Aircraft veering off course - Ferram & Deadly Reentry enabled

[ironclad]

I'm trying to get back into (space)planes, with Ferram Airospace & Deadly Reentry enabled, but my first training vehicle has a bad case of veering off to the side and tumbling over. Not every time, but quite often, especially during landing. Any advice what's going on?

Also general tips on how to improve this specific design would be appreciated, landing and turning this thing are a *****. . Small note: the tiny srbs at the cockpit are my emergency ejection system. I'm aware that they're not properly bound to the alert action group yet.

Craft file: https://db.tt/xsqptDNs

Screens: http://imgur.com/a/frQ2v

Edited April 18, 2014 by ironclad

[Amaroq]

Remove the control surfaces on the leading edge of the wing - that would be my first guess.

Also, I'm surprised that you don't have a small control surface trailing the tailfin.

Incidentally, a micro-light plane such as what you're building will be much more maneuverable (in this case, it seems "too maneuverable"); I actually find it easiest to fly if I build something that looks approximately like an F-14 Tomcat, using the Mk2 fuselages, two jet engines with full circular intakes, multiple control surfaces along the trailing edge so that I can assign some to roll & pitch, and others as pitch & flaps.

The trick is, the heavier plane is less maneuverable, which makes it easier to fly.

Finally, I tend to use "T" (SAS) to keep my plane level and straight down the runway and on my initial ascent. Once I'm level at cruising altitude, I'll enable the FAR controls (FAR "DCA" is a must if you're on keyboard), set the trim (Alt-S) to about what I observed SAS was at, and disable the SAS. It takes a bit of getting used to, but once you've got it, its fabulously fun.

Finally, if you haven't found it, read keptin's fabulous Basic Aircraft Design thread -- I re-read it on occasion, and learn something new to try each time.

Edited April 18, 2014 by Amaroq
Added link to keptin's Basic Aircraft Design thread.

[Othuyeg]

Could you take some pictures of the craft in SPH with the COL, COT and COM showing?

[ironclad]

Remove the control surfaces on the leading edge of the wing - that would be my first guess.

Also, I'm surprised that you don't have a small control surface trailing the tailfin.

Incidentally, a micro-light plane such as what you're building will be much more maneuverable (in this case, it seems "too maneuverable"); I actually find it easiest to fly if I build something that looks approximately like an F-14 Tomcat, using the Mk2 fuselages, two jet engines with full circular intakes, multiple control surfaces along the trailing edge so that I can assign some to roll & pitch, and others as pitch & flaps.

The trick is, the heavier plane is less maneuverable, which makes it easier to fly.

Finally, I tend to use "T" (SAS) to keep my plane level and straight down the runway and on my initial ascent. Once I'm level at cruising altitude, I'll enable the FAR controls (FAR "DCA" is a must if you're on keyboard), set the trim (Alt-S) to about what I observed SAS was at, and disable the SAS. It takes a bit of getting used to, but once you've got it, its fabulously fun.

Finally, if you haven't found it, read keptin's fabulous Ba Aircraft Design thread -- I re-read it on occasion, and learn something new to try each time.

The Tailfin is the stock AV-R8 winglet - it's fully flexible. And I almost always have SAS enabled. The thing with the craft is that I'm doing this in career mode, with limited access to parts - this wing is pretty much the biggest "wing" part I have available.

Could you take some pictures of the craft in SPH with the COL, COT and COM showing?

sure, just a sec.

here:

Edited April 18, 2014 by ironclad

[Jimbimbibble]

Increasing the length of the fuselage should give you much more lateral stability. Also, removing the control surfaces on the front of the wings would be a good idea.

[ironclad]

I would really like to know why the plane reacts the way it does. Basically it starts to veer a little to the left/right, and then ... seems to try to correct and starts rolling over. It almost looks like it hits a boulder and falls over, except that the runway is flat as a very flat pancake. It's not much of an issue in ascending, since if the pilot actively pulls the plane upwards it never reaches the instability that makes it fall, but landing it seems impossible...

[Jimbimbibble]

There are a few possibilities. If you did not restrict that winglet on the tail to move only a few degrees, it could be causing the roll you're talking about. Those winglets are very powerful. Also, because the distance between the CoM and the tail is so small, your tail is not very effective as a stabilizer.

[GoatRider]

because the distance between the CoM and the tail is so small, your tail is not very effective as a stabilizer.

If it was a real plane, this would be the reason. I have a model airplane that has a pretty short fuselage, and it's rather squirrelly on the ground.

[Taki117]

If it was a real plane, this would be the reason. I have a model airplane that has a pretty short fuselage, and it's rather squirrelly on the ground.

With FAR this is very proabaly the reason, just add more jet fuel and you're golden (Or even the structural fuselage if you have them.)

[ironclad]

With FAR this is very proabaly the reason, just add more jet fuel and you're golden (Or even the structural fuselage if you have them.)

I wish that were true, I still get landing gear instability, no matter how much mass I add

[Hodo]

Ok Ironclad, here is your problem with your aircraft.

The stability issues on the ground are because your landing gear are off camber. In simple terms they flex out when you are on the ground causing the aircraft to pull one direction or the other. This is caused by the fact they are under the wings, and the wings are not structurally strong enough to handle the load of the craft, thus they flex upwards as the aircraft attempts to pull up. Which pushes down on the landing gear.

The other issue is your landing gear are to far back from the CoM of the aircraft, this is crazy considering how short this airframe of this craft is. But it is true, your rotate point is almost in line with your CoL, which is a fair bit behind your CoM.

There are several options to fix this problem. You can add struts to the wings which will make them more ridged and fix the flex issue making the aircraft a lot more stable. And you can move the landing gear on the wings foward just a bit to get them closer to your CoM.

A couple of other minor fixes I would do for stability sake. I would remove those massive control surfaces and that tail, and go with smaller control surfaces so I can set roll and pitch on different ones so you dont have aileron-elevators, which will cause stability issues while flying. I would also ditch the leading edge control surfaces, there is a reason why you dont see many aircraft out there with leading edge control surfaces. Sure you see planes with slats, leading edge flaps but not control surfaces. As for the tail there is a winglet/canard part that has a built in control surface and doesnt move the whole part. This is perfect for a tail for an aircraft this small as it would reduce your loss of stability on sharp yaw meneuvers.

Good luck, and dont worry I have lots of experience with FAR+DRE, just look at my sig, that is ALL of the mods I run.