Great Dane - RDAF F-91 Thunderceptor

[CammNut]

Or not so great, maybe...

This is Planet Models' 1/72 Republic XF-91-III Thunderceptor, modeled as an operational Royal Danish Air Force F-91A. As a mixed-propulsion interceptor, this aircraft was obsolete before it flew and never progressed beyond a pair of prototypes, so no backstory really makes sense. But here goes.

Denmark was among a handful of Republic F-84 operators "persuaded" by the U.S. to take a few of the same manufacturer's supersonic F-91 Thunderceptors for use in air defence alongside their Thunderjet and Thunderstreak ground-attack aircraft.



The F-91 was an unusual aircraft. In addition to mixed turbojet and rocket propulsion, the Thunderceptor had a novel inverse-taper wing. This was designed to eliminate the propensity of swept-wing aircraft of the time to encounter dangerous tip stall.

As angle of attack increased, airflow on a swept wing would begin to turn spanwise toward the tips, rather than flow chordwise. This caused the tips to stall before the inboard wing. The loss of lift aft of the cg caused the nose to pitch up violently. A large number of F-100 Super Sabres were lost on landing to this phenomenon, known as the 'Sabre Dance'.



Republic sought to overcome this hazard by reversing the conventional taper on a swept wing so that the tips were longer and thicker than the roots. This prevented the tips stalling before the inboard wing.

The inboard wing sections were now too thin to house the main landing gear, so instead the unusual dual-wheel bogies retracted outward into the thicker wingtips. To add to the novelty, the F-91 had a variable-incidence wing to increase lift for takeoff and landing.



Two XF-91 prototypes were built, the first flying in May 1949 and going supersonic in level flight in December 1951. The aircraft was powered by a water-injected, afterburning General Electric J47 turbojet and a Reaction Motors XLR11 four-chamber liquid-fueled rocket engine.

The first prototype had a nose intake and was later fitted with a small gun-ranging radar in an inlet centerbody. After the tail burned off following an engine failure on takeoff, the aircraft was fitted with a butterfly V tail.



The second prototype retained the cruciform tail but was fitted with a radar nose and chin inlet. (Sadly no V tail.) As armament, the F-91 would have had a retractable pack under the cockpit for unguided rockets or four AIM-4 Falcon air-to-air missiles (not modelled unfortunately).

The XF-91 was one of generation of late-1940s U.S. Air Force fighter prototypes that never made the grade because jet engine technology was advancing so quickly that they were obsolete before they flew. That group included the McDonnell XF-88 (1948), Lockheed XF-90 (1949) and Convair XF-92 (1948) - all on my list to whiff one day.



Now back to whiffland. A competent point-defence fighter, the F-91 served alongside Denmark's F-84s until its entire Republic-made fleet was retired with the arrival of Lockheed F-104s beginning in 1964.

Planet Models' kit is, quite simply, beautifully moulded, in finely detailed resin so smooth and thin it could be injection moulded - only the finish is even better! Fit is good, allowing for my ineptness with resin glues. The wings and tailplanes where they join the fuselage and tail are thin, so drilling and inserting brass wire for alignment and strength required some care.



I am on my third resin kit in a row and I am learning – pin everything. I have now armed myself with a pin vise and an array of ultra-small drill bits, but I need more brass wire!

Markings are from a Modeldecal F-104G sheet and an AirDOC Decals F-84G sheet. Colour is Tamiya RAF Dark Green. I was never going to attempt the heavy weathering that Denmark's F-104s suffered so this is either an aircraft soon after delivery or the Danes used the right paint.



The XF-91-III is on display at the US Air Force Museum in Dayton. It has matt olive green atop the fuselage – which I carried over to the operational aircraft - and polished metal on the sides of the rear fuselage and where the wing pivots. I used Bare Metal foil for that – first time in years. As always, I struggled with the vacform canopy and framing.

[Weaver]

That's gorgeous!     

It's really quite credible too: there was nothing much wrong with the XF-91 and it could have given good service, it was just overtaken by events, competition, and the USAF's desire to make a "big leap forward" with the highly-automated "1954 Interceptor" that eventually became the F-102 (a lot later than 1954 though!).

I have a HUGE irrational soft-spot for the XF-91, and two 1/48th Lindberg ones stowed away, but I've always been shy of the Planet Models one because... resin, so it's nice to get the lowdown from you about it's quality: I may get one myself now.     

Part of the reason why I love the XF-91 is that I remember as a kid going and staring at the Lindberg ones in Riley's toy shop in Stockport every time we went down shopping (when I was old enough, Mum would let me go off on my own while she got the groceries, and we'd meet up at a pre-arranged time), but I just couldn't afford them. When I saw a couplegoing on Ebay a few years back, I had to have them for nostalgia's sake, so at least one will probably never be built. Also, one of the first profiles I ever did on here was an XF-91 with a MiG-21MF (big) nose intake, in the service of the Kingdom of Gwynedd, with a huge dragon painted down it's side, so the other one may get that scheme one day if I'm feeling brave.

[Dizzyfugu]

Odd operator choice, bit it looks very good. 

[McColm]

Well done 

[PR19_Kit]

What a superb model, very redolent of the period too.

As Weaver says, I've always liked the XF-91 if only because it had SO much weirdness all incorporated into one aeroplane!   

[zenrat]

Mate, you've glued the wings on the wrong way round.   

Weird looking but good job.   

[chrisonord]

Wow that's very nice, we need more obscure stuff like that 

[NARSES2]

That's come out really well   

I'm a fan of Planet, they sit at the "top table" when it comes to resin kit manufacturers and can be as easy to make a decent IM kit once you get used to using superglue. I have bottles varying from ultra-thin to ultra-thick which can give me more time to play with if I need it and of course the indespensible bottles of "Zip Kicker" and de-bonder.

[Pellson]

Looking really good! 

[CammNut]

Thanks, folks - and I am off to get a range of different superglues

[HarryPhishnuts]

That's really cool looking. 

[George the Cat]

Excellent modelling. 

[Glenn Gilbertson]

Really impressively modelled - and quite plausible!
  

[Captain Canada]

Odd operator choice, bit it looks very good. 

Not really. As stated, they were already operators of the F and G, and then they were 'persuaded' lol

[Captain Canada]

That looks so good in those colours and markings ! I have to admit, I'd never seen the one with the radar nose......looks right ! Great job on both the build and the back story. Cheers !