Propeller - need to calculate the area

[NRPI]

Propeller -- need to calculate the area

Hello

I am doing a research on different propellers, including how do different propellers ( different mass/size, number of blades ) with different speeds change the rpm and the thrust. However to continue my research and to be able to graph it, I need to calculate the area of the propellers. The information I have is the diameter and the pitch of the propeller. And i can also can also calculate the rpm and the thrust ( however I think that is not important to calculate the area ) Does anyone know how can I calculate the area of a propeller ?

PS : I am using airplane propellers

Thank you

 

[rcgldr]

You would need to get the actual specifications for the propellers you're interested in.

 

[A.T.]

Do you mean blade area ?
http://www.hydrocompinc.com/knowledge/whitepapers/HC135-BladeAreaRatio.pdf
http://www.teignbridge.co.uk/propeller_questions_and_answers.html

 

[CWatters]

The blade area is important, as is the aspect ratio. Props aren't that different from wings, long thin high aspect ratio wings are generally more efficient than short fat ones.

However the prop has to be matched to the motor and aircraft, even which part of the flight it's in (eg fine pitch for take off, coarse for cruise).

 

[mrspeedybob]

If you are interested in the area of the propeller blade then you'll just have to get the spec from the propeller, that's not something you calculate.

If you want to know the area swept by the propeller then that would be ∏r² of the whole propeller - ∏r²of the hub.

 

[NRPI]

So, being impossibly to calculate the area of the propeller ( and I can not just look to the specifications of the propeller ), because it needs to be something I can calculate, what do you think might be the best i can use to do a graph with rpm and other with thrust. It needs to be something that will differ on different size of propellers. I was thinking about the area but since it is not possible to calculate, what you think ?

 

[TheAbsoluTurk]

Like mrspeedybob mentioned, the area swept by the propeller may be worth calculating since you have the diameters.

 

[NRPI]

ohhhh , then I do cause i am using Radio control airplanes propellers and when I buy them, it has a measure. Which for example 12X8 . Where 12 is the diameter and 8 is the pitch. But imagining I have a 12X8 and 12X9, so changing only the pitch how will it change the area swept by the propeller ?

Thanks very much

 

[mrspeedybob]

I went back and re-read your original question. Now I'm not sure what exactly it is you're needing help with. At first you say...

I am doing a research on different propellers, including how do different propellers ( different mass/size, number of blades ) with different speeds change the rpm and the thrust.

which makes it sound like you are trying to calculate propeller rpm and thrust. Later you say...

...i can also can also calculate the rpm and the thrust .

So what exactly is you are trying to calculate? What is your end goal. Knowing that may help us help you more effectively.

 

[NRPI]

So i basacly seeing and looking for a relation between different propellers and rpm and thrust. By other words how do different propellers affect the rpm and thrust. And I need to include on my work graphs and i was planning to do something related with the propeller size ( what i thought about propeller area )rpm grap,and that same thing related with propeller size ( as I said i thought about propeller area )thrust graph. However when i started doing it I couldn't figure out a way to calculate the area of the propeller. The rpm and thrust will be measured with equipment. So those are easy however i don't know how to calculate the area of a propeller ( maybe there is a method or a formula). Does anyone know how to do it ?

 

[mrspeedybob]

OK. So the propellers you plan to study are ones you have physical access to, that makes things easy. You can't calculate the surface area of the propeller but you can measure it dirrectly. Place each propeller on a sheet of graph paper. Photograph it from above. Look at the photos and count the number of graph paper squares obscured by the propeller. The finer the graph paper, the more precise your measurement.

 

[NRPI]

Thanks you very much. However I have a question, actually it is more an opinion. Do you think area of the propeller is the best I can you for the work I want to do ? If yes, when i change the number of blades to 3 and 4 blades, should I use one to with the same size ( eg: 12X8 on 2 blades and then use a 12X8 on 3 and 4 blades ) or use a similar one ( so same area ) ?

 

[mrspeedybob]

Propeller design is a very complex topic. A solid working knowledge of fluid dynamics would be a necessary first step in understanding propeller design. That being said, sometimes a simple analysis will get the job done, though I'm still not clear on what the objective is.

I think the most useful measurements you can study are going to be the ones you find in the spec sheet on the propeller. You mentioned diameter and pitch, I'm sure number of blades is given also. The reason I say this is that If I was trying to create a method to determine what propeller I would need for a given application, I would want that method to give me an answer that I could take shopping with me.

If you create an algorithm that tells you that for a given application you need a propeller with surface area X, and you then take that information with you to the propeller store where all the boxes list diameter and pitch, you still won't know which propeller to buy.

An algorithm based on diameter and pitch would be more useful. You'll probably find that those are actually the most useful specs for predicting the propellers performance anyway. If other specs were more useful, the propeller industry would use those instead.

 

[NRPI]

Could not agree more that propellers is a very complex. But i will explain better what I need to do. So my research question is How different propellers ( when i say different i will change the size and number of blades ) change the rpm and thrust. And then on my conclusion based on rpm, and thrust tell the best propellers for thr different aplications . However on my work I need to include graphs. So I could just do a dimeter pitch by rpm graph or a diameter pitch thrust graph but to make it more interesting i was thinking instead of using diameter pitch , use the propeller area ( which is realeted with the size of the propeller ).

 

[billblack]

If I am not mistaken, propellers are designed with a particular airfoil profile. This site: http://www.aerodyndesign.com/PROP_10/PROP_10.htm has both a PDF and the Excel sheet for a NACA 4412 airfoil. Therre are several other pages and the forum may be helpful to you as well.
This site used to have a lot of resources on it, but it doesn't seem to want to load: http://www.mh-aerotools.de/airfoils/
and:
http://propdesign.weebly.com/
bit of reading but worthwhile: http://www.boatdesign.net/forums/design-software/there-free-software-propeller-design-9474.html
good luck

 

[NRPI]

Thank you very, those websites are being very useful. Right now i have no more questions, if later i have more questions i will ask. Thank you guys.