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#11
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Exceeding VNE may induce aerodynamic flutter, this can and almost certainly will cause catastrophic failure of the airframe. Put simply try and avoid both but if the choice is exceed the placarded G loading or VNE the G loading is the only choice. The potential for catastophic failure is much much greater if VNE is exceeded, Why? exceeding VNE is therefore not an option. Isn't there a built in safety margin for both G's and VNE? A modern sailplane is built to withstand a sudden updraft of 10 m/s at Vne. If you pull at the same time, it is more than likely that the wing won't make it. |
#12
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K.P. Termaat wrote:
Thanks for the discussion. Once one has exceeded Vne ... This whole discussion is somewhat bizarre. I've been doing spins on a regular basis and exceeding Vne has never been an issue. Certainly not when still spinning (no acceleration in spinning mode), but not during pull out either. I can't help assuming that no one contributing to this thread has ever done a spin himself. Stefan |
#13
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Nonsense. Exceed the structural g-load limit and you fly without wings.
-- Bert Willing ASW20 "TW" "Don Johnstone" a écrit dans le message de ... OK the answer to this one is very simple, VNE stands for 'Velocity never exceed' the never is not optional. Pulling the airbrakes or pulling back hard on the stick may cause structural damage to the glider, however this structural damage is not likely to be catastrophic. Exceeding VNE may induce aerodynamic flutter, this can and almost certainly will cause catastrophic failure of the airframe. Put simply try and avoid both but if the choice is exceed the placarded G loading or VNE the G loading is the only choice. The potential for catastophic failure is much much greater if VNE is exceeded, exceeding VNE is therefore not an option. I have no doubt there will now be lots of postings from people who say they have exceeded VNE and got away with it. Even idiots can be lucky sometimes. At 11:30 25 March 2004, Bert Willing wrote: If you are already very fast and pull the airbrakes, you have to be very careful during the pull up because the wing won't stand the same g-load as without airbrakes. -- Bert Willing ASW20 'TW' 'Erik Braun' a écrit dans le message de ... K.P. Termaat wrote: Yesterday evening I talked with a friend about avoiding excessive speed when recovering from a spin in a modern low drag glider with the somewhat larger span. He came up with the idea of pulling the airbrakes when still recovering from the rotating mode. I am not sure this can be done without disturbing the recovering action or without hurting the glider. Any comment will appreciated. Karel, NL Pulling the airbrakes is what most handbooks say on this subject. But if you're already very fast I'd do this carefully. |
#14
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Well, your contribution does make me assume than you never did a spin in a
large span glider. I once had to choose between exceeding Vne and pulling the airbrakes, and I didn't pull them. As someone said earlier, I was one of the lucky idiots who got away with it. -- Bert Willing ASW20 "TW" "Stefan" a écrit dans le message de ... K.P. Termaat wrote: Thanks for the discussion. Once one has exceeded Vne ... This whole discussion is somewhat bizarre. I've been doing spins on a regular basis and exceeding Vne has never been an issue. Certainly not when still spinning (no acceleration in spinning mode), but not during pull out either. I can't help assuming that no one contributing to this thread has ever done a spin himself. Stefan |
#15
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To put the record straight
1. When I referred to idiots and exceeding VNE I meant those who had done so deliberately, not those who had done so inadvertantly. 2. Pulling excess G can damage the airframe, however the damage is likely to be far less than the damage caused by flutter. I am not sure that enough G could be pulled at speeds below VNE to cause serious catastrophic failure as there is a margin between the placarded limit and the design limit of most gliders. (We are talking about avoiding exceeding VNE) For example from memory the Grob 103 Acro is placarded +3G -1G in the UK. (This might be the LBA limit). If I remember correctly Grob place a limit of +8G -3.5G for the airframe. I stand to be corrected but I suspect it is unlikely that 8G could be attained at an airspeed less than VNE. Other design limits may of course be closer to the placarded limit but again I suspect it may be difficult to exceed the design limit at speeds below VNE. 3. Airframe flutter can occur at less than VNE. The likelyhood of flutter increases dramatically above VNE and the severity increases with the speed. The flutter may mean that there is no control of the aircraft and therefore no way to recover. Aerodynamic flutter breaks airplanes (and bridges) and the failure is almost always catastrophic. The N really does stand for never. Excess G is the lesser of 2 evils, I know which i would choose. However whatever floats your boat but if you intend to exceed VNE I would be grateful if you did not do it over my head, all thos falling bits can really spoil your day. Yes Bert, you were indeed lucky if you exceeded VNE but read my first paragraph as to the rest. I have spun a large span glider (ASW17) and I have to say I have never got anywhere near VNE or the placarded G limit in the recovery. Will airbrakes effect the recovery from a spin, I don't know yet, I will let you know. At 11:48 26 March 2004, Bert Willing wrote: Well, your contribution does make me assume than you never did a spin in a large span glider. I once had to choose between exceeding Vne and pulling the airbrakes, and I didn't pull them. As someone said earlier, I was one of the lucky idiots who got away with it. -- Bert Willing ASW20 'TW' 'Stefan' a écrit dans le message de ... K.P. Termaat wrote: Thanks for the discussion. Once one has exceeded Vne ... This whole discussion is somewhat bizarre. I've been doing spins on a regular basis and exceeding Vne has never been an issue. Certainly not when still spinning (no acceleration in spinning mode), but not during pull out either. I can't help assuming that no one contributing to this thread has ever done a spin himself. Stefan |
#16
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Bert Willing wrote:
Well, your contribution does make me assume than you never did a spin in a large span glider. I did spins up and including a Duo. I've never flown an ASH 25 or a Nimbus 4, so I can't comment these from my own experience. However, JAR requires that they can be safely spun up to 5 full rotations. To my undertanding, "safely" means that they can be recovered without dirty tricks and without exceeding their operation limits. Stefan |
#17
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Why don't you check your glider's flight manual ?
Jean "K.P. Termaat" a écrit dans le message de ... Yesterday evening I talked with a friend about avoiding excessive speed when recovering from a spin in a modern low drag glider with the somewhat larger span. He came up with the idea of pulling the airbrakes when still recovering from the rotating mode. I am not sure this can be done without disturbing the recovering action or without hurting the glider. Any comment will appreciated. Karel, NL |
#18
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Don Johnstone wrote:
I am not sure that enough G could be pulled at speeds below VNE to cause serious catastrophic failure as there is a margin between the placarded limit and the design limit of most gliders. IIRC, JAR requires a safety margin of 1.5 Stefan |
#19
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Once I was in that situation I didn't behave as an idiot. But to get there,
I did all to qualify as an idiot. What speed you build up during recovery largely depends on how long the ship continues to turn after the counter measures. In my case the ship (26m) passed from spin through a form of spiral dive, and that makes builing up of speed very fast. Vne in this case was 200 km/h. What happens if you step outside the flight enveloppe - your guess is as good as mine. Flutter test on modern gliders is done up to Vne + 10%, but 10% is not very much in such a situation. If flutter starts, your day is spoiled. If you exceed g-loads during pull-up, you have a 1.5 design factor for a clean wing (that's more than 10%...), but pulling the airbrakes will shift the load distribution on the wing dramatically. So, you have to make a choice between two sub-optimal solutions. But, in a certified glider there is basically no reason to get there. -- Bert Willing ASW20 "TW" "Don Johnstone" a écrit dans le message de ... To put the record straight 1. When I referred to idiots and exceeding VNE I meant those who had done so deliberately, not those who had done so inadvertantly. 2. Pulling excess G can damage the airframe, however the damage is likely to be far less than the damage caused by flutter. I am not sure that enough G could be pulled at speeds below VNE to cause serious catastrophic failure as there is a margin between the placarded limit and the design limit of most gliders. (We are talking about avoiding exceeding VNE) For example from memory the Grob 103 Acro is placarded +3G -1G in the UK. (This might be the LBA limit). If I remember correctly Grob place a limit of +8G -3.5G for the airframe. I stand to be corrected but I suspect it is unlikely that 8G could be attained at an airspeed less than VNE. Other design limits may of course be closer to the placarded limit but again I suspect it may be difficult to exceed the design limit at speeds below VNE. 3. Airframe flutter can occur at less than VNE. The likelyhood of flutter increases dramatically above VNE and the severity increases with the speed. The flutter may mean that there is no control of the aircraft and therefore no way to recover. Aerodynamic flutter breaks airplanes (and bridges) and the failure is almost always catastrophic. The N really does stand for never. Excess G is the lesser of 2 evils, I know which i would choose. However whatever floats your boat but if you intend to exceed VNE I would be grateful if you did not do it over my head, all thos falling bits can really spoil your day. Yes Bert, you were indeed lucky if you exceeded VNE but read my first paragraph as to the rest. I have spun a large span glider (ASW17) and I have to say I have never got anywhere near VNE or the placarded G limit in the recovery. Will airbrakes effect the recovery from a spin, I don't know yet, I will let you know. At 11:48 26 March 2004, Bert Willing wrote: Well, your contribution does make me assume than you never did a spin in a large span glider. I once had to choose between exceeding Vne and pulling the airbrakes, and I didn't pull them. As someone said earlier, I was one of the lucky idiots who got away with it. -- Bert Willing ASW20 'TW' 'Stefan' a écrit dans le message de ... K.P. Termaat wrote: Thanks for the discussion. Once one has exceeded Vne ... This whole discussion is somewhat bizarre. I've been doing spins on a regular basis and exceeding Vne has never been an issue. Certainly not when still spinning (no acceleration in spinning mode), but not during pull out either. I can't help assuming that no one contributing to this thread has ever done a spin himself. Stefan |
#20
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Unless you are the designer, you don't know what was the limiting factor
which sets the limit speed. I once saw the wreck of an ASW20C just after it crashed at about 200 knots. It turns out that the stability and control characteristics of that type are such that above a certain speed it is impossible to recover from a dive even with the stick on the back stop; this is because the wing twists. I also saw the wreckage of a Vega where the trailing edge brakes had been deployed at too high a speed. If you exceed VNE you are taking a risk, if you pull too hard above manoeuvring speed you are taking a risk, and if you pull hard and roll at the same time you are taking a risk. If you pull the brakes you are increasing the bending load on the wings. If you get it wrong and have to take one of the risks, I am told that you should centralise the ailerons, then pull however hard is necessary not to exceed VNE, and make sure the brakes stay shut. It is clear that some types are marginal in recovering from an inadvertent spin entry without exceeding limits, especially if the entry is from an accelerated stall. An ETA broke up recovering from a deliberate stall/spin entered for certification purposes. W.J. (Bill) Dean (U.K.). Remove "ic" to reply. "Bert Willing" wrote in message ... Well, your contribution does make me assume than you never did a spin in a large span glider. I once had to choose between exceeding Vne and pulling the airbrakes, and I didn't pull them. As someone said earlier, I was one of the lucky idiots who got away with it. Bert Willing ASW20 "TW" |
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