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prop tip speed and noise

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Thom Riddle

Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

Posted: Wed Feb 03, 2010 5:16 am Post subject: prop tip speed and noise

This has nothing to do with Ted's rum-rum but rather the amount of noise (db levels) from props. 



I don't know how much of the prop noise one gets in the cabin of a Kolb is due to prop tip speed but believe that the tip speed is a major contributor to it. I normally fly my Slingshot w/ Jabiru 2200A engine at 80 mph which is 2,712 rpm. The 64" diameter prop at this speed has a rotational tip speed of 516 mph plus the advance speed of 80 mph equals 596 mph total tip speed.



My memory (which could be wrong) is that John H normally cruises at similar airspeed at 5,000 rpm with 72" WD prop and 2.43 PSRU which gives a rotational tip speed of about 440 mph plus the 80 mph equals about 520 mph total tip speed. 



Therefore my prop tip speed at normal cruise is about 14-15% higher than John H's. I have no idea how much more noise (db level) that difference makes but do know subjectively that when I fly at an engine speed (<2400 rpm) that produces the same prop tip speed as John H does at cruise, the noise level in my Slingshot is dramatically lower. At 2700 rpm I sometimes have difficulty understanding radio transmissions but no problems at all at 2400 rpm.



We have at least two Kolbers on this list who I think might be able to add something worthwhile to this discussion, if anyone is interested. One is Will Uribe who makes his living doing noise surveys and mitigation at industrial plants. I know he has a db level meter and may be able to tell us something about this from his experience. Then there is Rick Nielsen who originally flew his VW without a PSRU then added the PSRU. I would be interested to see how much difference (if any) the noise level was for him after adding the PSRU and going to a longer prop.



No need to comment on the difference in thrust between direct drive and PSRU drives. We all know that the PSRU increases thrust with larger prop, especially at lower airspeeds. My interest is in perceived or measured noise level differences.

_________________
Thom Riddle
Buffalo, NY (9G0)

Don't worry about old age... it doesn't last very long.
- Anonymous

John Hauck

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

Posted: Wed Feb 03, 2010 6:03 am Post subject: prop tip speed and noise

> I don't know how much of the prop noise one gets in the cabin of a Kolb 

is due to prop tip speed but believe that the tip speed is a major 

contributor to it. I normally fly my Slingshot w/ Jabiru 2200A engine at 80 

mph which is 2,712 rpm. The 64" diameter prop at this speed has a rotational 

tip speed of 516 mph plus the advance speed of 80 mph equals 596 mph total 

tip speed.

 	  Quote: 	
		  

 My memory (which could be wrong) is that John H normally cruises at 

 similar airspeed at 5,000 rpm with 72" WD prop and 2.43 PSRU which gives a 

 rotational tip speed of about 440 mph plus the 80 mph equals about 520 mph 

 total tip speed.



 Therefore my prop tip speed at normal cruise is about 14-15% higher than 

 John H's. I have no idea how much more noise (db level) that difference 

 makes but do know subjectively that when I fly at an engine speed (



 --------

 Thom Riddle


	


I think you fired a round before you were ready.  By the way, I am flying 

with a 71" prop now.  Have flown with 70 and 72" props.  John W flew with a 

68" prop.  Wonder if that helped give him a little more edge on cruise speed 

than me with the larger props?



Every notice how quiet a tractor 912ULS with Warp Drive Taper Tip Prop is 

compared to the same engine and prop on a Kolb?  Same engine, same prop, 

same rpm, but none of the nasty noise we have deal with in our pusher.



Got an idea most of the noise is being produced as the prop blades gnaw away 

at the air as it is disturbed by the engine, wing, flap leading edge, 

inboard end of flap, anything that disturbs the air in front of the prop 

blades.



Only way I know to fix that is protect myself from it.  I don't know how 

else to reduce the noise except convert to tractor configuration.



john hauck

mkIII

titus, alabama

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

jbhart(at)onlyinternet.ne
Guest

Posted: Wed Feb 03, 2010 6:43 am Post subject: prop tip speed and noise

At 05:16 AM 2/3/10 -0800, you wrote:

 	  Quote: 	
		  



This has nothing to do with Ted's rum-rum but rather the amount of noise 

(db levels) from props. 
	


 	  Quote: 	
		  


	


Thom & Kolbers,



Propellor tip shape can be a noise contributor too.  See:



http://jackbhart.com/firefly/firefly100.html



and:



http://jackbhart.com/firefly/firefly111.html



This is a nice way to reduce cockpit noise without adding any weight.



Jack B. Hart FF004

Winchester, IN

lucien

Joined: 03 Jun 2007
Posts: 721
Location: santa fe, NM

Posted: Wed Feb 03, 2010 6:56 am Post subject: Re: prop tip speed and noise

My titan is I think the only plane I've ever flown that was louder inside the plane than my FSII was. Even with the 3.47 C box turning the 68" WD slow, the prop noise in the cockpit was absolutely deafening. I could hardly even hear the cooling fan scream above it. 

There was no extension and the prop blades were only a few inches away from the back of the cage and the TE of the wing. 



Talk about rum-rum..... but vibration-wise it was completely silky smooth and gave really good performance. I just stuffed earplugs in under the headset and turned the radio up as loud as it would go.



Wish I'd had my telex 50-D back then. It's a miracle-worker on noise.



The other titan on the field is configured almost exactly like mine and I can hear him all over town when he's up. he's still audible at the airport when I hear him call the tower that he's made it outside the class D. I've been told I'm also similarly audible from miles away.

We have a Lockwood Aircam with 2 912ULS's based here as well and I can hear him pretty good too.



There're a couple tractor 912 equipped LSA's that fly in here from time to time and they're so quiet they almost sound like they're running electric motors. And one of those has a 3 blade prop.



I think it's that big ol airplane in front of the prop disk that does it for us....



LS

_________________
LS
Titan II SS

robcannon

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

Posted: Wed Feb 03, 2010 7:04 am Post subject: Re: prop tip speed and noise

When I was researching which prop to put on my mark II HKS with a 3:47 gearbox I talked to alot of people about airplane noise.  My goal was to be as quiet as the 85hp fleet canuck (cub like canadian plane), that flies out of my home strip.

   What I learned was that it is a combination of tip speed and pitch which determines noise. (and pusher or tractor) Basically the smaller the "bite"out of the air, each blade takes, the quieter you are.......so, more blades, less diameter, less rpms, = quieter.  I have been told by pretty much everyone that hears my plane that it is the quietest plane they have ever heard......it sounds really nice!!!

  It has a four blade 68 inch powerfin, with the 3;47 gearbox. Does the 912 not have the option for a higher ratio gearbox ?

    Although I realize performance is rather subjective, I am very happy with my combination. Empty weight = 550 lbs  HP = 60  Solo climb = around 1000 fpm. Cruise = faster than vne of 75 mph.

   ...............so, I believe now that Kolbs can be made quiet, with enough money and effort put into them........providing you can slow the prop down.  I'm not sure what the gains would be seen by simply adding more blades with reduced pitch, without slowing the prop down, but I'd love to hear about someone experimenting with that.  

  At the Wallaby ranch in Florida they use Dragonfly ultralights to tow hangliders, and they use two stacked three blade Ivo props, which they say gives them the best combo of quietness and thrust (they dont care about airspeed). cheers, Rob Cannon

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lucien

Joined: 03 Jun 2007
Posts: 721
Location: santa fe, NM

Posted: Wed Feb 03, 2010 7:29 am Post subject: Re: prop tip speed and noise

 	  robcannon wrote: 	
		  When I was researching which prop to put on my mark II HKS with a 3:47 gearbox I talked to alot of people about airplane noise.  My goal was to be as quiet as the 85hp fleet canuck (cub like canadian plane), that flies out of my home strip.

   What I learned was that it is a combination of tip speed and pitch which determines noise. (and pusher or tractor) Basically the smaller the "bite"out of the air, each blade takes, the quieter you are.......so, more blades, less diameter, less rpms, = quieter.  I have been told by pretty much everyone that hears my plane that it is the quietest plane they have ever heard......it sounds really nice!!!

  It has a four blade 68 inch powerfin, with the 3;47 gearbox. Does the 912 not have the option for a higher ratio gearbox ?

    Although I realize performance is rather subjective, I am very happy with my combination. Empty weight = 550 lbs  HP = 60  Solo climb = around 1000 fpm. Cruise = faster than vne of 75 mph.

   ...............so, I believe now that Kolbs can be made quiet, with enough money and effort put into them........providing you can slow the prop down.  I'm not sure what the gains would be seen by simply adding more blades with reduced pitch, without slowing the prop down, but I'd love to hear about someone experimenting with that.  

  At the Wallaby ranch in Florida they use Dragonfly ultralights to tow hangliders, and they use two stacked three blade Ivo props, which they say gives them the best combo of quietness and thrust (they dont care about airspeed). cheers, Rob Cannon 	




When I was learning to fly trikes, the trainer I flew in had a 582 with the stacked 6-blade IVO prop on it, with 4:1 C box. I think the prop on it was louder than my FSII was with 3-blade 3.47:1 C box. It was one of the loudest combos I think I'd ever heard on a 582 in fact. I have no idea why that combination is so popular on tow planes. Must be really thrusty?



More blades means a higher frequency noise which adds to percieved loudness. So I'd say that probably needs to be taken into account too.



I love my powerfin 3-bladed (70" model F) on my 912ULS titan, but it's louder than the WD (68") that was on the plane for a while by a significant margin. 



The WD taper tip is actually a pretty quiet prop in flight compared to something like our powerfins which have the big square blade ends. I wouldn't use anything other than a WD on a Kolb personally, tho I love my powerfin the WD is just the ideal there.....



LS

_________________
LS
Titan II SS

Thom Riddle

Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

Posted: Wed Feb 03, 2010 7:37 am Post subject: Re: prop tip speed and noise

Jack,



Your measured difference of 1 db between 2 and 3 blades of the same diameter and rpm was interesting to learn and unexpected, by me at least. I wonder if the lessor pitch was the actual cause of the slightly reduced noise level or the different beat. I suspect it was the change in blade pitch, as Rob stated. My prop is cut in a scimitar shape so the tip angle is a lot more laid back than the modified tip on yours.



John,



No question that the pusher configuration is MUCH noisier than tractors, but I can't control that factor as long as I'm flying a Slingshot. What I am thinking about though is going to a shorter prop with more pitch like Gary has on his Jab powered mkIIIX. BUT if additional pitch also adds to the perceived noise then it might be for naught.

scaled Jabiru Rt Rear.jpg

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_________________
Thom Riddle
Buffalo, NY (9G0)

Don't worry about old age... it doesn't last very long.
- Anonymous

rickofudall

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

Posted: Wed Feb 03, 2010 8:07 am Post subject: prop tip speed and noise

Rob, For what It's worth I have the exact same engine and prop setup on my trike. One of the comments I get at fly ins and EAA chapter events is that I can't be heard in the pattern. Personally I think it really is prop tip speed as much as anything else. I have a 4:00 to  1 C gearbox with a 66" 3 blade Warp Drive on my 582 Mk III and my neighbor across the runway complements me on how quiet it is, too. 



Rick Girard



On Wed, Feb 3, 2010 at 9:04 AM, robcannon <leecannon(at)telus.net (leecannon(at)telus.net)> wrote:

[quote] --> Kolb-List message posted by: "robcannon" <leecannon(at)telus.net (leecannon(at)telus.net)>

 

 When I was researching which prop to put on my mark II HKS with a 3:47 gearbox I talked to alot of people about airplane noise.  My goal was to be as quiet as the 85hp fleet canuck (cub like canadian plane), that flies out of my home strip.

     What I learned was that it is a combination of tip speed and pitch which determines noise. (and pusher or tractor) Basically the smaller the "bite"out of the air, each blade takes, the quieter you are.......so, more blades, less diameter, less rpms, = quieter.  I have been told by pretty much everyone that hears my plane that it is the quietest plane they have ever heard......it sounds really nice!!!

    It has a four blade 68 inch powerfin, with the 3;47 gearbox. Does the 912 not have the option for a higher ratio gearbox ?

     Although I realize performance is rather subjective, I am very happy with my combination. Empty weight = 550 lbs  HP = 60  Solo climb = around 1000 fpm. Cruise = faster than vne of 75 mph.

    ...............so, I believe now that Kolbs can be made quiet, with enough money and effort put into them........providing you can slow the prop down.  I'm not sure what the gains would be seen by simply adding more blades with reduced pitch, without slowing the prop down, but I'd love to hear about someone experimenting with that.

    At the Wallaby ranch in Florida they use Dragonfly ultralights to tow hangliders, and they use two stacked three blade Ivo props, which they say gives them the best combo of quietness and thrust (they dont care about airspeed). cheers, Rob Cannon

  

 

 

 

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Thom Riddle

Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

Posted: Wed Feb 03, 2010 8:23 am Post subject: Re: prop tip speed and noise

Rick,



Assuming your cruise rpm is about 5800 your prop tips are rotating at only 284 mph plus your airspeed of 50-60 mph I would guess for a total tip speed of about 330 mph or so. That is a whopping 45% less than my tip speed. That has got to be a BIG factor. 



How does it sound to you while flying it?

_________________
Thom Riddle
Buffalo, NY (9G0)

Don't worry about old age... it doesn't last very long.
- Anonymous

slyck(at)frontiernet.net
Guest

Posted: Wed Feb 03, 2010 9:56 am Post subject: prop tip speed and noise

Try a dovetail saw for that precise cutting job.

BB

On 3, Feb 2010, at 9:17 AM, Jack B. Hart wrote:

 	  Quote: 	

 At 05:16 AM 2/3/10 -0800, you wrote:

> 

> 

> This has nothing to do with Ted's rum-rum but rather the amount of noise 

 (db levels) from props. 

> 

 Thom & Kolbers,

 Propellor tip shape can be a noise contributor too.  See:

 http://jackbhart.com/firefly/firefly100.html

 and:

 http://jackbhart.com/firefly/firefly111.html

 This is a nice way to reduce cockpit noise without adding any weight.

 Jack B. Hart FF004

 Winchester, IN

rickofudall

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

Posted: Wed Feb 03, 2010 5:05 pm Post subject: prop tip speed and noise

Thom, The only time I see 5800 RPM is on climbout. If I need a workout pulling the control bar in I'll cruise at 5400, normally I use 5200. Those figures are with the little wing. With the 19M I cruise at 4700 when I have my wife with me and 4300 when flying it solo. I wear a Shoei full face helmet when I fly it without any ear plugs. It's a little louder with the visor open than when closed but it's pretty quiet.

Rick



On Wed, Feb 3, 2010 at 10:23 AM, Thom Riddle <riddletr(at)gmail.com (riddletr(at)gmail.com)> wrote:

 [quote]--> Kolb-List message posted by: "Thom Riddle" <riddletr(at)gmail.com (riddletr(at)gmail.com)>

  

 

Rick,

 

 Assuming your cruise rpm is about 5800 your prop tips are rotating at only 284 mph plus your airspeed of 50-60 mph I would guess for a total tip speed of about 330 mph or so. That is a whopping 45% less than my tip speed. That has got to be a BIG factor.

  

 How does it sound to you while flying it?

 

 --------

 Thom Riddle

 Buffalo, NY

 Kolb Slingshot SS-021

 Jabiru 2200A #1574

 Tennessee Prop 64x31

 

 

 We refuse to believe this country, so powerful to defend its citizens abroad, is unable to protect its citizens at home.

  - Ida B. Wells

 

 

 

 

 Read this topic online here:

 

 

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

jbhart(at)onlyinternet.ne
Guest

Posted: Wed Feb 03, 2010 7:04 pm Post subject: prop tip speed and noise

At 12:47 PM 2/3/10 -0500, you wrote:

 	  Quote: 	
		  



Try a dovetail saw for that precise cutting job.

BB




	


Not all tractor aircraft are quiet.



When I was working for a living, RCA Corporation, I used to travel to the 

RCA Labs located at Lancaster, PA.  To get there one had to fly to 

Newark and then board a commuter to Lancaster.  The commuter was an 

Irish built Short Skyliner, a dressed up version of a little slab sided 

cargo hauler that mounted twin turbo props.  Looked like a pregnant guppie 

with a very wide landing gear.  I dreaded those trips, because when the 

pilot took off, it was like being inside a drum.  You could not keep your 

hand on the wall unless you wanted to experience extreme wrist pain.  You 

just had to guts it out until he got to cruise altitude.  One learned to sit 

in the extreme tail to get as far away from those propeller blades as possible.



By today's standard, they would not allow anything living to be shipped in 

such noisy environment.  But back then that was the only way to travel to 

Lancaster and get back home in the same day.



Jack B. Hart FF004

Winchester, IN



do not archive

Thom Riddle

Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

Posted: Thu Feb 04, 2010 6:01 am Post subject: Re: prop tip speed and noise

Rick,



I've only owned one aircraft with a 582 and it was a CH701. It cruised at 72 mph at 5800 rpm, which is where I ran it most of the time. I can imagine how quiet your trike is at 5,000 rpm or less. That sounds like a nice set up for quiet sight seeing flight. 



Change of subject:

There are almost zero weight shift aircraft near Buffalo due to the strong winds here. The only one I ever saw never flew. Very few powered parachutes here either (I've seen only one fly once) for the same reason, and not many legal ULs of any type, probably for the same reason of very light wing loading in this perpetually windy area. This is also one of the reasons I'm glad I moved to a short wing Slingshot last year. It handles the winds, gusts and thermals very well. My old short wing (20') Titan Tornado 912 handled them even better with only 93 sq ft of wing area compared to the 110 sq ft on the SS.

_________________
Thom Riddle
Buffalo, NY (9G0)

Don't worry about old age... it doesn't last very long.
- Anonymous

lucien

Joined: 03 Jun 2007
Posts: 721
Location: santa fe, NM

Posted: Thu Feb 04, 2010 7:25 am Post subject: Re: prop tip speed and noise

 	  Thom Riddle wrote: 	
		  Rick,



I've only owned one aircraft with a 582 and it was a CH701. It cruised at 72 mph at 5800 rpm, which is where I ran it most of the time. I can imagine how quiet your trike is at 5,000 rpm or less. That sounds like a nice set up for quiet sight seeing flight. 



Change of subject:

There are almost zero weight shift aircraft near Buffalo due to the strong winds here. The only one I ever saw never flew. Very few powered parachutes here either (I've seen only one fly once) for the same reason, and not many legal ULs of any type, probably for the same reason of very light wing loading in this perpetually windy area. This is also one of the reasons I'm glad I moved to a short wing Slingshot last year. It handles the winds, gusts and thermals very well. My old short wing (20') Titan Tornado 912 handled them even better with only 93 sq ft of wing area compared to the 110 sq ft on the SS. 	




I know, not Kolb related, but real quick... 

We do have a group of trikers down south in the area around Albuquerque. Those guys are brave too, I don't know how they handle the conditions here during the spring and summer but they do when I dare not even try it. (the main guy in the trike community there is a guy named Frank Dempsey, one of the coolest, nicest most helpful guys I've ever met in all of aviation. The rest of the group there are great folks too, wish they lived nearer here I'd love to fly with them). They do all kinds of long xcountries and everything else so they could really teach me a thing or two or three.....

I think they've gone to MV several times now.



If I don't out and out build a new plane, I've given thought to building a spare short wing (23 1/2 footer) for my titan to extend the flying season a little bit. My 26 footer climbs great but can be a handful in gusty winds even with the aileron spades on it.



Anyway, sorry for the OT post, but had to comment...



Do not archive

LS

_________________
LS
Titan II SS

John Hauck

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

Posted: Thu Feb 04, 2010 7:52 am Post subject: prop tip speed and noise

>

 	  Quote: 	
		   I know, not Kolb related, but real quick...


	


 	  Quote: 	
		   Anyway, sorry for the OT post, but had to comment...


	


 > --------

 	  Quote: 	
		   LS

 Titan II SS


	




Lucien/Gang:



I have a friendly suggestion on how to handle those uncontrollable urges to 

write about trikes and Titans:



     Try going back copy to the individual(s).



If I am out of line, let me know, please.



john hauck

mkIII

titus, alabama

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

lucien

Joined: 03 Jun 2007
Posts: 721
Location: santa fe, NM

Posted: Thu Feb 04, 2010 8:21 am Post subject: Re: prop tip speed and noise

 	  John Hauck wrote: 	
		  >

 	  Quote: 	
		   I know, not Kolb related, but real quick...



	


 	  Quote: 	
		   Anyway, sorry for the OT post, but had to comment...



	


 > --------

 	  Quote: 	
		   LS

 Titan II SS



	




Lucien/Gang:



I have a friendly suggestion on how to handle those uncontrollable urges to 

write about trikes and Titans:



     Try going back copy to the individual(s).



If I am out of line, let me know, please.



john hauck

mkIII

titus, alabama 	




Apologies guys, will keep it on topic from now on....



LS

_________________
LS
Titan II SS

dalewhelan

Joined: 11 Nov 2008
Posts: 105
Location: USA ARIZONA fountain hills

Posted: Sun Apr 04, 2010 10:57 pm Post subject: Re: prop tip speed and noise

I am not sure why tip speed and forward airspeed are added together to come up with total prop speed as the speeds are in different directions.

_________________
Dale Whelan
503 powered Firestar II, Luscombe 8A
Projection, A simple and interesting Psychological concept

dalewhelan

Joined: 11 Nov 2008
Posts: 105
Location: USA ARIZONA fountain hills

Posted: Sun Apr 04, 2010 10:58 pm Post subject: Re: prop tip speed and noise

I am not sure why tip speed and forward airspeed are added together to come up with total prop speed as the speeds are in different directions.

_________________
Dale Whelan
503 powered Firestar II, Luscombe 8A
Projection, A simple and interesting Psychological concept

dalewhelan

Joined: 11 Nov 2008
Posts: 105
Location: USA ARIZONA fountain hills

Posted: Sun Apr 04, 2010 10:58 pm Post subject: Re: prop tip speed and noise

I am not sure why tip speed and forward airspeed are added together to come up with total prop speed as the speeds are in different directions.

_________________
Dale Whelan
503 powered Firestar II, Luscombe 8A
Projection, A simple and interesting Psychological concept

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