Back after a couple days of testing the
theory of differential pressure acting upon multiple airfoils in close proximity to each other (formation flying). But I didn't stay in a Holiday Inn Express, so I'm no smarter!
WOW!, Skylor! I think you're on the right track. You also noted that I put the observation about the pressure differences and lift in the form of a query, not an outright statement.
Paul, I thought Skylor made some good points too, and I was going to say that I get your points (er, I mean queries
) about whether its the outside air's pressure on the bottom...or the outside air's pressure on the top...or the differential pressure between them...or the differential in differential pressures (outside versus inside) between the top and bottom.
Being the goof pilot I am, I'm still looking for the "Answer D: All the above" option. That's the bubble I'd fill in...but then again, since this is all theory, if you added an "E: None of the above", I'd really be in a conundrum! In some ways, we've been saying the answer is "7". You're asking if that means 0+7, 1+6, 2+5, or 3+4. I'm wondering if it matters (and yes, I live in Nevada, thus my analogy!)
However, given that a solid wing, a rotor, a prop blade and a hollow wing (or hollow wings of various structures) all generate that amorphous force we call lift when moved through a medium (yes, I know, I'm already in trouble with that one, as the wing probably doesn't generate lift, it probably facilitates its generation)...but I digress...back to the point...I think (IMHO) that truly is all the above. We each try to explain it in our own best terms. And yes, both the mathemetician and the engineer have to be able to use the info. My guess is that in this case, the engineers use a best guess model as a baseline, then they (or in some case pilots
) test the model to failure, and the M's and E's scratch their heads and say, "well, that was wrong, lets try this", and we'll get Bob to test fly it.
My guess is they don't have the full mathematical answer, so they over-engineer it for some margin of safety. Sure if we had it perfect, we could save weight or strcuture, but as that test dummy, I like the margin.
I find it much more useful to be able to harness the resultant force than to be able to fully explain it, though it doesn't mean I (and others) won't try our best (please see my next part below)...
I'm really surprised at the number of respondents who skate and skirt around the whole issue with their "Lift is a result of the mass flow times the downwash velocity." and "It's the result of the summation of all of the force vectors." and such. What I've often found revealing in my discussions with others on various topics is that far too many are afraid of giving definitive answers, for fear they may look wrong in the eyes of others. This is especially true if they must put their answers down in print for all to see for all time. So what they do instead is rely on time-proven reponses to keep from showing their vulnerability, even if they are only generalizations.
I was on a jet flying a landing approach in rain, sleet, and snow (Even though sleet means a mixture of rain and snow, I threw the rain and snow in for those who have never been out of SoCal!). I was sitting ahead of the leading edge and marveled at the sight of these elements being swept up toward the leading edge as they were being illuminated in the landing light. A few days after I got home I asked an acquaintance who was an aero grad from Cal Poly SLO what caused this action. He replied that it was due to the low pressure being broadcast ahead of the wing. I asked him if that was AM or FM. When pressed, he said that was how the instructor taught the class. If only this instructor had known about the Coanda effect, he and the class would have had a much better understanding of the forces at work.
I also once acted as a TA, technical advisor, to two Cal Poly EE students on their senior projects. The one had an instructor who didn't undestand the biasing of an Op Amp in the middle of its applied voltage when operating from a single supply voltage, and the other didn't know that when you transmit 24 bits of TTL over wires that each bit wire must have its own return, or if only a single wire return was used for all 24 it would cause common-mode coupling.
The students only learn what the instructors teach them and then go on to become instructors themselves to teach some of the same falsehoods. Something along the line of educational entropy!
Try to get good propeller design in one of these aero classes. They're still discussing advance ratios and such.
Paul, we've met and had great conversations...I like talking with you, and wish I could figure out a way to test one of your props (still hung on the CS to FP engine/crank ramifications and how they relate to my pocketbook, but I'd still love to do it). That being said, seems to me (again IMHO) a lotta gentle (and not so gentle) bashing going on here brudda. Several great posts by guys putting it out there, and taking that risk. Several have checked out because their "time-proven responses" were seemingly dismissed (kinda felt my discussion on the canopy issue was as well, but what the hey, eh!)
You've asked some thought provoking questions...and have thrown some chum in the water to keep the discussion going...and many have responded. Some of us challenge some of the theories you (and others) postulate in response to your original query, some ask follow-on questions, and the discussion rolls on. But I need to remember that approaching and postulating responses to your queries is (and I mean this in a very complimentary way, honest) akin to trying to describe what something looks like with my eyes, to a guy that sees in the visual,
and the XRAY,
and the IR spectrums.
Guess all I'm saying is, if we are going to expand the plane (or sphere) of thought on these theoretical concepts via discussion, then perhaps attack innuendo, subtle though it may be, will turn some off. Rhetorical queries are fun, if we keep 'em fun. Nobody elected me counselor or mediator, but I like your postulations and learn a lot, so I'm just tossing a pitch for being (intellectually) nice to mere mortal pilots like me!
Now, do you have a theory on that initial query that we may be able to evaluate and take to that next plane (sphere)?
I tried to give all of the theoreticians a little hint when I spoke of the structure-less construction of the Atlas missile. Along this line, what if we were to make a totally hollow wing with no internal structure; no ribs, no spar, just an applied air pressure within it. Goodyear made an inflatable plane for the military to be parachuted to a downed pilot, which he would inflate and fly off.
How in this case are the lift loads transmitted to the wing and then from it to the rest of the struture? Through air pressure?
OK, so we've never really resolved how the force gets applied to the wing, so I'll stick my neck out and say its transmitted via the wing structure (however it gets there, and in whatever form that wing finally takes), via wherever it interacts with the rest of the aircraft structure (wing root, etc...if this conceptual aircraft has those). Otherwise it is magic (PFM, right!). At least that's what my aircraft structures prof taught me. Now I didn't go to CP SLO, but I am a product of the California State University system (SJSU), so that may be suspect!
(Yes, I'm kiddin' around).
So Paul, what do
you think the answer to your question is?
Cheers,
Bob