View source for Bell XV-15

{{Short description|American experimental tiltrotor aircraft}}
{{Multiple issues|
{{More citations needed|date=April 2010}}
{{Lead too short|date=December 2023}}
}}
<!-- This article is a part of [[Wikipedia:WikiProject Aircraft]]. Please see [[Wikipedia:WikiProject Aircraft/page content]] for recommended layout, and guidelines. -->
{{Infobox aircraft
|name= XV-15
|image= File:Bell-NASA XV-15 (cropped).jpg
|caption= XV-15 in a hover
|type=Experimental VTOL aircraft
|national_origin= United States
|manufacturer=[[Bell Helicopter Textron]]
|designer=
|first_flight= 3 May 1977
|introduction=
|retired= 2003
|status= Prototype
|primary_user= [[NASA]]
|more_users=
|produced=
|number_built= 2
|unit cost=
|developed_from=
|variants=
|developed_into= [[V-22 Osprey]]<br>[[AgustaWestland AW609]]
}}
The '''Bell XV-15''' is an American [[tiltrotor]] [[VTOL]] aircraft. It was the second successful experimental tiltrotor aircraft and the first to demonstrate the concept's high speed performance relative to conventional helicopters.
==Development==
===Early VTOL rotor aircraft===
The idea of building [[VTOL]] aircraft using helicopter-like rotors at the wingtips originated in the 1930s. The first design resembling modern tiltrotors was patented by George Lehberger in May 1930, but he did not develop the concept further. In [[World War II]], a [[Germany|German]] [[prototype]] called the [[Focke-Achgelis Fa 269]] was developed starting in 1942, but it never flew.
Two prototypes that made it to flight were the one-seat [[Transcendental Model 1-G]] and two-seat Transcendental Model 2, both powered by single reciprocating engines. Development started on the Model 1-G in 1947, and it flew in 1954. The Model 1-G flew until a crash in [[Chesapeake Bay]] on 20 July 1955, destroying the prototype aircraft but not seriously injuring the pilot. The Transcendental 1-G was the first tiltrotor aircraft to have flown, and it accomplished most of a helicopter-to-aircraft transition in flight to within ten degrees of true horizontal aircraft flight. The Model 2 was developed and flew shortly afterward, but it did not fly much beyond hover tests. The [[United States Air Force]] withdrew funding in favor of the [[Bell XV-3]].
The Bell XV-3 was first flown in 1955. Like its predecessors, the XV-3 had the engines in the [[fuselage]] and driveshafts transferring power out to tilting wingtip rotor assemblies.
Other rotor concepts, such as [[slowed rotor]]s, stopped rotors, folding rotors, and variable-diameter rotors, were investigated for subsequent designs, but Bell engineers [[Kenneth Wernicke]] and Bob Lichten deemed them unfeasible compared to experience with the XV-3 project.<ref name=as-xv3>Miller, Jay. [http://www.airspacemag.com/history-of-flight/origin-species.html "Origin of the Species"]. ''[[Air & Space/Smithsonian]]'', July 2004. Accessed: 17 March 2012.</ref>
===Technological advances===
[[File:XV-15 takeoff.jpg|thumb|left|XV-15 taking off at NASA Dryden]]
One of the major problems with the early [[tiltrotor]] aircraft designs was that the driveshafts carrying power from the fuselage out to the wingtip rotors, along with the gearbox and tilting mechanisms at the wingtips, had substantial loads placed upon them and were heavy. They were transferring large amounts of power and torque long distances for an aircraft power transmission system.
The XV-15 experimental aircraft introduced a major design concept advance: instead of engines in the fuselage, the XV-15 moved the engines out to the rotating wingtip pods, directly coupled to the rotors. The normal path for power was directly from the engine into a speed-reduction gearbox and into the rotor/propeller without any long shafts involved. There was still a driveshaft along the wings for emergency use to transfer power to the opposite rotor in case of engine failure, but that shaft did not normally carry any power loads, allowing it to be lighter.
The tilting engine concept introduced complexities in the design of the engines and engine pods to be able to shift from operating horizontally to operating vertically. Those problems were addressed fairly early in the XV-15 program.
In the late 1960s and early 1970s, [[NASA]] and other researchers worked extensively on theoretical and wind tunnel tests of various rotor pods. Two companies were involved in the research and proposing designs: Bell Helicopter and [[Boeing Vertol]]. The focus was on tilt-rotor pods, integration of the tilting rotors with the wings and fuselage of the aircraft, and studying the airflow as the rotors tilted. Tilt rotors with fixed rotors and with folding rotors were investigated.
===XV-15 project===
What was to become the XV-15 program was launched in 1971 at [[Ames Research Center|NASA Ames Research Center]]. After preliminary work, a competition was held to award two $0.5 million research and development contracts for prototype designs. Companies that responded included [[Sikorsky Aircraft]], [[Grumman Aircraft]], Boeing Vertol, and Bell Helicopter.
R&D contracts were issued to Bell Helicopter and Boeing Vertol on 20 October 1972. The two companies' design proposals were delivered on 22 January 1973.
====Competing designs====
[[File:XV-15 N703NA USCG.jpg|thumb|A XV-15 in [[United States Coast Guard|USCG]] livery landing on the lawn of the Pentagon, September 1999]]
[[File:Xv-15 inflight.jpg|thumb|right|XV-15 in forward flight]]
Boeing Vertol proposed its Model 222 (not to be confused with the later [[Bell 222]] conventional helicopter), in which the engines were in fixed pods at the end of each wing, and a small, rotating pod with the rotor was slightly closer to the fuselage on the wing. This design simplified the engine design by keeping it horizontal at all times without having very long driveshafts to the tilting rotors.
In the Bell design, Bell Model 301, the whole wingtip pod rotated between horizontal and vertical, with the engine and rotor assembly fixed together within the pod. This simplified the power transmission, but it had more complicated requirements for the engine design and was probably slightly heavier than the Boeing proposal.
After a review of both proposals, NASA selected the Bell 301 for further development, and a contract for further R&D was issued on 31 July 1973. Extensive engineering and testing took the next four years to complete the development of the aircraft. The first of two Bell XV-15s, tail number '''N702NA''', first flew on 3 May 1977. After minimal flight tests at the Bell test facility, the aircraft was moved to Ames Research Center in Sunnyvale, California, where it was then mounted in the large Ames wind tunnel and tested extensively in various simulated flight environments.
For the [[United States Department of Defense|U.S. Department of Defense]] Joint-service Vertical take-off/landing Experimental (JVX) aircraft program, Bell Helicopter and Boeing Vertol teamed to submit a bid for an enlarged version of the XV-15 in 1983. The Bell Boeing team received a preliminary design contract that year, which led to the [[Bell Boeing V-22 Osprey]].<ref name="Norton_p22-33">Norton 2004, pp. 22–33.</ref>
==Flight testing==
Following wind tunnel and flight testing by Bell, the aircraft was then moved to [[Dryden Flight Research Center|NASA Dryden]], which is at Edwards Air Force Base in the California High Desert. The XV-15 flight testing continued expanding its flight envelope. It was able to successfully operate in both helicopter and normal aircraft flight modes and smoothly transition between the two. Once the aircraft was considered sufficiently tested, it was returned to Ames Research Center for further testing.
The XV-15s were deemed sufficiently tested, and one aircraft was taken to the 1981 [[Paris Air Show]] for demonstration flights. The ''[[The New York Times|New York Times]]'' praised its performance. "And if ever there was a lovable plane, it is the Bell XV-15... The machine, the hit of the show, performed a series of maneuvers including bowing to the crowd."<ref>{{Cite news|url=https://www.nytimes.com/1981/06/14/business/the-paris-airshow-wining-dining-and-dealing-for-military-might.html?pagewanted=2|title = The Paris Airshow: Wining, Dining and Dealing for Military Might|newspaper = The New York Times|date = 14 June 1981|last1 = Anderson|first1 = Susan Heller}}</ref> Over the next year, Senator Barry Goldwater, Navy Secretary John Lehman, and other officials were offered guest co-piloting flights to promote tiltrotor technology for military development.<ref>R. Whittle, ''The Dream Machine''. pp. 95–100.</ref>
The XV-15s were a standard demonstration in the annual summer airshow at the co-located [[Moffett Federal Airfield|Moffett Field Naval Air Station]] for several years during the 1980s. Both XV-15s were flown actively throughout the 1980s testing aerodynamics and tiltrotor applications for civilian and military aircraft types that might follow.
The [[Fédération Aéronautique Internationale]] classifies the XV-15 as a Rotodyne, and as such it holds the speed record of {{convert|456|kph}},<ref>"[http://www.fai.org/fai-record-file/?recordId=1553 FAI Record ID #1553] {{webarchive|url=https://web.archive.org/web/20131203032031/http://www.fai.org/fai-record-file/?recordId=1553 |date=2013-12-03 }}" ''[[Fédération Aéronautique Internationale]]'' Record date 6 April 1990. Accessed: 18 November 2013.</ref> and the 3&nbsp;km<ref>"[http://www.fai.org/fai-record-file/?recordId=1551 FAI Record ID #1551 - Rotodyne, Time to climb to a height of 3000 m] {{webarchive|url=https://web.archive.org/web/20131203035628/http://www.fai.org/fai-record-file/?recordId=1551 |date=2013-12-03 }}" ''[[Fédération Aéronautique Internationale]]'' Record date 15 March 1990. Accessed: 18 November 2013.</ref> and 6&nbsp;km time-to-climb.<ref>"[http://www.fai.org/fai-record-file/?recordId=1552 FAI Record ID #1552 - Rotodyne, Time to climb to a height of 6000 m] {{webarchive|url=https://web.archive.org/web/20131203044149/http://www.fai.org/fai-record-file/?recordId=1552 |date=2013-12-03 }}" ''[[Fédération Aéronautique Internationale]]'' Record date 15 March 1990. Accessed: 18 November 2013.</ref> <!--still holds several others: http://www.fai.org/fai-record-file/?recordId=1549 , http://www.fai.org/fai-record-file/?recordId=1550 , http://www.fai.org/fai-record-file/?recordId=1553 , http://www.fai.org/fai-record-file/?recordId=1554 . Use Rotodyne as search name -->
===Further testing===
[[File:XV-15 Paris 1980.jpg|thumb|XV-15 N702NA at the 1981 Paris Air Show]]
The first XV-15 prototype aircraft, N702NA, was transferred back to Bell for company development and demonstration use. On 20 August 1992, the aircraft crashed while being flown by a guest test pilot. He was lifting off for a final hover when a bolt slipped out of the collective control system on one pylon, causing that rotor to go to full pitch. The aircraft rolled upside down out of control and crashed inverted. While significantly damaged, the aircraft was largely structurally intact and both the pilot and copilot escaped with only minor injuries from the crash. The cockpit of the aircraft was salvaged and converted for use as a [[flight simulator]].
The second XV-15 prototype, N703NA, was used for tests supporting the military V-22 Osprey program and [[AgustaWestland AW609|Bell/Agusta BA609]] civilian transport (still under development in 2023 as the AgustaWestland AW609). It continued in primarily NASA test operations until September 2003. The shortest takeoff distance was achieved with the nacelles at 75 degrees angle.<ref name=NASA_SP-2000-4517>Maisel 2000, p. 70.</ref>
After N703NA was retired from test operations, it was donated to the Smithsonian [[National Air and Space Museum]] in Washington, D.C. The XV-15 was flown cross-country from Fort Worth, Texas to the museum before being decommissioned for display. It is now on display at the [[Steven F. Udvar-Hazy Center]] at [[Washington Dulles International Airport]].
==Specifications (XV-15)==
[[File:Bell XV-15 line drawing.png|right|350px]]
[[File:Bell XV-15 tilt rotor research aircraft.png|title=Cutaway drawing|right|350px]]
{{External media |topic=|width= |float=right
|image1=[[Cutaway drawing]] of [http://www.flightglobal.com/airspace/media/experimentalaircraftcutaways/images/8965/bell-xv-15-cutaway.jpg XV-15 ] }}
{{Aircraft specs
|ref=Jane's All the World's Aircraft 1988-89<ref name=JAWA88-89>{{cite book |title=Jane's All the World's Aircraft 1988-89 |editor1-last=Taylor |editor1-first=John W.R. |year=1988 |publisher=Jane's Information Group |location=London |isbn=0-7106-0867-5 |edition=79th |pages=347–348}}</ref>
|prime units?=kts
<!--
General characteristics
-->
|crew=2 on Rockwell-Columbus LW-3B [[ejection seat]]s
|capacity=up to 9 passengers if seats fitted / {{cvt|3400|lb|0}} max. payload STOL
|length ft=
|length in=505
|length note=
|span ft=
|span in=
|span note=
|width ft=57
|width in=2
|width note=overall with rotors turning
|height ft=12
|height in=8
|height note=over tail fins
::::{{cvt|15|ft|4|in|0}} with nacelles vertical
|wing area sqft=169
|wing area note=
|aspect ratio=
|airfoil='''Wings''' - [[NACA airfoil|NACA 64A015]]<ref name="Selig">{{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}}</ref>
|empty weight lb=9570
|empty weight note=
|gross weight lb=13000
|gross weight note=VTO
|max takeoff weight lb=15000
|max takeoff weight note=STO
|fuel capacity={{cvt|229|USgal|impgal l|0}} in four wing tanks
|more general=
<!--
Powerplant
-->
|eng1 number=2
|eng1 name=[[Textron Lycoming LTC1K-4K]]
|eng1 type=[[turboshaft]] / [[turboprop]] engines
|eng1 shp=1550
|eng1 note=normal takeoff power (10 min max)<ref>Maisel 2000, pp. 130–132.</ref>
::::{{cvt|1802|shp|0}} emergency power (2 min max)
:::: (modified Lycoming T53-L-13B)
|rot number=2
|rot dia ft=25
|rot dia in=<!-- helicopters -->
|rot area sqft=981.8
|rot area note=total<br>
*'''Blade section (original):''' - '''root:''' [[NACA airfoil|NACA 64-935/528/118]]; '''tip:''' [[NACA airfoil|NACA 64-(1.5)12/208]]<ref name="Selig"/>
*'''Blade section (Boeing ATB):''' - '''root:''' V43030-1.58/VR-7; '''tip:''' Boeing VR-8<ref name="Selig"/>
<!--
Performance
-->
|max speed kts=332
|max speed note=at {{cvt|17000|ft|0}}
|max speed mach=<!-- supersonic aircraft -->
|cruise speed kts=303
|cruise speed note=max. at {{cvt|16500|ft|0}}
::::{{cvt|200|kn|mph km/h|0}} at {{cvt|20000|ft|0}}
|stall speed kts=
|stall speed note=
|never exceed speed kts=364
|never exceed speed note=
|minimum control speed kts=
|minimum control speed note=
|range nmi=445
|range note=with maximum fuel
|combat range nmi=
|combat range note=
|ferry range nmi=
|ferry range note=
|endurance=<!-- if range unknown -->
|ceiling ft=29000
|ceiling note=<br>
*'''Service ceiling OEI:''' {{cvt|15000|ft|0}}
*'''Hover ceiling IGE:''' {{cvt|10500|ft|0}}
*'''Hover ceiling OGE:''' {{cvt|8650|ft|0}}
|g limits=<!-- aerobatic -->
|roll rate=<!-- aerobatic -->
|glide ratio=<!-- sailplanes -->
|climb rate ftmin=3150
|climb rate note=at sea level
|time to altitude=
|sink rate ftmin=<!-- sailplanes -->
|sink rate note=
|lift to drag=
|wing loading lb/sqft=
|wing loading note=
|disk loading lb/sqft=15.2
|disk loading note=
|fuel consumption lb/mi=
|power/mass={{cvt|0.45|hp/lb|0}}<ref name=wickTilt>{{cite journal |last1=Warwick |first1=Graham |title=Tilting at targets |journal=Flight International |date=February 1992 |page=44}}</ref><!--url inactive. when flight archive re-opens unlikely to be the same-->
|thrust/weight=
|more performance=
|avionics=
}}
==See also==
{{aircontent
|see also=
|related=
* [[Bell XV-3]]
* [[Bell Boeing V-22 Osprey]]
* [[AgustaWestland AW609]]
|similar aircraft=
* [[Canadair CL-84 Dynavert]]
* [[Sikorsky S-69]]
* [[Sikorsky S-72]]
|lists=
* [[List of VTOL aircraft]]
}}
==References==
===Notes===
{{reflist}}
===Bibliography===
{{refbegin}}
* Maisel, Martin D., Demo J. Giulianetti and Daniel C. Dugan. [https://history.nasa.gov/monograph17.pdf NASA SP-2000-4517, "The History of the XV-15 Tilt Rotor Research Aircraft: From Concept to Flight" (PDF).] ''NASA'', 2000.
* Markman, Steve and Bill Holder. "Bell XV-15". ''Straight Up: A History of Vertical Flight''. Atglen, PA: Schiffer Publishing, 2000. {{ISBN|0-7643-1204-9}}.
* Norton, Bill. ''Bell Boeing V-22 Osprey, Tiltrotor Tactical Transport''. Earl Shilton, Leicester, UK: Midland Publishing, 2004. {{ISBN|1-85780-165-2}}.
{{Refend}}
==External links==
{{Commons category|Bell XV-15}}
*[https://web.archive.org/web/20050411052448/http://www.space.com/imageoftheday/image_of_day_030917.html Image of XV-15 in hovering flight]
{{Bell Aircraft}}
{{US STOL and VTOL aircraft}}
[[Category:Bell aircraft|V-15]]
[[Category:1970s United States experimental aircraft|V-15, Bell]]
[[Category:Tiltrotor aircraft]]
[[Category:NASA aircraft]]
[[Category:High-wing aircraft]]
[[Category:Turboshaft-powered aircraft]]
[[Category:Aircraft first flown in 1977]]
[[Category:Twin-turboprop tractor aircraft]]
[[Category:Aircraft with retractable tricycle landing gear]]