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stuart(at)harnerfarm.net
Guest

Posted: Thu Aug 28, 2014 12:42 pm Post subject: pitch?

Hi,

 

My Warp Drive prop (3 blade- 60”) arrived yesterday and I am getting ready to set it up.  It is going on my Firefly with a Rotax 447 (single carb),B-Gearbox with 2.58 ratio.

 

Is anyone running this same setup?

 

What amount of pitch do you think I should start with?

 

Do I shoot for 6500 or 6800 RPM static?

 

Just waiting for muffler mount and engine instruments so I can do the final assembly.

 

Getting anxious!

 

Thanks in advance,

 

Stuart

  [quote][b]

John Hauck

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

Posted: Thu Aug 28, 2014 1:04 pm Post subject: pitch?

If I was flying it, I would prop it to bump 6,500 rpm, wide open throttle, straight and level flight.  Without looking for the book, I think the 447 is rated at 6,500 rpm max continuous.  6,800 rpm is like military power, can only be run at that speed for 5 minutes max.  If you had an in flight adjustable prop you could pitch to turn 6,800 rpm, but a ground adjustable prop works best propped as described above.

 

I don't know what static rpm would be, probably 6,300.  Been too many years since I had a 447 on my FS.

 

john h

mkIII

Titus, Alabama

 

From: owner-kolb-list-server(at)matronics.com [mailto:owner-kolb-list-server(at)matronics.com] On Behalf Of Stuart Harner

Sent: Thursday, August 28, 2014 3:41 PM

To: kolb-list(at)matronics.com

Subject: pitch?

 

Hi,

 

My Warp Drive prop (3 blade- 60”) arrived yesterday and I am getting ready to set it up.  It is going on my Firefly with a Rotax 447 (single carb),B-Gearbox with 2.58 ratio.

 

Is anyone running this same setup?

 

What amount of pitch do you think I should start with?

 

Do I shoot for 6500 or 6800 RPM static?

 

Just waiting for muffler mount and engine instruments so I can do the final assembly.

 

Getting anxious!

 

Thanks in advance,

 

Stuart[quote]  [b]

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

beauford173(at)tampabay.r
Guest

Posted: Thu Aug 28, 2014 2:03 pm Post subject: pitch?

Brother Harner:

 

Cannot speak directly to the Warp… Mine has a 66 inch IVO… But load is load.  That said, I would suspect that anything over

6100 or 6150 static might  be a tad skinny on loading.  When I set 6150 static WOT, I get easy 6600 in level flight WOT.

Personally fer me, that is about enough. 6800 static would be like an argument with my first wife… makes my few remaining teeth hurt. 

(how mad are you at your bearings…?)

 

Worth What Ye Paid Fer It…

 

beauford

FF-076

Brandon, FL

 

 

From: owner-kolb-list-server(at)matronics.com [mailto:owner-kolb-list-server(at)matronics.com] On Behalf Of Stuart Harner

Subject: pitch?

 

What amount of pitch do you think I should start with?

 

Do I shoot for 6500 or 6800 RPM static?

 

Stuart 	  Quote: 	
		   	


  [quote][b]

t41pilot

Joined: 05 Sep 2011
Posts: 38
Location: Howard City, Michigan

Posted: Thu Aug 28, 2014 4:03 pm Post subject: Re: pitch?

I'm running a 447 on my firefly with a 60 inch IVO prop. 6500 WOT is by the book and typically 200 RPM less static on the ground would yield whatever WOT setting you are looking for.  That being said, I have found from a lot of reading on the subject that not all 447's are going to run identically. You should dial in your prop to whatever setting makes your CHT and EGT fall within the normal operating range during flight conditions.

On my particular engine that ended up being 6000 static and 6300 WOT. It took a few flights to get that figured out. Definitely 6800 WOT is too much. I would start at 61 or 62 static and see how she goes. Add more pitch if the EGT is too high.  Fiddling with carb jets to get the temps right can lead to a vicious circle of prop pitch changes and wrong conclusions. I did end up with my clip set rich and one size larger on my main jet but in most cases the stock size jets should work.

_________________
Gregg Kaat
2011 Firefly

Richard Pike

Joined: 09 Jan 2006
Posts: 1670
Location: Blountville, Tennessee

Posted: Thu Aug 28, 2014 5:48 pm Post subject: Re: pitch?

What John & the others said. Let me add a few remarks from my own experience: leave the jets alone and fine tune the EGT with prop pitch. When the pitch is ideal, your EGT's will stay roughly between 1050 & 1150 at any typical in-flight throttle setting except WOT, where they will be 1000-1050. As the EGT rises and falls from summer to winter, once again, leave the jets alone and add or remove pitch. 



I marked this on my Ivo hub abut 3 years ago, so the arrows are a bit faded, but coarse is one way, fine is the other. Takes less than 2 minutes, usually a half a turn is enough.

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_________________
Richard Pike
Kolb MKIII N420P (420ldPoops)
Kingsport, TN 3TN0

Forgiving is tough, being forgiven is wonderful, and God's grace really is amazing.

John Hauck

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

Posted: Thu Aug 28, 2014 6:05 pm Post subject: pitch?

If I remember correctly, ROTAX sets up their two strokes, before they leave

the factory, for operation from sea level to 3000 feet on a 70F day.  It has

the correct heat range spark plugs and is jetted correctly.  It will run

perfect right out of the box.



It is up to the operator to load the prop correctly.  Do it by pitch

adjustment and leave the engine alone.



My experience with two stroke aircraft engines, which are continuous duty

engines, is WOT, straight and level flight, just bump the red line, 6500

rpm.  I discovered if I set up the engine this way, my EGTs would be right

in the green.  Loading and unloading the prop by changing pitch attitude

also affects EGTs, but temporarily.  EGTs can be controlled with throttle

settings.



This info is nothing new.  We have been doing it this way since 1984, and

others long before me.



john h

mkIII

Titus, Alabama



 

What John & the others said. Let me add a few remarks from my own

experience: leave the jets alone and fine tune the EGT with prop pitch. When

the pitch is ideal, your EGT's will stay roughly between 1050 & 1150 at any

typical in-flight throttle setting except WOT, where they will be 1000-1050.

As the EGT rises and falls from summer to winter, once again, leave the jets

alone and add or remove pitch. 



I marked this on my Ivo hub abut 3 years ago, so the arrows are a bit faded,

but coarse is one way, fine is the other. Takes less than 2 minutes, usually

a half a turn is enough.



--------

Richard Pike

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

rickofudall

Joined: 19 Sep 2009
Posts: 1392
Location: Udall, KS, USA

Posted: Fri Aug 29, 2014 3:35 pm Post subject: pitch?

Stuart, As long as you're in the ballpark it will be okay. If, after first setting, you find the engine is winding out and EGT is running hot, put in more pitch. On the other hand if it's a bit boggy, doesn't rev up and the CHT's are running hot, take a little pitch out. Somewhere around John's or Beauford's recommendation should be the Goldilocks setting. Good luck and have fun.

Rick Girard



On Thu, Aug 28, 2014 at 5:03 PM, Beauford <beauford173(at)tampabay.rr.com (beauford173(at)tampabay.rr.com)> wrote:

  	  Quote: 	
		  

Brother Harner: 

 

Cannot speak directly to the Warp… Mine has a 66 inch IVO… But load is load.  That said, I would suspect that anything over 

6100 or 6150 static might  be a tad skinny on loading.  When I set 6150 static WOT, I get easy 6600 in level flight WOT.

Personally fer me, that is about enough. 6800 static would be like an argument with my first wife… makes my few remaining teeth hurt.  

(how mad are you at your bearings…?)

 

Worth What Ye Paid Fer It… 

 

beauford

FF-076 

Brandon, FL

 

  

From: owner-kolb-list-server(at)matronics.com (owner-kolb-list-server(at)matronics.com) [mailto:owner-kolb-list-server(at)matronics.com (owner-kolb-list-server(at)matronics.com)] On Behalf Of Stuart Harner

 Subject: pitch?

 

What amount of pitch do you think I should start with?

  

Do I shoot for 6500 or 6800 RPM static?

 



Stuart 	  Quote: 	
		    	
 

   	  Quote: 	
		  



get="_blank">http://www.matronics.com/Navigator?Kolb-List

tp://forums.matronics.com

_blank">http://www.matronics.com/contribution



	




	




-- 

Zulu Delta

Mk IIIC

Thanks, Homer GBYM

It isn't necessary to have relatives in Kansas City in order to be unhappy.

   - Groucho Marx

 

  [quote][b]

_________________
The smallest miracle right in front of you is enough to make you happy....

stuart(at)harnerfarm.net
Guest

Posted: Fri Aug 29, 2014 4:51 pm Post subject: pitch?

Thanks everyone for the replies.

 

Any idea where I should start, maybe 10°?

 

Stuart

 

From: owner-kolb-list-server(at)matronics.com [mailto:owner-kolb-list-server(at)matronics.com] On Behalf Of Richard Girard

Sent: Friday, August 29, 2014 6:35 PM

To: kolb-list(at)matronics.com

Subject: Re: pitch?

 

Stuart, As long as you're in the ballpark it will be okay. If, after first setting, you find the engine is winding out and EGT is running hot, put in more pitch. On the other hand if it's a bit boggy, doesn't rev up and the CHT's are running hot, take a little pitch out. Somewhere around John's or Beauford's recommendation should be the Goldilocks setting.

Good luck and have fun.



 



Rick Girard

 

On Thu, Aug 28, 2014 at 5:03 PM, Beauford <beauford173(at)tampabay.rr.com (beauford173(at)tampabay.rr.com)> wrote:

Brother Harner:

 

Cannot speak directly to the Warp… Mine has a 66 inch IVO… But load is load.  That said, I would suspect that anything over

6100 or 6150 static might  be a tad skinny on loading.  When I set 6150 static WOT, I get easy 6600 in level flight WOT.

Personally fer me, that is about enough. 6800 static would be like an argument with my first wife… makes my few remaining teeth hurt. 

(how mad are you at your bearings…?)

 

Worth What Ye Paid Fer It…

 

beauford

FF-076

Brandon, FL

 

 

From: owner-kolb-list-server(at)matronics.com (owner-kolb-list-server(at)matronics.com) [mailto:owner-kolb-list-server(at)matronics.com (owner-kolb-list-server(at)matronics.com)] On Behalf Of Stuart Harner

Subject: pitch?

 

What amount of pitch do you think I should start with?

 

Do I shoot for 6500 or 6800 RPM static?

 



Stuart 	  Quote: 	
		   	


 	  Quote: 	
		    get="_blank">http://www.matronics.com/Navigator?Kolb-Listtp://forums.matronics.com_blank">http://www.matronics.com/contribution 	




 



-- 

Zulu Delta



Mk IIIC



Thanks, Homer GBYM



 



It isn't necessary to have relatives in Kansas City in order to be unhappy.

  - Groucho Marx



 



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  [quote][b]

jbhart(at)onlyinternet.ne
Guest

Posted: Sat Aug 30, 2014 6:02 am Post subject: pitch?

 	  Quote: 	
		   

From: owner-kolb-list-server(at)matronics.com [mailto:owner-kolb-list-server(at)matronics.com] 
	


Sent: Thursday, August 28, 2014 3:41 PM



Hi,



My Warp Drive prop (3 blade- 60) arrived yesterday and I am getting ready to 

set it up.  It is going on my Firefly with a Rotax 447 (single carb), 

B-Gearbox with 2.58 ratio.

.......................

 	  Quote: 	
		  


	


Stuart,



I hope you have considered the following:



The B gearbox is rated for a max moment of inertia of 1025 lb-in squared or 

3000 kg-cm squared.



Ultralight News of Canada found the three blade Warp prop exceeded these numbers.



See: http://www.ultralightnews.ca/articles/driveselection.htm



Warp Drive should be able to tell you the moment of inertia of your propeller.  

Or, the above site can direct you to a Rotax Service Bulletin that explains 

how to determine the moment of inertia of your prop.



Jack B. Hart FF004

Winchester, IN

stuart(at)harnerfarm.net
Guest

Posted: Sat Aug 30, 2014 8:04 am Post subject: pitch?

Jack,



Some  others have raised that issue.  I was aware of the MOI limits on

gearboxes and quizzed Darrell at Warp Drive before I ordered the prop.  He

assured me it would be OK, but had no hard numbers for me.



Now I am beginning to wonder if I was fooled by a salesman.  



I can easily set up and run the MOI tests myself to get the true answer, but

I suspect I am not going to like it.



Options are buy a new milled aluminum hub, but that is saving all the weight

at the center, which won't help the MOI much.  I could convert to a two

blade hub, but the 60" is probably not able to put enough load on the engine

at any kind of a reasonable pitch.



I wanted to check out the Power Fin props at OSH, but could not find them on

the field nor in the list of vendors.



Now what I am going to say next is strictly personal and is NOT meant to

start any flame wars over props:



I know Travis recommends the IVO, but for me they are not an option due to

other's experiences.  End of story, no more gas for the flames.

I have a good regard for the Warp Drives, related to the above sentence,

again, no more gas.



I am completely open to any other prop that gets the job done that is

reasonably priced.  



I don't care about looks, but am concerned about vibration, price and noise,

but of course they have to take a back seat to proper application.



Some things I have read and conversations I have had led me to think that

the 3 blade would be a better choice as it would be smoother and quieter

than a 2 blade.  I also liked the idea of a lower overall folded size (my

hanger/trailer situation came into play here).



Anybody want to buy a new prop that has not even had the bolts torqued down?



Not the first stupid thing I have done, probably not the last either.....



Stuart



--

rowedenny

Joined: 09 Mar 2008
Posts: 338
Location: Western PA

Posted: Sat Aug 30, 2014 9:53 am Post subject: pitch?

I would think that the shorter blades of your 60"prop would drastically reduce it's inertia. Also if it's a tapered tip that would also make it lighter. 

Most Kolb props are 66-72" dia.



Dennis "Skid" Rowe

Mk3, Rotax 670, 

Leechburg, PA



[quote] On Aug 30, 2014, at 12:03 PM, "Stuart Harner" <stuart(at)harnerfarm.net> wrote:

 

 

 

 Jack,

 

 Some  others have raised that issue.  I was aware of the MOI limits on

 gearboxes and quizzed Darrell at Warp Drive before I ordered the prop.  He

 assured me it would be OK, but had no hard numbers for me.

 

 Now I am beginning to wonder if I was fooled by a salesman.  

 

 I can easily set up and run the MOI tests myself to get the true answer, but

 I suspect I am not going to like it.

 

 Options are buy a new milled aluminum hub, but that is saving all the weight

 at the center, which won't help the MOI much.  I could convert to a two

 blade hub, but the 60" is probably not able to put enough load on the engine

 at any kind of a reasonable pitch.

 

 I wanted to check out the Power Fin props at OSH, but could not find them on

 the field nor in the list of vendors.

 

 Now what I am going to say next is strictly personal and is NOT meant to

 start any flame wars over props:

 

 I know Travis recommends the IVO, but for me they are not an option due to

 other's experiences.  End of story, no more gas for the flames.

 I have a good regard for the Warp Drives, related to the above sentence,

 again, no more gas.

 

 I am completely open to any other prop that gets the job done that is

 reasonably priced.  

 

 I don't care about looks, but am concerned about vibration, price and noise,

 but of course they have to take a back seat to proper application.

 

 Some things I have read and conversations I have had led me to think that

 the 3 blade would be a better choice as it would be smoother and quieter

 than a 2 blade.  I also liked the idea of a lower overall folded size (my

 hanger/trailer situation came into play here).

 

 Anybody want to buy a new prop that has not even had the bolts torqued down?

 

 Not the first stupid thing I have done, probably not the last either.....

 

 Stuart

 

 --

John Hauck

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

Posted: Sat Aug 30, 2014 12:00 pm Post subject: pitch?

Daryl Heineman, President of Warp Drive, is probably the salesman you are

referring to that sold you the prop.   Normally, he is the only one selling

them.  Good man.  Knowledgeable when it comes to Warp Drive Props and engine

combos.



I've flown with Warp, and done business with them, for 21 years.  Tested

them, unintentionally, to the max.  They always come through and get me back

home.



I don't know what kind of flying you will be doing, but doubt you will ever

be able to over stress your gear box with this prop and a FS????



Daryl was not trying to fool you, I am sure.



I'd fly that combo.



My experience and opinion only.  Don't try this at home.



john h

mkIII

Titus, Alabama



--

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

rickofudall

Joined: 19 Sep 2009
Posts: 1392
Location: Udall, KS, USA

Posted: Sat Aug 30, 2014 3:07 pm Post subject: pitch?

Stuart, Before you get rid of your WD prop, know this. Most of the MOI problems on "B" gearboxes come from trying to make the engine idle at too low an RPM. Doing this beats up the dogs and wears out the spring washers in the gearbox. Just keep the RPM at idle at 2000 or more and you'll be just fine. You have one more option before you dump the prop. Have the blades tapered. It's going to mean putting another $200 or so dollars into the prop but tapering the blades gets rid of mass on the blade tips where you get some good out of it.

 My 2 cents, your $200 bucks if you decide to do it. 

Rick Girard



On Sat, Aug 30, 2014 at 2:59 PM, John Hauck <jhauck(at)elmore.rr.com (jhauck(at)elmore.rr.com)> wrote:

 [quote]--> Kolb-List message posted by: "John Hauck" <jhauck(at)elmore.rr.com (jhauck(at)elmore.rr.com)>

  

 Daryl Heineman, President of Warp Drive, is probably the salesman you are

 referring to that sold you the prop.   Normally, he is the only one selling

 them.  Good man.  Knowledgeable when it comes to Warp Drive Props and engine

 combos.

 

 I've flown with Warp, and done business with them, for 21 years.  Tested

 them, unintentionally, to the max.  They always come through and get me back

 home.

 

 I don't know what kind of flying you will be doing, but doubt you will ever

 be able to over stress your gear box with this prop and a FS????

 

 Daryl was not trying to fool you, I am sure.

 

 I'd fly that combo.

 

 My experience and opinion only.  Don't try this at home.

 

 john h

 mkIII

 Titus, Alabama

 

 

 

 --

_________________
The smallest miracle right in front of you is enough to make you happy....

stuart(at)harnerfarm.net
Guest

Posted: Sat Aug 30, 2014 4:47 pm Post subject: pitch?

John,



That was the exact impression I had, and the reason I did not question it

any further.  Seemed like he knew the plane, the engine and the gearbox.  I

did not get the "used car salesman" red flag.



I really did not give it much extra thought until some replies to my

starting pitch angle came back, indicating that this combo would not work.

The numbers back this up, Rotax did not put the limits in the book just for

the heck of it.



However, no one has replied that Yes, they are running this combination and

it is fine.  The flip side of that is no one has said "I tried that and it

tore up my gearbox", only some have warned that it would not work, according

to the numbers.



So, it would seem that it all comes down to whether I want to try it or not.



I have been doing some research on this subject today, some of it I did not

understand.  I like physics, but am not very good at it.



To me, a heavier prop (flywheel) would help smooth out the pulses of

combustion, at the expense of quick throttle response.  It seems to me that

a lighter prop would speed up and slow down "faster" so that it would

"hammer" the gears more.  More rotational mass (MOI) would be slower to

reach a set speed, but would also tend to continue rotating at that speed

(minus the drag of producing thrust) therefore carrying the inertia into the

next combustion pulse.  To me this should dampen the "hammering of the gears

effect".  Maybe I just don't "get it".



Something else I find interesting is that the Rotax manual warns never to

run the engine without a prop (load) as it will damage the gearbox.  They

give a max MOI, but wouldn't there also be a minimum MOI?



Maybe I am fretting over nothing.  Maybe I should bolt it on and fly!



I value EVERYONE's input, and thank you one and all.



Stuart

P.S. I still haven't heard a suggested starting pitch angle....



--

rickofudall

Joined: 19 Sep 2009
Posts: 1392
Location: Udall, KS, USA

Posted: Sat Aug 30, 2014 5:19 pm Post subject: pitch?

Stuart, I'm re-posting this response just in case it didn't come through. And I'm going to add something after.Before you get rid of your WD prop, know this. Most of the MOI problems on "B" gearboxes come from trying to make the engine idle at too low an RPM. Doing this beats up the dogs and wears out the spring washers in the gearbox. Just keep the RPM at idle at 2000 or more and you'll be just fine. You have one more option before you dump the prop. Have the blades tapered. It's going to mean putting another $200 or so dollars into the prop but tapering the blades gets rid of mass on the blade tips where you get some good out of it.

 My 2 cents, your $200 bucks if you decide to do it. 

 Rick Girard



In the winter of 2006, hot out of LSARM training I built a rig and did the rotational inertia per Rotax Service Instruction 11 UL 91E published December of 1992 (attached). At the time I had six props for various aircraft in the shop. As I recall only the wood two blade that came with my Firestar passed and being of multi-laminate constuction only did barely. Jimmy Young also did tests on two props, a WD and an IVO if memory serves. Both were three blade props.

 Anyway, I stand by the recommendations above.

I know I'm not alone in recommending WD props for one simple reason. They are great at holding up to the trials and tribulations of the pusher configuration. I put an AN 6 bolt through a Warp and didn't even know it until I landed. I put a cheap pair of bifocals through the Power Fin on my trike and it cost me two new blades.

 



Rick



On Sat, Aug 30, 2014 at 7:47 PM, Stuart Harner <stuart(at)harnerfarm.net (stuart(at)harnerfarm.net)> wrote:

 [quote]--> Kolb-List message posted by: "Stuart Harner" <stuart(at)harnerfarm.net (stuart(at)harnerfarm.net)>

  

 John,

 

 That was the exact impression I had, and the reason I did not question it

 any further.  Seemed like he knew the plane, the engine and the gearbox.  I

 did not get the "used car salesman" red flag.

 

 I really did not give it much extra thought until some replies to my

 starting pitch angle came back, indicating that this combo would not work.

 The numbers back this up, Rotax did not put the limits in the book just for

 the heck of it.

 

 However, no one has replied that Yes, they are running this combination and

 it is fine.  The flip side of that is no one has said "I tried that and it

 tore up my gearbox", only some have warned that it would not work, according

 to the numbers.

 

 So, it would seem that it all comes down to whether I want to try it or not.

 

 I have been doing some research on this subject today, some of it I did not

 understand.  I like physics, but am not very good at it.

 

 To me, a heavier prop (flywheel) would help smooth out the pulses of

 combustion, at the expense of quick throttle response.  It seems to me that

 a lighter prop would speed up and slow down "faster" so that it would

 "hammer" the gears more.  More rotational mass (MOI) would be slower to

 reach a set speed, but would also tend to continue rotating at that speed

 (minus the drag of producing thrust) therefore carrying the inertia into the

 next combustion pulse.  To me this should dampen the "hammering of the gears

 effect".  Maybe I just don't "get it".

 

 Something else I find interesting is that the Rotax manual warns never to

 run the engine without a prop (load) as it will damage the gearbox.  They

 give a max MOI, but wouldn't there also be a minimum MOI?

 

 Maybe I am fretting over nothing.  Maybe I should bolt it on and fly!

 

 I value EVERYONE's input, and thank you one and all.

 

 Stuart

 P.S. I still haven't heard a suggested starting pitch angle....

 

 --

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_________________
The smallest miracle right in front of you is enough to make you happy....

stuart(at)harnerfarm.net
Guest

Posted: Sun Aug 31, 2014 5:35 am Post subject: pitch?

Thanks Rick, that helps.

 

This list once again proves what a great bunch of guys make it up.

 

I have sent an email to WD about this and will wait for a reply.  Holiday weekend and all, plus I am on the road for work next week, so it may be a while before I find out what they say.

 

I will let you know what comes of this.

 

Thanks again to everyone!

 

Stuart

 

From: owner-kolb-list-server(at)matronics.com [mailto:owner-kolb-list-server(at)matronics.com] On Behalf Of Richard Girard

Sent: Saturday, August 30, 2014 8:20 PM

To: kolb-list(at)matronics.com

Subject: Re: pitch?

 

Stuart, I'm re-posting this response just in case it didn't come through. And I'm going to add something after.

Before you get rid of your WD prop, know this. Most of the MOI problems on "B" gearboxes come from trying to make the engine idle at too low an RPM. Doing this beats up the dogs and wears out the spring washers in the gearbox. Just keep the RPM at idle at 2000 or more and you'll be just fine.

You have one more option before you dump the prop. Have the blades tapered. It's going to mean putting another $200 or so dollars into the prop but tapering the blades gets rid of mass on the blade tips where you get some good out of it.



My 2 cents, your $200 bucks if you decide to do it. 



 



Rick Girard

 



In the winter of 2006, hot out of LSARM training I built a rig and did the rotational inertia per Rotax Service Instruction 11 UL 91E published December of 1992 (attached). At the time I had six props for various aircraft in the shop. As I recall only the wood two blade that came with my Firestar passed and being of multi-laminate constuction only did barely. Jimmy Young also did tests on two props, a WD and an IVO if memory serves. Both were three blade props.



Anyway, I stand by the recommendations above.



I know I'm not alone in recommending WD props for one simple reason. They are great at holding up to the trials and tribulations of the pusher configuration. I put an AN 6 bolt through a Warp and didn't even know it until I landed. I put a cheap pair of bifocals through the Power Fin on my trike and it cost me two new blades.



 



Rick

 

On Sat, Aug 30, 2014 at 7:47 PM, Stuart Harner <stuart(at)harnerfarm.net (stuart(at)harnerfarm.net)> wrote:

--> Kolb-List message posted by: "Stuart Harner" <stuart(at)harnerfarm.net (stuart(at)harnerfarm.net)>



John,



That was the exact impression I had, and the reason I did not question it

any further.  Seemed like he knew the plane, the engine and the gearbox.  I

did not get the "used car salesman" red flag.



I really did not give it much extra thought until some replies to my

starting pitch angle came back, indicating that this combo would not work.

The numbers back this up, Rotax did not put the limits in the book just for

the heck of it.



However, no one has replied that Yes, they are running this combination and

it is fine.  The flip side of that is no one has said "I tried that and it

tore up my gearbox", only some have warned that it would not work, according

to the numbers.



So, it would seem that it all comes down to whether I want to try it or not.



I have been doing some research on this subject today, some of it I did not

understand.  I like physics, but am not very good at it.



To me, a heavier prop (flywheel) would help smooth out the pulses of

combustion, at the expense of quick throttle response.  It seems to me that

a lighter prop would speed up and slow down "faster" so that it would

"hammer" the gears more.  More rotational mass (MOI) would be slower to

reach a set speed, but would also tend to continue rotating at that speed

(minus the drag of producing thrust) therefore carrying the inertia into the

next combustion pulse.  To me this should dampen the "hammering of the gears

effect".  Maybe I just don't "get it".



Something else I find interesting is that the Rotax manual warns never to

run the engine without a prop (load) as it will damage the gearbox.  They

give a max MOI, but wouldn't there also be a minimum MOI?



Maybe I am fretting over nothing.  Maybe I should bolt it on and fly!



I value EVERYONE's input, and thank you one and all.



Stuart

P.S. I still haven't heard a suggested starting pitch angle....



--

jbhart(at)onlyinternet.ne
Guest

Posted: Sun Aug 31, 2014 1:39 pm Post subject: pitch?

From: "Stuart Harner" <stuart(at)harnerfarm.net>

Date: Sun, 31 Aug 2014 08:34:47 -0500

 	  Quote: 	
		  >>>>>>>>>>>>>>>>>>>>>>

.................

I have been doing some research on this subject today, some of it I did not

understand.  I like physics, but am not very good at it.

To me, a heavier prop (flywheel) would help smooth out the pulses of

combustion, at the expense of quick throttle response.  It seems to me that

a lighter prop would speed up and slow down "faster" so that it would

"hammer" the gears more.  More rotational mass (MOI) would be slower to

reach a set speed, but would also tend to continue rotating at that speed

(minus the drag of producing thrust) therefore carrying the inertia into the

next combustion pulse.  To me this should dampen the "hammering of the gears

effect".  Maybe I just don't "get it".

 	  Quote: 	
		  >>>>>>>>>>>>>>>>>>>>

Stuart,

May be I can help you "get it".

The moment of inertia is the spread of the mass about the center of rotation 

times the radius of gyration squared.

    Take a large hex nut and tie to the end of a string.

    Give it a whirl in the horizontal plane with a short 

    radius and notice the tension in the string and the 

    revolution count.

    Double string length and try to keep the rotation 

    speed the same as before.  

You will find that the string tension more than doubles and the energy you 

have to exert to swing the whole thing goes way up.  In this case the system 

mass "the nut" is constant but as the mass is moved out from the center of 

rotation more torque is required to keep rpm constant.

These represent the loads as seen by the gear box and the crank.  It is 

desirable to have a low inertia propeller so that the propeller can 

accelerate and de accelerate and absorb some of the firing impulse exerted 

on the crank by the piston and connecting rod. This reduces the peak 

oscillatory torque loads in the crank and on the face of the gear 

teeth.

It is some what counter intuitive.  With a lower inert propeller, the 

engine and gearbox will jump around a little more on the mounts.  But 

internally the gear box and crank and piston rod bearing assemblies will be 

operating under lower peak loads while the system is delivering the same hp 

as it would with a higher inertia propeller.

Jack B. Hart FF004

Winchester, IN

baberdk

Joined: 23 Jan 2014
Posts: 53
Location: East Moline, Il

Posted: Tue Sep 02, 2014 12:59 pm Post subject: Re: pitch?

I started at 16 degrees and then adjusted for 6250 rpm static

stuart(at)harnerfarm.net
Guest

Posted: Thu Sep 04, 2014 1:14 pm Post subject: pitch?

Thanks, that is where I will start too.



Stuart

Do not archive



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