飞行员操作飞行手册Pilot Operational Flying Manual

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the engine's still going anyway. While

speed is of the essence, there is

usually time enough to verify actual

engine failure by looking at the

instruments while you're reducing to

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autorotation speed to maintain

height, certainly in a Bell, unless

you’re very heavy in a high hover

situation, such as long-lining, where

you have no time to do anything

other than dump the pole.

For all practical purposes, your

gliding distance is about equal to

your height or, put simply, what you

can see slightly above the bottom of

the windscreen. If you keep your

landing spot in the same place in that

area, your speed watch needn’t be so

critical (remember sight picture

approaches?). In fact, once you've

set your speed, keeping a mental

note of the attitude will enable you

to look out more. Loss of RPM at

the entry into autorotation is more

important—a higher angle of attack

from the new relative airflow as air

rushes up through the rotors will

cause enough drag to slow the rotors

drastically, especially if your weight is

high or air density low, meaning that

your blades will be at a higher pitch

angle anyway. Get that collective down,

and bring the airspeed back to autorotation

speed. Then accept the inevitable, that

you may hit something, so your

primary focus now is to ensure you

and your passengers' survival, that is,

to protect the cabin area as much as

possible. Of course, it would be nice

to save the whole ship, but don't

stretch the glide, for example,

towards a clear area and risk losing

the RPM, or having less control over

the rate of sink. Clear areas should

really be within a normal glide.

On this point, remember that the

helicopter is better able to cope with

a vertical rather than a horizontal

crash (oops, sorry, landing), since the

gear can usually take some

punishment, as is proven daily by

student pilots. You can use the tail

boom and main rotors, too,

especially in trees, mentioned below.

To ensure the horizontal element is

reduced, the best tactic will be to

land in a decelerating attitude, which

will mean making sure that the rear

skids hit first (this will also help you

keep straight. The reason a Jetranger

requires to be levelled during normal

autorotative landings is to preserve

the gearbox mountings, but this is

less of a consideration right now). A

couple of good reasons for avoiding

run-on landings are obstacles, and

soft ground, which would increase

your chances of nosing over, due to

the inertia of the gearbox, engine

and rotors, etc. against the drag of

the skids.

Reducing collective to compensate

for the extra drag will, of course,

increase the rate of descent, at which

point the inner 25% of each blade is

stalled, and the outer 30% is

providing a small drag force. In

other words, it is being driven:

The right hand view above is what

happens to the lifting area if you

vary the ideal speed – it moves

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towards the retreating blade side,

and when it reaches the edge, you

get your VNE for autos. The best

254 Operational Flying

lift/drag ratio in autorotation is

obtained at best endurance speed,

whatever that is (check the manual,

but most helicopters are designed

for a speed of about 45 kts).

Try to establish the cause of engine

failure—if it's fire, close the throttle,

but, if not, consider initially closing it

only to idle speed (or not closing it

at all) as the engine may be able to

provide enough power to help you

out a little, but this point is

controversial as many people think

you should secure the engine and

fuel in case the landing gets hashed

up, which may actually be caused by

a playful engine, or a fire caused by a

hot one (turbines cool down quite

fast after they are turned off). Also,

if the main drive shaft breaks in a

206 or a 407 (and others), you will

need the engine to drive the tail

rotor. However, the discussion

below will consider it closed.

Several factors may affect your rate

of descent, such as gross weight, air

density, airspeed and rotor RPM.

Changing airspeed, though, is about

the only one you have direct control

over that gives you some flexibility,

as the RPM must remain in a small

speed band to be effective—

remember that only the portions of

the blades between 25-70% of their

length provide any lift. In any case,

every 1% reduction in rotor RPM

results in a 2% loss of thrust, which

will be the same as if somebody

threw that weight in the back of your

machine. The other significant point

about keeping your RPM up

concerns the tail rotor, which runs at

a fixed speed relative to the main

rotors – if they go slower, the tail

rotor does too, and loses some of its

effectiveness.

Changes in airspeed can have

dramatic effects on the rate of

descent. If the recommended IAS is

60 knots (fairly common), for

instance, speeds of either 30 or 100

could increase RoD to as much as

3000 fpm, because the lift vector is

reduced when you alter a relatively

horizontal rotor disc, so if you want

to change your angle of approach,

don't forget to use collective to

compensate (when going for range,

you must use both collective and

speed to get the full effect—you can

pull collective until you get nasty

noises in your ear). As forward

airspeed increases, the driving region

of the autorotating blades moves

towards the retreating blade side –

the point where it meets the edge of

the rotor disc is where power off Vne

is found. If you go beyond it, your

driving region gets smaller, so your

rotor RPM will decay.

Turns will have a similar effect, but

the results will be worse if pedals are

used. Steep turns are good ways of

losing height if you find yourself

overshooting—if you are seated on

the right, turn right first, then go left,

so you have the best possible view

through the windscreen, and you

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of collective, used with some

machines to level better. Otherwise,

there should just be small pause in a

continuous movement, and you

should find the rear skids touching

the ground gently well before you

run out. Get used to the visual clues

required for the correct approach

256 Operational Flying

and flare attitude – there's no time to

look at the ASI, and the one on the

407 is dampened anyway, so is fairly

useless under these circumstances.

Get up on a nice day and practice

autos to a cloud, getting used to the

horizon's position through the

screen during descent, flare and

turns on your machine.

In every flare there is a point called

the apex, which is where the trading

off of airspeed for lift is essentially

all over and you just have to get

yourself on the ground. Put another

way, it is the point where there is no

further benefit from the flare

manoeuvre, so you may as well pull

the pitch (a little later in a 206). As

the flare ends, and the kinetic energy

of the rotors is used when the

collective is raised, the airflow

through the rotors is reversed,

assisting the level, ready to cushion

the landing with collective. This is

where correct use of airspeed during

the descent will have had the most

beneficial effects—as the kinetic

energy stored in the blades is what

slows you down, it follows that any

you have used already to slow an

unnecessarily fast descent is not

available for the final stages of

touching down.

But what if you are going into a

clearing? Or don't get that much

practice? The above method is fine,

but you need to be doing it a lot to

get it right every time. One way that

will cover both the above situations

is to start the flare very much earlier,

so that you are virtually stopped

quite high up. Then carry on as if

you had an engine failure in a high

hover, that is, dump the pole to get

going vertically downwards and haul

it all in at the end. In a vertical

autorotation, there is a phenomenon

known as dynamic stall that will help,

where an aerofoil that is rapidly

stalled can produce double the

normal lift, just for a moment,

because the breakup of the boundary

layer on top is delayed for a while, if

indeed you don’t actually create a

little vortex along it that improves

lift even further. Do not try to gain

speed, as you will split the lift vector

and increase your rate of descent.

If you're likely to be ending up in

trees, as you might if you have the

choice between them or power lines,

aim between two tops, tail first or

low, or at least moving gently

backwards. The worst thing to do is

go in nose first, because the engine

and gearbox will hit the ground

before you do. The height of the tree

is less important than the height at

which the branches start, and if you

are over them regularly, you might

like to carry a good length of rope to

help yourself get down. Having said

that, it will be easier for the SAR

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guys to pick you up from the top.

With short trees, denser areas

provide the most shock absorbency

– don't worry about branches

overlapping, as long as the trunks are

far enough to allow the fuselage to

settle and the main rotors to miss

them (actually, the main rotors can

be used as an umbrella to reduce

descent). Fewer trees in an area

actually become obstacles. Dead

ones provide no absorbency at all.

Pull the collective when you are in

the trees.

If the surface is sloping, try to land

nose up. If you flare a little, you will

increase your chances of getting it

right first time as the attitude of the

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skids will match the slope of the

ground better.

Whereas an aeroplane is better suited

to protecting the occupants from

forward impact, the helicopter is

better suited to vertical motion, so

forward movement should be

reduced as much as possible,

especially over hostile ground – the

cabin can be distorted badly just

from the couple between its forward

motion against the drag from the

skids on the ground. As it happens, a

zero speed touchdown at 1500 feet

per minute on soft terrain would

probably not result in many injuries.

If it looks like you are going to hit

hard vertically, do not lean forward,

but brace your back against the

complete area of the seat to maintain

a natural curvature. Spinal injuries

are most often caused by flexing.

In fact, there are two broad types of

injury to consider. Contact injuries

arise when you hit something, or

something hits you (such as loose

articles in the cockpit). Decelerative

injuries result purely from motion of

the body, or loads applied through

seats and safety belts. They are

internal in nature, such as the spinal

injuries mentioned above, or in the

abdomen. Other injuries, like

burning, may occur after the crash.

Although it helps to crash as slowly

as possible, dissipation of whatever

speed you have is the main

consideration, and this is never

usually uniform. Every obstacle the

fuselage hits is responsible for a peak

deceleration and the potential for

damage to the people inside, so it

makes sense to try and protect this

as much as possible at the expense

of rotors, undercarriage, tail booms,

etc. This is where the proper use of

shoulder straps is important – if you

don't wear one, you will jackknife

over your lapstrap and your head will

hit the instrument panel at a speed

over 12 times that of the cockpit

deceleration. Also, when only

wearing a lapstrap, your tolerance to

forward deceleration reduces to

below 25G, from a normal total of

over 40.

Some things you can do to prevent

injuries can be done before you get a

problem, by selecting clear routes

wherever possible, and flying higher,

which increases your range of

choices (but not so high that it takes

too long to get down in a hurry).

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Once you've landed:

· Close throttle & fuel valve

· Turn off Battery

· Evacuate aircraft

Power-On Recoveries

These are an increasing trend in

many companies, intended to reduce

the number of autorotative accidents

when practicing engine-off landings,

and ensuring that some pilots don't

get to practice real ones for years on

end. The examiner is looking for a

correct entry into autorotation and

flare initiation height, but, thereafter,

the process is a coordination

exercise, and you should treat it as a

rather fast transition to the hover—

be careful not to check and level, or

you can expect a large torque spike

(in a 206, anyway), and looking at the

torquemeter is not what you want to

be doing at that late stage.

258 Operational Flying

Tail Rotor Failure

When the tail rotor fails, it will be in

varying degrees of positive, neutral

or negative pitch, depending on what

you were doing at the time, so if you

can remember what it was, you will

have an idea of the state of the

pedals. Unless it’s a drive failure, or

you lose some of the components,

the chances are that you won’t

discover the problem until you

change your power setting, as it’s

very unlikely you’ll be flying along in

the cruise, for instance, and find a

pedal forcing itself completely over

to one side, as simulated by

instructors on test flights, unless you

have a motoring servo or similar, in

which case your problem is

hydraulics and not the tail rotor,

although the effect might be the

same. More typically, you will be in a

descent, climb, cruise or hover, with

the pedals where they should be and

won’t move when you want to do

something else. When descending,

for example, in the AS350, you will

have more left pedal (more right in

the Bell 206), both of which will aid

the natural movement of the

fuselage against the main rotors. The

pedals would be in a neutral position

if you were flying at medium to high

speeds, and the power pedal would

be forward in high-power situations,

like hovering. In any case, the spread

between the pedals is not likely to be

more than a couple of inches either

way, certainly in a 206 – try an

autorotation properly trimmed out

to see what I mean. You will notice

the same in the hover. My point is

that the situation may not be as bad

as frequently painted.

In fact, landing with a power pedal

jammed forward is relatively easy,

since the tail rotor is already in a

position to accept high power

settings (try also using a little left

forward cyclic in a 206, and pivoting

round the left forward skid), so you

may be able to come in very slowly

and even hover. If the pedals jam the

other way (right in a 206), look for

more speed because there will not be

enough antitorque thrust available.

A drive failure, on the other hand, or

loss of a component, will cause an

uncontrollable yaw, and maybe an

engine overspeed, so the immediate

reaction should be to enter

autorotation, keeping up forward

speed to maintain some directional

control (which is difficult in the

hover, so try to get one skid on the

ground at least), if you have time. If

you lose a component, the C of G

may shift as well, although an aft one

in general has been found to help

with this situation. Pilots who have

been there report that there is a

significant increase in noise with a

drive shaft failure, and that the

centrifugal force in the spin is quite

severe. Anyhow, an autorotation is

certainly part of the game plan, and

as speed is reduced towards

touchdown, you will yaw

progressively with less control

available in proportion, so it may be

worth trying to strike the ground

with the tailwheel or skid first (if

you’ve got one), which will help you

to keep straight—according to the

JetRanger flight manual, you should

touchdown with the throttle fully

closed, as you would if the failure

occurs in the hover, to stop further

yaw when pitch is pulled to cushion

the landing.

However, in some circumstances,

such as the cruise, sudden

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movements like this may not be the

best solution. If you can reduce the

throttle and increase the collective,

this would reduce the effect of the

tail rotor at the same time as keeping

the lift from the main rotors, as does

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beeping down to the bottom of the

governor range (difficult in most

AS350s or Gazelles, where the

throttle is not on the collective). The

tail rotor is there to counteract

torque, so if you give it less work to

do, you will be more successful.

Otherwise, you might find a power

and speed combination that will

maintain height until you find a

suitable landing area, then you've got

as much time as your fuel lasts to

solve the problem. Don't forget that

the cyclic can be useful for changing

direction and enabling you to fly

sideways to create drag from the tail

boom and vertical stabiliser, for

example. It's the sort of situation

where it pays to be creative

sometimes. After all, the aim is to

walk away, not necessarily to

preserve the machine. Two other

things you can try if you finally make

the hover—stirring the cyclic so as

to dump lift, and pumping the

collective to produce a similar effect.

Both will serve to confuse the

machine enough so it forgets which

way to turn! With a jammed power

pedal (left, in a 206), what also works

is to crab in the way the machine

wants to, come to a high hover

sideways and let the machine settle

by itself. You will find very little

input is required by you.

If you want to run-on for landing,

get the wind and/or nose off to the

retreating blade side, so the fuselage

is crabbing, and control your

(shallow) descent with a

combination of throttle and

collective, applying more of the

latter as the throttle is closed just

before touchdown so you run on

straight. Note that some helicopters

(such as twins, or the AStar) won’t

let you use the throttle as precisely as

that. Not only that, you may well be

so busy that worrying about minor

details like the wind’s exact quarter

will be the last thing on your mind.

For a running landing, on most

machines, about 30% torque at 30

kts will put you in a good position

for landing at 30 ft, and a little

power at the last minute will put

your nose nicely straight. For the

non-power pedal, keeping straight

involves either more speed or less

power, and you have to accept more

of a run-on.

In an AStar (or TwinStar), the

recommendation in the book is to

come in with some left sideslip (i.e.

crabbing right). Slow down until the

nose starts to move to the left, and

you have your landing speed.

Loss of Tail Rotor Effectiveness

This is sometimes known as tail rotor

breakaway, or a stall, which is not

strictly correct, as thrust is still being

produced – it’s just not enough for

the task in hand. It shows up as a

sudden, uncommanded right yaw

(with North American rotation), and

has amongst its causes high density

altitudes, high power settings, low

airspeeds (below about 30 kts) and

altitudes, and vortex ring, not

forgetting turns in the opposite

direction of blade rotation. Your

helicopter will be more susceptible

to it if the tail rotor is masked by a

tail surface, like a vertical fin, and it

can be especially triggered by tail and

side winds (this is actually a

260 Operational Flying

significant reason for maintaining

main rotor RPM – as the tail rotor

runs at a fixed speed in relation to it,

lower NR will reduce tail rotor

effectiveness in proportion).

Recovery in this case comes from a

combination of full power pedal,

forward cyclic and reduction in

collective, or autorotation.

Prevention lies in keeping into wind

and always using the power pedal

(left in a 206 or one with similar

blade rotation). If you use the other

one, not only will the fuel governor

ensure that the aircraft will settle

after a short time (using the power

pedal by itself makes it climb), but a

large bootful of the power pedal in a

fast turn the other way will create a

large torque spike.

Jammed Controls

Aside from jammed tail rotor pedals,

discussed above, your cyclic or

collective may jam as well. Both

cases will result in a run-on landing.

To get out of a jammed collective,

just bring the speed right back. This

will cause you to descend, and you

can use your speed to aim at the

ground. Hopefully, your cyclic will

jam in the centre. Anyway, leaning in

the desired direction (passengers as

well) will cause enough of a shift in

C of G to turn the ship in the

desired direction.

Hydraulic Boost Failure

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Indicated by feedback forces in the

controls, which will be negligible

when they are held in a fixed

position. Hopefully, your failure will

be just from fluid leakage, but it

could be a hydraulic pump drive

failure—in a JetRanger, this will be

confirmed by looking at the NR

gauge, as the pump is driven from

the transmission. Note that the

Hydraulic CB sometimes relates to

the switch as the idea is to have it

fail-on – electricity keeps the switch

off, so if it fails, it stays on and so do

the hydraulics. Reduce forward

speed and control inputs to a

minimum, making necessary

movements at a rate of travel not

faster than one full displacement,

stop to stop, per second. The failure

won't be sudden, so switch off early

to keep fluid in the system.

If you ever have to leave the

controls of a helicopter with the

engine running, do not switch the

hydraulics off, but use the control

locks only, in case the controls

motor by themselves.

Overpitching

In a helicopter, overpitching is

where the rotor RPM are too low to

maintain flight, giving the impression

of "labouring". It's the nearest

equivalent to stalling and is

commonly caused by being

overweight for the particular

conditions. Reduce power to

maintain RPM.

Engine Handling

One of the biggest things to unlearn

when transitioning from piston to

turbine is to keep your finger on the

starter button once things start

happening (with a piston, you tend

to take your finger off straight away

when the engine starts). You take

your finger off when the engine

becomes self-sustaining. Before then, it

relies heavily on the battery or start

trolley to keep it turning. It follows

that, if the battery is weak to start

with, the engine won't spin as fast,

Techie Stuff 261

the airflow is reduced, the whole

process becomes hotter and you

could melt the back end with a hot

start. You should always check the

voltage available from the battery

before starting a turbine engine. A

hung start exists when the engine fails

to accelerate to normal idle RPM. It

just sits there, weakening the battery

and leading to a hot start.

Pulling full power just because it's

there is not always a good idea.

Limitations may be there for other

reasons—for example, the

transmission might not be able to

take that much, which is why you

can’t go faster than 80 kts in a

Jetranger when pulling more than

85% torque (actually, in this case, the

transmission ends up in a strange

attitude). Excessive use of power will

therefore ruin your gearbox well

before the engine (and will show up

as metal particles in the oil). Many

turbine failures are the result of

pulling too many cycles from

minimum to maximum Ng, so if you

don't need 100% torque, it's best not

to use it. It's also best not to reduce

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the collective lever of your

helicopter to the bottom when

descending, either, and to make

power changes gently, avoiding over-

and undershoots.

Maximum Continuous Power is the

setting that may be used indefinitely,

but any between that and maximum

power (usually shown as a yellow arc

on the instrument) will only be

available for a set time limit.

While I'm not suggesting for a

moment that you should, piston

engines will accept their limits being

slightly exceeded from time to time

with no great harm being done.

Having said that, the speed at which

the average Lycoming engine

disintegrates is about 3450 RPM,

which doesn't leave you an awful lot

of room when it runs normally (in a

Bell 47, anyway) at 3300! Turbines,

however, are less forgiving than

pistons and give fewer warnings of

trouble because of their closer

tolerances. This is why regular power

checks are carried out on them to

keep an eye on their health. The

other difference is that damage to a

piston engine caused by mishandling

tends to affect you, straight away,

whereas that in a turbine tends to

affect others down the line.

In a turbine-engined helicopter,

power is indicated by the torquemeter.

Apart from sympathetic handling,

the greatest factor in preserving

engine life is temperature and its rate

of change. Over and under leaning

are detrimental to engine life, and

sudden cooling is as bad as

overheating—chopping the throttle

at height causes the cylinder head to

shrink and crack with the obvious

results—the thermal shock and extra

lead is worth about $100 in terms of

lost engine life. In other words, don’t

let the machine drive the engine, but

rather cut power to the point where

it’s doing a little work. This is

because the reduced power lowers

the pressure that keeps piston rings

against the wall of the cylinder, so oil

leaks past and glazes on the hot

surfaces, degrading any sealing

obtained by compression. The only

way to get rid of the glaze is by

honing, which means a top-end

overhaul. For the same reasons, a

new (or rebuilt) engine should be

run in hard, not less than 65%

power, but preferably 70-75%,

according to Textron Lycoming, so

262 Operational Flying

the rings are forced to seat in

properly. This means not flying

above 8000 feet density altitude for

non-turbocharged engines. Richer

mixtures are important as well. Also,

open the engine compartment after

shutting down on a hot day, as many

external components will have

suddenly lost their cooling. With

some turbine engines (like on the

AStar), you have to keep a track of

the number of times you fluctuate

between a range of power settings

because of the heat stress.

In the cruise, better fuel

consumption may be obtained at

slower speeds and lower power

settings, at the cost of extended

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running time, so you might not really

save that much. For example, leaning

to 10° lean of peak Exhaust Gas

Temperature (EGT), without

exceeding the maximum, loses about

5 knots. Typically, EGT probes are

fitted to one cylinder of the engine,

which is not necessarily the one that

reaches peak temperature first, even

though it may end up as the hottest,

so a margin of 25° rich of peak may

still not be enough to stop another

cylinder from getting too close to

peak for comfort, or even lean.

One consideration with using low

power when it's very cold is that the

engine may not warm up properly

and water that forms from

combustion may not evaporate, so

oil won't lubricate properly.

The reason the temperature cools

either side of the peak reading is that

on the one hand (rich), there is too

much fuel and, on the other (lean),

there is too much air (having said

that, the hottest CHT is between 25-

50° rich of peak EGT, because that's

where the peak cylinder pressure

occurs, with a high rate of heat

transfer to the cylinder head, so you

need to lean past it). However,

although being lean of peak works,

there is much more potential for

causing damage to the engine if it is

mismanaged – it needs more

monitoring to be used effectively, as

the temperature at the exhaust will

still be high, which is not good for

the valves, particularly acute with

high performance turbocharged

engines – Australian authorities

found that leaning causes lead

oxybromide deposits to cling to

various parts inside the combustion

chamber, which could become

hotspots and cause detonation (the

lead appears as a result of chemical

changes in avgas as it burns). At

richer settings, the lead either doesn't

form or is swept out of the cylinder

(this may be true for lower

performance engines, too).

Don't forget to enrich the mixtures

before increasing power when at

peak EGT or when increasing to

more than 75% power. Move the

engine controls slowly and smoothly,

particularly with a turbocharged

engine. Harsh movements that (on

older engines) will result in a cough

and splutter and having no power

can be embarrassing.

Although many flight manuals state

that as soon an engine is running

without stuttering it's safe to use it to

its fullest extent, try warming up for

a few minutes before applying any

load, at least until you get a positive

indication on the oil temperature

(and pressure) gauges. This ensures a

film of oil over all parts.

Even better, warm it before you start

it, because the insides contract at

different rates – in really cold

Techie Stuff 263

weather the engine may have the

grip of death on the pistons and

cause some strain when you turn the

starter. Equally important is not

letting an engine idle when it's cold,

as it must be fast enough to create a

splash (about 1,000 RPM is fine).

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After flight, many engines have a

rundown period which must be strictly

observed if you want to keep it for

any length of time. As engines get

smaller relative to power output,

they have to work harder. Also, in

turbines, there are no heavy areas to

act as heat sinks, like the fins on a

piston engine, which results in

localised hotspots which may

deform, but are safe if cooled

properly, with the help of circulating

oil inside the engine (75% of the air

taken into a turbine is for cooling

purposes). If you shut down too

quickly, the oil no longer circulates,

which means that it may carbonise

on the still-hot surfaces, and build

up enough to prevent the relevant

parts from turning. This coking up

could sieze the engine within 50

hours or less.

If the starter light remains on after

you release the starter button on a

piston engine, you should shut it

down, as it indicates that the starter

is still engaged with the engine and is

being driven by it.

The "LL" in 100LL stands for low

lead, but there is still about four

times more than is needed. As well

as the lead (in the form of TEL—

Tetra-Ethyl Lead), a scavenging agent

(Ethylene DiBromide, or EDB) is also

added to ensure that the lead is

vapourised as far as possible, ready

to be expelled from the cylinder with

other gases. Unfortunately, this is

not 100% successful, but the results

are best at high temperatures and

worst at low ones - the unwanted

extras result in fouling of spark

plugs, heavy deposits in the

combustion chamber, erosion of

valve seats and stems, sticking valves

and piston rings and general

accumulation of sludge and

restriction of flow through fine oil

passages, so it makes you wonder

which is worse (in fact, petrol is not

the only fuel you can use – Japanese

Zeros used to outfly American

aeroplanes because they used ethyl

alcohol). TEL, by the way, is actually

a liquid gas, which was developed by

a subsidiary company (Ethyl, Inc)

belonging to General Motors and I

G Farben sometime before WWII.

In June, 1940, just before the Battle

of Britain, it could only be obtained

through the Anglo-American Oil

Company, or Esso - when the fuel

was changed from 87 octane to 100,

German pilots got a real surprise,

because the Spit could suddenly

climb a whole lot quicker.

Oil

An engine that is not used enough

develops corrosion very quickly on

the inside, and rust flakes, which are

very abrasive, will circulate when the

engine is started, which is why you

have to change the oil even when

you don’t fly a lot. Another reason is

an increased water content, which

will have an acidic effect once it

mixes with the byproducts of

combustion. The most wear takes

place in the first seconds of a cold

start, after the oil has been allowed

to settle. Priming will wash whatever

is left off the cylinder walls, so don't