DA-50 Mod: Anyone seen this?    Gallery
View related threads: (in this forum | in all forums)

Logged in as Guest



Users viewing this topic: none
    Search This Thread  
 
Printable Version

All Forums >> Glow Engines, Gas Engines, Fuel & Mfg Support Forums >> Gas Engines >> DA-50 Mod: Anyone seen this?
Page: [1]

Tower Hobbies Get Coupon Codes Brands  
Login
Message << Older Topic   Newer Topic >>
DA-50 Mod: Anyone seen this? - 9/29/2006 5:19 PM   
plasticman


 

Posts: 328
Score: 105
Joined: 6/8/2005
Last Login: 5/13/2012
From: Xenia, OH, USA
Status: offline 		I have come across a very interesting mod on a DA-50 from a person who knows his stuff; this was based on a discussion about the balsa box. So, I did the best I could at drawing it up. The carb plate hole should be soldered shut (original diaphram vent) and the brass tubing should be soldered on both sides and then dremeled on the inside.

Anyone seen this mod?

P-man

Attachments
Click to see fullsize image.
Click for fullsize


< Message edited by plasticman -- 9/29/2006 5:21 PM >


_____________________________

Plasticman


Hide Signatures
       Post #: 1

RE: DA-50 Mod: Anyone seen this? - 9/29/2006 6:54 PM   
Crusty



Posts: 356
Score: 100
Joined: 11/9/2004
Last Login: 4/13/2007
From: Metropolis , ARUBA
Status: offline 		One question..why not use the original vent hole and solder a tube there?..seems like extra work for nothing
Anyway, looks like a good mod to eliminate pressure variations on the diaphragm so long as the carb throat is suitably located in the first place, a bit like the 3w venturi which locates the vent in the venturi opening

_____________________________

Who put that tree there?

Hide Signatures

(in reply to plasticman)
       Post #: 2

RE: DA-50 Mod: Anyone seen this? - 9/29/2006 7:01 PM   
Tired Old Man


 

Posts: 18600
Score: 662
Joined: 2/25/2002
Last Login: 1/16/2012
From: Valley Springs, CA, USA
Status: offline 		Concur. I fly with the guy that came up with the balsa box, and adding the tube is all that either one of us would do when required.

_____________________________

Never lie, and never minimize or gloss. Tell it like it is and let the pieces fall where they may. The truth always wins.

Hide Signatures

(in reply to Crusty)
       Post #: 3

RE: DA-50 Mod: Anyone seen this? - 9/29/2006 7:03 PM   
jongurley



Posts: 2830
Score: 100
Joined: 4/24/2003
Last Login: 4/9/2013
From: Goldsboro, NC, USA
Status: offline 		Me too, I don't really understand what this would accomplish,,,,

_____________________________

"Practice, confidence and arrogance makes you a better pilot, few can use these to the best of their ability" JONGURLEY 3:16

Hide Signatures

(in reply to Tired Old Man)
       Post #: 4

RE: DA-50 Mod: Anyone seen this? - 9/29/2006 9:36 PM   
rcbill


 

Posts: 479
Score: 100
Joined: 2/13/2003
Last Login: 1/6/2013
From: pleasant prairie, WI, USA
Status: offline 		I'm not sure what this would do also. I can tell you this though. I have a GP Pitts with a FPE 3.2 engine. The engine would run fine on the ground but the second the wheels lifted off the ground it would run so rich it was barely able to fly. The carb plate had 2 holes so I soldered one closed and soldered a nipple on the center hole and ran fuel line to the inside of the fuse just like I have read on these threads. Instead of building a balsa box I just plugged in a felt clunk to the end of the line. I also removed the velocity stack. The engine runs great with no changes from ground to being airborne. I'm happy with the engine although I don't really like flying the Pitts but it sure gets a lot of attention on the flightline. (Shoulda bought the Ultimate) Bill

Hide Signatures

(in reply to jongurley)
       Post #: 5

RE: DA-50 Mod: Anyone seen this? - 9/29/2006 10:04 PM   
JoeAirPort



Posts: 10260
Score: 116
Joined: 8/12/2003
Last Login: 5/19/2013
From: Milwaukee, WI, USA
Status: offline 		Looks like he's trying to make the diaphragm vent the same pressure as the air inlet on the carb. I don't know enough about carb's to tell what this accomplishes. If anything there might be a negative pressure at the carb air inlet causing the vent to go slightly negative. That's not good. You want the vent to be a constant atmospheric pressure.

I agree, plumbing the vent to the fuse or a balsa box works well for many people.

< Message edited by JoeAirPort -- 9/29/2006 10:06 PM >

_____________________________

Joe AP

Hide Signatures

(in reply to rcbill)
       Post #: 6

RE: DA-50 Mod: Anyone seen this? - 9/29/2006 11:09 PM   
plasticman


 

Posts: 328
Score: 105
Joined: 6/8/2005
Last Login: 5/13/2012
From: Xenia, OH, USA
Status: offline 		I have some more information on this: I just spoke to Mr. Jim Cline who is a freind of mine as we fly at the same field. He is the designer of the Cline Regulator which is essentially Walbro parts. I knew Jim would know something about this. He said this layout works and can solve the problem of air velocity problems on a DA-50. By positioning the brass tubing close to the venturi the diaphram will then see the same pressure as the venturi; and this is how the Walbro carb is supposed to work.

P-man.


_____________________________

Plasticman


Hide Signatures

(in reply to JoeAirPort)
       Post #: 7

RE: DA-50 Mod: Anyone seen this? - 9/29/2006 11:31 PM   
JoeVen



Posts: 81
Score: 100
Joined: 12/15/2005
Last Login: 5/7/2013
From: Cumana Sucre, VENEZUELA
Status: offline 		I known I saw it anywhere... , guys look at this:
http://www.rcuniverse.com/forum/m_4665248/tm.htm#
JoeAP your thinking is half right, this carb modification seems to work by equalizing the vent hole pressure to the intake carb pressure, this way the diference betwen these values keeps steady.
I´m suffering engine sags on flying so I´m traking whatever anybody post related the issue, this arrengement look like my final solution....

_____________________________

Good pilot leaving the ground, best builder landing on!

Hide Signatures

(in reply to JoeAirPort)
       Post #: 8

RE: DA-50 Mod: Anyone seen this? - 9/30/2006 12:19 AM   
RTK



Posts: 4892
Score: 116
Joined: 4/21/2003
Last Login: 5/16/2013
From: Left Coast , CA, USA
Status: offline 		plasticman, that should work in most situations. I had a particularly odd set-up in which it did not. That is when I made the magic dead air box. It cured 90+percent of my problem.

Hide Signatures

(in reply to JoeVen)
       Post #: 9

RE: DA-50 Mod: Anyone seen this? - 9/30/2006 1:19 AM   
rmh



Posts: 12307
Score: 252
Joined: 12/12/2001
Last Login: 5/19/2013
From: , UT, USA
Status: offline 		I only had one engine which had rich/lean problems - used a Bing carb
Anyway
here is what that darn hole does:
when the carb was designed - the DEMAND REGULATOR was adopted to supply fuel --upon demand
the theory is this : spring pressure holds a needle seated
that needle is attached to a diaphragm (think of a drumhead)

On a snare drum - notice there is always a hole in the side - this is to release air (or let in air) as the drum head is struck.
The hole in the lid of the demand regulator is for the same purpose - nothing more nothing less
It just lets the diaphram move with no pressure or vacuum on the outside
The engine -as it draws a slight vacuum (carb opening) ,lowers pressure on the underside of the diaphragm- this then, moves the needle attached to it . opening it ever so slightly admitting fuel to the airsream.-or as much fuel as the vacuum DEMANDS.
In order for this sensitive arrangement to work correctly - there must be no opposing force or air restriction on the other side of it.
So-- there is a small breather hole in the dirt cover plate .
Cowlings have air unbalances /changes inside them in some cases--as the plane changes attitudes and speeds.
The pressure (NOT AIRBLAST ) on the vented side, can and does change, becoming lower or higher
the demand regulator is then working aginst a different air pressure - giving a different fuel flow -higher or lower
When the carb was designed - the use of it in a model airplane was never even considered - but operating at different altitudes was consided -so -the cover is vented. to assure a normalized environment
If you took that vent and attached it with a line, to a large sealed plenum with a tiny pin hole in it -the diaphragm would never see fast air pressure changes
moving the vent by a line to inside a fuselage - often fixes the problem of pressure changes
anything done to provide a constant vent pressure will work
- there must be a pressure that remains close to atmospheric -that's it.
The vent plced at the inlet of the carb works for that reason - -it assures a rather constant vent pressure ( air pressure at carb opening.
so does a little wooden box - so will a small can/bottle --- whatever--- with a small leak in it to let it gradually normalize.
the little cover plates sometimes are enough- but if not -anything you do to create a constant vent pressure will work.

< Message edited by dick Hanson -- 9/30/2006 1:28 AM >

_____________________________

Libby is still watching you

Hide Signatures

(in reply to RTK)
       Post #: 10

RE: DA-50 Mod: Anyone seen this? - 9/30/2006 2:10 AM   
AndresAM


 

Posts: 206
Score: 100
Joined: 2/13/2005
Last Login: 5/17/2013
From: Tulua, COLOMBIA
Status: offline 		I had some issues with my DA too. It was air pressure building up in the cowl and making the engine rich in flight. My fix was the brass tube soldered to the carb cover but I routed the tygon tube OUTSIDE the plane in a place where was not affected by airflow . In my opinion the balsa box is not needed. Outside the plane the pressure is the same (atmospheric) not matter what the speed of the plane is and unless you point the tube direct to the airflow the carb will always "see" the same pressure.
Another good thing I observed was that you can tune the engine with or without the cowl and get the same results. My DA 50 runs exactly the same now whether it is on the ground, in the air, inverted, knife edge or whatever ....
Andres

Hide Signatures

(in reply to rmh)
       Post #: 11

RE: DA-50 Mod: Anyone seen this? - 9/30/2006 2:29 AM   
RTK



Posts: 4892
Score: 116
Joined: 4/21/2003
Last Login: 5/16/2013
From: Left Coast , CA, USA
Status: offline
quote:

ORIGINAL: AndresAM
I routed the tygon tube OUTSIDE the plane in a place where was not affected by airflow . In my opinion the balsa box is not needed. Outside the plane the pressure is the same (atmospheric) not matter what the speed of the plane is and unless you point the tube direct to the airflow the carb will always "see" the same pressure.

Andres


Just some more information to pass along to prevent what happened to me. Do Not let that tygon tube dangle outside the cowl pointing rearward in the air stream. In my experimenting I found that this creates a small enough vacuum which will keep your metering needle seated, this will lead to a dead stick about half way through the first pattern when higher speeds are hit. I know, it happened 3 different times, in 3 different rearward positions. Guess I am a slow learner

Hide Signatures

(in reply to AndresAM)
       Post #: 12

RE: DA-50 Mod: Anyone seen this? - 9/30/2006 2:30 AM   
rmh



Posts: 12307
Score: 252
Joined: 12/12/2001
Last Login: 5/19/2013
From: , UT, USA
Status: offline 		--your cowl should really see a low pressure in flight -- this means air is flowing in up front and then being extracted at an aft point.
this is important for best cooling - unless your entire cylinder is hanging out in airstream

< Message edited by dick Hanson -- 9/30/2006 2:31 AM >

_____________________________

Libby is still watching you

Hide Signatures

(in reply to AndresAM)
       Post #: 13

RE: DA-50 Mod: Anyone seen this? - 9/30/2006 2:34 AM   
rmh



Posts: 12307
Score: 252
Joined: 12/12/2001
Last Login: 5/19/2013
From: , UT, USA
Status: offline 		the dangling line is like the problem seen on many glo engined models - the tank vent dangling can create a low pressure in the tank
moral :
don't leave it dangling----

_____________________________

Libby is still watching you

Hide Signatures

(in reply to rmh)
       Post #: 14

RE: DA-50 Mod: Anyone seen this? - 9/30/2006 2:44 AM   
AndresAM


 

Posts: 206
Score: 100
Joined: 2/13/2005
Last Login: 5/17/2013
From: Tulua, COLOMBIA
Status: offline
quote:

Just some more information to pass along to prevent what happened to me. Do Not let that tygon tube dangle outside the cowl pointing rearward in the air stream. In my experimenting I found that this creates a small enough vacuum which will keep your metering needle seated, this will lead to a dead stick about half way through the first pattern when higher speeds are hit. I know, it happened 3 different times, in 3 different rearward positions. Guess I am a slow learner


As I said you have to locate the tube in the right place, but you are right, direct airflow or the tube hanging on the air will give a different pressure reading and the results you mentioned.
My DA is in a CA 27% extra and I found that a good place to place the tube was in the recessed area in the fuse where the landing gear is mounted. The DA runs great now,
Andres

< Message edited by AndresAM -- 9/30/2006 2:46 AM >

Hide Signatures

(in reply to rmh)
       Post #: 15

RE: DA-50 Mod: Anyone seen this? - 9/30/2006 2:57 AM   
RTK



Posts: 4892
Score: 116
Joined: 4/21/2003
Last Login: 5/16/2013
From: Left Coast , CA, USA
Status: offline 		One more thing, erratic air flow over the carb venturi and or changing air flow/pressure will cause a similar problem even with the diaphragm tube.

Dick, in a few more years mine will only be dangling

< Message edited by RTK -- 9/30/2006 2:59 AM >

Hide Signatures

(in reply to AndresAM)
       Post #: 16

RE: DA-50 Mod: Anyone seen this? - 10/7/2006 10:10 AM   
pierocapredoni



Posts: 16
Score: 100
Joined: 11/1/2005
Last Login: 12/29/2008
From: Mendoza, ARGENTINA
Status: offline 		I have some issues of performance of my DA50 in flight, even dead sticks. Once I done the mod in the carb, soldering brass tube to original vent hole and tygon tube to balsa box, all my problems dissapeared. My engine runs now same in ground than in flight. Here some pictures.....

Attachments
Click to see fullsize image.
Click for fullsize 		Click to see fullsize image.
Click for fullsize


Hide Signatures

(in reply to RTK)
       Post #: 17

RE: DA-50 Mod: Anyone seen this? - 10/11/2006 2:00 PM   
TW3DGUY


 

Posts: 38
Score: 100
Joined: 12/3/2003
Last Login: 5/17/2013
From: Taipei, TAIWAN
Status: offline
quote:

ORIGINAL: RTK

One more thing, erratic air flow over the carb venturi and or changing air flow/pressure will cause a similar problem even with the diaphragm tube.

Dick, in a few more years mine will only be dangling

RTK, so if erratic air flow over the carb venturi with the diaphragm tube to sealed box same problem occur, how to solve ? use velocity stack? I tried but doesn't work.

< Message edited by TW3DGUY -- 10/11/2006 2:02 PM >

Hide Signatures

(in reply to RTK)
       Post #: 18

RE: DA-50 Mod: Anyone seen this? - 10/15/2006 9:40 PM   
RTK



Posts: 4892
Score: 116
Joined: 4/21/2003
Last Login: 5/16/2013
From: Left Coast , CA, USA
Status: offline 		TW3DGUY-- Experiment with either a velocity stack or removing the erratic air flow from around the venturi. Make sure you have at least one inch between the venturi and cowl/firewall too, more is better from what I have found. Your mileage may vary though

Hide Signatures

(in reply to TW3DGUY)
       Post #: 19

RE: DA-50 Mod: Anyone seen this? - 10/16/2006 9:45 AM   
TW3DGUY


 

Posts: 38
Score: 100
Joined: 12/3/2003
Last Login: 5/17/2013
From: Taipei, TAIWAN
Status: offline 		RTK, thank,
I have 35% AM yak with DA100 and 37% AM YAK with 3W157, both engines with velocity stack and diaphragm tube to sealed box but still run rich when take off, yesterday I took velocity stack off and put one CF plate behind crab as a dam for creating air flow positive presure and routing more air into crab inlet, big improvement when take off and mid-range throttle in air.

Hide Signatures

(in reply to RTK)
       Post #: 20

RE: DA-50 Mod: Anyone seen this? - 10/19/2006 4:47 PM   
Hirobocool



Posts: 82
Score: 100
Joined: 2/28/2003
Last Login: 1/9/2013
From: Miami, FL, USA
Status: offline 		pics

CARBURETOR DIAPHRAGM COVER


Attachments
Click to see fullsize image.
Click for fullsize


< Message edited by Hirobocool -- 10/19/2006 4:55 PM >

Hide Signatures

(in reply to TW3DGUY)
       Post #: 21

Page:   [1]
All Forums >> Glow Engines, Gas Engines, Fuel &amp; Mfg Support Forums >> Gas Engines >> DA-50 Mod: Anyone seen this?
Page: [1]





Jump to:


 
Google 



Search | Marketplace | Event Calendar | Local Clubs | Magazine | Product Ratings | New Products | Discussion Forums

Photo Gallery | Instructor Search | Field|Track|Marina Search

Advertisers | Hobby Vendor Resources | Rate Manufacturers | Sign In/Sign Up

SITE MAP!   : :   FORUM RULES

RC Universe is a service of Internet Brands, Inc. Copyright © 2001-2013.

Charities we support that also need your help
Yorkie Rescue | Humane Society | ASPCA | Crohn's-Colitis America


0.625RCU1