Hey Crab , i see you revert to your old practice of attacking the man, nothing constructive to say? Could we agree to keep it on the technical points?
(i feel a circular discussion coming on unless you can keep to the points)
(the point about hydraulics was to make you think. why are hydraulics necessary on a helicopter tail rotor? (it's a rhetorical question). Bad design maybe? Especially if it involves introducing an unecessary system to a system that can kill you, once per 50,000hrs. As for your point about forces on an AS350 with the hydraulics turned off, I am sure you can see the flaw with your question, moving hydraulic fluid around is hard work. If the centre of pressure is too far behind the pitch change axis then there also a lot of unecessary work to do, (bad design; that could be offloaded by spring). The main rotor of an H369 is about the same size as the Tail Rotor of a Mil26, 5 blades too. The H369 does not have hydraulics, and moving it's collective lever forces, with your feet would not be at all difficult. So why do you need hydraulics on a helicopter TR (?) , answer is you don't.)
Crab wrote: "I suppose if you run out of fuel, the whole single vs twin argument becomes irrelevant........... "
Yes spot on, and very topical wrt the Glasgow thread. Pretty pointless having 2 engines there and killing all those people.
Better over a Hostile Congested Area in a single with fuel, than in a twin with no fuel.
Given the choice 'spare fuel' or 'spare engine' which one delivers real world benefits??
Fuel is a real world necessity. (anyone flying over long stretches of the worlds most inhospitable water has probably worked out their fuel. If their engine were to stop, for some strange reason, then their chance of survival (according to JimL) should be 10^-9. If they did survive then its not 100% fatal right? It's just inconvenient. Inconvenient requires 10^-3 reliability ? )
Complexity kills too, you have fuel but you can't figure out how to get it to the engines, this is NOT PILOT ERROR, this is inherent in complexity.
Complexity is dangerous, 2 pilots partially mitigates that.
Singles do fly over congested areas. They do so almost completely safely, relatively (with 2 very rare recent exceptions).
Please ge back and look at thread #97 to see what heavy twins do in congested areas.
If 'North Sea twins' flew over cities, then the Catastrophic outcome would be obviously unacceptable. IMAGINE G-REDL in central London, ouch, it would look like Glasgow but much worse. 'Leicester' catastrophe, in the city centre, no good). If the Tail Rotor failure that happened to the police AS355 helicopter in Wales had been an AW139 then imagine the impact damage to the house. Mass kills.
The only previously airbourne helicopters that have killed anyone on the ground in the UK are twins.
There is no justification for mandating multi engine for helicopters over congested areas, it will lead to more deaths not less.
The focus on engines is totally distorting the approach to the actual cause of deaths. It's 99% NOT engines.
If you want to set an Acceptable Level of Safety Performance then looking at engines isn't going to get anything achieved at all.
What is the ALoSP for a State?
1 death per person on the ground per million hours ? 10 million hours?
Where is that number? Currently for twins is it running at about 1 fatality per 100,000hrs, worse ? Who knows? WHO is in charge of this?
The ONE THING that it is very insensitive to is engine reliability. It is the single least helpful indicator of anything to do with safety.
(serious if you can please Crab)
212 the engine argument for aeroplanes is totally different to the consideration for helicopters for many fundamental reasons.
Aeroplanes don't combine the drive to a common output. Airliners have more independent engines. Airliners land very much more energetically than helis in autorotation.
Gearboxes and freewheel units and tailrotors make the mix of what gives best safety yeild different. By far the most important component is the pilot. Aeroplanes just HAVE to keep moving. Helicopters can land non fatally almost anywhere. In a helicopter use of 2 engines introduces additional mechanical risk factors. Sometimes you are better off in a helicopter having a bigger window than another engine, more chance to see the wires. Helicopters operate in environments where the biggest practical benefit is real performance margins and reliability. Reliability is not acheived by redundancy. Redundancy gives increased unreliability in exchange for (a degree of) fault tollerance.
Albatross, unlucky/lucky you. You must have had a few more hairy moments too i bet.
Crab, singles, good for you, PM me if I can help, don't lose too much sleep about what you fly over, it's the OTHER 99% ways to die you want to watch out for.
Last edited by AnFI; 19th April 2019 at 18:19.
Reason: adding