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Restricted takeoffs, VRS, and ground effect

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Restricted takeoffs, VRS, and ground effect

Old 30th Jul 2015, 08:52
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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?
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Old 30th Jul 2015, 10:27
  #42 (permalink)  
 
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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
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Old 30th Jul 2015, 12:50
  #43 (permalink)  
 
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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
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Old 30th Jul 2015, 15:59
  #44 (permalink)  
 
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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
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Old 30th Jul 2015, 16:18
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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 donít become limiting.

HT
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Old 30th Jul 2015, 17:56
  #46 (permalink)  
 
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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.
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Old 31st Jul 2015, 08:29
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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
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Old 31st Jul 2015, 08:31
  #48 (permalink)  
 
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...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.
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Old 31st Jul 2015, 12:59
  #49 (permalink)  
 
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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.
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Old 31st Jul 2015, 15:23
  #50 (permalink)  
 
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Any OEI power above PC2 with calculated exposure is wasted, and could have gotten you improved safety
You 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.
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Old 31st Jul 2015, 18:18
  #51 (permalink)  

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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.
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Old 31st Jul 2015, 22:42
  #52 (permalink)  
 
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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%.
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Old 31st Jul 2015, 22:59
  #53 (permalink)  
 
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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.
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Old 1st Aug 2015, 00:45
  #54 (permalink)  
 
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Great post thanks, NickLappos. Good to see there's still a place for plain common sense these days.
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Old 2nd Aug 2015, 00:28
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Thank you, Nick

"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?
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Old 2nd Aug 2015, 05:36
  #56 (permalink)  
 
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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
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Old 2nd Aug 2015, 06:36
  #57 (permalink)  
 
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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!
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Old 2nd Aug 2015, 08:22
  #58 (permalink)  

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Crab, that's because you were operating a hovering machine that flies, rather than a flying machine that hovers.....
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Old 2nd Aug 2015, 13:26
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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.
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Old 3rd Aug 2015, 01:09
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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.

Last edited by Devil 49; 3rd Aug 2015 at 01:11. Reason: Grammar...
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