thevirginian

A safety reminder for the RC enthusiast:
I was prepairing my Christian Eagle for the upcoming weekend and tried to tweak the carburetor of my Fuji 50 while sitting. The airplane was leashed to the garage door rail on my driveway. The wings and the cowl were off, since I would only adjust the high end needle. I started the motor and positioned myself behind the big prop on the left side of the airplane with a screwdriver in my hand. I let the engine warm up and then reved it up with my radio. All of a sudden the 20x10 Mezjlik flew off the motorshaft and landed fifty yards across the street in my neighbors front yard. Luckily it got stuck in a pile of mulch and hasn't hit anything. The prop followed a pretty straight projectory like a missile. If I would have been in front of the airplane a visit to the emergency would have been out of question. I remembered, the throttle was about half open when the prop came off. Not to imagine what could have happened with the throttle being wide open. First I thought I haven't tighten the M8 Hex bolt enough and it unscrewed from the shaft. I was wrong. That big fat bolt just snapped in two. The remainder was still attached to the crankshaft. Perhaps vibration could have played a role for this failure, I don't know. One thing I DO know, though: I will do all my stuff BEHIND the prop. Not that I wasn't doing that in the past but sometimes you forget and rev up while sitting in front of it. Not anymore, I swear.

aviti

My Feedback: (54)

You will get more vibration running an engine with the wings off. This is especially true of one piece wings that fit in a saddle as the lack of the wing allows more torsional movement. Not sure if this could have caused the bolt to break but never a good idea to run an engine with the wings off.

Point taken though on being behind the prop. I always do the same.

RK-Aircraft

My Feedback: (81)

Holy Sh@#!!! [X(]

PaulBK

the bolt breakage is rare...but it is one reason that i don't mind the 6 screws of a DA or 3W - although they shear too...but your point is well taken, and it shouldn't matter if it is a 50cc, a 100cc, or a .60. props do come off shafts, and when they do...%&$$%#$!!! i had a similar experience years ago with an os .61....it shed the prop in the garage, making for a very exciting few seconds as the APC shot forward. i don't let anyone stand in front of or to the side of the prop arc. it get tiring when flying big airplanes of constantly asking people to move, but its lessons like this that prove how important it is.

P

cwrr5

My Feedback: (32)

Good point, thanks for the reminder! [sm=thumbup.gif]


By the way, not to nit-pick, but what's a "projectory"?

Antique

My Feedback: (4)

When you get a replacement bolt be sure it's a grade 8..Metric grade 8 bolts should have 12.9 on the head....
Or...Tap the hub for a 3/8x24 made in USA grade 8....You will NOT be able to break that one

thevirginian

Hey, cwrr5;
I feel like a fool. I did invent a new word, didn't I? "projectory" : It must derive from a projectile being on a certain path What I meant was "trajectory". Sorry

thevirginian

Hey, Ralf
I forgot to mention that bolt had a thread thru the hex head. It was for a 10-32 SHCS that holds the Alu spinner to the back plate. I know that threaded hole did weaken the bolt considerably. But you'r correct. The prop bolt should be made of high grade steel.

rmh

easy on the "harder is better stuff - the harder -the more brittle -the worst case -- titanium - had some - NO more.

cwrr5

My Feedback: (32)

That's ok - I kinda like that word, I think I'll start using it.

projectory - The path a project (airplane) takes when falling from the workbench or other high surface. Also path followed when traveling through the air without control.(soon to be a "project" )

thevirginian

Or you can define it as a projected trajectory of a certain projectile