Confined area power check - tips and techniques

[GeorgeMandes]

1) I just read that thing a number of times and if you think that does not involve calculations, you may have a future as a flight engineer.

2) What the wind and upflow is at the LZ +500 feet may or may not relate to what the air is doing at your LZ.

[Flyting]

OK George.... so improve it so I and all can benefit...
As I said, it was an Aussie method I found

[Gordy]

Can anyone comment on the technique in post 3...? Is it not the easiest way of finding your IGE hover performance without any calculating?

Yep----you take off form 6,000 feet and are going to land at 12,000 feet---AND need ot take off again....tell me how your graph helps me....All it tells me is if I can hover IGE....Who cares---if I can't, I will settle to the ground and then figure what to do.

This chart is good for checkrides and those who do not work in the "real' world...That is about it.

[rotornut01]

There are two distinct parts to power checks, or as I like to call them power awareness when relating to landings in mountainous terrain.


They are:

1. Awareness of how much power is available to be used (what the engine(s) will provide).
2. Awareness of how much power is in use or for those with a crystal ball, will be used (we can never be 100% sure how much will be used prior to the landing due to all the variables in play).

The difference between 1. and 2, is your power margin. You can think of it as your power safety margin.

One simple way to ascertain how much power you have availble and whether it is enough to land at a given spot is to come to a hover (OGE) beside the proposed landing spot with plenty of air under you. The air below is your escape route should the helicopter not deliver the required power. Of course the result of this exercise could be a false sense of security if the approach to the landing spot is poorly excecuted, for example downwind or into a descending mass of air. In a downwind approach you could easily add another 10% power requirement, which would quickly erode that safety margin that you thought you had. For this reason this type of power check has its uses, but also has its limitations.

There a lots of rules of thumbs around for different helicopter types that are always useful to work out how much power you should need to use once you are in a stationary hover at the spot, but once again they don't help you out if the approach is miscalculated, or poorly chosen. They also all need to be combined with a procedure to check how much power you have available to be truly useful.

In my opinion, the best method to work out if you can land at a spot is to perform a low recce down to a low airspeed (not below translation, approx 20-30 kts depending on machine) as close as you can to your intended approach path. I like to aim for no rate of climb or descent when I am over the spot (will help to identify updrafts or downdrafts), and compare airspeed with groundspeed and power in use. Prior to this, you should have already pulled to the power limit to check that it is available. Sometimes this limit is given by graph, sometimes by progressively adding power till rrpm droop. This method does require having knowledge of how much power you will use at 20-30kts, vs what you will use in IGE or OGE hover. i.e. a bit of experience and a fair amount of practice.

Once you are very familiar with a particular machine and the difference between the power at 20-30 kts vs IGE or OGE hover then, the low recce approach will turn into the final approach without the need to use your escape route and a subsequent final approach.

Some spots on some days do not allow an escape route close enough to be able to make this assessment using this method. In this case, until you have a lot of time and experience in the mountains reading winds and know your machine extremely well, don't go there, choose another spot.

To sum up, firstly, you should have an idea of how much power margin you have available before you go in to a spot, have an escape route, use it if things don't feel or look right, and then after landing assess how much of that power margin you used. Repeat many times until the difference between the first answer and the result are the same 99 times out of a 100. Then it might be time to reduce your safety margin by a small amount and repeat the process over and over again.

Beware though there are a lot of bold pilots who have eroded their safety margins to nothing over the years, then had a bad day and payed dearly for it just because they weren't completely on to it that particular day.

[Flyting]

What the wind and upflow is at the LZ +500 feet may or may not relate to what the air is doing at your LZ

the extra 500' above the LZ gives you a little more positive margin (if thats the correct way of saying it) on the power check because of the higher alt. The wind checks get done at the LZ lower down.
or, you could just do the whole check at a lower alt above the LZ...

All it tells me is if I can hover IGE

exactly...! If you know what power you will be using to hover IGE then compare that to what you have available at your 12000', and make the decision whether to land or not according to what you have, versus the confine and what kind of take off you'll have to do...
Besides, isn't that the point of the power check...? To see what you have available...

I find with this method, I don't have to worry about which type or machine I'm in (as it differs quite often and I don't know each particular machine intimately - no not type - each machine is different to the next) and I've got into the habit of doing the initial hover/speed comparison check when I get airborne and it works out quite well... In the "real world" thanks Gordy... or maybe I've just been damn lucky until now...

A lot of the techniques described, and many that I have been taught, have put the machine smack in the middle of the dead man's curve for the initial power check. Ok if you're in a twin, which is what most of those instructors were used to (being military men) but I'd prefer to stay out of it as long as possible in a single over dense jungle.

[Gordy]

In the "real world" thanks Gordy... or maybe I've just been damn lucky until now...

I guess I could have phrased it a little better...

A lot of the techniques described, and many that I have been taught, have put the machine smack in the middle of the dead man's curve for the initial power check.

There is nothing wrong with being in the "dead man's curve" as you call it..I think it has been used to scare people into not going in there. I spend a fair amount of my flight time there---we prefer to call it the "money curve"...tis where all the money is made---it is after all what helicopters were designed to do... As I am sure you know, on an approach, the curve is not as bad as on takeoff.

I've got into the habit of doing the initial hover/speed comparison check when I get airborne

Again---this is good if you have the time to do it...In most of the work I do, I rarely get above 300 feet, and often times am landing in different places all day. I do not have the luxury of time to do these checks. I have HIGE/HOGE cheat sheets aboard the aircraft, that are laminated. I can look to see what I can and cannot lift very quickly. I have a standard 500lbs of fuel version, but I created it in excel, therefore I can adjust the aircraft/fuel/pilot weights as needed. Here is the one I use:

[paco]

"---if I can't, I will settle to the ground and then figure what to do."

So who's going to pay for the journey while you figure things out? Knowing as much as you can before you go is better for the customer!

"There is nothing wrong with being in the "dead man's curve" as you call it"

There's plenty wrong with it!

phil

[Gordy]

paco...

I guess I phrased that badly too huh?? (Note to self---quit posting in the early hours of the morning...)

In reality, I think it comes down to knowing your aircraft's capabilities. I attempt to have an idea of the capabilities of my aircraft prior to launching. Working for the USFS, we are required to work out a "load calc" daily, and for each specific mission.

For initial attack, we do a baseline daily calculation which will tell us the highest weight we can accept for a given alt/temp which is normally selected based upon worst case for the day.

We also are required to factor in a "weight reduction" or download based upon aircraft type---which for the L4 is 180lbs.

I have yet to land at a place where I could not get out. And why is it wrong to be inside the "dead man's curve"?

[paco]

It's wrong to be anywhere you don't need to be, but you're the guy in the hot seat - you may well need to be there. I'm not here to criticise!

I will pass on my own way of checking progress on the way in - having done the usual power check to see what you've got, coming in at 250 fpm (on the 206 at least, round about 60 kts) gives you more or less the same power as you would be using in the hover - if you are using 95% under those conditions, you won't cope with the windshear as you go past the treetops. A side benefit is that you shouldn't need to move the collective at all. It will stop nicely as soon as you get decent ground effect.

Phil

[valve guide]

"There is nothing wrong with being in the "dead man's curve" as you call it"

There's plenty wrong with it!

phil


I hate the above term, just like I hate the term "choppers". Its actually called an "avoid" curve not a "never go into curve". Helicopters were designed to get into tight confined areas and if that means going into the avoid area of the curve so be it. Sure lets minimise the time we are in it and take all the precautions but Phil lets not get too carried away!

[paco]

Did I call it the dead man's curve? I referred to it as the H/V curve, which is its proper name.

I don't think I'm getting carried away - manufacturers spend time and money establishing such parameters for our safety, so a statement like:

"I think it has been used to scare people into not going in there"

is not appropriate.

I also didn't say "don't go in there", I said "there's plenty wrong with it", in the light of the statement above. I just didn't think it was getting the respect it deserves.

phil

[Gordy]

so a statement like:

"I think it has been used to scare people into not going in there"

is not appropriate.

Not really fair to pull out one line from everything I have written. I think we are agreed that it is NOT the "dead man's curve". Some of us make our living working inside the H/V diagram. Does it demand respect?---YES, should one deliberately spend time there for no reason?--NOPE. I guess you and I really do agree---its just the interpretation and delivery of the argument.

My comment was referring to those who do not fully understand what the diagram is telling you. I once watched a pilot fly an approach at 60 kts all the way down to 10 feet off the ground and then flared all the way to a hover. When asked why, he replied that he was avoiding the "dead man's curve".

[paco]

OK, things are a bit clearer now - these early morning posts! You're right, though, people just do not know the basics.

Phil

[Flyting]

Guys.... sorry for calling it the dead man's curve.
For Phil's theoretical purposes, I refer to it as the H/V curve. Like Phil said, manufacturerers spend a lot of money coming up with it, and when you've seen a good friend and a full helicopter of pax burn to death in front of you because he had no time to react, you'll learn to respect it...
...but that's a curve post and is done already...

Gordy...
I like the "money curve".... much better, and it's true. I too, spend a lot of my time in it for work purposes - but that's it.
I also have done a similar chart like yours for all the types on my license and use it as much as possible. Works well, especially if you're flying one particular machine and you get to know it intimately.
We too have to do all that pre-planning stuff for the records, but where I mostly fly, we have no idea of conditions, let alone where we are going, so a good check is essencial.

p.s. didn't mean anything by this:

Quote:
In the "real world" thanks Gordy... or maybe I've just been damn lucky until now...
I guess I could have phrased it a little better...

just that I do fly in the real world... if you can call the jungles of central africa that...

[tyto]

HueyRacer:

Reference to your reply about having minimum 10% power margin available as you reduce speed while over flying the confined area may i know the Maximum Power available factor??? is it the Max Power Available for the day???? or some other value??? because while we fly at slow speed within translational lift i have never found myself close to 10% power margin figure.....its always been 40-50% less than max available in normal load conditions!

[Aucky]

I once watched a pilot fly an approach at 60 kts all the way down to 10 feet off the ground and then flared all the way to a hover. When asked why, he replied that he was avoiding the "dead man's curve"

And why not if you have the space? I appreciate you may spend most your time in helicopters with relatively high-inertia heads so auto at 30kts from 150' may not be a problem, but I know I'd rather have the 60kts at 50' if the engine quit in a 22... that ability to flare effectively would potentially save a very hard landing. I know it's not what we teach in the UK, and cannot be achieved into many helicopter site sites, but where you can i say go for it, especially in a helicopter with a low inertia head - also at 60kts (near the bottom of the power req'd curve) on approach your collective is lower on approach so less RPM decay if the donk quits... speed, rpm, flare. Yes please.

[lelebebbel]

And why not if you have the space?

I guess if you only land on runways it doesn't matter - if you are so worried about an engine failure on approach, you might as well auto it all the way down every time.

But on an unprepared landing site?

At 60kts you have zero chance of seeing or avoiding a wire or other obstacle that pops into view on short final. And a big flare, close to the ground at the end of every approach? No thanks.

Come in slow, controlled, with a loaded disc. An engine failure on approach should be quite manageable, a tail- or wire strike certainly isn't. Just look at the statistics, which is more likely to happen?

[Aucky]

You are somewhat twisting my words. Perhaps i should have been a little clearer in my meaning of 'if you have the space' I clearly mean where is is safe to do so i.e. Clear of obstructions, wires, hazards & aircraft, and of sufficient size. Obviously one is not going to do this into an unfamiliar site or particularly confined site. Few of us only land on runways, and few of us solely land in confined areas. I was simply suggesting that where the area is clear and of sufficient size I don't consider there to be anything wrong with flying something close to the reverse of the HV diagram. As pilots it is up to us to make the decision on where this technique is and is applicable just like every other decision regarding safety.

And a big flare, close to the ground at the end of every approach? No thanks.

No. Not every approach clearly. Also flaring from 60kts at around 50' does not have to be that "big" or aggressive. Passing 25' at 40kts. It's like a transition back from a quick hover taxi. Precision transition if your used to calling it that.

An engine failure on approach should be quite manageable, a tail- or wire strike certainly isn't. Just look at the statistics, which is more likely to happen?

As stated above, you shouldn't be doing this into a site with hazards such as wires. Engine failure manageable from 150' at 30kts in an R22 with already low rpm. I don't know anyone who practices this, wouldn't like to try. Of course we all accept that risk on the majority of our approaches, your in a helicopter, it's meant to fly, but where it's safe to do so why not reduce the risk...