Forum: General F-35 Forum

wrightwing wrote:

megasun wrote:

What if F-35 faces an opponent capable of both supersonic and stealthy in future?
For example for USN, who has no F-22 but F-35C to face such a challenge.

You mean post PAK FA/J-20? By that time, you'll likely see F-35 successors arriving in service

You don't really think there's a good chance the F-35 successor will actually be on time do you??? Unless they're building it right now then there's not a hope in hell of it being ready to coiunter J-20's.

F-16.net Sponsor

The last F-35 is not scheduled for delivery till 2037 which means that it's replacement will not be built till 2050 or so. Backup 15 years for dev and that puts the start of it's replacement dev in 2035.

If a replacement is required, the answer to the J-20/PakFa will not be the F-35's replacement, but the F-22's.

haavarla wrote:

As in Lateral stability in high apha. The engines airflow restriction(or the lack of it)! Its a large fighter, the weight follows it, its still very manuvereble, that would be Agility.

Ok, but you still need to understand a few things about this.
Back in '70s (when both Mig29/Su27 got conceived) carefree handling was a new fashion in design construction philosophy.
Since FBW and CCV, were still unachievable by then SU, they needed to devise an alternative way to cope with departures and post stall dynamics.
That resulted in Mig29/Su27 designs, in medium and heavy fighter class.
(btw, up to this day, Russia doesn't have a single major operational fighter that was originally conceived as a RSS vehicle)

Now, what I've spent a several recent posts on, was showing you that this doesn't matter, since the number of fights that will degenerate into such a slow/post stall fighting is next to none and that this doesn't have any meaningful impact on combat performance.
What matters though is that F15C beats Su27SK (if you want to compare these two) across the board in terms of Ps and IMO Sukhoi would have been much better of, if they put those two engines together to reduce drag, instead of insisting on high alpha performance.

Also, johnwill is right.
Directional stability is of a concern at high alphas.
Once your ailerons stall and you loose lateral stability, the rest of your wing is already stalled anyway and you're on the way down.

spazsinbad,
Thanks for the A-4 information. The functioning of those slats looks similar to the F-86 my good friend flew in the 50s. He's 85 now, in great health. The A-4 slats are really covered with band-aids, but if it works, fine.

A little more on high AoA rolling and yawing. When a fighter rolls it does not roll about the fuselage longitudinal axis, it rolls around the flight path axis. At low AoA, that is almost the same thing as the fuselage axis, but at high AoA, a roll generates a significant yaw rate and a yaw generates a significant roll rate. That is definitely a difficult condition for a stability and control engineer to resolve and maintain good handling qualities.

Quote:

Lateral stability at high AoA has been mentioned as part of "handling". I think the writer has the right idea, but the terminology is wrong. Lateral Stability is stability around the roll axis, which normally is not a concern. I think the writer really means Directional Stability, or stability around the yaw axis. Directional stability suffers at high AoA due to the fuselage masking or blocking airflow past the vertical tail or tails. Directional stability is what keeps the pointy end in front. Loss of directional stability is what causes spins.

Here is my definition of good handling. The airplane responds to all-axis control inputs in a predictable, linear fashion, with sufficient rate to accomplish the pilot's intent.

If an fighter lose all lift, the wings are fully stalled, you lose control normaly in roll direction first and then in yaw direction or sometimes both at the same time.

It has also to do with wing design and LERX, and those ventral fins too. Not only the Verticals Stabz.

Quote:

Ok, but you still need to understand a few things about this.
Back in '70s (when both Mig29/Su27 got conceived) carefree handling was a new fashion in design construction philosophy.
Since FBW and CCV, were still unachievable by then SU, they needed to devise an alternative way to cope with departures and post stall dynamics.

Upon the Su-27 entering service it fielded an FBW system. The Mig-29 did not.
Sukhois design construction philosophy was to design an wing that was as stable in the wide range of AOA.
They first designed the wing, then they understud that the aircraft had to have a long nose section and the way the air was feeded onto the wings was crusial(LERX).
Anyway, it was a lot of try and error, but they got it right in the end.

The overall goal of the Su-27 design was to best the F-15.

Last edited by haavarla on Apr 02, 2012 - 09:57 AM; edited 1 time in total

Quote:

Now, what I've spent a several recent posts on, was showing you that this doesn't matter, since the number of fights that will degenerate into such a slow/post stall fighting is next to none and that this doesn't have any meaningful impact on combat performance.
What matters though is that F15C beats Su27SK (if you want to compare these two) across the board in terms of Ps and IMO Sukhoi would have been much better of, if they put those two engines together to reduce drag, instead of insisting on high alpha performance.

On what parameters have you concluded this??
You make it sound like the Su-27 design is a very dragy design, i can assure you its not. It is a supersonic fighter that holds it own in higher speed regimes as well as slow speed regime.

Its by no account like the SH design which has clear compromises.
Thats the brilliant feature of Su-27 design, its very good over a wide range of kenetic and Aerodynamic. Not only in slower speed regimes.
Its a heavy interceptor and airsuperiority fighter, its a very large design, it has high MTOW and empty weight. More than the F-15C. Still its more agile, it allmost as fast as the F-15C(increase accelleration and climb ratio can be corrected with more thrust).
It has many more role than the F-15C.
It can do Carrier operation with small changes.
Its a two seater Combat trainer.
Its a short take-off and landing aircraft.
It has very long legs.
In short there are no compromises in this design in term of aerodynamics.. it sounds like you do not agree?

'johnwill' the 'band-aid' vortex generators were on the wing as well. And don't forget the rudder was 'inside out'! Smile

The prohibition on rolling was due to tumbling caused by the back end not rolling around the same axis as the front end while the result could be horrific after more than one roll - not that I ever did that myself. No one could roll an A-4 at maximum aileron deflection at 250 knots before centering the ailerons before the 'magic one roll' completed. Back seaters in the TA-4 were always bumping helmets on the canopy even when they knew the roll was coming. Sitting up high there the roll coupling experienced was horrendous! Smile

The KIWIS used to successive roll the A-4K KAHU going upwards releasing flares but I guess the rapidly diminishing airspeed helped with the 'roll coupling' problem.

Yes, the naked rudder. The T-38/F-5 also have unusably high roll rates. I have often wondered why some kind of mechanical stick stop was not used to limit the roll rates and accelerations. Did that extreme roll performance ever lead to serious problems?

I think I read somewhere the Kiwis are giving up on selling their A-4s and will donate them to museums. Maybe you could start a museum and get one.

Quote:

Does the Su-27 flight manual say the vanilla flanker becomes unstable beyond 24 degrees alpha (20 degrees with weapons loaded) and is limitted to 8G's maximum below mach 0.85 and 7G's max from 0.85 to 1.25?

I have no excact manual over the Vanila Flanker AoA with a load-up chart. I cant answer.

However, you could look at these two vids and come to your own conclusion.
Here by an British Test pilot. Start at 02.45

http://www.youtube.com/watch?v=zqcHXbO3 ... ure=relmfu

And here the Flanker with heavy load. Its not an Vanila Flanker though..

http://www.youtube.com/watch?v=UsyMUAfh6fg

Western press and pilot comunity critizised the Flanker, that it could not do high alpha in heavy load up.. Victor Pug said, ok watch me..
There was no more question by western press after this..

haavarla wrote:

Upon the Su-27 entering service it fielded an FBW system.

Well Su27's FBW worked only in longitudinal plane, so it wasn't really a CCV in the true sense, like F16 was f.e, let alone RSS plane.
Su27 really didn't need FBW to achieve carefree handling in terms of slow/post-stall, but designers used aerodynamics instead and that aerodynamics took the toll on performance.

Quote:

The overall goal of the Su-27 design was to best the F-15.

In which they essentially failed.
So, what was the point in having more carefree handling than F15, when Sukhoi designers couldn't match its performance, in the first place?

Last edited by spazsinbad on Apr 02, 2012 - 11:52 PM; edited 1 time in total

'johnwill' at 720 degrees per second one had to only 'think' about rolling and it was done. A first timer taking off would always wing waggle. There was no other way to keep the wings steady except to over correct initially - even in micro amounts. Being relaxed was the key! Smile

The high roll rate for carrier landing was excellent for lineup corrections. Nice to see the F-35C will have good roll rates at carrier approach speeds.

It was literally impossible to go to full aileron deflection without already exceeding the one roll restriction. So the method was (with an instructor in back of the T-A4 - about to spew) go to almost max deflection - about only half way [I don't believe anyone could ever get there at 250 knots] before having to go back again just as quickly and it was done, with always an 'over roll'. That would be the last time anyone would attempt such a suicidal trick. Smile

The A-4 roll rate was so fast it was not necessary to go to anything like full deflection; except perhaps at very slow speed when dirty. OR recovering from an inadvertant 'assymetric slat' situation (hopefully also at slow speed).

If I recall the term correctly now the 'inertial coupling' would lead to airframe breaking if continued (under adverse conditions) because the weight was so far aft. I have been in a bad 'non-spin' situation in a spiral dive rotating left with extreme nose down attitude but stalling as the nose came up almost to the horizon to stall and flick left again because the electrim trim had gone to full nose up (my fault) entering this state at around 30,000 feet ending up recovering (pulling out of the dive below 10,000 feet but under control) just in the time it took to get the trim back down near neutral so that the aircraft was controllable again. It was impossible to push/keep the nose down to unstall the aircraft during the violence of flick rolling left, nose up and down etc. It was the wildest ride of my life. Smile

Luckily I had just read a USN APPROACH magazine article about this 'full nose up trim' condition and I was able to identify the problem immediately to get the trim down again but in those few seconds lost all that altitude!
___________

That roll rate was useful when A-4 loaded up - everything slowed down then of course due to the mighty load carrying capacity!

Last edited by cola on Apr 02, 2012 - 02:02 PM; edited 1 time in total

haavarla wrote:

...Still its more agile, it allmost as fast as the F-15C...

How many times you need to be repeated the same thing?!
It isn't more agile then F15 in real world, due F15's higher speed and thus the ability to superimpose the combat tempo on Su's pilot.
I gave you several examples, but obviously I wasn't clear enough, so I'll try to type slowly this time.
Mustang could outturn Me262 across most of its flight envelope.
However, Me262 would outturn Mustang at higher speeds and that was exactly the place where Me262 fought Mustang, where its superior performance enabled it to choose the part of envelope in which he'll fight (if the pilot was even semi-intelligent) and Mustang couldn't do a damn thing about it.

Another consequence of what you call a brilliant idea behind Su27 aeroconfiguration is airframe life, which is meager 2k hours for Su27SK.
I'm sure johnwill can explain this better then me, but the problem of long tip chord (as a requirement to be able to cope with high alphas and another testimony to Su27's FBW), resulted in huge torques on the tips and required extensive strengthening of the wings and consequently the weight increase and all that just to meet 2k hours of airframe life.
Then the goal to squeeze as much of a sustained turn as possible, from already large portion of draggy fuselage lift, required comparatively high aspect wings (15% over F15) which also worsen wave drag characteristic.
Already mentioned separate engine nacelles also do wonders for interference drag, but in a bad way.
Long fuselage with lifting and control surfaces stuck back, sure don't help reducing trim drag in turns.
Etc, etc...I can do this all day...

So, you see this "brilliant" design is loaded with compromises and it isn't quite as brilliant as you seem to think, but an offspring of requirements and available technology of the time.

haavarla wrote:

Victor Pug said, ok watch me..
There was no more question by western press after this..

Its not doing a high alpha turn in those videos though, its doing high alpha departures. That was a bad movie to make a point IMO, every one of those maneuvers turned it into a brick. Was that prototype using the 117S engines, because if so, I'd be willing to bet the aircraft doing the rounds at airshows lately has been massively weight reduced? Either that or combat configuration completely destroys its performance.

Is there anything available where it does a high aoa turn and actually sticks the turn like in this example?

http://www.youtube.com/watch?v=PyKYw_p1Hrc

Su-27sk manuals:

http://www.secretprojects.co.uk/Su27_Rus_1.doc
http://www.secretprojects.co.uk/Su27_Rus_2.doc

http://www.secretprojects.co.uk/Su27_Eng_1.doc
http://www.secretprojects.co.uk/Su27_Eng_2.doc

Last edited by haavarla on Apr 02, 2012 - 02:44 PM; edited 3 times in total

Quote:

How many times you need to be repeated the same thing?!
It isn't more agile then F15, due F15's higher Ps and thus the ability to superimpose the combat tempo on Su's pilot.

The Su-27S/SK was not required to carry any A2G weapons, nor any ext DT. and could do with 4 tons+ of A2A missiles. The Su-27SK are absolete, its not exporting anymore. Its gone, save for a few 3rd world countries. Can i make my self more clear?

The Su-27SM have the same airframe improvments as the Su-27SKM.
The SKM has stengting in wings and airframes, which make your figures go up in smoke.
Any reason you pick the SK version?
The F-15C spawns from the F-15A you know.

Both Aircraft manufactors had to start somewhere. Your claims about the F-15C comes with higher Ps ended at the very early 2000.
The first operational Su-27SM entered service in Dec2003.

The Few Su-27S that are operational in VVS(if there are any?) Did see upgrades on airframe in their time of service.

That the Su-27SM/SKM entered that late was due to the cash strapped SU and Russia 90s. RuAF even received three Su-27M as early as 1996, but it did not see any contract, for reason above.

Last edited by haavarla on Apr 02, 2012 - 03:18 PM; edited 2 times in total

... Double post

Forum: General F-35 Forum

JSF High Wing Loading: why?