There are a lot of reasons to use bench runs first, Here are just two:

Not all engines come out of the same mold i.e. there are lapped piston engines, ABC/N, AAC and ringed types and they are not all run in the same. In fact breaking ins an ABC the same way as say a Ringed engine can ruin it as well as vice versa. Not all these running methods are condusive to good controlled flight especially on a new or unknown airplane to to. Simply put it ain,t much fun flying around for an hours worth of flight at a very rich setting with your new ringed engine.

Now you say, but my ABC should be broke in at higher RPM at a two stroke mixture? and right you are but what you are leaving out in that senario is the fact that what will do more for the brake in than anything else is 'Thermal Cycles". heat that puppy up and let it cool down every few minutes. Something thats hard to do on an airplane in flight.


In most case with only a few exceptions (yup there are always exceptions) I will break in an engine with the intended flight prop and fuel. Always on a stand and irreguardless of pistion/cylinder metalurgy will use short thermal cycles. I have mounts that will mount the engine in vertical sideways or inverted position so it can be broken in as it will be used.

The multi engine airplane in my avitar has Magnum .28's and all four where mounted on a single two by twelve with the
spacing and fuel tank positions as in the airplane. All four where broke in simultaniously with a gallon throuh each be fore they ever saw the airplane. I even wanted the same vibration harmonics for the brake in. Sure would not wanted the resultant wear and tear on the airframe. The reliability rewards was certainly worth it.

One last though I commonly see people running in an engine on the airplane and never even get the midrange needle set right for the life of the airplane. Simply because its to akward to get to, as a result they never even learn how to set 'that' engine. Of course every idividual engine is differant. All of this makes a whole bunch easier to do on a stand and not ignore it. I think the one that gets me the most is someone will come out with a beautiful new airplane ARF or kit or ?, with a new engine and not even provide a way to set the main needle through the cowling. Expect to brake in the engine, set the engine and flight test the airplane all in one setting. I don,t think so.

John[8D]