The CIAM is proposing to require engine shutoffs on F2D Combat planes in the event of a flyaway.  Sounds like a good way to kill participation in the event for a few years.  Only a couple of the current shutoffs used in AMA Fast work even fairly well, and they both have other problems.  Unfortunately, the proposed rule changes didn't get into any of the nitty gritty of how to handle all the situations that will occur with shutoffs.  Who times the 2 second run down?  When is the shutoff checked?  How is it checked?  What about a shutoff that will only work in the air, not on the ground?  Yet another way to win by getting your opponent on the ground instead of cutting streamers.

The accompanying report on the 2006 WC's in Valldollid was entertaining.  Apparently initially there were a number of very ugly matches and several flyaways.  Finally, in one, one pilot got too enthusiastic and they stopped the meet to reiterate that "dirty" flying would not be allowed and dq'd the guy from the contest.  It was protested a couple of ways, but stood.  Interestingly, there were 5 other protests that were not explained.  After the dq the flying cleaned up a lot, at least according to the organizers.

Line size doesn't help much.  If the lines get hit by a prop any size line will be cut.  If the lines are in a tangle and one set slides directly across the other set in one spot, it will cut them instantly.  About the only place larger lines seem to help is in a hopeless tangle.  Once the lines are locked up and twisted together the pilots are helpless.  The only thing that controls when the lines break then is the fatigue resistance.  Larger lines help then.

Apparently there were batches of lines in Europe the last couple of years that were unusually fragile and caused a higher number of flyaways.

Now is the  time to contact our FAI rep and tell him the proposed rule is not well thought out or tested, or complete.

I think the two line size changes you mentioned worked because the planes were pushing the strength limit of the lines, at the time.  An 18 oz. Nemesis with a G21 flying 110 mph(fairly realistic setup) is pulling well over 50% of the strength of a set of 015 cables.  Same applied to flying F2D's.  Early 80's folks were hitting over 100 mph with 15 oz. planes.  That puts the line pull at something like 80% of the line strength.  Current F2D's(15oz, .0151 lines, 90 mph) pull slightly over 2/3 of the line strength.  I use 018 7 strand stainless on F2D's.  that puts the breaking strength of the lines over 3 times the line pull.  But according to many reports, 4 strand high tensile .0151 steel wire will is just as strong and will cut the stainless easily.

I've had 021's cut by 018's so fast you couldn't blink.  The lines crossed, we stepped towards each other('cause we were a step apart) and my plane was gone.  Fortunately the shutoff worked just fine.

You can compare this to current fast ships- 110 mph, 23 oz, 018's, where the line pull(~19 lb) is just over half the breaking strength.  Going to 021's puts the line pull well under half the breaking strength, but doesn't do much for cutaways, except in special situations, like I said above.

At least around here, with 018 lines on everything and speed limits of 70-74 mph. any kind of a cutaway has been extremely rare.  Maybe once a year in 30 contests and 600 matches.

I've seen one where the plane started vibrating and fatigued the lines in level flight.  There have been a few between F2D planes, powered by 15's and bigger stuff.  The F2D planes are just to twitchy on 60 ft lines for precision flying.  There was one at Brodak where the leadouts pulled apart.  They passed the pull test and looked alright, but they were improperly crimped and pulled out when the plane went across the circle.