Instrument Flying From Cyclic & Collective

PtigiM ---- and instrument !=tying -

instnrment nying

ep

a:-D

Before beginning this section, a distinction must be made between Instrrtment Right Rules ( P B ) and ndmtrsment i%te~r~Eogical Conditions (IMC). IFR means following the rules of instrument flight - this can be in very good weather, clear of cloud, using radio navigation aids, Air Traffic Control and so on. IMC means flying with sole reference to the instruments - namely no visible horizon, no ground references, no way to determine the helicopters pitch, roll and heading except from cockpit instruments. A subtle difference, but very important, as will be shown shortly. F C can be simulated using an instrument hood, and it need not be in the airways structure . As far as the airways' (i,e. IFR) procedures are concerned, instrument flying in helicopters is very little different from that in an equivalent speed fixed-wing aircraft. Fixed-wing flying is a much cheaper way to learn instrument air sense, then it is only necessary to learn to fly a helicopter on instruments. This is a large enough step in itself why is it so =cult?

-

E R Flight ]Envelope The first thing to understand about instrument flying in a helicopter is, aside from helicopters fitted with very complex autopilots and special instruments, only half the flight envelope is usable for instrument flying, Most light helicopters that are instrument flight equipped have a minimum airspeed when IF^ in the flight manual. For the sake of argument, lets say this airspeed is about 60 knots. Why is this speed there at all? There are many good reasons for setting a minimum speed in IMC. Unless a low-airspeed sensing system has been fitted (discussed later), the airspeed system is pretty well useless below 40 KIAS. A 20 knot margin between minimum IFR speed and the speed where the AS1 stops making sense isn't too large, and might be acceptable, if it weren't for several other problems, namely: The shape of the power required vs. airspeed curve around 60 KIAS is relatively flat, but, as speed decreases below this airspeed, starts to go negative - that is, more power is required to maintain level flight at a slower airspeed. If you haven't tried maintaining 40 KCAS in level flight, under simulated IMC, it's an interesting exercise. I wouldn't recommend it in real IMC. The helicopter has very little directional stability a t these low speeds very small amounts of out-of-trim can cause large yaw rates, and that makes it difficult to maintain heading accurately. The slip ball is very insensitive a t these airspeeds, and a small amount of out-of-trim condition can cause large heading changes. Slip strings, of course, are not fitted to the inside of the helicopter, so it makes the instrument scan or cross check slightly awkward. There is very little, if any, static stability in the longitudinal axis below 60 I(TAS. I11 avoid a very complex discussion, and say that even when trimmed for a particular airspeed, if a gust changes the airspeed, the helicopter is happy to stay at the new airspeed and not return towards the original speed. Another way to say this is any small change in longitudinal stick position will affect a very large change in airspeed in this region. In simple terms, it is ditEcult to hold an airspeed around 60 RIAS in anything other than ideal, flat calm conditions.

-

-

Wrhy is He1lcopter All of this is merely to discuss why only half the flight envelope is usable, but doesn't tell us why it's difficult to fly helicopters on instruments in the first place. Unlike fixed-wing aircraft, which are more or less stable in both the longitudinal and lateral-directional axes, the helicopter is dynamically unstable in the longitudinal axis, and neutrally stable in the lateral directional axis. Big words - what do they mean?

* A safety pilot is needed however end someone to look-out on the same side as the pilot 'under the bag'is very worthwhile.

t See the confusion? Don't they mean when IMC?

94-@ Instrument Flying $3

MigM and hstrument Ffying

-- ----- -- ----There was some discussion earlier about instability in the hover. You may remember some discussion about the increasing oscillations and the requirement for small continuous controlinputs or corrections to stop this from developing - they are equally valid here. Left to its own devices, in forward flight a helicopter w i l l develop larger and larger pitch oscillations. The pilot must prevent these from starting, and in VMC, with good visual references, this is relatively easy. I n IMC,only the instruments to tell the pilot what is happening. In turbulence, the attitude indicator, which is the primary reference for attitude, has enough 'noise' to be difficult to interpret the exact attitude with any precision and decide what to do at an early stage. Just like the hover, in calm conditions, the pilot must make corrections to stop the oscillation from diverging about every 5 - 8 seconds. f remember many hours of flying on instruments in the UH-1N (without a stabilization system) when it was not uncommon for the altitude to change suddenly by 100 feet, or the airspeed to suddenly be 10 different with no perceived (i.e. seat of the pants) change. Add to this the effects on the yaw axis when vertical gusts change the torque balance on the main rotor, and the picture becomes very confusing. Most helicopters without an AFCS and that fly in IMCfIFR (and they are almost all military) end up with the two pilots trading flying every 30 minutes or so it's too tiring to keep it up for much longer than this at one time. Is it any wonder nearly every civil IFR helicopter has an autopilot in it? Why aren't more civilhelicopters flown IER?The simple reason is that most civilhelicopters are singleengined, and what happens when the engine fails*? Unless you have lots of clear air under the clouds so you have enough time to find a suitable place to land, it's not a good idea to be up there. In most European countries, it is not permitted to carry paying passengers in singleengine helicopters IFR.For the few given dispensation, there must be no cloud below 1,500AGL in order to carry out a safe engine off landing.

-

Disorientation One of the main problems of instrument flying in helicopters is that in real IMC, it is very easy to get disoriented (some people call it vertigo). Unless you are lucky enough to fly a big helicopter, the large amount of glass area provided to give you a good view of the world when hovering can easily provide ill distract you from the instruments. I've seen people get disoriented several times, powerful cues that w and had it happen to me. For this reason, nearly every helicopter that operates at night or in an area where there aren't really good visual cues for determining pitch and roll attitude, or height above the ground should have an attitude indicator, and the pilot should have an instrument rating. Interestingly, it is only the operating rules that require an attitude indicator for night flying - the basic certificationrules don't require it. Just another of the strange things i n this world. Hopefully when you get your instrument rating, you will be put in unusual attitudes and other situations where you will learn to trust your instruments, and also how to survive disorientation.

UseM Instrument FIying Exercises The following are useful exercises to develop instrument flying skills. It is noticeable that they concentrate on IMC skills, as opposed to procedural IFR skills. These should all be practiced with an instructor or competent helicopter pilot as safety pilot.

Slow BFHighk The first exercise is slow flight. Slow down to 60 RIAS and practice turns,climbs and descents and then combine turns with climbs or descents. While the maximum angle of bank you might expect to see for a standard rate turn is quite low (about 13"), you should try fmmto 30°, just for the practice. When changing power for climbs and descents, notice how difticult it is to keep the ball in the middle. When you get tired of doing this with all the instruments working, try partial panel with the attitude indicator failed, and if you have a turn and slip indicator, using the turn and slip to do a standard rate (rate 1) turn. Time turns through 60°, 90" and 180" of heading, on partial panel (i,e. no attitude indicator).

* Unfortunately,the engine failure rate on turbine single engine helicopters is still too high to permit carrying passengers

m.

Night I"fylng ----- and--InstrumenP --

Autorotations at Night, in Clouds, etc.

wed,

Once you get the hang of that, try slowing down to 40 RIAS and turning, climbing and descending. Be careful of letting the airspeed get too low, and also be prepared for very small angles of bank to generate large heading changes.

Changing Airspeed Change the airspeed while m a i n k i h g altitude, h m 40 HIAS to VH and back.

Pu~iirngIt All Together The best training exercise for learning to fly on instruments is the coordinated climbing turnor descent. Basically, starting a t a convenient airspeed and on a cardinal heading (East or South, for example) and at an easy-+remember altitude (2,50OYA1MSL,for example), start a climb at 500 feet per minute and then start a standard rate (3" per second) turn. Every minute you should be 500 feet higher, and 180" different in heading. Work at it until you can be sure of the heading being 30" different every 10 seconds, and the altitude being 125' different every 15 seconds. Minor corrections to power, rate of turn and so on will be needed. This exercise will sharpen cross check skills immensely, and make followingradials and ILS bars a piece of cake.

Ik3adv-t

mc

This is a touchy subject. There are numerous schools of thought on this, and lots of things to think about. Lots of helicopters which are very well equipped to fly in IMC crash while trying to stay in VMC conditions. Consider your options before you set out on a trip. If you're in an area without many obstacles, and you're not likely to encounter icing conditions, and you're current in instrument flying, and not likely to mess up instrument approach procedures, then I would seriously think of climbing to a minimum safe altitude rather than trying to scud run. rve had to do this three times in my relatively tame career. Each time, it was very straightforward. We had encountered deteriorating weather, and had the necessary conditions to be able to climb into IMC. We contacted the local controlling authority and were given permission to proceed IF'R. (In one case we were a long way away, and climbed to the minimum enroute altitude for that area and tried to contact Air Traffic Control we were so far away, it took us a while before we could get in touch with them, but we were well below any altitude they would have been using in that area anyway). Otherwise, no problems a t all. ATC weren't upset a t us, there was no grand inquisition to ask us why we did this, and everyone was happy I've done this in several countries, and no-one has complained about it. I was certainly happy to have this capability I ability! In some organizations, IMC is the last resort, and pilots are led to believe that using the procedure just described is a career-ending move. Far from it!

-

Just like we have no reliable long-term warning of when engines will fail, we have no guarantee they will not fail at night or other times of poor visibility. Even multi-engine helicopters can have occasion to use autorotations if they have fkel problems (a distinct lack of it, for example), or a tail rotor failure. What to do if the need arises when you are not sure of the ground underneath, and have no choice about autorotation? The answer is in a little known technique called the 'constant attitude autorotation', invented (I think) in the UK. The name derives from the constant attitude maintained throughout the maneuver, although the name 'constant airspeed' might just as well be used - there is no flare a t the bottom. Typically, this autorotation uses a lower-than-normal airspeed, about 35 to 40 KIAS, plus half the windspeed, with the helicopter facing into the surface wind*. Maintain this airspeed all the way to the time of pulling collective pitch, and if any margins are to be given, err just slightly to a higher airspeed. Slowing below this slow airspeed quickly increases the rate of descent and makes it d3Yicult to regain (or even hold) airspeed due to errors in the pitot static system. * which means it's a good idea to keep a mental note of the surfacewind direction and speed.

tnstrument Flying Rules (IFR)

Might and Instrttmmt Fiying

. The effect for most of the descent is quite serene - there is little sensation of plummeting towards the earth. This changes dramatically at about 10OYAGL,when the ground rush starts to become apparent in a real hurry. The philosophy of the constant attitude autorotation is that at night with the landing light on or in IMC (fog all the way down to low altitude), the ground would start to make its presence known a t about this point. A radar altimeter is really essential if you're going to fly in cloud for real, if only for this reason. In daylight (the best place to practice this), wait until the ground rush is really quite pronounced (at about 5OYAGL)before starting to feed in collective, slowly at first, and then as rapidly as needed. The amount of collective to apply is quite natural, but there is little room for error. Do not flare, accept the slight forward speed! It should be quite obvious to even the most casual observer that there is no point in flaring. From a technical point of view, there is not enough kinetic energy to change the flight path and it would only change the attitude on ground impact. The logic for this maneuver is something like this: a t night or in IMC, there are not enough cues for the pilot to judge height above ground for a flare to stop the rate of descent. The purpose of the flare is to stop the rate of descent and get rid of the kinetic energy of forward speed.A misjudged flare might mean hitting the ground with high forward speed as well as a vertical speed and is worse than hitting the ground with very little forward and relatively low vertical speed. So the constant attitude autorotation is a compromise. For those of you who say this is silly who would want to fly a single engine helicopter in cloud or at night - well, not only will people do it (it's normal in some militaries), but multi-engine helicopters can also have emergencies where an autorotation is the only way out. They fly at night and in cloud a lot! . -

""

-

I'm very disappointed that the Air Traffic system has not seen fit to recognize the special needs and capabilities of the helicopter. It is only within the last few years that we have seen helicopter-only instrument approaches which utilize a maximum speed on approach which is representative of the helicopter's capabilities. While this is a big step forward, there is still much to be corrected. We need to have fuel reserves which recognize that helicopters can't carry as much fuel as fixed wing airplanes, so it is impossible to be able to carry alternate fields and fuel reserves and a meaningful payload. The chances of achieving a successful approach with the slower approach speeds the helicopter uses would also ensure that less fuel reserves would be needed. One of the other reasons fixed wing aircraft carry fuel reserves, runway closure, is also less of a hazard for helicopters, as we typically don't need runways for landing. All in all, we are being hampered by yet another hold-overfrom the fixed wing world. With the advent of precision GPS approaches, perhaps it is time to revisit the fuel reserve requirement. As this book was going to print, I read that the FAA is relaxing these requirements - about time, too!

G B alld rn There is a great tendency to use a simple, hand-held GPS for a lot of helicopter flying. For VFR operations, this is a great idea (but see "Using GPS Intelligently" on page 434*). If you're planning to use GPS for IFR however, a hand-held machine can be lethal. One of the primary concerns of instrument navigation is reliability of radio navaid signals. For some of the radio navaids we use, (VOR, ILS) there are flags on the displays to tell when the signal is not correct or has been lost. For ADF, there is no flag to tell when the signal is lost, so it is necessary to listen to the audio signal during an ADF approach to tell if the signal suddenly goes away; GPS has an equivalent 'flag', and it's called RAIM, for Receiver Autonomous Integrity Monitoring, This is only found in IFR approved equipment, and its the GPS equivalent to the flags for VOR and ILS, or listening to the ADF.It tells the pilot that the required navigation accuracy for an IFR approach (0.3nm) is not available. For those of you who think this lessthan-accurate state of affairs with GPS is never going to happen, I suggest you think again. I've read lots of reports from hand-held users where the GPS was found to be up to 80 nautical miles off, with no warning. Not the sort of thing to have happen on an IFR approach in the mountains, you'll agree. So, if you're going to go IFR, get an appropriately approved GPS installation. And learn how to use it.

PdigM and lnsttumenZ Ffying -"

*-

f3

Instrument Flying --Rules -- {IFRj

: ;

" P

Just to reinforce the point, you wouldn't think of routinely using your hand-held Nav-Com transmitter with VOR receiver to do a VOR approach would you?You & remember to monitor the ADF signal when you're using that for an approach don't you?

Helicopter Only Approaches I've seen a few of these, and for the most part they help to utilize the unique capabilities of the helicopter. We need to learn from our fixed wing brethern though, as they have specialtests that must be satisfied when an airplane is approved for anything other than a 3" glideslope. We're slightly luckier in the helicopter world, in that most approach paths that are steeper than 3" don't cause a problem, but really steep ones (greater than go,for example) can be interesting to fly. The other problem with helicopter only approaches is %t they should only be carried out into the wind. Again, our firred wing brethern have a rule that anything more than a 10 Knot tailwind must be specificallyflight tested and approved. We seem to have ignored this, with the added peril that a tailwind on approach can lead to nasty things like vortex ring state. High crosswinds can also lead to some interesting crab angles a t the final stages of the approach. A lot of work needs to be done before we get to the next stage, which is-

Zero-ZeroApproaches The zerolzero approach is one where the visibility is zero, and the ceiling is zero. In other words, some pretty intense fog, This is actually extremely rare, and there is generally some vertical and horizontal visibility. We are a long way from achieving this in the helicopter world on an everyday basis. Previous comments on low airspeed sensing systems are very pertinent here, but more mundane things like how w i l l we be able to transition from the approach to a go-around, or land safely in the event of an engine failure* a t the very last part of the approach? What kind of lighting system wiU we need for the landing site? What kind of crosswind limits will be permitted? Related to this subject is the need to consider what type of helicopters we are going to permit to do these type of approaches. If we slick to our major concern of engine failures (and this itself may not be the real problem in helicopter flying) then it is probable that only multi-engine helicopters will be permitted to conduct these approaches. Even if we then accept that Category A helicopters have good single engine capabilities, they aren't able to fly away from all conditions the flight profiles are set up to make sure the helicopter can land safely from a failure on very short final, for example. So, if we have a zero-zeroapproach to the hover at some point the helicopter is going to be committed to land if an engine fails. So, being committed to land, it follows that we need guidance to touchdown (or some other low visibility) in case the visibility is really that bad. Given the capabilities of GPS and most especially Differential GPS (DGPS), this should be no problem. I've seen some zero-zero approaches in helicopters that were absolutely spectaculaq and if implemented would truly unlock the potential of the helicopter. A lot of work needs to be done to make this reality.

-

Single Pilot lFR The helicopter, being a more expensive machine to operate, has more impetus to have only one pilot on board, in order to maximize the number of revenue seats on the machine. So what about single pilot IFR? I find it interesting to note that for IFR,we r e q d e two of nearly anything. (?"he US is the only country to permit IFR in single engine helicopterswith passengers on board, although single engine fixed wing IFR with lots of restrictions is permitted in several countries.) We require two navigation aids, two altimeters, two radios, and so on. But the part that has been shown to fail most frequently, and in the most un-explained way, the part with the single information processor (brain) and single engine fieart), is permitted to operate without a

* Not well known or understood.It's buried in the airframe certificationrules, and not spelled out in Flight Manuals. -f You will note that I ' m not wen considering single engine helicopters for zerolzem approaches.

w? lnstnrment Flying Rules (IFR) a+.-

# ;a.-

-.--

"---

NigM and fnstrummt Rylng--

backup. After I read of a pilot flying IFR by himself with passengers, at night, having a heart attack and landing the aircraft safely at a conveniently close-by airport, I really questioned this philosophy

S

ry of Chapter 36

We've covered a bit of night flying and instrument flying- two things which are often considered the same in the fixed wing world. For helicopters, they are two different scenarios, and both need special trailling.