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Old Sep 22, 2011, 09:25 PM
The blade numbers go up to 11
stumax's Avatar
Sydney, Australia
Joined Aug 2002
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Stumax SM80-45, SM89-45 and SM100-45 rotor issue

Hi guys, I'm still in lovely China but still somewhat in touch with the rest of the world. I've just received a few emails detailing rotor blowups, one with an SM80-45 running very high power, and SM89-45 runing very high power and one with an SM89-45 running normal power. The SM80-45 rotor blades have rubbed inside the shroud and failed. Without being able to see the remains of the SM89-45's first hand I can't be sure what's happened but it's enough to make me worried that it's going to happen again. One of the SM89-45 failures could have been due to the fan mounts being out of alignment, causing distortion of the shroud, even with the mounting grommets, the wide spacing of the mounts will aggravate any misalignment, but it could also have been due to excessive blade stretch.

I have had two batches of rotor blades moulded for me, the second batch seems to be the one causing the problems. What I've noticed is the blades become a little bit more flexible over time. This is normal for Nylon, as it is pre-dried before it's moulded, and moisture content affects stiffness, but also it's brittleness - less moisture means it's more brittle. In the old days we used to boil Nylon props in a pot of water before use but modern Nylon formulations are supposed to normalise a lot quicker in the atmosphere. This could be allowing them to stretch a bit more and possibly strike the shroud. I do set a generous tip clearance to allow for stretching at big power levels, but if the material is getting more flexible then it may not be enough. BTW, I can't use high stiffness materials such as carbon reinforced Nylon as FOD with these narrow blades would be a serious issue. I am currently experimenting with a special higher modulus long glass fibre reinforced Nylon designed for high impact strength but it's not ready for release yet, if it turns out to be OK then I'll offer a free rotor upgrade.

Without my records here to check, I can't be sure who's fans may be at risk, but as it's the second batch of blades I would say that any SM89-45, SM100-45 or SM80-45 fans purchased from about May onwards would be from this batch. Both failures have been early in the fan's life, so I'd say if you've been flying for some time without issue then it's going to be fine.

What's the fix? If you're confident enough you can fold some 80 grit sandpaper over itself enough times to take up the tip clearance in the rotor and increase the clearance by about 0.5mm. If you're not confident enough to do that, please send your rotor to me and I'll fix it for you and return it at my expense. I'm very sorry about any inconvenience caused, and I may be over reacting, but without any more evidence at this stage I can't let people risk their models or worse while I wait to see what else may happen.

Stu.
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Last edited by stumax; Sep 23, 2011 at 12:16 AM.
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Old Sep 23, 2011, 02:27 AM
deltas are cool
AIR SALLY's Avatar
Tehachapi ,CA.
Joined Apr 2006
20,522 Posts
mighty BIG of you ...that is some great customer service ,and a safe thing to do .
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Old Sep 23, 2011, 05:21 AM
Life begins at transition
Australia, VIC, Sale
Joined May 2007
3,593 Posts
I've noticed a bit of rubbing on my 89-45, but it's limited to only a 10-15 degree section of the shroud. I assumed that's more an un-centered motor. Hasn't seemed to affect it at all - at only 2.5-3kw, is this considered a 'safe' level?

I'm happy to turn it down myself, but would prefer not to increase the tip gap beyond what's absolutely necessary...
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Old Sep 23, 2011, 05:42 AM
Dream Build Fly Scale
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Philadelphia, PA
Joined Oct 2004
2,866 Posts
I had this happen on my 100mm fan on 11S and turning down the tips 0.5mm was easy to do and has made no difference in the performance. Great support from Stu!!
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Old Sep 23, 2011, 06:39 AM
"Aircraftus Fragmentum"
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Motor City USA
Joined Mar 2007
3,561 Posts
This explains why I need to order a StuMax setup for my next big bird. Excellent Customer Service.
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Old Sep 23, 2011, 10:45 AM
Xtreme Power Systems
Lake Havasu, AZ
Joined Jun 2005
15,713 Posts
Thanks for the heads up, Stu!
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Old Sep 23, 2011, 11:22 AM
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St.Catharines, Ontario
Joined Jan 2009
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Originally Posted by kydawg1 View Post
This explains why I need to order a StuMax setup for my next big bird. Excellent Customer Service.
absolutely, 100% +1. how many other manufacturers would do this? most would wait to take action, or be forced into action after a gripe thread on a forum such as this. Stu seems like a class act and I'll deffinitely be looking at his stuff very soon.
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Old Sep 23, 2011, 12:34 PM
Pursuit of Happiness
Ron101's Avatar
Brentwood, California
Joined Jul 2007
7,190 Posts
Stu you have been all about customer support from day one
This shows the kind of company you run

Love your products
Some of the very best!

Thanks bud
Ron
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Old Sep 23, 2011, 12:52 PM
There was a crease in the plan
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Respect
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Old Sep 23, 2011, 03:32 PM
jean-claude Terrettaz
bidule's Avatar
Carp, Ontario, Canada
Joined Mar 2000
1,451 Posts
Stu do you think is what happen to mine...( disappear in Post Neverland when I shipped the fan to Stu)
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Old Sep 23, 2011, 03:37 PM
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United States, KY, Louisville
Joined Jul 2008
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Originally Posted by LuvEvolution7 View Post
absolutely, 100% +1. how many other manufacturers would do this? most would wait to take action, or be forced into action after a gripe thread on a forum such as this. Stu seems like a class act and I'll deffinitely be looking at his stuff very soon.

+1 We love you Stu!
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Old Sep 23, 2011, 09:04 PM
The blade numbers go up to 11
stumax's Avatar
Sydney, Australia
Joined Aug 2002
4,380 Posts
Quote:
Originally Posted by bidule View Post
Stu do you think is what happen to mine...( disappear in Post Neverland when I shipped the fan to Stu)
JC, you know I offered to replace it immediately, but I did want to see the bits to try and figure out what happened. I thought Mike was going to give you a new one at Ejets, that was our last communication. I'll get in touch with Mike and see what he says. I actually replicated your setup and was getting over 4.5kW, which is more than I set tip clearance for (bcause that's a crazy amount of power to put in a 90mm fan), so I think yours was probably a combination of too much power and not enough tip clearance, the blade material issue could also have been a contributing factor. When I get home I'll get in touch with the post office and try to find where the parcel has gone, can you email me a tracking number please? Also, let me know what motor you'd like to replace the old one with as I think that one was too hot.

One thing I'm considering is to make an all carbon rotor and offer an upgade to existing customers for small price, probably $60-70 as there will be quite a bit of work in making them. As we've seen from the original blades, if the material is moisture stabilised the way it should be (the parts are supposed to be steamed prior to packaging) then they are fine, I actually tested the 89-45 up to 5kW and the 100-45 to 7.5kW without issue, so an all carbon rotor is a luxury, not a necessity, the only real benefit from it (apart from its appearance having extreme woody value) is the power can probably increase to totally crazy levels, if you are totally crazy, of course

Thanks for your support guys, this is a tough situation to resolve, there are a lot of rotors out there for me to replace/fix, that's gonna have quite an impact on production but it's go to be done.

Stu.
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Old Sep 23, 2011, 09:27 PM
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St.Catharines, Ontario
Joined Jan 2009
10,377 Posts
hopefully it doesn't have an impact on your business. we'de hate to lose you over a major recall. we don't have enough choice as it is in high end fans. to lose Stumax because of financial troubles would be a major blow. let's hope that this situation is small and that you are indeed blowing it a bit out of proprtion........if that's what you can call it. I'm sure you know what I mean though.

Rich
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Old Sep 23, 2011, 09:27 PM
KingtechUSA
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Tampa FL
Joined Apr 2009
2,823 Posts
Great support Stu!

Stu you have bent over backwards for me in the past with great service with the special inlet duct and the crashed fan. Heck you even gave me better service then the last time I sent my EVF back to BVM. To beat out BVM in service is freaking great!! Keep up the great work Stu!
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Old Sep 23, 2011, 09:28 PM
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St.Catharines, Ontario
Joined Jan 2009
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by the way, we really need an outlet in Canada. can we get something going? paying import duty from the States is lousy.
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