V1 = Vr, Balanced field???

[Alpine Pilot]

hi there,

ok I know what balanced field lenght, ASDA, TODA and all that stuff is, so no explination needed here, but is it possible to have a balanced T/O with V1=Vr?

What advantages do I get of reducing V1 on a Turboprop on a long runway?

Thank you!

[Old Smokey]

Yes, it is possible to have a Balanced Field Length with V1=Vr.

The advantages of reducing V1 on any runway in any aircraft is to make the Accelerate-Stop manoeuvre less limiting. The Disadvantages lie in making the airborne portion of the Takeoff from V1 to Vr to 35 feet at V2 MORE limiting.

Regards,

Old Smokey

[Alpine Pilot]

Thank you Old Smokey,

well it sounds kind of strange either to lift off at a slightly higher speed as Vr and reach 35 feet after a few seconds, or stop at V1 (wich is the same as Vr in that case) and only need the same distance?? Must be a hard stop??

My problem here is my company usually always uses V1 = Vr, and they always talk about balanced T/O, and know from one day they suddenly decided to reduce the V1 for 6 knots for every runway. Yet they suddenly talk about unbalanced T/O.

In my opinion know it´s rather an balanced T/0 then before? Isn´t it?

Yes Old Smokey I understand that with a reduced V1 it´s "easyer" to stop, but with a Dornier 328 on a 3500m Runway never a problem.

And Old Smokey I saw you are quit familiar with performance, so I have another question: In our IRT´s of Innsbruck airport I noticed that with a certain level of contamination I can suddenly increase my T/O weight again. That´s not making any sence for me?? Or is there something I do not see??

Thank you!

[alatriste]

alpine pilot:

Yes you can operate balanced when V1=VR, BUT only if VR is reduced to V1. If V1 is increased ASDR will be longer than TODR and therefor the TO will be unbalanced.
Sometimes , very very heavy or very very light aircraft, V1 must be reduced or increased to comply with Vmcg, Vmbe restrictions, in this scenario V1 might equal VR BUT won´t be a balanced take off.

In a long runway does not make sense to reduced V1, What for?

Regarding taking off from a contaminated runway, YES it can happen that your RTOM or OTOW (however you call it) might be higher if the deposit is deeper. WHY? Consider that if this deposit is a fluid contaminant( slush, loose snow) it will decrease the braking performance but also will increase the precipitation drag( displacement and spray impigment drag). So as your max take off weight will be a "trade off" between the accelerate go and accelerate stop, with a bigger drag you may find out higher weights when the depht of the deposit is higher.

[Alpine Pilot]

Thank you for the good answer! So I´m right that it doesn´t make any sense to reduce the V1 on a long runway!

That´s interesting with the contaminated runway. But isn´t my acceleration due to the contamination slower i.e. my ASD get´s longer? Or is the drag of the contamination that great that I have a better braking action as on a dry runway?

Thanks!

[oldebloke]

With the developement of eficient braking,the stop' case is improved to allow guys to go to V!/VR and stop on runway(the reject actioned by V1 as per thr 'rules'..Ergo the 'go' case is the worst(longest distance)case..
And has been pointed out that the 'reduced V1'on a long runway simply gives you an 'early' stop,or a more leisurely Go' case to the distant screen height.
With the use of 'clearway'these days very few Takeoffs are Balanced...
cheers:ok:

efficient-that is

[Old Smokey]

Alpine Pilot,

Clearways are sometimes available, Stopways are sometimes available, often they are unequal, or one exists and the other doesn't. If they're available, why not optimise performance and use them?

There's nothing sacred about using the 'Balanced Field' technique, in fact adherance to such a policy can be restrictive. Personally, I'd prefer to work with an unbalanced field to optimise both the Stop and Go cases.

Most commonly, V1=Vr when the aircraft is NOT Accelerate-Stop limited, i.e. when V1 could have been above Vr, but as this is not allowed, V1 is reduced to Vr.

Considering the runways that you're operating from, it's strange that your company has opted for a lower V1 speed schedule. I sincerely hope that this was an AFM / Manufacturer's option, and not just something that some bright person in the company thought of.

Because of the permitted credit for Reverse Thrust for the Accelerate-Stop, and a reduced screen height for Wet Runways / Contaminated Runways, it IS possible in some circumstances to have a Wet / Contaminated Runway RTOW in excess of that for a Dry runway. Common sense, safety, and in some cases the regulatory authority, dictate that if this is so, the lesser of the Wet / Contaminated and the Dry Runway limit weights be used.

Regards,

Old Smokey

[Alpine Pilot]

Thank you Old Smokey for the answer.
That´s what I thought: it doesn´t make any sense to reduce the V1 on a long runway.
And in fact it was the idea of a bright person, but they will change it pretty soon again to V1=Vr on the long runways, since other pilots are also asking for the reason.

Ok but one is still not really clear, I understand if V1=Vr it can be a balanced T/O or unbalanced. (but depending on what??, stop perfomance Runway condition wind,...)
And if there is a split between V1 and Vr can it also be a balanced T/O, when we talk about the same aircraft (Dornier 328)??
I guess not?? Then the ASD is shorter then the TOD. (we only used to have the split on very short Runways)

Thank you!

[Old Smokey]

Alpine Pilot,

I’m not familiar with the Dornier 328, so a lot of what I say here will be generic, and possibly not specific to your aircraft.

It concerns me that “some bright person” reduced the V1 for your aircraft without verification from the AFM or the manufacturer. If we look at the Accelerate-Stop manoeuvre in isolation, we can reduce it to anything we like, 20 knots if you like, and the Accelerate-Stop performance will be impressive. Unfortunately, we cannot look at the Accelerate-Stop manoeuvre in isolation, as V1 is both a “Stop” and a “Go” speed. V1, Vr, and V2 are variable speeds, they may be adjusted by the performance engineer as necessary to achieve the desired performance, but there are both Lower and Upper limits to this variation. Whilst reducing V1 will have obvious benefits in improving Accelerate-Stop performance, for the “Go” case from V1 there are two major considerations –

(1) V1 must be equal to or greater than VMCg, to ensure directional control for the continued Takeoff, and

(2) The aircraft must be able, with one engine inoperative, to accelerate from V1 to Vr, become airborne, and achieve V2 by the screen height.

Arbitrarily reducing V1 by 6 Kt may well place the aircraft below VMCg, and directional control for the continued Takeoff may not be assured. John_Tullamarine can provide some pretty graphic illustrations of such a circumstance. Acceleration to an additional 6Kt of speed with 1 engine inoperative may consume a prodigious amount of runway, not considered in your certified Takeoff performance data.

On very short runways, Accelerate-Stop performance will obviously be limiting, and V1 must be as low as possible (but not below the minimums specified by the AFM). This will require a weight reduction, which will provide a “Go” performance better than required, and acceleration from V1 to Vr to V2 presents no problem. As the runway becomes longer, V1 and the weight may be increased, Accelerate-Stop performance is retained because of the longer runway, but, at the higher weights, continued acceleration from V1 to Vr for the “Go” case becomes more limiting, and the V1/Vr delta must be reduced to allow for this acceleration within the available Takeoff distance. If we continue with lengthening the runway, V1 may continue to increase until it reaches, and passes Vr. As we cannot have a V1 greater than Vr, the upper limit of V1 then becomes Vr, i.e. V1=Vr.

During all of the processes described here, Balanced Field performance may be retained, i.e. ASD=TOD, by manipulation of the speeds, V1, Vr, and V2. Now, if you throw in a Stopway, or a Clearway, we have Unbalanced field performance. Accelerate-Stop and Accelerate-Go performance must now be considered in isolation, and the operation performed at the lesser of the 2 limiting weights.

At the end of the day, it gets down to the individual performance characteristics for each aircraft. One earlier aircraft that I did the numbers for had a superb stopping performance, and a mediocre continued Takeoff performance. V1 was always equal to Vr. The last aircraft that I number crunched had a mediocre stopping performance, and a superb Go performance. There was always a significant V1/Vr split for this aircraft.

Regards,

Old Smokey

[Jet-Base]

Yes, but purely coincidental.

Why does it matter anyway, it happens in a blink of an eye. Can YOU call VR AND V1 at the same time to within a knot? No, I dont think so, so your question is answered. So please, no more replies about this, its boring now.

And to all those stupid replies to come after this about me being a part of a boring thread, I am only reading this because I am drunk.

Thankyou, and goodnight.

Prawn shark whale dolphin.

[punkalouver]

I think it best to just ignore the last post. We eventually read about those types.

Old Smokey....you stated
(1) V1 must be equal to or greater than VMCg, to ensure directional control for the continued Takeoff...


..but I thought V1 actuall has to be a certain amount greater than VMCG. Is that correct?

[oldebloke]

JAR25.107(a)(1)VEF.This is the CASatwhich the critical engine is assumed to fail.It is never less than VMCG and is always less than V1..:ok:

not enough Swatton readers about\'Aircraft performance theory\',covers all the JAR stuff..
Cheers:confused:

Ergo as VEF is at least one second prior to V1(average,could be as high as 3 seconds on a triple engine aircraft)the V1 is at least 4knots higher than VEF/VMCG:O

[mutt]

Jet-Base, please get back to us when you are:
A: Sober.
B: Flying an aircraft where V1 doesnt equal VR.......

Oldebloke, please be very very careful to state the aircraft that you are talking about, the FARs have various amendments, for example the B737-100/200 & B737-300/400/500/600 & B737-700/800/900 are all certified under the same FAR but the amendments are different.

Mutt

[oldebloke]

Amendment 42 applies to FAR25-107(1978)which applies to all Types..Thats why the VEF definition appeared in the AFM's,or should be..
cheers:ok:

True, not all types took into account the, Amendment 42,two seconds more of runway distance required for the accelerate stop distance..And to date only the B777 has complied to all the nes rules(Boeing give the non FAR carriers the JAA data in their AFMs-performance B)...Never the less ,should one have occasion to refer to the REGS,the current references only reflect post amendment 42..
Cheers:ok:

[Jet-Base]

im sorry for being drunk last night and for my inappropriate post, bad habbits die hard.:ugh: :yuk:

mutt, i dont see your point about v1=vr, last time i flew the concorde that was the case (in fact, v1 was even better than vr :p).

no seriously, what is your point about flying an aircraft who's v1 doesn't equal vr? doesn't it depend on the conditions on the day and any performance limitations....? any aircraft can have a v1=vr

jet-base
xoxo

[LGB]

I have been amazed why small turboprop pilots (not the DO328, but smaller like King Airs etc) have been using the "VEE ONE ROTATE" call, instead of just "ROTATE", as most of these are not able to continue the take-off with one engine out and still on the ground. Why even have a V1 in cases where runways are way over the ASD? If I had not retracted the gear yet and still visual, why not just land straight ahead when there is still thousands of meters available? As long as it is briefed beforehand, I cannot see the problem in this - but, I have never done it (on turboprops) because it wasn't a procedure. What I have done once, on testing the landing gear on a twin turboprop, and briefed to go airborne, retract gear, extend gear and flaps and if not even half down the 2500 meter runway, land straight ahead. Also requested this to the tower, and when coming to a stop, without using the brakes, there were still 1000+ meters left.

Point is, with a runway way over the requirement, why force a small twin prop with an engine failure at rotation all the way around the circuit, when land straight ahead is the easiest and safest? (look at all the engine out after take-off crashes).

As I am aware, the DO328 is not a heavy runway consumer, so lowering V1 will just force yourself in the air with no reason, unless you are on a really short runway.

With heavy aircraft it is of course a different story, as the large airport runway lengths are there for these types mainly, and brake energy limits and other nasties come into play here.

[Old Smokey]

LGB,

When V1=Vr MOST operators simply call "Rotate", as V1 has already passed and is now redundant.

Regarding your comments regarding the "land ahead on long runways", fine, go ahead do it, just as soon as you've done the certification, test flying, approval by the regulatory authority, published the approved data in the AFM / AOM, trained your pilots in the procedures required, and had it approved by the regulatory authority for the country which you're operating in.

Regards,

Old Smokey

[LGB]

Old Smokey,

As I wrote, I didn't do this myself, but I wonder why it hasn't been done. You can always use common sense and if you have a 2000+ meters of runway left on an aircraft that only uses 500 meters, why not just land straight ahead (if you still have the gear down)? Understand it this way, why isn't there a procedure for this ...

[Old Smokey]

LGB,

I hear loud and clear where you're coming from, but, at the end of the day, it depends upon whether you're flying an aircraft which has GUARANTEED one engine inoperative performance from V1 (e.g. FAR 25 aircraft and their equivalent), or flying an aircraft that DOES NOT have guaranteed one engine inoperative performance.

For aircraft that DO have guaranteed one engine inoperative performance from V1, accident statistics heavily favour the continued Takeoff. For the aircraft which has no guaranteed OEI performance after V1, then it is up to the pilot's judgement - Is the available OEI performance and obstacle clearance adequate to ensure continued flight? If so, there should be no fear in continuing. If not, then the best "controlled crash" possible is the only option, and, if there is sufficient runway remaining, putting the aircraft back on the runway expiditiously sounds perfectly reasonable to me.

You pose the question - "why isn't there a procedure for this ...?" To begin with, there's an enormous number of variables, the most important of which seems to me to be the height above the runway that the Takeoff is aborted. We'd require a new term, "H1", to replace V1, being the maximum height at which airborne flight could revert to a landing. The computations would be enormous. I've done performance analysis for Touch and Go landings for heavy (FAR 25) aircraft, which is essentially a OEI landing converted to a OEI Takeoff, and that's a complex process. What you propose would be mind-boggingly more complex to prove.

I've been fortunate (unfortunate?) enough to have had 2 complete engine failures after V1, and one RTO from very close to V1 in my career. The RTO was a heart-stopper, whereas the continued Takeoffs were exciting, but relatively uneventful. Added to that are dozens of deliberate RTOs from near V1, and deliberate engine cuts (fuel off) at Vef during certification flying, and personally rate the RTO as 10 to 20 times as dangerous as the continued Takeoff. Statistics back up my gut feeling.

In closing, be assured that if you're flying an aircraft with guaranteed OEI performance after V1, and choose to land on the remaining runway, you won't have a legal leg to stand on, even if you don't even scratch the paint. For other classes of aircraft, it's up to your judgement, and the accident enquiry will demonstrate much "wisdom in hindsight" in examining your case.

Regards,

Old Smokey

[john_tullamarine]

Some considerations ..

(a) the discussion is getting very much into weeds level

(b) the concern is a very dynamic aircraft motion environment which is trained for in the sim in a fairly narrow sort of way

(c) the more options which are available, the more training is appropriate and the more opportunity there is for the crew to get it wrong on the (rare) day when training is put to the test

(d) given that historicals suggest that continuing the takeoff post V1 has a better chance of favourable outcome, why load the dice against yourself ?

(e) physically, of course the takeoff/land scenario can work on a runway whose length is very much more than required for a particular aircraft .. but do you really want to trade a trained-for recovery for an ad hoc finger-in-the-wind-on-the-day procedure ?

[LGB]

Regarding the "land straight ahead" I did mention that it was for smaller turboprops and piston multi engine aircraft. Look in the accident statistics for these, and a great deal of these engine failures right after take-off result in an accident, especially the ones where the aircraft have been overloaded.

For JAR/FAR 25 aircraft I totally agree that I'd rather be go-minded, especiallt when the runway length and ASDA is limiting.

Has anyone here adressed the timing issue I brought up yet? I think not. So why not incorporate timing in the V speed calculations? (or was that another thread I wrote this in?)

[john_tullamarine]

Concur totally with the suggestion that one ought to separate the smaller Part 23 and Part 25 aircraft. One's engine failure at rotation in a light twin is a whole different ballgame to the equivalent event in a Boeing or Bus.

[moon_towers]

Gus,

Fokker Family applying V1 = VR

cheers

m_t;)