Hello All,
I am sure this has been done to death, but I would like to summarise the knowledge base. I have acquired 3 FP40s that are well used, but still have excellent compression. These are R/C models and they have all been fed on lots of castor. There are two ABN and one iron/steel engine (Ouch for the ABN models!). I have spent some time cleaning the castor crud both internally and externally and they still look good and still have good compression. So I intend to run them as follows.
1/ In profiles with RIGID front ends and some anti foaming agents in the fuel. Haynes type R/C tanks. Uniflow with or without pressure (what works!)
2/ 5% nitro and maybe 25% oil (a mixture of synthetic and castor).
3/ A 3 to 4 inch pitch prop and diameter to suit the model.
4/ Free flow tube muffler (because I don't like tongue mufflers. They are too noisy for me).
5/ Launch rpm to get a suitable airspeed, but probably 10,000 rpm plus, to get the engines closer to their design rpm.
6/ Line length to suit lap time.
7 Venturi ........well the FP20 venturi with OS needle valve and the FP40 venturi with ST needle valve have about the same free area. The FP40 with OS needle valve gives much more free area.
8/ Possibly one more head shim or maybe two depending on how they run.
9/ I intend to use them in a fast 2 cycle mode, 4-2-4 operation seems to be asking for trouble, which I can well do without!
There seems some conflicting advice about venturis, some say a large area is required , presumably to increase fuel / oil flow and hence promote cooling. The other school says small free area venturi to restrict fuel flow and hence throttle the engine back. So here we have a conflict, both ideas have virtue, but can they both be correct?
The dreaded FP40 runaway is generally ascribed to thermal runaway and this seems reasonable, hence the profile idea with everything hanging in the breeze, to promote cooling! Maybe even use high temp paint to increase the radiative transfer of heat (every little helps!)
One thing that puzzles me about the very real runaway problem is the following. I have seen plenty of R/C FP40s in action. If you do some violent maneuver on say 2/3rds throttle, then I have never seen one runaway, must be a lesson there, although I can't figure it out, unless you use the R/C carb for Stunt with it wired 2/3rds open!!! Don't laugh, no one has been able to tell me why it doesn't run away, in conditions that are very close to C/L maneuvers.
The engines only cost me a few bucks and I can always use them on the dark side if they don't work for C/L. Any comments would be welcome before I go down this well trodden route. Some people seem to have cracked it. The Philly fliers use stock engines and the larger area carb yet others have done it with the FP 20 carb! Comments Please?
Regards,
Andrew.