Veering aircraft

[MGCJerry]

I cant build anything more complicated than a speed car, or a ginormous mk3 monster. I tried building a small aircraft, but its veering off the runway to the left 6 out of 7 launches. I've reattached the landing gear probably 30 times and rebuilt it another 4 or 6 times, but it still rolls off the runway. I used to be able to solve this by restarting the game, but that isn't working anymore. The plane below has the COM & COL right next on top of each other. I've strutted the side engines, etc.

Maybe I should just stick with huge planes.

Offending aircraft:

Other ideas?

Edited June 24, 2015 by Claw

[Claw]

It's really hard to tell from just that picture, but it looks like you might have two wheels in front. Try to put only one up front. I'm also going to make a wild guess that you put the rear landing gear under the side fuel tanks. Sometimes this causes flexing, especially when you try to pitch up. The elevons on the back actually cause a downforce on the landing gear and make the fuselage bend.

Try adding some struts, putting on some canards, or moving the rear landing gear closer to the CoM.

Cheers,

~Claw

[MGCJerry]

Thanks for the reply Claw. I used this picture because it was easy to upload as-is.

* Only one gear is up front and it is at the back end of cockpit part.

* The rear gear are between the nacelle and the fuel tanks. I also have 2 struts securing the nacelles to the main body on the underside.

* Adding canards to the font makes it really-really flip happy which makes it excessively unstable and it reaches 20m above the runway, stalls and crashes. On the off chance it does make it to the end of the runway, it flips immediately at the end, even with no control input.

I've decided to abandon this the design entirely and stick with big stuff because this veering happen rarely with my mk3 sized ships 100+ tons on the runway, empty.

[Scarecrow88]

Do you have the craft file for download, as I reckon I could get it flying. In any event it would be a nice challenge to try.

[m1k3ol]

ok, I'm having this issue as well...

I have to note I've been doing planes for a while and didn't encountered this prior to 0.90 (didn't made aircrafts on that or 1.0 before)

playing on "easy" in sandbox, made a simple craft, it veers!

File:

https://dl.dropboxusercontent.com/u/35221678/Aircrafter%201.craft

funny thing, it veers more the closer the back wheels are to the center of mass, tried different angles with the wheels themselves (more or less closer to each other), the front wheel was installed using angle snap to avoid it being out of place...

if I use the ramjet engine it can get up fast enough to have the veering impact the take off at all, but if I use the basic jet engine (slower), the veering just takes me out of the strip with mixed results, I either fly or a wing hits the ground and brakes away...

if I add more weight (a small cargo bay in between the tanks) it just causes more veering, but I have no idea how this small design can impact the wheels like that when attached to the main body and no in the extra parts...

are the wheels more "weird" now with the current updates than it was before? (due to weight and other forces)

[Wanderfound]

Are you attaching the rear wheels with angle snap to ensure that they're perfectly vertical? Test with the rotation tool (set to absolute and angle snap on) if unsure.

Is the steering unlocked on your front gear?

[Mic_n]

I long ago gave up trying to figure that sort of thing out.. things veering off on the runway and randomly rolling or yawing to one side.. they're supposed to be symmetrical but I kinda get the feeling sometimes it's lying. Particularly annoying when you have a pair of jet engines and one of them is putting out significantly more thrust than the other (I suspect hogging air from the other, but even with "way too much" intakeair it seems to happen).

Yeah, it's "one of those damn things". Rip things off and put 'em back on.

[Wanderfound]

Particularly annoying when you have a pair of jet engines and one of them is putting out significantly more thrust than the other (I suspect hogging air from the other, but even with "way too much" intakeair it seems to happen)

That one is caused by order of part placement. There are manual ways to avoid it, but you're better off just installing the Intake Build Aid mod. Problem go away.

[FancyMouse]

For some reason I'm seeing quickload screwing my air intake - the same craft which I did IBA and worked just fine (confirmed when >100% intake KER reading), got screwed after a quicksave and quickload - it was the same flight! Probably I really should improve my landing skill to avoid F5/F9...

[Reactordrone]

ok, I'm having this issue as well...

I have to note I've been doing planes for a while and didn't encountered this prior to 0.90 (didn't made aircrafts on that or 1.0 before)

playing on "easy" in sandbox, made a simple craft, it veers!

File:

https://dl.dropboxusercontent.com/u/35221678/Aircrafter%201.craft

funny thing, it veers more the closer the back wheels are to the center of mass, tried different angles with the wheels themselves (more or less closer to each other), the front wheel was installed using angle snap to avoid it being out of place...

if I use the ramjet engine it can get up fast enough to have the veering impact the take off at all, but if I use the basic jet engine (slower), the veering just takes me out of the strip with mixed results, I either fly or a wing hits the ground and brakes away...

if I add more weight (a small cargo bay in between the tanks) it just causes more veering, but I have no idea how this small design can impact the wheels like that when attached to the main body and no in the extra parts...

are the wheels more "weird" now with the current updates than it was before? (due to weight and other forces)

It flew ok for me despite the splayed landing gear, dead straight on the takeoff roll and only wobbled on landing with the application of full brakes.

[DancesWithSquirrels]

Three things:

(1) The small retractable aircraft landing gear defaults to no steering - I always have to remember to enable steering on the front gear to stay on the runway, and also disable brakes on the front for more stability. Without that, I always run off the runway...

(2) The Intake Build Aid mod is really useful if you're having uneven flame-out; I thought that particular issue was fixed in 1.0.2, but if it isn't, just hitting F7 in the SPH/VAB rearranges the construction order to evenly distribute intake air.

(3) Make certain you have your rear gear parallel. It's easy to end up with a bit of splay or pigeon-toe angle, and that will definitely make you veer around.

[kStrout]

Make sure your center of lift is behind the center of mass, I did not know that when I started building planes and all of my planes would do exactly what you described.

[xtoro]

If your landing gear is straight, there are two things you can try.

1) Sometimes jets spool up at different speeds. Put your brakes on and fire the jets at 50% throttle. Once they spool, release brakes and go full throttle.

2) Sometimes due to flexing and slightly uneven lift, you will get yaw drifting. Try pulling up right from the start and all the way until you lift off. I find with heavier planes that this will keep even pressure on the rear wheels and also prevent uneven lift.

[Nich]

In my experience letting engines spool up to 100 fixes the problem. It may just be cross wind I find engaging SAS fixes it as well

[m1k3ol]

Are you attaching the rear wheels with angle snap to ensure that they're perfectly vertical? Test with the rotation tool (set to absolute and angle snap on) if unsure.

Is the steering unlocked on your front gear?

no, all locked, they are splayed on purpose (always used the same setup in past versions, no veering)

It flew ok for me despite the splayed landing gear, dead straight on the takeoff roll and only wobbled on landing with the application of full brakes.

uh, that's weird, I wonder if it might be a save issue then...

where you using SAS on take off?, I never use it (I turn it on after take off)

In my experience letting engines spool up to 100 fixes the problem. It may just be cross wind I find engaging SAS fixes it as well

I do what I do on games like IL2, I apply brakes and turn on the engines, let them spool fully and then go for take off...

I never use SAS on take off, maybe I should try with it...

[Mad Rocket Scientist]

I am about to fly your plane, and see what can do.

- - - Updated - - -

When I downloaded your plane, I got this:

I think you might have uploaded the wrong craft?

It takes off easily with SAS enabled, without SAS you need to correct some veering.

I figured it out, it's the main wings, since they have pitch enabled, they cause huge amounts of downforce, disabling pitch on the wings fixes it.

Edited June 16, 2015 by Mad Rocket Scientist

[m1k3ol]

Nope, not wrong, that's the correct craft (I'm not the OP, hijacked an abandoned thread with the same issue to avoid spam )

So, it was just the "pitch enabled" that caused all the veering?, who could have tell...I thought it was to let that control surface change pitch/roll/etc with my input...

Is there any wiki/tutorial explaining those " obscure" options?, or a way to know the downforce or other stuff affecting a craft? (I only have/use Kerbal Eng.)

Edited June 16, 2015 by m1k3ol

[xtoro]

Nope, not wrong, that's the correct craft (I'm not the OP, hijacked an abandoned thread with the same issue to avoid spam )

So, it was just the "pitch enabled" that caused all the veering?, who could have tell...I thought it was to let that control surface change pitch/roll/etc with my input...

Is there any wiki/tutorial explaining those " obscure" options?, or a way to know the downforce or other stuff affecting a craft? (I only have/use Kerbal Eng.)

You're right about the control surface options. It dictates what kind of input the surface will respond to. For example, you don't want the vertical tail fin at the back to respond to roll, only yaw.

To visually see the forces in action, launch your plane and hit F12. This will show you the aerodynamic forces at work. What you will be looking for is the yellow lines which react to the control surface movements.

[m1k3ol]

I think I solved the mystery, I need to check in game, but it seems that the problem for me and the OP is this: we're using control surfaces as lift surfaces

I'm using "tail fins" as wings, so is the OP (judging by the model), it seems we can't use them as simple lift surfaces like in past versions (planes revamp related I think) without having impressive amounts of downforce pushing the plane (affects flight as well, but works if plane is airborne), maybe that's why disabling pitch worked? (I guess it drops the control surface part?)

(use RMB to check if a part is lift or control surface, to know what you're using)

[DancesWithSquirrels]

m1k3ol - Control surfaces work with lift, directing it as desired (up/down, left/right, off-axis up/down for roll). If the landing gear is highly splayed, however, downforce from trying to rotate for liftoff may force them down more, with no guarantee of even distortion - and there's your veering.

Potential fix - set your gear vertically, rather than splayed, and use the offset tool to arrange the ground tilt to where it was previously.

What I've done in the past for this, when my wing layout was such that my elevator didn't have the required rotation lever (either squashing down smacking the back end into the runway, or unable to rotate at all) is to add some front control canards. Ahead of the CoG, so that rotating upwards uses upwards rather than downwards force on the canards, and far enough forward to have a reasonable lever arm around the CoG.

EDIT: Yes, when you pitch upwards with a rear control surface, there's an initial downforce in the rotation, followed (hopefully) by increased upforce as your wing angle of attack increases. That's a problem with a number of aircraft, one in particular that I've looked at being the Backstrom Flying Plank:

The lever arm on the pitch surfaces was so small that the required force on them initially drove the entire aircraft down - apparently the first few landing attempts resulted in some serious bouncing off the runway when attempting to flair for the touchdown.

Edited June 17, 2015 by DancesWithSquirrels
Added Backstrom plank

[m1k3ol]

uh, well, yeah I'm aware of all that, but I was trying to explain what I saw by looking at the F12 arrows...

the "tail fins" I used as wings on the image you can see above, just produced huge (quite huge) yellow lines upwards the craft (from the "wings") while moving down the runway with no input at all, no blue lines (lift I guess?) other than the ones coming from the MK2 body itself...

changed those fins which are cataloged as "control surface" for normal (ugly, uh...) wings which are noted as "lift surface" along an added elevon I put on them and problem solved itself, big "blue lines" and small yellow ones, no veering on the runway at all, with or without angled wheels and with or without SAS, faster take off with less speed, etc.

so, yeah...I guess I'll have to "mod" normal "pretty" control surfaces to be...just lift surfaces I guess?

[m1k3ol]

*knock*

can a mod please set this to "answered"?

[Claw]

*knock*

can a mod please set this to "answered"?

Sure.

For future reference, you can edit your original post and click "Go Advanced." From there, you can select Answered in the dropdown and save.

Cheers,

~Claw

[FancyMouse]

For future reference, you can edit your original post and click "Go Advanced." From there, you can select Answered in the dropdown and save.

except that this isn't his thread...

[m1k3ol]

Yeah, thanks for the help!

Maybe one day the OP will look here again and find that all the answers have been found