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Props

Old 09-25-2005, 04:47 PM
  #1  
sedonakevin
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Hi all, I'm new to RC and Electric fight in general after 30 years of building scale static models. I'm currently building a Turnkey RC Fiesler Fi-156 Storch with Speed 480, 30 amp ESC, and 7.4 V 2100 Mah Li-poly. My questions concern props:

1. Why do most electric plans fly plastic/nylon props rather than wood?
2. Why are most props only two blade when the actaul airplane might have had a three or four blade prop?
3. If the motor is geared properly is there any reason an electric motor cannot spin a wooden prop?

OK, OK I guess I'm one of those 'rivet counters' but I really would like to build my models as scale like and realistic as possible. In other words if the full-size plane used a 3 blade prop then i would like my model to fly with a 3 blade prop.

Anyway, any help is apprecieated, Kevin
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Old 09-25-2005, 06:51 PM
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Dr Kiwi
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Originally Posted by sedonakevin
Hi all, I'm new to RC and Electric fight in general after 30 years of building scale static models. I'm currently building a Turnkey RC Fiesler Fi-156 Storch with Speed 480, 30 amp ESC, and 7.4 V 2100 Mah Li-poly. My questions concern props:

1. Why do most electric plans fly plastic/nylon props rather than wood?
2. Why are most props only two blade when the actaul airplane might have had a three or four blade prop?
3. If the motor is geared properly is there any reason an electric motor cannot spin a wooden prop?

OK, OK I guess I'm one of those 'rivet counters' but I really would like to build my models as scale like and realistic as possible. In other words if the full-size plane used a 3 blade prop then i would like my model to fly with a 3 blade prop.

Anyway, any help is apprecieated, Kevin
My thoughts - not necessarily correct

1. Nylon props have some 'give' in them, so the shaft is less likely to snap on impact - electric motor shafts are far thinner (relatively) than I/C motor shafts. I/C props have to able to stand the stresses of higher rpm and of alternating firing strokes - electric props don't have to be as rugged, so can be made with very thin aerofoil blades.

2. Two bladed props are generally far more efficient than 3- or 4-bladed props. Any 'extra' blades generate additional drag.

3. Wooden props are relatively heavy and inefficient - they could be used, but nylon or CF works better, especially for small motors/aircraft.

Cheers, Phil
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Old 09-25-2005, 08:03 PM
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timocharis
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Like Phil, I'm basically guessing. But first let me point out some electric flyers (especially micro) actually make their own props from balsa. So.

Overall, I'd agree with the assessment above, but might add a few things.

I'd assume plastic/nylon props are cheaper and easier to make.

Another reason two-bladed props are commonly used: there isn't exactly a wide variety of three or four-bladed props in the sizes most electric flyers prefer -- very few, actually. You'd have to kind of design around the prop choice.

Flexing during flight is not necessarily a bad thing. I'm unsure of the effect of the forward curving of the longer/thinner props, but the torsional flex gives you something of a variable-pitch prop, particularly at the tips where stalling can be a problem. Electrics have evolved to often fly at a much broader range of throttle settings, and often use more RPM than torque, so anything that handles a broader "power band" is probably more important with electrics.

All these comments are completely seat-of-pants...


Dave North
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Old 09-26-2005, 01:37 AM
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watt_the?!
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if i may add...

more blades, more power needed.

to fit a power train to your plane that is relatively inexpensive then use the lowest power draw. to runa scale prop, multi bladed, youll need a large power train wrt the aircraft itself.

this plagues not only electric, but ic aircraft. the amount of power generated by scale powertrains is far in excess of what is needed, but carries the size/weight penalty as well.

alot of peeps just fit scale props for static display, and then swap out for flying...you cant see a spinning prop anyway.

the other way to do it would be to run a high reduction gearbox.

tim.,
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Old 09-26-2005, 03:15 AM
  #5  
pace_likethesalsa
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Wood ones can actually be lighter than than plastics. This is why they are common in freeflight flight time competitions.


Plastics are easier to mass produce, stronger, cheaper, and easier to quality control (hand selecting all the wood would be a pain in the arse, as would most other topics).


Seeing as you have experience in modeling, check out these two sites;

a good tutorial on making your own custom props
figuring out how to get the same power for 3 or 4 blade props as a 2 blade


These are more geared towards free flight, but if you have the tools it will definitly transfer over to R/C no problem.


Reading the second link will show you that if you use a 3rd prop, you only shorten the radius of the prop by 10%. You actually gain weight by doing this, hence the propensity of the two blade design. :P

Last edited by pace_likethesalsa; 09-26-2005 at 03:40 AM.
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Old 09-30-2005, 02:05 AM
  #6  
John Seidelman
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A new question I have the ParkFlyers Cessna 182 with a Speed 480. It has a prop adapter on it.( see photo) Is there a way to get around not using this adapter? As the supplyer is out of props and I only have one left.
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Old 10-07-2005, 10:26 AM
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Duster52
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Originally Posted by John Seidelman
A new question I have the ParkFlyers Cessna 182 with a Speed 480. It has a prop adapter on it.( see photo) Is there a way to get around not using this adapter? As the supplyer is out of props and I only have one left.
Not clear on why you need to "get around" using the adaptor. Something has to hold the prop on the motor. How would not using this adapter help just because the supplier is out of props? Do you mean out of props that have that size opening? If the shaft has threads, you can use a prop that has the hole the size of the shaft and put a nut on back and front of the prop. Otherwise, you will need an adapter of some type. They have different sizes.
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Old 10-08-2005, 02:49 AM
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John Seidelman
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The prop has a recess that fits the adapter in the shape of a nut to hold it from turning. I was wondering if there would be a simpler adapter or a way to get around buying props that only fit that type of adapter.

John
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Old 10-08-2005, 03:56 AM
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watt_the?!
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we removed the existing stock adaptor (i think we needed to heat it) and replaced it with a ''normal'' prop adaptor to suit the shaft size. Then we used any old prop (APC in this case) as a replacement.

Tim.
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Old 10-08-2005, 04:04 AM
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watt_the?!
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i uploaded a small video of the 3 channel cessna flying.

http://www.relexaustralia.com.au/rcs...techcessna.wmv

5.8mb

the guy doing the video had never flown before and spent a few weeks on the simulator, then went out and maidened on buddy box...didnt need any assistance either.

this plane is excellent IMO. FWIW.

Tim.
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Old 10-08-2005, 04:47 AM
  #11  
hoppy
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Originally Posted by John Seidelman
The prop has a recess that fits the adapter in the shape of a nut to hold it from turning. I was wondering if there would be a simpler adapter or a way to get around buying props that only fit that type of adapter.

John
All kinds of adaptors, all kinds of props, cheap shipping. Just match your shaft diameter to the adaptor. I assume your adaptor has a short threaded portion which demands the indentation in the prop. Longer shafts are available.
http://www.aircraft-world.com/shopdi...cat=propellers
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Old 01-05-2006, 02:40 PM
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slowmover
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Default Props

Please explain to me what the SF,EP, etc. means on the blades.
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Old 01-05-2006, 05:19 PM
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Don Sims
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SF is for Slow Flyer
EP is for Electric Power

I'll let one of the real gurus explain the differences in better language.
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Old 01-05-2006, 05:24 PM
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Rodneh
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Usually SF is for geared motors (lower RPM) while EP is for the direct drive motors where RPM can be quite high and needs more blade strength in the prop.
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Old 01-05-2006, 09:38 PM
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meatball
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http://www.smallflyingarts.com/Curre.../comprop_2.htm

how big a prop can you make doing that? Think you can make 9x3.8's with it? My hobby shop is 45 minutes away and I go through them.
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