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Edwards Five cylinder aircraft engine
- Thread starter Master
- Start date
Hi Master. I'm building a radial quite similar to the Edwards. My planetary gear layout is the same principle as Edwards other than my engine uses metric gears, the Edwards is Imperial.
My gear train goes: 15 tooth on crankshaft drives 15 tooth on an idler cluster. The 15 tooth is mechanically locked to 10 tooth face to face but running on same idler shaft. The 10 tooth then drives the 40 tooth internal (ring gear) which is mounted to (or integral to) the cam plate. So the resultant crankshaft to ring gear ratio is 1:4. However, there are 2 cam lobes on each of the inlet & exhaust cam plates, so the 4:1 gear yields the correct 2:1 crank:cam timing 'equivalent'. So the gear count on my radial is 15-15-10-40 vs. the Edwards is 18-18-12-48.
For both engines, the inlet cam lobes are on a cam 'plate' and the exhaust lobes are on another plate. So the plates are phased relative to one another & also clocked relative to TDC or some such piston reference. To make things interesting, the cam plate goes in the opposite direction as crankshaft & the tappets & push rods come off at slightly different angles relative to the valve rockers based on their 3D geometry, so the designer has to factor this into the lobe ramp & duration profile to yield correct engine breathing timing.
2 lobes @ 4:1 is typical for a 5-cylinder radial, but a 7-cylinder would have 3 lobes @ 6:1 and a 9 cylinder would have 4 lobes @ 8:1. There are only so many planetary gear combinations that 'work' meaning a) matching pitch diameter between 4 gears b) correct tooth count and c) tooth size. Some pretty smart guys back in the early 1900's LOL.
Are you considering building an Edwards? There are few build posts on HMEM. I hang out there too,
https://www.homemodelenginemachinist.com/
My gear train goes: 15 tooth on crankshaft drives 15 tooth on an idler cluster. The 15 tooth is mechanically locked to 10 tooth face to face but running on same idler shaft. The 10 tooth then drives the 40 tooth internal (ring gear) which is mounted to (or integral to) the cam plate. So the resultant crankshaft to ring gear ratio is 1:4. However, there are 2 cam lobes on each of the inlet & exhaust cam plates, so the 4:1 gear yields the correct 2:1 crank:cam timing 'equivalent'. So the gear count on my radial is 15-15-10-40 vs. the Edwards is 18-18-12-48.
For both engines, the inlet cam lobes are on a cam 'plate' and the exhaust lobes are on another plate. So the plates are phased relative to one another & also clocked relative to TDC or some such piston reference. To make things interesting, the cam plate goes in the opposite direction as crankshaft & the tappets & push rods come off at slightly different angles relative to the valve rockers based on their 3D geometry, so the designer has to factor this into the lobe ramp & duration profile to yield correct engine breathing timing.
2 lobes @ 4:1 is typical for a 5-cylinder radial, but a 7-cylinder would have 3 lobes @ 6:1 and a 9 cylinder would have 4 lobes @ 8:1. There are only so many planetary gear combinations that 'work' meaning a) matching pitch diameter between 4 gears b) correct tooth count and c) tooth size. Some pretty smart guys back in the early 1900's LOL.
Are you considering building an Edwards? There are few build posts on HMEM. I hang out there too,
https://www.homemodelenginemachinist.com/
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Hello Peter T. Yes I am building the Edwards 5 cylinder. I have the crankcase machined and working on the cam housing. I'm waiting for the G677 gear to arrive and that will complete the cam. The idler gear and crank gear are what baffles me. Looking at Sheet 29 of the plans would appear that the idler gear isn't meshing with anything. This is why I wonder if there are 2 S2412 gears. One on the crank meshing with the idler.
Yes, there are two 18-tooth gears required. One is for the crankshaft, the other is for the large gear on the idler cluster. These two 18-t mesh with one another. They are individually modified though. The crankshaft gear ID would be bored to fit to crankshaft OD & looks like a keyway slot. The idler gear ID would be modified to match idler shaft OD. And thickness reduced I suspect.
I color coded the section drawing, hopefully more clear. If not ask again, I don't mind. Took me a while to get my head around these things.
Glad to hear you are building one. Are you going to share pics here or HMEM or both? How did you hear about us?
I color coded the section drawing, hopefully more clear. If not ask again, I don't mind. Took me a while to get my head around these things.
Glad to hear you are building one. Are you going to share pics here or HMEM or both? How did you hear about us?
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Peter T, Thank you so much. It all makes sense. I kept doubting myself. I think I found this site by searching for the answer to my question. I also joined HMEM. It will be awhile before I finish this project. Just not as fast as I used to be. But, I will try to put some pics on. Have made about twenty engines in past twenty years. Mostly hit and miss. Thanks again.
Excellent! 20 engines, wow! Well, this is my first engine, so I'm kind of at the opposite end of the experience spectrum LOL. I posted a few pictures here.
https://canadianhobbymetalworkers.com/threads/radial-engine-build.68/ I've been kind of picking away at mine & had some interruptions along the journey. But I feel like I'm rounding the difficulty hump this fall & have some momentum. I found the heads to be challenging because there are so many important inter-related parts & issues. I guess we'll see....
If you haven't already, do a search on Edwards on HMEM. There have been a few builds documented for reference. Unfortunately one with lots of pics I recall was a victim of Photobucket. There is another one going on now. Some guys have cut the 45-deg valve seats directly in the head as per plans, but I think others have modified with insert bronze cages (that's what I'm doing). The other thing to familiarize yourself is the cam plate lobes. I wrote a spreadsheet to back-compute my own engine timing & through that conversed with a guy building an Edwards. I think we ultimately came up with the same numbers. Its posted somewhere on HMEM. Anyways make sure you have a handle on the tabular cam coordinates. I know of at least one oops where he assumed CW & it was CCW... something like that.
https://canadianhobbymetalworkers.com/threads/radial-engine-build.68/ I've been kind of picking away at mine & had some interruptions along the journey. But I feel like I'm rounding the difficulty hump this fall & have some momentum. I found the heads to be challenging because there are so many important inter-related parts & issues. I guess we'll see....
If you haven't already, do a search on Edwards on HMEM. There have been a few builds documented for reference. Unfortunately one with lots of pics I recall was a victim of Photobucket. There is another one going on now. Some guys have cut the 45-deg valve seats directly in the head as per plans, but I think others have modified with insert bronze cages (that's what I'm doing). The other thing to familiarize yourself is the cam plate lobes. I wrote a spreadsheet to back-compute my own engine timing & through that conversed with a guy building an Edwards. I think we ultimately came up with the same numbers. Its posted somewhere on HMEM. Anyways make sure you have a handle on the tabular cam coordinates. I know of at least one oops where he assumed CW & it was CCW... something like that.
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DPittman
Ultra Member
Yup and some of us could have the best "easel and palette of oil" and still never be able to produce art! It does take an artist!
New problem. My much anticipated Boston gear #677 arrived. It is the wrong size. The OD is larger than required. I wonder if there is a misprint in the plans. I've been finding errors in some of the measurements. Not this far off tho. Anyone know of the actual Part number of the Cam gear 012-3?
How does the ring gear OD compare to part 004 cam ring? Hopefully slightly larger & not smaller. I don't know for certain, but it certainly wouldn't surprise me the intent is to turn the gear blank down to match the cam ring ID. This might seem counter intuitive but the whole cam assembly probably has lots of dimensional constraints, so the resultant gear blank OD is 'to suit' those dimensions. But maybe post a confirmation question on HMEM if you haven't already.
If so, you'll need a reliable method to retain the ring gear concentrically on a fixture to do the machining. Pics show what I did, turned in-situ so it stands best chance of being reduced concentric. Other pics - my I/E cams are bolt on plates to the ring gear cup (turned, profiled, then hardened). Edwards is an integral cam/cup. One thing I would watch out for is do the complete part meaning also any hardening of the 004 cam cup before committing to turning the ring gear ID. Depending on how you harden (surface vs. entire body) I think its safe to assume you will get some dimensional change, then match the ring gear OD to that <less> Loktite annular gap specs.
If so, you'll need a reliable method to retain the ring gear concentrically on a fixture to do the machining. Pics show what I did, turned in-situ so it stands best chance of being reduced concentric. Other pics - my I/E cams are bolt on plates to the ring gear cup (turned, profiled, then hardened). Edwards is an integral cam/cup. One thing I would watch out for is do the complete part meaning also any hardening of the 004 cam cup before committing to turning the ring gear ID. Depending on how you harden (surface vs. entire body) I think its safe to assume you will get some dimensional change, then match the ring gear OD to that <less> Loktite annular gap specs.
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The Edwards is a bit different than my O-5 radial which has separate Int/Exh cam plates mounted to the ring gear cup. They are angle phased by their mounting holes to yield timing. Plates seem a little more manageable to make (and screw up with reduced consequences) but also a bugger to hold. I also had to thin the tool steel stock from IMP to metric. The O-5 'lift' (valve open) segment is basically a larger extended radius from inner radius (valve closed). He figured out the onset of open & close timing by a radius which is equivalent to an endmill of Xmm diameter fillet. So its basically rotary table work because the cam profile, lightening holes, screw holes... all have angle & radius coordinates. Then I had a bit of hand filing work to smoothly round over the tiny corners using a machined round as a guide.
Edwards has the cam bumps milled directly on the cam ring & 360-deg cam coordinates supplied. Note Intake & Exhaust are slightly different duration. So the nice part is you can grip the entire ring in the RT & perform the cam milling following the coordinates. On the transition segments I think you have no choice in the matter other than back off tool, set RT to table angle, in-feed tool to radius, back off tool... rinse & repeat. The degree increments should provide a micro faceted profile that you can Sharpie marker blue & smoothen. I used some cheap China abrasive rubber cylinders in my Dremel & it came out nice. The trick is to blue often & use magnifiers so you can see what you are doing. Now how you make the outer & inner ring in separate tracks & preserve the setup I think you need a thin key slot cutter to reach the underlying cam profile. Otherwise you would have to flip the cup to do the other side with a regular end mill, somehow re-orient the cup & reverse the coordinates.
The challenge on the integral cup cam is hardening & not distorting. I think most guys surface hardening? (plans say 4340). My plates used air hardening tool steel (for minimal quench distortion) which isn't particularly fun stuff to machine. But I found a knife blade guy to harden & that turned out well. I made the cams slightly harder than the (O-1) lifters because I want the lifters to wear, not the cam. Much easier to make/replace lifters than re-machining cam plates.
Hope this helps. If not just ask. I'm no expert, just how I went about it. Show us some pics when the time comes!
Edwards has the cam bumps milled directly on the cam ring & 360-deg cam coordinates supplied. Note Intake & Exhaust are slightly different duration. So the nice part is you can grip the entire ring in the RT & perform the cam milling following the coordinates. On the transition segments I think you have no choice in the matter other than back off tool, set RT to table angle, in-feed tool to radius, back off tool... rinse & repeat. The degree increments should provide a micro faceted profile that you can Sharpie marker blue & smoothen. I used some cheap China abrasive rubber cylinders in my Dremel & it came out nice. The trick is to blue often & use magnifiers so you can see what you are doing. Now how you make the outer & inner ring in separate tracks & preserve the setup I think you need a thin key slot cutter to reach the underlying cam profile. Otherwise you would have to flip the cup to do the other side with a regular end mill, somehow re-orient the cup & reverse the coordinates.
The challenge on the integral cup cam is hardening & not distorting. I think most guys surface hardening? (plans say 4340). My plates used air hardening tool steel (for minimal quench distortion) which isn't particularly fun stuff to machine. But I found a knife blade guy to harden & that turned out well. I made the cams slightly harder than the (O-1) lifters because I want the lifters to wear, not the cam. Much easier to make/replace lifters than re-machining cam plates.
Hope this helps. If not just ask. I'm no expert, just how I went about it. Show us some pics when the time comes!
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Good question. The crankcase is more voluminous than mine, but whether the master/link rod assembly can go in together preassembled vs attaching each of 4 rod bottom ends to the MR knuckle inside the case is hard to prejudge.
This person was making great progress but looks like its paused a bit. Doesnt show assembly but overall pics might give you rough idea.
https://www.homemodelenginemachinist.com/threads/another-edwards-built.30822/page-3
Some of the other Edwards build posts suffered from Photobucket-itis & dont show up.
This person was making great progress but looks like its paused a bit. Doesnt show assembly but overall pics might give you rough idea.
https://www.homemodelenginemachinist.com/threads/another-edwards-built.30822/page-3
Some of the other Edwards build posts suffered from Photobucket-itis & dont show up.