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SV: SV: SV: Re: wing lift/drag pins

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sidsel.svein(at)oslo.onli
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Posted: Mon Jul 01, 2013 9:00 am Post subject: SV: SV: SV: Re: wing lift/drag pins

 	  Quote: 	
		   > > A glider is

 > > "propelled" by the forward - in the direction of flight - component

 > > of the aircraft's WEIGHT only.

 

 And that´s why they (gliders) obviously fill also sometimes their

watertanks -
	


 	  Quote: 	
		   to get more load, to feed gravity and to get speed?

 

 Cheers, Raimo

 


	


Yes, Raimo, that is one of the main reasons for the water ballast.  At the

same glide ratio, you get higher speed with than without ballast.



Just look at the bottom illustration in my first e-mail:  Higher weight

gives larger gravity component in direction of flight at the same angle of

flight vs. horizontal.  Larger pulling force gives higher speed - the glider

accelerates until the higher pulling force equals the increasing drag.

Higher speed gives higher lift (square of speed increase) to carry the

higher weight, so that you can maintain the glide ratio (direction of flight

vs. horizontal).



Regards,

Svein

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sidsel.svein(at)oslo.onli
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Posted: Mon Jul 01, 2013 9:49 am Post subject: SV: SV: SV: Re: wing lift/drag pins

Frans,



The forces are as illustrated in my first posting.



If you throttle back the engine, all properly designed and built aircraft

automatically pitches down to gain speed.  The pitch-down is of course the

result of the stabilizer's design and angle of incidence vs. the wings' .



Why gain speed:  To give required lift.



To get enough speed to give the required lift, the pulling force must be

kept up.  Lost propeller thrust must be compensated by something.  As lift

CANNOT give force in the direction of flight (remember, BY DEFINTION it is

perpendicular to the direction of flight, thus it has no forwards nor

backwards component flight-direction-wise).



What is this "something" force that compensates for engine power?   Look at

the bottom illustration in my first posting:  To create a forward force

(forward meaning in the direction of flight) to maintain speed to maintain

lift, the only possible force available is the gravity's flight-direction

component.  The steeper the pitch-down, the larger this force becomes, and

the faster down you fly.  This creates more lift (perpendicular to the

flight direction), of course, but the vertical component of the lift remains

the same - equal to the weight of the aircraft plus the vertical component

of the downward stab. force.



The gravity component acts on every atom in the structure's molecules, but

we commonly consider them all grouped together at what we refer to as the

center of gravity (CG), and uses this as point as the one common point where

the total pulling force acts.  Neither the fuselage nor the wings pull the

aircraft forward, good ol' gravity does it all by itself!



Do this, Frans:  Shake off all your conceptions.  Look ONLY at my

illustrations.  The global airplane forces are actually this simple.



Alan,

Right on!



Regards,

Svein

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frans(at)privatepilots.nl
Guest

Posted: Tue Jul 02, 2013 2:58 am Post subject: SV: SV: SV: Re: wing lift/drag pins

On 07/01/2013 07:49 PM, Sidsel & Svein Johnsen wrote:



 	  Quote: 	
		   Do this, Frans:  Shake off all your conceptions.  Look ONLY at my

 illustrations.  The global airplane forces are actually this simple.


	


I think we are both right, but each of us looking at a different

situation. You are talking about the airplane as a whole.



But for me, as this was the topic of the original discussion, the

question is: what kind of forces do the wings pose on the fuselage?



As the fuselage doesn't want to go forward without the wings, but still

goes forward with the wings, it looks to me that it is possible that the

wings somehow pull the fuselage forward.



And of course I have some clues as why the airplane (as a whole)

actually flies and I agree with your drawings, but again, the topic was:

the rear wing sockets, do they push or do they pull?



To really answer this question you should drawn the vector diagrams not

for the airplane as a whole, but for each of the components that make up

the airplane. And then it would be interesting to see what resultant

force is acting on the rear wing sockets.



Mind you, I might be totally wrong on my idea. But I have a feeling that

it is beyond just our reasoning to really have a grasp which forces are

acting where on the individual interconnecting components. As I recall,

the "cuff" around the two wingspars was a "fix" for some unforeseen

force acting on the wing spars causing them to twist somehow around each

other. Despite the great souls working on the original design of the

wings, it was not foreseen that the cuffs would be necessary.



Has anyone actually ever tried to fly without the rear pip pins in? If

so, what happened? If not, what would happen? Could you get away with

it, or will the wings fold forward during the landing flare?

I don't think the forces are too large anyway, as the original Europa

design didn't have the interconnecting bar between the sockets, and the

original structure is not really that strong with respect to pulling and

pushing forces.



Frans

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