Author Topic: Ohrndorf 5 Cylinder Radial  (Read 1719 times)

Offline petertha

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Ohrndorf 5 Cylinder Radial
« on: January 19, 2021, 02:21:46 AM »
Iíve been working on this radial engine on & off for <ahem> more than a few years now. You may have seen some of my prior questions or random posts scattered elsewhere on the forum. Progress has been pretty slow with the usual factors - time constraints, distractions & learn-as-you go snailís pace. I also had a few unwelcome interruptions with my machines. The drive train on my í97 Taiwan 14x40 lathe developed problems which took some time to source parts & repair. Then shortly thereafter my same vintage RF-45 mill gearbox decided it wasnít happy with the world. Ultimately I decided to upgrade the mill but that required some shop shuffling & electrical work.

Anyway, rolling time forward to present day, I might actually be on the home stretch. So I figure itís a good time to post my prior construction journey and transition into present day work so it will appear as a normal, continuous construction exercise. Actually, looking back at some of my pictures & notes leaves me wondering what I actually did myself, so this documentation exercise will benefit me as well.

I really wanted to build a radial and avoid castings to mess up, so 5 cylinders is kind of the minimum order, at least of the more common radial plans available. The Ohrndorf seemed well designed from my amateur comparisons to other 5-cyl radials. Nothing stood out as radical or unconventional. There is a YouTube video of it running. Hard to tell, but possibly it is an early prototype. I liked the overall proportions & some aesthetic features. Anyways, it ticked most of the boxes for me at the time.

Experience wise, this is my first engine. Iíd made a few prior metalworking gadgets, but nothing remotely close to this level. I decided to attempt a single cylinder assembly prototype and if that turned out OK, then Iíd carry on with the rest of the engine. The engine has yet to run, so weíll ultimately see if that path was the right decision. Wish me luck!

Offline petertha

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Re: Ohrndorf 5 Cylinder Radial
« Reply #1 on: January 19, 2021, 02:23:20 AM »
Design
The engine is designed by Martin Ohrndorf of Modellbau & Technik (Germany). On his web site he offers various other plans if you are so inclined (no personal affiliation). There are also some YouTube videos of his engines running.
https://www.engineman.de/
https://www.engineman.de/produkt/bauplan-5-zylinder-sternmotor/

Engine Specs
Methanol fuel, glow plug ignition
Bore = 24 mm
Stroke = 22 mm
Displacement = 50 cc (10 cc per cylinder)
Weight ~ 1900 g
RPM ~ 950 Ė 5,500
Outer diameter ~ 225 mm
Length ~ 165 mm
Propeller size 18x14 to 22x12 inch

Offline petertha

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Re: Ohrndorf 5 Cylinder Radial
« Reply #2 on: January 19, 2021, 02:24:07 AM »
Plans
The 2D hardcopy plans are most certainly derived from a 3D CAD model. They are metric dimensions, corresponding to metric components & tooling. The instructions are in German & quite brief, however I was able to occasionally communicate with Martin by email to answer the odd question.

Once I had the plans, I set about re-drawing parts into my own CAD model. This isnít a necessity but it certainly helped me on multiple fronts. I was better able to understand the assembly details, make my (imperial dimensioned) shop drawings, design jigs & fixtures etc. Ultimately I made a few changes here & there which Iíll detail, but for the most part stuck to the original design.

Iíll use the abbreviations O5 & O9 for the (Ohrndorf) 5 & 9 cylinder engines respectively. The 05 shares about half its parts with the 09. Unfortunately you need to purchase both O5 & O9 plan sets in order to build the 05. I suspect the O9 came first & the O5 later. The O5 plans have a pseudo assembly sheet that specifies whether to use a stock O9 part, or modify an O9 part, or make a new O5 part. This involves a bit of juggling to keep straight. A single set of O5 plans would certainly have been more convenient, but it is what it is. Who knows, maybe Iíll build the O9 one day.

Offline petertha

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Re: Ohrndorf 5 Cylinder Radial
« Reply #3 on: January 19, 2021, 02:27:47 AM »
Plans overview & video link


Offline petertha

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Re: Ohrndorf 5 Cylinder Radial
« Reply #4 on: January 19, 2021, 02:29:39 AM »
Cad pics missing pushrods, carb, inlet/exhaust accessories & some other bits
« Last Edit: January 19, 2021, 02:45:09 AM by petertha »

Offline petertha

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Re: Ohrndorf 5 Cylinder Radial
« Reply #5 on: January 19, 2021, 02:33:11 AM »
Construction & Design
The engine is bar stock, no castings. Hardening is required on some specific parts. Remaining commercial components include metric fasteners, bearings, spur gears, ring gear, O-rings, circlips & such. I planned on cutting the spur gears for the learning experience, but ended up purchasing them along with the internal (ring) gear because all the gears require modification. Apparently ring gears are a bit involved to (properly) cut teeth profiles in the home shop. I found all the gears readily available at https://www.maedler.de/

RC glow plug ignition was my preference on a first build because it seemed simpler than spark in some respects. I have some RC experience so maybe it was more the devil you know, albeit no prior involvement with multi-cylinder engines or radials. Iíll have to figure out an igniter system when the time comes.

Lubrication is somewhat similar to other glow engines, oil is premixed with the methanol fuel. Specific to the O5, intake charge enters from the rear mounted carb into the crankcase where it mists over the moving master/link rod assembly, then flows backwards out through the induction tubes into the heads. One unique feature of the O5 is that the nose case is compartmentally sealed from the crankcase & partially filled with oil bath for the planetary gear train & cam plates to splash in. I liked this concept because it mitigates an oil pump system. But Iím also wondering what keeps oil from seeping out past the lower, submerged tappets (cam followers). He uses the same bath philosophy on the larger O9, although there seem to be seal differences between engines. Alternately, other glow radials allow the intake mist to continue further forward, flowing into the nose case via openings in the front gear plate. This option is still available to me with some modifications. So Iím still mulling this issue over in terms of how to proceed. I assume the rocker assembly gets lubricated by occasional maintenance oiling & fuel residue working its way between the valve stem & guide. At least thatís how commercial RC 4S engines seem to work.

The pistons have a single compression ring. My plan all along was to use commercial RC rings, specifically from an OS-56-4S engine because the nominal bore dimensions are very close to the O5. I thought this might provide some insurance against making inferior rings & experiencing running problems. I just assumed by matching the O5 bore & piston geometry to the OS-56, I would be good to go. What I didnít appreciate at the time is that this construction path actually requires more exacting work on multiple fronts, but Iíll save that for later. I still intend to make my own rings because thatís part of model engine building. Whether itís worth swapping them into this engine to see the difference remains to be determined. Because the liners are also cast iron, I assume they will run in together with the rings, as opposed to commercial RC liners which are typically hard chromed. Iím not sure I will ever fly the engine so I doubt Iíll wear them out between the test stand & trophy shelf.
« Last Edit: January 19, 2021, 02:42:21 AM by petertha »

Offline petertha

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Re: Ohrndorf 5 Cylinder Radial
« Reply #6 on: January 19, 2021, 02:40:49 AM »
Pics of the prototype. If only I knew what was ahead of me LOL.

Offline Laurentic

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Re: Ohrndorf 5 Cylinder Radial
« Reply #7 on: January 19, 2021, 11:03:25 AM »
Peter - this is an interesting project, and one close to me.  I am in the process of completing a 3 cyl radial that was part built before the originator died and a friend of his sold it on to me.  Mine came with crankcase and end covers, division plate to crankcase, cylinders, heads, crankshaft and conn rods done but no more.  And NO plans!  So I have had to laboriously measure all the bits I had then design the missing bits to fit into what existed, drawing it all up in CAD, and then go back and modify some of the drawn parts as my thoughts changed.

Interestingly, mine is also designed for glow fuel, as the inlets are plumbed into the crankcase, so I modified the division plate to the gear area to solid with JB Weld so the gearbox/cam area could be lubricated by oil bath.  I also arranged the gears and cams very similar to how yours looks, but not nearly so neat!!  I have been making progress on this area, having just made the cams, cam support ring and gears including an internals gear and am in the process of fitting it in all together to make sure all fits as it should.  Making the gears including the internal gear was all new to me.  Made the internal gear using my RF-25 derivative mill as a broach.  It all works, sort of, now needs running in.

Will follow your build with considerable and very close interest!!

Chris

PS Can't believe how readily the engine started in the video, it certainly is a runner!
« Last Edit: January 19, 2021, 12:47:57 PM by Laurentic »

Offline Vixen

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Re: Ohrndorf 5 Cylinder Radial
« Reply #8 on: January 19, 2021, 12:18:44 PM »
Hello Peter,

This is an interesting engine to build. As you said it looks well designed, quite conventional with no obviously 'quirky' bits.

The engine parts you have shown look great. Your write up and presentation are also a credit to you. I will be following your progress as you proceed. 

The Ohrndorf O5 and my Seidel ST540 are very similar in both design and size, so we should be able to compare notes.

Mike   :atcomputer:
It is the journey that matters, not the destination

Offline Mike R

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Re: Ohrndorf 5 Cylinder Radial
« Reply #9 on: January 19, 2021, 05:53:39 PM »
Iíve been working on this radial engine on & off for <ahem> more than a few years now.

Too painfully familiar with that phrase.  You're intro to this engine build reads very similar to my experience, but I dove into the radial engine world on a 9 cylinder with castings version! 
I will be following along closely as well.

Mike

Offline petertha

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Re: Ohrndorf 5 Cylinder Radial
« Reply #10 on: January 20, 2021, 04:57:35 AM »
Mike.R - Look forward to seeing your build progress. Hopefully my ramblings will inspire you as others have inspired me. Or put another way, provide you specific knowledge of how NOT to do certain things!

Laurentic - Same message. Sounds like a very interesting project. Would love to see some details when you are ready to share.

Vixen - thanks for the interest & nice comments

Offline petertha

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Re: Ohrndorf 5 Cylinder Radial
« Reply #11 on: January 20, 2021, 05:05:56 AM »
Crankcase 1. The crankcase is made from 2024 aluminum. My notes show that I started the first one in 2017, but there were a few binners along the way.

The turning operations went well, but I ran into issues cutting the cylinder facets. Possibly the setup shifted slightly. But I suspect it was my poor choice gripping the fixture OD with a 3J chuck and/or not properly confirming things where it mattered. Near the end of cutting depth, I noticed the facets were not breaking through quite equally to the internal master rod clearance groove. Not a good sign. Since the internal groove was turned in the same lathe operation as the OD, it could only mean one thing Ė radial runout. Therefore the facets were not equal distance relative to the CC centerline. Therefore each cylinder assembly would end up slightly up or down & a domino effect of bad things thereafter; piston geometry, compression ratioÖ. That that would never do. Lesson learned. Aluminum Gods = 1 point, Apprentice = Zero.

The dud part did provide some utility value. I used it to go through the motions of boring & finishing the cylinder skirt holes to tolerance as I was kind on new to boring head operations.

Offline petertha

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Re: Ohrndorf 5 Cylinder Radial
« Reply #12 on: January 20, 2021, 05:08:33 AM »
Crankcase 2. Turning operations went good. Repetition builds confidence. This time I reverted to an independent 4J chuck for the radial operations to ensure no runout & tight grip. I also made some improvements to the mounting plate. Radial & axial runout was confirmed, this time the facets came out good. The cylinder liner holes were bored. Then while tapping the proverbial last hole (or thereabouts) for the cylinder flanges, I experienced the dreaded broken off tap. ACK!

It was entirely my own fault. The holes were blind end M3 thread. A bit finicky but nothing onerous. After feeling quite confident with my shiny new tapping head, I decided this would be a good application. However, in hindsight, I didnít properly factor the over-depth allowance as the instructions clearly convey. So with tap firmly stuck in hole, what now. I tried drilling on the end with a carbide, no go. I tried heat. I didnít have access to EDM or anything like it. After some forum Q&A and very convincing YouTube testimonials, I decided to try the alum solution. It was a disaster. The process slowly turned the part into something that resembled an artifact from the Titanic. The tap was slightly smaller but still there. Rather than take up more space, Iíll just insert a few choice R.I.P. pics if you want to read the original saga on the other forum and weíll carry on. Aluminum Gods 2 points, Apprentice still zero.
https://www.homemodelenginemachinist.com/threads/broken-tap-in-aluminum-cranckase.26470/
« Last Edit: January 20, 2021, 05:45:05 AM by petertha »

Offline petertha

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Re: Ohrndorf 5 Cylinder Radial
« Reply #13 on: January 20, 2021, 05:14:02 AM »
Crankcase 3. After 2 warm up exercises, this was the keeper. WellÖ maybe. Dimensionally everything was good but as I look back on the pics of so-so thready finish, I think my lathe was trying to tell me something even at that point. Forewarning of ominous events around the corner. Anyways, pleasant thoughts for now. This is how it crankcase making SHOULD have gone.
« Last Edit: January 20, 2021, 05:46:32 AM by petertha »

Offline petertha

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Re: Ohrndorf 5 Cylinder Radial
« Reply #14 on: January 20, 2021, 05:18:50 AM »
Crankcase