Pursuant to the 21 June 1955 request for a study of the J79
engine for the Voodoo, Ship No. 1, 53-2418, was bailed to General Electric in
1956 and modified with a pair of YJ79 engines in place of its Pratt &
Whitney J57s. The keel area was reworked
to accommodate the new engines and the intakes were modified with longer
ramps. 53-2418 first flew with theYJ79
installation on 3 November 1956 with an initial fit of two YJ79 Phase 0
engines. Later that year, the NF-101A was modified with improved YJ79 Phase I
engines modified with the Basket Burner Test Package and the Parker afterburner
selector valve. During its service with
G.E., the aircraft also flew with YJ79-GE-3 and YJ79-GE-7 engines. In 1958, 53-2418 became the first aircraft to
flight test exotic borane-based high-energy “zip” fuel
(HEF). This was done as an adjunct to the General Electric J93-GE-5
program. The J93 was an enlarged
derivative of the J79 intended for use with the B-70 Valkyrie and F-108 Rapier.
The kerosene-fueled J93-GE-3 made it to the hardware stage and was
extensively flight-tested on the XB-70. Waiting on the drawing boards was the
J93-GE-5 engine, substituting borane compounds for traditional hydrocarbon
compounds as fuel.
Borane fuels were the focus of a great deal of research in the 1950s, with hundreds of millions of dollars quietly spent on their development. These materials reacted with oxygen like traditional hydrocarbon fuels, but offered nearly twice the energy for the same weight of fuel. In theory, an airplane using these fuels would need to expend less fuel to produce a given amount of thrust, resulting in greatly increased range. This made borane fuel an extremely attractive option for the B-70, a six-engine, Mach 3-capable aircraft that required intercontinental range without refueling. However, there were very serious drawbacks to the use of boranes as a practical fuel. Besides being extremely toxic, boranes are also extremely reactive. The same qualities that make them an excellent fuel also explain why they do not exist in nature—chemically, they are very unstable. Boranes have to be synthesized, a very expensive process. Diborane, the basic building block of all other borane compounds, is a gas that combusts simply on exposure to air at normal temperatures and pressures. Pentaborane, a liquid, spontaneously combusts at temperatures above 78°F and was itself too unsafe to use as a practical fuel. Decaborane, which is stable at normal operating temperatures, received serious attention from researchers as both a jet and rocket fuel, but is a solid at room temperature. Decaborane could be added to the air mixture of a turbine engine as a fine dust or mixed with a hydrocarbon liquid such as benzene. Unfortunately, the combustion products of borane fuels form a highly corrosive mixture of boric anhydride and water as well as extremely refractory deposits of boron carbide. (Slightly less hard than diamond, boron carbide is presently used as an industrial abrasive and has been used for cockpit armor on the Ling-Temco-Vought A-7D Corsair II). Injecting borane fuel into the combustion chambers of a turbojet would soon result in a wrecked engine.
In order to be usable, boranes had to be injected into the
afterburner section, well behind the more delicate engine components. This was the arrangement planned for the
J93-GE-5. Borane fuels were flight-tested with this
configuration for the first time on 28 September 1958, using the NF-101A with modified J79 engines as the test
bed. The flight tests themselves were
successful, but the borate deposits left in the nozzle and afterburner section
seriously degraded the usable life of the engines. Also, the borane fuel produced a great deal of smoke, enough
for some to judge it as being impractical and to be potentially unsafe during
takeoff. Despite the promise of borane fuels, their benefits were greatly outweighed
by safety concerns and by production and maintenance costs. Although not an important consideration in
the late 1950s, widespread use of these fuels with their acidic combustion
products could have also posed significant environmental problems. One borane compound, triethylborane (TEB) found use as a
catalyst for the ignition of the high-flashpoint JP-7 fuel of the SR-71. The Department of Defense abandoned work on
the J93-GE-5 in 1959, in large part due to the results of the flight test work
performed by the NF-101A. However, general research on borane fuels continued for some time afterwards.
By May of 1959, the NF-101A had had its J79 engines removed before the open
house at Edwards AFB that year. Thus,
the unwanted and little-heralded Voodoo played an integral part in what had
once been thought one of the most important and promising research programs of
the Cold War. Fortunately, this historic
aircraft has been preserved. After the
J79 installation was removed, 53-2418 was moved in 1960 to Amarillo AFB
Technical Training Center and used as a hydraulics trainer until placed on stands
outside of the base as a “gate guard”.
With the closure of the base in 1970, the aircraft was later sold as
excess property and purchased by Mr. Dennis E. Kelsey in February 1975. After residing on the grounds of Bell
Helicopter Co., 53-2418 was issued FAA Number N9250Z on 7 April 1976 and moved
to Pueblo, Colorado on 11 January 1977. At this writing, 53-2418 has been moved from
Pueblo and after extensive restoration work has been on display at the Evergreen Aviation and Space Museum in McMinniville, Oregon since 2013.
happy birthday bigron.... pats F106
ReplyDeleteGene, I am so sorry that I missed this, and now another year older, to boot! :-(. Thank you for the birthday wishes, and my very best to each of you guys over at Pat’s World of the F-106! Spare time for anything is in short supply these days, but I’ve been away for far too long over there. We need to stay in touch.
DeleteCheers!
Ron