Matronics Email Lists :: View topic - WRT M3X prop boom measurements.

Matronics Email Lists
Web Forum Interface to the Matronics Email Lists

Get Email Distribution Too! FAQ Search Memberlist Usergroups Register

Profile Log in to check your private messages Log in

WRT M3X prop boom measurements.
Goto page 1, 2, 3, 4 Next

Matronics Email Lists Forum Index -> Kolb-List

View previous topic :: View next topic

Author Message

captainron1(at)cox.net
Guest

Posted: Fri May 29, 2009 1:20 pm Post subject: WRT M3X prop boom measurements.

Folks I started the mating of the Suzuki motor to the Mounts. I need some measurements as to prop clearances and measured distance from the Boom the the center of the prop hub. I can't see where some of you reported where you had a 72 inch prop. I see where I can install a 70 inch prop on my mount but then clearance will be down to about an inch. These are preliminary measurements for my airframe.

Anyway I need to figure out what's what WRT that.



Thanks 

Ron (at) KFHU

mdnanwelch7(at)hotmail.co
Guest

Posted: Fri May 29, 2009 1:36 pm Post subject: WRT M3X prop boom measurements.

Ron C

  

   I have a turbocharged Suzuki G1.0. & a 68" inflight electric adjust IvoProp.  My measurements are:  from tip of prop to boom tube C I have close to 2 3/4" clearance.  Of course C you have a different redrive than I do C but it sounds like your prop position is very close to mine.

  

  

 Mike Welch

 MkIII

 

 

[quote] Folks I started the mating of the Suzuki motor to the Mounts. I need some measurements as to prop clearances and measured distance from the Boom the the center of the prop hub. I can't see where some of you reported where you had a 72 inch prop. I see where I can install a 70 inch prop on my mount but then clearance will be down to about an inch. These are preliminary measurements for my airframe.

 Anyway I need to figure out what's what WRT that.

 

 Thanks 

 Ron (at) KFHU

Hotmail® goes with you.  Get it on your BlackBerry or iPhone.   	  Quote: 	
		  [b]

John Hauck

Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)

Posted: Fri May 29, 2009 2:00 pm Post subject: WRT M3X prop boom measurements.

> Folks I started the mating of the Suzuki motor to the Mounts. I need some 

measurements as to prop clearances and measured distance from the Boom the 

the center of the prop hub. I can't see where some of you reported where you 

had a 72 inch prop. I see where I can install a 70 inch prop on my mount but 

then clearance will be down to about an inch. These are preliminary 

measurements for my airframe.

 	  Quote: 	
		   Anyway I need to figure out what's what WRT that.



 Thanks

 Ron (at) KFHU


	




I've flown with 70,71, and 72" props on my mkIII.  Clearances ranged from 

the "book" 1.5" to as little as .75".  Currently have 1.25" with my new 71" 

blades.



The lower the line of thrust the more efficient the system will be.



john h

mkIII

_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama

captainron1(at)cox.net
Guest

Posted: Fri May 29, 2009 8:55 pm Post subject: WRT M3X prop boom measurements.

Okay thanks, I guess and also based on what John H. said that the Suzuki motor crank is stationed lower on the mounts than the Rotax.

I would like at one point to have the SPG-2 turned down and have a 5 or 6 blade prop on it. this will place the center of thrust just about equal with the trailing edge of the wings. However for the moment and with the budget I got I'll keep it as is.

A friend of mine was looking at it today for the first time and she said "it has such a big motor on it".....  I guess the DOHC 1.3 is kinda large looking on the frame. 

---- Mike Welch <mdnanwelch7(at)hotmail.com> wrote: 



=============



Ron,



 



  I have a turbocharged Suzuki G1.0. & a 68" inflight electric adjust IvoProp.  My measurements are:  from tip of prop to boom tube, I have close to 2 3/4" clearance.  Of course, you have a different redrive than I do, but it sounds like your prop position is very close to mine.



 



 



Mike Welch



MkIII

 

 	  Quote: 	
		   Folks I started the mating of the Suzuki motor to the Mounts. I need some measurements as to prop clearances and measured distance from the Boom the the center of the prop hub. I can't see where some of you reported where you had a 72 inch prop. I see where I can install a 70 inch prop on my mount but then clearance will be down to about an inch. These are preliminary measurements for my airframe.

 Anyway I need to figure out what's what WRT that.

 

 Thanks 

 Ron (at) KFHU


	


_________________________________________________________________

HotmailÂ® goes with you. 

http://windowslive.com/Tutorial/Hotmail/Mobile?ocid=TXT_TAGLM_WL_HM_Tutorial_Mobile1_052009

--

kugelair.com

mdnanwelch7(at)hotmail.co
Guest

Posted: Sat May 30, 2009 3:38 am Post subject: WRT M3X prop boom measurements.

Ron C 

   Turning the SPG-2 redrive upside down (lowering the prop center) and then using a 5-6 blade prop would be a really bad idea. 

   This subject has been discussed numerous times before on this list.  The smaller the prop C the faster is has to spin.  Plus C because the prop is small C you have to add more blades C because a large engine will overpower a small 2 blade prop.  But C a faster spinning prop means more noise and is not as efficient. 

   IIRC C someone proposed putting on a multiblade prop (4-5 blades) a year or two ago.  They thought it looked "cool".  They were willing to give up some performance for "the look".  Not a

 good idea to just throw away some of an engine's thrust.

   Just my opinion.....

 Mike Welch

 MkIII

[quote] Date: Sat C 30 May 2009 00:54:30 -0400

 From: captainron1(at)cox.net

 To: kolb-list(at)matronics.com

 Subject: RE: WRT M3X prop boom measurements.

 --> Kolb-List message posted by: Ron <captainron1(at)cox.net>

 Okay thanks C I guess and also based on what John H. said that the Suzuki motor crank is stationed lower on the mounts than the Rotax.

 I would like at one point to have the SPG-2 turned down and have a 5 or 6 blade prop on it. this will place the center of thrust just about equal with the trailing edge of the wings. However for the moment and with the budget I got I'll keep it as is.

 A friend of mine was looking at it today for the first time and she said "it has such a big motor on it".....  I guess the DOHC 1.3 is kinda large looking on the frame. 

 ---- Mike Welch <mdnanwelch7(at)hotmail.com> wrote: 

 =============

 Ron C

 I have a turbocharged Suzuki G1.0. & a 68" inflight electric adjust IvoProp. My measurements are: from tip of prop to boom tube C I have close to 2 3/4" clearance. Of course C you have a different redrive than I do C but it sounds like your prop position is very close to mine.

 Mike Welch

 MkIII

 > Folks I started the mating of the Suzuki motor to the Mounts. I need some measurements as to prop clearances and measured distance from the Boom the the center of the prop hub. I can't see where some of you reported where you had a 72 inch prop. I see where I can install a 70 inch prop on my mount but then clearance will be down to about an inch. These are preliminary measurements for my airframe.

 > Anyway I need to figure out what's what WRT that.

 > 

 > Thanks 

 > Ron (at) KFHU

 _________________________________________________________________

 Hotmail® goes with you. 

 http://windowslive.com/Tutorial/Hotmail/Mobile?ocid=TXT_TAGLM_WL_HM_Tutorial_Mobile1_052009

 --

 kugelair.com

 ==========

Insert movie times and more without leaving Hotmail®. See how.   	  Quote: 	
		  [b]

captainron1(at)cox.net
Guest

Posted: Sat May 30, 2009 7:44 am Post subject: WRT M3X prop boom measurements.

It could have been me last year ( or 2 or 3 years ago) that spoke of a high number  multi blade propeller. However for me as evidenced by my own paint jobs, beauty or looking cool for looking cool is seldom a consideration. 

A multi blade prop all else being equal is  more efficient and effective. I truly don't want to delve into this subject again, but I think that real life experience and the math supports what I say. But again the last thing I want to start is another debate about this.  

I just felt for whatever strange reason to say the above fully knowing that this may yet start another thread..... LoL.

Anyway budgetary consideration will probably keep me more or less in a more popular configuration engine prop wise ( for the time being....). 

Ron (at)  KFHU

=============================

---- Mike Welch <mdnanwelch7(at)hotmail.com> wrote: 

=============

Ron, 

  Turning the SPG-2 redrive upside down (lowering the prop center) and then using a 5-6 blade prop would be a really bad idea. 

  This subject has been discussed numerous times before on this list.  The smaller the prop, the faster is has to spin.  Plus, because the prop is small, you have to add more blades, because a large engine will overpower a small 2 blade prop.  But, a faster spinning prop means more noise and is not as efficient. 

  IIRC, someone proposed putting on a multiblade prop (4-5 blades) a year or two ago.  They thought it looked "cool".  They were willing to give up some performance for "the look".  Not a

good idea to just throw away some of an engine's thrust.

  Just my opinion.....

Mike Welch

MkIII

 	  Quote: 	
		   Date: Sat, 30 May 2009 00:54:30 -0400

 From: captainron1(at)cox.net

 To: kolb-list(at)matronics.com

 Subject: RE: WRT M3X prop boom measurements.

 Okay thanks, I guess and also based on what John H. said that the Suzuki motor crank is stationed lower on the mounts than the Rotax.

 I would like at one point to have the SPG-2 turned down and have a 5 or 6 blade prop on it. this will place the center of thrust just about equal with the trailing edge of the wings. However for the moment and with the budget I got I'll keep it as is.

 A friend of mine was looking at it today for the first time and she said "it has such a big motor on it".....  I guess the DOHC 1.3 is kinda large looking on the frame. 

 ---- Mike Welch <mdnanwelch7(at)hotmail.com> wrote: 

 =============

 Ron,

 I have a turbocharged Suzuki G1.0. & a 68" inflight electric adjust IvoProp. My measurements are: from tip of prop to boom tube, I have close to 2 3/4" clearance. Of course, you have a different redrive than I do, but it sounds like your prop position is very close to mine.

 Mike Welch

 MkIII

 > Folks I started the mating of the Suzuki motor to the Mounts. I need some measurements as to prop clearances and measured distance from the Boom the the center of the prop hub. I can't see where some of you reported where you had a 72 inch prop. I see where I can install a 70 inch prop on my mount but then clearance will be down to about an inch. These are preliminary measurements for my airframe.

 > Anyway I need to figure out what's what WRT that.

 > 

 > Thanks 

 > Ron (at) KFHU

 _________________________________________________________________

 HotmailÂ® goes with you. 

 http://windowslive.com/Tutorial/Hotmail/Mobile?ocid=TXT_TAGLM_WL_HM_Tutorial_Mobile1_052009

 --

 kugelair.com

============

============

============

============

 	  Quote: 	

_________________________________________________________________

Insert movie times and more without leaving HotmailÂ®.

http://windowslive.com/Tutorial/Hotmail/QuickAdd?ocid=TXT_TAGLM_WL_HM_Tutorial_QuickAdd1_052009

--

kugelair.com

mdnanwelch7(at)hotmail.co
Guest

Posted: Sat May 30, 2009 10:14 am Post subject: WRT M3X prop boom measurements.

> But again the last thing I want to start is another debate about this.  

 	  Quote: 	
		   I just felt for whatever strange reason to say the above fully knowing that this may yet start another thread..... LoL.

 

 Ron (at) KFHU


	


 Ron C

  

   You are entitled to think whatever you want.  I'm not going to argue with you.  subject has ended

  

 Mike

Windows Live™: Keep your life in sync. Check it out.  [quote][b]

JetPilot

Joined: 10 Jan 2006
Posts: 1246

Posted: Sat May 30, 2009 1:21 pm Post subject: Re: WRT M3X prop boom measurements.

 	  captainron1(at)cox.net wrote: 	
		  



It could have been me last year ( or 2 or 3 years ago) that spoke of a high number  multi blade propeller. However for me as evidenced by my own paint jobs, beauty or looking cool for looking cool is seldom a consideration. 

A multi blade prop all else being equal is  more efficient and effective. I truly don't want to delve into this subject again, but I think that real life experience and the math supports what I say. 



	




How many blades do you mean by " Multi Blade ? "   One huge factor is power for the amount of prop area and speed.  For a turboprop going fast, I think the 6 blade prop works better, but they are trying to get 3000 horsepower into a limited diameter prop.



With all the LSA and experimental planes out there, no significant number of planes are using more than 3 or 4 blades.  If it were as easy as adding more blades to get significantly more performance on our class of airplane, many would be doing it.  Theory is nice, but nothing trumps real life performance, and by the lack of many bladed propellers on our class airplanes seems to indicate there is just noting to be gained by that.   If were as easy as changing a prop, and there were some reports of a 6 blade propeller significantly improving performance of our class planes, people would be lined up waiting to buy these props.



Mike

_________________
"NO FEAR" - If you have no fear you did not go as fast as you could have !!!

Kolb MK-III Xtra, 912-S

captainron1(at)cox.net
Guest

Posted: Sat May 30, 2009 1:43 pm Post subject: WRT M3X prop boom measurements.

It goes without saying that adding blades, will not do a thing for HP. We got what we got in that motor. The question is, well let me back up. I am thinking of lowering the thrust line further. With the SPG-2 it can be mounted 12-3-6- and 9 o'clock.

If I turn it down the thrust line gets be be pretty low. But now I am down to a 55 inch prop. If I use a two blades I will be nowhere near optimal conversion of HP/thrust. As you said it needs enough wing airfoil or prop to take the hp and make the thrust that the motor is capable of producing 

 thus I gotta put more blades. Or another way I gotta create more blade area. I guess we can figure out how much effective airfoil area two 71 inch props has and then figure out how many blades I gotta put on that hub to get the same total area. And then You can throw another blade in there for rotating disc efficiency and be done with it. Like I said the last I commented about this some experimentation is certainly required. One of the prop makers has a hub that can use six blades I guess if its not too expensive I buy it and start with 3 blades like everyone else and then add 3 more blades ( down sizing the whole deal as needed), and see the difference.

 I think that would be fun to explore. 



Ron (at) KFHU

==========================

---- JetPilot <orcabonita(at)hotmail.com> wrote: 



=============


captainron1(at)cox.net wrote:

 	  Quote: 	
		   

 

 It could have been me last year ( or 2 or 3 years ago) that spoke of a high number  multi blade propeller. However for me as evidenced by my own paint jobs, beauty or looking cool for looking cool is seldom a consideration. 

 A multi blade prop all else being equal is  more efficient and effective. I truly don't want to delve into this subject again, but I think that real life experience and the math supports what I say. 

 

 


	




How many blades do you mean by " Multi Blade ? "   One huge factor is power for the amount of prop area and speed.  For a turboprop going fast, I think the 6 blade prop works better, but they are trying to get 3000 horsepower into a limited diameter prop.



With all the LSA and experimental planes out there, no significant number of planes are using more than 3 or 4 blades.  If it were as easy as adding more blades to get significantly more performance on our class of airplane, many would be doing it.  Theory is nice, but nothing trumps real life performance, and by the lack of many bladed propellers on our class airplanes seems to indicate there is just noting to be gained by that.   If were as easy as changing a prop, and there were some reports of a 6 blade propeller significantly improving performance of our class planes, people would be lined up waiting to buy these props.



Mike



--------

&quot;NO FEAR&quot; -  If you have no fear you did not go as fast as you could have !!!



Kolb MK-III Xtra, 912-S





Read this topic online here:



http://forums.matronics.com/viewtopic.php?p 46065#246065



--

kugelair.com

JetPilot

Joined: 10 Jan 2006
Posts: 1246

Posted: Sat May 30, 2009 4:22 pm Post subject: Re: WRT M3X prop boom measurements.

For a slow flying plane like a Kolb, a larger diameter prop is far more efficient and provides more thrust.  As you make the prop disc smaller, the velocity of the air that you need to move becomes faster... A Kolb can not take advantage of High Velocity thrust.  Imagine putting a small jet engine on a Kolb, you would be using a huge amount of power and fuel just to cruise at 80 MPH.  It is an extreme example, but its the same thing as putting a small prop that depended on high velocity air on a Kolb, you would need about 200 HP to get the same performance as we get with our large diameter props.



A helicopter rotor is just a large prop that is very large diameter and optimized for slow speeds ( Lifting ).  An R-22 will have more thrust than weight with just 160 HP and fly...  If you took that same 160 HP engine on a helicopter and put a small high speed prop on it instead of a rotor, you would be moving a smaller volume of air very fast, but it would all be wasted energy, and it would not even come close to lifting the helicopter off the ground.  On the same token, the helicopter rotor would not fly very fast mounted on the front of a Cirrus or other high speed plane.



The idea of getting the thrust line much lower would be great, but it is not practical with this type of airplane.  You would need so much extra power to compensate for the small diameter high speed optimized propeller that you would create more problems than you would solve.  There has been a lot of experimentation with props and thrust lines on pushers, and what we have now as about as good as a compromise that you will get.  Again, if it were as easy as adding prop blades, and lowering the thrust line closer to the CG of the airplane, it would make a much nicer flying airplane, and it would have been done long ago.



Mike

_________________
"NO FEAR" - If you have no fear you did not go as fast as you could have !!!

Kolb MK-III Xtra, 912-S

slyck(at)frontiernet.net
Guest

Posted: Sat May 30, 2009 5:44 pm Post subject: WRT M3X prop boom measurements.

Ideally an Ultrastar should have the prop rotating around the boom  

tube.  Take a nice big bearing......

BB



On 30, May 2009, at 8:22 PM, JetPilot wrote:



 	  Quote: 	
		   



 For a slow flying plane like a Kolb, a larger diameter prop is far  

 more efficient and provides more thrust.  As you make the prop disc  

 smaller, the velocity of the air that you need to move becomes  

 faster... A Kolb can not take advantage of High Velocity thrust.   

 Imagine putting a small jet engine on a Kolb, you would be using a  

 huge amount of power and fuel just to cruise at 80 MPH.  It is an  

 extreme example, but its the same thing as putting a small prop  

 that depended on high velocity air on a Kolb, you would need about  

 200 HP to get the same performance as we get with our large  

 diameter props.



 A helicopter rotor is just a large prop that is very large diameter  

 and optimized for slow speeds ( Lifting ).  An R-22 will have more  

 thrust than weight with just 160 HP and fly...  If you took that  

 same 160 HP engine on a helicopter and put a small high speed prop  

 on it instead of a rotor, it would not even come close to lifting  

 it on the ground.  On the same token, the helicopter rotor would  

 not fly very fast mounted on the front of a Cirrus or other high  

 speed plane.



 The idea of getting the thrust line much lower would be great, but  

 it is not practical with this type of airplane.  You would need so  

 much extra power to compensate for the small diameter high speed  

 optimized propeller that you would create more problems than you  

 would solve.  There has been a lot of experimentation with props  

 and thrust lines on pushers, and what we have now as about as good  

 as a compromise that you will get.  Again, if it were as easy as  

 adding prop blades, and lowering the thrust line closer to the CG  

 of the airplane, it would make a much nicer flying airplane, and it  

 would have been done long ago.



 Mike



 --------

 &quot;NO FEAR&quot; -  If you have no fear you did not go as fast  

 as you could have !!!



 Kolb MK-III Xtra, 912-S





 Read this topic online here:



 http://forums.matronics.com/viewtopic.php?p 46074#246074

Dana

Joined: 13 Dec 2007
Posts: 1047
Location: Connecticut, USA

Posted: Sat May 30, 2009 7:03 pm Post subject: WRT M3X prop boom measurements.

At 09:42 PM 5/30/2009, robert bean wrote:



 	  Quote: 	
		  Ideally an Ultrastar should have the prop rotating around the boom

tube.  Take a nice big bearing......


	


Y'know, I've thought of that.  Suitable bearings _are_ available (I 

checked).  Replacing the redrive belt would be quite a procedure, though...



-Dana

--

  We wonder why the dogs always drink out of our toilets, but look at it 

from their point of view: why do humans keep peeing into their water bowls?

captainron1(at)cox.net
Guest

Posted: Sat May 30, 2009 7:27 pm Post subject: WRT M3X prop boom measurements.

See this is the thing I don't understand about the idea that a larger prop is more efficient. If say (  and its better if we use numbers as then we have a hard baseline) 55 inch blade. The 55 inch blade lets for the heck of it say six blades has a total  effective surface area which may be larger than three blades of say 72 inches.

Furthermore if the tips of the props remain under .8 mach ( which they will) and the prop is near its Ld / Max, where in the world a three blader will be better ( we are rich so money is not a limit ).



Its like the gears in a car, it will do 70 miles an hour as long as you get the rght amount of HP to the wheels, be the wheels 20 inch rims or be the wheels 13 inch rims with taller gearing at the same RPM  (more blades roughly speaking 35% more blades)  output at the crank. Not exactly aples to aples but close enough for us. 



---- JetPilot <orcabonita(at)hotmail.com> wrote: 



=============




For a slow flying plane like a Kolb, a larger diameter prop is far more efficient and provides more thrust.  As you make the prop disc smaller, the velocity of the air that you need to move becomes faster... A Kolb can not take advantage of High Velocity thrust.  Imagine putting a small jet engine on a Kolb, you would be using a huge amount of power and fuel just to cruise at 80 MPH.  It is an extreme example, but its the same thing as putting a small prop that depended on high velocity air on a Kolb, you would need about 200 HP to get the same performance as we get with our large diameter props.



A helicopter rotor is just a large prop that is very large diameter and optimized for slow speeds ( Lifting ).  An R-22 will have more thrust than weight with just 160 HP and fly...  If you took that same 160 HP engine on a helicopter and put a small high speed prop on it instead of a rotor, it would not even come close to lifting it on the ground.  On the same token, the helicopter rotor would not fly very fast mounted on the front of a Cirrus or other high speed plane.



The idea of getting the thrust line much lower would be great, but it is not practical with this type of airplane.  You would need so much extra power to compensate for the small diameter high speed optimized propeller that you would create more problems than you would solve.  There has been a lot of experimentation with props and thrust lines on pushers, and what we have now as about as good as a compromise that you will get.  Again, if it were as easy as adding prop blades, and lowering the thrust line closer to the CG of the airplane, it would make a much nicer flying airplane, and it would have been done long ago.



Mike



--------

&quot;NO FEAR&quot; -  If you have no fear you did not go as fast as you could have !!!



Kolb MK-III Xtra, 912-S





Read this topic online here:



http://forums.matronics.com/viewtopic.php?p 46074#246074



--

kugelair.com

Dana

Joined: 13 Dec 2007
Posts: 1047
Location: Connecticut, USA

Posted: Sat May 30, 2009 8:05 pm Post subject: WRT M3X prop boom measurements.

At 11:25 PM 5/30/2009, Ron wrote:



 	  Quote: 	
		  See this is the thing I don't understand about the idea that a larger prop 

is more efficient. If say (  and its better if we use numbers as then we 

have a hard baseline) 55 inch blade. The 55 inch blade lets for the heck 

of it say six blades has a total  effective surface area which may be 

larger than three blades of say 72 inches...


	


There are several aspects to this.



First, a prop creates thrust by increasing the speed of air passing through 

it.  It's more efficient to accelerate a lot of air a little bit than to 

accelerate a little bit of air a lot.  Thus a larger prop is better.



Second, there are tip losses, just like a wing.  A higher aspect ratio wing 

is more efficient (look at a sailplane).



Third, the closer together the blades are, the more each blade is operating 

in the air disturbed by the previous blade.  This causes inefficiency in 

the same way that a biplane is less efficient than a monoplane.



The ONLY reason for more than two blades is if you don't have enough room 

for a 2 blade prop that can absorb all the engine's power, or if it's 

turning too fast so that you get tip losses due to sonic effects and you 

can't increase the reduction ratio.



-Dana

--

  Ethernet (n): something used to catch the etherbunny

robcannon

Joined: 22 Jun 2008
Posts: 39
Location: British Columbia

Posted: Sat May 30, 2009 8:36 pm Post subject: Re: WRT M3X prop boom measurements.

A very good parallel for understanding the prop diameter / efficiency thing is to look at a tug boat prop.  A tug has a huge diameter slow turning propeller which is what it takes to produce alot of thrust, as opposed to a speedboat's small prop turning very fast to achieve high speeds.  I think it's fairly obvious that you need diameter to move alot of water or air, and create thrust. Hence, if you are limited in diameter, you will be giving up some thrust.  

  I hope that helps, Rob

russ(at)rkiphoto.com
Guest

Posted: Sun May 31, 2009 3:13 am Post subject: WRT M3X prop boom measurements.

BB , I like your thinking! -- long as you didn't take off or land,  

you'd be fine.

But I wonder about gyroscopic & P-forces??

do not archive

On May 30, 2009, at 9:42 PM, robert bean wrote:



 	  Quote: 	
		   



 Ideally an Ultrastar should have the prop rotating around the boom  

 tube.  Take a nice big bearing......

 BB



 On 30, May 2009, at 8:22 PM, JetPilot wrote:



> 

>

> For a slow flying plane like a Kolb, a larger diameter prop is far  

> more efficient and provides more thrust.  As you make the prop  

> disc smaller, the velocity of the air that you need to move  

> becomes faster... A Kolb can not take advantage of High Velocity  

> thrust.  Imagine putting a small jet engine on a Kolb, you would  

> be using a huge amount of power and fuel just to cruise at 80  

> MPH.  It is an extreme example, but its the same thing as putting  

> a small prop that depended on high velocity air on a Kolb, you  

> would need about 200 HP to get the same performance as we get with  

> our large diameter props.

>

> A helicopter rotor is just a large prop that is very large  

> diameter and optimized for slow speeds ( Lifting ).  An R-22 will  

> have more thrust than weight with just 160 HP and fly...  If you  

> took that same 160 HP engine on a helicopter and put a small high  

> speed prop on it instead of a rotor, it would not even come close  

> to lifting it on the ground.  On the same token, the helicopter  

> rotor would not fly very fast mounted on the front of a Cirrus or  

> other high speed plane.

>

> The idea of getting the thrust line much lower would be great, but  

> it is not practical with this type of airplane.  You would need so  

> much extra power to compensate for the small diameter high speed  

> optimized propeller that you would create more problems than you  

> would solve.  There has been a lot of experimentation with props  

> and thrust lines on pushers, and what we have now as about as good  

> as a compromise that you will get.  Again, if it were as easy as  

> adding prop blades, and lowering the thrust line closer to the CG  

> of the airplane, it would make a much nicer flying airplane, and  

> it would have been done long ago.

>

> Mike

>

> --------

> &quot;NO FEAR&quot; -  If you have no fear you did not go as fast  

> as you could have !!!

>

> Kolb MK-III Xtra, 912-S

>

>

> Read this topic online here:

>

> http://forums.matronics.com/viewtopic.php?p 46074#246074

>

>

slyck(at)frontiernet.net
Guest

Posted: Sun May 31, 2009 5:53 am Post subject: WRT M3X prop boom measurements.

Link belt

On 30, May 2009, at 10:59 PM, Dana Hague wrote:

 	  Quote: 	

 At 09:42 PM 5/30/2009, robert bean wrote:

> Ideally an Ultrastar should have the prop rotating around the boom

> tube.  Take a nice big bearing......

 Y'know, I've thought of that.  Suitable bearings _are_ available (I  

 checked).  Replacing the redrive belt would be quite a procedure,  

 though...

 -Dana

 --

  We wonder why the dogs always drink out of our toilets, but look  

 at it from their point of view: why do humans keep peeing into  

 their water bowls?

captainron1(at)cox.net
Guest

Posted: Sun May 31, 2009 8:37 am Post subject: WRT M3X prop boom measurements.

"First, a prop creates thrust by increasing the speed of air passing through 

it.  It's more efficient to accelerate a lot of air a little bit than to 

accelerate a little bit of air a lot.  Thus a larger prop is better. "

============== above is a quote==============

that's actually incorrect, it may be correct if we were talking about a Rocket motor or say a Turbo Jet but not a conventional propeller. The propulsion that a prop creates is directly proportional to how much lift the prop airfoil creates. Now if you look at the mechanic of lift you will see that to top of the prop creates a low pressure area. the air movement that you notice as the prop blast is to a large extent a stream of onrushing air filling in the low pressure area that the blades created. It can be accomplished by a large blade or many small blades. In fact the many small blades are way better at creating a vacuum in front of the propeller than a fewer blades attempting the same thing. This is not an opinion this is a fact of aerodynamics ( all else being equal ).

I sense that people have some problems in letting go of some constants in their minds, one of them is notion that a large because its large creates more propulsive force than an equally sized volume disc with multiple blades. Anyway I really gave out more information then I want, since who knows I may want to have a Kolb Air Race and I want to compete against the folks who hold a different concept.

slyck(at)frontiernet.net
Guest

Posted: Sun May 31, 2009 8:47 am Post subject: WRT M3X prop boom measurements.

I want a front row seat.

BB

On 31, May 2009, at 12:36 PM, Ron wrote:



 	  Quote: 	
		   



 "First, a prop creates thrust by increasing the speed of air  

 passing through

 it.  It's more efficient to accelerate a lot of air a little bit  

 than to

 accelerate a little bit of air a lot.  Thus a larger prop is better. "

 ============== above is a quote==============

 that's actually incorrect, it may be correct if we were talking  

 about a Rocket motor or say a Turbo Jet but not a conventional  

 propeller. The propulsion that a prop creates is directly  

 proportional to how much lift the prop airfoil creates. Now if you  

 look at the mechanic of lift you will see that to top of the prop  

 creates a low pressure area. the air movement that you notice as  

 the prop blast is to a large extent a stream of onrushing air  

 filling in the low pressure area that the blades created. It can be  

 accomplished by a large blade or many small blades. In fact the  

 many small blades are way better at creating a vacuum in front of  

 the propeller than a fewer blades attempting the same thing. This  

 is not an opinion this is a fact of aerodynamics ( all else being  

 equal ).

 I sense that people have some problems in letting go of some  

 constants in their minds, one of them is notion that a large  

 because its large creates more propulsive force than an equally  

 sized volume disc with multiple blades. Anyway I really gave out  

 more information then I want, since who knows I may want to have a  

 Kolb Air Race and I want to compete against the folks who hold a  

 different concept.

captainron1(at)cox.net
Guest

Posted: Sun May 31, 2009 8:47 am Post subject: WRT M3X prop boom measurements.

I don't know about that,,,,, .

 I just did a quick Google search for boat props and most of them are at least 4 blades, and their cross section support 100% just what I'v been saying all along. Submarine props are very much multi blade props, they almost look like the Propjets from the 80's.

---- robcannon <leecannon(at)telus.net> wrote: 



=============




A very good parallel for understanding the prop diameter / efficiency thing is to look at a tug boat prop.  A tug has a huge diameter slow turning propeller which is what it takes to produce alot of thrust, as opposed to a speedboat's small prop turning very fast to achieve high speeds.  I think it's fairly obvious that you need diameter to move alot of water or air, and create thrust. Hence, if you are limited in diameter, you will be giving up some thrust.  

  I hope that helps, Rob





Read this topic online here:



http://forums.matronics.com/viewtopic.php?p 46096#246096



--

kugelair.com

Display posts from previous:

	Matronics Email Lists Forum Index -> Kolb-List	All times are GMT - 8 Hours Goto page 1, 2, 3, 4 Next
Page 1 of 4

Jump to:

You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum