Akrobat Problems (late march)

After determining to finish the Akrobat that had been stored in the barn rafters for fifteen years, a suitable motor was sought.  Years ago, I'd bought an Enya 1.2 4 stroke for it but had used that engine in a Hanger 9 PT-19 and it seemed to be happy there.  After some inquiry, a friend had a deal on a never run YS-1.20 he'd bought several years earlier for an Ultimate bipe someone else ended up with.

The break in of the motor started out ok, but went south after a while.  Upright the motor adjusted reasonably well and after two tanks of fuel, the motor was moved to the plane in an inverted position where it would only idle under glow battery.  After some reading, I discovered that this older engine had no idle mixture adjustment and needed the throttle butterfly drilled to lean out a too rich idle.  

This required a step process of drill a little and test, which meant pulling the engine each time so it happened over a period of several days when time permitted.  Then one day the motor didn't seem happy and wanted to lean out and in the process kick and throw a tantrum.  From the reading about these engines, it was apparent they are temperamental with one plague being fouling of the regulator.  After cleaning the regulator, the engine wouldn't even run and again suffered a few kicking episodes spinning the prop and spinner loose.  Taking a hard look at things, two problems were discovered, the tank had shifted pinching a fuel line and I'd reinstalled a regulator spring the wrong direction. 

These fixed, the motor just didn't want to produce a good idle again even under glow power.  It will run up fine, allow adjusting of high end mixture and transition well but now won't idle well even upright back on the test stand.  I've lost ground with the motor and may have done damage to it during one of the kicking episodes.

I'd come to the conclusion shared by others that YS engines are high performance beast and more difficult to tune, especially this older model.  Having labored with it about a month off and on, I'd decided to send it to be checked and was cleaning it up in prep to ship when noticing hair line fractures on both sides extending from the forward corner of the mounting flanges.  The kicking episodes perhaps in conjunction with the hardwood beam mounts may have done this motor a death blow.  Subsequent reading has discovered that some of the YS engines would distort or crack if bolted to a fiber mount and that very solid aluminum mounts were reccomended.  My plane has hardwood maple beam mounts.

At any rate, I've given up on it, something my wife says must be serious because she says I rarely give up, usually making things work. 

What way to go?

Two choices emerge, a Saito 4 stroke, (either a 1.0 or a 1.25) or possibly the new Zenoa G20 gasser.  The Akrobat was designed for a strong .61 2 stroke with a prop drive unit to run a large propeller for more torque because the plane flies slow but adapted quite well to early 1.2 4 strokes without using the prop drive unit.  The YS weighed about 33 oz and the plane needed 2 oz additional nose weight plus an on board glow battery and a servo mounted up near the firewall to switch the OBG as well as it has large beam mounts with plywood gussets.  Adding all this up comes to 6-8 oz that could be stripped away if going gas not even considering the difference between an 8 oz fuel tank compared to 16 oz glow tank.

The G20 is designed somewhat lighter to try to get down into the power to weight ratrio of large glow.  Combined weight including muffler and EI battery is 41.6 oz with thrust being fairly similar to glow.  It of course remains 12 oz or so heavier than a new Saito but not much if any heavier than the old YS when factoring the ancilliary weight reductions if going gas.

I've three 4 strokes and love the sound compared to either 2 stroke glow or gas.  I've one gasser and the economy far surpasses even the 4 strokes and is far easier to clean up after flying.  4 strokes usually idle very well except the frigging YS :(

With the weight of this model fairly fixed,  a lighter Saito doesn't yield an advantage unless it is a slight thrust advantage as it would require additional lead.  The G20 would be about in balance after removing the beam mounts and glow battery and servo.  Actually, starting fly weight (full fuel tank) with G20 gas would be 8 oz less than glow.

Decision

What would the reader choose?  I've ordered one of them.  Which?  Answer