Propeller Basics

[okan]

Hi there,
I have been building a new airplane weighing 16.5 lb.s with a 5 lb. payload, I have found that i need a 25x12 or 25x14 propeller to use with Astro 90. But i can't find out what to buy... When i search internet, there are Kavan, Zinger, MA, APC propellers and they can be wood, plastic or carbon. What changes except the weight? Does selection of the propeller either wood or plastic matter if they both have the same diameter and pitch values?
Could you please inform me about these kind of propeller related sublect and maybe give some internet address from where i can find both data about them and buy?
Thank you...
Okan.

[agpilot24]

I'm sure that someone with more knowledge will chime in soon.
APC seems to be the best of those you listed.....but I base that on gas motor experience.....Zinger is lighter, but less efficient. Does APC sell a prop in the size you want? The best wood props I have ever used were "Rev-up", but I can't seem to find them anymore. The prop you want is larger than most that we modelers use......"Bolly"(sp?) makes some top of the line props for the large scale aerobat planes.....sorry I don't have an addy handy. i suspect that the prop you want hasn't yet been designed/built.....if RFM or Graupner built a folding carbonfibre prop of that size, it would be the top choice.....but I haven't seen any that large yet.
Good luck in your project!
-Jason

[steve lewin]

What changes is not only weight but also blade shape, accuracy, blade airfoil and overall efficiency. Props can also be optimised for the rpm you're intending to run. Look at a slowfly prop (very low revs) versus a similar size prop for an IC motor.

Martin Hepperle used to have an excellent site about prop design but he closed it down and I've never found another nearly as good. I've never used props anywhere near that size so I can't help with the specifics.

Steve

[leccyflyer]

It sounds like ypu need to talk to Les Bollhagen of Bolly Propellors in Australia. Bolly make a huge range of specialist props for all sorts of models, and even including microlight aeroplanes as well.

Have a look at their website and you might find what you need- they produce a document called The Bolly Book, which contains all you might ever want to know about props and tuned pipes etc and is full of tips for the aerobatics enthusiast as well.

http://www.bolly.com.au/

There are US and other distributors listed there.

hth

Brian

[okan]

Originally posted by steve lewin
What changes is not only weight but also blade shape, accuracy, blade airfoil and overall efficiency.
Steve
Yes as diameter and pitch changes the defined parameters may vary however none of the propeller sellers provide a catalogue giving their products' airfoil, efficiency data. So i can not want from one of the manufacturers to build a special one for me. I have to choose from the listed ones and all data they provide the diameter and the pitch values. So according to these variables i have to define my propeller. What i was asking is what changes if you manufacture the SAME (all airfoil, eff., overall data) propeller one wood and one nylon. What is the diffirence between them?
Thank you.

[Bill Glover]

Originally posted by okan
if you manufacture the SAME (all airfoil, eff., overall data) propeller one wood and one nylon. What is the diffirence between them?
Thank you.

That's a pretty academic question, if you did have two completely identical props the glass/nylon one would be heavier but less fragile. Performance wise they'd be identical assuming the glass/nylon one was rigid enough not to flex. That would depend on exactly what it was made from (and with the wooden one it would depend on what type of wood etc. ;) ).

Anyway APC make some props that are pretty close to what you want e.g. 24x12, 26x10. You can buy these online:

www.apcprop.com

The sizes you want are pretty specialised, you will have to take what's available and experiment a bit. Even if you can get them, you may find that the exact sizes you mention are not the best for your specific model when you come to fly it.

[Andy W]

I will say that pretty much any prop with a pitch:diameter ratio less than .5:1 is going to be fairly inefficienct..
..a