Biggles' Elder Brother - Moderator Posted April 3, 2012 Share Posted April 3, 2012 What I am saying is that statement you make - that I have quoted above - isn't true. There is no such minimum airspeed below which the model has to be in a stalled state. It may not be producing much lift - it maybe sinking rapidily, but none of that means its wing is stalled. BEB Quote Link to comment Share on other sites More sharing options...
Erfolg Posted April 3, 2012 Author Share Posted April 3, 2012 Are you really saying it is there is no minimum airspeed where the model can be in level flight. Or are you considering a model that is pointing vertically at the ground as an extreme example? Quote Link to comment Share on other sites More sharing options...
Martyn K Posted April 3, 2012 Share Posted April 3, 2012 Posted by Biggles' Elder Brother - Moderator on 03/04/2012 15:34:29: There is no such minimum airspeed below which the model has to be in a stalled state. It may not be producing much lift - it maybe sinking rapidily, but none of that means its wing is stalled. BEB I agree with that statement. A wing will only stall when a critical AoA is reached. Providing the airflow is moving over the wing and the wing is operating below the critical AoA then it hasn't stalled. However, if there is no airflow at all then the wing is quite simply no longer a wing and will be subject to Newtonian laws. Martyn Quote Link to comment Share on other sites More sharing options...
Erfolg Posted April 3, 2012 Author Share Posted April 3, 2012 What I do not get Martyn, is to be flying in the sense we have been describing, the model is moving relative to the air (not the ground, which is considered static, relative to the model)) the wing is supporting the mass, maintaining a constant altitude. With this set of conditions I am still at a loss to see how there is no minimum airspeed and still be flying. Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted April 3, 2012 Share Posted April 3, 2012 Posted by Erfolg on 03/04/2012 13:23:06: I am arguing that for a model of a given mass, there is a minimum flying speed, less than this the model stays put on the ground, or if in the air stalls,.... I don't see any reference to level flight there? In this statement you are saying that there is a minimum speed below which an aircraft stalls - I'm afraid that just isn't true. BEB Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted April 3, 2012 Share Posted April 3, 2012 Sounds to me as if Erfolg is considering the wing as if it was under test in a wind tunnel and not in the real world. Quote Link to comment Share on other sites More sharing options...
Martyn K Posted April 3, 2012 Share Posted April 3, 2012 Posted by Erfolg on 03/04/2012 16:08:07: What I do not get Martyn, is to be flying in the sense we have been describing, the model is moving relative to the air (not the ground, which is considered static, relative to the model)) the wing is supporting the mass, maintaining a constant altitude. With this set of conditions I am still at a loss to see how there is no minimum airspeed and still be flying. I agree that I am getting a bit pedantic. I think that the point is that when a model is in equilibrium (and flying), Then Thrust = Drag and Lift = Mass. If you increase the AoA, lift will increase but so will drag (at a faster rate). As Thrust hasn't changed, the aircraft will slow down (eventually). As the aircraft has slowed, the amount of lift will then reduce, and it wont climb (Mass hasn't changed). You can continue this process iteratively until the wing stalls, at which point the lift disappears and gravity takes over. That point is dependent on the airfoil characteristics and has nothing to do with velocity (airspeed) or mass of the aircraft. It just happens to be a characteristic for any particular model and the way it is being flown and this point will be reached eventually. You can force stall a wing - simply spin round with the wing held out at arms length. Keep spinning at the same rate and increase the AoA of the wing (you need 2 hands). You will feel it stall (or you will get dizzy and sick) Martyn Quote Link to comment Share on other sites More sharing options...
Erfolg Posted April 3, 2012 Author Share Posted April 3, 2012 BEB, The whole discussion has been with reference to level flight! Still beats doing Seduko, making a Rabbit Hutch, and preparing to Refit the bathroom (this will take a day, apparently, to remove window sill and replace, remove shower assembly, replace with thermostatic assembly, remove tiled wall on plasterboard and replace with aquapanel, re-tile etc). Anyway you can answer another problem, how is the relationship for MAC derived. I can see and read that it is a weighted average, based on what? I guess i now have time to start a Cleansweep Quote Link to comment Share on other sites More sharing options...
Myron Beaumont Posted April 3, 2012 Share Posted April 3, 2012 Anybody noticed that airspeed drops before a stall ? PILE on the power never mind the AofA & recover ie get to levelish flight (or a stall turn)and learn from what you did wrong .Cor Blimey Rant over! Quote Link to comment Share on other sites More sharing options...
Martyn K Posted April 3, 2012 Share Posted April 3, 2012 Anyway you can answer another problem, how is the relationship for MAC derived. I can see and read that it is a weighted average, based on what? I think that warrants a new Thread.. Martyn Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.