I forgot to ask this on my other post.
On the prop nut.
How tight is tight?
I never saw any info on that.
Any rule of thumb you go by?

I don't use a tork wrench but really put pressure on with a prop wrench (the ones that are also used for the glow plug). On some engines that have a tendency to spit the prop off the crescent wrench comes out. For most engines of the glow variety this is sufficient. Checking after a few flights and re tightening will normally hold quite well with an APC prop. Wood has a tendency to compress and needs to be checked more often.

EXCAP232

DARN tight! and then use a jamb nut against the prop nut if at all possible.

Hi EXCAP232,
I guess they have to be pretty tight.
So far I have never seen a torque wrench or any specs for how tight the nut should be.
After my 5th flight I did snug it back up and think I got close to 1/2 turn but it's TIGHT.
I guess like real aircraft it's best to do a pre flight and check it out.
Happy Flying
Thanks for the post

I did a rough check once using a largish torque wrench so I couldn't guarantee the accuracy at the low end of its range. What I did was to tighten a prop in the same way that's never given me a problem with them coming loose and then used the torque wrench. The nut started to move again at about 5 foot pounds or 60 inch pounds. This is between 1/3 and 1/2 the maximum torque that should be applied to a 1/4x28 bolt. Effectively, the crankshaft is a bolt and some are soft where others are hardened.

Tightening the nut puts the prop hub under enormous compression loads and if you overdo it then the hub could eventually fail.

Hi Downunder,
Well,
After I had to tighten mine only one time,
I realy cranked down tight the second time.
Never used any lock-tight and it's still OK but when it does turn on me again when I check it for looseness then i'll just replace it.
Thanks for the info

The first flight I ever had rolled out nicely, then snapped and just as I got the plane under control and climbing out, the prop came off. It made a nice silhoutte and went it's merry way. Now I use a teflon lock nut and I've never had one back off or loosen up since (although it's not a long time compared to some of you...). You can find 'em in the right thread if you look.

Ed

...WOW!!
Maybe a preflight check??
Well I have to agree with you that they come off and I check mine and I feel that I have the nut to tight.
Someone told me ther was a nut called a NY-LOCK
It's supposed to go on easy but very hard to unscrew the other way.
You said nothing about the Bird so I assume you made a nice no stick landing ??
Happy Flying

What exactly is a no stick landing?

I assume since this is the Beginners forum that we're talking about a garden variety .40/.46 two stroke.

The answer is tighter than you think. The little 4-way wrenches are too small for the prop nut. Get the correct sized box end wrench, which will probably be about 5" long. Bear into it a bit. If it's a wood prop, you'll know you've got it right when the washer sinks a little into the wood.

If you think about it, when the engine is turning the prop, the tendency is for the nut to tighten itself. The problem is when the prop is turning the engine, at which point the prop (i.e. the starter) is trying to loosen the nut.

Until you're sure you have it right, stand back when you start the engine. I saw a prop come off and embed itself in the pilot's forehead. It was not a serious injury, but if it had been an inch lower it would have hit his eye. If I hadn't seen it, I wouldn't have thought it possible.

"embed itself in the pilot's forehead. It was not a serious injury"

Holy smokes, what DO you call a serious injury??? Reminds me of the Monty Python "It's only a flesh wound! Come 'ere and I'll bite ya!"

.You havent see anything until you see a blade let go on a full size Benson Gyro.
Did a lot of damage to the rotor blades and caused a lot of vibration .
My friend was sweating it out coming down with a 15* nose down and no engine.
The landing was fine but new blades were ordered and we had the cheek plates and head forks X-Rayed.
Another pilot was flying and thought something let go and he also felt a sting in his upper back.
He decided to land even thought the Gyro was flying fine.
Getting out of the seat he saw blood.
Someone on the groung shot him with a 22 but the seat took most of the punch of the 22 and the bullett was just under the skin

Well pinball,
I see some dumb peope run that engine up to 18,000+ RPM with their face less then 2 feet from the prop.
If that prop went into the persons eye it would have gone far in enough to hit the front of the brain Some people don't think well today
Common sense is becoming more and more uncommon today.
Ever notice that many people answer your questions with a question?
I like the one where when you go fishing and you see a Guy sttting there and you ask if he caught any thing.
Amost all answeres are (I just got here a half hour ago)

I agree with using a box end wrench to tighten the nut, you'll never get the nut tighten enough with those 4-way wrenches. But I would add another piece of advice to that. Wear a leather glove on the hand that you are holding the prop with. I learned this when I had the sharp edge of a Master Airscrew prop make a really nice slice into my hand. If you wear a glove you can get it tight enough without hurting your hand.

Hope this helps

"Embed" was probably not the right word. It hit his forehead, leaving a nice prop end sized wound above his eye, no stitches required. It was still very startling, first because it happened so fast, and second, because the prop had to loose itself of the nut, and the spinner, and still jump up to the guy's face with enough force to break the skin.

I agree with the ability of MAS props to cut. I haven't gone to gloves yet, but I always get out the sandpaper and sand the edges until I can comfortably tighten the prop nut with the edge of the prop in my palm.

. PINBALL,
When you sand the edges down do you rebalance the propagain?

"Again"? I'm not particularly ashamed to admit that I don't balance 11" (or smaller) MAS props at all. I mean, it's a manufactured product (unlike wood, that grows), so how far off can it be? The amount you take off to round a sharp edge is so small in itself, that I can't see how one side could be more than the other.

I will even admit that I once posted a picture of one of my planes where the sticker was still on the back of the prop. Did I get flamed! (I don't usually do that, or recommend it, but I had to change props in the pouring rain, and I just didn't think about the sticker!)

And before you flame me, I want to comment that this is another area where the Internet is not like reality. At my field, if you ask someone how they balance their small props, they will look at you like you're from another planet.

OK, having got that out, I am willing to listen and learn. Is there any science that shows how much vibration is caused by the engine itself (just the piston going up and down) vs the amount of vibration caused by the worst case manufactured prop, and what bad things that vibration can do, assuming the receiver is isolated from the vibration?

Well thats why I asked .
TO EARN.
I have to agree that the piston going up and down at 19,000+ rpms and comes to a full stop each way would do more damage then anything else.
I cancelled the balancer because I feel that my home made one is just as good.
Plus I also question the nut being off balance.
I feel that if I need to balance it then i'll replace it.
I think maybe the manufacture of the engine is perhaps thinking of harmonic vibrations and they will run all along the model.
Thanks for the input

<<<---- I must be low on brain cells
My typos are getting bad
I really meant TO LEARN but this old lap top has some keys sticking and at times I need a hammer for that *L*
Sorry

If in doubt...
Cut two circles of sandpaper the size of the hub of the prop...glue the sides with out the grit on it together....drill a hole the same size as the crank shaft, install either between the hub and the prop or between the spinner and the prop....and give the prop nut one grunt and two grones of torque, (Just joking their)
Tighten well.....I've seen this work on the nastiest of motors that was throwing props....using 25% nitro...
Most of the problem is running the motor too lean and it's kicking back and loosing the prop nut....
Just two cents worth....

.BigBird,
What is the 25% have to do with throwing props
Please don't take this as a smart*** question.
I'm asking because I know others who fly dfifferent engines and use anything from 10% to 25%
Is it the more severe hammering of the piston?

Oh, no offence taken...

The pattern guys in the club use 25% nitro in their YS's...every one else uses 15% club fuel...
I've seen more props thrown with the YS's than with the other engines...and the sandpaper bit works well...
Most have to replace the rod every season because of wear on the bushings...Mo' bang in the fuel...
Some other motors are just plain 'finikie' with the needle settings.

Hope this helps some...

Whirley Bird,
BigBird1 is definitely correct about the YS engines. I fly a YS and it definately can kick back and throw the prop. In fact, kicking back and throwing the prop is usually the best that can happen in a YS. I have seen a YS 120 kick back and tear the engine, motor mount, and firewall right out of the plane (luckily this didn't happen to me). But what causes it???? Running the engine too rich. With a YS engine especially, and most engines in general the richer you run it the more change you have of it kicking back.

Remember that running the engine rich actually means "fuel rich", meaning there is more fuel than air in the engine. That's why an engine running rich "slobbers" out of the muffler, the excess fuel is pouring out of the muffler. And you have to also remember that although it is difficult to do, you can have ignition in the cylinder without a glow driver. Just the compression of the fuel in the cylinder can get ignition of the fuel. What is happening when running rich is that you are getting pre-ignition (the fuel/air is igniting before the cylinder gets to the top of it's stroke) which causes the piston to reverse direction and go back down. viola, the engine immediately reverses it direction and kicks the prop nut off. Now you can see that this happening can cause all kinds of other damage too. The higher end, higher compression engines like the YS are definitely more prone to this because of the higher compression they run. And running 25% fuel just adds the this problem because you have more nitro in the mix when the fuel ignites. More nitro means more bang, and more force reversing the engine. i.e. more force to kick the prop off.

I would like to thank my LHS for this info. The owner of my LHS is Mike McMurtry (a.k.a. father of Sean McMurty, of TOC fame). When I got my first YS motor he told me to NOT run it rich for this very reason. Even in the break in period you don't want to run rich.

So if you are having major problems with your prop getting kicked off, try leaning up your motor a click or two.

.Hi RCKen,Well I'm convinced that you can start a warm engine with no battery on the glow plug.
Saw it done several times on the bigger sized racing cars.
One person was having problem and he was not able to get the thing restarted with the recoil starter.
He removed the battery and gave that thin cord about 15 pulls like his life depended on it.
It fired up, he made some adjustments and it ran fine.
As of now my biggest engine is the OS 46 and I may order the next bigger one today.
Thanks for the input.
I guess the instruction book is not always right

Oh yes. I've seen it too....
Best way to go at it is play it safe, do equipment checks...and keep in mind that even if you know your motor etc...Murfey rules in the end....

Have a good season, I've tried many hobbies and this one is the most rewarding, simply because of something I've built rotating and going up in the sky is the most wonderful sight in the world..

BB1