CV-22 Incident at Addenbrooke Hospital
Looking at the video the matting that blew away is surrounded by lights, such as you would expect around the helipad itself. The presumed roadway can be seen leading away in the background with a sign post, might the sign say something like STOP, or some other directive to an ambulance driver? Don't know how an airborne recce by the crew could have detected anything amiss.
Last edited by megan; 24th Apr 2021 at 03:30. Reason: photo
I'm told that the matting that was thrown up was not actually the helipad but was a roadway for ambulances to get to and from the helicopter to transfer patients. The smooth surface provided by the matting is required for patients with some injuries eg spinal fractures. This explains why the matting is behind the Osprey as it starts to lift.
So why not land on the aluminium matting helipad?
Well it is a V-22 so, unsurprisingly, aluminium vs jet exhaust would not end well, even if the matting was of the required size & strength.
As an aside in the photo above you can see the rotors pushed to the first forward stop after landing. This minor change of angle made a big difference in reducing heat damage to steel decks & the thermal coating and as an added bonus it provides another option for dust management. They did aim for a slightly bigger angle but you then hit friction limits.
Still, a lesson learned and nobody has proposed a tilting nacelle on future tilt-rotors.
My favorite visualization of V-22 downwash...
...including bonus unfortunate Pongo, minding his own business, securing the LZ, and about to be engulfed in a tornado of sh1te.
No, the aluminium matting was indeed the helipad and the CV-22 landed as planned, ramp close to the matting that provides access to the normal helipad area.
So why not land on the aluminium matting helipad?
Well it is a V-22 so, unsurprisingly, aluminium vs jet exhaust would not end well, even if the matting was of the required size & strength.
As an aside in the photo above you can see the rotors pushed to the first forward stop after landing. This minor change of angle made a big difference in reducing heat damage to steel decks & the thermal coating and as an added bonus it provides another option for dust management. They did aim for a slightly bigger angle but you then hit friction limits.
Still, a lesson learned and nobody has proposed a tilting nacelle on future tilt-rotors.
So why not land on the aluminium matting helipad?
Well it is a V-22 so, unsurprisingly, aluminium vs jet exhaust would not end well, even if the matting was of the required size & strength.
As an aside in the photo above you can see the rotors pushed to the first forward stop after landing. This minor change of angle made a big difference in reducing heat damage to steel decks & the thermal coating and as an added bonus it provides another option for dust management. They did aim for a slightly bigger angle but you then hit friction limits.
Still, a lesson learned and nobody has proposed a tilting nacelle on future tilt-rotors.
I would have thought that pad melting would not be a factor. The Harrier was quite happy landing on aluminium planking and I never saw a melted pad. Aluminium is a very effective transmitter of heat, so local hot-spots disperse rapidly.
Mog
Mog
Hi Mog - The Harrier had no operational need to point the hot nozzles directly at the deck for 20 minutes or more, let alone at the temperature and gas velocity produced by the Osprey. Even when pointed at the deck the Harrier hot nozzle environment is partially offset by the cold nozzles - hence why you could do press-ups without killing the main gear tyres. In comparison, the M/CV-22 had little difficulty eroding & buckling coated steel decks that had been routinely operating AV-8A/B for decades.
Interesting I had two thought about why they didn't use the landing pad. First was the fencing around the site. It looked close to the pad and I was thinking that the nacelle might have ended up on top of the fence. Second was watching the video I assumed that the pad was a heavy rubber pad that I seen used for temporary construction roads here in Canada. If the pad was in fact aluminum then yes the engine exhaust likely would have melted the pads.
I suspect the CV-22 is too big to land on the pad comfortably, and chose to approach, land and depart the way they did to give themselves enough room against the fence, the lighting, the signage and what looks to be a waiting area on the way to the landing pad, but still allow the ramp to neatly meet the access pathway for transfer by gurney.
The only real issue for me is that the matting does not look to have been fixed to the ground so any blast of air impinging sideways on the matting was likely to lift it. For helicopter ops I imagine this isn't an issue, but I'd still want to do it anyway. This particular use case probably never occurred to the people planning it - maybe when it was designed there were only MH-53s and MH-60s around, or maybe those design assumptions were brought forward instead of re-assessed or maybe they didn't or couldn't consult this particular 'customer'. Lots of potential holes in the cheese, could have been filled with some pegs.
If I recall correctly, the damage mechanism in cases like this is not simply wind blast. Upon encountering the ground, the downwash flow has nowhere to go except sideways and expands as a high-velocity sheet, which results in lower-than-ambient pressure because Bernoulli, and since there is air under the matting there is a pressure differential, and it doesn't take a lot of delta-PSI over hundreds of square feet of matting to generate useful lift.
I recall John Fozard saying that this phenomenon was not fully understood before early P.1127 tests until a cast-iron manhole cover became airborne during a VTO event, to the general discomfiture of those present.
I recall John Fozard saying that this phenomenon was not fully understood before early P.1127 tests until a cast-iron manhole cover became airborne during a VTO event, to the general discomfiture of those present.
It could have been worse, the S$%& could really have hit the fan...
https://www.youtube.com/watch?v=XQcNwDuoxBk
https://www.youtube.com/watch?v=XQcNwDuoxBk
I quite literally did, what I was in there to do!
