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Sunday, April 8, 2012

Smoothing Out The 3D Landing


Sometimes these 48" 3D planes can be a little difficult to land. This seems odd because they otherwise fly so well, especially at low speeds. After a lot of research, flying, and tinkering, I think I have gotten to the bottom of it, and how to fix it.

First we fly these planes pretty tail heavy. We can get away with it because the planes have such light wing loadings but it does make the planes difficult to land. You can take any of the EXPs, move the battery forward, and they land like a baby. It's only when you get that CG near neutral that the plane gets a little weird at the stall. The critical moment is right as you are ready to flare the airplane out to land. That's when most guys get into trouble.

The pilot will fly the plane in, and the nose will rise a little. The pilot lets off the elevator but nothing happens. The nose won't come down on it's own, and the plane stalls and bounces. Typical 3D landing at most clubs.

This is why a lot of guys simply harrier land their 3D planes. With the wing already mostly stalled, it won't balloon up on you. The only problem is that when the tail wheel touches first the mains usually plop in harder than you want. A really smooth harrier landing is hard to hit perfect, but at least it doesn't balloon up on you.

In a bad balloon-type of landing, what happens is that since the rear stabilizer is so much smaller than the wing, it stalls first, and being tail heavy, the tail will drop. Since the wing is still flying, and now at a positive angle of attack, the plane will balloon up just enough to completely stall that wing. This would not be so bad if you were ready for it, but.....

You see it all the time with the newer 3D pilots who have not figured it out yet. They will go to flare out and the plane will start climbing on it's own, even after the pilot has let off the elevator. At that point, it is a little late to push in down elevator, and that low to the ground it's such a foreign thing that your instincts will fight you. These newer 3D pilots are used to a sport plane that you have to hold the nose up the whole way in.

So, the best answer would seem to be to make the plane behave more like a sport plane. You can do this by putting in some down trim when you are ready to land. You have to hold the nose up, and if it does balloon, all you do is ease off the elevator and the nose comes right back down. While this works beautifully when you can remember to do it, what a pain that is, and then you'de better remember to put your trim back before you fly again. Too much remembering required, but it would be a great solution if it was automatic.

Oh, wait....... with today's awesome computer radios, we can make it automatic! I use a 1% down elevator to low throttle mix. When you cut the throttle, the elevator goes down a little, about once click of trim worth. I have done this with both Futaba and Spektrum radios. It cures the ballooning problem, but outside of that it does not change the way the plane flies at all except it will give you a perfectly straight power-off down line.
With this mix you pretty much land like you would land a sport plane. Just drive it on in, and if the nose gets too high, just ease off the elevator a little, it will will come right back down.
Like with any new mix, I suggest that you put it on a switch. That way if you don't like it, you can flip it off, land like always, and clear it out of your programming. Try it and I think you will like it. I run this mix on all my 48" planes with no switch. I even dial it in on brand new planes because I know I am going to need it.
It just wouldn't be an Extreme Aviation report without a video, would it? This is a compilation of three flights that were not especially noteworthy, but once I edited out the lame stuff it was actually pretty decent. Add a spacey soundtrack and you've got a great video................

Notice on the very last landing, after the closing credits, that the plane comes in low and starts to rise back up again. It's trying to baloon up on me, but I instinctually ease off the elevator a bit, the mix does it's job and it's a perfect landing. I am doing my landings more and more like this because it is so much easier on the equipment than a harrier landing. Half my harrier landings are more like downward plops, but you can't beat a mains only roll out for soft and pretty.
Thanks to my friend Kevin for the superb camera work.

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