Sunday, July 12, 2015

The rapidly changing face of aviation technology


Regular readers will be aware that I worked on certain aspects of a fighter aircraft project in South Africa during the 1980's.  A few details may be found in Weekend Wings #39, #40 and #41.  As a result, I've maintained a passing interest in the field of military aircraft design.

I was therefore taken aback to read the very high demands being made by the USAF in terms of the capabilities of its new advanced trainer.  Flight Global reports:

The US Air Force is not backing away from the ambitious sustained g requirement for its T-X next-generation trainer that has sidelined at least two proposed aircraft types and driven the competitors toward clean sheet designs.

When the competition to replace the 55-year-old Northrop T-38 Talon got underway in 2010, pundits predicted the air force would favour price over performance, and vendors rushed to offer ready-made examples like the Alenia Aermacchi M-346 (offered as the T-100), BAE Systems Hawk Advanced Jet Trainer and Lockheed Martin/Korea Aerospace Industries T-50 Golden Eagle.

However, the initial set of requirements posted in March narrowed the field and caused the primes to reassess their initial offers, with General Dynamics parting ways with Alenia Aermacchi and Northrop reconsidering its Hawk offer in favour of a clean sheet design.

In a 10 July statement, Air Education and Training Command confirmed that the minimum T-X sustained g requirement of 6.5 g and objective of 7.5 g remains unchanged from the key performance parameter published in March, even though it would exclude a number of viable trainer options from the competition.

The requirement sets a high bar for manoeuvrability, requiring the T-X to sustain that load at a pressure altitude of 15,000ft for at least 140 degrees of a full turn with minimal loss of energy and altitude.

“Initiated at or above 15,000ft pressure altitude, at or below Mach 0.9, and at or above 80% fuel weight, the aircraft’s flight path angle during this manoeuvre can be no lower than 15 degrees nose low while losing no more than 2,000ft of vertical altitude and 10% of the initial airspeed,” AETC says.

There's more at the link.

The astonishing thing about that g-force specification (which is described in much more detail in the source article) is that as far as I'm aware, until the 1970's no front-line fighter in the world could sustain it - much less a trainer!  Even today the types of aircraft that can achieve that performance can probably be counted on the fingers of both hands.  They probably don't include the F-35, which will replace most of the F-15's and F-16's in the USAF inventory.  Such a specification means that the USAF expects its future fighter aircraft to exceed that level;  therefore, it wants its pilots to learn to handle it before they get into the cockpit of a combat aircraft, as opposed to a trainer.

It's strange to think that an advanced trainer of the 2020's will have aerodynamic and aerobatic performance far superior to the fighter jets on which I was working in the 1980's, or those that fought the Desert Storm air war in the 1990's.  This isn't just an evolutionary development;  it's revolutionary.  I suddenly understand much more clearly how designers of the final generation of propeller-driven fighter aircraft during World War II, the Spitfires and Mustangs and Bearcats and Corsairs, must have felt to see the jet age overtake them.

I think I feel old . . .

*Sigh*

Peter

7 comments:

RHT447 said...

Always fascinated me how the laws of physics led designers to more less the same place. For example, late model P-47s, the Tempest II, and the Nakajima Ki-84.

Wayne Conrad said...

I wonder if the actual goal is just to make the replacement cost more money. In a world where the F-35 is seen as a good thing, nothing has to make sense...

Angus McThag said...

It makes me wonder if this is some back-door deal to get some new F-16's...

And I'd be amused beyond words if the performance numbers mean a fighter has to be bought and a stripped version of the F/A-18F were the winner.

bmq215 said...

I'm no aerospace engineer but this makes sense to me in that A) it should be easier and cheaper to design a trainer for those requirements than a fighter due to reduced weight (from lack of weapons, complex avionics, fuel reqs, etc) and therefore reduced inertia and B) there's no point in designing a trainer that doesn't help pilots orient to the craft they'll be flying, especially when C) it took 55 years to talk about replacing the T-38 and I don't see that period getting shorter in today's procurement climate.

JoeMama said...

I think Angus might be on to something.

It would actually be pretty clever if the trainers had enough capability to press into service in the event that too many of the hyper-expensive (read, cannot afford enough units to sustain real conflict losses) fighters become in-op.

Not every mission requires stealth. Mounting hard-points are mounting hard-points.

Nathan said...

Faster, higher, farther...

the USAF's unofficial design motto can be such a curse. Alas, I do not think my generation has a John Boyd.

Billll said...

Sounds like a back door shortcut to an unmanned fighter.