pplm exam principles of flight confusion
 

Hello, I have been doing some mock exams on the Microisland website

Aircraft Techinal

And here, the answer to how much lift is generated from the upper surface of a wing, is opposite to what I have read in my textbook. As I understand it, two thirds of lift is generated from the lower relative air pressure on the upper surface of the wing, and one third from the airflow being deflected downwards by the lower surface of the wing.

The screengrab below however, has the answer different:

http://i.imgur.com/u3nJlwJ.jpg


So, am i missing something, or is the exam wrong?


Cheers

There is a never ending argument about how a wing produces lift.

The conventional wisdom though, is that 2/3 of the lift is produced by the smooth airflow over the upper surface, and 1/3 by the downward deflection of the air by the lower surface.

In reality, the two effects cannot be treated entirely seperately, as they each affect the other.


MJ:ok:

If you have any reasonable understanding of the principles of flight, then you come to realise that all of the exam syllabi are gross and often innacurate simplifications.

However, the objective in the short term is to pass the exams - and it is true that if you replaced the wing section with just the upper surface you'd lose about 1/3 of the lift. So, the answer works - but is still grossly simplistic and pointless.

Learn to pass the exam, then get a decent book on PofF like Kermode or Anderson, and learn it properly!

Daft, but the way to do it.

G

<i>"principles of flight confusion"</i>

That should be covered in the Human Performance and Limitations syllabus.

Sorry, I'll get my coat on the way out ....

The "trial" exam is wrong.

For this sort of exam question, the expected answer is:

The upper surface of the wing generates around 2/3rds of the total lift

Usually put that way, rather than "the lower surface of the wing produces about 1/3rd of the lift", since the idea is that in a stall the wing does not lose all its lift-generating ability.

You can always tell the smart student, they read this and ask: but what if the aircraft is flying inverted!

Or at zero 'G'. Or at negative 'G'. Shows why these simplistic explanations are such tosh.

Read 'Stick & Rudder'. Everything you need to know about why an aeroplane flys (and sometimes doesn't) is in there.

Oh come on, a great book, but there's stuff vastly more up to date and at-least as well written. Teaching PofF from Stick and Rudder, is like teaching aerodynamics from Glauert - you can do it, but there are vastly more up to date texts.

This is my current favourite:-


G

At £40 a copy I don't think I'll be reading that any time soon. Stick & Rudder is certainly dated, but I haven't come across another book that cuts through the crap quite as well as it does and tells a pilot what a pilot needs to know.

Should I start saving?

You spend how much a year on flying?

Or for something only 26 years old instead of 70 years old, you can have an earlier edition of Anderson for just over a fiver...


G

As usual in all these exam questions - go have a look which software is used in final real exam and then learn the pushbutton answers. Afterwards switch on again your brain ...

Genghis, there's a copy of 'Stick' on my bookshelf. It's far and away better than anything I've read before on 'pilot's aerodynamics'. Why do you think I'd need to supplant it?

I've no idea if those you've recommended are as good (the only thing 'Stick' falls down on is it's dated presentation). Since 'Stick', and not those other books, continues to be recommended, and it 'does it for me', it's the one I will stand behind as a recommendation. I'm not in the book review business so won't be buying those others to see if they're as good; I don't need to as I know 'Stick' does it just fine.

If you think the others are as good, by all means recommend them. But please recognise as well just how good 'Stick' is for someone who wants to fly aeroplanes, not design them.

One thing EASA have not yet been able to screw up are the laws of physics. Stick & rudder is still current.

I really do hope that we've learn a few things about aeronautics since 1944 however.

Newtonian physics and incompressible aerodynamics haven't changed yet, but our understanding of human factors, use of instruments, navigation, meteorology - certainly have.

G

Cheers guys, I have Brian cosgroves book call the microlight pilots handbook. Good to know the test answer is wrong in this case. Ive also come across afew other wrong questions from this site, so it might be an idea to avoid these online tests for now....


And to all those trashing the simplistic explanation of flight, well, we all have to start somewhere, and i think a simplistic explanation works for me now, much like a lot of GCSE chemistry and physics is not actually correct, and then retaught in a more complex (and contradicory) manner at A level.....

Um, 'Stick' doesn't address those other subjects so your comment is irrelevant. It's purely about pilots' aerodynamics. And it does it very well, perhaps because it doesn't dilute itself by addressing too wide a spectrum of subjects.

The exam question that the OP refers to is ridiculous. Definitely one just to learn the answer for the exam and then forget about.

Genghis and Shaggy - you're discussing different things. "Stick" is no good for learning about the science of aerodynamics, but is brilliant at getting across enough info for a pilot to understand what s/he needs. You don't need to understand the detail of how a car works in order to drive one safely - but you do need to know a little bit about how it works: flying is the same.

Neither "Stick" nor a good aerodynamics text book will help answer the OP's question though.

No one has mentioned Bernoulli yet...

Didn't write a single book on flying - ignore him.

G

Agreed! :)

Halfway through Stick and Rudder now. I thought I should read it, as some people rave so much about it.

I'll let you know what I think when I've finished it, but so far, if you can look past the rather dated style and language, it seems to explain things in terms that 'ordinary' people can understand, without falling into the trap of 'dumbing down' to a point where what it says is actually wrong.

From what I've read so far, I think you're a little harsh, Genghis. I think even Kermode, and Anderson seem a little highbrow to many.

Let's see how the other half goes.


MJ:ok:

From 1978. Just sayin'. ;)

SSD, an earlier edition is available as a PDF.