thanks for the great knowledge Sir..

Ah, this thread is a boon for guys like me who don't like reading thick books!
Thanks so much for explaining it so clearly and plainly Gusty sir!   

Waaaaaaaaa.... ...I am totally out of my depth. . :banghead:You can always say: 'Leave out if u can't follow.' But how can I ?  My technical knowledge is next to NIL. Now I have to learn the hard way. Otherwise, how to interpret the results of structural modifications I incorporated in to the model if I am scratch-building and experimenting? Gusty, man, you are taking me by the collar to think n learn.  I used to think that all I have to do is get a model, assemble it, put in electronics, power it up and fly.   But I still enjoy learning things, though most of these things you all are discussing are bouncers, going over n above my head. My situation is just like the man trying to walk forward n always back to square one, just like the figure of the man in SWAPNIL'S post. .
Thanks, any way.
eaaaargee.

Quote from: essaargee on April 08, 2012, 09:55:34 PM
...My situation is just like the man trying to walk forward n always back to square one, just like the figure of the man in SWAPNIL'S post. .

Haha! Actually that figure symbolizes the amazing nature of curiosity.
The more knowledge you acquire, the more curious you get. The more curious you get, the more mysteries you ponder upon. The more mysteries you ponder upon the more you study and acquire knowledge! And on and on it goes...it's a mystical cyclic process!

So the more forward the man walks, the more mysteries he stumbles upon and the more he enjoys it!

It's just shows how you perceive life...
For those who see acquiring knowledge and solving mysteries as difficult and pointless and do things just for looking 'cool', life is just a dull one way trip! 
For the curious and knowledge hungry folk life is a beautiful adventure!

This is why I respect Gusty sir and his knowledge sharing so much! 

yes..great sharing of knowledge..

Thirukural Couplet 396

தொட்டனைத் தூறு மணற்கேணி மாந்தர்க்குக்
கற்றனைத் தூறும் அறிவு

meaning

In sandy soil, when deep you delve, you reach the springs below;
The more you learn, the freer streams of wisdom flow

I strive to keep it simple

 

Gusty bhaiya, I have a silly question regarding camber line. Well it is simply the line that is equidistant from the upper and lower surfaces. Now, the problem is how do I obtain these mean points because if I draw a line from the top surface to the bottom surface on the cross-sectional plane and then I find the center of that line, someone else might draw a line that is slightly skewed to the line that I have drawn and so his center will different from mine. Therefore, there must be standard lines whose centers which when joined will give the camber line.

This is the first semester that I am having aerodynamics and I am really enjoying it. My favorite portion currently is shock waves. Thank You so much for your help(I hope you remember why!!). And thanks also to JD Anderson!

You are talking about Camber line and it joins the Centre of the Curvature of the LE and TE Radius, equidistant from Top and Bottom surface and it has to be drawn mathematically, there are plenty of tools, at NASA you have foilsim, foilsim 1.1 on joukowski aerofoil had my contribution, if you decompile the Java Class file should see one Flt Lt MJ Augustine

the book i gave was written by me, who is Mr Anderson ? is he from Matrix  

Any help on Shock Waves, do PM, Theoretically known it, practically seen it (Yeah when in clouds or high Humidity condition you can see it)

Check the attached picture. I basically want to know, the center of which line to consider when drawing the camber because as you see the center of all these 3 lines will be different even though they originate from the same point. So, if I have to plot the center from the upper surface at that point, which of these three lines will I choose?

Oh! I didn't know that. That is really brilliant! 

I also follow Anderson's books, they are very good.

Though I am BLUNT in aerodynamics, I think, it is the line generated by the CG of smaller area towards x-axis when the smaller area pieces having length of dx.
And, hope the angular shifting of x-axis will not differ the line generated with the camber line when dx=>0.

But the axis should be taken parallel to the wind flow always. And hence the lines are perpendicular to flow directions.

Line joining the tangents

Right! So, I did guess that correctly! Thank You 

Aerodynamics by LJ Clancy is good, esp the Chapter on stability, Momentum theory of Lift, M Cdr, etc, in fact i recommend it for all RC Pilots too, further reading will help you fly better , scratch build better

Sandy and I got discussing about his scratch built Bandit (EDF Jet), then it occurred to me i need to clear the cobwebs on Air Intakes and Duct Flow, for :-

(a)  To understand EDFs
(b)  To Scratch build EDFs
(c) this is the a common subject with the jets , therefore a link of this goes into Jet Engine thread as well

Airflow through Ducts

Before considering intakes in any more detail, the behaviour of airflow through a duct, and the consequent affect the cross sectional area has on the pressure, temperature, and velocity need to be understood.

With steady continuous airflow through a duct, the mass flow rate at any cross section must be the same, i.e. mass = Air Density (Density is less at altitudes than at sea level) x Area x Velocity.  It follows therefore that at a minimum cross sectional area the velocity is highest, and at a maximum cross sectional area the velocity is lowest. (However the limiting factor is the backpressure and choking of the intake)

Because of the change in velocity there is also an effect on the pressure and temperature of the airflow at these points.  Where the velocity is highest, the static temperature and pressure are lowest, and where the velocity is lowest, the static temperature and pressure are highest (See Image).

The above paragraph can be expressed using a modified version of Bernoulli's equation, representing the total pressure of the airflow.  The first term (pressure) is often referred to as the static pressure, and is the pressure of the surrounding air, whereas the second term (½RhoV2) is referred to as the dynamic pressure and represents the kinetic energy of the airflow.

   P     +   ½   rho  V2   =   Constant
   Where      P   =   Static Pressure
         rho   =   Density
         V   =   Velocity

   and from the Pressure law:   P   =   Constant
               T
   Where   P   =   Static Pressure
         T   =   Temperature

So that at constant density, any increase in velocity will cause a decrease in static pressure, and will be accompanied by a decrease in static temperature.  Conversely any decrease in velocity will cause an increase in static pressure, and therefore an increase in static temperature


Note:    At low speeds air density also decreases as velocity increases, but the effect is not very significant.

How much of aerodynamic - specially in terms of lift and drag actually affects the RC model?

I mean while the thrust to weight ratio of a normal plane is some where around 1/3, we are keeping a T/W to almost 1 in even the basic cases. So apparently, we should be able to cover up the ill affects of poor aerodynamics with the extra thrust available. Is this not the case?

to some extent yes, still, aeroplane flies due to interaction of the air (a) because the aerofoil (b) for example stall for a 12% T/C symmetrical aerofoil with no LE radius will occur at 12 deg alpha, whatever is the engine. the attitude it will occur will certainly depend on the engine. obvious question why  ? because air's interaction with the aerofoil has nothing to do with the engine.

PS

Above discussion pertains to EDF

http://www.rcindia.org/electric-planes/sky-surfer-from-rc-bazaar-build-and-fly-log/msg98379/#msg98379

read this and the subsequent thread for technique to launch high mounted engine glider

thanks for the guidance Sir..

To add to what Gusty bhaiya has said,
                   density at stagnation point/ local density = [1 + (gamma-1)/2 M^2]^(1/gamma-1) 
                   Gamma = 1.3 for air. (It is the ratio of specific heat at constant pressure to specific heat at constant value)
If the local density of air during flight is within 5% of the density of air at stagnation point(velocity of the flow and dynamic pressure =0), the change in density is ignored and we consider the flow to be in compressible and therefore Bernoulli's principle can be applied.
And if substitute the value in the above equation we get M(Mach number)=0.3 . So if the local Mach number is below 0.3 the flow is considered incompressible, above which the density change is significant and has to be taken into account.
     

Rohit K.I.S.S

Lol! Yes I know I crossed the line.
BTW Clancy is a very good book for beginners, was reading it the other day. Thanks for recommending.

here is the very basic discussion on control throws, Exponential and dual rates

http://www.rcindia.org/radios-and-receivers/how-to-increase-throws-of-rudder-and-elevator-flysky-th9x/msg99684/#msg99684

I saw a senior one aeromodellor entered the spin and for recovery opened power and continued pulling back and crashed, another, in a wall recovery,  flick and crash, on discussion with these people i understood, most people do not understand spin, its mechanics and recovery, subsequent posts are dedicated for Spin