Re: J-20... The New Generation Fighter III
"The damaged engine's nozzle was pointing 30 dregrees up, causing an uncontrollable pitch up"
what type of engine is that?
ah yeah a is a thrust vectoring nozzle that once damage doomed the jet, if you were right then the pilot could save it why?
Once again, what you are repeating is called the
. You are asserting that TVN failure was the cause of crash, when pilot error was the cause for both failure and the crash. From the following
, we see the investigators also attributed the accident to pilot error:
A joint probe by India and Russia into the crash of IAF's Sukhoi aircraft over Jaisalmer in April has given a clearance to the quality of the fighter plane, indicating that the mishap took place due to human error.
This debunks your claim that TVN failure is the cause of the crash. The TVN simply didn't spontaneously destroy themselves.
Because Song claims if an engine with TVC nozzle fails J-20 will bring the jet back to normal flight hahahaha, poor Russian pilots they did not know Song`s ideas it is so easy to control a damaged thrust vectoring nozzle in normal flight
See how easy is to control the nozzles once they fail
Dr. Song refers to TVN malfunction, not TVN having been destroyed. He made no requirement that J-20 has to continue to fly when the nozzles are smashed because of pilot's stupidity.
Now, if the jet is doomed as soon as TVN becomes damaged, then it only illustrates the unreliability of TVN. Aircraft such as F-22 and PAKFA requires TVN because their tailplane becomes ineffective at high AoA. For J-20 which uses canards, this isn't going to be a problem:
Control surfaces placed in front of the center of mass, like the canards, are negative load control surfaces. Since the main wing's ability to generate lift tends to saturate under high AOA conditions, the positive load control surfaces' pitch down control capabilities tend to saturate under high AOA as well. Therefore it will be wise to employ negative load control surfaces for pitch down control under high AOA conditions. Figure 7 compares the pitch down control capabilities of the canards and horizontal stabilizers. From the high AOA pitch down control stand point, it will be wise to use canards on the future fighter.
now let us go
"What the previous two observations mean is that an aircraft can still be flyable in the post-stall region provided that several criteria are met:
1. The aircraft has enough thrust to overcome the huge drag increase.
2. The aircraft has controls that will not be rendered ineffective by separated flow over the wings and tail."
do the MiG-29 or Su-27 stop using tailplanes ? no they do not
why?
Quoting this section of
does not support your claim, because no where in the above quote does it says tailplane is used in generating the necessary pitch-down moment to recovery the aircraft. The very paragraph which follows your underlined bullet points has this to say:
Hence the reason that the post-stall region has only been a fairly recent area of study: T/W ratios needed to increase, C[sub]L[sub]max[/sub][/sub] values needed to increase, and non-aerodynamic controls (such as TV) had to be developed before an aircraft would be capable of controlled flight in this very adverse aerodynamic region.
Two pages later, the author made the following statement:
The dynamic maneuvers possible in the post-stall region, the freedom from purely aerodynamic control surfaces, and the ability to aim the aircraft’s fuselage and weapons independent of the direction of flight combine to make a SF extremely lethal in the short range air combat arena.
It is very clear that when the statement "aircraft has controls that will not be rendered ineffective by separated flow over the wings and tail" was made, the author was specifically referring to TVN. The reason why TVN is needed is given in another
:
if the aircraft can fly at angles of attack of 80[sup]o[/sup] - 120[sup]o[/sup] with the ability to maintain stability in all channels. In this flight regime the ability for conventional control is usually lost.
Thus, the tailplane is ineffective, as pointed out by
:
A concentration of characteristic curves Cm for the tailplane setting angle φ[sub]t[/sub] being varied at post-critical AoA (i.e. very low sensitivity of pitch moment with respect to the tailplane setting angle) reflects the loss of effectiveness of a horizontal tail at higher AoA.
In another part of the
, says the following statement statement:
It can be explained by loosing of effectiveness of control surfaces... In the range of AoA up to 35[SUP]o[/SUP] the normal increases approximately linearly, then stabilises and practically the tail surface losses its effectiveness.
The MiG-29 or Su-27 wiggling their tailplane does not mean tailplane can provide the pitch-down moment for recovery. And as we have seen from the above quotes, the tailplane becomes ineffective at high AoA for recovery. MiG-29 and Su-27 uses passive mean rather than active deflection of tailplane for recovery. From the
:
The recovery from high angles of attack to the classical flight mode in a few seconds only is possible due to moving the center of pressure on main wing back and creating the strong nose-down aerodynamic pitching moment about the center of gravity.
The use of the word "only" excludes active deflection of tailplane as a contributor.
let us see
MiG-29 does this
"third phase, (recovery from the manoeuvre) characterised by full deflection of the horizontal tail for diving with the increasing, negative pitch rate (at the end of this phase the pitch rate for diving reaches its maximum, negative value"
From the same
of yours, the following is mentioned which you conveniently omitted:
It can be explained by loosing of effectiveness of control surfaces... In the range of AoA up to 35[SUP]o[/SUP] the normal increases approximately linearly, then stabilises and practically the tail surface losses its effectiveness.
This
analyzes the Cobra maneuver, a source that you brought into the discussion. Let us see what it has to say with regard to recovery:
The recovery from high angles of attack to the classical flight mode in a few seconds only is possible due to moving the center of pressure on main wing the center of pressure on main wing back and creating the strong nose-down aerodynamic pitching moment about the center of gravity.
The use of the word "only" excludes other means of recovery, such as active deflection of tailplane.
Su-27
"Angle of Attack and tailplane deflection depend very strongly on the flight path angle in the post stall region, and practically do not depend in the below stall region "
This statement doesn't say tailplane is used to generate pitch-down moment for recovery, thus does not support your claim.
ah your fallacy is to equal
inneffective=loss effectiveness
ah i see render inneffective means a 100% innefective, ah i see loss effectivenes means it does not completly stop working ah i see otherwise MiG-29 would not use it
see that
Ineffective does equate to loss of effectiveness, that's what the word means in English. It isn't a fallacy, it's just you being desperate trying to change the definition of the word because you have been proven wrong. Let see what dictionaries have to say about the word "ineffective":
From
ineffective [ˌɪnɪˈfɛktɪv]
adj
- having no effect
- incompetent or inefficient
ineffectively adv
ineffectiveness n
From
Pronunciation: /ˈiniˈfektiv/
adjective
not producing any significant or desired effect: the legal sanctions against oil spills are virtually ineffective a weak and ineffective president
Your fallacy is that you are employing
to claim "ineffective = 0% effectiveness" then proceed to argue with yourself about it.
"It can be explained by loosing of effectiveness of control surfaces... In the range of AoA up to 35o the normal increases approximately linearly, then stabilises and practically the tail surface losses its effectiveness."
stabilizes means it does not grow any more it simple remains the same ah i see so the tailplane has still a pitching moment ah i see
Wrong. Stabilizing does not reflect that tailplane is used in anyway. It is simply a result of the aerodynamic center shifting behind the center-of-gravity. From the same
, the following statement is made:
It can be explained by loosing of effectiveness of control surfaces... In the range of AoA up to 35[SUP]o[/SUP] the normal increases approximately linearly, then stabilises and practically the tail surface losses its effectiveness.
The tailplane being ineffective means it cannot generate the desired pitch-down moment to recover the aircraft. As pointed out by another
, the only mechanism for recovery is a passive mean via aerodynamics, not active deflection of tail surfaces:
The recovery from high angles of attack to the classical flight mode in a few seconds only is possible due to moving the center of pressure on main wing the center of pressure on main wing back and creating the strong nose-down aerodynamic pitching moment about the center of gravity.
This reason of the ineffectiveness of the tailplane is explained by Dr. Song's paper:
Control surfaces placed in front of the center of mass, like the canards, are negative load control surfaces. Since the main wing's ability to generate lift tends to saturate under high AOA conditions, the positive load control surfaces' pitch down control capabilities tend to saturate under high AOA as well. Therefore it will be wise to employ negative load control surfaces for pitch down control under high AOA conditions. Figure 7 compares the pitch down control capabilities of the canards and horizontal stabilizers. From the high AOA pitch down control stand point, it will be wise to use canards on the future fighter.
In short, to generate pitch-down moment, tail surfaces must increase their own AoA. When the aircraft is nearly in a stall or in a post-stall situation, these surfaces are also in stall and cannot provide the require pitch-down moment for recovery.
"3. CL remains great enough in post-stall to overcome the aircraft’s weight"
and this i what i like the most here your fallacy crumbled, the aircraft has stalled, me engineer say that! what does the paper say?
3. CL remains great enough in post-stall to overcome the aircraft’s weight
so it means the aircraft has lift because of what?
"Notice, though, that while CL decreases significantly after the airfoil or wing stalls, it doesn’t plummet to zero. It actually begins to increase again, and for a fighter aircraft with swept wings, it may increase to a second, smaller peak before finally tapering off"
and becuase what force is pulling the aircraft back to horizontal flight?
Just because the facts that I point out are contradicting your beliefs, that doesn't make my statements fallacious. It simply means it is time to re-evaluate your beliefs because they are incorrect.
CL remains great enough has no bearing whatsoever on whether stall has occurred. The definition of stall is simply that increase of AoA results in decrease of lift. One definition for stall is given in
:
The classical stall may be defined as a condition in which the airplane wing is subjected to an angle of attack greater than the angle for maximum lift coefficient.
The definition for post-stall (as in the case of Cobra) is synonymous with the definition of stall. Here is a definition of post stall from a
:
In the post stall regime, lift no longer increases but decreases with the angle of attack.
In another
, the following statement is made with regard to post-stall maneuvers:
The airframe agility may or not include the aircraft ability to fly and to maneuver at high angles of attack, also described as the post stall flight region, which give rise to new problems to the designer (aerodynamic stall, propulsion ignition,non linear and non stationary behavior, unstable configuration, control of the possible departure).
Note the use of the word aerodynamic stall. From
, the definition of aerodynamic stall is given:
An aerodynamic stall is defined as a condition in which the wing attains an angle of attack greater than the angle of attack for maximum lift, resulting in a loss of lift and an increase in drag.
Once again, stall simply means the decrease in lift with respects to increasing AoA. Stall does not mean lift has to disappear completely. Your desperation shows in your attempt to redefine the terminology of stall.
When the aircraft has stalled, the controls become difficult because they are ineffective. This is explained in
:
Stalls. The stall may be defined by either airflow separation with increasing angle of attack causing loss of lift, control difficulty, or excessive buffet/vibration (see 6.2.2 and 6.2.5)
"Normal Force Hysteresis
During the grant period, we were made aware of the interesting experimental results which show significant normal force hysteresis for pitching delta wings and for a Russian aircraft. Dynamic force coefficients can exceed static values by 30-50% on the upstroke portion of the pitch , and can undershoot static values by lesser, but still significant values on the down stroke portion"
Hysteresis has no relevance to the effectiveness of tailplane at high AoA. Notice that no where in the above quote of yours ever mentioned the use of tailplane. Your position that tailplane contributes to recovery by producing nose-down pitch moment remains unsubstantiated.
because this equals
"The pitch motion is highly dynamic (with the acquired kinetic energy of pitch) allowing the aircraft to overshoot its trim angle of attack at post stall region. The provision of high lateral stability, especially at angles of attack about 30 degrees, is sometimes referred to as a black art, and the only way to overcome this instability is to cross it in a reduced time before passing into the fully separate flow at higher angles of attack."
This says large initial pitch moment causes the aircraft shot up pass the trim angle of attack, and that recovery has to be done very quickly to avoid avert effects due to instability. It says nothing about the use of tailplane for pitch-down moment. Furthermore, if tailplane is effective at high AoA, it would be able to counteract the instability to allow the aircraft to stay at that attitude for a long time. There would be no need to perform Cobra maneuver quickly.
A concentration of characteristic curves Cm for the tailplane setting angle φ[sub]t[/sub] being varied at post-critical AoA (i.e. very low sensitivity of pitch moment with respect to the tailplane setting angle) reflects the loss of effectiveness of a horizontal tail at higher AoA.
From this
which analyzes the Cobra maneuver:
From
:
if the aircraft can fly at angles of attack of 80[sup]o[/sup] - 120[sup]o[/sup] with the ability to maintain stability in all channels. In this flight regime the ability for conventional control is usually lost.
So?
The recovery from high angles of attack to the classical flight mode in a few seconds only is possible due to moving the center of pressure on main wing the center of pressure back and creating the strong nose-down aerodynamic pitching moment about the center of gravity
where did i read what is center of pressure?
"the aerodynamic force can then be resolved into two components, lift and drag, which act through the center of pressure in flight
We call the average location of the pressure variation the center of pressure"
ah i see
So drag is dealt by thrust and gravity by lift
The recovery being "only is possible due to moving the center of pressure on main wing the center of pressure" means no other mechanisms can contribute to recovery. Thus, active deflection of tail surfaces cannot provide the pitch-down moment needed for recovery, debunking your claim.
From the
in which your above quote originates from, it is also explicitly stated that tail surfaces are ineffective at high AoA:
A concentration of characteristic curves Cm for the tailplane setting angle φ[sub]t[/sub] being varied at post-critical AoA (i.e. very low sensitivity of pitch moment with respect to the tailplane setting angle) reflects the loss of effectiveness of a horizontal tail at higher AoA.
