Disaster Averted

Airboat propeller discussion.
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digginfool
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Disaster Averted

Postby digginfool » Thu Sep 15, 2016 8:46 am

Some of you followed my post "Need Help 2A Now" and wanted to know what the final analysis was. The prop in question is a 72" Whirlwind Excalibur and the engine is an O540 narrow deck, SV with 10:1 pistons and a 290 cam. Now, you may be wondering why I said anything about the engine but the failure of the hub plate is directly attributable to it. Whirlwind said the plate failed due to metal fatigue and I agree; classic example. The question was why? I didn't know until just yesterday that the engine builder removed the counter-weights from the crank. It's a common practice for airboat engine builders but a practice that some builders are moving away from. From a post Patti made some time ago (2012):

" The crankshaft counter-weights are there to reduce the torsional vibration
stresses imparted on the crankshaft and the propeller by dampening the power
pulses from the combustion. You could think of it as a rotating shock
absorber. When the engine fires, it twists the crankshaft, and the
counterweights are there to reduce the phase angle between one part of the
crank shaft and the other (e.g. crank journal to prop flange). When
engineers designed the size and location of the counter-weights, they used
optical sensors to identify the phase angle between different locations on
the crank shaft.

Wood propellers are somewhat more tolerant of these torsional vibratory
stresses compared to today's modern composite propellers, but the benefits
of modern composite propellers far outweigh this characteristic. It would be
a wise idea to keep the counter-weights installed."


The fact that the engine has performance upgrades exacerbates the situation as the impulses are that much stronger. Plus, the shorty headers allowing the exhaust pulses to go through the prop disc could increase the effect as well. All of this fits with the odd harmonics I heard and often complained about. I do not dispute their analysis as it fits perfectly with what I theorized had happened (other than the part about the counter-weights; I honestly did not know until yesterday that they had been removed from my engine - it was also one of the first questions Patti asked when we initially discussed the issue).

Patti's suggestion was that I stick with the Excalibur since it is a more robust blade. This condition can affect the blade as much as the hub plates. She also suggests that I experiment with pitch and cruise RPM and try to find a combination that minimizes the harmonics that I heard. Re-clocking the prop would also change the way the blades interact with the exhaust pulses and was another suggestion Patti had made. While none of these adjustments will completely alleviate the condition, it could certainly help. Bottom line is that the hub plates will have to be considered a 'wear item' and will need to be thoroughly inspected on a continual basis, replacing them if/when a crack appears. It will tend to be a slow process, one that can be caught early with frequent inspections.

Patti has offered to replace the entire hub assembly free of charge, this one time only. This is exceptionally fair and very generous since the failure is not due to her product. She has also offered to keep the Excalibur and give me credit towards another Whirlwind prop of my choosing. At this time, I have not decided what path I'm going to take. I had used a 6 blade Saber for 3 months and really liked the smoothness and overall performance. Plus, it did not exhibit any of the harmonics I experienced with the Excalibur. Currently, I'm using a 6 blade Warp and also do not experience the harmonics but do not like the performance or sound signature.

Bottom line, it's very important to do regular and thorough examinations of your boat. I do a cursory look every time I go out but that will now be expanded to include a close visual inspection of the prop. I also go over all connectors and ensure they are tight (with a torque wrench when required) when I do an oil change. I do believe that whatever path I choose for a prop, it will be one that allows me to remove the prop for inspection without having to completely disassemble it and re-pitch. In the future, I will also stop at the first odd vibration I feel. That was my big mistake in this episode, one which could have resulted in catastrophic damage to boat, motor, prop and, potentially, passengers. The initial vibration I felt was so slight and I felt it only through the rudder stick but it was enough that I felt it necessary to ask my wife if she felt it. I should have followed my instincts. It's not that I blindly went on this time; I did stop, I did check visually, manually twisting, pulling and pushing on the blades to see if something was loose, and with a wrench. I just didn't see the crack, if it was even there to be seen yet. From here on out, you can be sure that at the first sign of something being amiss, my ass is off the boat and looking real hard for the reason. If I don't find it, I'll have myself towed in, put it on the trailer and start taking things apart until I do find it. No matter how slight the issue may seem. Not worth dying over.
“When plunder becomes a way of life for a group of men living together in society, they create for themselves in the course of time a legal system that authorizes it and a moral code that glorifies it” - Bastiat

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digginfool
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Re: Disaster Averted

Postby digginfool » Thu Sep 15, 2016 9:24 am

A reminder of what happened.

digginfool wrote:Image


[quote="digginfool"]Image

[quote="digginfool"]Image
“When plunder becomes a way of life for a group of men living together in society, they create for themselves in the course of time a legal system that authorizes it and a moral code that glorifies it” - Bastiat

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Re: Disaster Averted

Postby flcracker9 » Thu Sep 15, 2016 9:30 am

Greg, have you considered installing a full exhaust to eliminate any issues the exhaust could be contributing to premature failure?
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Re: Disaster Averted

Postby SWAMPHUNTER45 » Thu Sep 15, 2016 9:49 am

Very fair of Patti and the Whirlwind team! They should be commended.

This dynamic you refer to is also very present in the Cadillac direct drive engine. I can recall Darrin discussing the excessive forces the blade shank encounters and how they will reinforce an NGQ shank if the customer requests and advise it is going on a high performance Cadillac. Basically every time the cylinder fires it transmits a severe shock wave directly to the blade.

Excellent info on the modified crankshaft issue Greg, folks best pay attention and really pre-flight well!

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Re: Disaster Averted

Postby radtech » Thu Sep 15, 2016 9:52 am

Glad it wasn't any worse, Brother. Hate I missed you this spring. Gonna be down again next spring. Hope to ride with you then. Take care, Brother, and slide safe


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Deano
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Re: Disaster Averted

Postby Deano » Thu Sep 15, 2016 9:53 am

Airboats and motorcycles are two of the biggest instances of where any new, odd and/or different
vibration should not be ignored at all, and should be researched and identified as soon as is possible.

That sounds like a pretty obvious statement, but maybe somebody reading this will keep that more in the
forefront of their thought process and stop to check, instead of thinking "Oh yeah, I better check that later . . . . ".

Your example brings to light what should, and needs to be obvious for other people who haven't yet had
that experience. I could tell a similar story (without a bad ending) about a front wheel bearing . . . . :shock:
"The suppression of uncomfortable ideas may be common in religion and politics,
but it is not the path to knowledge; it has no place in the endeavor of science."
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Re: Disaster Averted

Postby John Fenner » Thu Sep 15, 2016 12:20 pm

Likely the exact same reason why I don't recommend a 3 blade on a 6 cyl in which I've seen 2 cracked Lycoming cranks and the crank gear bolts on a continental shear off, you can install counterweights without splitting the case but only if the bushings are still in the flanges, and or if flanges haven't been removed from throws.
I never finish anyth,,,.

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Re: Disaster Averted

Postby digginfool » Thu Sep 15, 2016 12:37 pm

John Fenner wrote:Likely the exact same reason why I don't recommend a 3 blade on a 6 cyl in which I've seen 2 cracked Lycoming cranks and the crank gear bolts on a continental shear off, you can install counterweights without splitting the case but only if the bushings are still in the flanges, and or if flanges haven't been removed from throws.


I had seen other comments about a 3 blade not being compatible with a 6 cylinder. Would that be the same issue with a 6 blade stagger hub?
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Re: Disaster Averted

Postby John Fenner » Thu Sep 15, 2016 12:45 pm

Quite possibly
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Re: Disaster Averted

Postby Seven3 » Thu Sep 15, 2016 1:08 pm

So is a multi-blade prop (5 blade razor or 6 blade razor non-staggered) the least stressful type of prop you can put on a 540? I was a big fan of the five blade razor I had on my last 540, and with plans to build a brand-new one for my new boat, if there is a prop type that will extend engine life by creating less stress on the crank, I'm all about that. Hopefully Patti will chime in on that.

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Re: Disaster Averted

Postby kwanjangnihm » Thu Sep 15, 2016 1:09 pm

diggin there are a lot of horror story threads on counter weight removal from AC cranks - why were yours removed? any idea?
" I don't care who you are back in the world, you give away our position one more time, I'll bleed ya, real quiet. Leave ya here. Got that? "

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Re: Disaster Averted

Postby digginfool » Thu Sep 15, 2016 1:19 pm

kwanjangnihm wrote:diggin there are a lot of horror story threads on counter weight removal from AC cranks - why were yours removed? any idea?


Honestly, I don't know. My engine was supposedly a runout when I purchased it and I had it rebuilt so that I wouldn't have to worry about doing it later. As I understand it, removing the counter-weights was a very common practice at one time. I would assume it is to reduce rotating mass, making a quicker revving engine. Perhaps that was the point, perhaps it's just because that's how my engine builder learned and it's how he's always done it. I'll have to ask.
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Re: Disaster Averted

Postby Doc jones » Thu Sep 15, 2016 1:51 pm

what would be the difference between the 3 blade prop for an air plane like the one pictured on Lycoming's web site and one on an airboat

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Re: Disaster Averted

Postby John Fenner » Thu Sep 15, 2016 3:46 pm

Yes, it was a common practice to remove the weights, however I have put crankshafts in bone stock gpus, with nothing else changed but the crank and rods, new crank had weights on it, old one didn't and it turned harder than before.
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Re: Disaster Averted

Postby 406 JAMIE » Thu Sep 15, 2016 4:06 pm

[b]my last boat 13x7 alumntec hull 88yr with a io540 widedeck fuel injected 300hp at 2750 and it had a whispertip 9.5wide blds and 74in long 3bld and that thung never had a problem i love whirl wind props. :rebel: /b]
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Re: Disaster Averted

Postby helicsher » Thu Sep 15, 2016 5:42 pm

If whirlwind knows it is common practice that airboat engine builders
remove these weights .why is there product not designed to withstand the way the motor operates
When your buy a prop they ask you about your boat and motor set up , shouldn'they ask if your weights have been removed
Holly cow if that thing would have come apart it would have been really bad
That's a big peace of metal moving fast someone's looking out for you!!!!!

We all need to inspect our boats like it's an airplane we are leaving the ground with
Can't tell you how many times I got to the ramp in the dark and was more worried if we had enough beer than if my rig had all the parts still working proper
That's fair warning for all right there!
"Success Requires No Excuses"

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Re: Disaster Averted

Postby digginfool » Thu Sep 15, 2016 6:55 pm

I appreciate your feelings but I reject the idea Whirlwind is doing anybody a disservice. Two things at work here; first, an issue beyond their control in the removal of the counter-weights. Second, I did not cease operating the boat once I definitively knew I had a problem; I allowed what they call in the pilot business a condition that kills many to get the better of me; get-home-itis. Thus my statement of stopping in the future if something is amiss.
“When plunder becomes a way of life for a group of men living together in society, they create for themselves in the course of time a legal system that authorizes it and a moral code that glorifies it” - Bastiat

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Re: Disaster Averted

Postby helicsher » Thu Sep 15, 2016 7:58 pm

bologna
I have a whirlwind prop and love it , not quite as high tech as yours but behind my 520 it does the job and I am not looking to change it


But the way I read the post she's saying they know it's not strong enough
Shore you ran it to the edge of catastrophic failure but it failed in a small place first form not being able to handle the power and vibration
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Re: Disaster Averted

Postby terrible ted » Thu Sep 15, 2016 9:02 pm

helicsher wrote:If whirlwind knows it is common practice that airboat engine builders
remove these weights .why is there product not designed to withstand the way the motor operates
When your buy a prop they ask you about your boat and motor set up , shouldn'they ask if your weights have been removed
Holly cow if that thing would have come apart it would have been really bad
That's a big peace of metal moving fast someone's looking out for you!!!!!

We all need to inspect our boats like it's an airplane we are leaving the ground with
Can't tell you how many times I got to the ramp in the dark and was more worried if we had enough beer than if my rig had all the parts still working proper
That's fair warning for all right there!




no prop manufacture ever asked me ses or ww. Now that was long ago. about counter weights that is

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Re: Disaster Averted

Postby helicsher » Thu Sep 15, 2016 9:54 pm

I read the fools original post about this subject a couple hours after he posted it, hoping I could come help someone who was in distress as I only live 10 min from the Sawgrass ramp and I am always ready to help a stranger and make a new friend but did see he got it going and made it back safe that's great

Then saw the pictures and read how world wind was going to look at it .
Thinking to myself this is a good safety lesson for all
" know your boats vibrations "
I remember reading this in the air boat safety post here's a good reminder

Today I read "Disaster averted " OK lets read what happened
What I got was patty says it you don't have balance weights on your crank that prop can fail
So I am thinking here's another safety lesson don'trun that prop with that set up
I don't think this should be bash post for world wind it should be a safety post I think that was the point of thre fools post to begin with

I have never bought a prop from a dealer but I have looked at them at Schmitt and the shows and was asked what kind of boat,motor and what do you want to do with it
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digginfool
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Re: Disaster Averted

Postby digginfool » Thu Sep 15, 2016 10:20 pm

Helicsher, I truly meant no offense. I completely understand where you're coming from. I just don't see it as a Whirlwind problem. However, I do realize everyone will see it in their own way. Peace and thanks for thinking of me that day I broke down.
“When plunder becomes a way of life for a group of men living together in society, they create for themselves in the course of time a legal system that authorizes it and a moral code that glorifies it” - Bastiat

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Re: Disaster Averted

Postby helicsher » Fri Sep 16, 2016 4:09 pm

I was never offended my skin is thicker then leather
Just having conversation
Now you now I am here for anyone
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Re: Disaster Averted

Postby kwanjangnihm » Tue Sep 20, 2016 6:50 am

Diggin have you decided to stay with the same prop setup, or will you go a different route?

Any thoughts on adding the counter weights back or is it cost prohibitive?
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Re: Disaster Averted

Postby digginfool » Tue Sep 20, 2016 7:55 am

I am going to a 5 blade 72" RazorX. As far as the counter-weights go, have not discussed that with the engine builder but I would imagine it would entail splitting the case to re-install. Plus, as it was explained to me, the counter-weights have their own issues. In an airplane, the motor runs at a steady rate with gradual throttle setting changes. In an airboat, you have constantly variable and sometimes rapid changes in throttle settings. The counter-weights sit on dowels that are only held in place with pins. They've been known to come off and destroy the case. They also weigh a lot. On the negative side, their removal does allow harmonics to develop, particularly with wider blades (so I've been told). However, I've also been told that the wider blades, being more robust, stand up to the harmonics and the power pulses better. Who knows? Sounds like fodder for another thread. My own experience is the harmonics I experienced with the Excalibur did not exist (at least audibly) with the Saber or Warp props that I have used. I guess we'll find out soon enough for the RazorX prop. I will certainly report what I experience. In the meantime, the Excalibur is being sent back to me with all new hub hardware; plates, bolts, spacers and clamps. It will be my backup until I determine the RazorX will do the job or not. At that point, I will have either an Excalibur, a RazorX or both for sale.
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Re: Disaster Averted

Postby flcracker9 » Tue Sep 20, 2016 8:10 am

I'm no engine builder, but I've been told if just the couterweights themselves were removed, they can be reinstalled by removing 1 jug, no splitting of the case necessary?
12' Open Palm Beach, IO-0470-L 260hp, 72" NGQ


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