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Is there a difference between Best Rate of Climb and Maximum Rate of Climb?

From my research, best rate of climb trades ground distance for altitude (i.e. steeper climb, more altitude per unit time). Since an aircraft cannot climb faster than its max rate, these appear to be two different labels for the same concept.

Am I missing some nuance between the two?

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Generally when GA pilots talk about climb performance we speak of two different airspeed values:

Best Rate of Climb speed (Vy) gets you the most altitude per unit time (feet per minute).
When you want to get to cruise altitude quickly for maximum efficiency you'll aim for the best rate of climb so you spend the least time at lower, less efficient altitudes.

Best Angle of Climb speed (Vx) gets you the greatest altitude per unit of ground distance (feet per mile).
When you've got a FAA-Standard 50-foot-tree at the departure end of the runway you'll aim for the best angle of climb to ensure you don't wind up in the tree.

Those speeds are useful to us as pilots, but the exact rate of climb (feet-per-minute) for those speeds will vary: A fully loaded plane will climb more slowly than one that's just got the pilot and a few gallons of fuel on board, and that's where the "maximum rate of climb" enters into the discussion:

Maximum rate of climb is the number of feet per minute you can get climbing at the "best rate of climb" airspeed.

If someone is being sloppy in their usage "Maximum Rate of Climb" could mean "Best Rate of Climb" (pitch for Vy and you get what you get), but if you're being precise in your usage and really talking about the rate of climb it would mean the theoretical maximum rate of climb in feet per minute based on the current conditions and aircraft weight.

Maximum rate of climb under a given set of conditions is useful information to know if you need to clear terrain at some point on your flight path and want to be sure you can climb fast enough to do so: If you're starting from sea level and need to clear a 5000 foot mountain that's 5 minutes away but your plane can't manage more than 500 feet per minute at best-rate-of-climb speed under the current conditions you'll need to reconsider your flight plan to either avoid the mountain or climb in a circle somewhere until you can clear it.

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    $\begingroup$ To help remember which is which, I imagine a chart where the x-axis is distance, and the y-axis is altitude. If distance (x) is a concern, then use Vx to minimize the x value for a given y. If reaching a given altitude (y) quickly is your primary concern, then use Vy. I imagine this is the origin of the notation as well. $\endgroup$
    – Steve N
    Commented Aug 27, 2014 at 18:26
  • $\begingroup$ An alternative memory device: the letter x has a lot of angles. $\endgroup$
    – 200_success
    Commented Aug 27, 2014 at 21:24
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    $\begingroup$ I think this answer would be better if best and max rate of climb were contrasted first, because that directly answers the question. Then perhaps describe best angle. $\endgroup$
    – rbp
    Commented Nov 20, 2015 at 15:03
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    $\begingroup$ @rbp I'm not sure how you would contrast them: "Maximum" and "Best" when talking about a rate of climb are, by definition, identical: Gaining the most amount of altitude for the least amount of some other resource (usually Time, Distance, or Fuel). The real question is What rate are you trying to optimize? (Feet-per-Minute, Feet-per-Mile, or Feet-per-Gallon) - optimizing each of these rates will give a different climb profile. $\endgroup$
    – voretaq7
    Commented Nov 20, 2015 at 23:30
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Although voretaq7 has already nicely answered it, I wanted to present a picture worth thousand words.

Vx vs Vy

VX

Best angle of climb speed

The greatest gain in altitude over a given horizontal distance. VX is used to clear 50' obstacles and so forth.

VY

Best rate of climb speed

The greatest gain in altitude over a given amount of time. VY is used on normal takeoffs and such.

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    $\begingroup$ I always liked this image. What's the difference between Vx and Vy? "At Vy you'll crash through the middle of the tower, but at Vx you'll just clip the antenna masts!" $\endgroup$
    – voretaq7
    Commented Aug 27, 2014 at 19:06
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    $\begingroup$ Shouldn't the aircraft climbing at $V_y$ be higher? $\endgroup$
    – user2168
    Commented Aug 31, 2014 at 7:06
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    $\begingroup$ user2168, I don't like this picture! Why the second aircraft is at the same height? Where is the "greatest altitude gain"? $\endgroup$
    – Electric Pilot
    Commented Sep 12, 2018 at 14:53
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Depends what is best in the particular case. Generally, best means highest climb speed, but there might be other things which should be optimized:

  • highest flight path angle: This might be desired to avoid noise on the ground, or to escape unfriendly fire near the airport. For propeller aircraft, the optimum lift coefficient is $$c_L = \frac{T\cdot\pi\cdot AR\cdot \epsilon}{4\cdot m\cdot g} + \sqrt{\left( \frac{T\cdot\pi\cdot AR\cdot \epsilon}{4\cdot m\cdot g}\right)^2 + \pi \cdot AR \cdot \epsilon \cdot c_{D0}}$$
  • lowest fuel consumption per altitude gained: The highest climb speed is reached with full power, but maybe a lower power setting is more economical. In general, this is very close to the schedule with maximum climb speed. For propeller aircraft, the optimum lift coefficient for highest climb speed is the same as for minimum energy loss: $$c_L = \sqrt{3 \cdot \pi \cdot AR \cdot \epsilon \cdot c_{D0}}$$
  • highest energy gain (the sum of both altitude and speed gain is optimized): This is desired when you want to reach a point far up in a hurry, like a supersonic interceptor would.

The graph below shows lines of equal total energy (black, dashed) and of maximum altitude for given climb speeds over true airspeed (blue, solid). The red line connecting the tops of the blue lines gives the flight schedule for fastest altitude gain, and the green line cutting through the blue lines at their maximum of total energy gives the schedule for the total energy gain climb. The higher you fly, the wider is the difference in optimum speed between both.

Isolines of climb speed

Nomenclature:
$c_L \:\:\:$ lift coefficient
$T \:\:\:\:$ thrust
$m \:\:\:\:$ aircraft mass
$g \:\:\:\:\:$ gravity
$\pi \:\:\:\:\:$ 3.14159$\dots$
$AR \:\:$ aspect ratio of the wing
$\epsilon \:\:\:\:\:$ the wing's Oswald factor
$c_{D0} \:$ zero-lift drag coefficient

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    $\begingroup$ Peter Kampf: single-handedly proving math is used after high school! $\endgroup$
    – CGCampbell
    Commented Aug 27, 2014 at 20:54
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    $\begingroup$ Kinda overkill though, maybe? (The question was really about semantics, not math...) $\endgroup$
    – Michael Hall
    Commented Jun 28, 2021 at 3:51
  • $\begingroup$ @MichaelHall Call it semantics, I call it physics. There are several "best" climbs, depending on what needs to be optimised. And using math makes the answer much clearer. $\endgroup$
    – Peter Kämpf
    Commented Jun 28, 2021 at 10:05
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    $\begingroup$ The question was whether two different adjectives, (best and maximum) when applied to a single noun, (rate) could be used interchangeably and mean the same thing in the context of aviation. You are welcome to call that physics, but that pretty much meets the definition of semantics. Look, we all know you are brilliant, but good teachers teach to the level of their students. Math may make some answers more clear, but that isn't universally true when it comes to simple questions. $\endgroup$
    – Michael Hall
    Commented Jun 28, 2021 at 14:17
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    $\begingroup$ I understand nuances, but from what I perceive as the OP's level of aviation knowledge I still think your answer was overkill. JMHO. $\endgroup$
    – Michael Hall
    Commented Jun 28, 2021 at 23:25
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No.

Best and Maximum (Rate of Climb = ROC) are usually$^1$ used as synonyms.

For completeness only: There is also the AOC (Angle of Climb), which is just another quantity to describe your flightpath (the angle of your climb).

In order to reach the maximum of:

  • ROC you have to maintain the airspeed $V_y$
  • AOC you have to maintain the airspeed $V_x$

Here is a nice picture illustrating the twoVx vs Vy

How to remember the two: x is before y in the alphabet. On take-off (for small planes at least), $V_x$ is used first because you want to climb as steep as possible to be free of any obstacles. Once you are free, you change to $V_y$ in order to climb faster.

1: I say "usually", because "best" may refer to something else, like "best in terms of fuel consumption", "best in terms of flying directly into the tree in front of us" etc. but then the meaning is unambigious

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Is there a difference between Best Rate of Climb and Maximum Rate of Climb?

There's no difference, end of story. This question inspired some good answers but many of them were really better suited to some other question!

From my research, best rate of climb trades ground distance for altitude (i.e. steeper climb, more altitude per unit time).

This is incorrect, the best or maximum or highest climb rate does not occur at the same airspeed as the steepest climb. The latter always occurs at a lower airspeed. Maximizing the vertical distance travelled in relation to the horizontal distance travelled gives you the steepest climb, not the maximum rate of climb.

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VY is similar to a transport aircraft v2 which will also get you to 1500 feet above the ground in the least amount of time possible ,VY will get you up to a pre-determined altitude usually between 1000 to 1500 AGL. The objective of getting to 1000 to 1500 feet as soon as possible is at that altitude you have more altitude to maneuver if an emergency occurs (example an engine failure) after obtaining such an altitude VY should no longer be maintained and aircraft should be transitioned to a cruise climb to increase visibility and engine cooling usually about 500 feet a minute, I hope this helps anyone that was looking for a clear explanation ....Good luck and stay safe thanks Joe

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  • $\begingroup$ A jet aircraft flying at V2 with all engines operating is way too slow. It is more closely related to Vxse. V2 and Vxse are not the same speeds however. $\endgroup$
    – wbeard52
    Commented Oct 3, 2016 at 3:42
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Despite the simple explanation that differentiates between the two types of climb (Vx and Vy) based on shortest distance and shortest time does not give clear assimilation unless you consider the concept of total energy and drag. At same power setting, thrust or total energy remains the same during both situations but the drag is more during best angle of climb which creates loss of energy and thereby lesser distance is covered as well as lesser height is gained compared to that of flying with best rate of climb speed. So in order to cross above an obstacle after take-off, we are intentionally trading off some height gain and distance covered to take the aircraft to a point above the obstacle. But, had we climbed at best rate of climb after take off, we would gain more height and distance within same period of time but ultimately hit the obstacle.

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