RE: OS 33GT Gasoline Engine for Pattern
Okay, here are some numbers from the first couple runs today
The short story is the engine now has 2 tanks through it, around 30 minutes run time. It runs well, as one would expect. I ran 3 different Pattern size props, 18x12, 18 3/4x10 and 20x10. All ran better than I expected and better than other engines I have been playing with for the same application. The 18 3/4x10 was an 18.1x10 originally; I extended the tips to tame the Webra 160 years ago so it was a natural to compare.....turned at 8300-8400 on the bench which is about 800 rpm more than the Webra ran the same prop. The 18x12 turned similar rpm but needed leaner needles to do it. A little lower load than the 18 3/4x10. The 20x10 was the real surprise for me, turning a much faster than anticipated 7800. You could hear air ripping and this gas engine is still new. I expect a little better after a few gallons
BUUUUT!! The proof of the pudding as they say...... I need to see what it does with any of these props in the air. If it bogs down anywhere for example. Also, we won't know how it runs in hot conditions until next summer, unless one our mates from down under gets some hot runs earlier
Very good field (bench) manners. After setting up and running the rig initially, hot starts were no more than 2 flips. Smoother than expected for a longer stroked engine. But OS should be expected to get all of that right.
The factory needles (1 1/2 HSN and 1 LSN) probably will work okay for a light load such a 18x8 as they quote in the manual. They were a little too lean for my props. I ended up at 1 3/4 on the HSN and 1 1/8 on the LSN. At these needle settings even the 20x10 displayed instant accel from extended idle.
I am fairly pleased with this choice so far. I will be putting into Temptress next week and get some serious break in in the air and hopefully the weather will cooperate.