Flight Characteristics




    The drone is a highly maneuverable helicopter of the coaxial rotor type. Under steady state fuselage heading conditions, the torque delivered to one rotor is exactly equal and opposite to the torque delivered to the other rotor. Thus, there is no need for any aerodynamic counter-torque device to keep the fuselage stable. Fuselage heading change is achieved by temporarily increasing the aerodynamic drag on the appropriate upper or lower rotor by means of the tip- brakes. Extending the tip brakes on the upper rotor introduces an unbalance torque, which feeds back through the transmission to turn the fuselage to the right; extending the tip brakes on the lower rotor causes the fuselage to turn to the left. Cyclic and collective pitch controls are conventional; i.e., directional (translational) flight is achieved by tilting the swash plates, vertical flight is controlled by moving the swash plates axially on the rotor mast.

The word "translational", as used in this sections and those part of this series and in general helicopter terminology, is taken to denote movement of the helicopter, with respect to the surrounding air mass, in a generally horizontal direction, in any azimuth direction, irrespective of fuselage heading.


    There are no pilot's controls on the drone. Control surface motion is achieved remotely by the manipulation of the deck and CIC control knobs and maneuver stick.

The maneuver stick has command authority, which can cause the normal cruise Vmax of the drone to be exceeded. This authority must be used with extreme care, and for command transients only. Refer to the operating limitations in the section “Operating Limitations”.



    The drone is capable of carrying one weapon centrally located or two equal weight weapons side-by- side. When a central weapon is dropped, the CG moves upward. When one of two side-by-side weapons is dropped, the CG shifts upward and sideward. When both side-by- side weapons are dropped, the CG shifts upward.

When the CG shifts upward there is a change in the pitch attitude and true airspeed of the drone, for any given airspeed command. Refer to the airspeed calibration data in the section “Performance Data”.

    When one of two side-by-side weapons is released the CG shifts laterally. With this asymmetrical CG the mast tilts approximately 3 degrees laterally about the center of rotor thrust. In order to maintain drone stability under steady state conditions, the thrust vector must pass through the CG. The servo system gains in the roll axis provide one degree of swash plate tilt, with respect to the mast, per degree of roll attitude, as measured by the roll pick-off in the roll and pitch gyro. Thus, as the drone cg shifts laterally, an approximate 3-degree roll attitude is introduced and the gyro senses the error. The roll axis servo system tilts the swash plate to compensate for the tilt of the mast and drone stability at this attitude is maintained.

Though the swash plate is tilted in roll with respect to the mast, sufficient authority remains for normal maneuvers.


It is not possible to land the drone in autorotative flight. 


    With the maneuver stick at center or zero airspeed commanded, the drone will assume a "no-wind" hover, i. e., it will remain fixed over a spot on the earth in calm air. By applying the appropriate directional command, the drone may be made to hover over the spot when the wind is blowing, or over the deck of the ship under way.

The power required for a "no-wind" hover is greater than the power required in directional flight at low and moderate speeds. Therefore, fuel is consumed at a greater rate.



    In the cruise mode, the drone is controlled through the heading (tip brake), altitude (collective pitch), and airspeed (longitudinal cyclic pitch) axes. In forward flight, turns are automatically programmed. The bank angle in turns is fixed at approximately 20 degrees, with respect to steady state flight attitude, and turn rate is automatically adjusted to satisfy the coordination requirement as a computed function of airspeed.

    Within the altitude limits set forth the section “Operating Limitations”, a collective pitch limiting system serves to prevent excessive drop in rotor rpm in the event of excessive aerodynamic loading. When an abrupt altitude command (or altitude error signal) causes aerodynamic overloading of the rotors, rotor rpm tends to decrease. If, as a result, rotor speed drops below approximately 600 rpm, a limiting bias is applied to the input to the altitude axis servo amplifier to reduce the magnitude of the error signal, and the collective pitch setting of the rotor blades is reduced. This rpm error cross feed limiting functions throughout all flight regimes in both maneuver and cruise modes.



    When the drone is a "no-wind" hover, it seeks to maintain its commanded altitude, within the range of tolerance inherent in the airborne altitude control system. As the drone moves into forward flight, a decrease in altitude will occur at an average rate of one foot of altitude per each knot of true airspeed. For example: as the drone accelerates from a "no- wind" hovering altitude of 300 feet to a forward air- speed of 50 knots, it will lose altitude at the rate of one foot per knot until it re aches 250 feet and 50 knots true airspeed, at which point it will level off and continue to fly at that altitude. Thus the drone always flies at an actual altitude that is lower than its hovering altitude by an amount (in feet) proportional to its true airspeed (in knots).

    This deviation from the hovering altitude is the result of aerodynamic perturbations in the region of the static pressure pick-up in translational flight. As the drone moves through the surrounding air m ass, a region of slightly reduced pressure is created above the circular air deflector at the top of the mast. This reduction of pressure is proportional to airspeed. The static pressure pick-up, above the air deflector, senses the reduced pressure and the barometric altitude control interprets it as a plus (or positive) altitude error. The collective pitch system seeks to correct the apparent error and the drone altitude de- creases until the pressure in the region above the deflector increases to that normally existent in undisturbed air at the original hovering altitude. At that point the altitude retention system nulls and the drone continues to fly at that altitude as long as its airspeed remains constant. Any change in drone airspeed will result in a corresponding change in actual altitude. Just as the drone altitude decreases during acceleration, its altitude increases at the same rate during deceleration.

    When the drone enters into a turn in the cruise mode, it may experience an additional loss of altitude, and the extent of such loss will be a function of the duration of the turn. Initially, the loss of altitude will result from the sudden lateral displacement of the thrust vector by approximately 20 degrees (the nominal fixed bank angle of the drone in a turn in the cruise mode), thereby altering the vertical thrust-to- weight ratio. In the event of misadjustment in the electrical turn coordination system, there may be superimposed on the initial loss of altitude an additional decrease in altitude if the drone tends to slip, or an increase in altitude if the drone tends to skid. As the barometric altitude control senses the deviation it will readjust the collective pitch system to compensate. Normal operations in the cruise mode should be limited to a minimum commanded altitude of 300 feet.



    The likelihood of entering into rotor blade stall in the QH- 50D drone is lessened by the reduction in range of certain factors, which normally contribute to blade stall, as follows:

1. The tactical altitude envelope is limited to 0 to 1000 feet by the command range of the system.

2. Rotor speed is fixed at a nominal 610 rpm by the regulating systems on the drone.

3. Bank angle in coordinated turns is fixed at approximately 20 degrees and turn rate is automatically adjusted as a computed function of airspeed to satisfy the turn coordination requirements.

4. The weight configurations of the drone are fixed within a well defined envelope.

With the reduction of the variability of the above factors, the only other contributory factors are airspeed, temperature, and high g-loading.

Ambient temperature has an effect on blade stall as it has on normal helicopter flight characteristics.

The low density usually accompanying high temperature reduces the airspeed at which the onset of blade stall might occur.

    In a helicopter, incipient blade stall usually manifests itself initially as a slight vibration of a non-critical nature. If this were to occur in the QH-50D drone, it would not be detectable since the drone is not equipped with tactical telemetry. In the QH-50D drone, blade stall can occur only under the following unusual circumstances, all of which relate to excessive airspeed:

1. Drone operations at Vmax in strong gusty weather. Under these circumstances, blade stall may be encountered in gusts on a short term or transient basis. Any resultant vibration should cause no damage to the drone.

2. Failure to observe safe operating procedures. Operations outside the operating envelope set forth in Section V should be avoided.

3. Misadjustment or malfunction in the automatic turn coordination system. During a mis-coordinated slipping turn, which is evidenced by a loss of altitude, it is possible for the drone to experience blade stall. In this case, the loss of altitude is more critical than the possible resultant blade stall. Corrective commands should be applied immediately in an attempt to arrest the slip and thus maintain altitude. These corrective commands (reduction of airspeed) automatically will reduce the magnitude of the blade stall effect and, as the drone recovers, remove it completely. 


    Power settling is a phenomenon inherent in all helicopters and is characterized by an uncontrolled and excessively high rate of descent. The possibility of entering into a true power settling condition is created when initiating a descent from a "no wind" hover or while at low airspeed, particularly at higher gross weights. It is normal in a hover for the down- wash velocity to vary along the span of the rotor, in- creasing from hub to tip, i. e. the downwash velocity is lower near the center of the rotor disk area than it is near the outer portion. In a rapid descent, the rotor literally "settles into its own downwash. " In the area of low downwash velocity (the center of the disk), rotor thrust will be reduced, and, as the rate of descent increases, the area of reduced thrust be- comes larger. If the rotor net thrust is reduced sufficiently, the helicopter is effectively free-falling. In the QH-50D drone, if a large reduction in altitude is commanded rapidly, the drone will descend and its rate of descent can be of such magnitude that the rotors can enter into their own downwash pattern.

The most effective recovery technique is to apply or increase translation airspeed command. As the rate of descent decreases, further changes in altitude can then be achieved by using the altitude rate switch or by manually applying gradual altitude commands.

Under any circumstances, the conditions contributing to incipient power settling should be avoided at all times.



    Airframe vibration is a phenomenon inherent in all helicopters. The characteristic frequency of these vibrations is generally a function of the number of rotor blades and the rotor speed. In the QH- 50D the common frequencies are approximately 5, 10, and 20 cycles per second. In a normally rigged and balanced vehicle, this vibration frequency will appear in one or more axes, and may be observed as small amplitude control oscillations. However any one of several factors may cause the control oscillation amplitude to increase to the extent that the attitude of the drone is visibly affected. This condition may be caused by mistracking, unbalanced rotors, bent rotor shafts, or marginal servo- actuator, etc. If this abnormal condition is noted, the drone should be landed immediately and the cause found and eliminated prior to further flight.




In all maneuvers in the vicinity of the ship, wind direction and velocity must be taken into account. When the relative wind is directly abeam, astern, or ahead, the ship superstructure causes the wind to become turbulent over the flight deck. This turbulence must be taken into account in launching and landing the drone. In contrast, wind striking the ship superstructure at an angle is deflected laterally, instead of vertically, and less turbulence over the deck results.



    When the ship is under way, compensation must be made, in launching, and landing the drone, for forward speed of the ship. If the drone is to hover over the deck, an equivalent airspeed must be maintained to compensate for relative wind velocity. Following the launch, it is imperative that this airspeed be maintained, and then gradually increased so that the drone moves out in the direction into the wind. If the airspeed is decreased and the drone is allowed to drift downwind, it is probable that settling will occur. At higher temperatures and normal gross weight configuration, this practice is dangerous. After switching to the cruise mode, downwind turns can be made with safety, provided that a minimum airspeed of 20 to 25 knots is maintained prior to entering into the turn.


    Launching and landing the drone when the deck is pitching, rolling, and yawing requires synchronization of commands with the movement of the deck. In general, it is preferable in a launch, that the drone breaks contact with the deck when the deck is moving in the upward direction and rolling in the direction into the relative wind. In landing, it is preferable that the drone makes contact with the deck when the deck is moving downward.  


End of Flight Characteristics Section


Home Up Description Normal Procedures Emergency Procedures Auxiliary Equipment Operating Limitations Flight Characteristics Systems Operation Crew Duties All Weather Ops Performance Data


Helicopter Historical Foundation
P.O. Box 3838, Reno, Nevada USA 89505

Because of SPAM, we ask that you copy the below address into your mail program and send us your comments!

Email us at: Gyrodyne_History@Yahoo.com

The name "Gyrodyne" in its stylized form above, is the Trademark of and owned by the Gyrodyne Helicopter Historical Foundation; unauthorized use is PROHIBITED by Federal Law.

All Photographs, technical specifications, and content are herein copyrighted and owned exclusively by Gyrodyne Helicopter Historical Foundation, unless otherwise stated.  All Rights Reserved ©2013.

The Gyrodyne Helicopter Historical Foundation (GHHF) is a private foundation incorporated in the State of Nevada as a Non-profit organization. 

GHHF is dedicated to the advancement of the education and preservation of the history of the Ships, the Men and the Company that built, operated and flew the U.S. Navy's QH-50 Drone Anti-Submarine Helicopter (DASH) System and to the preservation of the history of the U.S. Army's past use of DASH.
Your support will allow for that work to continue.