That might explain why there is also the drag chute on the J-20, since it's probably a must, that ground speed reaches a certain value before using the canards as speed brakes because those are also control surfaces that dictate pitch, unlike for example, a spine speed brake such as the one in the F-15 of Su-27/30/35, or those two little lip flaps on the back of the F-16.
I think if they're used as speed brakes, they're supplemental to the drag chutes.
The drag chute is a one-time use device, meaning for each landing, the pilot can use it only once -- deployment. Then once it is deployed, it must be ejected after a certain distance/time. So far, there is no design where the jet can retract the chute and redeploy as needed.
The drag chute is the most efficient way of slowing down a jet, however, the F-4 pilot operating manual have a drag chute section where certain landing conditions discourage deployment, namely high crosswind. So for the J-20, perhaps the speedbrake function using the flight control surfaces are supplemental to the drag chute for when landing conditions do not allow the use of the chute.
The aircraft that have dedicated speed brakes are just used for that purpose and are usually designed in a way to deploy while not to affecting the pitch of the aircraft in any significant manner, even in flight. I suspect that even as the J-20's canards are slowly pitched LE down after touchdown, they create a huge downforce on the front of the aircraft that the speed most certainly needs to reach a certain value before they deflect completely. Otherwise I just think that not only would there be some instability and possibly be too much strain on the front gear. I don't think that the movement of the canards is sudden or abrupt, but rather gradual.
Going back to the flight controls laws...And remaining with full FBW-FLCS designs for now...
When the landing gear handle is lowered, this command takes priority over other logic in the laws. Lowering the landing gear handle is not a virtual command but a physical one, complete with lockout switches built into the handle. The reason we design the system this way is because we want the system to have no uncertainty as to what the pilot want, and landing is obviously mandatory at some time in flight.
So when the landing gear handle is lowered, we want the wings to be at their most efficient shape to produce the highest lift possible. The logic then is to lower the landing gears, we can assume landing gear switches are engaged once they are fully down and locked,
AND to deploy wing LE and TE flaps to alter wing shape. The logic is not sequential but in parallel, meaning both actions takes place at the same time. The reasoning is that if there is something wrong with the landing gears, at least the wings are configured for landing, and if there is something wrong with reconfiguring the wings, at least the landing gears are down and locked.
And if both does not happen as the logic commanded, pull the ejection handle. Not sure if I want to try a landing with neither wing nor landing gear down even at the slowest speed.
At timestamp 0:04, even though the video is grainy, you can see the starboard wing's LE flap deflected down while there is no landing gear deployment. Faint, but discernible.
So what does this has to do with the J-20's speculative use of the flight control surfaces as speedbrake function? Plenty. As in the logic of the flight control laws.
http://www.ausairpower.net/SuperBug.html
2.2 The Virtual Speedbrake
The speedbrake function is produced by a balanced deployment of opposing flight control surfaces, generating drag without loss of flight control authority or change in aircraft pitch attitude.
...the raised ailerons, lowered trailing flaps, raised spoilers and splayed out rudders. Deceleration is smooth and there is no observable pitch change.
...the aircraft retains considerable control authority despite the fact that the rudders are splayed out, and the ailerons, spoilers and flaps are generating balanced opposing pitching moments.
Just like the TO/L logic where there are commanded and defaulted flight control surfaces' position, the F-18SH's speedbrake function has its own logic the moment the pilot activate the speedbrake switch. There is no dedicated speedbrake device. The jet uses all of its flight control surfaces in
DEFAULTED balanced positions to create drag
WHILE still giving the pilot full command authority to maneuver.
Assuming the J-20 uses the concept of 'balanced deployment of opposing flight control surfaces', the behaviors we see on the J-20 are inline with the concept. The logic maybe different with the inclusion of the canards and the delta wings, but the logic is definitely inferable based upon what we know of flight controls laws in general and with the F-18SH in particular as reference.
I can buy your hypothesis only if it's an SOP for all the pilots, and not just the occasional one who feels like leaving the speedbrake function switch in the on position since we saw 2 J-20's in a row do it as they exited the sun shelters. That's also assuming that the action is indeed a speedbrake function. Are there any other possibilities?
Possibly, but from my perspective, the odds of them are low.
Keywords search 'aircraft landing hot brakes'.
http://navyaviation.tpub.com/14014/css/Wheel-Assembly-Fires-348.htm
After a landing and once an aircraft is at end-of-runway (EOR), the EOR crew does a brief inspection of the jet prior to sending him to the chocks. Ground crews are trained to
NEVER approach the wheel from its face, but from either front or rear.
The J-20 maybe landing with a full fuel load -- air refueled. Or unspent ordnance because of no targets. Or battle damaged. Deltas are known for higher than normal landing speed. The drag chute seems to be a requirement rather than an optional feature for the J-20. However, local conditions such as high crosswind makes usage of the chute an option rather than a requirement. So
WHEN -- not if -- the J-20 pilot has to land his jet without the chute, he is stuck with only the wheel brakes? I cannot see that as acceptable by the J-20's designers.
