Sukhoi LTS "Checkmate" #2

GarryB wrote:

According to YouTube experts Russia cannot afford this aircraft. Yet another delusional fantasy.

Its core requirement is to be affordable and the prices they are talking about it costs less than a western LIFT and its operational costs are less than Gripen costs... and it is a 5th gen fighter...

They might not buy a lot because they don't really seem interested in light fighters... that job might go to drones instead.

Hole wrote:No new angles, but nice pics.

littlerabbit wrote:...I want to see 3 squadrons of these in Serbian AF...  

SeigSoloyvov wrote:The plan has only just started its development phase and even a "cheap stealth fighter" is by no means cheap to produce or develop.

The checkmate better hopes it gets some super-rich and patient backers otherwise this plane will become vaporware, after all the Russian Gov isn't assisting with funding for the aircraft.

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hoom wrote:Why do western commentators keep saying its got huge wings?  

They look pretty normal proportion to me, arguably a bit small given the absence of horizontal tailplanes or canards.

LMFS wrote:

hoom wrote:Why do western commentators keep saying its got huge wings?  

They look pretty normal proportion to me, arguably a bit small given the absence of horizontal tailplanes or canards.

We say they are big because they are big (almost 63 m2 according to Paralay, you can check that against the wing area of similar planes and for instance the F-15 has 56 m2), the proportion wing surface / thrust is 3.9-4.3 depending on the engine thrust taken. vs for instance 43 m2 for the F-35A for a thrust/wing area of 43 m2/19.4 tf = 2.21 or 62m2/19.4 tf = 3.19 for the F-35C. With izd. 30 the value would change to 3.48.

It is difficult to calculate the equivalent lifting surface of the fuselage, but in the LTS is not to be dismissed, because the "elevators" are part of it, so the transition between fuselage and wings works indeed as an airfoil.

LMFS wrote:
BTW, thinking about that eventual future unmanned platform, the huge wing area of the plane would make a lot of sense from that perspective, since unmanned aircraft with higher manoeuvrability requirements will require also more lift and the oversized wings of the LTS would help a lot there. Structure would need reinforcement vs. current overload limit, that is clear.

Lennox wrote:I'm not really sure why one would want to calculate the wing surface area/ thrust ratio though. The two don't seem to be related at all, except for you need to calculate lift-induced drag and total drag.

I think the huge wing area alone with high aspect ratio might actually make it somewhat less maneuverable. Intuitively, when the plane executes a maneuver, let's say the Pugachev cobra, the large wing area meets the incoming airflow, thus creating very high drag. And huge wing area would make the aircraft too stable in both static and dynamic senses (Think of HALE class UAVS)

The point is that the LTS has a special intake that extends to the sides, which may (I'm not really sure about this tbh) act as a weird-looking leading edge extension that can create vortex and improve the airflow at high AoA, thus making it maneuverable. Also its wings are similar to the Su-57's with low aspect ratio, so there's that.

Someone attempted a simulation of that vortex on CFD:

almost 63 m2 according to Paralay,... the F-15 has 56 m2... 43 m2 for the F-35A

hoom wrote:If those numbers are correct then ok yeah they're big wings.Whats the Su-57 area?

LMFS wrote:

On the one hand, we don't have clear weight parameters for the LTS, so I am using thrust instead, since TWR of fighters of similar role and characteristics are going to be similar.

On the other, you normally want to match your thrust level with your wing area in order to keep friction drag as low as possible. That is very clear in the F-35 or F-16 with their small wings.

I am not talking about post-stall maneuvers, but about sustained turning mainly. For the same airframe, achieving a 11 g turn is going to demand much more lift than a 8 g one.

I don't have any doubt that is the case, the MiG izd. 33 had a LERX that looked just the same and this is also the same kind of combined DSI intake/LERX setup already found in the F-35, only placed much forward and below the nose. Actually if you look it in detail at the bump and consider the wall splitting it in the middle, the intake of the LTS is configured as two DSI intakes, placed angled below the nose of the plane.

This LERX is the same kind of lift augmentation device used in the 4G planes, so this is the baseline we have to consider when comparing wing area with other existing designs. It is still a source of drag and not so flexible and effective as far as I know as the LEVCONS present in the Su-57, so apparently a further concession to cost, weight and simplicity.

Someone attempted a simulation of that vortex on CFD:

Lennox wrote:The Cobra maneuver was only an example to show how the large wing area meets the airflow when a plane executes a maneuver. In reality, the ability to turn sustainably has more to do with the stress and load on the wings, not the wing area. Delta wing aircraft, for example, have large wings but turn very poorly.