Space planes: How to fly??

[Recon777]

Hey all. I'm about fed up with the whole space plane thing. I love KSP, but I can't seem to fly even the most basic plane to save my life. The planes don't use anything close to real aerodynamic physics, it seems. I can fly a real flight simulator without any difficulty, but with this the plane gets a little bit up to speed and then goes completely out of control, pitching straight up or straight down and crashing.

A lot of the missions in KSP require the use of space planes to get to a specific part of the planet and perform some test. So, I concede that I need to figure this out, but I'm having no luck with it at all. Any videos posted online seem to be for old versions of the game, so I really need some up to date advice.

[Xannari Ferrows]

I will point you here. I can not explain the topic in question with the same efficiency as the other members here. Surely you can find something.

[selfish_meme]

Usually when planes go out of control it is a lack of directional authority caused by either Center of Mass too close or after Center of Lift, drag at the front exceeding drag at the back (this is usually the speed flip) or making to large a maneuver at speed.

[arq]

If your plane is flipping out of control, chances are that your center of drag is ahead of your center of mass. This means that if you go past a certain angle (that gets narrower and narrower at higher speed), the forces trying to flip your plane will be too much for your control surfaces to handle and your plane will turn around backwards and likely crash shortly afterward.

In the spaceplane hanger, enable both the center-of-mass and center-of-lift indicators. Make sure that the CoL is behind the CoM. Or try flying some of the stock planes before you do your own. Start with small, simple planes: a cockpit, single Mk1 fuel tank, basic jet engine, air intake, landing gear, wings, and a horizontal and vertical stabilizer. Make sure to use control surfaces for the stabilizers. Once it's built, move the wings backward until the CoL is a bit behind the CoM.

Once you get the hang of building and flying basic planes you can get more elaborate. Larger planes with more engines can be interesting and eventually RAPIER-equipped spaceplanes are a fun challenge. Just remember that your CoM moves as fuel is spent and if it gets behind the CoL your plane can become very unstable.

[Recon777]

Usually when planes go out of control it is a lack of directional authority caused by either Center of Mass too close or after Center of Lift, drag at the front exceeding drag at the back (this is usually the speed flip) or making to large a maneuver at speed.

This is the plane I'm trying to fly. I always crash at takeoff because it pitches WAY up without me telling it to.

How close does the center of mass and center of lift have to be?

[edit] I moved the wings slightly back to line those up perfectly and I was able to get it into stable forward flight, however it's still VERY touchy and apt to crash when I try to maneuver.

Edited May 28, 2015 by Recon777

[arq]

This is the plane I'm trying to fly. I always crash at takeoff because it pitches WAY up without me telling it to.

How close does the center of mass and center of lift have to be?

Move the CoL back so that is maybe a quarter of one of those 400 tanks behind, at least (in this picture somewhere slightly ahead of the rear landing gear). Personally I would change it down to a single fuel tank to start (jet engines are VERY efficient) and use one of the plane ones (liquid fuel only) if you can. If that still doesn't work try swapping out the Delta Deluxe Winglets for one of the canards or other surfaces where the entire thing moves.

[Vanamonde]

How-to question moved to the how-to subforum.

[Recon777]

Move the CoL back so that is maybe a quarter of one of those 400 tanks behind, at least (in this picture somewhere slightly ahead of the rear landing gear). Personally I would change it down to a single fuel tank to start (jet engines are VERY efficient) and use one of the plane ones (liquid fuel only) if you can. If that still doesn't work try swapping out the Delta Deluxe Winglets for one of the canards or other surfaces where the entire thing moves.

Moving CoL to that point makes it unable to lift off. So, centering it on the CoM and maybe *slightly* behind it gives stable flight. Though, I still can't land without something blowing up like the engine coming off. Even a very very gentle landing on the bumpy grasslands west of KSC blows something up. The whole flight model is so unlike real planes, maybe I'm just not knowing the rules. For some reason cutting the throttle to 0% still allows the plane to fly for ages and doesn't slow down enough to stall and stay on the ground for a landing.

Regarding the construction, well I had the T400 tanks on so that there would be room for all the parts. Removing one crams things together so tight that it doesn't all fit, so 3 tanks are needed. Also, I don't have any of the other parts because I'm trying to make a viable aircraft with just the initial set of spaceplane parts that are unlocked in the game.

[cybersol]

Can you successfully fly a included stock or spacecraft exchange plane built by someone else? If so, then you know its the plane design that needs improvement.

From your picture, that center of lift is too far forward and will easily get you spinning. Make sure to set yaw control only for the tail fin and turn off yaw for everything else. Also, arq has some good suggestions above. I also think you need more pitch control by switching the deluxe to av-r8 winglets or whatever the similar control ones are called.

[arq]

cybersol has more good suggestions for you. You'll still need to move the CoL back more. Larger controls surfaces will allow you to pitch up and get off the runway easier. Also, if you need to use the T400 tanks at least make sure you remove the oxidizer by right-clicking in the editor - that will dramatically reduce the weight which will make the plane easier to handle.

As for landing, trying to land anything above 80-100m/s is risky if not suicide. A plane this small can probably fly at 40m/s and that would be a good speed to try to landing. This may involve gliding for awhile to burn off speed. Try landing on the runway (if possible) or the flat area immediately surrounding KSC. Even small hills require some special consideration for landing and will be more difficult - the flatter the easier.

[Recon777]

Can you successfully fly a included stock or spacecraft exchange plane built by someone else?

I tried the Aeris 3A just now, and it seems pretty easy to fly, although it feels entirely unrealistic. I guess this is simply not anything like real life aircraft. I did notice that it wanted to pitch up, even with the throttle at 0%. I found that really strange because 0% throttle should cause the airspeed to go way down. It's almost like the plane has no drag.

Anyway, I was able to get from point A to point B pretty easily in the Aeris 3A, which I suppose is the whole point. It's not a flight simulator. I still found it very difficult to actually come to a stop once landed. The landing gear brakes are next to useless and forward momentum seems to be really hard to bleed off whether in the air or on the ground.

Regarding the plane I've been trying to build, yeah it's just meant to be whatever can be put together with the first science node having to do with spaceplanes. Maybe I need to just wait until I unlock some more advanced parts? Seems strange that the entry level parts don't give you enough to make a useful plane from. I did remove the oxidizer cause I saw someone's video recommend that. Also, very appreciative of the tip to switch yaw control only to the tail fin. I didn't know that was something you could do.

[SAI Peregrinus]

Your rear landing gear is too far behind your CoM to let you move your CoL back with the existing control surfaces. You want CoL a bit behind CoM, and the rear gear just under or barely behind the CoM.

[Recon777]

Your rear landing gear is too far behind your CoM to let you move your CoL back with the existing control surfaces. You want CoL a bit behind CoM, and the rear gear just under or barely behind the CoM.

Ah. Didn't know the landing gear was meant to be so far forward. I'll try that.

Out of curiosity, I looked up the parts for the Aeris 3A. I'd have to unlock the following:

90 science for Landing

90 science for Aerodynamics

160 science for SupersonicFlight

160 science for AdvancedExploration (Just for the ladder!)

Sooo... that's 500 science! Not gonna happen anytime soon, methinks.

[n0xiety]

Take a look at http://forum.kerbalspaceprogram.com/threads/52080-Basic-Aircraft-Design-Explained-Simply-With-Pictures and all your problems will be over my friend.

[Nansuchao]

[Rickenbacker]

Two basic things to check before takeoff:

- Your CoL should be slightly behind your CoM (i.e. your craft should be slightly nose heavy) at all times for stable flight.

- Your main gear should be slightly behind your CoM (or slightly in front of it for taildraggers), since the plane has to pivot around the main gear to lift off.

[KerikBalm]

I love KSP, but I can't seem to fly even the most basic plane to save my life. The planes don't use anything close to real aerodynamic physics, it seems. I can fly a real flight simulator without any difficulty, but with this the plane gets a little bit up to speed and then goes completely out of control, pitching straight up or straight down and crashing.

IRL, if CoL is ahead of CoM, the plane will be unstable, and you will crash. That is quite realistic. The problem is your flight simulators have properly designed craft, but your craft is not properly desiigned (by you, not the game)

Moving CoL to that point makes it unable to lift off.

Yor rear wheels should be either slightly behind the CoM, or you should move the wheels so that it has a positive AoA on the runway.

No AoA= no lift. Wheels too far behind the CoM means you can't pitch the nose up to lift off.

Makes perfect and real sense.

For some reason cutting the throttle to 0% still allows the plane to fly for ages and doesn't slow down enough to stall and stay on the ground for a landing.

This is probably due to the very slow throttle response of the jet engines in the game. If you action group them to shut them *off*, not just throttle down, you'll get a quicker response.

I'm not sure how accurate the throttle response is.

FWIW, I mainly fly my planes only at full throttle, or engines off.

Full throttle until orbit... and then I try to do my re-entries completely unpowered. (if I didn't time the deorbit right, I run them at full throttle to get my trajectory appropriate for landing at KSC, and then shut them off again and proceed for an unpowered landing) - of course, IRL, the only stuff I actually fly is all unpowered.

although it feels entirely unrealistic. I guess this is simply not anything like real life aircraft. I did notice that it wanted to pitch up, even with the throttle at 0%. I found that really strange because 0% throttle should cause the airspeed to go way down. It's almost like the plane has no drag.

Again, probably the slow throttle response.

What does its pitch trim have to do with airspeed. You simply need to adjust the trim of the plane, and then shut the engines down rather than throttling back.

I still found it very difficult to actually come to a stop once landed. The landing gear brakes are next to useless and forward momentum seems to be really hard to bleed off whether in the air or on the ground.

Brake torque by default is set to a measly 12, you can adjust it to 30, I would do that.

You can also add drogue chutes and airbrakes, which will really help a lot.

These are balanced around space plane (with rather OP'd engines), not something like a cesna.

Also, make sure you're not landing too fast. 80 m/s is 288 km/h

[Warzouz]

Air brakes are a MUST for landing, especially for cross-country landings (to get science from Kerbin).

[Wanderfound]

Sooo... that's 500 science! Not gonna happen anytime soon, methinks.

Hi tech is not required to start with:

Javascript is disabled. View full album

Craft file at https://www.dropbox.com/s/9vptzzhq8knsoaj/Kerbodyne%20Hiflyer.craft?dl=0

That's a suborbital hopper rather than a true SSTO, but it should give you some ideas of what is possible.

[Recon777]

IRL, if CoL is ahead of CoM, the plane will be unstable, and you will crash. That is quite realistic. The problem is your flight simulators have properly designed craft, but your craft is not properly desiigned (by you, not the game)

That's true, and I had considered it. Though, I have to say that even with the stock planes it still doesn't feel like real flight. Hop in FSX and fly around in an F-18 Hornet or P-51 Mustang, and the flight dynamic feels entirely different. KSP planes feel like a ball that just flies around the sky with the model of a plane that pivots around the ball acting on the air in various ways depending on what you do with the control surfaces. Not the best description I know, but it really doesn't feel like an actual plane. Maybe that's partially because these are planes made of rocket parts and they wouldn't fly like normal planes? I'm not sure, but it could be. The way momentum and drag behave feels all wrong. When do these things stall, anyway?

Something else I probably should try is using a joystick. Flying with keys is not only counterintuitive, but doesn't allow for graduated pressure on the control surfaces. In real life, slamming the stick around all-or-nothing is a fast way to crash your plane.

Yor rear wheels should be either slightly behind the CoM

When I try that, the plane starts off with its engine touching the ground. Even with CoM in front of the rear wheels (by a small amount) the game starts with a physics jolt of some kind which puts the plane on its ass.

It seems from what everyone is saying that there's a whole lot more to this than it seems. Maybe most of the parts which can make a nice spaceplane are unlocked much, much later. For me just starting out, I have the basic science node unlocked but that only gives you the parts to make essentially one plane - the plane I made. There really isn't much room for flexibility as far as I can tell. It'd take me 500 more science to unlock all the parts to get the Aeris 3A. I'd like to, but wow 500 science is a lot. And that's only three nodes!

Edited May 28, 2015 by Recon777

[arq]

It is definitely possible to build a simple plane with just the first aircraft tech, and for the sake of forcing a simple design probably easier. Yes, KSP aerodynamics are a crude approximation of the real thing, but they get the gist (and the aerodynamics now are waaaaay better than they were in beta). As it turns out, making 'flyable' planes in a flight simulator is a lot easier because they can have all their parameters input directly whereas KSP has to mash something together from a bunch of blocks stapled together and then try to figure out the aerodynamic implications.

However, there is a mod called FAR (check the modding section) that dramatically improves the aerodynamics model in the game. At the moment I believe it's still ironing out a few minor bugs, but it will make aircraft behave much more realistically. But FAR usually makes design and flight considerably more complicated so you may want to get the hang of stock aircraft first.

By the way, aircraft stall above 30deg AoA or so. It becomes obvious from a dramatic reduction in speed and (IIRC) a shuddering noise.

[KerikBalm]

Hop in FSX and fly around in an F-18 Hornet or P-51 Mustang, and the flight dynamic feels entirely different. KSP planes feel like a ball that just flies around the sky with the model of a plane that pivots around the ball acting on the air in various ways depending on what you do with the control surfaces. Not the best description I know, but it really doesn't feel like an actual plane. Maybe that's partially because these are planes made of rocket parts and they wouldn't fly like normal planes? I'm not sure, but it could be. The way momentum and drag behave feels all wrong. When do these things stall, anyway?

I agree, it doesn't feel entirely realistic, even considering that the plane you're flying is far from a fine tuned aerodynamic machine.

The other thing is that we often are flying around at really really high altitudes... 15km... who cares?

uhh.... that is 50,000 feet... higher than an airliner can fly. High enough that those air france pilots couldn't get the plane pointing in the direction it was flying (though the one definitely seemed incompetent, and kept the thing stalled all the way to the water).

I'm no expert in high altitudeflight, flight at significant mach numbers, or flight in craft that are not yaw stable.

The things i fly generally point the direction they are going -- but I know sailpalnes can slp and skid quite a bit.

This slipping and skidding in seen in KSP a lot, but I'm not sure if that is the aero model, or the aeroplane...

And KSP craft most certainly do stall when AoA becomes too high

[Docsprock]

I do a lot of kerbin flying. At first, the challenge was to get to the island runway and land. Many,many hours spent on that.

Landing in the boonies can be quite difficult. Fly as slow as practical, and glide to a landing. I will sometimes 'dolphin' to lose airspeed. (Kill throttle, dive/climb to achieve required airspeed.) In fact I always land with 0 throttle.

landing on the runway requires good rudder control to line up properly.

[ajburges]

Do note, the Aries A3 is not aerodynamically stable. CoL is ahead of CoM. It is a little flip happy as a consequence.

Most builders avoid aerodynamic instability. Space planes care about speed going up and stable glide going down. Science jets are designed to be flyable at high physics warp to reach survey sites quickly. Neither use case benefits from an unstable craft. Unstable craft are for buzzing KSC until we get better active stability options.

As a consequence most people here advocate more stable design choices over less stable ones. Not a lot of effort is spent making flyable unstable craft.

[Torquimedes]

Lots of good advice in this thread. Recon, definitely check out the "explained simply with pictures" link posted above.

The early landing gear are set to 20/30 braking force by default. Rightclick them in the SPH to crank up the brakes, but remember that braking too hard with the nosewheel could flip the plane over forward and/or wheelbarrow it sideways and crash while landing. Since you don’t have airbrakes or flap control early in the game, as soon as you are firmly on the ground, you can try pitching full down to create some control-surface drag to assist your braking. For landing in rough terrain like a mountain plateau, slap a radial chute directly over your CoM so you fall level on your wheels when you pop the chute and cut the engine.

It is possible to build useful low-tech planes. Download those and pull them apart to see how different configurations can work.

Less conventional layouts have their uses. For the sake of your engine on takeoff, I prefer to put my rear wheels as far back as possible, especially on an early spaceplane with a rocket bell sticking way back there. In order for this to work, you either need positive AoA on the runway, or you need canards to pull the nose up because your elevators won't be able to push the tail down. Then it is a matter of moving the CoL just far enough behind the CoM that full pitch can't slap the engine into the ground on takeoff, and you're golden. Don’t forget to limit the canards to pitch only.

Edited May 28, 2015 by Torquimedes