Vought XF5U-1 (oz11255)
About this Plan
Vought XF5U-1 (Flying Flapjack). Radio control sport-scale model. Unconventional twin.
Quote: "Vought XF5U-1, by Ken Stuhr.
Introduction: The real XF5U airplane was one of the many tragic stories I seem drawn to. It was built and taxi tested right up to the high-speed taxis, but destroyed by government edict before it could be flown.
As conceived, the XF5U was to be a carrier point-defense fighter, one that I like to think would have been used primarily against the Japanese kamikaze threat. its chief attributes included a great climb rate and great maneuverability. a very low landing speed, and a small overall size for efficient carrier 'packing.' Believe it or not, the real thing was powered by two P&W R-2000 radials! Estimates of its top speed range from 380 to more than 500 mph.
Background: Several years ago, in the May 1999 issue of S&E Modeler (the magazine that is now Quiet Flyer), my column featured this airplane as a possible power scale soarer (PSS) subject. I built a slope version, but owing to a lack of wind at my hill of choice, it has not yet flown. In the interim, I got a wild hair to electrify the thing. Naturally, it had to be a few percent smaller than the PSS version to match the motors I wanted to use at the time, which gave the 1 in =1 ft scale of this model. After scaling the big one down, construction took little time. I went to a thicker symmetrical airfoil, which was closer to scale, but retained the same sheet-balsa structure.
I planned to test fly this using Speed-280 motors and the 4.7 in Tipsy folding prop combination, with an ail-up weight of less than 20 oz. Instead of the full tubular shaft housings of the real thing, the test model had plywood keels sticking out front on which these motors were mounted. Well, it worked. Granted, I was running these motors on three Lithium Polymer (Li-Poly) cells, but the thing flew pretty well - I even got a roll out of it.
It has two modes of flight - low angle of attack, in which it goes fast and controls just like an aerobatic airplane, and high angle, during which the elevons lose most all roll authority. In this case, at least the elevons work to pitch the model down to fly out of the mush mode.
Feeling successful after this, I finished the model by adding the shaft housings, filling the surfaces and priming, leaving the model ready for paint. I thought to do another test flight at this point, as about 4 oz had been added. What followed was a very long, powered test glide; the model no longer had quite enough thrust to climb. Evidently, the 1-3/8 in diameter shaft housings covered up just enough of the 5 in diameter propellers to compromise the thrust.
At this point, two weeks before the fun fly I hoped to make, I decided to fit two AXI 2212/34 motors in place of the 280s. With some quick telephoning and quicker work, the motors were fitted a week later. I ended up using clunky 3-blade opposite rotation propellers from the gas world. That very day, I got word of new props from Windsor Propeller: 3-blade models available in both rotations. These were in hand about three days later and fitted for a test flight. The propellers produced a nice thrust level, allowing a near-hover on a 3s Li-Poly pack. The first test fight ended quickly due to way too much aileron throw, but repairs and dialing down the throw took only two more days and gave a perfect test flight.
This thing is very exciting to fly! It looks like nothing else and definitely sounds like nothing else. The AXi motors emit a whine that sounds for all the world like a turboprop airplane. That, coupled, with its looks got me going! I took the model to the Fern Prairie Club's Celebration of Silent Flight, put in almost two perfect flights, and won best multi-engined model to boot!
Construction: This model is comprised of two wingtips joined end to end with no wing in the middle. As such, it is all compound curves, so I'm thinking that only more experienced builders will want to build it. Therefore I apologize if I skip over some steps.
The 'wing' is symmetrical and built on a series of shadows as shown under each rib on the plan. These are glued to your flat table as a jig. For all the following, use only contest balsa and Sigment glue. I put a couple of the bottom pieces of sheeting on the shadows, and then pinned down the ribs, One of these bottom pieces near the mid chord should be glued to the ribs to keep the structure rigid after all the top sheeting has been added. Use the sheeting plan to cut approximate shapes for each piece of top planking, working from the center to each edge. Also, observe the grain direction called out, and try to make the planking pieces located near the center of the chord be full-span. The others can be butt-joined along the center rib. When dry, remove the frame from the jig, invert it, and add the rest of the bottom planks. Trim all the edges flush, add the trailing edge stock and the leading edge stock, and sand all to profile..."
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User commentsNice CAD file!
Gene Rock - 15/06/2019
Yes it is, but you'll have the Greens at your door for the amount of rain forest this Flapjack eats :-)
Miguel Morao - 15/06/2019
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