WARNING!!! Check your prop bolts!

[BEN S]

I had a close call today, I got up extra early so I could fly some egg McMuffins to my wife and her girl friends who had gone camping in the desert last night.
I preflighted my machine as I always do. Now I have been good about balancing my wood prop, a 64/32 GSC with epoxy leading edges, but after the last balancing, I haven't undone the safety wire to check the tourque on the prop bolts. I guess it hadn't occurred to me that if the bolt was still tie wired in place that the torque might not be correct anymore. Best as me Evan and Jim at Sportcopter can figure, the desert heat during the summer must have dried out my wood prop and the dimensions must have shrunk just enough to affect the torque on the prop bolts. Anyway, There I am on a Malapais in the desert and looking all awesome for delivering their breakfast, when I started the engine to leave there was a funny ping sound and the engine started to race a little. I immediately shut off the engine and was waiting for the prop to stop spinning before unbuckling my seat belt but the prop wasn't coming to a standstill, as a matter of fact it wasn't anywhere to be seen! The whole f**king prop and pre-rotator drum had sheared off the back completely and as neatly as if a laser had cut it!
Amazingly, the re was my prop sitting nicely on my tail Like I had laid it there! Not a mark on the prop, the tail or the drum(thank god)
After an embarrassing ride to the house (not as cool as I was earlier) my partner Bob and my son and I got some new bolts and went out to see if it was going to be an easy fix or were we going to have to get a trailer into the middle of 4 wheel country.
Long story short, it took less time to fix it than type about it, and as I only had to fly 10 miles to the hangar I decided to fly it back (of course after looking at EVERY screw and bolt and a couple of test runs),
The mental puckering on the way back was there, but I wouldn't have flown it if both Bob and I weren't certain it was OK. Tomorrow I'm going to tear it down to brass tacks and basically give it an annual.
After careful examination of the bolts, TWO were broken sometime before today!
I implore all of you, take the time and check those bolts, it's not worth the possible consequences for not checking them!
Ben S

[Master Roda]

Jeezus Ben, glad your ok. Those wood props need attention. Glad you caught that......

Your still a hero in my book :)

[RotoPlane]

Gee....I will now consider adding a couple .5" dowels or .75" through-bolt dowels to handle the shear-loads on my prop installation. I didn't think those six bolts would shear-off like that…..

[Passin' Thru]

Gee....I will now consider adding a couple .5" dowels or .75" through-bolt dowels to handle the shear-loads on my prop installation. I didn't think those six bolts would shear-off like that…..

Ed, my opinion is it wouldn't do you a bit of good if you don't maintain sufficient "crush" on the prop. Once the prop shrinks enough to lose the "crush" between the prop driver flange and the plates, torsional impulses cause an oscillating motion between the prop and the driver flange which fatigues the bolt threads where they enter the driver flange. Then it's only a matter of time (cycles) before they let go.
I would suggest that when checking and found loose, you replace the bolts.
This problem probably is not as prevelant with composite props and metal hubs, but it's a good to check them anyway.
There have been instances where the the fiction of the oscillating motion between the prop and the driver flange set the prop hub on fire! There was one case where the hub was chared enough to weaken it and permit the prop to sling apart resulting in a pretty serious accident.
As Ben sez, check those bolts!

[RotoPlane]

Thanks Pete, I'm sure you are correct on the crush factor and checking bolt torque. I'm using six M8 (.315 dia) studs to hold my aluminum prop hub and thought it may be better to allow dowels or bushings to take the shear loads (similar to the Lyc.180hp hub flange) and just have tension loads on the studs. But perhaps this would be overkill since I haven't heard of that happening with a metal hub….

[dinoa]

The GSC prop originally had six 1/4" AN4 prop bolts but these proved inadequate. For Rotax engines three 1/4" dowel head set screws were added to the prop flange to help with the shear loads and extended into the aluminum prop hub and prerotator drum.

Did your installation include the dowels as I can't tell from the pictures.

You may also want to read these links

http://www.ultralightprops.com/bulletins/bulletins.htm
http://www.ultralightprops.com/technical.htm


Dino

[Doug Riley]

Classic prop "theory" is that, with sufficient bolt tension, the driving torque from the engine flange passes to the prop via friction with the hub -- like a clutch. The bolts shouldn't be loaded in shear.

Charring and exploding props used to be a semi-common event in the Bensen-Mac era. Bensen used stacked-up Belleville washers (spring-steel washers that are dished into a shallow cup shape) that would crush flat when torqued. On preflight, if you saw the washers resuming their cone shape, you knew the prop had shrunk and a re-torque was in order.

It helps, too, to keep the idle on Rotaxes at or above 2,000, and avoid goosing the throttle like a dirt biker during ground ops. I recall one PPC pilot I used to see at flyins who tore around in his PPC cart as if were a go-kart. One day his prop sheared all its bolts (while he was taxiing) and rolled away like a hoop snake.

[Scary Gary]

You must be eating your vegetables , saying your prayers and living right .
So glad that this turned out well Ben .
Dick Wunderlich lost his prop once . But he was flying at the time . He never did fined that prop .
Just think of how tragic and devastating it would have been if you didn't fined your prop .

[BEN S]

Uhhh actually NO I didn't have any of the studs, only the 6 80x1.25 by 80mm metric bolts. Didn't see anything on GSCs website about the studs, is that from Rotax?
Also thanks for the tech bulletin. You know I haven't complained to GSC yet and that is my first responsibility to them, but as far as any kind of installation instruction sheets, I have purchased two props from them and neither had an instruction sheet with it.
Thanks for the post
Ben S

[BEN S]

I talked with Dave B last night about the bell vile springs idea, it occurs to me that part of the problem with safety wiring the bolts is that without undoing the wires there isn't a decent way to check the prop bolt torque. Would you be better off using nail polish to make a witness mark on the bolts and instead of wiring them just add a torque check to your weekly maintenance?
Ben S

[BEN S]

living right....yeah veggies, not so much and frankly if I never found this prop I would be OK, I never liked it much!
Ben S

[PW_Plack]

...Would you be better off using nail polish to make a witness mark on the bolts and instead of wiring them just add a torque check to your weekly maintenance?

Ben, if the looseness is coming from prop shrinkage, and not from the bolts or nuts actually turning, the marks wouldn't move, right?

[Passin' Thru]

Ben, if the looseness is coming from prop shrinkage, and not from the bolts or nuts actually turning, the marks wouldn't move, right?

Very good point!

[BEN S]

However the wire served two purposes, one as a sort of witness mark and two as a securing wire. Our discussion was about NOT using a wire at all so that you could frequently check the bolt torque. But this wouldn't provide you with any kind of a securing method. Some of the engines don't use tie wires on the prop bolts.
Ben S

[Flying_Lab_Rat]

Maybe it wouldn't be a bad idea to change the prop bolts every six months or so. As for torquing again, it's not a bad idea as long as you loosen the bolt first, then torque it. If you make another run on it while it's tight, it can artificially overtorque the bolt. Safety wire is still a good idea though; the bolts become projectiles and FOD if they depart the aircraft.

[dinoa]

Uhhh actually NO I didn't have any of the studs, only the 6 80x1.25 by 80mm metric bolts. Didn't see anything on GSCs website about the studs, is that from Rotax?
Also thanks for the tech bulletin. You know I haven't complained to GSC yet and that is my first responsibility to them, but as far as any kind of installation instruction sheets, I have purchased two props from them and neither had an instruction sheet with it.
Thanks for the post
Ben S

Ben,

8mm prop bolts under normal conditions are more than adequate.

The studs might have been an air command addition as they were long enough to go through the prerotator drum and into the prop hub. The links were from the GSC website.

Dino

[Alan_Cheatham]

Ok, here's my two cents worth.

Looking at the pictures it appears the prop bolts thread into the prop flange and this means that the shear load created by the engine driving the prop will be placed on the threaded portion of the bolt. Bolts should NEVER have a shear load on their threads, only on the un-threaded shank. Go to thru bolts and use nuts.

.

[BEN S]

Spent the entire day at the hangar tightening bolts and doing a very methodical once over.
The prop shrinkage was spot on, I have a prop balancer that used to balance the prop when I first got it. the spindle it sits on wouldnt even come close to going through the prop now!
Alan, I am using the standard Rotax set up and the flange is threaded, so I cant put the shank through those holes. The other ones maybe.
Ben S

[Timchick]

Ok, here's my two cents worth.

Looking at the pictures it appears the prop bolts thread into the prop flange and this means that the shear load created by the engine driving the prop will be placed on the threaded portion of the bolt. Bolts should NEVER have a shear load on their threads, only on the un-threaded shank. Go to thru bolts and use nuts.

.

Go back and read Doug's post. When the bolts are properly torqued there is not shear load on the bolts because the crush plate is holding the prop. The reason the bolts failed was because they weren't tight enough to provide the "crush" (due to the wood prop shinking) to keep the prop in place. Under normal circumstances the bolts are fine.

[BEN S]

Costanza!....."I got shrinkage!!"

It's a Seinfield thing.


Ben S

[Earthboundmisft]

Hey Ben, consider an Ivo prop. Lightest 3 blade, affordable. I love mine. My mounting bolts protrude through the prop flange, and I used acorn jamb nuts on the back side. 70 hours, no change in bolt torque.

[GyroRon]

Warp drive is better.... The prop is nearly indestructable, easily repaired and the bolts go through a aluminum hub. The Ivo is a good prop too, but the Ivo is the most critical prop out there for proper torque on the bolts, as the prop is held together and held on the machine from the crush forces of the bolts torque, not shear at all....

I also do like Earthboundy does and use slightly longer bolts, so I have some threads sticking out on the outside of the prop flange and I use a nut on the outside which works like a jam nut, keeping the bolt from loosening.

[BEN S]

Spent an hour on the confuser researching new props. My wife says to me why put on that older wooden one if the 3 bladed ones don't loosen up when the wood dries out? (gotta love that...shes practically begging me to buy a new prop!)
I tell her I always went with wood cause I love the look and it was cheaper, and she says so clean it up and hang it in our bedroom! But don't take chances go buy the composite prop!
So I am looking for a new prop setup. I have no particular favorites BUT I fly off a gravel runway and occasionally the desert floor. I'm not so into changing thee pitch and I don't care if its two or three blades.
I have a heavy (340lb) gyro and a heavy (205lb) pilot on a 503 dcdi at sea level.
What say you guys, whos got the best prop with a metal hub?
Ben S

[NoWingsAttached]

somebody saw the safety wire on my warp drive and told me it can actually be worse to wire it - that holds sheared prop bolts in position and you can miss it in pre flight. Better to have one break and fall out, and SEE it gone and take care of it b4 it is critical.

[BEN S]

I sorta feel the same way, that was what I was trying to say earlier but couldn't get the right words to come out.
Ben S

[CLS447]

I love the IVO prop ! So easy to adjust ! They don't want you to safety wire the bolts.

I should check the torque more often but I would have to remove the spinner cap.

I always check the threaded ends of the bolts by looking behind the drum.

Next flight I will check the torque but it will probably be right.

I could add some nylocks on the threaded ends......at least maybe thin nuts.

I also use red locktite on the prop bolts.

I also can't believe it snapped them all right off !!!!!

And George said......" I was in the pool ! " Elaine was also unaware of the shrinkage .

[GyroRon]

Spent an hour on the confuser researching new props. My wife says to me why put on that older wooden one if the 3 bladed ones don't loosen up when the wood dries out? (gotta love that...shes practically begging me to buy a new prop!)
I tell her I always went with wood cause I love the look and it was cheaper, and she says so clean it up and hang it in our bedroom! But don't take chances go buy the composite prop!
So I am looking for a new prop setup. I have no particular favorites BUT I fly off a gravel runway and occasionally the desert floor. I'm not so into changing thee pitch and I don't care if its two or three blades.
I have a heavy (340lb) gyro and a heavy (205lb) pilot on a 503 dcdi at sea level.
What say you guys, whos got the best prop with a metal hub?
Ben S


Two blade Warp drive prop, with as much diameter as you can stand.

The Ivo is a great prop, but again, look at how it is secured, the bolts going through the prop do not keep the blades from flinging off, it is the knurled crush plates on either side of the blades that is crushed into the prop that holds the blades from flying off the engine. The Ivo has the easiest adjustment of pitch, but it also is not nearly as durable or repairable as a warpdrive. I would not fly off gravel with any prop other than warp drive.

With a warp drive setting the pitch might take a hour or two, but once done you should never have to mess with it again.

[BEN S]

i have read about a lot of warp drive failures on the ultralight news web. Also their website is rubbish. I want tough but it makes me uneasy,,,smoke theres fire thingy.
also which one weighs less? and is it by a large amount?
Ben

[Vance]

I feel it is important to keep after the prop bolts.

I check mine at each oil change.

It only takes a few minutes to safety wire the prop blots.

Both my props have been plastic with a wood core.

They usually come out the same; I always loosen all of them before tightening them in the proper sequence and stages.

I also check for marks on the propeller hub that would indicate movement.

On the IO-320 there are dowels that fit into the prop hub that go a ways into the propeller. They have the threads in them. I feel and have read that it is still about the crush and not about shear.

I feel that the propeller is a flight critical component and should be handled with care.

Thank you, Vance

[GyroRon]

i have read about a lot of warp drive failures on the ultralight news web. Also their website is rubbish. I want tough but it makes me uneasy,,,smoke theres fire thingy.
also which one weighs less? and is it by a large amount?
Ben

Ben, I take it your somewhat sheltered aviation wise.... reason I am saying that is not to be a smartass, but if you have spent any large amount of time around this sport you would know Warp drive is one of the most popular and more reliable props out there. It is also one of the heaviest, but a 2 blade would be fine on your 503.

[BEN S]

You are most correct. I fly alone. really alone. The Utah fly=in was the first time I flew around anyone else. The cessna I rent is left with the keys on the pad waiting for me once a month and the fixed wings don't use anything but hartzell and sensenich from what I can see.
Im not saying that the warp drive is or isnt a great prop only that there was an article that said they have had over 30 failures mostly on two stroke rotax engines. I don't knw how old that is maybe they fixed whatever was wrong, but you aint gettin any info off the companys website!
I like the idea of the warp drive being rugged and easy to repair and will try tpo contact the company today to get some idea of what I will need.
Ben s

[Doug Riley]

I've been flying Warps for almost 20 years. They are tough and repairable. I certainly have not had a failure of any sort.

The company has been very reasonable about trade-ins and replacement blades. For example, I traded a used CW prop for a new CCW one when I switched from a Rotax 618 to a 912. They charged a very small cash differential.

[C. Beaty]

Use a ¼” carbide spade drill and drill out the threads in the prop flange (it’s hardened and will eat ordinary drills).

Then use longer bolts with self locking nuts behind the flange.

[helipaddy]

Ive done what Chuck says on every rotax 2 stroke engine I've had. Drill out the threads and fit longer bolts with locknuts. That material in the prop flange is seriously hard though.

[BEN S]

but there doesn't seem to be enough space behind my pre rotator drum to get a hand and socket.
And I'm not sure I like the idea of ME drilling through a hardend plate. Better chance of it cracking.
I'm sure this won't happen again as I will not be using a wooden prop here in the summer.
But I do appreciate the comments.
Anybody else got an opinion on the warp drive propellers vs other brands?
Ben S

[Chuck Roberg]

Anybody else got an opinion on the warp drive propellers vs other brands?

If it's durability that your looking for then Warp Drive Props fit the bill.

It is a heavier blade so you might have to adjust your idle speed a little higher to smooth out the engine.

[azdave]

Hello all you Gyro guys. I'm a trike flyer but have always wanted a Gyro. I'm in N.E. Az. and hope to meet up with you guys sometime. I fly a Rotax 912 and have owned Rotax 582's and 503's with a variety of props. I'm running an Aero Lux prop on the 912. It's much like the Kiev prop but it has nickel leading edges and a built in scale for pitch setting. I like it more than any other prop I've owned. I like warp props but they're heavy.I've seen them mow down big bushes more than once with no damage. I like the Ivo but it's heavy too believe it or not. The aero lux is a foam core/hollow prop. It will take some rocks because of the nickel leading edges but will disintegrate on hard impact. I've been told by many that is desireable because it will save the crank/gearbox. I have always checked torque every 25 hrs and have seldom seen any movement. To each his own but I wouldnt modify a prop or the flanges in any way without the manufacturers ok.

[BEN S]

Hello, I looked at the website for the Aerolux props. I don't know what it is about propeller manufacturers but they for the most part have some of the lousiest websites! I will agree with them on one point those ARE some beautiful looking props if not a bit spendy. I am using my old wood prop, the one I had been saving previously in a closet for just such an emergency, I can't understand why I ever changed it out, more thrust and what seemed like a better rate of climb to boot!
Thanks for the suggestion.
Ben S

[All_In]

Hi Buddy,

We pick of the PA-28-180 tomorrow!

So Dave and I will be flying out to see you for the GREAT adventure!

See ya soon!

[Flying_Lab_Rat]

PA28-180? Loved those....was my favorite plane at the FBO/flying club where I was last stationed. Always tried to land her light enough not to compress the struts...she'd usually settle about the time I'd turn onto the taxiway(was quite a surprise to the passengers!) Can also attest that the little vent window is JUST big enough to get a diaper out of when my son decided to try to kill us all while on a flight across Kansas. Ah, the fond memories...

[Scary Gary]

So you're the A$$ who hit me with the dirty diaper .