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Chris - always thoughtful and articulate - even when
pedantic. ;-) Seriously, I agree with your point about avoidance AND early, reflexive recovery to avoid a full-on spin. I used to work on wing-drop recovery in an early S/N Ventus A/16.6 - which had the most pronounced stall break of any glider I can recall. The control input was stick forward and into the turn plus top rudder. It takes some practice to make it reflexive. I recall the main reasons for teaching stabilized approach are to provide a consistent visual reference for the pilot and to keep from changing too many flight variables at the same time. Honestly, I don't know how they come up with recommended 'correct' pattern speeds - nor how scientific or precise the algorithm. My assumption is that the speed is picked as a tradeoff between stall margin and approach energy - but that there is an acceptable range. We regularly add 1/2 the wind speed - how exact is that? My personal experience is that it's quite easy to bleed off 5-10 knots by accident in a moment of distraction, but 15-20 knots takes longer and is more apparent. 9B At 15:36 30 August 2004, Chris Ocallaghan wrote: With the big spoilers on modern gliders, there's not much risk in adding 10 extra knots, and while your argument that it adds an increased cushion before stall is unarguable, I guess the measure of value comes in whether that reduced risk is a justified departure from the 'correct' pattern airspeed. I'm with Mark... it deserves some more discussion. BTW, as I noted in another thread, spins are not caused by lack of airspeed, but uncoordinated use of the controls -- at least in modern sailplanes. Two things must happen to enter a spin: 1) you must stall, and 2) you must fail to apply sufficient rudder during your attempt to pick up the low wing with aileron. That is, the sailplane is designed with enough rudder to stop autorotation, even with full deflection of the aileron throughout the stall break. As demonstrated by my thread last fall, a Ventus 2 won't spin if the controls remain coordinated (half stick/half rudder... full stick/rudder). It enters a controlable spiral, instead. However, half rudder and full stick (or half stick and no rudder) would induce a spin if the stick is held full back throughout the stall break. Avoiding the stall is the first most important step, but thorough training of the appropriate response during an inadvertent stall is a close, close second. And I could even argue that it's more important, since once you've stalled by accident, the outcome is determined by how well you've been trained to recover (that is, it becomes the failsafe for your stall avoidance error). Though I'm not a fan of axiomatic training, there's some value in remembering that you can stall at any attitude and any speed. If you wear that axiom on your sleeve, then you'd be best served by understanding and practicing superlative stall recovery technique in addition to practicing stall avoidance. That so many capable pilots have stall/spun in relatively docile aircraft indicates to me that there is a training gap. We are clearly handling the controls diffently at low altitudes. Why? If we can agree that this is the case, then adding speed is good insurance. But it doesn't address the cause. Andy, apologies for being the pedant. I'm spitting this stuff out at 60 words per minute, so I'm not giving much thought to 'balance.' |
#2
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I'd always assumed there were two factors in choosing a pattern speed.
First, safety, thus the +5 for turbulence. The other was to place the glider at best speed to fly. That way if you have to put the spoilers away, you are guaranteed to cover the maximum distance. If I recall, the simple formula for best speed was best l/d speed plus 1/2 the headwind. Don't recall the second ever being explained though. Just seemed to fit. |
#3
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![]() "Chris OCallaghan" wrote in message om... I'd always assumed there were two factors in choosing a pattern speed. First, safety, thus the +5 for turbulence. The other was to place the glider at best speed to fly. That way if you have to put the spoilers away, you are guaranteed to cover the maximum distance. If I recall, the simple formula for best speed was best l/d speed plus 1/2 the headwind. Don't recall the second ever being explained though. Just seemed to fit. up to plus 15 knots is currently being taught around here gust fronts and micro bursts make 30-50knot gusts relatively common during summer afternoons here if there's over-development two years ago we had a member landout in 70+mph cold front winds roaring in from the north. in some places along the front the winds exceeded 90mph. the pilot got about 8 miles in 7000ft to a landing about 4 miles south of the gliderport. he stayed in the glider, flying it on the ground until someone walked out and phoned for help. at the time I was playing father/son softball with my boy scout troop about 30 miles southeast of the landout location. large chunks of trees started flying by almost immediately as the winds hit we knew the front was coming, but no clue of the strong conditions. we usually expect some dust, but this was very different frank whiteley colorado |
#4
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![]() the simple formula for best speed was best l/d speed plus 1/2 the headwind. Don't recall the second ever being explained though. Just seemed to fit. Not a formula but a rule of thumb that's pretty close - judging by a number of polars I've looked at. The following article is very simplistic but was written for a student who had trouble grasping the concept of needing to stay upwind of the field in strong conditions: http://home.comcast.net/~verhulst/GB.../headwind.html Tony |
#5
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In article ,
Chris OCallaghan wrote: I'd always assumed there were two factors in choosing a pattern speed. First, safety, thus the +5 for turbulence. The other was to place the glider at best speed to fly. That way if you have to put the spoilers away, you are guaranteed to cover the maximum distance. If I recall, the simple formula for best speed was best l/d speed plus 1/2 the headwind. Don't recall the second ever being explained though. Just seemed to fit. http://www.stolaf.edu/people/hansonr/soaring/spd2fly/ was really useful for me. It sort of drove home the 1/2 headwind idea as being close enough, and was useful for deciding 30-45 deg of bank was fine for rope breaks. But look at it yourself. Of course the 2-33 data is in there, provided by yours truly ![]() -- ------------+ Mark Boyd Avenal, California, USA |
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