Edwards Radial 5 build thread --- PHOTOS!

@rgaal there probably is some merit to your method, but its probably also worth pointing out some of the some other issues in model engine radial cams.

- the cam plates are actually quite simple in principle: the inner diameter with no action (valve closed), the outer diameter 'bump' dictating (valve open) throw through the rocker assembly geometry. And the ramp curve connecting these 2 features which ideally has some smooth transition curve. The transition profile is more critical on engines with smaller cylindrical cam followers that see the cam as a point tangent. The Edwards is somewhat unique in that it has a profiled follower 'shoe'. But you will notice they are in line vertically coincident to the cylinder center line vs radially outward which is maybe a bit more common on other engines.

- I used to think cam timing was super critical on these radials. But I'm now of the opinion there is actually pretty wide margin where they run well for the task s long as the timing is reasonable & proven. Part of this stems from these radials are generally lower RPM, broader torque curve outputs, not high RPM 'peaky' horsepower type engines where cam tuning can moreso influence breathing. Back in post #140 I showed a comparison of OS (methanol glow) 4-stroke timing. You can see there is actually quite a wide deviation even normalized to the same manufacturer. (I have since found data for Saito so will add that in at some point). The Edwards has a slightly different exhaust vs intake profile but many model engines are the exact same cam plate for simplicity, just positioned different relative to TDC.

- valve lash (gap between valve stem & rocker) has quite a significant effect on actual valve open/close timing at model scale. Anywhere from 0.003 - 0.010" cold gap depending on the engine. Lash reduces open duration timing by a surprising amount on model engines, so we can't really look at the theoretical cam open/close duration in isolation. This is magnified on models because because typical lash is a higher percentage of cam throw vs full size engine.

- even with identical cam timing, different methanol (glow plug) engines will fire 'whenever they want to' within limits close to TDC. Its not an ignition driven event like a spark ignition, its a function of compression ratio, fuel etc. So an 8:1 will fire slightly different than a 10:1, which is why there is a requirement to equalize CR among the cylinders heads because the Edwards has an uncompensated master rod which would result in significantly different CR's that basis alone.

So not taking anything way from your observations or cam making proposal. I'm just saying (in my opinion) fortunately its probably not as critical as one might think. Now of course you cant have a jerky motion or a radical cam without consequences, but it seems like there is quite a generous margin within reason among similar model radial engines.
Thank you for the long and detailed explanation. I know a lot less about these engineering aspects as you, basically zero. My feeling was that if you cut away stuff at the two flanks of the lobes you will reduce valve open times and that will do no good to the engin.
The other issue is machining efficiency: we approach a smooth and non-trivial curved surface by cutting flats on it and do the smoothing with files, stones, emery paper or whatever at hand. If we do the machining part by cutting tangent planes there will be very little left to remove by hand.
 
An absolutely beautiful project. I hope it runs as well as it looks.

Six or so years ago when I bought my lathe, many friends asked what I was going to make. I quickly replied a scale model Harley Davidson engine. Then as I starting accumulating some materials and old engine parts to measure and scale from, and started thinking about the making process. I suddenly realised that I can't make this, because I don't have a mill, and I don't have the space to put one. I realise that many milling operations can be done on a lathe, but not all of the ones I will need to do.

So now my major project has been to make vertical spindle milling attachment for my lathe, but it is slow going.
 
So now my major project has been to make vertical spindle milling attachment for my lathe, but it is slow going.
A mill & a lathe are really a "set" that allow you to make a wide variety of things. You will be able to complete many more projects with a "set!"
Highly recommended.
 
Episode 1 || Introduction to My Build Thread


Background

After a brief search through the H-M.com archives, I was a bit surprised that nobody had documented their journey building an Edwards Radial 5-cylinder engine. These engines are reasonably complex and time consuming to construct, but as (1) detailed drawings are freely available and (2) it's a 'billet engine' requiring no castings, it tends to be a project commonly tackled by hobbyists like us (here's one nice example). There are several build threads for the Edwards in other forums, but apparently not here. UNTIL NOW!

The engine is a 5-cylinder radial designed and developed by Forest Edwards in the late 1980s. Edwards built about 30 of them for use in large-ish scale model airplanes. Robert Sigler drew up a set of plans (39 sheets total) for the engine in the early 2000s, which will form the basis of my build.

Overview of Engine
The Edwards is a methanol/nitromethane-fueled, glow-plug ignition, 5-cylinder radial engine with an overall diameter of about 10" and total displacement of 3.4 cubic inches (56cc). Running optimally, it reportedly spins a 22" propeller something like 6,000 rpm*. It packs a serious punch! The Edwards relies on a dry sump lubrication system to pump castor oil to the moving bits. The valve train in comprised of an intake and exhaust valve in each head controlled by pushrods activated by a 'cam ring' running concentric with, and geared to, the crankshaft.

Intent of this Build Thread
I hope that this build thread will serve several purposes:
  • First and foremost, I hope that the mere fact of starting it will keep me motivated throughout the process, and help ensure I end up finishing it.
  • Second, everyone on H-M likes a good build thread chock-full of photos, both for the entertainment value and for helping others undertaking a similar project; I intend to include lots and lots of photos along the way.
  • Finally, one thing that I wish other build threads had is an accounting of how much darn time everything takes. Is it just me, or do even seemingly simple components take a very long time to make, particularly if there's any special setup requirements? I'm reasonably new to the hobby, so it could be that I'll get faster as I go, but it's hard to believe I'll get much faster. Anyway, I intend to keep rough track of how much time each component takes, and a running total of how long the whole build is taking.

Side notes:
(1) I started this build about a month ago, so several components are already done. Accordingly, my first few posts after this one will be in pretty rapid succession, as I have time to write them up. Things will slow down precipitously after that.
(2) I have a full-time job, a 2.5-year-old son, a 1-month-old daughter, and a honey-do list a mile long. Shop time is hard to come by. Bear with me if there are stretches of inactivity...

*Edit: I originally said that this motor can produce 6HP based on something I recall seeing online. I can no longer find reference to that stat anywhere. I don't think I made it up, but perhaps I did. Let me know if you see the peak power referenced anywhere online by a reputable source.

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that is a beauty, will follow this
 
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