Sorry about that, I got a bit carried away there. What I meant to ask, more specifically, was in relation to the j-20 employing canards at the expense of LO. Based on my understanding of your posts in the past, regarding control surfaces, I was wondering if TVC (were it available) would be able to compensate for the lack of horizontal stabilizers and canards...in short, providing a similar level of maneuverability, while allowing for the elimination of a major contributor of RCS in canards. Ok, this sounds just as vague as the last post, I hope it makes a little more sense.
Delta Wings
While delta wings are critical to achieving high lift for supersonic flight, they also have a number of disadvantages for less high-performing aircraft. They require high landing and takeoff speeds and long takeoff and landing runs, are unstable at high angles of attack, and produce tremendous drag when "trimmed" to keep the plane level. Of these disadvantages, pilots and designers usually consider the high landing and takeoff speeds the most important because they make flying the plane dangerous. Indeed, when the Concorde had its first ever crash in 2000, after two decades of safe operations, the high-speed takeoff was a factor in this terrible accident, for the plane's high ground speed before becoming airborne placed major stress upon the aircraft's tires, which exploded upon striking an object on the runway.
Computer-controlled "fly-by-wire" flight control systems have allowed designers to compensate for some of the delta wing's poor control qualities. Canards are small horizontal fins (or small wings) mounted on the fuselage in front of an aircraft's main wings to provide greater control, particularly during high angles of attack. When they are part of a delta-wing aircraft, they improve its stability and maneuverability.
The decision to relocate the rear horizontal stabs to the front as canards is not to be made lightly and because I have far more respect for the Chinese engineers -- the real ones -- than the Chinese members here have for said group, I am certain they know the LO sacrifices necessary when they decided to go with canards.
The delta wing's advantages in a narrow region is considered to be inadequate when the aircraft that we operate must be flexible in many regions, from near-stall to stable subsonic to transonic to supersonic. I do not think that given what we know today, we would install TVC in an F-102/106 pure delta platform. But for speculation's sake, say we give the J-20 TVC and remove the canards, we would need to redesign the aircraft...
Area rule - Wikipedia, the free encyclopedia
The area rule was immediately applied to a number of development efforts. One of the most famous was Whitcomb's personal work on the re-design of the Convair F-102 Delta Dagger, a U.S. Air Force jet fighter that was demonstrating performance considerably worse than expected. By indenting the fuselage beside the wings, and (paradoxically) adding more volume to the rear of the plane, transonic drag was considerably reduced and the original Mach 1.2 design speeds were reached. The culminating design of this research was the Convair F-106 Delta Dart, an aircraft which for many years was the USAF's primary all-weather interceptor.
Is the J-20's fuselage sufficiently accommodating? Or may be it does not need to accommodate this rule?
Concorde supersonique jet / Engineering / Features / Delta wing
The wings were put through 5,000 hours of wind tunnel tests. As a result of the delta shape, the wings would be efficient for supersonic flight and also provide enough lift to allow the Concorde to land at a speed of 177 miles per hours.
Yet the delta wing also requires steeper angles of descent when landing. Instead of the traditional 3 or 4 degrees of traditional subsonic jets, Concorde must take off and land at angles of 10 to 11 degrees.
Keep in mind that even though canards and the engine are 'control effectors' they have different behaviors. A canard affect attitude changes through changes in its own lift. The engine does nothing of the kind. It provide thrust.
A delta winged aircraft have a surface area displacement issue, meaning there is more surface area
BEHIND the center of gravity (CG) than in front or in equal.
ch10-4
The delta wing is particularly well suited to tailless, all-wing configurations since the flap-type longitudinal controls can be located on the wing trailing edge, far behind the aircraft center of gravity.
This works in concert with the forward area of the wing where it is designed to generate lift at a certain AoA. The result is that even though the elevons are trailing edge up, which usually implies a nose-down direction, the forward part of the wings lift the nose up at the same time the elevons is forcing the tail down. The aircraft takes off. In flight, because of this surface area displacement issue, the delta wing is an inherently unstable aircraft, giving it a natural high maneuverability.
Given the current preference for highly blended body-wing design so our fighters can operate in as variety of conditions as possible, I do not see how the J-20 could be modified to accept TVC-ed engines without a redesign of the delta wings and possibly to include redesigning of the body to recover/replace the aerodynamic exploitation that was lost by the removal of the canards. Remember, the canards are not needed but they are preferred
IF there are performance desires, such as controlled flight at greater than 25 AoA. But once they are incorporated into the design and assigned certain burdens for flight, then for that aircraft design, the canards are indeed needed.
That was why NASA chose the F-15 to explore more complex flight control systems designs. The F-15 does not need canards to fly and to maneuver. But to have an increased quantity of flight 'control effectors' mean greater flexibility in assigning which effector group will do what tasks to what degree in in-flight experiments. For the ACTIVE F-15, there were test flights where the rear horizontal stabs were effectively disabled, meaning they were locked in neutral positions.
Another consideration that most people do not realize is the re-writing of the flight control laws. This is a fly-by-wire FLCS and it require constant inputs and feedbacks from all flight control elements and air data. Do not mistaken that a '0' v. response is a non-response. In flight control laws, a '0' v. response is a different response than a no volt response at all. No volt usually mean the expected input is not available. The '0' volt response mean the input is available but is not experiencing any changes. Lose power to one gyro and the system will flag as a potential catastrophic fail but nothing will happen if the gyro is sensing no aircraft movements.
Removal of the canards require the FLC laws to be rewritten to discard (not merely ignore) the canards as if the canards never existed in the first place. If there is an enlargement of the wings, this must also be rewritten in as an expansion of an existing parameter. Rate of attitude changes sensed by the gyros and accelerometers will be affected by these flight control effectors alterations so they also must be rewritten. The TVC-ed engines inputs must be rewritten to include additional axes of changes and to what extent. Previously, the engines was affecting the aircraft in only one axis, now there are two axes or three. If the TVC-ed engines are to be under arbitrary pilot control instead of purely under computer control, this exception must be written in as new and the laws must be able to compensate for when the pilot may do something funky and exceed safe parameters.
The list of reconsiderations and refactorings is long and financially costly enough that China might as well design a whole new aircraft.
. I'm egarly waiting for your reply.
