Author Topic: Ohrndorf 5 Cylinder Radial  (Read 22458 times)

Offline petertha

  • Full Member
  • ****
  • Posts: 784
Re: Ohrndorf 5 Cylinder Radial
« Reply #330 on: August 26, 2023, 10:50:12 PM »
With the sub-assemblies now coming together, I revisited my original master rod components & made a few re-doís. I decided I wanted a slightly better fit between the bronze crankpin bushing bore on the crank pin OD. So rather than ream the bushing which I think was the reason for slightly loose fit, I used a boring tool. The wall thickness is quite thin, maybe that influenced reaming. I also tweaked the front facing flange thickness while I was at it to accurately center the MR to the bores, even though it isnít really critical. I used Loctite to retain the bushing into MR body & with that done, drilled 3 oil passage holes at slightly offset positions down the crankpin length. The spacing had a domino effect on pin plate thickness & this time I made a bronze washer which will see some occasional rubbing from the retention clip

Offline petertha

  • Full Member
  • ****
  • Posts: 784
Re: Ohrndorf 5 Cylinder Radial
« Reply #331 on: August 26, 2023, 10:51:10 PM »
The spacing had a domino effect on pin plate thickness & this time I made a bronze washer which will see some occasional rubbing from the retention clip.

Offline petertha

  • Full Member
  • ****
  • Posts: 784
Re: Ohrndorf 5 Cylinder Radial
« Reply #332 on: August 26, 2023, 10:52:27 PM »
Around the same time, I came to notice how close the face of master rod occurred relative to the crankcase recess groove. I thought surely, I must have machined something incorrectly but everything checked out to plans. The MR is centered & nothing should really allow it to drift fore/aft too much, although the MR does have a bit of necessary clearance float between the crankpin bushing & retainer clip. It just made me a bit uncomfortable should a tiny fragment decided to lodge in there, or if I didnít seat the bearings quite right orÖ Not that we can predict disasters but I didnít think crankcase strength would be compromised by opening up the groove a bit. So, I made a holding fixture, dialed in the ID & took off some material either side of the groove, preserving the same depth. Made me feel better.

Offline petertha

  • Full Member
  • ****
  • Posts: 784
Re: Ohrndorf 5 Cylinder Radial
« Reply #333 on: August 26, 2023, 10:53:16 PM »
I donít think I showed pictures of the piston with the OS-56 rings. Here they are. I basically mimicked the groove dimensions to the stock OS piston including the same crown undercut to ease ring installation. As far as I could determine they were a good fit in the liner bores but will be proven later. For interest sake, the section dimensions are quite close to Trimble calculations. Next engine project I will have a go at making my own.

Offline petertha

  • Full Member
  • ****
  • Posts: 784
Re: Ohrndorf 5 Cylinder Radial
« Reply #334 on: August 26, 2023, 10:54:39 PM »
When my propeller arrived, it was a different nominal thickness than what the plans presumed which had a knock-on effect to the drive washer & therefore the split cone its mated to. So those parts had to be re-made. I made a slightly bit thicker bolt plate while I was at it & matching drill jig.

Offline Admiral_dk

  • Full Member
  • *****
  • Posts: 3777
  • SÝften - Denmark
Re: Ohrndorf 5 Cylinder Radial
« Reply #335 on: August 27, 2023, 08:35:56 AM »
It going to be a Magnificient Engine when you are finished with it  :praise2:

I reallt enjoy reading and watching the pictures  :cheers:

Per

Offline Roger B

  • Global Moderator
  • Full Member
  • *****
  • Posts: 6164
  • Switzerland
Re: Ohrndorf 5 Cylinder Radial
« Reply #336 on: August 27, 2023, 10:00:03 AM »
Nice work  :praise2:  :praise2:

Your thoughts on the cam drive are interesting  :thinking: I like the idea of being able to dismantle the system rather than using Loctite but I am not sure how your pin will cope with the alternating load from the cams.

Is that a special cut down digital caliper that you are using to measure the crankcase?
Best regards

Roger

Offline petertha

  • Full Member
  • ****
  • Posts: 784
Re: Ohrndorf 5 Cylinder Radial
« Reply #337 on: August 27, 2023, 05:18:03 PM »
Thanks Roger. That's a good point about alternating vs steady load from cams. I can't recall if this was the exact cross pin drill size I used, but I approached it rather simplistically to size the pin to meet or exceed shear strength of Loctite. I'm sure there are variables on both methods so rather uncharted waters. I was going to rig up some kind of torque measurement because the actual resistance during cam action is quite low. What gave me some degree of comfort is hand turning the assembly with a stub prop, I could easily rotate through the cam action with my index finger at maybe 2" radius. Not very scientific I know. I think its getting some mechanical advantage through the planetary gear drive? Anyways, pray that it works. Next engine I will have a proper key. The challenge is with these small gears, there really isn't a lot of hub material or assembly room to work with, but it is doable.

The caliper is called a hook caliper, Asimeto brand. But OMG the prices of these things have escalated over the years.

https://www.asimeto.com/category-Depth---Height-Gauges-03.html
« Last Edit: August 27, 2023, 07:49:25 PM by petertha »

Offline petertha

  • Full Member
  • ****
  • Posts: 784
Re: Ohrndorf 5 Cylinder Radial
« Reply #338 on: August 27, 2023, 07:48:06 PM »
The mechanical parts were basically complete at this point. I decided to make a leak down tester rig to sanity check the cylinders under pressure prior to running. The basic principle is you have two identical pressure gauges with a small diameter orifice restriction between them. Regulated pressure is applied to the input upstream gauge. The downstream gauge output is connected to the cylinder head by a fitting screwed into the glow/spark plug hole. With the piston at TDC & both valves closed mimicking combustion, the gauge pressures should read the same. If the downstream gauge pressure is lower and/or diminishes over time, it indicates a leak in the system. But it canít distinguish leak between ring seal, ring gap or valvesÖ because itís a collective system. This is why the tiny orifice restriction between gauges is important, we want to see any pressure change without the supply replenishing just as fast so to speak. I donít have a feel for how much pressure over how much time is acceptable. More of a Houston, we have a problem thing. My valve/seats were vacuum tested to the extent of negative pressure previously, so I was hoping this would show more ring related results at elevated positive pressure.

The parts were relatively inexpensive Amazon components including the hose & quick connect fittings. I machined an extended length spark plug adapter fitting to match the thread & incorporated an O-ring to seal.

Apparently on full size engine testers the orifice is of defined size. But because our model engine volumes are smaller, the orifice must be reduced. The smaller the hole, the more sensitive are the readings. Iím not sure if it should be reduced proportional to displacement, but I had a few data points from other model testers I came across. My friend used a #80 drill (0.0135"). I asked him how he came up with that & he said it was the smallest drill he had at the time & it works, ha-ha. Also, Don Grimm on the HMEM forum published his tester plans which I subsequently stumbled on & I believe he used 0.026Ē. I found a tiny restrictor we used on RC pneumatic retract gear systems, but the hose barb diameter is very small ~1/16Ē so would have required extra machining to integrate. So, I made a restrictor by plugging a standard pneumatic brass coupler fitting with a #80 pre-drilled orifice segment, glued with Loctite. It seemed to work. Then I realized what I thought was a regular on/off pneumatic valve I purchased was actually a pretty fine adjustable needle valve. It already has threaded fittings so I installed it in between gauges to compare. If I just crack the valve, it flows quite slow to the extent the downstream gage takes a while to equalize the upstream gage with the tubing blocked off. So for simplicity & some flow variability, I would recommend going that route if you build your own.

I went ahead & tested the 5 cylinders thinking it should at least be indicative of apples-to-apples comparison among all cylinders. I used about 45 psi initially & then 60 psi when nothing bad happened. The pistons had a light coating of oil normal for assembly. The good news is, no problematic leak off was seen. The gauges equal one another & will sit that way for several minutes at least. I left the crankcase open so I could see the underside of the pistons. Over time a tiny bubble could be seen which I attribute to ring gap & brand-new rings/liners. If I push on a valve, it blows down, re-seats & gauges re-equalize again. I put the same test rig on a known used RC engine & replicated the results (oops took picture with needle valve closed)

It is advisable to somehow mechanically lock the crankshaft at TDC before applying pressure. Otherwise, the engine will faithfully reproduce a combustion stroke with an unexpected & jump on the workbench. Ask me how I know.
« Last Edit: August 27, 2023, 08:36:44 PM by petertha »

Offline petertha

  • Full Member
  • ****
  • Posts: 784
Re: Ohrndorf 5 Cylinder Radial
« Reply #339 on: September 01, 2023, 09:40:18 PM »
Glow plug drivers have been discussed a few times on the forums so Iíll just try & summarize a few points as I understand them. A typical plug requires ~1.2-1.3 volts & draw 2-3 amps each depending on variables like the plug element, state of condition, how much fuel wetting, fuel composition variations etc. They can briefly take a bit more power but it shortens life. The wire glow elements come in various gauges & material flavors depending on the purpose. Most are exposed wire viewed from bottom, some plugs have an idle bar or shield.

For RC purposes the plugs are typically only energized for starting, they then sustain glow during running conditions every combustion stroke. 4-strokes engines usually benefit or require a heavier glow element vs. 2-strokes, presumably because of the extra dead time between combustion. FS (Four Stroke) plugs generally draw a bit more power but not much. In some installations glow plugs are switched on during idle for more reliability or for inverted cylinder arrangements which tend to run richer which would be the case for a radial. In that case a remote battery power must be carried by the model & of course weight may be a factor.

The simplest driver is a single NIMH cell (or NICD back in the day) typically integrated to a plug clip. These cells have output voltage quite close to plug requirements. It just needs to be of sufficient C-rating & maH capacity.  Some excerpts from OS 5-cyl documentation

Offline petertha

  • Full Member
  • ****
  • Posts: 784
Re: Ohrndorf 5 Cylinder Radial
« Reply #340 on: September 01, 2023, 09:41:49 PM »
Next are commercial or shop designed circuit-based drivers which may offer added features like regulated/adjustable voltage, self-compensating current to help if the engine becomes fuel loaded or degrade, responding to element resistance change, I guess. Many are trending to more modern lithium-based batteries especially where weight is a factor. They are quite prevalent, come in many mAH capacities, have much higher current rating & higher energy density. The downside is lithium packs are nominally 3-4 v/cell, so a 1S (single) does not make a good match to 1.2-1.3V plug voltage, hence some kind of circuit is required. There are also commercial, multi-cylinder airborne driver modules with more TX flight control features because they are plugged into the RX. For now, I am just in test stand mode. Weight is no concern, just portability, ease of use etc.

https://www.justengines.co.uk/shop/ignition-systems/on-board-glow/five-cylinder-glow-driver/?v=3e8d115eb4b3

https://www.sonictronics.us/glow-drivers/single-cylinder-drivers/3-9-cylinder-set-up/mcd475-4.8v-pulsed-on-board-glow-driver-five-cylinders/

https://rainbow-tronic.de/en/cartsearch/index.html

The wire harness to each of my O5 radial plugs works out to 6-10Ē length depending on where they would come together behind the firewall to meet the power supply. I had some inventory 2200 maH sub-C NIMH cells kicking around so as a test I soldered 5 in parallel (one per cylinder). A single cell ignited the dry plug sufficiently & confirmed the voltage/amperage range, so that was a viable option. But as the cells deplete, the glow intensity does diminish. There is also voltage drop along the harness wire & the clip, so a lower resistance multi-strand wire is preferable as is keeping oil off the clip so there is good contact.

Iíve seen various harness clips for RC use. Some are like an e-clip that snap to the stem groove. Some are like a push & rotate engagement that lock on the hex body. My plugs are recessed relatively deep in the head so I needed something physically longer to reach. I found some low- profile Ďremoteí RC harness / plug clips on AliExpress & ordered some to evaluate. The clip body is basically a brass cylinder with a spring captured inside which snugly grips the plug stem making electrical contact. Note that 2 sizes are offered, one for thinner (2S) and one for thicker (4S) plug stem diameters. The system looked as good or better than I could make & seemed like it would hold under vibration. One could also bend or re-solder the wire more at a right angle & re heat shrink, making it look like a faux boot.

Offline petertha

  • Full Member
  • ****
  • Posts: 784
Re: Ohrndorf 5 Cylinder Radial
« Reply #341 on: September 01, 2023, 09:43:14 PM »
While poking around AliExpress I also came across some on-board RC igniter modules. They are purpose designed to output the correct plug voltage. They also allow a wide range of input voltage which was desirable because I have spare LiPo cells & charging equipment. I bought one to try & it seemed to function as advertised with a bit stronger glow than on my NIMH pack. Iím not sure if the modules have features beyond voltage regulation since I am electrically challenged. I decided for the net cost to sandwich 5 together operating in parallel, one for each cylinder to common battery source. I also wanted to switch them on/off independently both to start & also to evaluate how idle/transition behaved on dedicated upright/inverted cylinders out of curiosity. I snipped off the pretty anodized & chromed clips for some other project.

Offline petertha

  • Full Member
  • ****
  • Posts: 784
Re: Ohrndorf 5 Cylinder Radial
« Reply #342 on: September 01, 2023, 09:44:35 PM »
I found a plastic project box to house the modules & switches & commenced my Neanderthal electrical construction. I needed something like a bus bar to tie the leads in common, but I didnít see the point in a bunch of screw terminals & the wires were pretty small gauge. So, I cut some copper from scrap 1/16Ē sheet & just soldered the wires directly. The modules were sandwiched together with heat shrink & everything sits on a G10 plate with standoffs. With the switches itís a bit of ratís nest but hopefully functional.

Offline petertha

  • Full Member
  • ****
  • Posts: 784
Re: Ohrndorf 5 Cylinder Radial
« Reply #343 on: September 01, 2023, 09:45:16 PM »
more pics

Offline petertha

  • Full Member
  • ****
  • Posts: 784
Re: Ohrndorf 5 Cylinder Radial
« Reply #344 on: September 03, 2023, 07:54:43 PM »
I made a test stand from 3/8Ē birch plywood. The joints were glued & screwed together for rigidity & a couple coats of 2K clear so it can be wiped down. My flying field has a very beefy wood table that was used for engine runups back in the day, so for now I will just screw the base down with deck screws which will save me making a dedicated sawhorse or buying a portable work table. The exhaust pipes will blow outboard of the firewall, thus providing copious lubrication to the operator, but I can rotate them within the head port so at least they donít blast directly at the firewall face as they are quite close right now. One day I would like to make an exhaust collector ring, but thatís a project for another day.

The engine is mounted on 5 aluminum standoffs which have M4 clearance holes, so basically bolt passing through the standoff into the threaded manifold mount plate part. The vertical ears give the firewall rigidity to the base & somewhat house the glow driver box. I routed the plug harness through a single hole to avoid the carb opening & then to individual cylinders. A LiPo battery is hooked up to the input power.

 

SimplePortal 2.3.5 © 2008-2012, SimplePortal