normal approach descent rate and VRS
My instructor is teaching me to perform 12 degree normal approaches in a hughes 269C.The 12 degree glide slope seems very steep to me and I do not understand why such a steep approach is used, as it is difficult to perform.My concern is that the descent rate is more than 300fpm and could lead to possible vortex ring state as the speed drops to 15kts just before landing.
Shawn Coyles book states "a good rule of thumb is to make sure the rate of descent is less than 300 ft per minute as you pass 100 AGL."
I drew a 12 degree slope with a protractor and calculated as follows:
50 knots = 1066fpm descent
25 knots = 533fpm descent
15 knots = 319fpm descent
I have an old "Basic Helicopter Handbook" that shows 12 degree approach angle as "normal" and 5 degree as "shallow". Shawn's book (1996 edition) doesn't discuss the approach angle or mention what is "normal approach angle"
What is considered a normal approach angle today?