Strange Flight Characteristics.

[Leszek]

I have made a plane that I am trying to fly north to tundra. It has an issue in that it always wants to fly crabwise. Here is a screenshot:

https://www.dropbox.com/s/cbsa33e17ihi449/screenshot8.png?dl=0

The air intakes show identical data when I click on them, the engines do as well. I checked all the tanks and they are draining symmetrically. I don't normally fly planes in KSP so I am inexperienced and am not sure where to look next to figure out the issue.

Edited May 23, 2015 by Leszek

[Chaos_Klaus]

Center of lift needs to be behind center of gravity. Is that the case? Also when the tanks are empty? You can see both if you activate the markers in the space plane hangar.

[Rodyle]

Yeah. I have had this as well with a few planes. Never could figure out for the live of me what causes it though.

Center of lift needs to be behind center of gravity. Is that the case? Also when the tanks are empty? You can see both if you activate the markers in the space plane hangar.

That's not really the issue. That wouldn't cause the aircraft to pull to the right consistently.

[Leszek]

The CoL is behind the CoG. I didn't check with the tanks empty but the mass non-expendable mass is forward of both, as the fuel goes down the CoG should move foreward. Finally I am not getting anywhere near empty tanks.

I moved the tail surfaces back a bit and added the smallest fins under the engines. It seems to help a small amount but not much. I am going to pump fuel from the aft-most tank to the fore-most tank to see what happens.

[Streetwind]

My educated guess:

Kerbin's rotation speed at the equator is 170 m/s. If you are flying close to the surface, you are rotated along with it; if you are flying further up, you get less and less of it as the atmosphere thins.

If you're flying directly north, the part of Kerbin's rotation that you are missing relative to the surface because of the height you fly at, causes you to deviate to the left with respect to the surface. Thus your plane must point slightly to the right to maintain its position above the surface and fly perfectly north.

The closer to the north pole you get, the less this effect should manifest itself.

[Leszek]

My educated guess:

Kerbin's rotation speed at the equator is 170 m/s. If you are flying close to the surface, you are rotated along with it; if you are flying further up, you get less and less of it as the atmosphere thins.

If you're flying directly north, the part of Kerbin's rotation that you are missing relative to the surface because of the height you fly at, causes you to deviate to the left with respect to the surface. Thus your plane must point slightly to the right to maintain its position above the surface and fly perfectly north.

The closer to the north pole you get, the less this effect should manifest itself.

Coriolis force (Change in course due to the rotation of the planet.) will turn you to the right in the north. My plane will sit crabwise either left or right but not straight. Also the air moves with Kerbin and you are flying through the air. However this isn't the issue as my other plane flies just fine.

Edited May 23, 2015 by Leszek

[DeMatt]

Is your trim clear? (Alt-X)

According to the screenshot, your plane is pointed to the right and is also steering to the right. The angled rudders are probably not doing you any favors, since by default they'll also activate for pitch adjustments. Try straightening out the rudders and setting them for yaw only (right-click in the hangar and hit the toggles).

If that doesn't work, post up the .craft file and a list of mods needed to run it.

[Leszek]

Is your trim clear? (Alt-X)

According to the screenshot, your plane is pointed to the right and is also steering to the right. The angled rudders are probably not doing you any favors, since by default they'll also activate for pitch adjustments. Try straightening out the rudders and setting them for yaw only (right-click in the hangar and hit the toggles).

If that doesn't work, post up the .craft file and a list of mods needed to run it.

Trim, a good idea, unfortunately it didn't work.

The tail surfaces are already set to yaw only. The elevons are set to pitch and roll only.

I think the plane is stock except for the science in the bay, I can remove that, I will have a craft file in about an hour +/-.

[cybersol]

In your picture, the tail surfaces are fighting each other. It's more boring, but for testing purposes does it still do it if the tails are exactly vertical and still set to yaw only?

[Leszek]

Sorry I did catch DeMatt mentioning that, I just forgot to say something in my post.

Anyway, I just tried that as I stockified the craft and low and behold it flies fine now. How annoying.

Thanks guys.