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What is the wisdom of allowing single-engine turbines for Medevac? AFAIK this is not legal in the EU.
Correct. All emergency service helicopters in the UK must be at least twin engined and if operated at night must have two pilots although the latter may have changed recently.
If it 'ain't broken........ Don't try to mend it !
Perhaps. Until you lose power at low forward speed and low altitude, at which point it becomes about as safe as a flying rock.
Gotta multiply that by how often it happens and factor in the poor suckers who die enroute in the SSSSLLLLOOOOWWW ground-based vehicle and the incidents of the ground base vehicle smacking something else head on. It's called scientific engineering and why we allow babies to die from sitting on their parent's laps.
Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.
What is the wisdom of allowing single-engine turbines for Medevac? AFAIK this is not legal in the EU.
I don't know that very many chopper crashes in general (and medevac specifically) have been due to engine failure (or engine problems of any kind). In fact, as some of my rotorhead friends tell me, an engine failure is one of those precious few helicopter problems that probably WON'T kill you.
I don't know that very many chopper crashes in general (and medevac specifically) have been due to engine failure (or engine problems of any kind). In fact, as some of my rotorhead friends tell me, an engine failure is one of those precious few helicopter problems that probably WON'T kill you.
A while back someone posted a link to a fatal jetranger crash that happened when it lost the engine as it was slowing to hover at about 150'. It's really alarming how it just drops out of the sky. You need airspeed to autorotate, either at that moment or you have to get it by pushing forward on the way down. You simply can't do that at low altitude and low forward speed.
Originally posted by 3WE
Gotta multiply that by how often it happens and factor in the poor suckers who die enroute in the SSSSLLLLOOOOWWW ground-based vehicle and the incidents of the ground base vehicle smacking something else head on. It's called scientific engineering and why we allow babies to die from sitting on their parent's laps.
It's not a helo vs ambulance issue. It's a single vs twin issue. Single-engine machines are perfect for certain markets, where operational costs must be keep down, such as private GA and aggie and surveillance, and for certain military roles. They should not be used for commercial passenger transport or medivac however. If you think medevac can't afford twin ops, I have a medevac bill that will pop your eyes out. But don't listen to me, listen to the EU, which wisely requires twins in these roles, and AFAIK for any flights over densely populated areas.
Bell developed the 427, basically a twin-engine 407, to meet this need, which was later replaced by the 429, a fairly common medevac chopper. Eurocopter developed the AS355, basically a twin-engine AS350, for the low end twin market.
And no, I'm not speculating that this crash was due to engine failure. I'm just pointing out that singles shouldn't be used in dedicated, for profit medevac roles.
And no, I'm not speculating that this crash was due to engine failure. I'm just pointing out that singles shouldn't be used in dedicated, for profit medevac roles.
That's your opinion, Evan. Years of experience suggest otherwise. Nor does what the EU does or doesn't allow necessarily germane in this case, they also don't allow single-engine fixed-wing "carrier ops" (including charter), making, for example, the PC-12 (a Swiss-built aircraft) not legal for ski charters to Switzerland, so here we are...
Just to clarify, if it's a dedicated but NON-profit medevac operation, they can fly all the single-engine choppers they want?
Just to clarify, if it's a dedicated but NON-profit medevac operation, they can fly all the single-engine choppers they want?
In situations where any helo is better than none, and the cost of operating a twin is truly prohibitive, I think exceptions should be made. This, however, does not include for-profit medevac operations that serve major communities in the developed world. In that case it has to be pay-to-play. And god knows they mark it up and pass it on to the customers. But we should also require twins for any non-profit providers who can charge fees that support the operating costs. Singles should be the exception and twins the rule. My opinion.
No you don't. You do need forward speed to arrest the high descent rate that develops during autorotation, though.
either at that moment or you have to get it by pushing forward on the way down.
If you really could not-autorotate without airspeed, pushing forward would not help. A rotor below low-speed limit is not very good at controlling pitch either.
You simply can't do that at low altitude and low forward speed.
But if you are at REALLY LOW altitude, you don't need to build forward speed: the inertia of the rotor is enough to arrest the very small decent rate that would develop, if you react in a split second. And if not the skids will take care of it.
That's why the dead-man curve has an open path between 0-0 and cruise.
--- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
--- Defend what you say with arguments, not by imposing your credentials ---
No you don't. You do need forward speed to arrest the high descent rate that develops during autorotation, though.
Sorry, you need airspeed to reliably autorotate to a safe, survivable landing. I should have been more... specific there...
And not while in ground effect. Need to be very specific round here.
Tridair was the first to produce a twin variant of the Bell 206. It was designed for service with the US Forestry Dept specifically with low altitude hover in mind for rappelling missions. The single engine 206 was rejected because an engine failure would not be considered recoverable in that scenario. The 212 was too costly to operate. Thus the twin Gemini ST was designed and certified. Bell finally got around to making their own with the 427.
That said, many twins have a dead-man's curve too. If you are hovering at a somehow high altitude (between ground effect and a few hundred feet) it may be not recoverable either.
Some of them (cat B) don't have enough OEI performace to achieve OGE hoover.
Some of them (cat A) do.
Some can be operated as cat B or cat A depending on the weight, altitude and temperature.
So are you suggesting twin Cat A ops only to be allowed?
--- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
--- Defend what you say with arguments, not by imposing your credentials ---
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