Take off V2

[Georgey]

If you apply all corrections for your RTOW figures and find out that V2 is less than VR what do you do?

[Pugilistic Animus]

Why did that occur with you?... sounds suspect explain more

[mutt]

Round V2 up to VR........

Mutt

[chornedsnorkack]

If you discover that you have a plenty of runway, so that you can accelerate to V2 while on the runway, do you then have restrictions on take-off weight?

If you have enough runway, you might consider derating engines. Or you could consider climbing above V2 if it improves your L/D.

[john_tullamarine]

.. and, more importantly, the book from which you derived your numbers should have some words as to what is expected/required in such circumstances

[Georgey]

No words to explain, only the usual make sure it is above vmu/min v2.
Nothing about if it falls below vr as it sometimes does for a lot of corrections.
But I presume all you can do is increase it to vr as mutt said.

[Pugilistic Animus]

while I'm not attempting to dispute Mutt,

I see looking at some old TO schedules for a Boeing 757-200 with RR's ---and the following annotation is stated---" If V1 exceeds Vr set V1 equal to Vr" , but I cant find any reference for setting V2 = Vr--- it must be an engineering decision covered under a few mind boggling layers:confused:--- to which type do you refer, just curious?

[Capt Chambo]

I have a hazy recollection that V2 and Vr have to be proportional, and that an adjustment to one needs an adjustment to 'tuther!
I am sure when Old Smokey sees this thread he will be able to answer the question.

[Mad (Flt) Scientist]

You can't legally set V2=Vr because of
§25.107 (c) V2, in terms of calibrated airspeed, must be selected by the applicant to provide at least the gradient of climb required by §25.121(b) but may not be less than—

(1) V2MIN;

(2) VR plus the speed increment attained (in accordance with §25.111(c)(2)) before reaching a height of 35 feet above the takeoff surface; and

(3) A speed that provides the maneuvering capability specified in §25.143(h).

Item (2) means you have to account for the "speed spread" between Vr and V2 - the aircraft physically MUST accelerate between Vr and v2, and that has to be taken into consideration.

But fundamentally JT is correct - the book should cover this, if it doesn't I'd strongly suspect an error - unless you're doing something so unusual you are the first person to encounter this....

[hawk37]

MFS, Dassault seems to choose Vr = V2 for the Falcon 50, at all times. There are no exceptions I'm aware of. It was once explained to me that Dassault choose to increase Vr to the value of V2. I believe for many of their other aircraft too, perhaps the falcon 20.
Hawk

[john_tullamarine]

the book should cover this

.. this applies generally for any operational document to which a pilot might refer .. unless the specific matter is so "standard" that it comes under standard practice considerations.

The problem is: while those in the know may be able to divine what was intended, but left out, it is totally unreasonable (not to mention potentially dangerous) to presume that all readers will have the deeper knowledge to "read between the lines" to determine how to handle omitted data.

If a manual does not have guidance to cover all eventualities in its use (other than for standard practice considerations) then the fault is with the book and the matter ought to be referred to the document sponsor for review and correction.

Many of us could rattle off a long list of horrifying workarounds developed in ignorance by well-intended folk in the face of badly constructed documents ....

Dassault seems to choose Vr = V2 for the Falcon 50, at all times

Not done much on the Falcons and not for a long time so I shan't try to dredge the memory ...

A couple of points

(a) the Design Standards (FAR 25 and the like) give the starting point .. in a specific certification, though, numerous minor workarounds and changes may be negotiated between the Authority and the applicant. If we wish to migrate a requirement from the Standard to a specific aircraft, then the information in the TCDS also must be consulted .. the bulk of changes are noted in the TCDS for the Type. Add to this a host of minor agreements which don't make the TCDS and it becomes very difficult to pontificate on the specific without access to the certification records.

(b) the Design Standards are an evolving beast and, generally, don't apply retrospectively. As for (a), it is a brave person who tries to migrate the current Standard's requirement to a specific Type without checking the TCDS first .. usually it is necessary to go to a superseded version of the Standard to get the starting story ...

[galaxy flyer]

I am dredging my experience, but also believe that any increase in Vr requires an identical increase in V2 up to some maximum Vr increase.

GF

[Mad (Flt) Scientist]

That rule relating Vr and V2 has been the same since the original release of Part 25, in 1964. I *think* that predates the falcon 50, though of course what regs the French were following at the time is another question....

I guess I don't really see why they are setting V2=Vr (or Vr=V2; I wonder which is the driver hmmmm). I'd hate to think people were actively trying to rotate so aggressively as to have no speed increase between rotation and the screen height. So the distance to the screen is surely based on a realistic V2, not the notional one equal to Vr? I'd have thought they must be penalising themselves by doing this? Unless it's some weird three-engine thing??

Quick check of the FAA TCDS for the Falcon 50 shows stated compliance up to Amdt 34, with one Special condition which does NOT mention takeoff speeds at all (it relates to the APU and max altitude, basically). I'm confused (as usual).

[Pugilistic Animus]

Exactly what I was thinking MFS ---that is what I'm so confused about---


--- I was thinking also about three and two engined 'ferry V2s' as the only acceptable case and FAR 25 leaves a good a lot to be desired in that scenario anyways:(

I don't see how there can be no Vr/v2 spread??? must be operator error???

[chornedsnorkack]

(2) VR plus the speed increment attained (in accordance with §25.111(c)(2)) before reaching a height of 35 feet above the takeoff surface;

What does that part require?

I have heard it alleged that, before the early jets came out with their huge runway requirements, it was the standard procedure to accelerate on ground to V2 and rotate then. Precisely what is wrong with setting V1=V2?

[Alex Whittingham]

MFS, surely the requirement to make V2 at the screen height only applies OEI? In the all engines case it would be V3 at the screen.

[john_tullamarine]

In the all engines case it would be V3 at the screen.

The bulk of the certification stuff for takeoff looks at the OEI case.

The basic risk management requirement is that the AEO flight path should stay somewhat well above the OEI worst case locus defined in the AFM numbers. By following the recommended OEM procedures, this should occur in a reliable and repeatable manner.

Often this might be a case of pegging the OEI body angle (say for lower performance props) or having two different body angle targets for OEI/AEO (higher performance aircraft) or whatever ... generally we are not too worried what the actual AEO speed is until well established in the initial climb.

[Mad (Flt) Scientist]

I guess my concern is mainly about the air distance part of the takeoff.

If the book is assuming V2 (or V2+10 AEO) at the screen, based upon some (unknown) Vr, and using those data to calculate the distance covered from rotation onwards (and, indeed, from start to rotate too) yet you arbitrarily round V2 upwards to a (possibly erroneous) "Vr", are all your distances now out of whack?

Plus, if the discrepancy is huge, are things like trim settings or forces during the rotate going to be wrong too? I agree you've probably got speed in hand, and thus plenty of margin to the stall, but there's a reason the regs put LOWER limits on the scheduled speeds - because if they didn't, the OEM would be tempted to set them dangerously low, to gain a bit more performance. Thus, overly fast speeds MUST be hurting you somewhere....

[411A]

In all old piston types, and most turbopropellor types, and yes, even a very few old CAR4b turbojet types (with certain exceptions)....Vr=V2 in nearly all cases.
Only on later types was it specified by the regulatory certificating authority of the necessary Vr/V2 spread, and yes, on those types, it is mandatory.

Read the book carefully, folks, and do not interpolate un-necessarily, for if you do, there are definite traps for the unwary.

[Pugilistic Animus]

Having carefully read every post very carefully,

My question is what would the TO procedure be using that method?

AEO--- rotate at V2 accelerate through Vlof, but cross the fence/screen at V3 or V4? i.e would V3=V4?

Vef occurs near V1 accelerate OEI to V2 [which is now Vr] and Cross the fence at V3 [V2=V3] perhaps V3 exceeding the V2 additive do you pitch up to V2+additive or to V3? if so call V3-- V2?

would it be like a V2 over speed?

---but I don't get how the increased distance would profit climb gradients, nor field length where's the benefit?----why would an OEM apply for such an amendment to the TCDS?

Sounds way too complex for a---while I agree that one shouldn't second guess the AFM, there must be some definitive guidance for pilots how to handle this situation the most limiting and critical scenario---hence my curiosity as to which type do you refer? [original poster]

:confused::confused::confused:

[I misspoke slightly above--- ferry V1max may equal Vlof]