Steve, I guess it's mostly a matter of preferences...

Both approaches move the heavy bits of the engine rearward some, and allow a more streamlined front end. We pretty much have as much access to the same European long-nose engines as fliers there have, so that part of it should be moot. A shaft extension on a plain bearing engine remains not the best way to lengthen the front end...

Also, nitro is still quite expensive everywhere, and worse in Europe than here. Many Western, and now Eastern, European engines are - or were - set up to run "FAI Fuel" (80% methanol, 20% Castor). Even though F2B CLPA is not a specified-fuel event like Speed or Racing, the cost of nitro and availability of low/no nitro engines may be a factor.

For rigidity of mounting, a six-bolt mount system seems theoretically better. Many FAI Racing engines have (had?) another pair of mount lug holes up around the front bearing area. For us, that might get in the way of playing with thrust offset...

There are no Appearance Points in F2B, but the models are usually very attractive and well finished. Impression on judges doesn't have to show up as formal points on a scoresheet. And a model that has seen "a lot of development" (read: wear and tear) isn't automatically at a scoring disadvantage in F2B. The flashes off a gleaming, well-finished model glinting in the sun as it flies can be impressive and contribute to a judge subconsciously favoring it...

Then there is the idea that many of the most famous European engines are limited production, pretty expensive, and usually a bit 'different' to live with. Replacement parts also may need to be considered: our better fliers usually pack in several hundreds of flights a year on a single model. Normal wear can more easily lead to need for replacing something. Higher-volume production and parts availability have advantages for many of us who aren't shooting at placing well at NATS or World's every time.

You raise an interesting thing to think about...

Steven,
Perhaps the 2 great American engines ( RO and PA) are stunt developments derived from the heritage of engine manufacturers who produced among the finest RC racing /speed engines in the world. It could be that the crankcase length demensions produced the best compromise to meet the needs of most of their diverse customers. This is just a guess on my part. Eastern engine designers who could work out the economic feasibility of limited production runs may have had more freedom in something as basic as crankcase length.
By the way I seem to remember seeing an extended prop driver that eliminates the need for a shaft extension on the RO website.  Again these are just guesses on my part but it makes sense.
                                                                   Pat Robinson

I've been thinking: how come East European stunt engine designers prefer engines with long crankshafts while US designed motors(PA and RoJett) have much shorter crankshafts. The use of extensions is a given with any US motor designs. Wouldn't it make more sense to use longer noses eliminating the need for prop extensions?

HI Steven
The PA line of engines are LONGER than ST 60s  and  do not need shaft extentions, and don't need to be any longer . I have senn hundreds of ships with PA engines and  NO  shaft extentions...zero problems with a nice looking faired-in nose , PA engines  are  NOT short engines, my 40 is longer in the nose than a ST 60.
As to why not make them longer..that is just much more weight. You can make a very nice faired in 1 3\4 or 2 inch spinner with the engines as they are.
Prop shaft extentions are BAD on any engine and I would advise staying away from them any time you can
All of my designs have zero problems making a nice clean nose with no extention
The PA 40 ultralight is a very long motor and is about the same lenght as a FOX 35 with a  1\2 to 3\4 inch prop shaft ext.. many people are now using the 40 UL in older Classic ships as is  without the extention they had to use on the old short motors
Why make them heavier if you don't need to?

Regards
Randy

Perhaps the 2 great American engines ( RO and PA) are stunt developments derived from the heritage of engine manufacturers who produced among the finest RC racing /speed engines in the world.

This makes the most sense! RC racing requires most aerodynamic form(needlenose spinners are not it) as well as the need to spin 30+ K RPM's. The longer the crankcase nose, the more metal is needed to keep it vibration free. While in stunt, we don't need either one, being based on racing cases, PA's and RoJetts inherit stubby nose characteristics. Hey Randy, is that it!?

Steven  I still do not get your point???

Randy, I had no point to prove. I just wondered if there was some reason for such a divergence in designs. You are right about not having to use extensions. I'm not using extensions on my PA75 and PA40Lite. Perhaps you can explain how you came up with the dimensions when you were designing the motors. If the dimensions are different from Nelsons, how did you come up with them?! You must have had a good reason for the dimensions you chose.

Randy,

Thank you for taking time to write up the development historyof PA's and the decisions that you made along the way. It is so rare that such a prolific engine designer such as yourself take time to tell the story of development of PA engines.