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F2D News – 8 April 2004
Mark Rudner

As promised, this month I’ll be doing a Q&A column in which I answer your questions about F2D combat. I didn’t get quite as good of a response on my call for questions as I would have liked, but there’s plenty of material for this column. Hopefully this will get the ball rolling and inspire more people to write in for future columns.

Q: Will helmets be required at the F2D combat events in New England?

A: Yes. Helmets are safety devices required explicitly by the FAI Sporting Code for F2D. Although we hope that everyone exercises good safety practices to minimize exposure to risk of being hit by a model, to be as safe as possible it is important for everyone directly involved a match to have the proper protective gear. As a result, all pilots and mechanics will be required to wear helmets while their match is in progress, as specified in the Sporting code.

Wearing a helmet is not a big deal, and there are plenty of options readily available to you. The rules do not specify any requirements about material, size, etc. The only requirement is that your helmet must have working chinstrap, and it must be fastened under your chin at all times during the match. Common types of helmets used by combat pilots are bicycle helmets, hockey helmets, and skateboarding helmets. If you go to look for a helmet for yourself, features you should consider are weight, breath-ability (will you be burning up in the summer months?), and shape. A helmet with a bill such as a baseball batter’s helmet may not be the best choice, as the bill could get in the way of your vision or your opponent’s lines.

Q: My Fora 0.15s came with a music wire contraption that held the pipe in place - I would believe these things are necessary - I would also believe the Cyclon needs something similar - If all this is true, what is the easiest accepted approach?

A: For those of you who don’t know what this reader is talking about, FAI combat engines are required to have mufflers, with dimensions constrained by the Sporting Code. Each engine maker has his own ideas about muffler shape and how the muffler should attach to the exhaust stack of the engine. One thing all of these engines have in common, however, is that the intrinsic muffler-attaching system of the engine is far from failsafe when subjected to the high forces of flying (and crashing). To ensure that the muffler does not pop off at a bad time, it is wise to use a supplementary restraint system.

A simple (but not necessarily the safest) way to improve the chances that your muffler will not try to imitate a Saturn-V is to bind or tie it to the engine with some twine. To do this, you can wrap the twine around the muffler’s outlet, loop it up and around the cooling fins of the engine, back around the outlet, and back around the engine a few times. If you decide to try this method, it’s important to have good tension in the twine at all times so that it is in fact applying a force to the muffler, pushing it onto the engine at all times. Note that the heat of the engine may damage the twine and cause it to fail eventually, so this method is good for a quick fix in a jam but isn’t necessarily a permanent solution. If replaced frequently, however, it may be sufficient.

Alternatively, you may fit your models with a more permanent muffler restraint device (muffler hook). As mentioned in the question, this device is usually made of music wire (0.0625” or 0.078”). In the drawing below, I have depicted a typical design for this device. The hook attaches to the model via the forward-most bolt that attaches the engine mounts to the model. From there, the wire extends straight back towards the rear of the model until becoming roughly aligned with the back of the muffler. Here there is a 90o bend towards the outboard so that the wire follows a line approximately parallel to the spar (but possibly tilted forward a bit). After passing under the muffler outlet, the wire loops up and back around the outlet. The exact shape of each hook must be custom bent in-situ to match your model-engine combination. The main point is to have a good tight fit so that the hook does its job of holding the muffler in place. It is good if the hook is actually bent forward a bit to apply firm pressure on the muffler when the engine is in place on the model. As always when bending wire devices that will be subject to high stresses and vibrational loads, be careful not to make any sharp bends or nicks in the wire; such places will become stress concentration points and lead to early failure of the part.

Q: Mark, why do you have so much time to write these columns for NECN? Shouldn’t you be doing your homework or something?

A: Ummm… no comment. NEXT!?

Q: In a line tangle/crash, do you just leave the mess and get the next plane up and going to continue till time runs out, or do you try to un-twist the mess?

A: Good question. If you get in a line tangle or a mid-air and both models come down, you may not do anything else until you have cleared the tangle completely. This means that no piece of your lines/model may be left lying on or across your opponent’s lines/model. If you leave your lines tangled up with his and try to take off with your spare, you will be disqualified. Also, be sure not to leave anything inside the pilot’s circle, as this is both illegal and a safety hazard.

Your mechanics are also responsible for making sure that your downed model is pulled all the way outside of the 20 m pitting circle. They may not work on the model before it is completely outside this line, and you may not take off with the spare if any part of the crashed model is lying over the line (no matter how it got there, i.e. even if someone trips over the lines and pulls it back into the circle).

As an additional note, I should mention that you also need to be careful not to set your crashed model’s lines on top of your opponent’s spare lines. Remember that each of you has two sets of lines running through the grass. If you set your first set down across your opponent’s spares, you will prevent him from being able to launch his spare which is clearly unfair conduct and forbidden by the rules.

These were all good questions, and I hope that they have answered some concerns for more than just those individuals who asked them. If you have other questions, please don’t hesitate to contact me so that I can address them in future columns. Happy flying!

If you have any questions or comments, please email Mark at rudner@mit.edu