Good, for you, I admire your tenacity (is that a word in English?). I still think you went the hard and slow way.

Anyway, you're enjoying yourself and that's what matters. I watched in horror how close you were to the houses in your first site, and advise you never to try to fly there again. Needless to say, a 2or 3 kg object with a metal tip hitting a child, car, pet, etc. is really not what you want, and, let's face it, you are still far from being in control.

The engine setup you're describing is most probably the reason the engine is quitting on you. When you carburate an engine, it is stationary, so it has to work a lot harder to push the air to the back of the prop. When you take of, the movement of the plane actually unloads the prop, increasing the final rpm's. Also, if your carburator is front mounted, the air is entering with more pressure. All this conspires to have a lean engine, prone to overheating, which I bet is what is happening to you. When the plane is flying, a lot of the time it has its nose up, so the tank being lower than when you set it up, also makes it harder for the engine to pressurize, also leaning it.

The proper technique is: start the engine, allow it to warm up for about 20 seconds. Remove the glow plug heater. Let it sit for a bit more, just to warm up and lubricate. Now lift the whole model (careful, it might be slippery) and accelerate to full. If it stops, open the carb a bit and start over. It was too lean. When you manage to get full rpm with the model facing about 45 degrees up, open it further 1 or 2 clicks. Now set it flat on the ground and check you have adequate throttle for a comfortable takeoff. It wont be full rpm, remember, you'll get those later when you are climbing.

This procedure will give you a much more reliable engine, and will help it last a lot longer than overheating it all the time. Do it every time you go flying,and again every time the temperature, moisture, pressure changes.

As for the sand, I suggest you get a commercial air filter for the carb and for the feed fuel line. Or at least tie a piece of nylon stocking stretched over the air intake.

Last, fly only rectangles, just like full size aircraft do over a runway. Decide where your runway is, and strive to fly directly over it every time. Then start reducing the throttle a bit more each time you pass, allowing the plane to glider lower and lower. On one of those you'll feel confident enough, stable enough, youll just idle the engine, flare a bit at about 1 meter over the ground, and you will have landed.

I wish you success, and hope you keep enjoying it as much as you have