Design challenge: next generation heavy-lift cargo plane?

[riggerrob]

Because a design challenge makes more fun with unusual approaches, I would like to propose a design which is a bit out of the box. My idea fairly conventional with some not so usual features. My idea that the resistance of very heavy plane will always be dominated by the induced drag and not by the parasitic drag. The design should therefor focus on maximum lift at take off and a lightweight structure, even if this will lead to higher parasitic drag. The amount of load largely depends on the take-off length on an ordinary runway, therefor the plane should be equipped with very strong turbo prop propulsion, (I added 6 propellers, so it will look automatically very powerfull ;-) .

Heavy load planes already do have something almost like stub wings at the bottom to house the landing gear (e.g. the A400m). In my design, these are more wider, so that they can create a ground effect. It is known, that these small wings helped a lot to lift the flying boats out of the water and Ecranoplanes used something quite similar for all of their lift. These stub wings are not effective in cruise flight, but they do help to get airborne and push the plane from the runway. On the other hand, these wings could also be used to produce downforce (by flaps, see the pics), so that the emergency breaking capabilities should improve. To switch between positive and negative lift, two different flap systems are needed, one aft for creating static pressure between the stub wings and the ground and one in the front to provide downforce when needed. If breaking is improved, the useful runway length can be increased which helps to take off with a heavier load. For take-off, the ground effect take-off flaps should extend at the beginning of the rotation, so that the maximum vertical acceleration can be achieved. By doing so, the rate of climb in the very early starting phase should be increased significantly, so that any nearby obstacles after the runway can be passed safely. Even if the additional ground effect of the stub wings is almost gone after reaching a flight high of about 5 m, the initial higher climb rate and steeper take off can make an important difference in the most critical part of the flight.

Since the stub wings take the load of the landing gear at hard landings, they can carry some of the main wing lift load during flight, so that a strut connection between them helps to reduce the root moment of the main wing and enables a higher wingspan (shorter take off, less induced drag). Struts can produce considerable amount of drag, but this depends very much on the angle, in a nearly rectangular angle to the main wing, as proposed here, this will be much lower than with the usual smaller angles.

My approach is not meant to be a high efficient, fast, long range or even a STOL aircraft, it is a proposal for a plane which should be capable of carrying super heavy loads from standard runways. Other than ordinary cargo planes, it is also not meant to be used as a regular freighter and should not fly in a regular schedule. The Antonov A225 made just few flights per year with a lot of preparation in between. The fuel cost and efficiency in this application will not be a major concern.

I made some drawings, which should demonstrate what it could look like.View attachment 676868View attachment 676869View attachment 676870

Good points Dear Nicknick,

Any specialized heavy-lifter is going to be STOL by definition, simply to allow it to use normal runways. STOL performance becomes doubly important when delivering drilling rigs to mines waaaaaaaaay back in the hills.
Few STOL planes cruise at Mach 0.99999 because of their huge wings. Those huge wings are needed for slow lift-off and landing speeds. The slower the touch-down, the shorter the runway you can use.
Also conisder installing reversible propellers to further shorten your landing roll.
As soon as you quit cruising at Mach 0.9999999, struts become more practical as their drag diminishes rapidly with cruise speed. Consider how several popular light singles (Cirrus, Lancair and RV series) cruise at 200 knots with fixed landing gear. I only worry about exposed struts attracting icing (see restrictions on flying Cessna 208 Caravans into known icing conditions).
For comparison, look at that fixed struts and landing gear on Shorts Skyvans ........ my all-time favorite jump-plane !!!!!!!!!

 

[Nicknick]

I read a paper about struts for braced wings and their resistance (found it in the internet). The strut itself is not the major problem, but the area where it is connected to the wing. The lowest resistance can be achieved with a 90° angle, but than you need to bend the strut which hinders its usefulness. With the low stub wings, a good compromise with a straight strut and close to 90° angle can be achieved. De-icing of the strut might be applied, but icing might also be acceptable since the impact on lift will be low (falling down of heavy chunks of ice might be too risky).

I agree about the STOL plane approach, a heavy lift plane should be designed like a STOL plane but for operation on ordinary runway length.

 

[Nicknick]

Hi all,
Thanks for the many replies, I have tried to incorporate as much as possible.
I had to do a lot of research-work to be able to implement the ideas.
I also noticed that my plane was a lot shorter then the 80 m of length that was allowed.
So I lengthened the plane and added canards in order to be able to change the CoG.
Now this design can carry a cylindrical shape that is 7 m in diameter and 50m long. ( The biggest cargo ever, if I am correct.)And it still has some room to spare...
The plane can do RoRo with regular cargo ( pallets, cars, trucks, tanks,...) But can only be loaded through the nose with extreme cargo. The rear-door is smaller then the nose-doors.
Controlsurfaces still have to be cut, but pretty much everything is there
I removed the fuselage and shaped the nose.( So now it has become a fuselage...)
Wheels also need to be added, two rows of 16 or so wheels should do it?

I thought about the Thunderbird 2 and its way to handle cargo, but that has been tried a few times and it never stuck... I think it is too dangerous... A pallet you can handle and through that you get an idea of how the mass is distributed in it. A car or truck you can secure to the floor and you know it will stay. A container can contain anything, you have no idea what is in it, if it is secured or not. The cargo inside of a container could be moving freely, you don't want some big mass sliding around in it. A container looks solid, but are thin-walled metal boxes that can hold some nasty surprises... Pretty much everything you don't want to be flying around with..

Feel free to comment,

Rob

I really like your design (looking better than my draft....), it could become a nice flying boat as well.

 

[MadRat]

Here's a horrible heavylift idea...

 

[Nicknick]

I’m glad, someone is picking up my ground effect approach . I’m not deep into aircraft design, but I think lifting bodies could be a good idea for heavy lift plane. In this application you don’t need to care about pressurization of windows for the passengers. A more or less square internal volume might be better suited for many purposes than the more roundish shape found in most cargo planes. Despite that, I would combine it with a high aspect ratio, we need all the lift we can get to maximize the useful load.

The fans should not be attached close to the wing surface by the way.

 

[OliverSedlacek]

Not sure I can add much to the wise words of those more knowledgeable in the area of plane design, but the oil exploration business seems to run on AN124s. This has led to equipment being designed with the constraint that it must fit in an AN124 for transport, reducing the need for a bigger plane. The Bloodhound SSC land speed challenger is a typical example as it was designed to be shipped to South Africa in an AN124 even if the fin had to be detached.
Transporting exceptional loads doesn't run on a schedule and takes a lot of preparation, so as others have commented, high cruise speed isn't really called for.

 

[Nik]

Funny thing, this design concept seems to be converging towards 'Burnelli'...

 

[Nicknick]

I was thinking the same

 

[Nik]

IMHO, China may, while Airbus could...

Sadly, I reckon anything Boeing offer would be shunned, due near-certainty of dire cost over-runs, while limping in a decade late...
{ Shakes head... }

Tangential, looks like NASA have handed Boeing a five-year, cost-plus 'Upper Stage' project. As the bemused reporter observed, gonna stretch to a decade...

Either NASA are tossing scraps to pacify Boeing's political backers, or they're spooling enough rope to hang Boeing's beset board from that stubbornly vacant launch-gantry...

 

[CiTrus90]

I've spent a few hours yesterday trying to think of a concept and came up with the following idea, inspired by NASA and Aurora Flight Science's D8.

A quick few renders for illustrations purposes only:





Double-bubble fuselage to allow for oversized cargo.
Same length of the A380 (to comply with possible existing airport limitations), but smaller wingspan (thanks to the lift generated by the fuselage).
4 engines in the same class as the GE90, with those in the rear using BLI propulsion to achieve lower fuel consumption.
RO-RO capabilities with a ramp in the front and one at the rear of the aircraft.

Besides the D8 style fuselage and BLI for the rear engines (with both concepts already widely studied and analyzed), I would tend to keep the design fairly conventional to avoid shouldering R&D costs and possible diffidence towards something looking extremely different to the aircraft already in service.

 

[yasotay]

As always my friend you impress with your logic. A question for those who might know; would a wider cord wing with blown flaps allow the aircraft to take off/land with reduced runway distance? Of course larger wings might reduce range/speed of the aircraft.

 

[Archibald]

Cytrus: I'm loving it. How about a high wing variant with the four GE-90 hanging below ?

 

[riggerrob]

As always my friend you impress with your logic. A question for those who might know; would a wider cord wing with blown flaps allow the aircraft to take off/land with reduced runway distance? Of course larger wings might reduce range/speed of the aircraft.

Wider chord and blown flaps will reduce stall speed, landing speed and landing distance.
We have already agreed that range and speed are less important when hauling weird-sized cargo.

 

[CiTrus90]

Cytrus: I'm loving it. How about a high wing variant with the four GE-90 hanging below ?

Although, I'm not sure the aerodynamic advantages would be the same by changing into a high wing configuration. For sure the removal of the engines from their position in the rear would negate the BLI propulsion gains.

Another thing I think would be necessary is the need to have a swivelling front part of the fuselage (similar to the one on the Super Guppy) to make maximum use of the cabin dimensions (which would otherwise be "limited" by the dimensions of the access ramps).

 

[yasotay]

I think the higher wing makes more sense as it provides more ground clearance for less developed areas where the airfield might not be pristine. I wonder if it would be more logical to retain the outboard engines in the original rear fuselage position to keep the thrust more centerline. The only other consideration I would ask experts about is if moving the wing above the fuselage, to keep the wing box from interfering with the cargo space, would drastically reduce the airframe aero-efficiency.

 

[aim9xray]

Think about aft C.G. problems with that forward wing and aft engine position with the design at post #50. Just sayin'.

Oh, and please pick up the white telephone, Boeing is on the line about: this Model 754 design.

Edit: added SPF thread reference.

 

[Nicknick]

The fans look much to close to the rudde/fuselage in the rear variant, a single one would look much better.

The Nose looks nice, but more horizontal floor length would be a better solution. I also believe the current design would produce downforce (on the nose) that's not desirable...

 

[Michel Van]

I prefer this design from Structural point of view
the wings are attach to main structure that also support cargo load.
it not need the complex frame structure of C-5 or C-17 with shoulder wing
making the hull easier to build
the only main problem that design face, is the conservative mind set of Management of Boeing & Co...

 

[CiTrus90]

I also believe the current design would produce downforce (on the nose) that's not desirable...

It might appear surprising, but it's actually the opposite:

Screenshot taken from The D8 Aircraft: An Aerodynamics Study of Boundary Layer and Wake Ingestion Benefit

Think about aft C.G. problems with that forward wing and aft engine position with the design at post #50. Just sayin'.

Oh, and please pick up the white telephone, Boeing is on the line about: this Model 754 design.

Edit: added SPF thread reference.

As I said, it's for illustration purposes only
I didn't even make proper pylons for the engines, I just lazily made them float above/under the wings. I'm no engineer, or aero expert, nor do I have any technical aeronautical background to fully evaluate this concept, so I hope you will pardon me, but I have absolutely no I idea how much forward or backward (or even what chord, profile and shape) the wing should be.

On the other hand though, I think (empirically) it would be easier (or less expensive/complex as Michel Van noted in his post above mine) to get a "buildable" aircraft from a structural point of view. For example, I think it would be easier to make a pressurization system to work on an aircraft similar to the D8 than any other aircraft whose structure is a departure from the classical tube and wing concept. But....I may very well be wrong about this.

I think the higher wing makes more sense as it provides more ground clearance for less developed areas where the airfield might not be pristine.

This is an interesting point and I think it should be looked at from the point of view of what exactly this aircraft would be called upon to do.

If we intend it to be used in a similar way to the An-225, I think that we would take into consideration only fully serviced civilian airports, so pristine runways, good logistical services in the surrounding areas and previously estabilished routes to bring the cargo to and from the airport where we are going to land in/depart from.
In that case, the aircraft is just one ring of a longer chain and we can decide how many capabilities we are willing to put into the airframe (and how much money we want to put into it, or rather not put into it) and then it's more of a case of "what do we want the aircraft to do?".

If we intended it to replace aircraft like the C-5M and C-17, then the ability to operate from more remote areas with less than pristine infrastractures should be our main concern, together with a possible need for more oriented STOL performances. In which case those capabilities should be the driving factor behind the design, and the answer we are going to face will be "what do we need the aircraft to do?".

 

[Jason Dykstra (Wyvern)]

What about something along the lines of the McDonnell Douglas Nation Builder, but using components of the A380?

Taken from here: https://www.secretprojects.co.uk/threads/mcdonnell-douglas-nation-builder.6139/

 

[MadRat]

As always my friend you impress with your logic. A question for those who might know; would a wider cord wing with blown flaps allow the aircraft to take off/land with reduced runway distance? Of course larger wings might reduce range/speed of the aircraft.

Did you mean lower or higher chord? Higher chord makes least drag. You want drag on takeoff and landing, because you're converting drag into lift. But while cruising you want minimal drag.

They have all sorts of tricks for adding lift while minimizing drag. One way is to increase fineness ratio and decrease camber of a lifting surface. You can run an extension off your fuselage, along the length of the body, as a sort of stubby wing, to get lift off your angle of attack. It unfortunately creates uneven lift in a crosswind. But if your extension runs at the bottom of ypur fuselage it helps minimize that uneven lift in crosswind. Mainly you see these edge extensions on fighters, not transports, where controls are more nimble.

 

[Jason Dykstra (Wyvern)]

Another thing I think would be necessary is the need to have a swivelling front part of the fuselage (similar to the one on the Super Guppy) to make maximum use of the cabin dimensions (which would otherwise be "limited" by the dimensions of the access ramps).

Would a swing nose be a possible option on this? It gives the benefits of the swing nose, without having to disconnect and reconnect the cockpit to the rest of the fuselage. Such options were proposed on designs for the CX-HLS (that led to the C-5), mostly by Douglas, but such a system hasn't been mounted on an aircraft this large.

 

[red admiral]

Swing nose might work. I was wondering about a clamshell like C-124. Or maybe just have a split ramp at the front rather than at the back?

 

[yasotay]

I agree that if the objective of the platform is to operate exclusively from well developed airports the lower wing proposal is likely to be somewhat simpler and likely lighter. However if the platform is to have a military mission, I would think that the rational that has led to almost every military heavy cargo aircraft developed over the last 60 years being a high wing design, would apply.

I am not sure I see that moving the entire nose aside creates an easier ingress to the cargo compartment if you still have to use a ramp to enter. Lowering the front or back gear to create less acute angle of entry might be a method, but you will need an innovative locking mechanism on the cargo floor to overcome the angle of the cargo deck while the aircraft is "kneeling".

 

[MadRat]

Swing nose might work. I was wondering about a clamshell like C-124. Or maybe just have a split ramp at the front rather than at the back?

I like clamshells better than a swinging nose.

They've had lifting noses on some very large aircraft including freight 747s.

 

[riggerrob]

Dear Citrus90,
A high wing eliminates the need to push cargo up and over the wing root structure when loading.
IOW A high wing allows you to almost drag the cargo floor on the runway, reducing the height that you need to raise cargo while loading. This also reduces the amount of special loading equipment needed at destination airports.

As an aside, your high-wing sketches could do with less or even negative dihedral (aka. anhedral) because wing sweep already provides plenty of roll stability. If you build in too much roll stability, it can create annoying "Dutch Roll." Most modern, high-wing military transports have drooping wings to minimize Dutch Roll (aka. too much roll stability).

 

[riggerrob]

Swing nose might work. I was wondering about a clamshell like C-124. Or maybe just have a split ramp at the front rather than at the back?

I like clamshells better than a swinging nose.

They've had lifting noses on some very large aircraft including freight 747s.

You can vastly simplify control, avionics and instrument routings by mounting the cockpit high enough that it never has to fold (see C-5A). Whether you hinge a nose hatch sideways or flip it up vertically is minor in comparison, because it uses hundreds fewer moving parts (e.g. control cables).

 

[BAROBA]

New design idea. I kept the fuselage and changed the wing layout to a box-wing-ish design.
I hope you guys like it.
The nose still has two clamshell doors and the rear a smaller loading ramp ( still need to be made)

Rob

 

[riggerrob]

New design idea. I kept the fuselage and changed the wing layout to a box-wing-ish design.
I hope you guys like it.
The nose still has two clamshell doors and the rear a smaller loading ramp ( still need to be made)

Rob

Good sketches.
Your tandem wing/box wing will be more stable in pitch ... even when un-evenly loaded.