Republic XR-12 Rainbow (oz16922)

About this Plan

Republic XR-12 Rainbow. Free flight scale model for rubber power. Wingspan 36 in.

Direct submission to Outerzone.

Quote: "REPUBLIC XR-12 RAINBOW
RC-2 CIVILIAN AIRLINER PROPOSAL

Development of the XF-12 photo-reconnaissance airplane began in 1944 when it appeared that a fast, specialized reconnaissance airplane would be needed during the final stages of the war in the Pacific. The XF-12 was roughly the same size as the C-54, but it was much heavier and had more than twice as much power. The four turbo-supercharged 3,000hp (2,200kw) Pratt & Whitney Wasp Major engines were enclosed in long, slender nacelles that extended well beyond the wing trailing edges. The wing and empennage shared a resemblance with those of the F-84 Thunderjet. The fuselage was a slender teardrop shape, unbroken even by the windshield. Each main landing gear had a very large single wheel to fit inside the confines of the laminar flow wing. The Rainbow had its own darkroom in order to develop reconnaissance images on the way back from a long photo mission.

The first of two XF-12 prototypes was completed and flown on February 7, 1946. Subsequent experimental flight tests showed that it had lived up to its promise, and it passed into the service-test phase in June 1947. The XR-12 delivered to the Air Force crashed on its second test flight. The other Rainbow was sent to a gunnery range.

Unfortunately, the day of high-performance reciprocating engine-powered military airplanes had passed and the anticipated contract for 20 production F-12As never materialized.

Republic still hoped to make the Rainbow into a 46-seat airliner, which they called the RC-2. Their selling point was speed, for which customers would pay a premium. Unfortunately, the expected postwar boom was not immediate and the airlines bought the slower but roomier DC-4 and Boeing 377 instead. —All Aero

CONSTRUCTION:

WING: The wing is built using the Dave Rees’ sliced rib method. Mike stuart has a great tutorial on his site on this method: https://www.ffscale.co.uk/rees.htm Use the wood dimensions as noted on the plans.

The nacelles basically pass through the wing so 1/32” ply and 1/16” half circles laminated over the spar after the wing is built allows the rubber motor to pass through the wing spars yet keeps the spars strong. One ply disc is usually enough with a 1/16” circle on the back side of the laminations. I hope the picture on the plan clears this up.

NACELLES: Nacelles are built using the ladder jig construction method. Use your favorite prop block and motor anchor method. The formers will be the same for all four nacelles. The inner nacelles are just a bit longer for the landing gear. Use the same method as for the fuselage and then slip the nacelles over the completed wing.

FUSELAGE: The fuselage is built in my favorite method, “Ladder Jig” and Maxfliart has a good tutorial on this technique in his Beech Staggerwing Twin video: https://www.youtube.com/watch?v=1yUYY1dqfH8 With the fuselage basically a round tube I planned on using reed instead of balsa. I bought my reed from Walmart’s hobby section Amazon has it as well. It comes in a loose roll of reed approximately 1/16” diameter. Enough for a lifetime of modeling. When soaked over-night in water is becomes very flexible and easy to wrap around a patter of foam board. I use plumber Teflon tape around the pattern for easy release of the reed or laminated balsa strips. I use masking tape to hold the reed in place till it dries over- night. I usually make a double circle of reed and after it has dried I use super glue to stick it together so it doesn’t unravel. Mark the demarcation lines on the dried reed and mount on the ladder jig..."

Supplementary file notes

Build notes.

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