F-106 DELTA DART

The first modifications done to N616NA was to remove the entire Weapons System and all it's wiring, over 700lbs of wiring. Then came the installation of the new underwing nacelles.

"To investigate airframe installation effects on exhaust nozzle systems mounted on underwing engine nacelles, a combined flight and wind tunnel test program is being conducted utilizing a modified F-106 aircraft. Flight tests were conducted in the transonic speed regime to determine nozzle performance and boattail drag for variable flap ejector, conical plug, and auxiliary inlet ejector nozzle concepts. Wind tunnel tests were conducted on isolated models of these nozzles and also on a 1/20-scale model of the F-106 aircraft with simulated underwing engine nacelles. Wing and nacelle pressures from these wind tunnel tests are used to qualitatively explain the observed installation effects. The 1/20-scale model was also used to evaluate the effects of changes in nacelle geometry and angle-of-attack".

It was intended to test various engine inlet and exhaust configurations for the future U.S. SST program, which was later cancelled. The test aircraft use was F-106B 57-2516 (NASA N616NA and later renumberd as N816NA). To fit the nacelle mounted engines under each wing, where the external drop tanks were normally mounted, the elevons were split to clear the engine exhaust. Auxiliary fuel tanks were mounted in the missile bay along with extra instrumentation. The engines used in this progam were J-85-GE-13 and some other slightly smaller (diameter) variants. Those who spent time in FLYTAF (ATC pilot training) might remember them from the T-38 Talon, MAAG people will remember them from the F-5A/B and another variant in the F-5E as well as in some AT-37s. These engines were not much larger in dia. size than the supersonic external fuel tanks used on the F-106.

This F-106B is now on museum display at the Virginia Air & Space Museum Hampton, VA
From NASA Test Pilot Earle Boyer [15 July 2013]
This is just a short recap of the NASA Lewis Research Center (LeRC), now Glenn Research Center, study of propulsion system performance in the transonic speed range. The objective was to determine propulsion system effects for a wide variety of air breathing inlets and nozzles, to aid in the development of Boeing's proposed SST. Most of the information is taken from previous publications along with some of my personal reflections.

Because of model size limitations, data obtained in wind tunnels were suspect due to the required large corrections for scaling effects.The F-106B was selected as a suitable test bed because of it's delta wing configuration and suitable underwing nacelle mounting capability,similar to proposed SST configurations. This information was necessary to make any future SST economically competitive,because of the excessive fuel required accelerating through the transonic speed range.

NF-106B 57-2516 (NASA 616) was acquired from the Air Force and flown to the LeRC, Cleveland, Ohio, in October l966. Extensive modifications were initiated to include the removal of all MA-1 associated wiring, which I recall was about a thousand pounds. All the missile bay rails and launchers were removed to provide room for an elliptical fuel tank holding 2100 pounds of A-1 fuel for the test engines. Aircraft and test engine fuel systems were separated and JP-4 was retained for the aircraft's J-75 engine. Fuel for the J-75 engine was reduced by 1443 pounds in each wing due to test engine mounting structure and research hardware.The forward electronics bay equipment and radar antenna were removed and replaced with data recording equipment andlead ballast. Lots of ballast was required to account for the aft CG tendencies with the test engines installed.

A portion of each elevon was fixed to permit the nacelle additions, each housing a J-85 engine with afterburner. Each nacelle was supported by two attachment links and a load cell assembly permitting direct thrust measurements of each engine. Each nacelle included a forward and aft interface permitting various types of inlets and nozzles to be tested. The starboard engine/ nacelle was normally flown with a normal shock inlet and reference nozzle to provide a constant base for thrust comparisons with the research engine.

Additionally, the standard pitot boom was replaced with a research boom containing pitch and yaw vanes. This necessitated recalibrating the airspeed system, conducted at WPAFB in June of l968. A pacer aircraft supplied by the Air Force was used for subsonic and supersonic comparisons. Two tower flybys at 600 knots and 100 foot altitude by the F-106 was also performed.

Taxi tests were performed at Cleveland to determine elevon effectiveness with a portion of each elevon fixed, and to determine angle of attack landing limitations with the test engines installed. Flutter tests were conducted to 1.5 mach on a 100NM supersonic corridor established over Lake Erie, beginning near Buffalo and ending near Cleveland. Chase was provided by a NASA Edwards F-104.Another 100NM corridor was subsequently established over Lake Hurron, beginning near Alpena,MI, when flight operations were conducted out of Selfridge AFB.

The aircraft was configured such that the front seat pilot flew the test plan and the rear seat pilot operated the test engines and data recording system. A chase aircraft was required on all flights. Myself and Clifford Crabs flew all the missions generally alternating between the front and rear seats,except on occasions when we flew the chase aircraft. On those occasions the rear seat was occupied by another LeRC research pilot. Depending on mission requirements either J-75 or J-85 fuel limited test time and on many occasions the RTB was flown with the test engines suppling most of the thrust. On some flights the TOGW exceeded 42,000 pounds. Since the landing GW was also heavy, final approaches were flown at 200kts with touchdowns not exceeding 10 to 12 degrees angle of attack to avoid test engine nozzles contacting the runway. Landings were typically made with less than 1000 pounds of J-75 fuel, enough for an aborted landing closed pattern.

Over 300 missions were flown on a variety of nozzles and inlets at various speeds,power settings,"G" levels and Reynold numbers.The lowest Reynolds number reached was on a flight requiring full pressure suits that reached an altitude of 57,000 ft. The program terminated with the transfer of the aircraft to the NASA Langley Research Center and re-designated NASA 816. Following completion of a Storm Hazards program and later a Vortex Flap program, the aircraft was ceremoniously retired on 17 May 1991. It is currently on display at the Virginia Air and Space Center, Hampton, VA.
--- Earle Boyer 15 Jul 2013