Thread: .020 size GLH
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Old 12-19-2013, 05:52 PM
  #149  
hllywdb
 
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OK, I spent a bunch of time last night going through FF sources on the TD 020. Yes, it is possible to get to the 27k to 30k range, but a little different than with a 1/2a motor. A great source is Bob Mattes at http://www.flyfreeflight.com. I agree with his findings 100% based on what I have been finding myself, he just drew better conclusions quicker than I did The steps are as follows:

1. Clean up the crank. This is always my first step. I usuallt clean it up with 1500 grit until it doesn't drag, then load it up with toothpaste, install a prop and hand lap it in. He also added that you can polish the inside passage.

2. The head. He makes a conversion head for a nelson flat coil plug (or Merlin) Most of us know from 1/2a stuff that while compression helps, it is the design of the squish chamber that helps these small motors perform. Doug Galbreath will also convert a burned out 020 plug to take a glow bee plug.

3. The 020 cylinders have bypass ports, but no boost ports. These can be added.

4. Apparently there is a wide range of manufacturing tolerances in the 020 size between the piton/liner/case combinations. Much more than the 049. Depending on the combination of all 3 of these at TDC your piston may be even with the top of the cylinder, below it or even above it. My findings agree as different combinations on my 020 will require anywhere from 1 to 3 shims to achive the same result. This is usually a $10 expenditure to find which combination. But the important thing is that he has found that this will cause exhaust timing varriances as much as 25 degrees. Again I have to agree where I have one setup that I can actually see bubbles being pushed backwards into the fuel line from the carb, much like the blow back you get in a small block V8 with a bad exhaust cam lobe. This timing would also contribute to the brick wall you hit. The solution is to shim the cylinder to get the exhaust timing correct, then shim the head accordingly.

5. Vibration. Most IC motors will have areas in the rpm range where they have balance issues. My Harley would hit it at 68mph and it would be gone by 73mph. These motors have a bad habit of hitting this at the 22k to 23k range. This becomes amplified by the plastic tank with only 2 mounting screws. I have seen this happen on my runs. It sets up some kind of harmonic occelation and the motor can't get past it. In my runs over 23k I was able to run past it only by leaving the glow clip on the engine, which helps to stablize it or put my finger on the side of the motor until it gets past this point. At first I thought it was a prop balance issue, but it is not. Bob does make and aluminum mount to overcome this issue.

6. Nitro. Yep, 40 to 65% depending on how fast you want to go, and replace parts. Bob calls 27k a safe max and 30k is do-able for competition. With his mods he accepts a minum of 27k with a 4.2X2 APC.

OK, sounds all well and good but the big issue for me right now is I'm not sure I WANT to run 27k on the ground with a 2.75 on this plane. I got a chance to fly the plane tonight. With it turning 20500 on the bench I was expecting a nice 35 to 40% boost in speed on a nice flying plane. Nope! These props UNLOAD. A LOT! Those of you who have played with CF props on re-worked TDs or AMEs can relate to this. I found the best setting to be very rich on the ground, just starting to 4 stroke. Within 15 feet after lauch it has gone to a high pitched scream and it's on. It then becomes not so much an act of flying the plane, but spending a tank of fuel trying very hard not to crash. It reminds me of when I was 9 years old. I had been flying 1/2a combat with lil satans with TD's on them. It was fun, but I figured moving up to 35's would be lots more fun. So I built a voo doo and installed a 36x with a bladder. Then, with all the wisdom of a 9 year old I set the elevator throws to match my 35 size ringmaster. Today was a lot like that flight. Part of the problem was my flying field. Its a huge field and I fly from down in the corner in the mornings, with the sun at my back and about 100 acres to fly in. I have flown a few times in the afternoon, but the sun is over the field and I fly down in the corner, which has water on both sides. Bad idea. There is no such thing as flying this close and in. Trim adjustments are made on the ground as there is no time in flight. It quickly becomes a small dot and loosing orientation happens in a fraction of a second. The control throws become way too much at this speed. Being a glutton for punishment I still made 3 flights like this. This makes flying the 28" glh at over 100 a liesure activity, almost boring.

So I will wait for a morning flight where I can make nice big circles around me to get things sorted out. I am also going to move the cg forward and reduce the throws quite a bit more. I have also contacted Bob Mattes and will start on some of his modifications and get some parts from him. I'm just not in such a darn hurry to put it on the plane right now
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