26 Sep 2018, 17:06
element1loop wrote:babybat{}.net wrote:The only one "but". If LFMS will appear, it will anyway be twin-engine like j-31.
These numbers are from specs, my calcs and some estimates (as noted):
J-31
Fuel Load ~12,000 lb (About all it could be given MTOW and implied empty weight plus claimed payload on Wiki page)
Empty Weight 37,363 lb (Obtained via claimed MTOW, minus the claimed available ‘payload’ of 17,637 lb. In 2015 Wiki claimed empty weight was 38,801 lb … so I’m being a bit generous)
Max Internal Weapons 4,409 lb (claimed 2,000 kg internal and 6,000 kg external)
TOW (with that configuration is) 53,772 lb
Remains under MTOW by 1,228 lb
MTOW is claimed as 55,000 lb
J-17 RD-93 (x2) engine thrust:
Dry Thrust lb=22,210
A/B Thrust lb=36,570
Resulting power to weight ratios with claimed full internal weapon payload used up:
Dry 100% fuel 0.41
AB 100% fuel 0.68
Dry 75% fuel 0.43
AB 75% fuel 0.72
Dry 50% fuel 0.47
AB 50% fuel 0.77
Dry 25% fuel 0.51
AB 25% fuel 0.83
Not good for a multirole fighter in the 2020s, but it's not unlike a fully-loaded Gripen E/F either. Wiki says this about J-31 payload:
“Payload
The J-31 can carry 8000 kg (17637 lb) of payload, with four munitions totaling 2000 kg (4409 lb) internally, and 6000 kg (13228 lb) carried on six external hardpoints; primary armaments include the PL-10 short-range missile and SD-10A medium-range air-to-air missile. It has a combat radius of 648 nmi (746 mi; 1,200 km) and a maximum take-off weight of 25,000 kg (55,000 lb).”
See the problem here?
Full-fuel of 12,000 lb plus the full-weapon payload gives a weight of 67,000 lb, or 12,000 lb over MTOW. In other words, you can have full-fuel, or you can have full-weapons--but you can not have both. So J-31, as it currently stands, would be unable to have full-fuel and to carry any external weapons, unless you first removed all of the internal weapons.
So external pylons on a J-31 will not be seeing a whole lot of action.
All of those computer pics of the J-31 flying about with a wide variety of nasty looking external stores … yeah ... dreaming.
In reality it would carry about the same internal weapon loads as an F-35B, and about 12,000 lb of fuel, into two fuel-inefficient engines, that will always have to be driven hard (even more fuel-guzzling) to produce acceptable cruise, or acceleration, or energy-recovery performance. So range would be less than half of that of an F-35, and performance and agility would be distinctly lacking after the first turn, and the practical weapons payload would be around one fifth that of an F-35A.
So basically you'd get something like a Gripen E/F in strike-range, and even worse than Grippen in deliverable weapon weights, but with added LO advantages (version 1.0). Which is useful but nothing like what the Chinese claim it as, nor clearly want it to be. So a Russian 5th-gen J-31ski is likely to run into similar limits, unless the engines are significantly better than RD-93s.
I suspect Russia could actually produce a better LO J-31ski over the next decade.
J-31 won't become an official program until China has a better idea of when WS-19 (think of it as Chinese equivalent to F414) will go into production. Does Russia have a replacement program for RD-33 with proper funding?
twin-engined fighter jet using RD-33 is quite underpowered. I would think it's a no-go.
