Engine Cowl Research Articles

New Ground Deicing Hazard Associated with Freezing Drizzle Ingestion by Jet Engines

A new ground deicing hazard is described, consisting of the accretion of freezing drizzle onto jet engine fan blades and cowlings, and subsequent shedding of the accreted ice during takeoff leading to damage to jet engine fan blades. Cases of damage to aircraft from hazardous surface icing conditions at Denver, Colorado and Oslo, Norway are described. The two cases at Denver cost United Airlines over $2 million in damage to 12 B737-300 engines. The hazard is identified as heavy freezing drizzle through examination of National Weather Service observations of upper level temperature and humidity, satellite, radar, and freezing rain sensor data. The official National Weather Service observation during these cases, however, was either light snow and mist or light freezing drizzle. The reason for this misreport and underestimate of intensity lies in the current reporting rules for determining freezing drizzle intensity by visibility and not by precipitation-rate. Theoretical relationships are presented that show that the variation in drizzle size distribution and the difference in determining visibility from day and night is the cause of the poor correlation of drizzle rate with visibility.

Loss of engine cowl door

Loss of engine cowl door

Designing hypersonic inlets for bow shock location control

The desire to match the bow shock of a hypersonic vehicle to the lip of the engine cowl provides for a design constraint on the hypersonic forebody. For in viscid flow, it is shown that there is one particular wedge angle which provides for shock matching which is insensitive to steady-state changes in vehicle angle of attack, though it is not possible to match against changes in flight Mach number. The angle-of-attack sensitivity of a hypersonic boundary layer makes this matching process more difficult. Design rules for cowl matching with secondary shocks are presented, though it is shown that it is never possible to fix them against changes in angle of attack.

Safety Topics

AFTER a 10‐hour direct flight a Boeing 707 had landed and clearance had been given to the stand. While the aircraft was travelling over a taxiway it was seen that a considerable quantity of unused fuel was being blasted rearwards by the jet efflux of No 1 engine. A ground operations vehicle driver also saw flames on the ground under the wing of the aircraft and informed the ground movements controller by radio who alerted the airport fire service. As the aircraft was turning to line up with the stand the captain called for No 1 and 4 engines to be shut down and later, for No 2 to be shut down. After the aircraft had halted he gave clearance for the emergency chutes to be disarmed and then continued with the normal shut down checks. Attention was however directed by someone outside to a ring of flames around the joint between thrust reverser cowling and the engine cowling of No 1 engine and flames also in the tail pipe area. Fire drill was immediately called for on No 1 engine.

Some Flight Simulation Experiments on Jet Noise from Supersonic Underexpanded Flows

Experiments on underexpanded cold jet flows from a convergent nozzle under simulated flight conditions have shown that a large periodic spinning motion of the jet can occur with greatly enhanced broadband noise production. Shadowgraph pictures indicate that this oscillatory jet motion accompanies the generation of random weak shock waves at the source. These waves appear to be generated at the point downstream of the nozzle exit where the shock cells in the jet begin to disappear. The weak shock waves propagate upstream and have been identified to be the cause of enhanced broadband jet noise production in flight. In addition, the results show that the boundary-layer flow conditions over the outside of the primary nozzle (simulating engine cowl flow in flight) influence the production of these random weak shock waves.

Effects of External Boundary-Layer Flow on Jet Noise in Flight

The effects on jet flow of the external boundary-layer flow emanating from the trailing edge of an engine cowl in flight has been shown to be the main reason for the disparity between predicted and experimental results obtained from flight measurements. Flight simulation experiments indicate that the external boundary-layer flow tends to shield the jet flow in flight. This in turn modifies the jet noise source in flight and consequently the radiated noise from aircraft in flight. Close to 0/ = 90° and in the forward quadrant, this study indicates that the far-field jet noise and its spectrum scales approximately with the absolute jet velocity instead of the relative velocity as has been assumed in the existing prediction models.

Automatic Temperature Control for Aircraft

AUTOMATIC temperature control for aircraft long has been neglected, and it is only during the war that adequate attention has been given to this important subject. The increased duties imposed upon flight personnel by the requirements of modern military aircraft, together with the necessity for reducing air drag to the minimum consistent with required cooling, have prompted aircraft designers to give consideration to automatic operation of cowl flaps, oil and coolant flaps, and intercooler doors. Automatic flap operation can be appreciated fully when it is considered that engine cowl flaps fully opened might represent an air drag as high as 40 miles per hour on a 400-mile-per-hour airplane.

Automatic temperature control for aircraft

AUTOMATIC temperature control for aircraft long has been neglected, and it is only during the war that adequate attention has been given to this important subject. The increased duties imposed upon flight personnel by the requirements of modern military aircraft, together with the necessity for reducing air drag to the minimum consistent with required cooling, have prompted aircraft designers to give consideration to automatic operation of cowl flaps, oil and coolant flaps, and intercooler doors. Automatic flap operation can be appreciated fully when it is considered that engine cowl flaps fully opened might represent an air drag as high as 40 miles per hour on a 400-mile-per-hour airplane.

British Reports on German Aeroplanes IX—German Cowlings

THIS note describes the arrangement of the engine cowlings on certain types of German aircraft. In each case the cowling is attached directly to the engine and not to the fuselage so that the engine can be removed complete with its cowling. The arrangement enables the engine to vibrate on its rubber mountings relative to the fuselage without any risk of distortion of the cowling. These cowlings all appear to be designed to facilitate rapid removal and replacement and to have the cleanest possible form when assembled.

U.S. Patent Specifications

An exhaust device for internal combustion engines, comprising in combination a toroidal manifold which is transversely of substantially round cross section, a plurality of flared mouth pipes opening individually from said cylinders in a common direction substantially parallel to the toroidal axis and connecting upon the exterior of the manifold tangentially into the interior of said manifold, an engine cowling, and a plurality of flared mouth outlet pipes opening tangentially from the interior of said manifold and tangentially to the engine cowling in a common direction substantially parallel to said axis into the open air.

U.S. Patent Specifications

The combination with an engine cowl having a front entrance opening, of a disc disposed therein, swinging links guiding the rim of said disc for approximately helical movement, and control means for effecting said movement.

Month in the Patent Office

A power plant for aircraft includes an engine‐cooling system, an oil‐cooling system, a super‐charging system, and means for preheating the air supply to the engine, some of which parts are formed integrally with, and others being attached to, the engine crank‐case which alone is adapted for attachment to the aircraft. As shown, a header tank n for the engine cooling system is connected by a pipe o to a radiator r disposed in a tunnel or recess of the engine cowling. The radiator r is connected to a pump u which delivers water to a water‐jacket w from whence it passes by pipes x to the tank n. Air passing through an oil cooler 11 is led to the carburetter air‐intake 13. Only a part of the air flowing through the radiator r may pass through the cooler 11. An oil suction pump 15 draws oil from the cooler.

Why Use Cowl Flaps

* I A HIS paper refers to the adjustable type of cowl •*• flaps, controllable from the cockpit, as used on the trailing edge of the N.A.C.A. type of radial engine cowling. Although these cowl flaps have been employed extensively, both in this country and in Europe (Plates 1, 2, 3 and 4) there still seems to be a considerable difference of opinion in the industry as to the desirability of using them. It appears to be the feeling among many designers that any advantage that may be gained through the use of cowl flaps is limited to the case of unbaffled engines, and that in the case of engines of high specific output, equipped with the conventional pressure type of baffle, the improvement in cooling or performance through the use of cowl flaps is negligible. This misunderstanding exists but the reason for it is not entirely clear since considerable test data have been published, which show that cowl flaps are not only effective in improving the performance of aircraft, but that in many cases their use is necessary in order to realize the full advantage of the modern high-powered engine. During the past year additional tests have been conducted on radial engine cowls by the N.A.C.A. and by the United Aircraft Corporation which, due to improved methods of presentation and a clearer understanding of engine cooling and cowl drag, afford conclusive data on the efficacy of cowl flaps. The purpose of this paper is to analyze these new data and to show that the use of cowl flaps accomplishes the desirable end of providing adequate cooling at all air speeds, including ground running, and at the same time limits the drag due to cooling at maximum speed to the minimum attainable with the conventional type of N.A.C.A. cowl. The N.A.C.A. has, as a result of theoretical analysis checked by actual tests, arrived at a fundamental criterion which clarifies the phenomena accompanying the cooling of finned cylinders to a point where it can be applied in an easily understandable form. The cooling {i.e., cylinder temperature) for a given enginebaffle-cowl combination is a function of the mass flow of air passing the cooling surfaces. The mass flow of air

Taste in Engine Cowlings

THE subject of air‐cooled engine cowling is one in which we have taken a special interest ever since the inception of AIRCRAFT ENGINEERING. In our first issue, in March 1929, we published the now famous Technical Note No. 301, which first gave the results of wind tunnel experiments with the then new N.A.C.A. cowling, and in the following month we published a full summary of Report No. 314, which developed the subject. Following with dramatic rapidity came rumours of the Townend Ring, the tests with which were first revealed to the public at the annual “Inspection” of the N.P.L. on June 18th, 1929, some of which were published in the issue of AIRCRAFT ENGINEERING for July of that year. Mr. Townend read his paper on his invention to the Royal Aeronautical Society on March 6th, 1930, and this appeared in full in these pages the following month.

Engine Cowl Rings

Abstract The radial air-cooled engine is a popular power plant. Its reputation with the public can be said to date from the summer of 1927, when it demonstrated its reliability and ruggedness in the hazardous long-distance flights of that year. Since then many refinements and improvements have been brought forth, but the drag of the radial engine has always been high. Large frontal areas are inherent with the radial engine, and as the power output of the present radial has increased, so has its frontal area. Until recently it did not seem likely that the radial engine could ever successfully compete with the liquid-cooled type as the power plant for use in high-speed airplanes. However, with the development of the N.A.C.A. type of cowling and the engine cowl ring by various aerodynamical laboratories, the big gap existing in actual ship’s performance between these two widely divergent power plants has been eliminated.