Douglas X-3 Stiletto

https://en.wikipedia.org/wiki/Douglas_X-3_Stiletto

The Douglas X-3 Stiletto was a 1950s United States experimental jet aircraft
with a slender fuselage and a long tapered nose, manufactured by the Douglas
Aircraft Company. Its primary mission was to investigate the design features of
an aircraft suitable for sustained supersonic speeds, which included the first
use of titanium in major airframe components. Douglas designed the X-3 with the
goal of a maximum speed of approximately 2,000 m.p.h, but it was, however,
seriously underpowered for this purpose and could not even exceed Mach 1 in
level flight. Although the research aircraft was a disappointment, Lockheed
designers used data from the X-3 tests for the Lockheed F-104 Starfighter which
used a similar trapezoidal wing design in a successful Mach 2 fighter.

It was originally intended for advanced Mach 2 turbojet propulsion testing, but
it fell largely into the category of configuration explorers, as its performance
(due to inadequate engines) never met its original performance goals. The goal
of the aircraft was ambitious—it was to take off from the ground under its own
power, climb to high altitude, maintain a sustained cruise speed of Mach 2, then
land under its own power. The aircraft was also to test the feasibility of
low-aspect-ratio wings, and the large-scale use of titanium in aircraft
structures.

The X-3 featured an unusual slender, streamlined shape having a very long,
gently-tapered nose and small trapezoidal wings. The aim was to create the
thinnest and most slender shape possible in order to achieve low drag at
supersonic speeds. The extended nose was to allow for the provision of test
equipment while the semi-buried cockpit and windscreen were designed to
alleviate the effects of "thermal thicket" conditions. The low aspect ratio,
unswept wings were designed for high speed and later the Lockheed design team
used data from the X-3 tests for the similar F-104 Starfighter wing design. Due
to both engine and airframe problems, the partially completed second aircraft
was cancelled, and its components were used for spare parts.

Two aircraft were ordered, but only one was built. It made 51 flights.

Role
Experimental

Manufacturer
Douglas

Designer
Schuyler Kleinhans, Baily Oswald and Francis Clauser

First flight
15 October 1952

Retired
23 May 1956

Status
Preserved at National Museum of the United States Air Force

Primary users
United States Air Force
NACA

Number built
1

The first X-3 "hop" was made on 15 October 1952, by Douglas test pilot William
Bridgeman. During a high-speed taxi test, Bridgeman lifted the X-3 off the
ground and flew it about 1 mi (1.6 km) before settling back onto the lakebed.
The official first flight was made by Bridgeman on 20 October, and lasted about
20 minutes. He made a total of 26 flights (counting the hop) by the end of the
Douglas tests in December 1953. These showed that the X-3 was severely
underpowered and difficult to control. Its takeoff speed was an unusually high
260 kn (482 km/h). More seriously, the X-3 did not approach its planned top
speed. Its first supersonic flight required that the airplane make a 15° dive to
reach Mach 1.1. The X-3's fastest flight, made on 28 July 1953, reached Mach
1.208 in a 30° dive. A plan to re-engine the X-3 with rocket motors was
considered but eventually dropped.

Tests would lead to the X-3's most significant flight, and the near-loss of the
aircraft. On 27 October 1954, Walker made an abrupt left roll at Mach 0.92 and
an altitude of 30,000 ft (9,144 m). The X-3 rolled as expected, but also pitched
up 20° and yawed 16°. The aircraft gyrated for five seconds before Walker was
able to get it back under control. He then set up for the next test point.
Walker put the X-3 into a dive, accelerating to Mach 1.154 at 32,356 ft (9,862
m), where he made an abrupt left roll. The aircraft pitched down and recorded an
acceleration of -6.7 g (-66 m/s²), then pitched upwards to +7 g (69 m/s²). At
the same time, the X-3 side-slipped, resulting in a loading of 2 g (20 m/s²).
Walker managed to bring the X-3 under control and successfully landed.

The post-flight examination showed that the fuselage had been subjected to its
maximum load limit. Had the acceleration been higher, the aircraft could have
broken up. Walker and the X-3 had experienced "roll inertia coupling," in which
a maneuver in one axis will cause an uncommanded maneuver in one or two others.
At the same time, several North American F-100 Super Sabres were involved in
similar incidents. A research program was started by NACA to understand the
problem and find solutions.

For the X-3, the roll coupling flight was the high point of its history. The
aircraft was grounded for nearly a year after the flight, and never again
explored its roll stability and control boundaries.

Specifications (X-3)

General characteristics
Crew: one
Length: 66 ft 9 in (20.3 m)
Wingspan: 22 ft 8 in (6.9 m)
Height: 12 ft 6 in (3.8 m)
Wing area: 166.5 sq ft (15.47 m²)
Empty weight: 16,120 lb (7,310 kg)
Max. takeoff weight: 23,840 lb (10,810 kg)
Powerplant: 2 × Westinghouse J34 afterburning turbojet, 3,370 lbf, 4,850 lbf
with afterburning (15.0 kN, 21.6 kN with afterburning) each

Performance
Maximum speed: 700 mph (1,125 km/h)
Range: 497 mi (800 km)
Service ceiling: 38,000 ft (11,600 m)
Thrust/weight: 0.40





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