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the only inflight breakups in such a situation
I ever heard of were the ASW-22 prototype (1981), the eta and the US Nimbus, the first two being test flights of prototypes. How about the DG-600 prototype? |
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John,
The airbrakes were designed not only to be used for approach and landing, but also to avoid reaching VNE. Look at your glider's POH and check what is the maximum speed to deploy the airbrakes, and what becomes the VNE with them deployed. In most modern design gliders, the airbrakes can be deployed up to VNE, and they will prevent the glider from reaching VNE when fully opened. The airbrakes are designed for this purpose. Once the airbrakes are opened and will prevent you from going over VNE, there's no need to pull at anything even close to the design limit G. Spin training therefore, is the best way to ease this fear and learn how to pull without overstressing the airframe. AP "John Galloway" wrote in message ... Through the contributions to the avoiding VNE thread runs the theme of the difficulty of avoiding overspeeding and/or overstressing some modern designs in accidental spin recovery. This is made more difficult than in older composite gliders because they had a little more drag and a little more (fortuitous) margin in the g limits. Is it not blindingly obvious that there is a need for an emergency drag device that does not reduce the G limits of gliders? Clearly if we all handled the recovery from inadvertent spins etc perfectly all would be well but equally clearly that does not always happen and it is a shame to lose pilots in this situation. As the Phoebus pilot pointed out a tail chute is ideal for this - providing that it can be made to actuate and jettison reliably. (I found the design used on the Kestrel particularly good and I never once had a failure for landing use) On the other hand they are expensive and inconvenient to replace and there are several ways that they can fail. So can anyone think of a better idea than a chute? The best I can come up with is some sort of flush fitted rectangular-with the-long-edge-horizontal rear hinged airbrakes (like old fashioned automobile suicide doors) located on the fuselge sides somewhere in the region below or below/behind the wings. If they opened to about 45 degrees with a spring actuator (and limited by sliding metal stays that hinge/attach to the front of the panel and whose inner ends slid along in runners) then they would provide a lot of drag without any deep internal mechanism (such as wing airbrakes have). Once they have done their job the rear end of the brakes could be released by a spring loaded mechanism similar to the front end so that the brakes would then instantly spring to as position set out from and parallel to the fuselage so that there would be very little drag - only that provided by the stays at both ends and the brake panels edge on to the wind. That configuration would be good enough to fly home with. It would only be possible to reset these brakes on the ground and they would not replace conventional wing airbrakes for approach control - although they could have a secondary use for emergency approach control. I am envisaging something the could be included in new designs although there does not seem to be any obvious reason why such a device could not be retrofitted as a fairly major modification. The contours of the brake panels would be specific to the individual fuselage type but the mechanism could be generic. The assembly would be fairly shallow and complete within itself apart from e.g. a cable release attachment. I am not advocating a technical solution to this problem in place of spin recovery practice but I do think that there must be something that the combined intellects of the gliding community can come up with other than observing that if we get into that particular overspeeding/steep attitude condition we are stuffed. Anyone got any simpler or better ideas? I am definitely not an engineer. John Galloway |
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NO. This is thoroughly misleading.
HISTORICAL. When the first gliders with good (for the day) performance were built, it was found that the good performance made them difficult to land. So they were fitted with spoilers as a landing aid. Then pilots started to cloud fly, and some lost control in cloud and overspeeded and overstressed their gliders, which broke up. This was countered by developing and fitting speed-limiting airbrakes (DFS, e.g. Weihe and Slingsby Sky, and Schempp-Hirth). These were intended to be speed limiting in a true vertical dive. In the U.K. it was a requirement that the glider was test flown to prove that at max. all up weight in a vertical dive Vne was not exceeded, I understand that the Slingsby Skylark series all passed this test. Note that max. manoeuvring and rough air speeds WOULD be exceeded. Later, it was found that with higher wing loadings, thinner wing sections and higher aspect ratios it became practically impossible to fit true speed limiting brakes (in the sense that Vne would not be exceeded in a true vertical dive at max. a.u.w.). The first U.K. built gliders for which this applied were, I believe, some at least of the Slingsby Dart series. Also, if the rules were relaxed life would become a lot easier for the designer, because it would save weight and cost. So the rules were relaxed, and "Speed limiting" came to mean "In a dive at X degrees", usually I understand of 45 degrees. TODAY Most gliders today, including I believe all those built in Europe, are designed to JAR 22. See: Joint Aviation Authorities, Europe. http://www.jaa.nl/ , JARs – Section 1 – JAR-22 http://www.jaa.nl/section1/jars/445499.pdf . The relevant clause is: "JAR 22.73 Descent, high speed "It must be shown that the sailplane with the airbrakes extended, will not exceed VNE in a dive at an angle to the horizon of: "(a) 45° when the sailplane is approved for cloud flying and/or aerobatics when certificated in the Aerobatic or Utility Category; "(b) 30° in other cases. "[Ch. 5, 28.10.95]" Some modern gliders, including some being built today, probably still have true speed limiting brakes by the strict old definition given above; my guess is that these would all be gliders with trailing edge brakes or braking flaps such as the early Pik 20; but this would not necessarily be true for all gliders with such brakes. Some gliders were built with tailchutes, either in an attempt to comply with the old strict requirement, or because it was necessary if they were to comply with the relaxed rule. I have always understood that the Janus was fitted with a tailchute to be speed limiting in a 45 degree dive at max. a.u.w. with full water ballast. At what dive angle would a Duo-Discus with full brakes go through Vne? I would be astonished if this is more than 45 degrees, it may very well be 30 degrees. So if in a spin recovery, or for any other reason, you are diving at a very steep angle your air-brakes are unlikely to save you from exceeding Vne. I am sure they won't in the Nimbus 3/4 series; it was not a requirement for certification. W.J. (Bill) Dean (U.K.). Remove "ic" to reply. "Arnold Pieper" wrote in message . com... John, The airbrakes were designed not only to be used for approach and landing, but also to avoid reaching VNE. Look at your glider's POH and check what is the maximum speed to deploy the airbrakes, and what becomes the VNE with them deployed. In most modern design gliders, the airbrakes can be deployed up to VNE, and they will prevent the glider from reaching VNE when fully opened. The airbrakes are designed for this purpose. Once the airbrakes are opened and will prevent you from going over VNE, there's no need to pull at anything even close to the design limit G. Spin training therefore, is the best way to ease this fear and learn how to pull without overstressing the airframe. AP "John Galloway" wrote in message ... Through the contributions to the avoiding VNE thread runs the theme of the difficulty of avoiding overspeeding and/or overstressing some modern designs in accidental spin recovery. This is made more difficult than in older composite gliders because they had a little more drag and a little more (fortuitous) margin in the g limits. Is it not blindingly obvious that there is a need for an emergency drag device that does not reduce the G limits of gliders? Clearly if we all handled the recovery from inadvertent spins etc perfectly all would be well but equally clearly that does not always happen and it is a shame to lose pilots in this situation. As the Phoebus pilot pointed out a tail chute is ideal for this - providing that it can be made to actuate and jettison reliably. (I found the design used on the Kestrel particularly good and I never once had a failure for landing use.) On the other hand they are expensive and inconvenient to replace and there are several ways that they can fail. So can anyone think of a better idea than a chute? The best I can come up with is some sort of flush fitted rectangular-with the-long-edge-horizontal rear hinged airbrakes (like old fashioned automobile suicide doors) located on the fuselage sides somewhere in the region below or below/behind the wings. If they opened to about 45 degrees with a spring actuator (and limited by sliding metal stays that hinge/attach to the front of the panel and whose inner ends slid along in runners) then they would provide a lot of drag without any deep internal mechanism (such as wing airbrakes have). Once they have done their job the rear end of the brakes could be released by a spring loaded mechanism similar to the front end so that the brakes would then instantly spring to as position set out from and parallel to the fuselage so that there would be very little drag - only that provided by the stays at both ends and the brake panels edge on to the wind. That configuration would be good enough to fly home with. It would only be possible to reset these brakes on the ground and they would not replace conventional wing airbrakes for approach control - although they could have a secondary use for emergency approach control. I am envisaging something the could be included in new designs although there does not seem to be any obvious reason why such a device could not be retrofitted as a fairly major modification. The contours of the brake panels would be specific to the individual fuselage type but the mechanism could be generic. The assembly would be fairly shallow and complete within itself apart from e.g. a cable release attachment. I am not advocating a technical solution to this problem in place of spin recovery practice but I do think that there must be something that the combined intellects of the gliding community can come up with other than observing that if we get into that particular overspeeding/steep attitude condition we are stuffed. Anyone got any simpler or better ideas? I am definitely not an engineer. John Galloway |
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Thanks Bill.
You detail the historical background to the paradox implicit in the 'Avoiding VNE' thread that a glider can be, at one and the same time, both technically within its operating limits, and also in an irrecoverable situation - i.e. if it is flying in a fast, accelerating, steep angle configuration (leaving those as vague terms as the values will vary between types) - even assumming a hypothetical empty airmass of infinite size and zero turbulence. This is a bit unfortunate for those who find themselves in that situation and I think that it would be nice if gliders that are within their limits had the capability of not exceeding them if it is technically possible. John Galloway At 15:18 31 March 2004, W.J. \bill\ Dean \u.K.\. wrote: NO. This is thoroughly misleading. HISTORICAL. When the first gliders with good (for the day) performance were built, it was found that the good performance made them difficult to land. So they were fitted with spoilers as a landing aid. Then pilots started to cloud fly, and some lost control in cloud and overspeeded and overstressed their gliders, which broke up. This was countered by developing and fitting speed-limiting airbrakes (DFS, e.g. Weihe and Slingsby Sky, and Schempp-Hirth). These were intended to be speed limiting in a true vertical dive. In the U.K. it was a requirement that the glider was test flown to prove that at max. all up weight in a vertical dive Vne was not exceeded, I understand that the Slingsby Skylark series all passed this test. Note that max. manoeuvring and rough air speeds WOULD be exceeded. Later, it was found that with higher wing loadings, thinner wing sections and higher aspect ratios it became practically impossible to fit true speed limiting brakes (in the sense that Vne would not be exceeded in a true vertical dive at max. a.u.w.). The first U.K. built gliders for which this applied were, I believe, some at least of the Slingsby Dart series. Also, if the rules were relaxed life would become a lot easier for the designer, because it would save weight and cost. So the rules were relaxed, and 'Speed limiting' came to mean 'In a dive at X degrees', usually I understand of 45 degrees. TODAY Most gliders today, including I believe all those built in Europe, are designed to JAR 22. See: Joint Aviation Authorities, Europe. http://www.jaa.nl/ , JARs – Section 1 – JAR-22 http://www.jaa.nl/section1/jars/445499. pdf . The relevant clause is: 'JAR 22.73 Descent, high speed 'It must be shown that the sailplane with the airbrakes extended, will not exceed VNE in a dive at an angle to the horizon of: '(a) 45° when the sailplane is approved for cloud flying and/or aerobatics when certificated in the Aerobatic or Utility Category; '(b) 30° in other cases. '[Ch. 5, 28.10.95]' Some modern gliders, including some being built today, probably still have true speed limiting brakes by the strict old definition given above; my guess is that these would all be gliders with trailing edge brakes or braking flaps such as the early Pik 20; but this would not necessarily be true for all gliders with such brakes. Some gliders were built with tailchutes, either in an attempt to comply with the old strict requirement, or because it was necessary if they were to comply with the relaxed rule. I have always understood that the Janus was fitted with a tailchute to be speed limiting in a 45 degree dive at max. a.u.w. with full water ballast. At what dive angle would a Duo-Discus with full brakes go through Vne? I would be astonished if this is more than 45 degrees, it may very well be 30 degrees. So if in a spin recovery, or for any other reason, you are diving at a very steep angle your air-brakes are unlikely to save you from exceeding Vne. I am sure they won't in the Nimbus 3/4 series; it was not a requirement for certification. W.J. (Bill) Dean (U.K.). Remove 'ic' to reply. 'Arnold Pieper' wrote in message . com... John, The airbrakes were designed not only to be used for approach and landing, but also to avoid reaching VNE. Look at your glider's POH and check what is the maximum speed to deploy the airbrakes, and what becomes the VNE with them deployed. In most modern design gliders, the airbrakes can be deployed up to VNE, and they will prevent the glider from reaching VNE when fully opened. The airbrakes are designed for this purpose. Once the airbrakes are opened and will prevent you from going over VNE, there's no need to pull at anything even close to the design limit G. Spin training therefore, is the best way to ease this fear and learn how to pull without overstressing the airframe. AP 'John Galloway' wrote in message ... Through the contributions to the avoiding VNE thread runs the theme of the difficulty of avoiding overspeeding and/or overstressing some modern designs in accidental spin recovery. This is made more difficult than in older composite gliders because they had a little more drag and a little more (fortuitous) margin in the g limits. Is it not blindingly obvious that there is a need for an emergency drag device that does not reduce the G limits of gliders? Clearly if we all handled the recovery from inadvertent spins etc perfectly all would be well but equally clearly that does not always happen and it is a shame to lose pilots in this situation. As the Phoebus pilot pointed out a tail chute is ideal for this - providing that it can be made to actuate and jettison reliably. (I found the design used on the Kestrel particularly good and I never once had a failure for landing use.) On the other hand they are expensive and inconvenient to replace and there are several ways that they can fail. So can anyone think of a better idea than a chute? The best I can come up with is some sort of flush fitted rectangular-with the-long-edge-horizontal rear hinged airbrakes (like old fashioned automobile suicide doors) located on the fuselage sides somewhere in the region below or below/behind the wings. If they opened to about 45 degrees with a spring actuator (and limited by sliding metal stays that hinge/attach to the front of the panel and whose inner ends slid along in runners) then they would provide a lot of drag without any deep internal mechanism (such as wing airbrakes have). Once they have done their job the rear end of the brakes could be released by a spring loaded mechanism similar to the front end so that the brakes would then instantly spring to as position set out from and parallel to the fuselage so that there would be very little drag - only that provided by the stays at both ends and the brake panels edge on to the wind. That configuration would be good enough to fly home with. It would only be possible to reset these brakes on the ground and they would not replace conventional wing airbrakes for approach control - although they could have a secondary use for emergency approach control. I am envisaging something the could be included in new designs although there does not seem to be any obvious reason why such a device could not be retrofitted as a fairly major modification. The contours of the brake panels would be specific to the individual fuselage type but the mechanism could be generic. The assembly would be fairly shallow and complete within itself apart from e.g. a cable release attachment. I am not advocating a technical solution to this problem in place of spin recovery practice but I do think that there must be something that the combined intellects of the gliding community can come up with other than observing that if we get into that particular overspeeding/steep attitude condition we are stuffed. Anyone got any simpler or better ideas? I am definitely not an engineer. John Galloway |
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John Galloway wrote:
Thanks Bill. You detail the historical background to the paradox implicit in the 'Avoiding VNE' thread that a glider can be, at one and the same time, both technically within its operating limits, and also in an irrecoverable situation - i.e. if it is flying in a fast, accelerating, steep angle configuration (leaving those as vague terms as the values will vary between types) - even assumming a hypothetical empty airmass of infinite size and zero turbulence. This is a bit unfortunate for those who find themselves in that situation and I think that it would be nice if gliders that are within their limits had the capability of not exceeding them if it is technically possible. It would be nice, and it is technically possible, but perhaps not economically viable, judging by the number of manufacturer that offer them. "Speed-limiting" gliders are available; for example, the Ka-6E and other gliders designed to the speed-limiting standards, and gliders with trailing edge dive brakes. Personally, I think other things are more likely to kill me, so I would prefer money and research effort be spent on more crash-tolerant cockpits, pilot rescue systems, spin resistance, spoilers and canopies that won't open when left unlocked, and simpler, more reliable self-launching systems. -- ----- change "netto" to "net" to email me directly Eric Greenwell Washington State USA |
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John Galloway wrote:
This is a bit unfortunate for those who find themselves in that situation and I think that it would be nice if gliders that are within their limits had the capability of not exceeding them if it is technically possible. You're right but it's the pilot task to think ahead and not to fall into such a situation. You cannot achieve high performance in a pilot-proof glider... The same when you are flying above unlandable terrain, there is nothing illegal in this but you are in a great risk. And you have to think ahead and stay within reach of a landing field... -- Denis R. Parce que ça rompt le cours normal de la conversation !!! Q. Pourquoi ne faut-il pas répondre au-dessus de la question ? |
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Nimbus 3 and 4 and Duo Discus brakes do not meet the
'speed limiting in a 45 degree dive' requirement, but do achieve that in a 30 degree dive. That's why they are non-aerobatic. At 15:18 31 March 2004, W.J. \bill\ Dean \u.K.\. wrote: NO. This is thoroughly misleading. HISTORICAL. When the first gliders with good (for the day) performance were built, it was found that the good performance made them difficult to land. So they were fitted with spoilers as a landing aid. Then pilots started to cloud fly, and some lost control in cloud and overspeeded and overstressed their gliders, which broke up. This was countered by developing and fitting speed-limiting airbrakes (DFS, e.g. Weihe and Slingsby Sky, and Schempp-Hirth). These were intended to be speed limiting in a true vertical dive. In the U.K. it was a requirement that the glider was test flown to prove that at max. all up weight in a vertical dive Vne was not exceeded, I understand that the Slingsby Skylark series all passed this test. Note that max. manoeuvring and rough air speeds WOULD be exceeded. Later, it was found that with higher wing loadings, thinner wing sections and higher aspect ratios it became practically impossible to fit true speed limiting brakes (in the sense that Vne would not be exceeded in a true vertical dive at max. a.u.w.). The first U.K. built gliders for which this applied were, I believe, some at least of the Slingsby Dart series. Also, if the rules were relaxed life would become a lot easier for the designer, because it would save weight and cost. So the rules were relaxed, and 'Speed limiting' came to mean 'In a dive at X degrees', usually I understand of 45 degrees. TODAY Most gliders today, including I believe all those built in Europe, are designed to JAR 22. See: Joint Aviation Authorities, Europe. http://www.jaa.nl/ , JARs – Section 1 – JAR-22 http://www.jaa.nl/section1/jars/445499. pdf . The relevant clause is: 'JAR 22.73 Descent, high speed 'It must be shown that the sailplane with the airbrakes extended, will not exceed VNE in a dive at an angle to the horizon of: '(a) 45° when the sailplane is approved for cloud flying and/or aerobatics when certificated in the Aerobatic or Utility Category; '(b) 30° in other cases. '[Ch. 5, 28.10.95]' Some modern gliders, including some being built today, probably still have true speed limiting brakes by the strict old definition given above; my guess is that these would all be gliders with trailing edge brakes or braking flaps such as the early Pik 20; but this would not necessarily be true for all gliders with such brakes. Some gliders were built with tailchutes, either in an attempt to comply with the old strict requirement, or because it was necessary if they were to comply with the relaxed rule. I have always understood that the Janus was fitted with a tailchute to be speed limiting in a 45 degree dive at max. a.u.w. with full water ballast. At what dive angle would a Duo-Discus with full brakes go through Vne? I would be astonished if this is more than 45 degrees, it may very well be 30 degrees. So if in a spin recovery, or for any other reason, you are diving at a very steep angle your air-brakes are unlikely to save you from exceeding Vne. I am sure they won't in the Nimbus 3/4 series; it was not a requirement for certification. W.J. (Bill) Dean (U.K.). Remove 'ic' to reply. 'Arnold Pieper' wrote in message . com... John, The airbrakes were designed not only to be used for approach and landing, but also to avoid reaching VNE. Look at your glider's POH and check what is the maximum speed to deploy the airbrakes, and what becomes the VNE with them deployed. In most modern design gliders, the airbrakes can be deployed up to VNE, and they will prevent the glider from reaching VNE when fully opened. The airbrakes are designed for this purpose. Once the airbrakes are opened and will prevent you from going over VNE, there's no need to pull at anything even close to the design limit G. Spin training therefore, is the best way to ease this fear and learn how to pull without overstressing the airframe. AP 'John Galloway' wrote in message ... Through the contributions to the avoiding VNE thread runs the theme of the difficulty of avoiding overspeeding and/or overstressing some modern designs in accidental spin recovery. This is made more difficult than in older composite gliders because they had a little more drag and a little more (fortuitous) margin in the g limits. Is it not blindingly obvious that there is a need for an emergency drag device that does not reduce the G limits of gliders? Clearly if we all handled the recovery from inadvertent spins etc perfectly all would be well but equally clearly that does not always happen and it is a shame to lose pilots in this situation. As the Phoebus pilot pointed out a tail chute is ideal for this - providing that it can be made to actuate and jettison reliably. (I found the design used on the Kestrel particularly good and I never once had a failure for landing use.) On the other hand they are expensive and inconvenient to replace and there are several ways that they can fail. So can anyone think of a better idea than a chute? The best I can come up with is some sort of flush fitted rectangular-with the-long-edge-horizontal rear hinged airbrakes (like old fashioned automobile suicide doors) located on the fuselage sides somewhere in the region below or below/behind the wings. If they opened to about 45 degrees with a spring actuator (and limited by sliding metal stays that hinge/attach to the front of the panel and whose inner ends slid along in runners) then they would provide a lot of drag without any deep internal mechanism (such as wing airbrakes have). Once they have done their job the rear end of the brakes could be released by a spring loaded mechanism similar to the front end so that the brakes would then instantly spring to as position set out from and parallel to the fuselage so that there would be very little drag - only that provided by the stays at both ends and the brake panels edge on to the wind. That configuration would be good enough to fly home with. It would only be possible to reset these brakes on the ground and they would not replace conventional wing airbrakes for approach control - although they could have a secondary use for emergency approach control. I am envisaging something the could be included in new designs although there does not seem to be any obvious reason why such a device could not be retrofitted as a fairly major modification. The contours of the brake panels would be specific to the individual fuselage type but the mechanism could be generic. The assembly would be fairly shallow and complete within itself apart from e.g. a cable release attachment. I am not advocating a technical solution to this problem in place of spin recovery practice but I do think that there must be something that the combined intellects of the gliding community can come up with other than observing that if we get into that particular overspeeding/steep attitude condition we are stuffed. Anyone got any simpler or better ideas? I am definitely not an engineer. John Galloway |
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The Type Certificate is Glider Utility Category for the Duo Discus, which
would seem to be inappropriate given the 45degree requirement of JAR22.73(a), unless this was subject to some caveat during certification. Never having seen a Duo POH, what does it say? Perhaps that's enough to satisfy the certification requirement. Frank Whiteley "Chris Rollings" wrote in message ... Nimbus 3 and 4 and Duo Discus brakes do not meet the 'speed limiting in a 45 degree dive' requirement, but do achieve that in a 30 degree dive. That's why they are non-aerobatic. At 15:18 31 March 2004, W.J. \bill\ Dean \u.K.\. wrote: NO. This is thoroughly misleading. HISTORICAL. When the first gliders with good (for the day) performance were built, it was found that the good performance made them difficult to land. So they were fitted with spoilers as a landing aid. Then pilots started to cloud fly, and some lost control in cloud and overspeeded and overstressed their gliders, which broke up. This was countered by developing and fitting speed-limiting airbrakes (DFS, e.g. Weihe and Slingsby Sky, and Schempp-Hirth). These were intended to be speed limiting in a true vertical dive. In the U.K. it was a requirement that the glider was test flown to prove that at max. all up weight in a vertical dive Vne was not exceeded, I understand that the Slingsby Skylark series all passed this test. Note that max. manoeuvring and rough air speeds WOULD be exceeded. Later, it was found that with higher wing loadings, thinner wing sections and higher aspect ratios it became practically impossible to fit true speed limiting brakes (in the sense that Vne would not be exceeded in a true vertical dive at max. a.u.w.). The first U.K. built gliders for which this applied were, I believe, some at least of the Slingsby Dart series. Also, if the rules were relaxed life would become a lot easier for the designer, because it would save weight and cost. So the rules were relaxed, and 'Speed limiting' came to mean 'In a dive at X degrees', usually I understand of 45 degrees. TODAY Most gliders today, including I believe all those built in Europe, are designed to JAR 22. See: Joint Aviation Authorities, Europe. http://www.jaa.nl/ , JARs - Section 1 - JAR-22 http://www.jaa.nl/section1/jars/445499. pdf . The relevant clause is: 'JAR 22.73 Descent, high speed 'It must be shown that the sailplane with the airbrakes extended, will not exceed VNE in a dive at an angle to the horizon of: '(a) 45° when the sailplane is approved for cloud flying and/or aerobatics when certificated in the Aerobatic or Utility Category; '(b) 30° in other cases. '[Ch. 5, 28.10.95]' Some modern gliders, including some being built today, probably still have true speed limiting brakes by the strict old definition given above; my guess is that these would all be gliders with trailing edge brakes or braking flaps such as the early Pik 20; but this would not necessarily be true for all gliders with such brakes. Some gliders were built with tailchutes, either in an attempt to comply with the old strict requirement, or because it was necessary if they were to comply with the relaxed rule. I have always understood that the Janus was fitted with a tailchute to be speed limiting in a 45 degree dive at max. a.u.w. with full water ballast. At what dive angle would a Duo-Discus with full brakes go through Vne? I would be astonished if this is more than 45 degrees, it may very well be 30 degrees. So if in a spin recovery, or for any other reason, you are diving at a very steep angle your air-brakes are unlikely to save you from exceeding Vne. I am sure they won't in the Nimbus 3/4 series; it was not a requirement for certification. W.J. (Bill) Dean (U.K.). Remove 'ic' to reply. 'Arnold Pieper' wrote in message . com... John, The airbrakes were designed not only to be used for approach and landing, but also to avoid reaching VNE. Look at your glider's POH and check what is the maximum speed to deploy the airbrakes, and what becomes the VNE with them deployed. In most modern design gliders, the airbrakes can be deployed up to VNE, and they will prevent the glider from reaching VNE when fully opened. The airbrakes are designed for this purpose. Once the airbrakes are opened and will prevent you from going over VNE, there's no need to pull at anything even close to the design limit G. Spin training therefore, is the best way to ease this fear and learn how to pull without overstressing the airframe. AP 'John Galloway' wrote in message ... Through the contributions to the avoiding VNE thread runs the theme of the difficulty of avoiding overspeeding and/or overstressing some modern designs in accidental spin recovery. This is made more difficult than in older composite gliders because they had a little more drag and a little more (fortuitous) margin in the g limits. Is it not blindingly obvious that there is a need for an emergency drag device that does not reduce the G limits of gliders? Clearly if we all handled the recovery from inadvertent spins etc perfectly all would be well but equally clearly that does not always happen and it is a shame to lose pilots in this situation. As the Phoebus pilot pointed out a tail chute is ideal for this - providing that it can be made to actuate and jettison reliably. (I found the design used on the Kestrel particularly good and I never once had a failure for landing use.) On the other hand they are expensive and inconvenient to replace and there are several ways that they can fail. So can anyone think of a better idea than a chute? The best I can come up with is some sort of flush fitted rectangular-with the-long-edge-horizontal rear hinged airbrakes (like old fashioned automobile suicide doors) located on the fuselage sides somewhere in the region below or below/behind the wings. If they opened to about 45 degrees with a spring actuator (and limited by sliding metal stays that hinge/attach to the front of the panel and whose inner ends slid along in runners) then they would provide a lot of drag without any deep internal mechanism (such as wing airbrakes have). Once they have done their job the rear end of the brakes could be released by a spring loaded mechanism similar to the front end so that the brakes would then instantly spring to as position set out from and parallel to the fuselage so that there would be very little drag - only that provided by the stays at both ends and the brake panels edge on to the wind. That configuration would be good enough to fly home with. It would only be possible to reset these brakes on the ground and they would not replace conventional wing airbrakes for approach control - although they could have a secondary use for emergency approach control. I am envisaging something the could be included in new designs although there does not seem to be any obvious reason why such a device could not be retrofitted as a fairly major modification. The contours of the brake panels would be specific to the individual fuselage type but the mechanism could be generic. The assembly would be fairly shallow and complete within itself apart from e.g. a cable release attachment. I am not advocating a technical solution to this problem in place of spin recovery practice but I do think that there must be something that the combined intellects of the gliding community can come up with other than observing that if we get into that particular overspeeding/steep attitude condition we are stuffed. Anyone got any simpler or better ideas? I am definitely not an engineer. John Galloway |
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