What is the convention to follow when I want to create two separate pull requests (to lower the size of the diff) but one of the pull requests depends on a change made in the other?
Well usually for bigger changes you would work on the first part and submit a pull request and won’t start working on the dependent feature until that PR is through or at least roughly working.
Other than that you can link pull requests by typing (e.g. #834) and then github creates a hyperlink to the other pull request (or just mention it). Most of the time the goal with separate pull requests is however to focus on the individual changes (so e.g. for the one you are about to create just assume that the plane constructor is already there).
Just another hint: You are creating your posts without a category, these would fit into the development category (but it’s just a note 
)
I’ve put it into the development category for him.
Yeah, in the example you are working on in particular… the first PR was an easy approval if it had been separate.
There are other ways to do so with git, but if you’re not too familiar with it, it may be difficult.
Basically work on the first change on a branch, and make a PR from this branch
Then create another branch from this branch (you’ll have the changes from the first branch), and work on your dependent change.
When your first branch is merged in master, rebase you 2nd branch on master (that means that your 2nd branch will be based on master instead of on your first branch) and since your changes have been merged on master… you still got them. Then, when you’re done, you can do a PR for your second branch.