Angle of climb/rate of climb

[dboy]

Hello

I don't know if this is the right place to put this topic but i need some explanation.
I don't seem to understand if you climb at vx you will gain an altitude in the shortest distance and if you climb at vy you gain the most altitude in the least time.

If you climb at vx and you reach 2000' in, let's say, 5nm while in the mean time you reach in 5nm at vy, 1300' why in the hell are going to climb at Vy to gain altitude in the shortest time?????

I've been looking up these things but they are always refering to excess power for Vy and excess thrust for Vx. Why not taking excess power into account for Vx.(too theoretically for me):ugh:

I simply do not understand, who can explain a bit?

Tx

[FlyingStone]

I'll try to simplify this a bit...

The simple vertical profile of a normal cross country flight (or every other one at that) is: takeoff, climb, cruise, descent and landing. So, since aviation isn't free (hope to see a day when Avgas/Jet A-1 will be free), you want to fly as many nautical miles per minute/hour you can. In order to do that, you need to have as high ground speed as you can, but if you want to save some fuel, you should fly higher - and to fly higher you need to climb.

The optimum between vertical and horizontal speed during climb is usually (C172/PA28/C152/....) Vy, Vy+5 or Vy+10, it depends on conditions... Climbing with Vy instead of Vx also gives you additional pros: engine cooling is much (MUCH) better since the forward speed is higher, margin from Vx to stall is usually only 10-15 knots, which means that if you get a 10 knot wind shear or forgot to check the ASI for few seconds, it wouldn't be nice... Also, most AFM/POH (especially Cessna's) say that climbing at Vy or higher gives you better forward visibility, which has proven useful many times in VFR where we follow "see and be seen" rule...

To extend the issue to IFR: which climb would expedite the traffic departing behind you - climb where you would be at a "safe" level (level at you must be in order that succeeding aircraft can depart) 2 NM from airport in 10 minutes or climb where you would be at the same level 15 NM from airport in 3 minutes? Do the math and it will come to you. :)

But still, if you need scientific explanations, there are million of books available which you can study...

[212man]

Think of it in terms of "not hitting the ground!" Gradient is the means to avoid terrain (or achieves minimum SID levels etc) whereas Rate gets you to more efficient or useful levels quicker, assuming that the gradient it gives is adequate to avoid terrain. If not, adjust speed to achieve the gradient required and accept the prolonged climb period. As they say "better to be late in this life than early into the next!"

[DFC]

The best rate of climb speed Vy will cause one to gain the most height in a given time period.

Imagine you are taking off with a 610ft hill 1nm ahead.

If the aircraft climbs at 60Kt (Vy) and tghis gives a rate of climb = 600ft/min the aircraft will be 600ft at the hill and will impact 10 ft below the top.

The whole idea of flying at the speed for best angle is to sacrifice a small amount of climb rate in return for a (proportionally) bigger reduction in speed.

Let's say that we now fly the same example at the best angke speed of 50Kt(Vx). This gives us a reduced rate of 550ft per minute.

However, even though we are climbing at a reduced rate it now takes longer to travel the 1nm to the hill and you can simply work it out that we will now

travel 5/6nm in 1 minute (climb 550ft)

and then climb 110ft in the remaining time it takes to travel the 1/6nm left to the hill.

Therefore despite climbing at a reduced rate we are now at 660ft as we safely pass over the hill.

[johns7022]

Gee wiz guys, why make it so complicated....

Think of these V speeds as tools you can use as a pilot..

Vx: Your flying along, you look forward and see a big hill up ahead...Vx is the speed in which you take to gain the most altitude in a given distance...and yes it is the steepest climb angle...but it's about obstacle clearance....you only have some much distance to get over this thing...in a small plane this speed might be 60kts...

Vy is more about the relationship between forward speed and vertical speed....meaning if your goal for example is to get up to altitude the quickest...you use Vy...now Vy on this same little plane might be 70 kts...it's a quicker speed then Vx, because speed translates into time, time can translate to FPM...and when it comes to getting up to alt...Max FPM is what we are chasing....

Another way to look at Vx vs Vy...imagine your need to get out of a canyon and there is no way you just fly straight out of it, so you do a circling climb, effectively making no forward progress to your destination......you could use Vy under these circumstances as that will give you the lest amount of time to get up and over...

Vx is a trade off of FPM and forward distance traveled, trading it for a higher climb angle vs Vy...

[flythisway]

Hello D boy-you must be wondering why nobody is answering your questions. I have highlighted your questions to make it easier for the experts

Hello

I don't know if this is the right place to put this topic but i need some explanation.I can answer this one--Probably not, because as yet no one on here has found the answer on the internet. (these types of question are outside the knowledge of most instructors)



I don't seem to understand if you climb at vx you will gain an altitude in the shortest distance and if you climb at vy you gain the most altitude in the least time.The question is why?

If you climb at vx and you reach 2000' in, let's say, 5nm while in the mean time you reach in 5nm at vy, 1300' why in the hell are going to climb at Vy to gain altitude in the shortest time?????The question is in bold

I've been looking up these things but they are always refering to excess power for Vy and excess thrust for Vx. Why not taking excess power into account for Vx.(too theoretically for me) I simply do not understand, who can explain a bit? Tx

The question is in bold

So D boy, has anyone answered your question(s) yet?

[Big Pistons Forever]

Flythisway

The purpose of this forum is to exchange information within the flying training sphere. If all you want to do is take cheap shots at instructors while providing no value added to this topic what so ever, than I strongly suggest you go find another audience to bother.

[dboy]

Yes some of the answers i knew already, but somehow i feel that i don't understand completely.

Why do they refer "Thrust" with Vx and why "Power" with Vy?
And pure aerodynamically? Do i have more drag with Vx or Vy??

grtz

[puntosaurus]

Well start with some definitions.

Thrust is a force, and power is a rate at which work is done. Work is the product of force times the distance moved in the direction of the force.

Vx is the speed at which you get the best angle of climb. Climbing is a matter of overcoming the force of gravity. Therefore the more force (excess of thrust over drag) you have, the better you can do it (ingoring all other considerations). So thrust is a key issue

Vy is the speed at which you get the best rate of climb. Rate of climb is connected to rate of delivery of work, and therefore power is a key issue.

Vy is the lowest point of the drag curve. Any other speed (including Vx if not the same) will have higher drag.

Hope that helps.

[24Carrot]

I'm not an FI, but by chance I was reading up on exactly this today.

Excess power matters for Vy because:

At max throttle, for any given speed, your engine produces constant power (ignoring tedious air density effects). This means some thing or things are steadily gaining energy over time. In this case, flying at a constant speed, your aircraft is NOT gaining kinetic energy (ignoring the tedious air density effects again).

However it is gaining height, which is potential energy. The more power that ends up in this category, the faster you go up. This is "excess power", and it is nice to have some.

As your wing generates lift and drag, you also disturb the air you pass through, handing out kinetic energy to the atmosphere at a steady rate. The more power wasted on the atmosphere, the slower you go up.

For aeroplanes, the power available from the engine depends on airspeed. Power lost to the atmosphere also depends on airspeed. There is a speed, Vy, at which you have the maximum difference between the two, leaving the most "excess power" left over to climb at the fastest rate.

==

The speed for best angle of climb is more complicated.

It also depend on the excess power, ie engine power minus power lost moving the atmosphere around.

You are trying to maximise Rate of Climb divided by TAS.

As we have seen, Rate of Climb is proportional to excess power, so if you plot Excess Power (Engine Power minus power lost to the atmosphere) versus TAS, the point on the graph with the steepest gradient gives you the best ratio of Climb Speed to TAS.

The reason eg Trevor Thom talks about excess thrust is that for a physicist or an engineer, a Power is a Force times a Speed.

Engine Power is Thrust times TAS.
Power Required is Drag times TAS.
Excess Power is (Thust-Drag) times TAS.

My "max gradient" is Excess Power divided by TAS, ie
Thrust - Drag or "Excess Thrust" as Trevor Thom calls it.

Hope that helps.

PS I see that puntosaurus made some of the same points while I was typing, but I've typed too much already, I think...

[dboy]

Tx, helped a lot more to understand.

But what do you mean with:"The more power wasted on the atmosphere, the slower you go up."

And if i inderstand well, with the angle of climb the engine delivers more energy into potential energy and less kinetic energy like in Vy.
cheers

[Piper.Classique]

See How It Flies (http://www.av8n.com/how/) Is a useful resource. Take a look at chapter 1 to clear up the differences between power and energy
But don't get obsessed by this small aspect of your flying, as long as you know that climbing at a lower airspeed than that for optimum rate of climb will cover less ground during the climb thus give you a steeper angle (despite the somewhat poorer rate of climb) For most light aircraft it doesn't make a lot of difference, much less than a few knots of headwind!


But what do you mean with:"The more power wasted on the atmosphere, the slower you go up."
I think he is saying the more induced drag you create, the slower you go up. Just another way of putting it......

[24Carrot]

The more power wasted on the atmosphere, the slower you go up.Every second, your engine releases some energy from the fuel it burns. Because of the Conservatrion Of Energy, it has to go somewhere. There are three obvious places:

1) Your aircraft can go faster, i.e. get Kinetic energy. But you are climbing at a constant speed, so no energy goes here.

2) Your aircraft can go higher, i.e. acquire Potential Energy. This is what you want.

3) The atmosphere can be moved about, i.e. acquire kinetic energy. You are right, this isn't really "wasted". I should have said it is an inevitable consequence of moving the aircraft through the air (parasite drag) and generating lift (induced drag). Parasite Drag involves a random swirling of air (Kinetic Energy but no momentum), and Induced Drag involves a downwards directed flow of air (Kinetic Energy and momentum).

The energy goes partly to 2, and partly to 3. The more that ends up in 2, the better for your climb.

Incidentally, if you are happy dealing with vector components of forces, there is a more direct explanation for "Excess Thrust".

Consider first a glide approach. Lets say Thrust is actually zero. Drag is still there, and because you are not accelerating (just moving steadily downwards) Lift equals Aircraft Weight (very closely) and Drag is Weight divided by the Lift/drag ratio.

Say LDR=10 so Drag is 10% of aircraft weight. If you descend at 6 degrees, (1 in 10) then 10% of Gravity (ie Weight) is pulling you along and making up the "Thrust Deficit". 10% of say 65kts is about 650 fpm so this makes sense.

If you extend flaps or the prop is windmilling the LDR might be 8, and you need to go down at 1 in 8 to overcome the Thrust deficit and maintain speed. This is about 800 fpm.

In the climb, you need Excess Thrust to overcome a component of Gravity which still depends on your angle of climb, but now works against you.

And I agree with Piper Classique, "See How it Flies" is a wonderful resource!

[bicha]

dear colleague , can you specify your knowledge level , flying experience, type of a/c flown :confused:, to help us to chose the most adequate way of explanation.
rgds.

[dboy]

Ok thanks guys for your help.

I just wanted to go a bit deeper in detail. Thi given link was just what i was looking for.

:ok:

[carldanner]

The height in meters that any vehicle can climb is found by using this formula:

ENGINE POWER IN WATTS
times
POWER LOSS FRACTION AT THE VEHICLE'S SPEED
times
DISTANCE TO OBSTACLE IN METERS
divided by
VEHICLE WEIGHT IN KILOGRAMS
divided by 9.81 ( Earth GRAVITY FACTOR )

The formula indicates that climb distance will:
A. increase in proportion to engine power.
B. decrease as efficiency decreases.
C. decrease in proportion to vehicle weight.
D. decrease as gravity increases.

For and aircraft the efficiency includes:

A Propeller efficiency which is typically about .3

B aircraft lift efficiency this could be about .8
Aircraft lift efficiency normally decreases with speed due to increased drag at higher speeds but lift efficiency also decreases at lower speeds near the stall speed due to increased turbulence.

If the numbers above are used then the total aircraft efficiency would be .3 times .8 which is .24

One horse power is 745.7 watts.
One mile is 1609 meters
One pound is .45359 kilograms

The calculations indicate that there is a sweet speed for maximum climb distance to an obstacle that is somewhere above stall speed and below higher speeds. That speed is the speed where the aircraft efficiency fraction is highest. This will probably be the lowest speed where you sense that losses due to turbulence and drag are minimum.

This sweet speed should also give the maximum climb distance in a given time because the maximum power from the engine is being transferred into the task of climbing. As far as clearing an obstacle goes, I would error on the side of going slower as long as efficiency seems OK since the aircraft will have more time to expend energy climbing before in hits the obstacle. This will also give you more time to think about how to avoid the obstacle as well as the fact that you will be going more slowly should you hit the obstacle.

My credentials.
I took flying lessons many years ago and soloed in a Cessna 152 but I
am not a pilot. I was working on electric vehicle charging systems when I came across this discussion while doing vehicle climb rate calculations. You can check out my site at EVfueling.com but I have not spent much time working on the site in the past year or more because I am working on a fueling calculator spreadsheet that will help quantify factors related to vehicle fueling.

Have fun flying.

Carl Danner

[Pilot DAR]

As to the OP's question, and applicable at lower altitudes, a climb at Vy (Best Rate) will get you the highest in the least time (greatest FPM), however, you're going to pass over lots of ground while you're doing it. A climb at Vx (Best Angle) will get you higher per given distance across the ground, though you will not be gaining altitude as fast as you would at Vy. Once you have cleared the obstacle, accelerating from Vx to Vy, will give the best climb overall. Flying either type of climb at a differing airspeed will reduce your climb rate to less than the most favourable for that condition.

As for determining climb performance numbers, there's a lot more required to gather actual climb performance data, and correct it for atmospheric and unique aircraft factors than the application of a simple formula. After gathering observed climb performance data (usually a minimum of a dozen or so test climbs per configuration), considerable data reduction is required.

This is in part, because the climb data must be expressed as sea level, standard day values, and you cannot test that way. The non standard altitude affects both power form the engine/propeller, the lift from the wing itself.

The propeller efficiency varies because of many factors, and is not fixed at one value. Generally, a factor around .7 is appropriate, though the application of that factor is complex. An email I received from a McCauley Propeller staff member on this subject recently, reads, in part:

I can say that most parameters the propeller runs about 77% efficient.

Just know which type of climb you need, and fly the numbers in the performance tables for the aircraft for that climb. For sure, having some understanding of the underlying factors is great.

[18greens]

I scanned this thread fast so apols if it has been answered.

'If you climb at vx and you reach 2000' in, let's say, 5nm (at eg 60 mph = 5 mins) while in the mean time you reach in 5nm at vy, 1300' (at eg 120mph= 2.5 mins and 2000' in 3.8 mins but 7.6 miles) why in the hell are going to climb at Vy to gain altitude in the shortest time'

Because in scenario 2 you are going faster, so you hit 2000' quicker ( less time) and you are 2.5 miles and 1.2 minutes ahead of your mate(but if the mountain is at 2000' at 5 miles the point is moot). I think the vx vy numbers you quoted aren't quite that divergent.

Another way of looking at it is if vx=60 and vy=65 and you had a 60 headwind you will clear any obstacle at 60 ( vertical take off) but at 65 you will go up faster ( vertical feet per minute) but will move forward towards any obstacle.

It took me ages to understand the difference. Now you have 17 different views of why it's different . Hope one works out for you.

[Crash one]

There seem to be a lot of mathematics based answers here that I'm finding hard to understand.
I understood the original question was concerned with the difference between best rate & best angle of climb.
My own idea to explain the differences would be that there are two different angles of climb. one is steep but slower, the other is shallow but faster.
Over a given time the steep climb will be higher but not so far "down range" the shallow climb will be not so high but further "down range".
Placing two 30deg right angle triangles on a table, one with the long "square" side down, the other with the short "square" side down.
The hypoteneuse is the time (identical), the horizontal is the airspeed, the vertical is the climbed altitude.
Experts please advise if this is bullsh*t.

[Pilot DAR]

Over a given time the steep climb will be higher but not so far "down range" the shallow climb will be not so high but further "down range".

Unfortunately not.

Two defined climbs are described as "Best Angle" and "Best Rate".

The "angle" is relative to the surface, so if you stood off to the side of the runway a way back, the airplane flying the "best angle" speed, would appear getting away from earth at an angle less acute relative to the ground, than a plane flying the best rate speed, which would have a more acute, flatter angle. The best angle plane will be moving more slowly across the ground, so combined with the steeper angle, will clear an obstacle that the best rate plane might not.

The "rate" is in feet per minute, for increase in altitude (does not care about distance over the ground covered). So flying the best speed rate speed will get you the greatest altitude in the least time, but you'll cover more ground doing it, so you might hit that same obstacle. So over a given time the shallow angle, faster airspeed, climb (at best rate speed) will get you to the highest altitude.

This is in part because there is more effect of drag at the lower airspeed of the best angle climb. You are flying with less than optimum efficiency, so you will climb at a slower increase in altitude per time (FPM) rate.

These speeds will change with increased altitude. When you get to the absolute ceiling for the plane, they will be the same, and alarmingly close to the faster stall speed way up there.

[Pilot DAR]

To further clarify this, an excellent depiction of these relationships is presented on pages 131 & 132 of this book. Note the Vx and Vy lines on the graph.

Flight testing of fixed-wing aircraft - Ralph D. Kimberlin - Google Books (http://books.google.ca/books?id=IdWmOwceEtIC&pg=PA129&lpg=PA129&dq=vy+vx+climb+kimberlin&source=bl&ots=3JBNPZbiRX&sig=P3gyy6duI-2Xz8-f_jBE8leYRfA&hl=en&ei=rReFTpa-BfGX0QX75sHoDw&sa=X&oi=book_result&ct=result&resnum=4&sqi=2&ved=0CDkQ6AEwAw#v=onepage&q&f=false)

[gulfairs]

BEST ANGLE OF CLIMB ALSO KNOWN BY THE HEAVY METAL AS BEST GRADIENT
SPEED THAT;
GIVE THE AIRFRAME MOST POWER AVAILABLE OVER POWER REQUIRED.
SAY THE SPEED IS 150 KTS FOR BEST GRADIENT.
THIS EQUATES TO A SPEED WHERE THE LEAST AMOUNT OF POWER IS REQUIRED TO FLY AT 150 KTS, AND ANY POWER AVAILABLE OVER THIS MIN POWER REQUIRED CAN BE USED TO GAIN HEIGHT.(increase ange of climb)
SAY 150 KTS NEED 40% OF THE POWER AVAILABLE, THE OTHER 60% IS WHAT IS AVAILABLE TO CLIMB.
THE OTHER SIDE OF THE ARGUMENT SAY 180 KTS GIVES THE BEST RATE OF CLIMB IN UNITS PER MINUTE BUT IT WILL NEED MORE POWER TO MAINTAIN 180 KTS BUT THE LD RATIO IS BETTER SO THE AIIRCRAFT WILL CLIMB AT A GREATER NUMBER OF UNITS PER MINUTE SO BE HIGHER THAN CASE A AFTER A FIXED TIME; BUT FURTHER DOWN TRACK., WHICH WOULD NOT AVOID A NASTY NOISE IF THERE WAS A NEAR OBSTACLE.

[Crash one]

The best angle plane will be moving more slowly across the ground, so combined with the steeper angle, will clear an obstacle that the best rate plane might not.


Pilot Dar thank you.
I seem to have got them back to front. Best rate is shallower/flatter, best angle is steeper.

[Heston]

Its probably worth remebering to emphasise to students (at PPL stage anyway) that if they are in a situation where the difference between best gradient climb and best rate of climb matters for terrain clearance... ...well they really shouldn't be there ;)

H

[Pilot DAR]

...well they really shouldn't be there

True indeed. Though if a pilot is realizing that they should not "be there", they are probably very much in need of the best information as to how to get out without delay.

If that pilot has recognized a need to outclimb rising terrain, best angle is likely most appropriate. If outclimbing changing weather, or traffic is necessary, and terrain is not a factor, best rate is probably more appropriate.

If you expect to climb for a long period, best rate will be much better for cooling.

[Pull what]

I seem to have got them back to front. Best rate is shallower/flatter, best angle is steeper. Except when they both become the same!

If that pilot has recognized a need to outclimb rising terrain, best angle is likely most appropriate.Not likely, ALWAYS, thats what it is there for and when you really need it you will appreciate that a foot the wrong way is the difference between flying over the mountain or being carried down it.

[italia458]

If you're looking for an explanation as to why max excess thrust will give max angle of climb and max excess power will give max rate of climb, you need to go over a TON of basics. Thrust and power are connected somewhat like torque and power. I wrote an article on torque and power that you can check out here: http://www.box.net/shared/tpby1m893e6mipiv6sjp (Power vs Torque)

When you talk about climbs you have to discuss power required and power available and thrust required and thrust available. I find it's best to start with power when discussing reciprocating engines and start with thrust when talking about jet engines. It can get incredibly confusing so take it one step at a time. The Advanced Pilot's Flight Manual has some good stuff on climbs that I suggest you read. You've asked such a broad question it's impossible to answer on here. I could write a book on it. Once you've read that and understand it a bit, I can help you with specific questions.

[KAG]

Dboy: just to confuse you a bit more:
sometimes when flying at max rate speed we choose best angle speed to increase our actual rate of climb over a period of time :eek:

Explanation/practical example: You are climbing at mach 0.76 and the atc ask you to expedite. You select max rate which is 266 KTS indicated speed today.
You are asked again to reach your level as soon as possible, you then select max angle (255 today?) which increases your actual angle AND your actual rate at the same time during the speed loss!

Let's go even further: you've just reached you best angle speed at 1200 feet below your level and the ATC is wishing you make it even faster, due to converging traffic (bad example).
You select then minimum speed for one engine out, maybe 242 today, (not a good procedure, but the result remains true for the subject of this thread): you find yourself increasing your actual angle AND your actual rate while the speed is decreasing.
Now you are reaching your level meanwhile you've just reached your minimum one engine speed, which is below both your max rate speed and best angle speed but have increased your actual max rate and actual best climb by doing so...

Hope I have confused you enough ;)

[italia458]

KAG, what you're describing is called a zoom climb. It shouldn't be related to holding a Vx speed for a limited time. A zoom climb is not sustained like Vx and Vy are. During sustained climbs, mechanical work is being transferred into potential energy (altitude). In a zoom climb, it's typically done at full thrust/power and a majority of the aircraft's climb performance is from it's kinetic energy being converted into potential energy (altitude).

[KAG]

You got it right.



A zoom climb is not sustained like Vx and Vy are.However if we want to be accurate, even if I agree with what you mean, NO climb speed, including best angle and max rate are sustainable on our aircrafts... ;););)


A "zoom climb" as you call it is sometimes the real answer to an emergency (wind shear at very low altitude, stall at very low altitude, imminent crash...) to avoid terrain, best angle speed won't be the one we will be looking for in those cases, the procedure will be to pull up to stick shaker (close to stall speed) to get the actual "best angle" and save your life, because the best angle speed remains in the real life a theorical speed that doesn't fit all real situations requesting the actual best angle performances from your airplane.

[italia458]

However if we want to be accurate, even if I agree with what you mean, NO climb speed, including best angle and max rate are sustainable on our aircrafts...

Oh you cheeky bugger! :E Now you're using a different meaning of "sustainable".

I agree with your statement about zoom climbs but they shouldn't be referred to as "best angle" climbs. That's incredibly confusing especially when trying to teach a student what best angle (Vx) climbs are. Discussing the benefits of the zoom climb, like you did, is good but it shouldn't be called Vx (best angle) because that is something different.

[Pull what]

Why complicate everything?

Best angle is thurst minus drag over weight and best rate is proportional to the amount of excess HP available over that required to fly the aircraft straight and level.

Instructors should teach people to fly not bore them to death trying to be clever.

[italia458]

Why complicate everything?

That's exactly the attitude that leads to crappy pilots. Rote learning doesn't "teach" you anything. Sure I can state exactly what you said but the problem with that is it doesn't explain anything. Although it might get you to pass the multiple choice questions on your exam.

Can you answer this question?... If a piston airplane's only way of moving is controlled by how much thrust is being created, then what does power have to do with it? Consider a fixed pitch, single engine airplane. Oh, and don't complicate it! :cool:

EDIT: Complicate is a very ambiguous word. To someone who just passed grade 5 math it would probably be considered complicated but to someone who has a PhD in aeronautical engineering it could be considered overly simple. What level of education should pilots be expected to have?

[KAG]

I agree with your statement about zoom climbs but they shouldn't be referred to as "best angle" climbs. That's incredibly confusing especially when trying to teach a student what best angle (Vx) climbs are. Discussing the benefits of the zoom climb, like you did, is good but it shouldn't be called Vx (best angle) because that is something different.

Thing is that what will give you your actual best climb angle and avoid a crash is not maintaining best angle speed in the real life examples I gave you.

A bit less focus on the physics and more concern about the reality and actual use of best angle concerning the actual operation of an airplane might be necessary to avoid speaking about matter of very little use when facing an emergency or having to deal with acceleration/deceleration change of flight level in a busy airspace.

[italia458]

KAG... This is really simple but obviously not obvious. If two words or sentences or phrases are spelt differently, they're NOT the same! A zoom climb is a zoom climb. Best angle of climb is best angle of climb. They should be discussed separately. Just like Vy and Vx both have a rate of climb and an angle of climb, so too does a zoom climb. And there are certain circumstances where one climb offers more performance than the others. That should be discussed, but it doesn't change the fact that they're different.

A bit less focus on the physics and more concern about the reality and actual use of best angle concerning the actual operation of an airplane might be necessary to avoid speaking about matter of very little use when facing an emergency or having to deal with acceleration/deceleration change of flight level in a busy airspace.

That statement is entirely irrelevant to what I've said. I never said that Vx should be used in all cases where you need to avoid an obstacle. I will say that if you're required to use a zoom climb to clear an obstacle without crashing then you're in a place you never should have been in. You should get a slap on the wrist for that.

[KAG]

I will say that if you're required to use a zoom climb to clear an obstacle without crashing then you're in a place you never should have been in.

Welcome to the real world.

[italia458]

Welcome to the real world.

...Ok. Been here for many years actually :ok:

[KAG]

I am sure about that, just a figure of speech.

[Pull what]

That's exactly the attitude that leads to crappy pilots.

I quite agree, over the last 28 years I have produced some crappy pilots but all excellent commanders.

[italia458]

I quite agree, over the last 28 years I have produced some crappy pilots but all excellent commanders.

You first need to teach someone how to be a pilot before you teach them how to be an airplane "commander".

[dboy]

Long time i've been here. First of all tx for your answers. But in the mean time i decided to quit with aviation. I'm moved back to my home country and found there another regular job (9 to 5) and having back a normal social life. Anyway, i stick around here because i like to keep on learning.

[Pull what]

You first need to teach someone how to be a pilot before you teach them how to be an airplane "commander".

But surely with your backward logic you would want to teach them to be aerodynamicists first!

[italia458]

But surely with your backward logic you would want to teach them to be aerodynamicists first!

.....:ugh:

[WaldoWho]

...aaaactualy, it's quite simple:
climb at a constant airspeed, lets say the advertised Vx for your A/C at a given altitude, climb for 1,000' noting the elapsed time to gain the 1,000'
Now climb at a constant airspeed. lets say the advertised A/C's Vy speed for your A/C at a given altitude (and the same starting altitude you started at for Vx), climb for 1,000' noting the elapsed time.

You now have 4 numbers; the Vx IAS, the Vx time to gain 1,000', the Vy IAS and its time to gain 1,000'
correct the IAS to CAS then into TAS for the temp and pressure altitude for both Vx & Vy then convert the Kts or mph as the case may be into fpm.
Take the recorded times (in minutes) and divide them into the 1,000', yielding the climb rate for each of Vx & Vy
Noe take the ARCSIN (or use Mr. Pythogoras's Theorem if you prefer) of the climb rates divided by their respective TAS in fpm.
The resulting 2 angles will be the angle of climb for Vx and Vy.

You will find the Vx angle to be greater than the Vy angle.
The reason for that is there was a trade off between Vx's lower airspeed than Vy's shortening its horizontal (ground) distance traveled while not reducing it's climb rate proportionally.

This is of course performed in a homogeneous, stable inertial air mass and totally divorced from earth, short of gravity.

Some of the confusion over this is when attempting to clear an obstacle the pilot is totally focused on the obstacle and therefore in a subjective earth relative reference frame while the A/C remains in that air mass reference frame although close to an obstacle/ground the air mass is probably not an inertial one any more.

...aaaactually maybe this is not so simple.

What is confounding thou is none of the POHs give the climb rate at Vx, and none give the ground roll and total distance to clear a 50' obstacle at the Vy speed, probably because that data is not specified to be included in the GAMA Specification No.1 for POHs.
So angle of climb for Vx and Vy cannnot be obtained from POHs directly, it has to be derived.

When it is the Vy climb angle is always greater than the Vx climb angle.

There, I hope I've cleared all that up.

[italia458]

Look at some thrust horsepower graphs.

Tangential line through origin is best angle climb speed. Highest point is best climb speed.

Speed is true airspeed.

[GlenQuagmire]

Thing is... its all a bit of certification nonsense isnt it? I cant imagine anyone ever sits at the threshold with an obstacle ahead that they will clear if they fly at Vx but hit if they fly at Vy and then goes ahead with the take off. That would be taking fine margins to a ridiculous extreme!

[WaldoWho]

Right!

For a representative example of ALL POHs consider;

The "805' of ground roll and 1440' Total distance to clear a 50' obstacle" (distances interpolated to 15 degrees C from the '78 172N POH specifying Vx TO distances at 10 then 20 degrees C) using a "Lift Off" speed of 52 KIAS and speed at 50' of 59 KIAS.

1) I have difficulty eye balling correctly 750' vs 1,000'. Am I supposed to go out and tape of the distances to the nearest foot??
2) If you subtract the ground roll distance from the total distance you would think you had the distance from "Lift Off" to the obstacle, but if you take the arc Tangent of the 50' divided by that distance you find the angle is always LESS than the Vy arc SINE angle of the Vy climb rate over the Vy KCAS - so Vy has a steeper flight path angle than Vx??
3) Of course not, so ALL POHs leave out the technique supposedly used to clear 50', most likely: lift off at just above power on stall (which incidentally is not specified in any POH), stay in ground effect until reaching 52 KIAS, then pull up to 59 KIAS.
4) If by some miracle you actually duplicate whatever the technique was to clear 50' (assuming there actually was one) do the wheels roll over the top of the 50' obstacle? or is there some unstated safety factor inherent but unstated in the numbers, e.g. is it really 60', or maybe 55' ?

There are many other omissions and commissions in POHs, this is just one glaring example of ; "If you want to know the actual performance of that commercially manufactured airplane, plan on spending 20 to 50 hours flight testing it yourself."

[MrAverage]

Still needs to be taught and tested, in case it's ever needed. If you know the pitchure (spelling error intended) you can set it and get Vx in a flash...............

[Alex Whittingham]

When it is the Vy climb angle is always greater than the Vx climb angle.

There, I hope I've cleared all that up.

Wrong way around?

[GlenQuagmire]

What a load of crap. I hope no early PPL or student is reading this thread and thinking any of it matters. Heres a top tip - if you ever find yourself thinking that flying a couple of knots slower will mean that the certain crash you are about to have will now become a close, but somehow heroic, shave you honestly need to get out of the plane and go and have a beer to make sure you dont get back in the plane for a bit. Its a load of flight testing nonsense. Let me explain how ridiculously stupid it all it. Nobody ever bothers to wind the gradient. In a rubber band powered single, the wind component will very significantly improve or degrade your climb gradient and it will do it by orders of magnitude more than messing about with Vx and Vy. Forget all about it because it just doesnt matter.

[MrAverage]

Where's Genghis when we need him?

[GlenQuagmire]

Pick an average single. Do the sums climbing still air to 1000 feet at Vx and then at Vy. I bet you find that you reach 1000 feet within 10 or 20 seconds of each other and I bet the difference over the ground is a few hundred feet. For both of those climbs you have been hammering your engine with the highest possible power demand with poor cooling due to the low airflow which significantly increases your chance of an engine failure. You are operating the prop in a speed range where it is less efficient and the engine won’t make full power anyway because the RPM will be lower. So you are a dillon if you do either of them. I totally disagree with Mr Average above - it doesnt need demonstrating and is of no use at all when you go flying. Its interesting and its a good idea to understand it so go and watch a video and spend your money in the aeroplane learning useful stuff. Learn some simple aerobatics, become really confident at crosswind landings, get really proficient at flying on the AH maybe, there are loads of things you can do in the plane that make your flight safer. I have an image of Alex W with his head in his hands saying, “Other way round, numbnuts”

[MrAverage]

Whether you agree or not is insignificant. It is a requirement to teach it and to test it. You'll need to convince the CAA of your opinion in order to remove the requirement.

[GlenQuagmire]

Whether you agree or not is insignificant. It is a requirement to teach it and to test it. You'll need to convince the CAA of your opinion in order to remove the requirement.

Well I am more than happy to take it up with them and I will let you chaps know the result. Incidentally, when have you ever selected a Vx or a Vy climb other than to demonstrate them? What departure have you ever undertaken which required their use? (I say you, its the royal you and open to the group, obviously). When you demo it do you discuss with the student when you would use it? Because I would venture to suggest that it would be highly irresponsible to suggest that using a Vx climb in order to clear obstacles is a good idea. I would think that if a departure is that limiting you should get out of the plane and do something else for the afternoon..

Also, do you actively calculate the effect of wind on the gradient and if not, whats the point of messing about with flying such a limiting departure anyway? My co-pilot looked at me like I was from mars when I showed him my calculations for a departure a few weeks ago. I explained that although APG said we could make the SID gradient we actually couldnt because we were taking off with a tailwind and the tailwind increased with height which would flatten our gradient. He asked why I had done that when there is no requirement. The gradient is predicated on missing the mountains..

[H Peacock]

GQ, I beg to differ.

Say you need to climb to FL430 before the FIR boundary (200nm). Are you telling me it doesn't matter if I elect to choose best rate (say 300/M0.8) or best angle (Vfto)? Okay, not doing this in a single piston, but rest assured that those in the know understand and do have a use for max angle of climb!

[GlenQuagmire]

If you chose to climb at Vfto you would be a complete dillon. Vfto is min clean after slat retraction. Other than fourth segment following an engine failure I would never climb at Vfto and even in hat scenario I would probably climb at a higher speed unless I was gradient limited - what would be the point? I doubt 300/M0.8 best rate either - thats almost certainly a cruise climb or high speed climb schedule and nothing to do with Vy. I commonly use 300/M0.8 or 0.82 but if I was trying to climb more quickly i may slow to 250 and use 78 on conversion but the calculations are not easy as it involves he mass of the aircraft, ISA, and the amount of power you get changes a bit with airspeed. So the last time I needed to get to FL450 in a hurry, which was for a NAT entry point out of Goose, I requested an orbit rather than fanny about trying to zoom climb just to get up more quickly. If you try to get too high a climb rate and the airspeed is reducing, the ITT rises and you arent doing the engines any good and I dont really want to cane a few million dollars worth of engines simply to reduce the track miles to an altitude.

[H Peacock]

Hmmm, well if you can't manage it without increasing the air-track you could do an orbit, but then if you've also wrongly elected to to go for the higher climb speed your turn is going to be fairly large, even more at altitude as the TAS increases. Therefore your rate of climb will suffer for a significant period. Of course the orbit can cause ATC a headache; not fair to give them half of my problem. Close but no cigar, when you can climb at a better speed in the first place.

Now, as for Vfto being for dillon's, you mention something about it only ever being of use for a 4th segment climb. I wonder how they came up with the Vfto recommended speed? Best rate?? Cruise climb??? Nope, its approx min drag and therefore best angle. Thats the whole point of Perf A OEI using a V2/Vfto climb, its best angle (gradient limited as you put it) to avoid the granite! So in my scenario, Vfto is just what you need when you want to achieve, er, best angle!

I think you're confusing yourself GQ. You refer to getting to FL450 in a hurry, = time and therefore best-rate is what you need. My scenario was clearly stated as limited ground-track therefore has to be solved with best angle.

[GlenQuagmire]

Best rate in the Global is achieved somewhere around max turb penetration speed but I hardly ever do that. I recently climbed to FL450 in 19 mins. Vfto is more likely to be best L/D than min drag but the engines dont produce maximum power at 160-190 kts. Even when you are OEI you still may get a better rate at a higher speed because he remaining engine produces a bit more power and you use less rudder so there is less drag. There are no climb figures for it, however, because here is no reason for a manufacturer to certify it. I am a current Glex and 6000 training captain and have flown the aircraft all over the world. I have had plenty of time to sit and look at the AFM and CCM and am pretty up to speed with what a 50 tonne swept wing jet aircraft can do. But hey, if you want to climb your global at Vfto, go for it....

[H Peacock]

GQ. My first post on this thread was to counter your statement that Vy & Vx and anything to do with them was "crap" and meaningless; I maintain you're wrong.

My scenario was based entirely on needing best angle for a climb, and that by using an appropriate min-drag speed (effectively Vx in a jet) I could achieve my goal. Same scenario, but flying at any other speed used a longer ground track. My scenario was extreme; any noteable tailwind during the 25 minute climb had an adverse effect.

You keep referring to rate and power - if you knew and understood the theory you'd know that these are not relevant to best angle climb, they are for best rate.

You state:
Even when you are OEI you still may get a better rate at a higher speed because the remaining engine produces a bit more power and you use less rudder so there is less drag.

So you acknowledge a speed/configuration that will give you a greater RoC than flying at Vfto; correct, Vfto is best angle - fly faster and you probably will get a better rate, but not the correct procedure when terrain is still an issue.

If you are indeed a Global Express expert I doubt you've ever looked and studied the Vfto graph. Vfto is not best L/D, it is approximately min-drag! Ask your instructor on your next Recurrent to explain why you must climb at V2/Vfto to get above safety alt when OEI.

If you've time to spare in your Global in the cruise why not refresh yourself on the theory and hence differences between climbing at Vx and Vy, you may well learn something that you presently don't appear to understand. And if you choose not to believe they are relevant, then kindly refrain from telling other aviators to ignore them until you demonstrate that you fully understand the theory.

[BEagle]

Climbing at V1.35+10 in the VC10K at Incirlik meant that we could make the correct level for the K-town transit corridor quite easily - whereas climbing at SOP best rate speed meant we couldn't. Not that many crews bothered - they were happy to ignore the Turkish limit...:rolleyes:

At Abingdon (before it was squaddified), on RW 36 if you taxyed as close to the RW threshold as possible, then took off and climbed at best angle, you were reasonably well placed in the event of EFATO as the fields at the end of the RW ran east-west. If you climbed at best rate, you would be too low to position for a field - but at best angle you could either jink round to RW 08 or make a descending steep turn to position for a field.

There are good reasons to climb at best angle, but to do so requires thought and quite careful handling.

[Pugilistic Animus]

https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.pprune.org/professional-pilot-training-includes-ground-studies/410673-atpl-performance.html&ved=2ahUKEwi1-M--0s_ZAhXRtlkKHWojAyYQFjAAegQIARAB&usg=AOvVaw2HlNRZjaF0TWyHMSJCupwc