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#1
August 24th 04, 12:33 AM
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want to hear about the very experienced pilot.. who in his first season with
his NEW ASW27B, found a thermal on downwind, thought he had it hooked.. only to get left low and dry and forced into a downwind landing.. and totaled it when it ground looped.. that extra tow back to that "found thermal" is cheap insurance Anyone found "thremaling out" from 300ft in the traffic pattern would not be asked to return. How many pilots did he block in the pattern while he climbed above pattern altitude. BT "Paul M. Cordell" wrote in message ... How Low to Spin?? I was proudly shown a IGC file this weekend. This file show the aero tow thru a thermal and a release into sink. Our proud pilot was unable to find the thermal and started a downwind leg for a landing. As he turned base leg, he flew into a 2-5 kt thermal. Instead of completing the pattern and landing, he turned and climbed in this thermal. The IGC file showed that his altitude at the time of encountering lift was 300 ft. I asked him 1 question as he displayed this flight on See You. How Low do you want to spin? His response scared me silly&&..My glider does not spin and there was no wind. He then continued to display the same flight where he bragged of spending a considerable amount of time in the mountains within 500 feet of the terrain. I am doubtful as to his ability to reach a landable area during this portion of the flight. This pilot is in his first year of private ownership, cross county soaring and may have almost 200 hours of total time. He has embraced soaring completely. I left the gliderport feeling that my suggestions as to his safety practices were just hollow words. I know that he reads RAS and would hope that the response to this post may give him some food for thought. 
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#2
August 24th 04, 02:01 AM
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that extra tow back to that "found thermal" is cheap insurance
A good point, and not forgotten at the time. I haven't shied away from relights in the past, but I wasn't out to volunteer for one either. How many pilots did he block in the pattern while he climbed above pattern altitude. None. As I told GY and Paul (before his post), I was careful to note as I entered the pattern that I was the only one near it. I'd noted when I launched that the entire commercial fleet was on the ground. In the air (when I entered the pattern) were one tow plane with which I had visual and radio contact, a motorglider several thousand feet higher, and another glider just off tow two miles to the west. Also, I didn't thermal at 300 feet -- that was the low point of the downwind leg (it was actually a little more than 300', but why split hairs). I was more than 100 feet higher when I started my first turn, to base. When the lift continued, I simply decided to continue the turn (over 400 feet now), plenty of altitude, airspeed and yaw string straight. At no point was it any more dangerous than a normal landing pattern, and if I'm wrong on that evaluation, I'm the first person who wants to know where why and how, because if it was a mistake for those particular circumstances, I care not to repeat it. I was far more scared when my CFIG pulled the tow release at 200' without warning in a heavily loaded trainer and I had to turn, line up on the same runway we launched from, all while managing the airspeed, and land downwind. (That's more than 180 degrees of turning, those of you who haven't enjoyed this exercise before.) I had to perform that maneuver twice, once before 1st solo and again just before my license exams. Was it safe? If so, then how is what I did less safe, with twice the altitude and no surprises? I'm not trying to be argumentive here -- I'm trying to understand what I should consider next time that I did not consider this time, if there is anything. Still I can't imagine "thermaling" at 300 feet unless there was terrain underneath me I could imagine landing on even less. I hope that goes without saying! -ted
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#3
August 24th 04, 02:52 AM
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Ted Wagner wrote:
yaw string straight. We've had this discussion on RAS before. I'm still gonna say that yaw string straight doesn't prevent a spin entry. Spins are when you're stalled and one wing is more stalled than the other. One wing is more stalled than the other if one wing has less AOA/more airspeed than the other. With the yawstring straight, this is still true in a steep bank, especially with long wings. It's also true if you're in a slip and then with a punchy foot coarsely correct it to center. The steeper the bank, the higher the stall speed AND the greater the difference in wing speeds, even with a straight yaw string. When I teach rope breaks, I do them at 300 ft and 30-45 degrees of bank, and best L/D for that bank angle. http://www.stolaf.edu/people/hansonr/soaring/spd2fly/ is a start. I also caution against super rapid roll rates and coarse use of rudder. I'm open to thoughts on this. I didn't do the math to see how MUCH the factor affects spins (somebody else did and came up with 3 degrees diff or so for 50 deg and 18m wings), but it sure surprised me. Now when I do spins in the L-13, I do them from string centered flight, and sure enough it always spins in the direction of the steep bank, and in a hurry too... P.S. Of course this assumes the rigging is right. If flaps are lower on one side than the other, hey man, there's yet another factor... -- ------------+ Mark Boyd Avenal, California, USA
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#5
August 24th 04, 08:52 PM
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Kirk Stant wrote:
I disagree with your conclusion about steep bank angles. It is usually a lot harder to spin from a steep turn, and a lot easier to recover from an incipient spin, for a simple reason (see Piggott for more details): a properly flown steep turn is flown at a significantly higher speed, and the elevator is limited, making it harder to reach stalling angle of attack, and much easier to reduce the angle of attack if needed due to the higher speed. Not always true. An aircraft that has done a complete 180 during the spin still has momentum, and is now to some degree flying backwards. The excess forward momentum translates into excess reduction of airspeed. 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. 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. But some of what you point out is true. Aircraft without enough elevator authority to stall, and with forward CG, won't have the ability to stall in a steep bank. But if the CG is back a bit, the elevator has a lot of authority because the glider is designed for a wide range of speeds, and the pilot has in aileron to resist overbanking, then whoa nellie! A properly flown steep turn at higher speed isn't what I'm talking about. I'm considering a 30-45 degree bank turn at low speed. You mention in an earlier post about making shallow, fast turns during a low save. Why shallow? If the thermal is narrow, you usually need to be steep (and fast) to stay in the (probably a bit turbulent) core. This thermal was very smooth and regular and wide. I was feeling it out on the first turn, and was not eager to make any coarse inputs or lose sight of my landing site or get vertigo during the circle. A shallow turn is asking for the classic base-to-final spin entry, 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... Too much rudder, maybe, but it wasn't because he moved it. It was because the pilot put in more dragging aileron without RELEASING inside rudder. unless you fly so fast that any climb is more luck than skill! This is usually the case for me on cloudless days (like that one). High over the terrain, I usually just bump into a thermal. Of course, at altitude, while thermalling, slow is good, and trim is your friend... Methinks your power background is showing (all those shallow turns!). Shallow turns in power? Why? Just jam the throttle all the way in, full flaps, and yo-yo base to final at 60 degrees. Gas is a good substitute for brains ;PPPP Power planes (except maybe the DA-20) often have lower aspect ratios. Some even have frieze ailerons. And if the left turns are flown with power off, there's even a little slip provided by the P-factor of the prop. There's enough differences between the two that the USA CFI practical tests require training and evaluation in each category seperately (CFI transition from one to the other requires spin training in the new class, except for Sport Pilots, but that's another thread). Even though I also have a power past going way back, I now find my glider bias showing when I fly a stinkpot; I find myself whipping into nice 45 to 60 degree banks, scaring the daylights out of my power-only friends... Power flying can be boring. If an autopilot can do it, why do they need me? Anyway Kirk, I welcome some more discussion. As you can see, there are quite a few points where we agree, and a few nuanced ones where we don't. I hope you have time to continue another response... -- ------------+ Mark Boyd Avenal, California, USA
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#6
August 25th 04, 05:59 PM
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#7
August 25th 04, 08:04 PM
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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
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#8
August 24th 04, 11:50 AM
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In article OrwWc.1538$4o.536@fed1read01,
"Ted Wagner" wrote: Still I can't imagine "thermaling" at 300 feet unless there was terrain underneath me I could imagine landing on even less. I hope that goes without saying! How about the opposite? I can't see much wrong with thermalling at 300 ft or lower if the ground underneath you is landable and unobstructed such that you can roll level and land in any direction. Or on one of those occasions where there is almost no lift about but no strong sink either. If conditions were at all boisterous then I wouldn't even consider it -- both because of the risk of a pin upset, and because of the risk of hitting horrid 500+ fpm sink just as you're facing away from the field -- but in the late evening when it's calm? Why not? -- Bruce | 41.1670S | \ spoken | -+- Hoult | 174.8263E | /\ here. | ----------O----------
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#9
August 24th 04, 08:59 PM
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Bruce Hoult wrote:
How about the opposite? I can't see much wrong with thermalling at 300 ft or lower if the ground underneath you is landable and unobstructed such that you can roll level and land in any direction. Or on one of those occasions where there is almost no lift about but no strong sink either. I've thermalled fairly low before. The main issues for me were to ensure there was no traffic nearby, and avoid wires and towers. But yes, we have a lot of flat, wide open dry plowed fields, so a landout is a no-brainer. I don't usually bother that low, however, because where I am, if I'm that low, it's usually because it's early and the thermals aren't really cooking yet. So that low there's often an inversion, and I'm gonna land anyway... -- ------------+ Mark Boyd Avenal, California, USA
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