john comp

I’ve been trying to get my OS 70fs to start, it’s mounted on a scale P6e , and had a 3 blade16/6 prop, plus a heavy hub. Well today it started with the electric starter, then it exploded with two blades off and who knows where the hub is.scared the heck of me, I was very lucky nothing got hit


Here ya go

End view of break

706jim

I guess it's harder to get the longitudinal fibers to line up in a three blade compared to a two blade. Another good reason to stay clear of the prop arc.

And maybe wear safety glasses until the plane is a safe distance from you.

1200SportsterRider

I can't imagine an OS 70 fs turning a 16 x 6 3-b fast enough to even hurt your fingers, let alone explode.

706jim

I just noticed the size. You're right it shouldn't be turning very fast.

rgburrill

Turning fast isn't the issue, it's that big boom every other cycle that generates a lot of torque trying to get the engine speed up. If that torque did that kind of damage to you prop you should make sure your crankshaft doesn't have any unwanted twist. There are prop sizes recommended in the user manual for a reason.

1200SportsterRider

It appears that the paint broke the prop material down and there is a saw mark on this blade.

Jesse Open

I thought that looked like a saw cut too. Just couldnt imagine ANYBODY actually leaving a prop like that on a plane! I immediately remove, destroy and discard nicked props. No prop is worth that risk.

john comp

Thankyou all that have replied, i errored in the prop size, it was a master airscrew 13-6, and that is recommended by OS, as far as the end view i took that to show the pocket in the molding, but there is no saw cut, sorry if it looks that way. Now as to the paint, i wanted an aluminum look to it. so much for scale.

Jesse Open

Thank you. That does make a lot more sense then. Yes, a void or two in the molding. For sure, and it was in a very bad spot as well!

GREG DOE

From the pictures it looks like there are stress fractures all across the blades. Take one of the blades and see how much effort it takes to to break them in your hands. I suspect you can
snap one in your hands. This prop was either made from bad plastic, or it was exposed to some chemical, or heat that degraded the nylon.

DGrant

My Feedback: (4)

It could have been something in that paint that attacked the plastic/resin of that prop. Certain plastics aren't compatible with certain chemicals. Think about it... It's highly recommended to not use Loc-Tite on plastic.. Why is that?.. because there's a chemical in it that will compromise any plastic it comes in contact with. Without know what type of paint you used, leaves a question as to if it was the paint the weakened the prop structure, but something definitely broke down/cracked that finish, and probably much of what's underneath. Something caused the problem, if it wasn't the paint, what was it?... it might remain a mystery, but I bet your done painting props.

Props aren't something to experiment with though. You're fortunate if it didn't just torque the nose right off that plane. I've seen a four-stroke throw a blade off, and it literally destroyed the front end of the plane. Don't paint them obviously, as you're just looking for trouble.

MasterAirscrew isn't the best prop for anything either. What they are is durable compared to wood, or carbon fiber, they're probably the most durable prop out there... but they lack in performance greatly compared to other props. Up to you what you want to use though. I hope nobody got hurt with it. It could have been very serious.