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Pressurized motors

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Thom Riddle

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

Posted: Mon Jan 12, 2009 6:05 am Post subject: Pressurized motors

..My Rotax 503 makes a claimed 52 HP (at) about 6,500 RPM.....

I've seen folks calling the 503 DCDI engine a 52 hp engine countless

times but none of the Rotax engine publications I've seen rate it at

more than 49.6 hp (37kw).



Anyone have any idea where this "52" comes from?



Thom Riddle

_________________
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: Mon Jan 12, 2009 7:05 am Post subject: Re: Pressurized motors

 	  Thom Riddle wrote: 	
		  ..My Rotax 503 makes a claimed 52 HP (at) about 6,500 RPM.....

I've seen folks calling the 503 DCDI engine a 52 hp engine countless

times but none of the Rotax engine publications I've seen rate it at

more than 49.6 hp (37kw).



Anyone have any idea where this "52" comes from?



Thom Riddle 	




I've seen this as the claimed HP for the free-air cooled version. I.e. 2 less HP that would otherwise be used to drive the cooling fan. 



LS

_________________
LS
Titan II SS

Thom Riddle

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

Posted: Mon Jan 12, 2009 7:11 am Post subject: Re: Pressurized motors

Lucien,

That makes sense but have you ever seen a 503 DCDI engine without fan cooling? I've never seen one.



do not archive

_________________
Thom Riddle
Buffalo, NY (9G0)

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

George Alexander

Joined: 10 Jan 2006
Posts: 245
Location: SW Florida

Posted: Mon Jan 12, 2009 7:26 am Post subject: Re: Pressurized motors

 	  Thom Riddle wrote: 	
		  Lucien,

That makes sense but have you ever seen a 503 DCDI engine without fan cooling? I've never seen one.



do not archive 	




Thom:

Many tractors (Phantoms, Flightstar, MiniMax, etc...) use free air.



Added image of Phantom with free air and fiberglass scoop.

freeair_phantom.jpg

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_________________
George Alexander
FS II R503
E-LSA N709FS
http://www.oh2fly.net

Last edited by George Alexander on Mon Jan 12, 2009 7:38 am; edited 1 time in total

lucien

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

Posted: Mon Jan 12, 2009 7:28 am Post subject: Re: Pressurized motors

 	  Thom Riddle wrote: 	
		  Lucien,

That makes sense but have you ever seen a 503 DCDI engine without fan cooling? I've never seen one.



do not archive 	




Yeah I've seen this on the Phantom. It requires replacing the fan housing with the one that doesn't have the fan on it and a free-air scoop in place of the regular cooling shroud.



The cooling is simply accomplished by ram-air from the prop and relative wind. 



I believe the replacement housing is a rotax option, but the cooling shroud is a 3rd-party deal....



LS

_________________
LS
Titan II SS

Thom Riddle

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

Posted: Mon Jan 12, 2009 7:32 am Post subject: Re: Pressurized motors

Live and learn. Still curious why I've never seen the 52 hp claim in any Rotax pubs. Maybe I've not dug into it deep enough.  



do not archive

_________________
Thom Riddle
Buffalo, NY (9G0)

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

jbhart(at)onlyinternet.ne
Guest

Posted: Mon Jan 12, 2009 8:34 am Post subject: Pressurized motors

At 08:34 PM 1/11/09 -0700, you wrote:

 	  Quote: 	
		  


	


Dale,



 	  Quote: 	
		  

The lean condition I was warning about is not from the increase in air 
	


density, it is from the decrease of vacuum in the venturi.

 	  Quote: 	
		  


	


I believe this must be where I am getting lost. I see that venturi vacuum is 

dependent upon throttle opening and engine rpm plus carburetor up stream 

losses and/or conditions.  Assuming engine timing is correct and 

mechanically sound and with no change in propeller pitch, what am I missing 

here?



The raising carburetor inlet pressure 4.73 inches of water represents 

lowering the altitude by less than 500 feet.



 	  Quote: 	
		  

The jetting on this bike may need to be changed several times per day, and 
	


is. This is why I made the comment about becoming a jetting expert. 

 	  Quote: 	
		  


	


This is why I worked on a cockpit adjustable air mixture control system.  In 

principle it works much like the HACman, except that it is manually 

controlled. With it I can hold EGT and the gph rate constant for a fixed 

rpm.  So far it appears to be saving fifteen cents of each fuel dollar.



No apology needed.  Another cold snowy day.



Jack B. Hart FF004

Winchester, IN

herbgh(at)nctc.com
Guest

Posted: Mon Jan 12, 2009 8:52 am Post subject: Pressurized motors

a lot of this propaganda is written by the same folks who write "if 

it lasts more than 4 hours , see your doctor" !!    Herb



At 09:32 AM 1/12/2009, you wrote:

 	  Quote: 	
		  



Live and learn. Still curious why I've never seen the 52 hp claim in 

any Rotax pubs. Maybe I've not dug into it deep enough.



do not archive



--------

Thom Riddle

N1208P RANS S6S, Tailwheel, 912UL

N197BG FS1/447

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

It is by universal misunderstanding that all agree. For if, by ill 

luck, people understood each other, they would never agree.

   - Charles Baudelaire





Read this topic online here:



http://forums.matronics.com/viewtopic.php?p 24219#224219

dalewhelan

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

Posted: Wed Jan 14, 2009 1:33 pm Post subject: Re: Pressurized motors

Let's say you have 1 bar of pressure in the float bowl and .9 bar in the venturi. The lower pressure in the venturi results in fuel delivery to the venturi.

Now if we increased the venturi pressure by .2 bar we would have fuel delivery to the bowl.

On my racing Yamaha the bowl and venturi are equally pressurized by putting the whole carb in the airbox. A fuel pump was also added to replace the gravity feed system and the float seats were replaced with smaller diameter fuel inlets. Honda chose to have solenoid controlled fuel tank vents, and pressurized the tank as well.



Just run the bowl vents into your airbox. Excessively long bowl vents have caused running problems on some motors I have seen, I am not sure why.

slyck(at)frontiernet.net
Guest

Posted: Wed Jan 14, 2009 1:52 pm Post subject: Pressurized motors

Good post.  If the airbox pressurizes the whole kaboodle then you  

would be compensating properly for altitude.

It looks like a good fix to me.

BB



On 14, Jan 2009, at 4:33 PM, dalewhelan wrote:



 	  Quote: 	
		   

 <dalewhelan(at)earthlink.net>



 Let's say you have 1 bar of pressure in the float bowl and .9 bar  

 in the venturi. The lower pressure in the venturi results in fuel  

 delivery to the venturi.

 Now if we increased the venturi pressure by .2 bar we would have  

 fuel delivery to the bowl.

 On my racing Yamaha the bowl and venturi are equally pressurized by  

 putting the whole carb in the airbox. A fuel pump was also added to  

 replace the gravity feed system and the float seats were replaced  

 with smaller diameter fuel inlets. Honda chose to have solenoid  

 controlled fuel tank vents, and pressurized the tank as well.



 Just run the bowl vents into your airbox. Excessively long bowl  

 vents have caused running problems on some motors I have seen, I am  

 not sure why.





 Read this topic online here:



 http://forums.matronics.com/viewtopic.php?p 24770#224770

jbhart(at)onlyinternet.ne
Guest

Posted: Thu Jan 15, 2009 8:04 am Post subject: Pressurized motors

At 01:33 PM 1/14/09 -0800, you wrote:

 	  Quote: 	
		  



Let's say you have 1 bar of pressure in the float bowl and .9 bar in the venturi. The lower pressure in the venturi results in fuel delivery to the venturi.

Now if we increased the venturi pressure by .2 bar we would have fuel delivery to the bowl.

On my racing Yamaha the bowl and venturi are equally pressurized by putting the whole carb in the airbox. A fuel pump was also added to replace the gravity feed system and the float seats were replaced with smaller diameter fuel inlets. Honda chose to have solenoid controlled fuel tank vents, and pressurized the tank as well.



Just run the bowl vents into your airbox. Excessively long bowl vents have caused running problems on some motors I have seen, I am not sure why.




	


Dale,



At the pressures you have given above, I agree with you and I belive this 

where I had the disconnect with your thinking.  It has to do with the size 

of the pressure differences.  I have been thinking about a maximum pressure 

difference of five inches of water, which is 0.012 bar.



The air box connection is good.  In my case I use the pressure below the 

wing as the maximum constant float bowl static pressure source.  For level 

flight, this source is independent of altitude or airspeed. But it's 

magnitude is dependent upon wing loading.  For the my FireFly at gross 

weight this static pressure calculates out to 0.989 inches of water.  Since 

my carburetor is set rich at this static pressure, I can lower the pressure 

to the float bowl and lean out the engine as desired.



As for the excessively long bowl vent problems, I expect it is caused by 

carburetor design.  Some carburetors draw jet percolation air through an 

internal passage way to from over the float bowl.  This means there is a 

constant flow through the float bowl vents.  Any constriction that would 

influence this flow, such as a long tube, would cause problems.  In the case 

of the Bing this is not a problem, as the idle and percolation air sources 

are independent of and not connected to the float bowl.  If this was not the 

case, I would not be able to move the EGT 150 degrees F with a five inches 

of water pressure change over the float bowl.



This has been interesting.  Four below zero, blowing snow and bright 

sunshine.  Late yesterday afternoon, I fired up the Kubota and blew snow for 

about an hour.  I will have to do the same before the school bus drops off 

the grand daughter.  Not as much fun as flying, but it does break up the 

day.



Jack B. Hart FF004

Winchester, IN

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