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#71
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Accident in Namibia, SH Ventus 2cxm
Read my post, at the begining it was not a spin
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#72
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Accident in Namibia, SH Ventus 2cxm
This comment has nothing to do with the latest Nimbus 4DM accident:
However, in regards to some comments about a glider spin developing into a spiral. If you have not had that happen it can be a real surprise. I was spin training in a 2-32 that would do 1/2 turn in a spin and then go in spiral. The sight picture was the same, only different was rudder opposite the rotation did not work. I spotted the problem after about ¾ of a rotation but was very surprised that the spiral did not look any different than the spin I had always assumed I could tell the difference. Now picture this is a slippery modern glider of any wing length, nose 70 degrees down or more. Would very quickly go through VNE. The most fun flying I have done is in a Nimbus 4D or ASH-25 as a shared experience is the essence of human nature. Two pilots can make one very good flight! |
#73
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Accident in Namibia, SH Ventus 2cxm
On Tuesday, February 2, 2016 at 5:02:50 PM UTC-5, Jonathan St. Cloud wrote:
This comment has nothing to do with the latest Nimbus 4DM accident: However, in regards to some comments about a glider spin developing into a spiral. If you have not had that happen it can be a real surprise. I was spin training in a 2-32 that would do 1/2 turn in a spin and then go in spiral. The sight picture was the same, only different was rudder opposite the rotation did not work. I spotted the problem after about ¾ of a rotation but was very surprised that the spiral did not look any different than the spin I had always assumed I could tell the difference. Now picture this is a slippery modern glider of any wing length, nose 70 degrees down or more. Would very quickly go through VNE. The most fun flying I have done is in a Nimbus 4D or ASH-25 as a shared experience is the essence of human nature. Two pilots can make one very good flight! You should be able to tell the difference. Look at your airspeed indicator. In the spin the air speed will be low or at least stable and in the spiral it will be high and quickly increasing. That was the case on all gliders I spanned. Turn and bank indicator ball in the spin will be all the way to the outside of the turn. |
#74
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Accident in Namibia, SH Ventus 2cxm
The 2-32 is not very slippery, no need to look inside when spin recovery did not work, I recovered from the spiral. Point being, if you had not considered this possibility and are in a slippery glider you might keep this in mind. This is the only aircraft I had intentional spun that would spiral out of the spin.
On Tuesday, February 2, 2016 at 3:05:29 PM UTC-8, Andrzej Kobus wrote: You should be able to tell the difference. Look at your airspeed indicator. In the spin the air speed will be low or at least stable and in the spiral it will be high and quickly increasing. That was the case on all gliders I spanned. Turn and bank indicator ball in the spin will be all the way to the outside of the turn. |
#75
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Accident in Namibia, SH Ventus 2cxm
On 2/2/2016 7:46 PM, Jonathan St. Cloud wrote:
The 2-32 is not very slippery, no need to look inside when spin recovery did not work, I recovered from the spiral. Point being, if you had not considered this possibility and are in a slippery glider you might keep this in mind. This is the only aircraft I had intentional spun that would spiral out of the spin. On Tuesday, February 2, 2016 at 3:05:29 PM UTC-8, Andrzej Kobus wrote: You should be able to tell the difference. Look at your airspeed indicator. In the spin the air speed will be low or at least stable and in the spiral it will be high and quickly increasing. That was the case on all gliders I spanned. Turn and bank indicator ball in the spin will be all the way to the outside of the turn. Having never spun anything more slippery than a 2-32 (at least four of which have been spun into the ground from well aloft), but having many times incipiently-spun a 15-meter glass bird, and having thoroughly spun a 1-26 (in both directions) for up to 17 turns (in one direction only), and having gained a modicum of knowledge concerning aeronautical industry practices and war stories related to spinning, I long ago concluded several things about spins: 1) they were then (and remain) beyond mankind's computational skills regarding "absolutely-predictable behavior," and (along with flutter testing) rightfully are one of the reasons within industry that test-piloting remains a well-respected, and reasonably well-paying occupation; 2) anyone who treats them complacently is either seriously ignorant or willfully blind; and 3) just because a bird is certified is no reason to complacently bet your life on the *next* spin behaving identically to past spins. I'm not trying to be dramatic here, just trying to convey the very real complexity of spinning aerodynamics. My present working conclusion is big, heavy, clean sailplanes (e.g. ASH-25, Nimbus 4DM) may well (likely do, for cleanliness & inertial reasons) have less "ham-fisted margin" between the time of stopping rotation and returning to level flight than "the rest of the glider fleet." Thoughtful pilots will fly them accordionly... As to "looking inside at ASI/needle-ball" to verify whether one is in a spin or spiral dive, I'd hesitate to make a sweeping claim one does or does not have to, but - assuming for the sake of discussion that ground clearance isn't an issue - if you choose wrongly as to which methodology to apply first in the face of "WTF is the ship doing?" I know I'd rather apply spiral dive corrective action *before* anti-spin corrective action, simply because being late on the former includes dire structural implications. Best, of course, to have confirmed what the ship is doing before attempting corrective action, and instruments are (used to be, anyway) a part of every instructors' teaching toolkit. I could never get that (still in the flying fleet) 1-26 I spent so much time with investigating its spinning behavior, to remain in a spin in one direction (I've forgotten which) for more than 5 (sometimes less than 3) turns; throughout it "hunted up/down in pitch" in phase with decreasing/increasing spin rate until on one of its downward-pitching excursions, it always exited in a skidding diving turn which showed every indication was about to become a spiral dive if left unaddressed. It spun rock-steadily in the other direction, but required ailerons to be strictly neutralized to avoid more or less instantly exiting in either a nose-low slipping turn (aileron out of the spin) or a nose-low skidding spiral dive (aileron into the spin). The transition from spinning flight to non-spinning flight was attention grabbing in that aerodynamically dirty bird. Quite audible and accompanied by obvious lateral accelerations. I never could convince myself to permit the skidding spiral dive entry aft-stick recovery to continue to nose level without quickly neutralizing the ailerons so cautious was I of spiral dive possibilities, though I think it would have safely recovered at that early stage of things. My "spin-now-stopped" recoveries involved rapidly neutralizing ailerons and maintaining full aft stick. I never managed to induce a secondary stall under those circumstances in that docile, forgiving, ship. The transition from spinning to non-spinning flight may well *not* be obvious in some other ship. You pays your money and takes your chances with spin behavior, ideally treading thoughtfully, cautiously and preparedly... Bob - so call me overcautious - W. |
#76
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Accident in Namibia, SH Ventus 2cxm
As glider pilots there are many things we do which are familiar to
us, we deal with these events very quickly, the so called muscle memory. If we are prudent we practise, on a regular basis so emergency situations, such as launch failures and every one we practise increases the chance of recognition and proper recovery action. As regards spinning we may practise in a glider cleared for intentional spinning but we seldom if ever practise a spiral dive which is uncontrolled, we have no experience of such an event. We may have been told that it can happen, briefed on the symptoms and warned of the consequences but never actually seen it and recovered unless we are one of the very few test pilots. The difference between a spiral dive and a spin may be bleedin obvious to a few but for most of us it is a situation which requires the processing of information which is completely unfamiliar. Some gliders are prohibited from deliberate spinning so we never have the opportunity to practice, it is likely therefore that the first time we see an event be it spinning or spiral dive is when it occurs unintentionally. One of the symptoms which distinguishes a spiral dive from a spin is the already high and increasing airspeed. To recognise the difference you have to see it. The problem is that the increase in airspeed, the acceleration, is very high, maybe approaching 18kts per second per second (32fps/ps). If we take just 3 seconds to see that the speed is in fact increasing we will have added 57kts and we still have to decide how to correct that and take the appropriate action. If we take a further 3 seconds to decide on and start to carry out the appropriate recovery we are already through VA, approaching or exceeding VNE and headed for the scene of the accident. It has been said that recovery will result in uncommanded airbrake deployment which transfers and increased load to the outer wing panels, which are likely to fail. When a test pilot carries out his tests he deliberately does so, he knows what to expect and has already decided on his recovery action, his recovery is likely to be close to optimum. He is likely to guard the airbrake control. I would suggest that anyone, including our test pilot might have difficulty if the event was completely unexpected. Even if the acceleration is only 90% of the maximun in a Nimbus 4DM, the speed will increase by 100kts in the 6 seconds. Assuming we started with 50kts the recovery will go through VNE (177kts). Max manouvering speed (VA) for a Nimbus 4 is 100kts, so full control deflection is not available after 3 seconds. It seems to me that if it happens unexpectedly it is not going to end well however lighting fast our reactions might be. |
#77
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Accident in Namibia, SH Ventus 2cxm
Don,
the answer is simple. Don't fly a Nimbus 4 if you do not feel competent to do so. There is a sh1t load of opinions in this thread and some frankly outlandish comments from people (most of whom) have not flown the aircraft. "I wonder how many other people have to die or parachute to safety before someone asks the question, should this glider be flying at all" A knee jerk response to a factually correct but ill-informed statement which lacked all of the information. So far as I can see, there are two people on this thread who has constructively contributed. JMC and Francois. I would happily fly a Nimbus 4DM with either of these people. At 11:05 03 February 2016, Don Johnstone wrote: As glider pilots there are many things we do which are familiar to us, we deal with these events very quickly, the so called muscle memory. If we are prudent we practise, on a regular basis so emergency situations, such as launch failures and every one we practise increases the chance of recognition and proper recovery action. As regards spinning we may practise in a glider cleared for intentional spinning but we seldom if ever practise a spiral dive which is uncontrolled, we have no experience of such an event. We may have been told that it can happen, briefed on the symptoms and warned of the consequences but never actually seen it and recovered unless we are one of the very few test pilots. The difference between a spiral dive and a spin may be bleedin obvious to a few but for most of us it is a situation which requires the processing of information which is completely unfamiliar. Some gliders are prohibited from deliberate spinning so we never have the opportunity to practice, it is likely therefore that the first time we see an event be it spinning or spiral dive is when it occurs unintentionally. One of the symptoms which distinguishes a spiral dive from a spin is the already high and increasing airspeed. To recognise the difference you have to see it. The problem is that the increase in airspeed, the acceleration, is very high, maybe approaching 18kts per second per second (32fps/ps). If we take just 3 seconds to see that the speed is in fact increasing we will have added 57kts and we still have to decide how to correct that and take the appropriate action. If we take a further 3 seconds to decide on and start to carry out the appropriate recovery we are already through VA, approaching or exceeding VNE and headed for the scene of the accident. It has been said that recovery will result in uncommanded airbrake deployment which transfers and increased load to the outer wing panels, which are likely to fail. When a test pilot carries out his tests he deliberately does so, he knows what to expect and has already decided on his recovery action, his recovery is likely to be close to optimum. He is likely to guard the airbrake control. I would suggest that anyone, including our test pilot might have difficulty if the event was completely unexpected. Even if the acceleration is only 90% of the maximun in a Nimbus 4DM, the speed will increase by 100kts in the 6 seconds. Assuming we started with 50kts the recovery will go through VNE (177kts). Max manouvering speed (VA) for a Nimbus 4 is 100kts, so full control deflection is not available after 3 seconds. It seems to me that if it happens unexpectedly it is not going to end well however lighting fast our reactions might be. |
#78
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Accident in Namibia, SH Ventus 2cxm
At 11:05 03 February 2016, Don Johnstone wrote:
The difference between a spiral dive and a spin may be bleedin obvious to a few but for most of us it is a situation which requires the processing of information which is completely unfamiliar. The instruction standard I teach by mandates spiral dive and spin recovery prior to first solo. Common sense dictates that if you can't distinguish between the two in your day-to-day glider (and their very different recoveries), you shouldn't fly solo IMHO. Granted, the differences are a lot more subtle in an advanced (open class) glider (and time to react a lot shorter), but it still suprises me how often students confuse the two and put in the wrong control inputs. |
#79
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Accident in Namibia, SH Ventus 2cxm
Le mercredi 3 février 2016 13:15:10 UTC+1, Justin Craig a écrit*:
Don, the answer is simple. Don't fly a Nimbus 4 if you do not feel competent to do so. Justin, "feeling competent to" is probably he cause of death #1 amongst glider pilots. I absolutely agree with you that if one doesn't feel competent to fly an open glass glider, then he shouldn't. But "feeling compentent" might be a different thing than "being competent". I'm not addressing that to any person in specific. However, having spin experience in a ASK21 or a Discus does not mean that you will survive a fully developed spin in an open glass ship. The momentum of the wing is about 3-5 times larger than that of a 15m glider, and when you do the right inputs to stop the spin, the large momentum means that until the actual rotation is stopped, you are accelerating nose down by 70-80 deg with negative flaps for almost a full turn. So if you wait for the rotation to have stopped before you pull up, there is almost no way that the wings would stay with you. If you don't wait long enough, you might re-stall the wing. The margin for a successful exit is very slim, while on a 15 m ship it is absolutely easy. Been there, done that long ago on a 26 m ship, happy to be still alive. After that event, any incipent stall on a ASH25 got my immediate attention. |
#80
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Accident in Namibia, SH Ventus 2cxm
On Tue, 2 Feb 2016 07:12:13 -0800 (PST), Tango Whisky
wrote: I think that the ASH25 happened in 1985 or 1986. Martin Heide told me about it a week or two later. .... actually it was the ASW-22 prototype. |
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