When you have an option of lowering your V1, as you do on the FOVE system, what are the advantages/disadvantages? I see it alters your max Alt level off hight, but how does it affect the four stages of your departure?
Lowering the V1, to me is a "ground" problem. Trying to get airborne with a lower V1, begs the question. Will the aircraft accelerate, in distance, between the reduced V1 and the rotate speed, should there be a power failure just after the reduced V1?
I would prefer to run off the end of the runway at low speed should there be a rejected t/o, than be off the end of the runway at high speed and at full power, trying to get airborne.
Joe, you need to do some research into V1 if this is your take on the subject:
I would prefer to run off the end of the runway at low speed should there be a rejected t/o, than be off the end of the runway at high speed and at full power, trying to get airborne.
Try a search of this site and then come back and write something sensible.
When you read through the whole procedure for calculating a V1 speed then it makes sense.
You have to go with the book values, otherwise why bothering trying to go fly at all? Is there anything intuitive that suggests hundreds of tons of aircraft should hoist itself off the ground using interaction with tiny molecules of air? Not to me! It works, though.
Think about a slippery runway. You will have trouble stopping, so that you use a low V1 speed because you will have a long accelerate-stop distance. Try to stop moving any faster than V1 and, yes, you will go off the far end, when low speed or high speed you are going to have an accident. Trying to go shouldn't be such a problem, though; the remaining engine or engines get you up to Vr and away you go!
If you are one of nature's pessimists who doesn't trust mechanical devices more than a little, tiny bit then aviation probably isn't for you in the first place. To see what I mean, try looking out the window the next time you are off to someplace or other in a 4-engine airliner to see just how long it takes, how far down the runway you are when that thing finally starts flying. You seriously think it would be a good idea to ignore having passed V1 to stomp on the brakes and hope to stop a 747 or A340 in the little bit of runway left?
No, sorry, it doesn't work that way even if it seems as though it should! If it did then we would all be much safer flying low and slow, eh?
chuks, we would be safer. I was once told "man is a low-level, low-speed, 1g animal" and that makes sense to me.
On a more serious note, (excuse me if I'm a bit rusty, I've been retired a little) the option to select more than one V1 can only occur if you are at a weight below the runway limit. There is then a range of available V1s and generally the airline decides whether it is a "go" or a "stop" airline, and publishes the V1 accordingly in the tables. Usually it's a "go", especially if the problem occurs at high speed. The aircraft will get airborne; you then have time to declare the emergency, brief the crew and pax, perhaps burn/dump fuel and arrive at the beginning of the runway at a lower speed rather than stopping from some way down the runway at the much higher speed of a reject.
If you have a range of V1s surely the selection depends on the situation? There are somes places where I would certainly not want to go off the end of the runway (Funchal or Luton spring to mind) but if I was a tad low on the screen height it wouldn't matter to much since there is a near vertical drop off the end of the runway!
On the other hand perhaps if I have stacks of field length but there is a significant emergency turn in the event of engine failure (Malage Rw 31 for example) then I would opt for a maximum V1 since I should be able to stop with space to spare whereas I would prefer not to do the ET through 180 degrees on one engine will high MSA after the clean up etc.
in our ATOGs we would use a lower V1 on a slippery runway and the MGTW is reduce to be able to get the plane in the air at a slower speed. so you can't change the V1 without changeing the MGTW, in my opinon. on the 737
Great to see a "sky god" on the boards!! Rare thing these days.
Let me give you a piece of advise sonny. Get yourself about 20,000 hours and some real heavy time on a/c at very heavy weights, (freighters) then you maybe in the running to make comments, in a way, such as yours. When and if you ever do come up with that sought of experience, you will be open minded enough to take on board what a person is trying to explain and not come down on a person like a ton of bricks.
I may not be an academic, such as yourself but know a little about aviation and enough not to try and re invent the wheel. None of us here know all the answers and that includes you.
Joe and fullyspooled are an aggresive pair! Ton of bricks indeed!
I was merely pointing out that your statement about sliding off the end of the runway showed a distinct lack of understanding of the methodology and application in producing the V1 figure. I merely suggested that you do some research before posting any further, what could be, misleading thoughts on a thread where the OP needs the correct information.
Incidentally, I do have over 20.000 hours, a lot over, and I do understand the concept of lowering V1 under certain conditions.
And why is a fully laden freighter heavier than a fully laden passenger aircraft? Such a statement leads me to believe you skipped a few Perf A lessons.
And don't call me, or anyone else on this site 'Sonny' ; it is a display of aggression, condescension and ignorance.
My advice in using the Airbus FOVE/LPC is to stick with the figures it gives you having made sure that all your selections on the F3 (T/o Perf) page are correct ie R/W state, anti-ice, contaminant depth, packs, optimum config ets. Airbus 'Grips' tell you a little about its logic, but it is clever and my take is that you mess about with it at your peril - unless, of course, you have good reason for doing so!
When you have an option of lowering your V1, as you do on the FOVE system, what are the advantages/disadvantages? I see it alters your max Alt level off hight, but how does it affect the four stages of your departure?
I've not used the system, so the following is guess work. By lowering the V1, the system may alter other variables such as MTOW which would have an impact on the max Alt level off height.
As for disadvantages, a lower V1 means you are slightly more likely to take a problem into the air with you. The advantage is it makes it less likely for you to take that problem off the end of the runway and into anything sitting at the far end should you react very slowly to the problem before V1
Low V1 will tend towards go. statistically safer. It will reduce climb perf so if obstacles are an issue it may restrict MTOW. It will reduce level off alt due to TO Thrust time limit. Got to be clean and on speed at the end of TO thrust time limit so to do this with a early Vef you need a lower accel height.
I'm not much of an academic and I don't have much over 20,000 hrs, but I do have some experience calculating slippery runway V1. First you figure your normal V1. Then figure it for your runway limit weight which (assuming that you are below your runway limit weight) will yield a larger number. Then go into the charts based on the difference between actual weight and runway limit weight to get an unbalanced field adjustment which you apply to your runway limit weight V1. There are a couple of more steps which aren't difficult when you have the charts, but are hard to explain. When you get to the end you have a range of several knots from which to chose your V1 any one of which will allow you to stop or go on that day on that runway. Where I worked last it was a crew decision whether to use it and what number to use.
