Sent as PM originally, now posted here at Deva's request.

"initially he used 9*4.5 and flying at full throttle say 1000rpm and changed to 9*6 and flying at little less throttle say 7500rpm

the thrust was reduced but how did the plane fly?  "

Hi Deva,
FACT: it flew
ASSUMPTION: thrust was reduced
HENCE: assumption must be incorrect.

Why incorrect? Because based on two other assumptions, which were not validated, namely, rpm on 9x4.5 and rpm on 9x6.
In general, when assumptions lead to a conclusion that differs from the observation, then the assumptions need rechecking.

Good effort. Wait till you get comments from Gusty sir, Sanjayrai sir etc!

The RPM will indeed drop, because the load on the motor is higher. This was discussed before : how to predict an RPM drop on a motor? Fact is it's tough; best is to ensure the motor has adequate power and torque so the effect is minimized!

Same doubt.
Think of a quad in hover. No velocity no momentum.

And for fixed wing, you need to know the power (not momentum) required to:
1. Maintain cruise speed (not just stall speed)
2. Accelerate reasonably quickly
3. Climb

Power = force X distance /Time = Torque X RPM

Should not this be RPS? Cause in general Power is expressed in Watts, and that is Joules/ Second.

And work done is circular motion = angular displacement(2 X pi X n) X Torque

Correct me if I am wrong.

I am trying to explain proportionality, not giving a formula

@devanesan Andrews,

Consider a glider.
With a given trim (i.e., stab/elevator adjusted to achieve a certain angle of attack of the wing)
it conserves momentum without any power source (except gravity  )
If you retrimmed for a lower angle of attack it will stabilize at a higher value of momentum.
Why does the momentum not go on increasing?
Because other factors are at play!

This, along with the points mentioned in my earlier post, make me doubt if momentum is a good yardstick for estimating the power requirements of an aircraft.

That is self evident.
Inboard ailerons will give inadequate roll rate.
Outboard flaps will increase the possibility (and effect) of tip stall during landing.

Deva,
Sometimes I ask members 'what's the objective?'
So I'll ask you what's the objective of asking this question.
Regards.

Not really for me to answer, but Iyer sir, many beginners would want to quantify some of the principles behind successful RC flight. There is some stuff on this forum, but it does tend to get extremely heavy from the experts, and dubious from the wannabees.

Why don't you put together a series on this in Iyer's Tech Talk which will be simple to understand: stick to easy terms, four letter words etc. 

outboard flaps will break the wings due to high bending moment in the centre.....

objective of the question is to tell this to all....

10000 members are there in rci 9000 may know this.... i am telling this to beginners like me

@ sanjay sir and  Iyer sir....

    in the beginning itself i told i am expressing my views

and this post is not just made for aeromodels.... more than that upto an UAV

iyer sir lets me get clarify about AOA first

considering an rc plane

              the air is stir and the plane is moving
 
 if the elevator is pushed up and the nose pitches up.....  so now the angle of attack has increased?

Deva,
Come on. You don't need my answer to that.

@rcpilotacro,
Gusty sir, where are you?
How to clarify without offending feelings of OP?
You have credentials which I lack...

iyer sir want to get clarified so only i am asking sir

Here is a proof that every thing could changed.... and the yardsticks are not yardsticks

https://www.grc.nasa.gov/www/k-12/airplane/wrong1.html

https://www.grc.nasa.gov/www/k-12/airplane/wrong2.html

https://www.grc.nasa.gov/www/k-12/airplane/wrong3.html

Yes.

Well.... guess the aerodynamics being propagated by DA are his assumptions..... a lot more happens actually because its not just one force acting on the aeroplane.  There are a multiple forces acting and many of them nullify the effect of the first force or compound it in many ways. 

All I can add to this confusion is...... leave the big daddy of aerodynamics apart.... Just follow the KISS rule.

OR Else DA please read "Mechanics of Flight" by AC Kermode.  This is the book all aviators read and study before taking their machines into the Air.  Otherwise for everyone else out here Guess the Humble book named "From the Ground Up" is more than sufficient.

If all theories are wrong ; what causes the lift?

Ok got the answer here : https://www.grc.nasa.gov/www/k-12/airplane/factors.html

@shobhit sir....  thank you so much sir...

but i have read

mechanics of flight and flight without formulae by kermode
introduction to flight  and aerodynamics by anderson
aicraft performance and design by anderson
stablitiy and control by perkins and a lot more

still the problem is why i dont know the thrust is measured in grams in aeromodelling instaed of newtons

Devanesan

Do read up 'Circulation theory of lift' 'Dimensional Analysis of Lift' of of course read clancy (not the famous Tom)

This is the simplest document you will find on 'Dimensional analysis of lift'

Dimensional Analysis of lift


PS
thrust x Velocity = Power (watts or Joules) do see Thrust power equation and how Jet engine recovers it with speed because of intake designs. We could even discuss intake designs, it, i guess will be too much for RC commuinty

@rcpilotacro sir,

 i agree with all you  said sir....

and i agree that its too much for an rc community....

this is what i want to change.... in india still its just a hobby... want to take that above  it

Dear DA..... Doing your studies on the subject you must have come across a lot of other books too and read them..... well.... the answer to your question.... on the topic u brought out in your earlier post.  Well.... you say most of us do not dwell much into Aerodynamics to understand the hobby better and to take it to a higher level or a new dimension.  Well... if you see here many of us fly helicopters or multicopters.  How many of us really know how a helicopter flies.  How do the blades function and how is the lift generated and a helicopter turned..... and what is stability...

Why do you not take some similar topics in Rotary wing AD and try and explain some of the baffling issues of helicoptrs..... it will be interesting.

Basically we all wish to keep it as a hobby and know what is required.  Knowing a little more will definitely help help each one of us.
  

in that case shobit sir... i ll definitely do that