[Somewhat edited]


Proposed alteration or addition:

Disallow use of solid control lines and re-define the multi-stranded lines to be used.

Sporting Code
4c4F2C4.3.5. b59

Remove: All of existing sub paragraph b) and replace with the following:

b) It is compulsory for models to fly clockwise and to be equipped with two multi-strand steel control cables, each constructed with a minimum of 3 wire strands all of circular cross section and of equal diameter, each resulting multi-strand cable to be coated overall with solder ("tinned"), or other coating material to bind the 3 strands together. The minimum thickness of each cable shall be not less than 0.380mm, as measured with a micrometer equipped with measuring surfaces ("anvil" and "spindle") of at least 5 mm diameter. Before every race a pull test shall be applied to the assembled control lines and model, and this shall equal 30 (Thirty) times the weight of the model in flying order, up to a maximum pull of 14 KGf. The control handle must be built so that the distance between the axis of the handle and the points of flexibility of the two control cables does not exceed 40mm.

Suggested date of setting in force: 1stJanuary 2001

Reason: SAFETY: The present solid control lines used in F2C have a tendency to "bind", especially during wet weather. In addition, solid lines are more "elastic" than multi-stranded cables. Both of these characteristics are potential safety hazards, and a number of accidents to models have already occurred which are attributable at least in part to the undesirable characteristics of solid lines. Although the present specification does also allow for the use of multi-stranded cables instead of solid lines, the present specification for multi-stranded cables imposes a penalty on competitors using them (increased drag/reduced speed potential), resulting in all competitors being forced to use solid lines if they are to remain competitive. The removal of solid lines from the present specification will remove this problem and will also offer a number of other highly desirable side effects - see Annexes attached.

Annexes:1. Report of practical trials of F2C models equipped as above, conducted on 17th October 1999 to evaluate flight and ground-handling characteristics. 2. Results of independent analysis conducted on 19th October 1999 to confirm cable strength and elasticity ("stretch") characteristics.


Results of practical trials held to assess effects on typical F2C model handling and speed
(plus cost and availability details)

  1. Flight Tests - 17/Oct/99, 15.00, "Schwalbennest", near Basel, SUI.
  2. Weather - 11 degrees Centigrade, sunny, generally breezy, some gusting (up to approx 15 Km/h in open countryside, but virtually nil wind experienced at site itself - for those not familiar with the site, it's well sheltered from wind from virtually all directions, being set into a "bowl" of steep, mostly thickly-wooded hills).
  3. Conditions - 2 x "standard" flying-wing type F2C models were flown, one of which placed 1st at the 1999 SUI C/L Nats (best heat 3:26.7 Giger/Studer), the other placed 3rd (best heat 3:31.8 Mueller/Saccavino V.). Both powered by CB (Zuriyev) motors. 1st model weighs 340 grams, 2nd model 320 gr. Throughout all, repeat all tests, both models were flown with their present "standard" race props, "standard" race fuels, and without additional tip weight (repeat, no prop changes, no extra tip weight added).
  4. Results 1 - Models were set up to run at their normal racing speeds and ranges (18.0/10, 33 to 36 laps) on present F2C standard spec lines (single wire, "solids"). These results were verified several times. Same models were flown on PAW "Staystrate" multistrand (3 strand) "tinned" lines of same length, 0.4mm diameter nominal (see 8 below). Results were that lap times increased by between 0.4 seconds over 10 laps and 0.6 seconds over 10 laps, and range was unchanged throughout (again, times & ranges were verified several times with these lines). Speeds were not timed with models flown in an F2A-type pylon.
  5. Results 2 - "Slow" take offs (motor badly set), slow/long landings (half lap & more ground rolls), one and a half laps whipping with motor cut, and take offs and landings from different segments were all specifically tried - but see comment re wind in 1. above. Result was that pilots reported nil adverse effects, but experienced improved, more positive/less "spongy" control response with the "Staystrate" lines compared to solid lines (present F2C spec), e.g. when operating shut off; e.g. possibly slightly less anticipation needed in preparation for overtaking. No deterioration with model on-ground performance was seen, or felt by the pilots; nor was any less-than-usual acceleration off the ground felt by either pilot (from both normal speed and slow speed take offs).
  6. Results 3 - Bearing in mind the above comments about improved controllability, plus other information received prior to the test which suggested that 7 strand lines have had stretching/unravelling/thinning problems in UK GY experience, a check of the oldest set of lines available for the unofficial STR class was also made (also made up from PAW "Staystrate"). These are now about one and a half years in frequent use. Further information - STR means an approx 440 gr model, but only running at speeds of about 23 seconds for 10 laps at best, often rather slower! As far as could be measured there was no diameter change on those lines from when they were originally made up, and there appeared to be no permanent stretching (increase in line length). The F2C "Staystrate" lines used on the above 17/Oct flight tests were also checked both before and after flying. Using a standard metric micrometer (6mm diameter spindle and anvil) at time of delivery, and a vernier calliper on site on 17/Oct, the line diameter measured exactly 0.4mm (i.e. no change before and after flying), and the length of both sets of lines also remained unchanged (as per FAI F2C spec).
  7. Results 4 - The pilot's comments about less "springiness" than the present FAI solid (single wire) lines then prompted a check of line length on both solid and "Staystrate" line types with a constant 10KG pull load applied. Both sets of the "Staystrate" 3 strand lines used for the F2C flight tests expanded in length by exactly 20mm, but the solid lines used in the F2C flight tests expanded by 30mm in length. These measurements were verified several times. All lines returned to the correct FAI length as soon as the 10KG load was removed. This prompted the use of the independent Test House, the results of which are detailed on the last page of this Annex.
  8. Availability & quality - Paul Eifflander of Progress Aero Works Ltd (PAW) in UK was contacted per phone and confirmed on 18/Oct that adequate supplies of "Staystrate" are readily available. Our own experience was that an order placed by phone quoting a credit card number on a Monday afternoon resulted in postal delivery of the reel in SUI the following Thursday morning. Paul added some further info - PAW produce "Staystrate" C/L lines from bought-in wire which they then twist and tin (with solder) themselves in-house at PAW. The bought-in wire has an ISO/BSI number. "Staystrate" is exactly 0.015 inches (0.385 mm) in diameter but although they have no records to confirm, Paul suspects that some small variations (increases) in finished diameter do occur during manufacturing.
  9. PAW contact details - Tel/fax: (+44) 1625 423 891
  10. Website: [ ]


  11. Costs - PAW pack "Staystrate" in 30 metre, 50 metre, and 100 metre reels, present costs are UK Pounds Sterling 6.25, 8.75, and 16.25 respectively, all prices excluding UK VAT and postage. It is stressed that neither I (Andy Sweetland) nor any member of Modelfluggruppe Breitenbach has any connection with PAW other than as satisfied customer. The 1 x 100M reel of "Staystrate" used in the above tests was bought direct from PAW approx 2 weeks before the flight tests at the above price and no one at PAW was advised of the purpose of the purchase at the time of ordering or until the above 18/Oct telecon. "Staystrate" was used for this test simply because it was "known to be available" and MF Breitenbach does not wish to promote any particular manufacturer’s product.
  12. Conclusions:- SUI finds that a rule change requiring the current F2C line specification to be changed to 0.385mm "tinned" multistrand (3 strand minimum, minimum cross-sectional area) offers several valuable safety benefits plus advantages to juries, officials, competitors, and to the overall future well-being and longevity of this particular FAI competition class.
  13. Reasoning: Primarily, the adoption of this rule revision will enhance safety - improved control response, especially under humid/wet weather race conditions when compared to the single strand (solid) lines currently used in F2C. Further, "tinned" multistrand lines also appear to offer reduced "stretching", improved damage and corrosion resistance during use, handling, and storage when compared to today’s solid wire lines. But to slow down F2C somewhat is also seen as beneficial and not detrimental to this class or to the sport in general, provided that the method chosen is universally applicable to all competitors - which does apply with this particular proposal. Juries, race officials, and competitors are all seen as benefiting positively from some degree of speed reduction, because this will result in a reduction of the considerable mental and physical fitness demands on all concerned by the competitive F2C models of today.

A.E. Sweetland

F2 Team Manager, Switzerland

Member, Modellfluggruppe Breitenbach.

Zürich, 19th October 1999



Independent Test Results - tests performed in Switzerland, 19th October 1999.

Parameters Table:


Roman Müller

Force measurement:

5,000 Newtons (N)


Daniel Lüscher

Stretch measurement:

"Multisens" (multi-test system)


3 strand steel wire, d = 0.385mm 1


10, 000 Newtons (N)

Test standard:


Test type:

Tensile ("Pull/stretch")

1 Note re above diameter - this was as marked on the packaging as received from the manufacturer and was NOT checked during this series of tests. Subsequent measurements at many points on a sample of approx 0.5 metres length with a metric micrometer with spindle and anvil (measuring surfaces) both of 6.5mm diameter showed diameters varying in the range 0.41 to 0.42 mm.




Rp 0.1
(extension limit at 0.1% stretch

Rp 0.2
(as Rp 0.1, but at 0.2% stretch

(tensile strength)

Ag (%)
(stretch at max tension)

A (%)
(stretch at breaking point

SO (mm2)
(cross section at start)









































[graphs omitted here]