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At 16:35 24 March 2009, bildan wrote:
Derek, I have more experience with ground launch than you are likely to achieve in your lifetime. No, Derek, Only YOU disagree. All you are doing is "Bible Pounding" hoping that by repeating the same thing over and over ever more loudly people will accept it on faith. I think people are smart enough to demand proof. I accept nothing on faith. I want engineering measurements to support each and every detail. Furthermore you are the sales representative for a particularly bad winch design seeking to discredit all other approaches any way you can. If you aren't being paid for this, you should demand to be. Bill, 1) So how many winch launches HAVE you done? I have made over 5000 autotow and winch launches at a number of sites over a 28 year period, both solo and as an instructor (combined that is). 2) What engineering measurements can you provide? To the best of my knowledge, nobody has yet found a 100% successful way of measuring winch cable tension. The cable speeds are too high for Rolling Line Tensiometers, so this generally has to be derived from torque or throttle settings. 3) Other than being a satisfied user of Tost and Skylaunch winches, I have no financial connections to any manufacturer. Derek Copeland |
#2
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On 22 Mrz., 03:24, bildan wrote:
And just as often I've challenged you to produce ANY engineering data to support your mere opinion. *You have not and I believe you cannot. That seems like elementary rigid body mechanics to me. In this case calculations trump measurements due to the well-understood nature of the physics and the inherent errors of any measurement. A simple longitudinal simulation model should be well sufficient to gain good insight into these types of accidents. Would be an interesting subject for a followup article. Best regards --Gerhard Wesp |
#3
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On Mar 20, 7:00*am, Derek Copeland wrote:
As I have tried to explain to Bill on numerous occasions, and on various forums, the uncontrollable over-rotation you get from an over-powered winch launch is caused by the pull line to the belly hook being below the glider's centre of gravity and centre of pressure. This causes a rotation for mechanical rather than aerodynamic control reasons. This is why high winged gliders, such as the K6 and K8 are most at risk. I understand this exactly and have wrote about it for many years. Almost all gliders currently in use have no risk at all of "mechanical" over-rotation. Does a G103 have "Uncontrollable Over- rotation"? The "Over powered" launches you speak of are strictly limited by the weak link to slightly over one G which is a trivial value. Nothing violent happens at one G unless the pilot initiates it. |
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No a Grob G103 is not prone to 'uncontrollable over-rotation' after
lifting off on a winch launch, because it has low set wings, hence a low centre of gravity, a slightly forward set belly hook, and it's quite heavy. Depending on the model, it either launches on a relatively weak red or brown link, so it is prone to weak link failures, as is identified in the Aerokourier report. So you need to be careful about overpowering it for a different reason. However there are many types that are prone to over-rotation, particularly K6, K7, K8, K13, Standard Cirrus, and many other types of single seater. In that it is very rare to break a weak link during the ground run, however violent, it is likely that you can get much faster acceleration than 1.2g. I think this is because of the fact that the glider is on wheels and unloads the weak link as it rolls and accelerates forward. If you where pulling against a concrete block set into the ground, you would break the weak link every time at the same force. If the weak link does break as a result of an overpowered launch, it usually does so sometime during or just after the rotation, which is at the worst possible time! If you drive a winch (which I do) you can feel the load on the cable increase as the glider rotates, even if the throttle or tension setting remains constant. Have a look at the following video showing a K13 being winch launched: http://www.youtube.com/watch?v=KUsqw0OwMZA Note that after a slightly protracted 'take up slack' the tailwheel goes down onto the ground when the winch driver opens the throttle and stays there until the glider lifts off, if anything slightly mainwheel first. This is despite the elevator being held slightly lower than neutral (stick forward of centre), as it should be. If you have a K13 available, try sitting two 180lb men plus parachutes in it and then push down down on the tail until the tailwheel touches the ground. You will find that this requires quite a lot of force, which illustrates just how powerful the rotational couple must be. Derek Copeland At 16:48 24 March 2009, bildan wrote: On Mar 20, 7:00=A0am, Derek Copeland wrote: As I have tried to explain to Bill on numerous occasions, and on various forums, the uncontrollable over-rotation you get from an over-powered winch launch is caused by the pull line to the belly hook being below the glider's centre of gravity and centre of pressure. This causes a rotation for mechanical rather than aerodynamic control reasons. This is why high winged gliders, such as the K6 and K8 are most at risk. I understand this exactly and have wrote about it for many years. Almost all gliders currently in use have no risk at all of "mechanical" over-rotation. Does a G103 have "Uncontrollable Over- rotation"? The "Over powered" launches you speak of are strictly limited by the weak link to slightly over one G which is a trivial value. Nothing violent happens at one G unless the pilot initiates it. |
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