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#1
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Why Isn't Vx The Best Rate Of Climb?
Here is something that I have always wondered about, but have yet to
hear a good explanation for. Vx is the best angle of climb speed for an aircraft. Vy is the best rate of climb for an aircraft. I can't seem to visualize why Vx is not the best rate of climb. To my feeble way of thinking, Vx - the best climb angle - gets you to the highest altitude in the shortest period of time, no? Why is that not the best rate of climb? I hope someone can enlighten me on this. I know that there must be a good explanation, but as I said, I just can't visualize it. Thanks... Randy L. -- Remember: Any landing that you can walk away from, is a landing that you can be fined, sued, or prosecuted for. |
#2
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Why Isn't Vx The Best Rate Of Climb?
RandyL wrote:
Here is something that I have always wondered about, but have yet to hear a good explanation for. Vx is the best angle of climb speed for an aircraft. Vy is the best rate of climb for an aircraft. I can't seem to visualize why Vx is not the best rate of climb. To my feeble way of thinking, Vx - the best climb angle - gets you to the highest altitude in the shortest period of time, no? No, Vx will get you to a given altitude while covering the shortest distance, but not generally in the shortest time. When climbing at a steeper angle the plane will be going slower so even though Vx will get you there in a shorter distance you'll get there a little quicker by choosing a slightly shallower angle that lets you go faster, i.e. Vy. It's similar to choosing whether to climb a mountain by either going straight up the side in which case you may need ropes and make very slow progress, or by hiking up the less steep switchback trail in which case you'll have to go farther but will be able to go faster. |
#3
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Why Isn't Vx The Best Rate Of Climb?
"RandyL" wrote in message Here is something that I have always wondered about, but have yet to hear a good explanation for. Vx is the best angle of climb speed for an aircraft. Vy is the best rate of climb for an aircraft. I can't seem to visualize why Vx is not the best rate of climb. Vy is time, and Vx is distance. The key, Randy, is to look at what the definition says and consider the words carefully. Best rate of climb considers feet of climb per unit of time past, without considering distance travelled at all. Best angle of climb considers feet of climb per unit of distance travelled, without considering time at all. .....To my feeble way of thinking, Vx - the best climb angle - NO. There's part of your difficulty, possibly. Stick with the proper terminology. Don't switch words around, because they mean something. "Best angle of climb" is not necessarily the same thing as "best climb angle". |
#4
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Why Isn't Vx The Best Rate Of Climb?
"RandyL" wrote in message
... Here is something that I have always wondered about, but have yet to hear a good explanation for. Vx is the best angle of climb speed for an aircraft. Vy is the best rate of climb for an aircraft. I can't seem to visualize why Vx is not the best rate of climb. To my feeble way of thinking, Vx - the best climb angle - gets you to the highest altitude in the shortest period of time, no? Why is that not the best rate of climb? I think the other two posts cover the basic definition adequately. I'll offer a mental view that sometimes helps me understand the relationship, and which might clarify the difference a little bit mo Vy is about the best *rate* of climb. That is, the most vertical distance over a period of time. Vx is about the best *angle* of climb. That is, the most vertical distance of a horizontal distance. That much has been explained. It may also be helpful to know that Vy occurs when you have the most excess power, while Vx occurs when you have the most excess thrust. Power, being a rate-based measure (that is, work (that is, force times distance) over a period of time), winds up contributing to the best climb performance over a period of time. On the other hand, thrust, being a measurement of the specific force acting on the airplane (and which is independent of time), winds up contributing to the best climb performance when time is ignored. I admit that the above may only be helpful if you already think in terms of physics. But perhaps it provides some additional insight into why there even are two different V speeds and how they relate to the definitions of them. Pete |
#5
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Why Isn't Vx The Best Rate Of Climb?
On Mon, 25 Sep 2006 23:21:44 -0700, "Peter Duniho"
wrote: "RandyL" wrote in message ... Here is something that I have always wondered about, but have yet to hear a good explanation for. Vx is the best angle of climb speed for an aircraft. Vy is the best rate of climb for an aircraft. I can't seem to visualize why Vx is not the best rate of climb. To my feeble way of thinking, Vx - the best climb angle - gets you to the highest altitude in the shortest period of time, no? Why is that not the best rate of climb? I think the other two posts cover the basic definition adequately. I'll offer a mental view that sometimes helps me understand the relationship, and which might clarify the difference a little bit mo Vy is about the best *rate* of climb. That is, the most vertical distance over a period of time. Vx is about the best *angle* of climb. That is, the most vertical distance of a horizontal distance. That much has been explained. It may also be helpful to know that Vy occurs when you have the most excess power, while Vx occurs when you have the most You might try the reverse order too. Look at best glide speed. In calm air the best glide speed gives you the most distance per time unit, but traveling either faster or slower will cause you to lose altitude faster. Now compare best rate of climb; a speed either faster or slower (Vx) will produce less climb versus time, so although the best angle for clearing an object at a given distance you will be going slower then the best rate of climb, but at a steeper angle. It's that slower speed with less lift that gives you less altitude versus time. Roger Halstead (K8RI & ARRL life member) (N833R, S# CD-2 Worlds oldest Debonair) www.rogerhalstead.com |
#6
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Why Isn't Vx The Best Rate Of Climb?
RandyL schrieb:
Vy is the best rate of climb for an aircraft. I can't seem to visualize why Vx is not the best rate of climb. Simple: The steeper you climb, the slower the airplane flyes (as long as you don't have excessive power). So you can climb steep but flying slow, or you can climb shallow but flying fast. Simple calculation shows that you can optimize for shortest distance or shortest time, but those optima need not be the same (and usually are not). Stefan |
#7
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Why Isn't Vx The Best Rate Of Climb?
RandyL wrote:
Here is something that I have always wondered about, but have yet to hear a good explanation for. Vx is the best angle of climb speed for an aircraft. Vy is the best rate of climb for an aircraft. I can't seem to visualize why Vx is not the best rate of climb. To my feeble way of thinking, Vx - the best climb angle - gets you to the highest altitude in the shortest period of time, no? Why is that not the best rate of climb? I hope someone can enlighten me on this. I know that there must be a good explanation, but as I said, I just can't visualize it. Thanks... You are forgetting that part of the equation for best angle of climb is also speed across the ground. For example, say best rate is 1000 fpm and best angle is 800 fpm. Now suppose that the groundspeed (assume no wind) is 120 knots for best rate climb, but only 60 knots for best angle. If you draw out the triangle you will see that the best angle airspeed really does give you the steepest climb gradient even though the rate of climb is 200 fpm lower than best rate. Matt |
#8
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Why Isn't Vx The Best Rate Of Climb?
"RandyL" wrote in message
... Here is something that I have always wondered about, but have yet to hear a good explanation for. Vx is the best angle of climb speed for an aircraft. Vy is the best rate of climb for an aircraft. I can't seem to visualize why Vx is not the best rate of climb. To my feeble way of thinking, Vx - the best climb angle - gets you to the highest altitude in the shortest period of time, no? Why is that not the best rate of climb? I hope someone can enlighten me on this. I know that there must be a good explanation, but as I said, I just can't visualize it. Thanks... How's this: I can get up a flight of stairs in around three seconds (best rate of climb). It will probably take me 20 seconds to climb a ladder the same height (I hate ladders). The ladder will get me up at a much steeper angle, hence best angle of climb. The stairs will get me there faster, hence best rate of climb. |
#9
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Why Isn't Vx The Best Rate Of Climb?
On 2006-09-26, Roger (K8RI) wrote:
You might try the reverse order too. Look at best glide speed. In calm air the best glide speed gives you the most distance per time unit, but traveling either faster or slower will cause you to lose altitude faster. Not quite - minimum sink (the speed at which you'll lose altitude at the lowest rate) is slower than best glide. -- Yes, the Reply-To email address is valid. Oolite-Linux: an Elite tribute: http://oolite-linux.berlios.de |
#10
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Why Isn't Vx The Best Rate Of Climb?
Roger (K8RI) wrote:
You might try the reverse order too. Look at best glide speed. In calm air the best glide speed gives you the most distance per time unit, NO! It gives you the most distance per altitude lost. |
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