How to get my SSTO to work?

[bgrif59]

Hey guys, probaly nooby question here but i cant seem to figure it out.

I have a space plane that is capable of reaching orbit with 3000+ delta-V, but every time i start it it heads down the runway, and before it can lift off it veers to the left and crashes and kills bob poor bob.

Is there anythin that i am doing wrong? i dont know how to post screenshots but if i knew i would.

Thanks in advance!

[thereaverofdarkness]

Craft veering is often caused by it being heavy and buckling under is own weight. If it veers slowly, you can probably adjust its course meticulously to keep it heading straight down the runway. Once it veers beyond about 1º, it's hopeless.

Also, you should be taking off going no faster than 125m/s. If you can't take off at that speed, you don't have enough lift. If you can't go fast enough to take off, you need more thrust. Most planes with a good wing area can take off at 80m/s, but heavy rocket-fuel laden craft sometimes need a little over 100m/s.

[Johnno]

What you're describing can usually be fixed a few different ways.

Lift

- Tilt your wings 5 or 10°

- Add wings

Control surfaces

- Add forward canards

Landing gear

- Move rear landing gear closer to center of mass

If you have enough lift and forward control surfaces, then it's usually down to your landing gear. The rear landing gear need to be pretty close to the Center of Mass (CoM for short) for easy takeoff. Also having your nosewheel on your cockpit can sometimes cause issues. To get a feel for how close the rear landing gear can be to the CoM Move them so that the CoM ball is centered on the wheel itself vertically. Your plane should tip over backwards. Revert flight and move the gear backward a bit, rinse repeat until your plane doesn't tip over.

[pokeman]

All solid suggestions. You also want to make sure that if you move the gears forward you keep an eye out for tail strikes when you do manage to pitch up.

Making the forward gear taller for more nose up on runway can work if you can't afford to angle the wings, it wont do anything for lift in the air but if the issue is purely getting off the runway it might help.

[RoboRay]

Actually, craft veering off to the side is caused about 99% of the time by landing gear being installed at an angle. They need to be attached straight up and down.

[shand]

I've heard that a good way to reduce veering is to accelerate slowly (low throttle) up to 60m/s before bringing it right up.

No idea if its true or just a placebo effect, but seems to work

[Brevillance]

Most of the time on the runway when my SSTO's (or just inter-kerbin) planes start to veer, i generally leave and go to the SPH. Once there, you can adjust the landing gear. Make sure all the gear is flat, this can be tricky when you put them on the side of a tank or such, so make sure to look at it, if it feel right launch it and see if they are all flat.

I also find that if you have long wings, adding a pair out on the side (i usually have the main body, then tanks right on the side, so i put them on the side tanks) can increase stability as well. Try to widen your rear wheelbase, make sure they are flat, turn on SAS, and see if it rolls straight.

If you do all that's suggested here, and still fail to make it roll straight. You can do 1 of two things.

1. Provide a craft file for us to look at

2. Alt-F12 and hack gravity to get it off the ground.

Best of luck

[bgrif59]

Ok guys good suggestions guys, thanks!

i will go and test this and of it doesnt work i will post a craft file of my ship, so you guys can have a look Also, first post and thanks so much for the responses, this forum is really great.

[Stochasty]

Craft veering before takeoff is always either a landing gear problem or a thrust imbalance problem. Here's a checklist:

1) Make certain your landing gear are vertical.

2) If you are using a tripod landing gear arrangement, be aware of what happens to the weight distribution during takeoff. As the plane accelerates and the wings begin to produce lift, it will often be the case that the weight distribution on the landing gear will shift. If the weight shifts onto the single gear, you will crash. (Often this will happen for craft with a nose-up attitude on the runway and a 1-fore, 2-aft gear arrangement; the wings will pull the rear gear off the ground shifting weight onto the forward gear.)

3) Landing gear attached to certain parts (structural pylons, certain struts, etc.) are not stable, and will undergo spontaneous rapid disassembly at high speed.

4) Always, always, always make sure your thrust vector passes through your center of mass. Asymmetric thrust produces torque which can lead to unexpected behavior on the runway.

[Hodo]

Stochasty, said it best

1) Make certain your landing gear are vertical.

Or as I like to say... make sure they go straight up and down.

If they have to much camber they will induce high speed direction changes. It will pull one direction or the other. Also make sure they are straight.

[Dispatcher]

Previous suggestions are helpful. Another thing which might help is to add a vertical tail fin (or a few vertical wing tip fins if you've already got a tail fin).

[bgrif59]

ok this is my craft design, i tried your suggestions but now it lift up and flips over and crashes

https://dl.dropboxusercontent.com/u/43468589/SSTO.craft

[Hodo]

bgrif59, can you post a pic of it.

If it lifts and flips over and crashes, it is the Center Of Lift (COL), being to far forward of the Center of Mass (COM).

[BubbaWilkins]

Landing gear attached to wings will flex along with the wings while holding the craft's full weight. Make sure you strut your wings to prevent this.

Also, try to configure your gear so that the nose is either slightly higher than the tail...

OR

that the rear gear is sufficiently near the CoM to allow the craft to nose up...

OR

You have forward canards which will bring the nose up.

Completely level gear often make craft harder to take off because you can't force the nose up no matter what speed you're going.

[Dispatcher]

I hope the IT people will restore the "reply with quote" ability for Safari users. Anyway, Bubba Wilkins, even with perfectly level gear, there is a way to get the nose up. Pitch the forward canards or wings up (shift A) or even all wings, so that they may get air pushing under them to initiate lift. I'm sure you knew that. :-) In practice I tripod my gear with the two rear gear "shorter" than the one forward gear, as well as pitching the wing surfaces up. I also do what some here advise against: angle my rear gear. Sometimes a take off can be a little scary but I prefer to place the rear plane mass load onto the gear instead of putting gear on wings. But that's the fun of KSP; we can do things differently and it sometimes works.

Edited September 4, 2013 by Dispatcher
Grammar.

[RoboRay]

Remember that the wings are supporting the full weight of the plane in flight, so the flexing from supporting part of the weight on the ground (assuming the nose gear is on the fuselage) is less than the flexing they will experience once you take off.

Landing gear under the wings is a total non-issue, from a load bearing standpoint... the wings must be capable of support loads significantly greater than that during banking turns in flight.

Considering the improved stability from the wider stance, along with the innate positive angle of attack during the takeoff roll, mounting the gear under the wings is frequently a superior option.

Edited September 6, 2013 by RoboRay

[lammatt]

mostly wheel problem

[ArmchairGravy]

Landing gear placement can be hyper-touchy. I had to tweak my gear several times so that a) the plane would stop veering, I wouldn't knock engines off when I angled up. Once I got it right it lifted off smooth as silk. If you have a really wide wingspan, you may want another set of rear gear to keep the wing flex minimized.