THE THEORY OF FLIGHT ETC

[Backpacker1uk]

Nephew going in for apprenticeship at British Aerospace what is a spoiler used for on a aircraft a aeirilon and a rudder and he has to write seventy words on the theory of flight.

All intelligent replies greatfully recieved.

 

[chieftiff]

For spoilers look here

http://www.grc.nasa.gov/WWW/K-12/airplane/spoil.html

For a good basic description of flight theory look here

http://www.physics.ubc.ca/~outreach/phys420/p420_99/sarah/welcome.htm

I could have written it all out but my diagrams would have been c*ap, 70 words isn't a great deal! I would concentrate on the fact that wings are designed to create a pressure differential between the upper and lower surface, this happens because air is forced to increase in velocity over the upper surface (reducing it's pressure relative to the ambient) It's all there in the physics tutorial.

 

[greenking]

For spoilers look here

http//www.grc.nasa.gov/WWW/K-12/airplane/spoil.html

For a good basic description of flight theory look here

http//www.physics.ubc.ca/~outreach/phys420/p420_99/sarah/welcome.htm

I could have written it all out but my diagrams would have been c*ap, 70 words isn't a great deal! I would concentrate on the fact that wings are designed to create a pressure differential between the upper and lower surface, this happens because air is forced to increase in velocity over the upper surface (reducing it's pressure relative to the ambient) It's all there in the physics tutorial.

Sorry to disagree with you chieftiff. Wings, or any airfoil for that matter, do NOT generate lift by making air go faster over the top than the bottom thus creating a pressure differential. Airfoils create lift by obeying Newtons Laws of Motion, specifically, "for every action there is an equal and opposite reaction". Simply, what airfoils do, is divert air downwards, the equal and opposite reaction being to move the wing (and whatever is attached to it), upwards. How do they make air do this? A combination of Coanda effect (basic fluid mechanics - a moving fluid will tend to 'stick' to a surface and follow it) and fluid viscosity (i.e. layers of a fluid will tend to follow each other to a diminishing degree proportional to the distance they are from the airfoil).
If what you say is true, how does a perfectly symmetrical wing generate lift (e.g. on a Pitts Special)? Or, if a curved upper surface is required to make the air go further and therefore faster, what happens when you turn it upside down? Will such a wing 'pull' the aircraft into the ground? Answer, no. You can go to the NASA website where they have film of smoke injected into fluid flows over all sorts of airfoils. What you will see is the fluid passing over the top of a curved airfoil actually arrives at the trailing edge well before the same timeframe fluid which passes beneath - therefore scotching the further/faster argument.
Preesure drops, like lift in fact, are just a by-product of the mechanical processes of making the air change direction.

Boy, have I got too much time on my hands..........!

Regards

Greenking

 

[chieftiff]

Greenking,
You are correct, but merely complicating the issue, all that stuff was reasonably interesting when those hours of aerodynamics made the days fly by.......but monitor the surface of an aerofoil and you get this crazy little diagram......

http://www.physics.ubc.ca/~outreach/phys420/p420_99/sarah/overhead04.html

Symetrical aerofoils only create lift when there is an angle of attack between the chord line and airflow, no angle of attack and the airflow break away point is the same above and below aerofoil, result equal forces so equilibrium.

My reply therefore: I couldn't have put that into 70 words and I am bloody impressed, but you are too clever, you will be talking about Reynolds numbers next!

 

[higthepig]

You are both wrong and i quote(Mel Brooks)its a simple theory.Matter is lighter thanair.You see,the motors, they pull the plane forward and they cause a draft,and then it taxies faster down the field and the motors go faster and the whole plane vibrates,and then,when theres enough of a draft and a vacuum is created,the plane rises off the runway into the air,from then on ,its a miracle.I dont know what keeps it up.end of quote.

 

[Backpacker1uk]

For spoilers look here

http//www.grc.nasa.gov/WWW/K-12/airplane/spoil.html

For a good basic description of flight theory look here

http//www.physics.ubc.ca/~outreach/phys420/p420_99/sarah/welcome.htm

I could have written it all out but my diagrams would have been c*ap, 70 words isn't a great deal! I would concentrate on the fact that wings are designed to create a pressure differential between the upper and lower surface, this happens because air is forced to increase in velocity over the upper surface (reducing it's pressure relative to the ambient) It's all there in the physics tutorial.

Sorry to disagree with you chieftiff. Wings, or any airfoil for that matter, do NOT generate lift by making air go faster over the top than the bottom thus creating a pressure differential. Airfoils create lift by obeying Newtons Laws of Motion, specifically, "for every action there is an equal and opposite reaction". Simply, what airfoils do, is divert air downwards, the equal and opposite reaction being to move the wing (and whatever is attached to it), upwards. How do they make air do this? A combination of Coanda effect (basic fluid mechanics - a moving fluid will tend to 'stick' to a surface and follow it) and fluid viscosity (i.e. layers of a fluid will tend to follow each other to a diminishing degree proportional to the distance they are from the airfoil).
If what you say is true, how does a perfectly symmetrical wing generate lift (e.g. on a Pitts Special)? Or, if a curved upper surface is required to make the air go further and therefore faster, what happens when you turn it upside down? Will such a wing 'pull' the aircraft into the ground? Answer, no. You can go to the NASA website where they have film of smoke injected into fluid flows over all sorts of airfoils. What you will see is the fluid passing over the top of a curved airfoil actually arrives at the trailing edge well before the same timeframe fluid which passes beneath - therefore scotching the further/faster argument.
Preesure drops, like lift in fact, are just a by-product of the mechanical processes of making the air change direction.

Boy, have I got too much time on my hands..........!

Regards

Greenking

Thanks for the info much appreciated I shall pass it on he has been studying French also with France being a big brother in the airbus thing

 

[chieftiff]

I wouldn't bother too much with the French thing Bae are in the process of selling their 20% share in Airbus to help fund their expansion into the US.

http://www.forbes.com/markets/2006/04/11/airbus-boeing-0411markets03.html

As discussed above I would get your nephew to follow the Physics tutorial about lift so that he understands the ideas and can put them in his own words. Greenking has a perception on lift, it is correct but really just another way of interpreting the pressure differential, it all depends on either how your brain works or moreoften how you were taught, some people prefer to visualise lift by Bernoulli's principles some are still stuck on Newton. (Unfortunately Newton is taught at school, so people like Newton, he's familiar, even if he was fundamentally wrong! see Einstein et al)

Once the lad gets the job BAe will no doubt bore him to tears with Bernoulli, divergent and convergent ducts, boundary layers, coanda, aspect ratio, Reynolds numbers, centres of pressure, pressure waves, shock waves, entropy and all the fine differential equations used to solve the problems of non-linear dynamics.

It's interesting stuff, no honestly!


Edited to add:
Greenking, this is worth a read, the calculus is a pain in the a*s but cut to the chase, you are interested in the velocity vector. Mathematics is my thing so I accept this explanation quite easily, an engineer may not. Comments welcome.

http://www.mathpages.com/home/kmath258/kmath258.htm

 

[greenking]

Oooh! Chieftiff you are naughty! People like Newton because he is taught at school?!! Purrrleeaase! People bang on about Bernoulli because that theory has been taught in flight schools for years, because it is a lot easier to explain (i.e. without diving into the world of Coanda etc). But it is fundamentally flawed for the reasons I highlighted in my earlier response. Newton will work for all airofoils of whatever descritpion, upside down or right way up. It's all about making fluid move in a different direction.

I agree, the Bernoulli/Newton argument rages on regarding aerodynamics. But I have to point out that your responses did not actually answer all of my questions (e.g. inverted airofoils?). Further your remark regarding angle of attack and lift generation is true of all aerofoils not just symmetrical ones - a highly cambered wing will also produce zero lift at a certain AoA.

Reynolds Number...............aaah, careful I will probably bang on all night!!

Fly Navy

Greenking

 

[chieftiff]

I'm not quite sure where this is going, I never said you were wrong Greenking.

Your description of what is actually going on is a little simplified, as was mine agreed. Are you saying Bernoulli was wrong, or the application of his theories to aerofoils? Read the maths article, not the maths though it's tedious, trust me I had to work it through at Uni, skip straight to the description, the reality is that there are many things going on here, oh and surprise surprise they adhere to Newtons observations (Laws?? I think not).

I didn't bother replying to your observation about symmetrical aerofoils and inverted flight because I know, as do you, that helicopters do after all fly and when they are on the ground (of the pilots choosing) they don't.

As for flight school, never went, flying is a confounded modern thing and it will never work, let alone catch on!

 

[greenking]

Not going anywhere really, just being argumentative!! CINCNAVHOME regualrly tells me to stop boring people to death with this - what does she know?!!

I actually agree with your assessment of things. There is lots going on and we haven't even got into the role of circulation yet!! I personally believe it's a combination of the whole bally lot.

The point I was trying to make (rather badly it seems) is that the accepted explanations of the phenomenon are extremely, necessarily, simplistic, but of all of them, the Bernoulli Effect is particularly badly applied.

I did read the article - very interesting. I also looked at the diagrams you linked in your first response - very misleading!

Aerodynamics - you gotta love it!

I think we should move on!!

 

[junglynx]

Greenking, are you perchance a Beefer?!

 

[Skunkmiester]

I thought helicopters beat the air into submission?

Have to agree Junglynx, Greenkings reply does come across as a bit hissy.