Spaceplanes == RAAARRRGHHHH!!!

[ZenithRising]

So, on two separate occasions, I've tried my hand at building some spaceplanes, worked at it all day, and ended up quitting in anger with no working plane designs. Most recently I did a lot of googling too to try and find some answers, and while I found a lot of things to try, it didn't seem to help me get a plane off the ground.

The big problem seems to be a fundamental instability that starts to affect my planes when they get up to a certain speed, causing them to roll and destroy their wings. I was able to get some minimalist planes (and the stock planes) into the air, but anything of any significant size I design is impossible to get off the ground.

I know this is a pretty common experience, but plenty of people out there seem to be flying successful planes, so I'm just wondering if those of you who have managed it could give me some tips to making my plane designs easier to take off and fly. Where should I put my CoM, CoL and CoT? Should I tie everything together with struts? What is a good mass to lift ratio? Do I just need to wait until Squad improves the plane physics? Etc etc

[Blaster]

So, on two separate occasions, I've tried my hand at building some spaceplanes, worked at it all day, and ended up quitting in anger with no working plane designs. Most recently I did a lot of googling too to try and find some answers, and while I found a lot of things to try, it didn't seem to help me get a plane off the ground.

The big problem seems to be a fundamental instability that starts to affect my planes when they get up to a certain speed, causing them to roll and destroy their wings. I was able to get some minimalist planes (and the stock planes) into the air, but anything of any significant size I design is impossible to get off the ground.

I know this is a pretty common experience, but plenty of people out there seem to be flying successful planes, so I'm just wondering if those of you who have managed it could give me some tips to making my plane designs easier to take off and fly. Where should I put my CoM, CoL and CoT? Should I tie everything together with struts? What is a good mass to lift ratio? Do I just need to wait until Squad improves the plane physics? Etc etc

1: Planes are super unstable due to how the game manages its unrealistic aerodynamic physics

2: Less is more. The fewer bits you have, the better it will fly. Don't be afraid to skimp on fuel, the weight loss can make a difference.

3: Center of Lift has to be bang on the center of mass, or the plane will dip or stall once you hit a fast enough speed. Again, this is due to the unrealistic aerodynamic physics, which adds force instead of drag, and doesn't respect "catching the wind".

4: Center of Thrust should also be on the same X and Y axis as the center of mass, or the plane will pitch or yaw violently in the not forward direction the moment you flip from jets to rockets.

5: Wing connectors are terrible.

6: Try and make your plane able to take off before hitting the end of the runway.

[Anton P. Nym]

Planes, too, need struts thanks to the way the game works. On big wings and heavy craft I try to put one or two struts between each wing panel to avoid flapping and snapping.

In the spaceplane hangar I put my CoL slightly behind the CoM, which makes takeoffs a bit trickier but helps with stability in flight; if the CoM every moves behind the CoL (because, for instance, of fuel burnt off) the plane will become unstable and your pilot will have a bad day. CoT, as pointed out above, must be aimed so that if it's extended forward it'll go through the CoM.

SAS helps. A lot.

The tip I didn't know that defeated my designs for so long; landing gear placement matters. Rear landing gear should be only slightly behind the CoM; if it's too far back, the plane can't rotate its nose up on take-off and it'll never leave the runway. (If it's too far forward, you'll tip back until the tail hits the runway which is bad for the paint. If you're worried about dragging the tail on take-off, put one extra set of gear near the tail so that when extended it barely gets below the tail... far enough to stop it from hitting the runway, but not so far that it prevents the nose from pointing up.)

-- Steve

[ChevronTango]

My Pro Tip is to angle the wings back by about 10-20 degree's using shift+[WASD]. If the wings are parrallel to the ground occasionally angles and things conspire against you and you can end up creating lift into the runway (rather counter intuitively). Angling them back ensures you are generating the lift up, and means at higher altitude you don't have to point your nose up as high (and therefore not waste as much fuel with engines that you'd ideally like pointing prograde)

[ZenithRising]

Thanks for all the suggestions guys. When I feel mentally prepared to take on spaceplanes again I will have much more to work with.

[RTK]

Yeah space planes did my head in for a bit, and definitely I have had the same experience in which making a space plane with what I presumed was perfect CoL & CoM however upon taking off it would roll.

Found this issue was caused by placement of wheels at the back of the plane. Most likely if you are placing your wheels onto the wings you will come across this issue often and will need to find the right spot of the wheels.

My only tip to resolve quickly is to firstly build the body of your plane (plane without wings) chuck the wheels on and test to see if it is stable down the runway. The wings only add lift and a bit of weight to your plane, however sometimes will need to place on the wings in which it becomes a case of trial and error.

[Dispatcher]

Try the space enabled (vectoring rocket, docking port, monopropellant) planes in my "self flying planes (mostly)" stock package at the Spaceport. You would probably want to remove the solar cells and ladders first, as these seem to affect flight behavior. You'll see that some of what I've done is in harmony with the advice given above. But I always try to get the fuselage (or if it were a rocket, the stack), landing gear and a tail fin figured out before I start with the lift (wings, control surfaces).

Note too that I had certain design goals which might not be the same as yours. Things to consider are: do I intend to send this plane up as payload on a rocket and use it from orbit? Or take it up from a runway? Both?

Good luck!

[ZenithRising]

Note too that I had certain design goals which might not be the same as yours. Things to consider are: do I intend to send this plane up as payload on a rocket and use it from orbit? Or take it up from a runway? Both?

Good luck!

An SSTO would be neat and all, but what I'd really like to do is get a flying rover to Laythe and Eve. Drive on zero fuel, fly great distances on little fuel. Just finished my first rover though, and the motorized wheels seem to have plenty of their own problems, so we'll see.

[allmhuran]

Yep, centre of lift slightly behind centre of mass.

You also, *ideally*, want the centre of mass to be somewhere in the first third of the way back from the nose. When something is flying through the air the centre of mass wants to lead the way (think abouta dart from a dartboard, or just stick some chewing gum on one end of a McDonald's straw and throw it). This, however, is a difficult condition to meet since you will usually have engines at the back.

The CoM can (and probably will) also shift around as fuel is used up. Engines draw their fuel in order from the furthest away fuel tank to the nearest, so for simple designs (fuel down the middle and engines at the back) this will usually mean the engine is draining the fuselage from front to back. This will shift your CoM backwards as you spend your fuel.

To fix this you can try to use fuel lines so that fuel is drawn from the middle, taking fuel from front and back equally. But this can require some tricky fuel line routing since you can no longer stick your engine directly onto parts that are crossfeed capable and are in turn connected to the rear fuel tank. One solution is to stick a structural plate at the back of the fuselage (these are NOT fuel crossfeed capable) and stick your engines on behind that. Then route fuel from the middle tank directly to the engines using fuel lines.

Doing this does not guarantee that your CoM won't shift: that will only be true if your middle tank is right on top of the CoM to begin with.

[Sauron]

One VERY helpful tip I picked up recently that has helped me go from 20 ton SSTOs to ~50 tons is wheel placement. Make certain your wheels are all perpendicular to the ground and that you only have 1 front wheel. This dramatically reduces swerving on the runway and makes takeoffs a lot easier. This incidentally means that there's less need to over-engineer your planes which leads to better performance.

[Anton P. Nym]

Doing this does not guarantee that your CoM won't shift: that will only be true if your middle tank is right on top of the CoM to begin with.

I get around this by locking the fuel feed of the foremost tank in the craft during ascent. (Right click, click on the green triangle next to the fuel gauge.) I reserve that fuel until landing, keeping that as a counterweight until I actually need that fuel.

-- Steve

[allmhuran]

Yep, that's what I do in case of emergency . But getting perfect fuel routing is much more elegant, just sit back and fly the thing. It can also be important when you've built something that doesn't have very visible fuel tanks, making them hard to click on, eg...

[Diche Bach]

Which mod(s) is most popular for muting the current aerodynamic effects?

[arq]

Ferram Aerospace Research (FAR) is the only mod that I know of that takes a stab at improving the stock aerodynamics. Procedural Wings is nice because you can make large wings instead of using 10 small ones.

My planes tip (stock aerodynamics) is to not worry so much about the CoL as the CoD (drag). Having many intakes on the front of the craft will tend to cause it to flip because of their high drag coefficient (~7 times higher than other parts). The most reliable way to control CoD is to place as many of your wings as possible near the back of the craft (with only a little bit at the front to keep it under control). The stock aerodynamics are made for rockets, which are fletched like arrows, so you do well to have arrow-like craft. Because they are behind the CoM, if the craft tries to flip or tumble they will help to get you pointed prograde again, and keep you there.

[iueras]

Yep, that's what I do in case of emergency . But getting perfect fuel routing is much more elegant, just sit back and fly the thing. It can also be important when you've built something that doesn't have very visible fuel tanks, making them hard to click on, eg...

Props for the battlecruiser, man, that's awesome! Although it saddens me to see another independent world fall to the Confederacy.