I am not sure how many of you use or have used this little engine for combat, but I had to comment on it's surprising power and durability so far.

   Dan Banjock and myself bought foam F2D wings from Phil C. at a GSCB swap meet a year or two ago. We both had good FP .15's so we decided to use them not knowing how well they would pull a 500sq" + wing.

   Our first flights/match was with a stock FP .15, .230 venturi, stock needle/spray bar, bladder pressure, 35% nitro and a Master Airscrew 7x4. The performance was good and fun to fly, but it didn't have what we were looking for. Were pro's at this remember (more on that later).

   In search of more power we removed the stock needle valve and venturi and replaced it with a ~.285 insert. The only reason for the insert is to push a piece a surgical tubing onto to prevent dirt getting in the engine in an event of a crash.

   To needle the engine we used a R/C style needle valve mounted behind the engine. This prevents broken needles, and lets the engine breath better.

   The flight results were so good (didn't sound to bad either ) we had to throw a tach on it. The FP .15, .285 intake, rear mounted needle, 35% nitro, bladder pressure, and MA 7x4 turned 20,400RPM!!!  Both Dan and I were surprised of the power they are making. We aren't sure how long they will last at this level, but we sure will enjoy it.

   As for the pro comment earlier, we have since backed off to 10% nitro to keep them in the air . Even though the performance won't touch a true F2D setup we have flown VERY little combat in the past few years and for some reason the circle gets very crowded very quickly . So much for MORE power........... lol

Mike         

Way to go Mike.  Now take the next step put in a Nelson plug head, jack the sleeve up 20 thou or so, adjust the head clearance, and open the crank up to ~200 degrees of intake duration, closing at 55 deg. or so.  That ought to get it up to 22,000 rpm or so.

For a benchmark, a typical F2D motor turns a 6.4/3.5 in. fiberglass prop around 28,000 rpm on the ground, on 10% nitro.

Not too surprising.. The Indonesians were using LA .15s for Combat, they were getting maybe 3.2-3.3 second laps. I've been doing the same except with the cheap ASP .15s (trying to shoot for the 3.2 second/lap Antipodean Speed Limit). You could probably pick up a little more speed by trying different props - most of the .15s we used back in the early 80s (ST G15s, ST X15, Rossi .15, Fox .15s, etc.) liked the 7x4 props cut down somewhat (6.5 usually). Never tached one back then, I wish I had now. A 500 sq. in. wing sounds too big, but should still work.

Good points Phil. I agree about the crashes. 

Mike

Nelson, Turbo, and "glo-bee" type work because the plug threads aren't exposed to the combustion chamber.  No pressure leak up the threads.

Assuming you have a lathe, IMO the easiest way to adapt a Nelson to any engine is to use the blanks made by Henry.  They have the plug recess cut, the combustion chamber needs to be cut and the rest of the head or button arrangement turned.  Along with the blanks he sells a steel lathe mandrel to hold the blank.

Hi Don,

Yes I do have a lathe, I was planing to do the whole lot from scratch as thats part of the fun.

Stephen

I have not done any nelson heads lately, but they are no big deal to do on a lathe. Set the compound rest at the proper angle, center, drill through hole, bore the body hole to proper depth, while on the final pass crank the compound to form the seat angle.   I stick the tap into the tailstock and turn the chuck by hand to get the threads. I then screw a dead plug into the head blank to use as something to grip with when I do the combustion chamber side of the head. Most of the time I use a ball end mill for the combustion chamber. After I face off the head to get the plug depth, I use the ball end mill for the cumbustion chamber. The dead plug is sacrifical as I try to get a feather edge to the glow plug hole, and the mill goes into the plug.  I don't have any numbers on hand,  I am sure I have them on a card or drawing someplace.

All this being said, I don't think making a nelson type head is worth the effort for a sport type engine.