Sukhoi’s new stealth fighter

Today Sukhoi announced the first flight of their new PAK FA stealth fighter-bomber, intended as a competitor to the US F-22 Raptor. The prototype is known as the T-50. (Click the picture below for a much larger view.)

A great deal of comment has already been heard from various sources, but a number of features stand out immediately.

1. This is a much larger aircraft than the US F-22 Raptor. Two weapons bays are beneath the fuselage, with two much smaller bays beneath the inboard portion of the wings. That gives it a significantly greater internal armament capacity than the US aircraft, both in quantity and in weight of weapons. This is, of course, part of the PAK’s heritage from the earlier Su-27/30/35 fighter series, which could carry a formidable array of weapons.
2. Given its size, it’s likely that the PAK FA will have a significantly longer range on internal fuel than either the US F-22 Raptor or F-35 Lightning II. That’s a real advantage in a combat situation. The PAK’s centroplane, extending well beyond the engines and terminating in a sort of ‘beaver-tail’ between the engine exhausts, will carry most of its extra fuel, as it does in earlier Sukhoi models.
3. The engines are almost certainly a limited development of those being fitted to the Su-35. It’s likely that these aren’t the final engines for the PAK FA, as those will still be under development; but they’ll probably be an evolutionary model of the Su-35’s engines, rather than something completely new.
4. The stealth features of the new aircraft are not well represented in this prototype. There are many joints in fuselage panels and protrusions of equipment that will wreak havoc with its radar cross-section (witness, for example, the infra-red vision system housed in front of the cockpit in the photograph above). Clearly, this first PAK model is a prototype to test engines and basic systems. It doesn’t carry the advanced materials that will be needed to provide true stealth, and its build quality will have to be significantly enhanced to achieve that status.
5. The new fighter doesn’t have forward canard winglets, as did the Su-30 (which were also dropped in the Su-35). What it does have is most interesting: a movable leading edge extension to the wing. This will provide some interesting maneuvering characteristics, but I’m not sufficiently engineering-oriented to be more specific. I’m sure more knowledgeable commentators will have a great deal to say about this in the near future.
6. The PAK’s control surfaces and twin tails are much smaller than I would have expected; but this is, of course, because a significant amount of its aerodynamic control is imparted by three-dimensional thrust-vectoring engine exhaust nozzles. This can be both positive and negative: it provides very rapid changes in attitude, but if you lose one or both engines, your maneuverability immediately degrades to the point of a real pucker-factor problem. In addition, the twin tails of the PAK are fully maneuverable, in similar fashion to the US SR-71 Blackbird. Again, that’s great as long as you have power and hydraulics to move them; but if you lose power or hydraulics, you’ve got a major problem.

This photograph of the PAK FA prototype in flight demonstrates many of the features identified above. I apologize for the fuzzy image: it was taken from a video clip of the flight. Again, click the picture for a larger image.

How representative is the prototype we saw today of the production aircraft? Bill Sweetman of Ares sums it up well, in my opinion:

How far along is the program? Russian practice historically has been to start development with a series of prototypes that successively conform more to the production design. That’s followed by an early series of aircraft that are “pre-operational” – flown by service units. Today’s T-50 is, in US terms, something between a technology demonstrator and a systems development and demonstration aircraft.

Here’s Sukhoi’s official video of the PAK FA’s first flight.

It certainly looks like a promising beginning. I’d expect at least four to five years to elapse before we see a version that’s close to the finished, in-service product: and that will take a great deal of money to achieve. If funding can be found (India has expressed interest in co-developing the PAK FA, and might be a source of capital) it’s likely to provide stiff competition to the F-22 and F-35 in years to come. Congratulations to Sukhoi on a good start to the program.

Peter