plane takeoff help

[jab136]

so should I drain them and then balance the plane? because that will probably result in a cp pretty far behind the cm at takeoff

[Hodo]

You don't have drain the fuel to get the balance right unless you are looking to keep the current shape. You could do something as simple as move the wings forward a bit, or just extend the inner edge of the wings just a bit forwards.

Right now your SSTO looks more like a rocket that takes off horizontally. This is fine if it has enough body lift to overcome gravity. But currently it does not.

The thing is if you look at the SSTO I posted the album of, the Center of Lift (CoL) is right behind the Center of Mass (CoM), and not by a large amount. You want it right behind it, so the cross lines touch it at the furthest, and at the closest, you dont want it more than just behind the center of the CoM ball marker.

Now mind you the CoM will shift as your fuel drains, I did not notice if you have the RCS build aid plugin. It helps a lot when figuring out the dry CoM and the wet CoM.

And looking at the second craft you posted, there are some other issues that will come up.

-all of the solar panels on the wings will cause excess drag, which will slow down the aircraft in the atmosphere. If they stay on during re-entry (if you have DRE) will be a miracle.

-The landing gear are to far behind the CoM rotate point. Ideally you want the landing gear just behind the CoM+CoL this gives you the rotate point for take off.

-Your tail stabilizers, are WAY to small for that craft, and they are canted at an odd angle that will actually cause them to act more like a spoiler than a rudder/stabilizer. Their current angle will cause the aircraft to pitch down.

-You also have to many intakes for that aircraft. From a quick count you have 10 intakes for 4 air breathing engines. That is a lot of excess drag that really isnt needed. The inline intakes you have on the engine nacelles and the stock turbine intakes are useless at the speeds you will need to be going to achieve orbital velocities.

Sorry to pick apart your craft, but I have a fair about of experience with SSTO, and space planes. I have built a few dozen of them if not a hundred, and a few that even work in the Realism Overhaul plugin.

Javascript is disabled. View full album

Edited April 16, 2014 by Hodo

[Redshift OTF]

I think as you use up fuel you the COM will move back any way. Looking at the picture I think you probably wont have enough wing to take off with all the weight. No matter, the most pressing concern is the rear wheels are to far back from the COM. The rear wheels are the pivot point the plane tilts at on the runway and if they are too far back from the COM there is too much force on them and they will buckle causing the plane to tip left or right. Move them more forward and then we will see if there are other problems with the plane. It's a badass plane BTW! Keep at it.

[Tex_NL]

yah but wouldn't the fuel drain cause the Cm to move back behind the cl creating an unstable plane?

Very well possible your plane will become unstable when the tanks drain. But be honest, what is more important at this very moment, stable flight 50 km up in the atmosphere after 30 minutes of flying? Or actually getting of the ground and fly?

My last piece of advice: Stop trying to build an SSTO spaceplane for a while and concentrate on basic atmospheric flight. Keep it small and experiment with things like wing size and landing gear placement.

You need to learn how to crawl before you learn how to walk. Only then should you attempt to run.

[GoatRider]

I haven't built many planes in KSP, but I fly both real and model airplanes. RL planes are usually designed with the fuel tanks centered on or near the empty CG, so that as they run out, the plane stays balanced. I wouldn't think that's hard to do in KSP.

[Claw]

I haven't built many planes in KSP, but I fly both real and model airplanes. RL planes are usually designed with the fuel tanks centered on or near the empty CG, so that as they run out, the plane stays balanced. I wouldn't think that's hard to do in KSP.

The problem with KSP is that you can't store fuel in the wings like most real planes do. Since the fuel is mostly in the fuselage and the engines can be quite heavy, you run into problems when the fuel drains.