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A welcome surprise Etudiant - I am far more used to abuse on this thread

drugsdontwork

Crab is very knowledgeable but be fair, you can be blunt to the point of insult on here, hence a least some of the ‘abuse’.

Also, re: BS, the MAUM of the S-92 you posted is incorrect 😁

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Don't fly it, don't have an RFM so blame the internet - perhaps 26,500 lbs is correct - the figures were after all just for illustration about disc loading and downwash.

One man's blunt is another man's truthful - all depends where you are standing - I have apologised in the past when I have actually insulted someone

drugsdontwork

Fair enough Crab, no problem with blunt if it’s truth. It’s the more subjective stuff that I’ve protested (such as your comments on civilian SAR pilots). Yes, 26,500lbs for S-92.

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Aren't they all civilian SAR pilots now? Much of my criticism at the time was slightly misdirected due to more organisational ethos concerns. I'm sure there are still good and bad in the Bristow setup.

dingo9

AW189 MAUM is Incorrect also. 8.6T

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Again, blame t'internet Even the Leonardo website says 8.3 or 8.6T - 8.3T is as close as to 18,300 lbs as make little difference

Hot_LZ

Throw the man a bone. 8.3T is certification, 8.6t is supplemental

LZ

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The high downwash in the hover is explained by dividing the rotor disc swept area by the AUM of the aircraft to give disc loading in lbs/sqft

For the previous examples, 189 and 92 come out at just over 10 lbs/sq ft compared to the Sea King at 7 lbs/sq ft.

The downwash of the Sea King could be problematic in light winds so it is no wonder the newer helos have issues.

Back to the Wessex for coastal and inland SAR 56 ft rotor, 13,600 bs MTOW, 5.5 lbs/ sq ft disc loading

dingo9

ok fair one

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And the 139 comes out the best - 15000 lbs (approx without supplemental increase to 7000Kg), disc 54' 8" - disc loading 6.37 lbs/sq ft.

It certainly seems clear from a downwash point of view that the 139 is the best option from the Leonardo stable for coastal SAR - oh wait, isn't that what was used when the 189s weren't available?

I like the 169 from a size perspective but it comes in at 9.5 lbs/sq ft - however, being less than 2/3 of the mass of the 189 it would have far less downdraught.

cyclic

What’s your calculations for the 175 Crab?

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Using rotor diameter 48' 7", MTOW of 16,535 lbs the disc area is 1850 sq ft and the disc loading 8.9 lbs/sq ft

jimf671

Not the entire story I suspect since the different blade tip and root designs along with the effect of the fuselage shape will have an effect on the working area under the aircraft. This subject was raised at the ICAR Air Commission a few years ago. Some makers had mapped the downwash under certain aircraft but I don't think we got any further with it since the science had never been done for most types. I am happy to work under the intense downwash of the new types since it is the same power that is keeping me safe in the air.

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Most of the tip design is to improve forward speed - hence the much higher Vne and cruise speed of the modern aircraft compared to Sea King etc. The Carson blades would have given another 25 kts of speed to the Sea King without changing the downwash.

You can have the extra power to give great OEI performance for safety without the horrendous downwash, you just make the rotors longer but that isn't the fashion amongst designers who like to make the overall aircraft more compact (shorter tailboom for example) to increase the useful space in the cabin.

You don't work much in the water under the aircraft I am guessing Jim?

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Second episode tonight, all mountain work, and every other word seemed to be downdraught. Modern helicopter design isn't focussed on what SAR needs.

jimf671

Although we sometime feel like the hills of Wester Ross are as wet as the nearby ocean, generally, that would be a no!

Where downwash is a problem for us is on steep ground, narrow ridges, and avalanche-prone terrain. One can train MRT to deal with working under heavy downwash but the problem remains of persons in distress, and other members of the public, who have no comprehension of the forces involved.

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So, given that the purpose of a SAR helicopter is to rescue people from difficult and dangerous situations - will we see a different choice of aircraft for the next contract or will it be more of the same?

Will any manufacturer actually design a SAR-specific helicopter rather than sticking a winch on the side of their offshore model?

Bravo73

No. The potential helicopter market is limited enough as it is. Why would they want to limit it further?

jimf671

There are ambitions in some quarters to turn some parts of this service into something like Choucas 74 or Dragon 76. While I admire the work under those c/s, I also believe those admirable approaches would have a limited applicability in this territory and there would be no appetite for their number of bases.

EASA Mountain HEMS? Non, merci.

Within the scope of the current spec one could see H215. H175? 525? ??? What else?

Smaller, faster? Faster: no such thing. Eh ... AW139? Well, fine until the day you are 150nm offshore with IMC at your destination and no space to do proper work on your casualty.


The money is in making stuff for landing on runways and steel decks or as a weapons platform. I suspect an SAR market divides up into 3 or 4 territorial sectors with different size and performance requirements. Nobody will service that kind of marketplace with dedicated types.