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#21
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Bert Willing wrote:
A Nimbus 4 has airbrakes. And as for different animals: A glider certified under JAR22 needs to have means which limit a dive to 45 deg at vne. Just nitpicking: JAR22 asks for a dive angle of 30 degrees. 45 degrees are only needed to be certificated for cloud flying or aerobatics. Stefan |
#22
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So it seems to be right that Scotch affects the memory...
-- Bert Willing ASW20 "TW" "Stefan" a écrit dans le message de news: ... Bert Willing wrote: A Nimbus 4 has airbrakes. And as for different animals: A glider certified under JAR22 needs to have means which limit a dive to 45 deg at vne. Just nitpicking: JAR22 asks for a dive angle of 30 degrees. 45 degrees are only needed to be certificated for cloud flying or aerobatics. Stefan |
#23
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At 21:48 10 July 2005, Denis posted the message ' Nimbus 4 Accident'
I don't understand your choice ! if there is a risk at high speeds, the best choice to avoid it is to avoid these speeds, and that's what the airbrakes are for, aren't it ? Pulling g's after loosing control is the best way to break any aircraft... ------------------------------------------ Denis The point that I was trying to make was that exceeding the positive flap limiting speed and then opening the airbrakes is also likely to cause damage to the wing structure. Gliders are certified to withstand +5.3g with the brakes shut, but only +3.5g with them open. Derek Copeland __________________________________________________ ____________________ This email has been scanned by the MessageLabs Email Security System. For more information please visit http://www.messagelabs.com/email __________________________________________________ ____________________ |
#25
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I think what Bert says is technically correct (wing load doesn't change
when you open the air brakes) - but the distribution does change a lot - especially on a ship like the N3 & N4 where the brakes are located inboard on the inner panels. Stated differently, when the brakes are opened the outer panels are being asked to do more work supporting the fuselage (and non flying portions or the inner panels) than before the dive brakes were opened. The Nimbus 3 and 4 are placarded against carrying water ballast in the inner panel tanks with the outer panel tanks empty for structural reasons. You also must dump the inner tanks first. The same structural problem occurs when the dive brakes are open and that part of the inner panel becomes "dead weight". So - while the brakes should be used to prevent the glider getting to extreme speeds - we need to be cautious about suggesting that nothing bad is going to happen if you open them at extreme speeds. Roy B. (Nimbus 3 # 65) |
#26
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I'll try again.
Positive flap limiting speeds have two justifications: 1) To prevent damage to the flaps themselves or more likely to their hinges. 2) To stop the wings producing more lift than is good for them at high speeds, remembering that lift increases with the square of the speed for a given angle of attack, and that flaps increase the camber and therefore lift produced by the wings. Airbrakes (when open) reduce the amount of lift produced over the portion of the wing they occupy and increase the drag. The rest of the wing (mostly outboard of the brakes) has to produce more lift to support the weight of the glider and hence the bending moment on the wingspar is increased. The fact that some stressing is taking place in the region of the airbrakes is often witnessed by the gel coat cracks that tend to appear in this area. Please also re-read my account of my test flight to check the double paddle airbrake mod! There have been two N4D break-up accidents where the common factor is that control has been lost in a thermal, either a spin followed by a spiral dive, or just a straight spiral dive. It is likely that in both cases that thermalling (ie positive) flap was selected and speed and g. increased very rapidly. In at least one case the pilot tried opening the airbrakes, but the glider still broke up. We had a fatality in the UK involving an ASW20 that dived vertically at very high speed into the ground after a similar thermalling upset. The flaps also to some extent act as elevators and it was thought that the pilot was unable to overcome the nose down pitch tendency by pulling back on the stick. My main original point was that the first action in any sort of loss of control situation in a flapped glider must be to select neutral or negative flap. If you have to open the brakes, do so before Vne is reached. Derek Copeland -------------------------------------------------------------------------- ---- Bert Willing wrote: you're mixing up things. Speed limits for positive flap settings have nothing to do with g-load; they are to limit the forces on the flap. ================================================== ========================== Any opinions expressed in this e-mail are those of the individual and not necessarily those of ADT Fire and Security. Any prices for the supply of goods or services are only valid if supported by a formal written quotation. This e-mail and any files transmitted with it, including replies and forwarded copies (which may contain alterations) subsequently transmitted from ADT Fire and Security are confidential and solely for the use of the intended recipient. If you are not the intended recipient or the person responsible for delivery to the intended recipient, be advised that you have received this e-mail in error and that any use is strictly prohibited. In this event, please notify us via e-mail at ' or telephone on 0121 255 6499 and then delete the e-mail and any copies of it. WebSite: www.adt-fire-and-security.co.uk ================================================== ========================== -- |
#27
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At 13:30 12 July 2005, Derek Copeland wrote:
We had a fatality in the UK involving an ASW20 that dived vertically at very high speed into the ground after a similar thermalling upset. The flaps also to some extent act as elevators and it was thought that the pilot was unable to overcome the nose down pitch tendency by pulling back on the stick. Not sure that is exactly right, the flaps tend to cause the fuselage and tailplane to 'pitch down'. Ergo the higher the ias the greater the angle of attack of the tailplane and elevator. (The AoA of the tailplance increases as the AoA of the wing reduces as the tailplane is trying to produce lift 'down' rather than up relative to the pilot). Pulling back on the stick increases the AoA of the tailplane which could become stalled and this would certainly cause it to be ineffective as you describe. My main original point was that the first action in any sort of loss of control situation in a flapped glider must be to select neutral or negative flap. If you have to open the brakes, do so before Vne is reached Absolutely correct, carve that in stone. Derek Copeland ------------------------------------------------------------------ -------- ---- Bert Willing wrote: you're mixing up things. Speed limits for positive flap settings have nothing to do with g-load; they are to limit the forces on the flap. |
#28
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You're point number two doesn't hold: At constant speed (whichever speed), a
wing of a sailplane will never produce more lift than corresponds to the weight of the glider. Otherwise you would be climbing. Your main original point is absolutely right. -- Bert Willing ASW20 "TW" "Derek Copeland" a écrit dans le message de news: ... I'll try again. Positive flap limiting speeds have two justifications: 1) To prevent damage to the flaps themselves or more likely to their hinges. 2) To stop the wings producing more lift than is good for them at high speeds, remembering that lift increases with the square of the speed for a given angle of attack, and that flaps increase the camber and therefore lift produced by the wings. Airbrakes (when open) reduce the amount of lift produced over the portion of the wing they occupy and increase the drag. The rest of the wing (mostly outboard of the brakes) has to produce more lift to support the weight of the glider and hence the bending moment on the wingspar is increased. The fact that some stressing is taking place in the region of the airbrakes is often witnessed by the gel coat cracks that tend to appear in this area. Please also re-read my account of my test flight to check the double paddle airbrake mod! There have been two N4D break-up accidents where the common factor is that control has been lost in a thermal, either a spin followed by a spiral dive, or just a straight spiral dive. It is likely that in both cases that thermalling (ie positive) flap was selected and speed and g. increased very rapidly. In at least one case the pilot tried opening the airbrakes, but the glider still broke up. We had a fatality in the UK involving an ASW20 that dived vertically at very high speed into the ground after a similar thermalling upset. The flaps also to some extent act as elevators and it was thought that the pilot was unable to overcome the nose down pitch tendency by pulling back on the stick. My main original point was that the first action in any sort of loss of control situation in a flapped glider must be to select neutral or negative flap. If you have to open the brakes, do so before Vne is reached. Derek Copeland -------------------------------------------------------------------------- ---- Bert Willing wrote: you're mixing up things. Speed limits for positive flap settings have nothing to do with g-load; they are to limit the forces on the flap. ================================================== ========================== Any opinions expressed in this e-mail are those of the individual and not necessarily those of ADT Fire and Security. Any prices for the supply of goods or services are only valid if supported by a formal written quotation. This e-mail and any files transmitted with it, including replies and forwarded copies (which may contain alterations) subsequently transmitted from ADT Fire and Security are confidential and solely for the use of the intended recipient. If you are not the intended recipient or the person responsible for delivery to the intended recipient, be advised that you have received this e-mail in error and that any use is strictly prohibited. In this event, please notify us via e-mail at ' or telephone on 0121 255 6499 and then delete the e-mail and any copies of it. WebSite: www.adt-fire-and-security.co.uk ================================================== ========================== -- |
#29
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Bert Willing wrote on 12th July.
You're point number two doesn't hold: At constant speed (whichever speed), a wing of a sailplane will never produce more lift than corresponds to the weight of the glider. Otherwise you would be climbing. Your main original point is absolutely right. -------------------------------------------------------------- Er, I'm only a humble gliding instructor, so what do I know about things? You are also right in that in steady flight lift must equal the weight of the glider. However in a spiral dive you are in accelerated flight and the glider could effectively weigh several times its own weight, and the wings (if not stalled) have to produce the equivalent extra amount of lift to balance this. If you are pulling more than 3.5 g at high speeds, opening the airbrakes could just be enough to finish things off, due to the extra bending load on the wings this entails. The correct recovery from a spiral dive is just to carefully reduce the angle of bank while keeping the stick fairly well back, by the way. As an instructor I do lots of spins and spiral dives, so can easily recognise what is going on. Many good cross-country pilots haven't done either for years, so could be caught out should either occur unexpectedly . The recovery actions are quite different. I also understand that Nimbus 4s have a non-standard spin recovery procedure, which further complicates the issue. Derek Copeland ================================================== ========================== Any opinions expressed in this e-mail are those of the individual and not necessarily those of ADT Fire and Security. Any prices for the supply of goods or services are only valid if supported by a formal written quotation. This e-mail and any files transmitted with it, including replies and forwarded copies (which may contain alterations) subsequently transmitted from ADT Fire and Security are confidential and solely for the use of the intended recipient. If you are not the intended recipient or the person responsible for delivery to the intended recipient, be advised that you have received this e-mail in error and that any use is strictly prohibited. In this event, please notify us via e-mail at ' or telephone on 0121 255 6499 and then delete the e-mail and any copies of it. WebSite: www.adt-fire-and-security.co.uk ================================================== ========================== -- |
#30
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Ok - you've got a point :-)
-- Bert Willing ASW20 "TW" "Derek Copeland" a écrit dans le message de news: ... Bert Willing wrote on 12th July. You're point number two doesn't hold: At constant speed (whichever speed), a wing of a sailplane will never produce more lift than corresponds to the weight of the glider. Otherwise you would be climbing. Your main original point is absolutely right. -------------------------------------------------------------- Er, I'm only a humble gliding instructor, so what do I know about things? You are also right in that in steady flight lift must equal the weight of the glider. However in a spiral dive you are in accelerated flight and the glider could effectively weigh several times its own weight, and the wings (if not stalled) have to produce the equivalent extra amount of lift to balance this. If you are pulling more than 3.5 g at high speeds, opening the airbrakes could just be enough to finish things off, due to the extra bending load on the wings this entails. The correct recovery from a spiral dive is just to carefully reduce the angle of bank while keeping the stick fairly well back, by the way. As an instructor I do lots of spins and spiral dives, so can easily recognise what is going on. Many good cross-country pilots haven't done either for years, so could be caught out should either occur unexpectedly . The recovery actions are quite different. I also understand that Nimbus 4s have a non-standard spin recovery procedure, which further complicates the issue. Derek Copeland ================================================== ========================== Any opinions expressed in this e-mail are those of the individual and not necessarily those of ADT Fire and Security. Any prices for the supply of goods or services are only valid if supported by a formal written quotation. This e-mail and any files transmitted with it, including replies and forwarded copies (which may contain alterations) subsequently transmitted from ADT Fire and Security are confidential and solely for the use of the intended recipient. If you are not the intended recipient or the person responsible for delivery to the intended recipient, be advised that you have received this e-mail in error and that any use is strictly prohibited. In this event, please notify us via e-mail at ' or telephone on 0121 255 6499 and then delete the e-mail and any copies of it. WebSite: www.adt-fire-and-security.co.uk ================================================== ========================== -- |
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