Losing stability at high speeds with my jet. (FAR)

[Lucy1nTheSky]

I need help building a science jet for visiting Kerbin's biomes. Like the title says, My jet seems to go into flat spins or flare up and exceed g-forces and kill my pilot after get get over 500-600 m/s in low altitude or even in higher altittudes at 1.5km/s+. How can i help fix this? More control surfaces? reaction wheels?

Also, my engines overheat if i keep them at more than just a tiny bit above 0 throttle even though i've got pre-coolers on them. I'd like to know how to fix that too, but stability is more important. Any help is greatly appreciated.

Edited February 4, 2014 by Lucy1nTheSky
FIXED PIC

[Jasmir]

Post a picture and the craft file...

[Starwhip]

Well, if you don't design the thing right with FAR, it will come and bite you in the rear. FAR simulates more realistic aerodynamics in all of its glory, including high-speed aircraft disintegration.

But yeah, a picture would be great.

[arq]

FAR has not caused overheating issues with overheating for me, especially as severe as you're reporting. I'm guessing something else is messing with that. Interstellar Mod does play with that, IIRC. Still, without a pic it is hard for us to see the problem.

The FAR VAB/SPH GUI is very helpful for building stable craft. In the simulation window, set mach number to 0.2 and pitch to 1 and do an angle-of-attack sweep. The 'Cm' curve should stay positive (at least out to 20deg) both with and without fuel. Change pitch to -1 and repeat, this time making sure that Cm stays negative. Now change the mach number to 3 and repeat the entire process. If your craft works in all these regimes, chances are good that it will stay pitch-stable.

As for flat spins, these are usually the result of unequal thrust or not having a sufficiently large vertical stabilizer that is set far enough behind the CoM. Try making it bigger or moving it back to improve this.

[Javster]

By overheating, do you mean an orange bar starts filling up, or your parts explode?

[Lucy1nTheSky]

I thought i posted a picture... [iM G]http://imgur.com/FXBTBSg[/iM G] is what i put in the OP. Thanks for the other info, gonna try the i've never actually used the FAR gui. I'll give it a shot. As far as overheating... i mean the orange bar filling up.

[ferram4]

The vertical fins that you have on the engine nacelles are worse than useless and are probably getting rid of a lot of yaw stability. You don't see any real life planes with fins like that, and there's a reason for that: they make the plane less stable in yaw. Getting rid of those might help with yaw issues. If that doesn't fix it, make the single vertical tail all the way at the back larger.

Engines overheating is a Deadly Reentry + Interstellar conflict; there's a fix sitting in the Deadly Reentry thread.

[Lucy1nTheSky]

Getting rid of the double fins on the body helped a bit, but i still flat spin... also uninstalling DRE did not fix my engines overheating. Am i just flying to fast? Just used to rockets being able to go pedal to the medal pretty much all the time. Thanks again.

[ferram4]

Dunno about the engine overheating, perhaps that's what's supposed to happen?

You need a larger vertical tail to balance all the drag at the front of your craft due to the center intake. Vertical tails need to be more substantial than afterthought-like little fins.

[Lucy1nTheSky]

I added a control surface to the tailfin and an inline radiator from interstellar and things are working pretty well now. It still gets hot, but with the radiator, i can just shut them down for a minute or 2 and they cool down pretty fast. Now i just have to learn how to land it