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Old Nov 28, 2012, 04:32 PM
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Bad props from HK.

I had one of these props this summer and, after several flights in an area with a few scattered rocks, it broke in the air. Luckily I was able to shut the motor down before it tore the firewall out. When I examined the piece that was still attached there was a definite nick in it and I figured that I had damaged it on a landing. Well?

I stupidly got a second one without reading the reviews and went out to fly with it for the first time. I got up about 50 feet and pow! One blade broke where the shoulder merges in to the blade. Luckily, for the second time, I was able to shut down before any airframe damage. (Which is also a pretty good endorsement for the strength of the Specter 1800.) Upon examining the remnant of the blade I could see a substantial void in the plastic. Now I wondering if that "nick" was really caused by a rock or just where the plastic broke.

Here's the link to the prop and, if you look at the reviews, you will see that others have had the same problem.

http://www.hobbyking.com/hobbyking/s...propeller.html
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Old Nov 28, 2012, 06:36 PM
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I may use some cheap Chinese motors or Lipos, but fast spinning thingies, no way
I've seen this issue come up before. I stick with the Freudenthaler CAM blades, but Graupners a fine as well
Pete
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Old Nov 28, 2012, 07:16 PM
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I have some of these cheap folders, After I received them and took a good look at them I threw them in a junk box out in the garage.

Some times cheaper isnt worth it.
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Old Nov 28, 2012, 08:49 PM
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Live and learn, as they say. Thankfully the prop was the only cost. I do have a couple props of a different brand that have held up. That being said, I think I'll stick with the Yak 54 until my proper CF blades arrive.
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Old Nov 28, 2012, 11:27 PM
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Australia, VIC, Cranbourne East
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Quote:
Originally Posted by peterlngh View Post
I had one of these props this summer and, after several flights in an area with a few scattered rocks, it broke in the air. Luckily I was able to shut the motor down before it tore the firewall out. When I examined the piece that was still attached there was a definite nick in it and I figured that I had damaged it on a landing. Well?

I stupidly got a second one without reading the reviews and went out to fly with it for the first time. I got up about 50 feet and pow! One blade broke where the shoulder merges in to the blade. Luckily, for the second time, I was able to shut down before any airframe damage. (Which is also a pretty good endorsement for the strength of the Specter 1800.) Upon examining the remnant of the blade I could see a substantial void in the plastic. Now I wondering if that "nick" was really caused by a rock or just where the plastic broke.

Here's the link to the prop and, if you look at the reviews, you will see that others have had the same problem.

http://www.hobbyking.com/hobbyking/s...propeller.html
What RPM did it break? I know that the plastic centrer folder lugs give way at 8k plus I have the dings in my workshop wall to verify it.
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Old Nov 29, 2012, 12:05 PM
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United States, DE, Seaford
Joined Sep 2008
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I bought a set of HK 13 x 6 CF series blades from them and they were the worst performing prop I've had on a sailplane. Lots of noise and no traction with a decline in climb with the same size Aeronaut or RFM from 2200 fpm to 1600 fpm. They did not get enough use to have a chance to fly apart and now are in the shop junk drawer.
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Old Nov 29, 2012, 12:31 PM
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I didn't get a chance to check the RPM, olmod, but it was around 8,000-8,300 based on my smaller props performance.

I decided to go with a couple Aeronaut props from Esprit, Leadchucker. I think I'll follow the other pete's motto of not beta testing "fast spinning thingies" in order to save a buck or three. Plus, now that I do have some personally collected data, I know what size props I need so there's no real incentive to try and get 2 or 3 sets of blades for the price of one from a name brand. Safety issues aside, I have enough excess motor power that I could lose a little efficiency but I think that the HK CF props just don't look right. They look, to me, like they went for a less efficient shape to save on production costs.
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Old Nov 29, 2012, 02:25 PM
B12
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Finland
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I am a huge fan of "China Junk" in general but on folding props I use only Aeronaut CAM Carbon. They are proven strength and efficiency and the price is not that bad either.

On the other hand I have used some "CAM" folders from RcTimer and those have not been bad at all for moderate power setups.
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Old Nov 29, 2012, 02:45 PM
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Me too, B12. Aside from this prop I have been very pleased with my "China junk" though I haven't been back at it long enough to speak about longevity. Since I'm now living on a fixed income I wouldn't be back in the hobby without it. Now that I have some experience with the new technology I can make informed choices based on the specifications of higher end equipment. But, as stated, I've learned my lesson on props. I get a very unpleasant chill down my spine when I think of where that blade could have gone.

Once I get my Aeronaut blades I will still probably keep the 10X6, that has given me countless flights, on hand as a spare but I will be even more careful about what's in line with it. And, since I started flying glow powered planes back when a nylon prop would occasionally explode for no apparent reason, I've always been careful about what's in line with a prop!
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Old Nov 29, 2012, 03:50 PM
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Australia, VIC, Cranbourne East
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Every Prop same as every grinding wheel should have a MSRPM (Maximum Safe Revoultions Per Minute) molded on the blades not hidden away on some online site or no information at all But how to change the situation
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Old Nov 29, 2012, 03:55 PM
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I agree, olmod. But, in this particular case, I would say there is no safe speed for these props. I tried to get a picture of the voids in the plastic but my camera just isn't quite up to the task. I also took a couple pliers to the unbroken blade and it had voids at the fracture points too.
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Old Nov 30, 2012, 03:15 AM
B12
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I have run $2 RcTimer 10x6 folder with 1350kv motor on 3s without issues. That makes something like 11000-12000rpm.
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Old Nov 30, 2012, 05:51 AM
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I have no experience with rctimer props ,but I do with lousy continuity of quality and aging of plastics that some use particlarly those orange horrors that go brittle after being out in the sun for a few days flying.
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Old Nov 30, 2012, 11:27 AM
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There are certainly cheap props that work very well and safely but, in hindsight, it's probably not something that most people would want to experiment with. Even with the most expensive CF blades one could still run into a manufacturing defect but it's obvious that the particular prop I, and quite a few others, had the problem with is from a very bad run. After I broke up the other one I could see multiple voids, or bubbles if you prefer, at the fracture points and the edges of the breaks feel like pumice when one runs a finger across them.
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Old Dec 06, 2012, 06:29 PM
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An update.

I have finally received a reply from HK customer service. I have waived my claim to a refund in the hopes that they will pull this dangerous product from their shelves. The rep asked for more information so I provided a complete breakdown of my setup and got a fair picture of the damaged prop. (NOTE: My new Aeronaut 11X6 blades give a first burst of 8250RPM.) I hope to get a better pic tomorrow when I can use outside light and play with backgrounds. I might even try a little chalk to see if it makes the bubbles and voids more obvious. Still, if one looks closely, one can see said voids and bubbles even though this pic is not as sharp as I would like. I'll keep you guys posted. Hopefully the word gets out and the product is pulled before anyone gets hurt.
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