Ace the Technical interview by G.Bristow

[gtaflyer]

Does anyone know which sections or answers (by page number if possible) are incorrect in the above book.

[Rainboe]

I bought the book following some good recommendations on this board. I read to about 1/3, and was staggered by the number of answers and articles I totally disagreed with and found plain wrong that I dropped it. Without wishing to cause an argument, I said nothing, but it's nice to see other people appear to be questioning the depth and accuracy of this book.

[ATIS]

Read it about a year ago, and if I remember correctly, his explanation of Dutch Roll was scary. Saying something along the lines that each downward going wing was caused as a result of that wing stalling.

[Hedncld]

His explaination of Epr on takeoff was way out there. It was simply wrong.
Take care

[gtaflyer]

thank you for your input, i will start rewriting the stuff although running out of time now with i/v approaching.

it is defeating the purpose of the book when you have to read other material to check the info out- time consuming but thanks again.

Anyone else have comments about the accuracy of the book i would love to hear from you.

cheers

gta

[MrBernoulli]

This book was a golden opportunity that was completely mishandled. Full of errors, almost too many to mention. How the bloke can keep his name to this and not die of embarrassment, I don't know. A complete rewrite is needed to save further embarrassment. And then all those who have purchased will want refunds/replacements!

[gtaflyer]

yep i know what you mean. if it had been written in the style of D P Davies - handling the big jets then it would have been a very good book.

gta

[Fogrunner]

yep i know what you mean. if it had been written in the style of D P Davies - handling the big jets then it would have been a very good book.
gta
I have Handling the Big jets......
thank you for your input, i will start rewriting the stuff although running out of time now with i/v approaching.
it is defeating the purpose of the book when you have to read other material to check the info out- time consuming but thanks again.
Anyone else have comments about the accuracy of the book i would love to hear from you.
cheers
gta
I too have found many errors. Can you gentlemen recommend another book.

[FlapsOne]

You could look at it positively.

If you have to verify all the incorrect facts by looking them up elsewhere, athough time-consuming, you will learn a hell of a lot in the process!!!!!!

[Rainboe]

Undoubtedly the advice I would give would be to totally avoid this garbage. There are clunky explanations, very poor writing, loads of wrong facts and poor reasoning. All round dangerous in that you would get the wrong idea about a lot of things. I get the impression he is a limited experience flyer writing way beyond his knowledge and capability. The contrast with DP Davies and his Handling the Biggies is just too great to mention. That was written by a highly experienced (and qualified!) TEST PILOT with an amazing amount of experience of all the civil jets and an expert pilot with good writing skills to boot. I was left by 'Ace' with a feeling of disgust. Maybe worth reading as a lesson on how not to write a book.

[gtaflyer]

1 Through search function on the net i found that for basic aerodynamics www.rmcs.cranfield.ac.uk/aeroxtra/olaeaero.htm is very good and has good diagrams.

2 another site is http://aerodyn.org/HighSpeed/sweepback.html is good also.

3 Some sample multiple choice questions that were good practice can be found at http://www.airwork.nl/examenvragen/atpl-principlesofflight2.shtm. these are similar to the Sample cathay multiple choice questions found on the pprune site.

[gtaflyer]

should be:http://www.airwork.nl/examenvragen/atpl-principlesofflight2.shtml

bye

gta

[Mr. Hat]

Yeah I was looking for some stuff to refreshen previous study and suspected in the first chapter that something wasn't quite right about this book.

This post has saved me another 250 pages of head scratching.

Off to find something else. I might go an get my old texts out.

Whats the best of the best in terms of website guys?

[ALTACK]

Good stuff


should be:http://www.airwork.nl/examenvragen/atpl-principlesofflight2.shtml

bye

gta

[Luke SkyToddler]

Hi all

Just brushing up on some *ahem* random reading in the 'Ace the Technical Pilot Interview' book and I have to warn anyone on here thinking of buying it, that the bloke who wrote it doesn't appear to know his @rse from his elbow.

Only a few pages in and the author has already tried to explain to me that

- The lift equation = 1/2rho + Vsquared + S + Cl :ooh:

- Dutch roll is perpetuated by the upward going wing STALLING and losing all its lift and then dropping :uhoh:

- it's better to lose your UPWIND engine in a max crosswind takeoff :eek:

What a useless publication, in fact it is worse than useless because you start to wonder if your understanding was wrong and then you have to go and check, and ask all your mates, and by the time you've decided you were right all along you've wasted a whole load of time.

I don't know whether I should read more of this book and maybe fill my head with wrong information, or keep reading it to try and pull some useful gen from amongst all the dodgy stuff. If I find any others I'll post them here, does anyone else have this book and can point out any extra clangers they've spotted?

[Dusty_B]

It also tries to explain lift as 'molecules above wing have to travel further...'

[G-IBBO]

I've had it gathering dust for a while now but I'll get it out and read through and, likewise, post any clangers that I come across. That's worrying to think that some poor sod could sit down in an interview and confidently bullsh*t his/her way out of a job.

[haughtney1]

luke theres a PM waiting for you dude

[ali1]

Unless i'm being v.stupid, it is better to lose your upwind engine.

If you have a xwind from the right and you lose your downwind engine ie left engine, the extra roll and yaw will be in the same direction as the wind therefore making it harder to stay on track???

Ali1

[ROI1900D]

Can anyone recommend a good book for Interviews??
Thanks beforehand.

[On speed on profile]

LST

I have the book and was intrigued by exactly those questions that you posed. I re-read them to check and I am still confused.

Dutch Roll- Isnt this due to the 'differential' (my own terminology used there) lift between the wing moving forward with an increased AoA therefore higher lift coefficient and the rearward moving wing having a reduced lift coefficient due to reduced AoA. If the rearward moving wing is indeed stalled, I am sure they are going to get more than a bit of dutch roll to contend with. I certainly have never been taught that the rearward travelling wing is stalled. Maybe he means in 'relative' terms and i use that term extremely loosely.

Engine Failures - If my memory serves me right. When I get hit by a crosswind, the nose of my aeroplane will swing into wind. This is due to the force acting on the tail. IE a left hand wind means swinging left and vice versa.

Quote, page 60:

"... a failed critical number 1 engine will cause a yaw to the left"

Correct.

" A crosswind component from the left will apply a restoring force to the aircrafts fuselage, whereas a crosswind from the right will aggravate the yawing moment further to the left due to the sideways force experienced on the right side of the aircrafts fuselage"

How does that work?

It doesnt matter if the critical engine is the number one or two (if there is a critical engine). If the number one fails, it will swing left, number two fails, a/c swings right. More or less depending on having a critical engine or not. As for the a/c swinging right with a left crosswind and left with a right crosswind? In what type of a/c does this happen. One with a tail in front of the C.o.G. maybe? Or maybe an a/c that has an engine failure while travelling in reverse? Sorry, bad joke.

Seriously, why is there mention of this force on the fuse and not on the tail.

Edited: Just read ali1's post. On the ground and in the air are a different matters. I agree with you totally although it is unclear what the book is talking about. I am talking about before you get airborne.


Dusty B

The 'molecules' that travel 'above the wing' do have to travel further. Look at a cross section of an aerofoil. How is that wrong, please explain what you mean.

Edited: This book while not perfect is a fairly good way of refreshing your ATPL information. I wouldnt write it off completely.

[scroggs]

If this is the kind of stuff peddled by this book, I'd avoid it. There are many problems with over-simplifying aerodynamics, as the ATPL exams regularly reveal. The 'molecules travelling further' bit is one obvious area where conventional simplified aerodynamics break down in the face of fairly casual scrutiny.

As for engine failure, it is indeed true that the yaw initially will be toward the failed engine (OSOT, my aircraft will yaw left if either No1 or No2 fails!). What happens thereafter depends on how many engines you have, whether you are considering a 'stop' or 'go' situation, and whether reverse thrust is used. Nevertheless, the aircraft will always tend to yaw towards a crosswind, as you would expect.

Scroggs

[Pin Head]

It isn't that bad. I bought it 6 months ago for an interview and got the nod. A 50K a year job is worth a £11.99 chance investment.

Everyones a winner:) :) :) :) :) :) :) :) :) :) :) :)

[ali1]

Just to clarify my comment. I meant eng failure once airborne. Apologies didn't read the comment correctly

[Luke SkyToddler]

Ali and on-speed, that was the one I had to think about for a while as well, but I'm reasonably sure of my facts (as they relate to my specific aircraft type anyway) because I've just had a chat with a bloke who recently joined Cathay from my company, and he got asked this very thing in his interview and explained it this way.

Picture yourself approaching V1 and taking off in a max crosswind from the right. The aircraft is wishing to yaw into wind, to the right, and therefore (in my aircraft anyway) you are holding a hefty boot full of left rudder to keep it straight on the runway.

Right hand (upwind) engine now fails between V1 and VR.

The aircraft now wants to yaw even harder to the right due to the engine failure. What you need to do, is apply further left rudder to counteract the yaw, but you can't, because you haven't got any more left rudder available, you've already used up 90% of your available rudder travel keeping the aircraft straight in the crosswind. The only place you can go from here, is into the grass on the right hand side.

Whereas if you lose the left hand (downwind) engine, then the yaw due to the failure will be towards the left. Since you're holding a bunch of left rudder anyway you need to reduce / remove the left rudder input, but you've still got all the available right rudder after that, and the yaw due to the crosswind will actually be helping you keep it straight in this situation.

This guy banging on in the book about 'restoring moments on the fuselage' sounds like a collossal pile of codswallop to me, I've worked at one or two different places as a multi engine instructor in my time and I've certainly never run into any other training notes that make any reference to such a thing.

Maybe it's different in jets with immensely long fuselages or something, but I'm definitely going to stick with what I know I can explain :ugh:

[On speed on profile]

Scroggs, thanks for stopping me going mad. I was talking about a light twin before getting airborne as you probably already knew. I seriously was starting to doubt my knowledge there for a second.

Ali and LST. Wasnt questioning you, just trying to gain further insight. The multi types I have been flying certainly wouldnt work very well if what was quoted in the book was what I would have to do for real. I agree with what you both say.

Dusty B. I am referring to the airflow over the wing (by saying molecules I could well be/probably am wrong). Please take what i said with a pinch of salt.

All of those other people out there. This book isnt complete crap although as has been proved, some of the stuff in there isnt totally accurate. It is good for reminding you what you already know. Particularly when it comes to relating questions to each other.

To give it (and the author) some credit. It has obviously helped a few of us get through interviews! On the other side. There is a box on the 4th page that says the authors do not "gaurantee the accuracy or completeness of the information". For the record, I would reccomend people to buy it.

[Dirty Harry 76]

I have to give this Book a massive :ok: :ok: :ok:

Myself and many others that I know have used this book and have been succesful at Technical Interviews. It came recommended.

For those who have never seen the book it is written as a refresher highlighting the key points to many questions and subjects that may be discussed at interview. It does not give full explanations from beginning to end and full back ground infromation as your already supposed to have covered that during your ATPL theory course. It can be described as more of a recurrency aid.

This book along with the cathay publication is essential in my opineon for anyone preparing for interview. You wont go far wrong. Gets my vote:)

[scroggs]

Maybe it's different in jets with immensely long fuselages or something

Nope, my A340-600 behaves entirely conventionally in this respect!

Scroggs

[Troy McClure]

I had a flick through said book that someone had left lying around at my flying school.

Spotted the L = 1/2 rho + V2 + S + CL bit soon after picking it up and immediately put it down again, not before suggesting to its owner that he burn the damn thing asap.

As for lift generation, having done a degree in Aeropace Engineering, I must say that I was pleasantly surprised during my PPL to see that the Trevor Thom and AFE books are both relatively accurate (within their albeit limited scope). At least there's no 'molecules must meet their neighbours at the trailing edge' crap as found in many school texts. Anyone doing their ATPL groundschool, or genning up for a technical interview, would be well advised to have a flick through these to refresh their memory.

I'd also recommend a website I found a while back while looking for info on Zhukovski's equation (don't ask):

http://www.av8n.com

It contains the complete text of an (unpublished) book by a guy called John Denker, who seems to know what he's talking about. It would be interesting to hear if anyone else has read it.

[Gingerbread Man]

Dutch Roll- Isnt this due to the 'differential' (my own terminology used there) lift between the wing moving forward with an increased AoA therefore higher lift coefficient and the rearward moving wing having a reduced lift coefficient due to reduced AoA.

Not quite, unless i've misunderstood you. Dutch roll is due to a yaw disturbance that couples into a rolling motion. If a perturbation causes the aircraft to yaw, one of the wings will move faster than the other as the aircraft yaws. It is the difference in speed that causes the rolling motion, not a change in angle of attack. The roll lags the yaw by about 90 degrees, which causes the 'wallowing' characteristic. A small fin combined with dihedral is the easiest way to start the motion.

GBM ;)

[On speed on profile]

GBman

Right on that chap. That is how I remember it. but...... Doesnt the wing produce more lift because the wing being presented in a more perpendicular way to the airflow effectively increases the angle of attack (I dont have my ATPL books to hand so cant remember the drawings) as well as increasing the speed at which its travelling through the air. Man that book has confused me.

Someone please elaborate on this...

Cheers

OSOP

Edited to say: GB Man, I know yaw is the precursor to dutch roll,I just ommitted it from my original post, its what happens to the wings when one is presented forward to the airflow that confuses me. And obviously the author of the book that prompeted this thread!

[tailwheel76]

The books a few inaccuracies but as a whole I found it pretty good and kept me ticking over before I had interviews. Whos going to ask you to recount a formula in an interview anyway.

[RoosterBoost]

This book is just great!

Look what it has made u guys do....... Carefully reading each sentence both forwards and backwards looking for errors - making you critical to every bit of information in the book. What better way to brush up on your knowledge?

One should always be a bit sceptic - Need I say more? - :cool:

[Cavallier]

I used the above book for my Dragonair interview and found it a great help. Yes there are a few errors, some of them embarassing but in general the book is thorough and the author has done his homework on some actual questions that specific airlines ask.
Some other useful publications I found were the 'Prepare Yourself for Your Cathay Pacific Interview' and 'Prepare Yourself for Your Emirates Interview'. These included both sample multi choice and verbal questions both with answers and explanations.

Good Luck

The Cav:cool:

[Canada Goose]

Personally I found 'Bluff Your Way on the Flight Deck' works a treat ;)

http://shop.pilotwarehouse.co.uk/product9210023catno2230023.html

CG.

[Luke SkyToddler]

Having gone through them all, I'd say that my pick of the bunch so far are 'handling the big jets' obviously, the Trevor Thom 'aerodynamics engines and systems for professional pilots' for the technical gen, and the Cheryl Cage 'checklist for success' is the absolute business for answering personal type interview questions.

I still reckon that 'Ace the technical interview' book is pants, admittedly I haven't found any other glaring technical errors apart from those ones I first listed, however the guy's style of writing is very verbose and wordy, and it's very poorly indexed. Trevor Thom wallops him if you're looking for technical knowledge that's well written and presented.

[wingbar]

Lets picture the scene a moment,

Made up in bed with a stonking bad cold. Pending interview the next day starting with a tech exam first thing, my one lifeline, and I MEAN lifeline, was this fantastic book.
And yes, sure, there are some small errors, but half an ounce of sense would mean the reader penciling in corrective actions for these...job done + rather keeps you on your toes.

What a fantastic book, covers everything, and even provides you with an emergency ATPL' cramming tool as well. 10/10 - Certainly not cr*p.

If you have an interview with a tech exam in it, get this book.

WB

[Gingerbread Man]

OSOP, you're probably right - My brain always starts to hurt when I try to work out when something changes the AoA. The speed thing is most likely a simplified explanation of what really happens, so i'd go with what you've been taught :ok: .

GBM ;)

[wheels up]

I was also suprised at the number of inaccuracies - and Ive only read about 30 pages.

One I noticed was his statement that best endurance occurs at min drag speed - incorrect - occurs at min power required which is slower.

[Wizofoz]

Has anyone else read this?

I bought a copy to bone up on a few things. The problem was it was so full inaccuracies and some down-right twaddle that I found it hard to trust the information on topics I wasn't that convercent with.

Some notable howlers-

* Got the Lift formula wrong (Used + instead of * and added some phantom factor S (Wing span area- a new one on me and redundent. L=CL*1/2RHO *V Squared-Period)

*In answering "Why does an aircrafts weight change during flight", went off on some tangent saying that the aircrafts weight varied as a function of it's speed (Something about "Apparent weight". I kinda see what he's getting at, but Weight = Mass*Gravity)

*In answering "How do you increase range with a headwind" tried to say that range INCREASES with a headwind!!!

*Gave some completely unintelligable response to "Why does a light aircraft descend more steeply than a heavy aircraft". Because the heavier one is descending closer to it's best L/D speed right? Ask a glider pilot about that one!!

* Had no real idea about what "G" was, and then said Negative "G" was "The Opposite" of what he'd just failed to explain!

* When talking about wide chord fans, thought the chord of a fan blade was the measurement of the hub to the tip! (I think they called this a Radius!!)

All in all,a pretty poor attempt. People are shelling out money for this in the hope it will help them in their carreer and should expect a supposedly authoritive text to not be so wildley inaccurate.

I think a chat with an aeronautical engineer and a "Revised edition" are called for!!

[1pudding1]

Lift does equal Cl*0.5*rho*V^2*S, where S is the wing area. :hmm:

[Wizofoz]

It isn't necessary to include wing area or any other factor into the formula as CL is just that-a co-efficient.

If one wing produces twice the lift of another wing at the same speed and air pressure, it has twice the CL. Could be because of wing area, aerofoil section, planform, angle of attack etc. etc.

In any case you multiply, not add, and "Wing span area" is still a nonsense term.

[Mercenary Pilot]

Agreed it needs a a revision but i think its a good book and gives simple straight to the point answers for most stuff. Good for refreshing the memory without having to dust off the old textbooks IMHO:ok:

[Jetavia]

The book is published through Mcgraw-Hill any errors should be brought to the attention of their editorial contacts, which for aviation related materials is Steve Chapman, e-mail: [email protected]

[john_tullamarine]

If one wing produces twice the lift of another wing at the same speed and air pressure, it has twice the CL

.. now, that statement should generate some discussion ....

[Wizofoz]

How about from you John? Am I right or have I missed a fundemental?

[Rivet gun]

It isn't necessary to include wing area or any other factor into the formula as CL is just that-a co-efficient.
If one wing produces twice the lift of another wing at the same speed and air pressure, it has twice the CL. Could be because of wing area, aerofoil section, planform, angle of attack etc. etc.
.

CL is a dimensionless coefficient. If you analyse the dimesions in the equation you will find that you DO need area in the right hand side in order that CL be dimensionless.

Do the analysis to prove it to yourself.

[InSoMnIaC]

Wizofoz

S is required as CL is only applicable to 1 section of airofoil. ie the wing is made up of many sections of airofoil so therefore S is required to find how much lift a wing with 'X' meters wingspan is producing.

I put it to u that CL is the same for a peice of airofoil with the same characteristics that is multiplied by S to determine how many peices of that particular airofoil is present.

[barit1]

Hmmm. A biplane has twice the Cl as a monoplane. What a concept! :ooh:

[Wizofoz]

Yep. Quite right. To get a force (KG*M/S^2) you need an extra M^2 on the right of the equation. I stand corrected.

barit- Absolutely not, that's why I resisted the idea that area should be part of the equation as twice the area does not mean twice the lift.

That being said, I think we hold the record for getting off topic the fastest as

1) He still should have known the difference between addition and multiplication.
2) "Wing span area" still doesn't mean anything, and
3) That was only one of the errors I highlighted, and my list was not exhaustive.

[Rainboe]

Wizofoz- you are right. Some of the information is outrageous. I found myself getting increasingly annoyed with it and dumped it 1/3 of the way through. There are some very dodgy areas and i concluded better to not trust anything in the book than try and sort the wheat from the chaff. There has been a previous thread about it.

[False Capture]

I almost bought the book but after speaking to a few friends who did I decided against it. I'd buy the revision if they act on the feedback they're receiving.

At least I didn't have an interview otherwise it would have been a case of "Ar$e the Pilot Interview".:}

[FougaMagister]

I reckon there were some answers in that book that I just didn't understand :confused:

If you have an interview, I would recommend reading "Aerodynamics, Engines and Systems for the Professional Pilot" at Airlife. Very thorough - sometimes more in-depth than needed for JAR (it's written by a group of Oz pilots). Well worth the 30 quid or so.

Cheers :cool:

[john_tullamarine]

A few comments on CL (now, if I could write in sub- and super-scripts, wouldn't that be wonderful ..) ...

CL, and a bunch of other terms (eg Re, M, etc.) are derived from a math technique called "dimensional analysis" - a typical story is given here (http://www.efm.leeds.ac.uk/CIVE/CIVE1400/Section5/dimensional_analysis.htm) but, unless you fancy brain strain, I wouldn't worry too much about the detail.

This technique arose as a result of the empiricism of the Industrial Age when some bright folk figured that there had to be an easier, more compact way of presenting data for engineering use.

Looking at forces generated in fluid flow, one considers all the parameters which might reasonably be involved ..

(a) mass (density is more appropriate for fluids)
(b) some sort of size measure (a big sheet of ply is harder to hold in a breeze than a little sheet)
(c) airflow speed
(d) viscosity (sticky-ness of the fluid eg compare honey with water)
(e) compressibility

.. viscosity and compressibility reflect the fact that we want to deal with real fluids in the real world.

The technique uses an exponential form of expression and, for force, gives a result that force is proportional to

dynamic pressure * Re * M * a representative area

If we hide Re (relevant to low speed) and M (relevant to high speed) within a constant of proportionality (this doesn't mean they go away .. have a look at any of the text books which will show the effect on CL slope at higher M values .. just that it would be a routine and not very useful complication to have them in the expression for normal use) we might write

force = constant * dynamic pressure * area

or, in the more usually seen form

L = CL * (1/2*rho*V2) * S

and, similarly, we can run up an expression for drag forces.

The area, S, need not be wing area, but that is probably the most important shape (area) consideration so it is conventional so to choose.

The advantage of DA to we boring old engineering folk is that we can put a huge amount of data into a very simple form rather than having reams of empirical data looking at the relationship between one variable and another ..

It is held, generally, that all the meaningful dimensionless values have been discovered .. find yourself a new one and you, too, could get your name in text book lights ...

As an aside, be aware that this use of the term "dimensional analysis" tends to be the engineers' view of life .. other meanings may be seen, including the simple dimensional checks of equations to make sure that the dimensions all balance out ...

I've never seen the book referred to in this thread so I can have no view on its usefulness etc.

[Wizofoz]

The area, S, need not be wing area,

True.

When you consider that in flight Lift=Weight, then lift is the total reaction of all surfaces (E.G Tail and Fuselage) producing a vertical force in either direction.

In fact the wind area in isolation is probably going to have to produce MORE lift than the aircrafts weight to counter the down force of the tail.

[john_tullamarine]

The point is that the S thing is just a reference area ... doesn't matter what area ... and depending on the actual size chosen, the CL values will fall out accordingly. Not really related to tails and wings as such ...

[Mad (Flt) Scientist]

In fact, it's not the real area of the wing anyway - most analysis uses some form of idealised wing area.

And often, when producing a derivative aircraft, it's simpler to keep the same reference area, even if the wing is physically increased in size.

[Wizofoz]

In light of the above two responses, is there any reason why S could not be assumed to be 1m^2 for all aircraft, thus making my original contention that the different lifting ability of different wings could be compared exclusivley by different values of CL?

[Mad (Flt) Scientist]

You can define it to be anything you want, so it's theoretically possible, but pretty pointless; the usefulness of the coefficients is in comparing the efficiency of different wing DESIGN FEATURES - by a more representative non-dimensionalisation, you can eliminate the influence of purely area changes and compare, say, the effect of sweep, or t/c, on the lift.

Knowing that a wing that is the same design but twice the size generates twice the lift isn't really insightful. Knowing that a change in t/c by 1% changed the CL by 3% for two DIFFERENT SIZED wings allows you to understand the influence of t/c on CL.

[SR71]

A few comments on CL (now, if I could write in sub- and super-scripts, wouldn't that be wonderful ..) ...

John,

Was it you I emailed about a year ago (or whenever) about getting TeX support for the Forum to make this alot easier?

I used to write my more mathematically inclined posts in TeX script, and various posters were/are conversant with it...

It should be possible for the administrators of the BB to get vBulletin to recognise [TEX] tags and voila.

My $0.02.

Wizo

barit- Absolutely not, that's why I resisted the idea that area should be part of the equation as twice the area does not mean twice the lift.


Twice the area does mean twice the lift.

It does not mean twice the lift coefficient.

The point of C_L is exactly as you suggest - to compare different objects ability to produce lift.

[Wizofoz]

SR71,

The suggestion was that a bi-plane would automatically have twice the lift of a mono-plane with half the wing area- Clearly not true as the airflow interference of the bi-plane configuration reduces it's efficiency.

In any case, doesn't Reynolds affect amongst other things mean that simply doubling the area of a wing DOESN'T automatically double the lift (A of A and Rho being equal)?

John, interesting CL discussion (I'm certainly learning a lot), but obviously completely off topic. Could we carve it off to a seperate thread?

[JonaLX]

add to your list of grievance the explanation of Dutch Roll. I imagine guys explaining it that way at an interview :}

[SR71]

Wizo,
Typically the kinematic viscosity of air is ~10^-5, which means that a commercial aircraft tends to fly in a regime where the Reynolds number is ~10^7.

You can see as a result, that you'd need to change the velocity of a flow by a hell of a lot to get a significant change in Re.

As John said, Re is a dimensionless number used to denote similarity of flow regimes. If you are testing a model of aforementioned commercial aircraft in a wind tunnel, you need to match the Re during testing.

Depending on what you're trying to measure you may need to match the Mach Number as well. Mach is just another dimensionless number like Re.

Re denotes the ratio of inertial to viscous forces in a flow.

In the regime we are typically interested in, inertial forces are large compared to viscous ones.

You won't see much dependence of lift coefficient with Re but, conversely, it will be important to match Re if you want a good drag estimate.

I remember when doing my PhD some colleagues trying to obtain laminar flow over wings at high Re with the intention of applying this technology to commercial aircraft.

They laser drilled thousands of minute holes in the upper surface of their wing and attempted to suck away the boundary layer, thereby delaying transition.

Of course, in any technical undertaking like this one has to deal with bugs.

In this case, the bugs kept blocking the laser drilled holes and the exercise was less than satisfactory.

NASA claim to have made progress on this front though:

http://www.nasa.gov/centers/langley/news/factsheets/HSR-Wings.html

with their F-16XL:

http://www.nasa.gov/centers/langley/images/content/69989main_Wings-fig1.gif

[Wizofoz]

SR71

Thanks- but we are now officially in WAY over my head!!

The reasearch on laminar flow is interesting though. At least one glider has reached production with a similar system, a venturi being used to provide suction to a series of small holes on the surface.

[john_tullamarine]

SR71,

.. as I recall ... indeed we discussed TeX (now that takes me back to the late 60s/early 70s if recollection serves me correctly) .. I'll raise the matter with those further up the totem pole ..

John

[barit1]

Wizofoz isn't the first to critique this book. Take a look. (http://www.amazon.com/gp/product/0071396098/104-8937499-7104736?v=glance&n=283155) :rolleyes:

[On speed on profile]

Just read a question on the use of the ILS and its limits. Page 297. The question: When, on the ILS can you descend on the GP?

1st part: When cleared for the ILS procedure. ..... Correct.
2nd part: When you have captured the localiser within +/- 5 degrees C...... absolutely incorrect.

Now the second part is obviously a huge mistake but, if the author meant +/- 5 degrees of the centreline (omitting the reference to temperature), which I think he did, isnt he still incorrect.

Please correct me if I am wrong here but I was taught that the approach should be thrown away when you are descending on GP and you go outside either half scale fly up or down or 1/2 scale fly left or right. And ......

On page 145, he says one dot on the ILS indicator = 1/2 degree (which I think is correct) so therefore on a normal HSI when flying the ILS, his answer should be +/- 1.25 degrees (or within half scale). This is a big contradiction to his answer (forgetting the reference to temperature).

I know what I used to know, but the numbers now have me confused big time!

To clarify this..........

Should the answers for the limitis of lateral navigation, when asked when one can descend with the procedure be:

+/- 2.5 degrees for a VOR approach. (full scale deflection = 5 degrees)
+/- 1.25 degrees for an ILS approach (full scale deflection = 2.5 degrees)

This book just gets more and more confusing!

barit1: It has been discussed in depth on Prune as well and the problems still crop up!!!

[santiago15]

Should the answers for the limitis of lateral navigation, when asked when one can descend with the procedure be:

+/- 2.5 degrees for a VOR approach. (full scale deflection = 5 degrees)
+/- 1.25 degrees for an ILS approach (full scale deflection = 2.5 degrees)


For a VOR app, is full scale deflection not 10 degrees? Therefore, should read +/- 5 degrees for a VOR approach.

[On speed on profile]

Yes, I was nutting it out with a colleague last night. On reflection I think it should be +/- 5 degrees for the VOR and +/- 2.5 degrees for the ILS or halfscale deflection for both.

[Rainboe]

I think that book is up to one major mistake per page. It was so outrageous I couldn't read it all. One volubly expletes trying to read it- the dog was hiding in the corner. I don't know how he got away with it. It's the Benny Hill Show of the aviation world. We should sue- a class action for fraud!

[On speed on profile]

We should sue- a class action for fraud!

Thats a bit harsh. We are all obviously smart enough to spot the mistakes. I still think its helpful for the questions (and for the most part the answers.)

I wonder if the man reads this site and the numerous threads on his book and is feeling a teeny bit embarassed. Or maybe he is laughing all the way to the bank! :hmm:

[Wizofoz]

We are all obviously smart enough to spot the mistakes.

Well, WE might be. But as this is a reference book intended for people to find things out, it should be incumbent on the Author to ensure at least a reasnoble degree of accuracy.