Incorrect Lift Theory
Join Date: Oct 2004
Location: Hunched over a keyboard
Posts: 1,193
Likes: 0
Received 0 Likes
on
0 Posts
Interaction between ships due to increased pressures at some points and reduced at others has caused quite a few accidents over the years - we always had to be wary of it conducting Replenishment at Sea operations, when ships approached each other and then steamed alongside.
Join Date: Sep 2005
Location: Inside the roster matrix
Posts: 617
Likes: 0
Received 0 Likes
on
0 Posts
Join Date: Sep 2004
Location: Jerez
Posts: 24
Likes: 0
Received 0 Likes
on
0 Posts
The NASA report is nothing new under the sun and it is what a lot of us already knew, that the little Italian isn't the only part of the equation. Unfortunately when we did 'professional' exams we just had to give a simplified answer that fitted the CAA's question rather than the whole story of lift that was learned at another institution at another time.
A bit like Georgraphy teachers at senior school never tell you about adiabatic lapse rates and tephigrams yet they teach about cloouds and they just say clouds form at a dew point which is zero degrees C. Always knew he was not so bright but bless. Pilots not knowing what they are actually on about is nothing new.
Lets not forget Kutta, Coanada, Joukowski et al.
What the R.A.F. taught it the pilots doesn't mean it was the whole story. It no doubt suited the purpose enough to give some understanding. The R.A.F. flight engineers maybe got more of the story and then ETPS went further and of the course the Marshall had a brain the size of a planet. That's how it works isn't it?
99% of pilots I ever meet just roll out Bernoulli's (two l's if I remember correctly) when it comes to lift and then dig themselves deep holes when probed.
A bit like Georgraphy teachers at senior school never tell you about adiabatic lapse rates and tephigrams yet they teach about cloouds and they just say clouds form at a dew point which is zero degrees C. Always knew he was not so bright but bless. Pilots not knowing what they are actually on about is nothing new.
Lets not forget Kutta, Coanada, Joukowski et al.
What the R.A.F. taught it the pilots doesn't mean it was the whole story. It no doubt suited the purpose enough to give some understanding. The R.A.F. flight engineers maybe got more of the story and then ETPS went further and of the course the Marshall had a brain the size of a planet. That's how it works isn't it?
99% of pilots I ever meet just roll out Bernoulli's (two l's if I remember correctly) when it comes to lift and then dig themselves deep holes when probed.
Last edited by Angels One Fife; 8th Dec 2006 at 22:04.
Join Date: Aug 2000
Location: Somewhere in Europe
Age: 53
Posts: 64
Likes: 0
Received 0 Likes
on
0 Posts
coanda effect
Found this on MS Encarta.
The theory would explain the flat plate phenomenon. It makes a very straight forward parallel between holding your hand out of a moving car window and adjusting the angle at which you present your hand to the wind. The speed through the air is also an important factor for the reaction force placed against the wind thus producing an "equal and opposite reaction" of the airfoil 'upwards'. It then goes on to describe how the bernoulii principle is an effect of lift but not its cause.
From this I understand that airfoils are given various shapes depending on the task at hand. A large slow moving heavy aircraft would benefit from having a concave undersurface of the wing (slats and flaps contribute to this)as this effectively acts like a parachute. With a forward force still being applied the a/c goes up (just like the boat towing parachute rides you get at the beach). To preserve this effect throughout flight, the a/c's wing incidence angle is usually set at around 4 degrees up w.r.t.o the horizontal thus always having a downward force.
Yes, there is low pressure above the wing and this is caused by faster moving air above - but has very little contribution to overall lift of the a/c. The camber of the wing is there to minimise drag as a flat plate would have severe vortices, hence drag above it.
Have a look at the Encarta CD. They quote 'Boeing' as their information source. There is an interesting diagram/video that goes along with it.
FJ
The theory would explain the flat plate phenomenon. It makes a very straight forward parallel between holding your hand out of a moving car window and adjusting the angle at which you present your hand to the wind. The speed through the air is also an important factor for the reaction force placed against the wind thus producing an "equal and opposite reaction" of the airfoil 'upwards'. It then goes on to describe how the bernoulii principle is an effect of lift but not its cause.
From this I understand that airfoils are given various shapes depending on the task at hand. A large slow moving heavy aircraft would benefit from having a concave undersurface of the wing (slats and flaps contribute to this)as this effectively acts like a parachute. With a forward force still being applied the a/c goes up (just like the boat towing parachute rides you get at the beach). To preserve this effect throughout flight, the a/c's wing incidence angle is usually set at around 4 degrees up w.r.t.o the horizontal thus always having a downward force.
Yes, there is low pressure above the wing and this is caused by faster moving air above - but has very little contribution to overall lift of the a/c. The camber of the wing is there to minimise drag as a flat plate would have severe vortices, hence drag above it.
Have a look at the Encarta CD. They quote 'Boeing' as their information source. There is an interesting diagram/video that goes along with it.
FJ
Join Date: Sep 2004
Location: Jerez
Posts: 24
Likes: 0
Received 0 Likes
on
0 Posts
Now let us just get those wings spinning round and round, about the lateral axis of course none of that helicopter nonsense here, bring in Mr. Magnus, for effect of course, and before you know it, Mr. Flettner will forget all about his strips and stick to ships. 
If Encarta says this then it is clearly wrong. The difference in surface pressure around the aerofoil accounts entirely for the lift the aerofoil produces. The difference in pressure is associated with a difference in speed. What causes what is a matter of philosophical debate.
