What is the target RPM for a Fox 35 and a OS 40 FP (Tower 40) for control line flying? Thanks, Tim

What RPM range do you look for when you adjust the needle valve using a digital tach before you launch? Fox is on a Ringmaster with a 10x6 prop and the Tower 40 is on a Twister with a 10x5 prop ( for now). Tim

     On the Ringmaster/fox.35, look for 8500 or so. You may be happier with a 10-5. The Tower .40 will be in the 9000 to 9500 range. It's all trial and error. You are just using the tach as a reference, so don't get hung up on numbers. If a certain number on the ground runs like you like it in the air, and does that consistently, that is what you are looking for. This is affected by plug and fuel, so stay consistent there also. Air temp can affect also.
   Good luck and have fun,
    Dan McEntee

Thanks Dan. That is close to what Bootlegger and I were doing today. I was just checking. I am really liking the digital tach but understand it is for reference. I will be glad when my ears have a little more experience. Tim

   Fox with a 10-6, set it so it is just at the richest possible 2-stroke on the ground, one click past the point that it cycles back and forth between 4 and 2. When you take off, it should fall into a fast 4. Once you get that to happen consistently, and the speed inflight is good,  measure the rpm and use that as a reference.

     Brett

  Now is the point in time to start measuring other things also. Start with your run time, so you can get consistent with fuel load and repeatable flight times. This is necessary for contest flying, but just plain handy for not running out of gas in the middle of an over head 8! Keep track of run time with a wrist watch or some one else with their watch. I time every flight I make, even just fun flights. Next is lap times. Just keep track of them for now as you find that sweet spot for the needle setting where the engine is performing like you think it should. If the engine run is awesome but lap times are too fast and you have trouble keeping up with the airplane, it's time for longer lines.Experience over time will help you pick a line length that is close to what you want.  A prop change may yield some acceptable results, but don't do that at the expense of good line tension everywhere, or by slowing the engine down too much. If you are already in the ball park for trim, fly the airplane a lot after each change, even small ones, to be sure you like it or dislike it. Make one change at a time. If it doesn't work, put things back where they were and re-evaluate. Take a pad of paper and a pencil, and make notes. Some might say that this all would be taking things too seriously and an early stage, but I say that it helps breed confidence and success, and that makes things more pleasurable and fun!
   Type at you later,
    Dan McEntee

When I'm setting the needle prior to launching, I also use the tach to tell me when the engine is fully warmed up. After it's started and the ignitor/battery removed, either pinching off the muffler pressure or blocking off the uniflow vent will lean the engine out. Do this a few times and watch to see what the baseline rpm is...when it stabilizes at the same rpm a couple of times, it is up to running temp and you can do your final rpm adjustment.

As the engine heats up, it will lean out. You can watch and see cold engines lean out as the flier heads out to the handle. It usually ends up being launched too lean. I have also had instances when the engine would not come up to the normal peak...say 10,400 when pinching off the pressure line (it was normally launched at 9,700). Bad glowplug, bad fuel, leaky tubing, or dirt in the fuel filter or NV, generally, tho if you scuff the prop tips on a takeoff, slight damage may also reduce peak rpm.   

You will also find that if you set the NV at 9am and it gets hot by noon, you will need to lean the NV to get the same rpm...OR, add Nitro content to get the same rpm at the same NV setting. Just leaning the NV will tend to give over-runs. Adding the right amount of Nitro and leaving the NV alone should not affect the run time as much. Personally, I haven't ever done that, but may take out an additional 5cc - 15cc of fuel from my normal amount removed. Start with a full tank when  you fuel up, and remove excess to get down to your desired run time. Quick starting is a key to this working out, of course! This stuff needs to get sorted before your first contest, but often isn't. At least, I didn't have it figured out then.  Steve