I was just reading in the POH a bit when I discovered a few strange points concerning high performance climbs and go-arounds. We all know Vx is 81 knots for the 20. And weren’t we all taught to not normally fly below Vx as this is neither efficient in terms of climb angle nor climb speed (adressed as “behind the power curve”?
Well, why does the POH, on page 4-3 suggest a go-around speed of 75KIAS? I’ve seen the same thing in a manual for a C172M. Then, in the section on short field take-offs, it says “climbs at speeds lower than Vx should be of short duration”. Should there be any? What am I missing, here?
Too further add to the confusion, in the section on balked landings/go-arounds (4-16), the “true Vx” of 81KIAS is used again.
Further down in the POH, in the performance tables for short field take-off distances, they recommend 76KIAS as “obstacle speed”.(BTW, I haven’t seen obstacles move that fast so far…wonder if the FAA knows this term…).
The only explanation I might have is that different flap settings might effect Vx, therefore the different numbers in the book.
CFIs. speak up please!
Maybe though, some of these things have now been corrected as I have these numbers from the copy on Cirrus’ website, which seems ever out-of-date.
You are correct, flaps will change Vx and Vy speeds. The use of flaps shifts the power required curve to the left and since climb is determine by excess power, Vx also shifts to the left (a lower value). I would say that 75 kts is the initial speed until the flaps are retracted.
I didn’t know that, and curiously, I can’t find a definitive statement of that in the POH. There are several references to an obstacle clearance speed of 75 or 76 knots (with flaps 50%) and there is a table of “Takeoff climb gradient” values that uses speeds of 84-80 knots depending on altitude, but it doesn’t actually say they are the best angle of climb speeds (and I suspect they’re not, since they are the same speeds as in the “Takeoff Rate of Climb” table, and both tables have a note “Airspeed: best Rate of Climb”).
Can you tell me your source for the 81 knot figure?
Can you tell me your source for the 81 knot figure?
Section 4 of the POH (Normal Procedures), right after the Introduction is Airspeeds for Normal Operation. As for the inconsistency with the climb tables, that is just another area of the POH figures which indicate that Cirrus did a poor job on the performance section of the POH. The figures not only don’t match actual SR20 experience they are not even consistent with themselves.
Ok, thanks for that. Not a figure that’s of much use, since it’s with flaps up, and best angle climbs would normally be done with 50% flaps, which would be why 75 knots is referred to elsewhere for obstacle clearance.