Why won't this low tech plane land?

[Fl1x]

Hi,

I'm a rather seasoned player with 400+ hours under my belt but so far I've only ever build rockets. In my new save I wanted to try out planes. So I dusted of my old joystick and started a career save. This is my first plane. It's not very good but it actually flies and I can control it pretty well. I just can't seem to get it to land. It explodes on touchdown. I have no idea why. I've attached some screenshots and I'd be happy to provide a .craft file if anyone wants to try it.

Gallery

[Popestar]

2 questions.

1. What is your speed upon attempting to land?
2. What is your angle of descent?

[bewing]

How much fuel do you have in it? Or alternately, what's it's mass?

Those cessna wheels you are using have very low weight tolerances. My guess is that you've greatly exceeded them. Try taking 90% of the fuel out of the craft, then see if it lands correctly. From your design, it looks like your landing speed should be below 30m/s, and make sure you touch down as much like a feather as you can. Don't slam your plane down onto the ground.

 

[The_Stinky_Broccoli]

my guess it that you were landing front gear first when you should be landing back gear first.

[18Watt]

58 minutes ago, The_Stinky_Broccoli said:

my guess it that you were landing front gear first when you should be landing back gear first.

Actually, the plane depicted appears to be a traditional (tail-wheel) design.  In that case, landing front wheels first is recommended.  Or a 3-point landing.  

As bewing said, looks to me like touch down should be around 30 m/s.  I don't think the mass is too much for the gear.  I would be concerned about the long wings, flapping down on landing.  Especially with the engines and fuel located so far from the centerline.

Perhaps try hitting F3 after an unsuccessful landing- it should tell you which parts were destroyed, and in what order.  That may give you a clue as to what is going wrong, by looking at the first few parts to explode.

Actually, taking another look at it, that is a lot of wing for that size plane.  30 m/s may actually be too fast for landing.

[Klapaucius]

Did you use rigid attachment anywhere?  It can make planes very brittle.  If you did, remove it and use autostrutting instead.

 

If you have not used it, well, what all the folks above said 

[jimmymcgoochie]

Next time you fly the plane and it crashes on landing, hit F3 and see which parts are exploding or breaking first- this will tell you what the issue is. Brittle landing gear is one possible cause, plus the fact that it’s attached directly to the cockpit means the force could easily push the gear into the cockpit and destroy both, or the gear snaps off and the cockpit immediately hits the ground.

I would recommend switching to a tricycle gear setup (but keep the tail wheel to avoid tail strikes) and adding a pair of elevators on the tail to greatly improve the pitch control; right now I see almost no pitch authority as the elevons on the wingtips are very near the mid point on the plane’s length, so they can’t apply much force.

Landing a plane can be tricky, so try to find out its minimum speed while you’re well above the ground and then stay above that speed when you’re trying to land. Kill your vertical speed when you’re just above the runway then let the horizontal velocity slowly bleed off and set the plane down gently. With a bicycle/tail-dragged setup you need to take it easy on the brakes or you can face plant the nose, something that plagued various WW2-era planes and which can easily destroy the cockpit on the nose of your plane in KSP too.

[Fl1x]

19 hours ago, 18Watt said:

Actually, the plane depicted appears to be a traditional (tail-wheel) design.  In that case, landing front wheels first is recommended.  Or a 3-point landing.  

As bewing said, looks to me like touch down should be around 30 m/s.  I don't think the mass is too much for the gear.  I would be concerned about the long wings, flapping down on landing.  Especially with the engines and fuel located so far from the centerline.

Perhaps try hitting F3 after an unsuccessful landing- it should tell you which parts were destroyed, and in what order.  That may give you a clue as to what is going wrong, by looking at the first few parts to explode.

Actually, taking another look at it, that is a lot of wing for that size plane.  30 m/s may actually be too fast for landing.

You were right, I was landing to fast. I also added some elevators to the tail to control the pitch better. And I found out that I could use the ailerons as flaps. That helped a lot. I'm beginning to think the rest is practice. I've made a video of one (unsuccessful) attempt, maybe it's good for a laugh.

 

[king of nowhere]

one counterintuitive thing i learned to land planes: you should not try to slow down as much as possible.

sure, you need to slow down, but not too much; you must still be fast enough to stay in the air. then, very carefully, you go down. your angle should be less than 5 degrees below the horizon.

in the beginning, i was trying to slow as much as possible while still in the air, that caused me to fall too fast because my plane could not fly anymore. and nobody explained it to me. i had to discover it by accident.

[18Watt]

4 hours ago, Fl1x said:I've made a video of one (unsuccessful) attempt, maybe it's good for a laugh.

Well, I’d call that a good landing.  I define a good landing as any landing you can walk away from.  Looked like the Kerbal was still alive to me!

A great landing is when you can use the plane again.

Looks like the plane handles well, but with all that wing you probably should be touching down much slower.  One additional thing to consider (after seeing the video) is that to get the plane that slow, your pitch will end up being +5 degrees, maybe more.  Due to the length of the plane, that may cause you to hit tail wheel-first.  Again, with a tail wheel airplane it’s better to land on the main wheels, or a 3-point landing.

Switching to a tricycle-gear (one nosewheel, two main wheels) configuration allows you to land at a higher nose-up attitude, thus slower speed.   I like tail wheels  too, but tricycle gear gives you a lot more design freedom, and is easier to control on landing- at least in my opinion.

[vv3k70r]

On 11/25/2020 at 8:53 PM, Fl1x said:

It explodes on touchdown. I have no idea why.

Tweak spring and dampers to max. This wheels are really bad to suport this mass. See where they have a pranet - wings are bad parent for heavy plane.

Landing is about loosing ability to fly, it is good to loose this ability as near and slow as possible - wheels gona be less stressed.

Edited November 30, 2020 by vv3k70r

[Spricigo]

15 hours ago, vv3k70r said:

Tweak spring and dampers to max

It's unnerving that sometimes is tweaking to min that works ...or max to one and min to another. ...or the other way around...or no way! Ahhrrrggg!!!

[AHHans]

8 hours ago, Spricigo said:

It's unnerving that sometimes is tweaking to min that works ...or max to one and min to another. ...or the other way around...or no way!

Indeed!

My impression is that you want to avoid maxing out the suspension travel - in both directions(!). I.e. don't have the spring strength so high that the spring doesn't really compress (mostly an issue on wolds like Gilly for obvious reasons), but also don't have it so low that you bump into the maximum compression with high speed. Getting that setting right is a PITA.

[vv3k70r]

31 minutes ago, AHHans said:

I.e. don't have the spring strength so high that the spring doesn't really compress (mostly an issue on wolds like Gilly for obvious reasons), but also don't have it so low that you bump into the maximum compression with high speed. Getting that setting right is a PITA.

It is something to be tweaked after situation. Generaly I set them on max (because cheap wheels to heavy construction) and if there is any issue with jumping I release them a bit and see if it helps. But if I set them too low there be no "after jumping" to twek them. It is why I consider max as good place to start testing.

It is quite funny on the begining whe there is no tech to choose and vehicle to be suported is as havy as it needs. In later game there is more stuff on the shelv. I have real fun making supersonics on cesna wheels.

Edited December 1, 2020 by vv3k70r