[FAR] Delta wings & deadly flat spin

[mielgato]

Hi dear kerbonauts, i'm doing some aircraft and try different models and wing types as I try to build a Hypersonic aircraft to do aerial survey missions faster using only liquid fuel

[imgur](http://i.imgur.com/q3qCWAL.jpg) (original size)

I have some troubles with delta wings and their flat spin tendancy when you go over the AoA limits and stall, Jebediah and Bill died while trying to change the bearing of their aircraft and entered a flat spin which brought them from 20 000m to the ground without any chance to recover

As I understand it, the aircraft do a flat spin because the center of mass and the center of lift are neutral, resulting in the aircraft not pitching down causing a stall of all elevon ? So the solution would be to bring the center of mass closer to the nose right ?

edit : in fact I just applied some overlooked basics rules in aerodynamics and my delta wings are now very stable and pull out of stalls... duh

Anyway, there come another question so the post doesn't go waste :

My aircrafts wobbles, even the smallest one,even using kerbal joint reinforcement and struts from B9... so I tried to strut every module to the wings, feel pretty rigid but the pitch still wobble up & down whenever I touch the commands, is that normal in kerbal terms or there is something i'm doing wrong ?

Edited December 1, 2014 by mielgato

[capi3101]

Since you're in FAR, whether or not you can recover from a flat spin depends on the plane's design and wing loading. You can try general spin recovery procedures recommended by the FAA -

*Set the throttle to idle (where this is in KSP is anybody's guess; I'd think maybe one or two notches above zero at most).

*Neutralize the ailerons

*Retract the flaps (if you have them)

*Apply full rudder in the direction opposing the spin (a reason to include a rudder in your design if ever there was one)

*Pitch to select zero angle of attack.

Like I said, whether or not that will work is going to depend on your plane. Sometimes the only thing that will save it is divine intervention...

[cantab]

Wikipedia discusses it at length http://en.wikipedia.org/wiki/Spin_%28aerodynamics%29

In a spin that is unrecoverable by control inputs, shifting the centre of mass forward can help. In KSP you can do this by pumping fuel providing you have multiple tanks, or by putting decouplable ballast on the rear.

Or you can simply use emergency parachutes, or an ejector seat/EVA parachute mod.

[Hodo]

Ok, looks like the first problem is your FAR is out of date. Update your FAR.

Next to recover from a flat spin in FAR you will have to have a dynamically stable aircraft first.

EDIT sorry was on a time crunch earlier.

Now I will give a decent answer.

Your FAR is out of date first. The current version is 14.4x so you will want to update it.

Next your craft has a very short profile and is pretty aerodynamically unstable, especially in the yaw category. I have to suggest you lengthen the craft slightly and add a bit more of a tail to it. Also check your numbers in the FAR tool in the SPH, check your AoA graph, and your speed graph at different mach speeds. Then check the numbers in FAR, if anything is in the red your craft will have some bad handling characteristics.

Ideally you want numbers all green like this.

That is at landing and take off speeds, .35mach

This is for mach 5 or near orbital burn speeds.

notice how the numbers are still in the green but they changed slightly?

This is the sign of a stable craft. Each of the numbers have a pop-up that comes up if you hover your mouse over them, which is handy if you don't know what they mean.

Edited December 2, 2014 by Hodo

[eddiew]

My aircrafts wobbles, even the smallest one,even using kerbal joint reinforcement and struts from B9... so I tried to strut every module to the wings, feel pretty rigid but the pitch still wobble up & down whenever I touch the commands, is that normal in kerbal terms or there is something i'm doing wrong ?

Does it still wobble if you turn off SAS? I get much a smoother ride by using only FAR's flight assistant, saving SAS for upwards of 25-30km when there's no real atmosphere to use control surfaces against. A stable aircraft can pretty much fly with just trim and patience

Alternatively, consider Pilot Assistant which will help tune your SAS to not make such large movements (it's designed for big unwieldy rockets, not planes with loads of control). Haven't used it myself, but it comes recommended by SSTO specialists, and it's on my list of stuff to check out.

Edited December 3, 2014 by eddiew
wrong link ^^;