why does my plane keep pitching up/flipping after take off?

[Mercyfon]

I have my CoL behind my CoM but yet my plane keeps flipping backwards and pitching up after take off

[desrtfox071]

A few things can cause this:

1) Way too much (or way too little) control authority
2) CoM behind CoL (I know you say this is not the case)
3) Aircraft fuselage/control surfaces are not rigid, i.e floppy craft syndrome.


Generally if the aircraft flips backwards and appears to be more stable backwards than forwards, this is the CoL being too far forward.

It's also possible there's something more subtle like a misaligned control module or something. As always, a screenshot of the aircraft can help a lot.

[Mercyfon]

Originally posted by desrtfox071:

A few things can cause this:

1) Way too much (or way too little) control authority
2) CoM behind CoL (I know you say this is not the case)
3) Aircraft fuselage/control surfaces are not rigid, i.e floppy craft syndrome.


Generally if the aircraft flips backwards and appears to be more stable backwards than forwards, this is the CoL being too far forward.

It's also possible there's something more subtle like a misaligned control module or something. As always, a screenshot of the aircraft can help a lot.

I do not think it is reason 3 cause all the mayor parts of my plane are autosturted.

here are some images of my plane: https://imgur.com/a/ogfdOsx

[FourGreenFields]

Not sure about stock aerodynamics, but at least for FAR it was allways said that CoM vs CoL placement is just a rule-of-thumb that has exceptions. So maybe try putting CoM further forward or CoL further back still.

EDIT: Having taken a look at those screens, it may be that your rear gears are too far back, requiring too much force to pitch up at all, and then overcompensating once airborne.

[Mercyfon]

Originally posted by FourGreenFields:

Not sure about stock aerodynamics, but at least for FAR it was allways said that CoM vs CoL placement is just a rule-of-thumb that has exceptions. So maybe try putting CoM further forward or CoL further back still.

EDIT: Having taken a look at those screens, it may be that your rear gears are too far back, requiring too much force to pitch up at all, and then overcompensating once airborne.

ow thanks for noticing that, ill try to adjust it

[desrtfox071]

Originally posted by FourGreenFields:

Not sure about stock aerodynamics, but at least for FAR it was allways said that CoM vs CoL placement is just a rule-of-thumb that has exceptions. So maybe try putting CoM further forward or CoL further back still.

EDIT: Having taken a look at those screens, it may be that your rear gears are too far back, requiring too much force to pitch up at all, and then overcompensating once airborne.

This looks like a strong possibility to me as well. This will cause the vehicle to feel like it "unsticks" and then rapidly pitches back, but this is due to holding too much pitch prior to enough wing lift. To avoid this, while still leaving your gear where they are, pitch back a little and then just hold that. Don't pitch back more. Then, just wait until the aircraft takes off on its own. Don't try excessive pitch to get it off the runway.

[.]

I try and put com slightly ahead and below col. But very very close to the same spot. As long as you have enough lift and some elevrons it should fly fine!

[doum]

Your engines ( Center of thrust) are lower then the COM. It may push your plane up too a little. May be.

[Mercyfon]

boys she flies! thank yall for the hints, it was the adding control surfaces that helped!

[desrtfox071]

Originally posted by Mercyfon:

boys she flies! thank yall for the hints, it was the adding control surfaces that helped!

I'm glad you got it to work!

[swatkats radical squadron]

Originally posted by Mercyfon:

boys she flies! thank yall for the hints, it was the adding control surfaces that helped!

now try and make her a spaceplane and send her to orbit =) (thats a challenge on its own)

[Mercyfon]

Originally posted by swatkats radical squadron:

Originally posted by Mercyfon:

boys she flies! thank yall for the hints, it was the adding control surfaces that helped!

now try and make her a spaceplane and send her to orbit =) (thats a challenge on its own)

now thats a good idea

[JohnRando]

Hi, i think @banditdoum nailed it, looks like the center of thrust is lower than center of mass, and when thrusting your engines produce upwards torque (that you successfuly compensated with more control surfaces). This works in dense atmosphere, but for a spaceplane you will need to take that into account because at some point theres no more air for the control surfaces to work on (and reaction wheels are a bit cheesy ;) ).

Congrats on your working plane still, it looks cool, bit like an Antonov. Tilted wings are hard to balance. And good luck with the next step.