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#11
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Wow.
Just... wow. What I still don't understand is how these aircraft are not overstressed, and are able to keep control at all. I realise that this story is an extreme example, but how about the "normal" flights? How do the planes survive? Is it just because they are built to take the load factors? "David Dyer-Bennet" wrote in message ... "xerj" writes: The site is down at the moment, but if I'm understanding it correctly, do these guys actually penetrate hurricanes in P3s and Gulfstreams? Do they go IMC flying into hurricane cloud??? If so, how the hell are they not constantly stalling as they are buffetted by the turbulence? I'm pretty sure that they'd slow down to maneuvering speed, and I'd assume that there'd be moments when windshear would be drastic How the hell are these flights even technically possible?? Fascinating article on a semi-accidental penetration of Hugo in a WP-3D (the accident was they didn't notice the storm had been upgraded, and they probably wouldn't have chosen to make the penetration given the actual state of the storm). With pictures. http://www.wunderground.com/hurricane/hugo1.asp -- David Dyer-Bennet, , http://www.dd-b.net/dd-b/ RKBA: http://noguns-nomoney.com/ http://www.dd-b.net/carry/ Pics: http://dd-b.lighthunters.net/ http://www.dd-b.net/dd-b/SnapshotAlbum/ Dragaera/Steven Brust: http://dragaera.info/ |
#12
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"xerj" wrote in message
... What I still don't understand is how these aircraft are not overstressed, and are able to keep control at all. I realise that this story is an extreme example, but how about the "normal" flights? How do the planes survive? High winds do not necessarily mean high turbulence or high wind shear. Of course, those characteristics *could* exist. But just because the wind is whipping around at 160 mph, that doesn't mean you can't fly into it without overstressing an airplane (any airplane). A hurricane involves a wide variety of meterological phenomena, including high winds, convection, rain, etc. My understanding is that the hurricane pilots use radar to avoid the strongest convective areas where severe turbulence and wind shear would be present. There probably are areas within a hurricane that would tear any airplane apart. Those who fly into them strive to avoid those areas. Pete |
#13
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I did fly through a hurricane (typhoon) at an altitude
of about 500'. Yes, it was rough! Yes, we were IMC a lot of the time. Back in the early '50s, before wx radar, we blundered into a hurricane in an R5C (C-46). Flew right through the eye. We were probably at around 10,000' altitude. It was not especially rough, but we had extreme rain that was causing problems with the Curtiss electric props and causing the fire warning light to light up. It took an unbelievable anount of drift correction to stay on the A-N range leg, and after the eye, an equally unbelievable amount in the opposite direction. We still didn't recognize that we were in a hurricane, till we were told after we landed. vince norris |
#14
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What I still don't understand is how these aircraft are not overstressed,
and are able to keep control at all. I realise that this story is an extreme example, but how about the "normal" flights? How do the planes survive? Is it just because they are built to take the load factors? Perhaps you are not a pilot and hence are not aware that if the plane is flown at "maneuvering speed," the wing will stall before the stress is sufficient to cause it to break. vince norris |
#15
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Peter Duniho wrote:
Perhaps you are not a pilot and hence are not aware that if the plane is flown at "maneuvering speed," the wing will stall before the stress is sufficient to cause it to break. For what it's worth "maneuvering speed" ensures only a certain degree of safety. A strong enough gust can still overstress the airframe, with or without a stall. Actually, the maneuvring speed is the max speed at which full deflection of the controls is still allowed and it is completely unrelated to gusts. What you both mean is the max speed for tubulent air. Both speeds are often indicated the same, but I suspect this is just to keep things simple for the average low time spam can pilot. The answer to why an airplane can be torn apart by a gust even when flying below the allowed speed for turbulent air is simple: When the gusts are strong enough, they will just "gust" you above that speed. Stefan |
#16
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"Stefan" wrote in message
... Actually, the maneuvring speed is the max speed at which full deflection of the controls is still allowed and it is completely unrelated to gusts. What you both mean is the max speed for tubulent air. Yes. I didn't see any point in further confusing the poster to whom I replied by trying to address the terminology issue at the same time. He clearly had a specific speed in mind that was related to gusts, but that speed does not guarantee airframe integrity under all possible conditions. [...] The answer to why an airplane can be torn apart by a gust even when flying below the allowed speed for turbulent air is simple: When the gusts are strong enough, they will just "gust" you above that speed. That "answer" is also incomplete. The airframe can be damaged without the relative wind rising above the relevant certificated maximum speeds. Pete |
#17
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Stefan wrote
Actually, the maneuvring speed is the max speed at which full deflection of the controls is still allowed and it is completely unrelated to gusts. Stefan...I've been fighting this common misconception here on this newsgroup for years and the spam-can pilots just don't seem to understand. It probably goes back to their basic instruction and a few well intentioned but misguided magazine writers. As you point out, maneuvering speed (Va) is related to pilot induced loads and gust loads are related to Vno, the top of the green arc on the airspeed indicator for small airplanes, it's Vb for newer and larger airplanes. There are actually two "g" envelopes for an airplane. One for maneuver loads and another for gust loads. When overlayed, they form the combined envelope. The gust loading envelope is required to accomodate the most severe gust that it is anticipated that the airplane will encounter in normal flying operations. Although both of these loads are actual physical phenomena, the FAA has defined them in the FARs via Part 23. The information is scattered in several sections of Part 23, but when specifying the gust loading requirements, nowhere is Va mentioned, and likewise, when specifying the maneuver loading requirements, there is no mention of Vb or Vno (the top of the green arc). From the FAR: Section 23.423: Maneuvering loads. Each horizontal surface and its supporting structure, and the main wing of a canard or tandem wing configuration, if that surface has pitch control, must be designed for the maneuvering loads imposed by the following conditions: (a) A sudden movement of the pitching control, at the speed VA, to the maximum aft movement, and the maximum forward movement, as limited by the control stops, or pilot effort, whichever is critical. Section 23.333: Flight envelope (c) Gust envelope. (1) The airplane is assumed to be subjected to symmetrical vertical gusts in level flight. The resulting limit load factors must correspond to the conditions determined as follows: (i) Positive (up) and negative (down) gusts of 50 f.p.s. at VC must be considered......... (ii) Positive and negative gusts of 25 f.p.s. at VD must be considered........... Section 23.1545: Airspeed indicator. (a) Each airspeed indicator must be marked as specified in paragraph (b) of this section, with the marks located at the corresponding indicated airspeeds. (3) For the normal operating range, a green arc with the lower limit at VS1 with maximum weight and with landing gear and wing flaps retracted, and the upper limit at the maximum structural cruising speed VNO established under §23.1505(b). Section 23.1505: Airspeed limitations. (b) The maximum structural cruising speed VNO must be established so that it is -- (1) Not less than the minimum value of VC allowed under §23.335 Quoted from Aerodynamics for Naval Aviators: "As a general requirement, all airplanes must be capable of withstanding an approximate effective +/- 30 foot per second gust when at maximum level flight speed for normal rated power. Such a gust intensity has relatively low frequency of occurrence in ordinary flying operations. The highest reasonable gust velocity that may be anticipated is an actual veritical velocity, U, of 50 feet per second." Now, I ask, why, when flying in gusty conditions, do pilots slow to Va? The airplane (by regulation) is designed to withstand the highest reasonable gust velocity at the top of the green arc? Slowing to Va presents a definate stall-upset possibility where the pilot is apt to induce a maneuvering overstress during the recovery. Bob Moore |
#18
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Peter Duniho wrote:
That "answer" is also incomplete. The airframe can be damaged without the relative wind rising above the relevant certificated maximum speeds. I think there is a maximum gust amplitude for which the integrity of the airframe is guaranteed. Don't know how much it is nor where that would be defined, though. (Most probably in the FARs (USA) or the JARs (Europe), but I'm not going to search.) Stefan |
#19
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"Stefan" wrote in message
... I think there is a maximum gust amplitude for which the integrity of the airframe is guaranteed. There is, and a gust greater than that may damage the airframe. Regardless of what airspeed one is flying. Which is what I said. The bottom line: there is no speed at which one can guarantee the airframe won't be damaged. Even sitting still on the ground, it is theoretically possible to have a strong enough wind to damage the airframe. "Safe" flight through a hurricane involves a LOT more than just picking the right airspeed. Pete |
#20
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vincent p. norris wrote:
I did fly through a hurricane (typhoon) at an altitude of about 500'. Yes, it was rough! Yes, we were IMC a lot of the time. Back in the early '50s, before wx radar, we blundered into a hurricane in an R5C (C-46). Flew right through the eye. We were probably at around 10,000' altitude. My dad has a ton of C-46 time. He was in a troop carrier squadron based out of Tachikawa, Japan during the Korean War until 1955. -- Mortimer Schnerd, RN VE |
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