EACH winged aircraft can trace its lineage back the Wright Flyer. That is no exaggeration. Go back one more step and you will touch the bird, of whom the Wright Brothers studied how birds flexes their wings to maneuver in flight.
Aerodynamics is the study of flow around shapes. So if you are an aerodynamicist, you would have a pretty good guess of an airframe based upon its shapes, from body to wings. It also mean that if you see two
SIMILAR shapes, meaning not
IDENTICAL, from the same knowledge, you would also have a pretty good guess as to their performance. You cannot in good professional conscience argue that the behaviors of a canard-ed aircraft is the same as a conventionally tailed aircraft. All of this came from observation.
Since the canard is ahead of the wing, shaping and positioning the canard is even more crucial than for a conventional tailplane assembly. Do it inefficiently and you will negative affect lift over the main wing. Do it wrong and your design will crash.
So when you see this...
It unlikely that you, as an aerodynamicist, will guess that the J-20 came from the older J-9. The shaping of the J-20's canards are too similar to the MIG's. The canards' dihedral (upsweep angle) exists on the MIG and J-20, but not on the J-9. Why do you think there is a canard dihedral on one design but not the other ? What about the quantity of flight control surfaces ? Which has more and why ?
When I transferred from the F-111 to the F-16, I do not need to know the aerodynamics of the F-16 to know that its flight characteristics will be different from the F-111. And I was correct based upon appearance alone.
YOU would, not merely could, make the same correct guess.
In rotary winged aircrafts, aka 'helicopter', just from noting the number of blades in the main rotor assembly, one can guess the performance of that helo to a high degree of accuracy. The more the number of blades, the more stable the flight but the less maneuverability. Which explains why the Cobra have only two blades because as an attack aircraft, it needs maneuverability to make quick aspect changes to deal with threats to self and to ground forces. On the other hand, the Apache, while also designed as an attack helo, it was also designed to carry more ordnance and other non-weapons related systems for other combat roles, hence four blades.
The point here is that while there are limits to appearances, noting similarities and differences can tell us much, even to origin of design.
