Achieving supermaneuverability

[Kerburettor]

I've been playing with FAR for the past three weeks month already and I wouldn't say I feel at home using it, but it's like sleeping with a heavy snorer. You get used to the pain.

After successfully managing to carry out lengthy survey missions in the upper layers of the atmosphere (still, I wouldn't have done it without Boris' atmosphere autopilot and its wonderful fly-by-wire capabilities), I think Cpt. Valentina 'Val' Kerman likes her planes with a bit more oomph. She asked her engineers to design a beast that will "take my breath away™".

After nearly two weeks of hard labour in an obscure soviet camp, this was the preliminary prototype:

Since last week, I've been tweaking some parameters a little bit, adding mass where needed to allow the center of mass to be noticeably in front of the aerodynamic center due to a tendency for the aircraft to flip over when subject to important angles of attack. Re-discovering KTech's Saturn AL-31FM1 engine was a true epiphany as it allowed me to care less about the very subtle trade-off between TWR, Dv and CoM-CoL positions. It also significantly increased my Dv and my ability to recover from stall (TWR going from 0.80-something to 1.15):

At an altitude of 2km at around Ma = 0.3, which is the typical flight regime where you want to attempt the Cobra (cf.

for instance... )

But the aircraft remained uncontrollable during stall. Here is my aerobatic attempt:

and here the way I configured my primary and secondary control surfaces:

My questions are:

1 - Why is my aircraft not post-stall maneuverable? I think I've got a rough idea why that would be the case: My pitch rate derivative is positive at the flight regime at hand, which means that the aircraft will tend to pitch over if the AoA becomes too important. What should I do to improve post-stall pitch control at a very high AoA WITHOUT having to change the geometry of the aircraft too much?

2 - What should I do to prevent my aircraft from obliterating when subject to intense g-loadings (I'm talking about g-forces > 6~7)? I mean sometimes I feel like native FAR structural parameters will cause structural failures even when my dynamic pressure is way lower than breaking point. My plane is profusely strutted, especially in the wings and wingroots. Additionally, autostruts were added and had to be set to "heaviest part" for most of the components otherwise I'd have parts colliding with each other at launch, which I suspect is due to the complexity of my build (88 parts). I sadly had to deactivate structural failure in the FAR GUI or my plane would not be capable to engage in any stunt.

3 - More particularly, what would you give as an input for parameters such as AoA% for each of my control surfaces? I understand that I'd better put -100 for my front canards as it helps them align with the airflow and energize the detached turbulent boundary layer over the wings to try and regain control after stall. What should I put for the rear stabilizers?

I didn't have much time to delve into knowledgeable resources but I'd be more than glad if you suggested me a few reliable pdfs or books for bedtime reading. A few interesting papers on supermaneuverability I had already found are Rick Cory's PhD thesis and Sibilski's article among others works, but I have yet to dissect them carefully...

Thank you for reading so far. Hopefully my design is not so deeply flawed that I'd have to start over

[Kerburettor]

Any idea? Or did I post this thread in the wrong subforum? 

[Xd the great]

15 hours ago, Kerburettor said:

Any idea? Or did I post this thread in the wrong subforum? 

Yeah probably wrong subforum...

Or maybe you should go to the FAR thread..

[Kerburettor]

22 hours ago, Xd the great said:

Yeah probably wrong subforum...

Or maybe you should go to the FAR thread..

Thanks for the indication.

I figured I'd open a new thread as per the forum recommendation because the FAR thread is getting a bit too long. But maybe this is the right way

[FleshJeb]

19 minutes ago, Kerburettor said:

Thanks for the indication.

I figured I'd open a new thread as per the forum recommendation because the FAR thread is getting a bit too long. But maybe this is the right way

I agree with the advice to check the FAR thread. You could also try finding knowledgeable folks on one of the FAR fighter challenges.

[Snark]

Moving to Add-on Discussions.

[Shadowmage]

On 2/11/2019 at 9:54 AM, Kerburettor said:

Why is my aircraft not post-stall maneuverable?

The #1 need for post-stall maneuvering is some form of thrust vectoring (or differential thrust to a lesser extent and on specific axes).  The second would be that your COG is very near your COM/COP, that way the aircraft will not have undue aero or mass related forces trying to make it 'fly the way it wants to'; you want it to fly where you  tell it.  The third would be a TWR sufficient for the maneuvers you are attempting;  your vectored thrust needs to not only support the aircraft during stall, but also affect changes to orientation -- therefore, more thrust = more maneuverability.

This aircraft can easily be controlled in all post-stall conditions.  Using thrust vectoring (and I guess the reaction wheel contributes some..) I can actually get it to fly backwards, controllably (flat spin, cut thrust, glide backwards).

Keep it small, keep it light, keep it balanced, give it lots of control surface to get into the stall, and then give it lots of thrust and vectoring for maneuvering during stall.

'Supermanueverability' is far less about 'good' aerodynamics, and far more about being able to put out the physical forces to force the craft to do the maneuvers.  The more 'aerodynamically stable' your craft, the more force you are going to have exert in order to break into the stall regime.

 

Edit:  The above is all taken in a 'stock' context for KSP.  But the basic theory is the same in FAR, and even in real life.  I have personally designed and built many RC (radio control) aircraft that were designed specifically for high-alpha/post-stall flight, and they all relied on the same basic premises for their control post-stall control -- neutral balance and strong thrust-vectoring.

Edited February 16, 2019 by Shadowmage