Assault on Bin Laden: mystery of the downed chopper

publiusr said:
Now Bin Laden's compound had a tall section and a solid wall perimeter...as opposed to low-buildings and chain-link fencing where you might imagine testing done.

Might the design of the compound have impeded flow?
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That's what I remember reading on another forum at the time of the raid. The chain link fences let the rotor downwash flow away from the area, while the solid walls forced the downwash upwards where it could get grabbed by the rotors again in a vortex ring state.
 
Scott Kenny said:
And a link to the 1978(!) report about designing a stealthy helicopter: https://apps.dtic.mil/dtic/tr/fulltext/u2/a058906.pdf
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Posted in this thread in 2012:

I recall it was posted here before that as well but can’t find it.

The Mystery Machine has nothing to do with that 1978 study.

One of these days - long after a certain tabloid website is gone - I’ll write up the parts of the development story I know (and have verified).
 
quellish said:
Posted in this thread in 2012:

I recall it was posted here before that as well but can’t find it.

The Mystery Machine has nothing to do with that 1978 study.
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Huh, how'd I miss that when I binged this thread?

I still expect the Mystery Machine to have some gross shape relationships to the original study (I'm guessing shape 3, shape 2 has way too much of a performance penalty), though I would bet that they used a much more sophisticated computer version for the finer detail shaping.


quellish said:
One of these days - long after a certain tabloid website is gone - I’ll write up the parts of the development story I know (and have verified).
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And I will happily read it!
 
I still find it very interesting that despite extensive modifications to the tail, the main rotor seems to be very conventional. It has few differences, if any, from a standard Blackhawk 4-blade rotor:


While there are rotor head covers, etc. that were destroyed by demolition charges the remaining hub/head and rotors do not seem to have any major modifications. This is surprising, as usually for a quiet or LO helicopter you want more blades (5, 6) and unconventional shaping - like on the tail rotor.
 
Perhaps the four rotor blades were of "exquisite" design (?)
 
yasotay said:
Perhaps the four rotor blades were of "exquisite" design (?)
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Must have been.

When the story first broke, I assumed that they used an H-3 transmission and rotor head with Blackhawk blades. 5 blades on the head, but being spun at about 220rpm instead of 300.
 
Don't forget the hot and high aspect of the mission that day. They might have options to relax LO with conventional hub rotor to better dynamic performances.

However, I think that a rotor that is trimmed to match known radar frequency and aspect ratio would de-facto present the best stealth means to defeat RCS. It's quite similar to a rotor or prop that appears static or slow turning in a camera.
 
TomcatViP said:
Don't forget the hot and high aspect of the mission that day. They might have options to relax LO with conventional hub rotor to better dynamic performances.

However, I think that a rotor that is trimmed to match known radar frequency and aspect ratio would de-facto present the best stealth means to defeat RCS. It's quite similar to a rotor or prop that appears static or slow turning in a camera.
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Gotcha.

And speaking of the bolded part, have you seen the video of a Hind where it looks like the main rotor is completely stopped due to shutter speed perfectly matching the rotation?
 
bob225 said:
Sandbox has also done a couple of videos, i've not had time to watch as yet, so not sure of quality:
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I watched one of them. Nothing new or interesting. I didn’t get the impression there was much research done beyond a few Google searches.
 
quellish said:
I watched one of them. Nothing new or interesting. I didn’t get the impression there was much research done beyond a few Google searches.
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I watched them all, thats time i'll never get back.

He makes claims but does not provide the evidence, much like the articles sadly.

Not really worth the watch, sorry all!
 
quellish said:
I watched one of them. Nothing new or interesting. I didn’t get the impression there was much research done beyond a few Google searches.
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Certainly was the case on the one he did exposing me as suffering from a temporal shift something or other. A very shouty man. Maybe take some presentation tips from the Tank Museum or The Chieftain.

Chris
PS anyone got the right time?
 

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