Do Jet Planes require a positive TWR to take off the runway? | Kerbal Space Center | Page 1

surreal ingot Jan 31, 2026, 1:36 PM

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Been wondering that since my plane have to go through the entire runway in order to take off and even then they still struggle taking off. This is with like FAR, RP-1 and procedural wings

flint temple Jan 31, 2026, 1:37 PM

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no

surreal ingot Jan 31, 2026, 1:38 PM

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flint temple no

Oh, then why is my plane taking a long time to take off?

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Do I just need wider wings?

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Or do I need like flaps?

flint temple Jan 31, 2026, 1:45 PM

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where is the com?
more lift or more speed help for sure

surreal ingot Jan 31, 2026, 1:50 PM

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flint temple where is the com? more lift or more speed help for sure

Sorry, the game crashed, let me reload the game

surreal ingot Jan 31, 2026, 1:53 PM

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flint temple where is the com? more lift or more speed help for sure

The center of mass is here

surreal ingot Jan 31, 2026, 2:43 PM

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flint temple where is the com? more lift or more speed help for sure

I forgot , is lift made from increasing wing size?

flint temple Jan 31, 2026, 2:44 PM

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yes

surreal ingot Jan 31, 2026, 2:46 PM

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Why is the plane doing this?

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@flint templeHow do I figure out why the plane I'm using is literally crashing instead of taking off?

flint temple Jan 31, 2026, 2:52 PM

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i have no idea

surreal ingot Jan 31, 2026, 2:56 PM

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flint temple i have no idea

Is it anything related to these landing gears?

feral lark Jan 31, 2026, 3:34 PM

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surreal ingot Why is the plane doing this?

I can't easily say straight up why there are issues, but have a read through this, it explains quite a lot, and simply: https://forum.kerbalspaceprogram.com/topic/47818-basic-aircraft-design-explained-simply-with-pictures/

surreal ingot Jan 31, 2026, 3:35 PM

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I did have a read through

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Though maybe I didn't read well enough

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I could try this

feral lark Jan 31, 2026, 3:37 PM

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At a glance, I suspect you're lacking in wing area / lift, Your craft has rather small wings. Giving them a bit of AoA (5 degrees or so) miiight be desirable.
Is your craft swerving on takeoff, or bouncing/rolling on takeoff? If it's the latter, I'd try stiffening the rear springs.

surreal ingot Jan 31, 2026, 3:38 PM

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Swerving on takeoff I think

feral lark Jan 31, 2026, 3:38 PM

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There are a few pages about swerving on takeoff in the document.

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If you were stock, I'd increase the friction of the rear wheels a bit and reduce that of the front ones too, but I don't see that option on your gear.

surreal ingot Jan 31, 2026, 3:40 PM

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Is this 5 degrees?

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Wait, wrong angle

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surreal ingot Jan 31, 2026, 3:41 PM

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feral lark There are a few pages about swerving on takeoff in the document.

I'm trying to find it but its hard when its an image you cannot press ctrl+f on

feral lark Jan 31, 2026, 3:42 PM

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That looks likea bout five degrees yes, is it me or is your control surface on the vertical stabilizer really small?

surreal ingot Jan 31, 2026, 3:42 PM

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feral lark That looks likea bout five degrees yes, is it me or is your control surface on t...

I forgot, which one is the vertical stabilizer?

feral lark Jan 31, 2026, 3:42 PM

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vertical fin control surface

surreal ingot Jan 31, 2026, 3:43 PM

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Oh, it is samll

feral lark Jan 31, 2026, 3:43 PM

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That thing ought to be able to control the plane's sideslip. Can't hurt to give it more oompf - especially since your tail is short (not much lever effect)

surreal ingot Jan 31, 2026, 3:44 PM

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So, like this?

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Also I notice my plane has a slight torque

feral lark Jan 31, 2026, 3:44 PM

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Now that's a control surface, yes!
Do note we're just trying slightly random stuff since we don't know for sure what causes your swerving issue.

surreal ingot Jan 31, 2026, 3:45 PM

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So, I guess Its time to simulate ,right?

feral lark Jan 31, 2026, 3:45 PM

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Yeah, give it a spin see if it improves or worsens first...

surreal ingot Jan 31, 2026, 3:45 PM

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feral lark Yeah, give it a spin see if it improves or worsens first...

Also I got front and back all moving wings, idk if that's bad

feral lark Jan 31, 2026, 3:45 PM

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'all moving wings'? Do you mean canards?

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'full control surface'?

surreal ingot Jan 31, 2026, 3:46 PM

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Yes, canards

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Weird, its moving this way instead of going straight

feral lark Jan 31, 2026, 3:47 PM

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'this way'???

surreal ingot Jan 31, 2026, 3:47 PM

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Its moving left

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Sorry, I'm bad with words

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Also idk if its lifting at all

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Crap, it just bumped

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I keep pressing S but nothing good happens from that

feral lark Jan 31, 2026, 3:49 PM

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I still think your main wings are too small, not enough lift.

surreal ingot Jan 31, 2026, 3:50 PM

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Yeah, i'll extend the wings

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Do I extend all wings?

feral lark Jan 31, 2026, 3:50 PM

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Focus on the main ones, they're the ones responsible for lift.

surreal ingot Jan 31, 2026, 3:51 PM

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How about now?

feral lark Jan 31, 2026, 3:51 PM

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check your COL vs COM.

surreal ingot Jan 31, 2026, 3:51 PM

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feral lark Jan 31, 2026, 3:53 PM

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That close makes a plane too maneuverable, imho. It might end up uncontrollable.

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I don't use FAR and am not familiar with everything you're using. But I do recognize AA.
Usually I activate stock SAS lock when taking off so it can prevent slight swerving, and I only activate AA after takeoff - I got the feeling AA can only get 'behavior' from a plane once its in flight and adapt.
Do you have other planes that takeoff well using your technique? No SAS and AA on?

surreal ingot Jan 31, 2026, 3:54 PM

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I don't have any other planes that take off

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Ok, I placed the wings further back

feral lark Jan 31, 2026, 3:55 PM

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Okay, try increasing your wing area even more. The goal is to make them 'too big' so we're certain we have enough lift, and we'll reduce afterwards, instead of edging upwards.

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Are you able to shorten your rear landing gear a teensy bit? And maybe stiffen the springs while you're at it?

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I see a 'strut angle', can you adjust that angle so the wheels are further apart, withough budging the boxes?

surreal ingot Jan 31, 2026, 3:58 PM

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Where do you see spring stiffening?

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Also these are wheels from Kerbal foundries I think

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Also these wheels are not attached to the wings

feral lark Jan 31, 2026, 3:59 PM

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'spring rating' at the top. Raise that. Maybe the damping too. Won't hurt to have stiff gear on takeoff.

surreal ingot Jan 31, 2026, 3:59 PM

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Ok, raised it

feral lark Jan 31, 2026, 4:00 PM

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Here we're purposefully makes a plane that will takeoff a lot easier, but may have a bit of trouble landing. But hey, if we can't takeoff, landing is a nonissue, let's get that bird in the air.
Hold on, is your steering active on the rear wheel? That should only be on the front wheel.

surreal ingot Jan 31, 2026, 4:01 PM

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The craft moves to the right in SAS when pressing s

feral lark Jan 31, 2026, 4:01 PM

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Stubborn weird thing...

surreal ingot Jan 31, 2026, 4:02 PM

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It swerves away out of control

feral lark Jan 31, 2026, 4:02 PM

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Altitude: 51 meters.

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But crazy stability issues... Odd, odd.

surreal ingot Jan 31, 2026, 4:03 PM

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Yeah

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Is it because I got too many elevators/canards?

feral lark Jan 31, 2026, 4:04 PM

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I don't know, don't ask me for a clear answer. We're in the 'try stuff till something works' method.

surreal ingot Jan 31, 2026, 4:04 PM

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Gonna try without elevons and instead just with canards

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Here's CoL Vs CoM again

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Weird, the plane swerves to the right and left whenever I press S and W

feral lark Jan 31, 2026, 4:06 PM

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Full stop
Sanity check: At a full stop, if you press W and S, look how the rear wheel and vertical control surface behaves - are they moving?

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Or the front wheel for that matter.

surreal ingot Jan 31, 2026, 4:07 PM

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the control surfaces do move

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wait I thought I mirrored these

feral lark Jan 31, 2026, 4:08 PM

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dum dum duuuuum,

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Big issue: found.

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But another question: At a standstill, if you move left-right,
1-The vertical control surface should react
2-The front wheel should react.

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3-The rear wheels should NOT`react.

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please check all three.

surreal ingot Jan 31, 2026, 4:10 PM

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It took off

surreal ingot Jan 31, 2026, 4:10 PM

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feral lark But another question: At a standstill, if you move left-right, 1-The vertical c...

the front wheel only reacts when I press A and D

feral lark Jan 31, 2026, 4:11 PM

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2: okay... what about 1 and 3?

surreal ingot Jan 31, 2026, 4:11 PM

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feral lark Jan 31, 2026, 4:12 PM

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don't look in SPH, look on the runway, test!

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Settings are hard to read, so there's no beating a visual sanity check.

surreal ingot Jan 31, 2026, 4:13 PM

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Only the canards move from S and W

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the ailerons move from q and e

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And the Rudder moves from A and D

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The front wheel steers from A and D

feral lark Jan 31, 2026, 4:15 PM

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And not the rear wheels? There you go, that's a good visual check of all controls. 🙂
Lesson learnt: Had we started with that, we'd have spotted your missing ailerons from the get-go. XD

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Congrats, that plane is now functional for takeoff!
I'm curious what speed it needs to lift...

Oh, to ease your landings I have a recommendation: Weaken the brakes a LOT on the front gear, (like 50%) it's a stronger gear than the rear ones, so for apparently equal braking power, it'll brake more.
And guess what happens to a fast landing plane that brakes more on the nose than the rear.

surreal ingot Jan 31, 2026, 4:17 PM

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The rear wheels don't move

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I do have the small landing gear version that's basically the same as the rear wheels

feral lark Jan 31, 2026, 4:18 PM

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If it was the same, I'd still reduce the braking of front gear to 70% or less... You want the braking to be firmly at the back of the plane.

surreal ingot Jan 31, 2026, 4:19 PM

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Ok, done that

feral lark Jan 31, 2026, 4:20 PM

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I think we're good now, the rest is up to you. The major issues were resolved. 🙂

surreal ingot Jan 31, 2026, 4:20 PM

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Why the heck are trees in the runway

feral lark Jan 31, 2026, 4:22 PM

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Mine doesn't. Odd, Parallax usually has a 'clear area' around the KSC

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At least Kerbal Konstructs has an option for that... Usually.

surreal ingot Jan 31, 2026, 4:23 PM

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How do I find the option for that in parallax?

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Also, this is not the kerbal space center, this is Korou in SOL I think

feral lark Jan 31, 2026, 5:40 PM

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It's not a parallax option, it's an option in Kerbal Konstructs to have an area be clear of scatters. And I just spotted it vaguely years ago, don't ask me to point it out.

surreal ingot Jan 31, 2026, 6:49 PM

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feral lark It's not a parallax option, it's an option in Kerbal Konstructs to have an area ...

I can't find the option sadly

waxen tiger Jan 31, 2026, 8:45 PM

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iirc the better lift to drag ratio a plane has, the lower TWR a plane needs.
(and on the other side, with enough TWR, a plane with any kind of lift to drag ratio can fly)

waxen tiger Jan 31, 2026, 8:46 PM

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surreal ingot How do I find the option for that in parallax?

it wouldnt fix it visually, but would fix the collision, you could change the parallax collision level, so that the tree doesnt have collision

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though hmm another way, if you get/have kerbal konstructs, and make a map decal (make sure setting to clear parallax scatter is enabled) and place it at same height as ground below runway and it should clear parallax scatters)

analog flicker Feb 1, 2026, 3:47 AM

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@surreal ingot check out the FAR stability stuff in the SPH

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you want all of the numbers to be green instead of red

surreal ingot Feb 1, 2026, 3:55 AM

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waxen tiger it wouldnt fix it visually, but would fix the collision, you could change the pa...

Is this like in a dot cfg file?

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What option do I set it at?

waxen tiger Feb 1, 2026, 4:03 AM

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well you could also change that in game but that also works, i think its collision level setting, that i think you set it to 0, but idk

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also this button here iirc tells you what each number means for the collision level, so if 0 doesnt work you could see what it says here

surreal ingot Feb 1, 2026, 4:24 AM

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Understood, I didn't notice it until now that it was in the gui menu

#Do Jet Planes require a positive TWR to take off the runway?