The New F2C Line Rule

19th March, 2004

Update April 2005: This rule change is now definitely reversed!

The actual rule text is not known, but this short briefing has been around:

Two control lines must be used. Each line shall have a minimum thickness measurement of 0.38mm for both stranded & solid wires. Stainless steel solid wires are allowed. Stranded wire must only be 1x7 strand uncoated stainless steel stranded wire. A minus tolerance of 0.011 mm is allowed.


My views:

NOW THE MOST FAR-REACHING F2C RULE CHANGE IN 38 YEARS HAS BEEN TAKEN

(The tank was reduced from 10 to 7 cc in 1967.)

Was this done with the eyes open to the consequences?
To me it seems NOT.

FIRST:

It was done on a proposal, which did not address the significant reduction in performance. One of the authors has even said (in the clracing forum) that there was no intent of reducing the speed.

I find it therefore likely that this quite significant consequence was not discussed as widely as its importance mandates.

I do not mind a proposal stating that speeds have become unmanageable, and that something is needed to tame the event. A line increase taken after carefully considering all the ramifications would be fine with me. But it wasn't done this way.

As it is now, this grave change was sneaked in through the backdoor, the true consequences not declared.

Besides, the argument that solid wire is unsafe in wet conditions is invalid, as a good remedy is found: Applying silicone oil.

 

WELL, THEN, WHAT ARE THE CONSEQUENCES?

PERFORMANCE

My estimate on the change in performance and immediate consequences for the models for a line diameter increase has been on my web site for quite some time:

linedia.html

As the change in line diameter is roughly 75% of the one I assumed, reduce the figures to 75%:

A model doing 10 laps in 17.50 seconds on .30 mm will do it in 18.43 seconds. This is after everything is balanced for the new situation, range kept, and so on.

We will see heat times becoming at least 9 seconds slower. This will be after people have gone down the learning curve with existing equipment, suitably modified. But note the prospects for radical model design changes, mentioned below!

AVAILABILITY

Why in the world specify a line diameter that is no even metric standard?? Why not use the same as for F2A, .40 mm, where sources are established since long??

Wire is standardized in .1 mm increments, with the exception of mainly one country, USA, which uses inch standards. (Some manufacture to inch standards is still going on in some British Commonwealth countries as well.) The smallest wire available to most people of the world in compliance with the new rule is .40 mm. At a 5% line drag disadvantage! The specified dimension falls quite close to .015". An undue favour to the inch countries!

Some manufacturers might offer wire of the specified dimension, but the suitability is totally unproven. The links provided (in the clracing forum) have not shown that a suitable line material is available.

It is incorrect to refer to F2D multi-strand lines (.385 minimum), since the lines of choice for F2D competitors are those that don't break in line tangles, not the ones fastest. The ones in common use are of a diameter of .40 mm or more. Such an oversize is of course unacceptable to a F2C competitor. Further, if the rule mandates stainless, the only F2D line type I know of is the one that (probably) caused the outbreak of flyaway-itis in Sebnitz 2002. :-( I most certainly hope the rule makers didn't refer to this type!!

SAFETY

There is an inherent danger in specifying "stainless" as a material, as this refers to something that is all over the place in tensile strength. While piano wire is quite an even product, stainless varies by a factor of three or more. Only the highest tensile strength grades should be considered for C/L, and a rule mandating "stainless" with no mention of a minimum tensile strength is out in the blue safety-wise.

Although there exists grades of stainless that approach the tensile strength of piano wire, the commercially available stainless C/L wire has about half the strength.

*** SO WIRE TO THE NEW SPECIFICATION IS LIKELY TO BE LESS SAFE THAN .30 MM PIANO WIRE! ***

.30 mm piano wire will withstand at least 147 N = 15 kilogram force = 33 lb. Better check that the new wire isn't worse!

SETTING THE MINIMUM FOR SOLID AND STRANDED LINES THE SAME

Stranded wires will have a smaller lateral cross-section for the same measured diameter, so the drag will be less. Therefore the only option I would seriously look for is 7-strand wire where the individual strands are .125 mm diameter with a guaranteed minimum of .123 mm. Eventually everyone will do the same, so the availability of solid wire is rather uninteresting.
- Know a source for my favoured wire, anyone?

VERIFICATION OF MULTI-STRAND WIRE

I have been a line checking official at one major event, for F2D at the E/CH 1987. It was a crazy task! The only thing that made it possible was that the lines were mostly well oversize. For lines not tin coated, the strands will slide on each other when the micrometer gauge is applied, and they could measure to just about anything, at the choice of the official. Given the well-known fact that teams in recent times have gone far and beyond in getting their lines near the legal minimum, we will see many instances of teams being refused entry due to lines deemed undersize, whether fair or unfair. It would have been better to allow multi-strand lines at a very slight dimensional disadvantage so that those seeking the utmost in line drag would go for the easily verifiable option.

WORLD RECORDS

CIAM failed to address the consequences for the World Record categories for 100 laps and 200 laps. Should the records stand, and the issue be dead until someone finds away to get the nine seconds back, should the existing records be translated, or should the records be scratched and everything started anew?

RAMIFICATIONS FOR MODEL DESIGN

The obvious changes are a move rearward of the line guide and an increased tip weight. However, there is also another issue:

With .30 mm lines, the models have settled on a low aspect ratio, as this is the lightest configuration. This in spite of a larger portion of the lines being exposed than for a high aspect ratio. With .38 mm lines, it is possible that the balance will shift in favour of high aspect ratio designs, as the gain in covering the lines becomes higher. At the same time, competitors will stretch the limits of how much asymmetry can be housed under the "semi-scale" rule. Maybe we'll see 1.5-meter wingspan flying wings! -And our usual D-shaped wings being regarded as out of touch as tailplane models today...

FINALLY

-Maybe I should be grateful that the rule makers didn't specify 2.375 cc maximum engine capacity.

Göran Olsson