Edwards Radial 5 build thread --- PHOTOS!

You've raised some really good points.

Where did you get the Edwards HP reference? I was wondering about that too. Power is not something one hears quoted often with home shop engines, I guess probably because most hobby mortals don't have a small dyno. A guy could probably estimate knowing rpm on a specific pitch & diameter prop, but usually those specs are kind of 'guidance'. I came across some equations & graphs once upon a time, I should get them into a spreadsheet or something. O.S. made a 3.03 CI 5-cyl radial but no power reference https://www.os-engines.co.jp/english/line_up/engine/air/twin/manual/fr5-300.pdf They say 8500 rpm but only referenced break in prop (18x10 or 20x8).

1144SP was nice to machine but I actually have essentially nil experience machining 4xxx series alloy to compare it to. Some of the model engine guys favor it especially inline or Vee crankshafts engines where the funky shapes are more prone to problematic stress relieving distortion. Our radials are a bit more forgiving from that standpoint I plotted the (annealed) hardness / strength coordinate just slightly above your curve cluster so will venture to guess probably similar. But now you have be wondering about heat treating. My radial plans are German & the instructions quite sparse. The 9-cyl big brother calls for 16 MnCr5 'nitride hardened' if that means anything to you. I naively assumed that was a surface treatment & not likely I was going to find that alloy in Kanuckistan where I live anyways.

I'm a long time RC guy but something tells me with the hours invested in machining this thing it will probably spend most of its life going putt-putt on a test stand. But there are braver souls....

Radial Engine Build

philsradial.blogspot.com philsradial.blogspot.com
 
One thing to consider on your crank pin. A Dremel cutoff disk will leave a groove with a bottom radii. ANy radius in the bottom corners of the groove will allow the clip to push off rather easy. Check your groove with a magnifying glass The spec allows only .003 R MAX. Where I work the grooving tool got dull and was leaving a .005-.007 R and we had a lot of warranty work on snap rings popping off even though there was very little load trying to push it off. A popped off ring could be real bad in a running engine.
 
I don't doubt the spec, but I am trying to visualize how a small radius in the groove could cause the clip to come off?
Robert
 
petertha said:
Where did you get the Edwards HP reference?
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For the life of me, I can't seem to find it now! I'm 90% sure I didn't make it up, would be a pretty strange number to pull out of thin air.... I'll let you know if I end up coming across it again.

petertha said:
My radial plans are German & the instructions quite sparse. The 9-cyl big brother calls for 16 MnCr5 'nitride hardened' if that means anything to you. I naively assumed that was a surface treatment & not likely I was going to find that alloy in Kanuckistan where I live anyways.
Click to expand...
Never heard of that before either. But a quick google leads me also to think it's more of a case hardening thing.

petertha said:
I'm a long time RC guy but something tells me with the hours invested in machining this thing it will probably spend most of its life going putt-putt on a test stand. But there are braver souls....

Radial Engine Build

philsradial.blogspot.com philsradial.blogspot.com
Click to expand...
This sort of video makes me want to toss my engine in a plane if I ever get it running... shame for it to sit on a bench, only to be fired up for 5 minutes a year to show off at a BBQ.


Flyinfool said:
One thing to consider on your crank pin. A Dremel cutoff disk will leave a groove with a bottom radii. ANy radius in the bottom corners of the groove will allow the clip to push off rather easy. Check your groove with a magnifying glass The spec allows only .003 R MAX. Where I work the grooving tool got dull and was leaving a .005-.007 R and we had a lot of warranty work on snap rings popping off even though there was very little load trying to push it off. A popped off ring could be real bad in a running engine.
Click to expand...
Uh oh..... you mean like this kind of radius? Based on the groove width of about 0.028", that looks to me like a radius of about 0.014....

1x
IMG_7360.JPG


30x
IMG_7358.JPG


100x
IMG_7359.JPG
 
I guess the point with the radius is that it gives an inclined plane for the snap ring to ride up, where flat sides don't. You're on a bit of a sticky wicket for modifying it now with it installed, though. Slitting saw and cnc program?
 
Lo-Fi said:
I guess the point with the radius is that it gives an inclined plane for the snap ring to ride up, where flat sides don't. You're on a bit of a sticky wicket for modifying it now with it installed, though. Slitting saw and cnc program?
Click to expand...

If it has a center in it (or perhaps even not!), he can hold the other end in a 4 jaw and use a ground tool to clean that up.
 
That would be an interesting setup!
 
Offset turning always is :) At least in this case though, you wouldn't have an inturrupted cut, which is my l least favorite part of offset turning.
 
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