Viv S wrote:
How much lift can you generate from the fuselage?! How DO you generate lift from the fuselage of F-22/F-35 type aircraft? How much more lift can you generate compared to say the Eurofighter
. How can it come anywhere
close to substituting the reduced wing area?
This is good question as lifting body is not very good if the lift is at a positive AoA. There is lift induced drag+aero-induced-drag(due to high aspect ratio)+greatly enhanced RCS. Actually this is used by "slow flyers" that we build as trainers (in aeromodels).
But you will be surprised to know that even in level flight fuselages can generate sufficient lift. This has been used many times in the opposite direction to generate down force for surface transport. Bullet trains, almost all maglev trains, F1 cars, sports cars, Richard Noble's Thrust SSC, etc etc. You see they don't have any (substantial) wings or AoA.
However its use in aeroplanes are not as well advertised. People start thinking straight to Burnelli. Few of the best exponents of fuselage lift generation are Mig-29, Su-27, F-15 and Pak-FA. It is not just the lift produced by a flat body at positive AoA. That happens for even airliners. But in the above examples, there is a gap between the engine nacelles. The air at the top flows above the cockpit and behind it , whereas the air below the fuselage blows straight through the channel between the engine nacelles. This creates considerable lift even in leveled flight. Imagine this "wing". How big is the camber? the height of the fuselage! how big is the chord? the length of the plane! I would not be very surprised if the lift generated by this part is 25-30% of the entire lift generated.
This is not just limited to the twin engined jets. The F-16's forbody is supposed to create substantial lift because of it's bubble canopy.
Many contest the 747's upper bulge has similar consequences. But that is not entirely true and makes for fascinating reading.
Viv S wrote:What would suggest I read? I don't see how I can apply anything learnt in SoM. I'm assuming I can treat it as a sheet of metal; simple Mechanics would suggest a bent sheet would experience a lower tensile stress than a taut one, leading to lower fatigue. So ... where am I going wrong? Or should one determine stress in shear (more common for aluminium) instead (though I don't see how the result changes)?
It is not strength of metal. It is the characteristics of shape. You should read about jigs and stingers. Anyways, just as an example, an uniform shape like circle has much more weight bearing capacity than an non uniform one. Hence a dome becomes a strongest shape. Archs are best bridges and buildings. And tunnels are thought to be self supporting, even if built underneath a mountain.
Fuselage of a plane is not built in the form of a tube because of just because it has the lowest drag possible. A hollow tube is not very flexible. You can take a sheet of any metal and fles it. But if you wound this up into a tube you will find it much harder to bend or flex.
I am sure you have sat in a plane and seen the wings flex all around. Did your fuselage flex as much?
Anyways here's a cutaway of Gripen. See the strengthening of wings relative to the fuselage.
Heres' the same for F-35
I was trying to find a similar one for Tejas, but couldn't find an image for the same.
Anyways go here
and check the sixth CAD image of "WalkThru assembly of structural components of LCA."
And this is how much the wings on the 787 are supposed to flex
. It would not be very nice if your fuselage flexed so much.
Viv S wrote:But, then this isn't a pylon we're talking about. The AVEL IIRC has to apply something like 40Gs to eject the missile and as the name suggests its designed for the 150kg AMRAAM not the 500kg JSOW (in F-35's case).
Yes that is right. But the 40G requirement rises from being able to launch the AMRAAM through the entire flying envelop, so that it can pierce through the boundary layer and to a distance beyond the plane (I have forgotten the distance). For A2G munition one doesn't need that king of acceleration. You might find this
Even with the F-35 the ASRAAM are going to be on external pylons. We will have to decide what goes internally and what goes externally.
Viv S wrote:The F-16, F-18 and Harrier II yes. Its can't really replace the A-10; the squadrons will probably be re-equipped with it and their operational role suitably modified.
I pointed you to official declassified documents. It is upto you to believe it or not.
Viv S wrote:The looks don't matter. Yes the requirements for a AF F-16, a naval F-18 and a STOVL Harrier II are different. But, the F-35A, F-35B and F-35C ARE different. 80% parts are claimed common, but the fact that the F-35A weighs 13.3 ton empty while the F-35C weighs 15.8 tons tells me, the CTOL variant isn't making allowances for a navalized version. The F-35C's wing area is almost 50% more than the F-35A. Compare that to a 'practically new' Super Hornet which has a 25% larger wing area than the Hornet. If I said the Rafale was intended to replace the Mirage-2000, would you disagree on the basis that the Rafale-M exists. Or that the Gripen would stop being a replacement to the Viggen if the Sea-Gripen materializes.
I see your point that there is many a slip between the cup and the lip. But F-35C houses the LiftFan, Engine to fan driveshaft, three-bearing swivel module (TVN), roll posts. all these are heavy machinery. The wing is 50% bigger not just for the added weight but also for providing lower landing speeds on ACs.
Viv S wrote:
As far as I have read they want a strike aircraft to complement the FGFA. Ofcourse it should be able to defend itself if attacked. It should be multirole to only that extent. I hope they stick to that rather than making it a jack of all trades and master of none.
As opposed to? I'm assuming it will have an AESA and the weapons bay will accommodate air-to-air weapons. That about brings it at par with the F-35 in terms of operational flexibility. If anything its the air to ground equipment like an internal/dispersed IRST system that will lead to any bloat. Point is its not as simple as making a trade-off between A2A and A2G capabilities. A super-cruising aircraft will be able to lob both missiles and PGMs a greater distance. A larger weapons bay will allow the aircraft to carry more weapons of either kind.
AESA-so? Are AESA's considerably heavier than other radars. I think not.
I pointed it out to you why going for a single engine design made F-35 thicker. It's height of the fuselage is not much bigger than the diameter of it's engines. With the Kaveri the diameter is 3/5 of the F-135/136!
Viv S wrote:
Thats only in your mind. IAF has strictly said that it has to be under 25 T. ADA has said 20T. You are throwing your hat around.
One could say the GoI/Armed Forces will do what they do, therefore BRF is redundant. The design is very far from being finalized and the crux of this debate is my questioning the viability/efficacy of a stealth fighter with a MTOW of 20 tons. The IAC-1's design grew from a proposed 20,000T to 37,000T to a further 40,000T - I don't think the AMCA's design has been frozen either.
There was a design given by the HAL/ADA which pegged the AMCA at 16-18T. IAF didn't like it. It was not on the basis of its payloads, but things like "semi-stealth" yada yada... IAF said give a fifth gen plane under 25T that is an extra allowance of 25-40%. Do you think it is not achievable. You seem to be suggesting all the guys at ADA/HAL/IAF who designed the preliminary prototype didn't have a proper idea of what we are speaking.
Viv S wrote:Here are you referring to the maximum load that can be carried by the aircraft (9 tons for the F-35) or the capacity of the weapons bay (4 AAM // 2 x JDAM + 2 AAM) or both? And just for general idea, what do you think a possible figure for the AMCA's payload will be?
AMCA was supposed to carry 2T of weapons internally and 4-5T of internal fuel. We can only expect the wings to carry 5T-7T or ordinance more. So its payload including internal fuel will be btw 11T -14T. (smack where a medium aircraft should have).
Viv S wrote:Yes a heavier plane would require design and production but it would be less challenging in terms of not requiring an as densely packed airframe, offer better a better range and payload, a bigger weapons bay (again less complex), longer intakes allowing for an S-bend with lower turbulence, and with a pair of F119s will offer a performance comparable to a re-engined F-22 or PAK-FA. And the downside to this of course, is a higher operating cost.
A smaller plane doesn't necessarily mean higher density. I read somewhere that a general rule of thumb for fighter planes is the useful load is around 1/4th of the MTOW. Ofcourse there is the Gripen on one side and the PakFA on the other, but in most cases I have found the same to be true. If you want AMCA to be capable of carrying 6-8 T of capable load, the 25T will do.
But you are right about the air intakes. That is why you see the air intakes of Rafale and EF underneath the cockpit itself. It will be interesting where the AMCA's intakes end up. I think it will not be very different from the CAD drawings we have seen so far.