Why the slanted glow plug on some Fox engines?

idk, several companies did the slant plug thing in the late 60's-early 70's (this was also a about the time a lot of larger R/C engines dabbled in dual plug head designed) i can only guess that there was some improvement in combustion with the element tilted into the direction of the intake?

This was also my first 'big bore' engine, went down to the new hobby shop that just opened in town, after school the last day of 6th grade. Bolted it onto a jr. Ringmaster, don't recall having any issues with it, it seemed to start decent enough and pulled the jr. ringmaster with good tension.

Kim wrote:.......wondering about the purpose of it's slanted glow plug.  

Cross threaded???

From what I have read it was designed to be a "swirl quench" chamber. Impoving combustion. I doubt it did a whole lot as it didn't last long. The 36X is the same.

Do these have a flat top piston or is it somehow contoured to utilize the plug angle?

The plug is positioned like that so the bottom of the plug is flush with the bottom of the cylinder head. The combustion chambre must be wedge shaped or maybe pent.

Thanks guys.  

Yeah Ron, I've heard that term "swirl quench" before, maybe in an engine review by Peter Chinn. Can't remember any of the other details, so am searching through my stack of old magazines to see if I can find a review on this or a similar engine.

KariFS wrote:Do these have a flat top piston or is it somehow contoured to utilize the plug angle?

Good question...gonna stick a flashlight in the exhaust port here in a bit to see if there's a web on the top of the piston.

There is a baffle on top of the piston

OVERLORD wrote:The plug is positioned like that so the bottom of the plug is flush with the bottom of the cylinder head. The combustion chambre must be wedge shaped or maybe pent.

Makes sense, although intuitively I would have made the combustion chamber angled the other way around

I am pretty sure those area all baffle piston engines. The angled plug suits the irregular shape of the baffled combustion chamber head better.

Phil

Ken Cook will know for sure.

I think I read somewhere that the slant plug had something to do with a side mounted engine close to the wing needing better access for start glow

When Fox updated the 36X design he went to the slanted plug.  His ads said it was to allow easy, faster plug changes on combat models.  But it may also have had to do with performance.  Over the years engine manufacturers have moved the plug location all over the head.  McCoy really did a lot of this and so did Fox of course.  Fox's first ad for the new 36X in the Sept. 1964 MAN showed the tilted plug pointing the wrong way.  

In the Nov. 1964 ad they got it right.


varied plug locations:
1958 35RC Special

1958 Fox 15

L&J modified Stunt 35s


1972 fox Eagle 60

1978 Fox Eagle 60 Export

1980 Fox Eagle 60 USA

Details of 1978 Export and 1980 Fox USA heads - both were designed for no or low nitro fuels


Fox 60 Stunt

Ah Ha!...that is what I remember....not for easier glow clip, but much easier to replace with slanted plug where the head is in line and close to the LE making plug replacement difficult if dead center and tool to knuckle limited space....

I do not have any slant plug engines but can attest that a straight plug near the wing does NOT allow the use of a typical 4 way tool to replace the plug and then a screw driver tool is needed ----but still a pain to do (fast)

I ... on re-thinking of this... wonder how many reading appreciate that a LOT of COMBAT matches are won on the ground

Cuts, kill (in some rules), and airtime are part of the scoring

If a plane flames out from dead plug the pit crew needs a strategy, tooling, and access to new plug FAST!

Same with prop replacement

Although I have never flown it, but seems that CL racing or speed have similar NASCAR style pit crew drills and speed thinking

I always assumed it was due to the easier access to the plug. From my experience, no matter where the plug is located in the cylinder head it doesn't seem to make a hoot of difference. Mccoy did this all the time. While there's mention of the plug location making it easier to pit for the Combat X series, the later Mark series had straight plugs. I wish they didn't alter this as I had to modify my wrenches to gain access to the plugs. My engines are recessed back into the wing making a T-wrench or cross handle style obsolete. I think the question was a very good one because no matter who I've asked, I get the blank stare initially. Ken

I think when the head button design became the performance standard most engines started using a central vertical plug.

From the top of my head:

In the fifties, when an engine was run hot (speed or racing) the hottest area in an engine was on center-top of the piston. It was known as hell's kitchen. Because of this heat, some engines failed at the top of the connecting rod or the wrist pin. Designs were tried that provided the best swirl of the incoming charge to cool off the top of the piston and a better burn of the fuel.

In 1960 Supertigre and K&B came out with a flat topped piston that used the intake porting to provide swirl. These were improved on with PDP (Perry Directional Porting) and eventually Schnuerle porting.

Another thing that came out during those times was the idle-bar glow plug. Be careful using them in old engines because some will allow the baffle to hit the idle bar...ungood!  

Besides, if the second generation Fox .15's didn't have the slant plug they may have been referred to as "drop-ins".

George