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Did I get myself into Vortex Ring State?

Discussion in 'Typhoon H Discussion' started by JulesTEO, Jul 13, 2018 at 2:34 AM.

  1. JulesTEO

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    Hello everyone,

    I'm not sure how to address this topic, since I would love to gather some true insight from this incident rather than starting a speculation brainstorm.

    Also I'm really not looking for advice; it is clear that this incident was self-induced, and as long as I don't repeat the same maneuvers the H will be just fine.

    So, long story short: I was trying to snap a cool image of my H tilted, (I did get it):

    [​IMG]

    But, in the process I believe I got myself into a Vortex Ring State, resulting in a minor crash with my H.
    • The scenario was as follows:
    ----
    Trying to get a snapshot of a fully tilted Typhoon H, I began to (very agressively) roll back and forth at maximum rate. (imagine tilting the aircraft as it is shown in the picture above, going side to side while remaining almost in the same position)

    After going, back and forth, 6 times in quick succession, the aircraft lost lift completely and it quickly sinked in a wobbly fashion.

    Since I was just very close to ground the aircraft made ground contact, but quickly recovered.

    I was able to regain altitude with only minor scratches on the camera.
    ----

    So, for those of you with knowledge on aerodynamics, my question is: Did I get myself into Vortex Ring State by tilting the H back and forth so quickly? Or was it something else?

    I have everything recorded, but I don't want to upload the video just now without first setting some context around it.

    Greetings!
     
    #1 JulesTEO, Jul 13, 2018 at 2:34 AM
    Last edited: Jul 13, 2018 at 2:39 AM
  2. Steve Carr

    Steve Carr Moderator
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    VRS would be my first guess. The back and forth movement could have set up an area of turbulence under the H.
     
    KEITH KUHN likes this.
  3. Dr Delta

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    Yup. Multirotors generate quite some propwash.
    Turbulences tend to stay noticable much longer then one would expect.

    :)
     
  4. PatR

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    My theory has the aircraft spending more time in an extreme bank where prop positioning will not generate the lift necessary to off set the weight.

    I have done similar and observed a fairly rapid altitude loss after several rapid oscillations. The aircraft quickly recovered and stabilized altitude after returning to level flight. In your photo, look closely at the angle the props are oriented. If you drew a straight line through the center of each propeller perpendicular to the blade length it would demonstrate the lift vector of the prop. As flight requires a balance of forces, lift over weight, thrust over drag to be successful we could view the lack of vertical thrust, which for a multirotor is lift. Too little lift is being generated to keep the weight aloft.
     
    MarkC and AeroJ like this.
  5. FlushVision

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    These days with modern drones it is quite difficult to get into VRS, particularly if it has six props. VRS was something to be very aware of on earlier quads. Descent speed limitations imposed on drones by the firmware has largely gone towards making VRS almost a thing of the past. However, it has not been eliminated completely and some thought should still be exercised to ensure it is avoided: Never descend straight down with full left stick...always come down in a diagonal fashion flying into the wind.

    Your statement: ' the aircraft lost lift completely and it quickly sinked in a wobbly fashion' tells me that this was VRS initially induced by making the aircraft go back and forth, 6 times in quick succession causing the aircraft to lose lift. The start of the descent wasn't VRS but VRS was quickly achieved once the aircraft had begun it's descent. The aircraft had been flown beyond it's capability to remain airborne.
     
  6. PatR

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    Also to consider is that load factor on an aircraft increases with angle of bank. Multirotors are a bit more complex in this area than fixed wing as they bank for every directional change due to opposing prop RPM increases and reductions. A 60* angle of bank doubles aircraft weight and thrust must be added to compensate. In the photos the aircraft is at a roughly 45* bank angle, increasing aircraft weight by ~1.3 times its weight in level flight. To obtain that photo the aircraft had to be spending a minimum time of at least twice what it spent in a level state due to opposing bank oscillations. Probably closer to three times longer. As the Typhoon H does not have an abundance of thrust reserves it could not compensate for increased loading.
     
    #6 PatR, Jul 13, 2018 at 11:35 PM
    Last edited: Jul 14, 2018 at 5:21 AM
  7. JulesTEO

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    Thanks for the feedback.

    Honestly I wasnt even familiar with Vortrex Ring State prior to this, mostly because as @FlushVision said, the H makes it almost impossible to achieve. I guess every flight is a new lesson.

    I will keep this incident in mind if (for any reason) I have to recreate these maneouvers in the future.

    As I mentioned, I didnt want to share the video without some context. Now it has been set, here's the video of the incident:



    Greetings!
     
  8. CraigCam

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    Check your telemetry and you will see that your power dropped during those 6 fast tilts. I use that maneuver indoors to fly down charged batteries to prep for charger storage. I’ve observed a battery at 14.8 drop to LVC of 14.3 on the ST meter during my stick stirring. So it can be a double whammy of wash and power loss and if you’d been higher up and just let go of sticks, it would have stabilized. Good to learn how far you can push your skills.
     
    Dr Delta likes this.
  9. PatR

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    I’ve done it with the gear down. The swings are a little more violent, but as mentioned, if higher it will self recover after letting go of the sticks before hitting the ground.
     
  10. KEITH KUHN

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    I like juuls he's like a surgeon when it comes to working on typhoon H
    he's the kind of guy if I needed work on my typhoon h i could trust him to do a good job.
    Keith Kuhn