Detailed Description of the Preferred Embodiment

Referring to Figures 1-3, the body 1 of a typical jet transport aircraft is generally divided into upper and lower lobes. Figures 1 and 2 show a typical cross section between adjacent ribs. The upper lobe comprises that portion of the body (fuselage) 1 that generally extends above the floor 2 to enclose the cabin 3 (which may in fact have more than one level), and is normally occupied by crew and passengers during flight. Conversely, the lower lobe comprises that portion of the body 1 that generally extends below the floor 2, and normally houses cargo bays 4. Both lobes can conveniently be subdivided into port and starboard sides, which will be symmetrical with exceptions such as doors. As may be seen in Figure 1, the present invention can be used to provide controlled ventilation within all four quadrants of the body 1 (upper lobe-port side; upper lobe-starboard side; lower lobe-port side; and lower lobe-starboard side). For simplicity of description, the following discussion will focus on only one quadrant (upper lobe-port side) of the body, it being understood that the same provisions can be made (with appropriate substitutions of components) within each of the other quadrants as desired.

An upper lobe envelope 5 encompasses the components of the body 1 between the outer skin 6 and the cabin liner 7. Similarly, a lower lobe envelope 8 encompasses the components of the body 1 between the outer skin 6 and the cargo bay liner 9. Conventionally, an anti-corrosion treatment 41 is applied on the interior surface of the skin and on structural members within the envelope. An insulation blanket 10 is normally provided within the upper and lower lobe envelopes 5, 8, and is typically secured to the stringers 11, so that a small gap 12 normally exists between the skin 6 and the outermost surface of the insulation 10.

The present invention provides an environment control system which operates by controlling flow of air within both the cabin 3 and the upper and lower lobe envelopes 5 and 8. The system comprises an airflow control device 13; upper and lower lobe envelope supply ducts 14P, 14S, 15P and 15S which communicate with the airflow control device 13 and which run generally parallel to the aircraft longitudinal axis; one or more ventilation air branch lines 16 which communicate with each of the upper and lower lobe envelope supply ducts 14, 15 and extend into the respective upper and lower lobe envelopes 5, 8; a plurality of return air controllers 17 which communicate with a respective main return air duct 18P, 18S; an outflow valve 19 communicating with the main return air ducts 18 ; a cabin air conditioner 20; a cabin supply air duct 21; and a control unit 22.

The lower lobe envelope supply ducts 15P and 15S and associated ventilation air branch lines 16 are independent of the main part of the system and can be omitted if desired.

Referring now to Figure 3, dry ventilation air 24, for example air bled from the compressor section of an engine 23 in a conventional manner and optionally conditioned (that is, cooled and possibly dehumidified) by conventional conditioning packs 23a, is supplied to the airflow control device 13. The airflow control device 13 operates in response to control signals A from the control unit 22 (or optionally is pre-set) to divide the flow of ventilation air 24 to create an envelope air stream 25, at least a portion of which is distributed to the upper lobe port side envelope 5 through the port-side upper envelope supply duct 14P and ventilation air branch lines 16, and a cabin air stream 26 which is supplied to the cabin air conditioner 20.

In the illustrated embodiment, the airflow control device 13 is provided as a unitary control valve. However, it will be appreciated that the airflow control device 13 may be provided as any suitable combination of one or more valves; dampers, orifices or duct assemblies, which may be used in combination with conventional ventilation ducts previously existing within an aircraft. Similarly, the ventilation supply duct 14P may be a separate air supply duct, or may be a supply air duct, such as cabin or gasper ventilation air supply lines, previously installed in an aircraft.

The ventilation air branch lines 16 are distributed at suitable intervals along the length of the upper envelope supply duct 14P so as to provide a distribution of envelope air 25 along the length of the upper lobe envelope 5. The number of ventilation air branch lines 16 will, in general, depend on the tightness of the envelope (i.e. leakage between cabin and envelope) and the presence of air-flow obstructions within the envelope. In aircraft with a particularly tight cabin liner and few obstructions to longitudinal flow within the envelope, as few as one ventilation air branch line 16 may be used. In other situations, a greater number of ventilation air branch lines 16 may be preferred. Conveniently, a single ventilation air branch line 16 can be provided in each rib space of the body 1. Each ventilation air branch line 16 includes a plurality (four are shown in the illustrated embodiment, see Fig. 1) of shell-side nozzles 27, which are designed to inject envelope air 25 behind the insulation 10, that is, into the space 12 between the skin 6 and the insulation 10. The shell-side nozzles 27 are distributed at suitable intervals around the circumference of the upper lobe envelope 5, so that envelope air 25 can be supplied to the envelope 5, behind the insulation 10. The number and spacing of shell-side nozzles 27 will depend on the tightness of the cabin liner, and the presence of obstructions to circumferential movement of air. Preferably, the envelope air flows are controlled to be sufficient to neutralize stack effect pressures (of up to 1.5 Pa with a least one flow blocker per side) and create slightly higher pressures in the envelope relative to the cabin (e.g., at least 0.5 Pa).

The " stack effect" is a phenomenon which occurs within the envelope and which tends to cause a circumferential flow of air within the envelope. In general, envelope air between the insulation 10 and the cabin liner 7 tends to rise (because it is lower density); passes through the insulation 10 where it contacts the fuselage skin 6 and cools; the cold envelope air between the insulation 10 and the skin 6 tends to sink (because it is higher density), and passes back through the insulation 10 near the floor 2 of the cabin 3. The amount of this natural convective flow depends on cabin height, the temperature differential across the insulation 10, and the presence of flow restrictions. In a conventional aircraft fuselage, stack effect pressures of up to approximately 3 Pa or more can be encountered at cruising altitudes.

In order to reduce stack effect, it is useful to provide at least one flow blocker 28 within the envelope 5, which serves to block circumferential movement of air within the envelope 5. Preferably, a flow blocker 28 is positioned between the panel 7 and the insulation 10, and squeezes the insulation against the skin 6 or stringer 11. In most conventional jet transport aircraft, a single flow blocker 28 will normally be sufficient. In such cases, the flow blocker 28 can advantageously be installed at approximately mid-height within the envelope 5 (i.e. just above the windows (not shown) on both sides of a conventional jet transport aircraft). This reduces stack effect pressures to approx. 3 Pa or less at cruising altitudes. In very large aircraft, particularly those with multi-level cabins, it may be necessary to install two or more flow blockers 28 on each side.

Optionally, one or more cabin-side nozzles 29 (two are shown in the embodiment of Figure 1) can also be provided in order to inject envelope air 25 into the upper lobe envelope 5 in front of the insulation 10, that is, between the insulation 10 and the cabin liner 7.

When the envelope air 25 is injected behind the insulation 10, the envelope air 25 will be cooled well below the cabin temperature (for example, by as much as 60C, going from +20C to -40C). This cooling promotes ventilation air contaminant sorption and condensation in the envelope. In particular, most VOCs identified in cabin air (see Figure 8a) may condense at temperatures well above -40C on cold envelope surfaces (for example the interior surface of the fuselage skin 6 and adjoining structural members), during cruising flight. Particles (e.g. oil aerosol) entrained within the envelope air stream 25 may impact and adhere to the interior surface of the skin (or adjoining surfaces), and/or will be removed (by physical filtration or electrical forces) as the air passes through the insulation blanket 10 toward the cabin.

It will be noted that any water vapor present in the envelope air 25 will also tend to condense on the cold surfaces within the envelope 5. However, because of the extremely low relative humidity of the envelope air 25, at least during the cruise phase of flight, the amount of moisture likely to accumulate within the envelope 5 is negligible.

Sorption of VOC's within the envelope 5 can be enhanced by replacing the conventional anti-corrosion treatment 41 with an improved composition having both anti-corrosive and enhanced VOC sorbent properties. The combined anti-corrosion/VOC sorption treatment 41 on the skin and structural members in the envelope is formulated to: not freeze at temperatures above -50C; maximize sorption of typical ventilation air VOCs in the temperature range 0 to -40C; and maximize desorption of these compounds in the temperature range 10C and higher. A particularly suitable formulation will be capable of performing multiple sorption/desorption cycles without hysteresis (i.e. it does not gradually become loaded with effectively permanently sorbed VOC's) or chemical degradation. It contains an anti-oxidant that ensures that it will not harden for several years and so will remain sorbent between regular maintenance cycles when it can be renewed.

The envelope air 25, after being cooled, passes through the insulation 10 to the cabin liner 7. During this passage, the air is heated by the dynamic insulation effect before it enters the cabin 3. If the envelope air 25 is injected in front of the insulation 10, contaminant removal through sorption and condensation is reduced. However, the envelope 5 is still pressurized with dry air throughout, preventing humid cabin air entry and thus allowing the cabin 3 to be humidified to desirable levels. Nozzles placed behind the insulation 10 improve the efficiency of VOC contaminant removal during flight at cruising altitudes through sorption and condensation, removal of ozone through surface contact with reactive materials, and deposition of particles through centrifugal and electrical forces. Nozzles placed in front of the insulation 10 simplify the installation and reduce heat loss. Either option, taken alone or in combination, can be utilized as required.

In order to ensure that air passes from the envelope 5 and into the cabin 3, the cabin must be maintained at a slight negative pressure relative to the envelope. This can be accomplished by drawing return air from the cabin 3, by connecting the return air ducts 18 in communication with the cabin space, for example via one or more simple return air grills.

In order to provide enhanced system capability, one or more return air control units 17 are provided at suitable intervals along the length of body 1, as shown in Figures 1 and 2. The use of such return air control units 17 permits return air to be selectively drawn from either the cabin or the envelope, as desired, thereby facilitating smoke removal, envelope purging, and fire suppressant injection while maintaining a negative pressure in the envelope relative to the cabin. Conveniently, a return air control unit 17 can be provided in association with conventional return air ducting arrangements previously provided within an existing aircraft. In the illustrated embodiment, a return air control unit 17 is provided in each rib space, at the floor level of the upper lobe envelope 5. Each return air control unit 17 comprises a housing 30 having an envelope opening 31 communicating with the upper lobe envelope 5, and a cabin opening 32 communicating with the cabin 3. A damper 33 within the housing 30 enables a selected one of the envelope opening 31 and the cabin opening 32 to be opened and the other to be closed. Thus return air can be selectively drawn from within the envelope 5 or the cabin 3, as desired and in accordance with the operating regime of the aircraft. The position of the damper 33 can be controlled by any suitable drive means (not shown), such as, for example, a solenoid, servo motor or pneumatic actuator in response to control signals B received from the control unit 22. Each return air control unit 17 communicates with the main return air duct 18 through which return air 34 (whether drawn from the envelope or the cabin) can be removed from the upper lobe of the body 1.

Return air 34 from the cabin 3 (or the envelope 5) flows through the main return air duct 18P and is supplied to the (conventional) outflow valve 19. The outflow valve 19 operates in response to control signals C received from the control unit 22 to maintain cabin pressurization, vent at least a portion of the return air 34 out of the aircraft as exhaust air 35, and (possibly) supply the remainder of the return air 34 to the cabin air conditioner 20 as recirculated air 36.

The cabin air conditioner 20 may, for example, generally comprise one or more conventional mixing and filtering units 20a, and a humidity control unit 20b, which operates in response to control signals D from the control unit 22. In operation, the cabin air stream 26 from the airflow control device 13, and recirculated air 36 from the outflow valve 19 are combined in a mixing unit 20a, then filtered, cooled (or heated) as required, and humidified by the humidity control unit 20b to create cabin supply air 37. The cabin supply air 37 is then supplied to the cabin through the supply air duct 21.

In the illustrated embodiment, fire suppression is provided by means of a container of chemical fire suppressant 38 , such as, for example Halon (trade name) or an equivalent, connected to the envelope supply ducts 14 and 15 via a valve (or valves) 39 which is responsive to a control signal E from the control unit 22 . Upon opening the valve 39, chemical fire suppressant is supplied to the envelope 5 to extinguish the fire. This fire suppressant supply could be from an existing cargo fire suppressant system or it could be added.

If desired, each of the envelope supply ducts 14P, 14S, 15P and 15S can be provided with its own valve 39, which can be independently controlled by the control unit 22. In this case, chemical fire suppressant 38 can be drawn from a single, common container, or from separate independent containers as desired. This arrangement has the benefit that chemical fire suppressant can be selectively delivered to any desired quadrant of the envelope 5P, 5S, 8P and 8S. Thus smoke/fire detectors can be strategically distributed within the envelope 5 (for example near electrical devices or other potential sources of ignition) so that the approximate location of a fire can be detected. Upon detection of a fire, the flight crew can choose to flood only that portion of the envelope in which the fire has been detected, thereby conserving fire suppressant and/or facilitating the delivery of higher concentrations of fire suppressant to those areas of the envelope 5 where it is most needed.

The control unit 22 can suitably be provided as an environment control panel within the cockpit of the aircraft. The control unit 22 can be designed as a simple switch panel, allowing the flight crew to manually control the operation of the airflow control device 13, return air control units 17, outflow valve 19 , cabin air conditioner 20 and fire suppressant valve 39. Alternatively, the control unit 22 can be at least partially automated, such that the operation of the system can be controlled in accordance with one or more predetermined programs and signals.

The environment control system of the invention can be incorporated into new aircraft construction, or installed as an upgrade or retrofit in an existing aircraft. Appropriate evaluation of the aircraft mission (e.g. requirements of moisture control, and whether or not air quality control and additionally fire/smoke suppression are required) and testing of the recipient aircraft type (e.g. configuration and geometry) will reveal the numbers, sizing and preferred locations for each of the elements of the system, as well as which ones (if any) of the optional elements (e.g. flow blockers, cabin-side nozzles, selectable flow return air control units, humidifiers etc.) are required in order to obtain desired operational characteristics. Upgrading an existing aircraft ventilation system in accordance with the illustrated embodiment, which incorporates all optional elements, can be accomplished by the following exemplary steps:

  • The cabin liner 7 and the insulation 10 are removed to obtain access to the envelope 5;
  • One or more lines of flow blockers 28 are installed on each side;
  • An anti-corrosion/VOC sorbent material 41 is applied on the metal in the envelope;
  • The insulation 10 is refitted as necessary to make a continuous blanket. Either new insulation can be used, or the existing insulation can be reinstated;
  • The fire suppressant container 38 (existing or new, if desired) and its control valve(s) 39 are installed;
  • Upper lobe envelope ventilation supply ducts 14 (and lower lobe envelope ventilation supply ducts 15 if desired) and the associated branch lines 16, including shell-side nozzles 27 and (if desired) cabin-side nozzles 29 are installed;
  • A cabin air conditioner (filter, humidifier) is installed and interconnected. The air conditioner outlet (cabin supply air) is connected to the existing cabin air ducting, which thereafter functions as the cabin supply air duct system;
  • The airflow control device 13 is installed and connected to the main ventilation duct and to the cabin ventilation and envelope ventilation supply ducts.
  • Return air control units 17 are installed in the existing return air plenums at the floor level of the cabin envelope 5. Care is required to ensure proper sealing around the housings of the return air control units 17 so as to minimize leakage;
  • Return air ducts 18 are installed on both sides of the aircraft and connected with the return air control units 17 and the existing outflow valve 19;
  • The system main control unit 22 is installed in the cockpit and connected to the airflow control device 13, return air control units 17, outflow valve 19 air conditioner 20 and fire suppression valve 39 in order to control the various elements of the system. In addition sensors for detecting temperature, humidity, smoke(fire) within the cabin and envelope and optionally an envelope/cabin pressure difference logger are installed at desired locations within the cabin and envelope and connected to the control unit 22 to provide information in respect of system operation;
  • If desired, heat exchanger units are installed in the lower lobe and interconnected with the return air ducts 18, and associated thermostats located in the cargo bay(s) 4, so that the cargo bay(s) 4 can be heated by warm return air 34.
  • Finally, the cabin liner 7 is reinstalled, with care being taken to close holes and gaps, so that desired pressures can be maintained within normal cabin ventilation air flow rates.

In use, the above-described system can provide controlled ventilation of the upper lobe envelope 5 and within the cabin 3, in various ways, depending on the flight regime of the aircraft. In the following examples, four exemplary modes of operation of the system are described, with reference to Figures 3 to 7.