If you had the model hovering, with the wind on the front. There has to be a change of speed, if you wish to go in any other direction, as you can no longer subtract the headwind, to that of the model to provide the apparent zero flying speed. As it is now on the side, a new vector calculation is required, it now needs a speed relative to the pilot greater than zero. Remember having mass there will be inertia effects, which the vectors do not account for, in addition to the fludics which will be affected, as all these things are not instantaneous or a steady state conditions . In my opinion it is a mistake to consider this issue as pure vectors. There are other considerations. A plane is not even a boat, which continues to float, where hydrodynamics can be ignored, when you are considering where the boat will be in 10 hours time and act of changing velocity or direction, is a small component in the mathematical model. Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted January 18, 2011 Share Posted January 18, 2011 Guys, do me a favour! As Bert so appropriately says - "Don't feed the Troll"! BEB Quote Link to comment Share on other sites More sharing options...
Steve W-O Posted January 18, 2011 Share Posted January 18, 2011 Posted by Biggles' Elder Brother - Moderator on 18/01/2011 15:47:13:Guys, do me a favour! As Bert so appropriately says - "Don't feed the Troll"! BEB Troll or not, he has started an interesting discussion. BEB, did you check the OPs IP address maybe it is a regular member Quote Link to comment Share on other sites More sharing options...
Tony Smith 7 Posted January 18, 2011 Share Posted January 18, 2011 Posted by Erfolg on 18/01/2011 13:51:34:I am surprised that modeller are that concerned about this issue. To me if a model has a stall speed of say 10mph. In a 10 mph wind a model could just about hover (relative to the ground) into a 10 mph head wind. With the wind directly behind it would need to fly at 20 mph relative to the ground, to remain at the stall. Going cross wind the relative velocity to the ground would need to be at least 10mph, although would probably need to be higher, as I would argue to side wind would not provide zero velocity, effective wind speed, mucking up the airflow over the wing. At 45 degrees i would suspect all should be well, in being at the stall. I assume you're sticking with 10mph airspeed, and 10mph wind speed. In that case if you fly heading 90 degrees to the wind your model will be doing just over 14mph over the ground, and its course will be 45 degrees downwind. It is not quite possible to maintain a course over the ground at 90 degrees to the wind. I don't think the principles are different from sailing "Course to Steer" or "Course Made Good" calculations. The only difference is that you're starting from a different frame of reference - ie what ground speed to I need to maintain my desired airspeed.. Quote Link to comment Share on other sites More sharing options...
Erfolg Posted January 18, 2011 Share Posted January 18, 2011 Tony You are only addressing part of the problem, the steady state part. An important set of components to the dynamic model which describe the changes to the steady state condition is not on your radar, dismissed as an instantaneous event which does not deserve any consideration. Biggles has a valid point.Edited By Erfolg on 18/01/2011 16:36:06 Quote Link to comment Share on other sites More sharing options...
Tony Smith 7 Posted January 18, 2011 Share Posted January 18, 2011 I'm not sure where we're in disagreement. Quote Link to comment Share on other sites More sharing options...
PatMc Posted January 18, 2011 Share Posted January 18, 2011 Time for the biggest Billy Goat Gruff to arrive methinks. Quote Link to comment Share on other sites More sharing options...
Tony Smith 7 Posted January 18, 2011 Share Posted January 18, 2011 I think I'll pop over to the sailing forum, and ask "Which anchor is best", or "should I lock the prop while sailing", or maybe something about Blue Ensigns. Quote Link to comment Share on other sites More sharing options...
Phil Brooks Posted January 18, 2011 Share Posted January 18, 2011 It's all down to PFM (Pure FFFFF...Flaming Magic) BUT don't forget that initiating a turn (downwind, upwind or crosswind) will induce positive G, thereby increasing the wing loading and raising the stall speed. If you are already close to stalling, very possible when turning onto the crosswind leg off the downwind, and seeking to lose height for a landing, that's all it takes. Don't bother asking how I found that out. Quote Link to comment Share on other sites More sharing options...
Steve W-O Posted January 18, 2011 Share Posted January 18, 2011 Posted by Erfolg on 18/01/2011 16:34:59:. An important set of components to the dynamic model which describe the changes to the steady state condition is not on your radar, dismissed as an instantaneous event which does not deserve any consideration. I thought we could only post in English????? Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted January 18, 2011 Share Posted January 18, 2011 Steve, but Erfolg, I have seen an apparently learned mathematical explanation of why the inertial effect is cancelled out and I must say I have no qualms about walking down the aisle of an Airbus flying at a ground speed of 500 mph and doing an about turn without falling over. Troll starting this or not, it's certainly an opportunity to try to raise the general understanding a little, Stewart, Please don't be offended or put off posting again if your post was made in good faith - it is a subject which evokes strong opinions and misunderstandings and you'll find this forum is a friendly one where differences in opinion are generally respected. Quote Link to comment Share on other sites More sharing options...
PatMc Posted January 18, 2011 Share Posted January 18, 2011 I think the last time this topic was raised the OP gave a plausible presentation arguing the opposite to the OP of this thread. When the flaws in her argument were pointed out she admitted that she had been trolling claiming it was in order to demonstrate how easy it was to convince those she thought gullible. Quote Link to comment Share on other sites More sharing options...
Steve W-O Posted January 18, 2011 Share Posted January 18, 2011 Posted by PatMc on 18/01/2011 17:30:48:I think the last time this topic was raised the OP gave a plausible presentation arguing the opposite to the OP of this thread. When the flaws in her argument were pointed out she admitted that she had been trolling claiming it was in order to demonstrate how easy it was to convince those she thought gullible. That thread was mentioned earlier, I read it and one of the first things that struck me was that her plane had inertia in one direction, but not the other In didn't know she was trolling, but to be honest, like here, it doesn't matter, judging by the differing opinions, there is a lot to be learnt. Quote Link to comment Share on other sites More sharing options...
MarkyMarc Posted January 18, 2011 Share Posted January 18, 2011 Hope we haven't put Stewart off! Conspiracy theory - maybe he's a ringer? Quote Link to comment Share on other sites More sharing options...
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