Hiller X-18

File:Hiller X-18 front.jpg

Design work started in 1955 by Stanley Hiller Jr and Hiller Aircraft Corporation received a manufacturing contract and funding from the United States Air Force to build the only X-18 built, serialized 57-3078.{{cite web|url=http://www.joebaugher.com/usaf_serials/1957.html|title=1957 USAF Serial Numbers|work=joebaugher.com|access-date=19 February 2016}}

To speed up construction and conserve money, the plane was constructed from scavenged parts including a Chase YC-122C Avitruc fuselage, 49-2883, and turboprops from the Lockheed XFV-1 and Convair XFY-1 Pogo experimental fighter programs. The tri-bladed contra-rotating propellers were a giant 16 ft (4.8 m) across. The Westinghouse turbojet engine had its exhaust diverted upwards and downwards at the tail to give the plane pitch control at low speeds. Hiller nicknamed their X-18 the Propelloplane for public relations purposes.[https://books.google.com/books?id=vtsDAAAAMBAJ&dq=true&pg=PA107 "Hiller's Tiltwing Transport if Largest VTOL Transport."]Popular Mechanics, March 1959, p. 107.

File:Hiller X-18 ground.jpgs]]

Preliminary testing occurred at Moffett Field Naval Air Station, CA. The first flight (hop) was on 11/20/1959 followed by the first real flight on 11/24/1959 with Hiller test pilots George Bright and Bruce Jones.{{cite web|title=The X-Planes|url=http://www.ais.org/~schnars/aero/x-planes.htm|access-date=5 September 2016}} Further test flights were held at Edwards AFB, ultimately recording 20 flights. A number of problems plagued the X-18 including being susceptible to wind gusts when the wing rotated, acting like a sail. In addition the turboprop engines were not cross-linked, so the failure of one engine meant the airplane would crash. Thrust control was through throttle changes, which were too slow for acceptable height and roll control.

On the 20th and final flight in July 1961, the X-18 had a propeller pitch control problem when attempting to convert to a hover at {{cvt|10,000|ft|m}} and went into a spin. The crew regained control and landed, but the X-18 never flew again. However ground testing of the tiltwing concepts continued. Eventually a VTOL Test Stand was built on which the X-18's vertical takeoff and landing and hover control was to be tested. One engine run was successfully conducted to the full {{convert|15|ft|m|adj=on}} wheel height on the VTOL Test Stand. The program was canceled on January 18, 1964, before further VTOL Test Stand testing could be conducted, and the X-18 was cut up for scrap.

The program proved several things that contributed to further tilt-wing VSTOL technology programs:

1. cross-shafting between the engines was necessary in order to avoid loss of control in the event of an engine failure.
2. direct propeller pitch control was necessary for precise height and lateral control during VTOL and hover.

This knowledge was employed in the successful development and flight tests of the Tri-Service XC-142A tilt-wing VSTOL transport.

File:Hiller X-18 3-view line drawing.png

{{Aircraft specs

|ref=Jane's All the World's Aircraft 1961-62,{{cite book |title=Jane's All the World's Aircraft 1961-62 |editor1-last=Taylor |editor1-first=John W.R. |year=1961 |publisher=Sampson Low, Marston & Co |location=London |page=265}} The X-planes : X-1 to X-29{{cite book |last1=Miller |first1=Jay |title=The X-planes : X-1 to X-29 |date=1983 |publisher=Speciality |location=Marine on St. Croix |isbn=0933424353 |pages=124–127}}

|prime units?=imp

|crew=2-3

|length ft=63

|span ft=48

|height ft=24

|wing area sqft=528

|aspect ratio=4.36

|airfoil=NACA 23015{{cite web |last1=Lednicer |first1=David |title=The Incomplete Guide to Airfoil Usage |url=https://m-selig.ae.illinois.edu/ads/aircraft.html |website=m-selig.ae.illinois.edu |access-date=16 April 2019}}

|empty weight lb=27052

|empty weight note=

|max takeoff weight lb=33000

|fuel capacity={{cvt|1000|USgal|impgal l|0}}

|eng1 number=2

|eng1 name=Allison T40-A-14

|eng1 type=coupled turboprop engines

|eng1 hp=5850

|eng1 note=equivalent

|prop blade number=6

|prop name=Curtiss-Wright

|prop dia ft=16

|prop dia in=1

|prop dia note=contra-rotating propellers

|eng2 number=1

|eng2 name=Westinghouse J34

|eng2 type=turbojet

|eng2 lbf=3400

|eng2 note=for jet reaction pitch control

|max speed mph=253

|max speed note=

• Maximum wing-tilt speed: {{cvt|178|mph|kn km/h|0}}

|range mi=224

|ceiling ft=35300

}}

{{aircontent

|related=

• Chase YC-122 Avitruc

|similar aircraft=

• Canadair CL-84 Dynavert
• Kaman K-16B
• LTV XC-142
• Vertol VZ-2

|lists=

• List of military aircraft of the United States
• List of VTOL aircraft

|see also=

• Tiltrotor

}}

{{reflist}}

{{Commons category}}

• [http://www.tiltrotormech.com/aircraftpages/hiller_x_18.htm Hiller X-18]
• [https://web.archive.org/web/20050116120216/http://www.studenten.net/customasp/axl/plane.asp?cat_id=12&ple_id=502&page=0 X-18 Images]
• [http://www.things-with-wings.com/VTOL/Hiller.htm X-18 Images and History]

{{Hiller aircraft}}

{{X-planes}}

{{USAF system codes}}

Category:Edwards Air Force Base

X-18, Hiller

Category:Tiltwing aircraft

Category:Aircraft with contra-rotating propellers

X-18

Category:Aircraft first flown in 1959

Category:Twin-engined four-prop tractor aircraft