Could you expand on this comparison? What goes into your rating? I would love to hear about the differences between the two. Thanks.

Dave thank heaven you changed the subject!

But do you really think a film changed the course of rotor craft history? I think it was a B-17 raid....

HC,

I shudder to think you might actually believe what you are saying.....

As I recall from my youth....the MET Forecasts for the North Sea on the odd occasion contained flawed data regarding icing....and did sometimes make life a bit interesting as rotor de-icing on commercial helicopters in those days was something we talked about over an ambient temperature beer but never saw on the aircraft.

Has the MET's crystal ball gazers improved to the extent that icing never occurs unless forecast?

Or...perhaps....there is a surplus of hot air that can be diverted to the rotor system in times of unscheduled need?

I would assume in the extreme....today's backup system is to seek warmer air just above the oggin if it can be found just as we did in those long ago years.

Nick,Naughty, naughty. You shouldn't answer a question with a question. :)


P.S. My lawyer has advised that a positive answer to your question might be construed as libel and a negative answer might be construed as nonsensical.
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Nick,
I must say that my tongue was in cheek when refering to a helicopter that doesn't crash. I am also not so naive to believe that old helicopters weren't without their teething problems. But it seems that lessons are not always learnt.

Would I be right to think that where old helicopters were designed with a slide rule and a bigger safety factor, the new ones are designed by computer and a lower safety factor? If so, why haven't helicopter manufacturers recognised that a small increase in safety factor for components might reduce costly re engineering at a later date? I am thinking of one or two specific cases here relating to a new design and of course the constant battle with airframe cracking.

I don't believe that modern analysis tools can model (with sufficient accuracy) the myriad of load cases that each component on a helicopter will see.

Also I don't believe that the oil companies are a) as bothered about safety as they make out and b) know as much about helicopters as they think. Politics (and personalities) have as much if not more to do with helicopter choice than technology, safety and reliability.

Well said, Droopystop! :D:D

bondu

HeliComparator said For the benefit of some of us that know less than you both have forgotten would you care to comment on these statements Nick?

Also sorry to be ignorant but what is PC2E?

Greetings,

Finalchecksplease

Droopystop;

I am sure that from the moment of design inception of a new aircraft or component, a fair amount of time passes. When the concept is at a point where it must be pegged before going to production, I would presume that many technological advances have been made known. The point is, that for the allocated budget of the design, will those advances be incorporated now or kept for a future design, maybe incorporated into after market production, possibly offered as an option, or whatever.

No matter how concious we are of the aviation world and its desire for safety, the harsh truth is that safety is dollars. A product will go to market with a sales estimate based on the thoroughness of the manufacturers sales team. That is why he decided to spend the money in the first place, he thought the design would produce a profit.

Then again, the design is pegged and the unit goes into production and a whole new world of tech problems are encountered. Look at the A380 problem with different software being utilised by the different manufacturers and the resultant delays and cost overruns this caused.

I am sure that when design improvements are found even during the design stage, they are seriously considered for incorporation at this time vs the investment or would they be better utilised downstream when the market may be much brighter. Possible even utilised in after market production to enhance sales.

I sometimes wonder if it is far removed from the automobile production. If you design the perfect unit, where will the future sales be after everybody owns one of these perfect units.

Regards

carholme

I feel a long post coming on so I will split into two and answer SAS and finalchecksplease first - cos that's easier!

SAS, I agree that the forecasting of icing is not particularly accurate but that does not really matter. If we are going to depart and fly at sub-zero temperatures, if by day I can avoid scattered clouds. If by night or where the cloud is unavoidable I will ensure that I have my "warm" band 1000' amsl and below. That is very predictable as its related to sea temperature, which only changes very very slowly. So if light icing is forecast but it becomes more than my aircraft's limited icing clearance can accept, I just have to descend into the warm band. Its a nuisance and reduces com range etc but not really a big deal. It would be a brave person who departed without an escape route into sub-zero cloud reliant on the fact that only light icing was forecast (brave = daft!).

So I maintain that rotor deicing does not improve safety, and unless its used cautiously (with an escape route) one day it will all end in tears. The fact the the RFM does not mention the need for an escape route is negligent IMHO.

finalchecksplease - you have not been keeping up with your reading of pprune! JAR-OPS3 used to allow Performance Class 2 (PC2) over a hostile environment (N Sea) only with conditions and only until end 2009, after which PC1 would be required. PC1 offshore is not realistic so JAR-OPS3 has been modified to allow PC2E which is Performance Class 2 Enhanced. PC2 had exposure time between the takeoff /landing decision point and achieving Vtoss/landing (exposure meaning you might crash or ditch if the engine failed during this time). PC2E uses manufacturers drop down data, deck edge clearance data etc to allow mass adjustment so that the exposure time is nominally zero. So its not PC1, but its probable (not certain) that with an engine failure at any time there will be a sucessful outcome.

HC

HC,

Guilty as charged your honour, better go and swot up on pprune, thanks for your answer.
I hope that Nick can comment on the points you made about the S92 and give straight answers and not like politicians avoid the though ones.

Greetings,

Finalchecksplease

The thought has crossed my mind :p

No helicopters are perfect
 

Gentlemen
Here are but a few opinionated views on relevant issues:

All helicopters suffer from vibration levels which are unpleasant and/or unhealthy both for man and machine. The interior noise leves are too high, and subjects a pilot to a significant risk of suffering damage to his/her hearing.

The problems of the S92A is not all the bells and whistles. High vibration levels leading to all sorts of cracks is. Also, parts falling off, dual failure of the lubrication system for the main gear box gives reason for consern.

Operating in the Norwegian sector of the North Sea the confidence in the aircraft seems to have been constantly fading since the introduction.

A few weeks back one S92A developed a crack in the main gesr box during final approach. This lead to all of the oil in the main gear box being drained. Even if the manufacuter claims dry-run capability, this is not a good thing.

The customers and the passengers organisations are not overjoyed by all of this. Still, the alternative aircraft types in the market are limited to the EC225, with its cramped cabin. According to colleagues flying the EC225, it does offer a smooth flight experience.

Since the EC products also suffer from its fair share of maintenance challenges, the whole selection process comes to down to a choice between poor alternatives, none of which really would be the preferred alternative if a smooth, quiet and reliable product entered the market place.

Keep in mind that none of the manufacturers are able to deliver aircraft in sufficient numbers at present, due to increased demand for new technology. To a certain extent this leads to the operators ordering aircraft from whomever can deliver in the next 2-5 years.

The good alternative should offer:
* Good ergonomics in the cockpit and cabin
* Standup cabin like the S61/S92.
* 5 blades like the EC225
* Performance in accordance with PC1
* De-icing, just in case, even though normal operations into known icing is not a preferred option
* Digital autopilot and flight director with quick and direct control of flight path, like the AS332L2 AND EC225, not like the S92A, which is a bit mushy
* Air conditioning, separate for the cockpit and cabin
* All sorts of bells and whistles to enhance work environment and reduce work loads, as well as impress wives, girlfriends and kids
* Etc.....


Regards, Olav

That would be the AS332 Mk3, pity they scrapped the project :{ (the 225 was known internally as the Mk2 plus)

From a frequent pax perspective, a couple of thoughts, if I may? I won't comment on servicability or front-end ergonomics and whistles and bells.

Having been invited to see inside the S-92, the school-bus style seating layout looks uncomfortable. The EC aircraft seats, which in many cases are offset from adjacent seats, offer an opportunity to stretch your legs.

A stand-up cabin isn't that attractive - once we're strapped in, we won't be wandering around too much. While the EC cabin may be cramped, again we're unlikely to do much more than grab some kip or read the Daily Sport. More serious an issue is having an adjacent window large enough to double-up as an emergency exit.

Vibration levels from a five-bladed head appear to be much lower than from four blades, which is particularly important from a passenger perspective on a long sector. (I have a susceptabilty to vibes, after 1000+ hours on Lynx, and I've only recently weened myself off Brufen after 10 years, so alighting at journey's end without buzzing knees is important to me).

A/c in the cabin has never been a problem, at least in the North Sea. If we want more, or less, the request has never gone unanswered when bleed-air is available. I'm sure an efficient a/c system would be welcome in warmer climes. A new job in Oz beckons, so I may well find out soon.

We work in an environment where we are constantly considering risk v probability. Having the fuel cells under the floor doesn't appear to be an issue that gives pax cause for concern. I has to go somewhere, or we don't get home, is how most of us would see it.

Thanks for the indulgence of intruding - please continue with the entertainment.

bobsaget123

I wrote a long tome about autopilots then clicked the wrong thing and lost it all! So here goes again...

Several books could be written about this but I will address 3 areas: 1) flight path prediction, 2) power / Nr awareness, and 3) flight envelope protection / Go-around (Flyaway) mode.

1) Most autopilots, including the 332L, L2 and S92, work by detecting a deviation, and a rate of deviation, from the required flight path. So for example when engaged on ALT mode, the datum altitude is compared with the actual altitude to get an altitude error. As that error starts to increase from zero, a correction is made according to the magnitude of the error and the rate of change of that error. This means that there has to have been an error in the first place before the autopilot does anything. In other words, the autopilot waits for an error and then fixes it.

The 225 uses accelerometer data to predict the flight path and correct it before an error has developed. In the case of ALT mode it would resolve the triaxial accelerometer data (lateral, longitudinal and normal) into the earth's plane using the pitch roll and yaw data and monitor the normal (relative to the earth) acceleration. In level flight this should of course be 1g, so if it sees the g falling to 0.99 then it knows that a descent will ensue. So before the descent has even started, it can make a correction to restore 1.0g.
This flight path prediction is why, for example, a 225 engaged on ALT and IAS in straight flight can be banked to 45 degrees by the pilot, holding it for 360 deg then rolling out and, with no pilot input to fore/aft cyclic or collective, throughout the whole manoeuvre the altitude will change by no more than 10'.

This is why it can level off at a preselected altitude having climbed/descended at 2000'/min with no more than 10' overshoot, more normally zero overshoot.

And the principle also applies to lateral navigation. Using gps ground track and wind data it of course knows what heading to fly to intercept and track the localiser (it doesn't just set the heading to match the localiser course and then adjust heading in response to a deviation), but its also monitoring the accelerometers to predict the flight path, so when a lateral gust occurs it knows that its flight path will start to deviate but doesn't have to wait for an error in the flight path to develop before it makes a correction. This is why it can hold the localiser and glidepath exactly in the centre, down to DA and below, when there is a 70kt crosswind blowing over the hills at Dyce.
This is why you can come down the ILS at 165kts / 80% torque and at 500' dial up 30kts IAS. As the torque goes from 80% to 20% in a couple of seconds to deccelerate, perhaps the glidepath might move a smigin but it would be no more that 5% of the scale.

And because its fixing acceleration deviations as they occur, its a very smooth experience for pilots and pax.

225 pilots relish really crap days because they love to fly down the ILS and have it auto-level off, slow it down to 30kts IAS and trickle up the runway exactly on the centreline, beep it down to 30' or so all on the automatics. If you can't see the ground then..... Not that we ever bust the minima, but we get a cosy feeling knowing that if despite the TAFS it all turned to rats# we are fine.

The 92 will of course fly a coupled approach but only on nice smooth days.
2) Unlike the 92 autopilot, the 225 is power and rotor rpm aware. Power is a limited commodity and the 225 will give priority to vertical mode when IAS is above Vy, and to IAS mode when below Vy. This means for instance that you can select 175 kts IAS and 5000' (or whatever) and the 225 will fly along at 5000', at max continuous power minus about 2% (allowance for turbulence etc), going as fast as it can (less than 175!) without fuss.

This means for instance that when going around from an ILS on one engine, it will climb at 1000'/min, washing off airspeed to achieve the climb rate. But as the IAS reaches Vy, priority will change to maintaining Vy and now it will sacrifice climb rate. So the OEI go-around procedure is to press go-around and watch it all happen.

The 225 is also rotor rpm aware so when an engine fails, of course there is no need to touch the controls as the collective is automatically lowered (if necessary) to give 96% Nr (the optimum Nr OEI). If the daft pilot pulls the collective up too far then lets go, it just adjusts itself to give 96% Nr again. If upper modes are engaged it will raise the collective as required to give no less than 96% Nr.

Because its power-aware if (on twin engine) you exceed MCP or takeoff power (according to airspeed), as well as an audio cue, if you release the collective it will automatically gently reduce to take you out of the transient range.

The cleverness of the S92 is limited to a statement in the RFM that tells you not to demand excessive power from the autopilot, otherwise the collective will rise without limit even though the rotor rpm slows down at the AEO FADEC stop.

3) There are various clever features - here is one: You have ALT engaged on cyclic, then you reduce power to slow down, but too much. The nose is raised to maintain altitude at the expense of IAS and in some helis this could result in excessive loss of speed so that either the mode drops out or worse, you enter a tail slide! Not in the 225 - at around 65kts it flashes a warning and then automatically engages IAS on the cyclic, moving ALT to the collective and increasing power to stabilise things.

The GA (Go-around) mode is really clever, eg you are in an OGE hover, when an engine fails. Of course there is no need to touch the controls - just press GA (under your thumb on the collective) and the aircraft will transition away by selecting 10 degrees nose down, adjusting collective to maintain 96%, then as the airspeed is around Vtoss-10kts, starting to raise the nose so that it gets to the climbing attitude just as Vtoss is reached.

We use GA mode on every takeoff. Preselect the desired IAS and altitude on the ground, preset the nominated Vtoss (if its greater than the actual Vtoss) then (for an airfield takeoff) press GA at decision point (V1) and let go. GA mode will set 1000'/min on vertical speed and raise the collective to MCP, climbing at whatever IAS it can muster. Should an engine fail, of course there is no need to touch the controls as it will reset the IAS datum to Vtoss (or current airspeed if that's higher) and climb away OEI. You do have to press the FADEC stop buttons to take the power down from 30 second power to 2 minute power, and again to continuous power. Its a hard life!

Now I am going to post this quickly before I lose it again!

HC

HC,
before you find someone jumping down your throat, you will need to correct your section 2 arguments: The S-92 became 'power aware' with the introduction of AMS 3.2.

AEO (DEO as they say) it respects the MCP limits. On the other hand, you can't fly it at MCP (86% Tq) as it would shake itself to death! Most operators either fly at 70-75% Tq, or a fuel flow or, in our case, an IAS. Many still fly the cruise in 3 axis coupling, for that reason (not us of course!)

In the event of an engine failure, it will re-datum the IAS to Vy and then respect the OEI MCP limits. This is a somewhat crude method, and the significant collective lowering to decelerate from cruise power results in a guaranteed 200 ft height loss (which slowly corrects.) One consideration is that the OEI Vne is 120 kts IAS so, it couldn't simply keep the ALT as that would posssibly result in Vne being exceeded, if the failure occured in the cruise. You couldn't use 120 kts as the datum, because in the event of a failure at a lower speed, the a/c would then accelerate, probably undesirably. So, Vy it is!

What it won't do, which ECF products do, is automatically couple the collective in the event of an engine failure, when previously 3 axis coupled. So, those operators who fly '2-cue' in the cruise will have to lower the collective promptly, whereas a 225 pilot flying 3 axis coupled would simply look up from his breakfast and say "oh, an engine failed, let's just monitor Monsieur Sagem dealing with it".

It is difficult to adequately explain in words, though HC has atempted well, how much more superior the 225 auto flight systems are by comparison to the 92: not just the physical coupling but also the MMI (Man Machine Interface) aspects. They are not perfect, but by golly they're good!

Its been a busy weekend, I haven't had the time to post some rebuttal to helicomparitor's drivel. His misrepresentation of the strength and safety shortfalls of the EC225, which is basically a 332 fuselage, with all the inherent weaknesses of that fuselage. Why did the 332MKIII not get built? Because the civil authorities would not let EC build it unless they also promised to meet the latest safety features, an impossible task in a short time and with only a few francs. That doomed the MKIII, and in its stead, the lesser 225 was born.

Helicomparitor says that it "meets" seat strength, but the FAA, JAR and EASA say he is simply either lying or misinformed (I prefer misinformed, because I think HC has integrity, he just doesn't have much else.) In the next few days, I will explain each 225 shortfall in detail. For now, let it suffice that a 332 is a 332 is a 332.
You can find this type data sheet easily, just Yahoo EC-225 TCDS and it will be one of the first hits. Note it is the same data sheet as all the other Pumas, all the way back to 1965! Change the chrome, change the paint, it is still an old, old helo. Note the shortfalls are things like overall structural safety, fatigue strength, fuel tank puncture resistance. Nothing important to HC, he will never crash.


http://webpages.charter.net/nlappos/225Oldsmall.jpg

It might have helped if in the early '90s oil wasn't $10-15 per barrel, the civil market wasn't in the doldrums and the MK3 would have been competing against the soon to be released NH-90!

Nick

Perhaps someone will go through the Gulfstream product line and look at its lineage too.

212 - thanks for the correction, I flew the 92 some time ago and I am glad to see that things have improved a bit since then.

Nick - if you read my post you will see that I said "our seats" not "the seats". When the 225 was certified it was with the original seats from the 332 family - not compliant with the latest regs as you say. But shortly after that (and probably thanks to Sikorsky) EC offered a new floor and seats that are compliant with the latest regs. Yes, its an "option" but an option that is standard for the offshore oil & gas support configuration and built into the price, and fitted to all the aircraft operating in the oil and gas sector both now and in the foreseeable future.

HC