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F2D News Ė 10 February 2004
Mark Rudner
rudner@mit.edu

While it may be hard to believe with all the snow and ice around these parts, the combat season is in full swing in some parts of the world at this very moment. Thatís right, for our friends in the southern hemisphere itís summer right now and that means one thing Ė theyíre getting better while weíre all forgetting how to fly. Do not fret, though, by the time our season is in full swing theyíll be back indoors competing in their other favorite event Ė mouth racing.

This month weíre fortunate to have a real combat legend of the southern hemisphere joining us as the Markís FAI News Foreign Correspondent and Model Trimming Advisor. In case youíre worried about his qualifications, despite his looks (see attached photo), Bryce Gibson is an excellent combat pilot and finished 4th place (see same photo for evidence) at the F2D World Championships in Germany two northern-hemisphere summers ago. Although he sent me all of this in whole (previously written), Iíll try to make it look like I did some work by casting it into interview format.

MR: Hey, long time no see. Thanks for helping us out this month. Why donít you tell the readers a little about yourself.

BG: † I am a Combat god in NZ and Africa, so I feel I can spread the dogma according to Bryce. †Probably 50% of this is wrong but it's what I have garnered in 25 years of combat!

MR: I see, interestingÖ Letís hope itís 50% right then. Last month I was telling them about setting up their models, and promised to talk about trimming them out this month. Do you have any thoughts on that?

BG: Models: trimming.

The first priority is setting the CG on the ground. If the model is one of a series, just set it the same as the previous one you liked. Once you fly it itís time to get the warps out. Are the wings level and the whole TE straight? I used to think that I could just bend the tip until the wing was flat in level flight and that was it.

That was wrong.

Unless the TE is a single straight line from tip to tip with no curves, when the speed changes the model will roll one way or another. Straightening the TE takes longer than bending a tip but gives a better result. However in an emergency if you need to bend the wing on the field without an iron, pull the wing to where you think is right then get someone else to put tape on the wing to hold it in that position.

MR: Ah thatís interesting. Another, slightly more destructive yet nonetheless pretty effective, method for iron-less warp correction is to put a dent in the leading edge with your thumb. For instance, if the outboard wing is hanging down when youíre right side up and tipping up when youíre inverted, you can put a dent in the bottom of the outboard leading edge.

BG: I didn't know that one. The tape can be removed afterward when you are in the luxurious surgically clean workshop. Once the TE is straight then you can start evening up the turn in either direction. Be aware that we often put down or up thrust into the motor when tightening the bearer bolts Note: this means that the engine is actually pointed up or down relative to the wing. This will have a huge effect on turn and wonít be consistent if you change the motor or reinstall it.

MR: How about CG placement for new models? And could you please be more philosophical in your responses?

BG: In all forms of combat you will have better results if you set the CG so you can fly the model without looking at it. I mean deliberately looking around the hemisphere while positioning your own model; you may get out turned but you wonít hit the ground unexpectedly. If you think about it, combat is simply the action of putting a model into the correct position on the hemisphere at the right instant. In spite of peopleís impression of combat as rough and tumble, it is in fact precision flying. If you canít look at where your opponent is heading (because you have to watch your own model the whole time) you are unlikely to put your model in the correct foot of space.

MR: Ah, thanks for using English units.

BG: Again set the cg to where you can fly eyes off then maybe a little further forward for the contest. The more you fly, the further back you can put the CG and still fly eyes off. Another point is that horsepower stabilizes models: the more power you have the further back the CG can go.

MR: Would you say thereís something even more important than turning?

BG: More important than turning in my opinion is line tension. Without Line tension there is no control. I donít like [engine] offset, I feel in repetitive turns it disturbs airflow causing one tip to stall before the other. I also donít like asymmetry for the same reason. At worst just slightly to the outside of straight ahead is plenty. Jari Valo and the Balievs use no offset, of course they have serious horsepower. A model with lots of offset is terrifying if the motor goes off song.

Airtime: +1 point for every second airborne, -1 point for every second not airborne

Another dislike is excess line rake. 2-3 degrees is tons, more means the model bangs on the lines as it slows up. What I do like is tip weight, about 15-20grams (half or 3/4 of an ounce). I sometimes make a hardwood out board tip but still add tip weight to the LE. I have been saying for a few years now that the further forward the tip weight is the better it works. This is incorrect. The nearer to a line extending from the Lead out Guide through the CG to the out board wing the tip weight is, the less yawing effect it has, hence the better and more consistently it works. This point is usually on the front of the Leading edge, I use lead shim and wrap it around the Leading edge and hold it in place with Filament tape. Be aware it does stress the Leading edge in a crash so I ought to think of a better way.

MR: Wow, thatís a lot of tip weight. The hardwood outer tip is a nice touch, but I usually stick with one or two pennies in addition to that. Okay, I think thatís about all the space we have this month. Stay tuned for next months column where weíll discussÖ something else. In the mean time stay warm fly lots of matches in your sleep.


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