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 11:59am

Are you using the ESC braking functionality? Most car ESC, and many plane ESC do have that.
Tj Bordelon September 10, 2010 at 11:52am

@Maik - Wish I had you at the first test flight. The prop unscrewed itself! I run a feedback loop so the error tends to build up slow enough. But I did have to add a delay of 1 second- if you cross over from forward to back it waits for 1 second with no throttle to allow the prop to slow down.
Ritchie September 10, 2010 at 11:43am

Reverse thrust I have no effective on my mind that I could implement easily.
Landing patterns however, I think TJ is spot on but the landing area would have to be of a certain size in every direction. A setup I had considered for mission planner software was waypoint based. With a "string" of waypoints with landing point and approach start at either end. With two waypoints between to help you setup for a gentle plop rather than a splat. My worry now is that without getting the wind right (predetermined points), this plop will be much more likely to be a splat.
However, what if TJs landing preparation could be used to lay out the waypoints for my "landing strip" idea. The landing strip could have definitions to the airframe to become more specific and allow better control during landings.
Maik 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.
Tj Bordelon 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.
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.
Moderator

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
Moderator

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
Bob Hvarven 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
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.

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