su27/Mig29 vs F15/F16 flight characteristic

[nevidimka]

No this is not a who is better thread.

The su27 and mig29 are very manourable in the lower subsonic speeds, while the F15/16 are better at higher subsonic/transonic speeds.

I would like to know what aerodynamic design characteristics that determine these differences?

[rjmaz1]

Where did you read that the su27 and mig29 are more manuverable at low speeds?

Thats a massive assumption and has never been proved. No one has published the sustained and instantaneous turn rates of these aircraft at various speeds.

The Su27 may have better high speed agility than the F-15 for all that we know.

Early block F-16's may have a higher instantaneous turn rate than any of the aircraft listed at both high and low speed.

The SU-27 performing the cobra only shows that it has good stall free characteristics. At 200 knots the F-16 may very well turn inside an SU-27.

Now to answer your question on what technical characteristics determine agility at various speeds..

High thrust is required to sustain high G turns as it bleeds off airspeed very quickly. Wing loading, apsect ratio, sweep angle and wing area all have play major parts in the agility of an aircraft. Thrust vectoring and canard foreplanes also help alot usually at low speeds. There is no perfect combination to acheive a certain result.

If the F-22 didn't have thrust vectoring it would probably be the worst when it comes to low speed agility due to its high speed wing design, this is shown by its high landing speed. The F-35 is desigend for slower speeds though still quick which means it doesn't require thrust vectoring. Thrust vectoring also adds weight and reduces the thrust to weight ratio, so thrust vectoring could reduce sustained turn rate instead of improve it.

Todays combat is at beyond visual range so the high speed agility of the F-22 is definitely preferred. Its safe to say that within visual range engagements will eventuall become a thing of the past. The good old dogfight light topgun is long gone as there are too many kill oppurtunities before the gap closes. If aircraft come within visual range the fight will be quick and speeds will drop no where near low enough to use ultra slow agility shown at airshows.

Within visual range combat may still occur occasionally when both sides get stealth aircraft but the fight will be quick and it will never turn into a dogfight as such.

Adding canards and thrust vectoring to the SU-30 is pointless as it doesn't improve high speed agility and the aircraft already had excellent low speed handling. The F-22 has some justification for thrust vectoring, the Eurofighter and Super Hornet hopefully never get it due to the extra weight.

Though US said this in veitnam which is why the F4 had no internal cannon. That was a mistake then but no

[qwerty223]

High thrust is required to sustain high G turns as it bleeds off airspeed very quickly. Wing loading, apsect ratio, sweep angle and wing area all have play major parts in the agility of an aircraft. Thrust vectoring and canard foreplanes also help alot usually at low speeds. There is no perfect combination to acheive a certain result.

If the F-22 didn't have thrust vectoring it would probably be the worst when it comes to low speed agility due to its high speed wing design, this is shown by its high landing speed. The F-35 is desigend for slower speeds though still quick which means it doesn't require thrust vectoring. Thrust vectoring also adds weight and reduces the thrust to weight ratio, so thrust vectoring could reduce sustained turn rate instead of improve it.


The turning part is not entirely correct. High G turns not necessarily rely only on high thrust. It happened when the aircraft is changing its direction rapidly, and all aerodynamic devices had to cooperate and well, in order to achieve such a maneuver. It is true that there is a ratio of lost in thrust in the process of directing it away from the axis of the engine, however, an co-axis thrust assist the airframe to maintain a high centripetal force, in other word a high G condition, but the tangential force from a co-axis thrust also laying much more pressure on to the lift devices which is inverse proportion to the radius of turn, while VT is a solution to bypass such a circumstances. VT achieve a small radius turn by changing the position of the longitudinal axis closer to and ideally on the barycenter of the airframe, in oppose to force the airframe to turn near a given axis. As a turning rigid body, regardless of method of turn, it creates G force proportion to the rate of turn.

Take note that the lost of thrust also happen on a co-axis thrust which act as a tangential force in the turn. When the airframe is well on the direction of flight, the nozzle rotate back to its position, lost of thrust no longer happen. Due to such a complex and precise mechanism control, thereby a digital flight control is a must as oppose to a conventional thrust design.

The so-call lost of KE in a VT turn is due to the congenital of the method of turn. When the longitudinal is very close to the barycenter (small radius) and a high turn rate (angular velocity), G force will increase such rapidly that easily exceed the limit, for the airframe as well as the pilot as a human being. To counter such a defect, flight control must maintain a low angular velocity, thereby a limit in low thrust cause a lost of momentum in the engine and the slower regain of KE. As a result, the aerodynamic become worse when there is no thrust to counter the stall effect. On the other hand, co-axis thrust powered aircraft can take a smooth turn upon a longer radius, keeping about the same amount of thrust under the limit of tolerance of the airframe, therefore not much lost of momentum in the engine in compare to a VT engine.

As you can see, there are pros and cons in both systems, but if there is a tech breakthrough to offer more endurance to G force, VT certainly has a brighter future.

[nevidimka]

I thought that the russian planes were more superior in low subsonic speeds compared to the American ones. Was i wrong?

If TVC and canards do not help the flanker much in its already good performance at low speeds, is that the reason why russian air force went ahead with a further development of the SU 35 which does not have canards n TVC, compared to the Su37?

[Chrom]

Mig-29 / Su-27 generally have better low-subsonic perfomance for exactly that reason - better stall control. While they "true" turning perfomance may be not much better than F-15 / F-16, but the ability to better control stall allow flying (and turning) much close to stall speed, and even taking risk to fall post-stall as Su-27 / Mig-29 engines do not easely shut off in reverse airflow and can recover quckly.

This is also major reason why TVC is better than normal engine - not only becouse better turn-rate, but mainly becouse pilot do not fear stalls with TVC. He can safely keep aircraft closer to stall-line.

Generally, SU-35 is a "cheap" version of Flanker, which can be described as "most bang for the bucks". With proliferation of all-aspect WWR missiles, coupled with HMS and the fact what new WWR missiles are better described as almost-BVR - turning perfomance became much less important.