Spaceplane SSTO Troubleshooting Guide

[Dragon1260]

Just some thing I learned in the last few hours. I wanted to post it in case it helps someone. There is likely this information posted somewhere on the forum, but I usually have to dig a bit for it. That or I am a dunce that can't find an existing guide. Hope this gets expanded or redirected to the appropriate guide.

1. My plane veers right or left on the runway, crashes into ground

=Problem: The back of the plane is lifting off before the front

-Solution: Make sure the Center of Lift is sitting behind the Center of Mass. Make sure that the wheels are level with eachother

2. My plane won't lift off before reaching the end of the runway

=Problem 1: Not enough lift.

- Solution : add a bit more in wings or reduce weight.

=Problem 2: Center of Lift is sitting in front of or too close to Center of Mass.

-Solution : Move Center of Lift behind Center of Mass.

=Problem 3 :Rear landing gear too far behind Center of Mass.

= Solution : Move landing gear forward.

3. Plane turns right or left in flight; hard to control right or left. Problem is more pronounced with more thrust.

=Problem 1: Asymmetric structure of plane.

-Solution : Check for asymmetry, make it symmetric.

=Problem 2: Uneven fuel usage.

-Solution : first check the tanks during flight to see if one tank is being used before the other. If so, this offsets the Center of Mass to one side. Reconfigure the fuel tanks / lines and do several test flights until fuel is used out of the tanks evenly.

4. Plane spins left or right around 23km up.

=Problem: Flame out.

-Solution: Watch your resources menu in the top right. When air intake reduces below 0.2, cut the turbine (or any other air-breathing engines). The plane is spinning because one engine cut out when the air became scarce, which left just enough air for the other engine to run for a second before cutting out, thus having thrust on one side for a sec.

5. Pulling up to quickly for takeoff knocks off my back engine (hits the ground).

=Problem 1: Landing gear is too far forward.

-Solution : The back landing gear decides where the plane pivots when taking off and landing. Move it further back to avoid scraping the engine against the ground as the plane pulls up.

=Problem 2: Poor Driving

-Solution : Hold Alt+S to adjust the trim to an upward pitch. Watch the pitch meter (in the lower left of the screen) rise as Alt+S is held. The trim sets a sort of "default" pitch/roll/yaw position. Setting the pitch up slightly will make the plane rise upward more slowly, rather than hitting S alone which maxes out pitch and dings the back engine against the ground.

6. I run out of fuel before reaching orbit.

=Problem: Bad ascent profile.

-Solution: Trying to run straight for the sky (like a rocket), often runs the plane out of fuel because the rockets are very expensive on fuel. The air-breathing engines are cheap. Look up ascent profile diagram for SSTOs. In general,

a. 45 degree angle to 10km,

b. lower to 5 degree angle, fly up to 20km at this low angle to gain about 1.5km/s velocity

c. Cut airbreathing engines when air intake gets below 0.2, angle to 80 degrees (like a rocket), kick on rocket to raise apoapsis to desired parking orbit

d. circularize orbit to about 2.2km/s velocity

7. How do I pull up the landing gear?

-Solution: G key

8. And the lights?

-Solution: U key

Edit:

July 16th, 2013 : Allmhuran : add to the "my plane won't get off the runway": Rear landing gear too far behind centre of mass. Move landing gear forward.

Edited August 17, 2013 by Dragon1260
allmhuran noted that plane not lifting off runway can be caused by landing gear being too far back.

[Tyren]

Nicetroubleshooting I dont even want to know how many tries u needed to get that compiled...

Ok, how many?

[ZenithRising]

THANK YOU!

Spaceplanes are so frustrating, and I've had trouble finding decent info about them in the past. I feel much more prepared to give them another try.

[thescientist]

wow! it's your First Post? it's a fantastic one

[Spyritdragon]

Very nice post. I'm just confused about one part:

"-Solution : Move Center of Lift behind Center of Mass."

Assume you have identical lift and gravity forces at your current velocity. Won't you have to continuously compensate for the torque generated by your lift, which is off-centred from your centre off mass?

EDIT: I noticed i made a mistake, my arrow is the wrong way around. Actual net torque would be the other way around. But you get my explanation i hope :-).

[SiliconPyro]

Very nice post. I'm just confused about one part:

"-Solution : Move Center of Lift behind Center of Mass."

Assume you have identical lift and gravity forces at your current velocity. Won't you have to continuously compensate for the torque generated by your lift, which is off-centred from your centre off mass?

EDIT: I noticed i made a mistake, my arrow is the wrong way around. Actual net torque would be the other way around. But you get my explanation i hope :-).

Don't think of it as a point of upward force because more importantly it is the center of pressure or drag. Think of the tail of a dart. It is where drag is greatest on the dart, so the center of mass stays in front of it. That's how a plane works. You want the center of pressure/lift behind the center of mass so the drag is keeping your plane pointing forward. Too far back, though, and you will indeed experience problems because there is also upward force applied there. That's why the COL should remain only slightly behind the COM. I encourage you to experiment. Make a plane with a long fuselage and place wings forward and back to experience different configurations. If the COL is too far forward, you will have stability problems. Too far back and you will have a lot of trouble turning at all.

[Dragon1260]

I drew a diagram; someone with a better physics credential, correct me if I am erroneous.

[Jackissimus]

I drew a diagram; someone with a better physics credential, correct me if I am erroneous.

Aaaand you got a reputation boost. Two posts only? Welcome to the forums!

[lammatt]

is it just me?

i find the phrase net torque pretty wierd

we use the convention net moment for the resultant quantity

and torque for each of the vectors

(well, at least this was how i learned in high school and used till i finished my postgrad)

[allmhuran]

Something to add to the "my plane won't get off the runway": Rear landing gear too far behind centre of mass. Move landing gear forward.

[capi3101]

Plane has tendency to not want to pitch or turn. Solution: Turn off SAS.

That may just be my problem; I suck at spaceplanes. Though switching the camera to Chase view does help.

[lammatt]

Plane has tendency to not want to pitch or turn. Solution: Turn off SAS.

That may just be my problem; I suck at spaceplanes. Though switching the camera to Chase view does help.

the 0.21 SAS allows tilting in one of the axis at each time.

so that means you can take off with SAS on.

[mellojoe]

My plane won't take off until end of runway: You can angle the entire plane backward by having the rear gear shorter than the front gear. You can slightly angle the rear ones outward, which reduces their overall height. Or you can put them on the wings instead of fusealage. You do have to be wary of scraping your buttocks, but as long as you aren't, the angle of attack on the runway will give you much faster liftoff.

My plane veers left or right on runway: Sometimes having the landing gear attached to the control pod can do this. Try putting your gear on fuselage or wings, not on the command pod.

My plane veers left or right in flight: Sometimes having a single tail fin can be treated as having a single wing, inducing a left / right lift. Try using two (symmetry) tailfins to offset the potential for the sideways lift.

[capi3101]

the 0.21 SAS allows tilting in one of the axis at each time.

so that means you can take off with SAS on.

Probably explains why I fared better flying that Dralthi last night......my first time trying to fly a plane in 0.21. Had this very issue a lot in 0.19 and 0.20.

[capi3101]

Okay...how about "plane pitches uncontrollably upward immediately on takeoff, loops over and then crashes into the ground?"

[ChevronTango]

I've found on some cases that a fractional downward angle of attack on a wing can cause lift down into the runway. It may not even be noticeable but a fix is to angle the wings back slightly. You get the most lift from a wing at 25 degrees to its velocity vector however just tilting it back 5 degrees I find is enough to fix the sticky runway problem. When you fall off the runway at the end, you pitch up in the fractional drop and thats usually enough to generate the lift needed on the wings, so if that matches your behaviour then your wings are generating lift into the runway.

[Zaeo]

Okay...how about "plane pitches uncontrollably upward immediately on takeoff, loops over and then crashes into the ground?"

your center of lift is too far behind or in front of the center of mass, OR you have thrust that is not in line with the center of mass*Important!!!*

By the way, The reason you want center of lift behind your center of mass, is because your center of thrust pushes your center of lift forward when "active" A perfectly balanced plane will do this to such a degree that the center of lift is at the same point of the center of mass.

[rpayne88]

Anyone know how well these suggestions would work with FAR?

[Jean Deaux]

This needs a sticky, I can never find all the one hint here, one hint there messages. Nice post, I may have to give planes another try cause I absolutely hate them right now.

[Jean Deaux]

After following all your easy to follow guides, I still find myself hating space planes. Apparently my methodology for assembly is not in line with real life (or simulated) physics. Still, the post is great and I've bookmarked it in the hopes someday it'll click for me. Some additional assembly tools may make this aspect of the game worth while, such as the center of lift icon changing colors from red/yellow to a green to indicate the current assembly has sufficient thrust/lift to safely fly the vehicle in it's current form.

[Zym3x]

Can someone help me with the elevons on my spaceplanes going in the wrong direction.

[Val]

9 hours ago, Zym3x said:

Can someone help me with the elevons on my spaceplanes going in the wrong direction.

This can happen if the elevon's hinge-axis crosses the centerline of the craft in front of CoM. For example if you have swept wings.

You should be able to reverse the direction in the elevon's right-click menu and setting control authority to a negative.

[Red Iron Crown]

@Zym3x Might be better to start a new thread in our Gameplay Questions section with a picture of your craft, this thread is quite old and contains some out of date information since the aerodynamics have changed so much since then. Closing this one.