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.

@Ritchie - I have specific landing bearings that effectively define runways. Right now there's a waypoint for the landing spot, and a list of up to 4 approach bearings. It picks the closest one. Now for landing patterns, I have 2 modes. One is beam follow, the other is radius follow. I radius follow around the landing point, then set up a new radius waypoint which is at the end of the runway, offset perpendicular by the radius length. So after I'm done orbiting and measuring winds, I fly to the other radius which lines me up with the runway. I added one last tweak which returns to beam following along the runway when I'm pointing perpendicular. That helps in cases when the wind is blowing and the last turn following the radius doesn't quite line you up.

Anyway, reverse thrust is pretty easy- just get a model car speed controller and allow your throttle values to go negative from a speed PID loop.

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Comments

AUQ September 10, 2010 at 2:01pm

I'm probably going to show how much of an amateur I am (if I could even be ranked as highly as that), but I figured I'd give my two cents, however devalued they may become.

What about some sort of arresting gear?
Tj Bordelon September 10, 2010 at 1:34pm

Can anyone give me some landing stats for their plane? Mine: From 200 feet up going 30 mph it takes me 600 feet to land.
Tj Bordelon September 10, 2010 at 12:30pm

@bGatti - I'm sure the prop is somewhat unhappy and stalling and/or otherwise being inefficient. Heck, it's running the airfoil backwards! But it does produce drag very well, and plenty of it.
Tj Bordelon September 10, 2010 at 12:01pm

Yep- using the breaking functionalty. Mostly because I am forced to with this ESC.
Tj Bordelon September 10, 2010 at 12:01pm

@Ritchie - I have specific landing bearings that effectively define runways. Right now there's a waypoint for the landing spot, and a list of up to 4 approach bearings. It picks the closest one. Now for landing patterns, I have 2 modes. One is beam follow, the other is radius follow. I radius follow around the landing point, then set up a new radius waypoint which is at the end of the runway, offset perpendicular by the radius length. So after I'm done orbiting and measuring winds, I fly to the other radius which lines me up with the runway. I added one last tweak which returns to beam following along the runway when I'm pointing perpendicular. That helps in cases when the wind is blowing and the last turn following the radius doesn't quite line you up.

Anyway, reverse thrust is pretty easy- just get a model car speed controller and allow your throttle values to go negative from a speed PID loop.
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.

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