A New "Slow" Combat Class (for Australia) ?

The international combat class, F2D, is very fast, intensive, expensive, complex. It is not at all suitable for beginners, nor for more relaxed combat. In Australia, there are some competing combat classes which attempt to cover the more casual "slow"/social/beginner's combat. None of these are official MAAA events, but one form is generally selected as an event at the MAAA Nationals. However, each has its own disadvantages (as I see it):

• NSW rules "Slow" combat - F2D rules, but with models that must "resemble a real aeroplane". The vague definition causes some problems, but most interpret it as needing a fuselage. One model per bout. Must have plain bearing engines, hard tanks, restricted propellors.

  • cannot buy mass-produced models commercially
  • line tension is a major problem in the wind if engine is not strong (common with hard tanks).
  • fuel supply can be a bit unpredictable with hard tanks
  • fuselage-based design + weight makes the model prone to damage in midair collisions and ground hits.

• Vintage combat (flown most frequently in Victoria and Western Australia?) - Roughly F2D rules, but with models (or at least plan outlines) restricted to pre-1970 designs, including no use of carbon-fibre etc. One model per bout. Must use hard tanks; no bladders. Must use pre-1970 engines, or modern plain bearing engines (diesel or glow).

  • cannot buy mass-produced models commercially
  • fuel supply can be a bit unpredictable with hard tanks
  • diesel engines restart well (and are suited to this type of combat) but fuel is difficult to get
  • line tension is a major problem in the wind if engine is not strong (common with hard tanks).
  • vintage construction techniques makes the model prone to damage in midair collisions and ground hits.

But, do we really want yet another class? Certainly not if it needs a whole new bunch of equipment. But if it used equipment that many of us already have ...

What do we want?

1. Models are slow enough to have less intense and more social style of combat, that might encourage people to compete more often on normal weekend flying days (outside of competitions).

2. Models are not so fast, such that midair collisions and line tangles are reduced --> reduce costs, lengthen combat time.

3. Models are of strong design so that they survive the (slow) ground hits and mid-air collisions very well --> reduce costs, maximise chance of relaunch.

4. Models are slow enough, engines less powerful and propellors softer (nylon?) for increased safety for beginners (pitting) and spectators (less fly aways, less need for nets and engine shut-offs).
5. Reduce the number of models required to enter a competition (1 model per bout).
6. Models fly well (good aerofoil, weight, stiffness) so that graduating to F2D is not a huge change in the experience.
7. Beginners can participate and not feel like they are "out of their depth" or wasting their time.
8. Have as much as possible, similar equipment and techniques as F2D to reduce costs and make transition to F2D easier for beginners.
9. Maximise use of commercially available models and equipment (for those who don't want to build).
10. Have designs and rules that create a reasonably level playing field for all competitors, so that lots of money and expensive gear doesn't give a competitor too much advantage.
11. Use equipment which maximises the reliability of the models and engine run consistency so that lots of experience is not needed to be competitive (e.g. hard tanks are hard to tune on-ground vs in-air, get leaner towards the end, get bubbles towards end of tank).
12. Have rules which inherently allow other "slow" class model types to compete without signficant modification.

What class/rules can satisfy this?

Well, New Zealand's National Combat Rules look like they fit really well. These rules essentially describe a Speed-Limit F2D class, consisting of F2D rules with the exceptions of:

• no engine restrictions (mufflers to suit flying site)
• speed limit imposed (min 3.5 sec/lap (~103 kph) with streamer, 3.3 sec/lap without)
• one model per bout (2 per competition, a third may be used in the final)

Some points in favour:

• ANY engine can be used, but powerful engines will have to be crippled in some way to conform to the speed limit. Cheap 2.5cc engines (plain bearing) should be able to reach the speed limit and so are at no disadvantage (in fact they are generally a little lighter). Cheap ball-race engines probably won't be more powerful but may last longer. Flexible props should also pose no disadvantage to performance.
• Typically, commercial F2D models are used. Commercial F2D models are very well designed and can sometimes survive ground hits at F2D speeds (up to 160 kph). Using these models at the specified speed-limit (65% of F2D speed, 45% of the F2D impact energy), these models are even more hardy and can survive up to 20 ground hits with minor repairs each time.
• Most equipment is compatible with F2D (planes, lines, bladders, fuel-line clips, etc.), but special mounts are generally required for plain bearing engine. These can be easily made up from commercial aluminium 10mm U-extrusion (from the hardware shop) or are available from NZ.
• The imposed speed limit makes sure that fancy engines or "tune-ups" don't change the character of the event.
• Use of bladders generally gives a better and more consistent engine run compared to hard tanks (which are still allowed), which makes for well-matched (level playing field) combat. Sometimes the needle-valve adjustment will be a lot more sensitive, but is still manageable. If this becomes a nuisance, restrictors in the fuel line can reduce the sensitivity. A competitor can choose a hard tank if they wish, but potentially losing fuel feed performance and not being able to use an F2D plane as-is.
• For those who fly F2D as well, repaired F2D models would be perfect for this class. They would be very cheap "hand-me-downs" and slight imperfections or extra weight from the repairs won't be noticed at the slower speed.
• All existing "slow" combat classes (NSW Slow, Vintage) qualify for these rules also, provided the speed-limit is observed. This means no-one would have to change model types to compete with these new rules. However, without some testing, it won't be clear whether NSW Slow and Vintage diesel-powered models will be able to reach the speed limit (although diesels have the compensating advantage of quick hot-restarts).

Some points against:

• Need to do some testing on a completed model to get the speed right, before a competition.

How does this go against our criteria?

There might be an argument to drop the speed limit rule and replace it with a plain-bearing engine rule. However, this removes the "level playing field" aspect of the rules (some engines and models will be much faster than others). Since NZ have imposed speed limits and kept them over a number of years, this element seems to have a good purpose. Also, having a speed limit is a good argument against the need for engine shut-offs in this class, because there is a guarantee of maximum model speed. Uniformity adds the potential of international competitions (at least with NZ) in this class. We won't be reinventing the wheel in that it is an already tried and tested competition format. I don't think we should reject something like this, just because its "not made in Australia".

Tips on this NZ Class from Bryce Gibson (NOCLASS MAC)

• NZ premade engine mounts available from Glen Lewis glenn@noclassmac.com

• ASP (or SC) 15 engines are popular in NZ (ball race engine, $40 USD from http://www.himodel.com/sort.php?brand=4&sub1=BS)

• We do permit a third model to be used for finals, that is to avoid any possibility of a fly over final.
• For speed adjustment, we just add flutter strips of self adhesive tape to the out board wing. 2" wide by about 6-8 in long adds 1 sec/10. Mixing Venturi's and Props also works. Adding the muffler takes it to 32.5, or the 4mm and a 7/4 and muffler is 33, 4mm, 7/4 open exhaust needs 2 bits of tape. Generally if both guys are pretty even we don't actually clock speeds.

Other Notes

• Tests of two different (slightly imperfect) F2D models with two different types of nylon prop on two different Norvel 15BB engines both gave 3.0 sec/lap without a streamer. So 3.3 sec without a streamer appears easily achievable with F2D models and cheap engines.

References

• NZ Combat Rules Page contains an extract of the important bits of the NZ National combat rules (as at Oct 2007)

• http://nzmaa.org.nz/rules/S03-CL.pdf - full NZ Control-line rules