littlera
Posts: 31
Joined: 3/22/2007
From: Advance, NC, USA
Status: offline
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Mesaflyer,
No, I did not receive a direct post to my questions about the vent, but did some further research and reached some decisions:
(1) I have located other postings where modelers have modified the diaphragm cover by adding a vent tube over the existing vent hole. I believe this is better than trying to drill another hole in the cover, near the center for example. Putting it over the existing hole ensures that the vent tube does not interfere with the movement of the diaphragm or the needle assembly (rivet) in the center of the diaphragm. A brass tube, end shaped with a Dremel tool to fit closely over the vent hole, is silver soldered over the hole pointing out radially. Center line of tube will point to center of cover, and will be in same plane. Don't forget to remove the zinc plating on the cover in the area to be silver soldered. The Dremel with grinding bit will be good for this. You will not have success soldering to zinc plating. Of course remove the cover from the carburetor before grinding or soldering on the cover. Failure to observe this will heat damage the diaphragm and ruin your whole day.
(2) After due consideration, I have decided to create a static port on the side of my plane, aft of the cowling. This will be a flush disk, maybe the size of a dime, with a hole in it of about 1 mm. A brass tube will be soldered over this hole on the back side and I will attach the vent line to this. There is precedence for this from full scale aircraft. which use such static sources and to provide reliable static pressure to air speed indicators and other instrumentation. They are used in this way in combination with pitot tubes (for total or dynamic pressure.)
Second best to this would be to run the vent line into the inside of the fuselage. This PROBABLY is at true static pressure, or very close to it, due to such side vents as pushrod exits, etc. This may not be the case, for example, if a high static pressure (fuel line hole in firewall into cowling area) is feeding the volume inside the fuse faster than it can vent through various leak points. Gaps at the bottom of a windshield can be a source for very high pressure air into the fuselage. It all just depends where openings are located on the fuselage as to their effect on the static pressure inside the plane.
A flying buddy advised me do try the engine without mods before creating the vent scheme, but I don't want to suffer a problem and have to retrofit. It is easier to do it up front for me. Anyway, I am an aerospace engineer and like the thoughts of such a functional relatively scale detail!
Engineers tend to worry about physical things, modes and effects that others of different disciplines are blissfully unaware of. Usually the concerns turn out to be of little or no consequence, but sometimes ............... 
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All Forums >> Glow Engines, Gas Engines, Fuel & Mfg Support Forums >> Gas Engines >> RE: CRRC PRO GF26I 
RE: CRRC PRO GF26I - 
I see on Brillelli's site that he provides his engines with the static nipple. I believe that I have seen pictures of engines were other people have just JB welded theirs on. I hope JB weld will work, as I only own a