Canard Community Forum  

Go Back   Canard Community Forum > Firewall Backward and Forward > Propellors
FAQ Members List Calendar Search Today's Posts Mark Forums Read

Reply
 
Thread Tools Display Modes
  #1  
Old 01-12-2006, 11:54 AM
rnbraud rnbraud is offline
Member
 
Join Date: Aug 2005
Location: Texas
Posts: 231
Default How about a four (4) blade prop?

Yes, this probably should go in the newbie section, but, wouldn't a four (4) blade prop be better than a two or three blade from the perspective of the blades pasing through the rough air?

Are four-blades louder or quieter?

Thanks for the discussion.
Reply With Quote
  #2  
Old 01-12-2006, 12:17 PM
Wayne Hicks Wayne Hicks is offline
Member
 
Join Date: May 2004
Location: Carrollton, VA
Posts: 1,376
Default

We went through this discussion month ago with the Cozy Builders email group. You might want to search Marc Z's archives.
http://www.cozybuilders.org/mail_list/

We also discussed it here, but I too have trouble locating past threads....

If my brain cells are functioning today (they weren't yesterday), I think the gist is:
() One blade is most efficient, but impractical, terribly hard on the crankshaft.
() Two blades probably most efficient and best compromise.
() Some three bladed props offer less vibration.
() The more blades you add, you reach a point of diminishing returns with efficiency.

I think that's how it goes. This is one of the reasons Mooney removed three-bladed props and put the two-bladers back on. They gained 5 knots. And decreased the plane's weight by a few pounds.
__________________
=============
Wayne Hicks, Cozy Plans #678
http://www.maddyhome.com/canardpages...cks/index.html
Reply With Quote
  #3  
Old 01-12-2006, 12:21 PM
Dust's Avatar
Dust Dust is offline
Super Moderator
 
Join Date: Apr 2004
Location: Troy, Michigan
Posts: 7,963
Default

Backwards logic here - the more blades the less efficient - 1 blade would be more efficient than 2 than 3 than 4

the main reason we like 3 blade is the individual blade passing through the wing dead spot is less felt than both of a two blader at the same time.

my guess - the prop is an airfoil and performs better the less the air is disturbed in front of it
__________________
Enjoy the build,njut av byggandet, godere il costruire, nyd bygningen, geniesse den Bau, apolafse tin kataskevi, disfrute la construcción, curta a construção, Pidä hauskaa rakentamisen parissa, bouw lekker,uživaj grade?inaslajdaites postroikoi, geniet die bou
dust

maker of wood, fiberglass, foam dust, metal bits and one day a Cozy will pop out and swiftly whisk me from meeting old friends and family to adventures throughout the world
Reply With Quote
  #4  
Old 01-12-2006, 12:28 PM
ekisbey's Avatar
ekisbey ekisbey is offline
Big man, little plane
 
Join Date: May 2004
Location: Tucson, AZ
Posts: 25
Default

Not really.

As a blade transitions through the airflow behind the strakes it makes a kind of a "pop" that an is felt through the whole aircraft. For props with an even number of blades, two blades transition through this zone simultaneously, and the "pop" is doubled. On a three bladed prop, only one blade is in this zone at a time, and on a different side for each "pop." This has the effect of making them seem smaller and closer together, reducing the amount of vibration that is percieved by passengers. I don't know if this fits your definition of "better" or not. If by "better" you're referring to efficiency, that's a whole 'nother can of worms. In general, for a canard, a three-bladed prop is widely considered the best choice overall.

As for noise levels, that depends on a lot more than just the number of blades. I'd suspect more blades would be quieter, but that's just an assumption.
__________________
--Evan Kisbey

There may not be any stupid questions, but I've seen LOTS of curious idiots...
Reply With Quote
  #5  
Old 01-12-2006, 01:19 PM
rnbraud rnbraud is offline
Member
 
Join Date: Aug 2005
Location: Texas
Posts: 231
Default I was thinking of vibration and/or noise

I have heard much about the "roughness: of canards due to the disturbed airflow throught the propellor behind the wing and the harse pulses of the 4-cyl Lyc imparted to the propellor blades. A 4 blade prop would seem more able to absorb the multiple pulses better than a 2 or three blade.

Another point is that if the main issue was the blades passing through the rough air, causing vibration and uneven forces imparted to the prop, a four blade would provide a more "symetrical" situation.

With a four blade two opposite blades pass through the rough air at the same time and would equalize the pulse, while at the same time the two "clean" blades are producing forward force.

This way the amount of time between push/nopush force would be reduced compared to a two blade prop. Further, the forces generated due to the blade passing throught he rough air wouldd be symetrical vs only one blade passing with a three blade prop.

As for the noise, I agree there are other variables to consider, however, all other variables being the same, it would seem a four-blade prop would provide a smoother tone since the rough air "pops" would be spread out over 2 pulses per rotation vs one per rotation.

The reason I ask this, is I am reading the archives of Nat's newsletter, and there is a picture of, I believe, Uli Walters rebuilt Cosy Classic in #6x, which has a four blade prop.
Reply With Quote
  #6  
Old 01-12-2006, 01:50 PM
David Staten's Avatar
David Staten David Staten is offline
Rotary Powered Velocity
 
Join Date: Jul 2004
Location: KEFD, Houston Area, Texas
Posts: 441
Default

Quote:
Originally Posted by rnbraud
I have heard much about the "roughness: of canards due to the disturbed airflow throught the propellor behind the wing and the harse pulses of the 4-cyl Lyc imparted to the propellor blades. A 4 blade prop would seem more able to absorb the multiple pulses better than a 2 or three blade.
I would be very careful before I correlated the number of blades with the dampning effect on torque pulses. I'm not an engineer, but some of the guys here are, and I would be interested to see how they weigh in on that premise.

dave
Reply With Quote
  #7  
Old 01-12-2006, 06:31 PM
argoldman argoldman is offline
Rich
 
Join Date: Dec 2004
Location: chicago area
Posts: 481
Default

Quote:
Originally Posted by David Staten
I would be very careful before I correlated the number of blades with the dampning effect on torque pulses. I'm not an engineer, but some of the guys here are, and I would be interested to see how they weigh in on that premise.

dave
An additional factor in number of blades is the following:

The blades must be of such a surface area that they are able to absorb the power put out by the engine, and convert that to thrust.

Three thin blades, if shortened may not be able to do this, and thus the fourth, or fifth (as was used in a Soob dragonfly) are necessary. You do loose some efficiency with multiple blades because each blade is closely following the one in front of it in disturbed air----

however look at the larger turbo prop planes with their four or more blade very wide chord props.-- what do they know that we don't?

On the other side of the coin (more blades, less length, less RPM) is the fact that propeller efficiency increase with propeller diameter.

It is a curious blalnce which props us up.
__________________
CANARDLY CONTAIN MYSELF
Rich
Reply With Quote
  #8  
Old 01-12-2006, 07:32 PM
Dust's Avatar
Dust Dust is offline
Super Moderator
 
Join Date: Apr 2004
Location: Troy, Michigan
Posts: 7,963
Default

Quote:
Originally Posted by argoldman
however look at the larger turbo prop planes with their four or more blade very wide chord props.-- what do they know that we don't?
they know that the prop tip speed can't go past, i believe, 110% of speed of sound for special props and about 91% the speed of sound for us mere mortals
__________________
Enjoy the build,njut av byggandet, godere il costruire, nyd bygningen, geniesse den Bau, apolafse tin kataskevi, disfrute la construcción, curta a construção, Pidä hauskaa rakentamisen parissa, bouw lekker,uživaj grade?inaslajdaites postroikoi, geniet die bou
dust

maker of wood, fiberglass, foam dust, metal bits and one day a Cozy will pop out and swiftly whisk me from meeting old friends and family to adventures throughout the world
Reply With Quote
  #9  
Old 01-12-2006, 10:35 PM
eracer113 eracer113 is offline
Member
 
Join Date: Nov 2004
Location: aurora, Illinois
Posts: 197
Default

I was just wondering how propellers on large boats compare with AC props. I had 40 to 60 ft boats for 25 plus years with gas and diesel engines running 2-3-4-and 5 bladed props. The boats weighed in at 20-25 tons. The 2 blade prop was hard to keep from cavitating upon acceleration, the 3 blade was probably the most efficient all around, the 4 blade was close to the 3 blade except was about 25% smoother, while the 5 blade prop was without a doubt the smoothest of all. The only problem with the 5 blade prop was you had very little back up thrust if you got caught docking in a heavy wind situation. The diesel powered boats all delivered 21 kts speed with 3-4-or 5 blade props, while the gas powered delivered in the 15-16 kt speed burning twice the fuel. All the twin engine boats I have owned, the diesel boats would average 1 mile per gal and the gas engined boats would average 1/2 mi per gal. I am not sure I am comparing apples with oranges but there seems to be a similarity between the two considering the load factor on the engines. Maybe a prop maker could respond to this thread. If a 5 blade prop would work on my AC, knowing what it gave me on my boat, I would have one made tomorrow.

Jack Morrison
E Racer113
Reply With Quote
  #10  
Old 01-13-2006, 12:01 AM
JonC's Avatar
JonC JonC is offline
LEz - N555LE Q - N555QA
 
Join Date: Jul 2004
Location: Mountain View, CA
Posts: 997
Default

Quote:
Originally Posted by Dust
they know that the prop tip speed can't go past, i believe, 110% of speed of sound for special props and about 91% the speed of sound for us mere mortals
That, and the fact that turboprops unlike piston engines run around at 90-100% power in cruise... so, we cannot turn the blades too fast and while having the blades turning slower, we must have enough blade to absorb the power of the engine, even at high altitudes.

The common "small" turboprop (not shaft) engines are around 600hp, so that is a lot of prop.
__________________
~Nathan
Reply With Quote
  #11  
Old 01-13-2006, 09:45 AM
rnbraud rnbraud is offline
Member
 
Join Date: Aug 2005
Location: Texas
Posts: 231
Default That's what I am looking for!

quoted: "he 3 blade was probably the most efficient all around, the 4 blade was close to the 3 blade except was about 25% smoother, while the 5 blade prop was without a doubt the smoothest of all."

This is what I thought would be the case for a 4-blade prop on a Cozy! I am indeed looking for smoothe and quiet. To me, the Cozy is a cross-country "SUV" and on long trips I would like quiet, smooth, with performance.

To this end, I am planning, (huh,like 2-3 years from now), for a quiet smooth propulsion package and considering the Jabiru 5100 with a 4-blade prop. The Jabiru 5100 even comes with mufflers! Eight cylinders, mufflers, and a 4-blade prop should make for a quiet, smooth package.

Question, nebie question that is, can the Lycoming O-360 be outfitted with mufflers? Just asking.
Reply With Quote
  #12  
Old 01-13-2006, 10:02 AM
Dust's Avatar
Dust Dust is offline
Super Moderator
 
Join Date: Apr 2004
Location: Troy, Michigan
Posts: 7,963
Default

WHY WOULD YOU WANT MUFFLERS, oops caps lock, to make it quiet for the spam cans you are leaving behind? they just rob power, add weight and take space under the cowling.

smooth - three blade is smooth and the conti has 6 cylinders, heh heh heh
__________________
Enjoy the build,njut av byggandet, godere il costruire, nyd bygningen, geniesse den Bau, apolafse tin kataskevi, disfrute la construcción, curta a construção, Pidä hauskaa rakentamisen parissa, bouw lekker,uživaj grade?inaslajdaites postroikoi, geniet die bou
dust

maker of wood, fiberglass, foam dust, metal bits and one day a Cozy will pop out and swiftly whisk me from meeting old friends and family to adventures throughout the world
Reply With Quote
  #13  
Old 01-13-2006, 11:28 AM
JonC's Avatar
JonC JonC is offline
LEz - N555LE Q - N555QA
 
Join Date: Jul 2004
Location: Mountain View, CA
Posts: 997
Default

Quote:
Originally Posted by rnbraud
Question, nebie question that is, can the Lycoming O-360 be outfitted with mufflers? Just asking.
Yes..
__________________
~Nathan
Reply With Quote
  #14  
Old 01-13-2006, 12:03 PM
rnbraud rnbraud is offline
Member
 
Join Date: Aug 2005
Location: Texas
Posts: 231
Default Mufflers are for me!

Hey Dust, the mufflers are for me not others!

Can I get some more feedback on the mufflers for the Lycs!

I said I was "planning" to use the Jabiru 5100, but I may need to go with a well worn Lyc initially. Remember Burt's saying, to paraphrase, "test an experimental airframe with proven motor, not both experimental.....


I just finished reading Nat's newsletters on the Franklin, anyone know if Franklin is still going? I thought I read they had been bought out then shutdown, but there is a website of a palce in CO www.franklinengines.com.
Any insights on using a Franklin six cylinder????

Just curious!
Reply With Quote
  #15  
Old 01-13-2006, 12:12 PM
Dust's Avatar
Dust Dust is offline
Super Moderator
 
Join Date: Apr 2004
Location: Troy, Michigan
Posts: 7,963
Default

Nat had a new prop made for the franklin - it would not spin it, i e it did not have enough HP.

then he put the one for the 180 hp lycoming on it - it would not spin it - ie did not have enough hp

He was not impressed with the franklin at all altho it had paperwork with it that it was 200 hp, it underperformed the 180 hp lycoming. it was smooth though.

the mufflers - don't think they will do you much - just buy anr and you're good to go - the noise goes straight out the back
__________________
Enjoy the build,njut av byggandet, godere il costruire, nyd bygningen, geniesse den Bau, apolafse tin kataskevi, disfrute la construcción, curta a construção, Pidä hauskaa rakentamisen parissa, bouw lekker,uživaj grade?inaslajdaites postroikoi, geniet die bou
dust

maker of wood, fiberglass, foam dust, metal bits and one day a Cozy will pop out and swiftly whisk me from meeting old friends and family to adventures throughout the world
Reply With Quote
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
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

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -4. The time now is 12:55 PM.


Powered by vBulletin® Version 3.6.7
Copyright ©2000 - 2018, Jelsoft Enterprises Ltd.