Props
09-25-2005, 04:47 PM
#1
New Member
Thread Starter
Join Date: Aug 2005
Posts: 5
Props
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
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
09-25-2005, 06:51 PM
#2
Super Contributor
Join Date: Aug 2005
Posts: 1,726
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
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
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
09-25-2005, 08:03 PM
#3
Dave North
Join Date: Sep 2005
Posts: 536
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
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
09-26-2005, 01:37 AM
#4
Super Contributor
Join Date: Sep 2005
Location: adelaide, south australia
Posts: 2,073
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.,
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.,
09-26-2005, 03:15 AM
#5
wheeee!
Join Date: Sep 2005
Location: San Francisco- Home. Los Angeles- School
Posts: 80
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
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.
09-30-2005, 02:05 AM
#6
Member
Join Date: Aug 2005
Location: Oswego , Il.
Posts: 203
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.
10-07-2005, 10:26 AM
#7
Member
Join Date: Jul 2005
Location: Newport, Arkansas
Posts: 138
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.
10-08-2005, 02:49 AM
#8
Member
Join Date: Aug 2005
Location: Oswego , Il.
Posts: 203
Props
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
John
10-08-2005, 03:56 AM
#9
Super Contributor
Join Date: Sep 2005
Location: adelaide, south australia
Posts: 2,073
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.
Tim.
10-08-2005, 04:04 AM
#10
Super Contributor
Join Date: Sep 2005
Location: adelaide, south australia
Posts: 2,073
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.
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.
10-08-2005, 04:47 AM
#11
Watts up Doc?
Join Date: Oct 2005
Location: Florida
Posts: 491
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
John
http://www.aircraft-world.com/shopdi...cat=propellers
01-05-2006, 09:38 PM
#15
Member
Join Date: Dec 2005
Posts: 225
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.
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.
Thread
Thread Starter
Forum
Replies
Last Post
aero007
Airplanes - Electric For Sale & WTB
1
03-11-2008 04:33 PM
Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
