Why does an entirely symmetrically constructed space plane yaw right?

[Zatie12]

I've constructed an entirely symmetrical space plane. On takeoff it yaws to the right. Why?

[KvickFlygarn87]

Ferram Aerospace Research? SAS active? Screenshots?

[r4pt0r]

perhaps accidental trim settings? i think alt+X will zero the trim. other than that i think even rovers will drift one way or the other if you spawn it on runway from the SPH

[Frank_G]

Still on the runway or already in the air?

[KerbMav]

There is this infamous bug that changes some numbers for a part placed with symmetry in VAB/SPH.

I never quite understood what it is about and why it does occur.

How intense is it yawing?

[Xetalim]

I believe the runway isn't exactly 0 degrees flat.

[Frank_G]

If it happens on the runway it could be the placing of the landing gear. To counter yawing try placing your gear straight down, not angled and sideways as far apart as possible.

[zarakon]

Screenshots?

If it has large wings that are only attached to the fuselage at one point, then I'm not surprised.

There was, and possibly still is, a bug where not all connection strengths are as equal as they should be. In most cases it's not noticeable, but there are designs where it becomes very obvious. One of the obvious cases I've seen is in planes with long wings, one will sag more than the other.

I think it has something to do with how the craft has to be constructed from its save file one part at a time. So two parts that are placed with symmetry won't actually be added at the same time, and somehow that can lead to them being treated slightly differently.

[Zatie12]

Ferram Aerospace Research? SAS active? Screenshots?

Thanks for the reply

FAR is active (I would never fly a space plane without it )

I've tried SAS on/off

The vehicle yaws to the right as soon as power is applied

Screenshots are here:

http://i.imgur.com/qGeSBTn.jpg

http://i.imgur.com/DrJ4T9E.jpg

It's just an Ion test craft, but I can't understand why it yaws so much to the right. There is a central unit. Everything else was constructed symmetrically around it.

[Kasuha]

It is ion-propelled. Are you sure your solar array is producing enough electricity to keep all your ion engines working? My guess is you got similar issues as asymmetric flameout, just with ion engines.

[vexx32]

Moved to Gameplay Questions.

[Zatie12]

I believe the runway isn't exactly 0 degrees flat.

I've launched many planes of this runway, few yaw like this does

- - - Updated - - -

It is ion-propelled. Are you sure your solar array is producing enough electricity to keep all your ion engines working? My guess is you got similar issues as asymmetric flameout, just with ion engines.

It's a good question. There are no power issues.

[Boosterspice]

It's an old mystery. Try to construct it from scratch again, see if that helps.

[linkxsc]

Try takimg the 2 delta wings on the far outer wing. Angle them up a few degrees (20-30) and that should clear out some of the instability that the plane looks like it has.

Also put the craft file so other players can fly it to check for problems.

[KvickFlygarn87]

It is ion-propelled. Are you sure your solar array is producing enough electricity to keep all your ion engines working? My guess is you got similar issues as asymmetric flameout, just with ion engines.

This is my best guess. They are VERY intense on power.

Try checking the ion engines' colours. If the engines have different colours, they are producing different amounts of thrust.

Also, try going into FAR build aid and checking stability derivatives. Anything red is bad.

If you have a red display, try adding a tail fin (large Delta wing maybe?)

EDIT: I just saw your post about power, scrap that.

[Zatie12]

How can I provide the craft file?

[KvickFlygarn87]

Upload it to... Err... Well, anywhere.

[Redshift OTF]

If it happens on the runway it could be the placing of the landing gear. To counter yawing try placing your gear straight down, not angled and sideways as far apart as possible.

This. If you can show a side shot of the plane with Centre of Mass showing that would help.

If the wheels are too far back from the CoM and the pitch control surfaces are too close to the wheels then it puts too much force on the wheels, they buckle and you yaw left or right on the runway.

[Kasuha]

It's a good question. There are no power issues.

Just to be sure: how big is your battery capacity on that plane? Notice that engines draw power from the battery, not directly from solar cells. If they manage to deplete the battery within single frame, they may be underpowered even though solar cells recharge that battery to full capacity within the same frame. When you're taking off, do all engines shine with the same intensity?

[Zatie12]

Okay all, here is the craft file:

https://drive.google.com/file/d/0B8Luetssz0ZxeGpGR2FGQXJGMjg/edit?usp=sharing

Please download and play. Let me know what I did wrong.

Please remember, this is not a production flier. I I just want to know why it yaws so much, before I balance it out

Thanks!

[Alfondoo]

It normally comes down to struts for me. If a plane isn't strutted tight enough the flexing will cause the landing gear to run out of alignment resulting in these symptoms, I notice that you don't have many on your craft, only a couple on the wings. At the very least I suggest a strut from the front wheel to both wheels on each side to keep it all pointing in the correct direction. Or you could try moving the landing gear inwards to stop the craft sagging in the middle?

This engineering flow chart should help in future

[Zatie12]

Play the craft prototype I posted and let me know

[Alfondoo]

Play the craft prototype I posted and let me know

I can't unfortunately, I am still playing an older version of the game and it says your craft file is incompatible. I hope someone else can come to your aid.

[linkxsc]

I can't unfortunately, I am still playing an older version of the game and it says your craft file is incompatible. I hope someone else can come to your aid.

Ill give a look when i get home from work in a few hours. (Bosses get a little mad about ksp in the workplace)

[Endersmens]

I've had this happen to me numerous times, and i've quadruple checked that they were symetrical. Even with only one engine some still yawed. Not all of them do, but every once in a while (a good design of course) it starts yawing for no reason.