It’s not always certain, lots of “depends upon…”
Which twin engines you are referring to? they are all connected to the same rotor (as the multi-piston SEP 
)
Unlike multi-engine aeroplanes most twin rotary (if not all) will not sustain S&L flight or hoover on ground effect with one engine, so you only get an extension of glide range from auto-rotation if one engine fails or higher cruise speed if running on two engines, you are going down anyway this is not the case when you loose one mag or one piston in a SEP or an engine in MEP !
The confusing case I can think of for twin engine helicopters are Chinooks, in the inside they are one engine (actually two engines but feed to one gearbox) but they have two independent propellers but I am not sure if they can fly on one prop or one engine?
In that case it is must be relatively dangerous to fly with a helicopter into the middle of a stadium bowl and later to take off from there again.
Only to repeat that most weekends, must be even more dangerous.
Oh, dear!
Ibra wrote:
Unlike multi-engine aeroplanes most twin rotary (if not all) will not sustain S&L flight or hoover on ground effect with one engine, so you only get an extension of glide range from auto-rotation if one engine fails or higher cruise speed if running on two engines, you are going down anyway this is not the case when you loose one mag or one piston in a SEP or an engine in MEP !
Definitely not all. Helicopter certification specifications provide for so-called categories A and B. Category A includes helicopters that can (in the given operating conditions) continue the flight in the event of engine failure. Takeoff and hover out of ground effect are indeed a lot more critical than level forward flight, but it essentially boils down to engine power vs. actual weight. The first generation of Soviet Mi-8 helicopter had two 1100 kW engines, while the latest one has 1860 kW ones with more or less the same airframe – go figure.
Ibra wrote:
Unlike multi-engine aeroplanes most twin rotary (if not all) will not sustain S&L flight or hoover on ground effect with one engine, so you only get an extension of glide range from auto-rotation if one engine fails or higher cruise speed if running on two engines, you are going down anyway this is not the case when you loose one mag or one piston in a SEP or an engine in MEP !
Wrong, wrong, wrong. There are many variables, notably mass and density altitude. The helicopter in yesterday’s crash appears to have been performing a Category A, Performance Class 1 departure. This is designed such that on take off, in the event of failure of a power unit, the aircraft is capable of rejecting safely onto the take off/landing area available or of flying away on the remaining power unit(s) avoiding all obstacles by a vertical margin of 35 feet. It is pretty much the same theory as Balanced Field and V1/V2 criteria for commercial multi-jet aircraft.
The AW169 (the type that crashed), is an extremely capable and powerful machine. I have absolutely no doubt that it would not have been performance limited in yesterday’s accident.
It such a terrible loss of life!
What could have gone wrong?
Yes, agree on aborted take-off or recovery for critical near ground manoeuvres (catA vs catB) but still it can’t maintain S&L flight in cruise with one engine, it needs 70% of power for that, of course in thermal/updraft it may only need only 30% but realistically it will be heading down before fuel goes empty !
I will be curious to see a helicopter type that does fly S&L flight with one engine (even beyond nominal max torque limit, say it delivers 120% on two engines), or than can “cruise hoover” for 4h (not just recover) on one engine?
In the other hand, I can find you many twin engine aeroplanes that can maintain S&L cruise flight with one engine while there is fuel in the tank and a big foot on the rudder
Twin helis I have flown S&L on one engine:
AS355
A109C
AW109SP
AW109SP Grand
Puma HC1
Bell 412
In fact, all of the above will climb on one engine.
What do you mean by “cruise hover(sic)”?
Please, stick with what you know.
Dave_Phillips wrote:
Please, stick with what you know.
I know about engines certification, I worked on Arriel 2+ & CFM56 leapx upgrades, which are by far the most common engines in twin helis/jets but good to know that there are some helis that can fully operate on one engine as most commercial jets do
