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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  • That is exactly what I learned. I usually fly in the Phoenix area around 1500 feet and was up in the mountains of Colorado at about 8500 feet with some light wind to push against. 

    See the last few seconds of my crash. All is good. My buddy ran and grabbed it for me. It got wet but not bad. We pulled the battery and dismantled it immediately to dry it out. Iris and GoPro both survived unharmed. 

  • I only fly at sea level where I am, but this is interesting and something most people probably wouldn't think about.

    Do you have any footage?  It must look great that high up even if you're not that far about the (elevated) ground.


    • Here's a little collection a friend edited together for me from some of my stuff: https://youtu.be/gMh8kM4o6tk

    • Very nice. Cool to see all the NM shots.

  • Just got a set of 10x4.7 CF props. Never tried carbon fiber before, but just the feel of them is promising. I have to repair my busted arm today and try them out ASAP. Along with general performance and avoiding the worst of the altitude penalty, I'm hoping the 10" props give me a little extra confidence adding FPV weight and possibly reducing vibration.

    • All props need to be balanced Justin...there are at least a few ways to do these props with the nut on em. I got a balancer for dji props off amazon...works well.
    • Yes, I was a big fan of balancing with the old APCs, but I've fallen off the wagon with the nut-on props both because I lack the nut-on balancer you mention and because the vibration logs have been quite good (and I haven't thrashed my props in months before this incident). These new CF props are standard through-axle so I'll be able to balance them first thing.

    • Please let us know when you try them! 

  • You can use this calculator to mess around with some of the parameters. It takes into account altitude/density/temperature and you can check the effect on flight times/range/etc of changing prop pitch and a bunch of other stuff:

    Aaron, your data matches what the calculator says:
    1000' MSL:

    11000' MSL:

    I've done some flying with an IRIS-like quad at around 12400' MSL and around 20 F a while ago. I normally got about 50-60% less flight time and had a scary RTL on one of the flights:

    • Cool! I've often used http://www.ecalc.ch/xcoptercalc.php, which is similar, but somehow didn't notice that it has temperature and air pressure -- duh!

      I wonder if this is an accurate way to answer the pitch vs diameter question... I'm guessing the deal is that both are ways to increase volume displaced per rotation, but pitch change comes with a higher drag cost... so you probably want to increase diameter as much as you can and THEN increase pitch if you still need more volume per rotation... right?

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