The Grove team missed the first two days of running due to delays in the production of automotive parts and went out on track for the first time Wednesday afternoon.
Williams said on Wednesday he was still waiting.
Kubica debuted at the wheel of the car on Thursday morning before handing it over to teammate George Russell for the afternoon session.
Kubica filed 48 laps before the lunch break. Asked what he had learned in his brief flight time in the cockpit today, Kubica said: "You can feel this is not like the car is completely shut down."
"I think there is still something to put on a car, probably not much, but there are certain things that have been compromised." It's not right to talk about them, as I said before I was here to drive, so I have to concentrate on that. [1
Kubica, who spent most of the morning with the aero rake mounted on the car, had only a dozen laps, in which I feel right
I feel like the fourth day of testing, I felt like one day, "he said.
"I have the opportunity for 12 laps to feel the car, which is of course limiting." At least, all of the things we did – not all, was not a mild morning, "I'm here last Friday. I've never waited so long to get 12-14 laps that I could
You just prepare what you can. It was not a nice day for the whole team, but finally we took the car. After all, the team did a good job to build it as quickly as possible.
"Of course, there are some compromises, I think so, but finally we took the car so we can concentrate on our work and look at next week."
Asked if he thought the car was a step , he said, "It's a step forward in some way. For others, it is not mandatory. "
" The question is whether we have made a bigger step forward and less back, due to regulations. Then it is a matter of balancing.
"It is not right at this stage to talk about the car or feelings of the car, and we will see the next weekend."