General Recommendations


Nelson Plugs - There are two sources for Nelson pugs that I use.  Doug Galbreath at has Nelson heavy duty plugs and other items for Free Flight.  Kitting It Together at  also has the Nelson heavy duty plugs.  For the Cox 049 engines and the Holland Hornet Nelson heads can be economically obtained from Doug Galbreath.  For most other engines I will gladly custom make a Nelson head to fit. I also use Merlin plugs in the Cox TD020 engine.  Please see the Cox 020 Rework Page for specifics on the Merlin plugs.

Plug Torque - Don’t go crazy with the torque you apply to the Nelson plug.  36 in-lb is plenty and do not torque while the engine is hot unless the lift is blowing through.  It is a good idea to get a torque screwdriver and use it for torquing head screws as well as the plugs.  You usually can get a Utica TS-35 Torque screwdriver on ebay for about $50 or less.  Retail is almost $300.00.

Fuel – Please use at least 25% oil in your NOS fuel with ½ of the oil or more being castor.  This is very important for those old sleeve main bearings and iron pistons.  I use about 15% nitro in all my NOS engines except for the few times I fly ½ or ¼ A  events.  With structurally strong engines you can easily push the nitro and many do up to 50% but I still do not recommend that practice.  K&B Green Heads, early Vecos, most NOS legal Foxes, and early Johnsons are not structurally strong.  OS MAX IIIs, later Vecos, the Johnson CS  and the Fox 35 Black Head Combat special and 29X all seem structurally strong.

Bladders –  A really neat bladder is something called “The Little Red Cap”.  It looks like a condom for a Gerbil and provides a pressure level that is lower than that of a pacifier but higher than for a penny balloon.  The lower pressure level makes many of the original needle valve assemblies work just fine and needle adjustment is very easy.   It can be cut off slightly longer than any of the various smaller diameter sections and used for engines from 0.020 to all but the largest engines.  If you mount it externally, where the sun can do it’s thing, you should protect it with a penny balloon.  The Little Red Cap web site is along with a list of retailers.  Cost is extremely reasonable from Rockler Woodworking and through  Rockler’s web site is .  I have been using the this bladder on my test stand for all but the largest engines and they last for months. It was discovered by Dick Covalt and we have been using it for many years with excellent results.  We don’t win more contests but our engines are happy and easier to needle.  I stock a limited supply of the “Little Red Caps” as described on the Commercial Parts page.