Top Turkey (oz7559)
About this Plan
Top Turkey. Radio control sport racer model.
Quote: "I have been participating in Sport 40 pylon racing for around two years now. I started with a Cotswold Kits Midget Mustang powered by a Super Tigre 40 which, despite the fact that it was horribly heavy (over five and a half pounds) and underpowered by today's standards, got me a fourth place at one poorly attended meeting. I moved from that to a Malina designed FAI racer, a P51 Mustang Miss RJ (oz5965) which was much quicker, and when powered by a Rossi was fast enough to be reasonably competitive. It required significant right rudder during take off and all the way down the first straight or it would jump off the ground and roll straight on its back. During flight it needed constant adjustments to stay straight which didn't leave me enough concentration to fly a good course. The best time I ever managed with the Miss RJ was 2 minutes dead. That's 2:00.00 on the stopwatch, not 2 minutes - crunch!
At the Sport 40 AGM, I voted with the majority to restrict designs to Formula 1 aircraft that had actually raced. This is an attempt to maintain the scale element and not to follow FAI pylon racing where anything goes. Although the rule changes do not come into force until the 1991 season, I reckoned it was time to start developing a new design whilst I could still use the Mustang as backup.
I chose the Top Turkey design from a number of three views to which I had access for the following reasons: The cheek cowls are in line with the wing, which minimises the frontal areas and hopefully the drag. The tailplane is slightly forward of the rear of the fuselage making it easy to install an internal linkage. It's reasonably pretty.
Top Turkey is a variant on a Shoestring to which this design could easily be converted if required, the only significant differences being in the wing, tailplane and rudder outlines. The design is almost scale in proportions, although the wing span is slightly larger to meet the minimum surface area requirements of Sport 40. The aileron position is further inboard than scale to keep the torque rods reasonably short. I didn't bother with spats because of the normally rough ground we fly off and the difficulty I have in making elegant arrivals. The other liberty taken, purely for constructional convenience (laziness), is that the rear canopy fairing should extend back another inch or so.
The prototype was completed and tested just in time for the winter meeting at HMS Daedulus on January 21st this year. On its first competitive flight I put in a blistering (for me) 1:49 with my two other heats well under two minutes. Fastest time of the day was 1:46 so I was more than happy with this performance. I was just squeezed out of the final, coming fifth. At the Yorkshire speed weekend in May, I put in .a 1:42 on an admittedly short course but messed up the semi final and had to be satisfied with sixth. I can only attribute the substantial improvement in my times to the design itself.
The engine and radio gear were taken from the Miss RI which was only slightly overweight so what else could it be? It's so much easier to fly than the Mustang that I wish I'd changed to my own design sooner. I have no doubt that in the hands of a better pilot the model is capable of an eight to ten second improvement. In the straight it is as fast as anything else and it will turn very tightly at the number one pylon without great loss of speed. So having established that the design is competitive, how do you build one?
Construction: The main aim is to get as close as possible to the 4 lb 8 oz minimum weight requirement without sacrificing strength. I did it by only using the lightest balsa I could find from three different model shops in the area. All the balsa used in the design should be the lightest you can find, the strength is gained from glass skinning. I believe this is a better construction method than using a glass fuselage as it can be made both lighter and stronger. Also, if you do break it, it's easier to repair. Since a Rossi .40 weighs a hefty 1 lb 3 oz, radio gear about 8 oz, pushrods, servo trays, engine mount, etc 5 oz, the completed, painted airframe needs to weigh just 2 lb 8 oz. Mine came out at 1 lb 5oz for the fuselage and tail and 1 lb 3 oz for the wings, spot on!
Perhaps the most important thing to watch weightwise is the glass skinning. I have seen articles in magazines advocating slapping on resin and placing inside a vacuum bag and the use of rollers to squeeze out excess resin. If you put enough resin on for either of these methods you will probably be overweight. I follow the instructions given by Barry Lever with his excellent System 2000 epoxy resin. This is a little thinner than SP113 so spreads better.
The fuselage: Cut the sides from 4 in wide 1/4 in balsa as indicated. The waste from the underside just does as the extra needed on the top. Cut out the main formers F3 and F5 and make up F4 from 1/4 x 1/2 in strip. Drill F3 for the throttle linkage. Cyano F3, F4 and F5 to one side at 90° and then glue on the other side. Cut out F2 and epoxy in place. Reinforce the F2 joint with 1/2 in triangular balsa. Sand or file the insides of the fuselage Sides at the back to make a parallel area for the rear joint and pull in and cyano the tail end. I find the easiest way to do this is to hold the back end together either side of a flat file and give it a few strokes.
At this stage, bolt the engine to an aluminium mount and work out how to position it on F2. For the Rossi, I found that for the silencer to clear the fuselage, I had to file a groove in the fuselage side and mount the engine not quite horizontal. This is indicated on the plan and is only noticeable on close inspection. Whilst F2 is clear of obstructions, drill the holes for fuel tubes and throttle linkage..."
Quote: "Hi Steve! Here is a Sport .40 pylon racer plan from Radio Modeller. Regular Competition Winner in the 1990 season. Thanks for your great job! Giovanni"
Update 23/05/2016: article pages, text & pics added, thanks to RFJ.
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Article pages, text & pics.
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