View Full Version : "CAT" (rejected) airplane design!

2005-May-24, 09:04 PM
Hello all!

As you might know, I'm quite busy with getting an aerospace engineering grade. My Bachelor is virtually mine: I need to wrap up this "can't go wrong" project (which is quite some work though), I need feedback on one small exercise, and a professor needs to find a lost exam of mine ( :evil: ).

Anyway, between the Bachelor and the Masters, a large design period of 10 weeks is held. This can be about anything: every year, there are about 15 aerospace subjects.

The subject of the design group I'm in, is working on an "future large aerostructures transportation system". This means that we have to design an aircraft that can carry aerospace constructions up to the size of a Fokker 50 fuselage, tail or wing (17m*3.1m*3.90m cargo) over distances up to a Pacific crossing. (10700 km in the design phase). Takeoff length is limited to just 1500m.

After some serious trade off work, the group was split in a group redesigning the A319 with an extended Beluga-like cargo bay, and a group working on a canard concept. The canard was chosen because it leaves the tail end free of any surfaces, which is easy to incorporate a large cargo door. In order to work from short runways, a low wing (ground effect at take off) was chosen.

Anyway, I was the lead aerodynamics and stability designer of this concept, and hence the external layout was determined mainly by me(placing and sizing of parts; profiles were chosen together with the performance guru :)). Of course the other design group members were very important as well: performance, which estimated the achieved range and takeoff length (among others) of my proposals; structures (which held my design within realistic proportions concerning construction :)), materials and business groups. All together formed the CAT (Canard Aerostructures transporter) concept. It is called "CAT" because the wing/canard combination gives it a catlike frontal view (to us at least :)).

Monday, this concept was thrown into the dustbin however, because it turned out the A319 did about the same job (the CAT had some minor technical and performance advantages, but nothing major) for much less money. As there is only a small market for these plane, the CAT concept was rejected. It is only a viable concept if this design is chosen as a technology demonstrator, giving way to future derivatives with a much lower design cost and extended expertise, allowing to optimize the canard technology as much as current technologies are optimized into the A319. As a technology demonstrator wasn't what the "customer" wanted, we went ahead with the A319.

So what you see below is a concept design of an aircraft which works and perform well in theory, but would cost more than an A380 per piece (20 planes world market)...

A nice detail is that the plane has flaps nor slats, because the canard surfaces take a large share in the lift generation.

Feel free to ask any questions/remarks!!

I've written this in little time, so it probably isn't too clear to all :D.


1280 resolution renders of the concept (the 2 renders above are included in 1280 resolution):

fully movable canards detail (http://upload.talk2.nl/files/768429canards.jpg)

engine details (A319 engine) (http://upload.talk2.nl/files/704970engine.jpg)

front view. Whiskers!!! ==> CAT (http://upload.talk2.nl/files/674763front.jpg)

loading impression (http://upload.talk2.nl/files/330395loading.jpg)

top view (above a well-known site!! 8) ) (http://upload.talk2.nl/files/140927top.jpg)

the wing (http://upload.talk2.nl/files/542092wing.jpg)

winglets (http://upload.talk2.nl/files/700012winglet.jpg)

side view (http://upload.talk2.nl/files/178302zijkant.jpg)

All the artwork presented here is done by me as well by the way, but I wanted to show the design in the first place. My graphics "artist" capabilities are less trained than my aerospace design capacities :wink: .

2005-May-24, 09:32 PM
Why did you choose a canard design?

Captain Kidd
2005-May-24, 09:38 PM
Why did you choose a canard design?

The canard was chosen because it leaves the tail end free of any surfaces, which is easy to incorporate a large cargo door.

2005-May-24, 09:43 PM
I meant, would you sacrifice stability for a better placement of a cargo door?

2005-May-24, 09:47 PM
:). You said it best Captain Kid.


the main philosophy behind a canard here was the completely free tail end, which allows for a very easy and simple cargo door design. This is quite a pro for an airplane that will need a rather huge cargo door, that otherwise interferes with all osrts of cables/wires/hydraulics...

We knew about the stability problems from the beginning. Those were solved as good as possible, but still the cargo placement requirements are very stringent. And the plane can't fly completely empty. To increase stability speed behaviour (the carft IS stable by itself, but with a moment arm of only about 30cm...) a pitch stability computer would have been added.

Other advantages of the canard are:
-increased sound damping of the on-wing engines by the winglets;
-free maneuvre area for cargo equipment between the wings
-IF DESIGNED CORRECTLY a lift gain compared to an aft tail. In most cases, there is a lift loss due to numerous reasons however. In our design, we seemed to go towards a lift gain, even allowing to drop the flaps and slats and STILL operate from 1500m runways!
-IF DESIGNED CORRECTLY the canard is more efficient in cruise. THis is of importance for the long range needed. A canrd design can be optimised for one very specific flight regime only however, and normally is worse than a standard plane outside that regime. Our design appeared to do par or better than conventional layouts in cruise, with high lift gain in takeoff. The lift gain was high enough that ground effect wasn't really needed. But it would be handy anyway, to give us some more slack on emergency procedures and the like.

So Argos:
we chose the canard because of the very easy cargo door design (which is of importance concerning a 1h TAT as well!). WE made this concept design (no details yet) to assess whether it was possible to achieve the other mentioned advantages of a canard as well, without running into too much stability problems.

The final result was that we did have the whole advantage package, with limited stability issues. Also, engine inlet air disturbances were an issue. In the end, the problems of the design were balanced by the advantages, and probably the advantages will further rise if this concept is used more widely. COst was the show stopper at this stage however.

2005-May-24, 11:17 PM
Very cool Nicolas.

Here's a project with a similar purpose that I happen to be working on:


2005-May-25, 06:07 AM
We've got that article hanging on the project room wall :D.

Very cool to be working on that one!

Just to make the scale clear: if the STANDARD 747 had full cross-sectional access to the upper deck, it would be large enough for 2 Fokker 50 fuselages!!

So we're designing a smaller plane. That's part of the problem: we need to have a large diameter for rather short cargo (16m max); it's hard not to make a huge plane (which isn't necessary in our case).

I'll show impressions of the rebuilt A-319 when they're ready! I don't have 3D renders of that one however.

2005-May-25, 08:23 AM
This is way outside my field of expertise (as if I have one :D ), but a few questions popped up.
1. Why the pointy tail? I seem to remember from the racecar discussion in the sixties (Lemans type) that it was a lot more effective to just cut off the tail: the aerodynamics stay the same, and you have a lot less weight (stability changes of course). I suppose that tail has no use in cargo capacity either, so... I know that car aerodynamics and plane aerodynamics are two different beasts, but that doesn't stop me wondering!
2. The position of the engines: the exhaust is above the middle of the wing (near the body, middle of front-back I mean): wouldn't this cause loads of turbulence and pressure on that wing? Wouldn't it be better if the exhaust was beyond the wing?

Apart from that: great! A pity that the A319 is cheaper (is that only because it already exists and so the development costs would be lower, or would the production itself be cheaper as well?).

2005-May-25, 09:23 AM
Hi Fram.

*The A319 is much cheaper in development of course. Production would be about the same. the high production runs of the standard A319 further lower production costs. If second-hand A319's would be used for a rebuild, it would be even cheaper. The Canard lowers its production costs somewhat by the lack of flaps and slats. The A319 cargo bay extension is made from FML, which increases costs and introduces a rather new technollogy in the A319 production, again increasing costs. So material and production costs per plane will be about equal, with the large production runs of A319 variants and the posibility of second-hand planes lower the production costs of the full series for the A319.

*The engines generate a high speed airflow above the wing, increasing the generated lift locally. Directly after the engine nozzle, this airflow isn't too turbulent as this makes the engine more efficient. Also, the engine is placed more than 50cm above the wing, so interference is limited. The outer cold flow protects the wing from the hot inner exhaust gasses.

*In racing cars, good flow attachment would be achieved by a pointy tail of several meters length. The drag decrease created by a pointy tail of 5 meters or more do not outperform the disadvantages in weight and handling. That's why they decided to just cut it off instead. You see this evolution in older racing cars: ever longer, pointier tails when aerodynamic knozledge increased, and then the change in cutting them off when the problems of a long enough pointy tail arose.
The problem with a cut-off tail is that a low pressure gap exist behind it ("the airflow continues where the car already stopped"), pulling the object backwards (drag). Certainly at airplane speeds, this drag is severe. That's why we made the tail cone pointy over 8 meters. it is a lightweight composite cone with no other functional parts in it.

2005-May-25, 09:39 AM
Thanks, Nicolas! I understand it a bit better now. A pity develoment is stopped. Perhaps it would be possible to make a small model, just for fun? I mean like 40 cm long or so...

2005-May-25, 09:47 AM
Go ahead! :D

2005-May-25, 06:53 PM
I just finished the tradeoff presentation. The CAT was presented and explained here, next to the A320 concept. The reasoning behind the decision to go for the A320 finished the presentation.

I guess that was the last thing the Aerospace world heard of the CAT :D :-? .

Oh well, we could keep the dead kitty alive for a while here 8-[

2005-May-25, 07:14 PM
Your team should consider applying for a patent. Seriously, you never know when it might pay off.

Just a couple of other thoughts:
1. I like the empty tailcone idea. Not having to route systems through the hinge is a major advantage. I speak from 2 years of personal experience!
2. I'm not sure about the pointy tailcone, however. A number of recent aircraft have used a laterally flattened tailcone -- various recent Douglas derivatives and the 777 come to mind. Pointy in the plan view, but not from the side. Adds yaw stability, I believe.
3. I think engines over the wings tend to cause pitching moment problems. The airplane tends to pitch down when you add thrust -- not what you want on takeoff.
4. I was surprised at the canard positioning -- I'd have expected it to be at the top of the body. Like the late, lamented Sonic Cruiser. Actuation for such a large all-moving surface might have been a problem, by the way.
5. Was your cargo area going to be pressurized? (Ours is not.) How about the A319 version?

2005-May-25, 08:01 PM
1. That was THE reason why we chose this concept: it seemed like an elegant way to get a completely free end on the plane, with out needing to place the cockpit on the rear (...) or down under (Beluga), and having the fuselage opening over its complete cross section.

2. It does increase the weathercock indeed. We needed the sideview slope for ground clearance during T/O rotation; but we could have done with a 1m end instead of a point. The point could have been rounded by the way, that was just an early design and easy to model in 3D :). The 777 is rather pointy from the side: the "point" is about 0 in top view, and about 1m in side view, which still looks rather pointy and is needed for ground clearance as well (or do I misunderstand you?). A reason to flatten the sides with tailed airplanes is to reduce the gap between aft fuselage and turned elevators; I don't know how much that one played in the 777.

3. Pitch down isn't ideal on take-off. During the rest of the flight, a pitch down moment adds to the pitch stability of the aircraft (nose down = stable pitch direction). In a Canard airplane having inherent pitch stability problems, every pitch down moment is welcome :).

4. High canards increase vertical separation with the low wing, which makes them more efficient (I did not understand the reasoning behind this). We put ours as low a possible, because we want to minimize the interference of the large canards with the wing and engine intake. So we tried to place them below the wing, as the downwash of a high Canardwould have hit the engine inlets anyway. Had the canards been small or further away from the wing, they might have been put on top, because interference was less problematic that way and vertical separation was the prime driver in that case.

5. We wondered whether your cargo bay was pressurized this very day!! We decided against it to save weight, increase internal dimensions, and make the cargo door easier (no bulkhead, no sealing etc). Living cargo isn't too well in the business case of a volume transporter anyway - unless you can sell lots of planes to wildlife parks in Africa (elephants, giraffes...:)).

The plane was scrapped in favor of the other concept after a short and limited design phase only. So there obviously still are quite some design improvements possible on the CAT. It appears now that we don't need the ground effect to get the takeoff length (given that our calculations are a bit correct), so we might put the engines down and the canard up (we lose the engine pitch down moment that way however). Just come to think about it: we didn't use the engine moment in the canard sizing calculations, so keep quiet about this!! :D . There's still the stability problem of course, which translates into stability computers (though the plane has -very limited- aerodynamic stability) and severe cargo placement restrictions. And the tail cone should be designed. Tail cone design went like this in this phase:
*we need X clearance for rotation, and [formula for airplane length and other parameters] about Y meters of length for aerodynamics, so *hoppa* here is our tail cone! :) Design work obviously would optimise the shape. But I do like the completely clear rear end: both in funciotnal parts inside the cone, and with the cone on top of the fuselage (see larger renders) during loading.

So we won't go into patenting now. Had it beendesigned to a more detailed level, and turned out to be rather good performing, we might have had a case.

Thanks or the interest!

I made the renders with SoftCad 3D Lite V1, and merged in Paint Shop Pro V7 by the way.

I saw the video of the "pregnant guppy" today: completely insane! They split the plane in half to load a fuselage into it. Turn around time was like 2 days :lol:.

2005-May-25, 08:12 PM
By the way what is your exact task in the 747 design?

2005-May-25, 08:36 PM
And another thing I forgot to post:

both in the CAT as in your 747 project, you could theoretically use Envirotainers if you needed to transport not too large goods requiring climate control in the plane, even when the cabin isn't pressurized/climatized.

2005-May-25, 11:37 PM
By the way what is your exact task in the 747 design?

I probably shouldn't be too specific, sorry. I'm on the Systems side of things.

You should see the bulkhead between the cargo area and front! Imagine an aluminum waffle the cross section of a 747 and over one foot thick....

Do you actually have waffles in Belgium, by the way? "Belgian waffles" are quite popular here.

2005-May-26, 12:14 AM
I saw the video of the "pregnant guppy" today: completely insane! They split the plane in half to load a fuselage into it. Turn around time was like 2 days :lol:.

I'm suprised you didn't go this method (http://www.globalsecurity.org/military/systems/aircraft/images/c-5-11.jpg) for quick cargo loading. Open up both ends :D

More cool pictures here of the C-5 Galaxy (http://www.globalsecurity.org/military/systems/aircraft/c-5-gallery.htm), if anyones interested.

2005-May-26, 01:27 AM
Have you seen these aircraft?

Carvair (http://www.aerofiles.com/carvair.html)

Conroy CL-44 (http://www.oldprops.f9.co.uk/props1/Canadair%20CL44%20Photographs.htm)

CL-44 (http://www.flyingtigerline.org/images/imageA24.jpg)

Flying Tiger's CL-44's had a swing-tail to permit the loading of long items.

2005-May-26, 04:34 PM
Trebuchet: I understand about not being too specific. But the combination systems and hinge issues makes it rather clear to me :).

We do have waffles in Belgium! Lots of them :D.
The compressed part of that 747 is only the front (cockpit) area, right? But with such a large fuselage that requires a huge bulkhead indeed!

Metricyard: Roll on - Roll off is very fast for (military) vehicles. A load ramp isn't handy to load things like wings and fuselages however. And it isn't compatible with the standard high loader equipment on airports. So it's a very good system, but in the environment where our concept is going to be used, it adds little value. With a fuselage that is easily accessible on one side, we get our 1h TAT as well. Furthermore, opening up your plane on both ends causes serious structural problems, and opening the fulseage on its full cross-section on both ends is really hard.

The Galaxy is just huge! the "small" bubble on top alone houses more space than many medium sized craft have... That plane is so cool! But certainly in the first version it was terribly expensive to maintain. The updated version improved this, but they remain very expensive in maintenance. And they plan on keeping them in use for many more years...

tmosher: We've seen all those craft indeed, and many more :) (on pictures, that is). Our current A320 concept is based on some of those concepts.

2005-Jun-08, 07:16 PM
I just wish the new Airbus plant (in Mobile AL I hope) is built big enough for AN-225. I would love to see that saved.

2005-Jun-08, 07:24 PM
I'm ging to the AIrbus plant in Hamburg on tuesday. I'll get the standard tour, plus a special Beluga tour 8). WE won't be able to go inside the Beluga normally, as it is being loaded and unloaded of course.

I don't think AIrbus will spend it's time and money building an Antonov aircraft - especially when it's not a new design.

2005-Sep-27, 07:53 AM
I forgot all about posting our final rebuilt A320!

I'll see if I still have an image here...

Here you go:

Huge I know, but hey it's probably the last post here.

All artwork except for the DoubleA logo done by me :).
(BTW runway length with full cargo is <2000, that's a mistake on the poster. It gets <1500m empty or with limited load).


2005-Sep-29, 08:26 PM
That is lovely!

2005-Sep-30, 10:20 AM
Thank you!

That Astra is one of my better Photoshop creations; it looked quite realistic up to A0 poster format :).