Flying knife !!!!!!

[Paul Taylor]

Boy was I lucky!!!
I take the day off in hopes of flying and of course it is windy as heck. Dang nab-it!
So wanting to mess with my planes I take my green plane with the OS .40 four stroke off the wall. I wanted to start it to make sure it was going to run now that I put a new tank in it. I fueled it up and pull out my electric starter. I had the plane sitting in a stand about 3 ft off the ground. I hit it to the front of the prop hub with my starter, and pow! The APC prop goes flying off at about 3 o’clock and into the middle of the drive way. I was bent over at about 12 o’clock. Had it came off sooner I might have been hit by the prop.
I drained the fuel and hung it back on the wall.

[Louis Rankin]

Paul,

You experienced the classic 4-stroke backfire.  You did make sure to install the prop nut and lock nut, didn't you?  If you do not install a lock nut, you will experience the prop popping off very often.

[Zuriel Armstrong]

Paul,

I have a lock set for this engine if you do not have one.  I am glad you did not get hit and decided to hang the "THANG" back on the wall.  The McCoy doesn't sound so bad now, does it?

You should have gone wind flying like I told you

[Paul Taylor]

No lock nuts,

Zuriel,
Let me know what you need for it. I will get it the next time we fly.
I will bring the green thing to fly in hopes of getting it in the air.

And next time I will listen to you.

[john e. holliday]

Go to ACE Hardware or any good hardware store and get a nut with the nylon insert to put in front of the regular nut.  I did that to my four stroke to keep the prop from flying off into vital areas.  Later,  DOC Holliday

[Harleyman]

Cover your face buddy!  You don't want that pretty mug to get hit.   

[Bob Zambelli]

Of all the 4S engines I've tested and flown, the ENYA .46 is not only shows the highest specific  powerful bit it really HATES PROPS.  You cannot believe all the instances of thrown props, no matter what means we used.

Second behind the ENYA is the Surpass .40. The best drill I've found so far with APCs is to re-tighten the prop a few times after installation. This seems to compensate for the initial "set" of the plastic. And, don't be afraid to lean on it.   

The comment about the "Nylock" nuts is excellent. They really help. the standard thread is 1/4-28 UNF but on some of the older ENYA and SAITO engines, the thread is 7 x 1 mm.

I've come up with quite a few 4S tricks in the past and this one really works: Before you put your prop on, wipe the threads with alcohol and then put the prop on. Then, coat the threads with RTV, put on the prop washer and run the nut down nice and tight.
Let it set overnight and then re-torque it. When it's all set, run the Nylock down against the regular nut. Finally, put a small dab of RTV over the bare exposed threads.
A big advantage of this on ANY engine is that if the prop loosens, even in flight, the nut will not spin off.

And, by the way, I've NEVER had a 4S engine do a shaft run.

Oh yes, regarding wooden props on 4S engines - I suggest that you check the nut torque every day that you fly because 

Bob Z.

[Tom Martin]

I think the prop throwing on 4 stroke engines is, in part, caused by the small amount of contact area between the prop nut & prop washer.
 
I have been using a onepiece spinner-nut tightened directly on to the prop. It has full contact at the prop & the shaft.
I have never had a prop come loose. Yes, I tighten it frequently. I use an electric starter.

No, this will not work when using a nose cone/spinner.

It works for me.

Tom Martin
Tulsa Gluedobbers Control Line Club member

[Bob Zambelli]

Good point, Tom.
I forgot to mention that I make ALL my own prop washers.

What I do is measure the largest width of the prop hub and then make the washer diameter around .03 larger. That way, the entire hub is covered.
Doing so, the prop washer will not sink into the hub.

I have also made a number of custom 4S shaft extensions with integrated spinner backplates. The thrust washer, extension and backplate are locked together to prevent relative motion.
Six small pointed protrusions engage the prop.
This setup has never failed.

For anyone interested, I will post pictures.

Bob Z.