Why does Vx increase, and Vy decrease with altitude? | Climb speeds explained
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- Опубликовано: 18 мар 2024
- You may know about Vx and Vy, and how they are derived, but did you know that while Vx, your best rate of climb speed, increases with altitude, your Vy, best rate of climb speed, actually goes down? Here's an illustrated guide to understanding why.
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After many hours of reading, this is what made it all make sense. Big Thanks!
This was one of those "just memorise it for the exam" things and I always wondered why! Thanks!
Most POH’s have a cruise climb that is 10 to 15 kn higher than Vy. This is because the manufacturer recommends for visibility, engine cooling and fuel consumption savings. If you are not concerned with getting to altitude fast, and you have a long cross country, you’ll gain more distance from your departure end before you reach cruise altitude. This always puzzled me when it came to flightplan because the book gave you time, fuel, distance based on a specific indicated airspeed, and as long it was zero wind. If you went, climbed via a cruise climb airspeed, your calculations were messed up because you burned more fuel being at power settings to get you to altitude, but traded off distance to destination. One other thing to consider, especially with constant speed propellers. Is the recommended climb setting which is about 90% power. Big planes like airliners have their engines reduce after they reach a safe altitude. Technically there aren’t too many airplanes that climb to altitude at full power, except for those with a fixed pitch prop.
This is something I always wondered and never was able to find a clear concise explanation! Thanks for explaining :)
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@flightinsight9111 Great video. I suppose when Vx and Vy are being referenced, these are Indicated (IAS) and not TAS?
Good presentation. Thanks
Brilliant as usual.
Outstanding!
Thank you.
So the altitude that Vx and Vy intersect in KIAS is the Service Ceiling of the aircraft?
Does that apply for jets as well?
I seem to remember in my early training that the curves intersect (regarding IAS) at the service ceiling. Apparently it is lower than that.
service ceiling is the altitude at which the climb performance drops to 100 feet per minute. absolute ceiling would be 0 feet per minute.
Good explanation of the math of Vx and Vy. The practicality, from an old crop duster's point of view, is that neither Vx nor Vy are generally appropriate. Watch an modern Ag pilot take off using the basic level in low ground effect takeoff. He has a much more powerful engine than the 235 hp engine on my Pawnee, but he is hauling eight times the load. Yet, both of us value the free energy acceleration of level in low ground effect so long as runway (or open desert) is available until cruise airspeed before pitch up to just over (not well over) the obstruction. Either Vx or Vy is a very dangerous low energy state, low airspeed state, when not absolutely necessary to miss things.
Vy is not "a very dangerous low energy state". Vy in a piston twin is the safest speed you can climb out. Even recommended Vx for a single is certified to be a safe speed for EFATO without resort to exceptional piloting skill. Having said that I agree that neither speed tends to be the best operational choice above a safe height.
@@XPLAlN Please see my comment posted just now. It should be at the top of the stack of comments if you sort by NEWEST FIRST.
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This really comes into play for jump pilots, who need to climb up to 12,000 feet or higher in the least amount of time. Both the jumpers and the drop zone owner will really start barking at you if they think you could be climbing faster-
Instrument rated commercial pilot and TIL.
Only comment, the characteristics are Complicated not Complex. Complex is not synonymous with Complicated. Complicated is ordered, deterministic, predictable, repeatable, regular. It requires analysis but it always gives the same thing. In Complexity, you may have patterns, but results vary. In Complexity, analysis fails you as the situation changes hence what you’ve previously learned no longer applies. You’re analyzing here, you’re working in Complication.
'Complex' is appropriate when describing "an aircraft's climb performance characteristics." Webster's definition of complex: "a group of obviously related units of which the degree and nature of the relationship is imperfectly known" applies here. The factors affecting performance being inclusive of all the characteristics of the atmosphere and environment, as well as airframe and power production, being imperfectly known, make analyzing results with certainty difficult. In fact using the word 'complicated' here would detract from the larger point, being that the analysis in the video was too simplistic to apply perfectly to a complex system like real world performance, where actual results are not knowable beforehand.
@@flightinsight9111those are old definition. Look up Dave Snowden’s Cynefin, look for the Scott Page Complexity lectures available here on youtube, try Rick Nason “It’s Not That Complicated.” You could also search Medium The Contrarian Aviator Sometimes Turns Right. Having the distinction between these two terms available to you opens up whole new ways to discuss concepts while knowing the distinction gives you different ways to approach problems. Climb performance is ordered hence not complex, though I’d argue it is actually closer to clear than complicated.
Vid didn't help me. Didn't really explan WHY Vx is increasing faster than Vy in terms of TAS.