At first glance, it might look like this month's issue represents pretty slim pickins', but as you will hopefully discover, appearances can be deceptive. Nevertheless, I have been as busy—work wise—as the proverbial "lizard drinking" for the past weeks and there is no let-up in sight this side of early July. Just as well I love my job! The long hours leave me with just sufficient time to drive home (in the new Boxter S ), cook, eat, take a glass or two of exceptional an Australian Shiraz, sleep, wake, then do it all again. Weekends are less hectic, but generally require some effort here as well, so time for playing around in the shop and flying models is regrettably low.
To brighten my days, and following on the high-temperature locktite received last month, contributions continue to be received from kind and generous folk whom I've never met. In the past month, a gentleman in England sent me some of the Model Engineers Workshop magazines that were missing from my library with complements for the work that has and is going into this web site. What can I say but thanks, and please keep the graft and corruption flowing in.
Finally, eagle-eyed readers will instantly spot that there's no Engine of the Month this month. Sorry guys, just plain ran outa time. Maybe next month. Hope the short treatments on the DA and the Kestrel make up for it a little bit.
By the way, there were 7,779 hits on last month's Model Engine News page, and there are now only 21 months remaining until Microsoft produces the cure for Spam.
A Four-Stroke Mk 17
What a beauty. Here we see a one-off conversion of the Russian Mk 17 1.5cc diesel to a four-stroke glow. The work was done by Mr Peter Tarn of England. The photos were sent by Ken Croft who reports that the engine sports titanium valves in phos bronze guides/seats. The anodizing job on the head is excellent too, as is the blacking of the rocker gear to provide a most pleasing color contrast (to my eye, at least). Mk 17's were made in great quantity and at one time could be had for the proverbial song, so obtaining an example for such a conversion should not be difficult. They are a darn good engine too—real "screamers"—wonder if the 4S conversion quieting them down a bit.
The Feeney is essentially finished. A mounting stand for it has been riveted up—each rivet a disaster in itself due to all I've managed to forget about riveting using pneumatic tools since I last did this nearly thirty years ago. Still, it's functional and I just won't take any close up photos of the job!
This month, two new pages for the Feeney saga have been written up and posted: Page 6 details the machining of the poppet valves and their attendant actuating gear. Page 7 shows how the cams and camshaft were fabricated using a table of tangential lift values that indirectly led to this month's Tech Tip (I'm nothing if not frugal with my output).
Piston rings for the Feeney have also been made using the well-known "George Trimble" method that appeared in the second volume of SIC. This worked quite well, although I'm a bit confused about an apparent dimensioning error in the article (repeated when it was published in a slightly different form in Model Engineer magazine). At least we know what next month's issue can address .
Last month, when describing the Westbury Kinglet, I made the Big Call that poo-poo'd any heritage between Westbury's Kestrel and Kinglet. I'll leave you to refresh your memory in regard to what I wrote as I'm now far too embarrassed. Having paid my old friend Russ Watson-Will a visit and borrowed his binder of Model Engineer for 1938 that contains the Kinglet construction series, I must retract my wild denouncement as The Man Himself not only states the connection, but having omitted small details like piston, rings, rod, wrist pin, and cylinder from the series, refers builders to the drawings published earlier for the Kestrel!! He makes no mention of it, but somehow I think the cross-flow baffle on top of the piston would not be a great idea in the combustion chamber of the Kinglet.
I'll have to go back to Russ for the Kestrel volumes. The picture here is photographed from Westbuty's Model Petrol Engines book, available again in reprint form from Tee Publications in the UK. The Kestrel has some unusual features, not all that apparent in this illustration. The inlet is timed by a rotary disk mounted in front of the the crankshaft web. This permits the inlet venturi to project forward into the prop slipstream, probably doing nothing at all, but, like a Zeiss Jenna, looking rather neat. The spray bar is mounted at an angle allowing it to intersect a passage drilled in a ridge running under the main crankcase to the rear mounted fuel tank. Ingenious, unnecessary, and very Westbury—I like it! It's a pity the photo of the completed engine was taken with the prop obscuring the inlet.
From the sectioned GA, it appears that thrust is taken up by the rotary valve. This has to have an adverse impact on friction. I'd have thought that the shaft bush could have been set to take this thrust, leaving the rotary valve with no more pressure on it than that exerted by primary compression on a rear rotary valve. Still, a nice enough design touch with enough unusual features to make it worth building, especially if paired with a Kinglet.
One last point before we leave ETW alone for this month: While the Model Engineer plans service offered the Kestrel plan, they do not appear to have ever listed the Kinglet as a plan for modelers. Leaving aside the parts it shares with the Kestrel, even the ME articles (which ran for only 3 issues: #'s 1936, 1938, and 1940) are sparse on detail with some parts drawn, but not dimensioned, and others—not shared with the Kestrel—not even drawn at all. Neither are specifications for the skew gear pair required anywhere to be found. Perhaps complete plans were supplied with the casting sets, which may have included the skew gear set. Certainly these existed; Westbury even noting that the head pattern and its complicated core was, to quote ETW, "not by any means a popular favorite at the foundry". Still, I'm sure a Kinglet could be built, even if some innovation and close guess-timation by measurement of the magazine drawings were required. Does anyone out there know of, or better still, have an actual Kinglet plan? Please let me know if so.
Tech Tip of the Month
As I've discovered from work on the Feeney, making cams by milling from a table of lift figures is quite easy. The method will naturally work for any "harmonic cam". The only hard part is generating the table of lift values verses cam rotation. Published designs seldom provide such a table, especially older designs. It can be done with CAD, or by drawing the cam several time life size and doing some measuring, but both of these methods are tedious. In SIC Vol 3, number 18, Roderic Jenkins published formulae for modeling such a cam mathematically. Having done that, deriving the lift as applied to a "mushroom" type cam-follower at any angle is simple, especially given today's desktop computing capability. The article included a program to perform this task written in a computer language whose mere mention would probably have me disbarred. In preparation for making the Feeney cam, I reverse engineered the program into a "command-line" driven utility, using my prime language of choice for the past 7 years or so: Java.
This was done just for the job at hand, but it's been in my mind to add a "Design Centre" page to this web site that contains somewhat more interactive pages and this looked like a good candidate. The work was comparatively simple. The command-line program had been written so formatted text strings could be redirected to files for printing in the best Unix traditions. This made it simple to wrap the utility in a Java Applet that could be invoked from a web page that first gathers the required variable values. The table, once calculated on the users' computer, is displayed in the browser ready for printing and taking out to the shop, ready to cut metal. So, if you look left, you'll see a new menu choice: Design Centre. At the moment, this only contains the link to the CamCalc Page (or you can click on the link here to go direct). The CamCalc page tells all, hopefully, that you'll need to know, especially if you read Page 7 of the Feeney Construction log first to see how the method is applied. Your comments and feedback are, as always, most welcome.
If you'd like to try reproducing the sample cam table from the SIC article, enter the following (Imperial units):
- Base circle: 0.128
- Valve lift: 0.09
- Cam action angle: 140
- Flank radius: 0.5
- Table increment: 3
- RPM: 10000
Yet Another YaHoo MICE List
You may remember mention of a YaHoo list dedicated to Real Model Engines (round ones). One of the posters to this list is none other than Robert Washburn, past editor/publisher of SIC magazine. It's good to see Bob (RAW as he signs himself) enjoying his third retirement, making chips and stuff. Last month he posted some pictures of a crankshaft grinding machine he's build. The post accidentally went to R_and_R_engines, the round engine guys, when he'd intended to send the announcement to Min_Int_Comb_Eng, a group for minature internal combustion engines. A fortuitous accident, as it alerted me to another relatively active group. So if you've a mind, and my little monthly ramblings are not enough of a fix for you, subscribe to one, the other, or both.
New Books and Magazines This Month
As mentioned earlier, the only "new" magazines added to the library this month were some old issues of MEW (that's Model Engineers Workshop, not the other one) kindly sent to me by a reader in the UK with complements and a request to keep up the good work. So I've dug back into the library to find something topical that I've not mentioned before and quickly decided on Dave Gierke's 2-stroke book. Back in the 60's and 70's, Dave was competing in C/L stunt with some of the most beautifully designed models ever to sit on the end of a pair of lines (remember the Novi series?). He also authored a series of articles in Flying Models on a torque reaction dynamometer for model engines. His book 2-Stroke Glow Engines for R/C Aircraft was first published by AirAge Publishing in 1994 (ISBN 0-911295-30-5).
It is not just an introductory text to how our engines work. In 23 chapters, Dave covers principals, design, and construction (12 chapters, 103 pages), then operation and maintenance (11 chapters, 66 pages). The book is lavishly illustrated with "3-D" art-work and truly outstanding, crisp, clear photography.
While the book title says "..for R/C..", don't let this put you off. The first 12 chapters are divided into engine subsystems (eg, "Induction Systems", "Scavenging", etc) and in each, Dave looks at just about all possible schemes and traces the evolution of designs from the spark era to current. The photos include examples drawn from private collections of rare and unusual engines, like the bar-stock prototype for that fabulous failure, the "Aero 35", designed by Augie Savage and John Piston (I kid you not). Pages 91 and 92 show the engines that led up to the production model, all retained by John.
If I have a criticism, it would be the lack of math (I'm a sick puppy), the lack of diesels (a very sick puppy), and the lack of twins (that's a fetish, not a sickness). If you are new to these things, you will find the book extremely informative and an easy read. I'll go so far as to say that even experienced folk who love model engines will enjoy at least the first 12 chapters. The link above will take you to the Amazon.com entry for the book, and if about 100 of you purchase through that link, I'll make enough credit to redeem a cheap paperback from them. Best of all, Amazon has placed a large chunk of the content on-line, so you can try before you buy!
Here's an example of one of Jan David-Andersen's designs. From the highly polished finish and use of contrasting material colors, you might guess it to be Les Stone's work, and you'd be right! DA apparently liked trying unusual features. One of his diesel designs varied the compression through an eccentric crankshaft bush (and hence, the cylinder desaxé as well). This engine features an "external contra-piston" arrangement. As the self-imposed monthly deadline is weighing heavily on me, I'm not going to go any further into this one right now, but expect this design to get "Engine of the Month" treatment some time soon.