Then & Now: LOX Operations at Selfridge

Published Sept. 11, 2013
By TSgt. Dan Heaton
127th Wing Public Affairs

SELFRIDGE AIR NATIONAL GUARD BASE, Mich. -- His hands covered by three layers of gloves despite the August heat, Staff Sgt. Scott Dykstra topped off the oxygen tanks of more than a dozen attack aircraft. It is a standard operation, performed at least twice a week at Selfridge Air National Guard Base, as the Airmen of the 127th Maintenance Group prep the unit's A-10 Thunderbolt II aircraft for operations.

Given the altitudes modern aircraft operate at - an A-10's listed maximum ceiling is 45,000 feet, relatively low by today's standards - supplemental oxygen for the pilot is as necessary as jet fuel is for the aircraft. Without it, things can start shutting down in a hurry. The advantage to dealing with oxygen in its liquid form is that it takes up considerably less space than it does when in gas form, a space savings of some 90 percent.

On this day, Dykstra, assisted by his safety spotter, Technical Sgt. Stan Wilson, will ensure that each of the A-10s at Selfridge have a full 5-liter tank of liquid oxygen (LOX) on board. The 127th MXG crew chiefs never allow their aircraft to fly with less than two liters of LOX on board. A converter onboard the aircraft changes the oxygen from liquid form to the more common gas for the pilot to breathe through his or her mask.

Once upon a time at Selfridge, things weren't so simple.

The U.S. Army Air Service's first cross-country flight in which all of the pilots used liquid oxygen took place on Nov. 3, 1931, on a flight by the 94th Pursuit Squadron, which took off from Selfridge Field and travelled to Bolling Field, near Washington D.C. Twelve aircraft made the flight that day, after several days of testing and training for both pilots and the ground crew who had to handle the LOX.

LOX is stored at around 360 degrees farenheiht below zero. It is, obviously then, dangerous stuff to deal with. Given that it is also pure oxygen and is, therefore, highly flammable, all operations around an aircraft quickly come to a halt when the LOX cart pulls up.

"You have to respect it," said Master Sgt. Doug Cox, a crew chief with the 127th Aircraft Maintenance Squadron. "That's why we always work as at least a two-person crew, with one person as the safety spotter."

A set of coveralls, a leather apron that covers almost the entire front of the body, a face shield and the three pairs of gloves complete the safety ensemble for the LOX work. As Dykstra connects the LOX tank to the aircraft, plumes of white mist surround him. That's the oxygen boiling off into a vapor as it returns to a gas form.

German zeppelin pilots during World War I are believed to have been the first airmen to experiment with the use of LOX. The zeppelins provided the room - and the lift - needed for a LOX canister on board. One of the limitations discovered during the 1931 flights at Selfridge were that the 5-liter LOX bottles used in the flights were just too big and bulky for the Curtiss pursuit planes of the day.

The 1931 flights at Selfridge, though they uncovered some problems with the operational use of LOX - the cold from the LOX kept fogging up the pilots' goggles among other issues - the tests, which also included the use of drop tanks filled with fuel, proved that should Washington D.C. come under attack, aircraft from Selfridge could reach the capital in a timely fashion to respond.

Throughout World War I, various air forces experimented with crude LOX systems. Then, in 1923, the U.S. Army began extensive testing on flight up to 20,000 feet. Among the biggest challenges was finding an oxygen mask that was acceptable. Numerous types were tried and rejected and, for the most part, pilots sucked on a tube that was connected to the oxygen tank.

Army Air Corps Technical Order 03-10 of 1927 was the first to specifically address the use of oxygen and it required the use of supplemental oxygen for all flights above 15,000. Still, most of the oxygen used then was stored in gaseous form. In 1930 a new order was issued, stating that above 22,000 feet, LOX was to be used due to problems with the gaseous oxygen delivery system. At the time, most cockpits were still open and the cold weather played havoc with a number of systems, including the oxygen tubes. Also in 1930, Navy Lt. Apollo Soucek, using LOX, reached an altitude of 43,166 feet. It was the last major altitude record set in an open cockpit. At the same time the military was trying to develop a LOX system, other engineers were working on the idea of a pressurized cabin for the pilot and air crew.

The Dec. 4, 1931, edition of the official Air Corps News reported on the successful flight of the LOX test at Selfridge. Among the lines included in summary: "... at high altitudes, liquid oxygen is superior to gas oxygen carried in tanks."

That article is reprinted in its entirety below:

High Altitude Formation Flying

The first cross-country flight at an altitude of 20,000 feet, in which all the pilots used liquid oxygen, was completed by the 94th Pursuit Squadron on November 3rd, when twelve planes, under the command of Lieut. Harry A. Johnson, flew from Selfridge Field to Washington, D.C., in two hours and five minutes. At Selfridge Field two days prior to the flight tests were run on gas consumption above 20,000 feet, and it was discovered that an economical consumption could be obtained at a fairly high r.p.m. Tests had also been conducted in training the pilots in the handling and use of liquid oxygen.

The flight took off at 1:45 p.m., with a heavy cloud bank covering this section of the country. Five miles from the field, a break in the clouds was discovered and the flight spiraled upward for a period of thirty minutes until the altitude of 19,000 feet was obtained, when the pilots started on their course, still climbing. After breaking through the clouds it was impossible, of course, to check any landmarks on the ground, and for about one hour there was nothing but a sea of white clouds below. As the Ohio River was crossed, a slight break showed the river and gave the Squadron Commander an opportunity to check the course. A short distance past Pittsburgh, Pa., the clouds broke, and from that time on the course was easy. The remarkable part of the flight was that after getting above the clouds a compass course plotted prior to the take-off, held directly on the course, and no change was needed when the clouds finally did break.

A short distance out of Washington, members of the flight noticed the plane piloted by Lieut. Hersam started cavorting crazily about the sky and then diving for the earth. Down he plunged out of sight of the remainder of the flight who, wondering, kept on towards Washington. They were delighted, indeed, to have him join the flight just before they landed. It was learned that Lieut. Hersam had accidentally detached the tube leading from his oxygen supply to his face mask while reaching for his map, He was soon unconscious, and his plane, out of control, dove towards the earth until at 7,000 feet the pilot recovered and righted his ship. He joined the flight over Washington, and the 12 planes landed as one unit at Bolling Field, Anacostia, D.C., the first one touching the ground at 3:50 p.m. A short time was lost spiraling down slowly so as not to make too rapid a change of altitude after a long stay at an altitude where the pressure density was much less than on the ground. The speed averaged 200 miles per hour and between 1900 and 1950 r.p.m. All the pilots made the flight to the place where they were ready to glide down and land on their auxiliary tanks of.55 gallons, with the exception of one.

Liquid oxygen was used on this trip, and it is a marked improvement over the gas oxygen carried in cylinders. The regulation of the amount necessary for the pilot is entirely automatic and cuts the number of gauges and instruments necessary to keep on a flight of that ty1)e. Face masks. in which a tube carried the oxygen to the nostrils, were used, and these proved superior to those which required the tube to be held in the mouth and, in addition, were much more comfortable on a long flight.

Most of the pilots encountered trouble through the fogging of the goggles, one pilot losing his goggles 15 minutes after taking off and flying the entire distance without them. The maximum temperature encountered was 20 degrees below zero centigrade, which seems to be the dead line on temperature where goggles either will or will not fog. At a temperature below that, all B-6 Goggles will fog until it is impossible to see through them.

As far as clothing was concerned, the flying suits (B-7) were apparently warm enough for the first hour. After that, all pilots began to chill and during the last hour hoped that Washington would show up soon. The opinion of the members of the flight upon landing was that the temperature of Washington was almost tropical.

On the following day the squadron returned to Selfridge Field by elements, for the purpose of navigation training. This trip required three hours and 40 minutes, and most of the pilots ran very close to the edge on gasoline prior to landing.

Lieuts. O'Donnell, Coleman and Hersam spent the greater part of the afternoon awing newspaper reporters with tales of the flight, having their pictures taken for future fan mail and basking in the lime light.

It can be seen from this flight that, should Washington be endangered by an attack, a squadron could take off from Selfridge Field, arrive at Washington, drop the auxiliary tanks, and have sufficient gasoline in the main tank to go into combat at ceiling just two hours after leaving Selfridge Field.

Flying above 20,000 feet, and handling and using of liquid oxygen, constituted some of the activities of the 94th Pursuit Squadron during the month of October. A considerable number of tests at high altitudes were conducted during April, but these were discontinued because of the fact that only five liter containers for the liquid oxygen were available. These containers were too large for a Pursuit type plane, as no pilot on any flight needs that amount of oxygen, and there were no means of determining the amount of oxygen carried. Difficulty was also encountered in filling these containers.

During September, a supply of 2 ½ liter containers were obtained and installed in the planes in such manner as to permit them to be quickly removed for filling. Representatives of the Materiel Division, Wright Field, were present at the preliminary tests. In the method they employed, it required from seven to twelve minutes to fill each container. The new type of can they furnished for pouring the liquid oxygen from the 25-liter storage tanks into the container worked very satisfactorily and cut down the large evaporation losses encountered in pouring. Modifications have since been made of the equipment, and the containers can now be filled in about two minutes after they are removed from the plane.

Flights were made on October 12th by twelve planes in formation to indicated altitudes of 27,000 to 28,000 feet, and considerable maneuvering performed. The temperature at that altitude was 27 degrees below zero, centigrade. Great difficulty was experienced by the pilots staying in formation at that altitude, due to goggles fogging and then freezing. The average gasoline consumption for one hour's flight, including climb, was 30.5 gallons.

Another high altitude journey was made by two flights on October 13th, for the purpose of maneuvering fast at between 21,000 and 22,000 feet, it being desired to avoid an altitude where the goggles were likely to fog and freeze. The temperature encountered was 15 degrees below zero, centigrade. The planes maneuvered very well at that altitude, and the pilots encountered no difficulties.

On October 16th, flights were made to determine the length of time required for a formation to reach 20,000 feet, also the gasoline consumption at that altitude at 1300 r.p.m. For this flight, 25 gallons of gasoline were carried in the auxiliary tank. The weather was cloudy, and it was necessary to climb through a hole in the clouds. The time required for the climb to 20,000 feet was 19 to 20 minutes, the speed of the slowest plane being the determining factor. The gasoline consumption at that altitude varied from 17 to 25 gallons per hour. A check was made of all the spark plugs in the planes and new ones installed. Trouble was encountered by all the pilots, due to goggles fogging, and all comp1ained of becoming cold.

On October 19th, another formation flight was made to 20,000 feet, and an objective of 100 miles away from the field was selected. The planes climbed to 20,000 feet over the field and then flew to the objective and returned at that altitude. The flight was made at 1800 r.p.m., and 25 gallons of gasoline carried in the auxiliary tank. The time required for the climb to 20, 000 feet was 21 minutes. At that altitude the gasoline consumption averaged 17 gallons per hour at 1800 r.p.m., and the temperature was 20 degrees below zero, centigrade. Some trouble was encountered, due to goggles fogging, and pilots complained of becoming chilled and of suffering much from cold hands.

Two days later, a flight was made to the same 'Objective "the test being the same as that carried out on October 19th, save that the r.p.m. flown by the leader was 1950. The 25 minutes required to reach 20,000 feet was unnecessarily long due to the leader falling out, making it necessary for the deputy leader to take the lead. The time required to fly, the 100 miles to the objective was 50 minutes., making the speed 120 m.p.h. The time required for the return trip was 30 minutes, or at a speed of 200 m.p.h. The'gasoline consumption varied considerably, but averaged 24.4 gallons per hour.

During these flights one 'pair of electrically-heated goggles and mittens were used and, aside from a slight amount of moisture forming between the double lenses, no trouble was encountered with them. The electrically heated mittens were quite comfortable, but could stand a little more heat, and a heating element should be in the palm of the hand where it comes in contact with the stick.

The deductions which can be made from these flights above 20,000 feet are:
(a) Our planes and engines function satisfactorily at that altitude with a little training of personnel.
(b) Our personnel flying at that altitude lose some of their alertness, after staying there for over an hour, due to becoming chilled.
(c) That it is almost impossible for the pilot to operate at that altitude without electrically heated goggles and mittens.
(d) That liquid oxygen fed directly into a face mask is much more satisfactory than taking oxygen into the mouth through a tube.
(e) That when it is desired to operate at high altitudes, liquid oxygen is superior to gas oxygen carried in tanks, as normally the pilot is assured of sufficient oxygen to keep him aloft until his gasoline supply is exhausted.
(f) That for the amount of oxygen carried; the liquid oxygen gives a large saying in weight.
(g) Studies are also being made of the desirability of heating open cockpits for the comfort of the pilot, and of oxygen flasks which may be filled as quickly and easily as the airplane is refueled when it comes to earth.

Comprised of approximately 1,600 personnel and flying both the A-10 Thunderbolt II and the KC-135 Stratotanker, the 127th Wing supports Air Mobility Command, Air Combat Command and Air Force Special Operations Command by providing highly-skilled Airmen to missions domestically and overseas. The 127th Wing is the host unit at Selfridge Air National Guard Base, which is also home to units of the Army, Navy, Marine Corps, Coast Guard, Border Patrol and Customs and Border Protection.

· Historical information on the use of LOX came from A Brief History of US Military Aviation Oxygen Breathing Systems by Christopher T. Carey (2002).

Selfridge Research

Selfridge Research

Then & Now: LOX Operations at Selfridge