Elevation impact on IRIS+ flight times.

Just a reminder that flying at high elevation can have a HUGE impact on flight times and can result in sudden failure. I flew at 9,600' this past weekend and my loaded IRIS+ (gopro, tarot 2d gimbal, secondary GPS) got to about 5:45 before the battery could not maintain enough thrust to keep it airborne and started dropping quickly. No warning, of course, since plenty of charge remained. Fortunately I was not flying past the cliff edge or the IRIS would have been unrecoverable; as it was, I suffered a hard landing that broke a leg off and took part of the motor housing with it. The more you know!

I normally get about 12:30 flight times from the same craft at 3,500'.

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    • Yeah, if you look at it on a per-inch basis, pitch change adds much more drag than diameter change.

      Changing diameter makes sense if you're after endurance.  If it's windy though, you want more pitch to be able to handle the wind.

  • I've done quite a bit of flying above 11,000. I got about 50% of sea level flight time (10 mins instead of 20 mins) flying at 12,000 on Mt Erebus with 1kg payload on an x650 X8 frame with 11" props and APM2. Worth noting that the "hot" part of hot and high is different electric craft (reversed, in the case of flying in Antarctica where batteries are below their optimal temperature). Combustion engines perform better in the cold (study the Carnot cycle to understand why).

    I'm still looking for a systematic field or simulation study of this that's relevant to small craft. You definitely want to push more air volume per rotation but I'm not clear whether thinner air means you should have higher pitch or longer props or both or what.

    • Jealous about flying at Erebus. All I got to do there was snow school. ;)

      What was the occasion and do you have video to share?

    • Hi Chris, here are some early flights: http://diydrones.com/profiles/blogs/arducopter-on-an-antarctic-volcano and here I am flying above the crater: https://www.youtube.com/watch?v=tA1cMbcm6bc . This was a recreational activity I did during my few hours of free time on Erebus, at no cost to the NSF, before any restrictions on UAS were in place. (I was hoping to turn it into a big research project after finishing my cave work, but that work is still ongoing.) After the USAP's "not a ban" ban on UAS I contacted the people in charge several times to inquire how I could potentially continue flying out there as a planned research activity, ensuring that I'm doing everything by the book, but I have received no responses to my emails to the point of contact listed here: http://www.usap.gov/News/contentHandler.cfm?id=4071 . I sent him email on 27 Sep 2014 and again on 9 Mar 2015. Don't know what else to do. Go to other volcanoes, I guess.

      What were you up to down south?

    • I was there summer 94/95 as a PC Tech.

      I'm super jealous of your opportunity to do work with multicopters on Erebus. I'm working on a stereo vision based system that might be interesting to your SLAM goals. Did you ever send a copter into a cave?

      I've also considered using a hybrid balloon/multicopter system to lighten the weight of the multicopter so it was nearly neutrally buoyant but retain the multicopter's ability to maneuver. But in MCM's windy conditions, that might not "fly" so well. Some kind of ducting and a tether might also help in specific cases.

      We should talk sometime.

      I have friends that still go back to the ice regularly.

  • Justin,

    I consistently launch from elevations around 9,000ft and sometimes from areas ranging between 10,000 to 11,000ft without indecent.

    My IRIS+ carries the same basic payload as yours and I typically see flight times of 6-8min, depending on conditions. I have never experienced the issue you described "not maintain enough thrust to keep it airborne and started dropping quickly."

    I do run the Slow Flyers that Christian wrote about, they are very good at these elevations and offer plenty of lift.

    I flew in some pretty windy conditions a week ago at 10,276ft and had very little problems controlling IRIS+.

    When flying, do you run with a tablet/phone so that you can receive and hear all the telemetry data? I have mine running everytime, it provides some valuable numbers and helps me keep track of how the IRIS+ is doing while in flight.


    • Hi Todd,

      Thanks, good to know. More evidence that 10" props should alleviate the problem.

      I use Tower if I think I'm going to be approaching flight time limits, but the range is so poor that I've found the "connection lost"/"connected" alerts come fast and furious at about 400'+ away and is more distracting than anything else. 

  • Thanks all, I wasn't clued in on the 10" prop advantage, and didn't consider them since I figured they'd have a negative effect on an already slim flight time, which is clearly not the case. I still have a set of APC props from the + upgrade, can't wait to try them out.

  • There was a thread on this a few months ago.

    You can improve lift (and thereby get longer flight times) with 10inch props. Here's a link with more info:

    • Need a smart math guy to model the tradeoffs on this one. Issue I see is that that the Iris batteries are low-medium discharge rate.
      The Iris was modeled in a wind tunnel flying certain prop sizes.
      And bigger props will heat the motors & ESC more.

      Our task here is to help Justin figure out his altitude flying issues... clearly we have found where he is losing duration due to altitude. Next step is slightly larger prop (lifting disc) to test performance.... mainly lifting potential.

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