Aerodynamics thread

[Engineer]

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.

That is not an indication of optimization. Rather, that is an indication that the smaller airframe has more limitations and that a larger airframe is more capable.

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.

Of course, engine scales, but this is not a linear scale. And while it is certainly possible to use smaller engine on smaller airframe to achieve the same thrust-to-weight ratio as a larger aircraft, doing so incur penalties in other performances. There are areas on aircraft that cannot be scaled at all, and the size of these area remain the same, taking up relatively more space in a smaller airframe. There is simply no free meal.

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.

So? I could show you a MiG-29 is smaller and has less range than a Su-27. I could also give you quotes like "

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" In these examples, similarities of the aircraft truly reveal the effects of performance due to change in size. These are unlike your examples that rely on fuzzy figure of combat range, with which a single aircraft can have multiple of depending on mission profiles.

You're engaging in strawman arguments; I never indicated that smaller is better, only that smaller aircraft tend to have more focus on maneuverability.

You are contradicting yourself now. You can't have never indicated smaller is better, while telling me in the very next sentence how smaller is better. It is like claiming "well, I never indicated the object is round, just that the object is somewhat spherical." Also, you can't have never indicated smaller is better, while having explicitly indicated so:

...if you are aiming to specialize in WVR warfare, smaller becomes better...

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.

The example does not need to explicitly show MiG-29 being less WVR focused. It is sufficed the show the MiG-29 does not enjoy an advantage in WVR engagements even though being the smaller fighter, which in turn indicates that MiG-29 is not anymore WVR focused than Su-27.

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.

The fact that F-35 having reduced stealth features is exactly what I mean about shaping. You assumed 10% increase in each of length, width and height would translate to 21% in RCS, but the fact that F-35 having smaller dimensions yet a bigger RCS than F-22 shows the assumption as incorrect. There doesn't need to be a pure example to illustrate the effect of shaping.

 

[latenlazy]

You know i hate discussions where ignorance and speculation is presented as facts.
Any simulation is math, any physical phenomenon is quantifiable, here all the discussion is sterile and stupid, what makes an aircraft turn is the total lift it generates with regards its weight speed and banking angle

Perhaps it would be less stupid and sterile if you stopped sticking words in my mouth. I did not argue that any physical phenomenon wasn't quantifiable or that simulations aren't math. The point I'm getting at is where is that lift coming from? (Answer, lift coefficient of object and thrust, the former of which depends on fluid dynamics, which varies based on design choices, and which isn't easily determinable just by looking).

see the equation and stop this stupid argument, see the equations, no equation is given aircraft has canards or not, it simply gives you speed banking angle Tan and gravity, the rest is pure non sense.

Once again I go back to the point about lift coefficients and L/D ratios.

The turn rate always will be given in math expressions and are these factors what matter regardless the aircraft is a fighter, a strike aircraft or an airliner, it does not matter it has canards or not or it is tailless.

The lift coefficient and L/D ratio matter too, not because they change the mathematical relationship between bank angle, gravity, etc, but because they change the input of one of the variables, the lifting force.

question for you why J-20 changed the shape of the LEX of its wing?

If you say you do not know, i just just recommend you google a bit about the F-16 aerodynamics and you will find the answer, the reason is not as complex as you think, in the same way the F-18E changed the shape of its LEX, the reason lies simply in what things do compromises between lift and low pressure vortices and drag.

simulation is not what you think, pretty much all designers do it before launching their projects.

There could be several reasons why they changed the J-20's LEX. One could aerodynamic optimization. Another could be RCS. I don't know what you thought I thought simulations were. I simply asserted that one cannot judge the J-20's performance without running a CFD or collecting actual flight data, and that advances in computation has enabled new designs to strike better compromises.

 

[Engineer]

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.

The above argument, with the use of fantasy numbers to battle cold hard figures, reeks of desperation. Even if economy of scale does reduce unit cost in the case of F-35, that only tells us making more drives things cheaper, not making things small drives things cheaper. It also is not unheard of for fighter aircraft with identical size and identical configuration to differ significantly in cost.

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.

It shouldn't cost that much, but it does. The excessive costs stem from piling a bunch of requirements into a small airframe, reflecting limitations. Some of those requirements are to enable the aircraft to do well in both WVR and BVR engagements to survive. It would be pointless to have an aircraft that "optimizes" for WVR engagement then have that aircraft easily gets blasted out of the sky due to deficiency in BVR engagement capabilities. So, the notion that small fighters do well in WVR engagement and large fighters do well in BVR engagement is just a form of black-or-white thinking.

 

[Air Force Brat]

Math is the phenomena since Physics is useless without it, and forces are vectors, vectors can be interpreted with math ie electromagnetic waves using electricity and magnetism as the quantifiable vectors or in aviation as the quantifiable forces of lift and drag.

Turn rates are quantifiable phenomena, lift will be measured with trigonometry on a turn, in fact they are vectors thus you just need to know the lift required for the jet to achieve the turn rate demanded

There is no simulation that does not use math in aviation, and not experiment without a mathematical interpretation.

Fluid dynamics is the science of the aeronaut, math, "quantifies" the relationship between the airframe and the invisible fluid medium. Since water is also a fluid, we are able to visualize the relationship, between the airframe and the fluid medium with-out a high tech wind tunnel, by observing our "airframe" in the water tank, math allows us to place a "value" on that interaction, and allows us to apply a formula to "predict" "values" outside of our test methods. No doubt the high speed wind tunnels at Arnold Air Force Base, allow us to "observe" those interactions in what approach "real world" velocities, in real time, and yes that is a more "accurate" means of predicting "values", but even simulation is unable with the most elaborate of equations to predict all the "behaviours" in the real world, otherwise there would be NO reason for test pilots or test aircraft, or telemetry, or "observation".

 

[F-15]

Perhaps it would be less stupid and sterile if you stopped sticking words in my mouth. I did not argue that any physical phenomenon wasn't quantifiable or that simulations aren't math. The point I'm getting at is where is that lift coming from? (Answer, lift coefficient of object and thrust, the former of which depends on fluid dynamics, which varies based on design choices, and which isn't easily determinable just by looking).
.

This is only blah blah blah, the total lift of a configuration is what counts, it does not matter it has delta or no delta wing or canards or not, twin fins of not

There could be several reasons why they changed the J-20's LEX. One could aerodynamic optimization. Another could be RCS. I don't know what you thought I thought simulations were. I simply asserted that one cannot judge the J-20's performance without running a CFD or collecting actual flight data, and that advances in computation has enabled new designs to strike better compromises.

more blah blah blah, i asked you why, it is very easy to say aerodynamic optimization, but is harder to say in specific why, you are dodging the question why?

I know simply you do not know and have no idea what really are LEXs

 

[F-15]

Fluid dynamics is the science of the aeronaut, math, "quantifies" the relationship between the airframe and the invisible fluid medium. Since water is also a fluid, we are able to visualize the relationship, between the airframe and the fluid medium with-out a high tech wind tunnel, by observing our "airframe" in the water tank, math allows us to place a "value" on that interaction, and allows us to apply a formula to "predict" "values" outside of our test methods. No doubt the high speed wind tunnels at Arnold Air Force Base, allow us to "observe" those interactions in what approach "real world" velocities, in real time, and yes that is a more "accurate" means of predicting "values", but even simulation is unable with the most elaborate of equations to predict all the "behaviours" in the real world, otherwise there would be NO reason for test pilots or test aircraft, or telemetry, or "observation".

Without math you can not make any model, experiments are just to collect data since in order to calculate you need real world data

If you paid attention to the equation, you can see is not a black art calculate lift, but pretty much math

You are not understanding what is he saying just blah blah blah and you are pretty much following the same line.

any aircraft has similarities due to similar technology and era, while exact dimensions are difficult to guess and airfoil types are varied any manufacturer has airfoil types for specific speeds and missions, so pretty much you can calculate approximations of the airfoil type in order to have the lift aircraft generate.

Nowadays computer simulation is pretty accurate so if you think aerospace engineers can not have a good idea of what an aircraft can do, you are wrong, the main problem is the engine and avionics which are really difficult to know their real performance

 

[Air Force Brat]

Without math you can not make any model, experiments are just to collect data since in order to calculate you need real world data

If you paid attention to the equation, you can see is not a black art calculate lift, but pretty much math

You are not understanding what is he saying just blah blah blah and you are pretty much following the same line.

any aircraft has similarities due to similar technology and era, while exact dimensions are difficult to guess and airfoil types are varied any manufacturer has airfoil types for specific speeds and missions, so pretty much you can calculate approximations of the airfoil type in order to have the lift aircraft generate.

Nowadays computer simulation is pretty accurate so if you think aerospace engineers can not have a good idea of what an aircraft can do, you are wrong, the main problem is the engine and avionics which are really difficult to know their real performance

Actually I do understand and yes I am a pilot, it appears that you are the one who does NOT understand, and there is NO reason for you to be insolent with latenlazy, who has an outstanding reputation on these forums, and clearly has a far greater understanding than you sir. To come on a forum and begin to make accusations and demands, after I explained a very basic principle that your math did not explain to you. I would suggest that you read forum rules and abide by them, no I don't give a "KRAP" about your math, and yes I do understand the drawing as well and a very nice wing,,,,, 15 posts and you're the "Lord of Flies".

After all the calculations, after being figured and calculated to death, none of the engineering or modeling enabled the designers of the F-35 to predict the aerodynamic "buffeting of the vertical stabs", it was discovered by a pilot in flight testing. My Daddy had a saying and that was "figures lie, and liars figure", it certainly does seem to be holding true.
If you're some great engineer or test pilot, please tell us a little about yourself, if you're just another internet troll, please don't bother........ the brat

 

[F-15]

Actually I do understand and yes I am a pilot, it appears that you are the one who does NOT understand, and there is NO reason for you to be insolent with latenlazy, who has an outstanding reputation on these forums, and clearly has a far greater understanding than you sir.

Does it make you an expert in aerodynamics? millions use computers and hardly can understand the Fourier series, millions use video games and hardly know how to finding the area between two curves using integrals that basically are the basis of programs like CAD and of their games they play.


If you are a bit more humble you will understand that airfoil section goes by generation and speed.

If you are humble you will understand math is the tool god used for nature and engineers fail when they fail in Math, therefore they need to test aircraft, but what you are pretending is to affirm you will know better for being a pilot, most modern test pilots are engineers with sometimes masters and PhD degrees in engineering.

So please, if you are a pilot love math and stop supporting a guy who is only pretending to know but what really just says is Blah blah blah

 

[vesicles]

Does it make you an expert in aerodynamics? millions use computers and hardly can understand the Fourier series, millions use video games and hardly know how to finding the area between two curves using integrals that basically are the basis of programs like CAD and of their games they play.


If you are a bit more humble you will understand that airfoil section goes by generation and speed.

If you are humble you will understand math is the tool god used for nature and engineers fail when they fail in Math, therefore they need to test aircraft, but what you are pretending is to affirm you will know better for being a pilot, most modern test pilots are engineers with sometimes masters and PhD degrees in engineering.

So please, if you are a pilot love math and stop supporting a guy who is only pretending to know but what really just says is Blah blah blah

OK, if you have ever done simulations/modeling, you would know that theoretical work has its flaws, serious ones. In order to get the math to work, i.e. solving the equations, theoreticians have to make assumptions. Most of the time, these assumptions do not work in the real world, like inventing multiple universes or extra dimensions. However, this is, in most cases, the only way to solve equations. As we typically get so many variables in an equation and this makes them unsolvable, we must simplify the equation by eliminating as many variables as we can. This is done by making assumptions. Take the Ideal Gas Law for example. We learn it in high school physics, then again in college, then again in grad school. It's so simple and straightforward that we take it for granted and assume it is a fact. But is it? The gas law has one major limitation: assuming the system is ideal. This means that the collision between the gas molecules in the system has to be perfectly elastic and there cannot be any intermolecular interactions. Does this ever happen in the real world? If you use the Ideal Gas Law in your calculations, then you automatically assume you have an ideal system, which does not fit the real world. So simulations and modeling has serious limitations. This is why ALL theoretical work MUST be validated by experiments. Even with experimental validations, the best models/theories typically can only work under certain set conditions. Take for example Newton's 2nd law. F=ma. However, this only holds when the mass is constant. As the Einstein's special relativity dictates, mass becomes a variable as extreme speed. So Newton's 2nd law F=ma is seen to be strictly a non-relativistic relationship. It no longer holds at extreme speeds.

Since we are discussing air planes, let's take a look at the development process of an air plane. After extensive designing and simulation and modeling on computers, a prototype is made and is put through years of extensive flight testing. IF the simulations and modeling are as perfect and as accurate as you claim, the engineers should have the confidence to immediately start production once they finalize the design on computers. Yet, they still must conduct exhausting flight testing and most of the time have to change their design based on data gathered from actual flight tests. This indicates that their models don't tell them everything. And often times, their model is wrong. That's why they have to go back and change their design. This is NOT because the engineers don't know math, as you claim. It happens because none of our physics theories is perfect. ALL of them have serious limitations because ALL these predictions came out of assumptions after assumptions in an attempt to simplify the equations. This includes the best of the best of us, like Newton and Einstein.

Any true theoretician would have full respect for experimentalists and engineers. This is because they know how much hoopla they have to jump through to solve their equations. And they also know that their models/predictions can only work in hypothetical world in most of the time because how much assumptions they have to make. I know this first-hand because I myself have done my share of simulation and modeling in my research (mostly thermodynamics). My dad is an inorganic chemist who does a lot of theoretical physics work. And my wife's uncle used to work at SAC as an aerospace engineer (designing cockpit of one of the early fighters. So yes, he is an expert in fluid mechanics) before coming to the US. After getting his Ph.D. in aerospace physics, he worked for NASA for almost 20 years. Then he decided to have an easier life. So he became a professor in the Math department at a university in the States. And my wife also has a cousin who is a theoretical physicist. So yes, I know how a true theoretician views his own work and views work by others. And the way you look at thing is NOT it! You are the one who should be humble.

 

[solarz]

Any true theoretician would have full respect for experimentalists and engineers. This is because they know how much hoopla they have to jump through to solve their equations. And they also know that their models/predictions can only work in hypothetical world in most of the time because how much assumptions they have to make. I know this first-hand because I myself have done my share of simulation and modeling in my research. My dad is an inorganic chemist who does a lot of theoretical physics work. And my wife's uncle used to work at SAC as an aerospace engineer (designing cockpit of one of the early fighters. So yes, he is an expert in fluid mechanics) before coming to the US. After getting his Ph.D. in aerospace physics, he worked for NASA for almost 20 years. Then he decided to have an easier life. So he became a professor in the Math department at a university in the States. And my wife also has a cousin who is a theoretical physicist. So yes, I know how a true theoretician views his own work and views work by others. And the way you look at thing is NOT it! You are the one who should be humble.

Awesome post!