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Dynamic Air Pressure Filter Housing

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jbhart(at)onlyinternet.ne
Guest

Posted: Wed Jan 07, 2009 12:33 pm Post subject: Dynamic Air Pressure Filter Housing

Kolbers,



In most tractor engine configurations, ram or dynamic air pressured air is 

fed into the carburetor.  With a pusher propeller and the engine mounted so 

that the carburetor is above the wing the carburetor inlet is being fed with 

lower static air pressure than can be found below the wing.  Last summer, I 

ran an experiment where I connected the carburetor inlet with a long tube to 

the air filter mounted on the main spar cross through at the root tube.  One 

flight told me that I could not tolerate the inlet noise that close to my 

head.  Also, the weight of the carburetor adapter and connecting tubing was 

a severe weight penalty.



I have been grounded by winds, cold temperatures, snow, and ice so I began 

re thinking the problem.  A dynamic air pressure scoop around the air filter 

seemed to be the way to go.  The result of this thinking can be seen at:



http://www.thirdshift.com/jack/firefly/firefly147.html



To keep the weight down, I attached it directly to the air filter.  This 

should more than make up for the 1.0 to 1.5 inches of water air filter loss 

that was found under cruise conditions.  When the weather improves, I will 

be able to measure the carburetor static inlet pressure.  The first test 

will be with the opening pointed upward or downward to simulate scoop inlet 

static pressure.  Then the second test will run with the opening pointed 

forward. I really do not expect a huge improvement, but when you have only a 

few horses, it is a shame to waste any of them.



Jack B. Hart FF004

Winchester, IN

Dana

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

Posted: Wed Jan 07, 2009 2:26 pm Post subject: Dynamic Air Pressure Filter Housing

At 03:34 PM 1/7/2009, Jack B. Hart wrote:

 	  Quote: 	
		  ...With a pusher propeller and the engine mounted so

that the carburetor is above the wing the carburetor inlet is being fed with

lower static air pressure than can be found below the wing....

...A dynamic air pressure scoop around the air filter

seemed to be the way to go....This

should more than make up for the 1.0 to 1.5 inches of water air filter loss

that was found under cruise conditions...


	


About 0.14 inches of mercury (1.9 inches of water) at 55 knots, or less 

than 1% of 1 atmosphere; 1/2HP for a 50HP engine (since output power is 

roughly proportional to intake air pressure)... seems unlikely it'd be 

noticeable.



Can't hurt though, unless it comes loose and goes through the prop...



-Dana



--

  In some cultures what I do would be considered normal.

NeilsenRM(at)comcast.net
Guest

Posted: Wed Jan 07, 2009 6:08 pm Post subject: Dynamic Air Pressure Filter Housing

Jack



Nice work. I would like to make two suggestions. One you may want to allow 

for a way for water to get out of the scoop. If you get in a rain storm you 

might flood the engine. Also why not add a long taper to the back of the 

scoop to cut drag.



I have had similar ideas for my VW. The big Webber air cleaners have 

considerable drag that I don't need. Also the small boost in air pressure 

would give me more horse power. I have been mulling over designs for some 

time and may steal some of your design.



Rick Neilsen

Redrive VW powered MKIIIC



---

jbhart(at)onlyinternet.ne
Guest

Posted: Wed Jan 07, 2009 6:21 pm Post subject: Dynamic Air Pressure Filter Housing

At 05:21 PM 1/7/09 -0500, you wrote:

 	  Quote: 	
		  



About 0.14 inches of mercury (1.9 inches of water) at 55 knots, or less 

than 1% of 1 atmosphere; 1/2HP for a 50HP engine (since output power is 

roughly proportional to intake air pressure)... seems unlikely it'd be 

noticeable.



Can't hurt though, unless it comes loose and goes through the prop...




	


Dana,



I believe the pressure change will be greater than 1.5 inches of water, as 

the air is passing through the propeller is much greater than IAS.  I won't 

know what it is until I measure it, but if air velocity past the carburetor 

has to be much higher than 55 knots IAS.



Jack B. Hart FF004

Winchester, IN

Dana

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

Posted: Wed Jan 07, 2009 6:51 pm Post subject: Dynamic Air Pressure Filter Housing

At 09:22 PM 1/7/2009, Jack B. Hart wrote:



 	  Quote: 	
		  I believe the pressure change will be greater than 1.5 inches of water, as

the air is passing through the propeller is much greater than IAS.  I won't

know what it is until I measure it, but if air velocity past the carburetor

has to be much higher than 55 knots IAS.


	


Good point... though I don't know how much faster it'll be on the upstream 

side of the prop, as compared to behind the prop.  Be interesting to see.



-Dana

--

  Come to think of it, there already are a million monkeys at a million 

typewriters, and the Internet is _NOTHING_ like Shakespeare!

jbhart(at)onlyinternet.ne
Guest

Posted: Wed Jan 07, 2009 7:06 pm Post subject: Dynamic Air Pressure Filter Housing

At 09:04 PM 1/7/09 -0500, you wrote:

 	  Quote: 	
		  



Jack



Nice work. I would like to make two suggestions. One you may want to allow 

for a way for water to get out of the scoop. If you get in a rain storm you 

might flood the engine. Also why not add a long taper to the back of the 

scoop to cut drag.




	


Rick,



I considered the rain/water problem.  If you look at the last photo on the 

page, you will see a series of little holes along the corner or edge of the 

assembly.  These are the relief holes for bending the tabs along the edge of 

the main body.  I did not seal them so that water could leak out.  Later if 

an oil slobbering problem develops, I will seal them and add a drain or 

relief tube so that I can run the oil and/or water to a catch bottle.  This 

will prevent oil spatter on the tail surfaces.



I did consider streamlining the scoop, but at this time I am more concerned 

with the added weight.  After, I get done testing and if it proves to be 

worth while, I may stream line it  with foam that is covered with organza 

fabric.  I worry about too much weight hanging out from the carburetor boot.



Jack B. Hart FF004

Winchester, IN

Thom Riddle

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

Posted: Thu Jan 08, 2009 7:42 am Post subject: Re: Dynamic Air Pressure Filter Housing

In the 1960s I flew Mooneys a good bit and really liked a couple of their unique features. One was the "poor man's supercharger" that came standard on the early Mooneys. It was a pilot controlled RAM AIR scoop that by-passed the air-cleaner and sent RAM AIR directly to the carburetor inlet. At typical cruise speeds (160 mph or so) it added about 1" of manifold pressure. It was to be used only at altitude of course where un-filtered air was not a problem... at least not back then. 



At the Kolb's much slower speeds you want see this much assist but any assist at all is worthwhile when you are pinching pennies.

_________________
Thom Riddle
Buffalo, NY (9G0)

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

aslsa.rng(at)gmail.com
Guest

Posted: Fri Jan 09, 2009 3:41 pm Post subject: Dynamic Air Pressure Filter Housing

Dale, Glad you brought all this up. Going to lunch after the Bing carb section of the Rotax mechanic courses at Lockwood, I asked Rotax guru Eric Tucker about my plans to build ram air into the cowling of my 582 powered Mk III. I covered pretty much everything you brought up and his advice was don't do it. The Bing is designed for ambient pressure and the design isn't conducive to ram air even if you do take all this into account. He's been working on Rotax engines for 40+ years since his snowmobile racing days so I figure he might know.   Still, it's experimental aviation and as they say, one good experiment beats a thousand expert opinions.

Good luck, Jack

Rick



On Fri, Jan 9, 2009 at 11:51 AM, Dale Whelan <dalewhelan(at)earthlink.net (dalewhelan(at)earthlink.net)> wrote:

   	  Quote: 	
		      

 I have read posts by other motorcycle mechanics and thought if they would just shut up I may not look like I am dumb by association.

 I have spent many years racing and tuning a two stroke Gran Prix road race motorcycle equipped with ram air.

 I am not formally educated, I read a lot and test alot both on dynos and at the track.

 I have some experiance that way be helpful and increase the safety of some experimenters.

  

 SAFETY FIRST

     If the veturi is pressurized without pressurizing the rest of the fuel system, the fuel mixture will be leaned out!

     The floatbowl vent need to be pressurized to avoid reducing the pressure difference between the bowl and the venturi.

     The tank needs to be pressurized to avoid reducing fuel delivery to the carb from the increased bowl pressure.

  

 PERFORMANCE

     At the low speeds I fly my firestar at the increase in pressure is not likely to be worth my effort as I need no more power to cruise at my desired speed. I would need power for climb but the ram effect is lower at climb. I could use more power at high altitude but here again I am not usually flying fast.

    

  CONSIDERATIONS

     Air inlet needs to be relativly small compared to tube feeding the airbox. Venturi effect, volune increases velocity slows, pressure rises.

     The airbox has a resonant frequency, some of the variables are, box volume, inlet length, and inlet area. The box seems to have about as much effect as the pressure.

  

 PERSONALLY

     If I were to modify my powerplant, (not sure I want to go throught the test tune fail learn process with my plane) I would go after power, without increase in RPM, and higher efficiency. POwer can be improved by reducing waste or by processing more fuel.

   My 503 could use more compression for the fuel I use, my friends looks like it can't. 

     I would build an exhaust that put the torque peak at cruise RPM if I wanted max fuel economy. The exhaust would be an expansion chamber, actually two of them. The tune would need to be just broad enought to cover the RPM range from cruise to climb. The ram air system would be simple, mount the carbs inside the airbox and vent the tanks to the airbox if I were to ram air the motor. I would rather just have the airbox.

       For me there are are aerodynamic considerations to offset some of the improved motor efficiency, but I would expect a net gain. The thing that concearns me the most is the addition of parts ahead of the prop, welded and designed by me.

       I would recomend becoming an expert in jetting and timing before attempting this kind of work, I expect some of you are.

  

 SIDE NOTE

     I have heard many say that jetting a plane is different than a motorcycle, When people say that to me I doubt they know how to tune either.

  

  

 Dale Whelan

 dalewhelan(at)earthlink.net (dalewhelan(at)earthlink.net)

 EarthLink Revolves Around You.

  

 

   [/b] 	




[b]

jbhart(at)onlyinternet.ne
Guest

Posted: Fri Jan 09, 2009 6:56 pm Post subject: Dynamic Air Pressure Filter Housing

Dale & Rick,



First of all, if my air fuel mixture control had not been effective, I would 

not be trying this.  Also, if I did not have an EGT sensor and gage, I would 

have to tune just as the snowmobiler and the motorcyclist do.  Although I do 

not motorcycle or snowmobile, I believe it may be impractical to monitor EGT 

while riding either one.  I assume one needs to maintain a high degree of 

diligence on the immediate surroundings.  This is similar to landing, 

takeoff and taxiing an ultra light.  But once in the air a pilot can devote 

some time to monitoring an EGT as well as looking out side the cockpit.  

Also, it is not easy to ground adjust for the current local atmospheric 

conditions when one wants to go for a ride in/on any of these vehicles.



It amazes me that Rotax, who manufactures aircraft engines, has not picked a 

carburetor that was cockpit adjustable.  This short coming ensures that 

these engines run richer than necessary. My Bing conversion may not be the 

solution.  I have only 13 and one-half hours on it.  I am very encouraged.  

If you have not see the conversion, it can be found at:



http://www.thirdshift.com/jack/firefly/firefly146.html

.......



Dale,



Yes, as the air density is increased, the air fuel mixture will move toward 

the lean side.  I really have no idea of the dynamic air pressure at the 

carburetor.  But assuming the FireFly is moving at 50 mph IAS and to 

overcome the drag the air passing through the propeller is 100 mph, the 

dynamic pressure will 4.73 inches of water.  I am assuming my system will be 

able to accommodate this pressure increase.  



The first flight will be made with the housing rotated vertical, so that, 

the carburetor is operating at it's normal static pressure.  Carburetor 

inlet static pressure will be measured to establish base line data.  On the 

next fight the housing will be rotated about thirty degrees from vertical.  

Hopefully I will see an increase in carburetor inlet static pressure over 

the whole cruise rpm range. And again hopefully, I will be able to maintain 

acceptable EGT over the entire range.  If that can not be done, the needle 

will have to be lifted.  This process will be repeated until the housing is 

pointed directly forward.  



This is how I foresee it, but it all has to wait until warmer weather.  If I 

see an increase in carburetor inlet static pressure, I would expect the 

engine to top out at a higher rpm, which will let me add a little more pitch 

in the propeller, and give me a little better climb rate.



My air fuel mixture control is based on varying the pressure over the float 

bowl.  So far it has not caused any problems.  At this time I can only hope 

it will accommodate the housing dynamic pressures.



Pressurizing the tank is a good idea.  The fuel pump has to lift fuel quite 

a distance on FireFly.



No argument about jetting.



I keep hoping the weather will break.



Jack B. Hart FF004

Winchester, IN

---------------------------------

Date: Fri, 9 Jan 2009 17:41:24 -0600

From: "Richard Girard" <aslsa.rng(at)gmail.com>



Dale, Glad you brought all this up. Going to lunch after the Bing carb section of the Rotax mechanic courses at Lockwood, I asked Rotax guru Eric Tucker about my plans to build ram air into the cowling of my 582 powered Mk III. I covered pretty much everything you brought up and his advice was don't do it. The Bing is designed for ambient pressure and the design isn't conducive to ram air even if you do take all this into account. He's been working on Rotax engines for 40+ years since his snowmobile racing days so I figure he might know. 

Still, it's experimental aviation and as they say, one good experiment beats a thousand expert opinions.



--------------------------------

On Fri, Jan 9, 2009 at 11:51 AM, Dale Whelan <dalewhelan(at)earthlink.net> wrote:



SAFETY FIRST

    If the veturi is pressurized without pressurizing the rest of the fuel system, the fuel mixture will be leaned out!

    The floatbowl vent need to be pressurized to avoid reducing the pressure difference between the bowl and the venturi.

    The tank needs to be pressurized to avoid reducing fuel delivery to the carb from the increased bowl pressure.

  

SIDE NOTE

    I have heard many say that jetting a plane is different than a motorcycle, When people say that to me I doubt they know how to tune either.

Dana

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

Posted: Fri Jan 09, 2009 7:40 pm Post subject: Dynamic Air Pressure Filter Housing

At 09:57 PM 1/9/2009, Jack B. Hart wrote:

 	  Quote: 	
		  ...Although I do

not motorcycle or snowmobile, I believe it may be impractical to monitor EGT

while riding either one.  I assume one needs to maintain a high degree of

diligence on the immediate surroundings...


	


More to the point, I think, is that you can't do an extended full power 

runup while a snowmobile is standing still; indeed I imagine you rarely are 

at full power for more than a few moments at a time.



-Dana



--

  Giving money and power to government is like giving whiskey and car keys 

to teenage boys.

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