US Navy: Naval Aviation Doctrine: Introduction to Naval Aviation, 1946 - Aviation Seamanship

INTRODUCTION TO NAVAL AVIATION  - RESTRICTED - ISSUED BY AVIATION TRAINING DIVISION OFFICE OF THE CHIEF OF NAVAL OPERATIONS U. S. NAVY. * JANUARY 1946 * OPNAV 33-NY-85; Chapter IX. Tactics and Flight Operations.

8. AVIATION SEAMANSHIP

Familiarity with the many demands of seamanship is required of every naval officer, whether he flies or stands deck watch. But a special knowledge of the effects of wind and sea is required of the pilots who fly ship-based seaplanes and flying boats.

Aviation seamanship is concerned with the water handling of aircraft under many conditions - launching and beaching flying boats, water taxiing, cruiser and battleship recoveries, water landings, and handling aircraft in the open sea.

An airplane, like a ship, is subject to currents and winds. It will weathercock into the wind like a ship, it will ride buoy in current and wind much like a ship, and maneuvers in the sea like a ship. There is an important difference between a ship and a plane, however, in that a plane is lighter and has little draft, so that the effects of wind and current are more pronounced.

Judging Wind Conditions

Wind direction and velocity usually will be found to be the most important factor in all normal surface operations, particularly water landings. The ability to judge wind velocity and direction from surface indications is a paramount requirement of aviation seamanship. Wind direction is indicated by the movement and condition of the waves, while velocity can be estimated from the degree of surface turbulence - a smooth sea, for example, indicates no wind, while whitecaps clearly indicate a wind of moderate force.

There are other indications:

1. When streaks on the water are long and straight, the wind is steady.

2. When streaks are curved, changes in wind direction are indicated.

3. When a distinct line appears on the surface, such as would be caused by a riptide, a reversal of wind direction is likely.

4. When swells are taken into consideration, it must be remembered they have no breaking crests and there is no relation between the direction of the swell and the direction of the wind.

There are no hard and fast rules for a water landing the governing factor will be the pilot's ability to estimate the situation. However, with more than 20 knots of wind, landings should he made directly, or as nearly as possible directly into it regardless of the direction of the swells.

Launching flying boat

The slower landing speed thus afforded outweighs other considerations.

Wind force predictions in knots can be made with reasonable accuracy front the following surface conditions:

Smooth sea to small ripples 0 - 3 knots

Well defined waves, smooth without breaking    5 - 6 knots

Pronounced waves. occasional whitecaps    6 - 12 knots

Whitecaps close together, clearly defined windstreaks 12 - 20 knots

Large seas with waves forming on them: whitecaps on every crest; windblown sea mist and occasional wind-blown crest 20 - 25 knots

Heavy seas with breaking, rolling waves; pronounced white streaks and frequent wind-blown wave crests 25 - 30 knots

Continual rolling waves with scud or foam streaks; wind carries along all wave crests; seas breaking and rolling 30 - 10 knots

Spray streaming from wave crests  10 - 50 knots

Taxiing Seaplanes

Because of the water-handling characteristics of seaplanes and the large area of surface exposed to winds, the principles of surface taxiing are much the same as the principles which apply to sailing boats. With one exception the use of power for directional control.

The techniques employed in taxiing sea-planes, therefore, will vary according to the condition of the sea, the strength of the wind, and the limitations of the taxiing area.

The broad unbroken side, the large rudder high above the water, and the heavy hull construction of multi-engine seaplanes make water taxiing of this type of seaplane particularly difficult. The tendency of all aircraft to weathercock is one of the most troublesome of taxiing problems, and consequently is the one which demands the greatest skill to control.

Generally, there are four main factors in control of waterborne aircraft:

1. Engines. They are of primary importance in effecting turns and for maintaining headway and direction.

2. Rudder. The rudder augments engine control but its effectiveness will vary to a large degree with wind conditions.

3. Sea anchors. They are used for directional control and for effecting turns at slow speed. They also serve to reduce the sailing speed of the plane.

4. Ailerons. They are helpful. but to a lesser extent than any of the other three factors.

Taxiing either into the wind or down-wind is relatively simple. A straight course can be maintained at most speeds with equal power on each engine and with the rudder centered.

Taxiing out of the wind is accomplished with rudder control alone, provided the new course is only slightly out of the wind. However, if the taxiing course is more than 30° out of the wind, full rudder will not suffice and more power must be carried on the upwind engine to correct the the tendency of the plane to weathercock into the wind.

Taxiing crosswind can be achieved by proper use of rudder, engines, and aileron provided wind velocity is not excessive. Full leeward rudder and aileron is thus employed, with the upwind engine used as the controlling factor in maintaining course. If the aircraft still tends to swing into the wind, a sea anchor must be streamed from the leeward after station.

To stop or turn, the pilot must consider the momentum of his plane as well as the strength and direction of the wind. At all times when executing a turn, the rate of turn must be maintained throughout or the plane will at once swing into the wind. In turning onto a downwind heading, for example, power and rudder control must he maintained until the plane reaches a heading within 90° of the wind line. Similarly, when turning into the wind, the weathercocking characteristics of the aircraft can be utilized substantially to bring the plane about. On multi-engine sea-planes the use of reversible-pitch propellers is a factor in slowing momentum. turning. or (in an extreme case) for backing. The reversible-pitch propeller, as its name indicates, reverses the direction of thrust by reversing the angle of the blades through electrical propeller controls.

Sailing without power down wind, or in the general direction of the wind, requires slight directional control with the rudder. With the rudder centered, the plane will sail directly down wind. When it is put to starboard or port, the direction of the aircraft is to starboard or port of the wind line. Sailing without power can have many practical applications such as leaving crowded buoy areas, or drifting down wind after failure to hook a mooring or beaching buoy.

Beaching flying boat

Sailing with power has many variations, and by using of engines a plane can be sailed 90° to the wind. It is the method used to facilitate entrance into narrow areas or in executing difficult ramp approaches where full directional control is essential.

Launching and Beaching Seaplanes

Multi-engine flying boats must be handled on shore through definite launching and beaching procedure. This procedure demands seamanship and a high degree of coordination among members of the ramp and plane crews.

Launching. While a flying boat is on land, it is moved by beaching gear corresponding roughly to the conventional wheel gear of a land plane save that it is removable. Side mounts of dual rubber-tired wheels are secured to either side of the hull forward of the center of gravity, and locked by pins to interjoining flanges on the hull. The third piece of gear is the "mule," which is a steerable wheel located at the aft point of the hull and controllable by hand to steer the plane while it is moving.

Seaplanes are taxied to the ramp for launching under their own power, with taxi directions given by the launching master stationed on the ramp. Taxi speed is checked by a tractor holding taut a tow line secured to the tail towing eye. Additional precautions against over-speeding are wooden chocks secured to each side mount by short drag lines. One man is stationed at each side mount to insert the chocks if required, while another steers the mule.

When the plane reaches the top of the slipway leading to the water, lines are attached to each float to hold it in position when waterborne until the beach gear is removed. While going down the slipway, the plane is braked by the tractor. When waterborne, the beach crew remove the beaching gear and the check lines are cast off. Upon the "all clear" signal from the beach master, the pilot is free to taxi to the take-off position.

Beaching. The approach to the ramp is one of the most difficult of all maneuvers for the multi-engine seaplane pilot. Ramp approaches must be varied according to the type of ramp, and the strength and condition of wind and sea. The pilot must always he prepared to take a wave-off, and so avoid placing his plane in any position which would make retreat, or a "go-around," impossible. The safety of his plane depends upon his ability in avoiding going aground or hitting the seawall and ramp.

Generally speaking, the ramp approach is planned to permit an approach into the wind so that, at any time, engine failure or deliberate throttling-back will weather-cock the plane away from the ramp. The approach speed is minimized by streaming sea anchors and intermittent cutting of the master ignition switch. Turning against a sea anchor should not be attempted; if a turn is necessary, the sea anchor should first be spilled and brought close aboard. To insure proper handling, close communication must be maintained by inter-phone between the pilot and crew members manning the after station and tending the sea anchors.

Ramp approaches normally are made by bringing the plane into position to catch a buoy off the ramp. Under circumstances where no buoy exists, it is necessary for the beaching crew to catch the plane with wing lines.

In making a buoy approach, crew members standing by in the bow catch the buoy with a buoy hook, temporarily securing the plane while members of the beaching crew swim or row out to secure wing and tail lines. When the buoy is caught, engines are cut. Under directions from the beach master, the plane is drawn toward the ramp into water sufficiently shallow to permit beaching gear to be attached. Once the gear is pinned into place, the plane is towed tail-first up the ramp by a tractor.

When a buoy is not available, a second type of ramp approach may be used. Assuming that an approach parallel to the beach (90° to the ramp) is to be made, the plane is taxied close enough to the beach to permit lines to be secured to the beach-side wing and the tail by beaching crewmen standing in the water. When both lines are secured, the engines are cut and the plane tailed into the ramp where beaching gear is attached.

Recovering Seaplanes at Sea

The recovery of battleship and cruiser (VO/VS) aircraft at sea must take into consideration the safety of the recovering ship, the safety of the aircraft, the efficiency and expediency of the recovery in relation to other ships of the force, and the necessity for making the recovery in a minimum time.

Seaplane taxies over slick to cruiser base

There are three methods of recovery:

1. The "Baker" method, in which the recovering ship comes to a dead stop to hoist aircraft aboard from alongside.

2. The "Charlie" method, in which the recovering ship takes aboard aircraft without stopping but after altering course to create a lee slick.

3. The "Dog" method, in which the recovering ship takes aboard aircraft without stopping or without altering course.

The Charlie method of recovery is most frequently used and is the most desirable from the standpoint of the pilot since it creates a smooth slick for landing and taxiing under open sea conditions. The Dog method can also be used if sea and weather conditions permit, particularly under combat conditions, because it allows the recovery of aircraft while the main batteries are manned. The Baker method is not usually used in wartime. inasmuch as the recovery ship, while stopped. is vulnerable to attack.

The recovery of aircraft under way involves the use of the recovery sled, a net towed from the ship's quarter or amidships which engages a hook on the seaplane's pontoon as it taxies onto it. When the plane is engaged, the sled is towed to position under the crane and the aircraft hoisted aboard.

Regardless of the method of recovery or the heading of the recovery ship, the landing is always made into the wind.

The Dog recovery may be used when no slick is necessary and when the wind is light enough so that the ship's course is immaterial. It is effective under battle alert, or when it is not desirable to interfere with the progress and disposition of the force. A Dog recovery is made by landing astern and taxiing up to overtake the ship.

The Charlie recovery is the most effective in the open sea under usual wind and surface conditions. The recovery ship makes a 90 ° turn, which begins 45° out of the wind line and finishes 45° inside the wind line at a speed of around 10 knots. The sharp turn skids the stern of the ship around and creates a slick for the pilot to land in. The landing is made across the longest diameter of the slick, and the pilot then overtakes the ship and engages the sled. The Charlie method renders ships less vulnerable to attack than the Dog method because they are required to maintain a steady course for only a relatively short distance and time.