Michael, for starters I would use Sig fuel if you can purchase it. I would recommend 25% nitro as I found this to work well for the Cox engines. The Little Satan does very well on a Cox Black Widow if you have one. Its just tricky getting the configuration of the pickup correct on that plane due to the firewall screws being the other way for the backplate. I believe you have to have the fuel pipes vertical on the inboard side while the pickup has to make a quick hard bend to the outboard corner. It would probably be best to place the needle on the inboard side as well. I fly my Cox equipment with lines typically no longer than 35'. I use .008 stainless but use a lot of care if doing so as they will kink and bend. You may find .012 to work better for you if you never had any experience in using the .008 as they're extremely fragile. Most fliers including myself use a braided line used for fishing known as Spectra or a similar line like Spiderwire. These products are not monofilament and they don't stretch but will take a lot of abuse assuming you tie the correct knot.I may be incorrect but I think you want the 35lb test. If I'm wrong maybe someone could respond with the correct pound rating.  Those particular lines are available at tackle and bait shops. The steel lines can be purchased through many vendors such as Brodak, S&S Hobbies etc. If your talking about Cox engines in reference to the .09 vs the .049, Cox only made 2 .09 engines. This was the Medallion and the Tee Dee series. These are considerably larger than the .049. The .09 has a glowplug approx the size of a nickle vs the .049 which is roughly penny sized. Both Medallion and also Tee Dee are beam mount engines as they share the same case. As for your Stuntman, its an excellent flying plane and will fly well with a Babe Bee, Black Widow, Golden Bee. The Black Widow is Black obviously with a larger tank and stunt pipes which enables inverted flight same goes for the Golden Bee. Depending on what era those engines may have been purchased they can be closely matched in power. The Golden Bee though came with a single ported cylinder early on just like the Babe Bee which doesn't deliver as much power as the dual ported cylinders. If you haven't flown these planes or have been away from the hobby for quite some time I would keep your line spacing at your handle to a narrow spacing. If your using a Cox handle try and keep your lines no further apart then 2 inches as this will tame the sensitivity down and keep you from overcontrolling the plane. In addition to your fuel question, its imperative to keep a oil content preferably castor to a level of least 20%. Sig fuels use castor and synthetic which keeps the varnishing down and works very well. The reed type engines can get pretty gummed up if not used for a while and the Sig fuels really help keeping things clean. I would also find some props in the 6x3 range and also 5x3. This may take some experimenting to find the correct prop. Some manufacturers like APc use a large hole in their hubs and this may require a piece of fuel tubing as a makeshift bushing but it will work. I like the APC 5x3 but they can be pricy and will break if in contact with terra firma. Good Luck, Ken

In theory APC has an adapter for their props that fits the Cox engines -- I've heard of it but haven't seen one (instead I had a fun afternoon making my own).

Get a variety of props.  A 6x3 is too much prop for a two-bypass Cox 049; the engine will unload and produce tons more power on a smaller prop.  It's a good prop to tone things down for beginners..  

I'm flying a "stunt-ish" plane on a Golden Bee (two bypass) with an APC 6x2.  The engine turns up as much as a higher pitch, smaller prop, but instead of going blazingly fast the plane accelerates quickly to a steady speed, and performs more smoothly on corners.

If you're a bit of a tight wad you can buy high nitro car or helicopter fuel, then add enough castor to bring the oil content up to 25%.  I only mention this -- you know if you're comfortable with it, and if you have the math skills to calculate the right amount of oil.  Sig products are always good, so if you can get Sig fuel go with it.

First, "Nylon" lines would be too stretchy, especially monofilament ones.  Spiderwire used to be Spectra thread, but isn't anymore (it may still be good, I just don't know).  At the fishing store look for line that has the Spectra logo on the box.  The smallest you can find is more than strong enough.  The stuff tends to slip its knots, so I apply a bit of CA glue to the knot after tying.

Second, Cox fuels had 18% Castor oil, not 22%.  Sport fuel was 15% Nitro and the Racing fuel was 30%.  I currently prefer half and half synthetic and castor fuels.  The castor protects the engine both when running and later from rusting.  22% oil is good, but will cut fuel economy by 4% compared to 18% fuels.  I usually buy Powermaster fuel from Hobby People and add more castor oil to bring it up to 22%.

I agree that 35 ft lines is about right for the two models mentioned, and that the Black Widow is appropriate power.

Forgive my carping about this...  After the clear consensus in favor of Spectra is established, why can't the AMA see the wisdom of allowing it, clearly and in writing, in the CL General rules?  It's abrasion resistant, much easier to handle than steel, very visible if you buy the high vis yellow variety, nonconductive and immune to kinking.  It looks to be about the same magnitude of safety advance as the spread spectrum technology was for radio.  Yet the CL General rules still call out lines of steel music wire construction.  The AMA should be advocating the adoption of new technology top down, not resisting it.  I'd invite all who feel the same way to jawbone this, long and loud, until it becomes SOP.  My humblest apologies for a thread hijack.

Paul - We don't need to outlaw steel lines, just make it so that guys who want to work with the newer technology can do so without fear of losing our all important insurance coverage.  Spectra should be allowed for sport flying in addition to steel lines, not to the exclusion of steel.  Combat allows spectra effective 1/1/2011.  Other events may choose to follow.

They'd be making a BIG mistake to allow fish line of unknown strength to be used in lieu of well-proven STEEL.

If certain types of fish line proved to have some sort of real or mythical competative advantage, the serious contestant would be obligated to use it, regardless of cost and danger.

Better to continue with the time-proven steel lines and compete with genuine building and flying skeels, not trickery with dubious fish line.

Maybe we should out law CA glue, electric power packages, carbon fiber, etc, etc ,etc.  Steel lines have failed pull test - that's way we have pull test.  Besides the rules do not specify a particular steel alloy. For a given diameter could be a big difference. Once again pull test!!!!  If it passes FLY!!!!

    

You can spearmint and sport fly all you want.  Just don't spect AMA to insure you if you violate esstablished rules.

As a CD, how would you pass judgement on some susposedly "equivalent" fish line that a contestant wants to use?   
Once it's off the reel, how do you tell Spider or Spector from any other kite string?