RC India

Since we know the formula of Reynolds number, Re.= 68459*V*L, where V= air speed in m/s & L= chord length of wing in meters. But i confuse about V  :headscratch: , What is the proper value of it for a trainer rc plane?  ???

Please tell me any one.
(If any data missing please asked to me)

Well, without getting into the details, a good estimate for V could be anywhere from 10 to 15m/s. But there are so many other factors and a correct answer depends upon the level of complexity of the problem and what you are trying to do with the Re value.

@ashwini06,
As mentioned by Mr Gupta in the last post, 10-15m/s is a good estimate for a trainer model.
And use round figures to do multiplication in your head without needing a calculator.
For example,
1. A small ~36" span model with 6" (15cm) chord at 10m/s. Re=70000x10x0.15=105,000
2. A medium ~54" span with 8" (20cm) chord at 15m/s. Re=70000x15x0.20=210,000

Many RC models (of this size) will have Reynolds Number in 100,000-200,000 range.

By the way, why do you want to estimate the Re number?

An excellent book is Model Aircraft Aerodynamics by Martin Simons. Available on Flipkart for about Rs 2500. Quite costly! If you have a friend in IIT, he can see if it is in their library.

Thanks so much iyer sir

  plz sir I want to know more about re number just simple explanation why it is calculated and
Where it is applied on the airplane

No math’s just for general idea and how this number effect the performance of the airplane

plz do not say Google or any link bec I had already gone through it and it seem me complicated

I want simple idea about this topic

Thank you, Mr. Gupta322,
Thank You, Mr. Iyer,

The rc plane, which i am going to make, is my 4th year project so i shall go for model analysis of it in the last with the help of wind tunnel. So for a good model analysis we have all the correct and accurate data.... so these days i am calculating all possible data regarding to this.... since it is beginning. I am going to post so many problems for all of you  :) ... please stay with me and guide me with your maximum effort....
Mr. Iyer, Thanks to you specially, because your answers are so much near to my calculations... so these are so much helpful to understand easily.


regards

@ashwini06,
Can you state the thesis or objective of your 4th year project?
If we knew clearly what you are trying to achieve, maybe we could help you better.
Regards

I repeat my question:
Why do you want to estimate the Re number?
What is its connection to your project?

V in RN is True Air Speed (TAS), aeroplane's performance is measured by Indicated Air Speed (IAS), see the difference in basic aerodynamics thread, to tell the difference at 40,000 feet IAS is 1/2 that of TAS

@rcpilotacro

Sir, Can you please elaborate to it deeply ..... with a realistic example.

what is the MISSION PROFILE????????

@Mr. Iyer,

Reynolds number is used to determine whether a flow will be laminar or turbulent. If Re is high, inertial forces dominate viscous forces and the flow is turbulent; if Re number is low, viscous forces dominate and the flow is laminar.
Reynolds number is important in wind tunnel experiments since it relates to the aerodynamic properties of lifting surfaces, such as airfoils, when extrapolating from small wind tunnel test models to full-size wings. Reynolds discovered that, if the same atmospheric pressure were used for experiments with wind tunnel models as a full-size aircraft would encounter under actual conditions, the experimental results would be invalid.

So this term will come in use when i shall go through my model analysis with wind tunnel.

Ashwini

upto 0.4 mach , air  is practically inviscid and incompressible, for model aerodynamics, RN is irrelevant, if you need to learn more about RN, then this discussion thread is insufficient and unnecessary, i could recommend some books to you for you to understand aerodynamics in the compressible regime, extremely interesting and the ways air behaves defies logic (In the compressible regime)

@pilotrcacro

Tell me only one best book. If you have pdf of that book then please send me at my mail- shukla.ashwini06@gmail.com

@rcpilotacro,
 
i repeat myself - if u have a best book regarding REYNOLDS NUMBER AND BOUNDARY LAYER, please tell me it's name, author name & publication.


I am extremely sorry for write your wrong user name.... :(

"Fluid Mechanics" by Streeter