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Pressurized motors

 
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Thom Riddle



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

PostPosted: Mon Jan 12, 2009 6:05 am    Post subject: Pressurized motors Reply with quote

..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


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Thom Riddle
Buffalo, NY (9G0)



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lucien



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

PostPosted: Mon Jan 12, 2009 7:05 am    Post subject: Re: Pressurized motors Reply with quote

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


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LS
Titan II SS
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Thom Riddle



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

PostPosted: Mon Jan 12, 2009 7:11 am    Post subject: Re: Pressurized motors Reply with quote

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

do not archive


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Thom Riddle
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George Alexander



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

PostPosted: Mon Jan 12, 2009 7:26 am    Post subject: Re: Pressurized motors Reply with quote

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.


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George Alexander
FS II R503
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http://www.oh2fly.net


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



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

PostPosted: Mon Jan 12, 2009 7:28 am    Post subject: Re: Pressurized motors Reply with quote

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


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Thom Riddle



Joined: 10 Jan 2006
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PostPosted: Mon Jan 12, 2009 7:32 am    Post subject: Re: Pressurized motors Reply with 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


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jbhart(at)onlyinternet.ne
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PostPosted: Mon Jan 12, 2009 8:34 am    Post subject: Pressurized motors Reply with quote

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


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herbgh(at)nctc.com
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PostPosted: Mon Jan 12, 2009 8:52 am    Post subject: Pressurized motors Reply with quote

a lot of this propaganda is written by the same folks who write "if
it lasts more than 4 hours , see your doctor" !! Smile 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



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dalewhelan



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

PostPosted: Wed Jan 14, 2009 1:33 pm    Post subject: Re: Pressurized motors Reply with 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.


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PostPosted: Wed Jan 14, 2009 1:52 pm    Post subject: Pressurized motors Reply with quote

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




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PostPosted: Thu Jan 15, 2009 8:04 am    Post subject: Pressurized motors Reply with quote

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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