ORIGINAL: Konrad
ORIGINAL: Kweasel
The newer two-stroke designs are generally lighter than the first generation schnurle engines of the 70s. They have basically taken durable high RPM designs and traded that durabillity for displacement and the torque at lower RPMs. The newest/lightest designs like Webras P5 series are too expensive for the average flyer. All the cheap engines are just OS clones that are not exceptionally light weight.
What makes an engine a clone? Looking at the OS of the 70's they actually look design wise very much like a McCoy. Even the OS of today still looks like a McCoy just that the materials are worse.
: Rcdude7
Having the lightest weight engine is not always best, a engine with some mass also tends to dampen vibration better, all else being equal of course. I certainly would not give up my rossi engines and they are as beefy as they come.
The brodak control line engine you refer to is a special purpose engine, it's much less powerful than a similar BB R/C .40 and turns about 5000 fewer rpms than we are used to.
That was Duke's point. That at some point the trade off for thermal stability and mechanical reliability would limit the power output of the engine. A displacement limit really doesn't limit anything for example an OS LA 40 might put out 1.1hp on 15% nitro yet a Nelson FAI 40 might put out 3+ hp on zero nitro fuel both engines are of 6.5 cc displacement.
Just a point, the Fox 25BB puts out more power than the old Fox 35 stunt on close to the same props. This is ''flyable'' power in a smaller engine displacement!
Now the Rossi and Webra are real performance engines. I agree all things being equal I wouldn't give up a Rossi for what passes as a high performance engine at most distributors today. I will admit that the Nelson was a competition engine and therefor way outside the scope of most pilots. Today's OS AX series is having thermal stability issues with the collapse of the cylinder mounting flange as the engine gets near its performance potential (hot). This is because there is little thermal mass and the case, head and cylinder configuration is not optimized for such a light weight engine.
You use the mass of the engine to dampen vibration? Why not balance the engine correctly to begin with for its anticipated rpm? The mass might be better placed elsewhere for mechanical or thermal integrityAll the best,
Konrad
A sport (high performance rossi like) engine is expected to be smooth running at all rpm, and single cylinder engines like this are inherently unbalanced, we can balance the engine rotation at 12 and 6 oclock but it will be out at 3 and 9, I am probably just repeating stuff you already know here. The extra mass of the case will help dampen and mask the inbalance.
OTH I have a Enya VT-240 and it is a V-twin in a 80 degree layout, this configuration can be made very smooth because one cylinder will balance the other at the 3 and 9 oclock position, neat. I have thought of selling this engine, but it is one of the best engineered glow engines out there, so cool, I just can't bring my self to part with it.