Losing controll in a well balanced plane.

[Turbojohn]

Hello.

I've been working on my airplane, the Stratoship.

It's well balanced, the center of mass is behind the center of lift.

99% symetrical, with the exception of the crew ladder.

But everytime I fly it in the stratosphere at roughly 1300 m/s it starts turning to the left even with SAS on and eventually loses control

It's not a flame out, neither an unbalanced empty fuel tank.

I've got no idea what it is, but at a certain stage it ALLWAYS does this

EDIT:

Forgot to mention, the ladder is to the right.

Here are 2 pictures of the airplane.

http://imgur.com/a/aiTJ5

Here's the craft

http://www./?8qppufs254kiqa5

Thanks.

Edited June 23, 2013 by Turbojohn

[Johnno]

Is your ladder to the left then?

[CaptainKipard]

... it starts turning to the left...

You're going to have to get used to terms like pitch, roll and yaw. The cause could be something else depending on what you mean by "turn".

[M5000]

It's probably the ladder... Without pictures, we're forced to assume that the cause of asymmetrical movement is caused by the asymmetrical part with drag and mass offset.

[Turbojohn]

You're going to have to get used to terms like pitch, roll and yaw. The cause could be something else depending on what you mean by "turn".

It's probably the ladder... Without pictures, we're forced to assume that the cause of asymmetrical movement is caused by the asymmetrical part with drag and mass offset.

Thanks for your feedback.

I added a few pictures, they may help.

It yaws first and then starts pitching.

It's almost as if I had an assymetrical flame-out, but it's slower.

[CaptainKipard]

I've not used the stock fuselage parts before. DO they have fuel? it could be that as you burn it the fuel shifts your center of mass backwards behind your center of lift. That might explain the pitching. Actually the four small tanks you have in front look like they have fuel routed towards the back. If I'm right those four tanks will empty first and that will DEFINITELY unbalance your plane.

As for the yaw, i agree with everyone else. Probably the ladder.

EDIT

When I build planes I try to have two main tanks. One in front and one in the back, and route fuel in such a way that both tanks drain at the same time equally.

Edited June 21, 2013 by Cpt. Kipard

[Turbojohn]

the only reason I've put those front tanks is to push the center of mass forwards. The thing is this moment where the plane looses controll the fuel is still pretty much full. It's 128/150 in each of those tanks.

I'm now going to remove the ladder, and test it when I have time

Thanks for the help.

Edited June 22, 2013 by Turbojohn

[Turbojohn]

So

I removed the ladder, and changed the fuel lines.

It still does it.

I don't know what does it.

But it may be that the faster I go, the plane has a bigger tendency to do it.

Perhaps it's my path that it's not really in the prograde direction that pushes the plane. But I still find it weird because on my other planes I can fly them easily...

[CaptainKipard]

What mods does it use? If you're using only (mostly) stock parts then upload the craft file and I'll be happy to tinker with it.

[Drokken]

Looking at the picture, the centre rear vertical stabilizer is a structural wing part?

I’ve had issues with these before, as they create lift, if you place them singly vertically they create lift to one side or the other only. When reaching high velocities and altitudes they can cause all sorts of crazy…

What I do now is always put them in pairs, off vertical, so the lift is balanced, or try a part with less lift if I really want just one perfectly vertical stabilizer…

Hope this helps?

[rryy]

Is there any loops in the fuel flow? Looping fuel flow can cause the fuel to be drained asymmetrically. In flight, alt+right click on the four radial tanks to check if they drain at the same rate.

[Tank Buddy]

Your center of lift is way out of whack. The center of lift should just be behind the center of mass, so when the fuel drains it moves the center of mass. Also, the center of lift and mass are not in line, in terms of up and down. This is probably because of the many wings placed in weird places, and those fuel tanks in the front. I don't know exactly how that affects the aircraft, but I would recommend simplifying the design. It looks like you are going more for aesthetic purposes, so you wouldn't want to do that. I would just fix up the center of lift not being in the middle of the craft in terms of up and down. Good luck.

[Jod]

So

It still does it.

I don't know what does it.

But it may be that the faster I go, the plane has a bigger tendency to do it.

-your aircraft goes out of control at high speeds?

-changing CoL and CoT positions does nothing?

-you've tried everything and nothing works?

My boy, you have Center of Drag issues. Move the air intakes as far back as possible. Also - if you use aerospikes they need to be in front of CoM.

It solves this problem for me anyway. Every time my craft goes nuts at high altitudes I find that it's because I placed aerospikes in the back or air intakes in the front. No exceptions so far.

[Turbojohn]

-your aircraft goes out of control at high speeds?

-changing CoL and CoT positions does nothing?

-you've tried everything and nothing works?

My boy, you have Center of Drag issues. Move the air intakes as far back as possible. Also - if you use aerospikes they need to be in front of CoM.

It solves this problem for me anyway. Every time my craft goes nuts at high altitudes I find that it's because I placed aerospikes in the back or air intakes in the front. No exceptions so far.

I've never touched the center of thrust.

I'm going to try removing the air intakes in the front.

Your center of lift is way out of whack. The center of lift should just be behind the center of mass, so when the fuel drains it moves the center of mass. Also, the center of lift and mass are not in line, in terms of up and down. This is probably because of the many wings placed in weird places, and those fuel tanks in the front. I don't know exactly how that affects the aircraft, but I would recommend simplifying the design. It looks like you are going more for aesthetic purposes, so you wouldn't want to do that. I would just fix up the center of lift not being in the middle of the craft in terms of up and down. Good luck.

Not really aestetical purposes, I put them there to increase lift and to separate the center of lift from the center of mass.

I'm going to try and remove some of them.

Is there any loops in the fuel flow? Looping fuel flow can cause the fuel to be drained asymmetrically. In flight, alt+right click on the four radial tanks to check if they drain at the same rate.

Yes. But it's not that because after losing controll I've checked and it's symmetrical.

What mods does it use? If you're using only (mostly) stock parts then upload the craft file and I'll be happy to tinker with it.

It's stock and I'm going to upload it.

Looking at the picture, the centre rear vertical stabilizer is a structural wing part?

I’ve had issues with these before, as they create lift, if you place them singly vertically they create lift to one side or the other only. When reaching high velocities and altitudes they can cause all sorts of crazy…

What I do now is always put them in pairs, off vertical, so the lift is balanced, or try a part with less lift if I really want just one perfectly vertical stabilizer…

Hope this helps?

I removed the winglets and the result was surprising.

The plane never lost control and I managed 1600 m/s at 25 km

The problem is that when I disabled SAS to correct my atitude it imediately started to yaw left

Thanks to everyone for the help!

Edited June 23, 2013 by Turbojohn