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propellors

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planecrazydld(at)yahoo.co
Guest

Posted: Sun Dec 10, 2006 4:45 am Post subject: propellors

[quote][b]

Eldo(at)unb.ca
Guest

Posted: Mon Dec 11, 2006 6:04 am Post subject: propellors

I thought I'd add a little to the propeller comment.  In considering diameter, some thought 

needs to go into rpm and blade tip speed as the tip approaches the speed of sound, in 

general the efficiency falls off.  This means that higher speed engines (most conversions) 

need to either be geared down or the prop must be of a smaller diameter to keep the tip 

speed down.  Of course a smaller diameter means less blade area and the prop will be 

unable to use available power... thus the need to add more blades to make use of the 

horsepower when the diameter is reduced.  



I am sure there are more specific guide-lines on the web with more equations and theory 

than this simple Civil Engineer wants to look at but this is a general view of the compromise 

of diameter-rpm-number of blades.  



Eldo Hildebrand, PhD., P.Eng.

Assistant Dean, Faculty of Engineering

University of New Brunswick

P.O Box 4400

Fredericton, NB

E3B 5A3

tel 506-453-4521

fax 506-453-3568

paulrod36(at)msn.com
Guest

Posted: Tue Dec 12, 2006 2:32 pm Post subject: propellors

<?xml:namespace prefix="v" /><?xml:namespace prefix="o" /><![endif]-->  An interesting comment. Your rough explanation being the case, it  suggests that a smaller diameter, wider-bladed, five blade prop might well be  worth looking at. Can't remember where, or what, but I do recall seing photos of  something that had a five-bladed prop. Anybody remember what it was?  Maybe  we really can use some of those high RPM motorcycle and sport car  engines????

  

 Paul Rodriguez

 601XL/Corvair

 [quote]   ---

dredmoody(at)cox.net
Guest

Posted: Tue Dec 12, 2006 2:52 pm Post subject: propellors

It doesn't help us Zenith builders at all but the last two airplanes with five bladed props that I saw in person were (A) a turbo-shaft powered Lancair Legacy (very highly modified airframe) that boasted a max straight-and-level speed of 313mph, and (B) a huge turbo-shaft Air Tractor ag-plane that was working in the forestry industry.



I don't recall ever seeing an engine light enough for us to use that could spin a five bladed prop. Would it not be cool if that existed though? Imagine the rate of climb....



Ed Moody II

Do Not Archive



---- paulrod36(at)msn.com wrote: 

 	  Quote: 	
		   An interesting comment. Your rough explanation being the case, it suggests that a smaller diameter, wider-bladed, five blade prop might well be worth looking at. Can't remember where, or what, but I do recall seing photos of something that had a five-bladed prop. Anybody remember what it was?  Maybe we really can use some of those high RPM motorcycle and sport car engines????

 

 Paul Rodriguez

 601XL/Corvair

billbutlergps(at)aim.com
Guest

Posted: Tue Dec 12, 2006 3:11 pm Post subject: propellors

http://www.warpdriveprops.com/

 I have seen 5 bladed props on trikes and on a 701 w/ floats. I would be interested in seeing some reasoning for going with a 3, 4 or 5 bladed prop over a 2 blade. I notice that most are running the 3 bladed prop. What is your take on having more blades?

 Bill

 

   

  

 --

dredmoody(at)cox.net
Guest

Posted: Tue Dec 12, 2006 3:29 pm Post subject: propellors

First, a disclaimer.... this is not authoritative.... it's basically just heresay because I have no direct first-hand experience.



What I've been told is that if you have the clearance and the torque to do it, swinging a long 2 bladed prop at lower rpm will give you the most climb performance for a given engine. A shorter 3 or four bladed prop at higher rpm is supposed to give you less climb performance but higher cruise speed and/or better fuel efficiency. Also, using more blades which are shorter helps with fuselage clearance on a pusher and ground clearance on a tractor arrangement.



I personally had not seen any prop with more than 3 blades that could be used on the Rotax 912S or Jabiru 3300, or similar lightweight engines. 



Ed

Do Not Archive



---- billbutlergps(at)aim.com wrote: 

 	  Quote: 	
		    http://www.warpdriveprops.com/

  I have seen 5 bladed props on trikes and on a 701 w/ floats. I would be interested in seeing some reasoning for going with a 3, 4 or 5 bladed prop over a 2 blade. I notice that most are running the 3 bladed prop. What is your take on having more blades?

  Bill

afterfxllc(at)aol.com
Guest

Posted: Tue Dec 12, 2006 3:57 pm Post subject: propellors

It would look cool but it is the least effecient prop you can use. The prop with one blade and counter balance weight was very effecient believe it or not. 

    

  

 --

dbortol

Joined: 02 Sep 2006
Posts: 46

Posted: Tue Dec 12, 2006 4:01 pm Post subject: propellors

There was a light plane in the hangar next to William Wynne's with a

five blade prop. I can't remember the name of it. Maybe somebody else

that was at the Corvair College last month will remember. Weirdest

construction I ever saw - aluminum wing spar with wooden ribs and

fiberglass skin. Little bit of everything...  Anyway, the engine was

an auto conversion (Subaru if I remember right) with the largest belt

reduction I've ever seen. The driven pulley was at least  12 inches in

diameter.



Personally I'm going to keep mine simple - direct drive Corvair with

two (2) blades.



Dino Bortolin

La Salle, Ontario

XL/Corvair



On 12/12/06, paulrod36(at)msn.com <paulrod36(at)msn.com> wrote:

[quote] An interesting comment. Your rough explanation being the case, it suggests

 that a smaller diameter, wider-bladed, five blade prop might well be worth

 looking at. Can't remember where, or what, but I do recall seing photos of

 something that had a five-bladed prop. Anybody remember what it was?  Maybe

 we really can use some of those high RPM motorcycle and sport car

 engines????



 Paul Rodriguez

 601XL/Corvair

   ---

craig(at)craigandjean.com
Guest

Posted: Tue Dec 12, 2006 4:16 pm Post subject: propellors

 	  Quote: 	
		  > swinging a long 2 bladed prop at lower rpm will give you the most climb

performance for a given engine.
	




Sounds like the backyard flyer: www.culverprops.com/back-yard-flyerA.htm



-- Craig

craig(at)craigandjean.com
Guest

Posted: Tue Dec 12, 2006 4:22 pm Post subject: propellors

 	  Quote: 	
		  > There was a light plane in the hangar next to William Wynne's with a five

blade prop.
	




I think this is what you are thinking of: www.flycorvair.com/32297.jpg



Read about it here: www.flycorvair.com/hangar1206c.html



-- Craig

dredmoody(at)cox.net
Guest

Posted: Tue Dec 12, 2006 4:32 pm Post subject: propellors

MY God! That's a long prop! I think that the longest 2 bladed prop that the engine can swing is probably the best bet but that one looks like a prop strike waiting to happen. 



While we're on the prop subject, there have been speculations about the blade tips going transonic at full throttle with the Jabiru 3300 and its (relatively) short prop (64"). Even if we could wind the engine up to the redline of 3300 rpm (which is doubtful) the tips would still only approach .85 mach. That doesn't sound like much cause for concern does it?



Ed Moody II



---- Craig Payne <craig(at)craigandjean.com> wrote: 

 	  Quote: 	
		   

 

 >> swinging a long 2 bladed prop at lower rpm will give you the most climb

 performance for a given engine.

 

 Sounds like the backyard flyer: www.culverprops.com/back-yard-flyerA.htm

 

 -- Craig

billbutlergps(at)aim.com
Guest

Posted: Tue Dec 12, 2006 5:33 pm Post subject: propellors

Here is a neat prop calculator that helps answer those questions. 

   http://www.hoverhawk.com/propspd.html

   Bill 

    

  

 --

paulrod36(at)msn.com
Guest

Posted: Thu Dec 14, 2006 11:00 am Post subject: propellors

<?xml:namespace prefix="v" /><?xml:namespace prefix="o" /><![endif]-->  Bill, my original thinking was as follows:  There are some neat  engines out there, but they run at high RPM. High RPM could push the  prop tip speed close to Mach 1, thereby reducing efficiency a great deal. A  shorter blade lets the tip move slower, keeping it in the efficiency range, but  you lose lift (thrust) with smaller wing (blade) area. To compensate, then, why  not have more blades, with wider chord, sort of the reason some very mean acro  ships are biplanes, with tremendous lift. (The AN-2 springs to mind.) However,  more blades mean more weight, so you would have to compensate by making them  very light, possibly hollow. I suggest it could be done, but it likely isn't  coming out of someone's garage. A high-tech prop manufacturer might have the  answer. I don't. But it makes my brain itch.

  

 Paul Rodriguez

 601XL/Corvair

 (and probably with WW's two-bladed prop)

 [quote]   ---

ggower_99(at)yahoo.com
Guest

Posted: Thu Dec 14, 2006 11:34 am Post subject: propellors

Hello Bill,



The reason od the five blades is noise...  In Europe are very carefull with the noise in airplanes,  Here we had two trikes that came from France with 5 blade props,  later were changed for 3 bladed ones for 3 main reasons:  One, the noise (very liitle in a 912 engine) is no legal problem here. Two,  There was a penalty in  performance,  messured against another similar trike.  and 3   I dont remember the brand or model of the propeller, but was a advise from Rotax to change that prop, because was too "inercia" heavy for the engine/transmission



A well chosen 2 or 3 blade in a 912 or 912S can be very effective,  in either climb and/or cruise...



Saludos

Gary Gower

Flying from Chapala, Mexico.



Saludos

Gary Gower.



billbutlergps(at)aim.com wrote:[quote]   http://www.warpdriveprops.com/

 I have seen 5 bladed props on trikes and on a 701 w/ floats. I would be interested in seeing some reasoning for going with a 3, 4 or 5 bladed prop over a 2 blade. I notice that most are running the 3 bladed prop. What is your take on having more blades?

 Bill

 

   

  

 --

bryanmmartin

Joined: 10 Jan 2006
Posts: 1018

Posted: Thu Dec 14, 2006 11:11 pm Post subject: propellors

The more blades you have the less the overall efficiency of the prop becomes. Each blade sees a bit of flow disruption from the blade leading it. The biggest reason for going with more blades is to allow the allow more power to be converted to thrust by the prop. That's why you often see high powered turbofans turning props with as many as seven blades. With all that power available, the lower efficiency is acceptable. If you don't have a lot of power available, the loss of efficiency of multiple bladed props can become a big deal.

The most efficient propellor is one with a single blade with a mass counter balance. There are a few motor gliders that use this configuration to squeeze every bit of thrust they can from a small, light-weight engine.



Another reason to go with more blades is that the more blades you have the higher the frequency of the noise generated by the propellor. Higher frequencies tend to dissipate more quickly over distance, resulting in a quieter airplane.



If you are running a direct drive engine at a relatively high RPM, you have to use a small diameter prop to avoid excessively  tip speeds and you may need more blades to get acceptable thrust, but you will pay a penalty in propellor efficiency. 

On Dec 14, 2006, at 1:59 PM, <paulrod36(at)msn.com (paulrod36(at)msn.com)> <paulrod36(at)msn.com (paulrod36(at)msn.com)> wrote:

[quote]Bill, my original thinking was as follows:  There are some neat engines out there, but they run at high RPM. High RPM could push the prop tip speed close to Mach 1, thereby reducing efficiency a great deal. A shorter blade lets the tip move slower, keeping it in the efficiency range, but you lose lift (thrust) with smaller wing (blade) area. To compensate, then, why not have more blades, with wider chord, sort of the reason some ..



[b]

_________________
--
Bryan Martin
N61BM, CH 601 XL, Stratus Subaru.
do not archive.

p.mulwitz(at)worldnet.att
Guest

Posted: Sat Dec 16, 2006 6:49 am Post subject: propellors

One factor with prop length doesn't seem to have surfaced in the 

latest discussion.  That is the fact that the propeller is mounted in 

front of the fuselage.  The airflow from the central portion of the 

propeller is blocked by the front of the fuselage, so this is mostly 

wasted energy.  A longer propeller has less of its rotation disk 

blocked by the fuselage, so more of the energy spent by the engine is 

converted to thrust.



An extreme case of adding shorter blades would have all the airflow 

generated by the propeller disrupted by the fuselage and a plane that 

could barely taxi.



Paul

XL fuselage

do not archive



At 10:59 AM 12/14/2006, you wrote:

 	  Quote: 	
		  Bill, my original thinking was as follows:  There are some neat 

engines out there, but they run at high RPM. High RPM could push the 

prop tip speed close to Mach 1, thereby reducing efficiency a great 

deal. A shorter blade lets the tip move slower, keeping it in the 

efficiency range, but you lose lift (thrust) with smaller wing 

(blade) area. To compensate, then, why not have more blades, with 

wider chord, sort of the reason some very mean acro ships are 

biplanes, with tremendous lift. (The AN-2 springs to mind.) However, 

more blades mean more weight, so you would have to compensate by 

making them very light, possibly hollow. I suggest it could be done, 

but it likely isn't coming out of someone's garage. A high-tech prop 

manufacturer might have the answer. I don't. But it makes my brain itch.



Paul Rodriguez

601XL/Corvair

(and probably with WW's two-bladed prop)


	


-

paulrod36(at)msn.com
Guest

Posted: Sat Dec 16, 2006 11:04 am Post subject: propellors

<?xml:namespace prefix="v" /><?xml:namespace prefix="o" /><![endif]-->  Neat explanation, Bryan. I guess I'll stick with WW's prop on my corvair.  (unless I borrow my friend's dragster engine, modify the cowling, mount and  firewall, get bigger landing gear, carve eight humongous holes in the top of the  cowling, .....hhmmmm)

  

 Paul Rodriguez

 DO NOT ARCHIVE

 [quote]   ---

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