Let me answer this question in two parts (a) Why Does a Vortex form (b) How can it's effect be minimised

(a) Wing Produces Lift agreed . in straight and level flight this lift needs to equal weight. This lifting force will translate to low pressure on top of the wing and high/not so low pressure on the bottom of the wing. This pressure differential for a given weight has to be same irrespective of the wing shape that means the vortex will remain same, because when air leaves the wing has to come back to neutral pressure

(b) how do you minimise its effect. Answer is simple instead of one big vortex, create multiple small vortex and one not so big vortex. advantage in this setup will be the core low pressure of the big vortex in case two will be less and consequently the loss (Also called the tip spillage) will be slightly less, HOWEVER the effect is only 10-12% overall, because of the pressure differential remaining same

A tip shaped like left wing of SLS's image will have multiple small vortex and one big vortex. Right wing will have one big vortex with much lower core pressure.

like the vg's we r using on the addiction x 

VGs induce Small vortex airflow which prevents separation of airflow at high angle of attack (Basically low speeds) because a turbulent flow is thick , has more energy and sticks to the surface longer (See image), VGs induce turbulent flow so that the flow doesn't separate at laminar stage itself. Thats how low speed handling of our addiction X is good. yeah small vortex by VGs analogy is bang on


Also read
http://www.rcindia.org/rc-general-topics/basic-aerodynamics-for-rc-flying/msg44317/#msg44317

Exact scaling of an aircraft, for testing purposes, isnt just scaling down the size, coz thats just static scaling. For dynamic scaling a lot of factors would have to be taken into account, Reynolds no., Froudes no., moment of inertia etc. I had read about this in a book called Modelling Flight, how do you go about this physically i.e. make a model that takes all this into consideration.

This is called Scale Effect, it is simply because of the relationship of forces vis-a-vis the size of the aircraft. if lift =CL ½ σ V² S. if i halved 'S' (Surface area, read post http://www.rcindia.org/rc-general-topics/basic-aerodynamics-for-rc-flying/msg41421/#msg41421) to see the same effect i need to adjust 'σ' and 'V'.this is where our dimensionless quantity called Reynolds number comes in. read more on Reynolds Number here (http://en.wikipedia.org/wiki/Reynolds_number)

Read for runway Orientation , downwind landing etc this whole thread

http://www.rcindia.org/chatter-zone/runway-traffic-90-minutes-compressed-into-230-minutes/msg64098/#new

Sirs,

I had read a book recently. "Flight without formulae" by A.C. Kermode. It deals with all the basic concepts of Flight/Aerodynamics.
Hope it will be a very useful to some beginers here.

try "Mechanics of Flight" by AC Kermode even that is good one!

Thank you Sir.
I will search for the book in my college libraray, once my college reopens.

As a beginner i kept wondering why do twin engine planes have propellers rotating in opposite directions 

found the answer here .....

http://www.aerospaceweb.org/question/dynamics/q0015a.shtml

Had the same question, & I thought I had partially the answer. The Bristol Beaufighter had a marked propensity to swerve on take off(It had propellers rotating in the same direction),whereas the P-38 lightning was given contra rotating props for improved handling.....but I knew there was more to it.thanks for the link!

The link is Inadequate , watch out for this space for prop induced swing , torque effect , ground loop etc.

Augustinev Sir,

Noticed your current total number of posts. It's 1234 ... 

Yeah, he's properly taught us the '1234' of RC through all those! 

Thanks! didn't notice that. I remember the 1000 th post of anwar bhai, if I am not wrong in Sushil sir post, be that as it may.
PIO( pilot induced oscillations) occurs when the aircraft lag and your control inputs match and is out of phase. There are long period oscillations called phugoid. This is not dangerous , dangerous is short period oscillations, occurs during landing. Margin of error is less. Remedy ? I case you get into oscillations (normally happens after touchdown) just hold the elev , do not move she will settle down. Happens in heli too, ESP during hover. Factors Affecting aircraft lag? Please read http://www.rcindia.org/radios-and-receivers/sanwa-the-choice-of-champions/msg72826/#new add air speed altitude and angle of attack to that list.

Now, contra rotating props and pusher props are same or different?
So if I understand correctly the difference between them, a pusher prop would throw wind forward while a normal prop would throw backwards right? In an electric setup, we often make the normal prop work as a pusher by interchanging any two leads of the motor/esc combine. How different it is from using a pusher prop?

Contra rotating props, on an aircraft, will BOTH push the air backwards (towards the tail) to make the aircraft fly forwards. One would be mounted on the port wing and the other on the starboard wing. While one would spin clockwise, the other would spin anti clockwise to negate the torque generated both by the engines. Alternately they could be both mounted on the same shaft as in the picture. Note the opposite pitch on the props.

Also, from what I know, to turn a normal prop (in an electrical setup), you not only have to interchange two wires from the ESC to the motor, you also have to mount the prop backwards on the motor shaft.

The above is my understanding and I would like to know if it is correct.

Thats exactly my point. In an twin motor electrical setup, if one is to move 'contra' then it will become a pusher. so one motor in tractor and another one in pusher configuration is not flying. PERIOD!!!
So think there is some problem in my understanding

Haha. Don't get confused. If one is tractor and the other one pusher won't they cancel each others thrust? It is just that the prop twist is so adjusted that both rotating in opposite diection still threw the air back , our man newton pushed the airplane forward, this setup cancelled each others torque reaction , but the swing is not only due to torque. It is also due to rotating mass of air and it's reaction with fin. This is a large contributor, then the question is why twin prop? The engine in this airplane though had enough did not have the adequate rpm . It could swing a larger prop but the Clearance was less. Therefore two props. That's about it.

then please answer the questions on #140. The main issue is if I am building a twin motor electric setup, how do I do it?

Not necessarily the prop should rotate anti clockwise it can rotate clockwise too, prop for that is twisted the other way, so that they both throw air backward while rotating in the opposite direction. Even for a Rc airplane such props are available.

What he means is, you put a tractor prop on one side and a pusher prop on the other side and rotate them in opposite directions. Then they will both push air in the same direction.

@sukurt
Thanks.... that is the answer that I can understand....

Quote from: VC on July 29, 2011, 08:11:59 PM

Also, from what I know, to turn a normal prop (in an electrical setup), you not only have to interchange two wires from the ESC to the motor, you also have to mount the prop backwards on the motor shaft.

The above is my understanding and I would like to know if it is correct.

VC

Not very clear what you mean. Reversing the prop does not reverse pitch It will still remain the tractor (or pusher) it was, but with lower efficiency.

from what I know, the marking in the prop always points to the front whether the configuration is a tractor or a pusher.