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Hartzell with a Loose Blade

Toobuilder

Well Known Member
Just a heads up for those with a Hartzel C/S:

I was just out in the hangar talking on the phone and since I was standing next to the -8 I just idly grabbed the propeller tip and gave it a shake. To my horror, it moved? A bunch! Fore and aft about ? inch; lead/lag about ? inch. Moved around like the shift knob in a VW bus.

Called the prop shop and yep, this happens sometimes. We have not opened the prop yet, but it?s likely a bolt that sets the preload on the shim pack simply broke. It?s a simple fix, but expensive to open the prop.

I bring this to your attention because it goes from ?good? to ?bad? instantly. Just in case you were wondering, this is not an old, junk prop. It?s a Blended Airfoil unit with less than 350 hours on it.

I?ll get back with a full report once it?s fixed, but wanted to give you all the ?heads up? to check this EVERY flight. This was a new one on me.
 
Wow

Michael, I sure am glad you found it, and how fortunate you found it without actually looking for a problem.
 
Its likely the stud that sets the bearing prelload came loose. There is a locknut that holds it in place. The whole prop needs to be disassembled to do this, one blade at a time since you have to go thru the open end of the hub to set the preload on the opposite blade.

Unnerving I agree but due to inertia it probably would be fine in flight.
 
Knowing the design of the propeller, I agree that the blade would be retained in the hub in all but the worst circumstances, but the issue with this is more insidious. I could easily imagine the roller bearing in the counterbore getting beaten to death and causing all kinds of (expensive) secondary damage to the hub or blade. Especially troubling is the lead/lag during the firing event.

I just hope I caught it early enough to get off lightly.
 
I always grab and shake my blades before every flight. I don't know why I do this or when I started doing it but now I have a very good reason for it.

Take some photos of the inside and what ever the issue ends up being. Would love to see.

Good catch and thanks.
 
I always grab and shake my blades before every flight. I don't know why I do this,,,,

Must be part of your pre-flight procedures. Good job. Way too many people who own their own planes get lackadaisical during their pre-flight inspection or worse yet,,,don't even bother at all!
 
Cleaning/wiping down the entire aircraft, including the prop, after every flight is a great opportunity to spot these issues.
 
As a side note, I was taught that you never push or pull a plane by the prop, if it is a constant speed.
 
Walt, Yes, I do wipe the bugs off in the summer including the prop. It seems to really collect bugs. I don't do it so much in the winter because there are no bugs and it is too cold to wipe with my detailing spray.

David, yes, it is part of my preflight. I just don't know when I started doing this.

As a side note, this caused me to go look at my prop log with the documentation from WW. Whirlwind has some movement allowances but not very much and so far, I haven't felt any movement in the blades. About 75 hrs.
 
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As a side note, I was taught that you never push or pull a plane by the prop, if it is a constant speed.
Best not go flying, then. Climbing, you're pulling the plane by the prop. Descending, the air pushes the plane by the prop.
 
In flight the blade shanks are loaded in the same axis as the bearings and races due to centrifugal force so all the balls are in contact and the load is spread. When pulling on the prop there are no centrifugal forces so when you pull on it depending on the preload there may be only a few bearings in contact tangentially. That said once you how the bearing races wear (brinnelling) and knowing how expensive the races are, it makes you think twice about pulling on the prop. I avoid doing it whenever I can.
 
As a side note, I was taught that you never push or pull a plane by the prop, if it is a constant speed.

Mike, I was taught this too.

But when you think about how much load is applied to this part in normal use, it is pretty hard to believe that I could cause any damage to it with my bare hands.

I dare say, it is an old wives tale...

My two...

:cool: CJ
 
As a side note, I was taught that you never push or pull a plane by the prop, if it is a constant speed.

This is one of those areas where I would love to hear what a Propeller manufacturer has to say. I have heard never push/pull on the prop. It doesn't matter. Only push/pull at the base near the hub etc etc.
Surely somebody out there in VAF-land has access to a manufacturer's engineering rep that can shed some authoritative light on the subject.
 
What Rocket Bob said is the same as I was told concerning the prop.

Loading on a spinning prop is a lot different than the load imposed by pulling on a not spinning prop.

Old wives tale??? Maybe so, but I think I will keep from using the prop as a handle anyway.

At least with the engine stopped---------
 
I always grabbed my hartzell on my Decathlon right near the hub and pull it out and push in to hanger. If its that fragile wear you can't pull/push it , then I don't need to be setting behind it while pulling a loop :D
 
Nah...

Mike and Bob,

I think you guys are both wet on this one.

I agree that using something in a manner for which it wasn't designed is a bad thing.

However, I dare say that the manufacturers designed our props strong enough to be used as a handle because they know that many pilots do exactly that.

Besides, they MOOR seaplanes using the prop!

If it is strong enough to drag my plane through the sky, it is strong enough to be ground handled by it.

Besides, I think that ALL the manufacturers are silent on this one???

:cool: CJ
 
Without any factual data, I believe Captain John has the best hypothesis going. With the list of cautions written for today's products - "warning, your new power drill should not be used for scratching your eye". I can't imagine the manufacturers wouldn't warn if the this act could be potentially harmful; especially an act that they know many owner/operators take part in.

That being said - maybe there is such a warning:confused: I'll have to dig out my manual.
 
Not all wet...I've had more than one apart myself and have seen how the races brinnell, which happens asymmetrically. There are plenty of other ways to push on these airplanes that aren't much more trouble to do.
 
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Just went to the Whirl Wind WEB page and could not find anything about pulling on the prop to move the airplane. Nothing pro or con.

I did find this:

2. BLADE FERRULES: Inspect each aluminum blade ferrule and blade intersection (located at the root end of blade where the silicone sealant is visible) for movement and/or signs of chafing. Gently flex the blade at the tip to check for any movement between the aluminum ferrule and blade root. No movement is allowed. There should be no movement between aluminum ferrule and blade. Notify Whirl Wind Aviation immediately if movement is detected.
3. BLADE MOVEMENT: Gently shake each propeller blade to feel for blade movement in the hub. Blade shake movement is allowed up to 1/8 inch, measured from the tip. Radial play of up to 2 degrees is acceptable. If the check shows values above these tolerances, contact Whirl Wind Aviation immediately. Movement is only allowed between the aluminum blade ferrule and the propeller hub, not as described in item #2 above.

So far, no movement in mine. :)
 
Pulling on the prop

This is from the Hartzell propeller manual: "Never attempt to move the aircraft by pulling on the propeller."
 
Blade Pre-Load

Based on the description of blade free-play, it sounds like a loose pre-load screw/plate. As mentioned already, the only way to correct the problem and rule out other more serious causes is to open the hub. This condition is very rare based on my time here but its easy to fix. If it is a loose pre-load then it should be fixed as soon as practical. We do have some info about blade free-play in the owner's manual FYI.

As others have said, the loading on the blade while operating is such that CF holds the blade shank in position against the bearings. The pre-load plate and screw keep it in contact with the bearings at low RPM and static conditions only. The pre-load is completely out of the picture once you have some RPM going.

Also, the loading on the blade is dramatically different during operation vs static when pushing or pulling on the prop. The total bending moment on the blade shank is relatively higher in some flight conditions (either static full power or closed throttle at high speed), the main difference is the blade is fully seated against the bearings under operation and the load paths are as-designed.

Yes, we have a statement in our owner's manual that says "never attempt to move the aircraft by pulling on the propeller." It is a rather general, nondescript statement. It seems that most everybody does this however and I've rarely heard of any damage caused by it. I have heard of other manufacturers having trouble with pitch change links breaking. The main concern is someone grabbing the blade fairly far from the hub (high bending moment) and pulling on the trailing edge of the blade (high twisting moment) at the same time. Minimizing the bending and eliminating twising moments on the blade is what's important.

Regarding this particular prop, if you or the prop shop have any questions, please call our Product Support folks at 1-800-942-7767. I don't know how old the prop is but if relatively new, it may be covered under warranty so call and check with them.

Les Doud
 
While it's good guidance not to move an airplane around by a C/S prop, I'd like to point out that the propeller in question has NOT been used as a handle... ever.

I only point this out in case someone tries to make that connection.

And yes, it's going to the prop shop on Friday.

...The Rocket gets pressed into service as a flying truck for the first time!
 
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Its likely the stud that sets the bearing prelload came loose. There is a locknut that holds it in place. The whole prop needs to be disassembled to do this, one blade at a time since you have to go thru the open end of the hub to set the preload on the opposite blade.

Unnerving I agree but due to inertia it probably would be fine in flight.

So it appears I never followed up on this...

Long story short:

Prop was disassembled and inspected. No internal damage, and the expected failure of the preload nut coming loose was not the case. It was still tight. The prop shop has no idea what happened for sure, but speculation centers around the previous shop setting the preload incorrectly without the races being seated. As said in the first post - all was well for 350 hours, then everything just settled in and the blade went loose.

It has been flying in the repaired condition for 50+ hours with no additional issues.
 
Mmmmm....and there it is. Thanks, Jim. Now...how to push my plane into the hangar... Edge of cowl opening?:confused:

Geez, I've been guilty of this myself. :( (pulling on my prop) Guess I'll go back to pushing on the roll bar behind the pilot's head. (RV 8) Not sure if this works on a side by side RV. For pulling it in the hangar, I have a small curved piece of PVC water pipe I got as junk from home depot, use that as a handle, and then inserted a 6' long waterski type rope thru that, (with a closable hook installed) and wrap it around my tailwheel strut. The tail wants to "wag" as you pull your plane, but you soon learn to master that. Works great. Got the idea here on VAF years ago, so the credit goes to that fellow. Oh, and it doesn't take up any room, ie easy to toss in your forward baggage comp.
 
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