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Vintage Forster .29 fuel and glow plug type

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Vintage Forster .29 fuel and glow plug type

Old 02-27-2023, 01:33 PM
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meowy84
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Default Vintage Forster .29 fuel and glow plug type

I have an old front-intake Forster .29 engine I want to get running and need glow plug suggestions. Does anyone know if OS #8 or equivalent would work or do I need one of those old style glow plugs with the idle bar?

As for fuel I assume 5% or 10% with at least 20% castor should do it?
Old 02-27-2023, 02:49 PM
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LLRCFlyer
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Default Forster .29 plug

MEOWY84,

Idle bar glow plugs were designed for use in loop-scavenged engines to keep raw incoming fuel from spraying on the glow plug's coil and quenching it during extended low power/low heat (idle) operation. Control line and free-flight engines without a throttle do not idle and therefore do not need idle bar glow plugs. So, unless your vintage Forster .29 (early 1950's) has been modified to add a throttle, then use a non-idle bar plug and determine the proper heat range by trial and error.

Unlike loop-scavenged engines, Schnuerle scavenged engines don't spray as much fuel on the glow plug and hence do not need an idle bar, but the .29 Forster was long out of production before Schnuerle porting was invented.

If you want more information on the Forster .29, go to Scepter Flight Model Engine Tests (Sceptre Flight). There is an engine review article on the Forster F-.29 taken from the August 1952 edition of Air Trails Magazine.

David
Old 03-02-2023, 11:23 AM
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meowy84
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Thanks LLRCFlyer for the info and the Scepter link. Funny you should mention adding a throttle, that was going to be my follow up question. If I did add a throttle I might need one of the idle bar plugs and the question arises of where to get one? I know Mecoa sells some but they're about $20 (a bit much for a plug is you ask me...). Any other sources?
Old 03-02-2023, 03:14 PM
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LLRCFlyer
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Default Glow plugs?

Meowy84,

I saw some idle bar plus on the Brodak website https://brodak.com/engines.html?p=7 Not quite the ones you want (4-C and tuned pipe) but $8-9. I have not bought glow plugs lately, but apparently finding idle bar plugs is like searching for dinosaur bones. Mecoa may end up being your source. Go easy on the nitro and the plugs will last longer. My bigger question is where are you going to find a carburetor to fit a Forster .29?

Good luck.
Old 03-02-2023, 03:29 PM
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LLRCFlyer
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Default Throttle for FOrster .29?

One last thought. Some non-throttle engines used sub-piston supplementary air induction to increase power. The bottom of the piston skirt would rise above the bottom f the exhaust port at top dead center and allow a little more air to enter into the crankcase. Many of the Cox reed valve engines used this. I had a Super Tigre .23 control line engine that had this porting. When I added a throttle, it would only idle when it was fitted with a muffler which prevented any fresh air from entering the crankcase via the exhaust port. The Super Tigre 23 RC engine did not have sub-piston supplementary air induction and idled well without a muffler. Check to see if the Forster .29 has the sub-piston porting. If it does, then don't waste your time with a throttle.
Old 03-03-2023, 11:33 AM
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meowy84
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Thanks again for the super info and for bringing up the issues I might run into. I have a few assorted carbs that I was going to try and I was going to try to fashion an adapter which I actually thought that might be easier on the Forster than on other engines because the venturi on the F-29 is threaded into the intake. One immediate problem I see is that the venturi assembly is so close to the actual engine case that there might not be enough room to accept a carb without making a longer intake to clear the crankcase which might then cause problems with venturi pressure and fuel delivery. And then of course you also have the issue of the sub-piston porting you mentioned that I have to look into also.

Anyways, at this point I'll just try to get the engine running as-is and see how it goes. The carb mod is further down the line and only in the dream stage at this point.

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