For a 10 x 4 the KV rating would be around 1000KV +/- 100.
Sai

Had a practical experience with the acromaster today  11 x 4.7 was very helpful in 3D whereas 11 x 7  was not effective in 3D but gave and immense thrust.
This  largely because when it covers 7 " per revolution it is not flying slow whereas in 4.7 it is better  so i am now waiting for my 3.8 props .

sai

Would someone please explain what is the Pitch Speed of a Prop and what is its significance.
---Rao

Here is question I was asked couple of days ago. 

Why are some electric props so flimsy that their blades can easily be bent ?  Why would anyone design/build them that way ?  Is it just a side effect of cost cutting or some other unintended end-result ?  What technical advantage would such props have compared to a sturdy prop of same dimensions and weight ?

Probably designed to be crash / hard landing proof?! As in, when the aircraft belly lands without an undercarriage, this flimsy prop scrapes against the ground and suffers the least amount of damage. Whereas, a rigid prop would possibly snap into two. Least resistance = Least damage, I guess!

Juvenile, as usual, however that was my two penny bit!

Cheers!

You get both types :
Rigid : APC and master Airscrew   : +  Don't break easily  - Bend the shaft on Impact  more expensive
Flexible : GWS Type  : + Break  easily on Impact  there by decimate energy   and save other  components especially   the Motor and shaft , less expensive 
- break easily   hence need to  carry a stock of them when going flying .

THE KEY HERE IS ENERGY DECIMATION ON IMPACT

Sai

Not my formula  picked it up from RCG  :

Quote
Pitch speed = RPM x Pitch x (60/63360)
eg: 8000rpm x 6" x (60/63360) = 45.45mph
The 60/63360 converts from inches per minute to miles per hour.

Plane speed can be anywhere from ~80% to ~95% of pitch speed depending on a whole host of variables including p-factor (prop efficiency), airfoil shape, size, weight, construction materials, yada, yada, yada.

Unquote

This is  a pure mathematical  calculation  but as mentioned   variables in flight  will affect the pitch speed  significantly .

Sai

Pitch speed is calculated by the formula given by sai above,

It is the actual speed an aircraft would Ideally move in a solid medium(in a metal for example.) But since our aircrafts move in air, Slippage happens, and hence we do not get that Ideal speed, but always below that. The most important factor that governs slippage is the Air density depending on the sea level we are. Higher air density - better the speed. Also make sure to keep the pitch speed slightly above 2 times the stall speeds. hope this helps.

Fair enough... how about flight characteristics. Can we always expect the flimsy ones to provide less thrust ? 

Not necessarily. I have tried on both, gws and apc. And the thrust is almost the same. Infact i like the flimsy gws  better as it balanced well, light weight, and slightly bended at high rpm to avoid turbulance, synched in smoothly with motor and reduced vibrations.

EDIT: But after a certain diameter, the stronger ones are better.

Are there any advantages in using propellers with 3 blades or 4 blades in the place of regular 2 blade propellers

Good Looks/ScalModels/Head turners. More thrust for lesser RPM. From my theory knowledge , I dont see any other. They are more expensive and probably difficult to balance I guess.

In general the higher the number of blades lesser is the efficiancy of the prop. The primary reason why full scale ones use multiple blades is for two reasons - 1. To keep the blade size to reasonable size and 2. Absorb the huge amount of energy produced by the improved engines.
For example when the Hawker Hurricane was first flown it had a 2 blade prop, but as the engine was upgraded it delivered more power which required larger blades, so if the prop size was increased to required size it would have touched the ground while the aircraft was horizontal (remember it was a tailwheeler). Thefore the solution was to put another balde and overall reduce the dia of the prop.
So now you get the picture?
In our models too when you are using high powered engines and do not have the luxury of ground/airframe(for multi's) clerance you would need to convert to multiple blades, apart from the bling factor.

On the flimsy props. A prop which flexes would again be less efficient and noisy than a stiffer ones, the best ones are wood or carbon composites which fles least but then are very brittle due to rigidity and thus become costly. While you may not notice much difference in general flying proper tests would reveal the truth.

Sai sir,
I am sure what you meant was immense speed. Since it was higher pitch it would translate into more distance being covered per revolution and thus speed. Dia being same a lower pitch would deliver higher thrust.
         

Agreed Capt  you got the right word

I am using a 3 blade on the easy glider pro ( converted to pusher )  for this very reason " lack of  prop leg room  "  as explained by Capt.

sai

Yes I got the Picture. Thanks Mr.Captain.

All Gurus,

Need clarification on thrust vs speed. What is generally said while choosing a motor is that we should have approx 100W per 500gm of AUW. So far so good. Now how does the prop fit into this equation of motor wattage and AUW? How does one go about choosing the various pitch sizes?

Another video on this topic is here :

http://www.rcindia.org/radios-and-receivers/fly-sky-fs-th9x-9ch-radio/msg38714/#msg38714

anwar bhai can you merge the video in this topic or make new topic called the "Basics of propeller" and add all the relevant videos in this thread

thank you
oh and Eid Mubarak to you and dear members of rcindia.org
Subodh

I have linked the video here via the earlier post (the video is not here, but it is pointed to by the link), and many prop related videos are already here, if you have read this thread from the beginning. 

This thread is the authoritative thread on pitch, dia etc.  "Prop selection" itself is not discussed here, that is a separate topic in itself as it involves motor parameters etc. 

If you find other good videos on prop itself (not "prop selection"), please feel free to post it here.

Hello to all RC Addicts!!
I have got a problem....
Can some one please explain me the whole concept of pitch and diameter of propeller...how it affects the thrust and velocity...
also how does the ratings of my motor affect the propeller that i choose...
Thankyou!!!!!

Hope this helps:

http://www.rcindia.org/multirotors/understanding-aerodynamics-of-prop-and-frame/msg103377/#msg103377

Propellor theory is big subject even to simplify. will try to do so soon in Basic Aerodynamics Thread. Some info is already there

http://www.rcindia.org/rc-general-topics/basic-aerodynamics-for-rc-flying/

Hello to all RC Addicts!!
I have got a problem....
Can some one please explain me the whole concept of pitch and diameter of propeller...how it affects the thrust and velocity...
also how does the ratings of my motor affect the propeller that i choose...
Thankyou!!!!!

Search on google first, there's valuable info hidden in thousands of threads.

to be more precise i wanted to know is there any relation between the motor that i have and the propeller that i choose