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.

Thanks everyone. Actually @mike-- You are spot on. With full reverse thrust, I can't hold the nose up on the plane beyond -15 pitch. Which when I'm trying to lose altitude isn't a problem, but during the last 30 feet I have to cut reverse thrust to regain my pitch authority. I think the negative is definitely the disturbed airflow situation. My landings have been perfect until this weekend when my reverse thrust had to stay on longer and closer to the ground. In both cases I had HARD landings.. .but my elevator was FULL UP going 25+ mph (plenty of airspeed) but couldn't hold the nose up.

All and all I think this technique works but has it's drawbacks.

Also, I purposefully descending too late. I am getting ready to land in my backyard, where I only have a few hundred feet and tall trees all around. I'm trying to practice :)

You are also right in controlling descent with throttle, but that requires more space. This was an experiment to see if I could do better by breaking all the rules.

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Comments

Tj Bordelon September 13, 2010 at 6:45am

Great idea! That sounds like a good solution. I had thought of:

1) Limiting the reverse thrust to 50% of what it is now
2) Just cutting out the reverse thrust when I get within 50 feet of the ground

but yours sounds the best...

3) Scale maximum reverse thrust with elevator command.

I hope I can encourage others to try reverse thrust as a valid way to slow down in a hurry. It works reasonably well.
Mike Lombardi September 13, 2010 at 5:36am

Sounds like a lot of fun doing these combat approaches! Maybe you could program the autopilot to reduce the reverse in proportion to the elevator command or maybe use less reverse for a longer time to keep control?
Tj Bordelon September 13, 2010 at 5:12am

One thing to point out again. I am trying to be VERY AGGRESSIVE here. That's why I'm diving and using reverse thrust.

I can land my plane in the same space because I circle in and avoid the trees. I am trying to program the AP to do it in one step. Dive in and land.
Tj Bordelon September 13, 2010 at 5:06am

Thanks everyone. Actually @mike-- You are spot on. With full reverse thrust, I can't hold the nose up on the plane beyond -15 pitch. Which when I'm trying to lose altitude isn't a problem, but during the last 30 feet I have to cut reverse thrust to regain my pitch authority. I think the negative is definitely the disturbed airflow situation. My landings have been perfect until this weekend when my reverse thrust had to stay on longer and closer to the ground. In both cases I had HARD landings.. .but my elevator was FULL UP going 25+ mph (plenty of airspeed) but couldn't hold the nose up.

All and all I think this technique works but has it's drawbacks.

Also, I purposefully descending too late. I am getting ready to land in my backyard, where I only have a few hundred feet and tall trees all around. I'm trying to practice :)

You are also right in controlling descent with throttle, but that requires more space. This was an experiment to see if I could do better by breaking all the rules.
Mike Lombardi September 12, 2010 at 6:30pm

Looking at your landing diagram again, it is looks to me that you are starting your landing descent too late. Try starting a decent when you are abeam the end of the runway on the downwind leg (pretty much where the road is in the picture). Turn your base leg when the plane is about 45 degrees from the end of the runway, then turn final when you line up with the runway.

Standard descent angle for most real real runways is about 3 degrees, which is 300ft/mile. So if you are 1 mile out from the touchdown point when turning final, you should be at 300ft, 1/2 mile final is 150ft, 1/4 mile final is 75 ft etc. Hope this helps.
Mike Lombardi September 12, 2010 at 5:55pm

I think it's fine to use reverse thrust if you have to, but I can tell you from my experience flying the full scale Piaggio Avanti (which is a pusher prop like the easy star), reverse thrust significantly decreases stability due to the disturbed airflow over the horizontal and vertical stabilizers. Just something to think about.
FlyMario September 12, 2010 at 2:09pm

Interesting discussion. I take it you can't just do tight circles on the way down. I can't imagine actually reversing the motor. Sure it can be done but props are not effecient running backwards. Heck, whatever works for you I suppose. Just doesn't sound very graceful :)
Andrew Jackson September 11, 2010 at 9:57pm

It seems to me that if the airframe can do the job when being controlled by a human and not when controlled by the computer, then the problem is with the algorithm.

You state that you have more success in low wind situations. Assuming that stability is not the issue, then I wonder if you are allowing for the "gradient effect". That is the reduction in airspeed as you get closer to the ground. I suspect that when you are flying it yourself, you are making automatic corrections for this. The autopilot is following some other rule.

And always remember - "There are three rules for a perfect landing every time . . . unfortunately, noone knows what they are."
Mike Lombardi September 11, 2010 at 3:06pm

You should be able to trim the airplane's pitch attitude to maintain your Vref speed (approach and touchdown speed) in level flight. I would fly at a safe altitude and slowly reduce the power while trimming the elevator to maintain level flight. Once you find a comfortable approach speed (about 1.3X stall speed), just reduce the power to start a decent. The airplane is trimmed and should maintain that approach speed even if you bring the power to idle. Now you can just use power settings to control your descent rate.

This is how real airplanes are flown, so I assume it should work fine with the easystar as well.
Ritchie September 10, 2010 at 3:11pm

I keep forgetting yours isnt a normal one :D
Once mine can be trusted, I'll start doing landings and give you all the data.

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