Need some help from some Ferram Aerospace Wizards

[Dtadrunk]

So I have the latest 14.3 FAR and I can't seem to get my planes working right. I have used far for countless hours in the past with no real hiccups after the first couple hours of using it. But now all the planes I build seem to flip out... I put the center of lift behind the center of mass a good ways. It's even far enough back that no matter how hard I pull up the plane won't go too far from prograde. BUT for some reason when I get up to high speed the plane flips out starting horizontally...

No idea how to fix this. Can you have too much lift? Like too many surfaces? The center of mass on my aircraft are usually located in the middle of the craft and the CoL some ways back.. Any help would be fantastic.

P.S.

When the plane spins out, it spins out in a way similar to when your lose intake air and flame out on one engine first.. Kind of like a flat spin left or right but in low altitude and no flame out.

[Master Tao]

That sounds like the plane isn't yaw stable at those speeds. You'll want to make modifications to the plane until the yaw stability derivatives, Yβ and Nβ, are green at those speeds. Try increasing the size of the vertical stabilizer, making two stabilizers instead of one, or shifting it farther back.

Pictures of the planes or craft files would help.

[Dtadrunk]

Ok, here are some pictures I hope this helps.

http://imgur.com/a/vIbaH

[ferram4]

Problem 1: You have no significant vertical tail to speak of. Add more vertical tail area further behind the CoM.

Problem 2: Your plane doesn't look like a plane. The closest thing it looks like is a relatively moderate speed plane, which means it won't really perform well above Mach 0.6. You should redesign it to look more like real-life supersonic designs if you're intent on going faster than Mach 1.

[Master Tao]

Yup, that'll have some yaw instability around Mach 1.

Take some time to read this aircraft design tutorial. The key points for this plane: wide, straight wings are good for gliding. If you want to go fast, you should use swept or delta wings.

Afterwards, I also suggest the Wikipedia page for wing configurations to give you even more ideas for how to build planes.

[Dtadrunk]

Problem 1: You have no significant vertical tail to speak of. Add more vertical tail area further behind the CoM.

Problem 2: Your plane doesn't look like a plane. The closest thing it looks like is a relatively moderate speed plane, which means it won't really perform well above Mach 0.6. You should redesign it to look more like real-life supersonic designs if you're intent on going faster than Mach 1.

Alrighty thanks I will try this. I just assumed all you needed was CoM in front of CoL.

- - - Updated - - -

Yup, that'll have some yaw instability around Mach 1.

Take some time to read this aircraft design tutorial. The key points for this plane: wide, straight wings are good for gliding. If you want to go fast, you should use swept or delta wings.

Afterwards, I also suggest the Wikipedia page for wing configurations to give you even more ideas for how to build planes.

I was looking for a tut like this but couldn't find it thanks!

[velusip]

Hi there! It's definitely a good idea to stick to the basics, but I would also like to encourage you to make nutty designs for fun! Let's tone back your design a bit...

Even under small amouts of yaw those wing tips will provide forces which the craft has no answer to. No amount of tail will help. So remove those.

Next, consider that the craft will produce a high positive feedback during high angles of attack due to two significant sets of wings (before and after the center of mass). You're flying like a leaf on the wind, and no this is not a good thing, Wash! Consider reducing the size of the leading "canard-wing" and rebalance your lift to suit. This new design will probably produce a noticable pitch oscillation, but overall, yield a less dramatic transition between positive and negative angle of attack.

Once the tips are gone and the lift is rebalance, fix that tail. You need some yaw control up in this ----- and there are a few ways to achieve it:

* Drop the v-tail and give it two wide-set, vertical tails with independent rudders (if possible). Have a look at some plane designs featuring wide-set tails for ideas: e.g. This one even has that nice canard-wing I mentioned http://en.wikipedia.org/wiki/Rutan_Voyager

* Drop the tail completely, move your main (rear) wing forward, and design it to produce more lift closer to the center of the craft. More reading material here: http://en.wikipedia.org/wiki/Flying_wing#Directional_stability

You might have to give it multiple, small tails over and under the main wing. Look up "Northrop flying wings" of the 1940s for ideas.

It might help to place winglets (90 degree tips) on the rear wings, but that only complicates things at very high speeds. However, this sort of design really isn't any use under high dynamic pressure anyway.