I machined a collar so I could chuck the head because the skirt flange is a larger diameter. Drill & tap 5 x M3 holes. Now I have a way of holding the head inverted on a fixture to drill & mill the flange.
Radial engine build
- Thread starter PeterT
- Start date
Amazing work Peter. Looks like most of the parts are finished. What's left to do?
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Now if that just isn't a thing of machining beauty I don't know what is.
Thanks for the compliments guys.
- just for scale it will fit in about 10-12" diameter circle with the head do-dads on
- remaining parts: cylinder liners, rocker perch's, rockers, valve covers, inlet/exhaust tubes, pistons, link rods, master rod, pushrod tubes, gear timing....
- my plan is to use commercial piston rings to get it baseline running. But I also intend to make rings & then swap them in to compare. It involves some fixtures & heat treating
- I already machined the rear induction manifold as per plans, but I can see some room for improvement so will cross that bridge come induction tube time. Might be a re-do.
- Another issue is to whether I adopt the partially oil filled nose case or not. That's what the plans call for but I just cant see how oil is not going to seep out of the lower tappet guides. Lubrication was kind of glossed over in the (very brief) description although he did the same on the 9-cyl big brother. Other engines have the gear plate open & fuel induction charge mist comes through the crankcase in & out which is how the rod assembly is lubricated anyways because the fuel is methanol+oil premix & quite common for RC engines. The Edwards radial you may have seen posted on the forum is quite similar in overall configuration but has a separate oil pump/re-circulation system. There are pros & cons to either (for model engines).
- just for scale it will fit in about 10-12" diameter circle with the head do-dads on
- remaining parts: cylinder liners, rocker perch's, rockers, valve covers, inlet/exhaust tubes, pistons, link rods, master rod, pushrod tubes, gear timing....
- my plan is to use commercial piston rings to get it baseline running. But I also intend to make rings & then swap them in to compare. It involves some fixtures & heat treating
- I already machined the rear induction manifold as per plans, but I can see some room for improvement so will cross that bridge come induction tube time. Might be a re-do.
- Another issue is to whether I adopt the partially oil filled nose case or not. That's what the plans call for but I just cant see how oil is not going to seep out of the lower tappet guides. Lubrication was kind of glossed over in the (very brief) description although he did the same on the 9-cyl big brother. Other engines have the gear plate open & fuel induction charge mist comes through the crankcase in & out which is how the rod assembly is lubricated anyways because the fuel is methanol+oil premix & quite common for RC engines. The Edwards radial you may have seen posted on the forum is quite similar in overall configuration but has a separate oil pump/re-circulation system. There are pros & cons to either (for model engines).
Well.. maybe, I dunno. I've been around RC forever so building & flying would be familiar territory although its been many years since I assembled a Crunchy as we call them. Some of my Composites Comrades are rediscovering scratch building, maybe a nostalgia throwback to their youth. I guess my goal & personal challenge is focused on the machining/mechanical side & (fingers crossed) seeing it run. So see what happens after that. I've also been around RC long enough to write a book titled 10,001 ways a plane can come to rest in a shallow grave LOL.
This guy built a nice 7-cylinder glow & promptly stuck it in a bipe. Gotta love the sound of 'round' engines!
http://philsradial.blogspot.com/
This guy built a nice 7-cylinder glow & promptly stuck it in a bipe. Gotta love the sound of 'round' engines!
http://philsradial.blogspot.com/
Yes, I have a friend that used to build rc planes as a kid and I was always intrigued with them and their engines. Crashing them seemed to be the end of them as opposed to wearing them out. He never had anything more than single cylinder engines. I'm love to see the size and complexity of the plane that your radial engine could fly. Heck if you built one or two more of them I think I could use them on my ultralight!
After spending all that time machining and building that engine there is no way in hell I would ever send it to an almost sure death on an RC plane!! Lol
Peter, what is the maximum safe engine speed of those radial engines? How do you prevent over speed?
Peter, what is the maximum safe engine speed of those radial engines? How do you prevent over speed?
I think I agree. Maybe Peter should make an air boat or a ground rig for that engine. A running engine is cool but making it do some work is cooler.
John I think the stated rpm range is 1500-5000 but its probably only rough nominal guidance. I know some of the commercial model radials say 7000 rpm but generally these have a power band that favors torque at lower rpms. In real life a prop pitch/diameter is selected for thrust at airspeed & sometimes practicalities like ground clearance. Compared to things like machines, prop load is always 'on' to a higher degree pushing air & load increases by some exponent (square?) of rpm. In my case bolted to a picnic table, it will be a glorified cooling fan. If the engine is static the prop load is also a bit higher than if moving in air as a function of the blade angle. Some guys cut down the diameter of a wider pitch prop just for walkaround safety on the test stand.
So I guess I'm saying there is no real independent rev limiter as such. The worst thing that can happen is a prop disintegrates with throttle stuck wide open. The load is instantly removed, probably lots of valve bounce bad things happen. This unfortunately happens too often on methanol racing 2S engines like a parted blade or mid-air. They generally have a high temp heart attack with piston permanently seized after about 10 seconds. Glow engines are kind of funky because there is no distributed spark to advance or retard (control) like a FS engine. Fuel fires when the compression is right. The carb selected has as much to do with trying to achieve a reasonable idle which usually favor slightly smaller throat over larger. Same thing with cam timing. So I think between the breathing & the disproportionately increasing load, this largely self-limit upper rpms under normal running load conditions.
Side note but radials are additionally quirky. If you phase the link rods equally around the master rod (for example 360 deg / 5 cylinders = 72 deg spacing) you actually get un-equal throw. That means with identical cylinder/head dimensions, un-equal compression ratio across the cylinders. Its just a function of the motion geometry. But that's a bad thing for a multi-cylinder glow engine to have say 10:1 on the #1 and 9.6 on #2 & 8.5 on #3 because glow ignition timing is largely influenced by CR. So on this engine, the master rod is 'compensated' meaning slightly adjusted unequal spacing to achieve ~equal CR. The Edwards radial has equal MR/LR angles but requires you to shave heads or add head shims, kind of volumetrically to achieve equal CR. Choose your poison. This effect was known on FS radials back in the day & different engines handled it differently. If you can pack the link rods very close to the MR crank pin, the effect is diminished (never eliminated). If you juggle geometry to have equal throw then TDC now occurs at non-equal crankshaft positions, which doesn't play as well with equal cam and ignition timing which is a function of crankshaft angle. I think the cam discrepancy is nearly negligible because of the high planetary gear ratio & cam lobe ramp. But I was told some radials had distributors (mags) with compensated non-equal firing phasing to match up with the mechanical discrepancy. Crazy stuff.
So I guess I'm saying there is no real independent rev limiter as such. The worst thing that can happen is a prop disintegrates with throttle stuck wide open. The load is instantly removed, probably lots of valve bounce bad things happen. This unfortunately happens too often on methanol racing 2S engines like a parted blade or mid-air. They generally have a high temp heart attack with piston permanently seized after about 10 seconds. Glow engines are kind of funky because there is no distributed spark to advance or retard (control) like a FS engine. Fuel fires when the compression is right. The carb selected has as much to do with trying to achieve a reasonable idle which usually favor slightly smaller throat over larger. Same thing with cam timing. So I think between the breathing & the disproportionately increasing load, this largely self-limit upper rpms under normal running load conditions.
Side note but radials are additionally quirky. If you phase the link rods equally around the master rod (for example 360 deg / 5 cylinders = 72 deg spacing) you actually get un-equal throw. That means with identical cylinder/head dimensions, un-equal compression ratio across the cylinders. Its just a function of the motion geometry. But that's a bad thing for a multi-cylinder glow engine to have say 10:1 on the #1 and 9.6 on #2 & 8.5 on #3 because glow ignition timing is largely influenced by CR. So on this engine, the master rod is 'compensated' meaning slightly adjusted unequal spacing to achieve ~equal CR. The Edwards radial has equal MR/LR angles but requires you to shave heads or add head shims, kind of volumetrically to achieve equal CR. Choose your poison. This effect was known on FS radials back in the day & different engines handled it differently. If you can pack the link rods very close to the MR crank pin, the effect is diminished (never eliminated). If you juggle geometry to have equal throw then TDC now occurs at non-equal crankshaft positions, which doesn't play as well with equal cam and ignition timing which is a function of crankshaft angle. I think the cam discrepancy is nearly negligible because of the high planetary gear ratio & cam lobe ramp. But I was told some radials had distributors (mags) with compensated non-equal firing phasing to match up with the mechanical discrepancy. Crazy stuff.
Interesting stuff. Thanks.
I think I'd like to buy you a beer (or coffee or tea or whatever you prefer) sometime, I think it would be fascinating to learn "stuff" from you Peter.
Looking at this radial engine connecting rod assembly I see what you mean Peter. The rod angularity is way different on the master rod compared to the others. The TDC events are not going to be evenly spaced
Work has commenced on the liners. They start out as drops of 1.25" diameter Class 40 grey cast iron, which comes delivered as more like 1.35" nominal. I think that overage is so that you get consistent machining properties under the skin. A while back I made some test liners out of 12L14 and 1144 stressproof but decided to stick with CI. I took a skim cut then pilot drilled 0.375, then 0.875, then bored to 0.940 which lands me with 0.005" to take off for the final 0.945" bore. I did the drilling & boring while I had more meat on the wall to try & keep a nice even bore. CI is quite inert compared to most alloys so you can hold dimensions quite well (just account for heat). It cuts quite well but is very messy so I cover the ways.
