Propeller Woes

[Richard Boyer]

I called Sensenich yesterday to check up on my prop. Boy did they freak me out. I sent it exactly 1 month ago today. At first they were just going to do a refinish, next they said it needed a rebuild. Now.... Throughout this whole process I had to call them every time for updates on what was going on. So yesterday I decide to call them to make sure they are on schedule for delivery next week. The conversation started with, "Mr. Boyer, I'm not sure how to tell you this.....".


Quite frankly that is not how a Doctor would start a conversation with a person that thinks they have cancer, when actually all they have is a pulled muscle!!!

Turns out that they had removed everything and was down to bare wood. Had re-laminated the hub and put the canvas tips on. At this point, someone noticed that the holes on the engine side of the hub were oblonged (little late wouldn't you think?). BUT, they were oblonged 90 degrees out of what they have ever seen. They asked if the prop were ever loose (which still wouldn't explain it being oblong in the direction they are).

Now, I'm fairly paranoid about the prop. There was an accident here in Georgetown with a guy that threw a blade on his Swearingen. Shook the engine right off the front of the airplane before he could even pull the throttle back! So, NO that sucker has never been loose (at least not in the 5 years I have owned it).

The proposed solution was to drill out the oblong holes, dowel it, and redrill. Sensenich says they will still YellowTag the prop, so I'm not too concerned (it JUST occured to me that It might change it's beautiful appearance though).

Any ideas on how that sucker got oblonged? Also, it would seem that I have overtightened it. I have NEVER gone beyone the 200 in/lb as listed in the bulletin. Theoretically I had another 25 in/lb to tighten it, that I never used. Maybe I should not use a torque wrench and just go with number of turns for the thread count. How are some of you guys doing this?

thanks
Richard Boyer
N95791

[VictorBravo]

Re: Propeller Woes

By "90 degrees out of what they had ever seen", I am GUESSING that means that the oblong was towards and away from the center of the prop hub, NOT in the direction(s) of propeller rotation. A Loose prop would work back and forth rotationally due to the pulses of the engine.

I have no personal experience with this, but the only way I could imagine a prop bolt hole getting elongated on a line radially out from the crankshaft is if it was WAY out of balance and/or track. That is the only thing I can guess would move the prop tips fore and aft enough to cause the holes to get worn in that direction.

Did they test how far off the balance and/or tracking was, before they rebuilt the prop?

BTW did you say CANVAS tips? They put canvas on...with glue...in 2005??? Fiberglass and epoxy work a LOT better. Kind of like a Fax machine works better than a teletype

[Richard Boyer]

Re: Propeller Woes

That would make sense. I am sure it was out of balance, but not real bad. I am also sure it was in track though. I checked the track everytime I retorqued the prop.

As for using fiberglass.....I'm sure they are just following the FAA rules, which we all know to be very modern and up to date.....
or maybe they do it for aesthetics?

I am hoping that since they are doing an overhaul of the prop that they would check it out completely. (of course, missing the egg shaped holes up until the stage they are at makes me wonder).

Richard Boyer
N95791

[Robert Lees]

Re: Propeller Woes

I assume they continue to use canvas because the 1940's design (and hence the 1940's TCDS) of the prop requires it. Of course, they make modern props with modern materials...but these modern props have a modern design (and modern TCDS). Care for a lawyer, anyone?

Richard: I cannot imagine why your holes should be egg-shaped in that plane, but I might throw some light on the torque: If you tighten to the correct torque in dry conditions (when the wood is tight), and then the weather dampens, the wood will swell slightly, so crushing the fibres in the hub against the bolts. This has the same effect as over-torquing.

Worse still is to torque in high humidity...drying out shrinks the hub, leaving the bolts slack a little.

This is why wood props need constant re-torquing (esp. after weather changes). In the UK we must re-torque every 25 hours, with a recommendation to re-torque after humidity changes (no percentage specifics recommended, however).

Dowelling & re-drilling sounds a suitable repair...this would be hidden by your crush-plate & spinner. You could, of course, get a metal prop?

[Chet Peek]

Re: Propeller Woes

Drilling out enlarged holes and putting in dowels used to be a quite common repair. I had to do it on the new OX-5 prop the manufacturer made for my Jenny, they missed-drilled the bolt holes. It makes it stronger than before, and it's hidden.
Chet Peek

[alwaysoar]

Re: Propeller Woes

Technical stuff aside, wouldn't it be about the same $ just to buy a new prop? I got a quote of #175 for each tip brass X's 2 for $350, and it would cost over $200 for refinishing. If you were also going to repair the bolt holes, put on new tip fabric, etc., plus shipping both ways, it's going to cost at least 75% the cost of a new one, and it won't be as pretty. Put your old one on the wall with a clock in the hub and get flying.

[Richard Boyer]

Re: Propeller Woes

$600 for a rebuild. I think a new one costs about twice that.

A rebuild from Sensenich: They take the prop all the way down to the wood, balance, put new canvas on the tips and new metal leading edges as well as new finish. And in my case, dowels in the oblonged holes.


Richard Boyer
N95701

[alwaysoar]

Re: Propeller Woes

Just about $1200.

[Richard Boyer]

Re: Propeller Woes

found out today that Sensenich wants 1600 for a wood prop like mine. yikes!

Anyone have a metal prop laying around? Pining for use in the beutiful blue skies? (C-85)

Richard
N95791

[Guest]

Re: Propeller Woes

found out today that Sensenich wants 1600 for a wood prop like mine. yikes!

Anyone have a metal prop laying around? Pining for use in the beutiful blue skies? (C-85)

Richard
N95791

Richard, try Univair or Wag-Aeo, in the past I got better prices from them.

Dave.

[Bill Fife]

Re: Propeller Woes

I paid $1500 for mine (change to metal) plus $150 for a re-pitch. Went through Barnstormers for a *rare* Lycoming-65 prop not sold by the other guys..

The wood one was laced with dry-rot but D.R. in Plant City said they could:
"shave the overtorqued hub down to remove (t)he broken wood fibers and refinish & rebalance the whole propeller for $200.00" (2003).

Since my Lycoming was just climbing with the wood prop I (after much soul-searching) decided to go with a more efficient choice. (Gained 2" pitch AND diameter over former, & about 50 on static.)

..Already have the wall ornament, without paying the $200.
(-So, I applied it toward polishing the metal one.)

No regrets here.

Continental - might've been different story. Not a '41 - also different. But like with synthetic fabric and epoxy, they probably would have used these if they'd had them.

T-Craft Deluxe. Full-swivel TW. It's a concept thing.

Have seen good used wood props for less than $1000 on the B'Stormers site. Worth doing a little shopping, IMHO.

Just my 2c.

Bill Fife

N29885
BL12-65

[Richard Boyer]

Re: Propeller Woes

Hello all,

I thought I would give you an update on the Propeller.

It's back on and spinning happily!! I received it last friday morning at 10:30am. My IA showed up and made me re-safety wire the thing 3 times! But, I didn't disagree with him once (even though he says he felt bad, I was grateful!). By 12:30 the dog and I took off and flew to houston to look at the next airplane that I would like to add to my collection.

Sensenich took 8 weeks and too much money, but the propeller is back on and absolutely beautiful. Both IA's that looked at it told me I was nuts for putting it back on the airplane. "Too pretty" they said. "Get a metal prop and put this one on the wall!" Everytime I would grumble about a metal prop, my wife would simply glare at me and tap her toe. She is an artist and loves the way the wood one looks. Absolutely refuses to let me put a metal one on the ole girl!

So far I have put about 4.5 hours on the new prop and it is working just fine!

Richard Boyer
N95791

[Jim Herpst]

Re: Propeller Woes

Richard AND ALL OUT THERE WITH WOOD PROPS PAALEASE check the torque
on a regular basis. I had one work loose several years ago . Thank the good lord I came down at my destination before the prop decided to come down earlier. The bolts were all working toward an even shear. Really would have been a spectacular death for my dad and I. He reminded me later that his T Craft had a metal prop when I was a kid as he was flying ME around. He said perhaps I should consider one!!! Well I never did and will not be putting a metal one on NC 24085 either. I like the lower vibration of the wood and they just look damn good too!!!

[Richard Boyer]

Re: Propeller Woes

I check the torque quite often, but obviously not often enough. They put a sticker on the prop that says fly it once and retorque it. Then retorque after 25 hours, and then 50 hours from then on.

Strangely enough, the yellow tag says to retorque every 5 hours or once a month??!!

That sure seems like a lot.......my problem hasn't been the prop getting too loose. It has been that it expands into the metal ring and crushing the hub. I might just do the one month thing. Gives me an excuse to do something to yellow bird.

later
Richard Boyer

[Guest]

Re: Propeller Woes

I check the torque quite often, but obviously not often enough. They put a sticker on the prop that says fly it once and retorque it. Then retorque after 25 hours, and then 50 hours from then on.

Strangely enough, the yellow tag says to retorque every 5 hours or once a month??!!

That sure seems like a lot.......my problem hasn't been the prop getting too loose. It has been that it expands into the metal ring and crushing the hub. I might just do the one month thing. Gives me an excuse to do something to yellow bird.

later
Richard Boyer

Hi Richard, what you describe sounds like what happened to me about 7 years ago.

Sensenich was telling me to torque to something like 175 in lbs, my memory may be off, but what they said was the same as on their sheet.

As I did that I could see my brand new taper shaft hub getting warped. It annoyed me as I had two new hubs that I have been saving for a long time and used one with my new wood prop.

I noticed a few things that convinced me not to use their torque table but to use their deformation table instead. The deformation table specs something like .53 nut rotations after contact with the wood.

The table they had at that time (1998) was for flanged hubs and mine is not flanged but taper shaft.

The old props made for a taper hub had a 3/8" hole in the back so the back of the prop made conatact with the hub directly adjacent to the bolt.

My prop had big holes in the back as it was made for a flanged hub so torque on the bolt is not pulling directly against the wood but against air space.

The above statement is true even when using the spacers because the spacers are shorter than the hole is deep.

So the bolt is deforming the hub by pulling the back of the hub into that big hole. ie. the hub is working as a circular plate (about 7/8" dia) with point load at the center rather than a direct compression onto a wood surface.

I used the deformation table and have had no problems at all.

My new hub is not so like new because of this but at least it will not get any worse.

If I understand what is happening to you correctly I would suggest that you look into using the deformation table too.

Hope this is useful, Dave.