aircraft control v1.1

[xendelaar]

Hi  everybody.

Ever Since version 1.1 I'm having trouble flying my spaceplanes.

I really have to pitch slowly in order avoid flipping the entire vessel .i've tried lowering and increasing the authority limiter but that didn't help.  The only workaround seems to be to use more SAS units, which doesn't feel right ... is there something I'm missing?i hope ypu guys can help.

Here's an example of a typical plane:

 

Edited May 7, 2016 by xendelaar

[bewing]

Are you experiencing this instability during takeoff, low-speed flight, or high-speed flight?

I had the same problem, but only during takeoff. Using a smaller canard, cutting the control authority to .65, and turning on "soft mode" steering with CapsLock all helped in my case.

During flight, I don't really touch the controls much. With SAS turned on, the nose rises all by itself. If I want the nose to come down, I click on "prograde" for a second until the nose drops as much as I want -- then go back to "stability" again.

In the case of your posted plane, it looks to me like your "canard" is just too small. It's unable to correct a deviation. So I'd think you need to push UP the authority to max on them.

[xendelaar]

I have difficulty remaining stable during take off and landing/re entry. As long as i stay prograde,  everything is just  fine. But When i try to adjust my course a bit too fast... all hell breaks loose.

Lowering the authority limiter doesn't seem to help. 

I never had these problems in 1.0.5 though. 

Edited May 6, 2016 by xendelaar

[AeroGav]

Three things I noticed -

1. The centre of lift is very close to the centre of mass.    I always play it safer in my designs,  generally i either have the back of the smaller blue ball touching the back of the larger yellow ball, or have the blue arrow at the rear of the yellow ball.   This means more up force is needed from the canard to hold the nose up , so make sure it is large enough to do so without requiring large deflection angles that produce drag.

2. You have two tanks holding 400 units of fuel each and the centre of gravity is exactly on the divider between the two.   That's pretty smart, but the front tank is all liquid fuel and the rear appears to  be LF/O.     Jet engines pull from every tank on the ship proportionate to their capacity.   So because the liquid fuel fuselage holds just over twice as much LF as the FT400 rocket fuel tank,  when in airbreathing mode it will take just over twice as much fuel per second front the front tank as the rear, making your plane increasingly tail heavy and unstable.   Once in rocket mode,  it'll then be emptying from the rear quicker than the front and the CG will move forwards instead. 

The simplest fix would be to use a liquid fuel fuselage with an FT200 rocket fuel tank immediately ahead of and immediately behind.    If the CG is exactly in the middle of all 3 you should have no shifts in CG.

3.  I've noticed you put incidence on the main wing but not the surface being used as a canard.         This does two things - first, the Centre of Lift indicator in SPH may be wrong, because in flight you will be angling this up to some degree , and it will be producing lift where the indicator in the SPH thinks it is producing zero lift.     Second, if you get to high angles of attack, the canard surface will be at lower AoA than the main wing so it will gain more lift than the main wing as AoA increases further, as the main wing will be getting into "diminishing returns".  This again will move the Centre of lift forward and could make things unstable.      Best to either not use incidence or apply it to the canard as well !

[herbal space program]

I concur with AeroGav that your COL is too close behind your COM. If you slide those wet wings backwards just a little, you'll both stabilize your plane and help it to maintain good aerodynamic trim as the fuel get used up.

Edited May 6, 2016 by herbal space program

[bewing]

6 hours ago, xendelaar said:

I never had these problems in 1.0.5 though. 

Yeah, well, 1.1 is a totally different game than 1.0.5 and nothing works the same as it did anymore. So that's not really a good argument, unfortunately.

6 hours ago, xendelaar said:

Lowering the authority limiter doesn't seem to help.

If you reread what I said above carefully, I was suggesting that you increase the authority to 150%. Your canard is the only thing keeping your plane from flipping at all.

Then you need to use the CapsLock to decrease the input from the keyboard. Or not use the keyboard at all to control the pitch.

[xendelaar]

Thanks for the advice! I'll will make the adjustments you guys suggested and report back after I've preformed some test flights

[xendelaar]

 

@Bewing: Sorry I misread your post.  Increasing the authority made my vessel even more flip-happy XD

 

12 hours ago, AeroGav said:

Three things I noticed -

1. The centre of lift is very close to the centre of mass.    I always play it safer in my designs,  generally i either have the back of the smaller blue ball touching the back of the larger yellow ball, or have the blue arrow at the rear of the yellow ball.   This means more up force is needed from the canard to hold the nose up , so make sure it is large enough to do so without requiring large deflection angles that produce drag.

2. You have two tanks holding 400 units of fuel each and the centre of gravity is exactly on the divider between the two.   That's pretty smart, but the front tank is all liquid fuel and the rear appears to  be LF/O.     Jet engines pull from every tank on the ship proportionate to their capacity.   So because the liquid fuel fuselage holds just over twice as much LF as the FT400 rocket fuel tank,  when in airbreathing mode it will take just over twice as much fuel per second front the front tank as the rear, making your plane increasingly tail heavy and unstable.   Once in rocket mode,  it'll then be emptying from the rear quicker than the front and the CG will move forwards instead. 

The simplest fix would be to use a liquid fuel fuselage with an FT200 rocket fuel tank immediately ahead of and immediately behind.    If the CG is exactly in the middle of all 3 you should have no shifts in CG.

3.  I've noticed you put incidence on the main wing but not the surface being used as a canard.         This does two things - first, the Centre of Lift indicator in SPH may be wrong, because in flight you will be angling this up to some degree , and it will be producing lift where the indicator in the SPH thinks it is producing zero lift.     Second, if you get to high angles of attack, the canard surface will be at lower AoA than the main wing so it will gain more lift than the main wing as AoA increases further, as the main wing will be getting into "diminishing returns".  This again will move the Centre of lift forward and could make things unstable.      Best to either not use incidence or apply it to the canard as well !

Wow, Shifting the centre of lift back fixed the problem! I feel so silly... I used to put the centre of lift always a bit more to the back, but it gradually shifted more to the front after each design...

I never would have thought of changing the incidence of the canard and using 2 FT200 to increase stability!