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9" Carbon Fiber Propeller - Possible warning

Discussion in 'General Discussion' started by map85086, Jan 28, 2014.

  1. map85086

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    I wanted to share my recent experience using 9" Carbon Fiber, Phantom 2-style propellers on my Phantom 1.1.1. I've been flying my Phantom using regular 8" carbon fiber propellers and decided to try something different, so I bought the propellers pictured below. When taking a test flight the first time, I took my Phantom up to about 150 feet. When I started to descend, the Phantom went out of control and crashed hard, breaking a couple of the propellers and a lot more.

    I assumed that something went wrong with the electronics. After repairing my Phantom, I tried flying it with regular 8" and 9" carbon fiber props. No problem. After buying replacement propellers for the ones broken on my first try, I tried to fly these again (I know what many of you are thinking...duh!). This time, I took it up to about 400 feet. I noticed that I wasn't getting the same lift that I got with the regular propellers, but it otherwise seemed to fly well. However, when I descended this second time, I lost control of the Phantom again, just like the previous time, and it crashed hard again. After repairing it a second time, I changed back to my old props and everything works fine.

    I'm interested to hear if anyone else has had this problem. At the very least, I would advise anyone not to try using these as I did.

    Thanks.

    [​IMG]
     
  2. ElGuano

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    Re: 9" Carbon Fiber Propeller - Possible warning

    How did you descend (pull throttle straight down, no other movement?) And how did you lose control (did it start wobbling like crazy and flip?)

    New props have different flight characteristics and you may have encountered extreme turbulence from descending in your prop wash. This is a pretty common effect with larger props and is mitigated by coming down slowly and at an angle. Improper gain settings (either too high or low) may exacerbate the effect too, though i've tried a few time to replicate it on my setup and haven't been able to get the quad to flip.
     
  3. map85086

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    I did descend straight down in both cases. Here's a link to YouTube where you can see the second crash.

    http://youtu.be/7m0rB54ct-w
     
  4. ladykate

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    Well... neat crash sequence anyway.

    It looked like the Phantom stabilized for a second just before hitting. However, it also seemed the motors shut off completely before the first stall - was that shutdown caused by you trying to stop it from tumbling or something? It was also windy (or it seemed so).

    Was that arm with the hole in it in the last scene a motor arm? Wow.
     
  5. ElGuano

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    9" props are a bit more susceptible to wind and turbulence (you have more surface area exposed to forces against the quad). People with P2/P2Vs with plastic props infrequently lose control when descending straight down and crash.

    The Phantom will naturally be wobbly on the way down - if you come straight down you are descending in your own prop wash. Best practice is to come down slowly, and always with a forward/backward/left or right angle, so you're never descending straight into self-generated turbulent air.
     
  6. ianwood

    ianwood Taco Wrangler
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    Isn't this a case of ring vortex state? I've noticed that the P2 needs a pretty slow descent if done in place. Slower than in the video at least! If you go too fast you can hear the sound of it descending into its own prop wash.
     
  7. ElGuano

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    Yes, I think it's likely that most of these cases are VRS/settling with power. The larger props seem a bit more susceptible to it (or at least we've been hearing/seeing it more with 9443s)!
     
  8. mtmilam

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    I had same thing happen with new Carbon Props on Vision…..A wind gust hit it after a descend and at 30 ft it rocked back and forth and then flipped over and hit the Cement……the CF props are so stiff that I think its forcing the Autopilot to overcorrect or something like that……the Regular DJI props have some flex, which is like Shock absorbers some…..at least thats my opinion, I could be wrong though… It flew Great After crash, with the DJI Props…that was my First Crash with it also….I was Shocked…. :D

    Just Say NO to CF props for your Vision… :D
     
  9. ElGuano

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    This happened just yesterday on someone's Phantom 2 with standard plastic props: http://www.rcgroups.com/forums/showpost ... count=3909

    I don't think carbon fiber is the culprit, I think it's the wider profile and surface area of the 9.4" props. The takeaway for all of us (cf, plastic, wood, 8", 9", triblade) is to take special care on descents not to come down too hastily or in a straight vertical descent.
     
  10. havasuphoto

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    That sure looks like settling with power in that video. I'm wondering if he just pushed forward on the stick, and added a bit of power, he could have flown out of the vortex?
    EDIT: I just read through the posts-and they're all over the place. Seems he was FPV and didn't realize he was in VRS until it was too late.
    Remember-sometimes you can get into your own down wash, on a windy day, while descending away from the wind-tail wind. It happens quickly, and sometimes quite violently.
    Always descend at least twice as slowly as you ascended, and always try and fly forward, into the wind, or a circle pattern-being careful that while "down wind", you don't enter your down wash.

    Also-I'm wondering if when the aircraft entered the "death wobble", did you user have any control at all?
    I get into VRS several times, while descending....but, I recognize it for what it is, and just fly out.
     
  11. ElGuano

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    Re: 9" Carbon Fiber Propeller - Possible warning

    I think the user said it happened so fast he couldn't really react. It's hard to tell from gimbaled footage, but it really looks like there wasn't a lot of time to react, and this happened so close to the ground. He did say he was descending with throttle all the way down, which I don't think I've ever done.
     
  12. havasuphoto

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    Re: 9

    Yea, I heard that too....zero throttle, I've never done that before. IRL, what I was seeing is exactly what settling with power looks like...but, it's easily recoverable with forwards stick.
    Guess I'll have to follow the other thread too-to see what the user did.

    Remember-the small size of the individual rotor discs on a quad, coupled with very high disc loading, easily lends itself to settling with power.
    For example; a Hughes 500(5 blades-small rotor disc), with a sling load on, in a descent, is constantly flirting with the edge of entering settling with power. Whereas a Huey(big rotor disk-not so heavily loaded), is much more forgiving of descents with weight on a sling.
     
  13. map85086

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    I think that ElGuano is right. It's the shape of the props.

    I was descending straight down when the crash occurred. I was also in GPS mode. Some have noticed that I almost pulled it out of the crash. I switched from GPS to ATTI mode and the Phantom began to respond. I then switched it back to GPS, which was a bad decision. The rest is history.

    Another observation about those props. I noticed immediately that the lift I got when accelerating on take-off was less then other props. There must be significantly different performance differences that should be considered when choosing props.
     
  14. ianwood

    ianwood Taco Wrangler
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    P2/P2V props (carbon or stock) are bigger all around which means more thrust (good) but also means when descending, you run a higher risk of creating turbulent vortices around your props that negate all the lift on one or more them, the so called vortex ring state. Switching from GPS to ATTI will not do anything to recover from it. And adding more throttle apparently only makes it worse.

    To avoid this, slow down your descent and/or descend while moving in a horizontal direction at the same time.
     
  15. ichi

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    This happened to me and I'm really glad I found this thread to understand it, at the time I thought something had happened to a rotor causing the violent oscillation. I couldn't recover in time (tried to throttle up out of it, which made it worse) and hit the deck, but luckily just snapped a rotor. Lesson learnt and thanks for the advice in this thread.
     
  16. Phantom_Menace66

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    Ok I'm going to throw my 2c worth in... CF props are getting a bit of a bagging lately & I think it is due to all kinds of 'knock off' so-called cheap CF props available on Ebay, most from China. Many are simply nylon props covered, or impregnated with CF & made via injection moulding. They're stiffer than plastic, but still flex at the tips & are usually horribly unbalanced. Especially the self-tightening ones.
    I use non self-tightening CF props I bought from Japan, ARRIS 9443's. They are solid CF & do not flex at all. The hubs are really thick & also keyed to fit on the Phantom2/Vision/Vision+ motor shafts but require prop nuts and a thread lock like blue loctite.
    However, it is worth noting that any CF props, particularly like the ones I use, are extremely sharp & will cause serious injury if they come into contact with a person or animal. There are some gory videos on YT showing the consequences of getting in the way of them.
    Also worth pointing out that they are NOT balanced out of the box & require balancing on a prop balancer.
    People seem to have the misconception that CF props are the 'Rolls Royce' of props. While I personally believe they make the Phantom more responsive & smoother when hovering, they are more easily affected by wind. Having said that, I have never experienced VRS as a result of using CF props & only resort to plastic props when flying in confined areas as they are more forgiving if they come into contact with an object, whereas the CF usually shatter like glass.
     

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  17. greenie65

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    I agree menace66 cf is more affected by wind imho. I was out flying the p2v with cf props near Big Bend TX yesterday and entered VRS at 400 ft. Air temperature was 92-94F and I had a ~15 mph wind at altitude. I noticed the p2v was starting to have some difficulty and I tried bringing her straight down. She started coming down with that "falling leaf" motion. Not knowing about VRS I wasn't sure what was going on. But I instinctivly started to try to push forward. That did slow my descent but didn't stop the fall. Luckily the cushioning ground effect softens the blow and I also landed in some wild grasses. No real damage to my bird. :)
    Thanks to these posts I've learned something new. I thought I had a mechanical problem with my motors. Thanks guys!
     
  18. hoosierdoc

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    Is there a concern with props being too rigid leading to motor damage when the prop doesn't break off as it should?
     
  19. MrGoodwreck

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    The blades were not loading after the quad entered into a vortex ring state. so the quad was descending faster than the blades could push...