Let's talk about Vx

Cooter143 said:
Correct, kind of. But the blind spot is larger at the slower airspeed (higher AOA). The higher the AOA, the less you can see in the direction of travel.
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Sure, and I said as much earlier. But my question is really about how much worse. Does it really make much difference? Is something that has really been examined or if its just an old wives tale. Is there somewhere that this is rally examined in depth?
 
dmspilot said:
You imply that at Vx the aircraft is going where it's pointed, which implies an angle of attack of 0°. Do you fly a rocket? :confused:
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Not at all. Look at my first post, second paragraph:

PPC1052 said:
I will grant that with the higher climb angle, you do need a greater angle of attack such that there would be a slightly greater difference between the angle you are pointing and the angle you are climbing comparing Vx to Vy. But it doesn't strike me as that great of a difference, and not "a lot worse" in terms of the difference between the angle you are pointing and the angle your are moving. And it's not like you cannot see below the angle of your plane's actual trajectory, even if you can't see as much of the ground. Is there any study that really examines this issue, or is this just one of those old wives tales that keep getting repeated?
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PPC1052 said:
Sure, and I said as much earlier. But my question is really about how much worse. Does it really make much difference? Is something that has really been examined or if its just an old wives tale. Is there somewhere that this is rally examined in depth?
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Jeez, get in an airplane and TRY it. It's just a Vx climb, not an inverted flat spin with one engine inop.
 
There are guys who believe Vx provides the best climb profile since it keeps you closer to the airport should you need to return after an engine failure. That may make some sense but in many planes the time it takes from climb to stall when the power quits in a Vx climb is shockingly quick. Many pilots wouldn't be able to prevent the stall and the corresponding altitude loss would more than offset the close proximity advantage. I climb at Vx when obstacles require it. In the absence of obstacles there's no reason and I use Vy and enjoy a much better view out the front, better cooling, more positive controls, and less stress on airframe and pilot.
 
Stewartb said:
There are guys who believe Vx provides the best climb profile since it keeps you closer to the airport should you need to return after an engine failure. That may make some sense but in many planes the time it takes from climb to stall when the power quits in a Vx climb is shockingly quick. Many pilots wouldn't be able to prevent the stall and the corresponding altitude loss would more than offset the close proximity advantage. I climb at Vx when obstacles require it. In the absence of obstacles there's no reason and I use Vy and enjoy a much better view out the front, better cooling, more positive controls, and less stress on airframe and pilot.
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Yup. Not saying it's gospel, but I was taught by one of them.

This is a short quote from Michael Church on his opinion why you should climb at Vx rather than Vy for gaining altitude while remaining near the airport to enable safe turnarounds:

The entire argument for Vx climbs in single-engine airplanes requires more space than available here. In a nutshell, it's safer to climb as close as possible to the airport (Vx) than to stretch your climb out over a greater distance (Vy). If you insist at climbing at Vy, as you were almost certainly taught in primary instruction, no amount of skill in turning around is going to do much good: Vy climbs maximize altitude gain [in the shortest period of time], but cover too much ground in the process. Experimentation will quickly demonstrate that an increase in climb efficiency is of no benefit if your angle of climb takes you so far from the runway that you can't glide back after a successful turn.
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2011 Plane&Pilot Article - "Safe Turnarounds" by Michael Church

He also promotes having a minimum turn-around altitude (e.g. 500 AGL), and climbing on runway heading until you have reached 500 AGL before turning to your departure heading. Thus, if you have an engine failure before you have started your turn, you already know that you're landing more or less straight ahead and NOT attempting a turn-around.
 
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Guys really need to consider what they're flying as part of their decision. My big engine 180 at 63mph is climbing very steeply at a speed that's 10% below best glide speed while offering mushy control response. Instant loss of power in that pitch profile would be very hard to manage. At Vy my controls are crisp and the transition from nose-up climb to leveled off glide is very simple. Therefore I 'd much rather have an engine quit at Vy than Vx. Other planes may warrant a different strategy. Think about your own airplanes rather than accepting anyone's opinions as gospel. Especially mine! ;-)
 
Maciej said:
It happens, look at KLDJ, the pattern altitude is 800' and the Bravo shelf is 1200'+.
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azpilot said:
Wow!!! That is close! :hairraise:
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At my airport (KVUO) it's not a Bravo but a Charlie (though ATC always says remain clear of the Charlie). Published pattern altitude is 1026' MSL; floor of Charlie is 1100' MSL.
 
My Cfi-I has me convinced of the following:

IMC takeoff- Vx until 400' agl. Make a decision on what happens next before takeoff.

VMC takeoff- I already adjust based on what kind of trouble I'm trying to manage the risk for. Vy for the grass strip if taking off on 18. Engine quits, I put it on the road south of the field. A takeoff on 36- Vx to avoid the BIG TREES!
 
azpilot said:
That's nuts! Whenever I have flown under Bravo, my flight instructor advised me to stay at least 500' under the shelf.

I fly out of KCHD. There are three Bravo layers that all converge there. Pattern altitude is 2200. The three bravo shelves bottom out at 4000, 5000, 6000. The class Delta at KCHD tops out at 3000. I fly a 172 (soon to be archer). I don't get too worried about the bravo.
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Hmmm, maybe I should redefine "close"? When I fly into 3DA, I'm 400' under Charlie at FNT, and when I fly under DTW, I'm usually also 400' under Bravo, at Bravo's lowest point.


And as far as Vx and Vy take offs, my POH states to limit them due to cooling. I let OAT decide how long I maintain Vy.
 
Pilawt said:
At my airport (KVUO) it's not a Bravo but a Charlie (though ATC always says remain clear of the Charlie). Published pattern altitude is 1026' MSL; floor of Charlie is 1100' MSL.
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Now that IS CLOSE!
 
tawood said:
Now that IS CLOSE!
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It is, but it's not nearly as scary as it sounds. BTDT. It's a nice airport, and the smell on the 45 is really good.

What's scary is getting out of Oakland at 1400 under a 1500 Class B floor, with a transponder that's broadcasting 200 feet high. BTDT, too.
 
MAKG1 said:
It is, but it's not nearly as scary as it sounds. BTDT. It's a nice airport, and the smell on the 45 is really good.

What's scary is getting out of Oakland at 1400 under a 1500 Class B floor, with a transponder that's broadcasting 200 feet high. BTDT, too.
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What's the smell on the 45???
 
tawood said:
Now that IS CLOSE!
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Flying off Long Island to the west, absent a class-B clearance from NY approach (great crew, and probably a 40-60 proposition that you'll get it if you ask), without extended over-water ops or climbing above 7,000, requires beach-combing at 500' off the Rockaways south of JFK. The floor of the bravo through there is +05 ("upward from above" 500 ft MSL). Talking to JFK tower through there, you get traffic advisories for departing traffic with "caution wake turbulence".

"Helicopter traffic, opposite direction" keeps you on your toes. :D
 
Stewartb said:
Guys really need to consider what they're flying as part of their decision. My big engine 180 at 63mph is climbing very steeply at a speed that's 10% below best glide speed while offering mushy control response. Instant loss of power in that pitch profile would be very hard to manage. At Vy my controls are crisp and the transition from nose-up climb to leveled off glide is very simple. Therefore I 'd much rather have an engine quit at Vy than Vx. Other planes may warrant a different strategy. Think about your own airplanes rather than accepting anyone's opinions as gospel. Especially mine! ;-)
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This is why I discourage Vx climbs unless needed in most single engine planes. An engine failure between 20 and 50 feet in most single engine planes at Vx will result in a damaged airplane without a lot of practice at it. By the time you realize the engine has failed and push the nose down you typically will not have enough airspeed left to flare and stop the decent.

This is why I read about the story of instructor giving a phase check in a Stearman, when he simulated a power failure on take-off the student pushed the nose down so fast that the instructor was ejected out of the cockpit since he forgot to fasten his seatbelt, He was able to stay with airplane while the student completed the landing. This was due more to the high drag of the stearman than Vx climbs, but in steep climbs it often requires a very aggressive nose over to land successfully after a power failure at low altitude.

Brian
 
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Pilawt said:
At my airport (KVUO) it's not a Bravo but a Charlie (though ATC always says remain clear of the Charlie). Published pattern altitude is 1026' MSL; floor of Charlie is 1100' MSL.
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That's it, I am never complaining about Phoenix airspace again.
 
PPC1052 said:
Not at all. Look at my first post, second paragraph:
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What you wrote is not my experience. If you're not worried about having a huge blind spot in front of you, I don't think I can say anything to change that. The FAA recommends periodic shallow banks to clear the blind spot ahead even in a cruise-climb.
 
SixPapaCharlie said:
After watching the video circulating of the POV engine out, I got to thinking, why not climb out at Vx every time you take off and get as much altitude as quickly as possible?
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Vx doesn't get you altitude as quickly as possible, Vy does.
Vx. gets you altitude over the shortest distance.
 
For me, no question. Vx for initial climb, at least the first 500-1,000 feet in most cases. I want to get as high as possible in the shortest distance.


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brian];2010510 said:
My Cfi-I has me convinced of the following:

IMC takeoff- Vx until 400' agl. Make a decision on what happens next before takeoff.

VMC takeoff- I already adjust based on what kind of trouble I'm trying to manage the risk for. Vy for the grass strip if taking off on 18. Engine quits, I put it on the road south of the field. A takeoff on 36- Vx to avoid the BIG TREES!
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That's probably not a bad practice. It's certainly not the be-all end-all, but it seems a good general rule of thumb.

Some home work is required. If you depart IFR you should know all about climb gradients. 3.3, 1.6, and so forth.
 
So the winds are gusting and swirling at 45* off runway heading at 20+. There are structures and trees that may promote mechanical turbulence. Do you Vx-ers still launch at Vx?
 
Stewartb said:
So the winds are gusting and swirling at 45* off runway heading at 20+. There are structures and trees that may promote mechanical turbulence. Do you Vx-ers still launch at Vx?
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Not sure the wind should be a factor. Like Kritchlow hinted at, the climb gradient (the departure x00 feet per NM) is. Once the wheels leave the ground, you are surfing the wind and the concept of crosswind is gone. The wind is just a force vector. Crab into it and go.

Oh turbulence. The grass strip I fly out of has a row of trees not far away. A strong easterly wind means some rolling action on takeoff and landing. Can be less than fun.

Vx >> Vs
Va >> Vx

Fly the airplane.
 
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The difference between choosing Vx on an airliner sized runway and needing Vx to clear the trees on a short strip is reflected in these comments. Close proximity to my home strip wouldn't serve any purpose. Having as much airspeed as possible to handle the wind rotors and clear the trees is what matters to me. If you use Vx for obstacle clearance for long enough you'll have a couple of close calls that'll help shape your attitude towards not favoring Vx. Airspeed is life.
 
Can you explain what airspeed has to do with clearing the trees, or dealing with turbulence? As a low time pilot I would think altitude would be what you're after in this scenario, so there's clearly something that I'm not understanding.


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Wind gusts can create sudden changes in airspeed. Especially a gust quitting or coming around to the rear can be problematic at planned slow speeds.

In a 172, climbing out at 59 into a 10 knot headwind component that goes away will lose all your climb. 20 knots will put you in the pavement. Things go better at 70 + half gust factor.
 
The difference 10 mph can make as you're clawing your way up over trees while fighting gust rotors that are trying to upset the airplane is important. I often will hold my 180 on the ground for as long as I can to gain as much speed as I can before I unpin it from the ground to wrestle with the winds. You hear about maneuvering speed as a maximum. In reality a pilot should have a minimum speed (depending on conditions) for turbulent air controllability, especially when trying to climb away from the ground and obstacles following takeoff.
 
wilkersk said:
It also depends on how much performance you have. If you're in a C-172 with a full bag of gas and mom and the kids on board, you're gonna wanna climb efficiently to an altitude the will allow you to return if you have a problem.



On the other hand, if you're flying a P-51, with all 12 cylinders on that Merlin humming along, You'll wanna be nice to the neighbors and resist the urge to do a max-performance climb out every time. ;-)
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Um, no I wouldn't. Hahahhaha. The neighbors can suck it and enjoy the sound of a Merlin screaming near an airport, as God intended. :)
 
http://www.planeandpilotmag.com/pil...st-speaker-safe-turnarounds.html#.VreIupWh4id

Interesting article. It is kind of vague though, since there is absolutely no mention of runway length. I wasn't crazy enough to try this for real, so I fired up the simulator and used a C172S at 2550 lbs. Flew the numbers right out of POH for short field at that weight and Vx after 50 feet all the way to 500' AGL. You can do a 180 turn with 300 to 400' loss with 45 to 60 degree of bank. The bad news, it takes just under a mile to reach 500' agl at Vx, so out of a 2700' strip you won't make it back to the runway with only 200' left. If you fly it perfect you will be about 800' short of the runway. Usually I fly out of a place with a 6500' runway and this maneuver would work there as long as you don't stall. Even at 2550 lbs climbing at 80 IAS I am usually 800' agl before the end of the runway, so I will continue to climb at Vx until I clear whatever I need to and then climb at Vy and if the fan stops I will not try a 180. I would rather fly into something than risk turning like that and stalling since now the stall speed would be 74 knots in that steep of a turn but training tells you to fly 68 knots for best glide.

Vy gets you to altitude faster, with better engine performance and less gas used.
 
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Hey - I'm not the guy that will be turning back to the runway if my nearly 70 year old engine decides its time to retire. (Might, but not my first choice - it's the insurance company's airplane at that point and I'm not going to kill myself trying to save their airplane.)

Still, being "afraid" of Vx isn't smart. It's like the Bonanza guys you see driving their aircraft onto the pavement at over 100 MPH because they don't like the pitch attitude. If you need Vx - point the nose up and go. The more I get into this IMC stuff the more I like to being "up there" before I'm "over the trees". Vx is the answer. Running into a tree (or a hill) trying to keep the engine cool or keep a passenger comfy is pretty dumb. (A local guy killed himself a few months ago because he didn't climb fast enough to clear a hill. Likely a mechanical issue - but lesson learned - get "up there" before you run into something.)

I guess my CFI-I is rubbing off on me. Don't be a one trick pony - Vx to clear obstacles. Vy to get to altitude. Cruise climb to keep the engine happy. All depends upon what you see out the windscreen just before takeoff.
 
Vx also drastically reduces momentum and if the engine quits the chance of a stall is greater. You might be closer to the airport, but you're also 10-15 knots slower. Now you have to pitch down and lose that extra altitude to gain that airspeed.

That's my non-scientific answer.

I climb out at Vy under normal circumstances. If it's a short field or there are obstacles, I climb at Vx for a short period.
 
fiveoboy01 said:
Vx also drastically reduces momentum and if the engine quits the chance of a stall is greater. You might be closer to the airport, but you're also 10-15 knots slower. Now you have to pitch down and lose that extra altitude to gain that airspeed.

That's my non-scientific answer.
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That is oft-repeated. Have you ever tried climbing at Vx and then pulling power off without changing your pitch input? You don't come close to stalling. Think parabolic arc.
 
Ok, I'm not an aerodynamic expert.

All I know is the deck angle is pretty steep on a Vx climb and I also usually have two notches of flaps(drag) out. Engine quits, you're losing a lot of energy.
 
fiveoboy01 said:
Ok, I'm not an aerodynamic expert.

All I know is the deck angle is pretty steep on a Vx climb and I also usually have two notches of flaps(drag) out. Engine quits, you're losing a lot of energy.
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Luckily I have a CFI-I with a lot of gray hair and ratings to match. I was a Vx chicken. My thought "this is a high performance airplane and the stalls are eye openers!" His thought was likely "you dumb newbie - with a few 4-letter words that were filtered out before he spoke."

You can't be afraid of Vx and you need to know how the aircraft behaves at Vx. Sounds to me like it is time for a few stalls at 5000' agl. Went through a series of power off and (gasp) power on stalls a few months ago in the doctor killer. I like knowing where the edge of the envelop really lives. At least for me, Vx is 80 MPH and the aircraft won't stall until around 60 MPH. Momentum is less than at Vy, but I'm convinced that if the engine suddenly stopped I'm not falling out of the sky. (Very quickly pushing the column forward is something you have to consider.)

(Just not sure how to test that rotor comment. Then again, I don't usually fly when the winds are a cracking like that..)
 
fiveoboy01 said:
Ok, I'm not an aerodynamic expert.

All I know is the deck angle is pretty steep on a Vx climb and I also usually have two notches of flaps(drag) out. Engine quits, you're losing a lot of energy.
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I tend to think you are right. By definition, Vx is close to stall and in order to intercept maximum glide you will have to lower the nose. The nose may have a tendency to drop with power removed but I'm willing to bet that at low altitude, the natural response will be to hold the nose up away from the ground. A little extra safety margin is nice.
 
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