The US Defense Science Board has just released its report on the VSTOL/STOL airlift requirements to support the US Army’s concept of “mounted aerial manoeuvre” – flying a fully equipped armoured force from an intermediate land or sea base directly to the battlefield.
The report is important to two camps: the US Army backing the Joint Heavy Lift rotorcraft (left) and the US Air Force backing the AMC-X (right, aka AJACS) replacement for the C-130.
(Artwork via www.secretprojects.co.uk)
Both camps are eyeing the Army’s requirement to airlift payloads of up to 30t over distances of 250-500nm, using either fixed- or rotary-wing aircraft. And the report has good news and bad news for both.
The DSB concludes that suitable aircraft, while technically possible, will be costly, risky and take a long time to field. The report says the “best single fit” is a hybrid aircraft combining rotary- and fixed-wing technology, but warns it is “likely to be very expensive”.
This is good and bad for the JHL camp, which is focusing on a large tiltrotor. Good because a tiltrotor is a hybrid aircraft. Bad because the report makes clear the cost, risk and time required to build a 30t-payload VTOL lifter are inconsistent with the Army’s near-term requirements.
As a result, the DSB recommends alternative concepts be explored. Specifically it believes a 20t payload and 250nm unrefuelled range is “a more achievable near-term goal for hybrid lifters”. But – and it is a big but – that would require the Army to change its operational concept.
The problem is the Army’s Future Combat Systems vehicles are getting heavier. They were planned to weigh 17-18t, so the original JHL studies assumed a 20t payload and C-130-sized cargo box. Now FCS vehicles are pushing 30t and JHL is growing to match. It’s now A400M size. No-one has built a rotorcraft that big, no engine exists to power it, and no existing or planned ship has a deck strong to carry it.
Quad Tilt Rotor – how big can it get?
So the DSB is recommending the US Army goes back and re-examines how big a force it really needs to fly direct to the battle, whether it really needs to airlift its heaviest vehicles, and how small and austere the landing site really needs to be. Tough questions – the answers to which will be key to the future of both JHL and AMC-X.