Moderator Comment by Gary Mortimer on September 10, 2010 at 6:51am

Power controls rate of descent Pitch controls speed. Putting the nose down just gets you to the accident quicker. A parachute is the way forward for tight spots.

Comment by Tj Bordelon on September 10, 2010 at 6:56am

That's the way real pilots do it. My AP generally does the reverse of that during flight and I wanted to avoid having to support yet another mode. (I always do airspeed on throttle, alt on elevator) But you are right in general.

I found though in my tests that doing exactly what you describe was a bit more sloppy-- and didn't work very well at all in winds. Basically it took more landing space, had me on the edge of stall (and I'd get tip stalls on landing), and had me tweaking even more parameters for different PID loops on landing.

I heard that this was "wrong" but I find that diving in and leveling out winds up working in gusty winds and seems like a more controlled way to get down and lined up. Of course the bad part is that you're going too fast.

I always imagined having throttle blaring, nose up 15 degrees, with a gentle touchdown. In practice I was never able to do that without stalling alot. Maybe I was doing something wrong.

Comment by Tj Bordelon on September 10, 2010 at 7:21am

OK- imagine this. You have a "beam" to follow that goes down at a 45 degree angle to "HOME" where you are to land, 200 feet below. You are going to do the "airspeed on elevator, altitude on throttle" thing. What happened to me is that you'd be up too high, so throttle would cut. Then you pitch down to get some airspeed. Well if you're trying to maintain the usual cruize speed of 30 mph, you're not going to dive fast enough. Even if you solve that problem, you're going to be coming in too hot.

My goals are to have the shortest landing possible without adding equipment. No sonar, no parachute. And without adding more feedback loops. This algo seemed to be the ticket. Do you know if anyone (including yourself) has gotten what you suggest to work coming in from so high with only 500 feet of space to land in?

The purist in me wants to do altitude on throttle, airspeed on elevator 100% of the time. I just can't seem to get the same level of accuracy with that technique if you are trying to fly on beams between waypoints PRECICELY.

Comment by Bob Hvarven on September 10, 2010 at 7:46am

Not sure how this would be integrated into your programming but - In my younger days we used to launch free flight gliders for duration contest. These gliders had a dethermalizer that when either a wick that burns down or a timer activated it causes the stabilizer to pop upward from it's horizontal position and the glider just slowly decends vertically to the ground. The stabilizer area on your plane would need to be modified and a way to stop the motor at the same time. It really wouldn't be difficult to do and there is a lot of info on the net under dethermalizers showing how free flight glider folks accomplish the task. FWIW

Moderator Comment by Gary Mortimer on September 10, 2010 at 9:17am

That would be a very neat solution Bob, I might try that myself. Perhaps the weight of UAS would not lend themselves to that technique, but I certainly stand to be corrected. I had completely forgotten DTs

Moderator Comment by Nathaniel Caner on September 10, 2010 at 9:22am

Sounds like what you really want is a speed brake, actuated when you are in LAND mode, your AIRSPEED is above a set value AND you have reached a given WAYPOINT, say the end of your runway. If all of these conditions are true, then speed brakes would be activated until you reach the desired airspeed. If any one of these conditions were NOT true, then nothing would happen, IE your airspeed is already below the desired speed. Perhaps this could be an alternate use for the 4th channel for those not using it for rudder. Suggest it as an enhancement in the issues section. Perhaps it could be considered in the next major revision.

Nathaniel

Comment by Maik on September 10, 2010 at 11:07am

If you modded your EasyStar with ailerons, you can also do a controlled slip to slow down. Pull the ruder and use the ailerons to keep the wings horizontal. Or you can use your ailerons as speed brakes, but then you reduce your aileron travel.

Comment by Scott Lencl on September 10, 2010 at 11:20am

I was thinking what Nathaniel was, air brakes all the way. Perhaps have the autopilot enable air-brakes and reverse power at the same time to get better effects. If you were to do that but with a bigger prop, that would help bite the air more too, so if you do vari pitch, 6" prop is a must. Although I think it would be interesting to see how to set up a variable pitch Easystar, theres mot a lot of room to set all that up I would imagine. great idea by the way, gave me a couple thoughts.

Comment by Tj Bordelon on September 10, 2010 at 11:23am

I like the slip idea. I've also tried spoilerons which helped, but not enough. The reverse thrust is the winner so far, assuming I am not out of juice. The spoilerons reduced my landing from about 1000 feet to about 800, but the reverse thrust has further brought that in to to 600 feet.

Right now I don't have a rudder hooked up, but that would be a neat thing to try (slip).

I like to think of this experiment as trying to land in a canyon in hurricane force winds. Scale wise it seems to be exactly that. You want to keep that speed up until the last second!

Awesome suggestions! I have to say that the reverse thrust produces amazing amounts of breaking. Almost too good. I had to dial my gains back. The first try I stopped in my dive almost instantly and tip stalled.

Comment by Maik on September 10, 2010 at 11:41am

If you can, set up some smoothing on your throttle, so you don't go from full forward throttle to full backward throttle. Otherwise I could imagine quite a bit of stress on the prop, motor and motor mount.

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