[Comments or questions]
Copyright © 1996-2001 jsd
Takeoff is optional.
Landing (sooner or later) is mandatory.
The most important part of taking off is making the
decision to do so. Discussion of decisionmaking (section 13.8)
will be postponed until after we have discussed normal takeoffs
— not because it gets lower priority, but just because it's hard
to appreciate an abnormal situation unless you understand the
13.1 Simplest TakeoffThis section presents a ``case study'' of
a takeoff in which the pilot
has to do remarkably little work. (In subsequent sections we
will describe ways in which you can get better results by doing
a little more work.)
This procedure applies when you have a well-paved runway with plenty
of length and no obstructions to worry about. As shown in figure 13.1 and table 13.1, part way
down the runway you rotate so that the pitch attitude is about 7.5
degrees. You then just hold that pitch attitude. Period.
Remarkably, at the moment of liftoff, the pilot doesn't have to do
anything. The plane lifts off when it is ready, that is, when it has
enough airspeed to support its weight at a 12 degree angle of attack.
This will occur a few knots below VY, assuming VY corresponds to
a 8.5 degree angle of attack (which is pretty typical; see also
section 2.4). To construct the last phase of the scenario
(asymptotic climb), I made some additional assumptions, namely that
your engine is just powerful enough to provide a climb gradient of
5° at a speed 10% above VY. In particular, I imagine
climbing out with airspeed = 83 knots and vertical speed = 735 feet
per minute, in an airplane where VY is 75 knots. These are
certainly believable numbers.
Angle of Attack
Angle of Climb
||6% below VY
||10% above VY
Note that before liftoff, most of the engine power is going into
increasing your kinetic energy; a little is needed to overcome drag,
and none is going into potential energy. Then, in the initial climb,
we have a funny situation where we are climbing and
accelerating at the same time.
Finally, in the asymptotic climb phase, most of the power is going
into potential energy; some is needed to overcome drag and none is
going to increase airspeed.
The technique just described is smooth, simple, and
elegant, but it has drawbacks. It does not give optimal climb
performance (see section 13.3), it can cause
problems if there is a gusty wind (section 13.2)
or a crosswind (section 13.5), and it can cause
problems if climb performance is impaired for any reason (section 13.8.1 and section 2.9).
13.2 Normal TakeoffImagine that you are using the simplified technique of the previous
section, that is, rotating early and letting the airplane ``fly itself
off'' whenever it is ready. Then imagine that just after liftoff, a
gust of wind comes along and robs you of a few knots of airspeed.
This will cause the airplane to settle back onto the runway. This is
not elegant. To get around this, use a different procedure: do not
rotate until the airplane has a
few knots more than the liftoff airspeed. This means that liftoff
will occur right then, while you are rotating. It also means that by
the time you are airborne, you can stay airborne even if you lose a
Here is a second refinement: Most runways are not perfectly smooth. If
the nosewheel hits a bump at 50 knots, it is likely to knock the nose
of the airplane into the air, which has several disadvantages: (1) It
will cause your passengers to be bounced around more than is
necessary. (2) It could cause a premature liftoff. (3) It causes
unnecessary wear and tear (and possibly outright damage) to the
airframe. Therefore, you can
semi-rotate. That is, fairly early in the takeoff roll
you can rotate to a pitch attitude of 3 degrees or so. This is
enough to get the nosewheel slightly off the ground, but not so
much that the airplane will lift off (at any reasonable speed),
and not so much that the nose will obstruct your vision (in most
airplanes). This semi-rotation involves a pretty tiny pitch attitude
compared to, say, proper landing attitude. When the airspeed
reaches VX or thereabouts, you should lift off,
by rotating another few degrees.
Finally, here is a third refinement: You know that
the airplane will climb more steeply at VY than
it will at a higher airspeed. Therefore, during the initial climb,
you should watch for the point where the airplane reaches VY.
At that point, you should make a pitch adjustment: increase the
pitch attitude a small amount (another 2.5 degrees, according
to the numbers in our scenario) and trim to maintain VY.
The whole scenario is depicted in figure 13.2
and table 13.2
The last phase of this scenario assumes your engine can sustain
a 6 degree climb gradient at VY. In particular,
I imagine 800 feet per minute at 75 knots.
Angle of Attack
Angle of Climb
|Just after rotation & liftoff
||just above VX
In the figure, the dotted-line flight path and the uncolored airplane
show the results you would have obtained using the simplified
procedure described in the previous section. Remember that by
climbing out at VY you gain more altitude (per
unit time) than you would at any other airspeed.
* Flaps for Normal TakeoffExtending the flaps for takeoff will improve
your ability to see over the nose. This is because it increases
the incidence; therefore the airplane will fly at a lower pitch
attitude (for any given angle of attack). If the Pilot's Operating
Handbook recommends flaps for a short-field or soft-field takeoff,
there's no law against using them even when the field is long
* Perceiving the AirspeedChoosing an attitude and letting the airplane ``fly itself
off'' as described in the previous section has the advantage
that you don't need to look at the airspeed indicator, meaning
you can devote all your attention to outside references. However,
this can get you into trouble if you choose the wrong attitude
(see section 2.9). Airspeed, not attitude, is your
best information about angle of attack (section 2.12).
At the opposite extreme, certainly it is not a good idea to
devote all of your attention to the airspeed indicator.
Fortunately, you can use your eyes (to
perceive your speed relative to ground references), your ears (to
perceive the sound of the engine and the
sound of the wind on the airframe), and your fingertips (to perceive the forces on the yoke). This means you
can get qualitative information about airspeed while keeping most of
your attention focused outside. Every so often, though, you should
glance at the airspeed indicator to supplement the qualitative
information with quantitative information.
13.3 Obstructed-Field TakeoffThis section describes the procedure to use when you have a
well-paved runway with an obstruction relatively nearby in the
Plan the takeoff carefully. Take into account density altitude,
runway slope, headwind or lack thereof, et cetera. Make sure you know
the value of VX under these conditions, and choose a suitable
rotation speed VR as discussed below.
Use the proper flap settings, as specified in the Pilot's Operating
Handbook. Here's a useful cross-check: on most light aircraft, when
you extend the flaps for an obstructed-field takeoff, you will observe
that the angle of the flap matches the angle of a fully-deflected
Start at the beginning of the runway. If the taxiway leads you onto
the runway some
distance from the beginning, you will have to back-taxi on the runway,
back to the very beginning.
Open the throttle smoothly, but not so slowly that you use up
significant amounts of runway before the engine reaches full power.
Some people advocate using the brakes to hold the
until the engine comes up to full power, but this is rarely necessary;
if you open the throttle properly the airplane will move only a few
feet while you're doing so.2
As shown in figure 13.3 and
table 13.3, you should choose a
rotation speed VR at or near
VX — that is, quite a bit
higher than what you would use for a soft-field takeoff (section 13.4) or even a normal takeoff. The idea is to use the
wheels to support the weight of the airplane until you have built up a
lot of energy. It's OK to semi-rotate a little bit, to take some load
off the nosewheel, but you don't want the wings to be producing
significant lift until you're ready to climb away. Then rotate
smoothly to the ``climb-out'' pitch attitude, whereupon the airplane
will lift off immediately. Climb away at VX. Trim for VX.
After you have cleared the obstruction, you
can accelerate to VY. Finally, after you have reached a
comfortable altitude, you can accelerate to
``cruise climb'' speed and trim again.
In the last phase of the example scenario, I imagine a climb rate
of 780 fpm at 63 knots, which gives a climb gradient of 7 degrees.
Angle of Attack
Angle of Climb
In the figure, the dotted-line flight path and the uncolored airplane
show the results you would have obtained following the normal-takeoff
procedure, that is, accelerating while climbing and then climbing at
VY. Note that using by using obstructed-field procedure, you have
not climbed as high, but you have better obstacle clearance because
you have not flown nearly so far horizontally.
It may seem paradoxical that you get better obstacle clearance by
staying on the runway longer, but it's true. The rationale is
as follows: You want to pass over the obstruction at a reasonable
altitude with a reasonable airspeed. This requires a certain amount
of energy. To maximize energy you want to minimize drag throughout
the maneuver. Keeping the airplane on the runway until reaching a
high speed is rough on the airplane, but supporting its weight with
the wheels usually involves less drag than supporting its weight with
the wings. To say it another way: rolling resistance is less than
induced drag, unless the field
is quite soft or bumpy.
Once airborne, you want to climb at VX for reasons discussed in
The idea of choosing VR to be equal to VX is only an
approximation. There are exceptions:
Still, for typical circumstances, choosing VR at or near VX is a
For example, if you are facing a 20-foot-high billboard that
is the only obstruction in the area, it is theoretically logical to
zoom over at a speed several knots below VX, then dive back
down on the other side.3 Short-term
altitude gain (as given by the law of the roller
coaster) is more important than long-term rate of climb (as
given by the power curve).
- On the other side of the coin, if the elevation of your
departure airport is near the absolute ceiling of your airplane (so
that you will have very little rate of climb once airborne) and if the
runway is long and well-paved but obstructed, then it makes sense to
say on the runway (or at least in ground effect) until the speed is
well above VX.
* Skimming versus Wheelbarrowing or Flap-PoppingThe procedure outlined above (staying on the runway at high speed,
with the flaps extended) may not be possible in your airplane.
Depending on the incidence of the wings, the airplane may fly
itself off well before you reach the desired rotation speed.
Usually the best way to deal with this situation is to let the
airplane come off the ground, and then fly along in ground effect,
rather like a soft-field takeoff.
Another possible procedure (which is usually not recommended) is
to keep the flaps retracted until you are ready to leave the runway.
Less flaps means less incidence. A big disadvantage is that
``popping'' the flaps like this increases your workload at a time when
there are lots of other things you should be attending to. Another
disadvantage is that you run the risk of extending the flaps past the
takeoff position to the landing position, creating lots of drag, which
is really not what you want in this situation. If your POH calls for
this procedure, go ahead, but be careful. Make sure you have some
sort of detent to block inadvertent over-extension.
An ever worse situation arises if you try to keep the plane on the
ground by pushing forward on the yoke. This is called
wheelbarrowing. What happens is that while you are holding the
nose wheel down, the main wheels come off the ground. You are
counteracting the incidence with a negative pitch attitude. The
steering becomes dangerously unstable. There is also a risk of the
propeller striking the ground.
13.4 Soft-Field TakeoffSometimes you want to get the airplane airborne at the lowest possible
using the shortest possible takeoff roll. For example, gooey
mud on the runway will cause tremendous amounts of friction on
the wheels. The sooner you become airborne, the sooner you are
free of that friction and the better you will be able to accelerate.
Additional reasons for using soft-field procedure will be given
The procedure is as follows: Extend the flaps as
recommended by the manufacturer; in the absence of a specific
recommendation, extend the flaps so that they just match a fully
down-deflected aileron. The idea is to get the most coefficient
of lift without undue drag.
At the beginning of the takeoff roll, pull the yoke
fully backward. Early in the takeoff roll, the nose will
rise, as indicated in figure 13.4. Allow it to rise
to the pitch attitude that corresponds to the stalling angle of
attack, or slightly less. This is typically about 15 degrees
To maintain this pitch attitude as the aircraft accelerates,
you will have to gradually let the yoke move forward. You will
become airborne at a very low airspeed — roughly the stalling
speed.4 If you were to maintain the liftoff
attitude, a typical airplane will accelerate poorly while climbing
poorly, but that's not what we want. (A lower-powered airplane
might get into a situation where it can neither accelerate nor
climb.) Instead, gradually lower the nose, so that you fly parallel
to the ground, remaining one foot above the ground. As the aircraft
accelerates in ground effect, the required
angle of attack will decrease, so you will see the pitch attitude
get lower and lower.
There are two ways of completing the maneuver.
You may be surprised at how well soft-field procedure
works. Just after liftoff, the airspeed is extremely low. In
ordinary conditions of flight, your airplane might well have a
negative rate of climb at that airspeed — yet in this case it
not only maintains altitude, but accelerates. The special ingredient
in this case is ground effect: a wing produces very little induced
drag while it is in ground effect (that is, roughly, within one
wingspan or less of the ground) for reasons discussed in
- If the field is unobstructed, remain in ground
effect until the pitch attitude (and angle of attack) have decreased
to their normal takeoff values, as discussed in section 13.2.
Then climb while accelerating to VY just as
in the normal takeoff .
- If, however, there are obstructions, it is better
to remain in ground effect until the speed approaches VX,
then raise the nose and climb out while maintaining VX
as in the obstructed-field takeoff (section 13.3).
Just after liftoff using this procedure,
The engine is producing full power, so if none of
it goes into drag and none of it goes into climb, the airplane
will accelerate like crazy.
- there is no rolling friction
because the wheels are not touching the ground;
- there is very little induced drag because you are in ground effect; and
- there is very little parasite drag because you are moving slowly; and
- no power is being used for climb because you
are moving horizontally.
There are many situations where this procedure is
In all cases you must be careful to remain in ground effect until you
have accelerated to a proper climb speed. If you try to climb at the
liftoff speed you will have a big problem: in many cases, you will
be unable to climb out of ground effect. That is, as soon as you
climb to a height where ground effect is no longer significant, the
induced drag will become so large that you will be unable to climb
- If the runway is covered with mud, tall grass,
sand, or snow, there can be troublesome amounts of friction against
the wheels. Soft-field procedure allows you to transfer the airplane's
weight from the wheels to the wings as early as possible, decreasing
friction and improving acceleration.
- If the runway is rough and bumpy, the problem
is not so much friction, but rather damage from hitting a bump
at high speed. The sooner you lift off, the less harm to the
airplane. Remember, the force involved in hitting a bump goes
like the square of the groundspeed.
- Suppose the runway is perfectly smooth and firm,
but very short — and suppose it is surrounded by open fields with
lots of bumps but no serious obstructions. You can become airborne
over the runway, and then accelerate in ground effect over the
- Suppose you are attempting an ordinary takeoff
from an ordinary field, but due to a gust (or perhaps even a lapse
in pilot technique) you become airborne at a too-low airspeed.
The best strategy is to accelerate in ground effect; you don't
want to re-contact the runway (especially if there is a crosswind)
and you don't want to try climbing at the too-low airspeed.
* Brief the PassengersIf you have passengers aboard who haven't seen a
soft-field takeoff before, give them the courtesy of an explanation.
Otherwise, they may find the procedure extremely disturbing.5 Just tell them
you will lift off at a low airspeed and they fly horizontally
for a few moments while you accelerate to the optimal climb speed.
Tell them that (a) this is standard procedure for getting best
performance, and (b) it minimizes jolts to the passengers.
* Maneuver by Reference to the Edge LineWhereas in a normal takeoff you can guide the airplane
by looking out the front, in a soft-field takeoff the nose will
block your view during most of the maneuver. Therefore you must
use the edge of the runway as your reference. Practice
this skill during taxi. You will need this skill for landings
and for soft-field takeoffs, but those aren't the best times to
be learning it.
13.5 Crosswind TechniqueThere is not a ``crosswind procedure'' that you would use
instead of normal procedure, soft-field procedure, or
obstructed-field procedure. Rather, you use crosswind technique
in conjunction with such procedures.
A crosswind takeoff is not as tricky as a crosswind
landing, but it does call for some special care. Consider the
following scenario: You are trying to take off in gusty conditions
using the (over)simplified techniques of section 13.1.
You've already rotated, and are accelerating toward liftoff speed
with the wings level. As the speed increases, the wings produce
more and more lift, lightening the load on the main wheels. The
wind is still blowing against the side of the fuselage as strongly
as ever. The ability of the wheels to provide a sideways
to resist the wind is proportional to the downward load
on the wheels.6 If you keep the wings level, there will
come a point — prior to liftoff — where the wind overpowers the
wheels and blows the airplane to the side, scraping the tires
across the runway.
So, here are the correct techniques for handling
a crosswind takeoff.
Regarding rudder usage: To counteract the
airplane's weathervaning tendency (section 8.11),
you must press on the downwind pedal to keep the plane going straight.
Before rotation, both the rudder and the nosewheel contribute useful
steering. After rotation, weathervaning continues, but the rudder has
to do 100% of the steering. Therefore you can plan on applying a
little additional pedal deflection following rotation.
Regarding aileron usage, there are two options:
Again, immediately after liftoff you must make a heading change to
establish a crosswind correction
angle, so that the fuselage is aligned with the airflow.
The less-common method is more or less the
reverse of a crosswind landing. During the takeoff roll, deflect the
ailerons into the wind, to place more weight on the upwind wheel. The
ailerons create force in proportion to airspeed squared, so at the
beginning of the takeoff roll you will need full aileron
deflection. As the airspeed builds up, gradually reduce the
deflection. Rotate normally, maintaining appropriate aileron
deflection, so that the downwind wing comes up while the upwind wing
remains down. Keep the upwind wheel firmly planted, so that it can
provide friction to resist the wind. Now the airplane is in a bank,
trundling down the runway on one wheel; the sideways lift of the
serves to counteract the force of the wind on the fuselage. As the
load on the remaining wheel decreases to zero, the airplane will lift
Since the ailerons are deflected one way and the
rudder another, you are commanding a slip. Indeed, the moment
before liftoff you are (as desired) in a nonturning slip. The
moment after liftoff you are still in this slip, but it is no
longer what you need. You should level the wings and swing the
nose to windward (to get the fuselage aligned with the airflow).
- The more-common method is as follows: You deflect
the ailerons into the wind, but not as much as in the previous
method. The idea is not to transfer all the weight to the upwind
wheel, but merely to equalize the weight, counteracting the wind's
tendency to flip the airplane over onto the downwind side. To
keep the wind from pushing you sideways, you keep weight on both
wheels, delaying rotation until you have almost 100% of flying
speed (rather like the obstructed-field takeoff procedure, section 13.3). You then rotate and fly away. This
method is not optimal for soft or bumpy runways (because it involves
driving along the runway at high speed).
Note that in both cases, the heading change that occurs right after
liftoff is not a normal, coordinated turn. The motion of the
center of mass
is already aligned with the
runway, so you do not want to change the direction of motion, just the
heading. Use the rudder, not the ailerons.
After you have lifted off, you must take care not to settle back onto
the runway. Since the airplane's heading is no longer aligned with
the runway, re-landing would cause a severe sideways force
on the landing gear.
As you climb out, you should expect that the crosswind
will be stronger at altitude than it was near the ground. To
compensate, make the appropriate heading changes.
13.6 Multi-Engine TakeoffIn a multi-engine airplane, an engine failure shortly after takeoff is
a very critical situation. It places considerable demands on the
pilot. Make sure you know what to do; brief yourself in detail before
the takeoff. Engine failures and related procedures are discussed in
Early in the takeoff roll, verify that both engines
are developing the same amount of power. If the aircraft is trying
to pull to one side, you've got a problem. Also, check the engine
gauges to make sure (a) you've got the normal RPM on both engines,
(b) you've got the normal manifold pressure on both engines, and
(c) you've got the normal fuel flow on both engines. The instruments
that measure these three quantities are usually a single gauge
with two needles, so if you notice that the needles are split
you've got a problem.
If anything funny happens while there is runway remaining ahead of
you, close both throttles immediately and stop straight
ahead. Even if you are airborne, close the
throttles and re-land if there is sufficient runway length. Indeed,
even if the remaining runway is not quite enough, you might want to
land on it: Suppose that because of density altitude or whatever, your
aircraft has poor single-engine climb performance. You will sustain
vastly less damage if you land and run off the end of the runway at
low speed, rather than making an unsuccessful attempt to climb out on
You really don't want to be airborne at a speed below
VMC, i.e. at a speed where you can't maintain directional
control on one engine. In many aircraft, you should aim for a
lift-off speed of VMC plus 5 knots. To make sure you
do not lift off too soon, you can delay rotation until reaching
VMC. You can semi-rotate earlier if you want; just
make sure you don't rotate to a pitch attitude that will cause
liftoff below the desired airspeed. After liftoff, climb while
accelerating to VY (which ought to be greater
than or equal to VYSE).
In many twins, VMC is essentially equal to the stalling speed. In
others, however, it is considerably higher, which makes soft-field takeoffs problematic. You don't want to
lift off at ``the lowest possible airspeed'' (like you would in a
single) since if you lost an engine at that speed you'd have a big
problem: uncontrollable yaw. It would be a lot safer to lift off at
VMC or higher, even if this means staying away from soft, bumpy
13.7 Other Elements of the TakeoffAt a tower airport, you will need to get approvals
and clearances before taxiing or taking off.
During the takeoff roll and climb-out, you will need
to apply right rudder to compensate for the helical propwash,
as discussed in section 8.4.
In an aircraft with retractable landing gear, you have to decide when to retract them. It is
not a good procedure to retract them the instant you become
airborne. The reason is that sometimes things go wrong in the first
seconds after liftoff, and you don't want to foreclose the option of
re-landing on the remaining runway. Therefore the usual procedure is
to retract the gear when it is no longer possible to re-land on the
departure runway. You should say aloud the checklist item: ``No more
useful runway; gear coming up''.
On a really, really long runway, it's OK to reduce drag by getting the
gear up somewhat before you've flown all the way down the runway.
However: (1) it's usually not worth the trouble, and (2) make sure
that you're high enough that, in the event you do want to
land immediately, you have time to re-extend the gear.
Very early in the climb, pick a landmark somewhere
a few miles along your intended flight path, so you can maintain
direction of flight primarily by outside
references. The upwind leg of the traffic pattern is supposed
to be an extension of the runway centerline. Similarly, note
the pitch angle relative the horizon, so you can maintain the
proper angle of attack and detect any windshear. You can cross-check
direction, pitch angle, and angle of attack using the directional
gyro, horizon gyro, and airspeed indicator, but you don't want
to spend more than a tenth of your time looking at gauges. You
need to be looking outside to check for traffic.
When ATC gives you a takeoff
clearance, it means you are supposed to have the runway to yourself.
This applies to the runway itself, not to the airspace, so as soon as
you are airborne, you are 100% responsible for seeing and avoiding
other traffic. Even on the runway, it pays to keep your eyes open;
there's always a chance that ATC has made a mistake, and an even
bigger chance that some other pilot has pulled onto the runway without
Upon reaching a comfortable altitude, say 500 feet
AGL, there are a number of things that might need doing: If your
aircraft has cowl flaps, check them. On a normal
takeoff they will already be open, but on a go-around you will
have to open them. This is also be a good time to throttle back
to normal climb power, which is less than takeoff power on most
aircraft with controllable-pitch propellers. This is also a good
time to retract any remaining flaps. Finally, this might be a
good time to accelerate from VY to a nice cruise-climb
You should not mess with the cowl flaps or other
items until you are several hundred feet up. Turbulence might
cause a pitch or bank excursion while your attention is distracted,
or you might bump the yoke. At low altitude, basic aircraft control
should get your undivided attention.
In some aircraft, the fuel-boost pumps should be
turned off at 1000 AGL; in other aircraft they stay on throughout
the initial climb. Other aircraft don't use boost pumps at all.
13.8 DecisionmakingThe most important thing a pilot can do to promote aviation safety is
to know when to leave the airplane tied down. Don't pressure yourself
— or let others pressure you — into making a questionable flight.
I advise all my passengers explicitly:
A flight can be delayed or diverted for many reasons,
including weather, mechanical trouble, pilot fatigue, et cetera.
If you feel they have to go or return at a particular time, you
should make alternate arrangements.
Different takeoff situations call for different takeoff
techniques. You have to ask yourself:
Use a takeoff checklist
that is appropriate to the particular aircraft you are flying (not a
generic substitute). Some airplanes require the fuel boost pump on
for takeoff, while others require it off. A C-152 requires 10
degrees of flaps for short-field takeoff, while a C-172 requires zero.
- Should I be making this flight at all?
- Is the runway long and unobstructed, or is it
short and obstructed?
- Is the runway firm and smooth, or is it soft
- Is there a significant crosswind?
13.8.1 Monitoring Takeoff Performance (wrong)I sometimes hear statements such as these:
People even claim to ``prove'' statement
#1, using physics plus a number of hare-brained assumptions, including:
#1 (wrong): ``On any runway, if you have attained 70% of your
takeoff speed before you have used up 50% of the runway, then you
will have 100% of your takeoff speed by the end of the runway.''
The following modified version is also wrong, and
even more dangerous:
- Assuming friction is negligible. In fact, friction
is much more important in the second half of takeoff roll.7
- Assuming the engine puts out constant thrust.
Although constant thrust might be a fair approximation for jets
or rockets, for piston engines (especially ones with constant-speed
props) constant power is a better approximation. Therefore
we expect considerably less thrust in the second half of the takeoff
- Assuming zero wind. This might be true sometimes,
but it's certainly not safe to assume this in general. With a
strong enough headwind, you can attain 70% of flying speed with
no engine power at all.
A little thought shows this cannot possibly be correct
in general. It cannot even be repaired by changing the percentages.
As shown in figure 13.5, consider a very, very
long runway and a density altitude slightly above the airplane's
absolute ceiling. You will able to reach
100% of flying speed
before you have used up even 10% of the runway. You will be able
to take off and climb a few feet, but you will never be able to
climb out of ground effect, no matter how long the runway. Therefore:
forget any X% — Y% rule you may have heard.
- Statement #2 (wrong): ``On any runway, if
you have attained 70% of your takeoff speed before you have used
up 50% of the runway, then the takeoff will be successful''.
: Takeoff Failure despite
plenty of airspeed and runway
13.8.2 Monitoring Takeoff Performance (right)Suppose that you are on your takeoff roll, and several subtle things
have gone wrong: (a)
you have underestimated the density altitude; (b) for various
reasons (see below) the engine is only producing 80% as much power
as it should, even at this altitude; (c) the parking
partially stuck so the brakes are dragging; (d) you didn't notice
a shift in the wind, so you now have
a few knots
of tailwind; (e) you didn't notice that the runway has a slight
up-slope; and (f) your mother-in-law has stowed away in the back
seat, so the airplane is 15% heavier than you planned for. You
may not be able to complete the takeoff safely. The question
is, can you somehow notice the performance deficit in time to
abort the takeoff?
If you are familiar with the airplane, you should know how the engine
is supposed to sound; if it sounds rough,
have it checked. Similarly, you may know what engine RPM to expect
early in the takeoff roll; if you get less, abort the takeoff and
Unfortunately, if you are not intimately familiar
with the airplane, it can be very difficult to notice a performance
deficit until it is too late. Careful planning and checking is
required, as we shall see.
Using the Pilot's Operating Handbook (POH), calculate
the takeoff ground roll distance that is expected for your takeoff
conditions. Also calculate the landing ground roll distance for
the same conditions. Choose a runway that is at least as long
as the two distances combined, plus a suitable
error. Observe and note well what part of the runway should be
consumed by the takeoff roll.8 Then commence your takeoff.
If you are not airborne by the predicted point, close the throttle
and apply the brakes immediately. Taxi back to the hangar and
figure out what's wrong.
Do not attempt to use ``extra'' runway length to salvage the takeoff
if there is a significant performance deficit.
If you've got a deficit, you should figure out why, and the takeoff
roll is no place to be doing complicated figuring.
Now let's consider the annoying situation where the
available runway is just a little shorter than the aforementioned
``takeoff plus landing'' ground roll distance. The POH
tells you that a takeoff should be possible, if everything goes
right, but it does not tell you how to make a timely determination
that you've got a problem. In such a situation, there are three
possibilities. One is to change the situation; that is, you can
offload some fuel, toss out some payload, wait for cooler air,
and wait for more headwind — so that you can attempt a takeoff
using the procedure described in the previous paragraph. The
second possibility is to figure out how much runway your airplane
should consume reaching various speeds less than flying
speed, so that you can have earlier opportunities to abort the
takeoff. This is a job for a test pilot; the typical POH does
not provide such information, and takeoff performance is notoriously
hard to predict accurately. Please do not try this; playing
``amateur test pilot'' is like playing Russian roulette.
The third possibility, if you have any remaining doubts about
your airplane's performance, is to stay home.
13.8.3 Causes of Diminished PowerThere are dozens of things
that could go wrong with an aircraft engine.
Such problems are not particularly rare; I have personally
experienced the first four items in this list.
- One of the exhaust valves could be burned or
stuck, so it won't fully close.
- One of lobes on the camshaft could be worn, so
a valve won't fully open.
- The magneto timing could be not quite right.
- There could be a bird's nest in the air intake.
- et cetera.
If some such thing goes wrong, the engine will usually
not stop cold. It will continue to run, producing a fairly
large percentage of its normal power. In flight, this resilience
is clearly an advantage.
During takeoff, this resilience is a two-edged sword.
Because the engine continues to develop lots of power, you might
not notice the degradation. You might be tempted to take off
with such an engine. This could lead to big trouble, especially
on an obstructed-field takeoff.
13.8.4 Plan & Practice Rejected TakeoffsThere are
many types of problems that you may not notice until you have
begun your takeoff roll. Early in the takeoff roll, scan the
airspeed, engine RPM, manifold pressure, and fuel flow to make
sure you're getting reasonable readings.9
You should always plan your takeoff. This
includes planning for a rejected takeoff, for reasons discussed
in section 13.8.2.
Be sure you practice this. The first few times the
rejected-takeoff situation arises, your expectation of a normal
takeoff will be so strong that it is difficult to accept the situation
and close the throttle. A rejected takeoff is psychologically
at least as difficult as a go-around. Actually, most single-engine
pilots find it more difficult than a go-around, if only
because it isn't given as much emphasis during training.
Instructors: here's an instructional technique:
During preflight, brief the student on the procedures for rejected
takeoff. Choose a runway that is plenty long. During the takeoff
roll, wait until the airspeed is about half of the liftoff speed.
Then slap a suction cup on the airspeed indicator and say, ``simulated
airspeed indicator failure''.
If something seemingly minor happens early in the
takeoff roll, reject the takeoff. The rationale is that during
the takeoff roll you don't have time to make an intelligent decision
about what is minor and what is not, so (assuming there is plenty
of runway remaining) the safest thing is to stop now and think
later. See also section 15.3.
Four of the most-common takeoff procedures are related
in a fairly logical way, as summarized in table 13.4.
Additionally, in each of the four cases, you must take into account
the crosswind if any.
Fully rotate at VR.
Climb while accelerating to VY.
|Rotate at VX.
Climb at constant airspeed: VX.
||Hop into ground effect just above VS.
Accelerate horizontally (1 foot AGL) to VR.
Climb while accelerating to VY.
|Hop into ground effect just above VS.
Accelerate horizontally (1 foot AGL) to VX.
Climb at constant airspeed: VX.
Proper planning is important. A wise ``no-go''
decision could save you a lot of trouble. Make sure you know
the proper procedures, including the critical airspeeds. Make
sure you know how much runway you will need. If, during the takeoff
roll, it looks like you are getting less performance than you
should, stop and figure out what's wrong. Practice rejected takeoffs.
Make sure you know what angle of climb you should expect. You need
this to check obstacle clearance. This also
affects your choice of initial pitch attitude.
When choosing an initial pitch attitude, remember that pitch attitude
is not the same as angle of attack. See section 2.9 for
information on the right (and wrong) ways to handle cases where the
correct pitch attitude differs from what you expected.
Keep the aircraft properly trimmed and fly with a light touch. Don't
forget the after-takeoff checklist.
- In your Pilot's Operating
Handbook, this is probably called ``short-field takeoff''.
However, as we shall see, this is definitely not the right procedure
for a short unobstructed field — it actually uses more runway
than a normal takeoff. If you have a really short but unobstructed
field, consider using soft-field procedure (section 13.4).
- I like to avoid
running the engine at high power when the airplane is not moving at
all, since this tends to suck up rocks, damaging the propeller. If
you are moving, by the time the rock gets off the ground you will be
somewhere else, possibly escaping damage.
- I wouldn't do this
except in an emergency, because it would imply operating without
adequate safety margins.
- ... but you shouldn't be
looking at the airspeed indicator. It doesn't provide any useful
information at these speeds.
- Imagine how it looks: The airplane is airborne but
not climbing, and you are flying directly toward the bases of
the trees at high speed. Just when they're convinced they're
about to die, you pop the nose up and climb out.
- Most types
of friction behave this way.
- Indeed, if friction were negligible, airplanes would
fly much faster and would use much less fuel.
are several good ways to do this. (a) Some runways have standard
markings every 500 feet. (b) Sometimes the required takeoff distance
is a half or a third (or some other convenient fraction) of the
total runway length. (c) Sometimes you can pace off the distance
between runway lights, and then count lights. (d) Sometimes you
just have to pace off the whole distance
problems you might notice during takeoff include: A door that
is not properly latched may pop open as the airspeed builds up.
A seatbelt hanging out can cause a very loud, aperiodic banging
noise. Neither of these is aerodynamically serious, so don't
[Comments or questions]
Copyright © 1996-2001 jsd