Author: Rich Lopez
Edition: Model Aviation - 2009/05
Page Numbers: 126,127
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Fuel-shutoff ideas from around the world

By Rich Lopez <[email protected]>

I have been writing about the new-for-2009 FAI F2D fuel-shutoff rule in all of my columns this year. As I suspected, the new requirement has unleashed an abundance of ideas from around the world.

Henning Forbech in Denmark continues to add information to his website and has included a "Fact Finding Mission" with a lot of data on line tension. I have not studied it in detail as I write this column. Rafael Unruh of Germany has posted information about his design. Henning has also posted an excellent 3-D interactive drawing of the design. The Italians have ideas worth looking at as well. Make it a point to visit Henning's site to see all of these concepts.

Swing arm

Some of the shutoff ideas came from the AMA .36-powered Fast Combat event. They have already proven effective and have found a new application in the F2D event.

Chuck Rudner designed the swing-arm device many years ago and has continued to refine it. Chuck was responsible for getting the Russians (Aleksandr Gievsky) to produce sufficient quantities to meet the demand of the Fast Combat market some 15 years ago.

Electronic devices

Probably the most exciting ideas involve an electronic transmitter built into a control handle and a receiver in the model.

The basic idea is that a button on the handle activates current flow from the transmitter to the model; as long as there is current, the fuel valve remains open. Each transmitter would carry an identification number for each pilot so there will be no unexpected shutdowns should lines touch or become tangled. Alex Prokofiev has postings that explain the concept in detail.

Sliding bellcrank

Jeff Rein and Bill Huber have been manufacturing the H&R bellcrank shutoffs for many years and have proven that this system works effectively time after time.

These bellcranks were developed for external-control-type models in which the control lines attach directly to the bellcrank. Similar bellcrank shutoffs have been in use for some time. Bobby and Andy Mears had a similar bellcrank shutoff that used an O-ring as the tension creator.

Coiled expansion spring

Pete Athans is thrifty by nature and always looks for the best deal; he developed the idea of attaching a spring to the engine mounts that connects to the leadouts via a line.

A piece of fuel line passes through one of the coils in the spring when it is stretched open by tension on the lines. When there is no tension, the spring pinches the line closed.

I purchased a variety of springs at the local Ace Hardware for about $1.29–$1.39 each. These can be cut in half to yield two shutoffs. The line through the spring can be 20- to 25-pound-test monofilament fishing line. A spool of this at Big 5 Sporting Goods costs roughly $1.99.

It takes some experimentation to find the correct length of line for the right amount of tension. I tried two of these for the first time, and both worked well.

Pete had the original idea, but Don Jensen adapted it to store-bought Eastern European models. Don also devised an arming/starting device consisting of a piece of wire embedded in the top inboard spar at approximately a 45° angle to the inboard; he simply used wire cutters to snip off the extra length.

I prefer to use a straight pin with a ball head, like those you get with a new dress shirt. A mini wood screw would probably also work.

How it works: the full-length spring has a loop at each end. When you cut it in half, bend one or two of the coiled loops to form a perpendicular loop at each end. Tie the fishing line to one loop, and attach the other loop to the engine mounts.

You will need to connect the two leadouts via a 4- to 5-inch length of fishing line. I use a Perfect-brand 1/2A line connector that attaches to the leadout line. The other end connects to the spring.

The line connector must be able to slide on the line between the two leadouts so that controls are not affected when the stabilator moves up or down. The loop of the spring is pulled over the arming/starting pin and held in place by the 45° angle.

It is important that the spring stretches just enough to permit fuel flow when hooked onto the arming/starting pin. The spring loop should pop out of the arming/starting pin when there is full tension on the lines. On one early attempt the loop did not want to pop out; slightly bending the loop angle cured the problem so it popped out effortlessly.

The whole setup weighs close to 4 grams and costs roughly $1.50. The downside is a slightly heavier feel on the lines during landing and the need to be careful.

2008 MACA Top 10

The Miniature Aircraft Combat Association (MACA) began keeping track of contest results in 1974. At that time, the only results counted were those for AMA Fast Combat and Western Associated Modelers (WAM) BC Combat.

The WAM BC class used similar equipment to AMA Fast Combat but with different rules. FAI, 1/2A, Slow, and Speed Limit were not included at that time.

The first MACA number-one pilot was Richard Stubblefield in 1974. He can still boast a Top 10 rating 34 years later. He also won the AMA National Championships that year in Lake Charles, Louisiana.

Current tabulations include all of the aforementioned events. Congratulations to the following pilots (ranked by MACA points):

  1. Roy Glenn
  2. Neil Simpson
  3. Jeff Vader
  4. Phil Cartier
  5. Brian Stas
  6. Louis Lopez
  7. Richard Stubblefield
  8. Brad LaPointe
  9. Dan Reedy
  10. Mark Rudner
  11. Mike Willcox
  12. Glenn Simpson
  13. Greg Hill
  14. Paul Kubek
  15. Ken Burdick
  16. George Cleveland
  17. Alex Prokofiev
  18. Allen Deveuve
  19. Chris Lopez
  20. Dave Fischer

Cyclon Fortune F2D

My testing of this engine has continued but has not yielded the results I was seeking. The piston-to-cylinder fit is a bit too snug, creating excessive effort during starting.

I have lapped one engine twice; it now starts relatively easily. I have managed times down to about 19 seconds per eight laps. The Fortune runs steadily and pulls strongly. It needed head clearance set at .0165" during break-in and is now running at .015". When I removed another .0015" gasket, it started blowing glow plugs. I will keep you posted.

Sources

Transcribed from original scans by AI. Minor OCR errors may remain.