Originally Posted by
Hueyman
But a point you didn't lighten up was.. the brake effect in flight.
If it's not an angle, what makes a turboprop plane able to make dive descent ( - 5500 Ft/min without going over 110 Kts ) ?
As you bring the power back the blade angle changes. Not directly from the throttle movement though. The constant speed unit is attempting to maintain the rpm you told it to maintain with the prop lever setting. It continuously does this as you retard the throttles until the blade angle reaches the low pitch stop. Then the CSU can no longer reduce blade angle. Then further throttle closing starts directly reducing blade angle which is now where you enter the beta range. Once the throttle is closed, you are at the minimum blade angle legally possible(on most aircraft). That is the other end of the beta range in flight. Once on the ground when reverse is selected, you go into the ground beta range.
When your blade angle reduces, there is more of it facing into the relative wind which means more drag which gives the higher descent rate. Similar can be said of an aircraft such as a Bonanza. If you have an engine failure with a windmilling engine, selecting course pitch reduces drag and increases glide distance.
Of course you could select reverse in flight and reduce blade ange even more but aircraft loss of control could result as airlow over the tail can be disrupted. On many aircraft and/or engines, damage may occur and has caused several turboprop accidents.