Confined area power check - tips and techniques

[birrddog]

I am interested in hearing your tips and techniques for confined area power checks (before making the decision to land if we have enough power to hover and get back out).

I have been shown a few methods during my training, the one being the OGE Hover, Power Check on Startup (MAP, or Torque/Temp margin) if in the same area (and ambient conditions).

I have been reading the other thread about approaches, and thought this would be a good compliment.

Discuss. :ok:

[kneedwondean]

For Pistons(R44 and R22) we teach - 53kts S+L over the site carb cold. Compare your MAP to your 5min rating. If you have 6"(R22) or 8"(R44) spare your have power to spare and can hover OGE. Wouldn't recommend going into a confined area with less. For departure, 2ft IGE hover and compare MAP with 5min rating, if more than 2" it will lift vertically. 1 1/2" and you could get away with a towering. Remember to actually pull your 5min rating(before approaching) at some point to make sure you can attain that power without rotor droop.

[Flyting]

Check out this... http://www.pprune.org/rotorheads/401436-flight-rules-thumb-only-2.html
The first on the list...
It's a technique I came accross that the Aussies use... and is the simplest that I have found
Confined Landing:
Do the P.A.W.S. check:

Power

http://i101.photobucket.com/albums/m78/whirleybirdsa/powercurve.jpg

Draw a horizontal line across the graph from point B (IGE Hover) to point C, which is X speed in straight and level flight. Point B and point C both use the same power. The trick is to know what the speed at point C is. To find this, when lifting off, stabilize into an IGE hover and read what power is being used. Now, using that same power, establish a S&L flight +-500’ above your IGE hover alt. Read what speed that particular aircraft gives at that IGE power setting.
Now when you come to land at a different LZ, reverse the process. Fly at the speed you obtained earlier, as you are approaching the LZ at +-500’ agl, and check what power you are using. This will give you an idea for what you will be using for an IGE hover at that LZ.
Obviously, the graph shifts according to altitude, temperature, etc, but it is an easy way of figuring it out instead of having to add/subtract Tq/MAP to give an IGE power required.

Area

Wind
Wires
Way in/Way out

Size
Shape
Sun
Surroundings
Slope

[Non-PC Plod]

The performance section of your RFM should be able to tell you whether you have hover OGE capability at the relevant weight, altitude and temperature.

As a rule of thumb, give yourself a 10% thrust margin for confined area - ie make sure your AUM is 10% less than the max for the altitude and temp for hover OGE.

Obviously, include this in your planning before takeoff, 'cos you dont want to be looking through the graphs in flight!

Do the manufacturers recommended engine power checks before take off, or check that you can pull to your aircrafts max continuous torque and takeoff power settings without topping out on Ng or temp (if we are talking turbines) or whatever other limitations you have in piston engines (manifold pressure?/temp?) at the altitude of the LS on the day.

[WikiRFM]

This topic has been beaten to death, revived, then beaten again elsewhere, but it's one that is worth figuring out (if for no other reason that CFIs think it's a good idea to teach something like this). Nobody taught me a "power check" during my training--beyond noting my hover power on pick up and checking my POH performance data--and there's nothing about it in the RHC Maneuver Guide. I looked at all the VR threads on the topic, and the advice was muddled and inconsistent at best. One school owner made an interesting comment: an examiner started asking his students who cited these rules of thumb to point out their sources.

Anyway, I tried to assimilate all I've read about it in this lesson plan (http://wikirfm.cyclicandcollective.net/ground-lessons/off-airport-pre-landing-power-check/). What I don't understand is why your published performance data aren't good enough, especially in a training environment. With a little pre-planning, you can guesstimate your fuel, LZ elevation, and temperature before the rotors even turn, and you'll know where you can land and where you shouldn't try landing. At your LZ, you can check your actual conditions to see how far off your expected condition is from your actual. For example, if the charts say you can land at 4500 MSL, is it reasonable for a <1000 hr CFI to take a student out and try landing there? Or even 4200 MSL? Seems like a lesson on ADM and understanding (performance, weather) minimums would be better for a student pilot rather than a rule of thumb.

[ralphmalph]

WikiRFM - Not really. There are many instances where a pilot has incorrectly calculated a weight/wind/pax which will mean that the aircraft is out of limits.

Look on youtube....there are scores of f*ckups to prove it

Before you land......check your weight and power.

you may get away with it for a couple of years.....but wait!

[GeorgeMandes]

"What I don't understand is why your published performance data aren't good enough, especially in a training environment"

Leaving aside whether you have a min spec engine, and if your weight is calculated correctly, none of this tells you what the effect of down flowing or up flowing air is at your landing area. Assuming a training environment, where weight is not be added to leave the confined area, you want to shoot an approach to the imaginary platform above your confined area, and before you slow below translational, determine what torque/temp/gas producer margins you have to get in and back out. Depending upon the up flow or down flow, you may be able to take more or less than the charts say.

Mel Schiller, instructor extraordinaire at Canadian Helicopters, has a whole program on confined areas developed there, that I can't do justice to, that combines wind finding, checking power and assessing the spot. This is just part of the whole procedure. It starts with the high recce, where he looks at 4 S's: size, shape, sun, starting point. Then he goes to the low recce and wind finding, the overshoot and option to land, maneuvering in the confined area and the departure.

[hueyracer]

This is a very simple way to check wether your power will be sufficient for a landing.....

1. Approach the area and bring the helicopter down to the obstacles.
2. Before reaching your area, reduce airspeed as much as possible, but keep it above translational lift-airspeed (mostly 18-25 knots)
3. Keep the heli with that speed straight and level (Vario=0) when flying over the are.
4. Check Torque/Power.

If your power leaves a minimum of 10% to max torque available, you can safely land (regarding to the wind...) and climb out of the area again....

[Torquetalk]

The value of the power check is that it tells you what you need to know in the situation you find yourself in. And if you do one for the aircraft you fly: the source of the values is no mystery :ok:

Stand to be corrected, but what is really clever about the power check is that the values work irrespective of DA and weight: that is you need x% torque or x" MAP margin to guarantee a particular manoeuvre. Depending on your weight and DA, wind etc, you will either have that margin or not.

Again, I may be wrong, but the values should work across aircraft types, ie. be the same for SE pistons such as R22, R44, H269. This is where 3" over hover power for a vertical take off has come from.

I have seen several different lists handed down by instructors to students and many have some form of error or another because the reasoning behind the chart has got lost. e.g Take-off = +1 is manifest rubbish. If you can hover, you can take-off: so hover power is take-off power (minimum for IGE normal hover height). More is nice to have. Lists with values so generous that there would never be an issue with power don't really help define the point where available take-off and landing techniques is limited.

TT

[[email protected]]

hueyracer - your technique has so many variables that it cannot be reccommended. 10% torque in hand does not equate to a 10% thrust margin which is a sensible performance level to keep when operating into CAs. Use your performance graphs to calculate OGE hover, anything else is guesswork. Unless your RFM has a graph for level flight performance at a specific speed that can then be equated to a power margin for landing, then the OGE graph is the only way and, as suggested earlier, taking 10% from the calculated max AUM will give you sufficent performance to deal with light turbulence/windshear etc.

[Heli-Jock]

I would be wary of doing this "carb cold", in a 22!
Ive always taught and been taught, to do it carb hot.
If you were carb cold, alone 53kts S&L that would take you below 18" manifold, which, as the gauge says "Full Carb Heat" applied.

Just a wee pointer. If i am wrong please tell me.

HJ

[choppertop]

Just blast it with heat for a minute before closing it to cold and doing the check...?

[hueyracer]

Like all "rules of thumb" my above mentioned statement does not have to be right for every situation and every helicopter.

For the last 15 years, i have been flying 205´s and 212´s in various countries-and the military.

After doing all the checks before landing, the "flying over" as described above gives you the last decision check wether to land or not...
I do not apply to be correct for all kinds of operations-but doing "confined area landings" is my daily business......but i have never flown a piston A/C.....so i don´t know about their performance...

Within Bell helicopters, 10% are more than enough to clear a confined area again-if the conditions stay the same for landing AND for take-off....

[Shawn Coyle]

My question for this situation - why are we continuing to put up with the dreadful level of information provided to us?
Turbine engines that are above spec lead us to not trust the charts, because the performance is better than expected. Turbine engines that are below spec get us into trouble. But at least with a turbine engine there is a way to know whether the engine is above or below spec.
Piston engines have no such check, but surely someone could develop one - Just to name one problem, piston engines can have poor compression, and the pilot wouldn't be aware of it till it's too late.
And none of the charts take into account wind.
Civil charts only publish one hover height for in-ground effect hover, and many out of ground effect charts are based on flying in to the hover, as opposed to climbing up to it.
So why are we putting our lives on the line for such poor information, when the technology surely exists to give us better, more clear and easily understood data???
Answers on a postcard please!

[Gordy]

Shawn...I guess until the industry demands such knowledge, it will not be given. It would be my guess that it has to do with liability---but I'm sure you knew that huh?

As for rule of thumb..I use the mountain flying technique that I learnt from Larry Doll, (former chief instructor at Rocky Mountain Helicopters). This technique supposedly works for all Bell products---I routinely land my L4 upto 10k and occasionally upto 12K during fire season and it works.

On final approach, flare the aircraft to a slight nose up attitude, (be slow and methodical with most of you power already applied), to be a little short and 100ft above any obstacles on your path---hold the slight flare till speed falls through ETL and you will feel a slight shudder, level, apply the last of the power and note:

1. Pedal position
2. N1
3. TOT

To hover IGE it will take an ADDITIONAL:

1. One inch of left pedal
2. 12% N1
3. 35 degrees TOT

To hover OGE will take and ADDITIONAL:

1. One and Half inches of left pedal
2. 15% N1
3. 50 degrees TOT

IF you do not have the additional pedal, N1 or TOT available before hitting any red line limits, you are in a position to nose forward and fly away.

If you have the available pedal, N1 and TOT, you can continue the approach in a nice controlled manner all the way to the ground. The mark of a perfect approach is to hold the collective in one position, the aircraft will settle all the way and "kiss" the ground and then lift off again to about 2 feet as ground effect kicks in.

I have tested this "rule of thumb" at most weights, lots of Alt/Temp variations and it works for me. The biggest thing to learn, if this is not your standard procedure, is the slow/methodical approach.

As for the original question of having enough power to get out---this comes down to being at "one" with you aircraft and understanding all the performance. I am lucky in that I fly the same aircraft most of the year---I know all of her quirks. By using the above technique, and having a cheat sheet in the aircraft, I am able to make a reasonable determination of whether I can get out or not.

[hueyracer]

This method applies to the same method i have mentioned above.....

[GoodGrief]

Hey Gordy,

that sums it up and works nicely, but only as long as you don't add weight after landing.
There you really need to know your machine.

[hueyracer]

It works the same way, when you plan to load weight...


As a rule of thumb (in Bell helicopters), you can subtract for each person (app. 100 kg including baggage) 0.1 kp/cm2 (Torque) which equals 3% Torque...



So-if you have 15% Power to Max left when overflying the area, you can just subtract the expected pax-weight and see, if you have enough power left for T/O BEFORE you land in that area.....:ok:

[b212hp]

You can plan based on where you're going and what the weather is, but you can bet that it'll change by the time you get there.

I'll do all the planning I can before I go, but I've found the off site power check is a good way to make sure you've still got the power before you commit to the approach. I use it with confined area/ridge line approaches and rappel ops, and I do it before every approach, even if I've been going in there all day.

When I set up on a long final I slow the helicopter to an OGE hover while I still have sufficient power to fly out of it, if I find I don't have the power. If I have the power to hover out there I should have the power in the hole. Keep in mind that things can change when you get close to the trees or the ridge. Winds defy physics some times, and the wind that's been helping you above the trees can drop to zero or shift to a quartering tailwind below the tops.

Departing a confined area I'll depart vertically until I'm above the obstacle so that if there's a problem I can go back down to a known spot instead having to bleed speed to land short of the trees.

[Flyting]

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

[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:

http://i76.photobucket.com/albums/j35/helokat/LaFawnduh%2008/57z-500.jpg

[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...