Landing patterns and reverse thrust!

I don't know how long of a distance it takes for most of you to land, but when diving in below the treeline from 200 feet I pick up tremendousspeed on my EasyStar to the point of hitting 50 mph and overshootingthe runway, ending up in the trees.

Of course I can land in 500 feet easy, but making my autopilot do it wasnot. I was curious if anyone wanted to chime in on how they solvedtheir landing issues and minimizing the length of space required.

I was able to get mine down to 500 feet diving in from 200 feet and leveling off. The attached photo is my landing pattern.

1) Circle the landing zone, sample the winds
2) Go downwind
3) Turn for final approach
4) DIVE! with a feedback loop on airspeed able to do reverse thrust
5) flare and land.

My reverse thrust is done with a car speed controller. I can get +1 lbthrust as well as -1 lb of thrust. (Wasn't expecting that either.) Thisis just by running a typical 5x5 prop backwards!

The end result is that I slow down from 50 mph to 20 mph in a few seconds after the dive.

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.

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Comments

Maik 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.
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Nathaniel Caner 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
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Gary Mortimer 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
Tj Bordelon 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.
Tj Bordelon 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.
Moderator

Gary Mortimer 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.

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