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#1
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Bruce Hoult wrote:
If you want, you can side slip and when close to the ground use the ailerons to level the wings. You are then in precisely the same situation as if you crabbed and then kicked in rudder, except that levelling the wings is probably easier and less critical than precisely timing and judging a bootfull of rudder. I think both are equally hard/easy in timing. Levelling the wings and yawing straight both start the aircraft moving sideways across the runway/strip and require the same accuracy of timing. Judging the required control input is different. You used the phrase "use the ailerons to level the wings". Why didn't you say "use rudder to yaw the glider straight"? The colourful phrase you actually used - "a bootfull of rudder" - from an instructor has probably caused more students to find crosswind landings difficult than any other aspect of the manoeuvre. Do you teach the final part of a slipped landing as "shove the stick over"? In my experience, old multiengine pilots like to crab and use rudder. Old single engine pilots like to slip and use aileron. Which technique is used just reflects the tribe you give your allegiance to. Both of them work well if taught properly. GC |
#2
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Graeme Cant wrote:
Judging the required control input is different. You used the phrase "use the ailerons to level the wings". Why didn't you say "use rudder to yaw the glider straight"? The colourful phrase you actually used - "a bootfull of rudder" - from an instructor has probably caused more students to find crosswind landings difficult than any other aspect of the manoeuvre. My opinion exactly. How many pilots use slipping to correct for wind while flying cross country? My wild guess is: none. We all crab without even talking about it. So what is the reason they don't do so during the landing? I can think of only two reasons: They've never learnt to master the rudder or they've never learnt to recognize and hold the runway axis unless it's right ahead of their nose. Both reasons claim for more training, not a change of method. Stefan |
#3
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Additionally, if you don't crab to stay centered during final, you stalling
speed will be higher. I never saw anybody slipping for wind correction in a glider in Europe... -- Bert Willing ASW20 "TW" "Stefan" a écrit dans le message de news: ... Graeme Cant wrote: Judging the required control input is different. You used the phrase "use the ailerons to level the wings". Why didn't you say "use rudder to yaw the glider straight"? The colourful phrase you actually used - "a bootfull of rudder" - from an instructor has probably caused more students to find crosswind landings difficult than any other aspect of the manoeuvre. My opinion exactly. How many pilots use slipping to correct for wind while flying cross country? My wild guess is: none. We all crab without even talking about it. So what is the reason they don't do so during the landing? I can think of only two reasons: They've never learnt to master the rudder or they've never learnt to recognize and hold the runway axis unless it's right ahead of their nose. Both reasons claim for more training, not a change of method. Stefan |
#4
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Bruce,
An even better way to think of this is simply to let the dihedral effect roll the wings level. An intent to "roll" the glider level will produce aileron drag with a yaw in the wrong direction. Since we're holding stick into the slip, the process only requires a relaxation of this force. And not even to neutral. That said, the majority of competent crosswind landings I've seen in open class ships usually involve flying the glider (wing low) onto the runway. The big gliders clearly require greater competence and a more flexible, not necessarily ideal approach to dealing with such problems. Also, I note that Don used the words "Kick off the drift." This is inaccurate. Since the crab is used to track down the runway, there is no longer a "drift." He is, in fact, kicking to align the gear with the runway. I point this out because sloppiness with terminology percolates up to our understanding of the model. And then back down to the control inputs we make. As for concerns of yawing while increasing angle of attack, remember you are near the ground. The real disadvantage of the wings level skid to align the gear is that you are introducing an unbalanced force. If your touch down is delayed, or you bounce, you will begin to turn downwind. It is an interesting dilemma. On the one hand, the alignment slip requires greater skill and understanding. On the other, the alignment skid requires a "touch" on both the rudder and the stick. I suspect the wings level approach is safer of low time pilots since they have greater controlability in the event of turbulence. But the wing low landing is easier since control movements are intuitive. There is a great big HOWEVER. A wing low landing into crops is completely unacceptable (as is flying the glider on). Each method has its role. We should be competent at both. But to be competent we need to clearly understand not just the obvious differences, but the similarities as well. Those of you who would prefer not to make the "additive" argument in public, please back channel. I am genuinely interested in understanding why this concept works... or perhaps, doesn't. OC Bruce Hoult wrote: In article , Don Johnstone wrote: Can't speak for 25 metres but I can for 20 metres and it's crabbing. I fly an ASW 17 and the tips are not that far from the ground, even when the wings are level, and sideslipping (using bank) near the ground has never appealed to me. My aim is to keep the wings level near the ground and kick off the drift at the point of flare but I have often wondered if it is a really good idea to apply yaw at the same time as increasing the angle of attack of the wing. Of course to conteract the further effect of rudder opposite aileron may have to be applied to keep the wings level but can be avoided by not being too heavy footed with the rudder. If you want, you can side slip and when close to the ground use the ailerons to level the wings. You are then in precisely the same situation as if you crabbed and then kicked in rudder, except that levelling the wings is probably easier and less critical than precisely timing and judging a bootfull of rudder. -- Bruce | 41.1670S | \ spoken | -+- Hoult | 174.8263E | /\ here. | ----------O---------- |
#5
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I fly a lot at a mountain site where the winds can be strong, gusty and
turbulent; 20 to 60 degrees (or more) off the runway heading, and constantly changing. The pattern there can be wicked at times. I am flying 18 and 20 meter gliders off a runway that is 75 feet (22.9 meters) wide with lights, sagebrush, and rocks past the edges. On days like that and at places like that there is no time for asking myself whether I should slip or crab. I just want to get the damn sailplane down in one piece. For flying like this you need to have your spurs on (be proactive and decisive). The only rules a Don't ground loop. Don't cartwheel. Don't hurt the pilot or glider. I would bet that if you debriefed me just after I stopped and got out of the glider, I would not be able to tell you very well what I had just done. One just does what is necessary to get down safely. When you get it slowed down somewhere near the ground in the middle of the runway and pointed pretty much down the runway, you had better plant it right then. Better safe than pretty. I do know that I have used a combination slip and crab many times, just so I don't run out of control travel before I get the desired response. Is that additive? You just lift the upwind wing before it hits the runway and use rudder as needed to establish/maintain heading. The upwind wing stays slightly down throughout the flare and rollout. At a sea level site with a steady wind and no upwind obstructions one can (yawn) take the time to worry about style points for slipping or crabbing approaches. :-) Teaching pilots to fly is, of course, a very different proposition. -Bob Korves wrote in message oups.com... Bruce, An even better way to think of this is simply to let the dihedral effect roll the wings level. An intent to "roll" the glider level will produce aileron drag with a yaw in the wrong direction. Since we're holding stick into the slip, the process only requires a relaxation of this force. And not even to neutral. That said, the majority of competent crosswind landings I've seen in open class ships usually involve flying the glider (wing low) onto the runway. The big gliders clearly require greater competence and a more flexible, not necessarily ideal approach to dealing with such problems. Also, I note that Don used the words "Kick off the drift." This is inaccurate. Since the crab is used to track down the runway, there is no longer a "drift." He is, in fact, kicking to align the gear with the runway. I point this out because sloppiness with terminology percolates up to our understanding of the model. And then back down to the control inputs we make. As for concerns of yawing while increasing angle of attack, remember you are near the ground. The real disadvantage of the wings level skid to align the gear is that you are introducing an unbalanced force. If your touch down is delayed, or you bounce, you will begin to turn downwind. It is an interesting dilemma. On the one hand, the alignment slip requires greater skill and understanding. On the other, the alignment skid requires a "touch" on both the rudder and the stick. I suspect the wings level approach is safer of low time pilots since they have greater controlability in the event of turbulence. But the wing low landing is easier since control movements are intuitive. There is a great big HOWEVER. A wing low landing into crops is completely unacceptable (as is flying the glider on). Each method has its role. We should be competent at both. But to be competent we need to clearly understand not just the obvious differences, but the similarities as well. Those of you who would prefer not to make the "additive" argument in public, please back channel. I am genuinely interested in understanding why this concept works... or perhaps, doesn't. OC Bruce Hoult wrote: In article , Don Johnstone wrote: Can't speak for 25 metres but I can for 20 metres and it's crabbing. I fly an ASW 17 and the tips are not that far from the ground, even when the wings are level, and sideslipping (using bank) near the ground has never appealed to me. My aim is to keep the wings level near the ground and kick off the drift at the point of flare but I have often wondered if it is a really good idea to apply yaw at the same time as increasing the angle of attack of the wing. Of course to conteract the further effect of rudder opposite aileron may have to be applied to keep the wings level but can be avoided by not being too heavy footed with the rudder. If you want, you can side slip and when close to the ground use the ailerons to level the wings. You are then in precisely the same situation as if you crabbed and then kicked in rudder, except that levelling the wings is probably easier and less critical than precisely timing and judging a bootfull of rudder. -- Bruce | 41.1670S | \ spoken | -+- Hoult | 174.8263E | /\ here. | ----------O---------- |
#6
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One advantage for the slip is that it has the upwind
wing low at touchdown. I prefer to have that wing just a bit down so that the wind is less likely to get under it on rollout. (Same reason I want that wing just a bit down for a crosswind launch. At 12:30 21 February 2005, Bert Willing wrote: Additionally, if you don't crab to stay centered during final, you stalling speed will be higher. I never saw anybody slipping for wind correction in a glider in Europe... -- Bert Willing ASW20 'TW' 'Stefan' a écrit dans le message de news: ... Graeme Cant wrote: Judging the required control input is different. You used the phrase 'use the ailerons to level the wings'. Why didn't you say 'use rudder to yaw the glider straight'? The colourful phrase you actually used - 'a bootfull of rudder' - from an instructor has probably caused more students to find crosswind landings difficult than any other aspect of the manoeuvre. My opinion exactly. How many pilots use slipping to correct for wind while flying cross country? My wild guess is: none. We all crab without even talking about it. So what is the reason they don't do so during the landing? I can think of only two reasons: They've never learnt to master the rudder or they've never learnt to recognize and hold the runway axis unless it's right ahead of their nose. Both reasons claim for more training, not a change of method. Stefan |
#7
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Nyal Williams wrote:
One advantage for the slip is that it has the upwind wing low at touchdown. I prefer to have that wing just a bit down so that the wind is less likely to get under it on rollout. (Same reason I want that wing just a bit down for a crosswind launch. One advantage for the crab is that it has the wings level. I prefer to have the wings level so that the grass is less likely to catch the wing and cause a ground loop. Especially important when grass and wings are both somewhat longer. (Same reason I carefully hold the wings level during the launch.) Stefan |
#8
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Excuse me... I slip for crosswind correction on final, rather than crab
(wich I assume is to correct the wind with heading; sorry, english is not my native language). I find it more effective as the fuselage is already aligned with the runway, and a more elegant manouevre as well. I live in Spain. Does it count as Europe? A lot of people does it here. I teach both methods, being crab easier to grasp at the beggining, slipping more effective and elegant when the student becomes proficient, IMHO. Jose M. Alvarez. ASW-24 'BR' At 12:30 21 February 2005, Bert Willing wrote: Additionally, if you don't crab to stay centered during final, you stalling speed will be higher. I never saw anybody slipping for wind correction in a glider in Europe... -- Bert Willing ASW20 'TW' |
#10
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At 16:00 21 February 2005, Stefan wrote:
Nyal Williams wrote: One advantage for the slip is that it has the upwind wing low at touchdown. I prefer to have that wing just a bit down so that the wind is less likely to get under it on rollout. (Same reason I want that wing just a bit down for a crosswind launch. One advantage for the crab is that it has the wings level. I prefer to have the wings level so that the grass is less likely to catch the wing and cause a ground loop. Especially important when grass and wings are both somewhat longer. (Same reason I carefully hold the wings level during the launch.) Stefan Amen to that. Long wings tend to be on the floppy side as well. Do we want to expand this thread to include launching? |
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