Example 1, Normal Cruising Flight

Under normal operation at cruising altitude, the flows of envelope air 25 and cabin air 26 are controlled such that the envelope pressure is slightly greater than that of the cabin.

The envelope air 25 supplied to the envelope 5 through the shell-side nozzles 27 contacts the cold skin 5 and contaminants are removed at least in part by sorption (e.g., by the anti-corrosion/sorption treatment 41), condensation and filtration (e.g., by centrifugal and electrical forces), and then stored on the interior surface of the skin 5 and other cold surfaces within the envelope or as an aerosol. The extremely low relative humidity of the ventilation air 24, and thus the envelope air 25 (typically less than approx. 5% at cabin temperatures) means that no significant moisture condensation will accumulate within the envelope 5. The envelope air 25 then flows back through the insulation 10 (as shown by the arrows in Figure 3), and enters the cabin 3 by leakage through the seams 40 between panels of the cabin liner 7.

For example, an envelope pressurization relative to the cabin 3 of between 0.5 and 5 Pa (preferably between approximately 1-2 Pa) and total envelope ventilation air 24 injection flows of less than the minimum cabin ventilation rate required for passenger transport aircraft of 0.55 lbs per person (which is equivalent to 10 c.f.m. per person at 8,000 ft. cabin pressure altitude) can be maintained for a cabin liner 7 paneling leakage area of less than 73 cm2 per person (or, equivalently, 440 cm2 per six passenger row). For a 5 c.f.m. per person envelope air flow rate, and a stack pressure of 2 Pa, the leakage area per six passenger row can be up to 100 cm2. For a leakage area of 440 cm2, moisture diffusion from the cabin to the envelope through typical panel openings is less than 5 mg/s per row (crack length) at a cabin humidity of 60%. At this rate, a 30 row 180 passenger plane would accumulate a maximum of about 1 pound of moisture during a three hour flight. Actually, it will be negligible because convective transfer from the envelope to the cabin will offset upstream or back diffusion.

To achieve the allowable leakage areas, the integrity (i.e. minimized leakage area) of the cabin liner 7 paneling must be maintained throughout and any openings at the overhead compartment must be sealed. With this degree of sealing, during a sudden aircraft depressurization event (for example, if a cargo door opens in flight), one or more panels of the cabin liner 7 will "pop" to equalize the pressure difference between the cabin 3 and the envelope 5. Additionally, the damper 33 of the return air control units 17 can be designed so that both the envelope opening 31 and the cabin opening 32 will open automatically in a sudden depressurization event. When insulation continuity is maintained, envelope air 25 entering the cabin 3 from behind the insulation 10 will be warmed by dynamic insulation heat recovery as it passes through insulation gaps.

As shown in Figure 3, during normal flight at cruising altitude, envelope air 25 is injected behind and/or in front of the insulation 10,and the cabin recirculation system is operating (that is, cabin supply air 37 made up of cabin air 26 and recirculated air 36 are being supplied to the cabin 3 via the cabin air conditioner 20). The return air control units 17 are set so that return air 34 is drawn from the cabin 3. In this mode, the cabin air conditioner 20 can be operated to maintain cabin relative humidity levels in excess of 20% (preferably between 40 and 50%). Moisture condensation within the envelope 5 from humid cabin air is prevented by the relative pressurization of the envelope 5, and the envelope is kept dry. Furthermore, contaminant gases and particles within the envelope air 25 are removed in part prior to entering the cabin 3 by sorption and condensation, and physical filtering as it passes back through the insulation 1,thereby improving cabin air quality over that typically encountered in conventional aircraft.

Return air 34 is drawn from the cabin 3 through the return air control unit(s) 17 and the main return air duct 18. If desired, this return air 34 can be used to heat the lower lobe through the use of one or more heat exchangers (not shown).

The outlet valve 19 operates to vent a portion of the return air 34 out of the aircraft as exhaust air 35, and supplies the remainder as recirculated air 36 to the cabin air conditioner  20.

Example 2, Taxi and Ascent

Figure 4 illustrates system operation during taxi and ascent to cruising altitude. Conventionally, the cabin pressure is maintained to an altitude equivalent of approximately 8000 ft., which means that the cabin pressure during the cruise phase of flight will be approximately three-quarters of sea level pressure. Thus during the initial portion of ascent, the cabin depressurizes, and approximately one quarter of the air in the envelope 5 at take-off would normally tend to bleed into the cabin 3. During this period, the envelope 5 will be relatively warm in comparison to cruising altitude temperatures, and VOCs sorbed and condensed in the envelope may volatilize. The airflow control device 13 is operated to pressurize the cabin relative to the envelope. At the same time, the return air control units 17 are controlled to draw return air 34 from the envelope 5, and the outflow valve 19 vents all of the return air 34 out of the aircraft as exhaust air 35. This operation effectively purges VOC contaminants (chemical and microbial, if any) within the envelope 5, and prevents them from entering the cabin 3. In a conventional aircraft ventilation system, these contaminants would normally be drawn into the cabin during ascent.

Example 3, Descent and Taxi

Figure 5 illustrates system operation during descent from cruising altitude as the cabin pressurizes, and taxi after landing. During this period the envelope is comparatively cold relative to the outside temperatures, and injection of air into the envelope during this phase of flight would cause accumulation of moisture condensation. Accordingly, for descent and taxi, the airflow control device 13 operates to divert all ventilation air 24 into the cabin air conditioner 20, and the return air control units 17 draw return air 34 from the cabin 3, thereby effectively isolating the envelope 5. The outflow valve 19 can be operated to vent all of the return air 34 as exhaust 35 or recycle some of the return air 34 back to the cabin air conditioner 20 as desired.

Example 4, Ground Purging

Operation of the environment control system of the invention during taxi and ascent (Example 2 above) is effective in purging VOCs from the envelope 5. However, in some cases it may be considered good practice to perform additional purging of the upper lobe envelope 5 as well as the lower lobe envelope 8 while the aircraft is parked (such as, for example, between flights). In this case, ventilation air 24 can be provided by a conventional ground conditioned air supply unit 42 connected to the two upper lobe ventilation air ducts 14 upstream of the airflow control device 13, as shown in Figure 6, and to the two lower lobe ducts 15. The airflow control device 13 directs ventilation air 24 into the envelope 5 via branch ducts 16 as envelope air 25, in order to volatilize VOCs adsorbing within the envelope 5 and to remove moisture. The ground conditioned air supply unit 42 is also connected to the lower lobe supply ducts 15 and branch ducts 16 to vent any moisture in this portion of the envelope. In order to accelerate this process, it may be desirable to operate the conditioned air supply unit 42 so as to heat the ventilation air 24 or use engine bleed air. The return air control units 17 are set to draw return air 34 from the envelope 5, and the outflow valve 19 vents all of the return air 34 out of the aircraft as exhaust 35.

This operation will remove moisture and air contaminant accumulation, if present, in the upper and lower lobe envelopes.

Example 5, In-flight Fire and/or Pyrolysis

Figure 7 illustrates the air handling system operation during an in-flight fire event in the envelope. When smoke (or combustion products) indicative of a fire is detected, the airflow control device 13 is set to divert all ventilation air 24 to the cabin air conditioner 20. At the same time, the return air control units 17 are set to draw return air 34 from the envelope 5, and the outflow valve 19 operates to vent all of the (smoke-laden) return air 34 out of the aircraft as exhaust air 35. Diversion of the ventilation air 24 to the cabin air conditioner 20 (with the cabin air conditioner 20 on) allows the cabin 3 to be pressurized relative to the envelope 5, and thereby prevent infiltration of smoke and combustion products into the cabin 3 if the fire is in the envelope 5. At that stage, fire suppressant can be injected into the envelope (either the entire envelope 5 can be flooded with fire suppressant, or, alternatively, the fire suppressant may be directed into a selected quadrant of the envelope). Maintaining a positive cabin pressure relative to the envelope ensures that smoke, fire suppressant, and combustion products are substantially prevented from entering the cabin, thereby providing effective separation of passengers from noxious gases.

If desired, however, the cabin air conditioner 20 can be turned off to stop the flow of ventilation air 24 into the cabin 3, after injection of fire suppressant into the envelope 5. This can be used to reduce the supply of oxygen available to the fire, but at the expense of allowing combustion products to leak into the cabin 3.

Alternatively, if the fire is in the lower lobe envelope, then fire suppressant can be injected into that portion of the envelope using ducts 15 and 16. This system has the advantage over current fire suppression systems of not exposing animals, if present, to the health and safety hazards of fire suppressants and their combustion products in combination with fire and smoke.

The above detailed description and examples describe a preferred embodiment of the present invention, in which ventilation air may be independently supplied to each of four quadrants of the envelope 5; shell-side and cabin-side nozzles 27, 29 are respectively used to inject ventilation air behind and in front of the insulation blankets 10; envelope air flows due to stack effects are restricted by the use of flow blockers 28; chemical fire suppressants can be selectively injected into the envelope 5; and means are provided for on-the-ground purging the envelope 5 by the use of a ground conditioned air supply unit connected to the ventilation air inlet ducts. However, the skilled artisan will recognize that these features can be used in any desired combination, depending on the design and mission of the particular aircraft in question.

For example, the skilled artisan will appreciate that the envelope 5 need not necessarily be divided into four quadrants, each of which are served by independent ventilation supply systems. It is not necessary to divide the envelope 5 into upper and lower lobes, if such a division is not desired by the aircraft designer. If desired, the envelope air stream 25, can be divided into upper and lower lobe supply streams, or alternatively both lobes of the envelope 5 can be ventilated using a common envelope air stream 25. Similarly, it is possible to utilize shell-side nozzles 27 alone; or cabin-side nozzles 29 alone; or shell-side nozzles 27 in one area of the envelope 5, and cabin-side nozzles 29 in another area of the envelope 5, all as deemed appropriate by the designer.

Similarly, the skilled artisan will appreciate that the envelope 5 need not necessarily be divided into upper and lower, port and starboard quadrants. In practice, it is possible to divide the envelope 5 as required to provide a localized ventilation regime appropriate to a specific portion of the envelope 5. For example, it may be desirable to provide a ventilation regime in the crown portion of the envelope 5 (e.g. to eliminate "rain-in-the-plane" phenomenon) which differs from that provided in the sides of the envelope 5. Division of the envelope 5 in this manner can readily be accomplished by means of the present invention.

Furthermore, the skilled artisan, will also recognize that, just as the envelope 5 can be divided radially into quadrants, it is also possible to divide the envelope 5 longitudinally into sections, such as, for example, by means of suitable flow blockers 28 circumferentially disposed between the cabin liner 7 and the shell 6. Each longitudinal section may also be provided with independent envelope and cabin air streams 25, 26, and may also include its own set of return air control units 17, and return air ducts 34 etc. to thereby allow envelope ventilation control independent of other sections of the envelope 5. For example, it may be desirable to provide independently controllable envelope/cabin ventilation (e.g. in terms of air pressures and flow rates) in the cockpit and passenger cabin. Furthermore, within the passenger cabin, in may be desirable to have differing envelope ventilation regimes within passenger seating and food preparation areas. This can be accomplished by longitudinally dividing the envelope 5 into appropriate sections, and providing envelope and cabin ventilation air ducts 14, 21, appropriate cabin and/or shell-side nozzles 27, 29, and return air control units 17 etc. as required to provide the desired ventilation regime within each section. Longitudinal division of the envelope 5 also creates a further mode of operation of the system of the present invention during a fire or pyrolysis event. In particular, in a case of smoke in the cockpit, it would be possible to control ventilation regimes in all of the sections of the envelope 5 to deliver maximum air flow to the cockpit (perhaps with reduced ventilation air flow to the passenger cabin), and thereby more effectively purge smoke and combustion products from the cockpit area.

In the illustrated embodiment, the return air control unit 17 and cabin air inlet 32 are located in the envelope space 5 near the floor 2 of the cabin. However, it will be appreciated that these components may equally be located elsewhere as deemed appropriate by the aircraft designer. Similarly, the locations or the envelope ventilation supply ducts 14, 15, the return air ducts 18 and the cabin ventilation supply duct 21 can be varied as deemed appropriate by the designer.

The ability of the system of the invention to pressurize the cabin relative to the envelope, or vise-versa, is inherent to the present invention, and may be utilized to achieve any of the operating modes (in terms of envelope and cabin ventilation, and return air recirculation and venting) described in the above examples. However, it will be apparent that one or more of the operating modes may be omitted, if such mode of operation is unnecessary for the mission and/or design of any particular aircraft. For example, in some aircraft, it may be desirable or necessary to omit operating modes in which the cabin is pressurized relative to the envelope. In such circumstances, all return air may be drawn from the cabin exclusively, in which case the return air control unit 17 may be replaced by a simple fixed return air inlet in communication with the return air ducts 18.

It is considered that the use of flow blockers 28 will reduce natural convective (stack-effect) air flows within the envelope, and that this would likely have the effect of reducing moisture condensation within the envelope, even in the absence of envelope pressurization. The capability of the system of the present invention to pressurize the envelope with dry ventilation air will serve to virtually eliminate moisture condensation within the envelope, at least during the cruise portion of the flight cycle. The skilled artisan, will appreciate that flow blockers 28 may be used independently of the other elements of the invention described herein. Thus the skilled artisan will recognize that flow blockers 28 could be incorporated into an aircraft, even in the absence of an envelope ventilation system. Similarly, an envelope ventilation system may be used either in conjunction with, or without, flow blockers 28.

Thus it will be appreciated that the above description of a preferred embodiment is intended to describe various elements, which may be used alone or in any desired combination as desired to achieve as appropriate to the particular circumstances. It will therefore be understood that the above-described preferred embodiment is intended to be illustrative, rather than limitative of the present invention, the scope of which is delimited solely by the appended claims.