Well Ahramin, There is no need to be derogatory! As the old saying goes. "it is sometimes better to keep silent and be thought a fool, than to open your moth and remove all doubt.
For the record I have been a test pilot for many years, I have been involved with prototype air testing and wind tunnel testing. Particularly, I have been involved with STOL aircraft and modifications to aircraft. I have also written flight manuals and supplements that cover just this kind of thing. I did not say that the airflow was going in that direction but that the pitot head is measuring a 'component' in that direction.
Some of you are correct with regard to Vfe and you have to bear that in mind when carrying out such manoeuvres. Also, as I am a qualified and licenced Aircraft engineer as well, I can assure you that some aircraft are prohibited from large slipping manoeuvres due to the side loads placed on the flap 'hangers'. I have never known a problem with a Cessna 152, 172, 182. The PA28 does not have that kind of flap 'hanger'. The Ralley MS880, 890 has a problem, big Flaps on wing 'hangers'. Furthermore, most Cessnas are well endowed when it comes to flap, slowing the aircraft down applying full flap then nosing the aircraft down can be just as effective as a side-slip in the amount of hight loss and you retain full control.