Official FAR Craft Repository

[Kitspace]

Thank you for your reply!

Angle of attack is about twenty degrees with maximum controls deflection. It is supposed to be slightly less though but the plane does get thrown above the calculated maximum values.

My wing load is high indeed because I am currently specifically trying to design something similar to the supersonic interceptors from the sixties.

Is it possible that planes of such proportions will not fly normally in game because kerbal parts are more dense than real life?

In this case how do guided missiles and various other things of that sort manage such high gee turns with wing loads much higher than any plane out there?

I do not have any active stability or piloting assist things enabled at all when flying these planes. They are not supposed to have any supermaneuverabilty features or be unstable or something so I consider that to be cheating to some extent.

But they just love being thrown beyond the values that they are to stabilize at even from smooth control inputs as mentioned above. The stability derivatives simulation shows almost infinite oscillation as well. It feels like the plane is stable but has no natural damping at all so it takes it a lot of time to settle into its sweet spot after any changes in the flight profile. Any suggestions on how to improve that?

As far as I understand it in the real life those kinds of sleek fast planes required input to stop rotating in roll axis because of small wingspan and aspect ratio but certainly did not wobble like this in the pitch axis.

In game currently actively attempting to stop it oscillating would probably make it worse until the plane goes out of control.

[FourGreenFields]

11 hours ago, Kitspace said:

Thank you for your reply!

Angle of attack is about twenty degrees with maximum controls deflection. It is supposed to be slightly less though but the plane does get thrown above the calculated maximum values.

My wing load is high indeed because I am currently specifically trying to design something similar to the supersonic interceptors from the sixties.

Is it possible that planes of such proportions will not fly normally in game because kerbal parts are more dense than real life?

In this case how do guided missiles and various other things of that sort manage such high gee turns with wing loads much higher than any plane out there?

I do not have any active stability or piloting assist things enabled at all when flying these planes. They are not supposed to have any supermaneuverabilty features or be unstable or something so I consider that to be cheating to some extent.

But they just love being thrown beyond the values that they are to stabilize at even from smooth control inputs as mentioned above. The stability derivatives simulation shows almost infinite oscillation as well. It feels like the plane is stable but has no natural damping at all so it takes it a lot of time to settle into its sweet spot after any changes in the flight profile. Any suggestions on how to improve that?

As far as I understand it in the real life those kinds of sleek fast planes required input to stop rotating in roll axis because of small wingspan and aspect ratio but certainly did not wobble like this in the pitch axis.

In game currently actively attempting to stop it oscillating would probably make it worse until the plane goes out of control.

(Quote please, as that triggers notifications if you enable that setting - doesn't matter much because I check this thread regularly, but others you're talking too may not)

 

If the wing area and weight are roughly the same as on the RL planes, they should turn roughly the same (if you're using the same wing shape, etc.). Maybe screenshot(s)?

[Kitspace]

Here are the screenshots of a typical example.

It is actually my most successful one so far even though it still wobbles a bit at low speeds and wobbles a lot if you are not careful with it.

I made it after realizing that the kerbal fuselage is too wide and it takes a bigger portion of the wingspan than the real prototypes so the wing area is likely to be incorrect when the overall proportions are more or less correct.

I am actually thinking of adopting it for the air defence force of the space center as it is actually good enough to be flown by someone other than drunken Jeb.  Of course kerbals do not drink and drive so Jeb had to be forced in the cockpit to test the previous versions.

http://imgur.com/a/YIUSC

Edited February 29, 2016 by Kitspace

[FourGreenFields]

2 hours ago, Kitspace said:

Here are the screenshots of a typical example.

It is actually my most successful one so far even though it still wobbles a bit at low speeds and wobbles a lot if you are not careful with it.

I made it after realizing that the kerbal fuselage is too wide and it takes a bigger portion of the wingspan than the real prototypes so the wing area is likely to be incorrect when the overall proportions are more or less correct.

I am actually thinking of adopting it for the air defence force of the space center as it is actually good enough to be flown by someone other than drunken Jeb.  Of course kerbals do not drink and drive so Jeb had to be forced in the cockpit to test the previous versions.

http://imgur.com/a/YIUSC

First things first: Clip the gear into the fuselage to avoid it killing your speed. Also, longer leading and trailing edges reduce drag as well (at least I suppose they reduce it - definitly not making it worse either way, except you can carry less fuel). And the wings seem kinda thick, might want to reduce at least the tip thickess too.

As for the turning, are you trying to turn with full fuel load? Pretty sure you don't need that much for an interceptor (assuming both white fuselage parts are LF tanks). Is the weight anywhere near the RL weight of Interceptors of that time? (max takeoff weight for the HA-300 would've been about 5450kg, and it's 8625kg for the MiG-21 F13)

Still no idea 'bout the wobble though. Going to try and make a new Heluan HA-300 replica now, and see how it goes.

 

EDIT: Pitch wobble isn't any worse than on other planes (= not noticable when pulling steadily), and turns good (except it bleeds all its speed) (but does have lower wing loading than the real thing afaIk)

Edited February 29, 2016 by FourGreenFields

[Kitspace]

The wings are half the default thickness and the fins are quarter the default thickness. Do you think it is better to make them even thinner? I assume it does not affect structural integrity in game?

Both of those fuselage parts are fuel tanks but the wing holds no fuel at all. I know that is an unrealistic amount but this configuration is required for balance as the empty center of mass is right between two sections and the plane does not have a lot of tolerance for the center of mass changes at all. Probably best way would be to try and replace both of those with structural parts and stick as much fuel in the wing as possible as it would be in real life.

It was never actually expected to fly with the full load all the time though. The maximum takeoff weight is nine tonnes as of now. Normal for short missions would be around seven probably. But still cuts through air like hot knife through butter and needs to be flown down the glideslope with the speed brakes open.

[FourGreenFields]

6 minutes ago, Kitspace said:

The wings are half the default thickness and the fins are quarter the default thickness. Do you think it is better to make them even thinner? I assume it does not affect structural integrity in game?

Doesn't affect structural integrity afaIk. Does affect cross section though -> affects drag. So unless you need the fuel, thin wings are better until FAR updates wing calculations.

[Kitspace]

1 hour ago, FourGreenFields said:

Pitch wobble isn't any worse than on other planes (= not noticable when pulling steadily)

So is that wobbling common for kerbal planes?

Any idea why is it so hard to get rid of it in game while in real world it seems to be harder than not to even notice? Even if you throw a brick with some fins at the back it will not wobble like this, right?

Edited February 29, 2016 by Kitspace

[FourGreenFields]

6 minutes ago, Kitspace said:

So is that wobbling common for kerbal planes?

Any idea why is it so hard to get rid of it in game while in real world it seems to be harder than not to even notice? Even if you throw a brick with some fins at the back it will not wobble like this, right?

It doesn't wobble the way you described it, it only wobbles at all with sudden change in pitch input (as said, not noticable when pulling steadily).

So no, it's not common for kerbal planes I'd say.

[Kitspace]

But real planes will just stall if you pull back very suddenly not start bouncing like a ball, right?

EDIT

By the way what is the capsule and parachute toolbar icon on the picture that says SR?

Edited February 29, 2016 by Kitspace

[FourGreenFields]

1 hour ago, Kitspace said:

But real planes will just stall if you pull back very suddenly not start bouncing like a ball, right?

Depends on the plane I suppose. If you can't pull enough AoA to stall, and even the inertia won't make you reach critical AoA, then the plane won't stall obviously.

 

1 hour ago, Kitspace said:

By the way what is the capsule and parachute toolbar icon on the picture that says SR?

Stage Recovery. Auto-recovers stages, calculating funds return on the number and size of parachutes vs weight (= speed) and distance from KSC.

[Hodo]

6 hours ago, Kitspace said:

But real planes will just stall if you pull back very suddenly not start bouncing like a ball, right?

EDIT

By the way what is the capsule and parachute toolbar icon on the picture that says SR?

An aircraft will "bounce" when you pull to much AoA and stall the wings out.  As the plane pitches back down the wings will suddenly bite into the air and provide lift again.  If you are still pulling back they will attempt the same move again.  

 

The Mig-21 was actually pretty bad for this affect in real life.  If you attempted low speed high G maneuvers it would buffet violently till it stalled hard.  

 

If you are flying with SAS turned on it will bounce in game due to the way SAS works in KSP.  I would suggest getting a PID tuner which will help you negate that bounce. 

 

Keep flying!

[Vegemeister]

On 2/28/2016 at 3:01 PM, Kitspace said:

Thank you for your reply!

Angle of attack is about twenty degrees with maximum controls deflection. It is supposed to be slightly less though but the plane does get thrown above the calculated maximum values.

My wing load is high indeed because I am currently specifically trying to design something similar to the supersonic interceptors from the sixties.

Is it possible that planes of such proportions will not fly normally in game because kerbal parts are more dense than real life?

In this case how do guided missiles and various other things of that sort manage such high gee turns with wing loads much higher than any plane out there?

I do not have any active stability or piloting assist things enabled at all when flying these planes. They are not supposed to have any supermaneuverabilty features or be unstable or something so I consider that to be cheating to some extent.

But they just love being thrown beyond the values that they are to stabilize at even from smooth control inputs as mentioned above. The stability derivatives simulation shows almost infinite oscillation as well. It feels like the plane is stable but has no natural damping at all so it takes it a lot of time to settle into its sweet spot after any changes in the flight profile. Any suggestions on how to improve that?

As far as I understand it in the real life those kinds of sleek fast planes required input to stop rotating in roll axis because of small wingspan and aspect ratio but certainly did not wobble like this in the pitch axis.

In game currently actively attempting to stop it oscillating would probably make it worse until the plane goes out of control.

The bouncing you're seeing is the short period pitch oscillation. I'm not sure what exactly is responsible for damping it, but it seems to be less severe with a smaller horizontal stabilizer farther from the center of mass, compared to a big one close to the CoM.  Unfortunately, it's difficult to avoid exciting it if you're controlling your plane with a keyboard.  The usual suggestion is to avoid sudden stick movements, but the keyboard only gives you full deflection or no deflection.  If you're PWM-ing with a keyboard, I think you'd be less likely to excite that mode if your PWM frequency was well above the frequency of the oscillation.  You might try moving fuel toward the nose and tail, away from the CoM, in order to increase the moment of inertia and therefore the period of the oscillation.

Remember lift is roughly proportional to the square of speed, so at high speed you don't need much wing to produce a lot of lift (and a high g-load). But also remember centripetal acceleration is v^2/r, and rate of turn (ω) is v/r. For a fixed g-loading limit (either of the plane or of the pilot), if you double the speed, you have to quadruple the turn radius, which means you halve the turn rate. Conversely, you can double the turn rate by halving the speed. If you want a high turn rate without ripping the wings off or chunky salsa ruling the pilot, you can turn at lower speed, but you need more wing to produce the same g-loading.  Interceptors were mainly designed for climbing fast and flying fast, with less emphasis on low-speed maneuverability.  At high speed, maneuverability is going to be limited by structure or physiology.

 

[NotAnAimbot]

How do you place struts without your plane looking like Frankenstein? I've heard about clipping them, but it doesn't work for me. The planes are solid enough, but they just look ugly.

 

Also, what pitch sensitivity do you usually choose? I'm oscillating between 20 and 40, which seem to be the treshold to make my planes turn well but not rip themselves apart.

 

[FourGreenFields]

8 hours ago, NotAnAimbot said:

How do you place struts without your plane looking like Frankenstein? I've heard about clipping them, but it doesn't work for me. The planes are solid enough, but they just look ugly.

I'm not placing struts. KJR (Kerbal Joint Reinforcement) ftw!

8 hours ago, NotAnAimbot said:

Also, what pitch sensitivity do you usually choose? I'm oscillating between 20 and 40, which seem to be the treshold to make my planes turn well but not rip themselves apart.

Depends alot on how you build your planes. Big elevator and low stability means you need less deflection to reach high AoAs - small elevator and high stability means you need high control surface deflection. A low wing-loading plane may also be able to get away with lower AoAs, and lower elevator deflection. And you can also use engine gimbal to assist you, if you somehow manage to pull enough when landing (maybe additional deflection as flap or stuff).

[Paul_Sawyer]

I'm having spaceplane fever

[Guest]

Ive been working on a new aircraft :

Edited March 16, 2016 by RevanCorana

[Good_Cat]

Has anyone got a working Skylon lookalike working.
I'm a FAR noob.
I've got the basics like area ruling down but i've nothing to compare mine to in terms of Cl and Cd figures along with what speeds / altitude should be stable at. Along with TWR's for FAR.

Edited March 19, 2016 by Good_Cat

[ss8913]

9 hours ago, Good_Cat said:

Has anyone got a working Skylon lookalike working.
I'm a FAR noob.
I've got the basics like area ruling down but i've nothing to compare mine to in terms of Cl and Cd figures along with what speeds / altitude should be stable at. Along with TWR's for FAR.

There's a lot of people that understand all of the actual numbers and what they mean; I'm in the process of learning this myself.  However that's the *science* of it.  What you really need to know is the *engineering* perspective of it.  Here's the quick guide to FAR plane design:

1. Go into the FAR menu in SPH and open the static analysis.  Click 'run analysis' and make sure there are no red numbers at 0.35 and 1.35 mach.

2. Lower the 0.35 until red numbers appear.  Never go below this mach # when flying.  (make sure to have the FAR window open in flight - also set your airspeed indication to indicated knots EAS.   This is what real aircraft use and is critical to knowing how much lift you're getting.  Your surface speed is pretty much irrelevant when you want to know your V speeds and stall speeds).

3. Now open the transonic design.  click the middle radio button for the yellow line.  The flatter it is the less mach buffeting you will get in the transonic zone (0.80 to 1.20 mach), and the less likely you are to have serious aerodynamic issues at high speed.

4. Are you using adjustable landing gear?  If not get it immediately.  This part isn't really FAR related but if you can't get the plane off the runway, FAR doesn't matter.  Use adjustable landing gear and never touch stock gear again.  ALG gives you an alignment indicator.  Make sure your wheels are not aligned to point away from the craft centerline.  If they are, use the rotation tool to fix that - about 1 degree of "toe in" towards the centerline will make the craft stable on the runway.  This does not apply to the nose gear.  Leave that alone as far as rotational alignment, but make sure it's shorter than the mains - you want 1 to 5 degrees of pitch down when sitting on the runway.  Set your spring and dampers to almost max on all gear.  Set main gear brake torque to between 60-100 depending on craft weight, and set the brake torque on the nose wheel to half of what you've set on the mains.  Turn shielding on for all gear.  Now FAR is relevant because you won't crash on takeoff or on your landing rollout

5. Use the FAR yaw stability helper when flying in atmosphere, even if you're using an autopilot.  This is like the yaw damper on real jets.  It helps.

6. Mechjeb even with the FAR helper module is not that great.  Kramax autopilot is a million times better than mechjeb for flying within atmosphere.  It is however completely useless in space, so I use both MJ2 and Kramax.

7. Kramax likes triangle shaped planes.  It can't follow a glideslope worth a **** if you have a plane with horizontal stabilizers and wings placed like on a commercial airliner.  Especially if you 1. have flaps and 2. use the flaps.  So you may need to control pitch yourself unless you have a triangle shaped plane (like the US space shuttle, with no independent elevators).


Follow the above tips and you too can have a fun and stable SSTO spaceplane that can land safely back on the KSC runway.  I also recommend KSP Interstellar Extended, because who *doesn't* like antimatter-powered thermonuclear hybrid turbojet/rocket engines giving you 80k dV in a Mark3 spaceplane?  I know I do

Here's a picture of one of my most successful designs.  This shape works well, and at about 25% fuel has a stall speed well under 200kts EAS, making it easy to land.  It's also got ATILLA arcjet VTOL engines with enough thrust to do a VTOL landing *anywhere*, even Eve.  The engines are also from KSPIE.  If you make a spaceplane using this layout (modify to suit), you'll have good results aerodynamically.

Edited March 19, 2016 by ss8913

[Good_Cat]

I've done a lot of reading but the information I've got nothing to apply or relate it to.

What the difference between the Cross Sectional Are Curve and Curvature Cross Sectional Area curve.
I understand how the Green line is calculated by lateral cross section area not the yellow, does it have something to do with Sears-Haack body.
The Blue line is air pressure so im expecting a positive spike at the nose followed by negative then shouldn't there be another positive spike on the leading edge and trailing edge, im thinking where the mach cones would be created or has this line something to do with aerodynamic drag??
Why the large spike on the trailing edge

I build this in stock and have tweaked it in FAR

[darkracer125]

it seems that stock airplane parts do not work in my game. 

c7 aerospace does not provide lift.  (centre of lift icon is set firmly on the ground)  and when right clicking control surfaces it does not allow me to set pitch yaw and roll.  

they are just structural parts.  

 

i do have other mods. but people have told me that ferram is the culprit. 

is there any fix for this. 

they do provide lift.  but in the same way as a fuel tank provides lift. 

c7 aerospace devision.  and the winterowl aircraft emporium.  any parts from those 2 manufacturers provide no control or extra lift.

[tetryds]

Hey @Good_Cat, @ss8913 and @darkracer125, I have moved your posts about craft design here.

I should make it a bit more explicit that this kind of discussion goes here, and poke @ferram4 about making that more obvious on the FAR OP.

Anyway, @Good_Cat, the yellow line is the second derivative of the green line, it basically means how "smooth" the green line is.

For example, if the green line is a straight line, regardless of the inclination, it will be zero.

If you put a straight line of fuel tanks of the same radius, the green line will be constant at the middle and have two sudden steps at the tips.
Every sudden step means a spike on the first derivative, a spike on the first derivative translates to two spikes on the second derivative (up then down).
It's not that complicated, but in order to decrease drag on the transonic region, you must decrease the Mach 1 wave drag area, and the closest to the zero the yellow line is, the lower wave drag area you get.

[Good_Cat]

1 hour ago, tetryds said:

Hey @Good_Cat, @ss8913 and @darkracer125, I have moved your posts about craft design here.

I should make it a bit more explicit that this kind of discussion goes here, and poke @ferram4 about making that more obvious on the FAR OP.

Anyway, @Good_Cat, the yellow line is the second derivative of the green line, it basically means how "smooth" the green line is.

For example, if the green line is a straight line, regardless of the inclination, it will be zero.

If you put a straight line of fuel tanks of the same radius, the green line will be constant at the middle and have two sudden steps at the tips.
Every sudden step means a spike on the first derivative, a spike on the first derivative translates to two spikes on the second derivative (up then down).
It's not that complicated, but in order to decrease drag on the transonic region, you must decrease the Mach 1 wave drag area, and the closest to the zero the yellow line is, the lower wave drag area you get.

Thx ,explained really well.:)

[winged]

Breaking the sound barrier with style:

 

 

 

 

[Rodhern]

On 2/22/2016 at 3:25 AM, Rodhern said:

I have this simple craft. It is a command pod, three girder boxes and four wing parts.

From looking at the picture I would guess that a positive pitch up rotation will induce a upward acceleration (negative Z-direction acceleration) as the wing surfaces are forced downwards. On the FAR stability derivatives tab however the Zq derivative is positive.

Hello @tetryds (and others)

I am  still missing the point of the sign in the above example. Can you tell me where the chain brakes:

1. An increased "q" means a faster pitch up rotation around the center of mass. The command pod will go (faster) towards up and the wing parts (faster) toward down.
2. When the increased "q" makes the wing parts move (faster) downwards the lift of the wings is increased.
3. The increased lift makes the entire craft (center of mass) accelerate upwards.
4. Upwards is opposite to the positive Z-axis direction; the acceleration caused by increased "q" is thus negative.

 

[Guest]

12 hours ago, Good_Cat said:

I've done a lot of reading but the information I've got nothing to apply or relate it to.

What the difference between the Cross Sectional Are Curve and Curvature Cross Sectional Area curve.
I understand how the Green line is calculated by lateral cross section area not the yellow, does it have something to do with Sears-Haack body.
The Blue line is air pressure so im expecting a positive spike at the nose followed by negative then shouldn't there be another positive spike on the leading edge and trailing edge, im thinking where the mach cones would be created or has this line something to do with aerodynamic drag??
Why the large spike on the trailing edge

I build this in stock and have tweaked it in FAR

Have you tried the mod Dynamic Deflection ? It links maximum deflection % to dynamic pressure and it's customizable, a staple for FAR basically.