THE SECOND INDUSTRY CONFERENCE (1958)

As North American was completing assembly of the first X-15, the Research Airplane Committee held the second X-15 industry conference at the IAS Building in Los Angeles on 28-29 July 1958. Forty-three authors (15 from North American, 14 from Langley, 6 from the High Speed Flight Station, 3 from the WADC, 2 from Ames, and 1 each from the AFFTC, Reaction Motors, and the Naval Aviation Medical Acceleration Laboratory at NADC Johnsville) presented 28 papers. There were 443 registered participants representing all of the military services and most of the major

(and many minor) aerospace contractors. Interestingly, there was no university participation this time. Notable attendees included Dr. David Myron Clark from the David Clark Company, Dr. Charles Stark Draper, and all of the original X-15 pilots. It is interesting to note how at least one of the participants registered; for instance, Harrison Storms listed his affiliation as "NACA Committee on Aircraft, Missile, and Spacecraft Aerodynamics" instead of "North American Aviation."[219]

The 1958 conference began, appropriately, where the 1956 conference had ended. Lawrence P. Greene from North American, who had presented the closing paper at the first conference, gave the technical introduction. One of his first statements summed up the progress: "It can be positively said that through the efforts of all concerned, the development of the X-15 research system has been successfully completed."1220

The airplane North American was building was the "Configuration 3" that had been inspected by the Air Force in mockup form. Configuration 1 was the initial North American proposal, while Configuration 2 was the one presented during the 1956 industry conference. Greene highlighted the important changes:[221

1. The side fairings were shortened ahead of the wing to improve longitudinal stability.

2. The horizontal stabilizer was moved 5.4 inches rearward, although the original fuselage location of the hinge line was retained. This modification moved the hinge line from the 37% to the 25% mean aerodynamic chord of the exposed horizontal stabilizer. Although flutter requirements dictated the change, this, combined with a 3.6-inch forward wing movement and the side-fairing changes, provided adequate longitudinal stability near zero lift at the maximum Mach number.

3. The vertical stabilizer area was increased to provide adequate directional stability with the speed brakes retracted and a 10-degree full wedge section was found to be optimum. The planform was then made nearly symmetrical (dorsal and ventral) for dynamic-stability considerations in the exit phase of the mission, since thrust asymmetry considerations in the zero to moderate angle-of-attack range necessitated a reduction in roll due to yaw.

4. Asymmetrical thrust effects also indicated the need for a low value of roll-due-to-yaw control in the low angle-of-attack region. For this purpose, an all-movable directional control was incorporated on the outer span of both the upper and lower vertical stabilizers. Incorporating the control in the lower vertical stabilizer was equally necessary for providing directional control at high angles of attack at high speed because of the ineffectiveness of the upper surface at these conditions. This, in turn, dictated some added complexity in the damper system.

5. In order to avoid compound flutter problems, the speed brakes were reduced in size and relocated on the inboard or fixed parts of the vertical stabilizers.

Although initially it had been decided not to increase the load factor of the airplane from 5 g to 7.33 g, sometime in the intervening two years the change had been made, much to the relief of the pilots and researchers at the HSFS. In mid-1957 the NACA had asked the Air Force to double the amount of research instrumentation carried by the X-15. This became a major design driver.

In order to keep the airplane weight (and hence performance) from being too seriously degraded, numerous details were redesigned to save weight. The two areas that received the most rework were the propellant system plumbing and the nose gear. This is when Charlie Feltz came up with the idea of keeping the nose-gear strut compressed when it was stored, allowing a much more compact and lightweight installation.-12221

Changes in configuration also brought changes in weight. To support the additional loads, North

American strengthened the structure of the wing, fuselage, and empennage. This resulted in a revised specification that showed an airplane that was 765 pounds heavier than originally expected (184 pounds in empty weight and 581 pounds in useful load; this included the pilot, propellants, and gasses, but not research instrumentation). However, by the time North American began building the airplanes, even this had changed. The empty weight had increased by only 61 pounds (instead of 184), but the useful load had decreased by 196 pounds. The research instrumentation, on the other hand, had increased by 522 pounds. The empty weight increases were the result of the following changes:[223]

1. The wing was changed from 7 to 15 intermediate spars, the skin gage was reduced, and the heat-sink material was changed from titanium carbide with a nickel binder to Inconel X, resulting in a net decrease of 131 pounds.

2. A 17-pound net increase in the empennage resulted from a 58-pound increase to meet thermal requirements and a reduction of 41 pounds for changing the leading-edge heat­sink material from titanium carbide with a nickel binder to Inconel X.

3. Chem-milling pockets in the skin and reducing the skin gage by adding Z-stiffeners and substituting aluminum for Inconel X in a portion of the intermediate fuel – and oxidizer-tank bulkheads saved 102 pounds in the body ground, but a 15-pound increase was caused by the additional structure to accommodate the engine weight increase. The net fuselage change was a decrease of 87 pounds.

4. The landing gear group was reduced by 73 pounds by eliminating the shimmy damper on the nose wheel and reducing the gage of the main-landing gear skids.

5. A reduction of 12 pounds in surface controls was realized by changing from four direct – acting speed-brake actuators to two actuators with a linkage arrangement.

6. The engine dry weight increased 296 pounds.

7. The addition of an engine purge system increased the propulsion group by 67 pounds. However, this was partially offset by a reduction in the internal liquid oxygen system plumbing of 29 pounds, giving a net propulsion system increase of 38 pounds.

8. The 4-pound increase in the auxiliary powerplant group was due to an increase in the weight of the APUs.

9. Changes in the fixed equipment resulted in a net increase of 9 pounds, consisting of a 76- pound increase in the ejection seat, an 11-pound increase in instruments, a 34-pound decrease in the nitrogen system, and a 44-pound decrease in the air-conditioning system.

ANHYIMJUS AWMON A

ІДКК (FULL:

QIC OXYGEN

.■ TANK (OXCIZER)

lIQJO NTKOGFN

і AUXILIARY

А ТІ I ULli

HVCROGEW

PEHQXIDF

EJECTION

SLAI

This is the configuration of the X-15 presented at the 1958 Industry Conference, and largely
represents the airplane as built. The major components are annotated. The large area immediately behind the cockpit was the primary location for the research instrumentation recorders and other equipment that required a controlled environment. (NASA)

Changes made in the useful load included the following:

1. The turbopump monopropellant was reduced by 196 pounds.

2. Trapped propellants in the engine increased 70 pounds.

3. The helium required to pressurize the propellant tanks increased 13 pounds.

4. The nitrogen required to pressurize the cockpit was reduced by 82 pounds.

All of this resulted in an airplane that had an empty weight of 10,635 pounds, versus an original specification weight of 10,390 pounds and a revised specification of 10,574 pounds. The total gross weight was 31,662 pounds, versus the original target of 30,510 pounds and a revised specification of 31,275 pounds. For high-speed missions, NASA could remove 370 pounds of altitude-related instrumentation, resulting in a gross weight of 31,292 pounds—only 17 pounds over the revised specification.-12244

Perhaps the most notable (though hardly unexpected) item to come out of the second industry conference was that the XLR99 was significantly behind schedule, and initial flight-testing of the airplane would be undertaken using two interim XLR11-RM-5 engines.-12254