[FerramAerospace] High-αlpha aircraft!

[deskjetser]

I have recently delved into the world of super-maneuverable aircraft with the fantastic Ferram Aerospace mod, and let me tell you, i've had some fun designing today!

There is going to be quite a wall of text, so brace yourselves!

So, I have created two aircraft to test high-alpha I want to show to you, the first is the KB XF-1 as seen below.

Note a few things:

[1] The forward canards completely unobstructed for airflow at huge varying angles of attack.

[2] The huge wing surface area and (not clearly visible in image) dihedral aspect of the whole lifting body.

[3] The enlarged tail.

The purpose of this aircraft:

I purposely set up this aircraft so that it had extreme pitch authority (note 1), because I wanted to see first hand how when obstructed airflow of the yaw controls during high-α, effects the aircrafts control-ability. You can see this in the example below, that I purposely blocked the yaw controls during high-α, to observe the effects for later use.

The observation:

Due to the lack of sufficient airflow passing over the yaw control surface, the lack of yaw authority wasn't too surprising. However, what was more surprising was the attribute that roll input brought along at high-α, which was yaw control. High-α + roll input = roll and yaw? What was happening!

After looking into it, I came up with a theory for this.

When both ailerons are in the same position, the airflow has to travel the same distance on each wing, thus creating no asymmetrical forces to the aircrafts yaw direction (Example 1 below). However, when one of the ailerons are pitched up, this forces the air to follow the contour of the control surface, effectively pulling the air down and out the back, creating a force pulling that side down and thus effecting the yaw (Example 2 below). It may not be the most bullet proof theory out there, but for my purposes it provided what seemed to be the correct solution in the end.

____________________________________________________________________________

The next aircraft is the, KB XF-3.

Note a few things:

[1] The forward and rear mounted canards, unobstructed through a wide variation of angle of attack.

[2] The elongation of the vertical tail beyond the bottom of the aircraft for airflow at extreme angles of attack.

[3] The upwards curved wingtips to improve wingtip high alpha performance.

[4] The substantially smaller ailerons mounted on the wingtips.

The purpose of this aircraft:

This aircrafts purpose was to test the possible solutions to the problems observed on the XF-1. For a start, the vertical tail was hugely enlarged to increase its effective width at high-α (Example below), not to mention it was also extended below the bottom of the aircraft to ensure maximum airflow over the yaw controls at all times. The addition of the rear mounted canard was to improve handling while at high-α, this is because with the XF-1, pitch is done by the canards only, however on the XF-3 pitch is controlled by three control surfaces. These are the forward canards, that only input pitch, the rear canards that input both pitch and roll, and finally the wing mounted elevators which only input pitch. Because of this layout, the pitch authority on the XF-3 is greater than the lighter XF-1.

Remember above, when we talked about roll having yaw affects, well that problem was fixed, by keeping the airflow on the wing symmetrical at all times. The elevators on the wing move simultaneously as not to create asymmetrical airflow, yawing the aircraft. The only ailerons on the wing are tiny to avoid the yawing effect at high-α, and the majority of the roll authority rests with the rear canards.

The observation:

All control surfaces on the new craft have much better authority, even when at extreme high-α, due to the open airflow allowance of all control surfaces and partially down to the placement (Example below). The XF-3 has exceptional high-α performance, and for the time being it is the peak of my progress.

Other issues are currently known, but there are no explanations I can offer to provide a solution, and thus this concludes the observation until I progress further.

(Above: Red represents airflow obstructions, in the case of the forward canard, it serves to create drag keeping the nose up. Dark blue and cyan blue represents roll controls, yellow and cyan blue represents pitch controls, and green represents yaw controls.)

Thanks for reading! Please comment or add suggestions for the next step in high-α tech!

Edited August 12, 2013 by deskjetser

[sidew]

remind me the X-31 project....

[deskjetser]

remind me the X-31 project....

Yeah, I guess, it's a pretty cool airplane the X31

[sidew]

The European EF-2000 Typhoon have similar aerodynamics: canard with delta wing for high maneuverability on high AoA...

[deskjetser]

The European EF-2000 Typhoon have similar aerodynamics: canard with delta wing for high maneuverability on high AoA...

Right, the Eurofighter has computer mixing for the ailerons and canards, virtually negating the need for under slung vertical stabilizers though, it's the same with most other combat aircraft, they compromise between actually being stable doing something and letting the computer handle it.

Unfortunately I have do do without a super computer that reacts instantly to wild movements

*Edit* "Unfortunately I have do do without a super computer that reacts instantly"

Sure the in-game SAS are good for going in one direction, but for this kind of stuff they don't react how I would need them too.

[Rune]

First, great post! I love to see other aerodynamics guys out there, and the scientific theme of the post speaks to the engineer in me.

Also, you are going to love the new 0.21 ASAS. No supercomputer is needed to perform fly-by-wire artificial stabilization, just good coding, and the KSP team (was it Nova? I forget) has finally worked out the bugs in the programming. According to the videos out there, it actually works now.

Rune. The XF-3 also has the looks, and that's almost as important.

[deskjetser]

First, great post! I love to see other aerodynamics guys out there, and the scientific theme of the post speaks to the engineer in me.

Also, you are going to love the new 0.21 ASAS. No supercomputer is needed to perform fly-by-wire artificial stabilization, just good coding, and the KSP team (was it Nova? I forget) has finally worked out the bugs in the programming. According to the videos out there, it actually works now.

Rune. The XF-3 also has the looks, and that's almost as important.

Thanks, and I'm sure the new SAS system is going to be helpful, but what would really be awesome is a semi-programmable SAS. It would be handy especially for awkward aircraft like this. Such as when at high-α when roll input is being applied, dampen the aileron movement and supplement it with rudder and rear canard input.