More POWER for my .020 TD

Better start looking for spare TD .020 cranks. I guess these tend to break easy.

Thanks Mike and Jason. I have not had crank problems yet, is that common? Anyone running these in a tach race? And know the fuel, prop, glow head, and rpm's?

If you keep the ball socket set correctly there is less chance of braking the crank.

With regards to breaking cranks, have you ever heat treated your cranks in the oven?

Ihave a TD020 with tons of hours of runtime on it and compression as well as ball socket setting are as original.

The only crank failure I ever had with COX engines was a broken, drilled pin of a TD050, and a similar pin failure on a regular product 049 reedie. COX engines do not often fail and in my eyes they still represent the benchmark of model engine longevity.

Running them up for free flight competion means running them close to the breaking point. I usually try to make enough modifications the get my TD's to run up to 23-23.5K on the bench on a 5.7x3 FF prop. 40% nitro is usually enough depending on head shims temp and humidity. If I go much higher on the bench they will blow up when they unload in the air. If you hit 25.5-26k the engine will often snap a journal or throw a rod. That is why I heat treat the crankshafts. This is only to get a few more runs out of them, not to solve the problem. Preheat the oven on the broil setting to 500 degrees and cook the crankshaft for an hour. Let it cool down in the oven. You will see it change color a bit.

You can hop up a TD .020 by drilling out the venturi to open it up a bit. You will have to run it using a fuel bladder. If you have some good GloBee or Nelson insert heads laying around, Matt's can turn a .020 glowhead down for you to give you a better fuel burn. Doug Galbreath my still do the machining if you ask but you will have to provide all materials.

These are the only two things I have done to maximize TD .020 RPM. I heat treated the cranks too. None of my TD .020 engines have blown up. (yet)

Thanks, I'll have to check the rules to see what they say about engine mods.  I ran this engine on 50% last weekend, on one shim, and it seemed to like it.

And bladders are no problem. My 049 free flight model runs a bladder.

Spending some time balancing compression vs fuel for your desired prop can go a long ways to getting good performance out of one of these engines WITHOUT excess modification. Get some brass or copper shim stock and make different thicknesses of shims, or order different brands anticipating different actual thicknesses (measure them).

35% nitro fuel is not outrageous by any means here, although on larger than 1/2a engines it is easy to say otherwise.

Phil

What a stock TD .020 can do without failure on 35% / 20% oil.

TD .020 Static test per prop calc:
Best read: 3.75x3 / 22,790 rpm / 65 mph / 5.3oz thrust / 37w
The engine prop combo is actually making over 5.3oz of thrust.
Lil Speedy TD .020 / unloaded 3.75x3 / 31,257 rpm / 148.37 km h / 92.19 mph
Best dive down wind / 31,419 rpm / 89.3 mph


Lil Speedy 3.5x3.5 Prop / 35% Nitro / 20% oil / 84F / 6 to 10 mph winds
Best static 24,644 rpm / 82 mph / Best pass 30,742 rpm /102 mph per prop calc.
Per Doppler Reading E-flite 3.5x3.5 best pass 105.12 mph

3x3 carbon porp best Static 30,684 / 87.2 mph / Per Prop Calc.
Static at launch 29,985 rpm / best pass 37,304 rpm /106 mph