Category NASA’S CONTRIBUTIONS TO AERONAUTICS

In contrast to STOL aircraft systems, which used wing lift generated by forward movement to take off, VTOL aircraft would necessarily have to have some provision for direct vertical propulsive thrust, with the thrust level well in excess of the airplane’s operating weight, to lift off the ground. This drove deflected propeller thrust, tilt wing, tilt rotor, and vectored jet thrust technical approaches, all of which NASA research­ers intensively studied. In all of this, the researchers’ assessment of the system’s VTOL control capability was of special interest—for they had to be able to be controlled in pitch, roll, and yaw without any reliance upon the traditional forces imposed upon an airplane by its movement through the air. The first two approaches that NACA-NASA researchers explored were those of deflected propeller flow and pivoted tilt wings.

At the beginning of 1958, the Ryan Company of San Diego unveiled its Model 92, the VZ-3RY Vertiplane. The Vertiplane, a single-seat twin – propeller high wing design with a T-tail, used propeller thrust to attain vertical flight and maintain hover, deflecting the propeller slipstream via a variable-area and variable-camber wing. The wing’s trailing edge con­sisted of large, 40-percent-chord, double-slotted flaps that transformed into a gigantic curved flow channel, with wingtip ventral fins serving to further entrap the air and concentrate its flow vertically below the craft. Roll control in hover came via varying the propeller pitch to achieve changes in slipstream flow. Power to its twin three-bladed propellers was furnished by a single Lycoming T53 turboshaft engine, which also had its exhaust channeled through a tailpipe to a universal-joint noz­zle that furnished pitch and yaw control for the airplane when it was in hover mode via deflected jet thrust.[1382]

Before the aircraft flew, Ames researchers undertook a series of wind tunnel tests in the 40-foot by 80-foot full-scale wind tunnel to define performance, stability and control, and handling and control characteristics.[1383] As a result of these tests, the aircraft’s landing gear was changed from a "tail-dragger” to tricycle arrangement, and engi­neers added a ventral fin to enhance directional stability in conventional flight. Thus modified, the VZ-3RY completed its first flight January 21, 1959, piloted by Ryan test pilot Pete Girard. Less than a month later, it

was damaged in a landing accident at the conclusion of its 13th flight, when a propeller pitch control mechanism malfunctioned, leaving the VZ-3RY with insufficient lift to drag (L/D) available to flare for landing. It was late summer before it returned to the air, being delivered to Ames in 1960 for NASA testing. Howard L. Turner oversaw the project, and Glen Stinnett and Fred Drinkwater undertook most of the flying. The aircraft was severely damaged when Stinnett ran out of nose-down con­trol at a low-power setting and the aircraft pitched inverted. Fortunately, Stinnett ejected before it nosed into the salt ponds north of the Moffett Field runway. Despite this seemingly disastrous accident, the aircraft was rebuilt yet again and completed the test program. The addition of full-span wing leading-edge slats to enhance lift production permitted hover out of ground effect (OGE). However, air recirculation effects lim­ited in ground effect (IGE) operation to speeds greater than 10 knots, as marginal turning of the slipstream and random upset disturbances caused by slipstream recirculation prevented true VTOL performance. A static pitch instability was often encountered at high lift coefficients, and large pitch trim changes occurred with flap deflection and power changes. The transition required careful piloting technique to avoid pitch – up. Although adequate, descent performance was limited in the extreme by low roll control power and airflow separation on the wing when power was reduced to descend. Despite these quirks and two accidents,

the VZ-3RY demonstrated excellent STOL performance, achieving a max­imum lift coefficient of 10, with a moderate to good cruise speed range. Thus, it must be considered a successful research program. Transitions were completed from maximum speed down to 20 knots with "negligible change in longitudinal trim and at rates comparable to those done with a helicopter.”[1384] Indeed, as Turner and Drinkwater concluded in 1963, "Flight tests with the Ryan VZ-3RY V/STOL deflected-slipstream test vehicle have indicated that the concept has some outstanding advantages as a STOL aircraft where very short take-off and landing characteristics are desired.”[1385] As well as pursuing the BLC and deflected slipstream projects, NASA researchers examined tilt wing concepts then being pursued in America and abroad. The tilt wing promised a good blend of moderate low – and high-speed compatibility, with good STOL performance provided by slipstream-induced lift. For takeoff and landing, the wing would pivot so that the engine nacelles and propellers pointed vertically. After take­off, the wing would be gradually rotated back to the horizontal, enabling conventional flight. Various research aircraft were built to investigate the tilt wing approach to V/STOL flight, notably including the Canadair CL-84, Hiller X-18, the Kaman K-16B, and the joint-service Ling-Temco – Vought XC-142. The first such American aircraft was the Boeing-Vertol VZ-2 (the Vertol Model 76). It was powered by a single Lycoming YT53L1 gas turbine, driving two propellers via extension shafts and small tail fans for low-speed pitch and yaw control. Conceived from a jointly funded U. S. Army-Office of Naval Research study, the VZ-2 first flew in August 1957 and was an important early step in demonstrating the potential of tilt wing V/STOL technology. On July 16, 1958, piloted by Leonard La Vassar, it made the world’s first full-conversion of a tilt wing aircraft from vertical to horizontal flight, an important milestone in the history of V/STOL. Vertol completed its testing in September 1959 and then shipped the VZ-2 to Langley Research Center for evaluation by NASA.[1386]

Subsequent Langley tests confirmed that the tilt wing was undoubt­edly promising. However, like many first-generation technological sys­tems, the VZ-2 had a number of limitations. NASA test pilot Don Mallick recalled, "it was extremely difficult to fly,” with "lots of cross-coupling between the roll and yaw controls,” and that "It took everything I had to keep from ‘dinging’ or crashing the aircraft.”[1387] Langley research pilot Jack Reeder found that its VTOL roll control—which, as in a helicop­ter, was provided by varying the propeller pitch and hence its thrust— was too sensitive. Further, the two ducted fans at the tail responsible for pitch and yaw control furnished only marginal control power. In par­ticular, weak yaw control generated random heading deviations. When slowing into ground effect at a wing tilt angle of 70 degrees, directional instabilities were encountered, though there was no appreciable aerody­namic lift change.[1388]

Reflected flows from the ground caused buffeting and unsteady aircraft behavior, resulting in poor hover precision. Because of low
pitch control power, lack of a Stability Augmentation System (SAS), and low inherent damping of any pitch oscillations, researchers pru­dently undertook hover trials only in calm air. Among its positive qual­ities, good STOL performance was provided by slipstream-induced lift. Transition to wing-supported flight was satisfactory, with little pitch – trim change required. In transitions, as the wing pivoted down to normal flight position, hover controls were phased out. The normal aerody­namic controls were phased in, with the change from propeller to wing – supported flight being judged satisfactory. However, deceleration on descent was severely restricted by wing stall. When power was reduced, lateral – directional damping decreased to unsatisfactory levels. Changes were made to "droop” the leading edge 6 degrees to improve descent perfor­mance, and the modification improved behavior and controllability so greatly that Langley test pilot Jack Reeder concluded the "serious stall lim­itations in descent and level-flight deceleration were essentially eliminated from the range of practical flight operation, at least at incidence angles up to 50°.”[1389] In spite of this seemingly poor "report card,” the awkward – looking VZ-2 contributed greatly to early understanding of the behavior and foibles of V/STOL tilt wing designs. All together, it completed 450 research sorties, including 34 full transitions from vertical to horizontal flight. The VZ-2 flight program proved to be one of the more productive American V/STOL programs, furnishing much information on wing- propeller aerodynamic interactions and basic V/STOL handling qualities.[1390]

In addition to the pioneering VZ-2, the Hiller and Kaman compa­nies also pursued the concept, the former for the Air Force and the latter for the Navy, though with significantly less success. Using an off – the-shelf development approach followed by many V/STOL programs, Hiller joined the fuselage and tail section of a Chase YC-122 assault trans­port to a tilt wing, creating the X-18, the first transport-sized tilt wing testbed. It used two Allison T40 turboprop engines driving three-bladed contra-rotating propellers, plus a Westinghouse J34 to furnish pitch control via a lengthy tailpipe. The sole X-18 made a conventional flight in November 1959 and completed a further 19 test sorties before being

grounded. Though it demonstrated wing tilt in flight to an angle of 33 degrees, it never completed a VTOL takeoff and transition. On November 4, 1960, a propeller malfunction led to it entering an inverted spin. Through superb airmanship, test pilots George Bright and Bruce Jones recovered the aircraft and landed safely, but it never flew again.[1391] Kaman undertook a similar development program for the Navy, joining a tilt wing with two General Electric T58-GE-2A turboshaft engines to the fuselage and tail section of a Grumman JRF Goose amphibian, creating the K-16B. Tested in Ames’s 40-foot by 80-foot tunnel, the K-16B never took to the air.[1392]

Despite these failures, confidence in the tilt wing concept had advanced so rapidly that in February 1961, after 2 years of feasibility studies, the Department of Defense issued a joint-service development specification for an experimental VTOL transport that could possibly be developed into an operational military system. After evaluating pro­posals, the department selected the Vought-Hiller-Ryan Model VHR 447, ordering it into development under the Tri-Service Assault Transport Program as the XC-142A.[1393] All three of these companies had previously employed variable position wings, with the F-8 Crusader fighter, the X-18, and the VZ-3RY, though only the last two were V/STOL designs. The XC-142A was powered by four General Electric T64 turboshaft engines, each rated at 3,080 horsepower, driving four-bladed Hamilton Standard propellers, with the propellers cross-linked by drive shafts to prevent a possibly disastrous loss of control during VTOL transitions. The combi­nation of great power and light weight ensured not only that it could take off and land vertically, but also that it would have a high top-end speed of over 400 mph. Piloted by Stuart Madison, the first of five XC-142As completed a conventional takeoff in late September 1964, made its first hover at the end of December 1964, and accomplished its first transition from vertical to horizontal flight January 11, l965, "with no surprises.”[1394]

The five XC-142A test aircraft underwent extensive joint – service evaluation, moving a variety of vehicles and troops, undertaking

simulated recovery of downed aircrew via a recovery sling, landing aboard an aircraft carrier, and even flying a demonstration at the 1967 Paris Air Show. With a payload of 8,000 pounds and a gross weight of 37,500 pounds, the XC-142A had a thrust-to-weight ratio of 1.05 to 1. In STOL mode, with the wing set at 35 degrees and with flaps set at 30 degrees, the XC-142A could almost double this payload yet still clear a 50-foot obstacle after a 200-foot takeoff run.[1395] Unfortunately, program costs rose from an estimated $66 million at inception to $115 million (in FY 1963 dollars), resulting in overruns that eventually truncated the aircraft’s development.[1396] The five aircraft experienced a number of mishaps, most related to shafting and propulsion problems. Sadly, one accident resulted in the death of test pilot Madison and a Ling-Temco-

Vought (LTV) test crew in May 1967, after a loss of tail rotor pitch con­trol from fatigue failure of a critical part during a hover at low altitude.[1397]

NASA Langley took ownership of the fourth XC-142A in October 1968, subsequently flying it until May 1970. The lead pilot was Bob Champine. When these tests concluded, the program came to an end. The Air Force Scientific Advisory Board’s Aerospace Vehicle Panel concluded that, "The original premise that the propeller-tilt wing was well within the state of the art and that it was possible to go directly to operational prototypes was essentially a correct one,” and that the tilt wing "has remarkable STOL capabilities that should be exploited to the maximum.” Indeed, "One of the major advantages of the propeller – tilt wing is the fact that it is a magnificent STOL,” but the panel also acknowledged that, on the XC-142A program, "The technical surprises were few, but important.”[1398]

The results of combined contractor, military, and NASA testing indi­cated that, as Seth Anderson noted subsequently, despite the XC-142A’s clear promise:

Some mechanical control characteristics were unsatisfactory:

(1) directional friction and breakout forces varied with wing tilt angle,

(2) non-linear control gearing,

(3) possibility of control surface hard-over, and

(4) collective control had to be disengaged manually from the throttles in transition.

Hover handling qualities were good with SAS on, with no adverse flow upsets, resulting in precise spot positioning. Propeller thrust in hover was 12% less than predicted. No adverse lateral-directional char­acteristics were noted in sideward flight up to 25 knots. In slow forward flight, a long-period (20 sec) oscillation was apparent which could lead to an uncontrollable pitch-up. On one occasion full forward stick did not arrest the pitch-up, whereupon the pilot reduced engine power, the nose fell through, and the aircraft was extensively damaged in a hard landing because the pilot did not add sufficient power to arrest the high sink rate for fear of starting another pitch-up.

STOL performance was not as good as predicted and controllability compromised IGE by several factors:

(1) severe recirculation of the slipstream for wing tilt angles in the range 40° to 80° (speed range 30 to 60 knots) producing large amplitude lateral-directional upsets;

(2) weak positive, neutral, and negative static longitudinal stability; and

(3) low directional control power.

Transition corridor was satisfactory with ample acceleration and deceleration capabilities. Conventional flight performance was less than predicted (11% less) due to large boat-tail drag-cruise.

Stability and control was deficient in several areas:

(1) low to neutral pitch stability,

(2) nonlinear stick force per "g” gradient, and

(3) tendency for a pitch Pilot Induced Oscillation (PIO) during recovery from rolling maneuvers.[1399]

A failure of the drive shaft to the tail pitch propeller in low-speed flight caused a fatal crash that essentially curtailed further development of this concept. The experience of Canadair with the CL-84 Dynavert, a twin-engine tilt wing powered by two Lycoming T53 turboshafts, was in many respects similar to that of the XC-142A. In October 1966, NASA Langley pilots Jack Reeder and Bob Champine had evaluated the CL-84 at the manufacturer’s plant, finding that, "The flying qualities were considered generally good except for a slow arrest of rate of descent at constant power and airspeed that could be of particular significance dur­ing instrument flight.”[1400] For a while after the conclusion of the XC-142A
program, the U. S. Navy sponsored further tilt rotor research with the Canadair CL-84, in trials at sea and at the Naval Air Test Center, Patuxent River, MD, looking at combat search and rescue and fleet logistical sup­port missions. Undoubtedly, it was a creative design of great promise and clear potential, marred by a series of mishaps, though fortunately without loss of life. But after 1974, when the CL-84 joined the XC-142 in retirement, whatever merits the tilt wing might have possessed for piloted aircraft were set aside in favor of other technical approaches.

The HSR Program Office assigned the six Phase I and one Phase II flight experiments reference numbers.

All six Phase I experiments were continued in Phase II and were iden­tified in their Phase II form by the letter "A” following the number. Only experiment 1.5 changed in nature in Phase II. All of the experiments
were assigned Tupolev principal investigator counterparts. The experiments and principal NASA-Boeing investigators are listed below:

• 1.2 Surface/Structure Equilibrium Temperature Verification: Craig Stephens (NASA Dryden).

• 1.5 Propulsion System Thermal Environment: Warren Beaulieu (Boeing).

• 1.5A Fuel System Thermal Database: Warren Beaulieu (Boeing).

• 1.6 Slender Wing Ground Effects: Robert Curry (NASA Dryden).

• 2.1 Structure/Cabin Noise: Stephen Rizzi (NASA Langley) and Robert Rackl (Boeing).

• 2.4 Handling Qualities Assessment: Norman Princen (Boeing).

• 3.3 Cp, Cf, and Boundary Layer Measurement and CFD Comparisons: Paul Vijgen (Boeing).

• 4.1 In-Flight Wing Deflection Measurements: Robert Watzlavick (Boeing).[1486]

Because the HSR program was the primary funding source for the Tu-144LL flight experiment, it followed that the relevant HSR Integrated Technology Development (ITD) teams would be the primary customers. Subsequent to Phase I, however, it became apparent that some of the exper­iments did not have the ITD teams’ complete support. The experimenters believed that data analysis would be accomplished by the interested ITD teams, but the ITD teams who had little or no input in the planning and selection of the experiments had no plans to use the data. This was com­plicated by the cancellation of the HSR program by NASA in April 1999.[1487] In retrospect, it appeared that the experiment selection process did not properly consider the ultimate needs of the logical customers in all cases. In deference to the HSR program, however, it should be noted that the joint U. S.-Russian Tu-144 project had political aspects that had to be considered and inputs for data from Tupolev that may not have fit neatly into HSR requirements. Fortunately, the bulk of the raw data from all of

the experiments, except Langley’s 2.1 and 2.1A, is maintained at NASA Dryden.[1488] The data from 2.1 were fully analyzed and reported in several NASA and Boeing reports.[1489]

The data from all but experiment 2.1, Structure/Cabin Noise, were collected by the Damien DAS and were for the most part managed in Zhukovsky by Tupolev engineers. Experiment 2.1 had a dedicated DAS and experienced none of the data acquisition problems suffered at times by the other experiments. NASA Dryden’s Glenn A. Bever was the NASA onsite engineer and instrumentation engineer for the dura­tion of the program. In this capacity, he supported all of the experi­ments, except Langley’s experiment 2.1, which had its own engineers and technicians. From 1995 to 1999, Bever made 19 trips to Zhukovsky, "a total of 8 months in Russia all told hitting every month of the year at least once.”[1490] Because Dryden had responsibility for instrumentation, Bever worked with Tupolev instrumentation engineers and technicians directly to ensure that all of the experiments’ data other than 2.1 were properly captured. Often, he was the only American in Zhukovsky and found himself the point of contact for all aspects of the project. He "wrote Summaries of Discussion at the end of each trip which tended, we discovered, to act like contracts to direct what work was to happen next and document deliverables and actions.”[1491] Bever utilized a rather new concept at the time, when he transmitted all of the collected data from the experiments under his purview to Dryden via the Internet. He translated the instrumentation calibration information files into English calibration files, wrote the programs that reduced the data to a manip­ulative format, applied the calibrations, formatted the data for storage, and archived the data on Dryden’s flight data computer and on CDs. One of his final accomplishments was to design the air data sensor sys­tem that collected altitude and airspeed information from the Phase II flights flown by the NASA pilots.[1492] Langley’s instrumentation technician,

Donna Amole, and Dryden’s Project Manager, Russ Barber, attested to the significant efforts Bever contributed to the project.

Experiment 1.2/1.2A, Surface/Structure Equilibrium Temperature, consisted of 250 thermocouples and 18 heat flux gauges installed on pre­determined locations on the left wing, fuselage, and engine nacelles, which measured temperatures from takeoff through landing on Mach 1.6 and 2 test flights.[1493] High noise levels and significant zero offsets resulted in poor quality data for the Phase I flights. This was due to problems with the French-built Damien DAS. For Phase II, a Russian-designed Gamma DAS was used, with higher-quality data being recorded. Unfortunately, the HSR program did not analyze the data, because the relevant ITD team did not believe this experiment was justified, based on prior work and preexisting prediction capability at these Mach numbers. The initial poor data quality also did not suggest that further analysis was warranted.[1494]

Experiment 1.5, Propulsion System Thermal Environment, sampled temperatures in the engine compartment and inlet and measured acces­sory section maximum temperatures, engine compartment cooling airflow, and engine temperatures after shutdown. Thirty-two thermocouples on the engine, 35 on the firewall, and 10 on the outboard shield recorded the temperature data.[1495] The data provided valuable information on thermal lag during deceleration from Mach 2 flight and on the temperature profiles in the engine compartment after shutdown. Experiment 1.5A in Phase II developed a Thermal Database on the aircraft fuel system using 42 resis­tance temperature devices and 4 fuel flow meters to collect temperature and fuel flow time histories on engines 1 and 2 and heat rejection data on the engine oil system during deceleration from supersonic speeds. HSR engineers did not fully analyze these data before program cancellation.[1496]

Experiments 1.6/1.6A, Slender Wing Ground Effects, demonstrated no evidence of dynamic ground effects on the Tu-144LL. This correlated
with wind tunnel data and NASA evaluation pilot comments.[1497] Effects were determined on lift, drag, and pitching moment with the canard, both retracted and extended. Forty-eight parameters were measured in flight, including inertial parameters, control surface positions, height above the ground, airspeed, and angle of attack. From these, aerodynamic forces and moments were derived, and weight and thrust were computed postflight. A NASA Differential Global Positioning System (DGPS) provided highly pre­cise airspeed and angle-of-attack data and repeatable heights above run­way accurate to less than 0.5 feet. Getting this essential DGPS equipment into Russia had been difficult because of Russian import restrictions. In Phase I, 10 good maneuvers from the 19 flights were accomplished, eval­uating a range of weights, sink rates, and canard positions. The data qual­ity was excellent, and the results indicated that there is still much to be learned regarding dynamic ground effects for slender, swept wing aircraft.[1498]

Langley’s Structure/Cabin Noise, experiment 2.1, was unique among the seven flight experiments, in that it used its own Langley-built DAS and had on site its own support personnel for all flights on which data were collected. Another unique feature of this experiment was its direct tie to a specific customer, the HSR structural acoustics ITD team. The two principal investigators, Stephen Rizzi and Robert Rackl, were members of the team, and Rizzi was the team lead. This arrangement allowed the structure of the experiment to be designed directly to meet team require­ments.[1499] Several datasets, including boundary layer fluctuating pressure measurements, fuselage sidewall vibration and interior noise data, jet noise data, and inlet noise data, were used to update or validate various acoustic models, such as a boundary layer noise source model, a cou­pled boundary layer/structural interaction model, a near-field jet noise model, and an inlet noise model.[1500] The size of the dataset and sampling rates was staggering. The required rate was 40,000 samples per second for each of 32 channels. The Damien DAS was not capable of sampling at these rates, thus necessitating the Langley DAS. Langley, as a result, provided personnel on site to support experiment 2.1. These included

Rizzi, Rackl, and several instrumentation technicians from Langley’s Flight Instrumentation Branch, including Vernie Knight, Keith Harris, and Donna Amole, the only onsite American female on the project. Amole spent about 5 months in Zhukovsky during 8 trips. Her first trip was chal­lenging, to say the least. The Tupolev personnel were not eager to have an American woman working with them. Whether because of supersti­tion (Amole initially was told she could not enter the airplane on flight days), cultural differences, or perhaps a misunderstood fear of poten­tial American sexual harassment issues, Amole for the first 2 weeks was essentially ignored by her Tupolev counterparts. She would not be deterred, however, and won the respect and friendship of her Russian colleagues. Glenn Bever and Stephen Rizzi provided essential support, but many times, she was, like Bever, the only American on site.[1501]

Experiment 2.4, Handling Qualities Assessment, suffered in Phase I from poor data quality, which predicted a very poor flying aircraft. The aircraft response to control deflections indicated a 0.25-second delay between control movement and aircraft response. Furthermore, angle-of – attack, angle-of-sideslip, heading, altitude, and airspeed data all were of suspect quality at times.[1502] These data issues contributed to the HSR pro­gram’s desire for U. S. pilots to fly the airplane to evaluate the handling qualities, because access to the Tupolev pilots was limited. Additionally, in Phase II, a new air data sensor from NASA Dryden corrected the nag­ging air data errors. This experiment will be covered in more detail in the following section on the Tu-144LL Handling Qualities Assessment.

Experiments 3.3/3.3A—Cp, Cf, and Boundary Layer Measurements— collected data on surface pressures, local skin friction coefficients, and boundary layer profiles on the wing and fuselage using 76 static pressure orifices, 16 skin friction gauges consisting of 10 electromechanical bal­ances and 6 hot film sensors, 3 boundary layer rakes, 3 reference probes, 5 full chord external pressure belts consisting of 3 on the wing upper sur­face and 2 on the lower surface, and angle-of-attack and angle-of-sideslip vanes. Measurements from the 250 thermocouples from experiment 1.2 were used in the aerodynamic data analysis.[1503] Data were collected at Mach

0. 9, 1.6, and 2 and included over 80 minutes of stabilized supersonic flight. Data quality was good, although some calibration problems with the pressure transducers and mechanical skin friction balances arose. On flight 10, the lower wing surface midspan pressure belt detached and was lost, and 4 tubes on the upper midspan belt debonded. Fortunately, the failures occurred after the minimum data requirements had been met. In Phase II, Preston tubes and optical-mechanical sensors devel­oped at Russia’s Central Institute of Aerohydromechanics (TsAGI) were implemented for additional skin friction measurements. The HSR pro­gram did not fully analyze these data, believing that prior XB-70 data already filled these requirements.[1504]

Experiment 4.1A, In-Flight Wing Deflection Measurements, pro­vided a limited verification of the wing geometry under in-flight loads. These data are needed for validating the aeroelastic prediction meth­odology and providing the in-flight geometry needed in computational fluid dynamics analysis. Boeing’s Optitrak active target photogrammetry system was used, and Boeing managed the experiment. The installed system incorporated 24 infrared reflectors mounted on the upper sur­face of the right wing, each pulsed in sequence. Two cameras captured the reflected signals in order to provide precise x, y, and z coordinates.[1505] The system was used on Langley’s Boeing 737 in the early 1990s high lift experiment, designed to quantify the precise effect of high-lift devices.

Not listed among the formal experiments was a Phase II indepen­dent "piggyback” experiment leveraging off the data collected from experiment 2.4, Handling Qualities Assessment, flown by the NASA research pilots. This involved a new longitudinal, lateral, and direc­tional closed-loop Low-Order Equivalent System (LOES) method of air­craft parameter identification using an equation-error method in the frequency domain. Because the data were accumulated by pilot-in-the – loop frequency sweep and multistep maneuvers, these were added to the test cards for the first four Phase II flights.[1506] Langley’s Dr. Eugene A. Morrelli requested theses datasets and developed the pilot maneuvers necessary to acquire them. This was a unique example of a researcher taking advantage of his colleagues’ work on a once-in-a-lifetime
experiment and of the spirit of cooperation among NASA researchers that allowed this opportunity develop.

The partnership between NASA and the FAA that facilitates that exchange of ideas and technology was forged soon after both agencies were for­mally created in 1958. With the growing acceptance of commercial jet air­liners and the ever-increasing number of passengers who wanted to get to their destinations as quickly as possible, the United States began explor­ing the possibility of fielding a Supersonic Transport (SST). By 1964, it was suggested that duplication of effort was underway by researchers at the FAA and NASA, especially in upgrading existing jet powerplants required to propel the speedy airliner. The resulting series of meetings during the next year led to the creation in May 1965 of the NASA-FAA Coordinating Board, which was designed to "strengthen the coordina­tion, planning, and exchange of information between the two agencies.”[187]

The Airspace Concept Evaluation System (ACES) is a computer tool that allows researchers to try out novel Air Traffic Management (ATM) the­ories, weed out those that are not viable, and identify the most promis­ing concepts. ACES looks at how a proposed air transportation concept can work within the National Airspace System (NAS), with the aim of reducing delays, increasing capacity, and handling projected growth in air traffic. ACES does this by simulating the major components of the NAS, modeling a flight from gate to gate, and taking into account in its models the individual behaviors of those that affect the NAS, from depar­ture clearance to the traffic control tower, the weather office, navigation systems, pilot experience, type of aircraft, and other major components. ACES also is able to predict how one individual behavior can set up a ripple effect that touches, or has the potential to touch, the entire NAS. This modeling approach isolates the individual models so that they can continue to be enhanced, improved, and modified to represent new con­cepts without impacting development of the overall simulation system.[251]

Among the variables ACES has been tasked to run through its sim­ulations are environmental impacts when a change is introduced,[252] use

of various communication and navigation models,[253] validation of cer­tain concepts under different weather scenarios,[254] adjustments to spac­ing and merging of traffic around dense airports,[255] and reduction of air traffic controller workload by automating certain tasks.[256]

During World War II, human factors was pushed into even greater prom­inence as a science. During this wartime period of rapidly advancing military technology, greater demands were being placed on the users of this technology. Success or failure depended on such factors as the operators’ attention span, hand-eye coordination, situational awareness, and decision-making skills. These demands made it increasingly chal­lenging for operators of the latest military hardware—aircraft, tanks, ships, and other complex military machinery—to operate their equip­ment safely and efficiently.[316] Thus, the need for greater consideration of human factors issues in technological design became more obvious than ever before; as a consequence, the discipline of human engineer­ing emerged.[317] This branch of human factors research is involved with finding ways of designing "machines, operations, and work environ­ments so that they match human capacities and limitations.” Or, to put it another way, it is the "engineering of machines for human use and the engineering of human tasks for operating machines.”[318]

During World War II, no area of military technology had a more critical need for both human factors and human engineering consid­erations than did aviation.[319] Many of the biomedical problems afflict­ing airmen in the First World War had by this time been addressed, but new challenges had appeared. Most noticeable were the increased phys­iological strains for air crewmen who were now flying faster, higher, for longer periods of time, and—because of wartime demands—more aggressively than ever before. High-performance World War II aircraft were capable of cruising several times faster than they were in the pre­vious war and were routinely approaching the speed of sound in steep dives. Because of these higher speeds, they were also exerting more than enough gravitational g forces during turns and pullouts to render pilots almost instantly unconscious. In addition, some of these advanced air­craft could climb high into the stratosphere to altitudes exceeding 40,000 feet and were capable of more hours of flight-time endurance than their human operators possessed. Because of this phenomenal increase in aircraft technology, human factors research focused heavily on address­ing the problems of high-performance flight.[320]

The other aspect of the human factors challenge coming into play involved human engineering concerns. Aircraft of this era were exhibiting a rapidly escalating degree of complexity that made flying them—particu­larly under combat conditions—nearly overwhelming. Because of this com­bination of challenges to the mortals charged with operating these aircraft, human engineering became an increasingly vital aspect of aircraft design.[321]

During these wartime years, high-performance military aircraft were still crashing at an alarmingly high rate, in spite of rigorous pilot train­ing programs and structurally well-designed aircraft. It was eventually accepted that not all of these accidents could be adequately explained by the standard default excuse of "pilot error.” Instead, it became apparent that many of these crashes were more a result of "designer error” than operator error.[322] Military aircraft designers had to do more to help the humans charged with operating these complex, high-performance aircraft. Thus, not only was there a need during these war years for greater human safety and life support in the increasingly hostile environment aloft, but the crews also needed better-designed cockpits to help them perform the complex tasks necessary to carry out their missions and safely return.[323]

In earlier aircraft of this era, design and placement of controls and gauges tended to be purely engineer-driven; that is, they were constructed to be as light as possible and located wherever designers could most conveniently place them, using the shortest connections and simplest attachments. Because the needs of the users were not always taken into account, cockpit designs tended not to be as user-friendly as they should have been. This also meant that there was no attempt to standardize the cockpit layout between different types of aircraft. This contributed to longer and more difficult transitions to new aircraft with different instrument and control arrangements. This disregard for human needs in cockpit design resulted in decreased aircrew efficiency and perfor­mance, greater fatigue, and, ultimately, more mistakes.[324]

An example of this lack of human consideration in cockpit design was one that existed in an early model Boeing B-17 bomber. In this air­craft, the flap and landing gear handles were similar in appearance and proximity, and therefore easily confused. This unfortunate arrangement had already inducted several pilots into the dreaded "gear-up club,” when, after landing, they inadvertently retracted the landing gear instead of the intended flaps. To address this problem, a young Air Corps physiologist and Yale psychology Ph. D. named Alphonse Chapanis proved that the incidence of such pilot errors could be greatly reduced by more logical control design and placement. His ingeniously simple solution of mov­ing the controls apart from one another and attaching different shapes to the various handles allowed pilots to determine by touch alone which control to activate. This fix—though not exactly rocket science—was all that was needed to end a dangerous and costly problem.[325]

As a result of a host of human-operator problems, such as those described above, wartime aircraft design engineers began routinely working with industrial and engineering psychologists and flight sur­geons to optimize human utilization of this technology. Thus was born in aviation the concept of human factors in engineering design, a disci­pline that would become increasingly crucial in the decades to come.[326]

NASA and a group of U. S. aerospace corporations began research for this ambitious program in 1990. Their goal was to develop a jet capa­ble of transporting up to 300 passengers at more than twice the speed of sound. An important human factors-related spinoff of the so-called High-Speed Civil Transport (HSCT) was an External Visibility System. This system replaced forward cockpit windows with displays of video images with computer-generated graphics. This system would have allowed better performance and safety than unaided human vision while

eliminating the need for the "droop nose” that the supersonic Concorde required for low-speed operations. Although this program was phased out in fiscal year (FY) 1999 for budgetary reasons, the successful vision technology produced was handed over to the previously discussed AvSP – AvSSP’s Synthetic Vision Systems element for further development.[430]

One of the more complex and challenging areas in aerospace technology is the prediction of paths of aircraft components following the release of items such as external stores, canopies, crew modules, or vehicles dropped from mother ships. Aerodynamic interference phenomena between vehicles can cause major safety-of-flight issues, resulting in catastrophic impact of the components with the airplane. Unexpected pressures and shock waves can dramatically change the expected tra­jectory of stores. Conventional wind tunnel tests used to obtain aero­dynamic inputs for calculations of separation trajectories must cover a wide range of test parameters, and the requirement for dynamic aero­dynamic information further complicates the task. Measurement of aerodynamic pressures, forces, and moments on vehicles in proximity to one another in wind tunnels is a highly challenging technical proce­dure. The use of dynamically scaled free-flight models can quickly pro­vide a qualitative indication of separation dynamics, thereby providing guidance for wind tunnel test planning and early identification of poten­tially critical flight conditions.

Separation testing for military aircraft components using dynamic models at Langley evolved into a specialty at the Langley 300-mph 7- by 10-Foot Tunnel, where subsonic separation studies included assess­ments of the trajectories taken by released cockpit capsules, stores, and canopies. In addition, bomb releases were simulated for several bomb – bay configurations, and the trajectories of model rockets fired from the wingtips of models were also evaluated. As requests for specific separa­tion studies mounted, the staff rapidly accumulated unique expertise in

testing techniques for separation clearance.[500] One of the more important separation studies conducted in the Langley tunnel was an assessment of the launch dynamics of the X-15/B-52 combination for launches of the X-15. Prior to the X-15, launches of research aircraft from carrier aircraft had only been made from the fuselage centerline location of the mother ship. In view of the asymmetrical location of the X-15 under the right wing of the B-52, concern arose as to the aerodynamic loads encountered during separation and the safety of the launching procedure. Separation studies were therefore conducted in the Langley 300-mph 7- by 10-Foot Tunnel and the Langley High-Speed 7- by 10-Foot Tunnel.[501]

Detailed measurements of the aerodynamic loads on the X-15 in proximity to the B-52 under its right wing were made during conven­tional force tests in the high-speed tunnel, while the trajectory of a dynamically scaled X-15 model was observed during a separate inves­tigation in the low-speed tunnel. The test set up for the low-speed drop tests used a dynamically scaled X-15 model under the left wing of the B-52 model to accommodate viewing stations in the tunnel. Initial trim settings for the X-15 were determined to avoid contact with the B-52, and the drop tests showed that the resulting trajectory motions provided adequate clearance for all conditions investigated.

During successful subsonic separation events, a bomb or external store is released, and gravity typically pulls it away safely. At super­sonic speeds, however, aerodynamic forces are appreciably higher rel­ative to the store weight, shock waves may cause unexpected pressures that severely influence the store trajectory or bomb guidance system, and aerodynamic interference effects may cause catastrophic collisions after launch. Under some conditions, bombs released from within a fuselage bomb bay at supersonic speeds have encountered adverse flow fields, to the extent that the bombs have reentered the bomb bay. In the early 1950s, the NACA advisory committees strongly recommended that focused efforts be initiated by the Agency in store separation, especially for supersonic flight conditions. Researchers within Langley’s Pilotless Aircraft Research Division used their Preflight Jet facility at Wallops to conduct research on supersonic separation characteristics for several

high-priority military programs.[502] The Preflight Jet facility was designed to check out ramjet engines prior to rocket launches, consisting of a "blow down’-type tunnel powered by compressed air exhausted through a supersonic nozzle. Test Mach number capability was from 1.4 to 2.25. With an open throat and no danger to a downstream facility drive sys­tem, the facility proved to be ideal for dynamic studies of bombs or stores following supersonic releases.

One of the more crucial tests conducted in the Wallops Preflight Jet facility was support for the development of the Republic F-105 fighter – bomber, which was specifically designed with forcible ejection of bombs from within the bomb bay to avoid the issues associated with external releases at supersonic speeds. For the test program, a half-fuselage model (with bomb bay) was mounted to the top of the nozzle, and the ejection sequence included extension of folding fins on the store after release. A piston and rod assembly from the open bomb bay forcefully ejected the

store, and high-speed photography documented the motion of the store and its trajectory. The F-105 program expanded to include numerous specific and generic bomb and store shapes requiring almost 2 years of tests in the facility. Numerous generic and specific aircraft separation studies in the Preflight Jet facility from 1954 to 1959 included F-105 pilot escape, F-104 wing drop-tank separations, F-106 store releases from an internal bomb bay, and B-58 pod drops.

Jeremy Kinney

Even before the invention of the airplane, wind tunnels have been key in undertaking fundamental research in aerodynamics and evaluat­ing design concepts and configurations. Wind tunnels are essential for aeronautical research, whether for subsonic, transonic, supersonic, or hypersonic flight. The swept wing, delta wing, blended wing body shapes, lifting bodies, hypersonic boost-gliders, and other flight con­cepts have been evaluated and refined in NACA and NASA tunnels.

N NOVEMBER 2004, the small X-43A scramjet hypersonic research vehicle achieved Mach 9.8, roughly 6,600 mph, the fastest speed ever attained by an air-breathing engine. During the course of the vehicle’s 10-second engine burn over the Pacific Ocean, the National Aeronautics and Space Administration (NASA) offered the promise of a new revolu­tion in aviation, that of high-speed global travel and cost-effective entry into space. Randy Voland, project engineer at Langley Research Center, exclaimed that the flight "looked really, really good” and that "in fact, it looked like one of our simulations.”[528] In the early 21st century, the pub­lic’s awareness of modern aeronautical research recognized advanced computer simulations and dramatic flight tests, such as the launching of the X-43A mounted to the front of a Pegasus rocket booster from NASA’s venerable B-52 platform. A key element in the success of the X-43A was a technology as old as the airplane itself: the wind tunnel, a fundamen­tal research tool that also has evolved over the past century of flight.

NASA and its predecessor, the National Advisory Committee for Aeronautics (NACA), have been at the forefront of aerospace research since the early 20th century and on into the 21st. NASA made funda­mental contributions to the development and refinement of aircraft and spacecraft—from commercial airliners to the Space Shuttle—for

operation at various speeds. The core of this success has been NASA’s innovation, development, and use of wind tunnels. At crucial moments in the history of the United States, the NACA-NASA introduced state-of – the-art testing technologies as the aerospace community needed them, placing the organization onto the world stage.

The history of composite development reveals at least as many false starts and technological blind alleys as genuine progress. Leo Baekeland, an American inventor of Dutch descent, started a revolution in mate­rials science in 1907. Forming a new polymer of phenol and formal­dehyde, Baekeland had succeeded in inventing the first thermosetting plastic, called Bakelite. Although various types of plastic had been developed in previous decades, Bakelite was the first commercial success. Baekeland’s true breakthrough was inventing a process that allowed the mass production of a thermosetting plastic to be done cheaply enough to serve the mechanical and fiscal needs of a huge cross section of prod­ucts, from industrial equipment to consumer goods.

It is no small irony that powered flight and thermosetting plas­tics were invented within a few years of each other. William F. Durand, the first Chairman of the NACA, the forerunner of NASA, in 1918 summarized the key structural issue facing any aircraft designer. Delivering the sixth Wilbur Wright Memorial Lecture to the Royal Aeronautical Society, the former naval officer and mechanical engineer said, "Broadly speaking, the fundamental problem in all airplane construction is adequate strength or function on minimum weight.” [648] A second major structural concern, which NACA officials would soon come to fully appreciate, was the effect of corrosion on first wood, then metal, structures. Thermosetting plastics, one of two major forms of composite materials, present a tantalizing solution to both problems. The challenge has been to develop composite matrices and production processes that can mass-produce materials strong enough to replace wood and metal, yet affordable enough to meet commercial interests.

While Baekeland’s grand innovation in 1907 immediately made strides in other sectors, aviation would be slow to realize the benefit of thermosetting plastics.

The substance was too brittle and too week in tensional strength to be used immediately in contemporary aircraft structures. But Bakelite eventually found its place by 1912, when some aircraft manufacturers started using the substance as a less corrosive glue to bind the joints between wooden structures.[649] The material shortages of World War I, how­ever, would force the Government and its fledgling NACA organization to start considering alternative sources to wood for primary structures. In 1917, in fact, the NACA began what would become a decades-long effort to investigate and develop alternatives to wood, beginning with metal. As a very young bureaucracy with few resources for staffing or research, the NACA would not gain its own facilities to conduct research until the Langley laboratory in Virginia was opened in 1920. Instead, the NACA committee formed to investigate potential solutions to mate­rials problems, such as a shortage of wood for war production of air­craft, and recommended that the Army and the Bureau of Standards study commercially available aluminum alloys and steels for their suit­ability as wing spars.[650]

Even by this time, Bakelite could be found inside cockpits for instru­ments and other surfaces, but it was not yet considered as a primary or secondary load-bearing structure, even for the relatively lightweight aircraft of this age. Perhaps the first evidence that Bakelite could serve as an instrumental component in aircraft came in 1924. With fund­ing provided by the NACA, two early aircraft materials scientists— Frank W. Caldwell and N. S. Clay—ran tests on propellers made of Micarta material. The material was a generational improvement upon the phe­nolic resin introduced by Baekeland. Micarta is a laminated fabric—in this case cotton duck, or canvas—impregnated with the Bakelite resin.[651] Caldwell was the Government’s chief propeller engineer through 1928 and later served as chief engineer for Hamilton Standard. Caldwell is cred­ited with the invention of variable pitch propellers during the interwar period, which would eventually enable the Boeing Model 247 to achieve altitudes greater than 6,000 feet, thus clearing the Rocky Mountains and becoming a truly intercontinental aircraft. Micarta had already served

as a material for fixed-pitch blades in World War I engines, including the Liberty and the 300-horsepower Wright.[652] Fixed-pitch blades were optimized neither for takeoff or cruise. Caldwell wanted to allow the pilot to change the pitch of the blade as the airplane climbed, allow­ing the pitch to remain efficient in all phases of flight. Using the same technique, the pilot could also reverse the pitch of the blade after land­ing. The propeller blades now functioned as a brake, allowing the air­craft to operate on shorter runways. Finding the right material to use for the blades was foremost among the challenges for Caldwell and Clay. It had to be strong enough to survive the stronger aerodynamic forces as the blade changed its pitch. The extra strength had to be balanced with the weight of the material, and metal alloys had not yet advanced far enough in the early 1920s. However, Caldwell and Clay found that Micarta was suitable. In an NACA technical report, they concluded: "The reversible and adjustable propeller with micarta blades. . . is one of the most practical devices yet worked out for this purpose. It is quite strong in all details, weighs very little more than the fixed pitch propeller and operates so easily that the pitch may be adjusted with two fingers on the control level when the engine is running.” The authors had performed flight tests comparing the same aircraft and engine using both Micarta and wooden propeller blades. The former exceeded the top speed of the wooden propeller by 2 miles per hour (mph), while turning the engine at about 120 fewer revolutions per minute (rpm) and maintaining a simi­lar rate of climb. The Micarta propeller was not only faster, it was also 7 percent more fuel efficient.[653]

The propeller work on Micarta showed that even if full-up plastics remained too weak for load-bearing applications, laminating wood with plastic glues provided a suitable alternative for that era’s demands for structural strength in aircraft designs. While American developers continued to make advances, critical research also was occurring over­seas. By the late 1920s, Otto Kraemer—a research scientist at Deutsche Versuchsanstalt fur Luftfahrt (DVL), the NACA’s equivalent body in Germany—had started combining phenolic resins with paper or cloth. When this fiber-reinforced resin failed to yield a material with a struc­tural stiffness superior to wood, Kraemer in 1933 started to investigate

birch veneers instead as a filler. Thin sheets of birch veneer impreg­nated with the phenolic resin were laminated into a stack 1 centimeter thick. The material proved stronger than wood and offered the capabil­ity of being molded into complex shapes, finally making plastic a viable option for aircraft production.[654] Kraemer also got the aviation industry’s attention by testing the durability of fiber-reinforced plastic resins. He exposed 1 – millimeter-thick sheets of the material to outdoor exposure for 15 months. His results showed that although the material frayed at the edges, its strength had eroded by only 14 percent. In comparison to other contemporary materials, these results were observed as "practically no loss of strength.”[655] In the late 1930s, European designers also fabri­cated propellers using a wood veneer impregnated with a resin varnish.[656]

A critical date in aircraft structural history is March 31, 1931, the day a Fokker F-10A Trimotor crashed in Kansas, with Notre Dame foot­ball coach Knute Rockne among the eight passengers killed. Crash inves­tigators determined that the glues joining the wing strut to the F-10A’s fuselage had been seriously deteriorated by exposure to moisture. The cumulative weakening of the joint caused the wing to break off in flight. The crash triggered a surge of nationwide negative publicity about the weaknesses of wood materials used in aircraft structures. This caused the aviation industry and passengers to embrace the transition from wood to metal for airplane materials, even as progress in synthetic mate­rials, especially involving wood impregnated with phenolic resins, had started to develop in earnest.[657]

In his landmark text on the aviation industry’s transition from wood to metal, Eric Schatzberg sharply criticizes the ambivalence of the NACAs leadership toward nonmetal alternatives as shortsightedness. For exam­ple, "In the case of the NACA, this neglect involved more than passive ignorance,” Schatzberg argues, "but rather an active rejection of research on the new adhesives.” However, with the military, airlines, and the trav­eling public all "voting with their feet,” or, more precisely, their bank accounts, in favor of the metal option, it is not difficult to understand the NACA leadership’s reluctance to invest scarce resources to develop
wood-based synthetic aircraft materials. The specimens developed during this period clearly lacked the popular support devoted to metal. Indeed, given the dominant role that metal structures were to play in aircraft and aerospace technology for most of the next 70 years, the priority placed on metal by the NACAs experts could be viewed as strategically prescient.

That is not to say that synthetic materials, such as plastic resins, were ignored by the aerospace industry in the 1930s. The technology of phenol- and formaldehyde-based resins had already grown beyond functioning as an adhesive with superior properties for resisting corro­sion. The next step was using these highly moisture-resistant mixtures to form plywood and other laminated wood parts.[658] Ultimately, the same resins could be used as an impregnant that could be reinforced by wood,[659] essentially a carbon-based material. These early researchers had discovered the building blocks for what would become the carbon – fiber-reinforced plastic material that dominates the composite structures market for aircraft. Of course, there were also plenty of early applica­tions, albeit with few commercial successes. A host of early attempts to bypass the era of metal aircraft, with its armies of riveters and con­cerns over corrosion and metal fatigue, would begin in the mid-1930s.

Clarence Chamberlin, who missed his chance by a few weeks to beat Charles Lindbergh across the Atlantic in 1927, flew an all-composite airplane. Called the Airmobile, it was designed by Harry Atwood, once a pupil of the Wright brothers, who flew from Boston to Washington, DC, in 1910, landing on the White House lawn.[660] Unfortunately, the full story of the Airmobile would expose Atwood as a charlatan and fraud. However, even if Atwood’s dubious financing schemes ultimately hurt his reputation, his design for the Airmobile was legitimate; for its day, it was a major achievement. With a 22-foot wingspan and a 16-foot- long cabin, the Airmobile weighed only 800 pounds. Its low weight was achieved by constructing the wings, fuselage, tail surfaces, and aile­rons with a new material called Duply, a thin veneer from a birch tree impregnated with a cellulose acetate.[661]

Writing a technical note for the NACA in 1937, G. M. Kline, work­ing for the Bureau of Standards, described the Airmobile’s construction: "The wings and fuselage were each molded in one piece of extremely thin films of wood and cellulose acetate.”[662] To raise money and attract public attention, however, Atwood oversold his ability to manufacture the air­craft cheaply and reliably. According to his farfetched publicity claims, 10 workers starting at 8 a. m. could build a new Airmobile from a sin­gle, 6-inch-diameter birch tree and have the airplane flying by dinner.

After a 12-minute first flight before 2,000 gawkers at the Nashua, NH, airport, Chamberlin complained that the aircraft was "nose heavy” but otherwise flew well. But any chance of pursuing full-scale manufacturing of the Airmobile would be short-lived. To develop the Airmobile, Atwood had accumulated more than 200 impatient creditors and a staggering debt greater than $100,000. The Airmobile’s manufac­turing process needed a long time to mature, and the Duply material was not nearly as easy to fabricate as advertised. The Airmobile idea was dropped as Atwood’s converted furniture factory fell into insolvency.[663]

Also in the late 1930s, two early aviation legends—Eugene Vidal and Virginius Clark—pursued separate paths to manufacture an air­craft made of a laminated wood. Despite the military’s focus on devel­oping and buying all-metal aircraft, Vidal secured a contract in 1938 to provide a wing assembly molded from a thermoplastic resin. Vidal also received a small contract to deliver a static test model for a basic trainer designated the BT-11. Schatzberg writes: "A significant innova­tion in the Vidal process was the molding of stiffeners and the skin in a single step.” Clark, meanwhile, partnered with Fairchild and Haskelite to build the F-46, the first airliner type made of all-synthetic materi­als. Haskelite reported that only nine men built the first half-shell of the fuselage within 2 hours. The F-46 first flew in 1937 and generated a great amount of interest. However, the estimated costs to develop the molds necessary to build Clark’s proposed production system (greater than $230,000) exceeded the amount private or military investors were willing to spend. Clark’s duramold technology was later acquired by Howard Hughes and put to use on the HK-1 flying boat (famously nick­named—inaccurately—the "Spruce Goose”).[664]

The February 16, 1939, issue of the U. K.-based Flight magazine offers a fascinating contemporary account of Clark’s progress:

Recent reports from America paint in glowing terms a new process said to have been invented by Col Virginius Clark (of Clark Y wing section fame) by which aero­plane fuselages and wings can, it is claimed, be built of plastic materials in two hours by nine men. . . . There is little doubt that Col Clark and his associates of the Bakelite Corporation and the Haskelite Manufacturing Corporation have evolved a method of production which is rapid and cheap. Exactly how rapid and how cheap time will show. In the meantime, it is well to remember that we are not standing still in this country. Dr. Norman de Bruyne has been doing excellent work on plastics at Duxford, and the Airscrew Company of Weybridge is doing some very interesting and promising experimen­tal and development work with reinforced wood.[665]

The NACA first moved to undertake research in plastics for aircraft in 1936, tasking Kline to conduct a review of the technical research already completed.[666] Kline conducted a survey of "reinforced phenol – formaldehyde resin” as a structural material for aircraft. The survey was made with the "cooperation and financial support” of the NACA. Kline also summarized the industry’s dilemma in an NACA technical note:

In the fabrication of aircraft today the labor costs are high relative to the costs of tools. If large sections could be molded in one piece, the labor costs would be reduced but the cost of the molds and presses would be very high. Such a change in type construction would be economically practicable excepting the mass produc­tion of aircraft of a standard design. Langley suggests, therefore, that progress in the utilization of plastics in aircraft construction will be made by the gradual intro­duction of these materials into an otherwise orthodox
structure, and that the early stages of this development will involve the molding of such small units as fins and rudders and the fabrication of the larger units from reinforced sheets and molded sections by conventional methods of jointing.[667]

Kline essentially was predicting the focus of a massive NASA research program that would not get started for nearly four more decades. The subsequent effort was conducted along the lines that Kline prescribed and will be discussed later in this essay. Kline also seemed to under­stand how far ahead the age of composite structure would be for the aviation industry, especially as aircraft would quickly grow larger and more capable than he probably imagined. "It is very difficult to outline specific problems on this subject,” Kline wrote, "because the explora­tion of the potential applications of reinforced plastics to aircraft con­struction is in its infancy, and is still uncharted.”[668]

In 1939, an NACA technical report noted that synthetic materials had already started making an impact in aircraft construction of that era. The technology was still unsuited for supporting the weight of the aircraft in flight or on the ground, but the relative lightness and durabil­ity of synthetics made them popular for a range of accessories. Inside a wood or metal cockpit, a pilot scanned instruments with dials and casings made of synthetics and looked out a synthetic windshield. Synthetics also were employed for cabin soundproofing, lights encasings, pulleys, and the streamlined housings around loop antennas. The 1939 NACA paper concludes: "It is realized, at present, that the use of synthetic resin mate­rials in the aircraft industry have been limited to miscellaneous accesso­ries. The future is promising, however, for with continued development, resin materials suitable for aircraft structures will be produced.”[669]

In the mid-1970s, coincident with the beginning of the fuel and litiga­tion crises that would nearly destroy GA, production of homebuilt and kit-built aircraft greatly accelerated, reflecting the maturity of light air­craft design technology, the widespread availability of quality engineer­ing and technical education, and the frustration of would-be aircraft owners with rising aircraft prices. Indeed, by the early 1990s, kit sales would outnumber sales of production GA aircraft by more than four to one.[869] Today, in a far-different post-GARA era, kit sales remain strong. As well, new manufacturers appeared, some wedded to particular ideas or concepts, but many also showing a broader (and thus generally more successful) approach to light aircraft design.

Exemplifying this resurgence of individual creativity and insight was Burt Rutan of Mojave, CA. An accomplished engineer and flight – tester, Rutan designed a small two-seat canard light aircraft, the VariEze, powered by a 100-hp Continental engine. Futuristic in look, the VariEze embodied very advanced thinking, including a GA(W)-1 wing section and Whitcomb winglets. The implications of applying the configuration to other civil and military aircraft of far greater performance were obvious, and NASA studied his work both in the tunnel and via flight tests of the VariEze itself.[870] Rutan’s influence upon advanced general aviation air­craft thinking was immediate. Beech adopted a canard configuration for a proposed King Air replacement, the Starship, and Rutan built a subscale demonstrator of the aircraft.[871] Rutan subsequently expanded his range of work, becoming a noted designer of remarkable flying machines capable of performance—such as flying nonstop around the world or rocketing into the upper atmosphere—many would have held impossible to attain.

NASA followed Rutan’s work with interest, for the canard config­uration was one that had great applicability across the range of air­craft design, from light aircraft to supersonic military and civil designs. Langley tunnel tests in 1984 confirmed that with a forward center of gravity location, the canard configuration was extremely stall-resistant. Conversely, at an aft center of gravity location, and with high power, the canard had reduced longitudinal stability and a tendency to enter a high – angle-attack, deep-stall trim condition.[872] NASA researchers undertook a second series of tests, comparing the canard with other wing planforms including closely coupled dual wings, swept forward-swept rearward wings, joined wings, and conventional wing-tail configurations, evaluat­ing their application to a hypothetical 350-mph, 1,500-mile-range 6- or 12-passenger aircraft operating at 30,000 to 40,000 feet. In these tests, the dual wing configuration prevailed, due to greater structural weight efficiencies than other approaches.[873]

Seeking optimal structural efficiency has always been an important aspect of aircraft design, and the balance between configuration choice and structural design is a fine one. The advent of composite structures enabled a revolution in structural and aerodynamic design fully as sig­nificant as that at the time of the transformation of the airplane from wood to metal. As designers then had initially simply replaced wooden components with metal ones, so, too, in the earliest stage of the com­posite revolution, designers had initially simply replaced metal com­ponents with composite ones. In many of their own GA proposals and studies, NASA researchers repeatedly stressed the importance of getting away from such a "metal replacement” approach and, instead, adopt­ing composite structures for their own inherent merit.[874]

The blend of research strains coming from NASA’s diverse work in structures, propulsion, controls, and aerodynamics, joined to the cre­ative impact of outside sources in industry and academia—not least of which were student study projects, many reflecting an insight and expertise belying the relative inexperience of their creators—informed NASA’s next steps beyond AGATE. Student design competitions offered a valuable means of both "growing” a knowledgeable future aerospace workforce and seeking fresh approaches and insight. Beginning in 1994, NASA joined with the FAA and the Air Force Research Laboratory to sponsor a yearly National General Aviation Design Competition estab­lishing design baselines for single-pilot, 2- to 6-passenger vehicles, tur­bine or piston-powered, capable of 150 to 400 knots airspeed, and with a range of 800 to 1,000 miles. The Virginia Space Grant Consortium at Old Dominion University Peninsula Center, near Langley Research Center, coordinated the competition. Competing teams had to address "design challenges” in such technical areas as integrated cockpit sys­tems; propulsion, noise, and emissions; integrated design and manu­facturing; aerodynamics; operating infrastructure; and unconventional designs (such as roadable aircraft).[875] In cascading fashion, other oppor­tunities existed for teams to take their designs to ever-more-advanced levels, even, ultimately, to building and test-flying them. Through these competitions, study teams explored integrating such diverse technical elements as advanced fiber optic flight control systems, laminar flow design, swept-forward wings, HITS cockpit technology, coupled with advanced Heads-up Displays (HUD) and sidestick flight control, and advanced composite materials to achieve increased efficiencies in per­formance and economic advantage over existing designs.[876]

Succeeding AGATE was SATS—the NASA Small Aircraft Transportation System Project. SATS (another Holmes initiative) sought to take the integrated products of this diverse research and form from it a distributed public airport network, with small aircraft flying on demand as users saw fit, thereby taking advantage of the ramp space capacity at over 5,000 public airports located around the country.[877] SATS would benefit as well by a Glenn Research Center initiative, the GAP (General Aviation Propulsion) program, seeking new propulsive effi­ciencies beyond those already obtained by previous NASA research.[878] In 2005, SATS concluded with a 3-day "Transformation of Air Travel” held at Danville Airport, VA, showcasing new aviation technologies with six air­craft equipped with advanced cockpit displays enabling them to operate from airports lacking radar or air traffic control services. Complementing SATS and GAP was PAV—a Langley initiative for Personal Air Vehicles, a reincarnation of an old dream of flight dating to the small ultralight aircraft and airships found at the dawn of flight, such as Alberto Santos – Dumont’s little one-person dirigibles and his Demoiselle light aircraft. Like many such studies through the years, PAV studies in the 2002-2005 period generated many innovative and imaginative concepts, but the

Agency did not support such studies afterwards, turning instead towards good stewardship and environmental responsibility, seeking to reduce emissions, noise, and improve economic efficiencies by reducing air­port delays and fuel consumption. These are not innocuous challenges: in 2005, airspace system capacity limitations generated fully $5.9 bil­lion in economic impact through airline delays, and the next year, fuel consumption constituted a full 26 percent of airline operating costs.[879]

The history of the NACA-NASA support of General Aviation is one of mutual endeavor and benefit. Examining that history reveals a surpris­ing interdependency between the technologies of air transport, military, and general aviation. Developments such as the supercritical wing, elec­tronic flight controls, turbofan propulsion, composite structures, syn­thetic vision systems, and heads-up displays that were first exploited for one have migrated and diffused more broadly across the entire aeronau­tical field. Once again, the lesson is clear: the many streams of NASA research form a rich and broad confluence that nourishes and invigorates the entire American aeronautical enterprise, ever renewing our nature as an aerospace nation.