Rules of Thumb for Airplane and Spaceplane Design - KSP-RO/RP-1 GitHub Wiki

Rules of thumb for airplane/spaceplane design:

  1. Tails should have a lower aspect ratio and/or more sweep than the main wing. This is reversed for canards, which should have higher AR / lower sweep.
  2. You need more vertical tail. No really, you do.
  3. It's easy to make things overweight in KSP without realizing it. You probably want more wing.
  4. Use FAR's analysis tabs. Sweep AoA at relevant mach numbers and make sure the Cm (yellow) curve is down-sloping. Use stability derivatives at various altitudes and speeds to ensure you don't have any red numbers.
  5. Never, ever, put wings/horizontal stabilizers/canards in the same line. You need them offset vertically or they will blank the airflow. A common pattern on early jets was a mid-body wing and a tail at the bottom of the fuselage. WW2 fighters generally reversed this. Modern canard-delta aircraft have the canard higher than the wing usually, and often with some anhedral.
  6. Give your wings a bit of dihedral for stability, but not too much. Also consider a degree or so of "baked in" angle of attack on the wing. Note this will alter your Cm curve.
  7. For more advanced transonic/supersonic design, you need to "area rule" your plane. This means minimizing the rate of change of frontal cross section. If you look at a plane from the late 50s, you'll see that for example the fuselage gets narrower as the wings get wider. To get FAR's help, open its display, switch to the Transonic tab, and turn on the first two curves (the green and yellow curves). The green curve is the total cross-sectional area, and the yellow curve is the rate of change in change of area (2nd derivative of area). You want a yellow curve that is as flat as possible. You can move the wings around, add small extra procedural structural parts (in aircraft design they're called drag bodies), etc, to smooth things out. Incidentally this is why swept wings help, because they lower the rate of change in area from "no wing then all the wing" to "gradually increasing wing span"
  8. Basic SAS + keyboard control is not a good way to fly a plane. Use Atmosphere Autopilot.
  9. If you want to go fast, go high first. 10+ kilometers, even for jet planes.