Aerodynamics?

[Nexus]

Oh I see now.
Sorry for jumping the gun on the issue
(hard to read a 3 page thread filled with information  :'( )

But I still stand pat regardless  :)

A cambered wing with zero geometric AoA (angle between mean chord and relative wind) will provide lift since there is a net diversion of the air down.
The same wing profile, with zero effective AoA wont produce lift.
Zero effective AoA =  0 lift

(sorry for the crappy pic, mobilecamera  :-/ )

So in order to get the aircraft up in the air, it has to deflect the air downwards.

[Brett_Henderson]

I was going to respond.. but anything I'd say is already in this thread

Summary: Getting enough mass, to move quickly enough to act as thrust simply by redirecting it (the act of RE-directing it would have to consume as least as much energy as any thrust generated) tickles with perpetual motion.. I can't sell myself on this theory anymore than I'd believe the wake a boat would create can help guide or propel it.

[Brett_Henderson]

Sorry for borrowing your image

[Brett_Henderson]

Uh OH.. I just had a mental break-through !

There is no horizontal component as the air isn't moving, the wing is. So....... the only redirection of the air IS downward..

HOWEVER... that still doesn't satisfy my perpetual motion problem (or does it ?)

[beaky]

You two just WONT give up a good fight, huh?

I think it's more of a friendly debate than a fight, and it was established long ago in this thread that we're both right to some extent.
At least I'm willing to admit that...

[beaky]

Ah, I see you're not giving in without a fight.

I don't think using a cropduster to demonstrate airflow gives the true picture as the spray is intended to fall as evenly distributed as possible. I'm sure there would have to be a reasonable pressure to form the spray & the nozzles would be directed downward. I really can't understand where this downward deflection is supposed to come from on a conventional wing that's flying straight & level.

You're free to think what you like. These are more than enough to convince me.

Okay; call it a draw. You have the formal training; I don't expect you to yield to a layman's observations. I'm not trying to change anyone's view so much as argue the case for downwash as best I can. As a pilot, I "feel" that downwash plays a role as well as pressure differential due to fluid dynamics, and without hard data about nozzle pressure and how much of an angle the deflection needs to be for a given weight and airspeed, blah blah blah, we're not going to really prove anything.
I think "aerodynamics" should be a sticky; these fact-and-theory-filled discussions seem to pop up every time some young innocent asks one of those "what does it all mean?" questions...
And in that spirit, I want to stir the pot with another something from Mr. Kermode... we are all probably familiar with the first four airfoils, and their specialized purposes are pretty obvious.... but how about the last one? Unfortunately, it's not explained anywhere in the book, as far as i can tell so far.
I figure if Hagar doesn't know, we're all stuck on this one. I've never seen a wing like that, as far as I can remember... and it definitely wreaks havoc with my ideas about downwash, although it seems unlikely to work well by anybody's reckoning. This type of wing must usually be mounted at a high angle of incidence, I think. Or maybe it's one of those shapes that never got off the ground (pun intemded!).

[Hagar]

I hadn't anticipated getting into a long scientific argument on this. It's a long time since I thought anything about aerodynamics & I must admit to not being familiar with these latest theories. In fact I'd not heard of them before reading the article from Jake's link. I've always thought there is more than one force at work here. It's quite possible the Newton/Coanda theory is valid in some circumstances but that doesn't appear to explain why there are so many different aerofoil sections or why they would be necessary. Not being a scientist I imagine several basic laws of physics apply here. I won't show my ignorance by continuing the argument but throw a few points into the discussion.

Most people tend to forget that it's the wing that's moving through the air & the term 'airflow' is a misnomer. This brings the whole argument about angle of attack into question as increasing the AoA involves lifting the nose of the complete aircraft & changing the direction of flight upwards. The thrust line remains constant so once a climb (or dive) is established the direction of the relative 'airflow' is no longer horizontal as shown in most diagrams.

I've dug out my old 'Flight Briefing for Pilots' that was considered the private pilot's bible for many years. I was given a signed copy by the author when it was first published in 1961 which is one of my prized possessions. I copied this short extract from the chapter on fundamentals. "If the Leading Edge of the airfoil is raised at a slight angle to the airflow, pressure will rise when the air makes contact with the undersurfaces of the wing because of its momentum. The net result is that the airfoil section will generate a lifting force approximately two-thirds of which is due to the decrease in pressure on top of the wing and one-third to the increased pressure below."

I suggest that this is only temporary during the change of direction & until the climb is established.

[Hagar]

And in that spirit, I want to stir the pot with another something from Mr. Kermode... we are all probably familiar with the first four airfoils, and their specialized purposes are pretty obvious.... but how about the last one? Unfortunately, it's not explained anywhere in the book, as far as i can tell so far.
I figure if Hagar doesn't know, we're all stuck on this one. I've never seen a wing like that, as far as I can remember... and it definitely wreaks havoc with my ideas about downwash, although it seems unlikely to work well by anybody's reckoning. This type of wing must usually be mounted at a high angle of incidence, I think. Or maybe it's one of those shapes that never got off the ground (pun intemded!).

Very interesting. I must hunt out my old modelling books that explain many of these things in detail. My immediate thought is that the reflexed section would be used on delta-winged aircraft. Not sure if there was such an animal in 1941 when your book was published.

I have a high-performance slope soarer designed by my old friend Chris Foss who is also a full-sized glider & power pilot. Not much this chap doesn't know about flying. The Phase 6 is still regarded as THE competition sloper & many championships have been won with it over the years. http://www.chrisfoss.co.uk/Phase6.htm
It comes in two versions, the fully-symmetrical 'pro' model & a 'sports' model with semi-symmetrical wing section. I have the pro version & remember he told me to make sure I sanded a reflex in the upper & lower surfaces (similar position as the upper surface in your example) as this makes all the difference to the performance. It flies extremely well & actually out-performs the sports version in low lift conditions. I put this down to carefully following his instructions on that reflexed aerofoil as he knows what he's talking about.

[beaky]

Very interesting. I must hunt out my old modelling books that explain many of these things in detail. My immediate thought is that the reflexed section would be used on delta-winged aircraft. Not sure if there was such an animal in 1941 when your book was published.

I did a little more research into this, and apparently it's a desired airfoil for all "tailless" aircraft, not just deltas... this would explain why it was being studied in 1941, as there are tailless and even swept-wing designs going back quite a ways.
I'm still not exactly sure why it's desired, but that little schwoop at the trailing edge seems to help with (lateral?) stability at low airspeeds and high angles of attack. Why it works so well with gliders is another interesting question; maybe the narrow fuselage aft of the wing puts sailplanes in the same aerodynamic realm as tailless aircraft in some situations. I wish I had more time to study this, but unfortunately I'm not getting paid to play aerodynamicist; got to get ready for work now.

This has been fun; maybe next we can all have a whirl with the old "downwind turn" debate... LOL...

[Hagar]

I did a little more research into this, and apparently it's a desired airfoil for all "tailless" aircraft, not just deltas... this would explain why it was being studied in 1941, as there are tailless and even swept-wing designs going back quite a ways.
I'm still not exactly sure why it's desired, but that little schwoop at the trailing edge seems to help with (lateral?) stability at low airspeeds and high angles of attack. Why it works so well with gliders is another interesting question; maybe the narrow fuselage aft of the wing puts sailplanes in the same aerodynamic realm as tailless aircraft in some situations. I wish I had more time to study this, but unfortunately I'm not getting paid to play aerodynamicist; got to get ready for work now.

Most deltas won't fly at all well without that reflexed trailing edge. I imagine the same applies to all tailless aircraft, not just gliders. The reflexed trailing edge can also be used near the wingtips of conventional aircraft to prevent tip-stall instead of washout.

This has been fun; maybe next we can all have a whirl with the old "downwind turn" debate... LOL...

Ah, that old chestnut. If you understand the difference between airspeed & groundspeed I don't see what there is to debate there.

[Brett_Henderson]

I'm Googling  "Downwind turn debate".. keepin' an eye open for the thread  ;)

[beaky]

Most deltas won't fly at all well without that reflexed trailing edge. I imagine the same applies to all tailless aircraft, not just gliders.

I wasn't referring to a tailless glider; I'm thinking that because of the lesser surface area of a glider fuselage behind the wing (compared to the average light single, for example), it needs a little help for lateral stability. In that department, a glider is a little more like a tailless airplane.Still a little vague on how the reflex curve helps, though...

The reflexed trailing edge can also be used near the wingtips of conventional aircraft to prevent tip-stall instead of washout.

Now that you mention using that upturned trailing edge in lieu of washout, i think I understand how it works. Or do I? I'm at a loss as to how to put it into words. Maybe I'm better off "understanding" it intuitively...not very logical, but ... (shrugs)  ;D

Ah, that old chestnut. If you understand the difference between airspeed & groundspeed I don't see what there is to debate there.

Yep. I think a lot of people are confused by the brief changes in "feel" and airspeed associated with windshear... but of course, the most stubborn proponents of the "tailwind will stall you" concept are non-pilots, based on what I've heard and read.

[beaky]

I'm Googling  "Downwind turn debate".. keepin' an eye open for the thread  ;)

Uhboy, here we go...

[Brett_Henderson]

Nah.. no worries..  I read 1/2 dozen posts about it on other boards and there's nothing to debate. If you consider the loss in lift/airspeed that you get any time bank the wings and use up some of that lift (no matter where it comes from  ::)   )  to "turn" the plane...  The plane's airspeed doesn't differ at all whether your in dead-calm air, or wind from any direction.

Throwing gusts or shear into the mix is a non-related complication to the "debate"..

[Hagar]

[quote]Now that you mention using that upturned trailing edge in lieu of washout, i think I understand how it works. Or do I? I'm at a loss as to how to put it into words. Maybe I'm better off "understanding" it intuitively...not very logical, but ... (shrugs)