Flight Testing Is a Sound Business

By Edmund T Allen
Director of Flight and Aerodynamics, Boeing Aircraft Co

Edmund T Allen gave his best efforts — and finally his life — to the advancement of the major science of flight testing. In this first of three significant articles comprising his last written contribution he has outlined the vital purpose of his work and revealed the careful organization of his personnel and the structure of his department.

A prototype of the test pilot, according to the usual story told by fiction writers and motion picture producers, is a daredevil sort of fellow, not infrequently long on courage and short on brains, who takes up a newly designed ship, whips it through the air a few times, then goes into a vertical dive that ends in a 9G pull-out. If the wings don't fold up, the ship is pronounce safe and the company goes into production of the new model. What happens to the test pilot during the intervening years while this model is being produced is never revealed by fictioneers.

Actually, flight testing today is not a spasmodic, haphazard, daredevil occupation. For some years it has been a sound, scientific business, operating to perform a design function on a quantitative basis.

Like any other product requiring engineering, an aircraft should fulfill completely and satisfactorily the purpose for which it is intended. On some occasions in the past it has been necessary to establish proof of this fulfillment by long usage and experience, most frequently not on the part of the manufacturer, but on the part of the owner or operator of the aircraft. Information pertaining to this type of operation seldom, if ever, reaches the manufacturer, and in the few instances when it does arrive the information is in such a form that it is of little or no use. In the past, a gap has existed between airplane design and operation. Bridging this gap is the function of modern flight testing organizations.

Flight testing can be, and at the Boeing Aircraft Co for the past three years has been, essentially quantitative. The spasmodic nature of flight testing as depicted in imaginative minds has long since been replaced at Boeing by a continuous project in keeping with the realization of the fundamental design objective. It is the opinion here that modern flight testing should consist of far more than merely the initial flight tests associated with newly designed aircraft. It should provide, among other things, a continuous, uninterrupted method of solving service operation problems and a means of providing operators with this information prior to delivery.

Very few design elements can be determined completely without information which can be obtained only through actual flight tests. The wind tunnel, the test shed, the cold room, and the stratochamber all work in complete unison to produce likely or probable solutions to the many engineering problems. However, the final and acid test can be obtained only from actual full-scale tests under actual flying conditions. Flight testing comprises:

  1. Testing a new model for performance and operational guarantees.
  2. Development testing to obtain design information corroborating
    1. mockups,
    2. simulated laboratory tests,
    3. theoretical studies, and
    4. model tests.

The outstanding example of an airplane whose essential components were designed through rigid and thorough flight testing is the Boeing B-17E Flying Fortress. With the capabilities of the flight test unit, in conjunction with the aerodynamics and engineering design units, all important items and changes were proved by actual flight on an earlier model of the B-17 series. Included in the items tested under flight conditions before the "E" was given a final stamp of approval and put into production, were details of the power plant system, structural innovations, aerodynamic refinements, such as the now famous Boeing dorsal fin, and other items involving stability and control.

Also tested under flight conditions were items associated with armament and also the tactical use of this now famous plane. When the first Boeing B-17E emerged from the production shop, it was a completed plane. No long period of service was required to prove the vital changes that had been incorporated. They had already been proved in hundreds of hours of quantitative full-scale flight testing. Following the customary checkout flights, the first and all subsequent Boeing B-17Es were ready and fit for delivery.

At the Boeing factory, the Flight and Aerodynamics Division has been organized on a parallel footing with Engineering, Manufacturing, and other divisions. The autonomy of the flight test unit permits it to:

  1. Establish the priority of tests if the authority is so delegated.
  2. Control tests and delegate items and equipment in proportion to the relative importance of the tests.
  3. Gather the background common to all design units on problems of flight testing.
  4. Obtain proper coordination with all design units.

This makes for individual integrity of all divisions and yields optimum results from flight testing.

Within the Flight and Aerodynamics Division are two separate, but not divorced, functions — flight testing and aerodynamics. These two groups work in close harmony with one another and enable close coordination with engineering, production, and other divisions of the company.

As a flight test unit's function is to provide the manufacturer with information dealing with either operation or characteristics of an aircraft in flight, the handling of this information is of paramount importance. Data obtained during flight testing are of equal, if not greater, importance than any other engineering information on the aircraft, for flight test information provides the proof, or final answer. The flight test unit should attempt to disseminate unprejudiced, unopinionated, understandable information of reliable accuracy as rapidly as possible. Information which is untimely is likely to be not only devoid of usefulness, but may cause misunderstanding or suggest inefficiency. Proper method, adequate personnel, and proper organization again are the solution.

At Boeing there has been established a hard and fast rule that immediately following a test flight, the entire crew gathers in the conference room, accompanied by a stenographer. The flight and all aspects of the tests are discussed by the crew, and tentative conclusions are reached. It is the purpose of these conclusions to direct the course of further testing, to indicate the results accomplished and the scope of those results, and to assure that the information is consistent and comprehensible.

The film from the recording camera is hastened to the flight test darkroom, where it is processed and the results projected on enlargement paper. The rough draft is corrected and turned over to the clerical group which mimeographs it during the night. The photographic results are sent to an analysis group which breaks down the various tests and prepares graphs and charts on the results of the test flight. This information is rapidly duplicated and added to the mimeographed report. By noon of the following day every interested person in the Boeing plant has a complete preliminary report on the flight test.

Every attempt is made by the flight test unit to avoid a blind collection of data which has not been evaluated for accuracy or usefulness in deriving results. The value of the results is decided upon through proper collaboration with the design units. The group must be thoroughly conversant with the details of the tests proposed and being conducted, in order to conduct the tests intelligently and contribute to the detailed technical solutions.

As the flight test group is the only unit in the company which comes into direct contact with the problems that confront the operators of aircraft produced, it cannot be casual or haphazard in its approach to these problems, nor should it be hampered in presenting the truths resulting from the actual flight test. The devotion of a flight test group to this policy will in later years be reflected in the volume of future business which the manufacturer enjoys.

Because a flight test unit, in the performance of its duties, is operating in conjunction with so many various engineering groups in an organization, this single group must determine the test priorities. Especially in these days of war, the importance of this phase cannot be over emphasized. In some instances the purpose of a test may be to obtain information of academic interest only, and, as such, is integrated into the over-all program by the Boeing flight test unit on the basis of importance for use in the final military article, which at present is the Boeing Flying Fortress.

In determining the priorities for test items, the Boeing company took cognizance of the fact that the tests were to be made on large four-engined aircraft, a manufacturing field in which Boeing pioneered. A major portion of the flight testing is in the stratosphere beyond the boundaries of general human knowledge. Sending an aircraft and crew into this region during the early days of Boeing's high altitude research was never considered as the safest occupation in the world. But every known safety precaution was taken.

Although the early hazards in this type of testing are now considerably reduced, the cost of high altitude flying has not been overcome. Sending a large four-engined aircraft such as the Flying Fortress to 35,000 ft or better represents a cost of about $1,000 per hour. For sound business practices it was necessary to devise a method of making each test flight as productive as possible. Single flights have accomplished tests on more than a score of items, and in some instances the item to be tested is checked for a dozen or more consecutive flights, depending upon the nature of the item.

When an engineering group at Boeing develops any item which will require a flight testing, a preliminary outline of the item and the test desired is submitted to the flight test unit. Here the flight test unit evaluates the item against the other tests that must be made.

From the preliminary outline, the flight test engineers work out the details of the test, planning and organizing the material necessary, and scheduling any special equipment installations which must be made on test airplanes for the inclusion of the particular test items involved.

In the event that the particular test item is of such nature that the information contained in the preliminary outline is insufficient for the flight test unit to make plans, a second and more extensive outline, including blueprints, is submitted. After the test item has been scheduled and the planning completed, the director of flight and aerodynamics, the chief of flight test, the flight test operations engineer, the flight test equipment engineer, and the flight test analysis engineer meet to discuss the test. Included in these conferences are also other parties concerned.

The discussion centers around the test in general, the portion of the aircraft involved, and the results desired. For each, an explanation of the manner in which it is related to the entire problem, and a statement of accuracy of data required, is given. The flight test equipment group will then obtain or design the instruments needed, with the range and accuracy required, and in the case of a new instrument, a description of it will be prepared.

Prior to the actual test flight, the test crew, usually composed of ten men, meets with the flight test operations engineer and the chief of flight test, and the entire test program for the flight is reviewed, with each item explained, so that every member of the crew will thoroughly understand his part.

Preflight conferences last from 30 min to 1 hr, and as a measure to insure that each member of the crew will fully understand his part in the test, the head of the engineering units involved in the comprehensive flight test, and the representatives of accessory manufacturers, if they are involved, stand by to answer any specific questions or provide additional information. The crew, each man armed with a flight test plan, a mimeographed form which includes every item on the test, and his particular function for each item, leaves the conference. Thus, each member has a thorough understanding of his duties for the test in question.

Part II … Training Flight Crews

Continuing the distinguished test pilot's significant three-part series, this second article deals with training systems and the equipment required for maintaining a flight test staff

In the not too distant past, curricula at the many aeronautical schools were almost devoid of those subjects which would particularly fit a man for position of flight engineer or instrumentation engineer in a large flight test organization. Most of the attention, in the past, was devoted to aerodynamic subjects, with an adequate amount of wind tunnel technique and detailed design and layout work.

So for some time now aircraft companies have found it increasingly difficult to secure graduate aeronautical engineers. Even a graduate engineer requires an extensive training period to fit him for the job of a flight test engineer.

In 1941, rea1izing the shortage of men properly trained for this type of work, the Boeing Aircraft Co initiated a survey among 18 colleges and 25 manufacturing concerns. This survey was partially successful and a cooperative program was worked out at that time which since has aided substantially in providing aircraft manufacturers with a few trained flight test engineers.

Meanwhile, it has been necessary for the flight and aerodynamics department to train the personnel required to conduct the extensive high altitude research program for the past three years.

Flight test crew training at Boeing is simple, direct, and to the point. It instills in the new men the basic principles of. the organization, discipline, self-reliance, self-control, safety and efficiency. Secondly, it results in attainment of a proficiency in specific procedure.

Before a new man is hired for a flight test crew, he is given a thorough physical check. The doctor making such an examination should be intimately conversant with the physiology of high altitude flying, flight crew maintenance methods, and the latest information regarding aeromedicine, which has been evolved in the comparative short space of time that high altitude flying has been practiced.

Having successfully passed a medical examination, the new crew member enters the first phase of training by attending an intensive two week course at Boeing's Engineering School. Operated under the auspices of the Engineering Division,the course is designed to familiarize new employees with the organizational scheme, engineering drafting procedures, and actual practice in drafting problems. Newly hired men for the regular Engineering Division continue this schooling for an additional two weeks. The flight test engineers leave, after the two-weeks indoctrination period, to attend the Boeing flight test engineering school.

Prior to the beginning of such classes, new men are given a tour of the entire manufacturing facilities of the plants, the operations centers, the wind tunnel facilities, model shop, and mock-ups, to familiarize them with some of the activities with which they may be concerned at a later time. It has been found that a general familiarity with the company must be obtained during the training period, because time may never be available for this later.

The flight test engineering school is designed primarily for junior flight test engineers. The curricula, however, are sufficiently broad that junior instrumentation engineers, junior analysis engineers, even pilots and copilots, may profitably attend these classes. Primarily, the schooling is divided into sections, the first comprised of 15 lectures extending over a two week period. A detailed outline of the lecture subjects is presented herewith.


Lecture 1. General Aspects of Flight Engineering
  1. . Company and departmental organization.
  2. . Flight test — general.
  3. . Test program survey.
  4. . Future flight testing.
  5. . Test airplanes.
  6. . Flight test organization, flight engineering, etc.
Lecture 2. Office Procedures
  1. . Emergency procedure (blackout, etc)
  2. . General procedure.
  3. . Relevant stenographic procedure.
  4. . Forms, etc — general survey.
  5. . Report and letter writing.
  6. . Miscellaneous.
Lecture 3. Flight Planning Procedure
  1. . Flight test procedure.
  2. . Preparation of test plan.
    1. . Details of various plans, significance of GW, CG, etc.
    2. . Coordination of plans.
  3. . Schedules.
  4. . Conferences and notifications.
  5. . Flight engineer checkoff list.
  6. . Procedure: Flight engineer.
Lecture 4. Flight Procedure
  1. . Preparation — data boards, sheets, etc.
  2. . Locker assignment.
  3. . Locker equipment and care of same.
  4. . Preflight checkoff lists.
  5. . Hangar procedure.
    1. . Preflight, denitrogenation, etc.
    2. . Post-flight.
  6. . Flight duties and conduct.
    1. . Use of interphone.
    2. . Description of exits.
    3. . Flight crew organization.
    4. . Radio contact.
    5. . Interceptor command.
Lecture 5. Physiology of Respiration & Circulation
  1. . Respiratory system.
    1. . General.
    2. . Effect of altitude.
  2. . Circulatory system.
    1. . General.
    2. . Effect of altitude.
  3. . Crew training and maintenance.
Lecture 6 Physiological Problems of Altitude & Oxygen Equipment
  1. . Afflictions of altitude.
  2. . Oxygen equipment.
  3. . Safety precautions in flight.
    1. . General.
    2. . Emergency procedures.
Lecture 7. Miscellaneous Physiological Problems
  1. . Hyperventilation.
  2. . Fear paralysis.
  3. . Fatigue.
  4. . Effect of accelerations.
  5. . Miscellaneous.
Lecture 8. Flight Test Information
  1. . Flight test documentation.
  2. . Running flight test jobs.
    1. . Log and alphabetical index.
    2. . Bi-weekly Air Corps summary.
    3. . Progress summary.
    4. . Test program.
    5. . Test item status.
    6. . Information circular.
    7. . Test item files.
    8. . Flight time estimates.
  3. . Weather.
  4. . Flight test handbooks.
  5. . Pilot's kits and map cases.
Lecture 9. Elements of Aerodynamics
  1. . Aerodynamics.
  2. . Application to flight test.
    1. . Airspeed calibration.
    2. . Flight polar.
    3. . Climbs and glides.
    4. . Stability.
    5. . Stalls, takeoffs, and landings.
  3. . Weather conditions for performance testing.
  4. . Miscellaneous formulas — bhp, etc.
Lecture 10. Temperature Measurement
  1. . Theory of the potentiometer.
  2. . Operation of the potentiometer.
  3. . Operation of automatic temperature recorder.
  4. . Data recording.
  5. . Tolerances.
  6. . Typical data.
Lecture 11. Pressure Measurement
  1. . Theory of the manometer.
  2. . Operation of equipment.
    1. . Camera.
    2. . Board.
  3. . Data recording.
  4. . Tolerances.
  5. . Typical data.
Lecture 12. Flight Analysis
  1. . General — Work of flight analyst group.
  2. . Photo recorder.
  3. . Reduction of data.
  4. . Test aims.
  5. . Miscellaneous.
Lecture 13. Powerplant — Installation & Flight Test
  1. . Engine and accessories,
  2. . Power measurement and power curves.
  3. . Engine performance tests.
  4. . Cooling tests.
  5. . Functional tests.
Lectures 14 & 15. Test Equipment
  1. . Installation and maintenance.
  2. . Demonstration.

The general lectures are followed by seven full-day lectures dealing with the Boeing Flying Fortress, on which flight test research is conducted. This Flying Fortress course includes actual practice in various operational procedures, familiarization with the kinds and varieties of equipment used for testing, and oral and written examinations. Instructors are men who currently serve in flight engineering capacities in the organization, making for ease of acquaintanceship between the experienced and the new personnel.

Aside from schooling new men on their duties in flight research, the indoctrination period includes a considerable amount of time devoted to safety procedures at high altitude. At the time the flight test department was organized, for the purpose of high altitude research, little was known about the stratosphere and the factors which limited man's actions in that region. Certain rules and regulations were laid down, and they are closely adhered to by all crew members. Each man must memorize and practice the three emergency high altitude flight procedures, until they become almost second nature to him,

The first emergency procedure is for bailing out of an airplane at any altitude, although most time is devoted to the high altitude phases of this practice. The men learn to take the following successive steps in this order: Unfasten safety belt; open all doors inside the airplane, unless a door is needed to isolate a fire; if a jump is necessary, turn on emergency oxygen system; remove flight oxygen mask, put emergency mask on; put goggles over eyes; exit from plane, making certain to clear the airplane; pull rip cord after the plane has been cleared and/or when warmer altitude is reached; try to land in the direction of drift; inflate life vests if over water, or if above clouds and water landing is uncertain; cross the feet and keep legs together, to make certain not to straddle trees or fences in landing; and if landing is made in water, unfasten parachute leg straps before striking water.

Emphasis is placed upon the fact that from high altitudes, a man might not reach ground safely if he were to jump and open a parachute immediately. The men are taught to stay inside the plane whenever practicable until the plane reaches a more moderate temperature, probably 15,000 ft. If the plane should be untenantable, the man should fall free until he reaches a warmer atmosphere before opening his chute.

The second emergency procedure deals with changing oxygen systems. This first entails opening the oxygen valve and tapping lightly. Put on standby mask if the regular supply of oxygen cannot be fixed immediately. Should stand-by system fail to function properly, turn on emergency bail-out oxygen supply and use bail-out mask. Help in any of these changes is to be given by another crew member, if required.

The third emergency procedure deals with collapse of a crew member, such as by failure of his oxygen system. First step is for another crew member to administer oxygen. The stand-by mask should be held tightly on the face of the stricken crew member, fastened into position, and checked to assure that the oxygen valve for this system is turned on. The aiding crew member should make certain that his own oxygen system is not cut off due to his movements. Should the stand-by system fail to function, the emergency bail-out bottle and mask are brought into use. Meantime, the pilot should be notified, so that he may take the plane to lower levels. Artificial respiration should be administered if the occasion requires.

The emergency bail-out bottle, which fits into one leg of the flying suit, contains oxygen which will last a man for about 20 min. Its uses are many, as is readily apparent. Aside from the regular oxygen supply, the stand-by system, which is checked for operation before each flight, provides three different oxygen systems.

After committing the procedures to memory, the crew members practice them until they become proficient. Having successfully completed their training program and safety precaution lessons, they are ready for a final examination, the passing of which will qualify them for a place in a flight test crew. The last test is a simulated flight in the Boeing Stratotrainer.

Differs From Stratochamber

The Stratotrainer, designed by the flight test department, is for the specific purpose of training crews in high altitude procedures. With accommodations for eight men at one time, it is considerably different from the dual-compartmented Boeing Stratochamber, the first low pressure chamber put into operation by an aircraft manufacturer for training work.

A typical training crew is composed of seven new men and one experienced man. As the air within the Stratotrainer is evacuated, the conditions simulate those of ascending. A refrigeration unit reduces temperatures inside the trainer to correspond to those within a plane on a high altitude flight. On a typical test, the motors are stopped when the interior atmospheric pressure of the Stratotrainer equals that encountered at 35,000 ft. Here each man performs the three emergency procedures under conditions which he may encounter on subsequent high altitude flights.

At this altitude, there is approximately a 40-sec margin of safety for changing oxygen systems. Failure to make the change within these limits means that the man will go into a coma from which he will never recover. Emphasizing the importance of these safety precautions, the Boeing flight test men have never suffered serious effects from high altitude flying. A doctor is always present, outside the trainer, ready if his services are needed.

New men, not yet ready for an actual Stratotrainer ascent may watch the proceedings through any of four large windows which have been provided in the Stratotrainer. After each man within the trainer has performed the three emergency procedures, the crew is taken to a simulated altitude of 40,000 ft, for the experience, and then the interior of the chamber assumes the pressure conditions of a plane descending.

Upon returning to a ground level atmosphere, the crew members are given a brief medical check to make certain that ears and sinuses have not been adversely affected. Any unusual effects or manifestations are reported to the doctor in charge. Those persons who do not pass the examination in the trainer are given a second opportunity of making a simulated ascent. Regular crew members must retake this examination at frequent periodic intervals to insure proficiency at all times.

Exit Practice

At the hangar, new crew members must demonstrate that they are intimately conversant with the various emergency exits from the plane. Each crew station has an evacuation exit and an alternate exit. Crew members must demonstrate that they are familiar with the ways of leaving the airplane by all exits.

Having completed this training, they are ready to take their place in a high altitude test crew.

Part III … High Altitude Flight Testing

Through case histories, "the greatest test pilot of them all" outlines procedures for safe, efficient test flying at all levels where nothing but perfect functioning of both men and machines is acceptable.

When a flight test unit is first organized, or begins to expand rapidly, operational procedures must be emphasized more strongly than. in an older and consequently more stable organization. It has been the experience at Boeing that the practice which will enable the key men in the department to stay abreast of the rapidly changing situation calls for a daily conference.

Meetings, therefore, are held each morning, presided over by the head of the flight test department. In attendance are the test pilots, the flight test planning engineer, the flight test equipment engineer, the flight test analysis engineer, the flight test secretary, and the crew leader of each test airplane.

Scheduled to last until 8:45 AM, this meeting briefly summarizes the work of the preceding day, the schedules for the day, report on the status of test airplanes, the weather, personnel report, test plans for the day, plans of other units or groups, individual schedules, action items, proposals for new tests, and miscellaneous items. Individual schedules result from the fact that during wartime, the entire flight test personnel must work long hours daily, including Saturdays and frequently Sundays and holidays. Occasions may arise when various individuals have personal business, such as a dental appointment, which would require a portion of the day for completion and might affect the flying schedules.

Decision for a test flight at any altitude is determined in the morning meeting, and is based on such factors as weather, personnel, and the status of the airplane. Schedules are prepared the night before, by the flight engineer in charge, and sent to the hangar in order that the airplane may be made ready for the flight. The hangar advises this man prior to the morning meeting if "ready" time can be met.

The flight engineer in charge notifies his crew and other interested personnel of the flight conference. He distributes the mimeographed "plan of test" to the entire crew and other interested parties at the conference, if this has not previously been done. This meeting is held in one of the conference rooms of the Boeing engineering building or at the hangar conference room, and each member of the crew becomes thoroughly conversant with his duties in regard to the particular flight. When the final engine run-up of the test airplane has been completed, the flight crew leaves for the hangar. If the conference should be concluded some time before the airplane is ready, the crew is dismissed with instructions to report to the hangar at a specified time.

Generally, the pilot and co-pilot arrive at the hangar 15 min in advance of the rest of the crew. This gives these men an opportunity to review the "changes since previous flight" report and the "weight sheet", in order that they may be familiar with the changes in the airplane. It should be pointed out that changes made in each airplane between flights will vary considerably. A large part of the high altitude research is done, not on the aircraft itself, but on special equipment, which may be designed by Boeing, or some other company, which has previously never been used and must be proven before it can become an actual part of the Boeing Flying Fortress.

Next step in the high altitude flight procedure involves assembling the test crew at the hangar. Here, each man obtains the necessary flying equipment. Trained to inspect the condition of his parachute, oxygen equipment, etc, each crew member must fill out a check-off sheet, signifying that he has performed these duties before he boards the test airplane.

After filling out the check-off sheet, the high altitude test crews report to the oxygen cart for denitrogenation. Complete denitrogenation is a company routine on all flights over 25,000 ft. Usually the exercise used is a snappy game of catch, throwing a basket ball, and calisthenics, the duration being 30-45 min. A doctor from the medical unit makes a brief examination of each crew member before he enters the plane, taking pulse and blood pressure and inquiring into the nasal and sinus conditions of each person.

The men then board the Flying Fortress, and while the pilot and co-pilot check the engine operation, the various crew members check their equipment.

During the progress of the flight, all crew members, with the exception of the radio operator, stay on the interphone. The flight engineer in charge announces to the crew members as each condition in the plan of test is established by the pilots, a signal for the crew members to play their role in that phase of the test. Once each hour, the flight engineer in charge reminds the crew members they should take a glucose capsule, to maintain peak efficiency during the course of the flight. If the flight is of long duration in the stratosphere,the flight engineer in charge reminds the crew members at frequent intervals to check on physical condition.

During normal high altitude flight testing, a ten man crew is used on each Flying Fortress. In the cockpit are pilot and co-pilot, the former being responsible for the safety of the crew and the airplane and of maneuvering the airplane in accordance with the plan of test. The co-pilot assists the pilot in his duties and shares the responsibilities. Just aft of the co-pilot the flight engineer in charge is stationed. This man is responsible for the coordination of the activities of the rest of the crew, at various stations throughout the airplane, and for making sure that all information called for in the plan of test is gathered. If, for some reason, this cannot be accomplished, due to physical limitations of the airplane or crew, the flight engineer in charge is the man who makes the decision for deviations from the original plan of flight in consultation with the pilots.

Normally the nose or bombardier's compartment of the Flying Fortress is given over to a potentiometer station where an operator and a recorder are located. The radio compartment of the ship is occupied by a radio operator who maintains communication with the Boeing radio station, and also by either a flowmeter operator and recorder, or a potentiometer operator and recorder. The aft portion of the aircraft, which normally is occupied by the waist gunners and the ball turret, contains a manometer station on test airplanes and is manned by a manometer operator and recorder. These crew locations can be varied, as tests demand, to accommodate photo recorders or special test instrumentation and operators and recorders.

Data on flights are obtained both manually and photographically. At Boeing, it is felt that there is a definite place for manually recorded data. In the instance of the flight engineer in charge, there is a complete log of the flight as well as the recording of the pilot's instruments. In the case of other stations, there is the necessity of knowing how any previously untried equipment is functioning at all times.

This is particularly important in high altitude testing inasmuch as most of this equipment is designed at normal atmospheric pressure and is untried in the extremely low temperatures and low pressures of the stratosphere. By manually recording the data, it is possible for the recorder to notify the cockpit at any time during the flight if a particular test item is not functioning properly. The pilot may then decide if the unusual operation will affect the safety of the crew or the airplane. On the ground, following a flight, the manually recorded data are immediately available at flight conferences, and is usually sufficient for determining the necessity of subsequent test plans of the same equipment. Manually recorded data also preclude the possibility of faulty recording equipment completely or partially failing to obtain the required data. It provides a double check on all flight test data, which is of paramount importance in stratosphere testing of large four-engine aircraft. The expense of sending a large four-engine aircraft such as the B-17 into the stratosphere is so great that the additional expense of a complete crew is justified in assuring that the necessary data will be available. As outlined in Part I of this series items to be tested are submitted to the flight test unit, where they are given a test number and assigned a priority which determines the importance of the test and aids in assigning this item to a test plane. Several such items are grouped together to be tested on a single airplane on a single flight. It is not infrequent that 20 or more items are tested on such a single flight. This reduces to an absolute minimum the expense of testing each item. A typical flight might include testing of the following items:

  1. A new or different type of propeller which might be designed to give better performance in the stratosphere, or might be equipped with heating or de-icing devices to reduce icing conditions at altitude. In the instance of a first test of such an item, one or two engines would be equipped with such propellers. If the first tests of such items proved satisfactory and further testing were required, all engines might be equipped with them.
  2. A new type cowl flap designed to provide better engine cooling in the stratosphere might be another test item. In the instance of the first such test, probably one engine would be so equipped; in subsequent tests, if the first merited more investigation, additional engines.
  3. Another item might be a new type buzzer signal to attract attention of crew members during an emergency in the stratosphere. Here, testing would involve radio interference and audibility.
  4. A new type bearing in a turbo-supercharger might be still another item.

On the ground, after the Flying Fortress had been thoroughly warmed up, the pilot would check the best adjustment for the operation of new type cowl flaps and check the time necessary for them to open and close.

After take-off, the plane would make a rated power climb to 30,000 or 35,000 ft. During the climb, the various test engineers of the crew would record data on the temperatures of the cylinder head and cylinder bases of the engine equipped with new cowl flaps and on an engine equipped with the standard equipment, thus getting a check on the efficiency of the operation of the new type at all times during the flight. The manometer operators would record the air pressures around the new type cowling and on a standard cowling. The performance of the engines equipped with new type propellers would be carefully noted, and the turbo-supercharger tachometers would indicate the performance of the turbos. A potentiometer reading would indicate the temperatures of the new turbo bearing. Photo recorders would gather other information, including a complete record of standard operating condition.

At the desired altitude, level runs would be made at varying engine power settings, during which time all operators and recorders would take data and make notes. The power conditions probably would include six or more variations from 2,500 rpm, with maximum manifold pressure down to 1,200 rpm. Carburetor mixtures would vary from auto rich to auto lean.

With the conclusion of this phase of the test, the plane would climb another 5,000 ft or so and repeat the test, with the test engineers reading and recording data throughout the various phases of the test. Sometime during the test the lesser important items, such as the buzzer signal would be tested. Those persons hearing it would signify that fact; radio operators would check for radio interference. It would not be at all unlikely that the buzzer signal test would be made during each of the conditions, to determine the exact conditions under which it could be heard.

Also during the stratosphere run, the cowl flaps would be opened and closed, to note the difference in engine operations of the new type cowling. The performance of the specially equipped engines would be carefully noted throughout the flight, and upon the conclusion of the high altitude runs, one of these engines might be feathered for a descent to 30,000 ft. Here, the Flying Fortress would level off and the prop would be unfeathered. The time interval involved in unfeathering and starting the engine would be noted and recorded. After the engine had been carefully warmed up, the plane would continue its downward course and land.

Immediately following the flight, the entire crew gathers in the flight conference room, where members discuss the flight and the various tests performed and also draw preliminary conclusions resulting from the tests. A reporter stenotypes the conversations verbatim and publishes the record at the earliest possible time (usually the afternoon of the next day). Meanwhile, the flight engineer in charge dictates a report of the test, and a rough draft is rushed out and is corrected before this man leaves for the day. The copy is then mimeographed and distributed as early as possible on the following morning to all persons involved in the results of the tests.

At the same time, all the manually recorded data are turned over to the flight test analysis group. The film from the photo-recorders is rushed to a flight test dark room, developed and projected, and the enlargements sent to the flight test analysis group, which breaks down the combined manually recorded and photo recorded information into a complete result of the test.

All of this information is then mimeographed and distributed to all parties concerned with the test, and one copy is hound in book form to become a permanent record of the results of the Boeing flight test department. The entire procedure for the execution of test flying at Boeing has been designed to complete each flight in the safest and most efficient manner.

Nothing that would contribute to obtaining the most complete and best information in the shortest possible time has been omitted. Safety precautions are never sacrificed. Because of its organization, the flight test department performs its work without conflict and with wholehearted cooperation from all parties involved. A flight test department operates very much like a well trained athletic team. Both require complete teamwork, without this coordination the final result cannot be satisfactory.

This three-part article was originally published in the April, May and June, 1943, issues of Aviation magazine:
Part 1 in the April, 1943, issue, vol 42, no 4, pp 109-112.
Part 2 in the May, 1943, issue, vol 42, no 5, pp 118-119, 417-418.
Part 3 in the June, 1943, issue, vol 42, no 6, pp 147, 149, 350, 353-355.
The PDF of this article [ PDF, 24.4 MiB ] includes an organizational chart of the Flight & Aerodynamics Division of Boeing, and photos of a wind tunnel model, a testbed B-17, a Boeing Model 40, a B-17E in flight, an altitude chamber, and the special instrumentation in a flight-test B-17.
Photos are not credited, but are certainly from Boeing.