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Breeze up the boom tube

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rickofudall

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

Posted: Wed Oct 05, 2011 12:39 pm Post subject: Breeze up the boom tube

Some time back I did an experiment to find the answer to the question of just how much air is flowing back up the boom tube of my Mk III. The post that describes what I did is in the archives, but as a rule of thumb you can figure that whatever your airspeed the air coming back up the boom tube is half that. For example, at an indicated airspeed of 80 mph the draft coming up the boom into the cockpit was 40 mph IAS. 



Rick Girard





-- 

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....

byoungplumbing(at)gmail.c
Guest

Posted: Wed Oct 05, 2011 1:03 pm Post subject: Breeze up the boom tube

Some  time back I did an experiment to find the answer to the question of just how  much air is flowing back up the boom tube of my Mk III. The post that describes  what I did is in the archives, but as a rule of thumb you can figure that  whatever your airspeed the air coming back up the boom tube is half that. For  example, at an indicated airspeed of 80 mph the draft coming up the boom into  the cockpit was 40 mph IAS.  



 Rick Girard

 



 

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

 when I built the mkiii.    I heat  formed a piece of fabric to fit inside the rear of the tube,  just ahead of  the elevator bell crank.  then I glued it in place with polly tack.  I  then cut small slits in it for the elevator and rudder cables.  I think if  I was doing it again.  I would take one inch of the 6 inch tube, split it  to fit it inside the main tube.  then glue the fabric to the outside  of the  1 inch piece ,  then slid it in the tail boom  tube.   that way it would have been removable if the need presented  itself.    that stops the wind movement,   I don't know  if it would stop critters or not.  I suppose you could do it with some  screen wire, then cover that with the fabric,  the fabric would create an  anti chafe buffer to the screen wire and the boom tube,
	


  

 Boyd young

 mkiii utah



   [quote][b]

Thom Riddle

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

Posted: Wed Oct 05, 2011 1:17 pm Post subject: Breeze up the boom tube

Rick,

That is an interesting observation. I have never noticed any reverse airflow up my Slingshot's tail but that does not mean it isn't there. IF that phenomenon is not characteristic of the SS but is for most Kolbs I speculate that it might be caused, or at least influenced by the relative positions of the horizontal stabilizer and boom tube. On most Kolbs the leading edge of the HS is well above the centerline of the boom tube, whereas on the SS it is even with (parallel) with the boom tube. There could be other factors too. I am not even sure what would be an easy way to detect/measure this reverse airflow up my SS tail. If it is dramatic as you say on my SS, I would think it would be obvious to me, but it is not at all. How did you determine the speed of roughly half of forward speed? Is it something I could easily replicate on my SS?

 

Thom 



On Oct 5, 2011, at 4:42 PM, Richard Girard <aslsa.rng(at)gmail.com (aslsa.rng(at)gmail.com)> wrote:



[quote]Some time back I did an experiment to find the answer to the question of just how much air is flowing back up the boom tube of my Mk III. The post that describes what I did is in the archives, but as a rule of thumb you can figure that whatever your airspeed the air coming back up the boom tube is half that. For example, at an indicated airspeed of 80 mph the draft coming up the boom into the cockpit was 40 mph IAS.  



Rick Girard





-- 

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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Thom Riddle
Buffalo, NY (9G0)

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

byoungplumbing(at)gmail.c
Guest

Posted: Wed Oct 05, 2011 3:00 pm Post subject: Breeze up the boom tube

Rick,

 



 That is an interesting observation. I have never noticed any reverse  airflow up my Slingshot's tail but that does not mean it isn't there. IF that  phenomenon is not characteristic of the SS but is for most Kolbs I speculate  that it might be caused, or at least influenced by the relative positions of the  horizontal stabilizer and boom tube. On most Kolbs the leading edge of the HS is  well above the centerline of the boom tube, whereas on the SS it is even with  (parallel) with the boom tube. There could be other factors too. I am not even  sure what would be an easy way to detect/measure this reverse airflow up my SS  tail. If it is dramatic as you say on my SS, I would think it would be obvious  to me, but it is not at all. How did you determine the speed of roughly half of  forward speed? Is it something I could easily replicate on my  SS?



Thom 

 

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

 i think the direction of wind flow in the boom tube  has more to do with the configuration of the cabin area, and whether it has a  high or low pressure,  this would be determined mostly by how the rear of  the cabin is closed in.  or lack their of.  all things being  equal.  the air going past the back of the boom tube should pull a negative  pressure on the rear of the tube.     but if there is a  larger negative pressure caused by the cabin enclosure,  then the flow  would be forward.
	


  

 boyd young

 mkiii ut



   [quote][b]

David d.

Joined: 04 Jul 2011
Posts: 60
Location: Fitzgerald Ga.

Posted: Wed Oct 05, 2011 3:53 pm Post subject: Re: Breeze up the boom tube

Interesting about the tail draft.   I have been trying to figure why my air speed reads about half.

Could this tube draft be causing my air speed to be off?

David d.

_________________
Kolb Mark IIIX 582 Blue head

Thom Riddle

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

Posted: Wed Oct 05, 2011 4:11 pm Post subject: Breeze up the boom tube

Boyd,

You are probably correct. Although I've flown a MkIII several times I've never owned one or flown one enough to get to the point that I notice that sort of thing. All my KOLB ownership experience is in Firestars and the Slingshot, both narrow bodied which have not shown the sucking tail syndrome, at least to a degree sufficient to get my attention.

 

Thom



On Oct 5, 2011, at 7:02 PM, "b young" <byoungplumbing(at)gmail.com (byoungplumbing(at)gmail.com)> wrote:



[quote]   Rick,

 



 That is an interesting observation. I have never noticed any reverse  airflow up my Slingshot's tail but that does not mean it isn't there. IF that  phenomenon is not characteristic of the SS but is for most Kolbs I speculate  that it might be caused, or at least influenced by the relative positions of the  horizontal stabilizer and boom tube. On most Kolbs the leading edge of the HS is  well above the centerline of the boom tube, whereas on the SS it is even with  (parallel) with the boom tube. There could be other factors too. I am not even  sure what would be an easy way to detect/measure this reverse airflow up my SS  tail. If it is dramatic as you say on my SS, I would think it would be obvious  to me, but it is not at all. How did you determine the speed of roughly half of  forward speed? Is it something I could easily replicate on my  SS?



Thom 

 

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

 i think the direction of wind flow in the boom tube  has more to do with the configuration of the cabin area, and whether it has a  high or low pressure,  this would be determined mostly by how the rear of  the cabin is closed in.  or lack their of.  all things being  equal.  the air going past the back of the boom tube should pull a negative  pressure on the rear of the tube.     but if there is a  larger negative pressure caused by the cabin enclosure,  then the flow  would be forward.
	


  

 boyd young

 mkiii ut



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Thom Riddle
Buffalo, NY (9G0)

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rickofudall

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

Posted: Wed Oct 05, 2011 6:22 pm Post subject: Breeze up the boom tube

I have a Winter ASI for which I made a pitot probe with about 3' of vinyl tube and 2' of aluminum tube. I took it out in my wife's car and stuck it out through the sunroof to calibrate it. Then I positioned it with the probe going back up the boom and went flying. I have lot's of cockpit vents in my Mk III, deliberate and not so and there's no seal at the top of the windscreen. The result is that there's a lot of airflow to create a negative pressure differential in the cabin to suck air in from the boom. That's my theory, anyway. 



Rick



On Wed, Oct 5, 2011 at 4:14 PM, Thom Riddle <riddletr(at)gmail.com (riddletr(at)gmail.com)> wrote:

 	  Quote: 	
		   Rick,

That is an interesting observation. I have never noticed any reverse airflow up my Slingshot's tail but that does not mean it isn't there. IF that phenomenon is not characteristic of the SS but is for most Kolbs I speculate that it might be caused, or at least influenced by the relative positions of the horizontal stabilizer and boom tube. On most Kolbs the leading edge of the HS is well above the centerline of the boom tube, whereas on the SS it is even with (parallel) with the boom tube. There could be other factors too. I am not even sure what would be an easy way to detect/measure this reverse airflow up my SS tail. If it is dramatic as you say on my SS, I would think it would be obvious to me, but it is not at all. How did you determine the speed of roughly half of forward speed? Is it something I could easily replicate on my SS?

  

Thom 



On Oct 5, 2011, at 4:42 PM, Richard Girard <aslsa.rng(at)gmail.com (aslsa.rng(at)gmail.com)> wrote:



 	  Quote: 	
		  Some time back I did an experiment to find the answer to the question of just how much air is flowing back up the boom tube of my Mk III. The post that describes what I did is in the archives, but as a rule of thumb you can figure that whatever your airspeed the air coming back up the boom tube is half that. For example, at an indicated airspeed of 80 mph the draft coming up the boom into the cockpit was 40 mph IAS.   



Rick Girard





-- 

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: 	
		  



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-- 

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....

rickofudall

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

Posted: Wed Oct 05, 2011 6:25 pm Post subject: Breeze up the boom tube

Yes, if you have no static source hooked up to your ASI (and assuming you need one, my little Winter that I used for testing doesn't have a static port).



Rick Girard



On Wed, Oct 5, 2011 at 6:53 PM, SS568 <david(at)paulowniatrees.com (david(at)paulowniatrees.com)> wrote:

  	  Quote: 	
		  --> Kolb-List message posted by: "SS568" <david(at)PaulowniaTrees.com>

 

 Interesting about the tail draft.   I have been trying to figure why my air speed reads about half.

 Could this tube draft be causing my air speed to be off?

 David d.

 

 --------

 Kolb Mark IIIX  582 Blue head

 

 

 

 

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-- 

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....

Richard Pike

Joined: 09 Jan 2006
Posts: 1671
Location: Blountville, Tennessee

Posted: Wed Oct 05, 2011 7:01 pm Post subject: Re: Breeze up the boom tube

No hard data, but in the winter the cold air coming out the boom tube opening was freezing me. I cut a round piece of foam with slots for the cables and stuck it in the tube at the front end and it improved things immeasurably. 



For what it's worth...

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

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

David d.

Joined: 04 Jul 2011
Posts: 60
Location: Fitzgerald Ga.

Posted: Thu Oct 06, 2011 3:36 am Post subject: Re: Breeze up the boom tube

I found this site that has a simple way of testing the ASI. 

http://www.n56ml.com/airspeed_calibration/

This is with plane in the hangar and the static air is very static. My instruments have their static airs tied together and a plastic tube runs up to a disc up near the pitot tube. What is the significance of this static air as opposed to just using cabin air? Can that disc be defective or stopped up perhaps?



David d.

_________________
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Thom Riddle

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

Posted: Thu Oct 06, 2011 3:56 am Post subject: Breeze up the boom tube

Thanks, Rick. Simple solution if you have a have a spare ASI.

Thom

  

do not archive

On Wed, Oct 5, 2011 at 10:20 PM, Richard Girard <aslsa.rng(at)gmail.com (aslsa.rng(at)gmail.com)> wrote:

  [quote]I have a Winter ASI for which I made a pitot probe with about 3' of vinyl tube and 2' of aluminum tube. I took it out in my wife's car and stuck it out through the sunroof to calibrate it. Then I positioned it with the probe going back up the boom and went flying. I have lot's of cockpit vents in my Mk III, deliberate and not so and there's no seal at the top of the windscreen. The result is that there's a lot of airflow to create a negative pressure differential in the cabin to suck air in from the boom. That's my theory, anyway.   



Rick



On Wed, Oct 5, 2011 at 4:14 PM, Thom Riddle <riddletr(at)gmail.com (riddletr(at)gmail.com)> wrote:

  

 	  Quote: 	
		   Rick,

That is an interesting observation. I have never noticed any reverse airflow up my Slingshot's tail but that does not mean it isn't there. IF that phenomenon is not characteristic of the SS but is for most Kolbs I speculate that it might be caused, or at least influenced by the relative positions of the horizontal stabilizer and boom tube. On most Kolbs the leading edge of the HS is well above the centerline of the boom tube, whereas on the SS it is even with (parallel) with the boom tube. There could be other factors too. I am not even sure what would be an easy way to detect/measure this reverse airflow up my SS tail. If it is dramatic as you say on my SS, I would think it would be obvious to me, but it is not at all. How did you determine the speed of roughly half of forward speed? Is it something I could easily replicate on my SS?

    

Thom 

On Oct 5, 2011, at 4:42 PM, Richard Girard <aslsa.rng(at)gmail.com (aslsa.rng(at)gmail.com)> wrote:





 	  Quote: 	
		    Some time back I did an experiment to find the answer to the question of just how much air is flowing back up the boom tube of my Mk III. The post that describes what I did is in the archives, but as a rule of thumb you can figure that whatever your airspeed the air coming back up the boom tube is half that. For example, at an indicated airspeed of 80 mph the draft coming up the boom into the cockpit was 40 mph IAS.     



Rick Girard





-- 

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: 	
		  



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-- 

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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[b]

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Thom Riddle
Buffalo, NY (9G0)

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

Ozarkflyer

Joined: 19 Jun 2009
Posts: 68
Location: Mtn. View, AR

Posted: Thu Oct 06, 2011 9:01 am Post subject: Re: Breeze up the boom tube

"Breeze up the boom tube......sucking tail syndrome"? Sounds like a Monty Python episode.

zeprep251(at)aol.com
Guest

Posted: Thu Oct 06, 2011 4:06 pm Post subject: Breeze up the boom tube

I flew my Firestar fully enclosed in zero degree weather,taped every opening I could find closed,using construction paper and silver tape around the spar carry thru and piped in heat via scat tube from the cooling shroud .Then is when I first discovered the cold draft roaring up the boom tube.Plugging that really did more than the addition of heat from the engine.The primary source of heat with my system was passive solar,and you could survive with that.I started going south for the winter after that.

 G.Aman MK3C Firestar 2

   

  

     

  

     

  

    --

Dana

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

Posted: Fri Oct 07, 2011 3:16 pm Post subject: Breeze up the boom tube

At 07:36 AM 10/6/2011, SS568 wrote:

  	  Quote: 	
		  --> Kolb-List message posted by: "SS568" <david(at)PaulowniaTrees.com>



 I found this site that has a simple way of testing the ASI. 

 http://www.n56ml.com/airspeed_calibration/

 This is with plane in the hangar and the static air is very static. My instruments have their static airs tied together and a plastic tube runs up to a disc up near the pitot tube. What is the significance of this static air as opposed to just using cabin air? Can that disc be defective or stopped up perhaps? 	


 The water manometer described in your link is a good way to calibrate an ASI... engineers have used water manometers in wind tunnels for years.



 Cabin air is notoriously NOT at static pressure.  Open a vent, pressure goes up.  Bad door seal, pressure may go down.  Open a window or slip the plane, who knows?  



 Your plastic disk is an external static air source.  It's generally placed on the side of the fuselage, parallel to the airflow, often in pairs to cancel any effects from yaw.



 -Dana

 --

 "If you're not a liberal at 20, you have no heart.  If you are not a conservative when you're 30, you have no head."-- Winston Churchill

    [quote][b]

Thom Riddle

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

Posted: Sun Oct 09, 2011 10:41 am Post subject: Re: Breeze up the boom tube

This summer weather in October was waaay too good not to fly, so I flew to Bob Bean's place and landed on his "mature grass" airstrip. No Brakes Required!



Enroute, I stuck my hand back under the rear seat and felt a light breeze, nothing like I think the wide body Kolbs get. It was a little cool to have my forward vents open so this slight breeze was with a bit of negative cabin pressure (presumably) because the aft vents were open in exhaust mode. By the time I got close to BB's place it was warm enough to open the forward vents, which I did. With this bit of positive pressure, I stuck my hand back under the rear seat and the air felt completely static to me.



My conclusion is that in MY slingshot, the breezy boom tube phenomenon is minimal and then only without forward vents open. Other Kolb types or even other slingshots may have a different experience.



After landing at BB's he gave me the grand tour of his brand new pole barn, just finished yesterday except for the garage door. Then we cranked up both the Kolbs and flew about 10 miles NW of his place to have lunch at Abe's Log Cabin restaurant, a very short walk from a very nice two runway grass airstrip, called Ridge Road West. After lunch we departed on our separate ways.



What a glorious October day for flying it was here in western New York.

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