Simviation Forums

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

"..predator had sex with a sky crane" 

Nice way to put it!

I actually think it is just a more developed NASA/AMES AD-1
http://en.wikipedia.org/wiki/NASA_AD-1

I would love to do a different type of aircraft for my senior design project, but the way it is done here at WMU is not very conducive to that....although some Mechanical engineer student managed to convince faculty to let him do a very standard airboat... :-?

At any rate, thank you very much Jake for posting it. I am doing a drawing halt on my design while I absorb the the info you gave including revisiting the wing.

One thing that is very daunting for this design though is what I saw last week at work. I was looking at our master drawing list for the YMF-5 when I discovered well over 3,000 different part/assembly numbers! This does not cover all the different dash numbers (like 51134-0,-1,-2) nor does it cover all the purchased equipment... Albeit the YMF-5 is a biplane, has excessive numbers of parts, and is much larger than my XS1.

I have to ask about your design though, I bet the take off and landing speeds would be really high with such a tiny wing even at 0sweep. Without reading through the report, do you remember an approximate what those speeds were?

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. 

[quote]"..predator had sex with a sky crane"

[quote]My only suggestion to your design, as a lowly pilot, is that is would be quite difficult to land with that landing gear arrangment.

[quote][quote]My only suggestion to your design, as a lowly pilot, is that is would be quite difficult to land with that landing gear arrangment.

As a UAV with a good flight control computer the landing gear would not be too much of an issue I would think.

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:

The mission was to carry a rocket to 50000 feet and launch it from supersonic speeds

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

As a UAV with a good flight control computer the landing gear would not be too much of an issue I would think.

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.

There are actually several UAVs that can land autonomously and modern fly-by-wire systems are extremely advanced. In fact, a recent test was conducted in which a USN F/A-18 had ~1/3 of a wing blown off by explosive bolts then the computer landed the plane by itself...it landed extremely close to the exact landing spot (with in 3ft I think). An aircraft also does not have to flare to land, the whole point of a flare is to slow down and lower decent rate to provide a smooth touch down. This could be achieved with appropriate use of air brakes and lift enhancement devices which when coupled with a modern UAV system would easily allow for minimal flare or even eliminate it. Rather than worry about the flare, I would have brought up cross wind tolerance..narrow track gear could spell disaster during the landing/takeoff rolls or while on the ground (as in taxi)

I would have brought up cross wind tolerance..narrow track gear could spell disaster during the landing/takeoff rolls or while on the ground (as in taxi)

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.

I've been a bit busy, I'll address a few points now and come back later for the rest.

The engine location was based on a recommendation from my professor, I was never fully sold on it but when the man grading the paper said I should do it, I should do it

There have certainly been podded engines on supersonic aircraft, and there's no reason they wouldn't work (besides my inlets being improperly sized and located, but that's a detail design feature that I didn't get into).  First aircraft that comes to mind is the B-52 Hustler, but I'm pretty sure there have been others.  On a redesign I would have used engines nested in a pseudo-fuse under or behind the wing.

The idea with the inlets would have been to use a
moving spike inlet as many other supersonic aircraft have used in the past.  These engines are not designed for supersonic flight, but that could have been remedied.  Inlet design was beyond the scope of this design. 


Landing would have been challenging but not impossible, especially since it sits level.  As I stated in the original post, landing gear design was definitely one of the weak points of my aircraft, and given the opportunity to redesign it would have been a traditional tricycle gear.

Many of my classmates designed fighter jets, that weighed as much as F-15's.  I focused on the ferry mission and maximizing cruise, centering my design around the oblique wing concept.  This meant compromises in powerplant configuration to meet the silly supersonic requirement.

Frankly, if I had the freedom to do ANYTHING, I would have written a 20 page paper describing the modifications I would have made to  retired F/A-18 A through C model to turn it into a cheap space launcher, as a new aircraft program would be excessive

[quote]
There have certainly been podded engines on supersonic aircraft, and there's no reason they wouldn't work (besides my inlets being improperly sized and located, but that's a detail design feature that I didn't get into).