A few questions

Ok, I’ve been searching google to find out a few things but to no avail. I was wondering if anyone here could help me with a few things. Here goes:

1. What is the difference between a “Mig” and a “Su” jet?

2. What does the A stand for for a Tornado GR4A?

3. Why does a Merlin helicopter have 3 engines for? Is it for better monoverability?

Cheers,

🙂