Are Planes Even Landable?

[Yeem]

I've had several plane models get off the ground and fly so far, and not a single one of them has been landable in any form. During my descent, I can't get the plane to drop below 70 horizontal m/s by any means. I've read posts about lowering my vertical speed below 5 m/s but even when I do that every single wheel still explodes on contact. I've read about making the back wheels lower than the front wheels so that they touch down first, but they just explode when they do. I've even gone so far as to pull my plane 5 feet up above the runway, kill the engine and attempt to touch down again -- somehow, in the 3 seconds the plane was in the air, the wheels go from perfectly functional to hot dynamite. Honestly I'm tempted to just start using parachutes and give up on landing being a "thing". Here are photos of my latest craft.

https://imgur.com/a/h7FsWva

[Cavscout74]

What game version & what wheels are you using?   I can't open your image for some reason, just shows up as text to me & copying it to a browser does nothing either. 

I've not run into any issues in 1.5.1 yet, but some previous versions had gear problems, primarily excessive bouncing.   But normally, the gear should not explode easily.  I've touched down in excess of 100 m/s, bounced repeatedly & broken off other parts of the plane without causing gear to explode.  Frequently, the gear are the some of the few surviving parts of catastrophic crash landings, so you definitely have something odd going on.

[Vanamonde]

Sounds like the plane could use more lift so that it's not relying on speed to remain airborne. Also, those are the weakest model of wheels, and are only suitable for very small planes. If you can get better ones I suspect you'll have less trouble. 

[bewing]

Welcome to the forums, yeem.

Those wheels are generally not capable of handling that much weight. Those ones max out at about 7 tonnes, iirc, for a tricycle arrangement.

For fancier designs like yours, you are going to need the next higher tech version of a landing gear.

 

Edited December 20, 2018 by bewing

[Mad Rocket Scientist]

There are a couple of things to consider when placing landing gear that aren't at all obvious:

First, the angle of the plane when resting on the ground. If the plane is nose up, it will take off easily, but land badly, since it will have to have a very high angle of attack (angle of nose relative to direction of travel) to land on the back wheels first. If a plane is nose down, it will land better most of the time, but may act weird in some circumstances, and will have trouble taking off. The Space Shuttle, which only even needed to land horizontally and never take off, had a very nose-down attitude on the ground:

https://www.nasa.gov/images/content/152546main_Landing2-lg.jpg

Second, the location of the landing gear relative to the center of mass (CoM) of your craft. There are two typical ways of doing this in the real world, but you shouldn't feel constrained to only using these ways in KSP. The first is tricycle landing gear. This is the most common in modern airplanes, and overall the best in most cases. It has one small wheel at the very front of the plane, and two or more large wheels right behind the CoM. As the plane increases its speed, it lifts the front wheel off the ground, the wings start to generate more lift, and the plane takes off. Placing the wheels only slightly behind the CoM means that the plane can pitch up easily while still on the ground. When landing, the plane touches down with its nose up, landing on the two large wheels first, then letting the nose drop to the runway.

The other way is called taildragger, and is essentially the opposite, with two large wheels well in front of the CoM, and one small wheel at the tail of the plane.

The first two planes in that image are taildragger, the last is tricycle. When taking off, the plane will quickly rise off the rear wheel, staying on the two main wheels for most of the takeoff. When landing, the plane comes in nearly level, then returns to all three wheels after slowing down.

From my experience in KSP, tricycle is harder to build, but easier to fly, while taildragger is easier to build but harder to fly.

What upgrade level is your runway? For some weird reason, the earlier levels are worse than the flat ground around the KSC for landing, so you may want to try that.

As others have said, upgrading to heavier duty landing gear will help. You may also want to look at the way the vertical wings that hold your engines on are attached. It looks like they are connected to the part of the swept wing that tilts slightly down, which can cause issues. Placing them slightly further back may help. This vs this.

[dire]

If your mission profile will allow it, you're going to want to cut down on your engines to just one wheezely, which should still be plenty of thrust for that much plane but reduces the burden on the landing gear. Also don't forget to throttle down on landing. You should be able to land on between 0 and 15% engine power.

Protip: If your plane starts acting crazy and doesn't want to steer straight when you're taking off, your wheels are overburdened and are more likely to explode when you land. Less of an issue with spaceplanes because they tend to burn so much fuel that they are many tons lighter on touchdown, but your plane is mostly engine and payload and very little fuel, so your takeoff weight is almost the same as your landing weight.

You'll also want to get in the habit of thinking about where your fuel is relative to center of mass, and try to keep your full and empty CoM at about the same spot. That's only important if your CoM slips behind your center of lift because your plane will then not want to fly straight, which again is more of a factor with spaceplanes whose CoM can potentially shift quite a bit thanks to all the fuel they burn.

I made a little mark-1 plane for you so you can practice landing and have something to go fast, and if you do give up you should be able to make a powered parachute landing: https://kerbalx.com/direstorm/Mark-1-Mach-1

The plane has a couple of more advanced spaceplane features that you can explore as well: the rear wheels are doubled up and you've got a small amount of oxidizer to let you hit some of the lower "altitude above" contracts -- probably can't get "suborbital tourist" in this one unless you want to start playing with SRB payloads, and there isn't really a small, thin SRB that would make a good spaceplane booster unless you want to tinker with the sounding rocket mod.

If you don't have sparks yet, you should definitely consider them as they're very handy for early-career science missions and remain good later for return vessels and landers. I'll also say you're right and those lander legs DO seem to be made of explodium, but if you pack spares it's not too big an issue If you get frustrated, try again when you can use the small folding wheels.

Edited December 21, 2018 by dire

[Yeem]

Thank you very much for all the advice. Turns out "get better landing gear" was the correct answer, as I can actually land now. I also found that I can reverse the thrust on my wheezelys to manually force the plane to slow down more than it wants to. Just did my first landing with no parachutes.