Cargo Spaceplanes

[Lukun7Rocket]

I need help making a mk3 or mk2 plane that can get into orbit. First, they steer off the runway, and I have to add 14-20 rapiers to even get off of the runway. What can I do?

[Arugela]

Veering off the runway might have to do with it being nose heavy. If It puts weight on the forward wheels it may go veer off. make the COM and COl be closer or maybe adjust the balance on the wheels so it's pointing up and not down.

Edited November 22, 2018 by Arugela

[Aegolius13]

Can you post  a screenshot of the existing craft?  That would help a lot in terms of figuring out what your specific issue is and how to fix it.

 

5 hours ago, Lukun7Rocket said:

First, they steer off the runway,

This is often due to wheels not being set perfectly (the game is insanely picky on this).  Click your wheel with the rotate gizmo, choose "snap" mode and "absolute" rotation ("F" key I think), and make sure they stick straight down and face forward.  Best to check all three axes of rotation. 

Other wheel things to try:

• Turn steering off on the back wheels.
• Increase friction on the back wheels, and/or decrease it on the front wheels.
• Try larger wheels if you have a heavier craft.  You may be overloading it.

This could also be related to your other problem re: taking off.  If the plane has to go too fast on the runway, or has unexpected forces pushing it down in front, etc., strange things can happen.

6 hours ago, Lukun7Rocket said:

. First, they steer off the runway, and I have to add 14-20 rapiers to even get off of the runway.

That sounds like... a lot of Rapiers.  Rapiers are not great at low speeds, but unless your plane is enormous, sounds like something unexpected is going on here.  

Difficulty taking off could be caused by, among other things:

• Insufficient wing area for your weight (add more wings, or lighten the plane).
• Insufficient pitch authority (add more control surfaces, use bigger control surfaces, and/or put them at the very front or back of the plane for better leverage).
• Center of mass too far forward relative to center of lift (move wings forward, or adjust design to shift mass backward).
• Rear landing gear too far backward (slide forward, but watch out for tailstrikes if you go too far).
• Unbalanced thrust making the plane want to pitch down (adjust engines so the center of thrust aligns with the center of mass).  The "RCS Build Aid" mod is great for checking engine torque. 

 

Again, a screenshot would do wonders for a diagnosis, preferably in the hanger with the Center of Mass and Center of Lift indicators on.

[Lukun7Rocket]

I couldn't get the pic so here;s the file

https://pastebin.com/vRkApVqY

[Aegolius13]

I gave it a quick try.  At least for me, the landing gear worked fine, and kept the plane straight on the runway up to like 140 m/s, which should be more than enough speed.  The bigger problem seems to be the difficulty taking off.  A couple points here:

• You've got your center of thrust well above the center of mass, due to the engines being placed high on the craft.  I think this is causing your nose to torque down. 
• You may want to try extending the forward landing gear down a bit, so the plane sits nose-up on the runway.  This helps it want to point up and lift off.  
• You might be light on wing area for a plane this size. You might also try rotating your wings so that they point up a bit when the plane is level (this is called angle of incidence, and helps generate lift).
• Your control surfaces are probably too small for a plane this size.  But the bigger issue is that they're in the middle of the plane, so they generate next to no leverage for pitch.  Mounting at the tail or the front (as a canard) will help.

One other point - this is not as directly related to taking off, but abrupt changes in form factor (e.g., Mk 3 to 2.5m and the like) generate tons of drag.  Your plane will perform much better if you smooth these out.  For example, I would get rid of that 2.5m monoprop tank in the middle, and put it in a spot with the same form factors.  (Or get rid of it entirely - you may have enough monoprop from just the cockpit).  Similarly, I would stick a Mk 3 to 2.5m converter on the back of your plane, before the coupler for the nukes.  

EDIT - one additional thought.  I think once you tweak some of this stuff, you'll find that you have more engines than you need to take off and get to space.  So you may be able to trim  down further, which can provide a cleaner design, and so forth in a virtuous cycle.  At the extreme end, you can check out posts by @GoSlash27, who is a master of making clean, low-drag planes that work with minimal engine power.

Edited November 22, 2018 by Aegolius13

[KerikBalm]

21 hours ago, Lukun7Rocket said:

I need help making a mk3 or mk2 plane that can get into orbit.

This is different request than making a cargo spaceplane (not that they are mutually exclusive)

As far as getting off the runway, does your spaceplane have some incidence, or some nose up angle when on the runway?

[Lukun7Rocket]

Thx for all the help. The plane took off and worked fine!

[Vanamonde]

This is going to be people sharing craft files, and so the thread has been moved to craft exchange. 

Glad your plane works now.