Airplane building skill issue

[Rihnami]

Every plane i build turns left and breaks its wings at speeds greater then 10 m/s.

For example, this plane made from parts from mod SXT. It turns left with stock aerodynamics and with FAR (Ferram Aerospace Research (SXT has compatibility with it))

I reinstalled the game and mods three times, so it`s not a bug
Screenshots:

Spoiler

And it`s not a gyroscope effect from prop engine, bcz jet planes turn to random side

Edited May 21 by Rihnami
correcting grammatical errors

[Vanamonde]

Try shifting the center of mass a bit farther forward for greater stability, and try adjusting the landing gear so the plane sits slightly nose-high, then apply a bit up upward pitch to your joystick while going down the runway. 

[Rihnami]

3 hours ago, Vanamonde said:

Try shifting the center of mass a bit farther forward for greater stability, and try adjusting the landing gear so the plane sits slightly nose-high, then apply a bit up upward pitch to your joystick while going down the runway. 

Thx, i tried and yes, plane became more stable, but now it starts jumping on speed 40 m/s (I think this bcz runway is 1 lvl). I decided that i should take off earlier, which means i need more lift.

And i make that. At least it flies, but not so stable

Spoiler

 

[king of nowhere]

if the plane turns left or right on the runway, often the problem is wheel drag. select the front wheels and manually reduce their friction, keep the rear wheels with a higher friction

[Superfluous J]

7 hours ago, Rihnami said:

Every plane i build turns left and breaks its wings at speeds greater then 10 m/s.

According to every single plane I've ever built, you're doing it exactly correct.

No don't listen to me the others are far smarter on how to build planes than I.

[Vanamonde]

I'd still suggest moving center of mass forward a bit or center of lift back. It will be more controllable in flight and will likely help with the "hop."

[DeadJohn]

@Rihnami If I understand correctly you're having a ground taxiing issue rather than a flying issue. That early landing gear in your screenshot can be twitchy. The later retractable gear is IMO much more stable and predictable. That doesn't help you right now if you are playing in science or career mode without spare points to buy better gear.

Sometimes getting more separation between the front and rear wheels can improve taxiing. In car terms, increase the wheelbase for stability. Slide the front wheel forward using the "2" offset tool. Slide the rear wheels backward a bit, but not so much as to cause difficulty pitching up for takeoff.

[Dinlink]

Hello!, in my experience with FAR, Is a common issue to have to iterate many times trying to have a laterally stable take off... Tipically I would iterate putting the tail farther from the center of lift, making it bigger and checking the following on the FAR design Interface:

1. Calculating the stability derivatives for runaway speeds (Mach ~0.2) and verifying everything is green

2. After that, simulating lateral stability plots, specially "q" parameter perturbation (if I remember well). I made a simulation setting "q" to 0.1 and plotting stability for 500-1000 steps... Then I verified that the curves were converging, I mean, oscillating but reducing it's value to a single value, not skyrocketing to infinity

3. Making a bigger tail and iterating again

 

I have tryied tweaking the friction on wheels too... But without too much success... In my experience what has helped is having a big fat far back tail... Or many tails... A multi tail could help... I hope you find my experience useful

[Rihnami]

On 5/22/2024 at 2:26 AM, king of nowhere said:

if the plane turns left or right on the runway, often the problem is wheel drag. select the front wheels and manually reduce their friction, keep the rear wheels with a higher friction

It`s only make it worse

On 5/22/2024 at 3:32 AM, Vanamonde said:

I'd still suggest moving center of mass forward a bit or center of lift back. It will be more controllable in flight and will likely help with the "hop."

I know, but biplane falls on it`s engine, when the engine is turned on and CoL is behind of CoM, bcz it`s CoM below than CoT

 

On 5/22/2024 at 9:00 AM, Dinlink said:

3. Making a bigger tail and iterating again

Thx, this is very helpful, the plane became more stable than before

And in career mode i can`t build my prieveous biplane, bcz it has 34 parts and i made this

Spoiler

And thanks you all for help, i knew something new about plane buildings

[RunaDacino]

One big advice I have for "weird turning right" is: NEVER ATTACH ANYTHING (except for ailerons, flaps, slats) to your wings. This includes other wings. Attach everything to your heaviest fuselage part (ideally in the centerish) and then use off-set to make space for more attachments. Do this until you have all wing panels (I recommend procedural wings to reduce part count) set up, then add control surfaces.

 

All my planes had really weird rightway turning, even on the runway, until I came to this realization. Super stable eversince.

 

You have also mentioned using FAR. If you are - I recommend either Kerbal Joint Reinforcement Next or Continued. FAR introduces far more aerodynamic stress that will bend and buckle your realistic and otherwise structurally sound designs.

Furthermore: I strongly recommend adding control surfaces on the front of your wings too (leading edge flaps/slats). I will forever advocate for them after learning just how much they can affect runway/takeoff/landing stability. It's insane.  Although, for your tiny plane it might not be needed.

Finally for taxiing: Reduce your frontal wheel friction significantly, and increase your rear wheel friction in turn if you are using wheels that allow such (Kerbal Foundries don't, unfortunately).