Shenyang FC-31 / J-31 Fighter Demonstrator

gelgoog said:

From what I understood from the interview with the FC-31 designer it is more of a concept platform to test new airplane design technologies. However from what I gathered from comments elsewhere there is a high likelihood that Shenyang *did* get funding from the PLAN to design a fighter but it is something larger than the FC-31 base design. Regardless of that we will get to see a new naval fighter design enter operations in a year or two I think.

Like I said here before I expect to see FC-31 v3 until May.

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I would not be surprised if we see FC-31 "v3" by the end of the year or early next year, but I'm not sure why you would specifically mention May so confidently.

And it will obviously take more than two years for the aircraft itself to enter service. I'm sure significant risk reduction and data from the many years of test flying FC-31 v1 and v2 would benefit the development of v3 and help to shorten it somewhat, however considering it is still a new naval fighter you can expect a development period of 4-5 years at least.

November 8, 2015

Sometimes there are details in old news that people miss out.

The Aviation Industry Corporation of China (AVIC) is "in negotiations" with the Chinese Air Force to buy the multi-role FC-31, AVIC project manager Lin Peng told reporters on Sunday. Peng declined to say when a deal would be finalized.
...
The test aircraft has been flying for more than two years, Peng told reporters after the briefing. AVIC is planning first flight of the production aircraft in 2019, with initial operational capability scheduled for 2022. The FC-31 will be fully operational in 2024.

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With regards to my guess about May 2019 it is just an educated guess. If you take into account the news from 2015, together with the time it took from v1 to v2, then v3 should come out this year. Typically the news for the new aircraft have shown up in September/October and it either gets displayed in the Zhuhai Airshow in China or talked about at the Dubai Airshow to try to sell it to Middle Eastern clients. Those airshows typically are in November.
However I expect the timeframe from v2 to v3 to be shorter than v1 to v2 because of the increased experience of the design team. Then there is also the fact that CV-16 and CV-17 look pretty much complete with their refit and trials respectively. They were painting the marks on the runway in CV-17 last time I heard about it. Regardless of which aircraft they actually deploy initially I think there is a decent chance they will try to align the unveil of the prototype with the end of the trials of CV-17. So I came up with that date.

But like I said it is just a guess. For all we know the naval FC-31 will be substantially different from the plain FC-31 similar to the differences between the F-35A and F-35C. It is supposed to enter service with more powerful engines. I think the naval concept might be larger than previous prototypes or even v3.

The F-35C is physically larger and heavier than the F-35A with a much larger wing area.

Bltizo said:

I would not be surprised if we see FC-31 "v3" by the end of the year or early next year, but I'm not sure why you would specifically mention May so confidently.

And it will obviously take more than two years for the aircraft itself to enter service. I'm sure significant risk reduction and data from the many years of test flying FC-31 v1 and v2 would benefit the development of v3 and help to shorten it somewhat, however considering it is still a new naval fighter you can expect a development period of 4-5 years at least.

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Do you expect to see modifications to the FC-31's weapons bay? The previous prototypes' bays seem very small and shallow, incapable of carrying serious strike munitions. I don't think we'll see the v3 take on the bulbous, bumblebee-like appearance of the F-35, but the bays strike my layman's eye as needing expansion. Is it too soon to see apertures on the next prototype similar to those on the F-35/J-20? Also, if accepted by the PLAN, do you think we'll see initial batches with interim engines or straight to the WS-19?

ZeEa5KPul said:

Do you expect to see modifications to the FC-31's weapons bay? The previous prototypes' bays seem very small and shallow, incapable of carrying serious strike munitions. I don't think we'll see the v3 take on the bulbous, bumblebee-like appearance of the F-35, but the bays strike my layman's eye as needing expansion. Is it too soon to see apertures on the next prototype similar to those on the F-35/J-20? Also, if accepted by the PLAN, do you think we'll see initial batches with interim engines or straight to the WS-19?

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I don't think we've had any pictures of FC-31's weapons bay internally yet.

But I think it might be similar in size to J-20's main ventral weapons bay, and we've read rumours of a small diameter stand off powered munition being developed to allow it to carry four internally and to be intended for the naval 5th gen fighter too. If it achieves performance similar to similar weapons like JSM, I think that's adequate. It's a smaller weapons bay than F-35 but that is adequate.

Almost certainly interim engines.

gelgoog said:

For all we know the naval FC-31 will be substantially different from the plain FC-31 similar to the differences between the F-35A and F-35C. It is supposed to enter service with more powerful engines. I think the naval concept might be larger than previous prototypes or even v3.

The F-35C is physically larger and heavier than the F-35A with a much larger wing area.

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A carrier based aircraft must be capable of a lower landing speed and more precise flight control during landings than required for a land based aircraft. This is the reason why the F-35C has a bigger wing area than the F-35A. It requires that the aircraft has to fly in a controlled prescribed approach path some four degrees below the horizontal to the flight deck at a precise, not-to-exceed speed into the arrestor wire as the wires have a limiting load beyond which they will break. This is an extremely challenging requirement and drives the design of the aircraft. The standard USN approach speed is around 130 to 135 knots, which delivers stable approaches and minimum ‘trap intervals’ (essential when numbers of aircraft are being recovered) at a speed that the arresting cables and engines can cope with. This speed delivers precision approaches, so that the ship needs only three cables for reliable ‘traps’. It also allows the aircraft to cope with the ‘burble’, which is the area of turbulent air immediately behind the ship, through which the aircraft must fly. The four degree downward approach path minimises the ‘burble’ effects and ensures that the aircraft will not fly into the stern of the carrier if it is pitching. Finally, this approach allows the aircraft, should it fail to engage the wire, or suffer a wire or hook failure, to accelerate immediately and take off again (a bolter) within one second of touching the deck.

Deck landing into arrestor wires requires precise control of speed, aircraft attitude and glide path. Any diversion from the prescribed approach parameters can and does result in various undesirable effects:
a) Too high an approach speed can cause the hooked wire to break leaving the aircraft with not enough residual speed to take off again but too much speed to stop on the deck: resulting in the loss of the aircraft.
b) Aircraft attitude (the angle of attack that the aircraft wings are presented to the air stream) must be accurately controlled. Too high a nose attitude at the prescribed speed will cause the loss lift from the wing surfaces and the aircraft will rapidly sink towards the stern of the ship. Too low a nose attitude will result in an increase in air speed, giving the aircraft to much inertia for the arrestor wire to cope with – and the latter will break.
c) Maintenance of the prescribed glide path is necessary to ensure that the hook does indeed catch a wire. If you are too low on the glide path, the hook can bounce over all the wires (or you may crash into the stern of the ship. If you are too high on the glide slope, your hook will miss the wires.

In other words, the correct air speed, attitude/angle of attack and glide slope must be maintained in a stable fashion all the way down the approach path to the deck. This means that the inertia of the aircraft, both horizontal and vertical, remains constant to the touchdown point: there is no reduction in rate of descent of the aircraft (as with landing on an airfield) and the forces that the aircraft under-carriage has to contain are markedly higher resulting from any pitching deck and “ship heave”.

The prescribed glide path for deck landing is steeper than that experienced ashore. On land, the prescribed glide path is 3°. But the land is stationary. With the ship moving at up to 30 kn away from the aircraft on the approach, the deck landing sight it is set at 4° which gives the aircraft an approach path through the air of just 3°. If the ship’s deck is pitching 2°, this leaves only 1° of clearance between the aircraft flight path and the stern of the ship.

The design has to balance a landing configuration weight and at speeds requiring very advanced flight controls. I suspect the J-15 crashes are connected to these issues and probably requiring the design to be tweaked if it is at all possible. Bottom line is even if you can check off 99.0 % of the boxes but if the design doesn’t allow for a safe aircraft recovery you don’t have a design – period.

Bltizo said:

And it will obviously take more than two years for the aircraft itself to enter service. I'm sure significant risk reduction and data from the many years of test flying FC-31 v1 and v2 would benefit the development of v3 and help to shorten it somewhat, however considering it is still a new naval fighter you can expect a development period of 4-5 years at least.

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A navalised version will be significantly different from the earlier versions and any flight testing data taken from the earlier version will have limited utility notwithstanding the fact that it was limited to single prototype testing for each version.

Carrier-based aircraft require heavier structures to withstand catapult launches and arrested landings. Put in perspective, the deceleration force experienced in arrested carrier landings is 24 times greater than that experienced by land-based aircraft, and the vertical impact force is over 3 times the level encountered by land-based aircraft. Inevitably aircraft weight is significantly added and will be different from any earlier versions.

In addition, there are a list of design limiting features unique to carrier based aircraft including :
(1) The landing gear and arrestor tail hook placement have to be compatible. Main landing gear placement is limited to allow for adequate wheel clearance from the edge of the carrier deck during catapult launch. Launch loads for a STOBAR design are not as bad as for a catapult launch, but the loads on the nose leg are still non-trivial. The arresting hook system appears simple but represents a major challenge for aircraft design. The dynamic interaction between the aircraft and the arresting system at around 135 knots is massive, and reliably bringing aircraft to a halt in around 350 feet is difficult and dangerous. The F-35C had to redesign the tail hook when it did not work when tested at sea.
(2)Balancing a minimum fuel and carry back weapons load weight against magnified stress.
(3)Size and weight limits imposed by carrier operations associated with handling an aircraft above and below decks. Strict size, weight, and configuration are not normally imposed on land-based aircraft. The need to park and maneuver a large number of aircraft while avoiding obstructions, not only limits the aircraft’s length and width but also necessitates folding the aircraft’s wings. Similarly, aircraft weight is limited by the capacity of the carrier’s elevators, catapults, and arresting equipment. In other words, the design has to fit carrier set requirements both with existing and those being build.
(4)It must provide the pilot with adequate visibility to make a safe carrier approach and landing. Steep approach angles, required for carrier landings, demand that the aircraft’s cockpit and front fuselage design provide the pilot with an unobstructed view of the carrier deck and stern. This degree of over-the-nose visibility is unnecessary for a land-based aircraft.
(5)Finally, the mother of all problems. The design requirement for excellent low speed flying qualities tailored to carrier approaches and landings including handling the pitching and rolling deck of an aircraft carrier at sea.

There is likely to be a number of iterations back to the drawing board type moments on top of the extensive testing at sea needed. For example, an initial design might end up with a weight and mission payload that is not suitable for deck recovery. It would then require a program to overcome the issues either through weight reduction or in wing lift design.

I doubt you can get to the end point in 5 years or less. In comparison, the X-35 first flew in 2000 and the F-35C will very likely declare IOC this month.

Brumby said:

A navalised version will be significantly different from the earlier versions and any flight testing data taken from the earlier version will have limited utility notwithstanding the fact that it was limited to single prototype testing for each version.

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I think that the utility of having had two flying demonstrators in the air since 2012 and 2016 respectively provides the carrier based FC-31 derivative with a far more advanced starting point than if SAC were to start off building a carrier based 5th gen fighter from a clean sheet design (i.e.: no land based tech demonstrators or airframes flying at all).

One way of judging this will be to see whether the initial FC-31 V3 prototypes we see are "tech demonstrators" similar to J-20 prototypes 2001 and 2002, or if they are more like J-20 201X prototypes which were of course far more structurally mature and with accommodation for key avionics that were either progressively more present or fully present among the successive 201X airframes.

Carrier-based aircraft require heavier structures to withstand catapult launches and arrested landings. Put in perspective, the deceleration force experienced in arrested carrier landings is 24 times greater than that experienced by land-based aircraft, and the vertical impact force is over 3 times the level encountered by land-based aircraft. Inevitably aircraft weight is significantly added and will be different from any earlier versions.

In addition, there are a list of design limiting features unique to carrier based aircraft including :
(1) The landing gear and arrestor tail hook placement have to be compatible. Main landing gear placement is limited to allow for adequate wheel clearance from the edge of the carrier deck during catapult launch. Launch loads for a STOBAR design are not as bad as for a catapult launch, but the loads on the nose leg are still non-trivial. The arresting hook system appears simple but represents a major challenge for aircraft design. The dynamic interaction between the aircraft and the arresting system at around 135 knots is massive, and reliably bringing aircraft to a halt in around 350 feet is difficult and dangerous. The F-35C had to redesign the tail hook when it did not work when tested at sea.
(2)Balancing a minimum fuel and carry back weapons load weight against magnified stress.
(3)Size and weight limits imposed by carrier operations associated with handling an aircraft above and below decks. Strict size, weight, and configuration are not normally imposed on land-based aircraft. The need to park and maneuver a large number of aircraft while avoiding obstructions, not only limits the aircraft’s length and width but also necessitates folding the aircraft’s wings. Similarly, aircraft weight is limited by the capacity of the carrier’s elevators, catapults, and arresting equipment. In other words, the design has to fit carrier set requirements both with existing and those being build.
(4)It must provide the pilot with adequate visibility to make a safe carrier approach and landing. Steep approach angles, required for carrier landings, demand that the aircraft’s cockpit and front fuselage design provide the pilot with an unobstructed view of the carrier deck and stern. This degree of over-the-nose visibility is unnecessary for a land-based aircraft.
(5)Finally, the mother of all problems. The design requirement for excellent low speed flying qualities tailored to carrier approaches and landings including handling the pitching and rolling deck of an aircraft carrier at sea.

There is likely to be a number of iterations back to the drawing board type moments on top of the extensive testing at sea needed. For example, an initial design might end up with a weight and mission payload that is not suitable for deck recovery. It would then require a program to overcome the issues either through weight reduction or in wing lift design.

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I'm quite well aware of the additional performance demands that a carrier based aircraft faces, however this doesn't take away from my argument that having had two flying tech demonstrators for 8 and 3 years respectively would have provided them with significant risk reduction and provided a starting point ahead of if they were starting development of a new clean sheet aircraft.

I doubt you can get to the end point in 5 years or less. In comparison, the X-35 first flew in 2000 and the F-35C will very likely declare IOC this month.

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I don't think a direct comparison between the PLAN 5th gen carrier fighter (assuming it is indeed FC-31 derived) and the F-35C is particularly useful in terms of extrapolating timescales given what we know about the respective programme structure of each type.

Bltizo said:

however this doesn't take away from my argument that having had two flying tech demonstrators for 8 and 3 years respectively would have provided them with significant risk reduction and provided a starting point ahead of if they were starting development of a new clean sheet aircraft.

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Typo, 7 or 6 years. but who's counting.

Although I don't sign up to the idea that FC-31 is the naval ship-borne fighter, I do think that there is a chance that SAC designed FC-31 from the beginning aiming for that purpose, so FC-31 as we see today does have the fuselage designed for catapult launch. This also means that we should be careful not to be locked to the thought of "land based aircraft to be modified for ship borne" and the prolonging of development time associated with.

The base of the thought that FC-31 was started as a land-based aircraft are 1) the HOPE of PLAF adoption (after failed to J-20) and an export opportunity. What IF PLAF has made it clear that they don't want a FC-31 sized aircraft and will never (chance lower than 1%) want? In this case, SAC designing FC-31 dedicated to the carrier will make much more sense.

If you compare the specifications of the Russian air force MiG-35 and the naval MiG-29K you can also see that the MiG-29K has more wing area. In that regard it is similar to the F-35A vs C.

Given the MiG-29K or the Rafale M's specs I think the FC-31 has too small of a wing to be usable as a naval airframe. The wing area is too low. But I could be wrong since the fuselage of the FC-31 might provide more of a lifting body effect than a MiG-29 or Rafale based design. I would not be surprised if things like the landing gear were already optimized for the naval role in the FC-31 prototype. However the wings, those I think would need to be larger. Perhaps even foldable. The fact that the design is built using modern manufacturing methods might mean that both versions of the FC-31 could be more different than something like the MiG-35 and the MiG-29K which seem to have the same basic fuselage to increase parts commonality. You would preferably design a naval version to have larger fuel tanks to increase range. You would want a lighter airframe on the frontal aviation fighter, not strengthened for hook landings, so you can increase the combat payload.

A carrier fighter needs to support lower landing speeds and it also needs to have more range than a comparable frontal aviation fighter. Thus a higher larger area makes sense.
A frontal aviation fighter will put more emphasis in maneuverability. So you use a smaller wing area.

So I think China is making a design which they can sell to foreign air forces, might be purchased in limited numbers by the PLAN, or the PLANAAF in land based formations, and a modified version optimized for the naval role. This is the scenario which seems to fit the available information better in my opinion.