Restricted takeoffs, VRS, and ground effect

[Chucklehead]

Hello all! I've come across an interesting situation that could lead to some good discussion. Thanks in advance for any input!

I fly a dual engine Huey out of a large city. We have a helipad sandwiched in the middle of the city at ground level that presents some interesting challenges, both on takeoffs and landings. This thread is specifically related to the takeoffs we do to try to give ourselves decent aborts and single engine options while trying to minimize risk to the surrounding populace.

We regularly have to come in and out of an approx 200'x200' helipad in the middle of the city, heavy weight with about a 5-10% power margin for OGE. The helipad is surrounded by 100' obstacles in the immediate area with taller buildings (up to 200' or so) within about 3-400' in some takeoff directions. On takeoff, we often come straight up vertically (sometimes backing slightly) to about 150' or so before moving forward to give ourselves the ability to clear obstacles OEI in the event of an engine failure. If we had any issues before this committed point, we would attempt to abort straight down, or down and slightly forward, to avoid the nearby populated areas.

If I had an engine failure right at about 150' before moving forward, I would pull into single engine power and attempt to come down to the pad, pulling cushion as necessary at the bottom to try to hit the ground softer. This scenario raises what I think are a few interesting questions.

By pulling single engine power while descending in this manner, could I potentially get into VRS? Would I come out of it at about 50' when the aircraft starts to reenter ground effect, or ride it all the way into the ground?

I'm guessing we wouldn't get to a high enough rate of descent to enter in the first place, but it's still an interesting question IMO. Would the downwash velocity decrease as you entered ground effect, allowing you to decrease your sink slightly but still negating your cushion?

As a sidebar, does anyone else have to deal with similar LZs? What are your preferred methods of dealing with them? Thanks again for the input!

[John Eacott]

Chucklehead,

By 'twin Huey' you may either be a 212 or 412 driver, but both should have vertical departure options to cover your situation. When coming up vertically you should always back up; not 'sometimes slightly' as you describe unless you have a suitable runway ahead for a SE landing. Essentially from a 4ft hover smoothly increase power and at 35ft commence moving backwards to keep the helipad in view, until at TDP you rotate and gain forward speed.

Best described in the appropriate supplement for your flight manual along with appropriate performance graphs: elevated helipad procedures give the best description but may not be suitable for a ground level operation.

Since a failure would require forward movement to regain the pad that you departed from, VRS should not be an issue.

[Geoffersincornwall]

If the RFM contains a back-up profile then there will be an associated WAT Curve to aid with 'mass management'. This may be your Achillies heel.

G.

[Chucklehead]

Thanks for the feedback!

John, it sounds like I should clarify the 'sometimes slightly'. When we have room to back up we'll do that in order to keep the LZ in sight, but in some takeoff directions you have buildings behind you as well and not very much room for backing. Unfortunately, our flight manual doesn't go into elevated helipad ops, and I haven't found any performance charts relevant to the situation. If it makes any difference, I fly a 212.

Geoffers, I'm not familiar with the "WAT curve", at least not by that name. What exactly is it that you're referring to?

[evil7]

@ John E.

He describes the landing zone as surounded by obstacles up to 100`!
So my guess is he cannot climb backwards as you should normally do.

[Non-PC Plod]

Geoffers is referring to the weight/altitude /temperature limitations for each takeoff/landing profile. It should be a graph in the performance section of the RFM.
So, for a given pressure altitude and outside air temperature, there will be a maximum all up mass that you can safely operate at for performance class one or 2.

[[email protected]]

From what chucklehead describes of the LZ, elevated helipad profiles don't seem appropriate and unless he reduces his AUM considerably, he is unlikely to get a PC1 profile that works.

Chucklehead - if an engine stops at 150' then I would pull until the Nr starts to decay and then back off slightly so that you are optimising the full power available on the remaining engine but preserving the Nr.

I am lucky to have a training switch to allow me to simulate engine failures during such profiles and the difference in rate of descent between just having normal/beeped up Nr and letting it decay by a few percent is quite marked. Nr is life and life is Nr as several wise people have said on this forum.

Don't worry about VRS - you won't get near the RoD required (probably somewhere around 12 - 1500'/min for your aircraft).

Presumably you do beep up your Nr for these arrivals and departures?

[krypton_john]

Can't comment on that highbrow multi stuff, but... man it must get interesting there on a windy day. With all the obstacles does it swirl around? How can you even tell the wind direction?

[Chucklehead]

Crab, I've never beeped the rotor above 100% (our "normal" range) for a takeoff, but it sounds like it might not be a bad habit to get into. I'm assuming you just mean to start out at a bit higher so you lose less in case of a failure?

That's definitely some good advice about the beeps. One instructor that I had in particular had a compressor stall and always said that the beeps were the difference between him flying out of it and hitting the ground.

I've considered trying it out a bit lighter weight on a training sortie just by decreasing power to single available, but was a bit worried about getting into VRS which I've never even approached before to my knowledge. I would imagine you'd get some decent vibration before it went full bore but the risk/reward hasn't been worth it for me to try yet.

Krypton, it does get a bit squirrely at times. It's not uncommon for the wind to shift somewhere in about a 90° range while on approach. I would compare it somewhat to mountainous flying, with some valley winds between the buildings and demarcation lines off some of the taller ones. With the exception that I haven't seen significant downdrafts.

There are a few flags and other wind indicators nearby, and there is a wind sock on a building just a bit above the pad itself, so you can get a pretty decent idea of what the winds are trying to do. It definitely makes me feel like a bad pilot some days though, makes me work too hard!

Thanks all for the replies!

[[email protected]]

Chucklehead - most aircraft have the ability to beep up the Nr for critical stages of flight, either manually or automatically and it would be specified in the RFM (well it is in mine) for PC1 profiles.

As you say, the point is that you start from a higher Nr figure which gives you more time to react to an engine failure. If you have a low Nr horn on your aircraft, that is what to pull to followinfg an engine failure, then lower the lever until the horn ceases again, that should give you optimum Nr and max single engine power.

It is worth noting that the helipad departure (up and back) often has a limited rate of climb specified in the RFM which is to keep the pitch angles lower in order to avoid rapid Nr decay following and engine failure; this is somewhat at odds with the military view where you get to height quickly to reduce exposure time to the reject option.

[Chucklehead]

Makes sense to me. It's always interesting to hear other people's perspectives on these sorts of things. A lot of techniques, such as the RFM vs military viewpoint, seem very much a matter of chance and opinion. Thanks for the input!

[[email protected]]

No problem.

However, it is worth stressing that if you are required to operate to PC1 (carrying fare paying pax for example) you have to comply with the RFM helipad profiles, including keeping inside the WAT limits for those profiles or legally you are on very thin ice if anything goes wrong.

[whoknows idont]

Interesting thread. It would be rounded off really nicely with a couple of pictures of the pad and the approach. :ok:

[Geoffersincornwall]

PC1 is an 'operating standard' and only relevant if your jurisdiction mandates it - most don't, EASA being the exception of course. You won't therefore find PC1 data in the RFM as that is produced to comply with 'certification standards'. Note that PC1 applies to EASA CAT (Commercial Air Transport) flights and not just 'fare-paying' passenger flights. You won't find any of the offshore workers putting their hands in their pockets for their tickets - not just yet anyway. Of course the US and other jurisdictions are a different story.

PC1 uses Cat A data and you will probably find the data for Cat A approved take off and landing profiles in the RFM along with the WAT chart as PC Plod explained.

Mass management is the key to safe operation as everything in our world gets more difficult at max AUW and for those souls that ignore the max-AUW limits it gets even trickier. I wish I had a fiver for every student I met doing 139 TR's that had no idea that mass was even important. After all surely no one would build a helicopter without giving it the capability of carrying full fuel with all seats occupied. :ugh:

If you wonder why the 139 is such a popular machine then the fact that it can cope with everything full means that those that don't do any pre-flight mass calculations are no longer putting their lives on the line to the same extent.

G.

[[email protected]]

Thanks geoffers - that's why I said 'if you are required to operate to PC1' since I don't know what rules and regs chucklehead is operating to - perhaps I should have said Cat A instead.

[Thomas coupling]

Chuckle ehad - don't you have governemnt rules to fly to? What are the national requirements for your type of a/c to fly into and out of public sites?
Geoffers has said everything I want to say on this.

IF you are making this up as you go along because there are no national limits then God help you when you stoof. What does your insurance company think of your profiles old boy. It won't pay out if you don't comply?:mad:

[Gomer Pylot]

One thing I have never, ever worried about is insurance, and whether it would pay. That's not my problem. If the boss is worried about it, he can dictate flight profiles. I've never worked for a manager who even considered insurance coverage, it was always assumed to be there, but there are other people being paid to worry about that. I worry only about complying with the ops manual and staying in one piece.

[John Eacott]

Chucklehead - most aircraft have the ability to beep up the Nr for critical stages of flight, either manually or automatically and it would be specified in the RFM (well it is in mine) for PC1 profiles.

I don't think that the Bell 212 (listed in his profile) flight manual allows Nr increase beyond 100%.

[[email protected]]

John, I'm assuming it is like the Brit Mil ones which can (I think) I know you can beep down the Nr - I'll ask my colleagues.

[John Eacott]

Sure you can beep the Nr on the 212, usually between 97-100%, but the FM limitations only allow those figures as the power on values.

The 412 allows an 'upbeep' for the Nr, the 212 does not.

[Chucklehead]

Lots of replies! For the legal matters, we are not required to follow a PC1 profile. To be honest I'm not 100% sure what that would entail, I assume it's a specific profile that gives a certain safety margin? For weight/power considerations, we maintain at least a 5% margin over OGE power during our ops. I'm with Gomer Pylot in that I don't know the details beyond that.

whoknows, I've been meaning to do that for quite a while now! I'll try to get a video and take some snips from it or something.

Crab, John is right in that our "normal" range is 97-100% Nr. It's definitely an interesting idea to have in the back pocket though, since the beep range does go up to 102.

[Sir Niall Dementia]

I fly two different types of twin, both with PC1 performance, and very different profiles, two areas I regularly see ignored are the max ROC on the vertical section of the take-off and also the torque limits. Both are designed to contain the Nr in the event of an engine failure.

The simulator provides fascinating lessons in this regard, when the book says "apply 10% torque above hover requirement" a lot of pilots just give it the full beans. When an engine stops the full beans guys find themselves with a sudden (and often catastrophic Nr droop) while the guys who fly the accurate proflie find the NR drooping to exactly the right spot for either a reject or fly away.

People with very clever science/maths qualifications who have graduated from complex test pilot courses work this stuff out, I wonder why when they've gone to all that trouble an average line driver ignores their work and puts themselves in a very difficult place to explain away if they have a problem.

In the last 28 years I have only once rejected for real off a PC1 take-off and that was actually when a front seat passenger dropped something in attempting to catch it turned off the hydraulics, so it isn't always an engine failure you're waiting for.

SND

[[email protected]]

Chucklehead - I have just been perusing my colleague's 212 RFM and it shows a vertical take off profile as follows:

Vertical climb to 40-60ft using a maximum of hover Tq plus 15%,

Continued climb with rearward movement to keep the LS in sight up to CDP of 160 ft with the same Tq limits,

Then rotate to achieve VTOSS (30kts plus windspeed) using not less than 72% Tq,

Climb to 200 ft at VTOSS.

You are right that the beeping up only comes following an engine failure.

I don't know what the certifcation of a 212 entailed but I am guessing with the age of the design it was well before the advent of Cat A and B. Hence there don't seem to be any graphs in the RFM which state Cat A or PC1.

Not sure where that places you in the modern era!

[John Eacott]

I uploaded this CAA Bell 212 Cat A supplement for a previous discussion some years ago; it is not an approved current copy, but may give some idea of the profiles available.

It is also based on very early PT6-3 engines:

Part 1 (http://www.eacott.com.au/gallery/d/6051-1/Bell+212+Category+A+Operations+Supplement+Part+1_001.pdf)

Part 2 (http://www.eacott.com.au/gallery/d/6054-1/Bell+212+Category+A+Operations+Supplement+Part+2.pdf)

Part 3 (http://www.eacott.com.au/gallery/d/6057-1/Bell+212+Category+A+Operations+Supplement+Part+3.pdf)

[chopjock]

It makes me wonder why backing up downwind to keep the LZ in sight and so enable a forward descent / run on in event of an engine failure has any real advantage when in so doing puts more stress on everything and thus more likely to have an engine / tail rotor failure in the first place!
I cringe when ever I see this, using all that power whilst backing up, when you could be doing a towering take off into wind and on your way in much less time.

[NickLappos]

Some discussion of why the twin behaves the way Crab and John E have so properly described:


In the vertical takeoff, the loss of an engine creates a power deficit that produces the need to descend, of course. The deficit is measured by comparing the power needed to HOGE as compared to the OEI power remaining. If the OEI power is very close to the OGE power, as is the case when very lightly loaded, the ride down is fairly slow and the landing easily cushioned. Since the speed of that descent is driven by the size of the power deficit, as the takeoff mass is made greater, the OEI power deficit is greater, and the rate of descent becomes greater. If the power deficit is appreciable, the aircraft doesn't stabilize in a fixed rate of descent, it actually accelerates downward, so that the stop at the bottom becomes pretty harsh at higher reject altitudes (higher barriers) and at higher weights. The flight manual WAT curve (Weight, Altitude, Temperature) shows the weights where the power ratio is acceptable to perform the published procedure. For vertical procedures, the WAT curve calls for much less all up mass than a ground level procedure where you can accelerate to somewhere close to VY before the engine failure. Of course, the ground level procedure rejects into a much longer heliport, because you have to bring that fast helicopter to a stop while in the protected runway length. In other words, the various procedures for Cat A swap all up mass for speed/runway length.


VRS is somewhat involved in a vertical reject, but the descent is more governed by the simple application of too little power and too much mass, so rotor thrust does not equal weight, and the helo falls, and accelerates as it falls.


Generally, for a vertical reject from over 100 feet to be successful, the OEI power must be an appreciable fraction of the OGE power required, perhaps 75 to 80%. That is almost exactly what HIGE power is as compared to HOGE, so a rule of thumb could be that if you can barely HOGE OEI, you probably have a darn good vertical reject capability.

[[email protected]]

Chopjock - you must understand that these profiles are, if flown exactly, guaranteed to permit a safe reject back to the helipad or a safe transition into forward flight and climb to 1000 ft providing the weight and temperature limits are adhered to.

They have been proven in flight testing whereas your pull pitch and pop out vertically has not.

The argument about exposure time is valid to a degree but with higher collective pitch comes more rapid and greater Nr decay in the event of an engine failure.

The profiles are actually quite gentle due, as Nick has explained, to the need to keep the power available and the power required quite close; your vertical departure will use more torque and therefore put more stress on the airframe and TR than the up and back version.

[Thomas coupling]

C'mon chopjock......stop it. How long have you been on this forum, now? Stop being a dickhe*d now.............................................:mad:

[ShyTorque]

Without the need for name calling, I believe that CJ flies single engined machines where the performance considerations are slightly different.

[John Eacott]

It makes me wonder why backing up downwind to keep the LZ in sight and so enable a forward descent / run on in event of an engine failure has any real advantage when in so doing puts more stress on everything and thus more likely to have an engine / tail rotor failure in the first place!

What 'stress', chopjock? And how does it create a greater likelihood of engine/tail rotor failure?

I cringe when ever I see this, using all that power whilst backing up, when you could be doing a towering take off into wind and on your way in much less time.

Using 'all that power'? SND and crab@ have both explained that it is a maximum of hover Tq plus10/15%. It is actually a relatively gentle application and very controlled, with little stress compared to many SE departures of 'pull max take off torque, nose forward and rotate'.

I've done a reasonable amount of both. I'm the guy that crab@ refers to as an ex-mil driver who would reef in power to get up quickly, and had to re-learn to be a bit more considerate to follow the correct profile.

[chopjock]

What 'stress', chopjock? And how does it create a greater likelihood of engine/tail rotor failure?


Ok is an engine or anti torque system more likely to fail / stall (LTE) at high loading or not so high loading.?
Yes I only fly singles and I know on a hot day with a light wind and quite heavy with fuel / pax etc it would require more power to climb out backwards down wind than to lift straight up off a cushion into wind. (I'm not talking about yanking up on the stick here).
I know the twins are doing it at a lighter than max weight to allow for this (helipad style), it just seems if the same power used for backing up was used to get going into wind, the exposure time to the risk would be less, or even be accomplished using less power (or an increased take off mass) and in my mind less risk of something breaking.

[[email protected]]

Chopjock - the profiles are designed so there is no exposure - at any stage of the process, an engine failure will result in either a safe landing or a successful flyaway.

Single engine is different and I would tend to agree (after 32 years of mil flying) that reducing exposure time is a good idea.

[Chucklehead]

John E, thanks for the references! With those numbers we may be close to cat A in the winter but pretty far out in the summer. That's more or less what I suspected, I've always expected to best case spread the skids if we had a failure up past 100'.

Crab, that RFM profile sounds pretty similar to what we do during normal ops. The only exception is that after 30 KIAS or so I normally climb while accelerating to about 60 KIAS for max rate of climb. Do you know why they would recommend climbing out at VTOSS instead? Does it give a better ROC when you take the acceleration into account? I would assume that this would only be valid up to a certain distance..


My reasons for backing up during takeoff would be a) keeping the landing area in sight, b) increasing your forward run available and therefore your obstacle clearance, c) to allow a bit of forward drift from the nosedown tendency when you reduce collective, and d) to allow for landing with a "skids level" attitude as opposed to nose up due to the mast tilt (at least for Hueys). Am I off base, or are there others that I'm missing?

Thanks for all the replies!

[Thax]

The other advantage of the rearwards departure is that the rejection profile (forward and down) allows a little additional airspeed (airflow over the disc) which improves performance, while the slight flare used to terminate helps with NR maintenance/recovery prior to landing. At higher weights the difference (according to the A109 simulator, at least) is significant.

[HeliTester]

I note that all published vertical takeoff procedures are not particularly gentle. At least one Category A vertical helipad procedure (S-76) uses rapid collective application from wheels light to full takeoff power for vertical climb to TDP’s up to 110 ft.

[[email protected]]

Chucklehead - I think the VTOSS climb is more to do with angle of climb than rate of climb which, as you say, will be better at 60 kts (I think it says 56 kts in the RFM).

Certainly following an engine failure at or after TDP, the attitude change to capture VTOSS for the climb ensures you get a healthy vector away from the ground.

i think all your reasons for backing up are extremely valid - that's probably why the profile is designed that way.

Helitester - perhaps Nick Lappos has an answer to that apparent anomaly.

[Thomas coupling]

Well chopjock another sterling job - reeling those innocent ones in....again tut tut.:D
Helitester, S76 do this because they have to break earth orbit @ 11k/mts/sec.:eek: Simples.

Next Q?

[ShyTorque]

Do you know why they would recommend climbing out at VTOSS instead? Does it give a better ROC when you take the acceleration into account? I would assume that this would only be valid up to a certain distance..

Yes, it's for obstacle clearance, rather than obtaining best rate of climb. For example, the profile for the type I fly requires the aircraft to be flown at Vtoss (30 kts) up to 200' above the takeoff surface, then an acceleration to Vy up to 1,000'

[Sir Niall Dementia]

Helitester;

Its' actually quite a smooth upward acceleration, the surprise comes on the reject, where in the words of the RFM you should "go light in your seat" Training for that profile is now done in the sim with occasional demos with both engines running in the aircraft. The problem is the propensity for pilots to hit the tail in the touchdown (RTO managed that a couple of times I believe) Certainly the S76 vertical, which is a true vertical with no rearward part is the most aggresive PC1 take-off I have ever flown (and I do it most days), but the power application should be smooth, yank it in and there are good opportunities for an over torque. Every other PC1 takeprofile I have ever tried is a very gentle and controlled experience,

SND

[Chucklehead]

On the subject of that S-76 takeoff, I'd like to poll the crowd on another "max performance" takeoff issue. I've met some proponents of a rather rapid power pull, vs a smoother, continuous pull into takeoff power. The argument being that the rapid pull can give you a higher vertical velocity vector and get you into a safe regime of flight faster.

I prefer the smoother pull because, in my experience anyway, the rapid pull tends to lead to a more unstable takeoff in which you lose a significant amount of what you gain, with a greater tendency to overtorque (esp due to tail rotor inputs). Any preferences, and arguments for one or the other that I maybe haven't considered?

Thanks again everyone! Interesting stuff all around.

[[email protected]]

SND - I am reliably informed that helitester is something of a subject matter expert when it comes to the S76 so perhaps he can tell us why its profile is so different to other aircraft.

Chucklehead - I'm with you on the smooth application of power. I know that some parts of the American military used to teach the 'champagne cork' style vertical but if you are maintaining a minimum of HOGE plus 5% thrust margin performance then you probably don't need to go for that technique for all the reasons so far discussed.

The only time I might use a quick pull to max power from a low hover is to get over lowish obstacles when I am really pushed for power (military scenarios really) where that sudden acceleration upwards can make the difference between clearing and not clearing the obstacles (VIGE transition).

Have you got a lat/long for your LS for google earth?

[Sir Niall Dementia]

Crab;

I wish someone would, I was in the SIM last month, flew one recently with a Skorsky test pilot at Coatesville and no-one I've met, or flown with so far can give me an explanation of why the profile is as it is, certainly it is unique in my experience of PC1 and I've been flying the beast for a good while, and PC1 twins an awful lot longer.

SND

[Margins]

I wish someone would, I was in the SIM last month, flew one recently with a Skorsky test pilot at Coatesville and no-one I've met, or flown with so far can give me an explanation of why the profile is as it is, certainly it is unique in my experience of PC1 and I've been flying the beast for a good while, and PC1 twins an awful lot longer

Lack of performance with an underpowred helicopter

[Sir Niall Dementia]

Margins;

I currently fly the C++ and that isn't underpowered, and I've flown the D which is way more powerful but has the same profiles.

SND

[HeliTester]

Crab,

The merits of dynamic vs. benign helipad vertical takeoff procedures have been debated for decades. The Category A vertical procedure WAT curve is based primarily on the ability of the helicopter to transition from AEO vertical climb to OEI forward flight. The dynamic procedure produces optimal performance with respect to payload and/or ground clearance during OEI continued takeoff, but causes the helicopter to climb (balloon) higher (especially at light weight) following engine failure thereby increasing workload during the vertical rejected takeoff maneuver. The same arguments for and against the dynamic procedure have been made with respect to helideck vertical takeoff procedures. The dynamic procedure produces better payload and reduced dropdown with more generous deck-edge clearances during OEI continued takeoff, but produces higher balloon heights for the rejected takeoff. Bottom line, the dynamic procedure yields better payload performance and can be used as long as the rejected takeoff issues don’t become limiting.

HT

[[email protected]]

Thanks helitester - that all makes sense, I presume since most PC1 profiles are gentle, it is the rejected landing capability that is the main concern.

[Sir Niall Dementia]

Helitester;

Thanks for that. It does make sense, but it does seem to add quite a lot to the workload during the reject, however the transition from AEO take-off to OEI climb out is surprisingly smooth and simple.

SND

[Torquetalk]

...and then there are colleagues who are are convinvinced that TDP is the moment pitch is pulled. Off we go like a rocket, the landing site dispappears and then the token "TDP" before rotating. Chances of a successful reject: zero.


The explanation unsually involves "reduced exposure" in an aircraft with enough performance to mean there should be none at any point in a correctly flown profile during landing or take off.


You can lead a horse to water, but you can't make it think.

[NickLappos]

I think this thread has disappeared into paranoid la-la land, and I smell some "manufacturer A is awful, B is so much better" creeping in. In this regard, the issue is physics, not brand labels. Some facts that I think every manufacturer's test pilots would endorse:


1) All approved procedure actually work, as tested by the national regulatory agency (FAA or EASA). If you don't think so, then I ask "Where does your paranoia end? Transmissions? Tire pressure?"
2) Having flown the development and certification of literally two dozen different procedures, I can attest that some vertical climb rate has a measurable effect of payload, to the tune of about 1 passenger, over a slow rise. The vertical inertia is of benefit popping over the TDP, where the most critical factor is the tail cone clearing the deck edge, or the 35 foot dip at the lowest point. That being said, the flyability of the procedure is the main point, so the observations that torque maintenance while climbing up is a big deal are correct. The most successful machines at the fast vertical portion are those where you don't have to look at the torque, just pull against a limiter that tends the power for you. That being said, passenger comfort and acceptance are important. I know of one noble VVIP who stopped at the forward window and asked his pilot "Do you have to do that F%#k-All over the top nonsense again today?"
2) Going straight up, or going slightly backwards are both roughly the same, going slightly backwards has the virtue of keeping the reject area in sight, it has the weakness of needing clear space behind you. There is no magic to it as opposed to going straight up.
3) The key to performance in vertical procedures is always and specifically the power remaining while OEI as compared to the power needed to HOGE at the procedure weight. There is some positive effect from rotor inertia, but it only affects the first few seconds, so its influence is usually only at the very bottom of the procedure.
4) Going vertical costs a lot in lost performance. Helos that are very good at vertical procedures throw away payload that could have been carried, a great 14,000 lb helo that can hover OGE on one engine is actually a good 19,000 lb helo that left 5,000 lbs of payload sitting on the ground.
5) Big OEI power ratios also mean a big gas bill at longer ranges. An engine that is loafing because it has an equally powerful twin sitting next door (both cruising at about 50% of max power) chews up about 20% more fuel for each mile, so that the payload at range for a super-vertical helo is actually less than a less capable vertical machine. In fact, in general single engine helos burn 10% less fuel than marginal twins, and 30% less fuel than powerful twins. Three engine helos burn 30 to 40% more fuel than singles, BTW.
6) The constant demand for superb OEI capability robs safety. The weight in engines, fuel and lost payload spent making you immune to engine failure in the 10 seconds of takeoff rob you of a hundred more important safety features that we leave off to save their weight. The issue is not engine safety, it is overall safety, which is not helped one bit by OEI immunity. Any OEI power above PC2 with calculated exposure is wasted, and could have gotten you improved safety.

[Margins]

Any OEI power above PC2 with calculated exposure is wasted, and could have gotten you improved safetyYou should start a campaign to advise arline passengers that a well defined exposure during takeoffs and landings can produce much lighter airplanes with a lot less thrust, therefore less costly, that would save a lot of money for airlines but they (as passengers) need to accept the associated risks.

I really do not understand why in the helicopter world we should not try to achieve the safety level of the airlines, and I mean ALL. Safety does not come free and requires additional costs in all fields.

Engine failures are remote but happen and when they happen they cause fatalities.

[ShyTorque]

Safety at departure and landing would be improved if helicopters were only ever operated from airports, negating the need for vertical profiles. But that isn't what helicopter owners/operators actually want.

[helmet fire]

Comparing airlines to helicopters..... not again.

If you want higher safety levels in helicopters, then let's stop buggering around with engine failure and tackle what is really killing us.

PC1 and the associated system may well suit offshore operations and they are a logical, very well thought out risk reduction methodology against the risk of engine failure. JimL has amazed me with his work in this area. But I feel they are a complication to onshore ops and are ensuring our time, energy, and dollars are diverted onto a minor threat and away from our major threats. I am not saying that there is a zero accident rate from engine failures, I am saying that we are at Mrs Footes Trolley.

This philosophically based dilemma puts you at the track change switch of a trolley/train line. You can see five people are tied to the rails on the path of the trolley, but you can divert the trolley onto a siding before it gets to the 5 people. Tied to the siding rails however, is one person. So, do you pull the lever and kill the one to save the five? What if the one was your mother, or a child? Etc, etc.

We are there at the lever. The trolley can either run over lots of people on the CFIT line or hardly anyone on the engine failure line. It is simply a matter of collective choice as which one we put our time and effort and dollars into.

I also suspect that the lever choice may well be different based on what sector of the industry you are in. I get that offshore have come to a contrary conclusion than I have, and I do not for a minute disrespect that choice given my lack of offshore exposure. I know that the limits of my experience also formulate the limits of my outlook, but from an onshore and EMS perspective the balance needs serious debate.

Our industry passion with engine failures has absolutely diverted focus from the major threats of my onshore/EMS sector (not the only threats - but the major ones). I get that there is a consequence of diverting the trolley.... I am not saying that no harm will come of engine failures, but put against the harm we continue to permit by a lack of focus???

I am with Nick 100%.

[Gomer Pylot]

Few people have died because of a single engine failure in a twin, and most of those died because one of the pilots pulled off the good engine. Happened in China in an S76. But given reasonably proficient pilots, people don't die from an engine failure, and seldom injured. A few more in singles, of course, but even then an engine failure should be survivable. I've been a pilot since 1968, and have yet to experience an engine failure. I worry most about what is the most likely thing to happen and hurt me, and engine failure is way down the list. I'm not thrilled by vertical takeoffs in the middle of the night from a highway or field in a single, but I do them, because the more likely killer is hitting wires that I can't see. I mitigate the most likely catastrophes in the order I think they are likely to occur, and engine failure isn't in the top ten.

[krypton_john]

Great post thanks, NickLappos. Good to see there's still a place for plain common sense these days.

[oleary]

"I think this thread has disappeared into paranoid la-la land, ... . Some facts that I think every manufacturer's test pilots would endorse:", says Nick.

Gee whiz, a man who actually knows what he is talking about - with the added virtue of country boy common sense.

People obsess way too much about engine failures, in my view. But I've only got ~22K (much of it on IFR twins) so what the hell would I know?

[paco]

Well, it's obvious really - two engines didn't help the Cougar guys in the S-92! I've always maintained that a twin is only "safer" when one engine fails. Well said, Nick.

Phil

[[email protected]]

6) The constant demand for superb OEI capability robs safety. The weight in engines, fuel and lost payload spent making you immune to engine failure in the 10 seconds of takeoff rob you of a hundred more important safety features that we leave off to save their weight. The issue is not engine safety, it is overall safety, which is not helped one bit by OEI immunity. Any OEI power above PC2 with calculated exposure is wasted, and could have gotten you improved safety. Not if you spend a lot of your time in an OGE hover!

[ShyTorque]

Crab, that's because you were operating a hovering machine that flies, rather than a flying machine that hovers..... :E

[Margins]

Operations with exposure in the Part 29 world belong to last century pilots that fly last century helicopters.
This century will see underpowered helicopters progressively disappearing with more and more powerful machines taking place. It's not just a possible OEI situation that will be definitely improved but, more importantly, the AEO power margins and aircraft controllability in low speed envelope will improve significantly allowing low speed operations to be conducted in a much safer way.
Anyway, all this combined with all the new technology that will be implemented in the avionics still need a proper education, therefore training is more and more the key factor for advancing in safety.

[Devil 49]

The argument that increased exposure in flying a profile that allows a return to the departure pad OEI isn't logically coherent with single engine best practice as commonly followed. A careful single engine pilot plans a track to keep a forced landing area available when possible. That requires more exposure, increases wear and tear on the air frame for a generally less predictable result.

I wish similar data was available in singles.

[Thomas coupling]

What about the guy who spends his entire life flying low level, in the weeds, dodging obstacles, hovering over hostile terrain close to solid (moving)objects and never hit anything after 30yrs? And in that same time frame experienced 3 engine failures. How do you think they view the risk of donk's stopping when they review their risk factors?
I guess - looking at it from a regulatory perspective - the authorities can only do so much towards risk assessing the human being who drives helicopters - after that it is all about pot luck and whether he got out of bed the right side on the morning of his CFIT. No amount of gadgetry will ALARP this guy.
However, if it is an object - like an engine - you can risk assess it 100% and hence engine failures, though they are rare (for some) - can be catered for to remove even the slightest risk during take-off and landing in particular. Hence the performance profiles designed to protect life in public transport - no?

[AnFI]

However, if it is an object - like an engine - you can risk assess it 100% and hence engine failures, though they are rare (for some) - can be catered for to remove even the slightest risk during take-off and landing in particular. Hence the performance profiles designed to protect life in public transport - no?

That's the problem right there - excessive irrational concentration on eliminating obscure and irrelevant risk levels for one particular cause for tiny time slices without the balance of looking at how that payload spent on excessive engines could be spent on other saftey yielding measures instead.

Irrational at the cost of helicopter effectiveness and performance.

The twin engined arguements are corrupt and wrong 1x10^-10 is a bogus theoretical figure damaging helicopter's future.

The attempt to increase the weight of helicopter per payload is a strategy designed to rip off government procurement processes and oil companies - especially in the military where the helicopter effectiveness was severely crippled by carrying spare engines around in Afgan rather than food ammunition etc. ridiculous (massive cost - poor effectiveness)

Agree with Nick.

[[email protected]]

The attempt to increase the weight of helicopter per payload is a strategy designed to rip off government procurement processes and oil companies - especially in the military where the helicopter effectiveness was severely crippled by carrying spare engines around in Afgan rather than food ammunition etc. ridiculous (massive cost - poor effectiveness)

So it should all have been done in single-engine aircraft in Afghan then????? Just need to find one big and powerful enough to carry what a Chinook does - especially at the high DAs of Afghanistan......... what a load of boll*cks.

Oh and by the way, military aircraft need more redundancy since they get shot at a lot so having a spare engine to get you home rather than crashing in enemy territory is quite a good idea.

if military effectiveness was crippled (which I don't think it was) then lack of performance by old aircraft at high density altitudes and OATs was the limiting factor (Sea King, Lynx and to some extent Merlin).

The military requirement is completely irrelevant to the PC1/2 performance considerations on this thread.

[Frying Pan]

Single v twin...again? Don't make it military either, from records Hurricanes and Spitfires had only the one donk - and yes I realise they're not helicopters. Single engine Hueys in Vietnam? The Afghan war highlighted lots of issues, especially DA. Even an old RN colleague had an engine failure in a Lynx resulting in n emergency landing in Greece, not enough power to get into a hover back to the ship....at sea level!

Twin engines really should be for niche markets, the money saved by the odds of an engine failure make it more than worth it. We all seem to be happy for one engine during training,

[Chucklehead]

"The weight in engines, fuel and lost payload spent making you immune to engine failure in the 10 seconds of takeoff rob you of a hundred more important safety features that we leave off to save their weight."

Forgive my ignorance, but what safety features are you referring to that get left out to save weight? Redundant systems? I fly an old aircraft so I guess I'm not up to date on what these safety features would entail. Thanks!

[[email protected]]

We all seem to be happy for one engine during training, perhaps because the risk is 2 peoples lives and that is deemed acceptable since few training sorties (on a basic syllabus) consist of hovering or low speed flight inside the avoid curve (ie operating in and around an OGE hover.)

Once you start operating with pax, the risk to life (in terms of numbers) increases and the size and power of that single engine has to increase to cope with the extra payload. Once you start moving pax and cargo you need even more power espeically at high DA.

At some point you come to the conclusion that 2 quite powerful engines are possibly better than one extra powerful one even though the mathematical risk of a single engine failure is very low - it is one of the few single point failures you can do something about relatively easily unlike double/no tail rotors or twin main rotors (clearly not impossible but they bring an increase in engineering complexity).

Anyone going to convince a regulator to go back to single engine ops for all helos??? Would you cross the Atlantic in a single engine A380? the probability of an engine failure is so theoretically low that by the arguments presented on this thread, it should be common place.

[AnFI]

Chuklehead : The thing to understand is that redundancy is not all it's cracked up to be. Better to have one system unlikely to fail than two dodgy ones one to catch the frequent failure of the other... don't think about having a spare tailrotor think instead of making one that can withstand the fabled test chicken. SIMPLEX theory is quite good. What do you want in your car a strong reliable braking system or a marginal one with a spare for when the main one doesn't work?

Instead of wasting payload on carrying a spare engine/gearbox and it's EXTRA fuel , spend it on critical components.

Engines are simple to duplicate and it is obvious to the layman that it sounds like a good idea... but what does the layman know? They think a helicopter falls out of the sky on engine failure, they also don't appreciate that engines are not allways a good thing... they explode catch fire and cause other problems .. so doubling the exposure to that is not such a great idea either.

This being shot at nonsense is just that - in Vietnam very few engines were hit despite taking fire often. The performance loss from carrying 2 engines is worse than the payload and performance loss, as Crab quite rightly points out in the Lynx, Sea king and to some extent the THREE ENGINED Merlin. (rubbish reliability/serviceability ratio etc chronically ineffective in Bang/Buck)

Sure good thing the Chinook was there (needing both engines)

When you need both engines to perform in a twin at altitude you are twice as exposed to engine failure than in a single - as well as carrying less life-saving supplies etc

It is not correct to say that higher DA favours 2 engines quite the opposite ref: AS350B3 compare to the almost useless AS355. Engine failure is not the problem in the B3 (and neither was it in the Gazelle - which would have done a better job bang per buck in Afgan surely?)

Crab: as for the single engined 380 you do have a good point and that is a matter of scale; the bigger the aircraft gets and the smaller the proportion of payload that is spent on carrying the spare engines around, the more it makes sense to carry 'redundant' engines around with you, like the payload rational for carrying a defribulator when you have 600 pax, small proportion of weight, high chance of it being useful. In the 380 also it's engine off landing characteristics are not as good as a helicopter. A 160kt arrival in a 300 ton aircraft is not going to be pretty. Landing gently at no airspeed (even at sea) is not such a bad thing.

[[email protected]]

Better to have one system unlikely to fail than two dodgy ones one to catch the frequent failure of the other.. but that is exactly what we don't have - we have 2 excellent and reliable engines in most modern twins.

The difference comes when an engine does fail in a single compared to a twin - if you are over a nice landing area with plenty of height to set up your EOL then no problem in a single BUT when you are at high AuM at low speed, low level or over inhospitable terrain/sea then a failure in a twin leaves you able to get home, a failure in a single leaves you dead....it's that simple.

In the car analogy, due you want single or dual circuit brakes, can you accept the weight penalty for ABS, traction and stability control, airbags etc etc none of which are essential for driving but all make it safer if something bad happens.

This being shot at nonsense is just that - in Vietnam very few engines were hit despite taking fire often. and you know this because you were there????? I reckon for the number of helos lost, quite a few will have taken rounds to all parts, including the engine.

[NickLappos]

Nice retorts, guys! Crab, you are quite right, my plea was to assess safety in the actual operation, and add the next thing that can measurably increase safety. If you spend your job in OGE hover or at low altitude and low speed, OEI safety is clearly an important safety option.

Where do we need more safety attention? Helicopter instrument procedures and kits, Night equipage, CFIT solutions, DVE solutions, expert copilot systems that tell you what actually happened in an emergency, etc, etc.

BTW, Crab, engines being shot seemed to be pretty rare in Vietnam. Once we read of a Marine pilot getting a DFC, and the citation read something about him getting an engine failure and flying for 30 minutes over enemy territory on one engine. We tore out the article and took it to our Awards and Decorations officer, asking for our DFCs, since all our aircraft were single engine and we had about 1,000 hours each "over enemy territory"! He threw us out on our bums.

[Sir Niall Dementia]

Go take a peak at CatPolH 305 (EASA regulation) the safety systems that demands as well as risk assessments and OEM reports on failure data will show you the future, and trust me its' no better than the past, but the legislature have covered their arses magnificently.

I spend a lot of time flying rotary at night/IFR (couple of hundred hours a year night and IFR, with 10 500 hour rotary and another 5 000 fixed wing total time) and the spare engine is welcome, as are the auto-pilots, nav systems, coffee cup holders and illuminated approach plate holders, HUMS is great for telling me when bits are as shagged as I am, I just fail to understand how last year EGLW and LFPI were fine for my aircraft and this year I've got to do a f***ing great paper work exercise to fly the same aircraft to the same LZ's I did last year. All that has done is take my time and effort and improved nothing in safety.

SND

[AnFI]

CRAB: In the car analogy, due you want single or dual circuit brakes, can you accept the weight penalty for ABS, traction and stability control, airbags etc etc none of which are essential for driving but all make it safer if something bad happens.

Yup I think the answer there is you want a reliable single system, and you can use the weight saving (weight not so critical in a car) to run the ABS, traction control, airbags etc etc

There's a much better safety yeild available in helicopters from other things than duplication the relatively complex and low yeilding engine at such a high cost to payload effectiveness, especially daft to carry enough spare engine to mitigate engine failure risk during the 8 second window of transition, especially considering the risk of prolonging, in an upwards and backwards takeoff, the exposure to tailrotors and other risks (about 30 seconds of that exposure instead)

Anyhow some twin maths can just work, if the helicopter is big and the risk of landing is most likely to be fatal, like over jungle.

[[email protected]]

Yup I think the answer there is you want a reliable single system, and you can use the weight saving (weight not so critical in a car) to run the ABS, traction control, airbags etc etc utter genius, I can't believe no-one has thought of that before - you should get yourself into the motor industry as soon as possible ANFI


Weight not so critical in a car????? do you know less about cars than you do about helos?

[AnFI]

Crab I am just never rude to you at all, but you are sarcastic, rude and unclear.

are you trying to suggest that weight is more critical in a car than a helicopter? (seems odd, if that is what you are saying (unclear), you'll have to explain why). You think you know more than i do about fundamental car 'PoF' too? (showdown? £10k says you don't, if I win proceeds to next pprune bash!)

and incidentally the only brake failure accident I know of happened in a car with a dual (redundant) brake system design (Bentley).

Ref VRS Crab: "Don't worry about VRS - you won't get near the RoD required (probably somewhere around 12 - 1500'/min for your aircraft)."
That I guess originates from the recent opinion that VRS won't occur untill half the downwash speed? I don't think that is true nor helpful and as such would constitute dangerous advice. I have found that you can neatly slip into VRS at about 1/8th to 1/4 of the downwash speed.

tread drift re cars sorry - I'll probably get in trouble again but I am only answering crab's rather rude thread drifting point, crab won't get in trouble for this since he seems to be 'teachers pet'. I'm already in trouble for suggesting that the multi engine maths gets better for more engines (3,4,5). Although I am not allowed to say that IMO it's not worth it since the reliability goes down, KISS is a dirty word around here.

PS according to Nick L, Crab also seems to be quite wrong about the risk of engines being shot out, the Huey experience in Veitnam being an excellent example of utility of payload vs redundancy. thank you Nick.

[[email protected]]

AnFI - If I am rude to you it is because you insist on trying to hijack threads with your own pet hobby horse ie singles are better than twins.

If weight is not important in cars (and I didn't say it was more important than in helos) why do car manufacturers, especially of performance cars, spend so much R and D reducing the weight of their vehicles? Oh yes...... it is to improve performance which is the whole subject of this thread!

I use Nick L's VRS figures since they are derived from testing as opposed to yours which are just your opinion and ignore any real evidence to the contrary.

Your childish bet is frankly typical of your posts - you don't like being criticised and react in playground fashion when you are.

Yes, I was wrong about the number of engines shot out in Vietnam - it still doesn't validate any of your hobby horse arguments though.

[krypton_john]

I think that's a bit unfair Crab - you mocked: "Weight not so critical in a car?" ... which is quite a silly thing to say. If course weight is not so critical in a car [as in a helicopter]. An overweight car can still be quite usefully and safely driven whereas an overweight helicopter either cannot get off the ground or cannot get safely back onto the ground!

But what is worse, is you went on to rewrite history:

You say "If weight is not important in cars" but that's not what was said and quite different to what you said which is "not so critical".

and I don't believe "improve performance" is the subject of the thread; it is "improve safety".

and "and I didn't say it was more important than in helos" - no, but you implied it was at least as critical.

[[email protected]]

Krypton John are you trying to suggest that weight is more critical in a car than a helicopter? is what AnFI wrote in reply to what I said which was Weight not so critical in a car????? it is your interpretation of my words which were meant to highlight that weight is indeed important in cars - I didn't say it was more critical which is what AnFI seems to believe I meant.

An overweight car can still be quite usefully and safely driven

I would suggest there are very many automotive safety experts who would disagree with that statement - I do know what you meant but that is what happens when you take every word literally and ignore context.

The thread was about helipad profiles which are all about performance which leads to increased safety.

You are encouraging the troll that is AnFI who only has one tune about singles being better than twins.

[AnFI]

Thank you Krypton John.

Yes Crab I am afraid it is just your misunderstanding which led to your frustration and rudeness and additionally I think if you insult my knowledge of cars as well as helicopters then I have every right to demand that you justify that rudeness which you refuse to do [insulting me further instead again], so you should retract that too please.

the only person who has been wrong here is you as you have admitted yourself - what you are not capable of doing is apologising for being so damn rude, being rude again to me in response to KJ, it's outrageous !

The way you chose to address the serious points I make through insult is demeaning to you, and I think you come from a better place than that (surely?)

The relationship of weight/power/payload is key [to safety[in a helicopter]]. As long as folk like yourself will not seriously engage in discussing these issues in a serious manner, relying on some bizzare gut feel, and DISHONEST MATHS (like the squaring of 1x10^-5) then longer we'll be condemned to the dark ages.

[[email protected]]

See what I mean KJ?

[AnFI]

As I said:

"The relationship of weight/power/payload is key [to safety[in a helicopter]].

As long as folk like yourself will not seriously engage in discussing these issues in a serious manner ...... we'll be condemned to the dark ages."

KJ?

[[email protected]]

Perhaps you should fly in situations you are not familiar with before you bang on about maths and single engine superiority.

Try 250 nm out into the North or South Atlantic (I've done both) in the dark and see how comfortable your maths makes you feel in a single instead of a twin.

Maybe sit in a hover against a mountainside in the dark and rain with 240' of winch cable and 2 pink bodies hung underneath you and see how comfortable you and your crew are with mathematical probabilities of engine failures in a single.

Perhaps IMC with a 200' cloudbase so you can get in on ILS or PAR with several important pax in the back - I'm sure your assertion that singles are at least as safe as twins will give great comfort.

Or North Sea with 15 bears in the back in shocking weather and a high sea state that would make ditching in a single (or anything else for that matter) very difficult.

"The relationship of weight/power/payload is key [to safety[in a helicopter]]. so where are your 3000 shp single gas turbines?

[ShyTorque]

This discussion is sounding like one of those pointless arguments in a pub about whose footaball team is best.

Irrespective of the reliability of modern turbine engines, the point about twin engined aircraft is that they have other duplicated systems, such as those which are required for flight in IFR e.g. generators, SAS/autopilot systems, hydraulics etc.

This rules out singles where continued flight is a safety and legal requirement. There is certainly no compelling evidence that a single engine is more reliable and therefore safer than two.

Having flown both singles and twins, I've always said that I'd rather have a well equipped, powerful single than an underpowered twin, some of which I've also flown.

But the latter came from "the dark ages" and modern twins do not generally fit into that category.

I'd say that both singles and twins each have their own "niche" and both will always exist. It's totally pointless trying to argue that singles should be exclusively manufactured and used because of a personal preference.

[[email protected]]

Completely agree Shy but you won't stop him doing it!

[AnFI]

Crab
Your assumption that I haven't had my share of dark and stormy nights in inhospitable places is a little harsh. Been more than 500nm from land just for starters.

Yes Shy is right to some extent and Crab's examples are the emotional ones that make people kneejerk to believing that the twin is obvious. BUT the point I am trying to make is deeper than that. Extending to the 'lazy' redundancy concept. The most unreliable part of some helicopters are the duplicated parts and I would prefer to spend the weight/cost/complexity on making a very reliable SIMPLEX system with minimal to zero need for backup.

Safety systems in general really ought to be evaluated with the cost to payload etc taken into account. Otherwise you get the daft situation where 3 flights need to be made in an 'engine failure immune' helicopter against 1 flight in an engine 'exposed' helicopter. [not a complete arguement]. AND duplication can be the answer sometimes, just nothing like as often as people's emotion leads them to believe.

3000shp? do you need 3000hp? 3000x 10 lbs/hp = 30000lbs that's heavy.
How many hp was the Huey (did pretty well, payload and performance wise)

As with the chinook if you need both engines to obtain enough hp then it's not the same thing as redundancy.

[[email protected]]

As with the chinook if you need both engines to obtain enough hp then it's not the same thing as redundancy. and that means if you need the payload then you need the power - that leads into your Otherwise you get the daft situation where 3 flights need to be made in an 'engine failure immune' helicopter against 1 flight in an engine 'exposed' helicopter. you have to make 3 flights to get the job done in a single when 1 flight in a twin would do it. What about exposure then???

Pie = sky...

Care to elaborate on your 500nm from land in a helicopter? Love to know what has that range.

3000shp? do you need 3000hp? 3000x 10 lbs/hp = 30000lbs that's heavy the Sea King has 2 1400shp engines for a MAUM of 21400 lbs and they are old technology compared to something like the S92 which I think is 26,500 lbs AUM.

Any one got any Skycrane figures?

[whoknows idont]

This discussion is sounding like one of those pointless arguments in a pub about whose footaball team is best.

So true... This used to be such a good thread one or two pages ago. Now round and round we go. :rolleyes:

[212man]

Care to elaborate on your 500nm from land in a helicopter? Love to know what has that range

A tuna boat?

[Geoffersincornwall]

We must all remember that whatever regulatory principles are handed down to us chopper pukes it will be the philosophies that apply in the fixed wing world that will dominate.

The old joke about the difficult journey - you know, the one that begins "well if I were you I wouldn't have started from here......"

Gentlemen, we are where we are, sad though that may be.

G.:{