http://www.rcuniverse.com/forum/fb.asp?m=10151700

The first page has some interesting points, especially things like "there is no real need to take off against the wind"

Interesting but lot of confusion in the discussion. , whats your take on this Anwar?

Quote from: anwar on November 23, 2010, 01:00:10 PM
The first page has some interesting points, especially things like "there is no real need to take off against the wind"

What do you define as "real need"? If the wind speed is substantial in comparison to the aircraft stalling speed, the difference between "into wind" and "downwind" take offs will be a lot. The ground speed will be stall speed MINUS wind speed upwind and stall speed PLUS windspeed down wind.  So, if you have a windspeed of even 15km/hr. the difference would become, effectively 30 km/hr. You would need more runway and power to accelerate to the take off speed downwind.

If you have a headwind of 160 Knots... you need no runway to take off a Boeing Jet when flying into the wind. As the Jet will takeoff as soon as you release the breaks ..... 

So is true to opposite direction, in a tail wind... same boeing will need amazingly long runway and power to just takeoff.

It would be fun to think about downwind landings along this line of thought ! 

Would a plane, that would tip stall at low speeds, land easier downwind due to the added help from wind

Quote from: asinghatiya on November 23, 2010, 05:08:29 PM
If you have a headwind of 160 Knots... you need no runway to take off a Boeing Jet when flying into the wind. As the Jet will takeoff as soon as you release the breaks ..... 

Very true.

I used to have a Senior Telemaster that was an aircraft with a high lift airfoil and very low wing loading. It would actually fly backwards and climb into a reasonable headwind!

It was originally designed for towing the "preliminary" cable across valleys and canyons.

Quote from: anwar on November 23, 2010, 05:20:11 PM
Would a plane, that would tip stall at low speeds, land easier downwind due to the added help from wind

The added tailwind would cause it to  - tip or otherwise- stall EARLIER

Bingo ! The key is to remember that air has to flow across the wings from the nose to tail, not the other way around.

Let me see if i can get across.
firstly in level flight weight= lift =CL ½ σ V² S. CL is coefficient of lift, which depends on your wing angle of attack (position of the nose in level flight) shape, camber etc, ½ σ V² is called the dynamic pressure, simply put, number of air molecules for a given time, ALSO CALLED THE INDICATED AIRSPEED, 'S' is your wing area.

Now, aeroplane has lift and weight acting as one couple (noseup or down will in RC language, will depend on the cg, because weight acts along it, and position of wings because centre of pressure through which the lift acts).

It also has thrust and drag couple acting on it. nose up or down will depend on position of your engine and wings, which if you are not designing, is pretty much taken care of,

For aeroplane to fly in level unaccelerated flight all these couple have to balance so that the residual is zero.
If the aeroplane is say designed to get airborne at 30 kmph, it will get airborne at 30 kmph, if the wind that is blowing is 30 kmph , the grd speed at which will get airborne will be zero. But remember the thrust drag couple will have to be zero, which means, you have to open power normally as you do in nil wind condition.
If the winds are 40 kmph the aeroplane after getting airborne into wind will travel rearward at 10 kmph. With respect to ground, however with respect to air it is still travelling at 30 kmph.
Bottom line CL and S being same it is the ½ σ V² (the number of air molecules for a given time above and below the wings) which matter.
Think about this.
With flaps & slats does the CL change? With an extending flap that comes out of the wings (called the fowler flaps) does the 'S' change. What happens to landing speed, pressure on the wings, in a CAP232 22' vis-à-vis RC CAP 232 5.5', (clue, Scale Effect and Reynolds number).
Thus spoke a Qualified Flying Instructor.
More queries? keep it coming.
Anwar bhai, thanks

ps

found this  http://www.av8n.com/how/htm/4forces.html

I made this couple of force to illustrate how you need to balance these forces to fly level and create an imbalance for manoeuvring the aeroplane, using my MiG, hope it is useful