Let's talk about Vx

SixPapaCharlie

SixPapaCharlie

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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?

That guys engine froze and he had taken off pretty flat.
I don't have the link handy but someone can post it for reference if you haven't seen it.
He had been airborne for a bit but didn't have enough altitude to have a lot of options.

So why not Vx every launch (excluding under a bravo shelf, etc)
 
It's what I do in the Skylane. Full Power/RPM and pitch for Vx on initial climb out, transition to Vy around 300-400ft AGL and reduce power/rpm to 23squared
 
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?

That guys engine froze and he had taken off pretty flat.
I don't have the link handy but someone can post it for reference if you haven't seen it.
He had been airborne for a bit but didn't have enough altitude to have a lot of options.

So why not Vx every launch (excluding under a bravo shelf, etc)
Click to expand...

Because Vy is the fastest climb. Vx is the steepest angle of climb (used when clearing an obstacle). Vx is altitude/distance, Vy is altitude/time.

And as for climbing at Vy, that's how I was trained. I understand some higher performance aircraft may get other treatment.

John
 
Vx is a less efficient way to fly. Vy gives you the maximum altitude in the shortest time. This saves fuel, as well as gets you to a higher altitude faster. Second, being at a greater altitude for the same given time, may offset Vx being closer to the field.
 
As several have said, Vy is the appropriate speed.

Another factor is that Vx climbs are rough on the engine due to reduced cooling. They also give you poor forward vision. In some airplanes, Vy is already a bit obstructed ahead, at full power. Vx is a lot worse.

Perhaps a better question is why not take off with as much flap as the POH allows (10 deg for a 172, 20 for a 182, 25 for a Cherokee), and climb at Vy for that configuration?
 
Well shave on me. Clearly I've misunderstood this.
I thought x got you higher quicker and y got you higher slower.

The distance part I got but the time part, I guess I need to rethink
 
I give up. My thumbs are to clunky for this phone
 
Vy unless you're in an RV, then you know what to do!
 
If EdFred was a bit more active on the board, this thread might make him develop a video that rivals this creation.

(where did he disappear to? Off galavanting with Henning?)
 
SixPapaCharlie said:
Well shave on me. Clearly I've misunderstood this.
I thought x got you higher quicker and y got you higher slower.

The distance part I got but the time part, I guess I need to rethink
Click to expand...
Vy is the speed that will give you the greatest altitude within a given time. Vx is the speed that will give you the greatest altitude gain within a given distance
 
this is a good pic of it:

1302vx-vy-climb.jpg


vx gets you more height with less travel, vy gets you more height sooner(in time).
 
In the SR22 I go Vy to CAPS altitude (here come the haters) and then I pitch down to keep my temps under 380.
 
If you are at Vx and have an engine failure you are closer to stalling (higher angle of attack and slower), than if you are at Vy with an engine failure.
 
MAKG1 said:
As several have said, Vy is the appropriate speed.

Another factor is that Vx climbs are rough on the engine due to reduced cooling. They also give you poor forward vision. In some airplanes, Vy is already a bit obstructed ahead, at full power. Vx is a lot worse.
Click to expand...

Is this really true? Sure, your plane is angled up more and away from traffic that is below you flying parallel to the earth, but your direction of flight is up too. What you don't see as well with a higher climb angle are planes that are currently in front of and below you. But why would they be any more likely to hit you than the planes that are in front of and higher than you? You can see the planes that are above you and descending better, which are the planes I would be most concerned about. Planes below me as I am climbing out which are heading towards me are probably heading to the airport, and thus are more likely to be staying at their same height, or descending for approach to landing--in which case I should be climbing out of their way. As a result, the greater angle of climb is an advantage in terms of seeing what may hit me, and avoiding them.

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?
 
RyanShort1 said:
If you are at Vx and have an engine failure you are closer to stalling (higher angle of attack and slower), than if you are at Vy with an engine failure.
Click to expand...

And don't forget, at a lower altitude, to boot.
 
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. ;-)
 
I don't like the letter 'x' so I try to avoid Vx, flying in Class X airspace, doing math problems such as x + 1 = 4, and I refuse to watch the new X Files. luckily I like the letter 'V' or I'd have NO speeds to fly at.
 
PPC1052 said:
Is this really true? Sure, your plane is angled up more and away from traffic that is below you flying parallel to the earth, but your direction of flight is up too.
Click to expand...

There are a lot of airplanes that climb faster than a 172 at Vx. And not all potentially conflicting traffic is departing, especially if the airport is uncontrolled. Obstructions and birds can also be issues. As can neighboring airports or helicopters.

You can't see directly ahead in quite a lot of airplanes at Vx.
 
MAKG1 said:
There are a lot of airplanes that climb faster than a 172 at Vx.
Click to expand...
Sure. But I am dense, and don't understand the implications of that fact in this context. (And I don't own a 172, so I am not sure if you are saying that's my plane or the other plane to be avoided.)


MAKG1 said:
And not all potentially conflicting traffic is departing,
Click to expand...
No, I would think not. In fact, the more likely conflicting traffic when I am taking off and still in the climb would be arriving traffic.


MAKG1 said:
Obstructions and birds can also be issues. As can neighboring airports or helicopters.
Click to expand...
Ok, sure.

MAKG1 said:
You can't see directly ahead in quite a lot of airplanes at Vx.
Click to expand...
This is really the crux of the matter. The only reason why you can't see "directly ahead," assuming you are meaning "directly ahead" as defined by the plane's trajectory is the increased angle of attack. But is that difference really that great? This is what I don't know if this has been studied.

Now, if you mean "directly ahead" as defined as "at my same altitude", then why am I more likely to hit that plane than some plane that is above my altitude (and likely descending toward me), at which my view is now less obstructed due to my upward pitch?
 
The difference works out to around 2-3 deg in pitch. It makes the difference between seeing the horizon ahead and not seeing it ahead in almost all the airplanes I fly. The horizon ahead is a danger point for midairs -- arriving traffic will be level at pattern altitude, and you might be climbing through it, for instance.

Maybe you're comfy with it, but I don't like to fly with a big blind spot exactly where I'm going, if I can help it. You can fly S turns, but it really is a much better option to climb out no faster than Vy. For a high performance aircraft, you can fly even faster if visibility is an issue; e.g., in a 182 at low DA, I'll generally fly Vy to TPA and then 90 knots afterward. In a Warrior, it's Vy (for weight -- it varies rapidly well below max gross) all the time.
 
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MAKG1 said:
Maybe you're comfy with it, but I don't like to fly with a big blind spot exactly where I'm going, if I can help it.
Click to expand...

But the blind spot is not right where I'm going. It's below where I am going. My plane is climbing and I am looking up. There is always a blind spot, no matter what my attitude. But it's not in the direction of travel.
 
PPC1052 said:
But the blind spot is not right where I'm going. It's below where I am going. My plane is climbing and I am looking up. There is always a blind spot, no matter what my attitude. But it's not in the direction of travel.
Click to expand...

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.
 
My first choice is to use the - I know, old school thinking - POH for Normal Procedures where it discusses Normal Takeoff climb airspeeds.
Unless obstacles or a short field, then use the Short Field Takeoff procedures also in the same section.
 
RyanShort1 said:
If you are at Vx and have an engine failure you are closer to stalling (higher angle of attack and slower), than if you are at Vy with an engine failure.
Click to expand...

If you're at Vx and have an engine failure, you're closer to the runway you took off from, so better chance of turning back. If you're high enough . . .

I climb at Vx initially, until I'm over nearby obstacles, then lower the nose to Vy to whatever cruise altitude I choose.
 
Hank S said:
If you're at Vx and have an engine failure, you're closer to the runway you took off from, so better chance of turning back. If you're high enough . . .



I climb at Vx initially, until I'm over nearby obstacles, then lower the nose to Vy to whatever cruise altitude I choose.
Click to expand...

Actually that can backfire on the impossible turn scenario. Especially in strong winds.
 
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wilkersk said:
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. ;-)
Click to expand...

:nonod: will not resist, c'mon man, we're talking Mustang here ;)
 
If you think about the actual direction the plane is going and that you might hit something along that line (other lines don't matter), then the higher your angle of attack, the more you are getting your view of that line blocked.
 
PPC1052 said:
But the blind spot is not right where I'm going. It's below where I am going. My plane is climbing and I am looking up. There is always a blind spot, no matter what my attitude. But it's not in the direction of travel.
Click to expand...

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:
 
PPC1052 said:
KEYE the pattern is 1800, and the shelf of the C is 2100.
Click to expand...

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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