1、SAE AIR*40b A7 m 8357340 0047229 A m K33-o9 AEROSPACE INFORMATION TheEngilk?e7-ngsociety Ih =For Advancing hfobiliiy -Laand Sea Air and Space INTERNATIONAL 400 Commonwealth Drive, Warrendale, PA 15096-0001 R E PORT Submitted for recognition as an American National Standard s, foliage (grasses, leave
2、s, During operation in icing conditions, ice that accumulates on the airframe can shed if aerodynamic and/or vibratory forces overcome the adhesive strength between the ice and the airframe structures. ice may then fall away from the aircraft or, on occasion, impact and damage the aircraft or be ing
3、ested and damage the engine. A slab or chunk of SAE AIRm4096 89 m 8357340 OULI9233 b m Page 3 .set, AIR4096 5.1 (Continued) : During flight operations outside of landing zones, the helicopter engine is subject to the same sources of FOD as fixed-wing power plants. These sources include birds, rain,
4、hai 1, snow, and ice. 5.2 Installati-onc: The engine inlet duct system and areas in front of and over the airframe inlet can be a potential source of FOD. The resulting damage from such items may be referred to as “Bi11 of Materials Object Damage.“ Mechanical fasteners within the inlet duct flowpath
5、 or on doors and access panels in front of or over the inlet can work themselves loose as a result of vibratory forces or improper installation and migrate into the engine, In the case of inlet ducts made of composite materials, pieces of the duct itself may delaminate and be drawn into the engine.
6、Low areas within the inlet duct flow path can trap water which, when subjected to freezing conditions, will convert to the solid phase. Upon engine start-up or under warming conditions, chunks of ice may become dislodged and be ingested. 5.3 Maintenance: Aircraft mechanics and other service personne
7、l, while performing their normal duties, may inadvertently leave hand tools such as screwdrivers, wrenches, sockets, inspection mirrors, etc. in the inlet ducting. Fastening hardware (nuts, bolts, cotter pins, safety wire, etc.) removed during service may accidently be left in the inlet or engine or
8、 may fall into areas that are not easily visible only to be later discovered lodged between rows of damaged compressor rotor blades and stator vanes. Parts bags, tags, rags, maintenance instruction sheets, plastic and metal caps and plugs are all examples of debris that have been left behind followi
9、ng service action only to become potential sources of foreign object damage to varying degrees. People working around aircraft invariably have pockets containing loose personal items (pens, pencils, pocket reference books, six inch scales, notebooks, magnets, flashlights, inirrors, etc.) that can un
10、knowingly fall out and into the inlet duct or engine, Rings, bracelets, necklaces, earrings, watches, and other types of personal jewelry and accessories can all cause extensive damage if allowed to enter the engine. Ground debris can be picked up by footwear and be deposited in the inlet system. 6.
11、 EFFECT OF FOD ON OPERATIONS: The most common effect of foreign object ingestion is damage to the compressor section of the gas turbine engine. The effects may be so minor that the operator cannot detect any change in the engines operating characteristics or be so extreme that the engine becomes ino
12、perable. Therefore, there are forms of FOD that may be considered to be “tolerable“ and those that are entirely “intolerable.“ SAE AIR*4Ob 87 W 8357340 004Z32 8 W 6AE AIR4096 -I Page 4 6.1 6.2 -I.-_.-. Tolerable FOD: _- Tolerable FOD can, in a general sense, be classified as damage which does not de
13、grade engine performance beyond the operating limits established by the engine manufacturer. compressor blade tips or actual loss of small pieces of the blade (tip leading edge) or minor local damage can be tolerated, but may reduce the life of the engine. reduced, ultimately yielding an engine that
14、 runs hotter to produce the same output power as before the ingestion of foreign objects. or overhaul manuals define the extent of damage that is acceptable and actions that can be taken to recover some of the lost performance and to reduce the potential for further damage due to crack propagation f
15、rom FOD i iiduced stress concentrations. The comparatively minor bending of The compressor pumping capacity and efficiency may be Engine maintenance Although the ingestion of “soft“ foreign objects such as paper, plastic bags, leaves, grasses, etc. does not generally cause physical damage to the com
16、pressor, these items can become lodged in front of inlet guide vanes and support struts creating airflow blockages and distorted airflow profiles. Inlet blockage causes an inlet pressure loss and reduces engine output power. The distorted airflow caused by the blockage can, in the extreme, drive the
17、 compressor into surge which, depending upon the condition of the engine and severity of the surge, may cause physical damage to the engine. In all but those cases where the hardware is deformed, engine performance should be recoverable by removing the foreign objects causing the blockage. The term
18、“tolerable“ as used in this section relates to the effect of the ingestion of foreign objects on engine performance. In economic terms, the effects of FOD may not be acceptable when consideration is given to the costs associated with the resulting increased fuel usage, reduced engine life, unschedul
19、ed tnaintenance and repairs, etc. &to.erabl.e FOD (Enqine Failure: Thi s refers to an engine shutdown resulting from physical damage to a mechanical or structural part or component of the engine. before the engine can be used again. the engine to be unable to perform within specification or service
20、manual limits or to be unable to sustain stable operation is essentially an FOD induced fai 1 ure. Mechani cal Pai 1 ures of the engine are defini tely within this classification which has here been expanded to include either blockage or damage short of complete failure that causes the engine to ope
21、rate in an unstable manner or at a speed, temperature, or torque limit while producing unacceptable output power. The damaged hardware must be replaced or repaired Foreign object ingestion that causes 7. FOD PREVENTION TECHNIQIJIS: The reduction and prevention of gas turbine engine damage due to the
22、 ingestion of foreign objects is the responsibility of the engine and airframe designers, the operators and the maintenance personnel . SAE AIR*409b 89 M 357340 0049233 T M AIR4096 I 7.1 7.2 - Engine/Airframe Desiun: must confront FOD as one of many factors affecting the engine design. order to be t
23、olerant of foreign objects, the number of parts projecting into the airflow path should be minimized (e,g., inlet temperature and pressure probes, mechanical fasteners, etc. 1. The use of capti ve bolts, retained nuts and washers, self-locking fasteners (versus lockwire) and other devices which limi
24、t the number of free small parts will enhance an FOD resistant design philosophy. The engine designer may wish to consider use of wide chord compressor blades having comparatively blunt leading edges that can more readily survive the abuse of impacting foreign objects. Similarly, variable inlet guid
25、e vanes (VIGVs) can help increase engine tolerance to FOD by acting as a crude fence to prevent the object from reaching the rotating machinery. This assumes that the object does not cause the VIGVs to break loose and collide with downstream rotor blades. Of course, the selection of a specific bladi
26、ng design is governed by many other considerations such as aerodynamic performance, weight, cost, producibility, reliability, and maintainability. FOD tolerance can be only one constraint on the selection of a specific compressor configuration. The engine designer is the first individual who In . An
27、 engine design objective of reducing the number of tools required for user level maintenance would have the effect of reducing the likelihood of FOD, Both the engine and airframe designer have the responsibility to assure that no liquid collection areas exist in the engine and airframe inlet ducting
28、. Should potential pooling areas be unavoidable, adequate drainage should be provided. The design should also be such that leakage of flammable fluids into the engine intake system is not possible. The airframe inlet ducting should not have mechanical fasteners of any kind in the airflow path. Acces
29、s panels or doors in front of or over the airframelengine inlet should have retained fasteners. possible on the aircraft in order to reduce the chances of ingestion of ground debris lifted into the air by the action of rotor downwash. The airframe inlet duct itself should be pitched away from the en
30、gine inlet such that it cannot be used as a shelf or surface on which service personnel may place parts. If angled away from the engine inlet, the airframe duct will not have the tendency to act as a chute which can naturally direct any object entering the duct into the engine. capable of being “eas
31、ily“ inspected up to the engine inlet face. Airframe inlets should be located as high as The airframe inlet duct should be - Foreign 0b.iect Inaestion Prevention Equipment: There are numerous devices available that can help reduce the potential for gas turbine engine FOD in rotary-winged aircraft. S
32、ome of these mechanisms are used exclusively for FOD protection, while others are used primarily for other purposes but provide FOD protection as an additional benefit. AIR4096 Page 6 7.2 (Continued): I Many aircraft include “FOD screens“ at either the airframe inlet duct entrance or at the interfac
33、e plane between the airframe inlet duct and the engine inlet. are constructed from 0.03 to 0.06 inch diameter wire. generally become nonuniform over the screen surface during forming such that they are quite small in some areas and large in others. Provisi-ons are made to allow airflow to bypass the
34、 screens in the event of blockage. Inlet screens should themselves be able to withstand the impact of foreign objects and should be constructed so as to preclude the possibility of loose strands of screen wire becoming a foreign object that could be ingested. Additionally, these screens should be ea
35、sily and routinely inspected. Airframelengine inlet ducting can be protected against ice formation and/or accumulation by the use of anti-icing systems. These systems usually involve heating of duct surfaces with engine bleed air or electrical energy. provide anti-icing capability. dependent on the
36、particular application. These screens are generally 4 mesh (4 openings per inch) and The openings The duct surface temperature is maintained sufficiently high to Heat rates and temperatures required are Inlet particle separators (IPS) of various designs are examples of components that are not specif
37、ically designed to prevent engine FOD but which do tend to reduce it. Although IPS flow areas are larger than the engine inlet area, the annulus gap is typically smaller and, therefore, prevents the larger foreign objects from reaching the engine core inlet. addition, separators that are designed to
38、 use inertial separation of particulates will allow fewer foreign objects to reach the engine core inlet. These comments generally apply to engine mounted particle separators, the larger scale airframe particle separators, vortex tube assemblies, and plenum chamber type inlet systems. Plenum chamber
39、 inlet systems have been included here as crude separators in that they act as settling chambers. In I FOD prevention can be considered during the design of engine mounted IPS systeins. Splitter lip radial location and scavenge vane spacing/throat area, for example, can influence foreign object inge
40、stion rates. 7.3 M&i?t.e.n-a-n.ce Clean1 iiiess: Conscientious maintenance and flight personnel can affect a significant reduction in engine FOD. People that are trained and aware of the potential hazards associated with allowing loose objects to exist in helicopter engine inlet systems are more lik
41、ely to check for such i tems prior to releasing the aircraft for flight. b D SAE AIR*409b 89 H 8357390 0049235 3 M Page 7 AI R4096 There are numerous things that maintenance supervision can do to help these individuals reduce the occurrence of engine FOD. exampl es : Consider the following Include F
42、OD as a topic in training prograins Include FOD as a topic in organization newsletters Install FOD-related posters or signs in hangar areas Use maintenance stands designed to account for each item used during Institute a maintenance and servicinq checklist aircraft servicing Ensure that engine inlet
43、 covers are sed Restrict the type of footwear allowed in flight (i.e., non-ridged soles) A checklist could consist of the following specifically performed on the engine and a when the helicopter is not the service a items and WOU rcraft inlet: ea n d pertain to work Ensure that all hand tools are re
44、moved from the aircraft Are all personal effects accounted for? Have all replaced parts been removed from the aircraft? Account for parts bags, tags, manuals and shop rags Check that all fasteners are tightened and secure Visually inspect rotorcraft and engine inlet for any loose objects 7.4 Effects
45、 on Engine: The use of inlet duct anti-icing systems, FOD screens, and particle separators will have an effect on engine performance and, therefore, aircraft capability. Engine bleed air anti-icing systems produce a loss of engine output shaft power since the bleed air is no longer available to prod
46、uce work in the turbines. Electrical anti-icing systems also reduce the available engine output power due to the increased generator load requirements. With FOD screens and inlet particle separators, a loss of engine output power will result from increased inlet system pressure losses. For an FOD sc
47、reen, the magnitude of the pressure loss is a function of the screen geometry and air velocity. The pressure loss of a separator is a function of the type of separator used and its airflow velocity characteristics. If a blower is required as part of the separator design, the power required to drive
48、it represents an additional loss. All three of the above protection systems produce weight penalties which, when combined with the lower engine output power, cause a reduction in aircraft mission capabilities. SAE AIR*4096 89 W 8357340 0049236 5 W I AIR4096 Page 8 7.4 (Continued): FOD screens and du
49、ct design influence how the airflow is presented to the engine inlet and the resultant compressor inlet distortion. This can impact compressor performance and stability and is a definite design consideration. distortion and testing is conducted to verify compliance, Maximum 1 imi ts are normally imposed on al lowable inlet Both FOD screens and particle separators must themselves be designed to provide acceptable operation under icing conditions. requirement adds complexity to the system and generally creates additional pressure and power losses. incorporate a bypass fl
