Prop nut coming loose

[kevin king]

Has anyone had a prop nut come loose when the engine was running? That happen to me on an LA 46. But i want to know from your experience how much damage, if any was done to the engine. My engine started right back up and i didnt notice any difference, but it was a new engine and i only had 3 flights on it, so i cant tell if there is any performance loss.

Kevin

[Perry Rose]

I've had the nut come off during a cold start several times but not in flight. If it runs without the prop I choke it to death to stop it. Wood props compress and loosen the nut over time.

[katana]

Don't the majority of engines have a run direction that is opposite to prop threads so they should tighten rather than loosen?

[Carl Cisneros]

Katana, in theory, yes it should work like that BUT in reality, no it does not.

If you are using a wood prop, by all means make sure that the prop nut is TIGHT.

The wood will/does compress over time as well as in weather (temperature) conditions.

As far as your shedding the prop in concerned, I had that happen on a new OS LA46 on the test stand with the motor
running away for a short time before I choked it to stop the motor.

I did take the motor apart later that afternoon to check it out carefully and there was no damage.
If your motor feels a bit funny compared to what it did feel like (if you can remember how it felt) take it apart and carefully check
everything especially the rod.

My motor that ran away after shedding the prop/ prop nut, ect. is still going strong.

This is just food for thought folks.

Carl

[Brad LaPointe]

My experiences with shaft runs have not ended in any catastrophic results. FAI combat engines would shed their props after a “light “mid-air bump. Unless you were unable to ditch the model immediately things probably would have gotten ugly .

For wood props I look through my box of old Fox prop washers with the grooves. These help keep wood props from getting loose…sort of . A good rule of thumb with wood props is to tighten / check before going to the flight line . Ask me why I know this and keep forgetting!

Brad LaPointe
MAAC 5418L

[Dan McEntee]

Has anyone had a prop nut come loose when the engine was running? That happen to me on an LA 46. But i want to know from your experience how much damage, if any was done to the engine. My engine started right back up and i didnt notice any difference, but it was a new engine and i only had 3 flights on it, so i cant tell if there is any performance loss.

Kevin

    If an engine kicks back and backfires it can knock the prop loose, but some times not enough that you would notice it. Sometimes you hear a soft "tick" when pulling it through by hand, and that is a good sign. If using wood props, a good habit to get into is to snug up the prop nut before each flying session, and the wood at the bub compresses, and then the tension on the nut relaxes a bit and it will come loose while running. The direction that the nut threads on is the standard right hand thread, or "lefty loosy, righty tighty" that most are familiar with but does nothing the ensure the nut stays tight. that would require left handed threads and I don't think that I have ever seen an engine with a left handed crank shaft threads. You see it on som eold cars on the lug nuts. Chrysler used to have left handed lug nuts on the left side of the car, with an "L" stamped on the end of the stud. The RPM that the engine is running during a shaft run isn't that extreme, and sounds worse than it is because there is no load on the engine. It the prop is broken during a shaft run, point the nose down and out the spinner into the dirt if flying over grass. Take a rag and covering the exhaust will snuff out a shaft run also. But like the others have said, I have never seen any harm done to an engine when it has happened to me.
  HAPPY NEW YEAR!!
  Dan McEntee

[Peter in Fairfax, VA]

What is harmful is if half the prop breaks off from flipping it or other reasons.  The first risk is the separated prop blade itself striking a person.  A massive imbalance ensues, sometimes ripping the engine off the plane by either wood breaking or fasteners loosening.

[Doug Moisuk]

Kevin you just need a bigger Wrench. 😈

[John Carrodus]

I store my wooden model props lose. Tighten in flight prep routine. Stops crushing and flyoffs.
Bill Bell, a big name in speed in these parts a few years ago . told me he had a runaway shaft run on one of his big speed jobs. He said after the shaft run, his engine was much faster and went on to set a new record!

[phil c]

I've more or less stopped using wood props because they tend  to break when used over grass.  Even though they aren't as relatively costly as molded and much cheaper than molded glass fiber.  When I was using, especially on combat planes, I drilled the mounting hole out and pressed in an aluminum, brass, or some plastic tubes.  Drill the prop, press in the bushing, and then stick it with CyA.  That usually fixed props getting tossed, or breaking and gouging you if the prop was bumped it while running.

It still works just fine these days on the planes that use bigger engines.

[bill bischoff]

Sorry to stray off subject, but back in the late '80's - early '90's, OS made a reverse rotation 46 SF, specifically for an F-16 pusher prop RC ARF. It had a left hand 6mm prop shaft thread. When they were closing them out, the hobby shop I worked for bought a bunch of them. I installed normal rotation cranks, and we were still able to sell them cheaper than a stock engine. Plus, I got a smokin' deal on the reverse cranks for my carrier pals and myself! BTW, when I needed to make heavy hubs, a 6mm left handed tap was actually not hard to find.

BB

[Brett Buck]

Has anyone had a prop nut come loose when the engine was running? That happen to me on an LA 46. But i want to know from your experience how much damage, if any was done to the engine. My engine started right back up and i didnt notice any difference, but it was a new engine and i only had 3 flights on it, so i cant tell if there is any performance loss.

     Probably no damage.

    Brett

[Leonard Bourel]

I highly recommend roughing up all surfaces All washers Props and use a proper wrench for tightening the prop Not just a little 4 way nut wrench .You just can't get enough torque on a little 4 way wrench Windy makes this very clear on many of his videos When I run that Rojett 90 I dont want that big  15 inch prop coming loose I check it before every flying session So far so good !!!

[kevin king]

I highly recommend roughing up all surfaces All washers Props and use a proper wrench for tightening the prop Not just a little 4 way nut wrench .You just can't get enough torque on a little 4 way wrench Windy makes this very clear on many of his videos When I run that Rojett 90 I dont want that big  15 inch prop coming loose I check it before every flying session So far so good !!!

Leonard, Do you have any video of you Ro Jett 90 flying?

[Leonard Bourel]

Hi Kevin I think there is a video of it flying at Brodaks around 2016 I will look for it on the tube

[kevin king]

I highly recommend roughing up all surfaces All washers Props and use a proper wrench for tightening the prop Not just a little 4 way nut wrench .You just can't get enough torque on a little 4 way wrench Windy makes this very clear on many of his videos When I run that Rojett 90 I dont want that big  15 inch prop coming loose I check it before every flying session So far so good !!!

For the tightening the prop nut on the RJ 90, this should do the trick.

[Leonard Bourel]

Good idea bud I will try that next time out Happy new year Kevin 

[Brian Hampton]

The only shaft run I've ever had was with a Series 70 K&B 40RR with a wood 7x10 prop. Never having flown a speed model before I took the advice of regular speed flyier who told me to put in a little down elevator as soon as it cleared the takeoff dolly to ensure it didn't go zooming up too high. Oops, it went straight down to the ground and sheered off both blades, instantly followed by a screaming shaft run for a few seconds before someone jammed the spinner into the ground. New prop and elevator level this time and it took off perfectly but speed was disappointing at only 120mph. At home I removed the engine to discover that all 4 front end screws were loose and, even worse, the disc valve had snapped along its shaft. The rest of the engine seemed fine but it's never been run again because disc valves for those K&B's are like hens's teeth in Australia.

As for props coming loose while flying this should never happen because the torque impulse after ignition is in the direction of tightening the prop nut. However, for engines with a removeable front end, if it's rotated 90 degrees towards the exhaust side, then it becomes a reverse rotation and in that case the torque impulse is in the direction to LOOSEN the prop nut. At one time, Enya were offering a pair of engines (IIRC 25's) where one was a reverse rotation (left hand thread) mainly for twin engined RC models.

[Dave Hull]

Yes, a shaft run can ruin an engine. I've seen it happen to more than a couple. The most recent was an Enya 60. It shed the wood prop and the engine was left with little to no compression, was hard to start and way down on power. The next wear/damage spot to check would be the fit of the big end of the rod.

The trick is not to have it happen, but if it does to get it shut down immediately.

I have also seen a good engine subjected to a shaft run and right afterwards it is the fastest it will ever run because it's loose. Bill Lee pitted a Cox Mouser that I loaned him at the Nats one year that did that. Best race that engine ever had....

The Divot

[Paul Van Dort]

In my opinion, stunt engines will run richer without load and this will avoid too much RPM.

I glue two pieces of rough sandpaper together back to back. Then I cut out washers from the double sided sandpaper and put them between the engine and prop and between prop and washer. Normal prop tightening and no more issue.

[Phil Spillman]

Make several disks out of medium to a bit more corse sand paper. Trace around a quarter cut out with your somewhat over the hill sissors and punch a hole at the center. Mount one disk at the drive washer and the other immediately behind the prop washer and tighten smartly. You should never have another prop come spinning off nor lossten up while pressing your starter against the spinner! This procedure has been working for me for many years! In addition make up several extra disks to keep in an envelope or flight box in case you need another sometime while out flying your old reliable whic suddenly sheds a prop!


Phil Spillman

[GERALD WIMMER]

Hello
In my time flying I've had lots of shaft runs.
 Most common cause was when my sons were learning with 35 sized combat models with nylon props , they'd hit the deck and we would restart the motor not knowing the sudden stop had loosened the prop nut and another shaft run would occur and they would slam them into the ground to stop the engine, retighten the prop if still in one piece and into the air again and normally the engine was fine.
The old Fox 19's and OS 15's and 19's used to strip the cogs/splines on the alloy drive-washer with a crash (and done quite easily too) and you would get the slipping clutch effect and freewheeling prop!
Bigger problem is if part of a blade was shed and the imbalance would often ruin the model and engine.
The other common cause of a shaft run was a backfire , especially if fitted with a spinner and it all comes loose if you continue starting.
Had more engines ruined by mud  (combat engines) or dust/sand (stunt engines) then shaft runs.

Regards Gerald

[john e. holliday]

A lot of good fixes here, but my Brodak 40 had a prop extension and the thrust washer would slip enough to let the prop come loose.  Finally after stripping threads on the extension nut and sandpaper didn't help.  I fianally J-B Welded the drive washer to the spinner back plate.

[Steve Helmick]

It would be nice to know if the prop in question was wood, plastic, or FG/CF. If the prop is not compressing, then it can help to put a "washer" made from 1/32" plywood under the prop washer to give something to compress. I haven't used a lot of wood props for stunt, and haven't had any problems with APC, Thunder Tiger or CF props coming loose.  Steve

[kevin king]

It would be nice to know if the prop in question was wood, plastic, or FG/CF. If the prop is not compressing, then it can help to put a "washer" made from 1/32" plywood under the prop washer to give something to compress. I haven't used a lot of wood props for stunt, and haven't had any problems with APC, Thunder Tiger or CF props coming loose.  Steve

The prop I
was using was a master airscrew 3 blade. I realize now that i should have probably not used a 4 way wrench to tighten the prop nut. Made me cringe because it was a brand new OS La 46 with all the extras from Randy Smith.