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Attitude Flying

Airspeed Control

Attitude flying is a simple concept which is used in both airplane and helicopter flying. The way it works is that the pitch attitude of the aircraft determines the forward speed, and power determines the altitude.

For instance, when flying a Robinson helicopter, the magnetic compass is mounted on the windshield in front of the pilot, and this can be referenced to the horizon to provide very accurate pitch information. For most pilots, holding the top of the compass on the horizon will cause the helicopter to fly along at about 60 knots. Holding the compass an inch below the horizon will cause it to fly at 70, and holding the compass an inch above the horizon will cause it to fly at 50 knots.

A Robinson R22 in a 60 knot attitude

Many people who are being introduced to helicopter flying assume they should use the airspeed indicator to control the speed of the aircraft. The problem with this approach is that there is a large time lag from the time that the pilot moves the cyclic control until the helicopter finally stabalizes at the commanded speed. This lag can be tens of seconds, and would make it very difficult to command the correct cyclic position, because feedback takes so long to occur.

Attitude flying on the other hand typically takes less than 1/2 second for the aircraft attitude to change. If the pilot knows the attitude required for the desired airspeed, the cyclic can be moved until the fuselage moves to the desired pitch attitude, and the pilot can be fairly sure the aircraft will accelerate/decellerate to the commanded airspeed within the next 10-15 seconds. After 10-15 seconds, the pilot can verify that the airspeed indicator shows the desired speed. If the airspeed indicator indicates a speed a few knots away from the desired speed, the pilot can make a small attitude change to bring it exactly to the desired value.

Altitude Control

Power setting determines whether the aircraft will stay in level flight, descend, or climb at the particular attitude the pilot has chosen. When attitude flying helicopters, large power changes do influence speed, so some compensation of attitude needs to be made for gross changes in power settings. This effect is fairly small, and pilots learn to do this easilly.

Pilots can quickly learn not only what attitudes will command a certain airspeed, but what power settings will give level flight at that airspeed. For instance, a Robinson R22 will take approximately 21 inches of manifold pressure to maintain level flight at 75 knots. This will be influenced by factors such as aircraft weight, density altitude, and the performance characteristics of the particular aircraft. Under most circumstances the value will be very close, and only a minor adjustment to power will be required to compensate for these factors.

By knowing what attitude will give 75 knot cruise, and what power setting is required, a pilot can very quickly make the pitch attitude and power setting adjustments needed to result in the desired performance. This is especially useful when converting from one flight configuration to another, such as from climb to cruise, or from cruise to descent.

Other examples of power settings for the Robinson are that 15 inches of manifold pressure at 60 knots will give between 300-500 feet per minute descent rates. This is a comfortable configuration for descending in the traffic pattern until approach angle intercept occurs.

Other helicopters have different power settings for the same flight configurations. Most pilots will quickly learn a few of the most commonly used configurations when they are first learning to fly a new make/model of helicopter. Interpolation will give them intermediate configurations which they have not memorized, and typically only 3 or 4 configurations need be memorized.

Turning (banking) Flight

A a pilot learns to attitude fly, he needs to learn how the pitch attitude should look during turning flight. Apart from attack helicopters, most helicopters have side by side crew seats, meaning the pilot is typically not flying from the middle of the aircraft, but is offset to the side.

A result of this seating is that the horizon will not roll about the center of the windshield during a level turn. Any reference point in the middle of the windshied (such as the Robinson compass, or a windshield vertical member such as in the Enstrom, Hughes 300, Bell 206, etc) will rotate up or down depending upon whether the bank is to the left or to the right, and whether the crewmember is sitting in the right or left seat.

The typical result of this is that pilots tend to pitch the nose up or down when entering a turn, and this will cause both the airspeed and the altitude control to be compromised. There are two ways to adjust for this. One is to simply learn through experience what the sight picture should look like in a turn. This tends to take a lot of trial and error, and changes depending on which seat you are sitting in. The other method is to pick a point on the windshield directly in front of the pilot's eyes, and rotate the horizon around this point while rolling into and out of a bank. This method is quick and easy to learn, and works from either seat. Focus on the horizon, not the windshield, but be aware of the out-of-focus windshield point as you roll into and out of banks.

Altitude Control during turning Flight

Both airplanes and helicopters have the problem that entering turning (banked) flight uses some of the lift component to perform the turn, and the reduction in vertical lift will cause the aircraft to lose altitude. There are two ways the helicopter pilot will typically compensate for this.

One possible way is to use some aft cyclic during the turn. This will cause a decrease in airspeed, but is normally acceptable for shallow banks. This technique has the advantage that since there is no torque change, no anti-torque pedal adjustment is required, decreasing the amount of inadvertent yawing that occurs.

Another possible technique to correct for this is to perform a power change. This is typically required if the bank is a steep one, or if the turn is made at an airspeed on the "back of the power curve" i.e. below the minimum sink airspeed. Power is increased during the roll into the turn, and decreased during the roll out. A proper adjustment maintains the vertical component of lift so that altitude remains constant.

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

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