|Quoting Tdscanuck (Reply 13):
It wouldn't be that bad. If the only difference was the rotation direction and everything was just mirrored, qualification by similarity would be pretty straightforward.
Quoting Dougloid (Reply 12):
That's not nearly as simple as it sounds. If you want to maintain the same prop speed, you're going to have to shoehorn those gears in there somewhere. This is not a freakin' bicycle, people.
Yes, but a counterrotating gearbox is a lot less work and cost than two types of engine.
Tom, it's not a question of mirror imaging everything. You folks are all assuming that this is easily accomplished by merely "putting in a counterrotating gear in there.
Listen. I spent a lot of time working on TPE331s and we had two flavors. One was a straight, 2000 rpm clockwise rotation engine with a supr gear train. The other was a counterclockwise, 1591 rpm number that swung a bigger prop.
I can tell you that the reduction gearing was entirely different between two engines with tthe same model number. Here's how they did it and I think that here's how Europrop will do it.
The 2000 rpm model had a spur gear train and a fixed planetary gearset. The 1591 rpm reverse rotation one had to have a floating planetary hearset and an extra bull gear to get the reverse rotation while making sure that all the accessories worked properly.
Think about it. Draw yourself a little picture of a geartrain that will reduce shaft speed to prop speed.
Then think about what you have to do to get the prop to run backwards. Never mind what you've got to do with your accessories, prop governor, whatever, but don't forget it's got to occupy the same physical envelope.
You've got to get one gear that's gonna take all that torque and reverse it in there that's gonna handle 15,000 hp reliably.
Easy? Simple? In an armchair maybe.
[Edited 2008-06-26 20:56:22]