Condensation in Aircraft: The Rain in Planes

There is no problem so complex that it cannot simply be blamed on the pilot.

- Dr Earl Weiner

Since people are made largely of water, transporting 350 of them thousands of kilometres through the air in a metal canister is a sweaty business.  On average, each person on board a commercial airliner gives off 100ml of moisture every hour.  That means a jumbo collects some 600 litres during a l7-hour transpacific flight, much of it as condensation in the gap between the cold outer skin of the aircraft and the insulated cabin wall.  Meanwhile, the people who have sweated off this moisture are being tortured by a cabin atmosphere that is too dry.  Its relative humidity is around 20%.  Comfort demands a figure nearer 40%.

CTT Systems, a Swedish company founded ten years ago by two Saab aircraft mechanics, sees an arbitrage opportunity in these two facts.  By adapting some 70-year-old Swedish air-conditioning technology, it has created a system that dries the air in the cavity between the hull and the cabin walls, while keeping the cabin itself comfortably moist.

CTT'S Zonal Drying System takes the moist air leaving the cabin and feeds it through a rotor impregnated with silica gel.  This removes the moisture.  The dry air is then blown between the cabin wall and the aircraft's skin, absorbing any condensation that has formed there.  Then, a stream of warm air is run through the rotor unit in the opposite direction.  This absorbs the moisture from the silica gel and feeds it back into the cabin whence it came, keeping the passengers comfortable.

Passenger comfort is important, of course.  But condensation in the gap between cabin and hull can be lethal.  This gap contains much of an aircraft's wiring, and water can damage that wiring's insulation.  Such a problem is thought to have contributed to the loss of a Swissair DC-11 off the Atlantic coast of America a few years ago.  Too much condensation causes other difficulties, as well.  There have been cases when ice has built up inside the tailplanes of aircraft, causing their rudders to freeze and thus preventing their pilots from steering them.

There is also the matter of weight.  An aircraft such as a Boeing 747-400 can accumulate as much as 700kg of condensation before it reaches equilibrium.  Even though that is only about 0.17% of the 400 tonnes such an aircraft weighs fully laden, it is enough to cause problems for the pilot when he tries to trim the balance of the aircraft.  And 700kg is about the weight of nine men.  So the aircraft is carrying the equivalent of at least nine non-fare-paying passengers, in an industry where every extra kilogram affects fuel consumption and profit margins.

So far, CTT Zonal Drying Systems have been installed by Swissair, KLM and Lufthansa, to deal with specific dampness problems in particular aircraft in their fleets.  This costs between $40,000 and $120,000, depending on the size of the aircraft.  Now, Airbus Industrie is planning to build the moisture arbitrageurs in at the factory.  It will offer the Zonal Drying System as an optional extra on its long-haul A33O and A340 models.

Source: The Economist 16 June 2001

-------- Original Message --------
Date: Sun, 17 Jun 2007

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Comments: I would suggest that Dr Earl Weimer do a little more research before he writes an article such as the one he wrote "Rain in the Plane" [above] about condensation inside the aircraft.  I was an Aircraft Mechanic/Avionics Tech for approximately 40 years and I can't for the life of me figure out where he came up with all this faulty information.

The first thing I want to comment on is his lack of knowledge of Aircraft Designation.  There never was an A/C "DC-11" there was a DC-10 and there was a MD-11.  Also in 40 years of working both hangar and line maintenance I never saw in the log books or verbally heard crew members complain about the rudder icing up and not being able to steer the aircraft because of that.

I might also add that even when there was ice on the outside of the aircraft, anytime I opened up a side wall I never found ice.  It would be very cold - but no Ice!

R L Sullivan

Aircraft Still Shine in Arizona Desert

I think historically, the airline business has not been run as a real business.  That is, a business designed to achieve a return on capital that is then passed on to shareholders.  It has historically been run as an extremely elaborate version of a model railroad, that is, one in which you try to make enough money to buy more equipment.

- Michael Levine, Executive VP Northwest Airlines 1996

by Jack Elliott

They stand proud, in long lines like old soldiers with a thousand memories of days of glory.

Once they roared through the skies, guided by bold, daring young men and women.  Now they stand in silence under the hot desert sun.  This is where old airplanes never die.  There are numerous aircraft here that once called New Jersey their home.  They still carry their home state designation, NJ, prominently displayed on their tails.  They once roared over New Jersey under the banner of the Air Force National Guard flying out of Atlantic City.  They are part of 4,524 aircraft here retired from active service.

This is the Davis-Monthan Air Force Base in Tucson, Arizona, the storage facility for military aircraft of all services.  The base was chosen for this mission because of the extremely low humidity in Arizona, which virtually eliminates corrosion.

A military base was established here in 1925, and the airfield was dedicated two years later when Charles Lindbergh, after his historic flight to Paris, flew his Spirit of Saint Louis to Tucson to dedicate Davis-Monthan Field - then the largest municipal airport in the United States.

After World War II, the base became a storage facility for hundreds of decommissioned aircraft, particularly B-29s and C-47s (the military version of the DC-3).  From 1946 to 1949, Davis-Monthan was home to the Enola Gay, the B-29 from which the first atomic bomb was dropped on Hiroshima.  (The Enola Gay has been restored and will go on exhibit at the new Air & Space Museum facility going up at Dunes Airport in Virginia, outside Washington, DC.)

Not all the aircraft here are military.  The first 727 to carry passengers is being stored here for the Smithsonian Institution.

"Twenty-two percent of the aircraft here are flyable," said Terry Vanden-Heuvel, the base's public affairs specialist.  There are 69 different types of aircraft stored here.  One line of F-16s has been sold, some to Thailand and some to Italy and some may go to Poland.

On one part of the field there is a line of old Boeing 707s bought to use for parts.  Most of them are missing tails and other structural parts and engines.  The engines were used on KC-135 tankers.

"Using parts from these aircraft has saved the military millions of dollars," said Terry. "For every dollar spent here we save $12.  That's why they call this place 'A Diamond in the Desert.'"  Another activity taking place here is the destruction of B-52s under START, the Strategic Arms Reduction Treaty with Russia.  There is a giant knife that is dropped on the aircraft to slice them in half.  A similar piece of equipment was built for the Russians.  Each side makes periodic inspection visits to see that the terms of the treaty are being carried out.

As Terry drives us up and down the long lines of aircraft in a van, we pass a group of A-7s, Carrier aircraft that were once based in New Jersey.  The field today is not only a storage facility, but an active airbase where A-10 Warthog pilots are trained for close support and forward air control missions.

As we near the end of our tour we stop at an F-106 Delta Dart with all kinds of markings on it, including an emblem that reads "Jersey Devils, 1972-1988."  This aircraft was part of the 177th Fighter Group of the New Jersey Air National Guard.  The aircraft, wore that emblem long before anyone dreamed of a New Jersey hockey team of that name.

"When a new commander of the group came aboard, he changed the name," said retired Brigadier General Francis R Gerard, World War II ace and former commander of the New Jersey Air National Guard.  "He thought it sounded too Satanic."  When that Group Commander left, in 1972, the name was restored.  Gerard was then commander of the state Air National Guard.  Painted on the side of the aircraft also is the notation that on December 15, 1959, the aircraft, broke the world speed record by hitting 1,525.95 mph.

"It was not this aircraft, which broke that record," said Major Roger Pharo, present Wing Executive officer of the 177th Fighter Group.  "This was the last aircraft, of its type to be flown," he said, "so all the major achievements of the 106 fleet are painted on its side."  Pharo, an avionics technician, had worked on that aircraft, many times.

There are so many aircraft here with distinguished service records.  And so many stories that nobody will ever know.

Source: The Sunday Star-Ledger Morris County, New Jersey 17 June 2001

Too Big to Bury...

B-52 at Davis-Monthan Air Force Base near Tucson, Arizona, United States (N 32°11' W 110°53')

Hundreds of B52 Stratofortress bombers are stored at Davis–Monthan Air Force Base in the Arizona desert.  These planes, whose flying days are probably over, are nevertheless preserved for spare parts.  After its first test flight in Seattle, Washington, in 1952, this plane was heavily used during the Vietnam War (1963 – 75), and a modernised version was flown in the Gulf War (1991).  The last models saw action during the 1999 bombardments in the Balkans and in Afghanistan in 2001.  This war plane symbolises the might of the world’s strongest military power, which has reasserted its dominance in this field as the world enters the 20th century.  Since the Gulf War the United States has played a major role in world conflicts, and it has a tremendous voice in international institutions such as NATO.  However, military power is just one of the many facets of the American model which, from trade to culture, is spreading throughout the planet.

Source: from Earth from Above by the incomparable photographer Yann Arthus-Bertrand.  Visit his site for some of the most stunning photos I have ever seen, of all kinds of things...

Lockheed C-141B Starlifters in Storage, Davis Monthan AFB

by Stan A Rothwell

Tucson is home to Davis-Monthan Air Force Base and the Aerospace Maintenance and Recovery Center (AMARC) as well as several private aircraft scrapyards.  Surplus and retired aircraft from all branches of the service are stored here due to the ideal climate (warm and dry).  Aircraft sent to AMARC are processed for long-term storage in the Arizona desert.  Sensitive instruments and high-value items are removed for safekeeping, and the airframes are drained and purged of fuel, oil, and hydraulic fluid.  Windows, doors, and hatches are sealed with protective material, but vents and aircraft undersides are left open to avoid condensation.

Most aircraft transferred to this facility are "cannibalised" (stripped for spare parts) and eventually scrapped, but some of the transport aircraft such as the older C-130s are made available to other federal agencies for nonmilitary purposes such as firefighting.  In the past some of these aircraft were offered for sale to private parties.  However, concerns that this would provide a cheap source of transportation for drug smugglers have resulted in most of the older transports being scrapped instead.

Tours of the facility are available courtesy of the Pima Air & Space Museum.  For more information, see

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