Well I was under the impression that if a plane has all up weigh (AUW) of 200gms then thrust of 220 - 300gms range is sufficient to fly it in normally. Anything less than 200gms and the plane wont even take off the ground.

Came across this thread which proves me otherwise 

http://www.rcpowers.com/forum/showthread.php?2286-My-Blu-Baby&p=17401#post17401

So now the question is: What should be the general thumbrule for weight to thrust ratio for any given airplane?  Also does the type of plane such as trainer, low winger, delta wing, f-22, odd shapes such as snow-ball, etc have an effect over thrust weight calculations   

check this thread
http://www.rcindia.org/electric-power/amp-rating-and-motor-size/

The thrust requirements for various types of aircraft are listed in the first post of this thread :

http://www.rcindia.org/beginners-zone/selection-of-power-system-and-components/

NO, the thrust should greater than the weight of the plane is not always true.It is applicable in the case of heli and 3d plane.

A plane having good wing shape with light weight and thrust 20 %  less than the weight of the plane can fly.I am not telling u any theory ,I have done some  experiment on  my plane using several size of propelleller.

The trust acts in the horizontal direction and is opposed by drag.
The weight acts vertically downwards and is opposed by lift.
The lift MUST exceed the weight for the plane to fly. laws of physics.
The lift depends on the airspeed and airfoil shape and wing area.
Remember Gliders and kites fly with zero thrust.
Read up the basic principles of flight.
Thrust more than weight is required for unlimited vertical flight.
Even in jet fighters the thrust is ussually less than weight. A airbus A380 certainly does.
In a rocket the thrust definitely exceeds weight.
regards
Avijit

hope this helps

http://www.rcindia.org/electric-power/a-basic-guide-to-electric-flight/

the thrust required depends upon the following factors...

weight of the plane
aerofoil shape of the main wing
aerofoil shape of the tail plane
amount of drag created
total lift created by the wing (wings in case of bipe)
location of the wing
thickness of the wing
shape of the leading edge
location of the thrust provider ( pusher or puller..... els prop or jet or on the wings)
thrust line
etc etc(will update as i remember)

I am making a rcpowers 300 using coro and the weight turned out to be 350gms(everything including electronics) and the motor is capable of around 600 gms. will it fly(the wing span is 35.5")?

Quote from: azhaguvel on May 17, 2011, 06:14:33 PM
the motor is capable of around 600 gms.

Can't understand this line .Is it thrust?

yes its thrust.

motor: 2210N 1000Kv Brushless Motor
GWS9050 @3S
Max Amp: 11.2A
RPM/Min: 8700
Thrust: 740g

Yes definitely it will fly .

Just talking in layman terms:

Consider you are pulling up a rolling bag on a ramp.I hope you must have done it while travelling.

So, its quiet easier to roll it on a ramp with very less slope(say 15 degrees).

If the slope is more(say 40 degree), you need more thrust to pull it.

And if you are just lifting it(slope is 90 degrees), you need the thrust just a bit more than the weight of the bag..

So, here flying is like just going on a air ramp, angle of attack being the slope of ramp.


Abhay

Thanks all for your replies. Actually i was expecting some formula for weight to thrust ratio. But guess there are multiple factors including location and thickness of the wing.

Came across a URL which calculates the theoritical thrust. In this URL i think the trick is to keep the Motor efficiency around 75-80% and if the thrust is around +/-20% of AUW then you got a decent flyer.
http://www.badcock.net/cgi-bin/powertrain/propconst.cgi?C_prop=123&RPM=&Volts=8&Current=8&Watts=64&Height=20&Temp=28