Evaluating Fixed Wing Aircraft in the Aircraft Carrier Environment
Total Page:16
File Type:pdf, Size:1020Kb
EVALUATING FIXED WING AIRCRAFT IN THE AIRCRAFT CARRIER ENVIRONMENT by Mr. C. P.Senn STIKE AIRCRAFT TEST DIRECTORATE NAVAL AIR TEST CE/TER PATUXENT RIVER, MARYLAND 20670-5304 UNITED STATES OF AMERICA The Aircraft Carrier Flieht Deck Layout Operating fixed wing aircraft from today's modern aircraft carrier is a demanding task. Evaluation of aircraft/ship compafi- The flight deck layout of today's modem aircraft carrier is bility, both during the concept development phase and FullScale shown in figure 1. Two steam powered catapults are located Development (FSD) ground and flight tests presents the evaluation forward (bow catapults) and two catapults are located amidships on team with unique challenges. The capabilities and characteristics the port side (waist catapults). Retractable let Blast Deflector of high performance carrier based tactical aircraft must be quanti- (JBD)panels are located aft of each catapult. The centerline of the flied for the catapult launch and subsequent flyaway, and the carrier landing area is angled relative to the ship's centerline, permitting approach and arrested landing tasks. Catapult launching involves simultaneous catapult launch operations from the bow catapults determining the minimum safe launch airspeeds while maintaining and arrested landing operations. Four arresting gear cables, acceptable flight characteristics in this low altitude, high angle of connected to arresting engines are located in the landing area. The attack (AOA) regime. Approach and landing requires the slowest first is approximately 170 ft (51.8 m) from the stern with approx. possible approach airspeeds while retaining the performance and imately 50 ft (15.2 m) between each arresting gear cable. Visual handling qualities needed for precision glide slope control. glide slope information is provided to the pilot by a Fresnel Lens Defining the lowest catapult launch and landing airspeeds reduces Optical Landing System (FLOLS). Aircraft are moved between the wind over deck (WOD) requirements, resulting in reduced ship's flight deck and the hangar deck by four elevators. operating speed and increased operational flexibility. The tight operating confines of the flight and hangar decks, in conjunction Capult Launch with the large number of other aircraft, support equipment, and personnel dictate unique design requirements which must be Evaluation of the catapult launch environment of an airplane considered in the earliest design stages of a new airplane. This covers many disciplines. These areasinclude: paper addresses the shore based and shipboard ground and flight tests which are conducted to assess the flying qualifies, perfor- a) Compatibility with the catapult accessories. mance. and structural suitability of an airplane in the aircraft carrier environment. OPTICAL .AJUUW r CATAPULT NO. 4 4 & FO. 4 'A L CATAPULT NO. I IU (43)- 1,0"7 Fir 1 ft = 0.3048 m -T lUGA CIum Figure 1 Plan View of Flight Deck NIMITZ Class Aircraft Carrier 9. b) Exhaust gas recirculation/reingestion and the ther- warranted to define a wind over deck envelope which reduces the mal/acoustic environment when operating at maximum power in ingestion to acceptable levels. front of the 3rD's. c) Tolerance of the engines to ingestion of steam emitted 3RD from the catapult during the power stroke. d) Structural integrity during the catapult power stroke. e) Minimum catapult launch airspeeds and characteristics during the rotation and flyaway phases. f) Shipboard catapult launch operations such as waist cata- pult operations, lateral/directional trim requirements for asymmet- ric external stores and crosswinds, etc. Airplane Positioned Airplane Positioned In Catapult Shuttle Aft of JBD Catapult accessories are the items of hardware necessary to Figure 2 attach the airplane to the catapult. Items considered are: Airplane Locations During JBD Testing a) Ease of installation of the repeatable release holdback bar on the nose gear. Steam Ingestion b) Tracking of the launch bar tee head and holdback bar in Steam catapults typically emit launch steam above the deck the catapult nose gear launch guide rails, during the launching operation. The design of the engine inlets and the proximity of these inlets to the catapult shuttle frequently c) Mating of the launch bar tee head with the catapult cause this above deck steam to be ingested through the engine(s) spreader. of the airplane being launched. The result is that the engine is forced to operate at off-design conditions and instabilities can d) Clearance between the airframe and external stores and occur. These instabilities can take the form of minor pressure above deck obstructions such as the catapult shuttle, catapult fluctuations within the compressor or the afterburner and could control station. etc. result in blowout, compressor stall or engine flameout. e) Holdback bar dynamics following release due to the The primary wnthod of determining susceptibility to stall is sudden release of high stain enegy. to conduct shore based catapult launches from a degraded catapult. The catapult is intentionally degraded by removing plugs in the Jaftermost plate of each piston assembly. This allows steam in the cylinders to travel forward of the aft face of the piston, bypass the catapult cylinder sealing strip as the shuttle assembly lifts the Exhaust gas recirculation and reingestion can occur when an sealing strip during the power stroke, thus allowing the steam io airplane is operating at maximum power levels when positioned in exit above deck around the catapult spreader. This steam leakage front of the JBD. Reingestion of exhaust gas can cause an exces- produces conditions that are more severe than those encountered in sive temperature rise in both the compressor and turbine sections, the actual shipboard environment. The airplane is launched a resulting in damage to the engine. Ingestion of exhaust gas by the sufficient number of times (about 30 launches) to reasonably airplane positioned behind the JBD can also result in damage to ensure that no instabilities are encountered. An appropriate it's engine. Impingement of the exhaust plume on the JBD panels number of additional launches will also be required if the engine is can result in local hot spots which can cause premature warping equipped with an afterburner. Testing is confined to those days and cracking. lBD operations can also result in a severe acoustic when the surface winds are less than 10 knots and ± 20 deg relauve and thermal environment. Shore based tests are conducted using a to the catapult centerline. Telemetered engine performance param- shipboard representative JBD installation. Testing consists of eters are monitored to ensure continued satisfactory engine perfor- placing one airplane forward of the JBD panels and a second mance. airplane aft of the panels as shown in figure 2. The position of the airplane in front of the JBD is varied from the minimum to the maximum engine tailpipe to JBD distances representative of shipboard TBD/caapult combinations. Military and afterbumer thrust (if available) runs are conducted for approximately 30 A typical catapult launch structural envelope is shown in seconds. Both airplanes monitor engine inlet and exhaust gas figure 3. This figure shows the longitudinal acceleration temperatures and other critical parameters. The acoustic and (NX)/aunch b,," load/maximum gross weight boundaries. thermal environment is monitored using microphones and ther- mocouples mounted on the airframe and in the vicinity of the JBD. Pole mounted instrumentation provides jet blast velocities and temperatures in the flow field beside and behind the JBD. Generally, the wind over deck during shipboard operations tends to alleviate any recirculation. reingestion. or thermal problems. However, if an airplane has demonstrated a tendency to have excessive exhaust gas ingestion. a shipboard test program may be Maximum) Deceasiesthe amount of energy imparted to the airplane M mresulting in conservation of water and fossil fiel/core life. A sThe catapult launch minimum end airspeed is defined by a set WOO Required -- of related criteria. Although these criteria generally have interre- lated effects, the following addresses each factor separately: a) Proximity to or warning of stall: The stall air- Zspeed/angle of attack defines an absolute minimum. The required safety margin is dependent upon the characteristics of the airpme under consideration. If stall warning (generally in the form of arti- 100 ficial stick/rudder shaker and/or airframe buffet) occurs at some AOA below stall and the warning does not increase in intensity as the airspeed is decreased to the stall, then the angle of attack (AOA) corresponding to stall warning will likely define the mini- mum end airspeed. b) Flying qualities/characteristics at high AOA: Frequently Catapult Endspeed/ an airplane may exhibit adverse flying qualities or characteristics Required Launch Airspeed - ki at high ADA. yet at airspeeds well in excess of the stall airspeed. Figure 3 The pilot must then determine the minimum airspeed/maximum Typical Airplane/Catapult AOA at which the airplane characteristics/flying qualities remain Structural Envelope acceptable. Examples of limiting characteristics include: buffet. wing rock, wing drop. pitch up tendency, nonlinear stick force The Nx and limit launch bar load limits are design numbers gradient, and unacceptable lateral/directional characteristics. which are defined by the mission requirements and maximum performance capabilities of the catapult types from which the c) Proximity to the airspeed at which thrust available equals airplane is to operate. The maximum gross weight is an airplane thrust required or "lockpoint": For practical purposes, the mini- design factor based on a 10% growth factor of the basic operating mum launch airspeed should be at least g kt above the lockpoint. weight of the design. Shore based structural testing consists of Pilots have indicated that the minimum level of longitudinai increasing the catapult end speed unti: either the limit NX or acceleration at which he has the sensation of accelerating is a h bapproximately I kti/sec. This level of acceleration must be avail, launch bar load is reached.