Flightdeck Friday: The F-101 Voodoo

So it’s like this – the Slavemaster Pops (aka SJS) is out of town this week and left us with a boooring article to post for this Friday (some biplane *bleh*).  Frankly, we think he needs to widen his view and we think the Voodoo is a perfect one  to start with.  Besides, it just looks cool and mean (say that about some biplane Pops).  Besides, who cares if it has a tailhook or not?  Our friend Mike likes the idea too and said he’d support us if the old grouch boss got too upset about it…right Mike?  Mike???  Oh sure — run off and hide in the mountains in Colorado will you…

 

The F-101 began life as the XF-88 – a design study in 1945 for a long-range bomber escort jet fighter that was penned and brought to life by McDonnell Aircraft Company (who was also working on the first Navy jet – Hey Pops, why don’t you do THAT next week? Has to be more interesting than a bleh-plane. -SJA#1). 

The first XF-88 made its maiden flight on 20 October 1948. It had non-afterburning engines and no armament. Like so many other jets of this period, It proved to be underpowered, leading to the decision to install afterburners on the second prototype, which was designated XF-88A Voodoo .  The XF-88A made its first flight on 26 April 1949 and the first prototype was modified to the same standard. In a paper competition against the Lockheed XF-90 and North American XF-93, the Voodoo lost to the XF-93, but the decision on production was later delayed until a ‘fly-off’ competition could be held. In that fly-off, held in the summer of 1950, the Voodoo proved the winner, but changes in Air Force requirements led the penetration fighter to be cancelled entirely.  Events in Korea showed the vulnerabliity of bombers to jet fighters and when SAC began casting around for a twin-engine long-range bomber escort, McDonnell provided an unsolicited bid based on a larger version of the XF-88A. 

 

Initially produced as a single seat fighter (and recce variant) the Voodoo showed impressive speed, setting several absolute speed records in the process.  In SAC’s configuration, a second person was required to operate the weapons system which served a battery of 4 missles, either 4 x AIM-4 Falcons (in either IR or semi-active radar homing) or 2 x AIM-4 and 2 X AIR-2 Genies that carried a 1.7Kt nuclear warhead.  The missiles were carried on a rotating bay door, two to a side.  The Falcons were typically fired in pairs (1 x IR + 1 x SAR), increasng the chance of a kill.  The  MA-13 fire control system that controled the intercept was linked to the ground and was integrated into the SAGE (Semi-Automatic Ground Environment) system which would allow ground controllers to steer the Voodoo to the intercept if enabled.  The MA-13 also performed automatic firing and post-firing maneuvering of the aircraft when launching the Genie.  This combination gave the Voodoo an all weather capability, but at the expense of speed.  Range was supplamented with drop tanks.

 

The Voodoo, again like many aircraft of the period, suffered from a variety of equipment and controllability problems.  With the addition of the MA-13 fire control equipment, a significant amount of heat was generated and subsequently vented off board.  Unfortunately it was vented offboard int he vicinity of the port side AIM-4 missile, leading to its degradation and unfortuante endancy to explode within two seconds of being launched.  Extensive airframe mods were mae in this area to screen the missile from further exposure to waste heat exhaust. 

As complex as the avionics cooling issue was, it, at least, was resolved fully.  Other issues, like nose pitch-up or down (unsolicited) made the aircraft a handful to fly in the pre-digital flight control era (unlike, oh, today’s Hornets… -SJA#2).  How bad was it?  Try this (h/t Fighter Planes):

Nose pitch up
At low speed or high speed/high ‘G’ and certain angles of attack it was thought that airflow separation occurred on the wing surfaces outboard of the wing fences. This down wash would envelop the horizontal and vertical tail surfaces and the aircraft would pitch up, airspeed would bleed off to about 110 kts.- and the stall would grow and progress inward and forward along the wing until only the inboard leading edge was producing lift. This would lift the nose of the aircraft and it would fall into an spin, oscillating between 20 and 70 degrees of pitch up.

In this oscillating stall condition the engines also stalled from lack of air induction. (In case you think this is an unusual action for a jet engine, just go out to your local jetport and watch the older ‘commercials’ idling on the taxi-ways in high wind conditions. Watch for the times that the wind blows across the intakes and you will see and hear the engines choking and burping and being not very happy at all.) There was not enough air across the controls to make a difference at this point so you just had to ride it out, or eject.

If you had lots of altitude and you hated parachutes the procedure was to wait for the aircraft to unload to the lowest angle of attack then deploy the drogue chute to try to keep the nose down. If your head stopped banging on the canopy you tried an engine restart and -if the engines lit- you firewalled the throttles and powered out of it until the aircraft was flying again at 230 to 350 kts., then you released the drogue. Below 15,000 feet standing orders were to eject since the Voodoo lost altitude quickly without lift. To remedy this problem the Air Force installed a hydraulic system, attached to angle of attack sensors on either side of the nose, that would not allow the stick to be pulled past specific points at specific speeds.

Nose pitch down

Similar to nose pitch up, this happened if the stick was pushed too far forward too fast at certain speeds. The flow of air over the upper wing seemed to separate in these conditions and cause the wing to loose lift. The aircraft would first fall nose first, then tumble as the tail (which still had lift) overflew the nose. The engines might stall and there might not be enough air over the control surfaces for control, but if you were quick and the engines remained lit you could catch it with the throttles it as you went through the horizontal again and fly out of it in sort of a non-spinning snap roll. The same hydraulic stick limiter designed for pitch up seemed to work as the remedy.

Inertial roll coupling

If you did a fast, large, roll at the same time as pulling G. the lower wing tip would stall outboard of the wing fence – causing an increase in the roll rate and dropping the stalled wing back – so that the roll became an asymmetrical bobble. Sort of like a snap roll again, but with no rudder fed in. If you tried reversing the controls to roll back, the ailerons would only cause drag on the stalled wing and the stall would worsen. The wing would drop until it really caught the slipstream then bounce up again… then stall again, etc. Unless you unloaded back pressure the condition would not stop, and in an oscillation or two you would find yourself in a nose pitch up condition… see above.

 

A total of 479 F-101Bs were produced and initially deplyed with Air Defense Command beginning in 1959.  Canada began deploying them as the CF-101 beginning in 1961 and lasting until 1984.  By the late 1960s the F-101 was being moved to the Air Guard as the F-106 was taking over primary interceptor duties.  By 1972 the last F-101B was withdrawn from ADC service and it was retired from active service altogehter in 1982.

 

Colorado State kept and operated one copy for a number of years while researching severe weather (read: thunderstorms).

General characteristics

• Crew: 2
• Length: 67 ft 5 in (20.55 m)
• Wingspan: 39 ft 8 in (12.09 m)
• Height: 18 ft 0 in (5.49 m)
• Wing area: 368 ft² (34.20 m²)
• Airfoil: NACA 65A007 mod root, 65A006 mod tip
• Empty weight: 28,495 lb (12,925 kg)
• Loaded weight: 45,665 lb (20,715 kg)
• Max takeoff weight: 52,400 lb (23,770 kg)
• Powerplant: 2× Pratt & Whitney J57-P-55 afterburning turbojets
  • Dry thrust: 11,990 lbf (53.3 kN) each
  • Thrust with afterburner: 16,900 lbf (75.2 kN) each
• Internal fuel capacity: 2,053 US gal (7,771 L)
• Fuel capacity with 2 external tanks: 2,953 US gal (11,178 L)

Performance

• Maximum speed: Mach 1.72 (1,134 mph, 1,825 km/h) at 35,000 ft (10,500 m)
• Range: 1,520 mi (1,320 nm, 2,450 km)
• Service ceiling: 58,400 ft (17,800 m)
• Rate of climb: 49,200 ft/min (250 m/s)
• Wing loading: 124 lb/ft² (607 kg/m²)
• Thrust/weight: 0.74

Armament

• Missiles:
  
  • 4×AIM-4 Falcon
  • 2×AIR-2 Genie nuclear rockets

Avionics

• Hughes MG-13 fire control system

P.S.  Hey Pops – the other thing we liked was the cool 50’s flight suit – not like you could fit in it

(For the record that was SJA#2  -SJA#1)

(No it wasn’t – you wrote that…liar  -SJA#2)

(It was #1 who wrote it but #2’s idea – *I* tried to tell them it wasn’t a good idea. – SJA#3)