Forrest Edwards 5 cylinder compression ratio?

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Hi, Folks. At the end of my build of Forrest Edwards 5 cylinder glow plug engine and at the commissioning stage. Cant find any build notes so my question to all is: as this is a glow engine using mix of nitro and methodology, what should the compression ratio be. At the moment I have it at 8.5 but being advised that Methanol needs a far higher ratio. Advise please 20220708_172128.jpg 20220708_172137.jpg
 

petertha

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I think you are fine. Many commercial 4S engines are +/- right in this range. I assembled this data from engine reviews within ScepterFlight web site.
And seems like lots of successful running Edwards engines.

 

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BTW, I like your engine stand. Are the joints brazed, welded or...?
Hi, thanks for the attachment, very helpful. I copied the stand from one I saw in Aerospace where I used to work. I brazed it, which I need to practise more as close up some of the joints could be better. However it allows good access plus I am going to be able tohang the fuel tank and control panel from it.
 

petertha

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Maybe the reason why you're asking about CR & apologies in advance if you already knew this, but just in case - my understanding of the Edwards is the head is shimmed (or maybe its liner top is machined?) to yield equal CR across the 5 cylinders. Because on this design the master rod rod is equally divided for the link rod positions, which then yields slightly unequal CR by default. Other radials such as the one I'm building have compensated master rod layout which achieves equal CR, but timing is slightly off relative to 365/5 CS position. Choose your poison. On a glow engine like this, I hear it doesn't factor significantly. What I'm not sure of is if there is an upper CR limit like valve/position proximity on the Edwards. My radial is working out to about 10:1 if I recall & that may be +/- with the OS-F plugs which protrude a bit deeper into combustion area which I didn't realize initially.

What carb did you select & how are you driving the glow plugs?
 
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Maybe the reason why you're asking about CR & apologies in advance if you already knew this, but just in case - my understanding of the Edwards is the head is shimmed (or maybe its liner top is machined?) to yield equal CR across the 5 cylinders. Because on this design the master rod rod is equally divided for the link rod positions, which then yields slightly unequal CR by default. Other radials such as the one I'm building have compensated master rod layout which achieves equal CR, but timing is slightly off relative to 365/5 CS position. Choose your poison. On a glow engine like this, I hear it doesn't factor significantly. What I'm not sure of is if there is an upper CR limit like valve/position proximity on the Edwards. My radial is working out to about 10:1 if I recall & that may be +/- with the OS-F plugs which protrude a bit deeper into combustion area which I didn't realize initially.

What carb did you select & how are you driving the glow plugs?
I have compensated the height of the sub con rods so they arenall the same in the bores. I have left material on the top of the cast iron liners for any needed removal. I have made my own carb to the Kiwi 2 drawings, on this engine without float chamber(at the moment), just positioning the tank just slightly below carb inlet level. I haven't bought the glow plug driver yet, currently searching for the best option, and also thinking about how to start it. I have a motor cycle starter motor I am thinking imight convert and put a huck boss on the prop nose
 

petertha

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I've fallen hopelessly behind my own build post, but just to experiment, I ordered one of harness wires with a spring connector end. They seem to fit very positive. Note they distinguish diameter of glow plug stem (OS-F slightly larger than regular plug).

And I tried one of these 1.5V, I'll call them 'regulator' module. I tried different configurations of LIPO/NIx source batteries & always got the same results, 1.5V & ~ 2.5A on new dry plugs. So I have 4 more on the way. The plan is to snip off the plunger plug thingy & hook up 5 in parallel through a rudimentary box with dedicated on/off switches.

There are also dedicated 'on board' RC ignition modules versions like the one offered through Just Engines, but that would involve a dedicated throttle servo & servo driver. Ends up being about same cost on my side of pond.
 

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josodl1953

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Hello Major,
You might consider purchasing a Glow-Control system from the German company Rainbow-tronic www.rainbow-tronic.de .
I am thinking about it , for my Edwards. They also provide glow plug connectors and cables .Shipping costs are 28 € for countries in Europe but outside the EU. The electronics seem to have an adjustable provision to keep glow power on at low revs. This is necessary because the engine cuts out below approx. 1/3 throttle if you do'nt keep the glow power on. The Edwards drawings ( version by Robert Sigler) have a note "on-board battery recommended". It is a bit unclear to me if Forest Edwards himself used glow plugs. I have a picture of Forest's own engine fitted to a Polikarpov biplane which has obviously spark ignition.

Jos
 

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I've fallen hopelessly behind my own build post, but just to experiment, I ordered one of harness wires with a spring connector end. They seem to fit very positive. Note they distinguish diameter of glow plug stem (OS-F slightly larger than regular plug).

And I tried one of these 1.5V, I'll call them 'regulator' module. I tried different configurations of LIPO/NIx source batteries & always got the same results, 1.5V & ~ 2.5A on new dry plugs. So I have 4 more on the way. The plan is to snip off the plunger plug thingy & hook up 5 in parallel through a rudimentary box with dedicated on/off switches.

There are also dedicated 'on board' RC ignition modules versions like the one offered through Just Engines, but that would involve a dedicated throttle servo & servo driver. Ends up being about same cost on my side of pond.
Thank you for this
 
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Hello Major,
You might consider purchasing a Glow-Control system from the German company Rainbow-tronic www.rainbow-tronic.de .
I am thinking about it , for my Edwards. They also provide glow plug connectors and cables .Shipping costs are 28 € for countries in Europe but outside the EU. The electronics seem to have an adjustable provision to keep glow power on at low revs. This is necessary because the engine cuts out below approx. 1/3 throttle if you do'nt keep the glow power on. The Edwards drawings ( version by Robert Sigler) have a note "on-board battery recommended". It is a bit unclear to me if Forest Edwards himself used glow plugs. I have a picture of Forest's own engine fitted to a Polikarpov biplane which has obviously spark ignition.

Jos
Thanks for this i will look at the web site
 

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