Author |
Messages |
Dirk Radewald
Private
Gender: Male
Location: Braunschweig, Germany
Registered: Sep 2011
Status: Offline
Posts: 2
|
Posted Thursday, August 16, 2012 @ 03:47 AM
Hi Folks,
please give me your feedback for a simple question:
does the CD-3 take regard to the thinner air in higher altitude?
Are there alternatives ?
|
Bob Grimstead
Captain
Gender: Male
Location: Perth, Western Australia or West Sussex, England
Registered: Dec 2006
Status: Offline
Posts: 2027
|
Posted Thursday, August 16, 2012 @ 06:05 AM
Hi Dirk,
Yes, the Stromberg CD 150 automatically compensates for the reduced oxygen at higher altitudes.
Yours, Bob
-------------------- Flying and displaying Fournier RF4Ds VH-HDO and G-AWGN, building replica RF6B G-RFGB and custodian of RF6B prototype F-BPXV
|
Mike-RM
Sergeant
Gender: Male
Location: East Sussex Gliding Club, Ringmer, UK
Registered: Mar 2007
Status: Offline
Posts: 38
|
Posted Thursday, August 16, 2012 @ 05:11 PM
How does it do that, Bob?
(Mine ran fine at 12000ft over the Alps earlier this year)
Mike
|
Bob Grimstead
Captain
Gender: Male
Location: Perth, Western Australia or West Sussex, England
Registered: Dec 2006
Status: Offline
Posts: 2027
|
Posted Friday, August 17, 2012 @ 05:21 AM
I don't know Mike, because I don't have one, but I'm guessing it will be something to do with that slidey/needly thing in the middle.
Ask Eugenio?
Yours, Bob
(PS Will you be at Old Hay on Saturday or Piltdown on Sunday?)
-------------------- Flying and displaying Fournier RF4Ds VH-HDO and G-AWGN, building replica RF6B G-RFGB and custodian of RF6B prototype F-BPXV
|
jb92563
Second Lieutenant
Gender: Male
Location: Lake Elsinore, CA, USA
Registered: Mar 2007
Status: Offline
Posts: 583
|
Posted Friday, August 17, 2012 @ 10:05 AM
I think that is the same carb as I have in the Grob 109. Dual carbs actually.
It seems to compensate based on barometric pressure. It only has two settings though, normal and lean and mine kicks in at between 5000' to 6000'.
I have some pictured instructions on adjusting the needle for mixture if you need it.
-------------------- Ray
RF4D #4057 N-1771 Rectimo 1400cc
http://picasaweb.google.com/jb92563/FournierRF4D
http://www.touringmotorgliders.org
|
Donald
Command Sergeant Major
Gender: Male
Location: Scotland
Registered: Jan 2007
Status: Offline
Posts: 489
|
Posted Friday, August 17, 2012 @ 11:36 AM
I think the compensating device in the Stromberg is the diaphram which in turn moves the needle jet. From a long ago memory the upper surface of the diaphram is exposed to the air pressure in the throat of the carb and the underside to ambient air pressure, so it responds to the differential between the two. As you climb the ambient pressure drops but so too does that in the throat so the differential is maintained.
Suddenly opening the throttle gives a lower throat pressure relative to ambient so the needle is lifted more thus enriching the mixture for acceleration until equilibrium is again reached.
I think that's how it works.
|
Mike-RM
Sergeant
Gender: Male
Location: East Sussex Gliding Club, Ringmer, UK
Registered: Mar 2007
Status: Offline
Posts: 38
|
Posted Friday, August 17, 2012 @ 04:51 PM
I agree with Donald. There is no mechanism to switch to lean. Thinking about it, lower atmospheric pressure would tend to reduce the pressure drop in the mixing chamber - between the pison and the butterfly so probably the diaphragm/pison drops as the altitiude increases causing the needle valve to lower and reduce the fuel flow. Clever really, no need for a mixture control.
Mike
[Edit by Mike-RM on Friday, August 17, 2012 @ 04:52 PM]
|
eugenio
First Sergeant
Gender: Male
Location: Str. Val S. Martino inferiore 133/7 I - 10131 Torino ITALY
Registered: Oct 2006
Status: Offline
Posts: 294
|
Posted Tuesday, August 28, 2012 @ 01:59 PM
I confirm the principle is correct. The outside pressure is taken from the upper port of the filter side and the manifold pressure is taken from the two holes in the bottom of the piston. The membrane takes up the piston and consequently the metering needle. This is the reason why the membrane must be checked for porosity and cracks.
Eugenio
|
Dirk Radewald
Private
Gender: Male
Location: Braunschweig, Germany
Registered: Sep 2011
Status: Offline
Posts: 2
|
Posted Thursday, October 18, 2012 @ 08:30 AM
Quote: | | This is the reason why the membrane must be checked for porosity and cracks. |
|
Hi Eigenio,
I checked the membrane last weekend: it does have some cracks ! !
but what is the result:
is the mixture leaner with a defect membrane or not ?
the sparkplugs have shown a good brown colour (with avgas)
Best regards !
|
eugenio
First Sergeant
Gender: Male
Location: Str. Val S. Martino inferiore 133/7 I - 10131 Torino ITALY
Registered: Oct 2006
Status: Offline
Posts: 294
|
Posted Thursday, October 18, 2012 @ 02:36 PM
If the membrane is craked you risk a too lean mixture, rough behaviour and at last an engine stop. If the membrane does not work it cannot lift the piston (kept down by the spring) and you have it always at idle (this is the case if the membrane is broken or with big cracks).
You have better to change it. If you don't find the original Zenith membrane, the Bing 64 (BMW, Rotax, Sauer etc.) membrane is the same. Remember to put some light oil in the dampener. Hydraulic oil is fine, don't use engine oil, it's too thick.
Eugenio
|