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F-101

A Tale of Two Voodoos - The F-101B versus the RF-101A/C

By Michael Benolkin

The McDonnell F-101 Voodoo concept started as the XF-88 in 1946, with the requirement for a penetration fighter to escort heavy bombers to their targets, essentially picking up the mission of the P-51 Mustang from World War 2. The newly-minted USAF wanted to carry the concept forward, but several factors intervened: first, the J-34 engines did not have the thrust, even with the newly added afterburners, to meet performance specifications; second, the revelation of supersonic flight potential after Chuck Yeager broke the sound barrier in the X-1; and third, the Korean war led to a new set of fighter requirements that required even greater range. The XF-88 was cancelled and the design was enlarged, re-engined with two J57-P-13s, and the plus-sized fighter was designated as F-101. By the time the F-101A entered service, the bomber escort mission had been abandoned and the aircraft re-roled (again) into a deep-penetration nuclear strike fighter, but it was unable to meet its 7+G maneuverability requirement. The airframe updates for 7.33G requirement and additional fuel for greater range led to the F-101C.

In the meantime, the USAF saw potential with McDonnell's F-101 airframe for the tactical reconnaissance mission and two F-101As were given new, longer, reconnaissance noses. Aside from the two F-101As that were modified into the RF-101A configuration, the remaining RF-101As were built on the production line. The RF-101C was very similar to the RF-101A as it too was built on the production line rather than modifed, but it featured the higher G-load limits of the F-101C and cooling scoops in the tail which would allow for extended afterburner use (> 2 minutes) without cooking off the drogue chute.

As the tactical strike and recce Voodoos progressed, the Air Force had another challenge - the Convair F-102 Delta Dagger interceptor was facing significant delays and they needed an interim solution - the F-101B was born. The F-101B adopted a tandem two-place cockpit with an operator in the rear seat to manage the MG-13 radar intended for the F-102 and the SAGE datalink. The F-101B was powered by a pair of J57-P-55 engines that pushed the F-101B to Mach 1.85. While the F-101A/C could fly low and fast, the F-101B could fly high and faster.

While not relevant to this discussion, a number of F-101As were modified into the RF-101G and F-101Cs were modified into the RF-101H, both of which remained single-seat aircraft with the fatter, shorter noses rather than the long sleek noses of the RF-101A/C. Likewise, a number of F-101B airframes were also converted into reconnaissance aircraft which rendered the only two-seat recce Voodoo configuration.

Until (somewhat) recently, the only Voodoo options available in 1/48 scale have been the Monogram F-101B and RF-101B kits. The only way to achieve an RF-101A/C in this scale was with the help of the C&H Aero resin conversion. In 2014, Kitty Hawk went where noone else had gone before - the F-101A/C Voodoo. Soon after, there was many discussions about intakes, afterburners, etc. This was followed by the F-101B and more recently, the RF-101C/G/H kits. What to do about the Voodoo?

We were recently visiting Fotios Rouch in Tucson and made the obligatory pilgrimage to the Pima Air and Space Museum. Fotios needed to take some measurements off the F-105 for another veteran modeler and it seemed like a good opportunity to look over their Voodoos as well. We'll look at the two aircraft side-by-side and you'll be able to tell which aircraft is which by their color-coding - the faded ADC Gray aircraft is the F-101B and the faded Southeast Asia camouflaged aircraft is the RF-101C.

F-101BRF-101C

In these first images, you can see the difference in length of the F-101B's -55 afterburners versus the RF-101C's -13 afterburners. You'll also note the smooth exterior shell of the -55 afterburners whereas the -13s have the bumps at the rear of the afterburner fairings that cover the nozzle positioning pushrod actuators inside.

Another noteworthy detail is the bare metal heat shield keels of each aircraft. With the F-101B, it appears rounded under the tail near the ends of the afterburner nozzles. A divider does form between the nozzles out of sight of this view. The RF-101C's keel maintains a wedge divider between the afterburner nozzles back to the rear of the keel. You'll note that we'll see this design feature again with McDonnell's F4H-1 Phantom II and later variants.

F-101BRF-101C

Looking slightly forward, you can see the bump with two antennas under the rear fuselage for the F-101B's SAGE datalink, while no antenna mount is under the RF-101C's fuselage. Along the top of the engine fairing are three air vents, a detail that exists on both aircraft. Under the wing trailing edge, you can see a large air scoop on the F-101B whereas there is an NACA flush air intake in the same position on the RF-101C.

F-101BRF-101C

Moving forward, you can see the difference in the air intakes of the two aircraft. While the basic shape of the air intakes is identical, the F-101B's intake face is angled forward while the RF-101C's intake face is almost vertical.

F-101BRF-101C

Looking aft, you can see the shapes of the two intakes are almost identical. Both intakes stand off from the fuselage sides to keep the intakes clear of the boundary layer airflow.

F-101BRF-101C

From the splitter plate to the edge of the intake, both measure out to 33 inches.

F-101BRF-101C

From the top to the bottom of the intake along the splitter plate, the intakes are 33 inches high, but the F-101B's measurement comes out to 36 inches due to the forward cant of the intake.

F-101BRF-101C

From the top to the bottom of the intake along the splitter plate, the intakes are 33 inches high, but the F-101B's measurement comes out to 36 inches due to the forward cant of the intake.

F-101BRF-101C

Looking at the splitter plates reveal some interesting details. With the F-101B, the splitter plate is about 41 inches measuring along the leading edge of the splitter. The leading edge of the RF-101C's splitter is about 36.5 inches. You can see the greater forward angle of the F-101B intake versus the RF-101C. While the RF-101C's intake almost looks vertical, you can see from the vertical line in the splitter plate how the RF-101C's intake also sweeps slightly forward.

F-101BRF-101C

The upper edges of the intake splitters are almost identical at 10-11 inches.

F-101BRF-101C

These photos reveal that the lower intake lip is angled further aft with a width of 14 inches to the splitter plate leading edge while the RF-101's width is 10.5 inches. There is one other detail with noting here, while the F-101B's splitter plate is essentially solid, the RF-101C's splitter plate has the distinctive vertical piano hinge that runs from top to bottom. When you look behind the splitter plates, the RF-101C's stand-off mounts have bolts to release the splitter plate to hinge outward to gain access to the auxiliary intake under the splitter plate. You'll see this hinge detail on other designs like the F-4 Phantom II and the MiG-23 Flogger.

The differences in these intakes reveal the evolution of the design where the F-101A/C (and RF-101A/C) were designed for low-level supersonic flight, the intakes only needed to handle up to Mach 1.5 airflow. The F-101B with its larger engines could reach Mach 1.85 at higher altitudes and those intakes were designed for that flight regime. Even so, the differences are more subtle than the MiG-23/MiG-27, for example. The MiG-23 was designed for Mach 2+ flight at altitude, so those intakes and splitter plates were designed for higher Mach cruise, while the smaller splitters on the MiG-27 were tuned for transonic (up to Mach 1.1) flight on the deck.

While the afterburner details are hard to miss, the differences in the intakes are more subtle and easy to overlook if you don't know what to look for. Hopefully this quick comparison will help you with your Voodoo builds.

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