In wahubna's thread about his first aircraft design, I promised to post some pictures of my design.  So I present to you, Aethos:
As I summarized the aircraft when I completed it:

"The Aethos ASBA (affordable space booster aircraft) is a lightweight unmanned low-cost space booster aircraft. It features a
unique oblique swing wing configuration designed to maximize efficiency for long range cruise
and to provide an ideal shape for supersonic flight operations. Powered by commercially
available turbofan engines, the Aethos provides unmatched reliability, maintainability, and
affordability for future satellite launch missions."

The mission was to carry a rocket to 50000 feet and launch it from supersonic speeds to place a small satellite into orbit.  In addition, the aircraft was required to complete a 1500 nautical mile ferry flight carrying the missile to a launch site. 

I went with my favorite of all aerodynamic breakthroughs; the oblique swing wing.  There has been research that shows that supersonic drag is a factor of a ratio of length to width.  By swinging a single wing at an oblique angle, we can maximize this ratio while maintaining an efficient design at low speeds.

The key is that in supersonic flight, an oblique shockwave forms at the front of any body.  The only airflow that the wing 'senses' when there is an oblique shockwave is the air normal to the shock.  With an oblique wing, the entire leading edge is separated from the shockwave and sees only the normal flow, versus a traditional design where shockwaves attach to the wing.  This allowed me to use a normal, efficient airfoil, again maximizing performance at subsonic speeds.

I will give a link to my 5th and final report, this summarizes most of the major design work.  Theoretical performance was excellent, at subsonic long range cruise the aircraft had a lift to drag ratio of 12!  It required very little fuel and as such was extremely light, less than 10,000 pounds max takeoff weight.  (Admittedly now that I have real world experience, I know that wouldn't be attainable.  I would guess it would weigh closer to 18,000 pounds).

Enough about that, here are pictures. 

From the 4th report, 3 of them in formation with wings fully swung


This is a view with a groundcrew.  It illustrates how shockingly small the aircraft is


For the final report, I had to ruin it by putting the engines further out so the gear was further apart to prevent tip over on the ground.


3 view with the wing straight.  It's pretty much 40 feet wingspan 40 feet long


Systems and (crude) structure.  The last report was all this detail work, which was when I realized I should have done the whole thing differently.  I started to redesign but got too busy, it was going to look like a predator had sex with a skycrane: a nose section to house the electronics, with the payload mounted externally, the engines closer to the middle, and landing gear in a traditional tricycle. 


A nice detail, my main gear retraction


To read the report (be warned, it's technical): http://www.mediafire.com/view/?1ggae7g1gjqv26h

I'll answer any questions, but it's been a while since I've looked at it

My only suggestion to your design, as a lowly pilot, is that is would be quite difficult to land with that landing gear arrangment.  If you flared at all, you would land on the single rear gear first, which could cause some directional control issues, if not structural issues due to the impact on a single gear.

DaveSims wrote on Aug 27^th, 2012 at 8:20pm:


Indeed. You need a lower tail attitude, either shortening the tail wheel or (probably more easily) by lengthening the mains. The problem would also manifest itself on take off, as any traditional rotation would immediately stress the tail wheel(s). You're U-2 analogy is worth looking at  - you'll note on the ground it has a distinct tail down attitude. If you were planning to land on a single stressed undercarriage leg, you'll need it on or around the CofG (think U-2, Harrier etc), not as far back is it is here.

The only other potential issue I see is with the stub wings and engines, ie, shockwave interaction with the stub wings, and airflow into the engines. I can't think of a successful supersonic design with standard podded turbofans; there needs to be a way of ensuring the supersonic airflow is in a ready "state" to be sucked in through the compressor, avoiding compressor stall where more air is being sucked in than the engine can actually cope with.

Not criticism, just things the small engineer part of my brain thought.

What would I suggest? I'd mount the engines side by side at the base of the tail, with sufficient ducting coming from the top/sides of the fuselage. This would also eliminate the majority of any potential asymmetric trust issue in an engine failure case.

Doing this would lost the stub wings (potentially a good thing), but leave you with a narrow track undercarriage, whether you go tricycle or taildragger. With a high CofG this isn't ideal. You could go the similar route to the U2, and have guys chasing it in a Subaru Impreza or Mitsubishi Evo...

wahubna wrote on Aug 28^th, 2012 at 2:01pm:


Aren't most landed by the mk 1 human being. It's doesn't matter whether a computer is landing it or not anyway, with any layout with more wheels at the front than the rear, in a conventional aeroplane you have to be able to flare.

Going back to the original post:

Quote:


As I said, simple podded engines just wouldn't work at that speed (certainly not efficiently). High subsonic maybe, but transonic/supersonic? 

wahubna wrote on Aug 28^th, 2012 at 3:16pm:


With the current design, that isn't really an issue.

As for flaring, I stand by my point. Yes you could design an aeroplane and fly it onto the ground in the three point attitude every time, but, IMHO as a passing engineer (once upon a time) and operator, would it be the best solution for what would be a fairly expensive bit of kit. You'd need a very forgiving undercarriage.

I'm not deliberately picking holes, I just offered a couple of points for consideration.

Jayhawk Jake wrote on Aug 31^st, 2012 at 12:26am:


The B-58 did indeed use podded engines. Looking at it, about the first 1/3 of the engine nacelle is devoted to airflow control (with the spike too)


Quote:


Fair enough, you've answered the question then I raised then!

Just playing devils advocate. I'm sure you'll get far more difficult questions to answer from more experienced people when you present your final solution!