Forward slip- rudder into the wind and ailerons in the opposite direction. Using the fuselage against wind to create drag to descend quickly
Side slip- ailerons into the wind (wing down into the wind) and opposite rudder to keep nose lined up with runway
You have a misconception there. You can forward slip or side slip either direction. And you can do it without any wind.
And the only difference between the two is the relationship of the aircraft's fuselage (longitudinal axis) to the ground track. The slips themselves are identical.
Easiest to explain and give a mental image example that they're all the same thing (a slip), with a no wind scenario...
Line up on a totally calm day with a road, now offset yourself to one side of it and fly parallel to it. Let's say the road runs north, 360 degrees.
You can bank toward the road and then put in enough rudder to stop the turn, and you'll appear out the window to "slide" back into alignment with the road sideways... A "sideslip". Putting yourself back over the road without allowing the nose to not be parallel to the road. Nose always stayed pointed 360.
Let's say you did it to the left, for clarity. Left aileron and right rudder.
Now imagine there's a runway over there to your left about 20 degrees off of the road you're lined up on. Heading 340.
Same slip... Exact same...
What you did to "sideslip" to the real road, is a "forward slip" to that imaginary runway over there. Nose wasn't pointed at it. No difference on the controls once established in the slip.
But, you would normally be aimed at it when you started. And that's where the two names come in. They're just teaching aids. If you were flying 340 and aimed at that imaginary runway, you'd have to add rudder first to get the nose OFF of that (and lined up with your 360 road), thus... a "forward" slip. Once established, you'd be in a "side slip" for the road.
See how that works? Same slip, different ground reference angle to the longitudinal axis/fuselage of your airplane.
Can reverse it and do both styles the other direction, too.
They're aerodynamically the exact same slip. You just entered them differently by starting with aileron first or rudder first in order to make the desired angle between the ground track and the longitudinal axis easier to obtain.
Most of the time folks eventually learn to just apply both controls simultaneously and adjust as desired. The whole "side" vs "forward" thing is just a teaching aid to show how to keep or move the longitudinal axis to where you want it.
Or as they say, "Aligned with the runway", or not.
If you have enough rudder (light crosswind) you can make a "side" slip steeper/more draggy by adding more of both aileron/bank and rudder. You've now got both a "side" and a "forward", component... or in reality, just a steeper/harder slip. More drag.
Once you bottom out that rudder pedal, you can't add any more aileron/bank without turning. That's your limit. (Well if you're landing out of it, your limit is below that, because as you slow down at the round out/flare, the rudder will lose some authority. If you're out of rudder before you've slowed to landing speed from approach speed, it's only going to get worse from there... Heh.)
Good mental exercise to think about. Same slips, different name, only difference is whether you've aligned the fuselage with something on the ground while holding the slip.
