Tail keeps hitting the ground.

[FlexT_ape]

So, I just made a HUGE cargo plane that is transporting a rover. I've been flying for over 30 minutes going to the north pole.  Everything went well except when I touch the ground the tail slams into the snow. I've  tried  going as slow as I can but it happens everytime.... Help anyone?

[ARS]

Picture of your craft would help us a lot in determining what's the error and how to fix it

In general, tailstrike usually happened because you're pitching up too high on landing, which caused rear section hit the ground, bad design with long structural element jutting up from behind which makes it very easy for getting tailstrike, or incorrect placement of rear landing gear. The rear landing gear is especially unique, when your plane takes off, the rear wheel acts like a lever, where the lifted part on the frontal section of your craft used the rear landing gear as the point of leverage to lift the rear section. When building aircraft, it's important to note that rear landing gear must be placed a bit behind the center of mass, if you put it too far behind the center of mass, your plane would have difficulty in taking off, if you put it too far ahead, the craft becomes prone to tailstrike since the center of mass behind the craft pulls the rear section into the ground

Hope that helps

[FlexT_ape]

10 hours ago, ARS said:

Picture of your craft would help us a lot in determining what's the error and how to fix it

In general, tailstrike usually happened because you're pitching up too high on landing, which caused rear section hit the ground, bad design with long structural element jutting up from behind which makes it very easy for getting tailstrike, or incorrect placement of rear landing gear. The rear landing gear is especially unique, when your plane takes off, the rear wheel acts like a lever, where the lifted part on the frontal section of your craft used the rear landing gear as the point of leverage to lift the rear section. When building aircraft, it's important to note that rear landing gear must be placed a bit behind the center of mass, if you put it too far behind the center of mass, your plane would have difficulty in taking off, if you put it too far ahead, the craft becomes prone to tailstrike since the center of mass behind the craft pulls the rear section into the ground

Hope that helps

Thanks! I'll upload a pic of the craft

SCREENSHOTS: https://imgur.com/a/05ez9Wr

 

Edited August 24, 2018 by FlexT_ape
link

[ARS]

Based from your screenshot, I can say:

Your rear fuselage is too long, and your rear landing gear is placed too far forward, that's why your center of mass is behind the rear landing gear, making it prone to tailstrike and highly unstable on the ground. I suggest you remove the fuel tank on the forward fuselage to make it shorter (So it becomes "cockpit-cargobay-rear door", with no fuel tank in between. When you fly for a long time with fuel tank behind the cockpit, the fuel drained will make forward section lighter, shifting the center of mass behind) move the fuel reserves to the wing (The largest wing for airplane part have internal fuel tank, right click it in hangar to fill it with fuel). Other than that, make sure your center of lift and rear landing gear is slightly behind the center of mass (Use the center of mass and lift indicator in hangar to adjust it by offsetting the wing forward/backward or adding mass/ additional lifting surface (Like radial fuel tanks or canards) to balance it).

In conclusion, your problem is:

1. Your rear fuselage is too long, fuel tank placed behind the cockpit shifts center of mass to the rear when it's drained during long flight

2. Rear landing gear placed too far forward, prone to tailstrike

Solution:

1. Remove forward fuel tank and move the fuel on internal tank on airplane wings

2. Adjust center of lift and landing gear slightly behind the center of mass

Hope that helps

Edited August 25, 2018 by ARS

[JoE Smash]

16 hours ago, ARS said:

Based from your screenshot, I can say:

Your rear fuselage is too long, and your rear landing gear is placed too far forward, that's why your center of mass is behind the rear landing gear, making it prone to tailstrike and highly unstable on the ground. I suggest you remove the fuel tank on the forward fuselage to make it shorter (So it becomes "cockpit-cargobay-rear door", with no fuel tank in between. When you fly for a long time with fuel tank behind the cockpit, the fuel drained will make forward section lighter, shifting the center of mass behind) move the fuel reserves to the wing (The largest wing for airplane part have internal fuel tank, right click it in hangar to fill it with fuel). Other than that, make sure your center of lift and rear landing gear is slightly behind the center of mass (Use the center of mass and lift indicator in hangar to adjust it by offsetting the wing forward/backward or adding mass/ additional lifting surface (Like radial fuel tanks or canards) to balance it).

In conclusion, your problem is:

1. Your rear fuselage is too long, fuel tank placed behind the cockpit shifts center of mass to the rear when it's drained during long flight

2. Rear landing gear placed too far forward, prone to tailstrike

Solution:

1. Remove forward fuel tank and move the fuel on internal tank on airplane wings

2. Adjust center of lift and landing gear slightly behind the center of mass

Hope that helps

Good explanation....I just laughed out loud when I saw the plane....

[Stephen Locksley]

If your spacecraft/aircraft's tail hits the ground on launch, then it's probably heavy in the back.

[archiebald]

On 8/25/2018 at 3:51 AM, FlexT_ape said:

Thanks! I'll upload a pic of the craft

SCREENSHOTS: https://imgur.com/a/05ez9Wr

 

WOH!!! I'm surprised you even got that thing off the runway in one piece.

[Hotel26]

On 8/25/2018 at 4:46 AM, ARS said:

fuel tank placed behind the cockpit shifts center of mass to the rear when it's drained during long flight

Precisely right.

Good practice in the SPH to note the position of the CoM with full tanks and then again with empty tanks.  Little movement (fuel balancing) is highly desirable.

Edited May 1, 2020 by Hotel26

[jimmymcgoochie]

Stick a wheel at the back of the fuselage, tail-strikes solved. Now you can work on why that plane is so ludicrously long and why the main landing gear is so far forwards. What are you doing at the north pole to need such a huge plane anyway???

[linuxgurugamer]

5 hours ago, Hotel26 said:

Precisely right.

Good practice in the SPH to note the position of the CoM with full tanks and then again with empty tanks.  Little movement (fuel balancing) is highly desirable.

The mod FillItUp is designed for exactly that

[Stephen Locksley]

Tailstrike will also happen if your plane is improperly designed, it's possibly due to the plane's back being heavy The wheels on the wings should be moved much closer to the back, so you do not get a tailstrike upon launching your plane.

[jimmymcgoochie]

28 minutes ago, Stephen Locksley said:

Tailstrike will also happen if your plane is improperly designed, it's possibly due to the plane's back being heavy The wheels on the wings should be moved much closer to the back, so you do not get a tailstrike upon launching your plane.

That's not actually a solution, as while the wheels further back will increase the angle of attack needed to hit the tail on the ground it also reduces the pivot force that the elevators can exert while on the ground and makes taking off harder, plus it doesn't do anything at all about the tail hitting the ground on landing.

Better to add a small wheel or two on the tail to mimic the anti tail strike devices on real airliners, which won't affect the rotation on takeoff but will still protect against tail strikes on landing.