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#11
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New 29 Palms Winchfest Video
Speed is not controlled by the pilot on a conventional winch. Though
you can temporarily speed up by pulling on certain winches, that is only a temporary effect, as the tension increases and the glider is accelerated for a short burst. However, that is really not a technique or effect that has much practical meaning, one way or the other. If the speed is too slow, the pilot has to slack off and be prepared to release. How can the pilot know the reasons for the lack of power?......pulling more just assumes it's only a winch driver related issue - when it could be any number of reasons for the slow speed. So yes, pulling will increase speed temporarily but only slightly and pushing will decrease it, again only slightly depending on the particulars of the winch - the effects are really not very noticeable on a conventional winch. Pulling will reduce motor and drum RPM, reducing the water skier effect. Pushing will also not really reduce airspeed too much or perhaps not at all depending on the winch, because motor and drum ROM will increase when pushing. But this is the wrong area to focus on in any case and can vary from one winch set up to another - depending on the engine torque, glider weight and engine RPM at which point the push or pull happens. But again, it's academic and not practical from a pilot point of view: I was taught this way: - Wings level, not matter the wind direction -Take off when sufficient air speed is reached with wings level - If a wing drags on the ground for more than 1second - release -Gradually rotate and increase rate of climb to normal climb attitude within the safety zone to 200ft as airspeed remains constant or increases -If airspeed falls bellow a certain speed, be ready to push forward and release ( In that order!) -If airspeed falls even lower, quickly push forward and then release -On the last 25% or so of the launch, gradually decrease the stick back pressure. Remember that the launch is an arc with a constantly changing climb angle relative to the horizon. So at the top of the launch, the pitch is almost horizontal - so the aircraft nose should also be almost horizontal there. There has never been a case of a glider over stressing due to excessive speed on winch launch, so that is not really a danger point. But if it seems excessive, one can always just release and I've seen that happen a few times, though rare. In any case, that is what the weak link is for. The only quick pitch movement should be when pushing over to release in an aborted launch due to lack of winch power and speed. Otherwise the pitch changes should always be smooth. Keep it simple and do not try to micromanage the launch from the pilot's point of view. There is no way the pilot can know what the troubles are, if any - so he can not possibly know what effect pushing, pulling or signaling will have. This is all just my 2 cents. |
#12
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New 29 Palms Winchfest Video
Discussing this brought more memories and perhaps I should fine tune
this by discussing some sceanrio's: If the airspeed never picks up enough, but not low enough for a release, just do not go into full climb mode even above the safety altitude, just remain in a shallow climb till either the airspeed increases or it falls further, where you push over and release if it does fall off. But keep some tension on the rope so that the chute doesn't open. So don't follow the rope or level off completely unless you're aborting and releasing. The signal to the winch driver that the airspeed is too slow is the fact that the glider is in a shallow climb mode. The winch driver may or may not add power. In no case can the pilot know. So the pilot should not pull more and increase climb rate to speed up. That's dangerous. The same is when the speed starts falling off bellow a certain point. I'm not talking about when it fluctuates and starts falling. But only when it falls bellow a certain point. Then, for safety reasons, you gradually shallow the climb angle when it falls too low, in case the power dies or there is some other problem. If power picks up again, you can resume the climb angle. This is done for safety reasons and not to influence the air speed. The winch driver can see if you're shallow or haven't started climbing normally yet. Then again maybe he can't.............. But the reasons for the lack of power can be totally outside the fault of the winch and the driver. For instance there can be strong and sudden wind shears at certain altitudes at the beginning of the day that nobody knows of, or when wind conditions change during the day. There might also be a traffic conflict with another plane somehow that the winch driver sees, but the pilot does not............... This can result in a crappy launch with a low release altitude. So what? Get another launch! It's cheap. Bad launches are fixed by talking to the winch driver. In Germany, the winch drivers usually called up to ask when that happens so they can make adjustments. So pilots trying to influence speed is a good practice. The airspeed will vary during a winch launch anyway. The best practice in this regard is to have well educated winch drivers who know what power settings are required for the different types of gliders being launched and on the known wind conditions. If this results in a crappy launch anyway, inform the winch driver of the problem you had, (..."at 300ft the speed increased/decreased 15 knots, at 1,000ft it reversed again...") , and the driver can adjust the power settings throughout the launch accordingly for good launches there after for all types. Of course tension controlled winches do not have these problem, but there are none in the U.S and few even in Europe. It's not the launching pilot who can really control the airspeed or power application on a conventional winch. So please, do not pull to increase speed as the low speed may be due to some problem you are not aware of and where pulling may not help - rather you'll only increase the risk should something else then happen - which you also can not predict. |
#13
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New 29 Palms Winchfest Video
I erroneously said:
"So pilots trying to influence speed is a good practice" I wanted to say: "So pilots trying to influence speed is NOT a good practice" |
#14
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New 29 Palms Winchfest Video
I fly off a powerful winch and pulling back has never sped it up. It
increases the tension and, with the throttle held constant at the winch, simply slows the engine down. I've never pushed forwards on a launch unless the speed has been falling away (not very clever to be nose-up with no speed). In the UK winch drivers are trained to notice a glider "nosing over" and thus gently feed in more power until the glider returns to a normal climb. I think someone suggested buying a copy of the BGA Instructor's Handbook and having it shipped to the US. That sounds a good idea. You can buy a copy he http://www.gliding.co.uk/shop/produc...products_id=65 It covers both theory and practicalities of winch launching well. Dan |
#15
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New 29 Palms Winchfest Video
Dan G wrote:
I fly off a powerful winch and pulling back has never sped it up. It increases the tension and, with the throttle held constant at the winch, simply slows the engine down. The one time I consciously tried to slow down by pulling was in a K21 on a Supacat 8. Airspeed kept increasing, but that may have had more to do with the wind gradient that day... Marc |
#16
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New 29 Palms Winchfest Video
Winch launch has nothing to do with free flight, and "angle of attack for
best L/D" has no meaning. On a winch launch, you simply try to fly at Ca/max. On my 1,200+ winch launches, I never felt the need of an AoA meter (nor did I after releasing). "Marc Ramsey" wrote in message ... 3. Pilots were told that while on winch launch they are flying at zero angle of attack. Is this possible? Not zero, but at a normal (i.e., not 45 degrees) positive AOA, ideally that for best L/D. Hence the interest in AOA meters. Marc |
#17
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New 29 Palms Winchfest Video
tommytoyz wrote:
[an over slow launch] can result in a crappy launch with a low release altitude. So what? Get another launch! It's cheap. Bad launches are fixed by talking to the winch driver. In Germany, the winch drivers usually called up to ask when that happens so they can make adjustments. A very good point, and one that is seldom if ever mentioned here. If you have a bad launch, talk to the winch driver and calmly discuss the problem with him. Equally important, if he gets it spot on, let him know! He'll appreciate that and remember what he did the next time he launches you or another glider of the same type. For instance, those of us flying 1st generation glass very often get over fast launches because the drivers are used to heavier, more highly loaded gliders. In my club the only 1st Gen glass is a pair of Libelles, but we also have two SZD Juniors, which all our drivers are very familiar with. The Junior has a similarly light wing loading to a Libelle but is draggier and has a Vwinch of 70 kts against the Libelle's 65. A request to a winch driver who hasn't launched me for a while to "launch me like a Junior, but 5-10 kts slower" gets a good launch every time. -- martin@ | Martin Gregorie gregorie. | Essex, UK org | |
#18
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New 29 Palms Winchfest Video
At 13:06 11 December 2007, Martin Gregorie wrote.
If you have a bad launch, talk to the winch driver and calmly discuss the problem with him. Equally important, if he gets it spot on, let him know! He'll appreciate that and remember what he did the next time he launches you or another glider of the same type. For instance, those of us flying 1st generation glass very often get over fast launches because the drivers are used to heavier, more highly loaded gliders. I have been reading with great interest the past few months the threads about winches and launching on them. And just a small observation about our own club in Prescott is that we have a medium powered winch. Which gives the heavier gliders, ie the Blanik and 2-33 fully loaded, a full power launch with the pilot pushing to increase speed once the winch driver has reached full power and the lighter ones, 1-26 with light pilot, a 60%or so power launch. But what I havent heard here in these threads is any one communicating via radio to the winch driver during the launch? We use a simple method on the radio by calling out the speed we are seeing. In other words we start by telling the winch operator who, what, how fast, and ready for launch. Then during launch we call out our speed and the winch driver adjusts accordingly. Example: Blanik to winch, I am fully loaded, wings are level, traffic pattern is clear, I am ready for a tow at 55 (short for 55mph). Winch to blanik, roger, here we go tow at 55, no delay. (after intial saftey climb to 200 feet and rotation into 45 degree climb angle) blanik says: five zero, five zero (winch reacts with full throttle and says): Full power. blanik says: Roger. (and decreases angle of attack to increase airspeed to target of 55). We then continue to call out airspeed every few 5 or 6 hundred feet. Until the winch driver tells us to: Stand by------level off level off. At which point we level off and release. Winch driver then waits to see the chute and announces: I have the chute. There are many scenarios with different gliders and weights but you get the picture. I have driven the winch and this seems to work very well. You get an idea of where the throttle has to be to start with each glider and it usually is a small if any adjustment throughout the launch. I have not flown on any other winches, only car tows, so my question is why no communication? |
#19
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New 29 Palms Winchfest Video
I have not flown on any other winches, only car tows, so my question is why no communication? Did a similar thing in Oklahoma, using noise canceling headsets on the winch and traffic frequency for speed hacks, but this was a new winch and some new pilots, so had to shake things out. Works okay in a remote area with today's low volume of transient power traffic. So you visit or move to another club. Now, forget what you've used and learn standard techniques. As a frequent winch driver, I'd rather everyone was practiced in standard signals and is well ahead of the glider and the process on each and every launch. Radio calls may not work well at a big site where multiple winches or aero towing operations are operating in parallel, or where the traffic frequency is otherwise cluttered. I am also concerned about pilots in singles using a hand held radio or mic for this, and even in two seaters, as there may be very little time to react if something goes pear-shaped, as there's the ever present danger of dropping either into a control at the worst possible time. Sod's law. If you have boom or headset mics and push buttons on the stick, okay, but this is generally no the case in trainers and many singles. Some may not even have radios. We use GMRS radios and/or flags to keep off 123.3 for staging and starting the launch (as there are plenty of other users of the frequency out there), but use the visual signals for speed control during the launch. One day soon, perhaps we'll have additional tools for this. Frank Whiteley |
#20
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New 29 Palms Winchfest Video
Bert Willing wrote:
Winch launch has nothing to do with free flight, and "angle of attack for best L/D" has no meaning. On a winch launch, you simply try to fly at Ca/max. I don't agree. Common sense (and the mathematics) make it clear that the most effective (highest altitude) launch is achieved by maximizing the lift and minimizing the drag given the varying cable tensions delivered during the climb phase of the launch. For a specific cable tension, that speed will be equivalent to the best L/D for the polar adjusted to the effective loading resulting from that cable tension. The AOA for best L/D, however, is independent of the effective loading. So, the optimal speed could be maintained during climb by keeping the AOA at best L/D (which also, of course, keeps one below the stall AOA). On my 1,200+ winch launches, I never felt the need of an AoA meter (nor did I after releasing). Well, in my 20+ winch launches I haven't been much concerned with anything beyond getting to release without breaking anything. From a training perspective, however, particularly in places (like the US) where there isn't much overall experience with winch launching, an AOA meter should be a great deal of help with learning to fly the launch optimally. Marc |
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