Why don’t we use Vx instead of Vy during normal takeoffs?
Posted by Frosty_Yak_4124@reddit | flying | View on Reddit | 182 comments
I have always wondered why we don’t use Vx initially during climb out as we gain higher altitude when compared to Vy in shorter distance.
This will give us advantage incase there is an engine failure we will be at a higher altitude.
CarbonCardinal@reddit
If you're in a 172 climbing at 62 KIAS and the engine quits, you need to immediately show the yoke forward to avoid stalling and in doing so you lose a ton of altitude. The extra energy from climbing at 74 KIAS gives you more margin to transition to bes glide if the engine cuts.
zemelb@reddit
This is probably the most helpful explanation I’ve heard
tempskawt@reddit
It’s also the most… iffy. You don’t lose much altitude from pitching, not sure what he’s on about.
The__Stig_@reddit
No he is right. You will lose a lot of altitude in that moment. It will take you some time to even realize that your engine has failed, and in that time your airspeed will continue to decrease. Vx is somewhat close to a stall, and under certain conditions, it can be very very close to a stall. Hence, the danger.
And, any time spent at those slower speeds will result in poor glide performance. Altitude will be lost from that.
And I can continue. Think of how high you have to hold the nose, even in underpowered airplanes, to achieve Vx. Or Vy. Neither speed is very safe from that perspective. You can’t see traffic in front of you, and you can’t see possible landing spots.
For that reason I am in favor of almost always using a cruise climb on takeoff. A cruise climb will be easier on the engine, be much more fuel efficient, it will be less likely to scare the pax, it will be safer, and it won’t even result in that much of an altitude difference in case of engine failure.
The only time Vx or Vy should be used is in situations that necessitate performance takeoffs, like unusual terrain. I think the speeds are very overemphasized in training these days. When you fly you should not take a one size fits all approach, you should be able to adapt to the situation at hand. ADM.
tempskawt@reddit
Huh? Are you seriously saying it would take you significant time to react to an engine failure on climb out? That’s the time that you’re supposed to be the most vigilant and ready to react at a moments notice by getting the nose down.
If you lose an engine at Vx or Vy you will not lose any appreciable altitude by pitching down. Get in the plane, try it out.
The__Stig_@reddit
Have you ever flown a bonanza? If you are at Vx in a nose high climb, and you lose your engine, you will pretty much instantly stall. You will die. Vx is an extremely unsafe speed from that perspective. Sounds like you’re the one who needs to try it out.
tempskawt@reddit
Only if you maintain back pressure. It's a glider at that point, losing an engine doesn't make it stall, breaking critical AoA does.
The 4 second engine failure reaction isn't referring to pushing the nose over to break a stall, it's referring to the more complex side of an engine failure, i.e. beginning checklists, comms, troubleshooting. If it takes you 4 seconds to prevent a stall, I'm not sure how you passed a checkride. That immediate reaction should have been baked into you early on.
The__Stig_@reddit
It takes a near aerobatic maneuver to prevent a stall, in that case. You lose so much airspeed instantly upon engine loss. It’s basically already stalled before you can even begin to push over the nose. If you don’t believe me you need to try it.
It’s a problem in any high performance single.
tempskawt@reddit
You're going to have to describe this near-aerobatic maneuver to me.
The__Stig_@reddit
A stall recovery without an engine close to the ground.
tempskawt@reddit
Go on, what's the maneuver for that? Is it something like... pushing the nose forward? Breaking the stall?
Or is there something special about the Bo? Gotta do an aileron roll or something?
The__Stig_@reddit
https://m.youtube.com/watch?v=dXvyjogOpc0&t=308s&pp=2AG0ApACAQ%3D%3D&ra=m
Here is a video describing what I am talking about. With video evidence.
tempskawt@reddit
Completely based on the premise that the nose over reaction takes 4 seconds. If it takes you 4 seconds to nose over in that scenario, that should be the subject of your next flight review. They held back pressure the entire time, that's a panic response, not a delayed response.
The__Stig_@reddit
When your engine fails, it will take you an average of 4 seconds to even realize it has failed and take action. Yes, like a panic response. When you are in your takeoff climb, as an average pilot, you are not going to be mentally prepared to nose dive the aircraft, 100 feet above the ground. That is what that 4 seconds is all about. In an emergency situation, humans don’t respond instantly, especially if that response must fight all human instinct.
Losing an engine unexpectedly at 100 ft is not the same as practicing stalls at 3000 ft. You cannot practice true emergencies in a flight review. Taking 4 seconds to nose over in that scenario is the normal, average response. Emergencies never emulate practice. Obviously you have never experienced a real engine failure.
tempskawt@reddit
No, that's no excuse. If we're nitpicking climb out speeds, but you still think you might panic and pull up on an engine failure, that's a problem with your training that needs to be addressed now. Engine out? Push. Stall horn? Push. No 4 seconds about that.
The__Stig_@reddit
No it’s not about pulling back. It’s about responding by pushing down. No one in the video pulls back lol. That would be irrational.
The 4 seconds is literally a proven statistic. That’s the facts idk why you’re arguing with the data. Yes, you can train an automatic response to a stall horn, but you cannot train an automatic response to an engine failure that will take place in less than 4 seconds on average. Think about it. You are not even going to realize the engine failed right when it fails. It takes some time for that to even register. Especially depending on how it fails. I am not pulling the 4 seconds out of thin air. That is just a plain and simple fact. If you disagree with it you disagree with a majority of pilots.
tempskawt@reddit
The dude in the yellow taildragger with the wheels that broke off is pulled all the way back
The__Stig_@reddit
Yes, in an attempt at a landing flare, right above the runway. What else can he do, at that point? Pushing forward would not have made any difference in the outcome.
I am referring to the rest of the video where the guy analyzes the scenario.
When your engine fails as low as the guy in the yellow airplane, you’re basically cooked. There’s no proper response.
tempskawt@reddit
Yes it would have! Pushing down would break the stall, generating lift, generating ground effect, doubly reducing the impact greatly.
The__Stig_@reddit
did you watch the video?
tempskawt@reddit
Ya
The__Stig_@reddit
Then you would have realized that the point is to establish that pushing forward or pulling back would have done nothing. The only way he could have saved the situation is if he used a faster climb out speed.
tempskawt@reddit
I’m not trying to be a jerk, but you’ve got to go back to the basics. Pulling back kept them fully stalled, they were a rock. Pushing forward would have broken the stall and they would have had *some* lift.
In a power out situation, if you are coming up short on your intended landing point, you PUSH FORWARD. Pulling back will put you in a stall or even spin, at least pushing forward will generate lift and ground effect.
The__Stig_@reddit
Great video btw.
But not super relevant. That airplane is not flying anywhere near its Vx.
tempskawt@reddit
Why would it be flying at Vx? I'm not arguing for Vx over Vy, I'm arguing for using Vy as your default climb-out speed.
The__Stig_@reddit
If you go back up the comment thread, you’ll see that I mentioned the “near aerobatic maneuver” in the context of a Vx climb.
Of course, a Vy climb would improve the situation, and give you a better chance at survival. My point is, again as I have said earlier, why treat Vy like it is set in stone? Different situations demand different climb out speeds, and sometimes the safest climb out speed may be above Vy.
The faster you fly, the more benefits you receive, at the expense of a minimal (depending on speed) loss of altitude. The article discusses that tradeoff and comes to a conclusion that I find convincing. That is all.
tempskawt@reddit
Give me a scenario where you want to climb out at an airspeed exceeding Vy. Perhaps I'm just not creative. And I'm only talking about climb out to 1000', so babying the engine is not a valid reason. If you want to baby it and cruise climb after 1000', that's completely fine.
The__Stig_@reddit
Flying a bonanza at Vy is nose high maneuver. Your view of what’s in front is very limited. If I am in busy airspace, trying to keep the traffic in front of me in sight, flying at a slightly lower aoa might be the safer decision. That’s just one example. I can give you lots more.
tempskawt@reddit
That's pretty niche, why would you be barreling after someone on upwind in a Bo? Like you're staying in the pattern? Even then, you can just bump the nose over periodically instead.
_VNAV_PTH_@reddit
If you lose an engine, would you rather be higher or lower altitude?
The__Stig_@reddit
Obviously a higher altitude is more desirable, my point is simply that there’s more to the equation than raw altitude. Just something to take into consideration when trying to decide the safest course of action.
If you like to always use Vy, great! Do it. I just don’t like people who blindly do it. Do it after thinking through all the possible contingencies and other options. And if that’s the one you’re most comfortable with, and the one you think will make you safest, then who am I to judge you.
tempskawt@reddit
You're acting like you have this refined opinion on the matter, but you're saying the equivalent of "Sometimes you have to ride on the highway without a helmet because you can see better". You really haven't provided anything other than "This is the way I like to do it."
Cruise climb is great... when you are in cruise flight. Until that point, you should be doing everything in your power to give you the best chance of surviving your emergency. That means optimizing how much *total* energy you can get out of the aircraft, hitting an optimal ratio of lift to drag.
There's the idea of the "impossible turn". It's not really impossible, you just need to know what altitude you can do it from. But following your logic, you seem to want to keep the impossible turn impossible for longer. Airspeed decays quickly, altitude does not. Unless you're flying the OV-101.
The__Stig_@reddit
This isn’t just some crazy opinion I have. Theres many who agree with me and research that has been done. Here take a look at this if you want a more intellectual opinion. https://www.advancedpilot.com/articles.php?action=article&articleid=1842
tempskawt@reddit
He had to call in a professor to draw some basic line graphs? That's hilarious
The__Stig_@reddit
Yeah you’re missing the point. As hominem.
tempskawt@reddit
That's not what ad hominem is. It's directly related to the subject at-hand.
The__Stig_@reddit
Um yes it is. You’re attacking the author of the article instead of the content of the article, ridiculing him for bringing in a “professor” to draw some simple graphs. That’s the literal definition of ad hominem.
Who drew the graphs is irrelevant. The data is the subject at hand, not who generated it.
tempskawt@reddit
His stance hinges entirely on graphs that anyone with such a strong opinion should be able to draft up independently. It's the entire backbone of his argument. It suggests that it is not his opinion after all, rather that of the professor. Not sure why you put professor in quotes.
Also the most hilarious part of the entire article:
"This shows a total of only 7 seconds difference between Vx and Vy, arriving at 1,000 feet!"
"Further, the average reaction time to an engine failure is four seconds."
So... we're not trying to give ourselves precious seconds? That's almost double the reaction time!
The__Stig_@reddit
I’m confused by your comment here. Again who cares about who generated the data? Why are you so hung up on that?
As to your critique of the 7 seconds of difference, i fail to understand it. According to his data, you arrive at 1000 feet 7 seconds earlier if you fly at Vy, rather than Vx. But the author is not arguing that we should fly at Vx! So you are critiquing a stance that the author does not hold. Your point is pointless.
tempskawt@reddit
You're ad homineming me by coming after me for ad hominem. (That's a joke)
He's criticizing that Vy and Vx are both bunk. Vy gets you to 1000' the fastest. There's no speed that's better at getting you to 1000' the fastest. He's suggesting you could climb out at a faster airspeed and you'd only be late to 1000' by a few seconds. But that undermines his whole point -- you need those seconds.
I hope we're not disagreeing on the wrong thing here. I'm agreeing with the guy that said Vy 90 percent of the time. I'm also saying that anything over Vy under 1000' is misguided.
The__Stig_@reddit
To go back to that article, and to answer both this comment and the other one you just made…
Using his method, Deakin pinpoints 4 factors that are in his favor. If you need to review his method to understand, do. I don’t wanna spell the whole thing out here.
He admits there is one flaw with his method, time. You will be at a significantly lower altitude per unit time, to 1000 feet. However, he concludes this is a small price to pay because, as he shows with his charts, the increased distance available to glide only increases 500-1000 feet with that conventional takeoff. He calls this a small price to pay in return for the factors he mentions. And it is a relatively small price, all things considered. Maybe you think that it is not a small price. Idk.
tempskawt@reddit
You’re citing the article to prove the article.
The__Stig_@reddit
I’m not attempting to prove the article. I am citing the article so that we both are on the same page as to what the argument is. You haven’t as yet made an argument against his method. All you have said is that you would rather have those extra seconds, and extra 500-1000 foot radius. His argument is literally that the cost of those extras outweighs the benefits. So taking that cost benefit analysis into account, what then is your verdict? Is the extra few seconds and 1000 feet really worth all the cost?
_VNAV_PTH_@reddit
Vy is the right solution 90+% of the time because it gives you more altitude faster than any other method, simple as that. Altitude is life. The only main exceptions are 1) Vx on a short runway and poorly gliding airplane where Vy might put you impossibly far from the runway should you lose an engine on departure and 2) obstacles.
The__Stig_@reddit
Vy does not give you as much extra altitude/gliding distance as you might think compared to the cruise climb method. In this article it’s all laid out in graphs in the second half.
Flying a takeoff at Vy has some significant disadvantages that outweigh the tiny benefit of ever so slightly more height, especially in more powerful airplanes. Take a look at this and tell me what you think.
https://www.advancedpilot.com/articles.php?action=article&articleid=1842
CarbonCardinal@reddit
I would rather have more energy. Airspeed gives you more energy than altitude and gives you an extra second to react.
cleardarkz@reddit
Tell me you are not a pilot without telling me you are not a pilot.
Thats the stupidest answer anyone could come up with.
Altitude IS energy.
CarbonCardinal@reddit
I'm a CFI dude. Speed gives you energy per velocity squared. Altitude gives you energy linearly with height. The extra altitude you get from the initial Vx climb is marginal when it already puts you slower than best glide.
_VNAV_PTH_@reddit
False lol, not even close. Especially in draggy piston aircraft like we're talking about. Altitude gives way more energy than airspeed.
CarbonCardinal@reddit
When you lose your engine at 100' AGL at the bottom of the drag curve, losing 50' just pitching over is a lot.
Affectionate_Ask4364@reddit
Heat
topdollar38@reddit
Vx does give you more altitude in a shorter distance than at Vy. But it takes longer to do so. Given the same amount of time, you will gain more altitude at Vy.
saksoz@reddit
Also Vx is a more vulnerable place to be, keeps you low and slow on takeoff.
paulyshorebreak@reddit
A DPE once told me, "If you're asking yourself what Vx is, that's often a pretty good clue that you shouldn't do that thing."
vtjohnhurt@reddit
One loses airspeed faster when climbing at Vx attitude The only reason to take that risk is to clear an obstacle or simulated obstacle (for training).
Here's what it looks like to recover from a loss of power at 250 AGL at an attitude that is higher that Vx https://youtu.be/gbQtkLI24dA?t=257 In an airplane you'll have a bit more time, but Startle Factor will delay your response.
maverck_0@reddit
Why do no CFIs add the time variable?? This finally makes sense
autonym@reddit
It's right there in the definition. Vx maximizes vertical distance gained per horizontal distance (highest angle of climb). Vy maximizes vertical distance gained per time (highest rate of climb).
qzy123@reddit
Commercial multi and you didn’t understand Vy? 😬
topdollar38@reddit
Meh. I'm an engineer and still have plenty of "ah ha" moments at work when I finally understand how something works that I should have theoretically should have already known.
Lightlychopped@reddit
Yeah but in this case it’s like you finally learning the concepts of algebra while sitting for your state board exam
iflyfreight@reddit
Meh. Not really. Clearly he knew what to say and when to use which. Not being able to get to the highest level of comprehension in every topic is slightly unrealistic. I agree, Vx vs Vy is a junior concept. But in my experience most schools have some systemic area of deficiency. I, for example, cannot tell you how many times I’ve had an ATP student that transferred into my school to teach give me a spiel about how the engine is “horizontally opposed, naturally aspirated blah blah engine” and freeze when I ask them what they mean by “naturally aspirated” and my primary training was very lackluster when it came to weather. It’s a license to learn. The trick is knowing or figuring out where you’re weak and continuing to expand your knowledge over time while not extending yourself into bad situations in the interim. At least that’s what I’ve been doing.
coldnebo@reddit
“naturally aspirated” is the turbo effect I get when turning carb heat off, right? 😅
definitely not judging.
one of the questions that broke me was: at what altitude are Vx and Vy the same?
but that opened up a really interesting deep dive that taught me a lot about performance. only knowing trainers, I had assumed they were constant values. hell, I assumed IAS was a constant value. I’ve never seen a flight level. 😅
maverck_0@reddit
I didn’t understand that Vx would take longer. The shorter distance was all that was emphasized.
poisonandtheremedy@reddit
If vY is the best rate of climb then by default vX is slower.
HLSparta@reddit
Did you not read the POH, the FAR/AIM, or a textbook?
LearningDumbThings@reddit
What’s your bigger threat, obstacles ahead or engine failure at low altitude? Choose Vx/Vy appropriately to mitigate the more imposing threat.
deezknots78@reddit
You hit the nail on the head.
qzy123@reddit
Always more to learn ✌️
Taskmaster and Volfpeck, clearly an aviator of culture.
floatinthrough@reddit
Oof
haveanairforceday@reddit
What do they describe Vy as if not time?
deezknots78@reddit
Is it not in the definitions?
HLSparta@reddit
It's very clearly spelled out in every POH/AFM I've read, in the FAR/AIM, in multiple textbooks, in the PHAK, and I'm sure in a few other common places I'm not thinking of at the moment.
TheDornado13@reddit
uh mine did as did my ground school textbook. Where in the heck did you learn to fly?
Icy-Bar-9712@reddit
I teach:
Vx, most altitude per unit of forward distance traveled.
Vy most altitude per unit of time.
iheartrms@reddit
It's best *rate* of climb. For me, the time was implied. Rate is feet/min.
ApatheticSkyentist@reddit
I guess I always thought it was intuitive. Best angle versus best rate. Rate = get there faster (sooner).
AtiumMist@reddit
Omg, i finally was able to visualise vx vs vy
Old-Trouble-8830@reddit
What helps me is Vx look at the X it has 4 45 degree angles inside the X and it reminds me Vx is your best angle.
BarnacleBeanz@reddit
I remembered the difference between vx and vy the same way. X has more angles than Y hence best angle of climb.
Also double check your angle math 45x4=180 ☝️
AtiumMist@reddit
Yeah, if you give me a minute i can tell u vx is best angle vy is best rate. But besides the definitions i never really was able to visualise it lol
ronerychiver@reddit
https://mediafiles.aero.und.edu/aero.und.edu/aviation/trainers/vx-vy/
Someone’s already visualized it for you
coldnebo@reddit
really nice vis! thanks!
AtiumMist@reddit
Thanks!
topdollar38@reddit
It does seem counter intuitive. Especially when you're sitting at that higher angle of attack at Vx. I'm not a CFI, but a fun exercise is to use a stopwatch to time how long it takes from takeoff to 1000ft both at Vx and Vy to see the difference.
Wild-Language-5165@reddit
When you think about it, it's not so counter intuitive. The steeper your climb, the slower your speed, ergo, the longer it takes to get to altitude. Unless you have a ridiculous thrust to weight ratio, then you can accelerate as you climb like an F15.
matthewlai@reddit
It does depend on the airplane though. For some low drag airframes they can be very close, because they don't lose as much speed at higher AoA, so increasing AoA still give you faster and higher angle climb, until you are limited by getting too close to stall. On the DA-40 for example, Vx isn't published because it's basically the same as Vy (maybe 1-2 knots slower).
Desirable_Username@reddit
If you're fortunate enough to have a digital VSI, you could just look at that when you're at altitude. You'd probably demonstrate this during a climbing and descending lesson.
Mithster18@reddit
Vx, you're abseiling a cliff, Vy you're walking up a hill path.
e_pilot@reddit
Vy is most altitude over time vs Vx is most altitude over distance
Carre_Munuts@reddit
It also reduces visibility during your climb since you can’t look through your cockpit unless you have a 400k custom fitted F-35 JHEMCS helmet
coldnebo@reddit
heh. I used to fly out of a 1400 ft field with 50 ft trees on the end in a C150.
can confirm: couldn’t see the trees over the front, but got to know Vx real well. peak over the front, dead. get scared and pull back more, dead.
I didn’t get to contingency planning until later and I don’t know a lot has changed, but now I wonder what my safety brief would have been?
if we engine fail before this point, abort. basically right at Vr.. 700 feet? oof.
if we fail before 600, landing Vg into the trees? oof. no side escapes.
if we get to 600 maybe? but surrounding terrain isn’t great (9B1).
it seems like a bush strip kind of. and honestly I felt better about it back then because I didn’t know as much.
now the other thing I puzzle about was two six foot guys in a C150 under gross weight? maybe? 😂🤷♂️
I’d appreciate pilot perspectives here on how they might do contingency in such a place.
Neither_Cap6958@reddit
Also better engine cooling for piston.
Professional_Read413@reddit
It took me like 90% of the way through PPL before i understood this
Po-Ta-Toessss@reddit
Think about it this way. During Vy you run out of runway faster. With Vx you don’t. You’re traveling in the same direction but slower, while gaining the most altitude per foot traveled. Useful when you need to clear an obstacle.
alexdwilliams91@reddit
Timey Y-mey, that’s how I always remembered it
sat1290@reddit
ball of wibbly wobbly timey y-mey... stuff
makgross@reddit
If your goal is to turn back to the airport in an engine failure, you’re mostly right. In Cessna and Piper trainers, you’ll be short at a faster climb in no wind.
If your goal is to survive a low altitude engine failure, the equation is very different. Turnbacks are very risky. Landing in a field or even in a forest or in mountains under control is much less so. So, we train people to land ahead, and higher altitude is advantageous, whereas higher angle is not.
Relevant-Train5317@reddit
I don’t think you understand the purpose of Vx and Vy.
Launch_Pad_Flagada@reddit
I see people already mentioned angle vs time.
Also Vy provide
Better forward visibility
Better engine cooling
Gets you to your destination quicker.
PG67AW@reddit
That it do, that it do...
Launch_Pad_Flagada@reddit
Lmao
PG67AW@reddit
Vy provideth, and gravity taketh.
nhorvath@reddit
A better way of saying angle vs time is: more altitude in the event of engine failure. if engine fails 1 min after takeoff you will be in a better spot with Vy. also less abrupt control inputs required to avoid a stall if it quits.
Launch_Pad_Flagada@reddit
I'll grant you angle vs time is poorly worded. Angle vs rate is what I obviously meant.
Difficult-Put9586@reddit
If you have obstacle clearance concerns, you would use Vx. Once clear of the obstacle, continue the climb at Vy.
Vy is more fuel efficient, gives you more visibility through the windscreen, and gives the engine better airflow for cooling.
Aggressive_Lime2214@reddit
Vx gives you best climb angle with no regard to time. Vy gives you best climb rate with no regard to distance. Vy will get you to altitude quicker than Vx, but you will have flown a greater distance. Vx will get you to altitude within a shorter distance than Vy, but you will have taken longer to get there.
autonym@reddit
If you compare an engine failure during a Vx climb with an engine failure during a Vy climb, you'll be at a higher altitude during the Vx climb if the two failures occur at the same horizontal position, but you'll be at a higher altitude during the Vy climb if the two failures occur at the same number of seconds into the flight.
Incase isnot aword. (Encase is a word, but it doesn't fit the sentence.)
CarryTheBoat@reddit
For the scenario you describe, you would actually want Vy, it will get you higher faster. You will travel further crossed the ground yes, but that’s doesn’t matter if there isn’t actually an obstacle to clear.
slendermanboxedwine@reddit
Everyone is correct with it takes longer to climb but also less airflow means engine temps gonna get hotter. I’d use VX a lot if we were departing off a north runway but we’re heading south. VX till we get above everything then VY/Cruise climb when I’m headed in the direction I wanna go.
flyingron@reddit
Gain altitude quicker... altitude gives you choices usually.
Better visibility over nose.
Better cooling.
Further from the stall.
draggingmytail@reddit
In a lot of aircraft, you’re hanging pretty close to stall speed when you’re at Vx speed. Not somewhere I want to spend a lot of time at with low AGL.
dhempy@reddit
Speed is life.
thegolfpilot@reddit
“I have always wondered…”-some guy that did his first discovery flight earlier this year
R5Jockey@reddit
So what? We can’t learn here or ask questions until we’ve got a cert?
Aromatic-Run-287@reddit
Because VY gets you to a safer altitude faster, it minimizes the amount of time that the plane is at a low altitude, therefore minimizing the chance that an engine out would happen without gliding distance. You may have heard of the impossible turn and most people agree that it's very difficult to turn back around to the airport after an engine failure If you are below 1000 feet. And v y minimizes the amount of time that the plane spins betweeAnd VY minimizes the amount of time that the plane spends below that altitude. Also VX is closer to stall speed. So if you did lose an engine, traveling at VY would give you a little bit more speed to be able to trade-off for maneuvering.
anonymeplatypus@reddit
Your engine doesn’t care how much distance you have covered when it fails. It is gonna fail when it is gonna fail, and vy means you will be at a higher altitude when that happens. Yes, you will have traveled more distance, but vx is best altitude per nm, vy is best altitude per minute (what is relevant here).
Unless you have an obstacle, always use VY. And sometimes even with an obstacle Vy is better (windshear)
luckyhendrix@reddit
We do ? You dont ? Ivhave always beeen taught to aim vx untill obstacles are clea or 400ft agl then vy
SheepherderNo5877@reddit
PPL student, but another advantage of Vy is prolly just mitigating against the moment of startle after an engine failure. You will have to push the nose over before you fall below your no-flap stall speed. (Short time at Vx, not quite as short at Vy). Get light in the seat before you stall it close to the ground.
WhiteoutDota@reddit
You are fundamentally misunderstanding what Vx is if you think it gets you higher than Vy in less time
DingleBurg2021@reddit
Plus additional speed so you’re still flying by the time you realize what’s happening.
PlasticDiscussion590@reddit
Plus you can see better!
Whole-Hat-2213@reddit
And it's better cooling airflow for your engine
WhiteoutDota@reddit
Indeed
primalbluewolf@reddit
To be fair to them, they've not said that it does. They've said that it gets them higher than Vy in less distance, which it does.
Its not clear in their argument why that's beneficial.
KITTYONFYRE@reddit
could be beneficial if there’s a situation where the airport is very safe and landing outside of it is extremely dangerous. eg maybe if there were zero options off the departure end of a 7,000’ runway, so you clim at Vx to stay more on top of the runway? even then you probably wouldn’t climb at Vx for more than 300-500 feet or so (at whatever point the runway isn’t an option any longer)
not sure though. just trying to think when Vx would be appropriate other than obstacle avoidance
CommonRequirement@reddit
I trained in a busy area and they taught vx because being high over the airport was preferable to getting a little higher further away. It was all buildings and 50mph packed streets. The airport was pretty big so it seemed plausible
primalbluewolf@reddit
Yeah, maybe. Going to be quite type and airport dependent, in that scenario.
I have that scenario pretty frequently in my work, and I still cruise climb as my SOP. Keeping the engine cool is the key objective!
Perhaps if you climbed Vx to 300 ft, then took an early crosswind turn at Vy... trying to stay close for a hypothetical turnback. I just finished Flying High Performance Singles And Twins, and it has an interesting appendix on exactly this topic, the maths behind the single engine turnback after engine failure (either the "impossible turn" or the "the possible turn", depending on altitude and distance from the runway). Eckalbar asserts in it that a departure from overhead or downwind is safer for an engine failure, which jives with common sense - but he's also considering the case of an engine failure at 1000 ft, rather than say 300 ft.
For me, I can't get away from the CHTs - climbing at Vx repeatedly may well induce the engine failure you're trying to avoid.
DankVectorz@reddit
They said distance, not time
VileInventor@reddit
rate vs time. Go watch a youtube video. You’ll get to the same altitude faster via Vy.
dodexahedron@reddit
-Vx
-Vy
haveanairforceday@reddit
Shortest distance to get altitude is not as helpful as shortest time to gain altitude
falcopilot@reddit
Depends on what's off the end of the runway. Might take us a few seconds longer to get to 100' but if we need to clear the tree at the end of the runway, Vx is your friend.
Icy-Bar-9712@reddit
Technically barrier speed would be your friend. Vx is probably a little faster.
If you fly a recent skyhawk the short field process will have a climb out speed lower than Vx. This used to be called barrier speed and in trainers is often reeeeealy close to Vr.
primalbluewolf@reddit
"Short Field Takeoff, Flaps Up, Speed at 50 Feet ... 59 KIAS" "Best Angle of Climb, Sea Level ... 59 KIAS"
That's from a 172N POH. Your numbers are probably a little different for a newer model - but not that different.
Vx at SL for that plane, 59 KIAS. Vy at SL for that plane, 73 KIAS.
Say you have a new 172S, though. For a new one, you'd be right apparently:
"Best Rate of Climb, Sea Level ... 74 KIAS" "Best Angle of Climb, Sea Level ... 62 KIAS".
"Short Field Takeoff, Flaps 10, Speed at 50 Feet ... 56 KIAS"
Vx is the best speed for best angle, full stop. Vx is different under different conditions, though - different power settings, different altitudes, different configurations. Fly high enough and Vx and Vy and Vs are the same number - that's your absolute ceiling.
If "barrier speed" gets you higher in a given distance, that's closer to Vx in that configuration at that altitude and power setting than the published Vx figure you were using.
haveanairforceday@reddit
That sounds uncomfortable
Icy-Bar-9712@reddit
For PPL students it really is. Many of them get fucked over by bad primacy of teaching of climb at Vx (~65) when the procedures and checklists call for a climb out of 56.
But they are also holding Vx till sometimes 400 to 500 feet. None of which is right.
It is essentially rotate into a power on stall pitch for about 4 seconds, lower the nose and slowly retract flaps once over 60.
topdollar38@reddit
That's correct. But OP was specifically asking about engine failure. Vy for altitude faster is preferred in that scenario.
Pilotreggie@reddit
Time is money
GryphonGuitar@reddit
Where I fly from we absolutely do the initial climbout at Vx since clearing a tall tree line at the end of the runway is the primary concern. Once that's done we transition to climbing at Vy.
ArrowheadDZ@reddit
Think of it this way. An engine failure is a function of time. That crack forming in the engine doesn’t “know” how high you are, it just knows how many seconds of full power from now it has left. (It doesn’t literally know.) If the crankshaft is going to fail 8,000 rotations from now, do I want to be lower, closer to the airport, and slower (that’s Vx) or higher, farther from the airport, and faster? (That’s Vy.)
The answer is always Vy. Vy is the maximum amount of energy (kinetic energy + potential energy) that you can store in the plane, period, and that’s why it is an important number. At any faster speed you are trading more potential energy in than you gain in kinetic energy. At any slower speed, you are trading more kinetic energy in than you gain in potential energy.
A Vx climb for obstacle clearance is an increased risk maneuver that should only be performed only for the minimum time required for obstacle clearance, and then immediately transitioned to Vy. And should only be performed as a fully briefed maneuver.
At Vy, when the engine fails you will be (a) higher; (b) faster, meaning more margin over stall speed while recovering from startle; (c) shallower, and thus bleeding speed off slower during startle time delay.
Always Vy.
atmatthewat@reddit
> do I want to be lower, closer to the airport, and slower?
well, my home airport has a 11,000 foot runway and my ground roll is only a bit over 1000 feet... so "closer to the airport" isn't the worst thing. YMMV of course.
PlaneShenaniganz@reddit
Do you need to clear an obstacle? Then use Vx: you will gain more altitude per unit distance traveled.
Are there no obstacles and you just want to get to cruising altitude faster so that you can burn less fuel? Then use Vy: you will fain more altitude per unit time traveled.
ronerychiver@reddit
Altitude buys you time if you have an engine failure. The second you’re off the ground. Unless there’s a mountain in your way, your goal is to get up there quickly so if something happens, you’ve got altitude and therefore more time to deal with it
Flapaflapa@reddit
Because Vx sucks donkyballs for almost everything.
Our goal is to get away from terrain. Vy does that sooner.
We want to see potential traffic, Vx puts our nose up in the air blocking the view.
We wan to have good cooling on the engine when it's working hard, Vy puts more airflow through the cowl,
We don't trust engines. Recovery from Vx attitude is dicey on an engine failure, you're slower, you have more push to react and get the nose down, and then you have to recover more airspeed to flair. For multi engine planes Vx is often pretty close to Vmc and Vy puts a much nicer buffer.
You want to clear the pass up ahead...oh hear's Vx's time to shine, but nope Vy and a couple S turns and you'll top the terrain sooner.
Oh ok so we have a short field and need to clear the trees maybe Vx is good for that? Nope, Vx for a bit, then as you see you'll clear the trees accelerate toward Vy, as it's better to clear the trees by 10 feet and have more speed (gusts, sheer etc) than 30 feet hanging on the prop.
The only thing Vx is good for is if you get yourself stuck in a blind canyon and don't have room to turn, then it's Vx and pray your stupidity doesn't kill someone.
Attackpilsung@reddit
Hotter engine temps as well in the summer.
Alternative_Pace6132@reddit
Cirrus pilots do.
AV_NAV_COMM_PROFIT@reddit
"x is angle, y is rate" more altitude in a shorter amount of time
FluffusMaximus@reddit
I’m just poking fun here… you weren’t strong in math class were you?
bhalter80@reddit
Scott Perdue did a video on this with the impossible turn, https://youtu.be/HqdusJ7P-R4
His conclusion was that from engine failure at Vx to pitched for best glide was almost a 30* pitch change from climb to glide and because of the energy loss there was no option but to land straight ahead. In the Vy case he was able to make a 180. Cruise climb had the least pitch change and you have a lot of airspeed which gives you options to maintain altitude or descend
mtconnol@reddit
Energy is life. It can take the form of airspeed or altitude roughly interchangeably.
primalbluewolf@reddit
At about 9 feet per knot, per hundred knots.
If you wind up in a high drag scenario, you're bleeding energy, whether you trade away airspeed or altitude for it. The attitude you're in for Vx at takeoff power in all aircraft I've flown, and I suggest most aircraft period, is very nose high compared to the attitude for best glide or tightest power off 45 degree bank turn - and you're going to incur a great deal of energy loss maneuvering the aircraft to get out of that state.
bhalter80@reddit
I encourage everyone to do a Vx takeoff in a Baron once. It's so nose high and you're so slow that you know that if something goes wrong you're a goner.
bhalter80@reddit
It's really not if you end up slow in a PO180 you're going to have to burn a lot of altitude to get that speed back
primalbluewolf@reddit
Interestingly none of his results were optimal. He didn't bank enough, and maintained too high a speed in the turns. 45 degree bank angle is the optimal for the turn, as a general rule.
bhalter80@reddit
I was trying to figure out how he picked the altitudes for the engine cuts
Old-Trouble-8830@reddit
The definition of Vx is it’s your greatest angle giving you your best climb over distance. Vy is your best Rate giving you your best climb over time. It’ll be the shortest time to cruise via Vy vs Vx otherwise yeah we would always use Vx. You are correct the goal is to gain as much altitude as possible in the shortest time.
Far_Top_7663@reddit
If the engine will fail x seconds after lift off, you will be higher AND FASTER if you are using Vy instead of Vx, making it safer for controlling the engine failure situation. Vx is only used to clear obstacles because it gets you higher in a shorter distance but not in a sorter time.
Frederf220@reddit
Flight at Vx is closer to stalling and has reduced engine cooling. Two engines about to fail on takeoff will failer sooner, lower, and slower at Vx than Vy. You do Vx strictly for the geometrical advantage. If the world was flat as a pool table you'd do Vy every time.
White_Hawk33@reddit
Also once you’re at 500 ft off the ground clear of obstacles you should use climb airspeed. More vis and honestly ft/min is the same
deezknots78@reddit
Why not use both? Vx to clear obstacles then Vy thereafter. Forgive my ignorance, but how is it being taught now?
Antique-Kitchen-1896@reddit
No one list engine cooling..
primalbluewolf@reddit
You're not reading the many comments listing engine cooling.
phliar@reddit
How's this: if an engine fails on takeoff (which is the likeliest, since that's the first time on this flight it has been at sustained full power) it will fail a certain time since full power was applied. So we want the highest altitude with time, that's Vy.
primalbluewolf@reddit
Not typically the case - I would suggest that the more common outcome is directly related to engine heating. Cracked spark plug causes mild detonation, CHT rises in that cylinder, heat encourages further detonation, becoming moderate, reducing power and further raising CHT, cylinder starts to go out of round due to uneven heating, causing scuffing and further heating, until parts of it melt - at some point it'll hole and lose compression, and spread molten aluminium through the crankcase and oil galleries.
Or if you keep the engine cool enough, it won't happen at all. Climbing very slowly and steeply is how to get the highest engine temps without touching the mixture knob.
PutOptions@reddit
Two reasons to my mind. Most important, Vy gets you HIGHER for a given measure of TIME. Unless you have an obstacle to clear near the approach end, use Vy. Hit the books.
Second -- and this is IMO -- if the engine quits and you are at Vx, you are not allowed to have startle effect which most humans (not me of course) suffer from. Welcome to the deadly low altitude stall/spin. Vy gives you that extra 5-15 seconds to gather your shit, push, and make the best of a bad day.
primalbluewolf@reddit
If you need 15 seconds to gather yourself after an engine failure on takeoff, it doesn't matter what speed you choose to fly at - and respectfully, if this applies to you, I suggest you fly with a safety pilot until it no longer does.
PutOptions@reddit
Just thinking a buffer estimate for startle might be suitable if ur thinking Vx climb (without reason) is a good idea. Engine roll back is a thing too that really catches people out.
primalbluewolf@reddit
A realistic buffer for speed is going to put most light singles and many twins back up to Vy anyway. If that's a 15 second buffer you're now doing a cruise climb... which I would advocate for anywhere, where obstacle avoidance isn't a priority.
classysax4@reddit
Climbing at such a low airspeed means you'll have to trade altitude for airspeed to make best glide.
Plus there are other factors than simply getting altitude as quickly as possible.
redditburner_5000@reddit
Vy gets you to 500' in one minute but you use 1.5 mi to do it. You'll climb faster in terms of vertical speed on the VSI, but you'll use more distance doing it.
Vx only gets you to 350' in one minute but you only use 0.75mi to do it. You don't climb as fast in terms of FPM on the VSI.
Those are made up numbers, but that's the idea.
You'll get higher in 1mi at Vx than in 1mi at Vy
You'll get higher in 1min at Vy than 1min at Vx.
Vy gets you higher is less time. Use this speed to get away from the ground as fast as you can. This speed gives you the biggest possible number on your VSI.
Vx gets you higher over the shortest distance. Use this speed to get higher than that mountain that's 2mi in front of you.
They're both useful, but you need to know what they're doing for you.
braided--asshair@reddit
Your understanding of Vx and Vy is not entirely correct. Yes Vx will get you to your target altitude in a short distance, but Vy will get you there in a shorter time. Let’s say that failure happens 3 minutes after takeoff, at Vy you’ll be at A) a higher altitude and B) higher airspeed.
Total energy is a function of altitude (potential) and airspeed (kinetic). Vy gives you an advantage in both altitude and airspeed giving you more total energy. Vx gives you less altitude and less airspeed giving you less total energy. The only advantage Vx has is a marginally closer distance to the runway. Even then, if you had a low altitude failure, pulling an impossible turn is going to be impossible whether you’re close to the runway or not.
Canadian47@reddit
Add to other comments...
Engine cooling. Vx provides less airflow over our air cooled engine at the time they need it the most.
dumbassretail@reddit
Assuming the engine stops at the same moment, you will be higher and further forward if you’ve been climbing at Vy vs Vx.
Mispelled-This@reddit
Vy gives you the most altitude in the least *time*, which is what you want if the engine is going to fail.
Vx gives you the most altitude in the least *distance*, which is only what you want if there’s a danger of hitting terrain or obstacles when climbing at Vy. And you switch to climbing at Vy as soon as that danger passes.
primalbluewolf@reddit
The reasoning to use Vx is straightforward: there's an obstacle in front of you, and you need to clear it. Climbing at Vx will give you the steepest climb angle, so that you stay the furthest away from the obstacle. Climbing at any other speed will get you closer to it. You'll also have a very high nose attitude, a difficult recovery in case of engine failure, and very high CHTs.
Climbing at Vy will get you closer to the obstacle, if there is one, but with a lower nose attitude, a higher speed, an easier recovery in case of engine failure, and cooler CHTs. You'll also be higher and faster for a given engine failure, if the engine was going to fail a given number of seconds after takeoff - and you'll be less likely to have an engine failure, if the failure is related at all to engine heating/cooling.
Vy is the speed where there's the maxmimum excess power. This means you'll have the maximum climb rate at this speed.
If there's no obstacles, and the terrain in front of you is smooth, you might consider forgetting both Vx and Vy and climbing at a cruise speed, depending on type. Accelerate, clean up, if there's houses around possibly reduce RPM slightly at a safe altitude, and cruise climb. Much lower nose attitude means an easier recovery from an engine failure, far better cooling means you're less likely to cause an engine failure, your CHTs will be much cooler, and you'll have more speed if you do have an engine failure - although you'll have less total mechanical energy (speed plus altitude) if you were always going to have an engine failure, say, 30 seconds after takeoff, compared to the Vy climb.
cazzipropri@reddit
I do routinely. We are in an area that is surrounded by forests, hills and water, and the smartest thing to do is to reach the highest altitude while remaining over the field as much as possible. We do all takeoffs at Vx unless demonstrating Vy.
Purgent@reddit
I fly out of a field surrounded by suburbs and terrain not suitable for off field landings. This is also why I climb out closer to Vx.
chupchupandaway@reddit
Probably to be further away from stalling speeds if it isn’t necessary to clear an obstacle would be my theory on that.
EliteEthos@reddit
Stall margin
Mountain-Captain-396@reddit
Incorrect. Double check the definition of Vx and Vy.
BornInTheSFRA@reddit
Good question. Not a CFI, but I would bet that it’s because we want to minimize the time we are too low. Vy gets us higher, faster.
rFlyingTower@reddit
This is a copy of the original post body for posterity:
I have always wondered why we don’t use Vx initially during climb out as we gain higher altitude when compared to Vy in shorter distance.
This will give us advantage incase there is an engine failure we will be at a higher altitude.
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