Beginners Beginners in RC start here for help.

problem 2 or 3 blades

Reply
Old 06-28-2009, 09:11 PM
  #1
RegFlyer
Thread Starter
 
RegFlyer's Avatar
 
Join Date: Dec 2003
Location: Virginia Beach, VA
Posts: 161
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default problem 2 or 3 blades

I an using a 10x7 2 blade prop, but flying off of grass turns my plane green. what I was wondering is if i use a 10x7 3 blade will it be as bad? also i was told that 3- blades = less power.
RegFlyer is offline  
Reply With Quote
Old 06-28-2009, 09:29 PM
  #2
el_xero
 
Join Date: Sep 2005
Location: Castries, SAINT LUCIA
Posts: 492
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: problem 2 or 3 blades

I'm not so sure about that.. I'd love to know though. I think I read somewhere that as you go up in blades you can go down in blade length a bit and get the same performance. I suppose if you did use the same length blade it would mean less power then because you're having the engine do more work, but lest see what others say on this.
el_xero is offline  
Reply With Quote
Old 06-28-2009, 09:39 PM
  #3
ChuckW
 
ChuckW's Avatar
 
Join Date: Jun 2006
Location: Clovis, CA
Posts: 5,165
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: problem 2 or 3 blades

The 10x7 3 blade is the same diameter as the 10x7 2-blade so ti will cut up just as much grass.

You'll also suffer in performance since the 10x7 3-blade will be harder to spin than the 10x7 2-bladed. You'll want to drop in diameter and/or pitch when going to the 3-blade.

I've also read that 3-blades are generally less efficient than 2-blades on small aplications liek RC planes. I can't personally verify that though since my 3-blade experience is limited to briefly messed with a couple 3-blade props on small electrics.
ChuckW is offline  
Reply With Quote
Old 06-28-2009, 10:27 PM
  #4
OzMo
 
OzMo's Avatar
 
Join Date: Sep 2002
Location: OZark, MO
Posts: 2,688
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: problem 2 or 3 blades

Drop 1" of length for a 3 blade. IE 10-6 two blade + 10-5 three blade. agood example id the alpha trainers that are popular. They speed up quite a bit when the 3 blade gets swapped out for a two blade.
OzMo is offline  
Reply With Quote
Old 06-28-2009, 10:28 PM
  #5
rgm762
 
Join Date: Jul 2008
Location: KS
Posts: 1,127
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: problem 2 or 3 blades

according to Zinger propellers, when going from a 2 blade to a three blade, you drop the diameter and keep the pitch, so if your running a 10x7 2blade, you will need a 9x7 3blade or cut the grass shorter


http://www.zingerpropeller.com/_2_blade_.htm
rgm762 is offline  
Reply With Quote
Old 06-28-2009, 10:38 PM
  #6
brett65
 
brett65's Avatar
 
Join Date: Dec 2007
Location: Oklahoma City, OK
Posts: 2,505
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: problem 2 or 3 blades

I'm gonna be using a 3 blade on my new fw-190, I want it to look as good on the ground as it does in the air. My personal opinion is that if two blades were actually more efficient then you would see them on all modern propped aircraft. It depends on the use and application. The alpha 3 blade prop is purposely made to be a slow prop, its on a trainer. I got a 10x5 3 blade I'm gonna try on my Extra 300.
brett65 is offline  
Reply With Quote
Old 06-28-2009, 10:58 PM
  #7
Campgems
 
Join Date: Feb 2006
Location: Arroyo Grande, CA
Posts: 4,465
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: problem 2 or 3 blades

""My personal opinion is that if two blades were actually more efficient then you would see them on all modern propped aircraft.""

Actually a one blade prop is more efficient, but the off set thrust causes some problems. The "modern Propped aircraft" will not turn in the 8K to 12K RPM range that our props turn, and the pitch is greatly different. Scale looks and scale performance seldom exist in the same setup. If you look at the scale planes in compentition, they will usually have two props, one for static judging and one for flight.

If the three or four blade props were more efficient in models, there would be a limited selection of two blade props and a huge selection of the three and four blade props. That is not the case though.

If we propped for a max RPM of around 3K and an Idle RPM of around 500RPM, then the 3 baldes may start to come into play. Most RC planes though at 3K are on final for landing, and at 2K rpm, they will only move if pushed by hand.

Don
Campgems is offline  
Reply With Quote
Old 06-29-2009, 12:01 AM
  #8
JohnBuckner
 
JohnBuckner's Avatar
 
Join Date: Dec 2001
Location: Kingman, AZ
Posts: 10,256
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: problem 2 or 3 blades

Quote:
ORIGINAL: RegFlyer

I an using a 10x7 2 blade prop, if i use a 10x7 3 blade will it be as bad?


Yes this will be very bad and accomplish nothing just adding a blade will only serve to drag the RPM's and reduce performance and incrasing heat thus causing running problems.

Three blades are less efficient than two so normally if you really must use three blades then you would reduce the diameter by one inch to a 9X7 three blade assuming you could find one-However-It will not be as efficient as a two blade.

For grass clearance it is always a better idea to lengthen the nose strut or use a larger wheel or mow the grass.


For scale purposes using three or four blade props for flight results in props so skinny and short that the result often looks laffable and thats why all scale contests allow using scale props for judging and changing to flight props for flight judgeing. In scale applications often the larger and\or fatter two blade flight prop actually looks better than than a shorter and usually skinnier three or four blade.
I bit if irony here is the earliest varients of the Spitire, Hurricane and 109 actually had two blade propellors.

John

This is arguably the most efficient propellor possible but not often used because of certain other problems that must be delt with:

Attached Thumbnails
Click image for larger version

Name:	Tr50795.jpg
Views:	10
Size:	67.0 KB
ID:	1226687  
JohnBuckner is online now  
Reply With Quote
Old 06-29-2009, 02:45 AM
  #9
redfox435cat
 
redfox435cat's Avatar
 
Join Date: Mar 2005
Location: Lompoc , CA
Posts: 1,469
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: problem 2 or 3 blades

it would be a 9x7 3 blade to match a 10x7 prop, you'll loose efficiency but gain braking and ground clearance. also be very patient because balancing 3 bladed props can be frustrating
redfox435cat is offline  
Reply With Quote
Old 06-29-2009, 06:10 AM
  #10
bingo field
 
bingo field's Avatar
 
Join Date: May 2004
Location: Mt. Morris, NY
Posts: 1,695
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: problem 2 or 3 blades

Solo props builds blade sets and hubs that more or less match the profile of certain 3 and 4 blade equipped machines, Mustangs, Corsairs, Thunderbolts, etc, and uniquely, you vary the pitch at the hub, it is adjustable. The problem is, they don't do it for the smaller planes. The Evolution trainer prop is a 10.5 x 3.5 (according to Horizon), and it flies the plane fine for training, and yes, it does slow down the plane well for landing.
bingo field is offline  
Reply With Quote
Old 06-29-2009, 07:20 AM
  #11
CGRetired
Moderator
 
CGRetired's Avatar
 
Join Date: Sep 2004
Location: Galloway, NJ
Posts: 8,999
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: problem 2 or 3 blades

There are also some definite advantages to three bladed props. Just ask any knowledgeable pattern flyer.

As for me, well, if I want ground clearance, I use larger wheels. Simple fix. Dubro makes some light-weight 3" and 3.5" wheels that work just fine. They look sort of wierd, out of place, so to speak, but hey.. you want ground clearance? They do the job.

http://www3.towerhobbies.com/cgi-bin...?&I=LXAZF2&P=7

for instance. These are 3" wheels and weigh in at only 14 grams (about a half ounce).

CGr
CGRetired is offline  
Reply With Quote
Old 06-29-2009, 07:36 AM
  #12
jetmech05
 
Join Date: Jul 2005
Location: Jacksonville, FL
Posts: 4,800
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: problem 2 or 3 blades

Leave the prop alone and cut the grass....I learned on a grass strip, we kept it short...the only time I ever got grass stains is when I ran into the longer grass at the sides of the strip.....there is more to short grass that just grass stains......grass resists free movement of the wheels and slows your prop....requiring a longer takeoff roll.....on landing can cause you to nose over....
jetmech05 is offline  
Reply With Quote
Old 06-29-2009, 08:08 AM
  #13
TexasAirBoss
 
TexasAirBoss's Avatar
 
Join Date: Oct 2002
Location: Houston, TX
Posts: 2,972
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: problem 2 or 3 blades

I was faced with this very situation when building my Bonanza. So I made new landing gear. These gear are an inch taller and the wheels are nearly 50 % larger than stock. So far, no one has noticed.
Attached Thumbnails
Click image for larger version

Name:	Jh15843.jpg
Views:	15
Size:	31.3 KB
ID:	1226775  
TexasAirBoss is offline  
Reply With Quote
Old 06-29-2009, 11:28 AM
  #14
bingo field
 
bingo field's Avatar
 
Join Date: May 2004
Location: Mt. Morris, NY
Posts: 1,695
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: problem 2 or 3 blades

Wow - Super job Pilotfighter. I wish I could get the gear doors on my Thunderbolt to look nice. I used the 3.5 in tires on it, it doesn't look out of proportion. I would have gone even larger if I could have fit them in the wheel wells.
bingo field is offline  
Reply With Quote
Old 06-29-2009, 11:34 AM
  #15
hogflyer
 
hogflyer's Avatar
 
Join Date: Mar 2005
Location: Wichita, KS
Posts: 2,036
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: problem 2 or 3 blades

PilotFighter,

Is that the old Sig Bonanza?

Hogflyer
hogflyer is offline  
Reply With Quote
Old 06-29-2009, 10:18 PM
  #16
TexasAirBoss
 
TexasAirBoss's Avatar
 
Join Date: Oct 2002
Location: Houston, TX
Posts: 2,972
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: problem 2 or 3 blades

Yep, the Sig Bonanza, but kinda Foosed up with an OS 50SX .
TexasAirBoss is offline  
Reply With Quote
Old 06-29-2009, 11:52 PM
  #17
RedGN
 
RedGN's Avatar
 
Join Date: Sep 2007
Location: Toronto, ON, CANADA
Posts: 542
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: problem 2 or 3 blades

This is a great little article that should shed a little more light on the subject.
[link]http://www.hartzellprop.com/pressroom/pr_htm/pr_09_11_96.htm[/link]

The only thing i can think of is that the 3+ blade props will provide greater thrust at lower revs.
RedGN is offline  
Reply With Quote
Old 06-30-2009, 07:18 AM
  #18
RCVFR
 
Join Date: Feb 2002
Location: Keller, TX
Posts: 2,050
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: problem 2 or 3 blades


Quote:
ORIGINAL: brett65

My personal opinion is that if two blades were actually more efficient then you would see them on all modern propped aircraft. It depends on the use and application. The alpha 3 blade prop is purposely made to be a slow prop, its on a trainer. I got a 10x5 3 blade I'm gonna try on my Extra 300.
3 and 4 blade props are used on full scale aircraft to make use of the available power from the engine(s) where a suitable 2 blade would be too large for practical use.
RCVFR is offline  
Reply With Quote
Old 06-30-2009, 08:55 PM
  #19
jeffie8696
 
jeffie8696's Avatar
 
Join Date: May 2007
Location: Muscatine, IA
Posts: 5,280
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: problem 2 or 3 blades

Just try it and see if you like it. You are the ultimate judge anyway.
jeffie8696 is offline  
Reply With Quote
Old 07-01-2009, 01:05 AM
  #20
DRC1
 
Join Date: Oct 2002
Location: Evansville, IN
Posts: 446
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: problem 2 or 3 blades


Quote:
ORIGINAL: RegFlyer

I an using a 10x7 2 blade prop, but flying off of grass turns my plane green. what I was wondering is if i use a 10x7 3 blade will it be as bad? also i was told that 3- blades = less power.
For my wife's trainer we had a situationwith the prop for a 90 4-stroke (Magnum) ona 60 size trainer only allowed for a 1/2 clearance on pavement. I decided to go to a 3-Blade prop for two reasons...

1) The 2-bladed prop pulled very well and would cause flutter in straight level flight at full power. Since my wife is learning, throttle management isn'ta natural reflexand the 3-bladed prop slowed the plane down.
2) The other reason was due to prop strikes on the softest landing and using an inch smaller diameter provided another 1/2 clearance...No more problems.

I went to a 3 bladed prop with a 1" smaller diameter and the same pitch (13 x 8 to a 12 x 8). Performance was not as good due to engine RPM being down. I lost a lot of power as I couldn't fly the Intermediate Pattern Sequence with her trainer any more. However, It does have more power than it needs for a trainer and she is more comfortable as it's more forgiving regarding the airspeed with throttle management.

Larry Diamond
DRC1 is offline  
Reply With Quote
Old 07-01-2009, 02:40 AM
  #21
redfox435cat
 
redfox435cat's Avatar
 
Join Date: Mar 2005
Location: Lompoc , CA
Posts: 1,469
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: problem 2 or 3 blades

go to a 12x7 3 blade and you'll get your power back
redfox435cat is offline  
Reply With Quote
Old 01-29-2010, 01:02 PM
  #22
ece8893
 
Join Date: Sep 2009
Location: Abu DhabiUnited Arab Emirates, UNITED ARAB EMIRATES
Posts: 29
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: problem 2 or 3 blades



I would like to send my query and I would like to see your recommendation.

I have A World Model P51 size 60 (WM product code A155).  Engine is OS FS-110a 4-stroke.
I installed a Tru-Turn Spinner and Master Airscrew 14x8 3-blade.

OS engine recommended as per the manual is 15x8 and 16x6 (2-blade).

Looks great in 3-blade with tru-turn spinner (anodized blue)....BUT would like to hear your comment if I am
doing the right was....or should I go back to 2-blade ?! 




ece8893 is offline  
Reply With Quote
Old 01-29-2010, 03:58 PM
  #23
jaka
 
Join Date: Dec 2001
Location: Upplands Vasby, SWEDEN
Posts: 7,634
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: problem 2 or 3 blades

Hi!
Master A makes some of the worst props on the market!
Go back to a 2-blade RAM or APC or ...any!
jaka is offline  
Reply With Quote
Old 01-30-2010, 10:54 AM
  #24
redfox435cat
 
redfox435cat's Avatar
 
Join Date: Mar 2005
Location: Lompoc , CA
Posts: 1,469
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: problem 2 or 3 blades

the prop will do just fine, spend some time balancing it and make sure it never hits 80% of top rpm on the ground. I recommend breaking in the motor with the recommended 2 blade prop
redfox435cat is offline  
Reply With Quote
Old 01-30-2010, 09:04 PM
  #25
Stick 40
 
Join Date: Jun 2003
Location: quincy, MI
Posts: 1,174
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: problem 2 or 3 blades

don't know if anyone said this ( did not read every post ) , but I have had very good luck with Graupner 3 blade props.

you should be able to go to a 9x7 and get away with it, and I do believe we loss a little performance with the three blade props. I was told it is due to dirty air, in other words the blades are soo close to each other they don't get a good " bite ".

sticks
Stick 40 is offline  
Reply With Quote
Reply


Thread Tools
Search this Thread
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off



All times are GMT -8. The time now is 10:06 AM.