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Black Hawk Down.

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Black Hawk Down.

Old 23rd Aug 2019, 12:52
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Black Hawk Down.

There is an interesting video on Live Leaks that might be worthy of a discussion if somebody could kindly post the link.
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Old 23rd Aug 2019, 17:59
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Is this the one?

A Chinook Crew with a sense of humor....and timing!



https://www.liveleak.com/view?t=uVDm2_1566553540
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Old 23rd Aug 2019, 18:28
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This was dropped on purpose as part of accident investigation research.
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Old 23rd Aug 2019, 19:20
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Was it a smashing success?
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Old 23rd Aug 2019, 19:21
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Originally Posted by SASless View Post
Was it a smashing success?
no, the whole thing fell flat.
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Old 23rd Aug 2019, 19:24
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the new look is kind of flattering dont you think?
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Old 23rd Aug 2019, 20:38
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Definitely caused by over pitching.....as evidenced by the Coning Angle of the MR Blades.
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Old 23rd Aug 2019, 21:43
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Thanks SAS, that was the one I mentioned!
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Old 23rd Aug 2019, 23:23
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IIrc, the original UH60 requirement called for a survivable heavy landing, with the undercarriage collapsing to take up part of the shock and the cabin remaining sufficiently intact to allow the passengers to survice.
The flattened airframe in the pictures shows that these requirements were not met in this test.
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Old 23rd Aug 2019, 23:28
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Perhaps the Test Engineers forgot to factor in the rotor downwash of the Chinook when they did their calculations.
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Old 24th Aug 2019, 00:27
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Originally Posted by etudiant View Post
IIrc, the original UH60 requirement called for a survivable heavy landing, with the undercarriage collapsing to take up part of the shock and the cabin remaining sufficiently intact to allow the passengers to survice.
The flattened airframe in the pictures shows that these requirements were not met in this test.
A quick search reveals the UTTAS crashworthiness requirement is a 42 ft/sec vertical sink rate.
The test case shown had an approximately 3 second drop time, which equates to 144 ft altitude, and 96 ft/sec sink rate at impact (ignoring vertical drag and Chinook downdraft).
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Old 24th Aug 2019, 01:17
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The Army had, as a result of Vietnam experience, created a crashworthy design requirement document which they cited for the UTTAS Request for Proposal. Both Sikorsky and Boeing designed to these very new requirements for their UTTAS competing aircraft. About the same time both of us were ready for first flight, they published these criteria as Mil-STD-1290. You can look it up and get an idea of the difference between designing for these combat related design crash survivability requirements, and where the various other helicopter structural design requirements are. One that stuck out was that as a fallout of the drop requirements in para 4.2 and the table 5.1 and following is that we had to drop the fuel tank, full of fuel and enclosed in the same structure enclosing it in the real aircraft, from 65 feet and not spill anything.

DS re the 42 ft/sec. Not sure I recall that number from the spec data ( and that could be age interference, I admit ). But we did have an occurrence during the test program wherein we overdid it a bit and smacked the tail down with a tail wheel vertical velocity of 42 ft/sec. You may have seen the video, as marketing put it out all over the place.The thing about it was that it occurred at 1530hrs local in CT. It was 652, ship 3. Sent the asst crewchief inside the tail three times looking for structural issues-there were none. The tail wheel tire was flat and the rim needed replacement. And, the rear 1-2 inches of the stabilator trailing edge was scrapped and bent up slightly. We did not have one and so the stabilator trailing edge was straightened with a pair of vice grip pliers and 652 flew at 0630 in the morning. There is a story about the asst crewchief going back into the tail the second and third times, but it has to do with human nature and not the technical facts. DS, this might be the source of that 42 ft/sec number?
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Old 24th Aug 2019, 01:28
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Dropped a Bell UH-1H C&C helicopter once......the Doughnut at the top of the recovery sling (the bit that actually rode inside the cargo hook of the Chinook) broke....and away off went the Huey.

It had less than 25 flight hours on it at the time....and was being recovered due to a hydraulics failure.

Some Einstein in his infinite wisdom decided since there were Chinooks headed south to our base at Chu Lai....why not just sling the Huey back rather than fly a Huey and Maintenance Team north to there grounded aircraft that was in a "safe" base camp with an airstrip.

It was after dark and out over the South China Sea....cruise altitude of 3000 feet.

The Huey did not survive that drop test.

We made darn sure we retained the broken Doughnut as evidence as we just knew some Colonel whose ride it was that got dumped would be looking for some heads to lop off.
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Old 24th Aug 2019, 02:12
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Originally Posted by Droop Snoot View Post
A quick search reveals the UTTAS crashworthiness requirement is a 42 ft/sec vertical sink rate.
The test case shown had an approximately 3 second drop time, which equates to 144 ft altitude, and 96 ft/sec sink rate at impact (ignoring vertical drag and Chinook downdraft).
at design MGWT 16825.
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Old 24th Aug 2019, 02:35
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Originally Posted by JohnDixson View Post
The Army had, as a result of Vietnam experience, created a crashworthy design requirement document which they cited for the UTTAS Request for Proposal. Both Sikorsky and Boeing designed to these very new requirements for their UTTAS competing aircraft. About the same time both of us were ready for first flight, they published these criteria as Mil-STD-1290. You can look it up and get an idea of the difference between designing for these combat related design crash survivability requirements, and where the various other helicopter structural design requirements are. One that stuck out was that as a fallout of the drop requirements in para 4.2 and the table 5.1 and following is that we had to drop the fuel tank, full of fuel and enclosed in the same structure enclosing it in the real aircraft, from 65 feet and not spill anything.

DS re the 42 ft/sec. Not sure I recall that number from the spec data ( and that could be age interference, I admit ). But we did have an occurrence during the test program wherein we overdid it a bit and smacked the tail down with a tail wheel vertical velocity of 42 ft/sec. You may have seen the video, as marketing put it out all over the place.The thing about it was that it occurred at 1530hrs local in CT. It was 652, ship 3. Sent the asst crewchief inside the tail three times looking for structural issues-there were none. The tail wheel tire was flat and the rim needed replacement. And, the rear 1-2 inches of the stabilator trailing edge was scrapped and bent up slightly. We did not have one and so the stabilator trailing edge was straightened with a pair of vice grip pliers and 652 flew at 0630 in the morning. There is a story about the asst crewchief going back into the tail the second and third times, but it has to do with human nature and not the technical facts. DS, this might be the source of that 42 ft/sec number?
John...
I recall seeing stills of the landing, but not sure I ever saw the video. Thanks for, as usual, adding plenty of meat to the bones of that story. I'm sure every development program has had many events like that, and of course the UTTAS was no exception.

I'm not a crashworthiness guy, and didn't remember the actual specs. A Google search quickly found USAARL Report No.93-15, "Basic Principles of Helicopter Crashworthiness by Dennis F. Shanahan." It's not a very clean reference, but it does refer to the "42 ft/sec design pulse." and that number rang a bell with me. But it seems questionable that the inadvertent demonstration would precisely meet the spec requirement.

If my maths is correct, a 65 foot drop corresponds to a 65 ft/sec impact velocity. The energy in the test, which goes as the square of the velocity, would be over twice that of a 65 foot drop (96/65)^2 = 2.16.

It would be interesting to know if the test that is the subject of this thread closely duplicates an actual accident, or is being used to gather data and perhaps validate a mathematical crash model. We'll likely never know.

DS
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Old 24th Aug 2019, 07:59
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So 42 ft/sec is approx. 2500 ft/min, to be able to walk away from that is impressive, we had a Black Hawk crew here in Australia stuff up on a night approach many years ago to a FARP , impacted the PSP matting at about 500ft/min made three large dents in the mating , bounced into the air and spun around, landed refuelled and took off, we weren't told about it by the crew but the refuellers told us the next day when we inspected all the machines we had on Ex one had the dust pushed about half way up the upper main struts, , the tail strut upper part just bottomed , when we questioned the crew they admitted they did it and stuffed up big time, aircraft was inspected for heavy landing, nothing found and cleared to fly , anything other than a Black Hawk we would have had a smouldering pile at the FARP .
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Old 24th Aug 2019, 13:08
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BH9, wait a second: you’ll be having me doing the marketing ploy! In that errant landing I referred to, the tail wheel hit at 42 ft/sec, but not the main, which was substantially less. Ship 3 was the one used for engine/airframe interface test/systems test/pitot-static system test/fuel system incl hot fuel test etc. On that day, someone decided they needed another power off landing for some piece of data. Ch. Pilot was one of the pilots and said ok ( Dick had done the first power off touchdowns ). But the wind was 0-15 and they had to use the approach over the river, which has a bluff on the far side, accentuating the updraft. Point is, when they flared they didn’t have 80, where the rotor bites cleanly and the vertical rate goes to zero, but they had 65, where the flare creates a change in pitch attitude, and that’s all. We looked at the data traces afterwards and this auto looked, flying-wise, like all the rest.
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Old 27th Aug 2019, 09:48
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Interesting variation on the old airshow act where an incorrectly parked car is in the way.... 'we'll just move it for you.... Oops...'.

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Old 27th Aug 2019, 12:19
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We did the Car Thing at every annual airshow....using a Huey to lift the prepared car....no engine or transmission...fuel tank removed.

It made a very pleasing sound upon hitting the ground from about 300 feet up!

That was until one year our guy almost took out the VOR Transmitter by delaying the drop just a bit too long.

The FAA guy monitoring the Show was not amused.
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Old 27th Aug 2019, 17:41
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I remember an HH-53 dropping a Ford Anglia from what looked to be about 1000' at Mildenhall.
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