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In the below video, the guy sets "launch mode" for hand launch where he adds a little bit of elevator.

Will a glider always loop up when launched horizontally, even if the tail is set to produce zero lift?

And what determines whether the glider will loop up or loop down (and crash, if possible) during launch?

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  • $\begingroup$ Do you see how the Spoilerons change the CP of the wing? (Launch/CruiseThermals) $\endgroup$
    – Robert DiGiovanni
    Commented Jan 15, 2021 at 19:53
  • $\begingroup$ @RobertDiGiovanni No $\endgroup$
    – user53913
    Commented Jan 15, 2021 at 19:57
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    $\begingroup$ Most of what you're seeing here is nearly unique to discus style hand launches. There are also javelin-style launches (which are rather different) and hi-start launches (different again) and winch launches (yup, different still). Oh, and although they're unusual in RC models, a few people do towed launches (which are completely different). $\endgroup$
    – Jerry Coffin
    Commented Jan 15, 2021 at 20:05
  • $\begingroup$ And there is also scale (Reynolds) too. One can see we want a thin wing with little camber, adding more camber as we slow down. Oh, yes, airliners do this too. $\endgroup$
    – Robert DiGiovanni
    Commented Jan 15, 2021 at 20:16
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    $\begingroup$ It's just being launched way above its trim speed, so it pitches up to regain trim speed and doesn't slow down back to its trim speed until it's completed a loop. If you set the elevator to a position that trims to the launch speed, it would go straight. $\endgroup$
    – John K
    Commented Jan 15, 2021 at 20:55

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No, it doesn't loop when launched correctly.

If you launch it so fast that lift is greater than weight, if will pitch up, and may either stall (as happened to me with my foam plane) or may enter a phugoid cycle where it climbs, dives, climbs again, and so on.

But if you launch it at the right speed and right angle (usually slightly down) it will fly smoothly to a gentle touchdown far away. This is the"trim speed" John K was talking about.

By angle I mean direction of flight, not pitch angle, or angle of attack. A stable glider will correct these as a rule.

But if your launch leaves too little lift, it will pitch down. This usually results in an immediate crash, due to the small altitude budget available.

The more lift your elevator is trimmed to create, the higher the optimum speed will be But it must always have lower angle of attack than the wing, or the plane will be unstable or will nosedive and crash

I often threw my plane at the ground as hard as I could, just to watch it nearly crash, and then zoom up to twice my height.

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  • $\begingroup$ The more lift your elevator is trimmed to create, the higher the optimum speed will be If CG is in front of wing 1/4 chord line,then elevator must procude downforce(negative lift). If CG is behind 1/4 chord line then elevator must produce lift.. to keep forces in balance...Isnt it? $\endgroup$
    – user53913
    Commented Jan 16, 2021 at 17:48
  • $\begingroup$ @EBV821 correct. But the CG does not directly set the trim. It merely sets how much force is required from the elevator. You still need to trim for speed. S slower airspeed at a given altitude will need the plane to fly more nose high, and vice versa. The forces will remain the same, despite the different trim settings. $\endgroup$
    – Abdullah is not an Amalekite
    Commented Jan 17, 2021 at 5:11

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