Hub Bars and Fatigue Cycle Life

[Brian Jackson]

Hi Gents & Gentesses.

I was following a thread frequented here recently on multiple blades and thought about something puzzling. Why don't we have more stick shake than many of us do? I'll plead the 5'th on this one only because others here have told me "there are no stupid questions."

The advancing blade generates more lift than the retreating blade. OK. That static model is pictured with the blades left and right, and makes perfect sense. Rotate the blades 90 degrees (forward & backward) in that static model, both generate equal lift. In that instance their airspeed is the same. Since their pitch is too, I assume so is their lift.

But as the blades swing around, say, 1/4 turn or so, the advancing blade developes a little more lift while the retreating blade loses an equal amount. Teeter bolts take care of much of that from what I understand. But here's where my understanding gets nasty:

Consider this... A force offset in one direction doesn't guarantee a smooth resolve in another. Angular force on the teeter? No. Every force is ultimately passed onto the Hub Bar. Though you may not feel it because these forces are equally and oppositely balanced (hopefully), stresses are still distributed.

Have there been any studies done on the fatigue or cycle life of Hub Bars? Seems that would harbor a high concentration of cyclic stresses.

Thanks,
Brian Jackson

[KenSandyEggo]

"Have there been any studies done on the fatigue or cycle life of Hub Bars?"

Don't know, but a Hershey bar in my mitts has a life-cycle of about 14.276 seconds.

[quadrirotor]

Martin Hollman.