This is soooo not good!

[stangflyer]

After yesterdays successful maiden of the Sukhoi, I got to thinking about that monster motor and the way it ripped the prop so badly. I talked with Dave, @Planebender this afternoon and it was suggested that perhaps that prop is not the best choice right now. Maybe better for slower 3D but not for the kind of paces I put her through yesterday. Since I have a new Falcon 32x11 I decided maybe I would give it a try and see if I could calm down that rip a bit. Well, as it turns out... I was much-much more successful than first thought. More along the lines of damn lucky. I removed the spinner this evening and I was very dismayed to find carbon fiber filings falling out as I removed the spinner. Now I have heard from many people that it is not a good idea to run a carbon back plate as they have a tendency to loosen and cause some serious damage. I have however been very cautious and payed very close attention to the ones I have run thus far and not even a single issue. The 260 now has 45 flights on it with the exact same spinner as the one I am using on the Sukhoi. It is still like brand new. I've been running the same manufacturer on my smaller motors and not even one issue. So how can it be with just one "8" minute flight I could have this happening?

Upon removing the prop hub bolts, I found they were "ALL" loose. Two of them finger loose. Much more dismay lay ahead. Two bolts sheared side by side. What the heck??? Have the gremlins finally caught up with me? This I do not know and thus the reason I am posting this thread. That and also to filter out to everyone some insight and some knowledge in case they are as in the dark as I am.

First: Carbon Fiber filings from inside the spinner.
Second: Two sheared prop bolts.
Third: Prop damaged on two sides.
Fourth: Back of prop damaged.
Fifth: Inside of spinner back plate damaged.

A couple of things come to mind. First, I am certain I torqued the bolts down. As I used my new torque wrench when I did them. I set them all to 110 in. pounds. Question: Was this enough? Next, Nord locks: I have been using them with super success however when I purchased them for this motor, I could not find 6mm. The ones I purchased were an SAE between 6 and 7 mm. They were not a perfect fit, but I felt they would be fine. Question: Is it possible there was enough play in them to allow this to happen? Since the back of the back plate is not damaged and only the contacting surface of the spinner and the prop are damaged, Could there have been enough heat from the hub that would cause the bolts to loosen? I kind of feel this would not be the case as the back of the back plate is perfectly un-damaged.
Is that motor making so much more power that a carbon fiber back plate just can not be used? My personal opinion is: The culprits are the non perfect fitting Nord Locks. Or is it possible that it is a combination of all factors? That is why I am posing the question to all you out there that have more experience with issues like this.

What did I miss or overlook? I would be very grateful if any of you that know, would jump right in and help me (and others) out with some answers.

And by the way, Is the 3W prop toast? Or is it possible to save it and safely use it later?

 

[Terryscustom]

Wow!! Yup, although not to that extent I did have a carbon prop and spinner that became bin filler material.....only aluminum backplates for me from then forward! Thankfully you did not get a big "bang" while flying to cost you a cowl too!

 

[Yakman]

On the first flight of my AW Yak was with a 3W80 for power. I had a brand new cabon spinner and a 3W 26x10 carbon prop,just like yours. My freind Flycanic was the test pilot, after a few minutes it started sounding funny. He landed the plane and got it over to pits and the spinner was gone. Well for some reason the prop bolts all came loose, surely thought i had them tight correctly. But it destroyed that new prop and never did find the spinner. I read somewhere, that some backplates are made with somewhat cheap plastic which can go awry. I don't know for sure but.. As for your damaged prop, i would be inclined not use it.

 

[yakpilot]

You were very lucky! 110 in.lbs is what I torque to also with good results. It is my strict policy not to use CF back plates on engines above 120cc. I use Mejzlic spinners on everything.
I'm not sure what prop to recommend to you. I tried a Falcon 30/14 at first as it worked well on my piped DA170. On my 176evo with pro flows it ripped way too easily. I'm now using a Mejzlic 28.5x12 3 blade and it works pretty good. Nice consistent speeds on up and down lines. Your engine being on pipes will be loud with any 2blade I can think of so I would recommend looking at a 3 blade. Maybe a 29/12 (not the narrow) would be good.

 

[stangflyer]

Wow!! Yup, although not to that extent I did have a carbon prop and spinner that became bin filler material.....only aluminum backplates for me from then forward! Thankfully you did not get a big "bang" while flying to cost you a cowl too!

On the first flight of my AW Yak was with a 3W80 for power. I had a brand new cabon spinner and a 3W 26x10 carbon prop,just like yours. My freind Flycanic was the test pilot, after a few minutes it started sounding funny. He landed the plane and got it over to pits and the spinner was gone. Well for some reason the prop bolts all came loose, surely thought i had them tight correctly. But it destroyed that new prop and never did find the spinner. I read somewhere, that some backplates are made with somewhat cheap plastic which can go awry. I don't know for sure but.. As for your damaged prop, i would be inclined not use it.

Its funny...(not really but you know what I mean) that you both mention a "bang" and "sounding funny". I watched the video of the maiden again and I am pretty much certain of when the bolts broke. As I was flying out of the first knife edge circle and made one bank at about the 6:25 mark, the motor just did something really odd, kind of weird sounding. I also noticed a difference of power. It concerned me, but then it sounded okay again after that. I think it was at that point the bolts broke. I am so glad it started raining. I really was going to put her in the air for a second flight. Terry, any ideas on where I can pick up an aluminum back plate? Tru-Turn doesn't seem to show them for 5" spinners.

 

[Bunky.F.Knuckle]

Get a 6 bolt spinner from TailDragger RC in 5". Aluminum backplate, carbon cone. All you have to do is drill the backplate for the prop indexing.

 

[HRRC Flyer]

Hey Stang,

Sorry to hear about your issues, but I'm glad you got the plane back on the ground with no damage. Your story sounds very familiar to me too. I was flying with my friend who just put a new 3W110CS in his Carden Extra after the DA100 self destructed. The same thing happened as yours. I was standing next to my friend on the flight line and the plane was flying along just fine. Then, all of a sudden, it made a funny noise, then the motor sounded like it went lean so he landed the plane. When my friend landed the plane, we took the spinner off and found some loose prop bolts and one that broke off, right where it screws into the hub. There is however, one difference in our experiences. My friends plane had a carbon fiber Mejlick prop, but had an aluminum back plate & spinner. Like you, my friend was certain he tightened down the prop bolts as well. I don't know if it makes any difference, but were any of your broken bolts loose in the hub? The reason I ask is that the one on my friend plane was. He was actually able to take a #11 exacto blade and push against the edge of the bolt and back it right out of the hub.

I'm sorry I cannot offer any wisdom as to what caused the problem, but hopefully someone on here can help shed some light on what happened.

Not, to change the subject, when is it ever warm enough in Idaho during the month of February to maiden an airplane?...........

 

[Pistolera]

You WERE lucky Stang. Glad you got it back down OK. I have seen and read so many such instances with CF back plates that I will never use one again.

Steve Johnston at SMJ Spinners might be able to machine you an AL backplate, or for that matter sell you one of the best looking spinners on the market.

 

[yakken]

Check your front bearing they are known to fail on the gp176's. They will fail early if they are going to.

 

[N726AC]

I know of one other that had this happen. Fergus/Dave will take care of ya.