Flying Spaceplanes: Rudder or Roll to turn?

[Diazo]

I'm currently struggling with flying spaceplanes and was looking to see how people handle turning specifically.

I'm also having issues with trying to use the on/off control states the keyboard allows to handle the analog control you really need to control a spaceplane smoothly, but I'm really asking about turning in this thread.

I've poked around and the forums and read some general airplane theory and it looks like there are 3 main options.

1) Force the turn with the rudder and only using roll to keep the plane level. While this method seems to work in KSP, at least for smaller planes, I was unable to find any example of using this on larger planes in KSP.

2) Roll into a bank and let the plane carry you through the turn. This seems to be the 'ideal' way to do things if you can manage it, but it is somewhat imprecise, at least in KSP as we don't have a panel full of instruments in front of us.

3) Roll into a bank to turn, but tweak as needed with the rudder. This sounds like the way things end up being in KSP. Let the bank do most of the turning, but tap the rudder as needed to end up on our desired course. If this is the method you use, how much rudder do you end up needing?

So, for those that are able to take off and land with their space planes, how to you tackle your turns?

D.

[RocketPilot573]

If I need to do a hard turn. I roll 90 degrees over and pitch up. If close to the ground, I roll over like 45 degrees while using pitch AND rudder.

[Link]

3) Roll into a bank to turn, but tweak as needed with the rudder. This sounds like the way things end up being in KSP. Let the bank do most of the turning, but tap the rudder as needed to end up on our desired course. If this is the method you use, how much rudder do you end up needing?

That's essentially how it's really done, or at least that's my understanding from the years of playing flight simulator. I'm sure a real pilot could chime in better. Unfortunately for me, and my time playing in flight simulators, I sort of tackle planes in ksp the same way as my flight simulators. I'll do a 15-20 degree bank roll, let my prograde turn and use my rudder to try keeping my nose level to try not gaining nor loosing altitude. On stock ksp, I have severe issues trying to use rudder controls, as I usually end up loosing control. Obviously FAR fixes *most* of that. Quite honestly tho, since it is just a game, it's all a matter of preference and controls available. I use a joystick, so it's much easier for me to roll than trying to use Q or E. Also, using just your rudder to turn can lead to some proper instability. While not exactly noticed in stock, it's noticed with more realistic aerodynamics. Personally, I consider the rudder to be used for small course corrections only, not for large deviations from the current vector. But again, I guess it's all more of a personal thing. I hope this helps a tad

[cantab]

I've not flown planes much, but when I have my approach has been to do more or less as in the real world.

First set up my control surfaces. Elevators/canards do pitch only, ailerons do roll only, rudders do yaw only. Of course some ships might have ruddervators, elevons, etc. And pod torque goes OFF.

In level flight I tend to use SAS to hold my heading. I can use pitch trim instead, but SAS is easier.

Then to make a large turn I turn SAS off, bank the plane, and use pitch to keep the nose up if need be. I tend to ignore the rudder. If I want to make a fine tweak I might instead do a rudder turn for that.

Digital controls are indeed difficult to fly with. I've ended up having to rapidly tap them, and often have to settle on not making a perfect level flight but rather letting the plane slowly climb or descend.

Edit: To quote Wikipedia,

Coordinated flight is usually preferred over uncoordinated flight for the following reasons:

it is more comfortable for the occupants

it minimises the drag force on the aircraft

it causes fuel to be drawn equally from tanks in both wings

it minimises the risk of entering a spin

The first, second I think , and third of those are irrelevant for stock KSP. So only if spinning is an issue do you need to coordinate your turns.

Edited June 30, 2014 by cantab

[LethalDose]

I use number 3 (roll and rudder) for hard turns and number 2 (roll only) to adjust my heading, typically to land or adjust my orbital inclination during insertion. If it matters, I use FAR, instead of the stock aero model.

[Khorso]

Seeing as how there are usually many more control surfaces for rolling than for ruddering, I find rolling to be more efficient, and always opt for that.

You can maximize the effect(yaw?) of a rudder by having it placed far away from the center of mass, however. That's part of what makes elevators so powerful for pitch control, alongside tail-fins.

With that being said, you'll get an extra boost to your turn using both roll and rudder- I just find rudder control gains alone to be lost too quickly. Roll is always my primary.

For overall controllability, the rule of thumb is that the closer your center of lift is to your center of mass, the more reactive your control will be. This is linked to, yet still separate from the distance of the control surface from your CoM/CoL. You'll want your CoM to always nudge a bit in front of your CoL however, or you run the risk of your tail-end leading in any 'controlled' fall/stall. I just installed TAC Fuel Balancer for precise in-flight fine-tuned Center of Mass rebalancing.

As for instrumentation- I use RPM for IVA, and KER for general tuning.

Ultimately - How fine do you want your turning control to be?

-Khorso

[Sky_walker]

I usually do Roll+Yaw with slight pitch correction. Yea, plenty of clicking, but this allows very precise manuevers and at the same time it's quite intuitive with current weird areodynamics. Pure roll+pitch somehow doesn't work for me too well - i tend to loose attitude too much and roll back a bit too late... Or too early :/

[Epthelyn]

For smaller, agile, aircraft I use option 2. For larger aircraft option 3, mostly because pitching up in anything less than a 90* roll will increase altitude slightly. To be honest I don't usually care about that altitude gain unless I'm attempting to land; in those cases I make sure I'm on course for the runway long enough before the landing to ensure that anything awry can be fixed with time to spare.

The amount of banking depends entirely on the aircraft you're using and the control surfaces providing the yaw force.

[Master Tao]

There's also my favorite option:

4) Roll about 80 degrees over and pull up. Results may include rapid turns, high gees, and unplanned aerodynamic failures.

I tend to use the rudder for the slight adjustments when landing and maintaining attitude while turning.

[EdFred]

This is actually an argument in real life (although the argument comes down to semantics really).

In real life you use all three axes to turn. You initiate a roll with the ailerons which causes the vector of lift to rotate to the left or right - creating a smaller vertical component of lift, and adding a horizontal component of lift. At the same time the plane will start to slip, so rudder in the direction of the turn is needed to keep this from happening. Some planes have more tendency to do this than others. And since the vertical component of lift is now decreased, you also need elevator (stabilator in some planes) to raise the nose to keep from losing altitude. Although when I only need a few degrees of left/right correction, I will make turns with only rudder - like when I am on final approach segment of an instrument approach.

I fly the same say in KSP as I do real life.

Edited June 30, 2014 by EdFred

[costermonger]

This is actually an argument in real life (although the argument comes down to semantics really).

In real life you use all three axes to turn. You initiate a roll with the ailerons which causes the vector of lift to rotate to the left or right - created a smaller vertical component of lift, and adding a horizontal component of lift. At the same time the plane will start to slip, so rudder is needed to keep this from happening. And since the vertical component of lift is now decreased, you also need elevator (stabilator in some planes) you raise the nose to keep from using altitude. Although when I only need a few degrees of left/right correction, I will make turns with only rudder - like when I am on final approach segment of an instrument approach.

I fly the same say in KSP as I do real life.

The way I teach it is that the banked condition redirects some lift and causes the slip as described, but the weather-vane effect of the vertical stabilizer is what actually causes the yaw.

From my relatively limited time flying aeroplanes in KSP, it seems like it doesn't quite compute the physics for turns the way it should (mainly the slip and resulting yaw), but an exaggerated version of the real life control inputs (mainly, more rudder) does the job.

[EdFred]

The way I teach it is that the banked condition redirects some lift and causes the slip as described, but the weather-vane effect of the vertical stabilizer is what actually causes the yaw.

From my relatively limited time flying aeroplanes in KSP, it seems like it doesn't quite compute the physics for turns the way it should (mainly the slip and resulting yaw), but an exaggerated version of the real life control inputs (mainly, more rudder) does the job.

Yep as you make the initial turn the relative wind impacts the vertical stabilizer pushing the tail inside of the turn, and the nose to the outside of the turn. A slip. The nice thing about a slip, is even if you stall it is pretty much impossible to enter a spin. I will sometimes have students do a stall while in a slip. Too much inside rudder though, and you've got the classic overcompensating base to final spin.

I've found planes with more dihedral have less tendency to yaw. Which is why we joke that the rudder pedals in the PA28 series are just for foot rests. Cessnas seem to need more rudder input on turns.

[Hodo]

As in real life it is generally better to bank turn then yaw turn. This is mainly for the reasons someone else listed, fuel flow issues, aerodynamic drag forces, and crew and passenger comfirt. But it is also more effecient to roll and turn. This is because your wings are the largest lift generating force on the aircraft, so why not use them to change direction.

[iFlyAllTheTime]

I fly the same say in KSP as I do real life.

This is off topic but, what do you fly in real life?

[EdFred]

This is off topic but, what do you fly in real life?

If I go through my logbook, I've probably got about 20 different types of airplanes I've flown - though I'm sure I've forgotten some. The largest I've flown is a King Air. Anything larger than that, and you get into needing a type rating for each specific aircraft. The most fun was flying aerobatics in an Extra 300. I currently own a Piper Comanche.

[Claw]

Not only does it depend highly on the airplane (as others have said), It also depends on how much AoA is on the airplane. Generally speaking, more AoA means the rudder is more effective at turning, while the ailerons are less effective. Which one works better at any given time will depend on the airplane.

The thing is for most typical flight though, it generally isn't the rudder that does the turning. It's because you are in bank. You might need to add rudder to overcome the sideslip and/or induced yaw from establishing and holding the roll angle. That's actually what you're doing to coordinate a turn.

That's all great and all, but KSP isn't exactly real life. However, stock KSP actually does a half way descent job replicating these things. (Which is part of why I think stock aero isn't totally horrible.)

So, for example, if you have a plane with a lot of wing (like a sail plane) then it will require a descent amount of rudder WHILE you have roll in to get it to turn faster. Even in KSP.

And if you add some pitch up (while rolled into turn) it will turn faster. Some pitch up is required if you want to maintain level flight. Some designs will require pitch up to turn at all when in roll.

[Starlionblue]

In heavy jets we don't touch the rudder pedals at all except on the ground, while decrabbing on touchdown and in an engine-out situation. We only use pitch and roll inputs to steer the aircraft. You roll into a turn and apply backpressure on the stick/yoke to maintain the nose level. Backpressure is needed because load factor on the wings increases in a turn.

Importantly, this doesn't mean the rudder doesn't move. We just don't make the inputs ourselves. The yaw damper system moves the rudder to ensures turns are coordinated, in other words we're not "skidding" in a turn but the longitudinal axis of the aircraft follows the turn neatly. Same as you (should) do in a lighter aircraft with your feet on the rudder pedals.

Why the yaw damper? Swept wing planes typically have a tendency to enter a coupled roll-yaw motion known as Dutch Roll, which is uncomfortable and potentially dangerous. Apart from turn coordination, the yaw damper counters Dutch Roll tendencies. You can easily see Dutch Roll in KSP planes if you don't have enough stability in yaw (not enough vertical fin area basically). The plane will rock side to side while rolling with the nose drawing a figure of eight.

I'd love to see a yaw damper mod for KSP, because frankly any plane with that kind of geometry performance should have one.

Edited April 18, 2016 by Starlionblue

[EnderKid2]

There's a 4th option: roll 90*, then pull up hard. It's called bank n yank, often used in 3 channel RC flying wings or jets.

[Starlionblue]

7 hours ago, EnderKid2 said:

There's a 4th option: roll 90*, then pull up hard. It's called bank n yank, often used in 3 channel RC flying wings or jets.

Indeed, but this only really works with very maneuverable aircraft. Since you can't hold altitude (without rudder application) it's not very practical for larger aircraft with a slower roll rate.

[HebaruSan]

When turning in the atmosphere as opposed to space, you don't just want to turn the craft, you also want to rotate your velocity vector.

On 6/30/2014 at 1:13 PM, Diazo said:

1) Force the turn with the rudder and only using roll to keep the plane level. While this method seems to work in KSP, at least for smaller planes, I was unable to find any example of using this on larger planes in KSP.

This is great at turning the craft, but with minimal lift/drag to affect your velocity vector, the main thing that turns your velocity vector is going to be your engines pointing off prograde. This is a less effective option than...

On 6/30/2014 at 1:13 PM, Diazo said:

2) Roll into a bank and let the plane carry you through the turn. This seems to be the 'ideal' way to do things if you can manage it, but it is somewhat imprecise, at least in KSP as we don't have a panel full of instruments in front of us.

Just rolling won't do a huge amount to turn the craft or your velocity vector by itself. But for both this item and #3, if we also pitch up, now the force of our big wings and control surfaces is pushing against the air that's speeding at us and deflecting us to the direction we want to go, like a sail on a boat. This is added to the engine angling that we had in option #1, so as compared to #1, we now have a larger force turning our velocity vector directly, and the craft can follow prograde as it moves.

On 6/30/2014 at 1:13 PM, Diazo said:

3) Roll into a bank to turn, but tweak as needed with the rudder. This sounds like the way things end up being in KSP. Let the bank do most of the turning, but tap the rudder as needed to end up on our desired course. If this is the method you use, how much rudder do you end up needing?

I don't see this as a separate option from #2. If your nose starts to drift away from prograde too much, you have to adjust with yaw to maintain control of the plane.

To sum up, as others said, I roll, then pitch up, then use yaw to keep the navball's nose marker upwards of the prograde vector.

[Geschosskopf]

On 6/30/2014 at 1:13 PM, Diazo said:

I'm currently struggling with flying spaceplanes and was looking to see how people handle turning specifically.

I'm also having issues with trying to use the on/off control states the keyboard allows to handle the analog control you really need to control a spaceplane smoothly, but I'm really asking about turning in this thread.

I've poked around and the forums and read some general airplane theory and it looks like there are 3 main options.

1) Force the turn with the rudder and only using roll to keep the plane level. While this method seems to work in KSP, at least for smaller planes, I was unable to find any example of using this on larger planes in KSP.

2) Roll into a bank and let the plane carry you through the turn. This seems to be the 'ideal' way to do things if you can manage it, but it is somewhat imprecise, at least in KSP as we don't have a panel full of instruments in front of us.

3) Roll into a bank to turn, but tweak as needed with the rudder. This sounds like the way things end up being in KSP. Let the bank do most of the turning, but tap the rudder as needed to end up on our desired course. If this is the method you use, how much rudder do you end up needing?

So, for those that are able to take off and land with their space planes, how to you tackle your turns?

Well, my spaceplanes don't need to turn except during the landing approach, which can range from a minor dogleg to account for a slight inclination issue, to doing a split-S after an overshoot.  So generally, my spaceplanes only turn at subsonic speeds.  Turning at higher speeds is usually both wasteful and destructive .  As a result, my spaceplanes turn the same as my planet-side planes.  But they also have to fly perfectly straight on ascent, which requires proper control mechanics, and that's just as important as turning.

IMHO, the single biggest problem with controlling ANYTHING in KSP is engine gimbal.  I find it totally counterproductive so I always disable it.  This is VERY important on spaceplanes because a twitchy engine will throw you off your ascent path with ease.

Another thing I always do on spaceplanes (and usually on planet-side planes, too), is to put my rudders out on my wingtips and have just a fixed vertical fin for stability.  This prevents the rudder from introducing adverse roll.  For rudders, I use the small, square control surfaces, sometimes 2 per wing on larger planes.  They're vertically mounted on the wing trailing edges, and the wings are centered on the fuselage.

As for actually turning, I roll into it, pull the nose around with the elevators, and use top or bottom rudder as needed to control my altitude during the turn.

[FullMetalMachinist]

ummm.... @HebaruSan and @Geschosskopf, you guys know that this is a necro from almost two years ago, right?

[HebaruSan]

Just now, FullMetalMachinist said:

ummm.... @HebaruSan and @Geschosskopf, you guys know that this is a necro from almost two years ago, right?

Nope, hadn't noticed.

[Starlionblue]

 

Only noticed it was a necrothread after I responded to it. Oops!

 

5 hours ago, FullMetalMachinist said:

ummm.... @HebaruSan and @Geschosskopf, you guys know that this is a necro from almost two years ago, right?

[Diazo]

Heh, it's actually worthwhile as I actually have a half written mod on my computer that I started back when I created this thread. It's a basic mouse control for pitch/roll with automatic rudder input that I think qualifies as "yaw damper", at least a rough one so I may actually finish it one of these days.

Can't look at it at the moment due to 1.1 updates on my other mods, but it's not something I'm going to say is abandoned at this point.

D.

Edited April 19, 2016 by Diazo