Why are these planes hard to control?

[jlcarneiro]

Hi, I have hard times trying to pilot my planes... These are from 0.24 and, except from L-Tech, DMagic and Universal Containers are pretty much stock.

• They tend to swerve during takeoff - when they are faster than 60m/s I have to take off quickly or they swerve and crash. Although I've structured and checked the back wheels...
  
• They oscillate (like little stalls) when I pitch (up/down) or turn (pitching after a roll to turn left or right)...
  
• They tend to point down their noses when I'm about to land and very frequently I hit the ground too fast. They don't keep pointing up even with SAS or trim...
  
• When I get a reasonable touchdown, I can't brake or they swerve (or raise one side) and crash...
  

Here the screenshots and .craft files of the planes (KP-1C, KP-2, KP-3, KP-4 and KP-5):

• Screenshots: http://imgur.com/gallery/Ztk1k
  
• .craft files: http://www.filedropper.com/crafts
  

Edited August 11, 2014 by jlcarneiro
typo

[neamerjell]

I just looked at your screenshot. First off, your center of lift is way too far behind your center of mass, that's why it noses down and swerves on the runway (too much weight on the front landing gear).

Try shifting the overall weight to the rear by adding another fuel tank up front and drain it (right click it and drag the sliders left), or add a structural fuselage if you have unlocked that far up the tech tree.

Next, move the wings forward until the center of lift is just barely behind the center of mass. The front half of the blue ball should be inside the yellow one. You could also add canards up front as well to fine tune the center of lift and increase your control authority but be mindful that it might end up being a little twitchy pitching up and down.

I'm going to download your crafts file and see if I can get it to fly for you and report back what I did.

EDIT: Apparently, I don't have the same mods installed as you do. I opened it in sandbox and it is telling me several parts are missing...

This guy helped me a lot with take off troubleshooting:

Edited August 11, 2014 by neamerjell

[Wanderfound]

1) Have you unlocked the steering on your front gear?

2) Your rear gear is way too far back. Think of the gear as a pivot in a see-saw, with your CoM sitting on one end and your pitch-relevant control surfaces at the other end. Put the gear between the two.

3) Wing-mounted gear is dangerous unless you have very rigid wings (i.e. not too long, and heavily braced with struts). As the wing flexes, it alters the geometry of the gear, which messes up your steering. It's usually better to mount the gear to the fuselage.

4) Planes do not glide well under stock aero. Most flyers use FAR or NEAR.

5) It looks like you're using stationary winglets as your only yaw-relevant control surfaces. That helps to stabilise yaw, but it doesn't do anything to control it. Get some control surfaces or all-moving winglets up there.

6) Your CoL is too far behind your CoM. This makes it hard to lift the nose. CoL should be behind CoM, but only by a bit. Make the indicator spheres overlap.

7) SAS and RCS aren't just for rockets. A well-built plane doesn't need them, but they make things more forgiving while you're still working out how to do it.

[Kryxal]

Your CoL is well back of where it should be ... move it up until it's at least half-inside the CoM, with the landing gear removed.

Speaking of landing gear, that's quite the wide wheelbase, you might want to move them inwards...

[Sirine]

Below solution apply to KP-1~4. Just make sure your front wheels are not angle.

Please list your mods use...I have try to load your craft file...about 2 hrs trying to figure out what mods did you install....

for KP 5. Just make sure your side wheels are 'straight', when your craft hit the ground. Normally, The middle section of your craft will be pull down-worth by gravity. Hence, creating angled wheels.

Including fixed craft file for KP 5. Download here.

Edited August 11, 2014 by Sirine

[jlcarneiro]

Great, guys! Very detailed explanations!

I'll implement these suggestions, thank you very much!

Edited August 11, 2014 by jlcarneiro

[jlcarneiro]

[...]

Please list your mods use...I have try to load your craft file...about 2 hrs trying to figure out what mods did you install....

[...]

Sorry, Sirine! I was so excited about all these tips and suggestions I did not notice your request about the mods...

I use many mods but the only ones with parts I currently use are: L-Tech and DMagic (science devices) and Universal Containers (the grey and black containers)...

BTW, this Cruzan AK on Youtube also has many good tips and tutorials, thank you!

Well, using all your tips I managed to land for the first time, Yay! Thanks!