I need help making this plane airworthy

[RocketPilot573]

So, I was building this space shuttle:

After I was able to get this thing to stop flipping during the flight tests (the usual), something weird happened. The plane takes off, and it flies level... Now here is were he problem starts: It quickly begins to drift from pro-grade, I try to correct, but it just doesn't listen. The orbiter continues to drifting off in random directions, as if the control surfaces aren't even there! The test fights always end in the whole thing pitching, rolling, and yawing out of control, followed by the poor pilots hammering the abort button; the cabin ejects, and the rest goes boom... (Sorry if this description isn't understandable, but that's why I'm providing a download link.)

I have never seen this behavior in any other KSP aircrafts I have made, not even my previous shuttle of a very similar design. This is by far the most unstable contraption I have ever created...

Does any one know what causes this?

Here's the .CRAFT file if anyone is interested:

http://www.filedropper.com/orionshuttlea-8-2

NOTE: This craft needs that big drop off at the end of the runway to achieve liftoff. (But that's fine, since this is a space shuttle and will only be required to land, not takeoff)

EDIT: Whoops, the craft has Mechjeb 2, I'll fix that shortly...

EDIT 2: Fixed!

Edited October 7, 2013 by RocketPilot573

[RocketPilot573]

Anyone?

(10 char)

[CalculusWarrior]

I'm by far no expert in building planes in KSP, but I think your problem might be the vertical cargo bay walls you've constructed out of wing parts. KSP's aerodynamic system doesn't play well with wings at odd angles. Nice looking shuttle though!

[RocketPilot573]

I'm by far no expert in building planes in KSP, but I think your problem might be the vertical cargo bay walls you've constructed out of wing parts. KSP's aerodynamic system doesn't play well with wings at odd angles. Nice looking shuttle though!

Umm, I kinda got that... However I'm still not sure why my other shuttle with pretty much the same design does not include any of this behavior. I've tried messing with the cargo bay, but I can't seem to narrow down exactly which section is at fault. Basically, I'd rather not do a complete redesign until I'm sure that this ship is completely wrecked. So, can anyone come up with a way to fix this?

[LexDavis]

i'd say that its all the oddly placed wings. could use the structural panels that have no lift rating

[M5000]

If you're having trouble correcting, try checking to make sure you have enough control surfaces, and that they are placed in good places. For example, that tail fin looks fairly small for a craft of that size. It looks good, but it might not be providing enough control authority.

[AletzN1]

Check yout center of thrust, if it isn't aligned with the center of mass, it will drift as long as you have the engines turned on.

Edited October 8, 2013 by AletzN1

[ferram4]

The first thing I'd try is flipping the craft on its side in the SPH to help see the yaw characteristics of the vehicle; the default orientation of the vehicle will only show if it is stable in pitch, while flipping it on its side will allow you to see if it is stable in yaw (same principles as before, CoL should be behind CoM).

Another possibility is that the CoL indicator isn't correct. The CoL indicator isn't affected by the placement of non-wing parts, such as intakes, even though the true CoL is affected by the drag characteristics of those parts. Since the drag of a part is based on its mass * maximum_drag (where maximum drag is almost universally 0.2), the drag characteristics of most parts is complete cancelled out; if you have lots of high maximum_drag parts at the front and low maximum_drag parts at the back, that could be an issue.

The final thing I can think of is that your cargo bay doors might be subtly deforming under the lifting forces applied to it; if it doesn't warp symmetrically (note: it will never warp symmetrically) it could cause phantom-like forces to be applied to your craft. I understand that you'd prefer not to strut the doors down so that they can open properly, but if strutting them in place fixes your problem then you know you'll need to redesign that part of the vehicle. Keep in mind that parts on the same craft do not calculate collision, so this might be more of an issue than you think.

Otherwise, nice design; probably needs more vertical tail to look right though.

[Cheaterman]

Quick, dirty and easy fix: put a few rotation wheels & RTGs near the center of mass of your craft. Results guaranteed!

[Runboy]

The best solution that I see is to make the wings larger,as the wings that I currently see on your plane are quite small to lift a beast of that size.Also,try adding more control surfaces in order to be able to pull up off of the runway better and faster.

Leave a reputation if this was helpful (The sheriff star symbol on the bottom left)

[Cal'Mihe]

Okay so I took this for some testing across a few hours and have the following to report:

Main problems:

Critical Yaw instability

Landing gear overload

1) The capsule ejection system gets caught in the fuselage (the delta wings jutting forwards) and the cockpit get stuck to the craft (test pilots Merrie, Geoffrey and Gregfrey would like to complain)

2) The cargo bay doors are a nice idea, but it appears they cannot open, merely jiggle a bit, and they interfeer badly with the aerodynamics

3) The center of trust is below the center of mass

4) The landing gear is not enough to carry the weight of the craft! Critical point, this cause the gear to buckle when the craft is under power and do a partial collapse, leading to a runway crash.

5) Even when empty of fuel, it is WAY too heavy to do a glider landing

6) The ailerons are misaligned and cause Yaw instability!

7) The spoiler flaps buried in the outer wings are a nice touch, but they are poorly aligned and contribute to the yaw control problems

8) The main cockpit section is not well connected to the rest of the fuselage, causing it to sway and pitch from side to side (look at it from front when it slowly rolls Down the runway, move the control surfaces fully around, notice the swaying cockpit)

9) The fuselage itself cause yaw instability. This is the most critical one. By having the fuselage constructed of wing surfaces, as soon as the craft is aligned away from the direction of travel, it will get lift acting on it with an angle in the yaw, corresponding to the angle away from the direction of travel. This compounds the problem! Basically it means that as soon as you start to yaw even the slightest, the entire fuselage wants to yaw more and more, and the other control surfaces are unable to compensate.

10) Many redundant parts and girders, adding weight and parts Count.

Other comments: Makes a very nice fireball when doing a runway crash.

I was able to get it airborne several times with numerous modifications and even fly around a bit under reasonable control, but in no cases was it particularily stable.

Only by stripping off the complete cargo bay and the entire fuselage, strutting the cockpit section to the engine section and re-working the aileron setup was I able to have some control over it.

Conclusion: Revise design and fuselage completly, otherwise might make a good storage closet

Edited October 8, 2013 by Cal'Mihe
Found the real reason, fuselage