@@dannyCOTW We fly in rivers of air. Thermal lift, cooler air descending, ridge lift, descending air below the declination line of a ridge, and wave are natural things that make these calculations just calculations. I have been lifted from 7,000 to 13,500 in a minute in a 65 hp Taylorcraft. I have been dumped from 13,500 to a hundred feet off the desert floor in a Tri-Pacer. A Huey at the Army's Mountain Flying School at Ft. Carson went from 7,500 to 17,500 at flat pitch. We got oxygen like the zoomies after that.
@@williamk5998 Vy and Vx intersect at absolute ceiling (as dannyCOTW wrote). It is conventional to determine this altitude by extrapolation from climb data gathered in tests up to about the service ceiling. In the performance flight testing, climb rate is recorded over a range of speeds and altitudes (sawtooth climb tests). The data is then processed graphically into 3 or more curves of climb rate vs speed (ie curves for 3 or more suitably different density altitudes). By striking a line through the peaks, and another through the tangents, you get the two straight lines that will intersect at absolute ceiling. Although you could determine absolute ceiling directly with a simple climb test, the sawtooth climb data provides Vx and Vy profiles and even the drag polar can be extracted.
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.
Vx and Vy occur at very nearly the same speed for jets. Due to ram effect, thrust is approximately constant with airspeed by contrast with the characteristic thrust curve of a propeller.
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.
Hi sir. That’s very interesting and I’ve thought about it before. Help me understand. So you are saying that on takeoff, accelerating using ground effect to a cruise airspeed so long as runway length allows, and the pitch up to clear the obstacle, you will actually clear the obstacle by a greater height than just taking off and maintaining Vx? That is what I’m taking away from your post . It makes sense. Here’s a scenario I have a question on: So when you accelerate to cruise using ground effect and then pitch up, let’s say the obstacle is still not cleared. Then you would maintainVx until you’ve cleared it? Step 1. Using ground effect on takeoff for its benefits on building energy. Step 2. Accelerate to cruise speed in ground effect so long as rwy length allows and then pitch up to clear the obstacle. Step 3. If obstacle is not cleared yet in the initial pitch up then maintain Vx? Thank you for your input and wisdom. I actually have my CFI check ride in 8 hours from writing this comment. It’s 12:30am now haha. I always find myself wanting to learn more and your comment intrigued me because it really does make so much sense yet is not taught at least not during my training. And I’m curious if you are aware to any references or tests done to back this up. -Derrick
@@derrick2251 Yes, staying level in low ground effect provides enough greater acceleration vs pitching up to Vxo or Vy pitch attitude as soon as Vx or Vy airspeed is attained to climb faster in a zoom climb when Vcc is attained. No, we would not be higher over the obstacles nor is that the objective. The purpose of accelerating level in low ground effect is to gain the free energy for safety and so the outcome of the maneuver is never in doubt. Having gained more airspeed safely over the runway, we don't then want to spend all that extra safe airspeed on altitude over the obstacles. We want to just clear the obstacles at the airport and cruise climb safely to altitude. If over the crop on a spray run, we want to use the full power level in low ground effect acceleration advantage to zoom climb just over the obstacles and gain only enough altitude to safely apply this potential energy in the 1 g turn of whatever bank angle is required to return to the next swath run only fifty feet upwind from where we left the field. What we are avoiding, at the airport especially, is picking to a Vx or Vy pitch attitude while that slow in ground effect and quickly climbing out of ground effect where Vso, an out of ground effect number, will cause stall. At slower than Vso in ground effect we can safely fly, especially low ground effect, with the outcome of that flying never in doubt. Either Vx or Vy, just climbing out of ground effect, is much closer to Vso than Vcc. We don't want to quickly climb just high enough to kill ourselves in the stall and fall of being a bit slower than Vso, or getting there in the startle of engine failure. Neither Vx nor Vy are ever appropriate on long runways where Vcc, especially in low ground effect, is easily doable with the outcome of the maneuver never in doubt.
@@XPLAlN It is not exceptional piloting skills. I soloed many students in 65 hp trainers in less than ten hours using the basic level in low ground effect takeoff. At high DA, say Monte Vista midday in summer, low ground effect energy was 50% of our total energy available. We couldn't have safely trained using Vx or Vy, neither being safe. Yes, in normal conditions most do so. Only a couple hundred or so yearly overdo the getting up quickly and stall just as they reach the out of ground effect altitude where flying slower than Vso is generally fatal. With thousands of feet of runway remaining, acceleration level in low ground effect is safer at any speed than Vso at fifty feet or so.
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-
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.
@@flightinsight9111 The dictionary is behind the times. It also failed to account for linguistics and etymology. Complex came from a Greek root for entangled while complicated came from a Roman for folded. You can unfold things though it is much harder to unentangle. Look into Cynefin and Dave Snowden. See also Sidney Dekker’s work. Appreciating the distinction between ‘complex’ and ‘complicated’ has significance when we look to safety work. This is especially true as most our safety tools are built for clear and/or complicated and therefore fail in complexity. You’ll note there are ties to naturalistic decision making and Klein as well as Twersky/kahneman. And Boyd, John Boyd’s Destruction and Creation really tie to these. Though for easier reading, I’d suggest Ron Butcher on Medium with his view of overlaps yet also disparate and contrasting features between “safety” (read too heavily as ‘compliance’) and “survival.” Note ICAO is moving to learning these concerns as is BALPA. American Airlines is making some inroads too. The EU has fully incorporated the ideas in their recent Crisis Response manual while the Marine Corps is probably the best in applying. In complexity, relationships are not obvious.
This was one of those "just memorise it for the exam" things and I always wondered why! Thanks!
This is something I always wondered and never was able to find a clear concise explanation! Thanks for explaining :)
These videos are hitting what I think about each week… I think of something and that’s what you solve .. it’s awesome
After many hours of reading, this is what made it all make sense. Big Thanks!
the best channel ever
Exceptional explanation
@flightinsight9111 Great video. I suppose when Vx and Vy are being referenced, these are Indicated (IAS) and not TAS?
Always enjoy your vids.
I absolutely love your video's!
So the altitude that Vx and Vy intersect in KIAS is the Service Ceiling of the aircraft?
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.
@@dannyCOTW We fly in rivers of air. Thermal lift, cooler air descending, ridge lift, descending air below the declination line of a ridge, and wave are natural things that make these calculations just calculations. I have been lifted from 7,000 to 13,500 in a minute in a 65 hp Taylorcraft. I have been dumped from 13,500 to a hundred feet off the desert floor in a Tri-Pacer. A Huey at the Army's Mountain Flying School at Ft. Carson went from 7,500 to 17,500 at flat pitch. We got oxygen like the zoomies after that.
@@williamk5998 Vy and Vx intersect at absolute ceiling (as dannyCOTW wrote). It is conventional to determine this altitude by extrapolation from climb data gathered in tests up to about the service ceiling. In the performance flight testing, climb rate is recorded over a range of speeds and altitudes (sawtooth climb tests). The data is then processed graphically into 3 or more curves of climb rate vs speed (ie curves for 3 or more suitably different density altitudes). By striking a line through the peaks, and another through the tangents, you get the two straight lines that will intersect at absolute ceiling. Although you could determine absolute ceiling directly with a simple climb test, the sawtooth climb data provides Vx and Vy profiles and even the drag polar can be extracted.
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.
Brilliant as usual.
Vid didn't help me. Didn't really explan WHY Vx is increasing faster than Vy in terms of TAS.
Good presentation. Thanks
Does that apply for jets as well?
Vx and Vy occur at very nearly the same speed for jets. Due to ram effect, thrust is approximately constant with airspeed by contrast with the characteristic thrust curve of a propeller.
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.
Hi sir. That’s very interesting and I’ve thought about it before. Help me understand. So you are saying that on takeoff, accelerating using ground effect to a cruise airspeed so long as runway length allows, and the pitch up to clear the obstacle, you will actually clear the obstacle by a greater height than just taking off and maintaining Vx? That is what I’m taking away from your post . It makes sense. Here’s a scenario I have a question on: So when you accelerate to cruise using ground effect and then pitch up, let’s say the obstacle is still not cleared. Then you would maintainVx until you’ve cleared it? Step 1. Using ground effect on takeoff for its benefits on building energy. Step 2. Accelerate to cruise speed in ground effect so long as rwy length allows and then pitch up to clear the obstacle. Step 3. If obstacle is not cleared yet in the initial pitch up then maintain Vx? Thank you for your input and wisdom. I actually have my CFI check ride in 8 hours from writing this comment. It’s 12:30am now haha. I always find myself wanting to learn more and your comment intrigued me because it really does make so much sense yet is not taught at least not during my training. And I’m curious if you are aware to any references or tests done to back this up. -Derrick
@@derrick2251 Yes, staying level in low ground effect provides enough greater acceleration vs pitching up to Vxo or Vy pitch attitude as soon as Vx or Vy airspeed is attained to climb faster in a zoom climb when Vcc is attained. No, we would not be higher over the obstacles nor is that the objective. The purpose of accelerating level in low ground effect is to gain the free energy for safety and so the outcome of the maneuver is never in doubt. Having gained more airspeed safely over the runway, we don't then want to spend all that extra safe airspeed on altitude over the obstacles. We want to just clear the obstacles at the airport and cruise climb safely to altitude. If over the crop on a spray run, we want to use the full power level in low ground effect acceleration advantage to zoom climb just over the obstacles and gain only enough altitude to safely apply this potential energy in the 1 g turn of whatever bank angle is required to return to the next swath run only fifty feet upwind from where we left the field.
What we are avoiding, at the airport especially, is picking to a Vx or Vy pitch attitude while that slow in ground effect and quickly climbing out of ground effect where Vso, an out of ground effect number, will cause stall. At slower than Vso in ground effect we can safely fly, especially low ground effect, with the outcome of that flying never in doubt. Either Vx or Vy, just climbing out of ground effect, is much closer to Vso than Vcc. We don't want to quickly climb just high enough to kill ourselves in the stall and fall of being a bit slower than Vso, or getting there in the startle of engine failure. Neither Vx nor Vy are ever appropriate on long runways where Vcc, especially in low ground effect, is easily doable with the outcome of the maneuver never in doubt.
@@XPLAlN It is not exceptional piloting skills. I soloed many students in 65 hp trainers in less than ten hours using the basic level in low ground effect takeoff. At high DA, say Monte Vista midday in summer, low ground effect energy was 50% of our total energy available. We couldn't have safely trained using Vx or Vy, neither being safe. Yes, in normal conditions most do so. Only a couple hundred or so yearly overdo the getting up quickly and stall just as they reach the out of ground effect altitude where flying slower than Vso is generally fatal. With thousands of feet of runway remaining, acceleration level in low ground effect is safer at any speed than Vso at fifty feet or so.
Outstanding!
Thank you.
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-
And not a word that these are Zhukovsky curves
🛩️🛩️🛩️🛩️💪🏼💪🏼💪🏼 excellent 👌🏼
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.
@@flightinsight9111 The dictionary is behind the times. It also failed to account for linguistics and etymology. Complex came from a Greek root for entangled while complicated came from a Roman for folded. You can unfold things though it is much harder to unentangle. Look into Cynefin and Dave Snowden. See also Sidney Dekker’s work. Appreciating the distinction between ‘complex’ and ‘complicated’ has significance when we look to safety work. This is especially true as most our safety tools are built for clear and/or complicated and therefore fail in complexity. You’ll note there are ties to naturalistic decision making and Klein as well as Twersky/kahneman. And Boyd, John Boyd’s Destruction and Creation really tie to these. Though for easier reading, I’d suggest Ron Butcher on Medium with his view of overlaps yet also disparate and contrasting features between “safety” (read too heavily as ‘compliance’) and “survival.” Note ICAO is moving to learning these concerns as is BALPA. American Airlines is making some inroads too. The EU has fully incorporated the ideas in their recent Crisis Response manual while the Marine Corps is probably the best in applying. In complexity, relationships are not obvious.