# Is Vy closer to Vbg with a variable pitch prop

My experience with fixed pitch props is that Vy is generally higher than Vbg due to engine efficiency issues. If I set my prop pitch so optimal engine rpm is at Vbg, will Vy = Vbg?

• Vbg = V best power-off glide speed? Or are you thinking of a different definition? Oct 16 '18 at 1:12
• Vbg = V best lift to drag ratio, in other words, greatest aerodynamic efficiency. At the higher speed the engine with fixed pitch prop likes, AOA would not be as optimal. In other words, could I increase my climb angle and climb at 65 knots rather than 70 if my engine/prop had peak efficiency at 65 knots (Vbg). Oct 16 '18 at 4:34
• @quiet flyer came across someone who published thrust data for Cessna 172P, actually close to 800 lbs with no forward motion, dropping to 600 lb near Vy, and around 400 lbs over 100 knots. So, please go ahead and ask, this may really help to add to our knowledge. These engineers really freak when we don't use the proper definitions, but thrust force at one given moment in time seems to be more applicable to compare with lift and drag. Apr 21 '20 at 18:26
• I'm thinking that if you set your prop pitch so that the engine rpm was optimum (maximum amount of engine power generated at wide open throttle) at V bg, the optimum prop angle-of-attack would occur at some slightly different airspeed, so the maximum power output from the whole system would occur at some airspeed other than Vbg. Would it be higher, or lower? Then on top of that consider the fact that that theoretical maximum climb rate ought to occur at Vmin sink, not Vbg. So I think the answer to your question would be "probably not", but I don't know in which direction Vy would be shifted. Apr 21 '20 at 21:38

Too long for a comment:

My POH does not show Vbg, only the 'normal' V's listed below, and even then only some of these are indicated on the Airspeed Indicator with the Green, Yellow, Red color bands. How would you determine Vbg? Experimentally?

VA, Maneuvering Speed is the maximum speed at which you many use abrupt control travel.

VFE, Maximum Flap Extension Speed is the highest speed permissible with wing flaps in a prescribed extended position.

VNO, Maximum Structural Cruising Speed is the speed that should not be exceeded except in smooth air, then only with caution.

VNe, Never Exceed Speed is the speed limit that may not be exceeded at any time.

VS, Stalling Speed or the minimum steady flight speed at which the airplane is controllable.

VSO, Stalling Speed or the minimum steady flight speed at which the airplane is controllable in the landing configuration at the most forward center of gravity.

VX, Best Angle-of-Climb Speed is the speed which results in the greatest gain of altitude in a given horizontal distance.

VY, Best Rate-of-Climb Speed is the speed which results in the greatest gain in a given time.

• Need answer from someone with variable pitch prop. On your plane we'll go with Vy. Oct 16 '18 at 20:09