Talk:V speeds

Italics?

These are all variables; should they really be V speeds? E.g., V_S rather than V_S?—Ben FrantzDale 17:39, 9 June 2006 (UTC)

Merge with Speed article?

User:Iancarter has added a tag suggesting that this article be merged with speed.

no: V-speeds are a detailed and technical topic, and there's too much information here to be merged in a general article on speed — it would be like merging Lake Ontario into Lake. David 01:32, 12 June 2006 (UTC)

but: both this article and the speed article are not too detailed and actually I was missing the V speed information in the speed article. You are correct, V-Speed is a technical aviation term but speed itself is also a physical property that should include all the different variations - it is where the non-expert would look first. (Lake Ontario is a specific lake while V-Speed is a variation of speed) However, I get your point - let's get some more discussion input... -- Iancarter 02:00, 12 June 2006 (UTC)

Please don't merge. These speeds are not even true speeds but speeds relative specifically to the air. Even then some of them are not relative to true airspeed but rather the speed as indicated by an airspeed indicator so as to ignore pressure (altitude & temp) differences. Link from speed to here if you like. Paul Beardsell 07:05, 14 September 2006 (UTC)

I concur with the above; this article should NOT BE MERGED with "speeds". V-speeds are not real velocities, but rather limitations on operations of an aircraft as indicated in KIAS. V_NE is a limitation, not a measurement of movement. Kob zilla 00:03, 31 October 2006 (UTC)

LOWER CASE subscripts

As far as I can remember the subscripts are lower case. It's V_fe not V_FE in all (UK and NZ) flight training manuals and (US written) aircraft manuals. Paul Beardsell 07:02, 14 September 2006 (UTC)

I don't think it's universally upper or lower. I've certainly never seen V_ne or V_d - these two, at least, are upper-case in all my reference books. Tevildo 23:21, 22 September 2006 (UTC)

If it could be considered an authority at least for US use, FAA Publications that I've read such as the Airplane Flying Handbook (FAA-H-8083-3A) and the Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25) both write with the subscripts in uppercase. My copy of the 2007 FAR/AIM (ASA-07-FR-AM-BK) also uses uppercase in the subscripts. I have generally assumed that lowercase is used when superscript isn't easily available to the person creating the document. Aaron Landry 22:42, 4 November 2006 (UTC)

I can't stop!

I've seen reference to a "refuse speed", above which an aircraft is unable to stop before running out of runway. Anybody know what the V speed ID is? Trekphiler 09:11, 22 October 2006 (UTC)

To the best of my knowledge there isn't one. We've always just used "V_refusal" as the written form and called out "refusal" when we pass it on takeoff roll.Kob zilla 00:03, 31 October 2006 (UTC)

I think this is V₁, commitment velocity, for single engines, and for multi-engines when V_refuse is lower than single engine takeoff speed. If you have a long runway, i.e., V_refuse is greater than single engine TO speed, V₁ may be set anywhere between the two.RandallC 07:10, 17 December 2006 (UTC)

Proposed merge with various V-speeds

I propose that these other articles on specific v speeds be merged and redirected to this article. Most of these articles are stubs. This iformation is also much more useful together. -- Chrislk02 (Chris Kreider) 20:00, 23 January 2007 (UTC)

• Support. Paul Beardsell 23:59, 23 January 2007 (UTC)
• Support. —Ben FrantzDale 00:07, 24 January 2007 (UTC)
• Disagree. Shane Pinder 16:00, 29 January 2007 (UTC)

I note that, while you took the opportunity to place this on a talk page, you carried on with the edit almost immediately. Stubs are just that, stubs. They are meant to be expanded, not deleted increasing our problem with the Reliability of Wikipedia. Your suggestion has been made in the past, and reverted. Perhaps you could spend your time expanding as opposed to making me once again revert a drive-by edit. V₁ speed, for instance, is a topic on which a few dozen PhDs have based their careers because of the importance of the concept in the aviation world. If you have nothing to add, leave it there for someone else to amplify. For my part, I will wait until I have put together a substantial article that will not be removed by every student pilot with a thirst for increasing their number of Wikipedia edits. Perhaps this comment is mean-spirited, but you won't catch me editing the Wikipedia page on the C programming language just because I've spent a few hundred hours using it, because I know there are contributors who have much more knowledge on that topic.Shane Pinder 16:00, 29 January 2007 (UTC)

Vno

Vno is generally understood to be the speed below which you can make abrupt control inputs. This is true with regards to elevator and ailerons, according to the regulations, but not necessarily true for the rudder. Particularly, the rudder is not required to be strong enough for a "checked" (back and forth) manouver to be made, even when flying below Vne. This is believed to be the cause of the crash of at least one commercial, passenger-carrying airliner. Only aerobatic aircraft have to have a rudder strong enough to withstand these forces. I don't know which airliner it was that crashed, but I'm pretty sure references could be found. It has been published in Flyer Magazine (UK) a while ago. (that information can be found here http://en.wikipedia.org/wiki/American_Airlines_Flight_587)

Vne Elaboration

Hi, I noticed the V_NE paragraph mentions 'TAS' (I assume it's an abbreviation for True Air Speed?). If someone more knowledgeable could add the full version of this acronym at some point I think it would help make it clearer for us 'laymen'. Many thanks IE 20:43, 6 November 2007 (UTC)

Yes, TAS means what you said. I've removed the paragraph in question, though, because it was an unnecessary digression on aerodynamic damping, TAS/IAS ratio and so on, with no additional information on the Vne itself.
Giuliopp 23:03, 6 November 2007 (UTC)

Presentation format into table?

Upon first viewing this article, I noticed that many entries are repeated in the various sections. I'm wondering if a multi-column tabular format would enhance the presentation. For example, a line would be a specific entry (in alphabetical order), and columns would provide the name (Vx), definiton (Best angle of climb), Airspeed type (TAS, IAS, etc), and any other of the characteristics as currently noted in the article (specified by regulatory authority, etc). Jasmantle (talk) 00:09, 20 January 2008 (UTC) —Preceding comment was added at 21:31, 19 January 2008 (UTC)

America and Canada

The information is now nicely ordered in a table, but it has two columns: "America" (FAA) and "Canada", is it possible to make a new column for ICAO, or merge it into the "Canada" column?

Stefanlinden (talk) 17:30, 25 June 2008 (UTC) Yea, it is possible. Do you have a link to a source for the ICAO values/definitions? Chrislk02 ^{Chris Kreider} 17:32, 25 June 2008 (UTC)

The image is wrong?

Seems to me that the arrows aren't pointing to the correct locations. For instance, Vfe would be the END of the white arc. And Vne right on the red line. And Vno the end of the green arc.

I'm a student pilot, so I admit I may be incorrect. But it looks wrong to me. I know it's direct from the FAA handbook, but I don't see how it's correct. W@ntonsoup (talk) 22:29, 30 July 2008 (UTC)

Well you are a good student, because your observation is entirely correct. That diagram did come from the FAA, but the arrows that label it are displaced and pretty much every one of them points to the wrong place. I think that in the interests of not confusing people that diagram ought to be fixed or removed. - Ahunt (talk) 22:57, 30 July 2008 (UTC)

I agree. The website(s) that are quoted as the source for this image is not available so it isn't possible to see exactly what the original image looks like. However, the image on V speeds is clearly misleading and should be removed, at least until it is repaired. Dolphin51 (talk) 23:09, 30 July 2008 (UTC)

Dolphin51: Thanks for taking care of that. - Ahunt (talk) 23:22, 30 July 2008 (UTC)

I will see if I can get a good ASI photo and construct a better labeled image, - Ahunt (talk) 23:33, 30 July 2008 (UTC)

I like the new picture. I used the old one because I had cut it directly our of FAA material but the new one is much better. Chrislk02 ^{Chris Kreider} 16:49, 31 July 2008 (UTC)

Glad that you like the new one better! I decided to make it an assignment and biked down to the local airport to take a photo specifically for this article. User:Poocat9 did the lettering and arrows for me. Hope it makes the article better! - Ahunt (talk) 17:25, 31 July 2008 (UTC)

Globalization

User:GW_Simulations tagged this article on 21 Aug with a Globalize tag. In looking at the article I think he is right. V speeds are used everywhere, but the top table, due to its US and Canadian checkmarks, is rather US/Canada centric. In looking at the table I don't think it hurts to remove the checkmarks and make the article more international by doing so. This opens the list up to additions from other sources. I have made this change. - Ahunt (talk) 13:46, 24 August 2008 (UTC)

My iniitial goals were to find the other sources of governmental defined v-speeds and compare them in the checklist. I however could not find any other governmental sources to finish the project. Chrislk02 ^{Chris Kreider} 14:38, 24 August 2008 (UTC)

No problem - if we find other countries we could just revert it! - Ahunt (talk) 20:48, 24 August 2008 (UTC)

Citations

I have been going though all the sources I can find and have referenced every V speed that I can, so far. The remaining uncited ones are all in the V_speeds#Other_V-speeds section and have been fact tagged. If anyone can cite any references for those remaining uncited speeds that would be great, otherwise eventually they will be deleted as unref. - Ahunt (talk) 01:24, 20 January 2009 (UTC)

I haven't checked to see if you have deleted unref-ed V-speeds but I do not think you should. If we removed all uncited statements in WP a lot of correct statements would be removed. May I suggest that the criteria for removing a V-speed or anything from WP are these: (a) the statement is unref-ed AND either (b) you think it is wrong, and having said so, no one disagrees or (b) you know it to be wrong and you have said so on the talk page. This corresponds roughly to accepted WP practice. Paul Beardsell (talk) 21:26, 22 September 2009 (UTC)

I think I managed to find sources for all of them, except where they were clearly duplicates of existing ones already in the other section. Finding sources has sometimes been a challenge but I don't see any that have been missed lately and it is worthwhile to make sure we have an accurate article. - Ahunt (talk) 22:00, 22 September 2009 (UTC)

V₁

An IP editor (at Boeing apparently) recently changed the definition of V₁, replacing the existing text and refs with a copy and paste of the FAA definition from the FARs. While the FARs are public domain and this is therefore not a copyright infringement, there are two reasons not to do this:

1. The definition of V₁ is different in different countries, although all have definitions that are generally along the same lines. Using the exact FAA definition is Americo-centric which Wikipedia seeks to avoid.
2. If Wikipedia were just going to duplicate the FARs then we wouldn't need Wikipedia at all - we could just publish the FARs again.

The aim with Wikipedia is to provide a global view and also to not just copy and paste text from other sources, even if they are not copyright infringements. Furthermore please do not remove valid references as this will be mistaken for vandalism. - Ahunt (talk) 18:21, 25 August 2009 (UTC)

Once again I agree: But something else that should be avoided is the use of references which do NOT support what is being said! That is more annoying than the removal of a reference as the use of a citation means someone is saying this has been fact checked and here is the proof. Paul Beardsell (talk) 20:36, 22 September 2009 (UTC)

It is now almost three years since the various articles on specific V speeds were merged into this article, against my objection. There is now more discussion on this talk page regarding V₁ speed than there is text in the entire parent article! My compliments to Dolphin51 and Ahunt for your efforts to question other contributors. I wish I had your endurance. Perhaps now some might agree that separate space is deserved for some specific V speeds? If not, I'll wait another three years, and see where we are then. Shane Pinder 16:00, 15 October 2009 (UTC)

Nice to hear from you. The section explaining V1 is pretty short and concise right now, but I can see that if other V-speeds need more lengthy explanations that it might make sense to have individual articles linked from this one to explain them in more detail. At this point I would want to see enough text added here that each would be long enough to stand on its own as more than a stub, otherwise that would only invite proposals to merge back in here!! - Ahunt (talk) 14:41, 15 October 2009 (UTC)

Hi Shane. Thanks for your complimentary remark. My contribution to V speeds has been miniscule compared to the Herculean efforts of Ahunt. His perseverence and attention to detail have been truly remarkable. If he didn't already have the Aviation Barnstar he would certainly have qualified for it through his contribution to V speeds alone. Perhaps we should develop the Airspeed Barnstar with Ahunt as its inaugural recipient.Dolphin51 (talk) 22:34, 15 October 2009 (UTC)

V₁ - two definitions

I take on board that written above by Ahunt and I agree but the problem with re-interpreting the definitions and putting them in our own words is that it can introduce uncertaintly, inaccuracy or perhaps even make them incorrect! So the difficulty is making sure we get it right. And I don't think we have with V₁. Currently we define it in this article as quoted below but I claim it is defined twice and that these are not mutually compatible, and I insert (a) and (b) to identify them:

"(a) Maximum speed during takeoff at which a pilot can safely stop the aircraft without leaving the runway. (b) This is also the minimum speed that allows the pilot to safely continue (to V2 takeoff) even if a Critical engine failure occurs (between V1 and V2)."

No. (a) must be wrong if (b) is correct. Example: If the runway length is 10km and the aircraft is a small twin the above cannot be true. The small twin can takeoff, climb to 1000ft, land and stop in the 10km available. The V1 of (a) would be much higher than the V1 of (b).

And, no: (b) must be wrong if (a) is correct. Example: If the runway length is only 1000m long and the aircraft is a 747 then the brakes better be applied well before the pilot could safely continue to V2.

Now I know that the second example is contrived - the pilot would have had to make a mistake to attempt a take off - but the situation occurs at hot and high runways - sometimes a heavy aircraft must offload weight or the departure must be delayed til the evening. And if the flight is not a commercial passenger op then often a take off is performed where not enough space is available toeither safely continue or to stop should an engine fail.

So the definition of V1 is wrong. It is either (a) or (b) but cannot be both. Which is it?

Paul Beardsell (talk) 20:36, 22 September 2009 (UTC)

You make a good point - the main challenge of re-writing in our own words is to get it right! So let's have a look at the three cited sources and see what they say about V1.

FAA says:

"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."

TC says:

"Critical engine failure recognition speed *" and adds a footnote: "This definition is not restrictive. An operator may adopt any other definition outlined in the aircraft flight manual (AFM) of TC type-approved aircraft as long as such definition does not compromise operational safety of the aircraft."

and From the Ground Up (a Canadian ground school text) says:

"Critical engine failure speed. Take-off decision speed. The speed above which the take-off is continued, and below which the take-off is abandoned in the event of an engine failure."

The article currently says:

"Maximum speed during takeoff at which a pilot can safely stop the aircraft without leaving the runway. This is also the minimum speed that allows the pilot to safely continue (to V2 takeoff) even if a Critical engine failure occurs (between V1 and V2)"

All are different and the article text doesn't conform well to any of them (none mention V2 for instance), so we have to decide whether we should create one definition from these (plus any other refs that can be found) or detail the national differences. I think it is worthy of note that the TC definition allows air carriers to create their own V1 definition, subject to TC approval of their procedures. This pretty much guarantees that the FAA definition is too rigid to be uniformly applied world-wide as the sole single answer. - Ahunt (talk) 22:39, 22 September 2009 (UTC)

My position is that there is no single definition of V1. In the USA prior to 1978, the airworthiness standards applicable to transport category airplanes (CAR 4B and FAR 25) V1 was called Critical Engine Failure Speed. At amendment 25-42 to FAR 25 in 1978 V1 was changed to Takeoff Decision Speed. A new speed, V_EF, called Engine Failure Recognition Speed was introduced at amendment 25-42.

Transport category airplanes that have been type-certificated to a standard prior to FAR 25, amendment 25-42, have flight manuals using the former name for V1. (That is the majority of transport category airplanes in service at present.) Transport category airplanes that have been type-certificated to FAR §25.107 Takeoff speeds at amendment 25-42 or later have flight manuals using the modern name for V1. It is only a minority of airplanes that have been type-certificated to amendment 25-42 or later. For example, among the Boeing products, the 767 and earlier are all pre-amendment 25-42. The 777 was type-certificated to amendment 25-82 and is the only Boeing type to include the effects of the revised standards.

So that begs the question – how should Wikipedia explain V1? Should it use the most numerous definition, albeit long superseded? Or should it use the definition currently found in the FAA and EASA libraries? That is what we should be debating.

Alan Hunt has written that each country has its own definition of V1. I challenge that view. For the purpose of operating transport category airplanes the relevant information is published in documents written to conform to the applicable airworthiness standards such as FAR 25 or EASA’s CS-25. Transport category airplanes should not be operated to definitions or rules that vary from one country to another, and in my experience different countries don't have their own versions of §25.107.

FAR 25 and CS-25 are consistent on matters such as definitions of V speeds. These are the only airworthiness standards in current use around the world, so I don’t agree that it is Americo-centric to use FAR 25 as a source for statements about V speeds. (I am an Australian so my view is unlikely to be excessively pro-USA or pro-Europe.) Dolphin51 (talk) 01:34, 23 September 2009 (UTC)

User talk:Dolphin51: You make some good points there, but it is worth noting that Transport Canada is approving different definitions of V1 for different air carriers. These may be the same as the flight manuals, which as you note vary depending on the certification basis or they may be the ones the carrier has developed and TC has approved, there is no way to know as air carrier operating manuals are not public documents. I would bet that carriers that are operating pre and post FAR 25, amendment 25-42 aircraft, like Air Canada, are using one fleet-wide definition of V1, but that is just a guess. Even though Canada does manufacture quite a number of airliners (Dash-8s, Bombardier CRJ, etc) they are certified to Canadian Standards, CAR 525, which is similar to FAR 25. You mention that we have a choice between the old and new FAR definitions, I would say there is good evidence that the range of definitions in use is greater than that.

At this point in the discussion I would say we have two choices - to either give all the definitions and their contexts, including the before and after FAR 25, amendment 25-42 ones or go for a simpler and more direct definition, something like what TC says: "Critical engine failure recognition speed" and leave it at that. Given that this all has to fit into what is essentially a summary table and not an essay I would opt for the latter option at this point, unless you would like to see both, a simple definition in the table and then a section below that explains the variations. Maybe that would satisfy all without making the table too messy? - Ahunt (talk) 01:55, 23 September 2009 (UTC)

Outdent. The definition(s) we settle on ought to be suitable for an encyclopedia, not for an aeronautical engineering text book. Further I believe it perfectly possible to give a defintion which the layman can understand with minimal extra reading. The problem I identified was that defintion (a) and (b) are not equivalent but the current defintion says (a) and (b) are equivalent. I am going to amend the article appropriately pending better defintion(s). Paul Beardsell (talk) 04:43, 23 September 2009 (UTC)

I don't see much problem with the existing explanation of V₁. I regard V₁ as a speed that is only applicable to transport category airplanes because it is only formally defined in sources applicable to such aircraft. Paul's example about the light twin, and his view of BFT, suggest to me that he doesn't see V₁ as applying only to transport category airplanes. If so, that will present a serious problem in finding consensus because it will prove impossible to explain V1 in a way that is equally relevant to a Beech Duchess and a Boeing 777.

V₁ is relevant to two parameters - accelerate-stop distance and one-engine-inoperative takeoff distance. Hence the two elements in the current explanation of V₁. My suggested approach to explaining V₁ is that we only attempt to cater for V₁ in transport category airplanes, and we use the following explanation:

Proposed definition of V₁: In an attempted takeoff, the maximum speed at which the pilot can safely stop the airplane in an emergency without leaving the end of the runway. Also the minimum speed at which the pilot can recognize an engine failure and safely continue the takeoff.

Dolphin51 (talk) 05:52, 23 September 2009 (UTC)

Dolphin51, please excuse the minor edit of your text. I like the above definition in that it is simple, and to the point. But (original research / synthesis warning) your proposal describes TWO different speeds except for a BFT. A 737 on a 10km runway will calculate two different V1 speeds using your description. And this is the problem I originally described. May I suggest that V1 is in fact the LOWER of the two speeds! So we should amend your suggested definition to read:

Proposed definition of V₁: In an attempted takeoff, V₁ is the lower of (a) the maximum speed at which the pilot can safely stop the airplane in an emergency without leaving the end of the runway and (b) the minimum speed at which the pilot can recognize an engine failure and safely continue the takeoff.

Paul Beardsell (talk) 15:53, 23 September 2009 (UTC)

Or, is it the higher of the two speeds? Does the pilot of a 737 on a 10km runway hold the a/c on the ground until he no longer has enough room to stop? Paul Beardsell (talk) 15:56, 23 September 2009 (UTC)

Hi Paul. Spot on! You are learning fast. You have realized that when runway length exceeds the Balanced Field Length there is a range of V1 speeds that permit compliance with both the OEI takeoff distance and the accelerate-stop distance. Boeing calls it Multiple V1. When excess runway length is available, a reduced-thrust takeoff is one option. Another option is to use a reduced V1 and this is especially recommended when the runway is wet or slippery. A third option is an increased V1 and this has advantages in certain circumstances.

Yes, I'm glad to see you're keeping up. Compliance with the two requirements, but compliance does not make it a BFT. A BFT is defined as being when the remaining distance to V2 and the remaining required stop distance are the *same* - the regs do not say that, they say the "the same or greater". The two distances are never equal on a longer than necessary runway when a max performance takeoff is performed - the remaining available stop distance is always more than the remaining distance to V2. That is NOT a BFT, by definition. Paul Beardsell (talk) 01:12, 24 September 2009 (UTC)

The multiple values of V1 are of interest to an operator's Performance Department in optimising operations. The single value of V1 determined by the BFT will always lie within the range of multiple V1 so this range of speeds is usually of little interest to pilots. Dolphin51 (talk) 00:00, 24 September 2009 (UTC)

So, how *exactly* does the pilot arrange for a BFT when there is excess runway length? There is ONLY one way. Reduced thrust. Otherwise you will NEVER (on a too long runway) (and no matter what V1 you select) have a situation where the remaining available&required stop length equals the remaining distance needed to attain V2 (because V2 is a question of physics not of selection). And that is what I have been saying all along! I'm sorry to repeat the thought experiment again but it is, I think, necessary. 10km sea level hard runway, normally loaded 737, no wind, STP. On a full thrust take off at what point in the take off roll does the distance remaining to V2 = the distance remaining required to stop? At no point. A BFT can therefore only be done with reduced thrust on a long runway! Shall I run thru that again? Paul Beardsell (talk) 01:12, 24 September 2009 (UTC)

(I wrote the above while you were writing the below - edit conflict. Merged.) Paul Beardsell (talk) 01:12, 24 September 2009 (UTC)

The B737 on a 10 km runway could takeoff safely and legally even with V₁ set to the minimum value (Vmcg). It could also takeoff safely and legally even with V₁ set to the maximum value (VR). The most attractive option is usually to set V₁ equal to VR. Alternatively, by using reduced thrust it might be possible for the 10 km runway to be limiting, in which case there will only be a single value of V₁ possible, and that will be the value determined by BFT considerations. (VR is directly related to aircraft weight rather than runway length, so regardless of runway length the pilot would never hold the aircraft on the ground past VR.) Dolphin51 (talk) 00:53, 24 September 2009 (UTC)

Finally you agree! A BFT is only possible on an overly long runway by reducing thrust. I will go now to balanced field takeoff and make the mandated change. Paul Beardsell (talk) 01:18, 24 September 2009 (UTC)

---

I can now summarise our two positions. Imagine an airplane taking off at a weight and V1 that require an accelerate-stop distance of 2000 meters, and an OEI takeoff distance also of 2000 meters. I say this value of V1 causes the takeoff to be described as a BFT. However, there is actually 2500 meters of runway available, so you say it is not a BFT unless thrust is reduced to extend both the above distances required to 2500 meters.

I say the two distances are balanced so it is a BFT. You say 2500 meters is not equal to 2000 meters so it is not a BFT. That is the nub of our different positions.

The current citation from John Anderson’s Aircraft Performance and Design talks about the same distance to clear an obstacle or to brake to a stop. The aircraft doesn’t actually need the extra 500 meters to clear a 35 foot obstacle or to brake to a stop. Consequently my reading of the citation is that it supports my position, but I don’t yet see how it supports your position. Can you cite a source that supports your position? Dolphin51 (talk) 01:44, 24 September 2009 (UTC)

You again provide a citation which does not seem to actually support your view. Anderson does not define BFT in the text you quote but you use the quotation to support your suggested redefinition of BFT. Who am I to challenge a professional aircraft performance engineer? But I am qualified to tell you that 2500 does not equal 2000 and that the defintion of BFT (in the article and in the refs) says they MUST BE EQUAL for a BFT. No specialised knowledge required. I'm not trespassing on your turf, I'm just saying that if what you say is true then other things are false. And I can say WP is not a place for WP:OR. Perhaps you need to write a paper and submit it to an aeronautical journal? Until then WP rules require us to use only verifiable sources. Your *opinion* does not count. Nor does mine. Paul Beardsell (talk) 02:13, 24 September 2009 (UTC)

I reference all the authorities cited including your last one. If you cannot say *how* I am wrong then we'll just have to let the logic stand. If you disagree with me then you disagree with how the balanced field takeoff article now reads and how it read before I touched it. I think that article is now logically self-consistent, it agrees with the cited refs. So let it be, even if you're right, you're wrong because you have to be able to cite refs in support. Sorry. Paul Beardsell (talk) 02:13, 24 September 2009 (UTC)

I am willing to propose a compromise position where we define a BFT as a takeoff in which the length of the runway available is equal to the Balanced Field Length. I can offer no source, so it is a bit of original research, but it is probably something we can both live with. What do you think? Dolphin51 (talk) 02:25, 24 September 2009 (UTC)

Dolphin51, I've been giving this a think and re-reading the refs. It seems I may have overstated my position. You correctly identify the current difference in our understandings to be whether the definition of BFT refers to the TODA being the distance required or the distance available. I apologise for rejecting that suggestion and for being perhaps too adamant. It all comes down to the definition of BFT. Paul Beardsell (talk) 03:12, 24 September 2009 (UTC)

I do suggest that the correct place for the discussion is at Talk:Balanced field takeoff, not here. I'm going there now. Paul Beardsell (talk) 03:12, 24 September 2009 (UTC)

V₁ and the Balanced Field Takeoff

I suggest that the V1 of (a) [in the above section] equals the V1 of (b) [in the above section] only on a balanced field takeoff and I'm arguing there about the correct use of that term, please feel free to contribute. The correct defintion of V1 is pertinent to that discussion.

The way V1 is discussed there you would think that the pilot increases V1 on a long runway and decreases it on a short runway. So I refer the reader to the above section.

Paul Beardsell (talk) 20:52, 22 September 2009 (UTC)

Later: And he does so vary V₁, but if he varies it away from the unique V₁ required for a given BFT the take-off no longer is a BFT. By definition. (And no matter if the definition is "remaining stop distance available" or "... required".) Paul Beardsell (talk) 13:04, 24 September 2009 (UTC)

As takeoff distance available increases, runway-limited takeoff weight also increases; so too does stalling speed so VR and V2 also increase. Conversely as takeoff distance available decreases.

As runway-limited takeoff weight, VR and V2 increase, so too does V1 for the BFT. Conversely as these parameters decrease. It is not the pilot who is doing this. It is the laws of physics. These things are reflected in the takeoff performance section of any flight manual or performance manual for a transport category airplane. Dolphin51 (talk) 02:28, 23 September 2009 (UTC)

You vary too many independent variables. *Obviously* I was talking about the same a/c at the same weight on the same surface in the same config at the same density altitude and with the same wind. What I am varying here is the runway length. Paul Beardsell (talk) 04:24, 23 September 2009 (UTC)

I think I'll let you propose a definition of V₁ suitable for an encyclopedia (not an aeronautical engineering text book) and then we can proceed. Of course it is physics and not the pilot - I was speaking loosely and should have said "pilot calculates a higher V1 on a long runway". No. Surely V1 is the same for all runway lengths where the runway length is at least the minimum BFT length required. Or is it? We await a definition of V1. Paul Beardsell (talk) 04:20, 23 September 2009 (UTC)

V₁ new definition request

Currently V₁ is defined in the article thus:

"Maximum speed during takeoff at which a pilot can safely stop the aircraft without leaving the runway. Alternatively, the minimum speed that allows the pilot to safely continue (to V2 takeoff) even if a Critical engine failure occurs."

My recently much improved understanding is that this is not (quite) true (enough), in that for most takeoffs there is a range of speeds which can be nominated by the pilot as being this speed. The rules which place upper and lower limits on this speed are (1) Vmcg <= V1 <= Vr and (2) at V1 the required-distance-to-stop <= available-distance-to-stop and (3) at V1 the available-distance-to-stop >= required-distance-to-attain-V2.

I think the WP definition should reflect this information. How about:

The decision speed nominated by the pilot which satisfies various safety rules, above which the takeoff will continue should an engine fail.

Or:

The decision speed nominated by the pilot above which the takeoff will continue should an engine fail. Regulations mandate Vmcg <= V1 <=Vr and that at V1 the remaining available runway stop distance is longer that the distance required to stop and is also at least the distance required to reach safe takeoff speed with one engine inoperative.

Paul Beardsell (talk) 13:44, 24 September 2009 (UTC)

While it maybe accurate, that is a rather long and confusing to the casual reader. How about the TC definition, which is the most straightforward: "Critical engine failure recognition speed" in the table and then a separate section below the two tables dealing with all these subtleties of V1 for anyone who wants to read more on the subject? I really think it needs a more detailed treatment than can be or should be done in just a table. - -Ahunt (talk) 13:57, 24 September 2009 (UTC)

Good sense. I like a definition saying Critical engine failure recognition speed or takeoff decision speed. And then a separate statement saying The decision speed nominated by the pilot which satisfies all safety rules, and above which the takeoff will continue even if an engine fails. Dolphin51 (talk) 22:53, 24 September 2009 (UTC)

Lacking any objections in the last few days I have gone ahead and done that - see what you think needs to be added to make this correct. - Ahunt (talk) 18:11, 27 September 2009 (UTC)

I like your re-work of the subject. I will refine it a little by making mention of the influence of wing flap setting on V₁, and removing mention of wind. Runway wind component influences the permissible weight at takeoff, rather than having an independent influence on V₁. Dolphin51 (talk) 22:48, 27 September 2009 (UTC)

That looks good! I think we have the right approach here - keep the table text simple and direct and then explain things in the para below linked from the table. There is probably room for more explanation there, or variants used in different countries or airlines. I am interested to hear what Paul Beardsell has to say on this too when he has a chance to have a look at it. - Ahunt (talk) 00:08, 28 September 2009 (UTC)

V_A - Doesn't centrifugal force in manoevering increase wing loading ?

The last sentence for V_A says: "The heavier an aircraft is loaded the faster this speed."

Now I'm not a pilot but I know a little basic physics. Surely, by centrifugal force, the structural stress on an aircraft turning at a certain speed is increased when it is more heavily loaded, therefore this sentence should say:

"When an aircraft is more heavily loaded, this speed becomes lower."

(If I've missed something obvious, please educate me.) Darkman101 (talk) 15:51, 30 August 2010 (UTC)

The article is right as it is - as gross weight increases Va goes up, not down. All of these are pretty accurate explanations. - Ahunt (talk) 19:11, 30 August 2010 (UTC)

V_A is determined simply as the speed at which the load factor at the stall is equal to the limit load factor. Imagine two aircraft of the same type flying at the same speed but different weights. The limit load factor for this type is 3.8. Both aircraft are turning at 3.8G (about 75 degrees bank angle) but getting progressively slower. The first aircraft to stall will be the heavier of the two; not the lighter of the two. Therefore the heavier the aircraft, the faster is V_A. Dolphin (t) 23:11, 30 August 2010 (UTC)

There is only one published value of V_A and it is called the Operating Maneuvering Speed or simply the Maneuver Speed. It is always the speed appropriate to maximum takeoff weight. There is an anomaly here. Pilots believe that if they fly at a speed equal to the published value of Maneuver Speed the aircraft will stall before reaching limit load factor, thereby protecting the structure from being overloaded. If the aircraft is at a weight less than the maximum takeoff weight that won't be true. At a weight less than the maximum takeoff weight the aircraft at speed V_A will be capable of achieving a load factor greater than the limit load factor. However, because the weight is less than the maximum takeoff weight the loads and stresses on the aircraft structure will be less than if the aircraft was at maximum takeoff weight. Dolphin (t) 23:25, 30 August 2010 (UTC)

Quite true. The only item I would add is that later Cessna POHs (post 1975) do give Va for lower weights than maximum gross weight. - Ahunt (talk) 14:22, 31 August 2010 (UTC)

TAS vs IAS

The article says: "The actual speeds represented by these designators are true airspeeds specific to a particular model of aircraft, ..." That's not true for many of the most important V-speeds, like Vs0: stall "speed" is actually a specific AoA, which roughly corresponds to a specific IAS, but not a specific TAS, which depends heavily on density altitude. This is a crucial insight to understanding V-speeds, and so I think this misleading sentence in the article should be revised. 204.11.73.2 (talk) 13:43, 20 October 2010 (UTC)

I agree!

• FAR §23.49 begins V_S0 and V_S1 are the stalling speeds or the minimum steady flight speeds, in knots (CAS) ... (where CAS is calibrated airspeed.)
  
• FAR §23.335 begins the selected design airspeeds are equivalent airspeeds (EAS) ... and goes on to specify V_C, V_D, V_A, and V_B.
  

Dolphin (t) 21:52, 20 October 2010 (UTC)

Yup, that is right, most are IAS or EAS, feel free to correct that. - Ahunt (talk) 22:58, 20 October 2010 (UTC)

Done. Dolphin (t) 01:34, 21 October 2010 (UTC)

That reads much better - thanks for bringing it up and thanks for fixing it!—Preceding unsigned comment added by Ahunt (talk • contribs) 11:15, 21 October 2010

Vne overstress

Another nitpick: the caption of the airspeed indicator photo reads "... Vne – i.e. the speed beyond which the airframe will be overstressed." But in many (most? all?) general aviation aircraft, Vne is actually limited by aerodynamic instabilities or "flutter," not stress. Often the airframe is quite capable of taking stress beyond Vne. 204.11.73.2 (talk) 13:49, 20 October 2010 (UTC)

I agree it was wrong. Also the caption was far too long and detailed for a caption, even if it was right, so I have fixed it. Thanks for pointing this out. - Ahunt (talk) 14:13, 20 October 2010 (UTC)

Vg?

Best glide speed (best/least gradient). —Preceding unsigned comment added by 58.165.22.25 (talk) 00:05, 19 April 2011 (UTC)

If you can find a reference we can add it. - Ahunt (talk) 00:30, 19 April 2011 (UTC)

V2

V2 is defined as "The speed that vies an adequate climb angle from 35' agl to 400' agl (second segment climb), with an engine inoperative." You cna figure out your V2 speed by 1.2 x Vs (some airplanes are 1.15 Vs) or 1.10 x Vmca See "Notes on Flight Technique Analysis for Professional Pilots" by Les Kumpula for more information.—Preceding unsigned comment added by 155.31.55.240 (talk) 22:29, 25 July 2011

What is the source of your definition? I would say it is not the speed that ensures an adequate climb angle, but the choice of weight. (If the aircraft is too heavy the climb gradient with the critical engine inoperative will be inadequate for the purposes of the second segment climb requirement, and obstacle clearance.) In the US airworthiness standards for transport category airplanes (14CFR Part 25) minimum V2 is defined as a multiple of the stalling speed, exactly as you have described. Dolphin (t) 22:49, 25 July 2011 (UTC)

Design maneuvering speed V_A

Our description of V_A, design maneuvering speed, is supported by four in-line citations. This description says it is also known as the speed for maximum control deflection. As far as I can tell, only one of those cited sources supports the idea that V_A is known as the speed for maximum control deflection – that is the source by John Brandon.

Brandon's source is tailored for recreational pilots and pilots of ultra-light aircraft. The more I read of this source the more I am convinced it is not a particularly reliable one for Wikipedia’s purposes; certainly not when compared with other reliable published sources that are readily available. Also these articles by Brandon make numerous references for Australian audiences whereas Wikipedia is intended to be international.

I think a superior source for information about V_A is FAA Advisory Circular 23-19A Airframe Guide for Certification of Part 23 Airplanes, section 48 (page 27). See AC 23-19A.

On the question of V_A, Brandon states that it is known as the speed for maximum control deflection. FAA AC 23-19A doesn’t support this alternative name. Brandon also suggests V_A is possibly known as rough air speed and is the recommended indicated cruising speed when flying in moderate turbulence. He does not say who makes this recommendation. FAA AC 23-19 contradicts this advice by stating, at paragraph 48 b., V_A should not be interpreted as a speed that would permit the pilot unrestricted flight-control movement without exceeding airplane structural limits, nor should it be interpreted as a gust penetration speed.

I am in favour of amending our description for V_A by:

1. removing the citation of Brandon’s document and replacing it by citation of FAA Advisory Circular 23-19A, section 48 (page 27)
2. changing the text so that it matches the information provided in the cited sources.

What do others think of these two sources?Dolphin (t) 07:19, 1 January 2012 (UTC)

I agree with you. Brandon is confused. The rough air speed is Vno. Va is the maximum speed that back elevator can be applied without exceeding the maximum design "g", not any control deflection. It has been demonstrated in the past that due to vector additive effects that full elevator and aileron at the same time at Va can overstress the aircraft. When I flew CT-114s this was emphasized as "rolling g" or "pulling g while rolling" and indicated that there was no easy way to avoid an overstress in this condition (back elevator to the limit (7.33 g) and then roll). - Ahunt (talk) 12:59, 1 January 2012 (UTC)

Thanks for your agreement. Inevitably, there must be a compromise between sufficient information to address the topic, and so much information that it begins to look like something other than an encyclopedia. Here is my first attempt at an improved description of design maneuvering speed. All comments and suggestions will be welcome.

Design maneuvering speed. The aircraft empennage must be sufficiently strong to withstand full deflection of the elevator alone at all speeds up to V_A. The empennage must also be sufficiently strong to withstand full deflection of the rudder alone, and the wing must be sufficiently strong to withstand full deflection of the ailerons alone, at all speeds up to V_A. V_A must not be less than $V_{s}{\sqrt {n}}$ where V_s is the stalling speed of the aircraft at maximum take-off weight and n is the design maneuver load factor. At speeds less than $V_{s}{\sqrt {n}}$ the aircraft will stall before the load factor exceeds the design maneuver load factor.

When we finalise this description, the article Maneuvering speed will need to be tweaked to make it compatible.

FAA AC 23-19A, section 48 (page 27) has reminded me of a new speed V_O, the Operating Maneuvering Speed, which cannot be greater than $V_{s}{\sqrt {n}}$. (The designer can choose V_A to be faster than V_O and that is why this topic is becoming more complicated than it used to be.) For aircraft that have a V_O it is the speed at which the aircraft (at max weight) will stall at design maneuver load factor. Our article V speeds appears not to have V_O at present. Dolphin (t) 03:05, 4 January 2012 (UTC)

On second thoughts, perhaps the best approach would be to simply state that V_A means design maneuvering speed and provide all the relevant information in maneuvering speed. Dolphin (t) 12:36, 4 January 2012 (UTC)

Now that sounds like a good idea. Since we have an article on maneuvering speed, let's just link to that, rather than duplicate it all in this article! In looking over the brief description we have now and the link, I think it is fine as it is! You should add V_O, though. - Ahunt (talk) 12:43, 4 January 2012 (UTC)

I added V_O Maximum operating maneuvering speed, citing US 14CFR §23.1557 as the source.

I edited our description of V_A Design maneuvering speed by deleting Brandon as a cited source and replacing it with FAA Advisory Circular 23-19A, Section 48, as discussed above.

I deleted the sentence also known as the Speed for maximum control deflection because the only source to support that claim was Brandon.

I also deleted the sentence The heavier an aircraft is loaded the faster this speed because it is incorrect. V_A is a design speed, selected by the aircraft designer. It is true that $V_{s}{\sqrt {n}}$ increases with aircraft weight, but V_A is a single speed selected by the designer; it does not vary with aircraft weight; and it can be faster than $V_{s}{\sqrt {n}}$ at all weights. Since 1993 (amdt 23-45), $V_{s}{\sqrt {n}}$ is approximated by V_O (approximated because V_O can be less than $V_{s}{\sqrt {n}}$.) See the diff. Dolphin (t) 02:01, 6 January 2012 (UTC)

I have substantially re-worked Maneuvering speed. Dolphin (t) 03:27, 6 January 2012 (UTC)

The only problem remaining is that there are authoritative refs that contradict your changes. For instance The Cessna 172N Pilot Operating Handbook, dated 1978, makes no mention of the V_O at all. Instead it offers this definition of V_A:

"Maneuvering Speed is the maximum speed at which you may use abrupt control travel" (page 1-6)

that isn't contradictory, but it then continues:

"V_A Maneuvering Speed, Do not make full of abrupt control movements above this speed

2300 lbs 96 KCAS 97 KIAS
1950 lbs 88 KCAS 89 KIAS
1600 lbs 80 KCAS 80 KIAS" (Limitations, page 2-4)

This clearly indicates that V_A is not just a design parameter, but is an aircraft and pilot limitation and that it decreases with aircraft weight. As this contradicts your changes we may have to indicate that there is disagreement on this issue. - Ahunt (talk) 13:19, 6 January 2012 (UTC)

Your observation is a very valid one. It doesn't demonstrate disagreement in the sense of two people with irreconcilable views. It demonstrates the differences that occur when an authoritative document is subjected to periodic amendment. Prior to 14CFR 23, amendment 23-45, V_O did not exist. V_A was probably explained in terms of the stalling speed that incurs design maneuver load factor. POHs for aircraft whose certification bases preceded amdt 23-45 will give examples of the kind you have quoted from the C172N POH. Those POHs can be cited as sources for the older and alternative meanings of V_A. 14CFR and AC 23-19A, at their current amendment statuses, can be cited as sources for the current meaning of V_A. If it can wait a few days I am willing to write some additional words to cover the former meaning attached to V_A, and to explain the change in meaning.

We have previously observed the same thing with the definition of V₁ for transport category aircraft. Prior to amdt 25-42, V₁ was the engine failure speed but at amdt 25-42 it became the take-off decision speed and V_ef was introduced and called the engine failure speed. Dolphin (t) 10:54, 7 January 2012 (UTC)

That makes perfect sense! I agree then if essentially the use of V_A as used by Cessna in 1978 was subsequently amended to V_O in the FARs then we need to explain that. Sure no rush. Since you have a better grasp on the history of when this happened then I do by all means take some time and add the clarifications when you are able to do so. - Ahunt (talk) 12:13, 7 January 2012 (UTC)

One problem with a discussion of Va is that one must remember which component of the aircraft is subject to overstress in any given maneuver. If the aircraft is at gross weight, a full-elevator deflection will stress both the horizontal tail and the wing to the design limit load (3.8 g for a small normal-category airplane). The other components in the airplane, such as the seats and the engine mount, will also be subjected to the 3.8 g load. Now if you are flying at less than gross weight and at a slower speed than Va, a full-deflection pull on the elevator will not subject the horizontal tail and the wing to the design limit load, but you will still feel the limit g-force on the seats and engine mount. SO, if you pull a full-deflection maneuver at Va at anything less than gross weight, you will overstress the engine mount. This is the danger of any facile discussion of Va; it is full of complexity which too easily gets lost in the shuffle.

On a different note, I am removing the explanation of Vc that was contained in the previous version of the article. Vc IS NOT NECESSARILY the most efficient flying speed of the airplane; that has nothing to do with efficiency (if you want "efficient" you should look at the best-rate-of-climb speeds). Vc is the speed at which the airplane must be subjected to the specified gust speeds for its category. Since the response to a gust increases with speed, the certifier must show that the structure can handle the resulting gust loading, which is usually greater than the maneuvering load. For example, a light normal-category airplane's Vc must be at least 33*(wing loading)^.5 in knots. This is a speed SPECIFIED by the regulation, and is not necessarily an economical cruise speed. (not saying it is a bad speed to travel, but it is a regulatory speed for structural certification, and nothing else). Regards. --Raymondwinn (talk) 04:39, 14 April 2012 (UTC)

Hello Raymond. Welcome to this thread! I disagree with some aspects of your comments on maneuvering speed. We agree that if the aircraft is at gross weight and the elevator control is moved progressively backwards, the maneuvering load factor will increase progressively until it reaches the design maneuver load factor (eg 3.8) when the aircraft will stall and the load factor will increase no further. There is no reason to assume that the stall and 3.8g will coincide with the elevator reaching full deflection. In many aircraft the stall will occur when there is still further deflection of the elevator available. In some other aircraft, when the CG is close to the forward limit there is not sufficient elevator deflection to achieve the stall.

I think we also agree that at maneuvering speed, regardless of weight, it must be possible to fully deflect the elevator without damaging any part of the elevator, elevator ciruit or surrounding structure. At full upwards deflection of the elevator the aircraft may have already stalled.

Have a look at Maneuvering speed. It is still work in progress but it contains some useful information, and some good references. Dolphin (t) 12:45, 14 April 2012 (UTC)

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