This maneuver is used to transition from a hover into forward flight.
Assuming Negative Translational Lift
Assume that the wind is calm, and that the helicopter is not in
translational lift at a hover.
The power setting will normally be very high in this case. The takeoff can
be initiated by lowering the nose slightly (a couple degrees). A very slow
acceleration should take place, with the skids still basically level with
respect to the ground. Some altitude will normally be lost as the front
vortex is overrun by the rotor system. The collective should not normally
be raised. If the pilot is patient and uses good technique, translational
lift will be achieved before the helicopter touches down. There should be
no problem if the helicopter does touch down assuming a normal surface,
because the skids are level.
During this acceleration, the anti-torque pedals should be manipulated
such that the skids remain alighned with the ground track. This insures
that a touchdown onto the landing gear will not result in a rollover.
As the helicopter accelerates into translational lift, an aggressive
lowering of the nose with cyclic will be required to avoid initiating a
climb. Also, as the tail rotor goes through it's own effective
translational lift, anti-torque thrust will increase greatly, and the
pilot will have to make a pedal adjustment to maintain his skids aligned
with the ground track.
Assuming Effective Translational Lift at a Hover
Assuming that the wind is strong enough that the helicopter is in
effective translational lift at a hover, the initial part of the takeoff
will be slightly different. Typically, the power setting will be quite
low in this situation, and the pilot will want to increase power as he
lowers the nose to begin the takeoff. Power should be brought up to a
normal power setting for takeoff. Skids should be maintained alighned
with the ground track using the pedals. The nose will be lowered more
than for the previous case, since translational lift is providing us
with an excess of vertical lift, and we still want to avoid begining
the climb too early.
The rest of the maneuver
Now that the helicopter is accelerating well past effective translational
lift, the trick is to prevent an early climb. Before the flight, examine
in the performance section of the pilot handbook. There will be an airspeed
at which you can start gaining altitude without entering the shaded areas
of the HV curve. This should be your target airspeed on a normal takeoff.
You can choose to accelerate to a faster airspeed, as long as you don't
hit the high speed shaded section of the H/V curve. Also, it usually does
not make sense to accelerate much past the minimum sink airspeed.
While the helicopter is accelerating from low airspeed to high airspeed,
transverse flow effect will require
lateral cyclic adjustment. At very low airspeed the cyclic will have to
move to the left, and then as airspeed is gained the cyclic will move back
to the right again.
As you encounter the target airspeed, bring the nose up until the helicopter
is in an attitude that will eventually result in the target climbout airspeed.
Holding the nose down until the airspeed indicator reads the target airspeed
will almost always result in an airspeed overshoot. By rotating to the target
attitude, the helicopter will slowly gain airspeed until it stabalizes at the
As the helicopter begins to climb out, trim the aircraft into the wind
with the anti-torque pedals. Continue the climb out until you reach your
Dumping the nose to accelerate
Many pilots begin the maneuver by dropping the nose many degrees. While this
will give a quick acceleration, it also decreases vertical lift substantially.
Most pilots raise collective to compensate. The problem occurs on the day
when you are already at maximum torque and you try a maneuver like this.
Either you exceed torque limits trying to avoid hitting the ground, or bleed
down rotor RPM, or hit the ground in a nose low attitude. None of these are
desirable. Dropping the nose a little, gaining airspeed and lift, and then
dropping the nose more to prevent a climb is a more conservative way to
initiate a takeoff. If the helicopter touches down, the skids are level, and
the helicopter will usually just skip off the runway and then climb out.
Usually the helicopter won't touch down because more vertical lift remains
available during the entire maneuver.
Failure to keep the skids alighned
As the helicopter accelerates, the tail rotor is going through it's
own translational lift, plus main rotor downwash will have an influence
on tail rotor thrust. It is important that the pilot be in the habit of
preventing any yaw in case the helicopter touches down during the takeoff
roll. Also, in the event of an engine failure any yaw will be immediately
apparent, and if the pilot is automatically keeping the skids alighned, the
helicopter can set back down without risking a rollover.
Allowing the helicopter to climb out early, and thus going through the
height velocity curve's shaded area invites disaster if the engine quits.
The "knee" of the HV curve is the most difficult portion to recover from,
even for pilots who are current in autorotations in make/model. Making
life more difficult by actually flying the knee portion in the shaded area
just makes things worse. Of course, if you have to clear an obstacle, you
have to climb out early. But if there is no reason for it, accelerate low
until you have passed the "knee" airspeed.
There are other pilots who will accelerate well past minimum sink before
they start their climb. This has the effect of keeping you lower over any
given point downrange than you would be if you climbed out closer to
minimum sink airspeed. Since altitude is useful in the event of an
autorotation, most pilots would rather climb at a steeper angle if it is
possible. Usually a steeper climb is benificial from a noise standpoint as
well, by being higher before overflying other property.
paul at copters.com
(replace " at " with "@" to email me - this avoids SPAMMERS I hope)