Taking off, flying and landing airplanes in KSP

[QF9E]

This started as a feature request for a longer runway, but evolved into a discussion on how to take off and land airplanes in KSP. To prevent us hijacking that thread, I made the current one.

In order for this to become a bit more general, it seems that many KSP players have trouble taking off or landing airplanes on the KSC runway, to the point that they believe that the 2.5 km stock runway is not long enough. I haven't had this experience: my 40 ton Shuttle is able to land on the KSC runway (and, in a pinch, the Island Airfield) just fine, even loaded with 80 tons of cargo, or with an asteroid on its back. And my hope would be that players with lots of experience with airplanes in KSP - perhaps including me - can answer questions of less experienced players and help them on their way to become better aircraft designers and pilots.
 

Spoiler

So what qualifications, if any, do I have to pretend that I can give hints and tips on this topic? To begin with, and apart from my recently completed Shuttle challenge, I have quite a lot of experience with flightsims, having played most versions of Microsoft Flight Simulator starting with version 3.0 - I have more than 250 sim-flight hours in MS Flight Simulator X alone, having completed all of its checkrides successfully, and I am very much looking forward to MSFS 2020. I also played a lot of Orbiter, which is a spaceflight sim that is more focused on piloting spacecraft and controlling their various systems and less on spacecraft design than KSP. If that is your thing, I can highly recommend it. I also played Condor quite a bit, which is a dedicated Glider sim, with excellent simulation of atmospheric conditions such as thermals and updrafts. I regard being able to sim-fly a glider a real bonus in KSP, as it made landing Space Shuttles and spaceplanes much more intuitive for me, especially when making a unpowered descents and landings.

And on top of that I used to design and build my own model airplanes. So even before playing KSP I had some idea of things like the Center of Mass, Center of Lift, wing dihedral, Angle of Attack and so on.

Ok, that being said, how to go about designing, testing and flying your own airplane designs in KSP? I believe this is one of the hardest things to do in the game. The reason is that your job is a combination of two things that are both seen  as very difficult in the real world: aircraft design and test piloting of high performance aircraft. Here's a few tips that I gave in the previous thread:

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• Add enough wings to your craft that it is able to fly at a reasonable speed, no more than about 100 m/s.  For comparison: touchdown speeds of real-life high performance aircraft vary from about 70 m/s (F-16) to 100 m/s (Space Shuttle), 105 m/s (X-15) with 123 m/s (F-104 with its blown flaps inoperable; with these flaps touchdown speed was 85 m/s) the maximum I have been able to find. 
• Don't have the nose of the craft pointed down too much when it is on the runway. That way it will be hard to lift the nose (a maneuver called "rotate" in aviation) and get the wings to generate lift. If the wings point downwards with respect to the airflow, you are generating downforce. Useful if you are building a Formula 1 car, not so much for a plane.
• Put the main landing gear slightly behind the center of gravity. If the landing gear is too far back you will not be able to rotate. I see a lot of spaceplanes that are only able to take off by running off the end of the runway, and often the problem is that the landing gear is too far back. A good test is to do a high speed taxi on the runway, and see if you are able to rotate. If your craft is well-balanced you should be able to taxi your plane a considerable distance on the main gear alone at a speed just below touchdown speed. A high speed taxi run also enables you to test the brakes.
• Try to land with as little speed as possible while still flying. Approach the runway somewhat above this speed, and once you reach the runway threshold (at about 20 meters altitude or so), pull up slightly to lose more speed - this is called a flare. If done correctly you will start losing speed without gaining altitude. If you do gain altitude when flaring, try again with a lower approach speed. 
• A more general tip is to try to design aircraft that are able to fly with SAS turned off. With SAS turned on, a KSP plane does not fly like a real plane at all, as the SAS will try its best to keep the nose of the craft pointed in the same direction, whatever you do. Learn to use pitch trim (Alt-S for trim up, Alt-W for trim down). Pitch trim is used in real aircraft to keep flying level without applying any force on the flight controls. The higher the speed of your craft, the less pitch trim you will need.
• And another general tip: consider playing a different flight sim to learn to sim-fly. I for one can't wait for MS flight simulator 2020. Building and flying planes in KSP is in some respects much harder than, say, sim-flying a Cessna in MSFS: in KSP you take on the roles of aircraft designer and high performance test pilot, two jobs considered very hard in the real world. Whereas the flight characteristics of a Cessna are very well known, the performance of any KSP airplane design is anyone's guess untill you start flying it.

One tip that I want to repeat because I think it is a very important one and it is in danger of disappearing in the mass of text is this one: If at all possible, fly your plane with SAS OFF. SAS will try to keep the nose of the airplane pointed in a fixed direction in space. This has a couple of unwanted consequences:

* It is virtually impossible to make fine course corrections, as you are in effect fighting the SAS system

* It makes it impossible for the plane to find its own balance, often forcing the plane into a slip (which means that it flies with the nose of the plane pointing to the right or left instead of straight ahead, adding extra drag)

* On long overland flights, it forces your plane to climb ever faster, which is due to the curvature of Kerbin. SAS keeps the nose of the plane in a direction which is fixed in space.

* It appears that SAS is momentarily switched off when you are giving control inputs. This has the rather nasty consequence of nullifying pitch trim when you give small roll or yaw inputs as course corrections, often dropping the nose of the airplane. If this happens on final approach, you are in real danger of crashing your plane.

Seriously, SAS is a lousy autopilot. I only use it for long overland flights.

 

But enough from me for now: I'd love to hear your tips and tricks, as well as your questions and any problems that you might have in flying or landing your airplanes. And maybe someone is able to answer a question of mine:

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How do you properly install a flightsim joystick or yoke in KSP? I tried, but I was unable to get it to accept small inputs. I could not remove the large dead center of my yoke, which resulted in almost keyboard-like behaviour: If I tried to roll a little bit, nothing happened, and with larger roll input on the yoke I suddenly get very large roll input in KSP. The same is true for pitch and yaw, making precision flying of an airplane impossible.

 

Edited May 24, 2020 by QF9E

[Guest]

I usually fly with SAS on. I tune out the twitchiness by balancing the plane and adjusting control authority. I do not find it difficult at all to land them precisely.

When flying spaceplanes to orbit I set it to prograde, and alternate between surface and orbit to fine-tune the ascent. When just tooling around I keep it in standard mode.

Other than that, good advice and I fully agree with it. There's an absolutely fantastic tutorial on designing planes here, anyone who's interested in making them would do well to take a close look:

https://forum.kerbalspaceprogram.com/index.php?/topic/47818-basic-aircraft-design-explained-simply-with-pictures/

[QF9E]

@Fraktal posted this in the old thread:

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What yaw does for me 100% of the time is make the plane yaw a bit to the side, then rubber-band back, then start rolling the plane to the side and pitching towards the ground.

I don't even know what it's supposed to behave. I mean, I'm an Ace Combat player so I know what yaw does, but not how it works in KSP. So basically, each and every single one of my attempts to line up with the runway use pitch/roll only and end up diving headfirst over the edge of the runway because I've got no fine control. Hence why I'd like a wider runway.

Already doing this, I use 2° most of the time and tweak until SAS is slightly pushing the nose down while supercruising. Don't use dihedral because I don't even notice a difference.

And that's the thing: I can't precision-decelerate without airbrakes or thrust reversal. I can cobra to decelerate from supersonic to subsonic in a hurry, but that's it. Flaring always results in me either overshooting the entire runway because I'm approaching at 150 m/s minimum or stalling out into a 30 meter vertical drop onto the runway.

My takeoff speeds are usually around 80 m/s. No problems with takeoff, only landing.

 

Maybe we should be taking this discussion elsewhere?

Welcome to this new thread! From what I read here you are quite an experienced flight-simmer, and I understand your frustration. From what you describe I think you play with SAS on, as you describe some of the very behaviours that I outlined in my previous post. KSP, especially if you play with mouse and keyboard as I do makes it almost impossible to fly a plane like you would do in other flightsims (or when flying for real, for that matter), by giving small control inputs.

If your approach speed is 150 m/s while your take-off speed is 80 m/s your approach speed is way too high, and a flare at that kind of speed will result in overshooting the runway, simply because the plane will keep on flying. And if your flare results in a stall 30 meters above the runway you started the flare too early. I'm sorry if this sounds blunt, but that would be no different in a real airplane. Perhaps you don't give yourself enough room to get your airspeed right? Have you tried doing an extra long final approach where you focus on getting the glideslope and approach speed correct? Problem with KSP is of course that you have no real way of knowing what the correct approach airspeed is for your aircraft design, and what glideslope you need to maintain that speed, so you'll have to do some testing.

With SAS off it is possible to side slip in KSP, by giving opposite rudder and stick inputs, and it will slow down your plane. If I have the time I will make a video with an example.

 

23 minutes ago, Brikoleur said:

I usually fly with SAS on. I tune out the twitchiness by balancing the plane and adjusting control authority. I do not find it difficult at all to land them precisely.

When flying spaceplanes to orbit I set it to prograde, and alternate between surface and orbit to fine-tune the ascent. When just tooling around I keep it in standard mode.

Other than that, good advice and I fully agree with it. There's an absolutely fantastic tutorial on designing planes here, anyone who's interested in making them would do well to take a close look:

https://forum.kerbalspaceprogram.com/index.php?/topic/47818-basic-aircraft-design-explained-simply-with-pictures/

Thanks for the link! I use pitch trim to fine-tune my ascent with a spaceplane, and leave SAS off. With SAS on it feels like I am fighting the SAS system instead of flying the craft.

Edited May 24, 2020 by QF9E

[Vanamonde]

This helpful advice about how to play the game has been moved to the Gameplay subforum. 

[Corax]

One thing I see over and over again is new players calling something difficult or impossible, and then mentioning they're just trying to land going no more than 200... or their rover flips and crashes at only 100... you really need to burn that into your brain to automatically and instinctively convert those m/s into the system you're familiar with, be it kph or km/h, or whatever else that may be.

For me, it's km/h, and there it's as simple as taking any speeds KSP throws at me and multiplying them by four. Usually it's close enough if you even leave off the last one or two digits and only consider the tens and hundreds. That doesn't take more than a moment.
If you really need to know the exact value, you can simply take ten percent off that and you're spot on, but that precision is rarely needed, and even then, it's a simple calculation anyway.

Edited May 24, 2020 by Corax

[QF9E]

11 minutes ago, Corax said:

One thing I see over and over again is new players calling something difficult or impossible, and then mentioning they're just trying to land going no more than 200... or their rover flips and crashes at only 100... you really need to burn that into your brain to automatically and instinctively convert those m/s into the system you're familiar with, be it kph or km/h, or whatever else that may be.

For me, it's km/h, and there it's as simple as taking any speeds KSP throws at me and multiplying them by four. Usually it's close enough if you even leave off the last one or two digits and only consider the tens and hundreds. That doesn't take more than a moment.
If you really need to know the exact value, you can simply take ten percent off that and you're spot on, but that precision is rarely needed, and even then, it's a simple calculation anyway.

Good advice. Almost no-one will be accustomed to m/s. Mach 1 is "only" 340 m/s or thereabouts, so speed can be deceiving.

[Corax]

speed can be deceiving

...and even more so when you're in a game that gives you nearly none of the visual clues like buildings and trees like you'd have in real life.



Originally as postscriptum to my previous post:

I'm not too familiar with miles per hour, but I think a good quick approximation there should be multiplying by 2.5 (add a zero to the end, and divide by four), and for extra precision, again subtracting ten percent.
And for knots: times two, less five percent.

For km/h, the conversion is correct; knots and mph are just my estimates, without sources–don't use them where your life depends on it, like for real aviation, or in maths exams.
For a quick reality check, and definitely for use in a game, they should be good enough.

[Klapaucius]

I think folks new to aircraft would do well to learn to fly before trying to build planes.  I spent a whole day trying out every stock plane and flying each one from the Island Airfield to the KSC. That was the day I learned how to fly and to land.  Once you have a grasp of how planes work in KSP or don't work (and some of the stock planes are terrible) you get a better sense of what you want to achieve.

It should also be noted that if you are in career mode, it is actually very difficult to build a good plane with the limited parts available to you, especially the landing gear.  Better to learn in sandbox, get the basics down and then try building in career.

Edited May 25, 2020 by Klapaucius
typo

[Corax]

What yaw does for me 100% of the time is make the plane yaw a bit to the side, then rubber-band back, then start rolling the plane to the side and pitching towards the ground.

I don't even know what it's supposed to behave. I mean, I'm an Ace Combat player so I know what yaw does, but not how it works in KSP. So basically, each and every single one of my attempts to line up with the runway use pitch/roll only and end up diving headfirst over the edge of the runway because I've got no fine control.

I don't know Ace Combat, or how it models its physics and flight controls, so it may well behave very differently from what you experience in KSP.

How the aircraft reacts to rudder will depend on its design. Basically, the farther away the rudder is offset from the longitudinal axis (the higher up it is), the more roll it will induce in addition to yaw, to the point where it acts more like an aileron if it is far enough. Which is actually one way to think of the rudder, as a single, asymmetric aileron.

When your aircraft rolls because you applied rudder, what I think happens when you release the rudder is one wing will create more lift, and depending on the design, roll the plane back towards the starting point. You can either apply opposite roll at the same time you apply rudder to lessen the reaction, or you can apply roll afterwards to stop the plane from rolling back on its own. You'll probably also need to apply some pitch at the same time if you want to keep the nose pointing in the same direction. This also ties into the sideslip technique mentioned above by QF9E to reduce your airspeed.

All of this is significantly more difficult if you're flying with keyboard controls, but it is definitely something one can learn. Use short, small taps on the keys, observe how the aircraft reacts, and repeat until you get a feeling for it. Of course, you need to turn off SAS (you really shouldn't have it on to begin with) or it will simply mask your inputs with its attempts to counteract.

[Meecrob]

I think the biggest point to be made regarding rudder is that it is literally secondary. Control the aircraft with pitch and roll and then use yaw to fine tune. When you roll using ailerons placed outboard on the wings, the ailerons will induce a yaw away from the direction of roll due to differential drag (remember all lift creates drag!). So unless you are way advanced and trying to squeeze the DV out of your craft, just don't use rudder. It will just increase your drag if you don't know how to use it. It does not change your aircraft's velocity vector, It just changes where your nose is pointed.

[Klapaucius]

44 minutes ago, Meecrob said:

I think the biggest point to be made regarding rudder is that it is literally secondary. Control the aircraft with pitch and roll and then use yaw to fine tune. When you roll using ailerons placed outboard on the wings, the ailerons will induce a yaw away from the direction of roll due to differential drag (remember all lift creates drag!). So unless you are way advanced and trying to squeeze the DV out of your craft, just don't use rudder. It will just increase your drag if you don't know how to use it. It does not change your aircraft's velocity vector, It just changes where your nose is pointed.

In KSP I find the rudder almost useless. In fact, i was so used to that I got caught out playing a flight simulator where it actually did something useful.

[Meecrob]

What did it do? Out of curiosity...not to be a jackass haha

Edited to add: its interesting how people react to flying controls. And makes me sit down and think.

Edited May 25, 2020 by Meecrob

[QF9E]

51 minutes ago, Meecrob said:

I think the biggest point to be made regarding rudder is that it is literally secondary. Control the aircraft with pitch and roll and then use yaw to fine tune. When you roll using ailerons placed outboard on the wings, the ailerons will induce a yaw away from the direction of roll due to differential drag (remember all lift creates drag!). So unless you are way advanced and trying to squeeze the DV out of your craft, just don't use rudder. It will just increase your drag if you don't know how to use it. It does not change your aircraft's velocity vector, It just changes where your nose is pointed.

Your point cannot be stressed enough. Airplanes DO NOT TURN by giving yaw input (well, technically they can do a flat turn but it will look really awkward). Airplanes turn by banking them, which means the lift vector points to the side a bit. This sideways force pulls the plane into a turn. It also means that the lift vector isn't pointing upwards as far, so if you don't correct for it the nose will drop in a turn. The correct way to execute a turn is to bank, then pitch up slightly. If it is a sustained turn, then use pitch trim to keep the plane in that orientation.

The fact that KSP by default enables all control axes for all control surfaces does not help either. You really should disable roll on the vertical stabilizer or else your plane will do a combined roll / yaw every time you want to do a roll. I hardly ever give yaw input in KSP, unless I want to do a side slip.

Edited to add a little story that I find quite amusing: I have had a few real-world glider flying lessons, and my instructor was surprised and a bit annoyed that I knew all this going in. My nerdy attitude at the time would not have helped with his annoyance either: He asked me when telling about the plane on the ground what happens when you pull back on the stick. I answered "the elevator will turn upward". "And what happens next?" "Nothing. This plane is stationary on the ground at the moment." In hindsight he probably was looking for the answer "the nose will pull up". Same will roll input: "What happens when you apply roll input?" "The plane will yaw in the opposite direction." Which is true, especially gliders suffer quite badly from adverse yaw due to their aerodynamics. But not what he wanted to hear ("The plane rolls in the direction that you move the stick"). Should not be surprising that I quit after just a few lessons.

Edited May 25, 2020 by QF9E

[Meecrob]

1 minute ago, QF9E said:

Your point cannot be stressed enough. Airplanes DO NOT TURN by giving yaw input (well, technically they can do a flat turn but it will look really awkward). Airplanes turn by banking them, which means the lift vector points to the side a bit. This sideways force pulls the plane into a turn. It also means that the lift vector isn't pointing upwards as far, so if you don't correct for it the nose will drop in a turn. The correct way to execute a turn is to bank, then pitch up slightly. If it is a sustained turn, then use pitch trim to keep the plane in that orientation.

The fact that KSP by default enables all control axes for all control surfaces does not help either. You really should disable roll on the vertical stabilizer or else your plane will do a combined roll / yaw every time you want to do a roll. I hardly ever give yaw input in KSP, unless I want to do a side slip.

 

Something about what you said makes me want to say this...If you need to hold nose up attitude when banking less than 45*, you don't have enough wing.

 

And the other part of me feels stupid for not suggesting what @QF9E said...uncouple all your control surfaces...you don't want your roll control to influence your pitch, but by default, KSP connects them.

[QF9E]

5 minutes ago, Meecrob said:

Something about what you said makes me want to say this...If you need to hold nose up attitude when banking less than 45*, you don't have enough wing.

I am going to disagree with you on that one. Whenever you roll the plane, regardless of the amount, the vertical component of the lift vector will be less than when flying straight. This is even true for real-life gliders. It is not very pronounced, and certainly not in KSP with its simplified flight model, but I've also experienced it in KSP. In KSP I use pitch trim to keep the nose up.

 

[Meecrob]

We will probably agree to disagree, but I feel that unless you are designing an aerobatic aircraft or fighter jet, 45* of bank is useless unless you messed up. So I guess what I am saying is that there are KSP players wondering why their planes won't do certain things, and I think they are trying to bank basically airliners to aerobatics standards...treat your space shuttle like a baby in a carriage kinda thing.

[QF9E]

2 minutes ago, Meecrob said:

We will probably agree to disagree, but I feel that unless you are designing an aerobatic aircraft or fighter jet, 45* of bank is useless unless you messed up. So I guess what I am saying is that there are KSP players wondering why their planes won't do certain things, and I think they are trying to bank basically airliners to aerobatics standards...treat your space shuttle like a baby in a carriage kinda thing.

On that point we agree. Cessnas and airliners *can* do high bank turns (don't discount the maneuverability of an empty airliner with just enough fuel onboard to complete a demo display) but it should not be necessary in normal operation. In my space shuttle I'll do high bank turns mostly to shed excess speed. I have been doing 90 degree banked turns and even split-S, but that is because my energy management is something that I need to work on. As you say, if everything goes right you don't need that kind of maneuvers.

[Meecrob]

I think this is the biggest issue...you and I and a  bunch of other players are experienced in atmospheric flight...and KSP introduces orbit and transfers...so a bunch of players understand orbital mechanics but not atmospheric flight. Here is a vid about what you can do with low weight!

 

[Klapaucius]

3 hours ago, Meecrob said:

I think this is the biggest issue...you and I and a  bunch of other players are experienced in atmospheric flight...and KSP introduces orbit and transfers...so a bunch of players understand orbital mechanics but not atmospheric flight. Here is a vid about what you can do with low weight!

 

I studied Russian and lived there 1996-98. It was amazing in the very opposite sense to watch an IL-86 take off at Sheremetevo.  I have never seen anything that seemed less keen on getting in the air (some of my early KSP designs excepted).  

[Meecrob]

Well, of course there is always this classic video...and to make this on topic, this is the result of overloading your aircraft/having not enough wing for the weight you are trying to lift. There is nothing wrong with this approach necessarily, but that's like saying "its fine to scare old people, just make sure they don't have a heart attack and you're good!"

 

[AHHans]

2 hours ago, Meecrob said:

Well, of course there is always this classic video...

Hmmmm... Is it also a liftoff when you get the wheels of the runway by raising the gear?
(Assuming that you don't fall back to the runway.)

[Meecrob]

But seriously, when you get a bunch of pilots together, anytime you leave the ground and don't bend metal is a successful take-off! Even that 12-foot hop you did in the tail dragger going over a bump while trying your actual take-off!

 

Edited to add: The B-52 has such an angle of incidence it points nose down while gaining altitude.

 

Mods, please tell me if I am breaking rules by linking these pics and videos, I can host them, but I'm lazy. Just say the word and I'll do this properly haha

Edited May 25, 2020 by Meecrob

[Meecrob]

Actually, let me share a story from my flight training regarding take-offs. So like most student pilots, I flew a crappy Cessna since I'm not a billionaire. I was doing a check ride to renew my currency (you need to fly within two weeks to keep flying solo before your license and I had not flown in 3 weeks). I was to do two circuits (laps around the airport to those who are smart enough to not pour all their money into flying)...when I did my pre-flight checks, I had a bad mag drop on the left magneto, but my instructor said it was fine...so I flew one circuit...no problem...then did a touch and go...and the engine basically said "screw you" so I was in this position where I knew the Cessna had crap brakes...I'm doing basically a wheelie down the runway with 50% engine power and hoping that I make 67 knots for best climb rate... I dragged that plane into the air and ATC was saying "Land anywhere you can, just get it down safely, We declared emergency for you". In hindsight this was really really stupid of me, but I was 16 and invincible...so my point is that just because you can take off, doesn't mean you should. Engineer extra lift into your designs so the aircraft leaps off the runway...If you wait for the drop off at the end of the runway in KSP, your plane needs more power or lift or both.