FAR Analysis

Information InformationCoefficient of lift.
Information InformationCoefficient of drag.
Information InformationPitch moment coefficient. This determines pitch stability and control authority and is dependent on the relationship between the center of lift and to the center of mass. Notice how it changes with AOA and speed? Notice how the stock game's CoL tool doesn't reflect this reality? That's right, it's garbage, don't use it!
Information InformationLift over drag.

The pitch moment coefficient determines the pitch stability and responsiveness of your aircraft. The steeper the downward slope the more stable, but the slower it is to pitch change. An upward slope is unstable and will not fly for very long, but will do impressive back flips! The further back the CoL (and the more stable and sluggish) the more the craft will want to pitch down. This is often negligible but will need to be taken into account if very high stability is sought.



A high lift to drag ratio is desirable for carrying cargo, but as lift is inexorably tied to drag (you can't produce one without the other) a low drag coefficient is of prime importance for very high speed vehicles.



Where a line splits and then rejoins shows a wing stall condition (a sudden reduction in lift). The more significant and sudden the separation the more future you will hate present you.

Lower:

0

Upper:

Warning WarningFor high performance aircraft don't leave the upper AOA range at only 25°. What if your spaceplane is unstable at 45°?
25

Num Pts:

Information InformationHow many points of data it will calculate. Different resolutions can cause drastically different results, so using a higher resolution (like 1,000 points) can be a good idea if you need higher precision or are experiencing unexpected results.
100

Mach

Warning WarningDon't think about going hypersonic if you don't know if you can get off the ground! Before all else make sure that your craft is stable at a reasonable take off speed.
0.2
Sweep AOA

Flight condition:


Planet:

Information InformationIn case flying planes on Kerbin is too easy for you.
Kerbin

Altitude (km):

Warning WarningIt is very important to test your vehicle at multiple altitudes. If you're building a spaceplane don't forget- very high altitudes and speeds change flight characteristics quite a lot!

0

Mach Number:

.35

Information InformationThe speed at which you would like to test the vehicle relative to the speed of sound. Mach .8 is simply 80% the speed of sound (which changes with altitude).

Flap setting:

Information InformationNot currently using flaps? You should be! Other than assisting take off, using the first setting of flaps allows for a better descent and more control of your glide slope (the angle of your descent path, not the orientation of your plane; usually 3° in real life). Using full flaps on final (the last turn if flying a traffic pattern, otherwise just use when you're very close) while using throttle to maintain airspeed allows for fine glide slope control that simply isn't possible without flaps, and allows for much slower, safer, and easier landings. Use them!
0 (up)

Spoilers:

Information InformationYou can slow your plane down without heavy airbrakes using spoilers. You're not going back to stock aero now, are you?
Calculate Stability Derivatives
Information InformationMake the magic happen!

Aircraft Properties

Moments of Inertia

Information InformationA measure of an object's resistance to changes in a rotation direction. Moment of inertia has the same relationship to angular acceleration as mass has to linear acceleration. See link in resources side bar for more info.

Products of Inertia

Information InformationIf a rotating object is not symmetric about all three axes than it will not actually rotate about the axes that we have used and described so far, but around some other axes. These off-axis moments of inertia are products of inertia and may be thought of as the measurement of dynamic imbalance caused by asymmetrically distributed mass. See link in resources side bar for more info.

Level Flight
Ref Area: 0 m²
Information InformationLifting surface area including lift from the body and vertical surfaces.
Ixx: 0 kg * m²
Information InformationResistance to roll change.
Ixy: 0 kg * m²
Information InformationResistance to roll due to pitch. Is equal to resistance to pitch due to roll.
u0: 0 m/s
Information InformationAir speed determined by the mach number entered earlier and temperature.
Scaled Chord: 0 m²
Iyy: 0 kg * m²
Information InformationResistance to pitch change.
Iyz: 0 kg * m²
Information InformationResistance to pitch due to yaw. Is equal to resistance to yaw due to pitch.
Cl: 0 Cd: 0
Information InformationCoefficients of lift and drag during level flight at above speed.
Scaled Span: 0 m
Izz: 0 kg * m²
Information InformationResistance to yaw change.
Ixz: 0 kg * m²
Information InformationResistance to roll due to yaw. Is equal to resistance to yaw due to roll.
AoA: 0 deg
Warning InformationMake sure to check that you don't need to maintain an extreme angle of attack at a speed you wish to travel. Always try to maintain a takeoff AoA that is less than 10°, ideally less than 6°. If too high an AoA is required to maintain level flight than more lift is necessary, either by an increase in speed (never fly that slowly at that altitude) or wing area.

Longitudinal Derivatives

Down Vel Derivatives

Fwd Vel Derivatives

Pitch Rate Derivatives

Pitch Ctrl Derivatives
Zw: 0 s-1
Information InformationLift. If this is incorrect than you are very talented.
Zu: 0 s-1
Information InformationHow vertical velocity affects lift. Can be negative.
Zq: 0 m/s
Information InformationHow vertical velocity changes with pitch rate. May make minor changes under very large amounts of pitching.
Zδe: 0 m/s
Information InformationHow vertical velocity changes with elevator deflection.
Xw: 0 s-1
Information InformationHow angle of attack affects forward velocity. Can be negative.
Xu: 0 s-1
Information InformationDrag. Ferram writes, and I quote, "If Xu is incorrect, you have summoned the Kraken and should file a bug report."
Xq: 0 m/s
Information InformationHow forward velocity changes with with pitch rate.
Xδe: 0 m/s
Information InformationElevator performance: how forward velocity changes with elevator deflection, or drag.
Mw: 0 (m * s)-1
Information InformationWhether or not your center of lift is positioned correctly. Larger negative values are more stable and sluggish, lower is more unstable and responsive, positive is a Kerbal mechanical bull.
Mu: 0 (m * s)-1
Information InformationHow pitching moment changes with forward speed.
Mq: 0 s-1
Information InformationPitch damp: the ability of the craft dampen pitching.
Mδe: 0 s-1
Information InformationElevator performance: pitch control authority. Get as large as possible while trying to minimize Xδe.

Lateral Derivatives

Sideslip Derivatives

Roll Rate Derivatives

Yaw Rate Derivatives
Yβ: 0 m/s²
Information InformationHow sideforce changes with sideslip: yaw stability. Makes the plane want to fly straight instead of skating sideways.
Yp: 0 m/s
Information InformationHow sideforce changes with roll rate. Not important on its own but if other roll and yaw derivatives are also poor can turn the plane into a dutch roll-happy nightmare to fly.
Yr: 0 m/s
Information InformationHow sideforce changes with yaw rate. Not important on its own but if other roll and yaw derivatives are also poor can turn the plane into a dutch roll-happy nightmare to fly.
Lβ: 0 s²
Information InformationRoll due to sideslip, which can be very significant. For this reason, inadequate vertical stabilizer can cause roll as well as yaw instability.
Lp: 0 s-1
Information InformationRoll damp: the ability of the craft dampen rolling. If too large it can make rolling difficult, and if large enough may make turning impossible.
Lr: 0 s-1
Information InformationHow rolling moment changes with yaw rate. Not important on its own but if other roll and yaw derivatives are also poor can turn the plane into a dutch roll-happy nightmare to fly.
Nβ: 0 s-1
Information InformationStatic yaw stability, exactly analagous to Mw. Higher values will increase stability but reduce your ability to yaw quickly, in case you care about that for some reason.
Np: 0 s-1
Information InformationHow yawing moment changes with roll rate. Not important on its own but if other roll and yaw derivatives are also poor can turn the plane into a dutch roll-happy nightmare to fly.
Nr: 0 s-1
Information InformationYaw damp: the ability of the craft to dampen yawing.

Coming soon.

Coming soon.

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