Open thread on Edwards 5 Radial

[tornitore45]

Peter, we can consider our self lucky that modelenginenews.org website is still operational albeit limping. The user login validation does not work either.
Ron Chernich demise was a great loss to the model engine community.

 

[WOB]

The 4-stroke glow fuel is little different from the 2-stroke version. It might contain a little more oil and maybe a little less nitro, but that is about it. I wonder about the design philosophy behind the Edwards radial 5. With standard 4-stroke glow fuel widely available and the principle of lubing the crankcase with oil blow-by being a well proven technology, it seems to be an unnecessary complication to have a separate oil-lubed crankcase. It only makes sense if the fuel is oil free, hence my question.

My favorite fuel is Powermaster: https://vpracingfuels.com/rc-fuels/#aviation They list their fuel mix recipes on the web page. Most of them are listed as suitable for both 2 and 4-strokes.

The commercial multi-cylinder, glow-ignition 4-strokes like the OS Sirius, Pegasus, and Gemini use blow-by lubrication with great success. Good luck on your project.

WOB

 

[petertha]

The Edwards is a bit unique for typical glow in that it specifies methanol/nitro (only) as fuel, but has a pumped oil lubrication system. People that run it that way don't seem to have adverse issues from what I hear, including the designed ring system. Although some still opt to blend or dilute commercial 4S RC fuel into the mix for insurance. Most RC 4S glow engines use pre-blend fuel on a single compression ring, including radials but no auxiliary lubrication system. The Ohrdorf 5-cyl & 9-cyl radials use pre-mix but the nose case is oil filled for the planetary gears & cams to splash around. It is sealed from the crankcase internals.

I have yet to figure out how the upper cylinder rockers are lubricated (over and above maybe manual squirts). On many RC 4S engines the push rods are within O-ring sealed tubes & rockers under gasketed alve covers. I know the rockers are nice & oily from experience but not sure if its migrating up the pushrod or there is enough blow-by leakage from the valve stems & the tubes are intended to drain it somewhere?

 

[tornitore45]

Thank you Peter for shedding some light on the fuel issue.
Since buying nitromethane is nearly impossible I plan to dilute a commercial 10% nitro with equal parts methanol to halve the oil and the nitro down to the 5% recommended. It also seem that this approach allows the adjustment of nitro to the sweet spot.

 

[tornitore45]

On other engines I built it seems that the rockers need so little lubrication that one can wet them before a run and the effect last at least for a 10-15 minutes usual flight. Not planning to fly it though.

 

[WOB]

The 4-stroke crankcase operates at a low positive pressure due to blow-by and a restrictive vent and I'm sure there is enough oil vapor present to go up the push rod tubes to the lower pressure area in the intake rocker boxes. Exhaust valve-stem blow-buy would likely lube the exhaust rocker box internals. This is a good reason to have a little looseness in valve-stem to valve-guide clearance. For engines with both rockers in the same box, it is likely both. Most hobbyist model 4-strokes are designed with open rocker arms and push rods. I never liked that feature and my 4-strokes have sealed rocker boxes and push rod tubes.

WOB

 

[tornitore45]

The 4-stroke crankcase operates at a low positive pressure due to blow-by and a restrictive vent and I'm sure there is enough oil vapor present to go up the push rod

That finally explain to me how the Malcom Stride LYNX works. It has no push rods because is a OHC but it has a small pipe from crankcase to the cam case.

 

[josodl1953]

I omitted the oil pump and everything that goes with it because if all goes I want to fly it ( in the distant future).Like WOB says, almost all commercial 4-stroke model engines depend on crankcase lubrication by blow-by of oil-containing fuel.
I use only one piston ring and no oil scraper. With my limited machining capabilities I see no way to make a slot in a 1 mm wide piston ring. To provide adequate lubrication for the cam gear I separated the cam housing from the crankcase by omitting the holes and using sealed crankshaft bearings. I use outboard gearbox oil in the camhousing, so far I did not have any problems.

 

[tornitore45]

Any of you that run this engine can share the size of the carburetor throat?

 

[aka9950202]

Rule of thumb sizing a carburetor is 10% of piston area.

Cheers,

Andrew in Melbourne

 

[WOB]

As a point of reference, the OS FR7-420, 7 cylinder radial ( 70CC) uses a # 80T carb. Don't know the throat size. Good price on Amazon.

WOB

 

[josodl1953]

Andrew, do you mean , on a mutli-cylinder engine, the combined area of all pistons or only one piston?

Jos

 

[bobden72]

Andrew, do you mean , on a mutli-cylinder engine, the combined area of all pistons or only one piston?

Jos

Multi cylinder or single cylinder only one cylinder is firing at once so just the area of one piston to determine the carb size.

 

[bobden72]

Any of you that run this engine can share the size of the carburetor throat?

Just been out and measured the throat on mine which runs OK and it is .226".

 

[aka9950202]

Andrew, do you mean , on a mutli-cylinder engine, the combined area of all pistons or only one piston?

Jos

The rule applies to single and multi cylinder engines.

Cheers,
Andrew in Melbourne

 

[Brian-in-Oz]

Hi Edwards Radial enthusiasts.
I finished building my engine in 2015 and it has been running happily ever since on a Perry 2100 carb.
At the time I emailed Gary Conley at Perry carbs. and described the engine and this is the model he recommended for the application.
It has a throat dia. of .270". I just looked at their web page and this carby is still listed.
The build can be viewed at this HMEM link. http://www.homemodelenginemachinist.com/showthread.php?t=6923
Here is the link to the engine running on its second startup.
Cheers all and keep up the good work.
Radials Forever - Cheers from Brian in South Oz.

 

[tornitore45]

Thanks
Somewhere in the 0.250" matches my calculations.

Up to 4 cylinder the carb is sized based on single cylinder displacement.
Above 4 the intake air volume is increased by a factor N/4.
A 2 cylinders draws air pulses contiguous but not overlapping
A 4 cylinders draws air in a continuous/constant manner equal to the maximum speed of the single cylinder.
An 8 cylinders doubles the air stream of a 4
A 5 cylinders should run well on the same carburetor feeding a single of 1.25 times the radial single displacement.

Some latitude is allowed
A smaller throat may starve at high rev but keeps sufficient air velocity to nebulize the fuel at low rew

A larger throat may allow higher power at the expenses of a higher stable idle.

Since I do not plan to fly this engine at top power but like to see a low RPM idle I will lean toward the 0.226"

 

[tornitore45]

Brian-in-Oz Great Video, an inspiration to finish mine.

 

[tornitore45]

I

 

[tornitore45]

After loading the picture could not enter text.
Got it running today, started right up with no fuss.
I was concerned about the oil pump being such a fiddly design/construction but it work well. One can see the sump return flow speed away.
I tried to post a video but .MOV is not accepted.
I ran it first with a fly wheel because I dis not want to reach around a 20" prop to get to the carb. But after it started reliably I felt safe walking around. On to the next project: Lanz Tractor