T/O Downwind -v- power available ?
 

Hello Rotorheads,

As I have progressed up into the realms of Turbine power, I have been shown, and then been allowed to execute a downwind and/or crosswind T/O to see what this entails and feels like, whilst I am very aware of the problems associated with this type of T/O, is there any rule of rough calculation which equates wind speed to power available that would allow for this sort of T/O, I hasten to add I always T/O into wind but one of the FI's has shown me downwind and crosswind T/O's in the B206, and said with the power increase over piston engines you are safe to consider this , can any of you confirm this?

The wind direction really has little effect on the rotor performance in a hover, any wind is good wind if you don't take off. The rotor really doesn't know which direction the wind comes from, and tail rotor power increase is nearly always less than the performance gain from the wind speed.

In a downwind takeoff, three factors complicate the matter (let's use 15 knot winds as an example):
1) The aircraft must accelerate from minus 15 knots velocity through zero velocity. At the zero velocity point (where the aircraft is scooting along at 15 knots groundspeed) the power will be at the maximum for the procedure. (If you were foolish enough to have been at max power when in the steady downwind hover, at this point you will settle and ground contact is a real possibility.) As you then continue to accelerate, the power will decrease (or the climb will begin) and you are off.

2) The takeoff distance (when compared to still air) will be the sum of that needed to get to zero plus that needed for a normal take off. With a 5 degree nose down as "normal" you will take you about 110 feet just to get to zero knots airspeed. Additionally, the acceleration will seem very flat relative to the ground and obstructions, since you are always 15 knots faster, so your climb angle will be considerably shallower than a still air takeoff.

3) If you have a power failure anywhere along the takeoff, you will not be able to stop the aircraft prior to touchdown, because that would require that you decelerate to zero, then continue decelerating to a rearward 15 knots. Count on needing to run it on at about the wind speed.

That was all for a dead downwind takeoff. For a cross wind, the issue is much cleaner. Let's assume the same 15 knot wind.
Since the rotor doesn't know where the wind is coming from, the performance is better from the start, it takes much less power to hover, so your acceleration for takeoff is greater, if you chose to use the extra power. The distance to takeoff is less than that of a zero wind takeoff, so you are ahead there, too. The only two complications are:
1) You gave up the chance to shorten your takeoff by about that 110 feet if you had taken the headwind.

2) If you have a power failure, you will not have the advantage of that extra 15 knots of airspeed on touchdown, plus you must compensate for the cross wind on touchdown, thus complicating the touchdown a bit.

All in all, the rules might be:
1) Take a headwind component as often as possible, always if it allows good takeoff paths and barrier clearance.

2) If dictated by the scenario, take a cross wind with the assurance that it is better than still air.

3) As a last resort, take the down wind if you have good power margin above the "steady" hover and if the takeoff path allows extra distance for barrier clearance and allows a running touchdown if the engine quits.


I have been trying to boil down a rule of thumb, but its a complex situation. If you have a 15 knot wind, and a helo that climbs at 500 FPM at 45 knots:
At 20 knots, the upwind allows a 40% climb gradient (40 up at 100 across), still air allows 7% and downwind allows 4%. In other words, for a slow speed climbout, you have 10 times the climbout gradient into the wind as down wind! Rule of thumb might be, if there are barriers, don't go downwind.
:cool:

[ 03 September 2001: Message edited by: Nick Lappos ]

Vfr,

Orthodox UK mil teaching discounts the windspeed, as Nick Lappos mentioned - all downwind departures are treated the same. A hover check downwind is carried out and the power noted, then the max power available is confirmed. If the difference between the 2 is 20% or greater, then the power margin is considered adequate for a downwind transition. However, all the comments appended by NL are agreed - we only carry out downwind transitions if there are over-riding (that's not flying across Yorks, by the way...) operational factors or considerations.

Great bunch of info there,

I'd add that while turbines do have more power then pistons they actually use that power in working situations. That power margin difference you mentioned is nice for a lightly loaded ship but not for one doing work near mgw.

An 11,ooo pound ship slinging a 9,000 pound load has lots of power but most of it is already in use. You may only have a small percentage of power left to stop you or direct your flight path.

In this case the downwind/ into the wind decision you make will be more critical due to the inertia that you're trying to control.

A rule of thumb for power required I was told a while ago was that a downwind approach/ departure requires 2% additional NG. It may not be exact but it does make you look at the problem prior to becoming involved in it.

NL ,T&B & T,

Thank you for that very interesting break down of my seemingly simple question, I have noted the feeling of what could be described as drifting with power when in the down wind T/O which was and is a very errie feeling, I did notice that height gain was indeed very slow, the cross wind situation was better and the B206 seemed to act very similar as when into wind, but I have taken in what you have all said, and I fully understand the problems that could and would be associated with down wind T/O's, thank you all, I envy your experience, thank you for sharing it>
My Regards

By the way Thud, only a Yorkist or a lad from Lancashire would understand the Over riding bit, I think!!

And a good bit of advice, load up your Jetranger to max gross and then go for a flight, you may not feel it has so much power any more (try to do it before things cool off much more).

This will help you get a feel for when downwind departures are and are not acceptable.

mr Vfr man,

regarding downwind takeoffs in a Robbie, a good rule of thumb is that if you have 2" in hand in the hover from your 5 minute rating then you should be able to do it safely(however if the engine fails in the early climbout, things are looking v.bad)

also I agree with heloteacher about the 206, if you have got 4 heavy punters in it as well as you then you have to be real careful to keep torque below 100% while hover taxying.

if you want a bit of power then try a super puma, they really have got power

stay lucky

Let me establish an argument here to keep things lively -

It takes no more power to take off down wind than it does to hover in still air. That means that the rules of thumb presented above (good ones, I think) are for you to use if you don't know what the capability of your aircraft is, and you have to judge by what you are seeing right now on a windy day.

The power rise due to downwind takeoff is never more than the power increase experienced between a windy day and a still air day.

The transition needed for the private pilot to move to the next stage is to begin to understand the performance of the machine against the charts, so the power needed on a given day is known before the liftoff to a hover. Then the downwind takeoff is a choice, not a chance. :cool:

Um...sorry to butt in but here's my two penny's worth.

Don't.

If you went in Clear Area, you can get out Clear Area by back tracking.
If you went in Helipad, you can get out Helipad.
If you're going to approach to land downwind, ask why.
If you have to take off downwind, ask why.

Even during Police Ops I avoid downwind landings unless it's life or death & even then there has to be no viable alternative.
At worst I'll take a cross wind, but I haven't come across a good reason to take off downwind in my very humble 12 years flying.
It can be done & reasonably safely....but why? The machine prefers being into wind, chances of successful reject, after donk, are much better into wind (not least because the tail hangs lower downwind).
Into wind is the safest option (I don't think anyone can argue with that? Except Chinook drivers?)
Cheers!

A general rule would be to calculate your Out of Ground Effect(OGE)+5% hover performance calculation or equivalent for your machine, and ensure you have that performance. Due to your movement across the ground you will not have In Ground Effect(IGE) performance i.e. ground effect benefits, when you are at zero airspeed therefore requiring OGE performance.

OGE +5% should allow you to hover in free air and overcome light turbulence without exceeding the power limits. Light turbulence is defined as updraughts and downdraughts not exceeding 2-300' per minute (met office). Therfore you should be able to climb vertically in still air in the hover and acheive a rate of climb of 300' per minute. Alternately you could increase your aircraft weight by 5% and maintain a hover but drift up and down with the turbulence.

If you haven't calculated OGE +5% then for SA342 a rule of thumb is 10% torque in hand before attempting the departure. Regards!

Nick,

I would agree that the transitioning pilot needs to know the charted performance parameters inside and out of the aircraft they are flying.

But I think it does require more power for a downwind takeoff.

Let me throw this out for consideration.

On a zero wind, standard day aircraft "A" loads up to a specified weight and sits at a hover.

The aircraft is transitioned to forward flight slowly and maintains a three foot skid height along the way.

Just prior to ETL the aircraft settles a little. We'll call it one foot per second. The rate of acceleration applied by the pilot up to this point (with power) means that the aircraft will take 2 seconds to go from the onset of that settling into ETL and clean air. Only having lost 2 feet, the aircraft can accomplish this maneuver with no additional power applied.

Aircraft "B" is identical in all respects but is doing the takeoff with a ten knot tailwind.

I believe his settling rate would be the same but this aircraft will be in that settling rate for a longer time, lets say 4-5 seconds :eek: as it fights it's way to the clean air just ahead of the disc.

Requiring more power. (to not hit the ground)

Acorn,

The OGE power plus 5% is a very high margin indeed. The difference between OGE and IGE is about 15% and if you add 5% on top of that you lose about half your payload. That is a very conservative rule.

No performance is lost because of the downwind at all. The ground effect does not change because of movement of the air or the ground, that is an ancient piece of pilot lore. Think of the big bombers, with 1 of 4 engines running, limping back across the channel, 1/2 wing span above the waves. They had no trouble gaining ground effect!

For all the ppruners who would like to try, I invite you to make a careful downwind landing and note the power (use manifold pressure or engine turbine temp) needed to complete a careful approach. Compare downwind to that needed for still air, there is no difference. Ground effect is not lost because the aircraft is translating, that effect is nil.

Regarding the safety of downwind takeoff or landing, it is clearly less safe, due to barrier clearance, failure tolerance and ground covered (roofus shows great wisdom, why not back up across the clear area to the rear?)

On the other hand, I have had to do hundreds of downwind landings, and dozens of downwind takeoffs in my career, and knowing how is part of our craft.

Tgrendl,
Your thought experiment is a good one, and clearly illustrates the issue. However, the settling you describe is caused by the aircraft running into the ground vortex created by its main rotor wash. In a steady, no wind hover, the rotorwash spreads outward evenly in all directions, at about 8 to 12 knots on average, as a thin sheet close to the ground. On takeoff, the aircraft moves into this outward spreading air, and it causes the air ahead to roll up and interact with the forward part of the rotor disk. This causes a loss of efficiency, and thus the settling. It also causes the lateral stick shift and the ruffling prior to ETL.

A great paper was prepared by a Boeing team during their development of their YUH-61A UTTAS (the one that lost to the Black Hawk) which defined this effect.


In any case, that interchange between the aircraft and its wake takes place up wind, down wind and even in sideward flight.

In the case you describe, the only difference between the still air aircraft and the up wind or downwind aircraft is the speed at which the ground is moving. All the aerodynamics stays the same.

The power to land downwind is exactly the same as the power to land in still air. The negative point is that you did not gain the power that is inherent in landing up wind, where you never have to make your aircraft slow down below windspeed.

Nick,

Happy labor day to you and to all on the board.

Two quick questions and then the thread. Is it possible to go to your plant and get a tour without causing too much grief for the workers?

And is the RAH66 scheduled sometime to get to ADTA at Rucker as a J serialed aircraft?

The thread,

I believe and can intuitively agree with all you said except the part about rotor wake interaction and groundspeed/airspeed.

It seems like in this example you would be in this region longer because it's taking you longer to accelerate through it. (result of the ten knot tailwind)

The relative airspeed over the disc would be the key here regardless of groundspeed.

Continuing to scrape my knuckles in the dirt when I walk,

Tom

Just to add fuel to the flames.... With a conventional helicopter, it often takes less power to hover downwind than into wind. Blade vortices/downwash impinge on the tail rotor making it less efficient when into wind?

The above remarks about crosswind takeoffs are strictly accurate, but from a practical point of view there can be problems. Some types have very benign handling qualities when crosswind, others can be a real handful (or foot-full!) If operating at high weights, the ensuing pedal 'dancing' as you transition while applying full power, can lead to inadvertant overtorqueing.

Nick, I'm not attacking you, just responding to all your posts at once.

You said, "It takes no more power to take off down wind than it does to hover in still air. "

I don't agree with this. When you take off with a tail wind, you must accelerate your helicopter first to zero airspeed, then beyond. Hovering in still air requires less power than accelerating and climbing from the still air hover.

If you meant to compare power required to take off with a tail wind to the power required to take off from a still air hover, I wouldn't argue. I think if there is a difference it would be small.


You also said, "any wind is good wind if you don't take off."

I always thought that in wind speeds slower than translational lift speed, the power required to hover with any relative wind would be greater than that for still air.


Finally, you said, "...make a careful downwind landing and note the power...needed to complete a careful approach. Compare downwind to that needed for still air, there is no difference."

The power required to approach along the same path, with the same speed gradient will be greater if you have a tailwind.

Practically, you can do the approach with the same power requirement down to zero airspeed by shallowing your approach angle with a tailwind.

What really amazes me in this discussion is the strength of the tail winds that have been mentioned. We have a published limitation of 15 kts for downwind takeoffs and landings. Even without that limitation there would still have to be considerable mitigating circumstance before I'd consider any downwind approach/landing in 15kt or stronger winds.

Matthew.

Nick + tgrendl,

The requirement for the additional power is to ensure you are able to overcome the additional settling described as 1' per second. A rate of climb capability of 2-300' per minute is more than adequate for that purpose. OGE +5% in temperate climates at heights below 3000' i.e UK would rarely limit your AUM performance. Should the temperature or density altitude preclude OGE performance then you would be in the realms of appropriate into wind techniques from the outset.

With regards payload, an SA342 in UK with 340 KGS of fuel would carry 2 pax with about 50 KGS spare. OGE +5% performance during Spring through to Autumn would be achievable to 3-4000' at AUM. The 5% thrust margin equates to being able to increase the aircraft AUM by 95 KGS and still hold a free air hover without being able to compensate for turbulence. Therefore the reduction in AUM would not affect routine UK operations. Assuming the same generic calculations are used across types the same would be so although this I cannot confirm.

As an asside, with regards tail rotor effectivness downwind, assuming the downwash from the main rotors is therefore blown away from the tail rotor, if the tail rotor is optimised to utilise downwash as in the case of the Lynx then the loss of translational lift from downwash would cause an increased power requirement downwind. Regards

[ 04 September 2001: Message edited by: ACORN ]

vfrpilot
Don't be put off by DW transitions, sometimes they are the only option - but always think far enough ahead so you have as many options as possible....
Is it safer to t/o into wind but over a substantial infrangible object - or depart downwind over a clear area?
Personally, I'd always go for the clear area.....with only one engine, one can sometimes lose the big picture!

With all the other good points raised, don't forget the downwind wind limit for B206 - 17kts

Must admit, bit surprized to hear our EMS pilot restrict his 2-eng, dw approaches to "life and death" tasks only! That's not meant as a side swipe, just surprized, that's all.

I have often found that I am able to to do an out of wind approach that has a far better approach angle than a directly into wind one. For example approaching to a particular wharf coming from one direction requires a verticle descent of some 100', where as approaching from over the ocean has an approach angle of almost 0. Even though the sea brezze is almost always behind me it still uses far less power if handled carefully. What I am saying is (as with all aspects of RW flying) flexability is the answer.

One word of caution though!! Approaching with a even moderate down winds with a heavy aircraft may see you not slowing as fast as you expect. Add to this a higher than normal rate of descent and you have the following situation. Hi ROD, Low-Nil forward IAS (Due to the tail wind), High power. You guessed it the result is Vortex Ring (sometimes called power setteling), and at low alt you may be unable to recover before the ground.

Also watch out for flap forward it can surprise you with how much cyclic is required to overcome it, and if you are flying an aircraft with limited Tail Rotor authority or one that is susceptible to LTE (as in the B206) it may start to weather cock and swap ends on you without you being able to do anything at all.

Don't want to make a big deal out of it, but for tgrendl, heedm and acorn your method of thinking about the power needs is earth-centric, so you picture the power needs as somehow "knowing" what the ground speed is. The aircraft is a beast driven by aerodynamic forces, and its power needs are highest at 0 knots. If we did the maneuver in the dark, and simply decelerated from + 50 to -15 knots while holding a constant angle, the power would be seen to be at a maximum at the 0 knot point, and that power would equal the power of the still air approach we discussed. There is no -1 foot per second descent or such. I ask you to try it on a quiet day with a moderate wind and see. I have tested helicopters to rearward speeds up to about 80 knots in Comanche, and 55 knots in the S-75 and Black Hawk. There is no mystery, guys, but it is a place you don't often go, so I understand your questioning.

Regarding a rule of thumb to need +5% over OGE hover power, acorn, you should keep that rule if it works for you, but the cost in payload is large in most climates and conditions, if not in your helo in UK. In 33 years of professional helo flying, I can count on one hand the times I had that much extra power (read it another way, that much too little payload).

Your UK scenario is a good one where you feel that you do not lose payload until 3000 feet or so, but try that at 3000 feet in an equitorial climate and you will find your rule of thumb has cost you all the reason why you are flying to begin with.

Rather than use power as the way out for downwind approaches, I suggest the barrier clearance issues, and forced landing issues are much more the safety drivers.

When a US Army crew is inserting a SOF team in the black of night, they do not calculate the wind, I assure you, they simply fly carefully, and place their aircraft where the mission dictates. Similarly, when a helo minesweeper is tied to a sled and sweeping precise lanes at night, it goes where it has to, and lets the wind do what it will.

I do not advocate downwind operations blithely, but I do believe, like vfrpilot's instructor in the original post, that they are part of our bag of tricks. :)

EESDLI'm surprised that you're surprised! No offence taken.
I must ask though...you state better to take off down wind using a clear area than take off into wind over something nasty. Um....why not back track the clear area & then take off into wind? or use helipad departure?
I'm not a single engine pilot so...is there such a thing as helipad in singles?
I'm no wise man & certainly open to others views. I've been taught down wind techniques, but everyone who has had an input into my training....Navy, North Sea & Police have emphasised (is that spelt right?) Why you shouldn'tdo down wind approaches.
So yes...to reiterate....I will only do a down wind approach if I absolutely have to. &, as I stated, in 12 years I haven't had to; except for training puposes.
Obviously I'm in a minority group...fine...I also believe in each to their own.
But my OPC's every six months do not include down wind approaches & take offs! I'm fairly sure that if it was anticipated I'd need to do down wind approaches, the CAA would have written it into my Base Checks?
Hand on heart I can see very little reason to do one.
That said there are some amazing facts & figures flying around on this thread & I shall continue to follow it with interest! :D

To all of you, thank you for your answers, I have learnt quite a lot from reading,and re-reading the answers as you people see it, today I have very carefully with a CFI sat at my side, plus two other passengers undertaken what was suggested, to see what the power would be like whilst only hovering down wind, the R44 without hydraulics, ran out of rear cyclic in a 7/8 knt wind at a hover height of around 8/10ft, I was forced to turn into wind to stop the movement of the A/C, the power being pulled was 25", had I gone beyond that I would have been in the area of overpitching, so after reading all that you have put into this thread, and doing this little rather gentle test, I can see that the D/W operation should be treated with great caution, I also see what Roofus is saying, but there must sometimes, be a time when this sort of take of is the only one availble, with the only alternative of staying on the ground. Thank you for sharing your thoughts and experience with us who need to understand more.
My Regards

Nick,
I was led to believe that there is a slight decrease in power required in a no-wind hover due to a 'cushioning effect' that is lost when a few knots are attained. Could it be that those on this forum who are arguing that the power required is not the same for a downwind take off and a zero-wind take off are referring to this? Assuming there is such an effect, it would seem that the power required to take off from a zero wind speed/positive groundspeed hover would be the same as that for a zero wind speed hover. However, taking off or hovering with a finite, yet small wind speed would in this case take slightly more power than hovering or taking off with zero airspeed.

I realize this explanation is a bit garbled, but perhaps this is at the crux of the disagreement.

P.S. Got your msg. Thanks. Will do..

Nick, I was not referring to the sterile laboratory that you fly in. I was referring to a real world comparison between actual zero wind and downwind approaches. In both I assumed starting with the same airspeed, and taking the approach to landing, thus to zero groundspeed.

I know that slowing from one airspeed to another does not depend on the wind.

The power needs don't "know" what the groundspeed is, but they are based on decelerating the helicopter and controlling it's descent. To fly the same approach path with a tailwind requires more decelerating. QED

As far as this not being "a place I don't often go", wrong. I don't fly comanches backwards at 80kts but I fly a heavy underpowered machine in the rocky mountains, frequently in the worst weather conditions (SAR). Mountain approaches sometimes are dictated by terrain and weather rather than winds. Considering downwind safety and power requirements is a place I frequently go.

Matthew.

[ 06 September 2001: Message edited by: heedm ]

Matthew,
Sorry if I tweeked a nerve, all opinions are valid around here, don't take my post the wrong way, please.

Regarding the time to decel the extra few knots, that is all relative. If you do the typical approach that holds constant airspeed until the appearant groundspeed gets to the old proverbial brisk walk, you will atuomatically adjust the downwind approach to start at the right ground speed point, and that will have nil effect on power. Besides all this interesting theory, why not just try it?

Kyrilian,

The cushion is not lost at forward speed, contrary to pilot lore. It has less effect, but only because ground cushion acts to reduce the induced power by about 15%. But since induced power falls off rapidly with airspeed, so that profile power begins to predominate, the power savings shrinks with speed.

The proof of how ground cushion is independent of speed (and how much it depends on induced power) is to recall how a big airplane gains ground effect at high-for-helicopter speeds as it comes within 1 wing span of the ground plane.

[ 07 September 2001: Message edited by: Nick Lappos ]

Nick, I'd love to try this, but we have a new baby so I'm on parental leave, and I can't fly the FS2000 206 well enough to do the experiment.

I think maybe we're talking about different things. My position is that two approaches flown identically, but one in zero wind and one downwind will have different power requirements. In practice, downwind approaches are extended and shallowed so the power requirement could be made identical. I believe this may be your position.

I think my argument is one to consider because the ideal approach over flat land would keep the energy state of the helicopter ideal for engine failure. To take that approach and shallow it due to being downwind would put you in a less than ideal energy state during your approach. I agree then that a downwind approach doesn't have any added power demand, if flown appropriately, but that comes with a tradeoff.

I took a mountain flying course with Canadian Helicopters, who teach techniques based on decades of mountain flying. They teach a flat or nearly flat approach (depending on terrain) to keep power requirements as low as possible. The safety is there because the approaches are flown well above terrain, until the short strokes.

As far as taking things personally, I respect your knowledge and look forward to your posts, but in that one I did feel a bit of condescension. I should have responded with wit rather than rapier. Sorry.

Matthew.

hi guys,

I have gotta go with Nick on this one. While the AC speed relative to the ground is higher when the airspeed hits zero, once you you have gone below translation whether you are into wind or out of wind is irrelevant in regards to the power required. Given a cautious approach profile I will go with a clear obstacle free approach downwind over the alternative 99 times out of 100.

Regarding takeoff's over obstacles... when youre heavy and theres the option of a large clear area downwind of the take-off point, again I will generally go with the downwind option. I figure that if the engine quits or there are any problems its preferable to try and sort these out over a clear area downwind, rather than an obstacle ridden environment into wind. Falling through those trees can really hurt!

The key to all this I guess is good technique and plenty of practice with people who are confident in this environment.

Food for thought maybe?

Roofus
Thanks for the info.
I'm now off to take my instructor to court for all those dw approaches he made me do at Chetwynd/Shawbury/Ternhill!!
Joking aside, appreciate the differences between mil and civvy.
Civvy pressures that I have come across so far have all been commercially based, funny old thing. Would dearly love to back track the clear area but the extra time spent backtracking (269m I think) would not make the flying financially viable (ie Pleasure Flying)
Roughly, allow 1 minute for hover taxi/turn, 60 trips a day = 1 hour of flight!
The good book wants you to be at 100' over the obstacle on departure, my logic tends me to try and remove the obstacle completely.
Loads of ways to skin a cat, and if your engine is going to fail, it will fail at the most awkward time!!
You are just showing off if you have 2 engines:-)

Is it better to do a towering (Helipad? Profile) takeoff to clear obstacles or downwind over open area, Id say downwind as you are you dont need to go inside the HV curve,whereas upwind towering you do.And its far easier to run it on than drop vertically from 150 feet! but id be interested in everyones more experienced views.

Regards
Hover Bover

[ 07 September 2001: Message edited by: hoverbover ]

Hoverlover,
I think you are right on, a towering takeoff is a prescription for a bruising if an engine has a problem, downwind over reasonably good ground is a much better bet.

Matthew,
For condesention, just spray Rain-ex in my eyes. :D

:( Thou Shall Not Hover(Takeoff) Downwind or Else The Ground Will Rise Up and Smite Thee! And you can take that to the Bank. :(

Gutless,

Bring that to where I work and the only thing you'll take to the bank is your unemployment check. You need to learn where, when and how to do them.

[QUOTE]Thou Shall Not Hover(Takeoff) Downwind or Else The Ground Will Rise Up and Smite Thee! And you can take that to the Bank.

Now I'm intrigued!
Firstly...are we talking singles or twins?? I'm talking twins! I've only got 200hrs in singles & as such I'm not aufait with the Cat A profiles for singles.
'A helipad take off into wind isn't as safe as a down wind departure' did I understand you guys right??
Helipad approaches & departures are taught to allow you to safely get in & out of areas much smaller in area than the proverbial 'Clear Area'.
'Towering' take offs are not a recognised CAT A profile (at least not in the helo's I fly).
A donk stopping during a Helipad allows for a safe reject....that's what the profile is designed to cater for!
Even in a very fat Squirrel you can reject post donk failure back into your site without too much grief.
Of course it does mean that you have to fly the profile well & accurately! Surely that isn't a problem?
I am presently too stunned at the answer 'commercial pressure' to allow coherent thought. I cannot believe that commercial pressure forces pilots to ignore into wind profiles.
I therefore am pleased to say that I work for a commercially liberated company in an ideal world! :D
Oh...by the way....there are no Cat A performance profiles, Cat A restricted performance profiles or Cat B performance profiles in the Flight Manuals for the two helo's I presently fly that allow for downwind T/O's or landings.
Obviously flying under an AOC or a PAOC, an aircraft captain has to satisfy himself that his aircraft can meet the relevant performance criteria.
Perhaps that is why this all comes as such a shock to me. :eek:

[ 08 September 2001: Message edited by: Roofus ]

Roofus,

I agree hat a twin is a whole different ball game, I believe a helipad profile allows you to reject back to the pad if you suffer OEI prior to CDP, am I thinking correctly ? (only being a PPL on singles such things are for the future !) But the same profile in a single if you go OEI (OEI inthat case is ONLY engine inoperative) Just puts you slap bang in the middle of the HV curve and only allows you to crash on the pad from a great height, rather than the downwind TO that keeps you within it.

Regards

Hover Bover

Roofus,
You point out the extreme difference between airline type Cat A operations and utility operations. Cat A is a regimented method of assuring single engine getaway for every millisecond of the journey, a very nice thing. It is achieved at the expense of the flexibility of doing what the machine is capable of doing physically.

There are towering Cat A takeoffs (which involve whistling down Cat A rejects!).

Certainly, any points we were making in these posts were not to condone inventing Cat A ops. I know of no downwind Cat ops, although some Bells and EU's have you back up while climbing vertically to keep the small heliport in sight during thier heliport Cat A procedures. (oh goodness, that means you fly in rearward flight downwind in the first segment of the takeoff, I wish I'd remembered that while we were discussing this earlier!)

The issue is not single or twins, otherwise the advantage of allowing single engine fly out would become a liability if you always had to fly Cat A. Sometimes the thicker fellows in the FAA forget that. There will be times that the tiny risk of engine failure is acceptable when balanced against the ability to do the job. BTW, tiny is correct, data from the North Sea tells us that engine failure during the first seconds of a rig (or towering) takeoff is likely to occur about once each 100,000,000 takeoffs.

In commercial operations under Cat A operations (as dictated in the Company's Ops Manual), you must follow published procedures, upwind or downwind as they are written, of course.

[ 08 September 2001: Message edited by: Nick Lappos ]

Nick,

To declare my hand, I was an unquestioning fan but now I am concerned.

The downwind scene is something I am forced to live with in aeroplanes because the poor bluddy things need runways and lots of factors cause me to take an undesirable solution.

In helicopters, however, there are generally two distinct scenes: one - military and two - commercial.

In my military role, I may well be forced to operate downwind due to tactical imperatives. History has forced miltary machines to be specified with the specific problem in mind. In my commercial role, I can usually avoid it because it does have significant problems. The machinery is rarely specified to cope.

In any event, it should not be underestimated and the risks should not be diminished.

I am disappointed that the posts thus far are in my view a touch cavalier. If I had my bum strapped to a Commanche, I certainly wouldn't be overly concerned about tail rotor power and critical azimuths or downwind autorotations or a sh*tload of other things. If I happen to be in a Robbo or a H269 or similar, then I sure as hell am not going to be so comfortable.

For my sins, I have swapped ends with pedals on the stops and have shuddered to a halt with severe pylon rock and little lateral control and I have investigated three vortex ring/settling with power accidents that have resulted from downwind landings. I have also put my skids through the trees on marginal power take-offs when the wind stopped being my friend.

Roofus - you get my vote.

As for performance margins, I am again a little disappointed. Nick, forgive me for being cynical but I am old and no longer bold - your job is to produce performance figures that sell helicopters and how much your experience/conscience interferes with that commercial imperative is not known to me. I am not for one second suggesting that you lack any desirable personal attributes - my emphasis was only on the unknown - but there are any number of junior helo drivers out there who may read this thread and feel supremely confident that downwind operations are OK and no big deal.

It is a fact of life that they will be operating machines of very limited capability in performance and control power. I just hope that they do not get confused between what you can do and what they (and I) cannot!!

Well said, 4dogs,
The limits of each machine are very important and must be part of the equation. I don't condone cavalier downwind operations, and I think the whole thread so far has been about "What are the issues to deal with"

The one place we have concentrated on is the detail the possibility of more power being needed for downwind operations, several posters say yes, I say no.

We all say to perform downwind operations judiciously, and if one operates outside of his machine's limits, he is foolish.

To believe that a Robinson can be handled like a Black Hawk is suicidal. To believe that a Black Hawk must be limited to a Robinson's capabilities is as wrong, but at least it is a safe belief, if not a productive one.

hoverbover thanks for pointing out differences in helipad singles v twins. Agreed helipads in singles are out! :eek:
But without Helipad profiles how do you guys get into the more restrictive landing sites?

Nick Are we calling Helipad profiles Towering? Towering to me means vertical. Helipad profiles are not vertical.

IAW the ANO any aircraft flying whilst carry pax must conform to Performance Profiles as laid down in the Flight Manual.

Yep...they restrict you. Yep...they ensure single engine climb...um...that's exactly the point! That is why they are there!

To say not to use the published profiles to allow you flexibility, is shocking! (fingers crossed I misread that!)

Professional pilots have a responsibility to those they carry. As such the published profiles must be used...thus giving the greatest chance of a safe conclusion to any 'mishap'.

To use commercial pressures as justification for going against the aircraft Flight Manual is equally shocking!

I stand by my earlier statements.
If you're considering downwind approaches or T/Os ask WHY???
Look for an alternative....or use the statement 'I can't get in there'

So...I also stick by my earlier statement.... I fly Police & will only consider a downwind approach & T/O if it is Life or Death & I have no other alternative.

Yes helicopters can take off & land downwind, yes instructors teach you these techniques, NO they shouldn't be taken lightly.
I'm not saying they can't be done...they can But not as safely as into wind & in some cases not legally.

I'd merely like to think that upcoming helo pilots would use the same caution when considering it as I was taught to.

I've only been flying 12yrs, a tiny amount compared to some, but in that time I've yet to have to do a downwind departure or approach.

Play nicely & Fly Safely :D :p

Edited 'cos I just noticed I've past 100 posts :D Is that good or bad? :rolleyes:

[ 08 September 2001: Message edited by: Roofus ]

Nick,

The one place we have concentrated on is the detail the possibility of more power being needed for downwind operations, several
posters say yes, I say no.

How about a downwind approach at or steeper than the FAA shallow approach? Seems to me that you will reach zero airspeed OGE or at least at the very limits of IGE. The critical part of this approach is to replace the loss of ETL with engine power before a higher than normal rate of decent is established. It takes a LOT more OGE than IGE.