Aerodynamics thread
- Thread starter siegecrossbow
- Start date
Correct all is math
all is how much lift versus gravity and speed
Aerodynamics is not as simple as understanding some force diagrams. We actually won't have discovered everything there is to know about aerodynamics until we have experimented or simulated every possible shape in every possible flow condition with every possible surface interaction.
thunderchief
Senior Member
Compared to what ? Is J-20 faster and more maneuverable then lets say J-10 ? Don't think so .
Well, even your diagrams show that a) vortex lift is just a fraction of total lift and b) canards "work" only when deployed at high AoA . Nobody disputed that. What your diagrams fail to show is increase of drag with deployed canards.
Fighter loses energy when generating vortices, canards or no canards. Bigger vortex means more energy is lost . So, if your canard equipped fighter goes for higher AoA then it will lose more energy, but it will also turn tighter for a time. There is no magical source of energy in canard
, it is just piece of metal . It converts kinetic energy (speed) into lift (form of potential energy) . That is all.
thunderchief
Senior Member
I never said it wasn't . But point of building 5th gen fighters is not to have similar characteristics as 4th gen fighters .
Turn is aircraft flying at high AoA for 15+ seconds. If you really want to see how tightly could J-10 turn watch video below from 8:34 . I lasted around 20 seconds , giving turn rate of 18 degrees per second (maybe a bit better ,19 degrees per second) . It exhibited usual characteristic of delta-fighters , good ITR with a bit sluggish STR in latter part of the turn. Not bad, but remember that J-10 has lower wing loading then J-20.
We should look at how other fighters turn in airshows, but I suspect no fighter is turning at their max when they're being show pieces.
How would you know.
Well, even your diagrams show that a) vortex lift is just a fraction of total lift and b) canards "work" only when deployed at high AoA . Nobody disputed that. What your diagrams fail to show is increase of drag with deployed canards.
Fighter loses energy when generating vortices, canards or no canards. Bigger vortex means more energy is lost . So, if your canard equipped fighter goes for higher AoA then it will lose more energy, but it will also turn tighter for a time. There is no magical source of energy in canard
I think the point is whether designs are bleeding more energy (which always takes the form of drag) with those vortices to achieve the same amount of lift. This always goes back to the L/D ratio. It's not about the conversion of energy from one vector to another, but how much energy loss occurs as you make that conversion. If you are achieving the same amount of lift with less drag because of vortices, that IS an advancement. There is no free lunch, but some lunches cost more than others, and the whole point of studying complex aerodynamics and engineering new solutions is to find ways to make that lunch as cheap as you can. Suggesting that because vortex lift still creates drag means that aerodynamics has not improved or that certain designs can't compromise less is like saying it doesn't matter whether your car is boxy or curved, because both cars will experience drag.
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I also note you're comparing pre-IOC F-35s to full production F-22s. The current schedule is that by 2019, increases in scale efficiency of F-35s should have reached the point where new F-35As cost 90 million current USD. That's compared to current USD cost of ~160 million for the F-22s. Even if costs only plateau to 110 million it's substantial savings and is approximately proportional to the empty weight of the F-35s.
I also note that in the case of the F-35, the engine, just by itself, and only sporting 190kn afterburner output, the F-135 costs more than 30 million to produce in its current LRIP, with the full aircraft costing 160 million. Two F-22 engines combined, with TVC, thrust vectoring, and outputting more than 320kn of augmented thrust cost only $20 million. Given that the excessive cost in roughly in proportion, and that the F-35 shouldn't cost anything similar to what it is currently costing now, it's reasonable to expect that once the F-35s reach full-scale production, their costs will drop to the levels one would expect from their airframe. But your sophistry is appreciated.
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Latenlazy, concerning decoy Al-31s, the problem is that in an actual production scenario involving both existing WS-15 powered J-20s and Al-31-powered J-20s, you will end up with having substantial numbers of unupgraded J-20s for quite some time. Let me outline the scenario.
Let's say the J-20 project is targeting 400 planes. That's a reasonable number, and twice the inventory of American F-22s, while presumably having enough tactical superiority to deal with F-35s, and in the worst case, run away, refuel, and fly to a Sichuan or Xinjiang airbase. Okay, now, you've built 100 J-20s already with Al-31s for training purposes and to provide a minimal fifth-gen capability to match or outmatch Japanese F-35s in the region, your J-20 factories are humming at full speed, and all of a sudden, your WS-15 engine is ready, and your WS-15 engine has been successfully trialled with the J-20 airframe.
You have options with regards to WS-15 production levels. The first thing you can do is to build WS-15s at high-scale, so that you'll immediately have the ability to retrofit all your Al-31-equipped J-20s with WS-15, as well as make sure all your future J-20s are equipped with WS-15s. The other alternative is to simply not retrofit any of your Al-31-equipped J-20s with WS-15s, while all your new J-20s use WS-15s instead of imports or weaker domestic engines. The disadvantage of the first option is that you'll have huge amounts of surplus WS-15 production capability, while not having the airframes equipped or designed to use them. That means that after all you finish producing the required amount of WS-15s, you'll end up shuttering your excess capability, resulting in fiscal waste in unused industrial capacity.
The disadvantage of the second option is that you'll end up being equipped with large numbers of J-20s that, for want of, I'm guessing, $20 million in engines a piece, perform like fighters half their cost.
A solution to the problem is probably something in between these two extremes, meaning that while all of your J-20s will be retrofitted to use WS-15s at some point in time, not all your J-20s will be retrofitted immediately. In that span of time, tactics involving the use and manipulation of inferior look-alike J-20s will be necessary and employed.
I also note that in the case of the F-35, the engine, just by itself, and only sporting 190kn afterburner output, the F-135 costs more than 30 million to produce in its current LRIP, with the full aircraft costing 160 million. Two F-22 engines combined, with TVC, thrust vectoring, and outputting more than 320kn of augmented thrust cost only $20 million. Given that the excessive cost in roughly in proportion, and that the F-35 shouldn't cost anything similar to what it is currently costing now, it's reasonable to expect that once the F-35s reach full-scale production, their costs will drop to the levels one would expect from their airframe. But your sophistry is appreciated.
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Latenlazy, concerning decoy Al-31s, the problem is that in an actual production scenario involving both existing WS-15 powered J-20s and Al-31-powered J-20s, you will end up with having substantial numbers of unupgraded J-20s for quite some time. Let me outline the scenario.
Let's say the J-20 project is targeting 400 planes. That's a reasonable number, and twice the inventory of American F-22s, while presumably having enough tactical superiority to deal with F-35s, and in the worst case, run away, refuel, and fly to a Sichuan or Xinjiang airbase. Okay, now, you've built 100 J-20s already with Al-31s for training purposes and to provide a minimal fifth-gen capability to match or outmatch Japanese F-35s in the region, your J-20 factories are humming at full speed, and all of a sudden, your WS-15 engine is ready, and your WS-15 engine has been successfully trialled with the J-20 airframe.
You have options with regards to WS-15 production levels. The first thing you can do is to build WS-15s at high-scale, so that you'll immediately have the ability to retrofit all your Al-31-equipped J-20s with WS-15, as well as make sure all your future J-20s are equipped with WS-15s. The other alternative is to simply not retrofit any of your Al-31-equipped J-20s with WS-15s, while all your new J-20s use WS-15s instead of imports or weaker domestic engines. The disadvantage of the first option is that you'll have huge amounts of surplus WS-15 production capability, while not having the airframes equipped or designed to use them. That means that after all you finish producing the required amount of WS-15s, you'll end up shuttering your excess capability, resulting in fiscal waste in unused industrial capacity.
The disadvantage of the second option is that you'll end up being equipped with large numbers of J-20s that, for want of, I'm guessing, $20 million in engines a piece, perform like fighters half their cost.
A solution to the problem is probably something in between these two extremes, meaning that while all of your J-20s will be retrofitted to use WS-15s at some point in time, not all your J-20s will be retrofitted immediately. In that span of time, tactics involving the use and manipulation of inferior look-alike J-20s will be necessary and employed.
Re: Chinese Engine Development
If you're talking about avionics, that's my entire point. Larger aircraft can more easily utilize larger sensor systems, while smaller aircraft have to take aerodynamic penalties for having outsize radars. Hence, due to having superior sensors, larger fighters tend to be more optimized for BVR fighting, as they are intrinsically better at BVR than their smaller counterparts.
Regarding engines, umm, the thing is, engines scale. Smaller engines on smaller airframes give you constant T/W ratios. And smaller engines can be said to be easier to design, read up on the square-cube law of how larger objects tend to be subject to larger proportional forces than smaller objects.
As far as less range goes, if your aircraft is lighter, it needs less thrust to go a given distance. If your aircraft needs less thrust to go a given distance, it needs less fuel to go a given distance. Proportionally speaking, there's no reason that smaller aircraft are necessarily shorter-ranged than their larger counterparts, in the F-22's case, the F-35 actually exceeds the F-22 in range, being designed for a combat range of about 1,100 km on internal fuel, while the F-22 sports 750 km in combat range. I could also show you the example of the F-15C vs the Rafale; the Rafale is a mid-weight fighter at about 14,000 kg loaded, while the F-15C is at 20,000 kg loaded. Yet both the Rafale and F-15C are listed at the same combat radius of 1850 km / 1000 nm.
You're engaging in strawman arguments; I never indicated that smaller is better, only that smaller aircraft tend to have more focus on maneuverability. In the same way, while the Su-27 outperforms the MiG-29 as a WVR airframe, that doesn't actually prove that the MiG-29 is less WVR-focused than the Su-27. Using the MiG-29 and Su-27 relationship to prove that point would require the MiG-29 beating the Su-27 in BVR but losing to it in WVR, something we know doesn't happen, given that the MiG-29 has an 700mm radar aperture while the Su-27 has a 950mm radar aperture, and that the latest MiG-35 has an RCS of 1-1.5 m^2 while the Su-35S has an RCS of 2-2.5 m^2. Even worse, when you add the effects of externally-mounted air-to-air missiles on airframes, smaller aircraft with low RCS suffer disproportionately compared to larger aircraft optimized for BVR.
That's called shaping, and in fact that supports my argument. The F-35 is a lot less oriented towards BVR fighting than the F-22, given that the F-35 has a smaller radar aperture, as well as having reduced stealth features. To actually disprove my point you'd need to show that the F-35 is better than the F-22 in BVR action simply based on airframe.
And no, RCS, if held independent of shaping and materials features, does in fact work that way. You can point to all the real-life examples you want, but you can't get a sufficiently pure example to make your point that way, because in almost all the listed cases loss in radar effectiveness due to smaller radar aperture is not compensated for by reduced detection range through an equivalent change in RCS to the fourth power.
If you're talking about avionics, that's my entire point. Larger aircraft can more easily utilize larger sensor systems, while smaller aircraft have to take aerodynamic penalties for having outsize radars. Hence, due to having superior sensors, larger fighters tend to be more optimized for BVR fighting, as they are intrinsically better at BVR than their smaller counterparts.
Regarding engines, umm, the thing is, engines scale. Smaller engines on smaller airframes give you constant T/W ratios. And smaller engines can be said to be easier to design, read up on the square-cube law of how larger objects tend to be subject to larger proportional forces than smaller objects.
As far as less range goes, if your aircraft is lighter, it needs less thrust to go a given distance. If your aircraft needs less thrust to go a given distance, it needs less fuel to go a given distance. Proportionally speaking, there's no reason that smaller aircraft are necessarily shorter-ranged than their larger counterparts, in the F-22's case, the F-35 actually exceeds the F-22 in range, being designed for a combat range of about 1,100 km on internal fuel, while the F-22 sports 750 km in combat range. I could also show you the example of the F-15C vs the Rafale; the Rafale is a mid-weight fighter at about 14,000 kg loaded, while the F-15C is at 20,000 kg loaded. Yet both the Rafale and F-15C are listed at the same combat radius of 1850 km / 1000 nm.
You're engaging in strawman arguments; I never indicated that smaller is better, only that smaller aircraft tend to have more focus on maneuverability. In the same way, while the Su-27 outperforms the MiG-29 as a WVR airframe, that doesn't actually prove that the MiG-29 is less WVR-focused than the Su-27. Using the MiG-29 and Su-27 relationship to prove that point would require the MiG-29 beating the Su-27 in BVR but losing to it in WVR, something we know doesn't happen, given that the MiG-29 has an 700mm radar aperture while the Su-27 has a 950mm radar aperture, and that the latest MiG-35 has an RCS of 1-1.5 m^2 while the Su-35S has an RCS of 2-2.5 m^2. Even worse, when you add the effects of externally-mounted air-to-air missiles on airframes, smaller aircraft with low RCS suffer disproportionately compared to larger aircraft optimized for BVR.
That's called shaping, and in fact that supports my argument. The F-35 is a lot less oriented towards BVR fighting than the F-22, given that the F-35 has a smaller radar aperture, as well as having reduced stealth features. To actually disprove my point you'd need to show that the F-35 is better than the F-22 in BVR action simply based on airframe.
And no, RCS, if held independent of shaping and materials features, does in fact work that way. You can point to all the real-life examples you want, but you can't get a sufficiently pure example to make your point that way, because in almost all the listed cases loss in radar effectiveness due to smaller radar aperture is not compensated for by reduced detection range through an equivalent change in RCS to the fourth power.
Surplus issues are smoothed out by requirements for spares for maintenance. Furthermore, given the WS-15 core is meant to be developed into high bypass variants production can be offset into a variant once capacity requirements ramp down. If they had to retrofit 100 airframes (which I think is on the high end of how many they may build with AL-31s) it would take some time, and decisions would certainly need to be made about how they're used in the meantime, but unless they absolutely need to sortie more fighters than the number of ws-15 equipped fighters they have it's far more likely the Al-31 variant will be relegated to training strike and counter 4+ generation fighter missions.
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The SF-A project is parallel to the WS-15 project and is not going to wait for the success of the WS-15 to be deployed. Besides that, skipping spares are not a solution to a shortage of WS-15s. Flying J-20s without WS-15 spares just means that the moment any engine needs to be replaced or serviced, the entire airframe is going to be grounded until a replacement can be produced.
Also, let me do mention that if we're talking about divided fronts issues between China and Japan; Japan has both the advantage and disadvantage of being a small, rather compact country. It's a disadvantage in that it lacks anything resembling strategic depth, but it's an advantage in that you have a very small area that can be covered by a small number of bases.
So, while China needs to protect its southwest (India), southeast (South China Sea), east (East China Sea), and northeast (Bohai, North Korea, Japan), Japan only has its southwest and northeast to cover with air defense. As a consequence, it can concentrate more of its airpower against one front.
So, while China needs to protect its southwest (India), southeast (South China Sea), east (East China Sea), and northeast (Bohai, North Korea, Japan), Japan only has its southwest and northeast to cover with air defense. As a consequence, it can concentrate more of its airpower against one front.