Over the past few days Russian media sites such as Sputnik and Russia Today have been reporting on plans for a new super-heavy transport aircraft for the Russian Air Force, under the title "PAK-TA". There were conflicting statements about the specifications, although the aircraft would undoubtedly be huge, carrying 200T+ of cargo over 7000km (4350 miles). However what stood out most was the unusual design presented in all the articles.

It is unclear why the design is coming from the Volga-Dnepr (a specialist cargo-charter airline), when other sources claim that Ilyushin (an actual design bureau) will be designing the aircraft. What is however clear is that Volga-Dnepr Group knows how to make fantastic promotional videos:

Vimeo/Volga-Dnepr/Alexey Komarov

Analysis

Unfortunately even a quick analysis shows that the aircraft in the video, however innovative in appearance, is pure fantasy and will never fly. It is clear it is not a serious concept, and may indeed have no connection to the new requirements coming from the Russian military.


General Configuration

A broad lifting body is an excellent choice for a cargo aircraft, especially with regards to its large internal volume. However the choice to place the wing under the fuselage raises questions. The cargo floor would be several meters above ground level (on top of the wing structure) requiring a large and steep access ramp, and the landing gear would probably have to be lengthened to prevent the wing striking the ground during rough landings or steep take-offs.

The design would seem to have a reduced radar signature (always beneficial for military aircraft) and the use of electric fans and a shielded engine would seem to suggest a very quiet aircraft.

Structures

There is little information on structures, however the video presents an approximately square cross-sectional cabin. This would clearly be impractical to pressurise, forcing the aircraft to fly at low altitude and calling into question the range target.

Aerodynamics

The design has a wonderful aerodynamic shape, smoothly blending the wings and fuselage. However the intakes for the main fans are clearly too large and would have a detrimental impact of the overall wing aerodynamics around the critical wing root area. Furthermore none of the intakes are fitted with boundary layer splitter plates and the engines would suffer reduced performance as a result.

Finally the location of the tail engine inlet puts it in the shadow of the fuselage at higher angles of attack. This could lead to pressure loss and engine stall during takeoff rotation.

Propulsion

The video mentions the use of thrust vectoring, although it is not clear why this technology, usually applied to supermanoeuvrable or vertical take off fighter jets, would be relevant. Furthermore the exit-nozzle is mounted quite close to the aircraft centre of gravity and would not be very effective.

The video also mentions an "energy storage" medium, presumably between the turbine and the electric fans. Since the turbine is running in flight it is unclear why energy storage (other than normal aviation fuel) would be needed, and indeed the problem would seem to be more of energy transfer.

Since the electrical fans are dependent on the main turbine for power, this leaves the aircraft effectively single-engined. This could of course be a problem from a reliability/survivability perspective, especially for an aircraft that may take enemy fire, but would also require the development of an entirely new engine on a scale never seen before, at least eight times bigger than the biggest turboshaft/turboprop engine ever made.

In general, the use of electrical fans is questionable, a simple mechanical connection to the main engine would be more efficient and simpler. Furthermore the largest aircraft to have flow until now on electrical power weigh around 2-3T or perhaps less than 0.5% of the expected PAK-TA weight.

Finally the location of the engine seems like a nightmare for maintenance crews, being located on the highest surface of a very large aircraft.

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