Is it a bug? or intended? (V-tail abnormal lift)

[Efour]

Link to youtube video regarding this behavior

is it a bug? or intended behavior? I had no problem like this until 1.7.3.

just after takeoff, v-tail makes abnormal lifts so I can't control my plane's pitch midair.

.craft file is here

Edited November 25, 2019 by Efour
adding craft file

[OHara]

The V-tail starts to try to lift up for me as well, as soon as I rotate the nose to take-off with your craft. 

That looks correct and normal to me, because the nose is high enough at take-off speeds that the air is coming from 5° below the craft.  Only part of the tail-fin moves as a control surface, and the rest is lifting the tail up more than the moving part tries to push it down.

That doesn't cause me any trouble in takeoff or climb.  I climb well with the pitch control at the letter 'P' in the P-I-T-C-H labels.

The big cargo bay is the root part of your craft, which causes an annoying bug on re-load and on revert-to-launch (link) that makes KSP count drag on the contents as if the bays were open.  You can use the re-root tool (number 4) in the VAB/SPH to make some non-cargo part the root.  Maybe you tested with more parts in the cargo bay and their drag was causing a pitch-down ?

The only other thing I notice is that the main-wing flaps/ailerons are active for pitch, and they try hard to help with pitch, but mostly give drag because they are so close to the center of the ship they don't have a good lever arm for pitch.

Edited November 26, 2019 by OHara