Aerodynamics thread

[fasiiih]

I agree that flying the J-31 at Zuhai is both risky and gutsy, and while we both wish she had something other than those old smokey RD-93s, she does very well even with those, in spite of some commentary about her being "underpowered". I noted that she is not carrying the movable- up or down LERX devices associated with PAK-FA, and no doubt there are very likely vortex generators of some type, but they seem to be more along the line of traditional leading edge slats and "strakes", but I will definitely give the J-31 a little closer perusal... and welcome to the Sino Defense Forum fasiiih, there is a thread for new members introductions there, and we would all love to know a little more about you, and of course read the rules.

very nice response to my post by the way, and its always nice to have an informed discussion on the aeros of all these beautiful airplanes.

Thanks Air Force Brat .. well i am actually not new to this forum, i´ve always been on an observing level since i joined.. didnt took part in conversations much...but learning by observing, even checking daily, sinodefence is actually one of the sane forums .. very very interested in aeros of fighter planes...professionally i am doing Chartered Accountancy ..

about FC-31, the pace of development on this program is what excites me the most, you are right about the strakes... i dont think that it is underpowered for its purpose (17.5 tons combat weight)... the article which said that j-31 was sinking neglected the fact that .. they are seeing a prototype aircraft, having very few hours of flight time (i think), flight control laws may have been limiting or they might not be complete, and the pilot´s experience required to perform airshows on this particular type.. anything could have been a factor.. but it definitely need a more powerful less smoky engine.. something like a 100+ KN medium thrust enigne.. but there has been no news of ws-13 from some time. which is worrying..

what are the advantages of cropped tail fins shown in the FC-31 model vs f-22 style tail fins.. can we say that they are less draggy or it has something to do with stealth.. also what are the possibilties of installing uprated rd-93s with tvc.. as far as i know having tvc may require higher thrust to recover from extra drag and maintain energy.. which again brings us to uprated thrust, AKA more powerful engine..

Can anyone compile known confirmed Officially revealed Data of FC-31 or j-31/31001/AMF( last years Zuhai)

 

[Air Force Brat]

Thanks Air Force Brat .. well i am actually not new to this forum, i´ve always been on an observing level since i joined.. didnt took part in conversations much...but learning by observing, even checking daily, sinodefence is actually one of the sane forums .. very very interested in aeros of fighter planes...professionally i am doing Chartered Accountancy ..

about FC-31, the pace of development on this program is what excites me the most, you are right about the strakes... i dont think that it is underpowered for its purpose (17.5 tons combat weight)... the article which said that j-31 was sinking neglected the fact that .. they are seeing a prototype aircraft, having very few hours of flight time (i think), flight control laws may have been limiting or they might not be complete, and the pilot´s experience required to perform airshows on this particular type.. anything could have been a factor.. but it definitely need a more powerful less smoky engine.. something like a 100+ KN medium thrust enigne.. but there has been no news of ws-13 from some time. which is worrying..

what are the advantages of cropped tail fins shown in the FC-31 model vs f-22 style tail fins.. can we say that they are less draggy or it has something to do with stealth.. also what are the possibilties of installing uprated rd-93s with tvc.. as far as i know having tvc may require higher thrust to recover from extra drag and maintain energy.. which again brings us to uprated thrust, AKA more powerful engine..

Can anyone compile known confirmed Officially revealed Data of FC-31 or j-31/31001/AMF( last years Zuhai)

Actually if you will note the SU-35 performance, the pilot actually slows the aircraft and then "hangs it on the pipe, much like a solid rocket climbs away, and the J-31 is slowed and then pitched up as full burner is applied, just part of the airshow style program. As for the cropped tips, my suspicion is that is mostly "cosmetic" although it may provide a reduction in RCS? No real concern either way, other than you lose a small amount of control surface, hence some reduction in control effectiveness... In the old days lots of aircraft companies swept vertical stabs and rudders for a largely cosmetic reason, when the upright vertical stabs/rudders were actually more effective. You are right about the FCS, I imagine the the control laws have not been fully written, but the brat is somewhat limited in the nuances, but the J-31 must fly fairly well to be out on parade.

I'm all in on OVT, although the trend is to engage BVR and not get caught up in the furball???

 

[fasiiih]

Actually if you will note the SU-35 performance, the pilot actually slows the aircraft and then "hangs it on the pipe, much like a solid rocket climbs away, and the J-31 is slowed and then pitched up as full burner is applied, just part of the airshow style program. As for the cropped tips, my suspicion is that is mostly "cosmetic" although it may provide a reduction in RCS? No real concern either way, other than you lose a small amount of control surface, hence some reduction in control effectiveness... In the old days lots of aircraft companies swept vertical stabs and rudders for a largely cosmetic reason, when the upright vertical stabs/rudders were actually more effective. You are right about the FCS, I imagine the the control laws have not been fully written, but the brat is somewhat limited in the nuances, but the J-31 must fly fairly well to be out on parade.

I'm all in on OVT, although the trend is to engage BVR and not get caught up in the furball???

I have a suspicion that the furball will eventually come one way or the other.. but a fighter aircraft will still need clean aerodynamics to maneuver away from incoming MRAAMs as quick as possible.. sure it wont be engaged in a knife fight with the missile but the seeker heads on MRAAMs are getting smarter with second shot capability coupled with high g maneuvers.. to deceive such missiles the aircraft will have to employ a number of different counter measures flares, chaffs , decoys, including high g maneuvers .. this is just the air to air scenario .. i have not touched the SAM threat .. but u can imagine, more and more variants of AAMs are coming out as SAMs these days.. so i think OVT is something that should be looked at for fc-31.. especially if PLAAF or PLAN have any plans to acquire j-31

i know j-31 will be looking alot like f-22.. but it is actually not .. i dont think it was designed with such high parameters in mind ... it is supposed to be an affordable 5th generation fighter aircraft .. but if the aerodynamics can improve more it will give a tough competition to competitors from Turkey, South Korea & India..

 

[Air Force Brat]

I have a suspicion that the furball will eventually come one way or the other.. but a fighter aircraft will still need clean aerodynamics to maneuver away from incoming MRAAMs as quick as possible.. sure it wont be engaged in a knife fight with the missile but the seeker heads on MRAAMs are getting smarter with second shot capability coupled with high g maneuvers.. to deceive such missiles the aircraft will have to employ a number of different counter measures flares, chaffs , decoys, including high g maneuvers .. this is just the air to air scenario .. i have not touched the SAM threat .. but u can imagine, more and more variants of AAMs are coming out as SAMs these days.. so i think OVT is something that should be looked at for fc-31.. especially if PLAAF or PLAN have any plans to acquire j-31

i know j-31 will be looking alot like f-22.. but it is actually not .. i dont think it was designed with such high parameters in mind ... it is supposed to be an affordable 5th generation fighter aircraft .. but if the aerodynamics can improve more it will give a tough competition to competitors from Turkey, South Korea & India..

Interesting that it has been almost 4 years since the J-20s first flight, and that aircrafts delta main wing and distant coupled canards continue to be tweaked, though the now 4 pre-production proto-types logging flight time. Sadly it seems that we know far less about 2011 and 2012 than we do about 2001 and 2002, although the new kids are likely in the mold of production aircraft and seemed to fly well, we simply did not have the pictures and videos that we all enjoyed so much after 2001s launch. We are seeing how politics affects aerodynamics, and even flight testing. The previous presidents openness and forward movement on many fronts has been "pulled back", possibly due to "security concerns", or maybe just a general desire for more "clandestine" operations.

No doubt all governments are concerned about security and rightly so, but it has certainly been disappointing to see this "regression", even as we were excited about Chinas participation in RIM-PAC 2014. So it was a very pleasant surprise to see the J-31 flown to Zuhai two weeks early, and to perform several outstanding flight demonstrations during the International Air Show, and as you have observed, it is a more traditional platform, the J-31 itself looking very kool and futuristic until shown side by side with the FC-31, which promises to be an even more exciting airplane. While lots of folks are concerned that the RD-93s are very limiting, my own perspective is that you use what is available, and work from there. As we have noted on another thread, it would seem the RD-93s will need to be upgraded before this aircraft becomes a "money maker", but it sure is slik, and I can't wait till we see the FC-31 first flight?

 

[Air Force Brat]

Interesting that it has been almost 4 years since the J-20s first flight, and that aircrafts delta main wing and distant coupled canards continue to be tweaked, though the now 4 pre-production proto-types logging flight time. Sadly it seems that we know far less about 2011 and 2012 than we do about 2001 and 2002, although the new kids are likely in the mold of production aircraft and seemed to fly well, we simply did not have the pictures and videos that we all enjoyed so much after 2001s launch. We are seeing how politics affects aerodynamics, and even flight testing. The previous presidents openness and forward movement on many fronts has been "pulled back", possibly due to "security concerns", or maybe just a general desire for more "clandestine" operations.

No doubt all governments are concerned about security and rightly so, but it has certainly been disappointing to see this "regression", even as we were excited about Chinas participation in RIM-PAC 2014. So it was a very pleasant surprise to see the J-31 flown to Zuhai two weeks early, and to perform several outstanding flight demonstrations during the International Air Show, and as you have observed, it is a more traditional platform, the J-31 itself looking very kool and futuristic until shown side by side with the FC-31, which promises to be an even more exciting airplane. While lots of folks are concerned that the RD-93s are very limiting, my own perspective is that you use what is available, and work from there. As we have noted on another thread, it would seem the RD-93s will need to be upgraded before this aircraft becomes a "money maker", but it sure is slik, and I can't wait till we see the FC-31 first flight?

Well it does seem that Christmas has come to the SDF, and some of our posters must have been nice as opposed to naughty, as Santa Clause/Chengdu Aircraft has gifted us with two additional J-20 prototypes 2013 and 2015, bringing the total to 6 aircraft. So this has been an exciting year here on SDF, particularly in light of the J-20, hopefully we will be getting some good pictures of flight testing out of Chengdu, but with the new laws it will depend on how they are interpreted and applied?

Heres hoping we get to see some new aspects and elements of flight test, hopefully someone will catch some exciting video as they did with 2001?

 

[Air Force Brat]

Oh, you are too modest. I can't half compete with you even if I did cherry pick. For one, I am not the one who uses imaginary value that can subject to change in the next five years to argue against hard figures currently published by US Air Force. For another, I am not the one who argue about aircraft performance based only on WVR engagement.



There is nothing sound about using LRIP as a premise, because the issue of contention is not whether scale of economy can drive down cost. The issue is whether smaller fighter aircraft have lower unit cost compared to larger ones, which is an entirely different concept to that of economy of scale. Moreover, economy of scale isn't unique to F-35, and if F-22 had production up to thousands of units, we would see lower unit cost for F-22 as well. In other words, economy of scale doesn't help your argument.


You can go on and on about specifics of the two engines, but the F-35 cannot super-cruise and has a lower thrust-to-weight ratio than F-22. That's go against your generalization that a smaller fighter is more optimized for WVR than a large fighter.


The flaw of the above statement is the assumption that fighters don't have to be good in both BVR and WVR. A fighter aircraft that's optimized for BVR engagement can at least choose to avoid getting into WVR, whereas a fighter aircraft that's optimized for WVR engagement has to survive through BVR first. So, a fighter can have the best performance in the world at WVR engagement, but that's useless if that aircraft gets blown up at BVR and can't make use of the advantage.

Well, where is the Engineer, you still onboard with us Chief?

Time to upgrade that lovely avatar, and what better thread than the old aerodynamics thread?? LOL

 

[Air Force Brat]

Well, where is the Engineer, you still onboard with us Chief?

Time to upgrade that lovely avatar, and what better thread than the old aerodynamics thread?? LOL

This guy is like smoke, he wafts in unoticably, makes the kill, and evaporates, who knows about you Eng??? you're not tryin to lay low are ya bruda?

 

[Scratch]

The lift is created by a vortex around the wing. Imagine a two dimensional airfoil in an air steam under an angle of attack. The speed of air on the suction side is larger than on the pressure side. If you subtract the free airflow you see a vortex around the airfoil, with something strange near the trailing edge.

I'm sorry if I'm bugging you here. I'm just keen on wrapping my head around this one.

Am I to understand that the velocity of upper side air is slightly larger than free stream velocity while underside air velocity is slightly lower than free stream?
If I now subtract the free steam velocity value, the result is a slightly negative v beneath, and a positive v above the wing. That in essence leads to a circular motion of the air around the wing?

Furthermore, is that the same "concept of circulation" that forms the basis of the Prandtl lifting-line theory for the three dimensional wing?

If so, then in that context I wonder if it is the correct term to speak of that lift-causing circulation as a vortex, in contrast to the vortices that form at the tip, or the trailing edge, as a result of lift being produced.
As in all the respective explanations, that I find and understand as a layman, I only find the term vortex being used in the latter context.

Thanks allready for your time.

 

[delft]

I'm sorry if I'm bugging you here. I'm just keen on wrapping my head around this one.

Am I to understand that the velocity of upper side air is slightly larger than free stream velocity while underside air velocity is slightly lower than free stream?
If I now subtract the free steam velocity value, the result is a slightly negative v beneath, and a positive v above the wing. That in essence leads to a circular motion of the air around the wing?

Furthermore, is that the same "concept of circulation" that forms the basis of the Prandtl lifting-line theory for the three dimensional wing?

If so, then in that context I wonder if it is the correct term to speak of that lift-causing circulation as a vortex, in contrast to the vortices that form at the tip, or the trailing edge, as a result of lift being produced.
As in all the respective explanations, that I find and understand as a layman, I only find the term vortex being used in the latter context.

Thanks allready for your time.

You have understood my post just as I intended.

 

[Air Force Brat]

I'm sorry if I'm bugging you here. I'm just keen on wrapping my head around this one.

Am I to understand that the velocity of upper side air is slightly larger than free stream velocity while underside air velocity is slightly lower than free stream?
If I now subtract the free steam velocity value, the result is a slightly negative v beneath, and a positive v above the wing. That in essence leads to a circular motion of the air around the wing?

Furthermore, is that the same "concept of circulation" that forms the basis of the Prandtl lifting-line theory for the three dimensional wing?
If so, then in that context I wonder if it is the correct term to speak of that lift-causing circulation as a vortex, in contrast to the vortices that form at the tip, or the trailing edge, as a result of lift being produced.
As in all the respective explanations, that I find and understand as a layman, I only find the term vortex being used in the latter context.

Thanks allready for your time.

I wouldn't use the word "circulation" to describe "air-flow", and I wouldn't allow the Prandtl wing to cloud my understanding of "airflow". Its like trying to understand the box kite, in order to get a get a grasp of the aerodynamics of "flying" a kite.

"Air Flow" is a linear affair, with the vortex created by the pressures above and below the wing attempting to achieve equilibrium being incidental. To "corral" that vortex and make it do something beneficial, is rocket science.

The Typhoon is sprouting LERX and delta shaped ILS housings below the cockpit, in order to maximize low speed aircraft agility and handling, and enable the aircraft to achieve a much higher angle of attack before experiencing "separation" or departure of that "airflow".

I would suggest that would be a much better place to start thinking about the beneficial effects of vortices, and hopefully find a video of "blue smoke" in the wind-tunnel, in order to help you visualize what is actually occurring??