T-50 LERX?

[shep1978]

Let me try to explain aerodynamics.

Err, I don't want to appear rude but I think Johnwill is just a tad more knowledgeable in field of aerodynamics then yourself my friend. Sometimes it pays to listen to those who have real hands on experience in these matters...

[1st503rdsgt]

1. The F-22 does benefit significantly from the vortex lift generated by the sharp edges along the upper edge of the inlet. Call them anything you want, they work.

2. The F-22 lifting tail does not result in any more drag or frontal area than a down-loaded tail, plus it results in a lower required angle of attack, thus less overall airplane drag and frontal area.

3. On what basis can you claim the F-14/Su/MiG tunnels produce more lift than the flat F-22 bottom? Pure speculation on your part. I can assure you the tunnel design results in more drag than the flat bottom due to increased wetted area.

Layman's question johnwill:

Do you think the Russians went with the wider-spaced engines to to make better use of 3D TVC?

[johnwill]

I don't have any insight why the Russians (and Grumman) went with widely spaced engines and can only speculate. One reason Grumman did that for the F-14 was to get straighter inlet ducts into the engines, to reduce stall problems on the TF-30 engines. RCS was not much of an issue in 1968. TVC is primarily used for two reasons, pitch authority at high angle of attack and low airspeed, where the tails lose effectiveness, and pitch trim at supersonic speeds, to reduce trim drag from using the tails. It is possible they use roll differential TVC with widely spaced engines, but normally the ailerons, differential tail, and rudder are still effective in roll at very low speeds. The use of differential TVC should result in no weight or cost penalties, so there's no harm in doing it.

Something not obvious about using TVC for roll is that it can produce an undesirable yaw (sideslip) effect. Let's assume the airplane is at low speed, high AoA, and the pilot wants to roll. Using normal control surfaces, the airplane rolls around its flight path axis, not its body axis. That way, AoA stays the same and sideslip angle stays near zero. However, differential TVC rolls the airplane around its body axis, and the AoA is changed into sideslip, possibly resulting in control difficulties. Normal flight controls could be used to counteract that undesired condition, but then why not just use the normal controls to roll the airplane?

Another positive effect of widely spaced engines is it results in more widely spaced main landing gear, for more stable ground handling.

The design of all airplanes is a compromise. Wide or narrow engine space, flat bottom or tunnel bottom, etc. are only a few of the choices design teams have to make. Each team has different goals, different constraints, different budgets, so the resulting airplanes reflect those items.


Edited;

Let me add that if the Su-XX have lateral TVC, that would help with the roll/yaw control problem.

[haavarla]

[quote]Err, I don't want to appear rude but I think Johnwill is just a tad more knowledgeable in field of aerodynamics then yourself my friend. Sometimes it pays to listen to those who have real hands on experience in these matters...[/quote]


I did not claim to be working within fields of Aerodynamics.
I did not state Johnwill knows nothing about Aerodynamics.

And i do listen, what i want is for him or anybody else to explain why a flatt and wide planform airframe body have an advantage with high-lift vs a more boxy(fat) airframe body.

It is not the tunnel design in it self, but the fact that the short(flatt) space between top and belly of the Su-xx serve as an extension of the wings, thus creating additional high-lift.
It is not that hard to understand, but perhaps my limited English could be a problem.
Another advantage with such tunnel design is stability.
Stability in Yaw more spesific.
That coupled with the pair of large Stabz, the small ventral strakes underneath makes the Su-xx a very stable design in a wide range of high AoA.
I agree with johnwill, each fighter designed is aimed at spesiffic goals and requirements, and in the case of Su-xx, it goal was to best the F-15.
At least in Aerodynamic performance, which history shows it did.
The Su-xx design was i dare say way ahead of its time.

PS. Why does not my quote text work here

[SpudmanWP]

hehe.. a quote of your quote works.

Does it work when you "preview"?

[johnwill]

haavarla,

I am not offended by your statements. Please continue to ask questions freely, and to question my statements as you wish. Your English is not a problem for me, as I have worked with ESL people for many years.

To answer your questions, no one says the F-22 wide flat body is better than than Su-XX in generating lift, but I'm saying you have no basis for stating the reverse. The fact is you don't know and I don't know which is better. Both are evidently effective in doing their job. Let me give you an example of fuselage lift. The F-16 does not appear to have a very effective lifting fuselage, but in fact it provides as much as 45% of total airplane lift. The flat F-22 fuselage would likely be at least as effective as the F-16. Is it better than the the Su-XX? The only way to know is to look at actual engineering data from wind tunnel test, CFD analysis, and flight test. The entire fuselage generates lift, not just the space between the engines in the Su.

My point is that you cannot tell how effective the fuselage lift is just by appearances.

Yes, the Su-xx would appear to be quite stable in yaw, but at the expense of added drag from the very large vertical tails and the small ventral strakes. Notice the F-15 does not need the strakes and it has excellent yaw stability. Likewise the F-18 has no need for ventral strakes.

[1st503rdsgt]

The design of all airplanes is a compromise. Wide or narrow engine space, flat bottom or tunnel bottom, etc. are only a few of the choices design teams have to make. Each team has different goals, different constraints, different budgets, so the resulting airplanes reflect those items.

Another question:

Do the large size, novel control surfaces, and 3D TVC reflect an effort to surpass the F-22/F-35, or could they be design crutches that reflect an inferiority in Russian avionics and other systems?

Also, on the subject of low-observables, do the Russians stand a chance of achieving the levels of workmanship necessary to obtain a low RCS? Even their best 4th generation fighters were roughly built by western standards.

[johnwill]

Sorry, I can't comment Russian systems as I know nothing about them. But, I find the recent Russian airframe designs to be clever, innovative, and effective. Same story concerning RCS effects of Russian workmanship, other than to say It may not be the workmanship that results in "roughly built" airplanes. It could be it's the detail design that's rough.

[haavarla]

The Russian made TVC has been around for some time now.
What i find more interesting than the TVC, is the new FCS which is said to incorporate the TVC with the rest of control surfaces.
I'm not sure how its done exactly

Perhaps the TV nozzles movements increase progressivly as the speed drops and vica verca..

Anyway this was never acheived on earlier models. Where the pilot had to engage the TVC with a switch.

The new FCS is said to increase the flight safty of pilots, like deny pilot making dangerous manuvers in low altitude etc and in effect making the aircraft easier to control(reducing pilot work load).
It also uses the Stabz as airbrakes, deflecting both stabz inwards for slowing down.

[haavarla]

...

[Scorpion82]

What i find more interesting than the TVC, is the new FCS which is said to incorporate the TVC with the rest of control surfaces.
I'm not sure how its done exactly

Not that difficult, on the Su-30MKI for example the nozzles were manually activated and didn't interact with the control surfaces. On aircraft with like the T-50 the TVN movement is commanded by the FCS and interacts with the other control surfaces.

[johnwill]

The new FCS is said to increase the flight safty of pilots, like deny pilot making dangerous manuvers in low altitude etc and in effect making the aircraft easier to control(reducing pilot work load).

F-16 first did this 37 years ago with its YF-16 prototype.

[sprstdlyscottsmn]

They even had a 50% gain reduction with the gear down after the accidental first flight. Brilliant solution IMO to an agile platform becoming more docile for landing.

[haavarla]

[quote="johnwill"]
The new FCS is said to increase the flight safty of pilots, like deny pilot making dangerous manuvers in low altitude etc and in effect making the aircraft easier to control(reducing pilot work load).

F-16 first did this 37 years ago with its YF-16 prototype.[/quote]

Sure.
Still, fatalities occurs.
Remember back in the 80's, when one RNoAF F-16 went down in the swamp after some low flying.
It was deemed pilot error.

I was in the army back then and the crash site was not that far from base.
We was dispatch on ski(winter time) to secure the crash site.
A weird sight.. completly white snow everywhere except a big black hole and very litte to recover..