Glider speed and issues stalling? - RC Groups
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May 17, 2017, 06:40 AM
Registered User
Discussion

Glider speed and issues stalling?


First time flying the HK mini-DLG pro today and found that as long as it kept up speed it wouldn't stall. It had a tendency to glide but slow down and stall unless i gave it a very gentle downwards trajectory, sometimes i could get it very level and glider but a lot of times it would tend to just stall, but not stall and dive.... just kind of stall and drop to the ground in a horizontal position.

It didn't dive presumably because I got my centre of gravity right (tested multiple times, 80mm from the leading edge)

Is that just how it is with dlg gliders? Every time this thing in the air I am nervous about it dropping out!
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May 17, 2017, 08:03 AM
Registered User
Sorry if this is obvious, but..

Gliders don't have an engine to generate thrust. But they still have aerodynamic drag. The energy to overcome drag has to come from somewhere. Gliders get this energy by converting altitude into speed, just like driving a bicycle downhill without pedaling. If you try to fly at level altitude, you will eventually run out of airspeed and stall, just like trying to drive a bicycle on level ground without pedaling. The only way to maintain or increase altitude is to fly in an ascending airmass, but even then the glider must be decending relative to the air around it.

Gliders are powered by gravity and must be flown downhill all the time.

If your glider doesn't do this on its own and the cg is correct, add a few clicks elevator down trim until it does.
May 17, 2017, 11:21 AM
Registered User
Yes, you must trim the elevator so that it will glide hands off in calm air. Gliders tend to have the CG more rearward so you can see them react to thermals making them pitchy, so it would be best to trim it out on a nice clam day with few thermals.
May 17, 2017, 11:32 AM
Drone offender FA377YHFNC
Here's where a bit of trial and terror is called from. Every plane has a certain speed for minimum sink rate. Flying above or below that airspeed means the plane comes down quicker. DLGs tend to like to fly faster than floater type gliders. Slow them down to floater speed and the descend level, but very fast, like they're on an elevator. You have to experiment to find the speed it likes to fly. Remember, airspeed is determined by elevator position: down elevator speeds you up, up elevator slows you down.

Long ago, sailplane designers found that the lowest sink rate for a given wingspan wasn't the key to longest flights. Every thermal has a lifespan, either because it peters out or it drifts downwind to a position from which you can't fly back to launch point. So you have to bail out of a thermal. Every thermal is surrounded by a donut of sink, and the plane which can fly through the sink on the way to the next thermal, taking the shortest time (flying fastest) through the sink will have more range to find that next elevator ride. Therefore modern sailplanes are designed for much more speed than old school floaters.

Your report on stall behavior is spot on. A well designed sailplane won't dive when it stalls. The nose drops a tiny amount, the plane shakes side to side a bit and drops almost vertically while in level attitude. You gave about the best description I've ever read. It becomes a falling leaf! Blip down elevator for a split second, the nose goes down and the plane resumes flying without any fanfare about it at all. That's what a well-behaved sailplane does.

Find the speed it likes and feed it that! Have fun!
May 18, 2017, 08:30 AM
Registered User
thanks guys, much appreciated


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