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Lift %, Upper/lower wing sections

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Lift %, Upper/lower wing sections

Old 20th Jul 2022, 08:20
  #41 (permalink)  
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Many thanks, Clive.

The simplest, briefest story generally proves to be the best, one thinks ? I shall remain envious.

Given that you have somewhat more than a passing interest in deltas, might you be able to comment on Megan's ground effect observations in post #32 ? (We might have been able to entice him down for a meal had my misreading of your email been correct.)
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Old 20th Jul 2022, 16:27
  #42 (permalink)  
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I had never thought of it before, but:
For there genuinely to be nothing else happening the lift and pitch balances must be satisfied simultaneously.
If the aircraft started in trimmed 1g flight then the incremental wing and elevon lifts must be equal and opposite to remain in 1g flight
Applying that condition to the pitch balance the algebra says the aircraft can only stay in pitch trim if the wing incremental lift and elevon lift act at the same point.
For normal flight/free air one would throw this out as a load of cobblers, but as a delta wing flies into the ground cushion the wing lift moves a long way aft - possibly to around 70ish% chord. I do not know what the elevon lift does in ground effect, but would not expect it to go any further forward than that.
So technically it could be possible, but would depend very much on the airplane and the height at which the manoeuvre was attempted.
I seem to remember somewhere in the Concorde question thread a pilot posted that allowing the stick to move forward during the flare was a prelude to disaster.
I tries to find the posting but gave up at #600!
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Old 21st Jul 2022, 01:27
  #43 (permalink)  
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Originally Posted by john_tullamarine View Post
An interesting thought, I shall have to ponder it a while. Or, perhaps enlist the expertise of a couple of our aerodynamicists on the matter. Ah, looking back, again, I see Dave has been here already ...
So long ago for me that it strains the memory and I dare not comment. I recall doing this stuff over 50 years ago and then more fancy stuff: Subsonic Aerofoil and Wing Theory | Aerodynamics for Students

I amuse myself these days by helping some with the "cesspit of misinformation, half-baked truths and misshapen facts" mentioned in https://www.flightsafetyaustralia.co...y-unteachable/ Unfortunately it is the regulator which is often the root cause of it. Incidentally, I don't mind them calling me a dinosaur. Aerodynamicists these days tell me that my CFD wasn't really CFD (stretching the capability of mainframe computers back then). CASA's current Flight Instructor Manual is pretty much the same as the 1967 version at the time I was doing my flight training. I've learnt a lot since.

Originally Posted by CliveL View Post
I wasn't going to post anything as it has all been said, but since you ask: .... That being so, the usual explanation fits, that is to say:- ... Newton tells us that to change something's state there must be a force applied ...That reaction is the force we call lift acting on the airfoil .. That’s Newton’s contribution ... So much for lift generation .... Force can only be applied to an object immersed in a fluid by changes in pressure of the fluid in contact with the body. ... The distribution of those pressures and forces is best calculated using Bernouilli’s theorem ... That covers Bernoulli
That's it really
Sums it up nicely.

Last edited by djpil; 21st Jul 2022 at 02:13. Reason: typo in date
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Old 21st Jul 2022, 01:40
  #44 (permalink)  
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I think the three of us probably qualify for saurian status ?

Good to see a link to Sydney. Auld and Srinivas were after my time (I was there during Bird's and Steven's tenure). That's a useful link for folks.

Many thanks, both, for your comments. Somehow I don't think we will change the imaginative waffle that passes for elementary pilot theory training in the Industry, though.
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Old 21st Jul 2022, 03:11
  #45 (permalink)  
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Somewhat off topic but I thought a beautiful demonstration of air flow from a real wing is in part of the video below (around about 35 seconds in)

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Old 21st Jul 2022, 04:16
  #46 (permalink)  
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I'd have to take issue with the video.

Cubs are fun, for sure, but Supercubs are betterer fun ... and do just the same sort of max rate cross controlled landings .... I can recall, during my outfielder paddock retrieve checkout, being shown steep turns under the crown of a large tree. Probably stupid (actually, definitely stupid) but, for young chaps with no brains and far too much testosterone, great fun as is the norm for young chaps with no brains and far too much testosterone.

The turning flare to land we used to do off glider launch recoveries in a Callair, many years ago, at a well-known RAAF base. Hopefully the boys don't do them, these days. Callair was fun, too, even if the ailerons were a bit strange (ie useless) at low speed.

However, a nice shot of trailing vortex flow.
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