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Plane tumbling upon landing


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Question

Has someone ever had a problem like this ? 

Also it has a weird bug with the brakes when loaded, if I try to begin taking speed it won't move, I have to toggle the brakes on and off. It might be related, or it might just be my bad designing or piloting. The weird thing is that generally on test flights, it lands correctly the first time and then when I quickload it tumbles upon landing.

 

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I think if you manually set the friction of the front wheels to 0 in the SPH, it will work much better. I think the front wheels are grabbing the ground when you touch down. Also, your airspeed seems very high when landing. When you are down to a few meters above the ground, I think you need to "flare" more to reduce your airspeed.

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There's a few problems going on here.  As @bewing mentioned, you're coming in way too fast and too level, you should come in at about half that speed, and let it roll a bit on the back wheels before you bring the nose down, especially with that extreme of a downward rake to the aircraft when the wheels are level.  In addition to reducing the friction, you should also reduce the springyness of the suspension, as that could induce a bounce at higher speeds.  The extremely compact design is probably not helping, increasing the length between the nose and main gear will make the plane less likely to flip.

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Your plane is too short, the wheels are too close together and the front wheels are higher than the back ones. The rear wheels will land first and friction will pull the nose down, but the front wheels are too high so it can pivot a lot before they touch the ground and will make them ‘dig in’ and flip the plane. The short distance between the wheels and short overall length make it easy to rotate on its pitch axis so you’ll front flip very easily, the wheels are really close to the centre of mass which reduces stability.

To fix it, make the fuselage longer, move the rear wheels further back and keep the front and rear wheels as close to level as you can, or have the front wheels slightly lower. This will make the plane more stable on the ground and easier to land as the wheels are further from the centre of mass, although moving the rear wheels too far back will make it harder to pull up when taking off unless you use nose mounted fins or canards to lift the nose.

You’re also landing quite fast, it’s entirely possible to get a much larger and heavier plane to stay in the air at under 40m/s. Cut the throttle and glide for as long as you can at an altitude of 5m or so until the plane runs out of lift and drops gently to the ground, then go easy on the brakes- set the front brakes low to avoid making the plane pivot forwards and crashing it’s nose into the ground.

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