Departures: Vx, Vy, or Zoom

Jay Honeck

Jay Honeck

Touchdown! Greaser!
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Jay Honeck
In another thread, there has been a lively discussion over whether a zoom climb to pattern altitude is as safe (however safe is defined) as the more normal Vy climb out.

Here is the plane:

An RV-8A with a 180 HP Lycoming O-360, and a Hartzell constant speed prop.

Temperature: 91 degrees.

Procedure: Start stopwatch at brake release. Record time as altimeter hits 1000'.

Results:

Vy Climb at 100 knots, from brake release to 1000' took 59 seconds.

Zoom Climb. Break ground and accelerate to 120 knots in ground effect, with a +1G pull, took 61 seconds to 1000'.

(I didn't try a 140 knot version of this pull up. That will wait till next time.)

Vx Climb at 75 knots. Within ten seconds, I aborted this departure when the deck angle exceeded 45 degrees up. The feeling of impending doom so close to the ground had Mary muttering sweet nothings to me in the intercom. :D

So there you have it -- a COMPLETELY unexpected result. A "normal" (in a lower performance plane) Vy departure felt so unsafe that we aborted and dropped the nose to Vx.

A Vx departure would be quicker over an obstacle, and may be as fast to 1000', but the discomfort and lack of forward visibility made this option too unsafe for our tastes. YMMV.

Note: Original post edited to correct Vx versus Vy error.



Sent from my Samsung Galaxy S3...
 
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Jay Honeck said:
In another thread, there has been a lively discussion over whether a zoom climb to pattern altitude is as safe (however safe is defined) as the more normal Vy climb out.

Here is the plane:

An RV-8A with a 180 HP Lycoming O-360, and a Hartzell constant speed prop.

Temperature: 91 degrees.

Procedure: Start stopwatch at brake release. Record time as altimeter hits 1000'.

Results:

Vx Climb at 100 knots, from brake release to 1000' took 59 seconds.

Zoom Climb. Break ground and accelerate to 120 knots in ground effect, with a +1G pull, took 61 seconds to 1000'.

(I didn't try a 140 knot version of this pull up. That will wait till next time.)

Vy Climb at 75 knots. Within ten seconds, I aborted this departure when the deck angle exceeded 45 degrees up. The feeling of impending doom so close to the ground had Mary muttering sweet nothings to me in the intercom. :D

So there you have it -- a COMPLETELY unexpected result. A "normal" (in a lower performance plane) Vy departure felt so unsafe that we aborted and dropped the nose to Vx.

I have no doubt that a Vy departure would be quicker to 1000', but the discomfort and lack of forward visibility made this option too unsafe for our tastes. YMMV.



Sent from my Samsung Galaxy S3...
Click to expand...

I think you have VY (best rate) and VX (best angle) mixed up.
 
Jay Honeck said:
Vx Climb at 100 knots, from brake release to 1000' took 59 seconds.
[...]
Vy Climb at 75 knots.
Click to expand...

You have these reversed. Vx (best angle) is always less than Vy (best rate). They become equal at the service altitude.

So you've done the experiment at Vy vs zoom. Vy wins.
 
I'm a vy guy, however pitching for vx ain't that mad of a idea, after all you would have the max altitude for remaining runway that way, if your plan is to land on the remaining runway, if you're flying out of a OK sized runway in a 7AC, vx might be the safer route.

My home drome has fields to the right of centerline, I will visualize a landing on those fields on takeoff, our plane won't get down and stopped before the end of runway on most take offs, if a failure occurs.

The biggest thing is know your outs around the airport, what field, road, etc would you land in for a t/o engine failure? Can you get down & stopped on the runway in your airframe?
 
No further questions of this witness.

Jay Honeck said:
In another thread, there has been a lively discussion over whether a zoom climb to pattern altitude is as safe (however safe is defined) as the more normal Vy climb out.

Here is the plane:

An RV-8A with a 180 HP Lycoming O-360, and a Hartzell constant speed prop.

Temperature: 91 degrees.

Procedure: Start stopwatch at brake release. Record time as altimeter hits 1000'.

Results:

Vx Climb at 100 knots, from brake release to 1000' took 59 seconds.

Zoom Climb. Break ground and accelerate to 120 knots in ground effect, with a +1G pull, took 61 seconds to 1000'.

(I didn't try a 140 knot version of this pull up. That will wait till next time.)

Vy Climb at 75 knots. Within ten seconds, I aborted this departure when the deck angle exceeded 45 degrees up. The feeling of impending doom so close to the ground had Mary muttering sweet nothings to me in the intercom. :D

So there you have it -- a COMPLETELY unexpected result. A "normal" (in a lower performance plane) Vy departure felt so unsafe that we aborted and dropped the nose to Vx.

I have no doubt that a Vy departure would be quicker to 1000', but the discomfort and lack of forward visibility made this option too unsafe for our tastes. YMMV.



Sent from my Samsung Galaxy S3...
Click to expand...
 
Zoom is the most fun. Then VX if you have enough poop to be hanging from the prop. VY is boring.

I can't believe you bailed on the VX because the deck angle was too high.
 
So a vx departure was too scary to continue, but zooming 140 without enough runway left to land on felt fine? Got it.
 
Altitude as soon as you can get it is your friend if you have a problem.

RT
 
When it comes to sub 4K runways in these spam cans, I'm a Vx guy. The concept of 'runway remaining' is critical to these engine out scenarios. Vy is not always ideal; it doesn't matter if you get to altitude quicker, if it takes your gliding bubble way the heck out of the field.

In most scenarios you simply are NOT gonna have sufficient runway remaining. Vy hurts you in that category, Vx helps you. Furthermore, Vx makes the impossible turn possible because in energy states where insufficient runway remains straight ahead, the Vx climb will have you significantly closer to the departure runway than Vy.

Once you resign yourself to the idea that you won't have sufficient runway remaining, then ninethreekilo's advice rules: I.E. you're better off doing a good pre-takeoff study of the suitable surfaces available to you directly left and right of your departing runway environment. In many instances, your departing field has cross runways or grass fields to the left or right of your departure corridor, and perhaps similar options just outside the airfield, which make a 1/2 to 3/4 of an impossible turn all of a sudden very possible energy-wise.

All in all, I rather take the fence at a nice, slow and lightweight 20-40knots with the rims on pavement and my boots thru the firewall, than take the Earth at 90Knots and overbanked while short of the intended spot.... which is why part 23 twins are an oxymoron, but I digress.
 
Jay Honeck said:
In another thread, there has been a lively discussion over whether a zoom climb to pattern altitude is as safe (however safe is defined) as the more normal Vy climb out.

Here is the plane:

An RV-8A with a 180 HP Lycoming O-360, and a Hartzell constant speed prop.

Temperature: 91 degrees.

Procedure: Start stopwatch at brake release. Record time as altimeter hits 1000'.

Results:

Vx Climb at 100 knots, from brake release to 1000' took 59 seconds.

Zoom Climb. Break ground and accelerate to 120 knots in ground effect, with a +1G pull, took 61 seconds to 1000'.

(I didn't try a 140 knot version of this pull up. That will wait till next time.)

Vy Climb at 75 knots. Within ten seconds, I aborted this departure when the deck angle exceeded 45 degrees up. The feeling of impending doom so close to the ground had Mary muttering sweet nothings to me in the intercom. :D

So there you have it -- a COMPLETELY unexpected result. A "normal" (in a lower performance plane) Vy departure felt so unsafe that we aborted and dropped the nose to Vx.

I have no doubt that a Vy departure would be quicker to 1000', but the discomfort and lack of forward visibility made this option too unsafe for our tastes. YMMV.



Sent from my Samsung Galaxy S3...
Click to expand...

45 degree up pitch? For how long? :rolleyes2:


You really need to do a basic flight review and try to understand the correct terminology. :nonod:
 
GCA319 said:
I think you have VY (best rate) and VX (best angle) mixed up.
Click to expand...

I concur.

And, what's a +1 G pull? All constant speed climbs at any rate are +1 G. No accelerating climb is +1 G. And if it's really +1 G all the time, you're still flying around in ground effect.
 
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I just watched the fun of the last thread, and now it's gotta be repeated??

Seems Veffinstupid to me to keep beating the horse.
 
THere needs to be an investigation on who signs Jay's flight review.

Every post he makes digs a deeper hole.
 
Can only hope the NSA is watching who will inform Homeland Security who will tell the TSA and the FAA and eventualy a notice of investigation letter will be in the mail while the local FBI watches.
 
Give it up Jay. Now you're not only wrong, you look like an RV-idiot. Maybe you actually are.....

FTLOC, would you just admit you like the macho fun.
You're much farther from the end of the runway and you give up any option to get it stopped on the runway, when the engine fails at 120 knots, intending to do a 140 kt zoom climb.

GIVE IT A REST.
 
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I think there is one set of data missing from your stopwatch timings. You also need distance so you can compare Vx to Vy to zoom in that axis, too.

When you start/stop the timer, you need the mark the distance traveled.
 
Matthew said:
I think there is one set of data missing from your stopwatch timings. You also need distance so you can compare Vx to Vy to zoom in that axis, too.

When you start/stop the timer, you need the mark the distance traveled.
Click to expand...


Good idea.....:yes::yes:

Just have Mary note the lat/lon where you launch from and then hit store waypoint when getting to 1000 agl....

It will be an interesting experiment for sure...

Do that for a VX climb... a VY climb and a zoom climb...;)
 
So, he went out, did some tests and learned something and had the guts to post it here... Perhaps some here can learn as well. How many believed the difference would be under 5% in time to altitude? Not really that significant...

What he hasn't yet determined is how far down the runway 1000 ft is reached for each method. This is good info to know as well. With his info better known, he can then determine his tradeoffs vs risk, etc... for any particular takeoff situation.
 
Rotate 92kts, positive rate gear up, nose down accelerate to Vyse+5(117 kts) to 200' or obstacle clearance, nose down for 125kts props back to 2450 and mixture back to 50°LOP and climb out to whatever my cruise altitude will be. That's the first 5-10 seconds depending on departure altitude, I'll be through 1000' in under 30 seconds.
 
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skidoo said:
So, he went out, did some tests and learned something and had the guts to post it here... Perhaps some here can learn as well. How many believed the difference would be under 5% in time to altitude? Not really that significant...

What he hasn't yet determined is how far down the runway 1000 ft is reached for each method. This is good info to know as well. With his info better known, he can then determine his tradeoffs vs risk, etc... for any particular takeoff situation.
Click to expand...
He also needs to determine V1.
 
Jim Logajan said:
You have these reversed. Vx (best angle) is always less than Vy (best rate). They become equal at the service altitude.

So you've done the experiment at Vy vs zoom. Vy wins.
Click to expand...

Ha! They are reversed on our checklist!

Stupid homebuilt. :D

Two pilots with years of experience testing a departure procedure and neither of us noticed that Vx and Vy were reversed. D'oh! :rolleyes:
 
MAKG1 said:
I concur.

And, what's a +1 G pull? All constant speed climbs at any rate are +1 G. No accelerating climb is +1 G. And if it's really +1 G all the time, you're still flying around in ground effect.
Click to expand...

+1G over normal gravity = 2G. Unless you're on the moon. Then it's 1.25 Gs.
:D
 
RotorAndWing said:
45 degree up pitch? For how long? :rolleyes2:


You really need to do a basic flight review and try to understand the correct terminology. :nonod:
Click to expand...

You really need to develop a civil tongue.

+45 degrees was what the plane required to hold 75 knots at full throttle at takeoff. Is this difficult to understand?
 
How many cared about the time difference when so many other obvious stupidities were involved in the maneuver?

skidoo said:
So, he went out, did some tests and learned something and had the guts to post it here... Perhaps some here can learn as well. How many believed the difference would be under 5% in time to altitude? Not really that significant...

What he hasn't yet determined is how far down the runway 1000 ft is reached for each method. This is good info to know as well. With his info better known, he can then determine his tradeoffs vs risk, etc... for any particular takeoff situation.
Click to expand...
 
jmn444 said:
I just watched the fun of the last thread, and now it's gotta be repeated??

Seems Veffinstupid to me to keep beating the horse.
Click to expand...

The difference in time to 1000' AGL between the two techniques was an inconsequential 2 seconds -- well within the margin of measuring error.

I personally find that fascinating and surprising, but if you don't wish to participate I'm sure there's something on the cooking channel...
 
skidoo said:
So, he went out, did some tests and learned something and had the guts to post it here...
Click to expand...

Agreed. I think he did great by performing the experiment. I should have posted that sentiment earlier.

I try to treat my knowledge of the world as always provisional. Sometimes mistakes in important things can last decades. For example, in 1921 zoologist Theophilus Painter published his count of human chromosome pairs - 24. Others confirmed his count. He was held in some regard, so it is possible that any other number might have been dismissed by the counter as an error. After all, perhaps if someone else counted only 23 pairs it was likely they simply missed a pair.

It was not until 1956 that the count was corrected to 23 pairs.

Perhaps some here can learn as well. How many believed the difference would be under 5% in time to altitude? Not really that significant...

What he hasn't yet determined is how far down the runway 1000 ft is reached for each method. This is good info to know as well. With his info better known, he can then determine his tradeoffs vs risk, etc... for any particular takeoff situation.
Click to expand...
In theory he could get approximate values using an app on his tablet computer that records GPS track over time. He'd need something similar to the CloudAhoy app available for iPads.

The one textbook on my shelf that goes into the theory of estimating values like Vx and Vy is "Aerodynamics, Aeronautics, and Flight Mechanics" by McCormick (not a great text, but adequate for my purposes when I first bought it years ago.)
 
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kgruber said:
THere needs to be an investigation on who signs Jay's flight review.

Every post he makes digs a deeper hole.
Click to expand...

When IS the last time you actually flew? Do you really have no curiosity about this sort of thing? Is it that you resent those of us who can actually go out and test this stuff, or are you just naturally a curmudgeon?

Why are you on a piloting group again?
 
Matthew said:
I think there is one set of data missing from your stopwatch timings. You also need distance so you can compare Vx to Vy to zoom in that axis, too.

When you start/stop the timer, you need the mark the distance traveled.
Click to expand...

I agree. After we were done I asked Mary if she had noted our position in relation to the runway as we passed through 1000', but sadly she did not.

I was too busy flying to notice. Next time we will note that position, because that's an important parameter.

My gut feel is that they were very similar, perhaps with the zoom climb having a bit of an edge. (AKA: I think we were closer to the runway environment when we reached the 1000' target.)
 
Matthew said:
Well - now you have an excuse to fly again!
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Yes, but oh, how Gruber will pout and whine, along with his buddy Bower! I would hate to aggravate them so by actually FLYING! :D

Alas, I'm done flying now till Sunday -- when we go up with our aerobatics instructor. I can't WAIT to hear the grounded kiwis here whine and moan when I post about THAT experience!

:rolleyes:
 
Jay Honeck said:
You really need to develop a civil tongue.
Click to expand...

What, for asking a simple question? :dunno:


Jay Honeck said:
+45 degrees was what the plane required to hold 75 knots at full throttle at takeoff. Is this difficult to understand?
Click to expand...

Your aerodynamics aren't making sense. Are you stating that the airplane maintained a 45 degree up pitch maintaining 75 knots indefinitely? 1 minute? 5 minutes? From ground to 1000'?

I find it hard to believe an RV8 with a 180hp engine is capable of 45 degree sustained climb from take off roll to top of traffic pattern.

As far as my other comment:

You really need to do a basic flight review and try to understand the correct terminology.
Click to expand...
Sorry, sometimes the truth hurts. :rolleyes:
 
Why don't you list the credentials and experience of those who support your half-asx theories with those who have pointed out the idiocy and see how they stack up?

Jay Honeck said:
Yes, but oh, how Gruber will pout and whine, along with his buddy Bower! I would hate to aggravate them so by actually FLYING! :D

Alas, I'm done flying now till Sunday -- when we go up with our aerobatics instructor. I can't WAIT to hear the grounded kiwis here whine and moan when I post about THAT experience!

:rolleyes:
Click to expand...
 
So what I learned in PPL training still holds:
Vx(best angle) is a slower speed which gives me the most altitude in the shortest distance traveled but takes longer to get there, and Vy(best rate) is a faster speed which gives me the most altitude in the fastest amount of time but requires a longer distance to get there. Any other speed is a compromise and provides an intermediate result. Vx is good for clearing an obstacle, but otherwise Vy is best because it gives you a better safety margin if your engine fails you.

The physics remains the same.

Did I mess it up.
 
Did you fly VY corrected for weight?
 
Henning said:
Rotate 92kts, positive rate gear up, nose down accelerate to Vyse+5(117 kts) to 200' or obstacle clearance, nose down for 125kts props back to 2450 and mixture back to 50°LOP and climb out to whatever my cruise altitude will be. That's the first 5-10 seconds depending on departure altitude, I'll be through 1000' in under 30 seconds.
Click to expand...

Can you say that three times in rapid succession?
 
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