forrest edwards radial

[josodl1953]

Hi, I,m Jos from Rotterdam, the Netherlands. After having model racing boats as a hobby for about 40 years I changed to RC model flying a few years. Being fascinated by radial engines, I found the complete set of drawings for the Edwards Radial engine. I am considering the build of this engine in a slightly downsized version, with all dimensions converted to metric and some other modifications. I wonder if there is someone who can advice me on this subject.
The obvious step would be to send an email to Robert Sigler who had digitalised the drawings but I found on the internet that he has passed away
some time ago. Is this true and if so, is ther someone else who has experience with this project?

Greetings from Holland,
Jos

 

[petertha]

Hi Jos. Sounds like we have RC flying & radial interest in common.

I'm (slowly) building the Ohrdorf 5-cyl radial which is somewhat similar to Edwards in displacement & design. Link shown below. Its entirely metric, CAD drawings from 3D assembly model. The only downside is he sells the 5-cyl version plans as additional/modified parts to the 9-cyl engine plans which share several components. In other words you need to buy both the 9-cyl + 5-cyl plans to have the whole 5-cyl picture. At least that was the case at the time for me. I guess the positive side is if you were going to build the 9-cyl one day anyway http://www.engineman.de/

Another similar 5-cyl radial is by Jung. Again all metric, but standalone complete drawings.
http://www.cad-jung-shop.de/epages/62479729.sf/de_DE/?ObjectPath=/Shops/62479729/Categories/Baupläne
Here is a very nice build of the 7-cyl version which should give you an idea of construction & result.
http://philsradial.blogspot.ca/

Edwards uses straight methanol fuel but has separate lubrication pump system. The 2 euro designs use typical RC premix (methanol/oil) somewhat similar to commercial RC radials. The Ohrdorf uses kind of a crankcase sump chamber to semi-bathe the gear assembly. All use glow plug ignition.

I suspect you might find 'scaling down' these plans somewhat involved - to the extent of pretty much a complete re-design by the time you are done. One key challenge & heart of the engine is cam ring gear drive assembly. You need to get specific tooth count (gear ratios) between the shaft gear/idler gear/ring gear cluster in order to yield appropriate cam timing & direction. And you have to fit this package inside the crankcase with bearings etc. Ring gears & spur gears only come in limited tooth count flavors at that scale. And a smaller subset of those available will yield appropriate gear ratios with the spur gears. Sourcing ring gears is the next potential headache. In that regard you are one step ahead being located in Europe. All plans show suppliers, but I found it easier & less cost to source the module ring gear than IMP (Edwards) gear. Pic shows roughly what you are looking at (Ohrndorf example)

Then you have the other scale reduction issues: smaller bore means different rings, valves, springs, rods, crankshaft, carb.... And things like pins & fasteners & bearings which must mate or fit within one another typically don't scale to the same multiple maybe you have in mind. Not trying to talk you out of anything but just providing opinion as to what it likely entails.

 

[xpylonracer]

Hi Jos
A UK plan which may still be available is for the Radian, approx 40cc total volume. This is glo plug ignition with methanol/oil fuel.

 

[josodl1953]

Thanks everybody for reacting. About the cam gear: I think I have a solution for the ring gear problem. Being a bicycle mechanic, I found a ring gear and a sattelite gear from gear hubs of different makes ( Sachs and Sturmey Archer) which in combination gave the all-important reduction of 1:5 . With an outer diameter of 53 mm of the ring gear I think I can make a nice compact cam gear. As far as the re-sizing/ metric conversion is concerned: I consider this as a project for at least 3 years. On long winter evenings when my workshop is too cold to work in, I think there is plenty of time to do the necessary maths. I made an Excel sheet which should make life that more easy....

Jos

 

[petertha]

I found a ring gear and a sattelite gear from gear hubs of different makes ( Sachs and Sturmey Archer) which in combination gave the all-important reduction of 1:5 . Jos

The Edwards and the 2 other 5-cylinder radials mentioned have combined gear ratios of 4:1 using the Crankshaft > Idler1 > Idler2 > Cam ring cluster arrangement. So 4:1 drives 2 lobes positioned 180-deg apart. Similar arrangements exist like 6:1 drives 3 lobes, 8:1 drives 4 lobes ... Can you elaborate on your 5:1 arrangement?

 

[josodl1953]

Whoops.. you're right, the reduction is 1:4..it's been a while since I last checked my radial data.... The bike hub ring gear has 60 teeth, the sattelite gear 15, so no problem there. I purchased two gears , 25 teeth, mod.0.7, from the German Maedler company( www.maedler.de) for the 1:1 drive, albeit withe a slight play on the teeth. I think I'll make a test rig first before starting the actual fabrication to see if this play adversely affects the cam timing.

Jos

 

[petertha]

Maedler is the recommended supplier mentioned on Ohrdorf plans & where I purchased my gears from. Reasonably priced & good to deal with, especially from far away N-Am where I'm located.

Maybe I'm misunderstanding your gear layout or what you mean by 'slight play', but I don't quite follow your math. I'm not in front on my own spreadsheet but I'll take a crack at it. Pitch diameter = Module x Teeth. Your 60 tooth 0.7mod ring gear will have a pitch diameter of 42mm, or radius of 21mm. The 25 tooth has 8.75mm radius, 15 tooth has 5.25mm radius. In order to have coincident pitch circles and achieve 4:1 gear ratio, you add the spur gear radii train like: 8.75mm (25T crankshaft) + 8.75mm (25T idler) + 5.25mm (15T satellite). That distance sums to 22.75mm. But this does not equal 21mm radius of ring gear PD. ??? (The idler gear & satellite gear are on same shaft center, assume that is what you are contemplating).

 

[petertha]

Maybe this image will help. The O5 engine uses mod-1 gears, 15 tooth crankshaft, 15 tooth idler, 10 tooth satellite (on same shaft as idler) which drives 40 tooth planetary. When you work out the distances same method as described, the pitch circles are coincident with dimensions as shown.

 

[josodl1953]

The 0,7 mod goes only for the 25 t gears, the ring /sattelite gears have mod 0,80. The only problem is that the nominal centre distance
of the sattelite gear to the crank centerline is 18 mm and the centre distance of the 25/25 gears is 17,5 mm which would result in more
gear clearance . Problems could arise with inaccurate timing and gear hammer. I don't know if there are known issues with cam drives
of model radial engines, maybe the proof of the pudding is in the eating here.

 

[royal-corsair]

Hi, I,m Jos from Rotterdam, the Netherlands. After having model racing boats as a hobby for about 40 years I changed to RC model flying a few years. Being fascinated by radial engines, I found the complete set of drawings for the Edwards Radial engine. I am considering the build of this engine in a slightly downsized version, with all dimensions converted to metric and some other modifications. I wonder if there is someone who can advice me on this subject.
The obvious step would be to send an email to Robert Sigler who had digitalised the drawings but I found on the internet that he has passed away
some time ago. Is this true and if so, is ther someone else who has experience with this project?

Greetings from Holland,
Jos

I just got an email from Robert Sigler this morning, he is alive and well. Don't know where you heard about him passing away.
[email protected]

 

[josodl1953]

Well, I wanted to send him an email but before doing that I looked for him on the internet and I found an announce of someone called Robert Sigler who passed away.I thought it would be very embarassing to send an email to someone who is not with us anymore but I'm glad he's well.

Jos