Back Hughes Model 385 / XV-9A "Hot Cycle"


Convinced that the use of gas pressure to drive rotors, as used in the XH-17 and proposed for the XH-28, was superior to conventional methods as the elimination of the transmission drive system resulted in a lighter, less complex, and more easily maintained system, Hughes engineers sought ways to improve the propulsive efficiency of pressure-jet rotors. Eventually concluding that much improvement would result from ducting the hot efflux of gas generators directly to cascade vanes at each blade-tip instead of piping cold air to tip-burning nozzles, they succeeded in attracting the interest of the US Army.

Funded by the Army beginning in 1962, the multi-phase development programme for the Model 385 began with 60 hours of test running of a prototype hot-cycle rotor mounted on a ground rig. As results were encouraging, Hughes proceeded to the next phase, 15 hours of bench testing of the Model 385 propulsion module consisting of two General Electric YT64-GE-6 gas generators mounted at the tips of stub wings and driving a three-bladed rotor. Each blade was of two-spar construction with the hot efflux of the gas generators being taken to vanes at their tips by means of a Rene 41 high-temperature steel duct passing between the spars. Cooling air was forced through the leading and trailing edges of the constant-chord blades and was exhausted at the tip, fore and aft of the hot efflux. Results remaining promising, Hughes was authorized to proceed with the manufacture and testing of a research vehicle, the XV-9A (serial 64-15107), which was given a VTOL mission designator instead of the more traditional H helicopter designator.

As the XV-9A was only intended as a demonstrator for the hot-cycle system, the Army requested that manufacturing costs be kept to a minimum by using components from other aircraft. Thus, the cockpit of a Hughes OH-6A (with side-by-side accommodation for a pilot and a co-pilot/flight test engineer) and the undercarriage of a Sikorsky H-34 were mated to a specially-built fuselage and V-tail. The hot efflux from two General Electric YT64-GE-6 gas generators, which were loaned by the Navy and mounted at the tips of a stub wing, drove the three-bladed rotor. Bleed air from these generators was ducted to a yaw control system at the tail.

First flown by Robert G. Ferry at Culver City on 5 November, 1964, the XV-9A remained at the manufacturer's facility until it had completed an initial 15-hour flight test programme. It was then transferred to Edwards AFB, where an additional 23 hours were flown. From an engineering point of view, tests proved highly satisfactory and in 1965 Hughes confidently predicted that the hot-cycle system would be used for heavy-lift military helicopters and for compound civil helicopters. The latter, which were to have been fitted with short wings and forward thrust fans, were expected to fly at speeds of up to 480km/h. From the environmental and economic points of view, however, the XV-9A was less successful as the exhaust of hot efflux through cascade vanes at the tips of the rotor was noisy and unacceptable in urban areas and as fuel consumption rate was high. To mitigate these deficiencies, Hughes proposed a refinement of the pressure-jet concept based on the use of turbofans in lieu of gas generators. This warm-cycle system was tested in a wind tunnel and on a whirling stand but improvements were insufficient to warrant the manufacture and testing of a flying prototype, thus bringing to an end the development by Hughes of pressure-jet systems successively based on the cold-cycle principle, as used for the XH-17 and XH-28, the hot-cycle principle, as featured by the XV-9A, and the warm-cycle principle, as evaluated during whirling stand tests.

Rene J. Francillon "McDonnell Douglas Aircraft since 1920: Volume II", 1997

Test pilot Robert G. Ferry in front of the XV-9 at the Hughes Airfield in Culver City

This was a large experimental heli-copter built in 1964 to study blade-tip nozzle jet propulsion. Some of the parts were taken from existing aircraft. The version for the US Army was designated XV-9A and had a three-blade constant chord metal rotor. There was room for two pilots seated side by side in the cockpit.

G.Apostolo "The Illustrated Encyclopedia of Helicopters", 1984

In 1962 Hughes Helicopters was awarded an Army contract for the development and construction of a research helicopter utilizing a hot-cycle propulsion system. The resulting XV-9A (serial 64-15107) made its first flight in November 1964.

Though rather ungainly-looking the XV-9A was of essentially straightforward construction. Indeed, in order to save time and money in the building of what was certain to be the only vehicle of its type Hughes' engineers assembled the XV-9A using the cockpit of an OH-6A, the landing gear of a Sikorsky H-34, and a simple purpose-built cylindrical fuselage with a twin-rudder V-tail. It was, in fact, the XV-9A's experimental propulsion system that made the otherwise mundane craft unique. The system was built around two pod-mounted General Electric YT64-GE-6 engines fitted to the ends of two high-set stub wings, one on either side of the fuselage directly below the main rotor hub. Each engine's turbine section had been removed, and hot exhaust gases were ducted directly through the rotor hub to be expelled at near-sonic speeds through vaned cascades in each of the three blade tips. Smaller exhaust ports on either side of the tail boom just forward of the rudders provided some additional directional stability.

The XV-9A's flight test programme was completed in August 1965, with a total of 19.1 hours having been flown. The hot-cycle propulsion system had proved to be overly complex and the aircraft itself had been plagued by stability problems; the Army therefore returned ownership of the XV-9A to Hughes and abandoned any further hot-cycle research.

S.Harding "U.S.Army Aircraft since 1947", 1990

Technical data for XV-9A

Crew: 2, engine: 2 x General Electric YT64-GE-6 gas turbines rated 2125kW each, rotor diameter: 16.76m, fuselage length: 13.72m, height: 3.66m, empty weight: 3856kg, loaded weight: 6940kg, maximum weight: 11567kg, rotor loading: 31.5kg/m2, maximum cruising speed: 222km/h, range: 240km

Bob Meuse, e-mail, 26.03.2014

March 25, 2014
I began my career at Hughes Aircraft Company in 1954 and retired with Hughes after 38 years. I used to go into the big hangar (where they built the Spruce Goose) every noon to eat my lunch. The XV-9A "Hot Cycle" helicopter was being worked on. Also in the hangar was the huge HX-17 "Flying Crane" helicopter. I used to climb up into the cockpit and eat my lunch; play "helicopter pilot", and watch them build the smaller Hughes helicopters; I think the 500s. I never did see the HX-17 in operation but I understand that it met the lifting requirements although very unstable in flight. It was designed to lift and transport a 12 ton semi-trailer radar van. I'm told that it was frighteningly noisy and could be heard for miles. The rotor spun at 80 RPM.
Hughes also had plans for an even bigger helicopter, the HX-28. It was I'm sure, never built but I'm told that there was a mock-up of it and it was simply gigantic. I've seen photos of the mock-up and it is so surreal that it reminded me of some of those bizarre Russian aircraft like the Kalinin K7 monster that were obviously too large and could never fly.
"Did you ever meet Howard Hughes?" I hear you cry.
"No, and I never knew or met anyone who did".

shoes, e-mail, 17.06.2011

I would love to make a model of the type.

melon, e-mail, 23.04.2011

i am joint the works

Zac Yates, e-mail, 03.11.2010

Long shot, does anyone know where I can obtain a DVD of a 1980s doco called "The Chopper"? I have no idea who produced it, exact year, or who the English-sounding narrator is. It includes interviews with Hanna Reitsch and Bart Kelley (coworker of Arthur Young at Bell), and other techs and pilots, as well as footage of the prototype NOTAR, Apache, Sikorsky ABC and the XV-15 as well as the XV-9A. And Vern - many thanks for your information :) a sad fate, but at least parts and the model remain.

Vern, e-mail, 10.10.2010

Re what happened to the Hughes XV-9A Hot Cycle Helicopter

During my USAF career, I received an invitation for the “dedication” of the Hughes XV-9A to the Smithsonian Institution in Washington DC on May 6, 1970. In the course of trying to ascertain where the A/C was, I searched the Smithsonian website and did not find it in their inventory. Subsequently I received a response from the Smithsonian Aeronautics Division regarding the history of the “dedication”.

The aircraft was scheduled for delivery to the Smithsonian collection in May 1967 but actually arrived in August. It was shipped via railcar from Ft. Eustis and arrived as a wreck, which was not the Smithsonian's understanding of the aircraft's condition. The cockpit had been picked clean and there were multiple holes in the fuselage. Smithsonian correspondence does not make clear how much of this was due to improper handling and security by the railroad and how much was due to inadequate storage by the Army.

As it turns out my invitation is not related to the actual full size aircraft airframe that was never publicly displayed, but rather to a fairly small scale model (which is now on display at the Steven F. Udvar-Hazy Center).

The net result was that at some point in the early seventies, the aircraft was deemed beyond reasonable restoration and scrapped. The Smithsonian did retain most of one of the hot cycle blades and it is still in storage at their facility in Suitland.

Dave Stern, e-mail, 07.04.2010

Hi and this is very nice site. I enjoyed the XV-9 data and gained comm helio license on 269A and briefly owned a Hughes 500, but never flew it. I'd trade photos for several shots of the XV-9. Can you assist me on this? Thank you.

David rs Greer, e-mail, 15.05.2009

hot-cycle propulsion I like it .No missiles or computers for 1960ts.A lot of that was put on afterwords But good director of Expermentel principally bachk then and can do attude . This Has A weight prolbem Im sure its made from metel but that old flying mechine thay had no carbon fiber
the new Heli - Plane can do 500km/h + stock standard streight from the factoy that you can take the wife and kids in .
We have to respect how many lives were lost in makeing our avation safer And to hughes Aspergers autistic spruice goose.Nx376 02

Zac Yates, e-mail, 22.02.2009

Does anyone know what became of the XV-9A? I would love to make a model of the type.

RICHARD GING, e-mail, 26.04.2008


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