Normal Takeoff

This maneuver is used to transition from a hover into forward flight.

Maneuver Description

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 the manufacturers H/V curve 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 desired airspeed.

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 desired altitude.

Common Mistakes

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.

Early Climbout

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.

Late Climbout

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 Cantrell
paul at copters.com (replace " at " with "@" to email me - this avoids SPAMMERS I hope)

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