Radio Control Pylon Racing

Author: Matt Russell

Edition: Model Aviation - 2008/02
Page Numbers: 148,149

MA's new columnist starts with a review of Pylon basics

WHEN I SAY I race model airplanes as a hobby, I get many different reactions. The majority of the time people say, “Oh, that’s nice.” The more interested ones ask about the airplanes, racecourse, scoring, and so on. I enjoy explaining these things, and I will try to explain some of them now for those of you who are not racers.

We generally compete in three classes in the US today: two classes of Quickie 500 (Q-500), which has its roots in a model designed by Glen Spickler approximately 30 years ago, and Quarter 40 (Q-40), which replaced Formula 1 in the 1990s. All are generally raced on the same triangular course for 10 laps that are 1/4 mile each.

The slower of the Quickie classes is Sport Quickie (AMA event 424), which is the best place for a new racer to start. The rules require a 500-square-inch wing attached to a box cross-section fuselage. You can build your own airplane from scratch if you like, but the Great Planes Viper ARF and the Lanier Predator are so competitive you might as well start with one of those.

The only common failure with these models is the firewall, which isn’t built tough enough at the factory. Without modification the entire firewall pops out with the first hard landing.

A generous fillet of epoxy and milled glass fiber applied to the backside of the firewall where it meets the fuselage sides will remedy this weak spot. You will need to remove the factory-applied glass cloth in this area; it is simply ineffective, particularly on the Viper. I recently used a sharp chisel to remove the factory glass cloth, but a Dremel tool with a small pointed bit will do the job as well.

Make this modification before you fly the model. Repairs made to the broken airplane never seem to hold up well, and it’s much easier to do before you glue on the hatch that covers the fuel tank.

There is currently one approved engine for this event: the Thunder Tiger Pro .40. It runs great, but there are a couple things to do to increase its reliability in preparation for racing.

Back out the idle needle most of the way and glue it in place with cyanoacrylate. This will improve fuel flow and ensure that the engine dies when the throttle is closed, to shut down for landing.
A weak link is the carburetor-barrel retaining screw. When it backs out, the barrel comes loose and the spring behind it can be ingested in the engine, causing great damage. Most people toss the spring and glue the retaining screw in place with cyanoacrylate. Some cyanoacrylate or thread lock carefully applied to the needle-valve assembly where it screws into the carburetor body is not a bad idea either.
The factory rear bearing can occasionally fail, causing considerable internal damage. Boca Bearings sells a replacement for less than $20 that will hold up better than the factory-installed unit. That is some cheap insurance.

The bolt that holds the front and rear halves of the muffler has been impossible to obtain in the past, but it is now available as a replacement part. At operating temperature the aluminum muffler expands more than the steel bolt, which stretches somewhat, allowing the rear half of the muffler to rotate and eventually leak. Tightening the bolt and jam nut at the rear of the muffler solves this problem only temporarily. The bolt will stretch some more, and multiple cycles of stretching and retightening will eventually result in a broken bolt and lost muffler parts.

I have seen various attempts at preventing these problems. One method is to apply a 2-inch length of bicycle inner tube with cable ties over the joint between the front and rear halves; that prevents the loss of parts when the bolt finally gives up. I have seen the muffler halves welded together, but the weld broke after several runs. Replacing the bolt with a length of 4-40 threaded rod and multiple nuts at both the front and rear has worked for some. If you have another fix for this problem, let me know and I will include it here for everyone’s benefit.

Also included in this column:

Tips for getting started
Thunder Tiger Pro .40 tips
The new Profi 6.5cc RC engine
Winter contests not to be missed

Once you get the airplane together, go fly it and trim it out. You will find that the models track well and have no tendency to pitch up with increased speed. With the CG set properly, they will fly on knife edge for quite some time with no need for a rudder input. Now it is time to find someone to race against.

If you do not know anyone who races in your area, a good place to go is one of several pylon racing forums. The National Miniature Pylon Racing Association (NMPRA) is the SIG that provides support to the AMA.

Forums on the NMPRA Web site will help you find races and racers in your area. If you are looking for other online information about racing, check out the sites listed at the end of the column. Dig around in the corners of those sites, and you will find tons of helpful tips.

For those of you who race in the expert Q-500 class (AMA event 428), there is a new engine available: the Profi 6.5cc RC. The same people who manufacture the MB .40 that is used in FAI-class F3D produce this engine, which has some of the same features as the MB .40.

The inner race of the rear bearing is eliminated since the crankshaft has a groove machined in it that serves as the inner race. The crankshaft/bearing assembly is inserted in the case as a single unit. In addition, the crankshaft is bored off-center to help with balance and fuel feed. The piston is domed to provide for better combustion.

At this time the engine has not been used much in competition. It may take some experience to learn how to optimize its performance, but the potential is there.

Jim Booker is importing the 6.5cc, and he claims that its superior-quality materials will prove to be its strength. Tom Strom Sr. operated one of the prototypes at Whidbey Island in Washington this past summer and entered it in the race unofficially to compare with other airplanes. He felt that the engine had great promise; it was the fastest at the meet, flying roughly 1:05.

On the topic of Tom, he bested Travis Flynn’s Q-40 record at the Shelton, Washington, race in August, flying a blistering 57.83 in a heat against Jerrett Cangee, who flew a Bruce DeChastel/Dan Kane Polecat. I witnessed the race, and Tom’s flying was extremely consistent. He backed that up with a win at the North-South Shootout in Medford, Oregon, two weeks later.

I have known Tom for more than 25 years, and he is always the one to beat in our district. He has worked hard and persistently to achieve this goal. Congratulations, Tom!

My daughter and I just returned from the final West Coast points race for the year, which was held in Phoenix, Arizona. On the first day of the race, eight of the 11 Q-40 contestants (I was included and set my personal best time) flew approximately 1:04. This was a tremendously competitive event!

If you have not had the opportunity to attend a Phoenix race, try to schedule it in. The SpeedWorld club can always find volunteers who are willing to man the racecourse, and the electronics that Jim Allen and Hank Kaufman developed are world-class. Jim is a great CD, and he gets everyone organized so things start on time and the races proceed at an amazingly fast pace.

The Winterfest Q-500 race will be held January 19–20 for both slow and expert Quickie, and the Q-40 Classic will be held February 23–24. Last year 70 entrants from more than eight countries competed in Q-40. Check the NMPRA Web site for more information.

When my 14-year-old daughter tells her friends she races model airplanes as a hobby, she gets a slightly different reaction than I do. Most of her classmates think she is a bit of a geek. If having this much fun means being labeled “a bit of a geek,” I guess we will just have to get used to it!

If you have information you would like for me to publish here, contact me. Thanks for your time. I’ll be back in two months. MA