another one on v1
Guest
Posts: n/a
another one on v1
I'm finding the concept of v1 a bit confusing. According to my manual v1 increases with t/o weight. My question is that doen't it take longer to accelerate a fully loaded aircraft and to bring it to a full stop due to its momentum. That in turn should reduce v1. This point can be made with the fact that v1 decreases with high ambient temperatures. Again due to reduced engine performance it should take the a/c longer to accelerate to a predetermined speed.
I think I need a bit of training on this topic.
Also why is Vmcg not affected by xwind component
I think I need a bit of training on this topic.
Also why is Vmcg not affected by xwind component
Guest
Posts: n/a
Many pilots find the concept confusing, so don't feel you're alone. <g> Perhaps I can help clear it up.
First, we must understand that V speeds are based on "balanced field length". This has NOTHING to do with the amount of runway available. It simply means that the distance to accelerate-stop equals the distance to accelerate-go.
Second, if you are heavier, it will take longer to stop. But, it will also take longer to "Go". So, your balanced field length will increase.
When the balanced field length equals the runway available (some carriers/countries also figure stopways and clearways) you are at maximum t/o weight. When there is an increase in density altitude, you decrease your max t/o weight. The V (basic) speeds will change very little. They will increase approx. 2 kts. per 5000'.
It's also important to recognize that there are "basic" V speeds and "minimum" V speeds. V1 min is driven by Vmcg. Vr min is driven by Vmu and Vmca, and V2 min is driven by Vmca and Vs. In no case may any of the V speeds be less than the corresponding Vmin speeds. That is why on some very short runways, you can't go even if you're very light.
AT higher density altitudes, many of the Vmin speeds will decrease due to the lesser thrust output of the engines, therefore lowering Vmcg and Vmca.
Actually, V1 basic and V2 basic will INCREASE with higher density altitudes (either temp or pressure altitude). It is the V1 and V2 MINIMUM speeds that decrease. So, if you are limited by V1 min, for example, and you find the temperature has increased, you will see a reduction in V1. Recognize also, that your max t/o weight will be reduced.
To summarize: You determine the t/o weight first. Then get you V speeds corresponding to it. I bet you'll find that the speeds for a 10,000' runway will be the same as for a 20,000' runway.
P.S. Sure, in real life the X-wind will have an effect on Vmcg. The trick is in knowing WHICH engine will fail!
------------------
[This message has been edited by quid (edited 15 September 2000).]
First, we must understand that V speeds are based on "balanced field length". This has NOTHING to do with the amount of runway available. It simply means that the distance to accelerate-stop equals the distance to accelerate-go.
Second, if you are heavier, it will take longer to stop. But, it will also take longer to "Go". So, your balanced field length will increase.
When the balanced field length equals the runway available (some carriers/countries also figure stopways and clearways) you are at maximum t/o weight. When there is an increase in density altitude, you decrease your max t/o weight. The V (basic) speeds will change very little. They will increase approx. 2 kts. per 5000'.
It's also important to recognize that there are "basic" V speeds and "minimum" V speeds. V1 min is driven by Vmcg. Vr min is driven by Vmu and Vmca, and V2 min is driven by Vmca and Vs. In no case may any of the V speeds be less than the corresponding Vmin speeds. That is why on some very short runways, you can't go even if you're very light.
AT higher density altitudes, many of the Vmin speeds will decrease due to the lesser thrust output of the engines, therefore lowering Vmcg and Vmca.
Actually, V1 basic and V2 basic will INCREASE with higher density altitudes (either temp or pressure altitude). It is the V1 and V2 MINIMUM speeds that decrease. So, if you are limited by V1 min, for example, and you find the temperature has increased, you will see a reduction in V1. Recognize also, that your max t/o weight will be reduced.
To summarize: You determine the t/o weight first. Then get you V speeds corresponding to it. I bet you'll find that the speeds for a 10,000' runway will be the same as for a 20,000' runway.
P.S. Sure, in real life the X-wind will have an effect on Vmcg. The trick is in knowing WHICH engine will fail!
------------------
[This message has been edited by quid (edited 15 September 2000).]
Guest
Posts: n/a
I think: Refering to the 1st segment of the Perf A climb out which ends at around 35ft. Start at rotate and at the 35 ft point you will be in the engine out pitch attitude with the gear retracting at V2 assuming a post V1 engine failure...I Think!!! 
Guest
Posts: n/a
On a Bae 146-200 series ONLY above 29,500Kg Vmcg = 82 and increases 5Kt/10Kt of crosswind
Bae146-100 Vmcg = 88 Kt no X-wind add
Bae 146-300 Vmcg = 86 KT no X-wind add
Can any pilots tell me why X-wind has no effect on the 100 series Vmcg (shorter fuselage) or 300 series Vmcg (longer fuselage)?
I used to operate on a 30 m large runway, has it been taken into account in Vmcg calculation?
thanks in advance.
Bae146-100 Vmcg = 88 Kt no X-wind add
Bae 146-300 Vmcg = 86 KT no X-wind add
Can any pilots tell me why X-wind has no effect on the 100 series Vmcg (shorter fuselage) or 300 series Vmcg (longer fuselage)?
I used to operate on a 30 m large runway, has it been taken into account in Vmcg calculation?
thanks in advance.
Guest
Posts: n/a
Except in the balanced field length case there is a choice of V1 from V1min to V1max.
V1 max is the accelerate/stop case and V1min is the accelerate/go case.
The reason that in tabulated V speed charts the V speed increases with increasing mass is that you must be able to accelerate from the point at which the engine fails to VR and meet the screen height at the end of the TODA.
Incidentally the first segment is from 35 feet to the end of gear retraction.
V1 max is the accelerate/stop case and V1min is the accelerate/go case.
The reason that in tabulated V speed charts the V speed increases with increasing mass is that you must be able to accelerate from the point at which the engine fails to VR and meet the screen height at the end of the TODA.
Incidentally the first segment is from 35 feet to the end of gear retraction.
Guest
Posts: n/a
fart-
The 35 feet is important in so far as the obstacle clearance in the t/o flight path is concerned. You must miss all obstacles by the net climb gadient (this is different depending on low many engines you start with) plus 35 feet. So at 35 feet at the start of the t/o, you are just starting your obstacle clearance path.
stardust-
All other conditions the same, i.e. rudder throw and square footage, thrust, etc., the Vmcg WILL vary with the fuselage length. Your carrier (for whatever reason) may not choose to use any modification of Vmcg for x-wind on those models. A longer fuselage has a greater lever, so the Vmcg will be lower.
The width of the runway has nothing to do with the value. The only concern is how close you can keep it to centerline, not how far from the edge.
------------------
The 35 feet is important in so far as the obstacle clearance in the t/o flight path is concerned. You must miss all obstacles by the net climb gadient (this is different depending on low many engines you start with) plus 35 feet. So at 35 feet at the start of the t/o, you are just starting your obstacle clearance path.
stardust-
All other conditions the same, i.e. rudder throw and square footage, thrust, etc., the Vmcg WILL vary with the fuselage length. Your carrier (for whatever reason) may not choose to use any modification of Vmcg for x-wind on those models. A longer fuselage has a greater lever, so the Vmcg will be lower.
The width of the runway has nothing to do with the value. The only concern is how close you can keep it to centerline, not how far from the edge.
------------------
Guest
Posts: n/a
Working out a V1 for every single runway in order to achieve max payload would not be practical or efficient, especially since the airplane is rarely limited by the runway length. So the manufacturer or contractor tasked to do this for the company will produce charts for each runway based on balanced field performance. When this is done the computer (or mark one eyeball) is used to determine the "best" V1/VR. (V1:VR Ratio). VR is based on the value of V2 and so is a weight related number. This makes V1 weight related too, for this type of assumption. This ratio is used for the whole chart, and is not necessarily the best for every case on that chart. Most jet airplanes use about 85% as a ratio for balanced field. This optimises the "STOP" ability. Turbo props or pistons are happier with 100% (or 1, ie V1=VR since their problem is usually a "GO".
So you see the V1 is an arbitrary figure for most cases. There are always two V1 figures for a real calculation, if it was considered necessary to work it out; a Min V1 which would allow for a continued flight, and a maximum V1 which would allow for the stopping case. In many cases, with a long runway, the minimum V1 is below the Vmcg and the max is above the V2, so the pilot would have a choice of any figure in that range. As the runway is shortened, the two V1 figures come together so that at a true balanced field they would be equal.
Way too complicated for the average pilot and usually not necessary. Although it would be nice if we knew the max V1, so that in extreme cases we could opt for an abort rather than be forced to continue the takeoff simply because the speed is above the charted V1 figure But this opens a real can of worms, especially for the training people, and is best left alone.
So the company (or manufacturer) will chart every airfield for you, using an assumption that each takeoff will use only enough runway to satisfy the balanced field performance, and an arbitrary V1/VR ratio. Much easier.
If you have time some day, look at the performance charts in the Flight Manual.(The Ops Manual charts and the FMC calculations use the same assumptions as the RTOW charts). There are explanations on the use of the Flight Manual charts and an example. Pick a runway that is way too long and work out the V1(s). You will have to teach yourself how to do it, since most companies do not cover this manual in training. Look again at a short runway and do the same. Illuminating.
So you see the V1 is an arbitrary figure for most cases. There are always two V1 figures for a real calculation, if it was considered necessary to work it out; a Min V1 which would allow for a continued flight, and a maximum V1 which would allow for the stopping case. In many cases, with a long runway, the minimum V1 is below the Vmcg and the max is above the V2, so the pilot would have a choice of any figure in that range. As the runway is shortened, the two V1 figures come together so that at a true balanced field they would be equal.
Way too complicated for the average pilot and usually not necessary. Although it would be nice if we knew the max V1, so that in extreme cases we could opt for an abort rather than be forced to continue the takeoff simply because the speed is above the charted V1 figure But this opens a real can of worms, especially for the training people, and is best left alone.
So the company (or manufacturer) will chart every airfield for you, using an assumption that each takeoff will use only enough runway to satisfy the balanced field performance, and an arbitrary V1/VR ratio. Much easier.
If you have time some day, look at the performance charts in the Flight Manual.(The Ops Manual charts and the FMC calculations use the same assumptions as the RTOW charts). There are explanations on the use of the Flight Manual charts and an example. Pick a runway that is way too long and work out the V1(s). You will have to teach yourself how to do it, since most companies do not cover this manual in training. Look again at a short runway and do the same. Illuminating.
Our company's performance department produces V1 charts for every intersection on every runway we use on the network, and tabulates the data in a big book. This allows maximum weight uplift for each take-off.
Guest
Posts: n/a
quid, the answer to your Q. is yes, yes, and yes for the mob I`m with. (and I think it`s the same mob as CB`s
Temp in increments of 2 deg C
QNH in 10 hpa inc.
Two best flap configs.
Wet/Dry rwy.
Every applicable intersection.
It`s a lot of pages.
[This message has been edited by jtr (edited 25 September 2000).]
Temp in increments of 2 deg C
QNH in 10 hpa inc.
Two best flap configs.
Wet/Dry rwy.
Every applicable intersection.
It`s a lot of pages.
[This message has been edited by jtr (edited 25 September 2000).]
Guest
Posts: n/a
quid
I think some of your marbles may be on the ground.
1.The V speed concept applies for balanced as well as non-balanced take off performance calculations.
2. V1 goes up withe the weight as it is also related to V2 wich only depends on weight as it is in IAS wich equals EAS at low speeds and density altitudes. As long as there is enough runway ahead to stop it's OK to increase V1 with the weight.
3.As far as Vmcg is concerned:
Regulations do not require that x-wind is taken into account.
If one day this would become a requirement then the case of the most critical engine (similar concept like on the piston thing) would be applicable, hence it would not matter wich engine would fail.
------------------
Smooth Trimmer
I think some of your marbles may be on the ground.
1.The V speed concept applies for balanced as well as non-balanced take off performance calculations.
2. V1 goes up withe the weight as it is also related to V2 wich only depends on weight as it is in IAS wich equals EAS at low speeds and density altitudes. As long as there is enough runway ahead to stop it's OK to increase V1 with the weight.
3.As far as Vmcg is concerned:
Regulations do not require that x-wind is taken into account.
If one day this would become a requirement then the case of the most critical engine (similar concept like on the piston thing) would be applicable, hence it would not matter wich engine would fail.
------------------
Smooth Trimmer
Guest
Posts: n/a
Quid,
We produce takeoff charts for every runway that we operate to and also include commonly used intersections. This gives the maximum takeoff weight for a balanced field situation for these runways.
If the takeoff weight is less than the maximum, reduced thrust can be used to utilize the whole length of the runway.
The V-speeds are dealt in different ways depending on the aircraft type. With the Airbus and optimized V-speeds, the V-speed is printed for each takeoff weight on each runway.
For the older Boeings, tabulated V-speeds are presented showing temp, pres alt, weight, thrust rating, flaps and necessary corrections for slope, clearway, packs.
On the newer Boeings the FMC will provide Balance Field v-speeds for whatever weight you input. The FMC doesn’t care what the runway length is, it only uses the weight and actual conditions.
Mutt.
We produce takeoff charts for every runway that we operate to and also include commonly used intersections. This gives the maximum takeoff weight for a balanced field situation for these runways.
If the takeoff weight is less than the maximum, reduced thrust can be used to utilize the whole length of the runway.
The V-speeds are dealt in different ways depending on the aircraft type. With the Airbus and optimized V-speeds, the V-speed is printed for each takeoff weight on each runway.
For the older Boeings, tabulated V-speeds are presented showing temp, pres alt, weight, thrust rating, flaps and necessary corrections for slope, clearway, packs.
On the newer Boeings the FMC will provide Balance Field v-speeds for whatever weight you input. The FMC doesn’t care what the runway length is, it only uses the weight and actual conditions.
Mutt.
Guest
Posts: n/a
B747-400 or B777-200
The easy answer is YES, the FMS would allow you to takeoff from any runway. It presumes that you have gotten the field length limit weight from another source!
Anyone care to tell me where there is a page for you to enter the runway length in the FMC?
Mutt
The easy answer is YES, the FMS would allow you to takeoff from any runway. It presumes that you have gotten the field length limit weight from another source!
Anyone care to tell me where there is a page for you to enter the runway length in the FMC?
Mutt
Guest
Posts: n/a
Streamline-
answer to 1. Don't really know what you're saying here. We use balanced field (theoretical) numbers to operate in unbalanced (real life) situations. Most pilots in their whole career will never be faced with a true balanced field takeoff.
2. V1 only increases with weight if you are heavier than the weight that drives V1min. That in turn is determined by density altitude. Below that, V1 is the same for all weights.
Once a V1 is determined for your weight, (unless your carrier has adopted an increased V1 speed procedure) it is not increased if you have a longer runway.
V2 may or may not depend on weight. Once again, V2min may be driven my Vmca requirements. The IAS-EAS statement is not a factor in this case.
3. My remarks concerning Vmcg were in response to questions by av8r76 and stardust. In most cases, "Vmcg" in jet aircraft is not adjusted for winds. In actual practice, however, your actual ability to control the aircraft IS greatly affected by the x-wind.
jtr-
Sounds like a helluva complete book.
------------------
answer to 1. Don't really know what you're saying here. We use balanced field (theoretical) numbers to operate in unbalanced (real life) situations. Most pilots in their whole career will never be faced with a true balanced field takeoff.
2. V1 only increases with weight if you are heavier than the weight that drives V1min. That in turn is determined by density altitude. Below that, V1 is the same for all weights.
Once a V1 is determined for your weight, (unless your carrier has adopted an increased V1 speed procedure) it is not increased if you have a longer runway.
V2 may or may not depend on weight. Once again, V2min may be driven my Vmca requirements. The IAS-EAS statement is not a factor in this case.
3. My remarks concerning Vmcg were in response to questions by av8r76 and stardust. In most cases, "Vmcg" in jet aircraft is not adjusted for winds. In actual practice, however, your actual ability to control the aircraft IS greatly affected by the x-wind.
jtr-
Sounds like a helluva complete book.
------------------
Guest
Posts: n/a
av8r76 & quid
May I try to put it in a nutshell
It’s easier to explain when you reason it out backwards
V2 = 1.2 Vs
Vr must be such as to reach V2 at the latest at 35 ft and above the runway end in the balanced case.
So the bigger the difference between V1 and Vr (the one engine acceleration part) the more runway you need, hence the reason to increase V1 closer to Vr (it accelerates better with two then one) as long as there is enough runway left to stop at this increased V1.
V2 depends only on weight when expressed in EAS (and IAS=EAS in the low range of speeds and density altitudes)
So if weight goes up, V2 goes up, so Vr goes up and hence V1 goes up if enough runway is left over otherwise the weight can not go up and you have reached the maximum for that runway.
I know there are some factors as Vmu, Vmca ,Vmcg Vmbe involved as well but these do not affect the aforementioned principle of reasoning to a large extend if we concentrate on the original question "How does weight influanse V1" or am I overlooking something here ?
I know that V1 has some upper and lower limits dictated by brake energy, tyre speed and Vmcg but thats besides the original question I think ?
But do you agree with the following?
In the case of balanced Take Off we set TOD = TOR as a condition for the calculations.
If you want to squeeze out a bit more performance you can go unbalanced and use clear and stop-way to a larger extend.
As far as I know balanced or not has nothing to do with the practical or theoretical concept they are both theoretical but any feedback on this is welcome.
------------------
Smooth Trimmer
[This message has been edited by Streamline (edited 28 September 2000).]
May I try to put it in a nutshell
It’s easier to explain when you reason it out backwards
V2 = 1.2 Vs
Vr must be such as to reach V2 at the latest at 35 ft and above the runway end in the balanced case.
So the bigger the difference between V1 and Vr (the one engine acceleration part) the more runway you need, hence the reason to increase V1 closer to Vr (it accelerates better with two then one) as long as there is enough runway left to stop at this increased V1.
V2 depends only on weight when expressed in EAS (and IAS=EAS in the low range of speeds and density altitudes)
So if weight goes up, V2 goes up, so Vr goes up and hence V1 goes up if enough runway is left over otherwise the weight can not go up and you have reached the maximum for that runway.
I know there are some factors as Vmu, Vmca ,Vmcg Vmbe involved as well but these do not affect the aforementioned principle of reasoning to a large extend if we concentrate on the original question "How does weight influanse V1" or am I overlooking something here ?
I know that V1 has some upper and lower limits dictated by brake energy, tyre speed and Vmcg but thats besides the original question I think ?
But do you agree with the following?
In the case of balanced Take Off we set TOD = TOR as a condition for the calculations.
If you want to squeeze out a bit more performance you can go unbalanced and use clear and stop-way to a larger extend.
As far as I know balanced or not has nothing to do with the practical or theoretical concept they are both theoretical but any feedback on this is welcome.
------------------
Smooth Trimmer
[This message has been edited by Streamline (edited 28 September 2000).]
Guest
Posts: n/a
Hello Mutt
As far as the field lenght limit is concerned referring to your Boeing FMC 747/777 wonder.
Suppose ATC or any other reason asks you if you can take an intercection for T/O, how do you know if you can make it with your 747/777 FMC.
I have flown on the 777 but the company I worked for didn't use the FMC for their V speeds yet ?
Thanks for your feedback
------------------
Smooth Trimmer
As far as the field lenght limit is concerned referring to your Boeing FMC 747/777 wonder.
Suppose ATC or any other reason asks you if you can take an intercection for T/O, how do you know if you can make it with your 747/777 FMC.
I have flown on the 777 but the company I worked for didn't use the FMC for their V speeds yet ?
Thanks for your feedback
------------------
Smooth Trimmer