Wheel Brakes Research Articles

Dynamic Reactions in Hop Dampers for Bogie Undercarriages

THE function of hop damper units as fitted to modern multi‐wheel bogie undercarriages is to dissipate the kinetic energy of the bogie, wheels and brakes due to their rotation about the bogie attachment pin. This rotation of the bogie may be caused by impulsive application of the wheel brakes, and the purpose of the hop damper is to reduce the angular velocity of the bogie, so that when it comes up against itsstops, the angular velocity is substantially zero, thereby reducing the mechanical shock which may be felt in the undercarriage as a whole.

Aircraft Engineering Reference Sheet

The pneumatic system operates the undercarriage, wheel brakes, flaps, windscreen wipers, fuel priming pumps and air intake shutters, Fig. 7 and its accompanying key show the principal features and the location of the major components where this is not obvious.

A New Tyre, Brake and Undercarriage Testing Machine

DURING the war the young aircraft industry in Australia made great strides. Design and development of new types of aircraft were undertaken and a need was soon felt for an undercarriage testing machine. A small drop tester was built by one of the firms for the undercarriages of small aircraft and a larger one was under construction by the Government when, towards the beginning of 1944, serious operational difficulties were experienced in the South Pacific area due to the short life of the tyres of medium and heavy bombers, complete failure occurring in as few as five or six take‐offs and landings. Thus to the need for an undercarriage tester was added the need for proper facilities for developmental and type testing of tyres and wheel brakes.

Reverse-Pitch Propellers as Airplane Landing Brakes

Reverse-pitch propellers, operating with full engine power, may be as effective in decelerating an airplane during the landing ground run as are conventional wheel brakes. The factors governing the effectiveness of reverse-pitch braking are power loading (W/P), wing loading (W/S), and such propeller characteristics as number of blades, diameter, and activity factor in comparison with conventional wheel braking. The result of varying the first two of the above factors is studied for the case of an airplane with a tricycle landing gear, and the method of calculation is developed. The great safety advantage of reverse-pitch braking for large airplanes landing on ice-covered, snow-covered, or wet runways is emphasized; the possibility of reducing the landing airport length required by the C.A.A. is discussed; and the reduction in tire and brake maintenance and replacement costs due to everyday use of reverse-pitch braking is considered. Also considered is the feasibility of reducing the glide plus transition distance by applying reverse-pitch braking during the final stage of the transition to eliminate floating.

Propeller Design Requirements

Functional requirements which have formed the basis for propeller development by the U.S. Army Air Forces in recent years are separately discussed in considerable detail. The importance of feathering and reverse pitch with a maximum rate of pitch change of 45° per sec. is emphasized. Experiments show that reverse-pitch propellers are at least as effective in ground braking as the best wheel brakes. They are more effective than any known flap-type dive brakes in retarding aircraft in flight. Air-line experience indicates an emergency feathering of the propeller to stop a damaged engine occurs every 3,000 enginehours on the average. The full-feathering propeller is without doubt the most valuable single contribution in the past decade to safety in flight of multiengined aircraft. Tracings are included of oscillograph records of propeller governing response to propeller and engine control changes for different types of governors and rates of pitch change. I t is shown how improved governing to prevent overspeeding has permitted increasing engine ratings by 10 per cent during the past few years. Further developments in anticipatory governing promise to give an additional 10 per cent improvement. I t is pointed out that refinements in hollow steel blade design permit saving as much as 25 per cent in the weight of a given propeller. The effect of weight-savings of this magnitude on transports and military aircraft operation is illustrated by factual examples. A survey is made of current experiments on propeller ice elimination, and attention is focused on the promise of pastes and thermal means to solve this difficult problem. Numerous other items which must be included in a propeller design to make it successful are briefly discussed.

Aeroplane Brake Development

AEROPLANES are now being built of from 25,000 to 60,000 lb. gross weight, and to comply with these loads it has been necessary to construct wheels and tyres capable of sustaining these machines when taking off with a minimum resistance and weight of structure. Complications arise from the provision of wheel brakes, which are an absolute essential on modern aircraft.

Wheel Brakes and Undercarriages

Until recently an aeroplane undercarriage has generally been called upon to serve two purposes only :—To absorb the energy due to the vertical velocity of the aircraft when landing;To enable the aircraft to be flown off from, and manoeuvred over, ground which may be very rough or very soft.To these requirements are now added a third :—To absorb the energy due to the horizontal velocity of the aircraft by means of wheel brakes.These three duties must be carried out with the minimum possible weight and head resistance, for the undercarriage must be as self-effacing in flight as it is all-important on the ground.The problems connected with wheel brakes are very specialised in themselves and have a particular interest at the present time. For this reason it was decided to deal with them first, and later to turn to the more general aspects of undercarriage development.

Hydraulic Brakes for Aircraft

IN a previous article the subject of wheel brakes for aeroplanes was surveyed and the various types of brake in use briefly described. It is now proposed to deal in exact detail with hydraulic brakes, which are receiving more and more attention for installation in aircraft.

Aero Wheel Brakes

The trade was only just emerging from the stage when aero wheel brakes were merely adapted forms of automobile wheel brakes, and the aeroplane industry from the point of view of wheel brakes is now in about the same stage as the motor industry was with car brakes six years ago. In this respect the United States is very far ahead of us.The aircraft industry is now realising, however, that the brake needs of an aeroplane have to be specially catered for, and it is to this end that research is being made, the ordinary motor car two-shoe brake being abandoned as inefficient.The lecturer stated that the average reduction in the landing run of machines fitted with the modern Bendix-Perrot brake was 50 per cent., and that the fitting of brakes has the effect of assisting Ground Crew.