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#51
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Don't get me wrong: I am very cautious close to the ground, even though I
did extensive spin testing with my ship. I actually very often do not come to the conclusion that this or that low level IS safe, and then I don't do it. It's just statements like "never thermal below 400ft" which I don't like, although I agree that in many (maybe most) cases it would be unsafe. "Never" and "always" don't help people to practise actively thinking about every single situation they're in, and I think that it this lack of active situational awareness which is a main cause of fatal accidents. If you keep telling that "never below x feet", some will think "well my alti reads x+100ft, so I can safely thermal" - and that might be totally wrong for a special situation. -- Bert Willing ASW20 "TW" "Bruce Greeff" a écrit dans le message de ... Bert Willing wrote: Putting spin behaviour of a modern glass ship in this general way is pure nonsense. Spin behaviour is different for every model, and even a model with and without winglets enters differently. I wouldn't think about 300ft revoveries with a Ventus b, but on my 20 w/ winglets I would at least think about it. But as a general rule, I avoid flying ships in the mountains which depart violently and use 500ft to recover. Sorry all - I was generalising, but even the ASW20 spins interestingly, and will sometimes reverse it's spin direction instead of recovering if the pilot's technique is poor. Under the right (wrong) conditions even a K13 will depart violently. My point is that you should have a very good idea of exactly how much height your aircraft uses in a spin, including the half second or more it takes you to realise you have lost it, for you to recover in. Not the absolute minimum, in a factory perfect example in still conditions with a test pilot at the controls. Winglets, repairs, control wear and slop and build variations all change the behaviour. I think if you set up a logger and tested you might be a little more conservative close to the ground. |
#52
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Bert Willing wrote:
Don't get me wrong: I am very cautious close to the ground, even though I did extensive spin testing with my ship. I actually very often do not come to the conclusion that this or that low level IS safe, and then I don't do it. It's just statements like "never thermal below 400ft" which I don't like, although I agree that in many (maybe most) cases it would be unsafe. "Never" and "always" don't help people to practise actively thinking about every single situation they're in, and I think that it this lack of active situational awareness which is a main cause of fatal accidents. If you keep telling that "never below x feet", some will think "well my alti reads x+100ft, so I can safely thermal" - and that might be totally wrong for a special situation. Hi Bert In this case I am entirely in agreement - situational awareness and evaluation of the possible outcomes is fundamental. The "I will never spin THIS plane unintentionally so it is always safe" is equally dangerous to the "never thermal below x feet rule" Know your aircraft, evaluate the situation and the weather and make a reasoned decision as to how much risk to take. This is OK, and some people will accept different risk levels, and what is dangerous for a low timer may be safer for an experienced pilot. Note I did not say safe - just safer. Flying gliders is dangerous - accepting that and managing the risk is the key step to being safer. There has to be some motivation to take risk though, and hubris is a poor reason. The complications arise with objectivity - most people are less objective about their own capabilities than they think (me included) If you are low and in the circuit I still believe you should land unless there is some hazard on the runway that increases the risk of landing above the risk involved in thermalling low down, possibly below spin recovery height, where there is the probability of conflicting traffic. Under pressure objectivity tends to decrease - rather err on the side of caution, as you said. To paraphrase a bumper sticker - A bad day retrieving beats a good day in hospital. Bruce |
#53
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#54
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Barb ,
Perhaps "routine" isn't the right word, as like you, it's not something I see our fellow (local) pilots doing. I have however heard several of them talk about contests where the only way to a particular turnpoint was to fly a stretch with no known landing options from the top of the lift, and I *have* heard at least a couple of them talk about "no option" situations they knowingly entered. (There are parts of GW's flight from Turf to Moriarty in April where I have no idea where he could have landed without another thermal, and I recall him mentioning something to that effect in his discussion of that remarkable flight.) Of course, I've participated in only one sanctioned contest, so the frequency that competitive pilots (not to be confused with me!) actually do this, and how they handle it, is something I have to accept at face value from other competitors. -ted "BMacLean" wrote in message news:zJMWc.60231$wo.50491@okepread06... I fly with the same group as you Ted and I wonder where you get the idea that it is "routine" to fly with no landing options, even in hardcore competition. I don't believe this to be the case and I agree with Eric. I have found that when a pilot is relating a story of some scary situation they got themselves into and I ask them where they would have landed, 99% of the time they have an answer. Barb |
#55
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Kirk Stant wrote:
(Mark James Boyd) wrote in message news:412b9c97 Think about it for a minute. If you're going 50 knots in one direction, and then one-half second later the nose of the glider is 180 degrees pointed the other way, does this mean you are doing 50 knots in the other direction? That's some G's, and I don't feel them in a spin. And what do you mean by doing "a complete 180 during the spin ...and is now to some degree flying backwards." That isn't a spin, it's a frisbee! As far as G's, if you enter a spin at low speed (not accelerated), you can't pull any G's - as the plane unloads and goes down there is actually a decrease in G's! Some aircraft have a very nose low spin (Blanik), others have a much flatter spin (Katana). The Katana, which spins very flat on the horizon, is going North at 30 knots. I stall it and spin. Over the course of a second, the nose is now pointed South. Is the Katana moving South with an airspeed of 30 knots? No, it is not. This is part of the reason why, during the first turn or two, the pitch oscillates more violently than in a fully developed spin. Because of momentum, the airspeed from front to back of the wings is less during the South pointed nose part of the spin than during the entry of North. And yes, this is a frisbee. At least for the first 180 anyway... This is why aircraft oscillate pitch up and down for a few turns before stabilizing in a spin. For the first few turns, the aircraft momentum is still slogging through the air. I don't have a spin text handy, but I would think the oscillation is more due to angular momentum and changing AOA as the glider rotates around it's pitch and roll axes than from "flying backwards". Yes, and part of this changing AOA is due to momentum in the Northerly direction. Even with an aft CG, any glider is fully controllable up to the spin - it's recovering that would be interesting. True, true. The more aft the CG, the more controllability. It's pretty hard to get the CG that far aft (it can be done, especially if you are light, but any sort of preflight should find it) Ms. Campbell is the Hawaii state altitude record holder. She worked at Dillingham as a CFI. She told me during a ground session she was in an uncontrolled spin for more than 5,000 feet at one point, with a passenger, before recovering. She said after landing, she weighed the glider and the CG was well aft of what was on the 10+ year old "official" form. And her new calculated CG for that flight was well aft of limits. In my experience, the older the calculation, the further back the actual CG is from it. Dirt and crap on the long lever arm of the tail do a lot more than crap in the short nose. and if discovered the plane is still fully controllable - unlike a too far forward CG that can lead to a heavy landing. Just my opinion, but I bet there have been very few spin accidents caused by aft CGs (CG out of the aft limit, not just at the aft limit). Except for that 1 in 10 case, I'd guess aft CG is just a contributing factor, not a cause. But I'd like to see data. When I hear of a winch launch by an experienced pilot during the first flight of the season, ending in a fatality, I have to wonder if he took something out of the nose, or put something in the tail, and so his stick pressure feel and initial trim setting were off... Of the stall spin fatalities on record, I'd bet most, if not all, had CG further back than the 60-70% forward that Eric described... Sounds like trying to turn via ground references down low - a big no-no This is required to fly a rectangular pattern with wind correction, and still part of the PTS... and probably the real reason for low altitude "stall-spin" accidents. Clearly true. If one weren't trying to land on a particular bit of ground, and the world was just one big flat runway, I'm certain landing accidents would be more rare. The classic spin entry from a shallow bank is uninteresting. I won't be jamming in the rudder for a skid at some obviously low speed close to the ground. I think the focus on the classic case is niave and dangerous. Yes, it's easy to teach and demonstrate, but it ignores too much. The more complex, less discussed spin entry is the one in the accident reports: tight pattern, higher speed, steep bank, lots of inside rudder, pilot focussed on keeping the yaw string straight, quite a bit of opposite aileron in the steep bank, in vertigo, pulling stick back to tighten up the turn, and then wham! I'll look back through the accident reports, but the ones I recall, and the B-52 and the DG spin I saw on video, involved stabilized, 30-45 deg bank turns before each of the spins. In each, it looked like the craft was overbanking, and the pilot put in more opposite aileron and more elevator and WHAM! Instant spin... Again, you are describing a pilot who has no clue how to fly his glider. Hard to quiz them, the dead are VERY quiet... A stabilized steep turn doesn't call for a lot of inside rudder. Many of the 10 reports seem to indicate the spirals/spins happened during the roll, not the turn. High roll rates require a lot of rudder (and then rudder release), used quite precisely. And I am a bit confused by your reference to vertigo - again, this is avoidable (don't stare at the ground, no rapid head movements, etc) and should be taught. I commonly induce vertigo in students to demonstrate unusual attitude recovery. Although easiest to induce by rapid head movements, I can also induce it with nothing more than a rapid, perfectly coordinated roll into a steep bank, and then a rapid coordinated roll to level flight. I've done this with pilots from 10-30,000 hours. In all of them, if I cover all the instruments on a nice dark night with foggles on, they get vertigo. Not staring at the ground and avoiding rapid head movements is a start, but is an incomplete solution...rapid roll rates and dramatic G changes are another factor. When I fly gliders, I have to remind myself to fly at least a 1/4 mile out pattern. I normally fly a power plane (day VFR only) with a 5:1 glide ratio, and a tight pattern, with steeper banks and faster roll rates at higher airspeed. I don't do this when in a glider approaching an unmarked landout field with mountains and no horizon around. If a pilot continually gets vertigo in steep turns (and I have some really good friends who do, unfortunately) they need to seriously consider the ramifications of it and fly accordingly! I see we are agreeing again -- ------------+ Mark Boyd Avenal, California, USA |
#56
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In article ,
Marc Ramsey wrote: Mark James Boyd wrote: One flat skidding turn, the others were in a bank. At least one looks like an aileron spin (this can be done with feet off the rudders completely, but is very hard to time correctly). Several don't look like spins at all, but overbanking that led to a steep spiral close to the ground. In others, it seems possible the steep bank was after the spin entry, perhaps not before it. I've witnessed three stall/spin accidents over the years, two gliders turning base to final, and one power plane during departure. At the end, all of them looked like a steeply banked turn into the ground. Most eyewitnesses, particularly non-pilots, aren't going to notice anything is wrong until after the spin has started, at which point it will look very much like an abnormally steep turn. I've also been in a G103 that was about to depart into a spin from a low shallow left turn after a botched low finish at a contest. I was PIC, but a CFIG (!) in back was flying. I noticed things were getting a bit quiet, the left wing was starting to drop, and the stick was moving toward the right. I reflexively slammed the stick forward, which was probably what prevented us from making like a cartwheel. In most gliders (and there are exceptions), when you stall in a turn the inner wing is going to start dropping. If you release back pressure at this point, you'll be fine. But, the natural reaction of too many pilots is to try to pick up the low wing with aileron, which increases the angle of attack on the already stalled wing, increasing drag and decreasing lift, resulting in more bank, until the nose drops and you're spinning for real. Marc It's too bad we can't tell the "well-trained" from the "poorly-trained" pilots until after they've done something wrong, don't you think? ;P -- ------------+ Mark Boyd Avenal, California, USA |
#57
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Mark James Boyd wrote:
Some aircraft have a very nose low spin (Blanik), others have a much flatter spin (Katana). The Katana, which spins very flat on the horizon, is going North at 30 knots. I stall it and spin. Over the course of a second, the nose is now pointed South. Why do you think it takes only one second? Even a aerobatic glider can't reverse direction that quickly - that would be such a violent manuever. Think about it: a 60 knot change in one second takes over 3 gs, and a spin entry produces nothing like that. Try timing a spin entry sometime with stopwatch or a recorder on board. Is the Katana moving South with an airspeed of 30 knots? No, it is not. It's probably still got about 30 knots airspeed (do they really stall at such a low speed?), but because it is pointed down, the southerly component is less than 30 knots. snip Except for that 1 in 10 case, I'd guess aft CG is just a contributing factor, not a cause. But I'd like to see data. When I hear of a winch launch by an experienced pilot during the first flight of the season, ending in a fatality, I have to wonder if he took something out of the nose, or put something in the tail, and so his stick pressure feel and initial trim setting were off... Of the stall spin fatalities on record, I'd bet most, if not all, had CG further back than the 60-70% forward that Eric described... Just to be clear here, the convention is: 0% is at the front of the range; 100% is at the aft end of the range. It sounds like you have it backwards. -- Change "netto" to "net" to email me directly Eric Greenwell Washington State USA |
#58
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Eric Greenwell wrote:
Just to be clear here, the convention is: 0% is at the front of the range; 100% is at the aft end of the range. It sounds like you have it backwards. My mistake. I wasn't expecting you to have flown aircraft in such an aft CG range, and inverted it in my mind. Really. So the aircraft were in the aft 1/3 of the range? And still wouldn't stall at 45 deg bank? Interesting... I believe you, I'd just like to see this myself as well. As far as stalls in a steep bank, without uncoordinated inputs, I've noticed many aircraft roll wings level, just like the GFH and AFH (and Marc, it seems) say... One thing I haven't tried that I recall is banking into a turn and then just failing to take rudder out while rolling level at a high rate (all while at low airspeed). This should get a nice spin entry too... Maybe there are spin fatalities in this category too...steep bank close to the ground, more elevator to tighten the turn to final, then an attempt at a quick roll to level wings... -- ------------+ Mark Boyd Avenal, California, USA |
#59
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Mark James Boyd wrote:
Eric Greenwell wrote: Just to be clear here, the convention is: 0% is at the front of the range; 100% is at the aft end of the range. It sounds like you have it backwards. My mistake. I wasn't expecting you to have flown aircraft in such an aft CG range, and inverted it in my mind. Really. So the aircraft were in the aft 1/3 of the range? And still wouldn't stall at 45 deg bank? Interesting... 70% is a common CG location, because (for many/most gliders, especially the newer they are) the glider handles pleasantly, recovers easily from spins, and is close to the optimum CG for cross-country performance. I believe you, I'd just like to see this myself as well. The limit on elevator "authority" isn't so much the force it can generate (except at the most forward positions) but more the angle of attack reduction on the elevator that occurs in steep turns. I'm sure the bank angle you can stall at is higher with a more aft CG, but in the commonly used 60-80% range, you do run out of elevator in the steeper turns. -- Change "netto" to "net" to email me directly Eric Greenwell Washington State USA |
#60
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