V1 and light plane

[Dariuszw]

Need some help understanding why for example Cessna Citation (light craft) has V1 speed ? Assuming sufficient runway length why restrict and deny myself an option of aborting takeoff at speeds much higher then V1 ?

CJ2 can accelerate to takeoff speed and then land few times before running out of distance to land on 11.000ft long runway. Why continue takeoff after hearing loud bang in the back only because aircraft is at V1 ? That makes no sense and more importantly it takes decision from pilot. Let Concord accident be an example of that. I can understand big iron which is limited by runway length but not light twin. So why ?

[bingofuel]

To keep it simple, you might be attempting to take off from a runway that is a lot shorter.
Essentially V1 is the speed on the ground above which you cannot stop in the runway remaining but can safely continue the take off in the remaining runway length in the event of an engine failure.
It may well be that the V1 speed is the same as the Vr speed so at V1 you pull back and fly.
Of course if there was a catastrophic failure just as you took off and you had 10,000 ft of runway remaining there is an argument for landing back on but the theory is you continue to fly.

Search the other threads as there was a recent debate about stopping after V1 or even landing back in certain circumstances.

Performance is a fairly complex subject and there are many factors to consider.

[zero1]

Even when I fly my TB-10 we use V1 at a decision point in the take off roll (2/3 speed check (V1) available runway length) very useful for short field operations.

[KBPsen]

Dariuszw, you should acquaint yourself with the definitions of V1, Vr and V2. Particularly what they can not be less than.

I am not sure what you think you have debunked?

[bingofuel]

Need some help understanding why for example Cessna Citation (light craft) has V1 speed ?

Because it is a performance A aircraft and requires one by law, will that suffice?

[deltahotel]

Because V1 can't be greater than Vr - once yr past that, you're airborne and RTO is no longer an option. If you (knowing yr ac capabilities) decide that up to eg 50',100',200' whatever you plan to land back on straight ahead then that's a different matter.

Hope this helps

[MarkerInbound]

V 1**means the maximum speed in the takeoff at which the pilot must take the first action (e.g., apply brakes, reduce thrust, deploy speed brakes) to stop the airplane within the accelerate-stop distance. V1**also means the minimum speed in the takeoff, following a failure of the critical engine at VEF, at which the pilot can continue the takeoff and achieve the required height above the takeoff surface within the takeoff distance.

Many people look at V1 as the maximum reject speed only. But it is also a minimum speed. If you didn't have a decision speed and an engine went bang at say 82 knots, how would you know you could keep going and clear your 35 foot trees?

[bingofuel]

With your ' thousands of hours ' flying experience did you ever study the subject? If you had any knowledge of performance planning at all you would not be asking the questions you are.
I will ask you the question, how much runway do you require to accelerate a CJ2 to flying speed and then stop it again? At what point do you say the runway is so short you are unable to land back?

[bingofuel]

Because the runway may not be 12000 ft long. Can I ask, you are 16 years old and claim '. Thousands of hours ' experience, have you ever flown a real aeroplane ?

You seem unable to grasp the basics of aircraft performance and will not listen to those that have. Perhaps others may help you from now on.

[keith williams]

It is certainly true that when looking up the various V speeds (V1, Vr V2 etc) you do not need to know the field length.

Vmu is the minimum speed at which the aircraft can generate enough lift to rise up off the runway surface. But if we permit it to lift off at Vmu then any minor reduction in airspeed, due for example to a drop in headwind, will cause the aircraft to sink back onto the runway. To avoid this we plan to make the aircraft lift off a Vlof (Velocity lift off) which is slightly higher than Vmu. I cannot recall the exact figure, but it is about 5% higher than Vmu.

To ensure that the aircraft lifts off at Vlof we must begin to rotate it into the take-off attitude at the correct speed. The speed at which we must begin this rotation is Vr. The difference between Vr and Vlof is determined by aerodynamics.

Before beginning the nose up rotation we must make the decision to continue or to abort the take-off. The time between rotation and lift-off is often very short. So if we rotate then change our minds and push it back down again, it is quite possible that we will have-lifted off and landed again. That may be OK when you have lots of spare runway available, but that will not always be the case.

V1 is the take-off decision speed. There has been much debate over the years about how exactly it would be better described as the take-off action speed. Essentially V1 is the speed at which, the take-off must be continued unless the first actions have been taken to reject the take-off. But there may of course be some overriding reason to prevent the take-off from being continued. If for example a wing drops off at V1 + 1 knot, your only choice is to attempt to stop.

Logically we must made the decision to take-off at or before the point at which we begin the rotation to the take-off attitude. So V1 must not be greater than Vr.

We now have a logical sequence of speeds V1, Vr, Vmu, Vlof. The magnitudes of these speeds are determined by aerodynamics and have nothing to do with the field lengths available (TORA, TODA, ASDA).

But that does not mean that V1 has nothing to do with field lengths available!

Imagine that we have an extremely long field in which the distances available are far in excess of those that will be required by the aircraft at its current take-off wait.

We start the take-off roll and accelerate down the runway. Eventually we will reach the speed at which we can suffer a single engine failure and still have enough TODA to reach screen height at V2 within the remaining TODA. The speed at this point is called Vgo and it is the minimum value for V1 for this combination of aircraft weight, atmospheric conditions and field length.

Now let’s suppose that instead of rotating, we keep the nose on the runway and keep on accelerating. We will eventually reach a speed at which we have just enough ASDA remaining to bring the aircraft to a stop if we decide to reject the take-off. This speed is called Vstop and it is the maximum value of V1 for this combination of aircraft weight, atmospheric conditions and field length.

Because the field is much longer than the aircraft requires, there is a gap between Vgo and Vstop. But at any speed within this gap the aircraft is capable of continuing the take-off following a single engine failure, or aborting the take-off, within the distances available. This means that we have a speed range within which we can select our decision speed V1.

If we gradually increase the aircraft weight, the value of Vgo and the amount of runway used to accelerate to Vgo will increase. And the value of Vstop and the distance required to accelerate to Vstop will both decrease. This means that the allowable range of speeds between Vgo and Vstop, within which we must select V1, will gradually reduce.

If we continue to increase the aircraft weight (or reduce the field lengths available) we will eventually get to a point where Vgo and Vstop are equal. We then have only one choice for the value of V1. In this condition when we reach V1 we have just enough TODA available to complete the take-off, with one engine failed, and get to screen height at V2 within the remaining TODA. We also have just enough distance to abort the take-off and stop the aircraft within the remaining ASDA. In this condition the aircraft is said to be field limited.

We now have a relationship between V1 and the field lengths in that when carrying out a field limited take-off V1 is the speed at which we have just enough TODA available to complete the take-off, with one engine failed, and get to screen height at V2 within the remaining TODA. We also have just enough distance to abort the take-off and stop the aircraft within the remaining ASDA.

[MarkerInbound]

Historically, for every case where continuing did not work out (Concorde), there are many more where the reject led to damage and injuries.


I guess I'm having a problem when you say runway length does not matter. I'll put my dispatcher hat on and say runway length always matters. Your TO weight is controlled by the length of the runway and V1, Vr and V2 are a function of your weight, adjusted for temp, PA and other things.

Or are you asking for a particular flight at a particular runway where you are not runway limited? I don't have a 525 manual and it's been a long time since I've flown a 500 so we'll make some numbers. Say for MTOW ISA day at SL we need 4000 feet to take off and 3500 feet to land. Throw in 4 seconds of "What was that?" and you're looking at 8000 feet. Are you saying if the runway is more than 8000 feet (in this example) you shouldn't reject at V1? I'll grant you that on a 12,000 foot runway you could most likely start rotating, change your mind and still stay on the runway. So now we have a new question - When are we committed to flying? Rotation? Lift off? Gear retraction? At some point you will be out of runway and you don't have any data to find that point.

You say it takes away the pilot's choice. I'd say it gives them more. You've got the time to think through and deal with the problem.

[mutt]

Welcome back SSG :{:{:{

[BOAC]

Please note this appears to be 'son of SSG'. I guess Daddy bought him a Flt Sim programme for the X-box, sat him on his knee and told him ALL about us.:)

"And because I do fly CJ2" ..........................................

[galaxy flyer]

Fanatic is someone who won't change the subject and can't change his mind.

Whoever Mr V1 is, he does seem to migrate around the globe based on his location. Most of us here have rather fixed locations and advancing ages. :{

[redsnail]

Assuming what you've written about yourself is correct,

Join Date: Dec 2011
Location: Poznan
Age: 16
Posts: 5

Then I doubt you're flying a CJ2 at all...

You can play the "what if" game forever.

[Bealzebub]

DariusZW,

You seem very reluctant to accept and understand what all these good people are trying to tell you.

V1 is simply an accelerate/stop distance speed. Where the runway length and environmental factors do not result in an earlier limit, VR the point at which rotation to an airborne phase takes place, becomes the co-incidental point. Once you have rotated to become airborne, or actually become airborne, the accelerate/stop distance speed is irrelevant, since it is only measured on the ground.

Could you land in the remaining distance? Maybe. The problem is how do you know. What is the distance once you are airborne. What is the landing distance from that variable height with only take off flap and not landing flap? What effect will a weight possibly well in excess of your maximum landing weight have on the stopping distance and brake energy limits?

What you as an individual decide to do, is ultimately up to you. The purpose of the V1 speed is to provide a safety calculation based on a set of defined criteria.

It isn't unusual for engine failures to go with a "big bang," however getting airborne, resolving the issue, and landing with a full runway ahead of you is what a competent pilot is trained to do. Safety cannot be deemed to exist unless those charged with it are both competent and fully understand the rationale on which they make their decisions.

The question is fair enough, but you are not accepting the rationale on which the answers are being provided.

[gorter]

Do you really expect me to take aircraft and passengers into the air with unknown problem after hearing loud bang and become a test pilot

Yes we do. It's what what the manufacturer certified the a/c to do, and if you hold a type rating (and considering your poor attempt at playing devils advocate, highly unlikely) it's what you would have been trained and tested on then, and unless you want a TRE to hit you, what you would do every 6 months in the sim or on the A/C on LPC/OPC.

If you do become airborne and attempt to land, or reject after V1, then you really do become a test pilot. The manufacturer of the aircraft sure as hell won't have done it.

Your aircraft is certified to fly on one engine. Past V1 that is the only thing it is safely tested (by actual test pilots) to do.

Once airborne (even only 2 or 3 feet) you then have to cut the (take-off) power control the yaw, re-flare and land. How much runway does that use? The manufacturer of your perf A aircraft never tested that and if you survive, well good luck in court.

[Old Smokey]

Hey, SSG, Dariuszw, and all of your offspring, have I got an early Christmas present for you!:ok:

It's called Reduced Thrust (or Flex as your fellow Europeans from the Poznan region would call it). An added extra is that you could further apply Reduced Thrust to Derated Thrust. As you seem to have a problem with excess runway (I wish that I did), Flex, Reduced Thrust and Derated Thrust can eliminate your excess problem in an instant, no kiddin!:E

Go check with Daddy SSG, he knows a lot about Reduced Thrust, quite an expert in fact, just ask him, he knows it all. Us other dumb pilots and Performance Engineers know nuthin.....really! He knows that we all 'take it to the fence' on a flight by flight basis, airborne criminals the lot of us.

He knows too, that these airborne criminals regularly take aircraft into IMC and Icing conditions, on some mistaken belief that that's where REAL pilots go. Shockingly, these same real pilots actually accept that the Performance Engineers who created their performance data actually know a tad more about performance than they do, so naive:yuk:. Now, we wouldn't want you to do any of that Real Pilot Stuff would we?

Show us the way in 2012 SSG et al, we eagerly await your moderation of the sanity of these forums (although I sometimes wonder in which direction you modify it).

Seasons Greetings to the Real Pilots.

[Bealzebub]

Cessna Citation will never have V1 increase to Vr in any foreseeable circumstances. So I object to be categorized like that for math simplicity.

I am sorry, but you have lost me completely. I thought you were torturing this point on the basis of long runways, when V1 would presumably equate to VR in virtually all of those "forseeable circumstances?" You don't appear to understand what V1 actually is. It is an accelerate/stop distance speed that is limited by VR. You could have a runway that spans the Earth if you can imagine one, but it wouldn't change the mathematics. I suspect you are wrapped up with the idea that V1 is a decision speed when in fact it is used as a speed by which time a decision should have been made based on the fact that is an accelerate/stop distance speed that ceases to have a function once VR has been reached. In other words VR becomes the ceiling.

In your premise, I suppose you could accelerate on the ground well beyond VR. Presumably your tire limits would be the next performance barrier? However this is nonsense, because the premise of what the performance calculation is being done for, is nonsense.

As the above posts have already made clear, a very long runway can become a performance critical runway (and nearly always is) by the use of reduced thrust take offs.

there are some many stupid regulations that your eyes open wide and you start to think twice everything you see.
Examples: oxygen requirement for any small jet is the same as for jets flying oceanic crossings which is 2h. Why when we are never more then half an hour away from farthest airport and descend to 10.000ft will take no more then 10min ? Or this stupid FAA requirement which no one ever complies with of using oxigen mask at FL350 and above.

By "never more than 30 minutes from the fatherest airport" I assume you are being erroneous again, and actually mean 30 minutes from the nearest airport. There are no end of places where a small business jet can be more than 30 minutes from the nearest (suitable and adequate) airport. This is before you even begin to take things like "weather" into account. Believe it or not, there are even parts of the world where terrain can preclude decents below 10,000ft for periods longer than 30 minutes.

There have been some famous accidents where oxygen mask none use was a major factor. The regulator rules to protect against a repetition of those factors. The idea being that protection is afforded by learning from the mistakes of the past.

I suspect the people you are referring to as "clueless" are in fact very intelligent and knowledgeable. They are simply alluding to the "information" you have chosen to display in your profile. That it is erroneous doesn't surprise me at all.

There is nothing wrong with asking a question, but you seem woefully reluctant to digest and listen to the answers that other people provide.

[500 above]

Any real CJ2 pilot would have told us that there are no charts for reduced thrust takeoffs Smokey.

The nearest Dariuszw has been to a reduced thrust takeoff is when he forgot to push the carb heat in on the Cessna in FS4... :)

[Old Smokey]

Dariuszw,

Thank you most sincerely for adding me to your ignore list, now that is indeed a compliment!:ok:

For the record before leaving this thread forever, yes, I do indeed accept it as truth that Jet aircraft at high altitude do indeed spend most of their time above Mcrit, even during climb. No, I don't believe it, belief is a matter of faith, I accept because it is FACT'

See you in the next incarnation.

[500 above]

Dariuszw take a look here http://www.pprune.org/tech-log/407225-confusion-machcrit-mach-trimmer.html and don't confuse MMO and Mcrit.

You can also look here Mach Crit, Mach Number Buffet, Mach Tuck, and Mach Trimmers [Archive] - PPRuNe Forums (http://www.pprune.org/archive/index.php/t-131271.html) May I suggest (if it's not too late) putting a request to Santa in for Handling the big jets?

[500 above]

Perhaps you can now explain FLAT RATED to us. Reduced thrust t/o in a CJ! I think you're a little confused! But thanks for the lesson on flying jets...

[mutt]

Flying a jet full power is not an option due to ITT limits

Priceless..........

[Dariuszw]

Old Smokey - As Im reading into this Mcrit business more and more I see that you might be correct. As we use Mmo and Mcrit is not a factor Im perhaps bit rusty on the subject. For now seems you are correct...but only for now and if I find something otherwise I will shove it back. But I do admit confusing it with something else. So ther you go :ok:

[Bealzebub]

V1 is always less then Vr. So explain that phenomena when takeoff is not ASDA limited ?

No. V1 can be co-incident with VR (and often is.) I am not sure what "phenomena" you are referring to? If you are not runway length limited or limited by another factor, then your V1 speed is the same as your VR speed. What is it you want me to explain?

However I assure you there is no such place in US nor Europe where you cant descend to 10.000ft for more then two hours with jet speeds. Care to point one out
I didn't say there was. What I said was:
Believe it or not, there are even parts of the world where terrain can preclude decents below 10,000ft for periods longer than 30 minutes.
The regulatory requirement is no doubt based on a conservative set of assumptions.

You are clearly arguing simply for the sake of arguing.

[mutt]

http://farm8.staticflickr.com/7024/6564294365_8371dbcbff_z.jpg (http://www.flickr.com/photos/pprunemutt/6564294365/)

http://farm8.staticflickr.com/7003/6564294861_a4751a51cb_z.jpg (http://www.flickr.com/photos/pprunemutt/6564294861/)

All rights to Mr Boeing......... I would presume that he understands how airplanes fly :)

[mutt]

And just so you can educate yourself about V1.....

http://farm8.staticflickr.com/7143/6564422595_2419945e6a_z.jpg (http://www.flickr.com/photos/pprunemutt/6564422595/)


Once again, all rights to Mr Boeing.....

[galaxy flyer]

One point of confusion here--airlines are provided with more performance charts than are provided to business jet operators. The airlines have performance engineering departments that have all the "raw" charts--Vmcg, accelerate-stop, accelerate-go, brake energy limits, OEI climb gradients etc.

The AFM data provided business jet operators is "dumbed down" to presuppose every operation is a field length-limited take-off, that is only balanced field data only. We do not have all the charts to optimize performance because no operator wants to pay for it, to get trained in using them and to be legally responsible for any misuse. So, unless an operator uses a runway analysis provider, a lot of take-offs are done without all the facts, but the performance available is usually so much greater than the limiting case, it is not an issue.

To our fanatic poster, here's a suggestion. Go into the tab data, select the highest weight that the conditions will allow for take-off. IF the V1 for that weight is equal to or greater than Vr for your actual weight, your V1 can equal your Vr for the actual TOGW. You have "unbalanced" your field lengths i.e your actual accel-stop distance, based on the V1, will exceed your actual accel-go distance but both will be less than the TODA.

As to landing after rotate, you and the plane are much safer in the sky than trying to be a test pilot and landing again.

Call it the assumed weight method, but my heirs would appreciate if you don't reference me at the inquiry, if you overrun. BTW, I am pretty authoritative on the cost of providing performance engineering data prohibiting the provision thereof.

[deltahotel]

Blimey, this is hard work! Read again "Because V1 can't be greater than Vr - once yr past that, you're airborne and RTO is no longer an option. If you (knowing yr ac capabilities) decide that up to eg 50',100',200' whatever you plan to land back on straight ahead then that's a different matter"

I stick by that - if you are able to land back on and stop safely then why not? I guess you would probably have to initiate that before gear retraction.

The important thing is to make these decisions before you set off down the runway. So perhaps (not knowing yr aircraft type so doinbg a read across from my previous experience) the following might work (having considered the runway/weight/wx etc on the day) "up to rotate I shall carry out RTO iaw with our SOPs, after that before gear retraction I shall lower the nose and land on the rw remaining. Once the gear has started to retract I shall continue with the SID/carry out SOP EFATO actions whatever etc etc."

Hope this helps

[Meikleour]

Dariuszw: What makes you think that thye O2 requirements are only to cater for depressurisation? Do your drills not consider smoke scenarios?

PS I realise this may be a pointless post...................

[Dariuszw]

It is pointless. Because if you got smoke or fire you will land much quicker then when simple decompresion. It takes just two minutes from the moment you see first smoke to fully engulfed craft according to NASA studies. In all cases checklists will call for landing as soon as possible and not practical. If you argue that fire has been extinguished and only smoke persist you have cabin dump and fresh air options which will get rid of smoke. Hope that answers this question.;)

[Piltdown Man]

Regarding Perf A & Bureaucratic regulation: You don't get the choice. Once the regulators get involved, you just have to comply. However, their involvement has forced some idiots to fly with fatter margins.

If runway is long enough why not reland rather then continue with unknown perhaps catastrofic problem into the air ( like Concord crew), perhaps into IMC, icing and God knows what else.
You can - that's your choice. But if you are flying an aircraft within its limitations it could mean you are legally in both IMC and icing conditions. So if you have a problem when just airborne, just how will you perform a safe land-ahead manoeuvre?

Would you continue takeoff with unknown huge bang in the back into IMC/icing conditions
Yes - that is what you are paid to do. If you decide not, that's your choice. But don't ask for sympathy or understanding if you foul it up. I would also wish you the very best in stopping lawyers from climbing all over you.

In general, you appear to obsessed with re-landing after a failure. Were you taking a day off when Performance A was started? Have you not read the overviews of certification standards? It is intended that modern aircraft will be safe to operate from the start of their take-off roll until they are stationary after having commenced their takeoff roll. Basically Take-off Performance considers engine failures, wind, runways etc. and make an assumption that you'll either fly or stop. Flying and landing are NOT considered because it's too complicated and I'd also suggest beyond that capability of most people here, excepting yourself of course. If you want to do it that's fine. Fill your boots but don't try to sell it here.

[Dont Hang Up]

According to wikipedia the US Federal Aviation Administration (http://www.pprune.org/wiki/Federal_Aviation_Administration) defines:


V1 means the maximum speed in the takeoff at which the pilot must take the first action (e.g., apply brakes, reduce thrust, deploy speed brakes) to stop the airplane within the accelerate-stop distance.

but strangely also


V1 also means the minimum speed in the takeoff, following a failure of the critical engine at VEF, at which the pilot can continue the takeoff and achieve the required height above the takeoff surface within the takeoff distance


In the case of the Citation on 12000 feet then
Definition 1 V1 would be VR
Definition 2 V1 could be as low as zero knots

Now I understand why there is so much discussion. ;)

[galaxy flyer]

Correct, mostly, on definition 1; not so much on definition 2. By definition, V1 cannot be less than V1mcg. That means it must be a two engine take-off to Vef, which cannot be less than Vmcg.

GF

[GlueBall]

..."Assuming sufficient runway length why restrict and deny myself an option of aborting takeoff at speeds much higher then V1..."

Have you considered brake energy limitations...? Take a scenario of max gross weight and abort 20kts beyond V1 [Maybe you've briefly rotated and put it back on the pavement]. Now you're "off the charts" because you're over max landing weight and rolling faster than your normal max landing weight brake application speed. Your brakes will go on vacation before a full stop. And then you'll be standing on the pedals, but just continue rolling and rolling. Think about it. :rolleyes: