I don't agree with this FAA ATPL Question

[aviationluver]

Hello from the states. I'm doing some review for an upcoming interview and I was reviewing my FAA ATP material.

There's one question and answer that I don't agree with. I wrote the FAA two weeks ago about this question (because I have no life) and never got a response.

FAA Airman's Information Manual (AIM) 7-3-3 and FAA ATPL question 9119:

"Which flight conditions of a large jet airplane create the most severe flight hazard by generating wingtip vorticies of the greatest strength?

A. Heavy, slow, gear and flaps up.
B. Heavy, slow, gear and flaps down.
C. Heavy, fast, gear and flaps down."

The FAA says the correct answer is A.

However, I disagree. I think the correct answer is C because when a plane has it's flaps down, the plane is generating more lift and drag, thus creating a greater disturbance in the air. Also, with the gear down, there is more turbulence from the disturbed flow off of the gear. Finally, when a plane is traveling fast, the wing is generating much more lift than when the same plane would be flying slower.

Does anyone agree with me? What are your opinions?

Thanks.

[Exup]

It really doesn't matter, if the FAA say A Just put A then let experienced guys teach you how it should be done,

[Port Strobe]

generating wingtip vorticies of the greatest strength

This is a function of the wing. Disregard the gear position.
The strength of wingtip vortices is a function of angle of attack - large AoA leads to stronger vortices. Which conditions give greatest AoA?

Heavy and slow or heavy and fast? Flaps up or flaps down?

Answer A is correct.

Once you get that job this will be backed up by real world experience when you're asked to maintain 230 knots and you're following a 757 that's clean.

[aviationluver]

The strength of the vortex is lift of which AOA is just one component.

Factors which effect lift are air density, circulation, wing area and velocity of the relative wind.

Therefore, assuming density plays no factor, the circulation will increase with flaps down as will the wing area, thus producing greater lift and stronger a stronger vortex. Also, a higher relative wind means the lift on the wing will be stronger, thus a stronger vortex.

Correct?

[_Phoenix]

When a wing generates aerodynamic lift the air on the top surface has lower pressure relative to the bottom surface. Air flows from below the wing and out around the tip to the top of the wing in a circular fashion. An emergent circulatory flow, vortex is induced. Slow and flaps up = larger AoA, then larger pressure difference between lower and upper surfaces.

Not correct.
The lift is constant = weight, larger wing(flaps down) = lower delta pressure required, then less "leakage" from lower to upper.

[Aerozepplin]

Finally, when a plane is traveling fast, the wing is generating much more lift than when the same plane would be flying slower.

I think you should figure out why this statement is incorrect first. Understanding lift vs weight vs air speed, and the mechanism through which the lift is generated is more important that a specific issue such as vortices and configuration.

[FlightDetent]

I agree with the OP, that's what my study books said.

FD.

[underfire]

generating wingtip vorticies

answer

D. There is no such thing as wingtip vorticies. :}

Also, with the gear down, there is more turbulence from the disturbed flow off of the gear.

The gear down affects the rollup of the vorticies....so less vortex creation...while the Lazy B doesnt agree, there is lift from the center wing...

[mikedreamer787]

Gear down mitigates votexes but to a negligible degree. And yes being clobbered behind a clean 757 teaches one about wake turb very quickly! :uhoh:

[Pontius]

It's 'A'. Read what Phoenix has written.

[underfire]

Gear down mitigates votexes but to a negligible degree.

unless it is an A388 or B748...

Much better chance of getting clobbered if you are answer A for certain!

I was at the wakenet US, the FAA presented the new guidance for wake encounter mitigation for drivers...
The guidance made the mistake of saying watch the leader depart, and rotate before that point....the rep for A went ballistic...yelling, "you rotate when the ac tells you to rotate"...that guidance is bull****.... oh well.

on the short final issue, if you are that close, technically, wouldnt your FAF move to the beginning of the turn, so that you still have decision and the stabilized approach? FROP is 500 feet min, but you also must have 30 seconds of stabilized approach....FAP would be where you intercept the glideslope, and FAF is not coincident?

[ahwalk01]

The gear position is to be disregarded, it is testing your understanding of flaps up AoA (and therefore additional lift, stronger vortices) vs flaps down.

[Solidfuel]

Hello from the states. I'm doing some review for an upcoming interview and I was reviewing my FAA ATP material.

There's one question and answer that I don't agree with. I wrote the FAA two weeks ago about this question (because I have no life) and never got a response.

FAA Airman's Information Manual (AIM) 7-3-3 and FAA ATPL question 9119:

"Which flight conditions of a large jet airplane create the most severe flight hazard by generating wingtip vorticies of the greatest strength?

A. Heavy, slow, gear and flaps up.
B. Heavy, slow, gear and flaps down.
C. Heavy, fast, gear and flaps down."

The FAA says the correct answer is A.

However, I disagree. I think the correct answer is C because when a plane has it's flaps down, the plane is generating more lift and drag, thus creating a greater disturbance in the air. Also, with the gear down, there is more turbulence from the disturbed flow off of the gear. Finally, when a plane is traveling fast, the wing is generating much more lift than when the same plane would be flying slower.

Does anyone agree with me? What are your opinions?

Thanks.

You are alarmingly incorrect. Going faster or putting out flaps does not generate more lift - not if the yoke monkey on board is maintaining level flight..... Think about it....

More flaps or higher speed will indeed create more drag, and I suppose 'disturbance through the air'. However this question is limited to one specific aerodynamic phenomenon.

This is all about angle of attack. With flaps out you have larger wing area, therefore you reduce angle of attack to maintain level flight .This creates less pressure under the wing and hence a weaker vortex. Going faster also requires a lesser angle of attack to achieve the same lift, with the same result .

[Jetpipe.]

The strength of Wingtip vortex is proportional to the value of Induced drag. Ask your self what is Induced drag and when is it the highest and you 'll understand the question.

[Avenger]

They use this as ref:


2.2 Historical Examination of the Wake- Turbulence Hazard
Wake turbulence is a natural by-product of powered flight, but was not generally regarded as a serious flight hazard until the late 1960s. Upsets or turbulence encounters associated with other aircraft were usually accredited to “propwash” and later on, with “jet wash.” Interest in this phenomenon greatly increased with the introduction of large, wide-body tur- bojet aircraft during the late 1960s and a con- cern about the impact of greater wake turbulence. This was the impetus to conduct research to gain additional information and determine what safety considerations were necessary as more and more large aircraft entered the industry fleets.
An investigation of the wake-turbulence phe- nomenon, conducted by Boeing in mid 1969 as part of the FAA test program, included both analysis and limited flight test and pro- duced more detailed information on wake vortices. The flight tests provided a direct comparison between the B-747 and a repre- sentative from the then current jet fleet, a B- 707-320C. The smallest Boeing jet transport, the B-737-100, was used as the primary wake- turbulence probing aircraft along with an F- 86 and the NASA CV-990. Smoke generating
towers were also used to observe the wake turbulence generated by aircraft as they flew by. Several observations were made.

• The strength of the wake turbulence is governed by the weight, speed and wing- span of the generating aircraft.

• The greatest strength occurs when the generating aircraft is heavy, at slow speed with a clean wing configuration.

Initial flight tests produced sufficient infor- mation about the strength, duration and move- ment of wake turbulence to come to conclusions and recommendations on how to avoid it. The wake was observed to move down initially and then level off. It was never encountered at the same flight level as the generating aircraft or more than 900 feet be- low the generating aircraft. Therefore, a fol- lowing aircraft could avoid the wake turbulence by flying above the flightpath of the leading aircraft. While this can be accom- plished in visual conditions, an alternative was developed for instrument meteorologi- cal conditions. Aircraft were placed into cat- egories determined by their gross weight. It was noted that a division based on the wing- span of the following aircraft was a more technically correct way to establish catego- ries; however, it did not appear to be an easily workable method. Since there is a correlation between aircraft gross weight and wingspan, gross weight was selected as a means of cat- egorizing aircraft and wake-turbulence strength. Minimum radar-controlled wake- turbulence separation distances were estab- lished for following aircraft. The separation distances depend on the weight of both the leading and following aircraft. Adjustments in separation distances were made as more information on the wake-turbulence phenom- enon was gained during the 1960s, 1980s and 1990s, but the basic concept of using aircraft weights remained constant.

[m39462]

Assuming the same aircraft weight and speed, A and B will generate similar initial vortices but B's will dissipate more quickly. To quote the FAA (http://www.skybrary.aero/bookshelf/books/1959.pdf) ,
The greatest vortex strength occurs when the generating aircraft is heavy-slow-clean since the turbulence from a “dirty” aircraft configuration hastens wake decay.

[Togue]

Heavy, slow and clean is when an aircraft produce more wake turbulence.

[Radix]

.............

[Mr Optimistic]

Interested pax.

At slower speeds the volume and mass of air swept by the wing in unit time is reduced. To maintain 1g you need to generate a fixed rate of change of momentum and with less mass to deflect you must induce a higher downward speed change to the air.

With flaps deployed speed needed to maintain 1g will be reduced so at first sight would expect higher circulation again but the wing has changed and isn't uniform along the span. The outboard section is unchanged but without flaps you couldn't maintain 1g. So the lift generated by the outboard section is reduced compared to the clean configuration.

Hope this didn't annoy......

[underfire]

flap setting are everything, even on the same variant,
it also depends on the crosswind component,
or if the flap edge discontinuity is ingested into the vortex or not...

ingested..adds to the rollup velocity from the small core outward...strong initial vortex, may dissipate faster....
http://i68.tinypic.com/28whyle.jpg

not ingested...large core vortex is not accelerated by discontinuity vortex...not as strong as above, but may be longer lasting
http://i67.tinypic.com/vpx5yo.jpg

then there is crosswind, just like the FAA says, the vortex is generated normally, then drifts away from the flightpath.. really?
reality...one really strong vortex, not coupled, on its own..VERY strong vortex...long lived and indeterminate behaviour

http://i67.tinypic.com/2qlaook.jpg

[Tourist]

The obvious addendum to this is the fact that there are various factors that affect the strength of the vortices, and the dominant factor may be changeable.


What I mean by this is that whilst heavy slow and clean is the standard answer, it is not quite so simple because a dirty aircraft can fly much slower.

A generic clean aircraft might have a min clean speed of 200kts.
This aircraft might have a fully configured speed of 130kts.

This means that the "clean" and "slow" aspects can be trading off against each other.

Yes, if you could fly clean at 130kts it would give greater vortices than dirty, but you can't, so on some aircraft dirty at 130kts may give a greater wake than clean at 200kts

Part of the reason that clean gives a large vortex is because the vortex comes only from the wingtip when clean, but once flaps are deployed, there is another vortex at the flap tip giving more than one vortex per wing which shrinks each vortex plus they can destructively combine reducing it further.

Boeing has even got plans to deliberately help this along:
Aero 14 - Airplane Trailing Vortices (http://www.boeing.com/commercial/aeromagazine/aero_14/vortices_story.html#1)

Gear down has also been shown to have an effect on wake turbulence in some aircraft, but this is due to interference with the vortex formation through mechanical turbulence and as such will differ between aircraft.

NASA - NASA Dryden Technology Facts - Wake Vortex Research (http://www.nasa.gov/centers/dryden/about/Organizations/Technology/Facts/TF-2004-14-DFRC.html)

Another aspect that must be considered is full length flaps. these will obviously cause entirely different effects.

[Amadis of Gaul]

I've disagreed with numerous FAA answers throughout the ages. I've managed to get over it.

[CONSO]

However, I disagree.

Uhh I learned in the 2nd or 3rd grade that the teacher is always right and is GOD.

The correct answer is what the teacher says it is- if you want to pass. :D

As to wingtip vortices- keep in mind that the various winglets work by taking a lot of the vortex " energy " and redirecting it in such a manner that a few percent better lift is generated. Thus the improved takeoff performance. And in some cases, by ' reducing' the trailing vortex during landing, closer separation **could** be allowed for trailing aircraft.

[cwatters]

In level flight total lift is constant irrespective of speed.

Vortices are proportional to the lift generated near the wing tip. With flaps down lift is increased at the root and reduced at the tip. So vortices are worse with flaps up.

Answer A.

[Feather44]

Heavy: because the heavier the weight, the higher the lift requirement
Slow: because the slower the speed the greater the AOA
Flaps up: because the smaller the surface wing, again the greater the AOA

As for the gear down; yes it creates indisputably a disturbance, but nothing to compare with the magnitude involved in the wake turbulence itself.

[Tourist]

In level flight total lift is constant irrespective of speed.


But below a certain speed, level flight cannot be maintained clean.

The question might be rephrased "Is the wingtip vortex worse at min speed clean or at min speed fully configured" because if the aircraft was to be flown at min speed fully configured without configuring, then the vortices will be very small indeed.....

There are two variables, ie speed and configuration which work against each other.
You cannot be slow and clean.
The dominant variable will be different for different aircraft wings.

[Radix]

.............

[Tourist]

"slow" is a variable, not fixed though. It invalidates the question to declare speed to be one of the available variables and then declare 2 different speeds to be "slow"

This means that the answer is not as simple as "A"

Different wings will have different characteristics, and speed may dominate under some circumstances.
A full length flap will cause a different effect.

Most of the trials that feed the received wisdom seem to have been performed a long time ago on a limited number of aircraft with old fashioned wings.

I have seen no experimental data from trials of the 787 or A380 wake turbulence.

[Tourist]

There is of course another variable not mentioned which is g loading. an aircraft in a turn will obviously have more wake all other things being equal, and that goes for the flare too......

Plus, on many aircraft, an increase in flap requires greater downforce from the tailplane due to the shift in the centre of pressure, which acts as an increase in weight thus affecting the third variable.

[No Fly Zone]

I refuse to to debate the question, but you are missing a vitally important point: for better - and often for worse, in the U.S. of A., the FAA makes the rules and we have to live with them. Have they imposed bad rules or asked wrong questions before? Of course they have. It will happen again. I promise. The FAA is an arm of Government and G'ment makes LOTS of very stupid mistakes. even in 'merika, where most G'ment is is a committee function.
Why are you wetting your pants over One Single Question, or becoming frustrated after only two weeks? Responses from G'ment often take months. Don't know where you are from, but a two week turn around is a :mad: dream for a response from the U.S.'s FAA. If you still do not have a response by July, 2016, please post your question afresh. While I do not wish to sound snarky here, two weeks for a response to a non-emergent question posed to the FAA hardly unusual. Heavens, even in emergent case, you are not likely to hear back that soon. As note, please write to us again in July, 2016 if this is still bothering you. If it helps you sleep better some engineers would favor two of the three responses offered, for different reasons. IMO, all three responses have some merit, but in Amerika, our testing procedures require the best of of the best. Sometimes. When G'ment gets involved, logic and reason tend to 'fly' out the window. Good luck.:D

[Tourist]

I think most on here are aware that the FAA just wants the answer they want. That doesn't stop the debate being interesting.

[Radix]

.............

[wanabee777]

http://www.rwf2000.com/atc/gifs2012-06/FAAB-727-A.jpgWhat happened to them??

[Air Swimmer]

High speed==>less angle of attack==> less wingtip vortex.
wingtip vortex is a result of air pressure differential at wing tip.
With flaps down another wake vortices created at the tip of trailing edge flaps. I believe this will reduce the span wash which consiquently weakens wingtip vortices.

[Tourist]

I don't think anyone is arguing with that, however the large vortices can now form at the flap tip rather than the wingtip.

[Natstrackalpha]

Well, I wanted B but you know what - what`s happening when you have no flaps and heavy and slow. Well, apart from you just got a good deal from your insurance man - you `aint got the lift with the flaps, I know, I know, but it is all generated by the lift from the wings. So - no flaps needs a greater angle of attack which mean more lift - more vortex - taking vortex to be the secondary effect of lift (and by passing drag altogether - just to make a point. Drag it on if you want. Swimmer seems to have got it in one! but my call is that with less "help" from the flaps you are generating more lift from the greater angle of attack -of the wings- and therefore more spanwise flow as that nice person just mentioned. . . . and so more Vortex. Trust me am a test pilot. (was)

[Um... lifting...]

Is the aircraft on a conveyor belt?

[Tourist]

Natstrackalpha

I honestly hope you are joking about being a test pilot.


The lift is the same, ie equal to weight however you get it in un-accelerated flight at any speed. (except that due to downforce being greater on the tail, slightly more lift is required from the wing is required fully configured unless you can shift the CofG)

The difference is how much air the lift is being generated from/acted upon.

Lots of air a tiny bit at high speed, or not much air a lot at low speed.

[Natstrackalpha]

Wait on, wait on Mr. Tourist - I like what you say - but you are also suggesting, are you not that there is the same amount of vortices at fast speed level flight as there is at - look, there is more Vortex at slow and level and heavy than there is at fast - level and light - take it from there. Because if you are slow and fat and heavy then there is loads of lift generated by the wings (logically) and the angle of attack - You are suggesting that because the lift is ~ the same ~ then the vortices are the same at any speed - despite the fact that they are all fluff and all bunched up in a small amount of space in the sky during (in this case) a flapless approach in a heavy aircraft. Whereas screaming along at M0.82 level and clean (obviously clean). . . . . I hate you Tourist.:bored::ugh:


There is something missing here - How can the lift be the s, oh yes ok, . . ~?
because Lift <> weight . . . . ah, there it is - as you said if you are going slower you need more lift because there is less air . . . so to generate this lift you increase the angle of attack -

so if you are increasing the angle of attack that is producing more lift, then you must be chuffing out more vortices - THAN if you are flying along light and fast. As the lift is there but it is not being produced by a high angle of attack meaning there is less drag to overcome - howz that?

Also fully configured? WWe are clean in this scenario/question.

Ok anything - a train . . A train is going along at fantastic speed - it wants to maintain that speed so the driver opens the throttle a little.

Same train - At the station, ready to leave Drive uses loads of power to overcome inertia - clean big fat aeroplane is creating more inertia/drag due to increased angle of attack needs more lift - causes more spanwise flow - Seriously, what has the tail got to do with it. Looking at the Longitudinal Dihedral (I`d rather not) but that has no bearing on this. If there is not enough air pushing the Tail down then . . well, there is - I don`t know why you brought the tail into the equation . . ~~~? If you are saying the speed is too low for the tail so you use more power and greater angle of attack then fine - but you are still creating more vortexx as there is more to overcome Why? Because it `aint being generated by speed, or in your case lots of air. (on the wings)

Or rather than write all that - to simply quote you in your previous statement Quote: "Part of the reason that clean gives a large vortex is because the vortex comes only from the wingtip when clean" Unquote.
And, you also said: Quote "The lift is the same, ie equal to weight however you get it in unaccelerated flight at any speed. " Unquote - well, not really confusing - considering the Lift is equal to weight - yes, so, if yo increase the weight, you have to increase the Lift - if yo increase the Lift (especially Clean then you increase the Vortices. Or, you would get the same Vortices from a balsa wood model as you do from a 283 ton 744:)

Also, Oh retired one, A 747 cruising at max chat (forget VNE and any other obvious restrictions like ISA, mach crit etc) and level flight light as possible with minimum fuel except for this experimental flight +> then the lift required from the wing is less than that required (from the wing`s upper surface) than at heavy, Clean and slow. At fast speed, really light there is a comparative nose down attitude i.e., little or no angle of attack . The airflow from the Rel Air Flow (R.A.F.) is max under the wing - so that the wing is verily surfing across the air and is having a dramatic affect of the Lift whilst the airflow over the wing is also providing lift - the wing is at max efficiency in the the span wise flow and the subsequent vortices are flowing, twisting from the tips causing powerful yet small and concentrated vortices, as you know. Light, unloaded, fast 747. Level flight Clean.

Now take same aircraft - load to max payload and or fuel and make it real heavy and slow it down to as low as you dare without reaching going to near the stall-WARNER - the air under the wings is minimal compared to fast flight - there is a high nose attitude due to the increased angle of attack due to the wings having to grapple for height (think of it that way - (unless of course you are and engineer) The wing is using its design to stay airborne with little help from the Rel Air Flow - The airflow over the wings is no longer as laminar as it was at the fast speed run and some vortices and airflow break up is occurring perhaps, the airflow over the wing is being pushed up - not only close to the boundary layer but also continues up above the wing and flows down to the tailing edge (Bernoulli) - also the Centre of Pressure CP is starting to move forward more than before - animatedly, its hanging by its teeth, so all of the air is being actively utilised to provide all of the Lift - so, massive Vortices. Heavy, Slow, Clean.



Test pilots try to see if it won`t break.

[misd-agin]

Flaps can break up the vortices if they're partial span flaps vs. full span flaps.


The 757 produces larger than expected wake turbulence due to the continuous nature of it's flaps vs. the inboard/outboard flap design of many jets.


Just looking at the 787 flaps you'd think they'd be in the 'more' group like the 757 flap design.

[Tourist]

Natstrackalpha

I did not say any of the things you suggest I say in your gibberish.

Please don't put words in my mouth, it's rude.

I will give you the benefit of the doubt that English is not your native language, but I refuse to believe you are or were a test pilot since you have no understanding of flying.