Building With Ferram

[Dizzle]

Hey guys. I just installed Ferram Aerospace, and I'm not quite sure what I'm doing. I learned pretty quickly that it hates ASAS, but that a stable plane flies just fine without it. The question is, what makes a stable plane? I looked at some of the pre-made designs and saw that the CoL should be above and behind the CoM, but that alone doesn't seem to do the trick.

Any and all tips are much appreciated.

[AndreyATGB]

You'll want pretty good tail fins and adequate surface area for your wings. You CAN have a CoL in front of CoM but it won't be very friendly to adjustments (it'll basically always pitch up). Also try and put the CoM in the middle of your plane as possible, then CoL behind it. If you stay in reasonable distances, it'll be stable and maybe take off from the runaway before it runs out. I'm no expert but you get the hang of it after many fails. 0.21 will probably fix ASAS with FAR too, also if you want more technical and in-depth tips post your problem with a pic of the plane in the FAR thread, ferram often answers too.

[Autochton]

There's a few tricks you can use to improve stability. For roll stability you can add dihedral (wings tilted so they point a little bit up when viewed along the fuselage), or, I think, if your CoM is below your CoL. I prefer the former, myself. For yaw and pitch stability, add a good set of large tailplanes. I'm prone to V tails myself, and using big stabilator type surfaces - where the whole surface turns to control the air flow - but a set of vertical and horizontal stabilizers work too. But yeah, make those big enough.

You'll want to have enough lift. Use the CAS to make sure you have a plane that will lift off - sweeping AoA will give you a good idea of how it'll behave. The higher the L/D line, the easier it is to get lift. If your plane doesn't lift, or needs a too high speed to take off (i.e. runs out of runway), bigger wings are a good way to go. (Or bigger engines so you hit takeoff speed in time - but beware of having to land, then!)

The CAS is your friend. I typically use sweep calculator to get an idea of overall performance under different regimes. Sweeping AoA gives me an idea what the typical flight attitude will end up being, and whether it might be worth it to change the angle of mounting, or the gear attitude. Generally, you want the plane to sit on its gear with a little nose-up (or wings-up, in the case where the wings are tilted upwards). That way, you may get a plane that takes off on its own, or which will at least take off easily. Sweeping Mach tells you how the plane will behave as speed changes - expect lift to drop and drag to rise around Mach=1, then things will even out again. AoA sweeps well from 0-25 for a basic calculation - expand as necessary - and Mach usually is good when swept from 0 to 5 or so, if you plan on going that fast. Make sure to set Mach number for AoA sweeps, and AoA for Mach sweeps appropriately for what you're trying to learn. As for stability derivatives, try to match up the suggested signs of each derivative (as given in the tool tip of each one), it'll make the plane a bit more controllable.