3D Robotics

Predator build and fly thread (tip stall warning!)

For those of you interested in the Nitroplanes/Hobbyking Predator (they're essentially the same plane), here's a great build thread on how to make it, along with a very sobering set of warnings and lessons learned the hard way about how it flies. Basically, tip stalling is a huge problem and you have to land it with long, straight and fast glide paths or it will crash (I've already lost one that way). Basically, it's a poor airframe for UAV/FPV/AP use; we just use ours to show off at conferences.
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  • I think it would be worth getting one for my kids ceiling might make a decent decoration.
  • I suppose I'm a fool for aesthetics. I'll look for a more stable platform and hopefully get my predator flying, any suggestions of planes would be appreciated.
  • T3
    This is Lancair GP EP for GreatPlanes,
    a TERRIBLE UAV platform.
    underpowered in my case, very small wing chord, wing loading some 60g/dm2 and high torque effect on roll.
    Barely flyable in RC mode without turbulators, with turbulators can accept very high AOA but still needs hot approaches that you flare at 0.5m altitude (without turbulators any attempt to flare ends in stalling above ground). Don't even think using landing gear unless got exceptionally smooth airfield. Needless to say it 'feels neutral' on roll and that you cannot toss it reliably since it is a low wing plane,.
  • Krzysztof,
    Where did you buy your Lancair from? It look like an excellent UAV platform.
    I'm working on a Predator but hope to expand in the future.
  • Am in process of installing FMA CoPilot on my TMPro Predator ARF from HobbyKing. Anyone here care to share their actual flight reports with this combination? My experiences are posted here; build thread
  • T3

  • Quote: Hope you fix it, also where was your CG. If its too tail heavy it will TIP STALL ALL DAY Long.
    Agree with that, and why not try with the old, always working rules:
    - accurate wing incidence measuring.
    - some light negative tip warpage (-0.5/-1 degree)
    - ailerons up on landing (not down!)

    Just a thought to make life easier.


  • Chris,

    A tip stall is recoverable at altitude though, it's not impossible to recover from a tip stall. An AP could be programmed to avoid a tip stall happening by settings and sensors noticing critically low speed - high angle of attack and wing dip. At that point the AP could inject correction, level out, dive a little and wing level to avoid the stall occuring. I have had so many different planes do tip stalls, especially my turbine yellowaircraft F-18 which is prone to it at high angles of attack on final approach. Its recoverable, just need to be able to see it, feel it, and respond quick enough with the right corrections. Can an AP do it, haven't seen a DIY one that could, but im sure someone could make it with wing sensors to sniff the rough air occuring at the wing tips.
  • 3D Robotics
    Jack, once that tip stall starts it's essentially impossible to stop. The plane is going to fall 100ft before you can get control, and if you're less high than that you're going to crash. What determines a tip stall is a combination of airspeed and roll angle, so I suppose you could program an autopilot to keep that combination above a certain threshold. But it would be hard to tune, and hardly worth it when you can just switch to a better airframe that doesn't have this problem. And once you've gone into a tip stall, I don't see how an autopilot can save you since you're basically non aerodynamic at that point.
  • Jack,

    I have FMA on mine for pure FPV only flight, and I never turn it off. It works like a charm on my other one, for paparazzi it has stability modes so I get the same effect as FMA with the paparazzi. Like ardupilot would provide if it had say AileronAssist like the UAV devboard has. Stability mode rocks for planes that are inherently not so stable. I have a delta wing UAV that I use FMA to maintain stability mode for aerial photography and video recording. This plane is a challenge to maintain stable flight, especially durring the hand launch. But with the fma copilot I turn it on on hand launch and its smooth sailing all day long. IR Sensor stabilization in any un-stable plane, or gyros will improve drastically the stability of that airframe.
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