Editing Bell X-1 (section)

===Research studies===
[[File:XLR-11.jpg|thumb|upright|right|XLR-11 rocket engine]]
The XS-1 was first discussed in December 1944. Early specifications for the aircraft were for a piloted supersonic vehicle that could fly at {{convert|800|mph}} at {{convert|35000|feet}} for two to five minutes.<ref name="ley194811">{{Cite magazine |last=Ley |first=Willy |date=November 1948 |title=The 'Brickwall' in the Sky |url=https://archive.org/stream/Astounding_v42n03_1948-11_cape1736#page/n77/mode/2up |magazine=Astounding Science Fiction |pages=78–99}}</ref> On 16 March 1945, the [[U.S. Army Air Forces]] Flight Test Division and the [[National Advisory Committee for Aeronautics]] (NACA) contracted with the Bell Aircraft Company to build three XS-1 (for "Experimental, Supersonic", later X-1) aircraft to obtain flight data on conditions in the transonic speed range.<ref>Miller 2001, p. 15.</ref>

Bell built a rocket plane after considering the turbojet alternative. Turbojets could not achieve the required performance at high altitude. An aircraft with both turbojet and rocket engines would be too large and complex.{{r|ley194811}} The X-1 was, in principle, a "bullet with wings", its shape closely resembling a [[.50 BMG|Browning .50-caliber]] (12.7&nbsp;mm) [[machine gun]] bullet, known to be stable in supersonic flight.<ref>Yeager et al., 1997, p. 14.</ref> The shape was followed to the extent of seating its pilot behind a sloped, framed window inside a confined cockpit in the nose, with no ejection seat.

For the design of the XS-1 the many unknowns relating to transonic and supersonic flight meant seeking every available source of information from governmental agencies, powerplant manufacturers and research institutions. Foreign information became available in early 1946, shortly after the first glide test of the XS-1 in Jan 1946, when the British Ministry of Supply cancelled the Miles M.52 and ordered all research reports and other information be sent to Bell Aircraft.<ref>{{cite book | url=https://archive.org/details/projectcancelled0000wood/page/30/mode/2up | isbn=978-0-356-08109-0 | title=Project cancelled : A searching criticism of the abandonment of Britain's advanced aircraft projects | date=1975 | last1=Wood | first1=Derek | publisher=Macdonald and Jane's }}</ref><ref>{{cite book | url=https://archive.org/details/planespeakingper0000guns/page/168/mode/2up | isbn=978-1-85260-166-9 | title=Plane speaking : A personal viewof aviation history | date=1991 | last1=Gunston | first1=Bill | publisher=Patrick Stephens }}</ref>

Bell Aircraft aerodynamicists working with NACA laboratories predicted significant longitudinal trim changes during transonic flight. [[John Stack (engineer)|John Stack]] and [[Robert Gilruth]] at NACA recommended that Bell mount the elevator on an adjustable horizontal stabilizer.<ref>https://www.amazon.com/Meeting-Challenge-Supersonic-Flight-James/dp/B0006QV0BQ p.9</ref> Bell incorporated the stabilizer with rapid adjustment in pitch to accommodate large changes of trim.<ref>{{cite web | url=https://archive.org/details/sim_aerospace-engineering-1942_1947-08_6_8/page/22/mode/2up | title=Aeronautical Engineering Review 1947-08: Vol 6 Iss 8 | date=August 1947 | publisher=American Institute of Aeronautics }}</ref> A contractor test flight by [[Tex Johnston]] showed an unacceptable lost motion between the pilot's input to the horizontal stabilizer and the stabilizer actuator which was corrected before the XS-1 was handed over for the high speed research program.<ref>{{cite web | url=https://archive.org/details/texjohnston00john/page/112/mode/2up | title=Tex Johnston: Jet-Age Test Pilot | date=2014 | publisher=Smithsonian }}</ref> The whole tailplane could be moved or just the elevator at fixed stabilizer settings.<ref>High Speed Test Flying, Yeager, The Aeronautical Journal, December 1956, p.788</ref> It was placed as high as possible above the wing wake with a thinner section than for the wing to separate the high drag rise from the wing from compressibility effects on the tail. Initially, as increases in speed were made in small steps towards possibly unknown control difficulties the horizontal stabilizer was left at its pre-launch angle set on the ground as there was concern that adjusting it at high speed would cause severe control problems. Nevertheless, in October 1947, when test pilot Yeager ran out of elevator authority (no pitch control) at Mach 0.94 it took the test team by surprise until they realized that extra control was available by moving the horizontal stabilizer. The tailplane trim setting had to be accurately set on the ground to ensure a controlled drop at the beginning of a flight. [[Scott Crossfield]] relates an inadvertent one-degree error flipping the X-1 on its back after being dropped from the mother plane.<ref>https://archive.org/details/alwaysanotherdaw0000cros/page/n7/mode/2up  p.128</ref> The tailplane configuration was carried over to the X-1A series. All subsequent supersonic aircraft would either have an all-moving tailplane or be "tailless" [[delta wing]]ed types.<ref>Pisano, ''et al.''. 2006, p. 52.</ref>

[[Swept wing]]s were not used because too little was known about them. As the design might lead to a fighter, the XS-1 was intended to take off from the ground, but the end of the war made the [[B-29 Superfortress]] available to carry it into the air. {{r|ley194811}}

The rocket engine was a four-chamber design built by [[Reaction Motors Inc]]., one of the first companies to build liquid-propellant rocket engines in the U.S. After considering [[hydrogen peroxide]] [[monopropellant]], [[aniline]]/[[nitric acid]] [[bipropellant]], and [[nitromethane]] monopropellant as fuels, the rocket burned ethyl alcohol diluted with water with a [[liquid oxygen]] [[oxidizer]]. Its four chambers could be individually turned on and off, so thrust could be changed in {{convert|1500|lbf|abbr=on}} increments. The fuel and oxygen tanks for the first two X-1 engines were pressurized with [[nitrogen]], reducing flight time by about {{frac|1|1|2}} minutes and increasing landing weight by {{convert|2000|lb}}, but the rest used gas-driven [[turbopump]]s, increasing the chamber pressure and thrust while making the engine lighter.<ref>Miller, p. 23</ref>{{r|ley194811}}