Model Engine News: June 2003

 

Editorial

May was a full-on month for me, work wise, and while some very, very innovative software has being built, but not a lot else has. So if you need a Dublin Core based metadata server, editor and harvester that is AGLS and ANZLIC capable, go see MetaSuite on our Demos and Downloads page, and if you've got no idea what that means, you can probably count yourself among the more fortunate.

That said, I did manage to complete the pair of Sparey 5cc diesels mentioned last month. Both have now been run and the prop flickin' finger of my right hand is healing quite well, thank you... The construction series on this engine has been updated with final photos and a few words on what I had to do to make them run without causing serious physical trauma--this latter may be of some use to prospective builders. One of the pair has now been traded for an DC Bambi 0.15cc diesel--that's 0.009 cuin--smaller in capacity than the Cox 010. In fact, it would not be out of scale if used as the tommy bar for the Sparey 5! The Bambi will get a little resoration done (re-anodizing the head), then we'll see if it will run. Ken Croft says that Bambis fall into two categories, those that start as easily as a Mills .75, and rest, that don't!

Books and Magazines

Volume 2, Issue 2 of Torque Meter, the quarterly journal of the Aircraft Engine Historical Society Inc arrived in May. Nothing of explicit interest to the model engine builders, but good reading never the less. Contents include an account of engines at this year's Reno air races (these seeming to subdivide into "blown"--as in supercharged, and "blown up"--as in supercharged too much) and an article on the hollow boss prop hub design for the P-39 Aircobra--designed that way so a cannon could fire through it.

Issues 89 and 90 of "Model Engineers Workshop" (the other MEW) also arrived this month. Again, nothing explicitly targeted at model engine building, although an add for sister magazine Model Engineer shows that a construction series on a quarter scale model of the Aeronca two cylinder, opposed, four-stroke has begun in issue 4187. If they follow their usual practice, installments will appear in alternate issues (they publish roughly twice per month), so buy all odd numbers if you feel the need to built an engine designed to form the actual nose of the world's ugliest airplane. Sorry I can't tell more (that magazine is hard to find and prohibitivly expensive here in Oz).

Issue 90 of MEW contains an article on twist drill sharpening using the Quorn. The Kiwi author first describes how to adapt the "Duplex" drill sharpening jig to the Quorn work head, then describes his own jig for the Quorn. This led to some digging: the Duplex jig appeared in Model Engineer over four issues in December 1963 and January 1964. It is based on a design that appeared in ME in 1913 (!) that follows commercial practice and applies a conical back-off relief to the drill lips. Bill Morris's jig on the other hand uses the so-called "Fout Facet" grinding which many say is superior in that twist drills sharpened this way are better able to "self-start", less likely to wander, and drill closer to size. The cutting edge geometry is similar to that on a slot drill, having flat-ground primary and secondary relief to the cutting edge and an actual point rather than the "chisel point" formed by traditional conical grinding. The down-side (there's always a down-side) is that four facet drills are more likely to "grab" on thin sheet and brass of any size, so if you sharpen all you drills this way, you'll need another set with conical relief anyway (perhaps with reduced rake for brass work). It's all very interesting and I may actually make one of these...

A Little Larger Than Usual

Early last month I received an email to inform me that a group called the White 1 Foundation, Inc are in the process of restoring a BMW 801 radial, and the Focke Wulf FW 190 it goes in, to flying condition. They are trying to attract new members and hopefully, raise some of the much needed money required to bring a project like this to completion, then maintain it! Their web site is at http://www.white1foundation.org and I sure wish them every success with their efforts.

Cams and Gearing for Radial Engines

There people out there doing amazing things, undertaking fabulous projects. With little more than grand ambitions and enthusiasm they overcome all hurdles--hurdles of the type that stop those with a little knowledge from even starting. All this is leading to an email I received from an innovator in the US who is building a 3 cylinder radial engine to a very compact design, using VW cylinder assemblies that will be fitted with his own head assemblies. Ultimately, this engine will power a motorbike. His research on cams led him to my Morton M5 pages (which will be finished, Real Soon Now). In discussing the relationship between the cam gearing ratio and how this relates to cam lobes, I recalled an article published by the HCI radial engine designer in Torque Meter, the quarterly journal of the The Aircraft Engine Historical Society.

The answer seems simple. The number of lobes depends on the gear ratio between the cam and the crankshaft, which in turn, depends on the relative directions of rotation and the number of cylinders. If the cam and crankshaft rotate in the same direction, the required ratio is the number of cylinders plus one; if opposed, it's the number of cylinders minus one. Since the number of cylinders will usually be an odd number to achieve an equal firing sequence, the ratio will be even (but see the item on the Bristol Hydra below before taking this statement as the Last Word). The required number of cam lobes, regardless of the relative directions of rotation between cam and crank, is one half the ratio. With an odd number of cylinders, this will be an integer since we are guarenteed of an even number for the gear ratio (half a cam lobe would be a right muthur to machine ).

As mentioned in the Morton piece, it's possible to make a single set of lobes lift both the inlet and exhaust tappets, although conventionally, a separate set of lobes are used. When separate (but joined) cam rings are used, the tappets will have to be staggered fore-aft, but the push rods can be set at whatever radial location the designer wishes. Also, the cam shape can be tailored to the job of exhaust, or inlet timing. If using just the one set of cam lobes like the Morton (and LaBlond on which it's based), the push rods can all be in the same plane, but relative timing must be achieved by angling the push rods to achieve a specific angular separation of the tappets on the cam. And the cam shape will have to be a compromise between the ideal shape for inlet and exhaust. The fixed angular separation at tappet and rocker (set by head design and valve spacing) means the push rods and stuff will be subject to some probably undesirable side loads. This, plus the less than optimum cam profile would seem to be why the LaBlond/Morton design has so rarely been used.

The Vivell 099 Redux

The Vivell 099 was a rear rotary valve induction, two stroke, available in 1949 as a glow, or diesel (the latter with either fixed, or variable compression). Plans for this engine appears in the Motor Boys Plans Book (available from the AMA) and a casting kit is available from Roger Schroeder's Classic Engines. Last month--or maybe the month before, I got an email asking me to explain a throw-away line appearing in the construction article that refers to a "cunning two-piece aluminum contra-piston" as the original plan does not show this feature. The Vivell 09 has a comparitively low side profile for a diesel which makes fitting of a conventional contra-piston impractical. Vivell's own contra on the variable compression model was not ideal either, so Motor Boy Stan Pilgrim (one of Oz's foremost C/L Team Race experts) devised a smart way to fit a low-profile, aluminum contra-piston into a steel liner and not have it lock solid after things heat up. My correspondant is building one and wanted to know the details, so I've pulled down the engine, taken photos and measurements, and included details on the relevant page.

Bristol Hydra Redux

My Big Monthly BooBoo (MB^2) for May was calling the Bristol Hydra a sleeve valve engine (just how dumb is it to have a big, expensive library and not use it before demonstrating one's ignorance?) Still, it did lead to an exchange of very enjoyable emails with Brian Perkins about said engine, which, to set the record straight, has poppet valves. The Hydra was also unusual in being a dual bank, air-cooled radial with an even number of cylinders in each bank. But wait, there's more: the cylinders in the two banks were positioned directly in-line rather than staggered as has become normal practice for multi-bank, air-cooled radials. The Hydra was installed in the other Hawker Harrier--the between-wars biplane, not the modern V/STOL used by the Royal Navy, US Marines, and Spanish, Italian, Indian and Thai Navies (I believe--please, please let me be right). Brian has supplied some pics of progress on the Hydra and I've added these to the Engine Gallery together with some of his comments regarding both the original engine and his scale model of it.

Other New Stuff This Month, Really!

Last month I promised new engines in the Engine Finder including a Mamiya, and others. What can I say? I lied. Somehow, the necessary entries never actually got made, which caused some readers to embark on a fruitless search (sorry). To make sure I don't make that mistake twice, here are direct links to the new entries in the Engine Finder. Hopefully I'll test them before publishing this page, and good things will happen:

• Taipan Series 66 Diesel
• Taipan Series 67 Glow
• Mamiya 60

Model Pulse Jets

Another email from last month caused me to go looking for pulse jet sites to confirm the spelling of a name. I found a couple of very interesting sites in the process which I pass along to those of you who, like me, have some affinity for these hot, noisy things.

• Pulse Jet plans
• Inside The Pulse Jet

The first link gives full working drawing reproductions for three commercial pulse jets that are no longer in production, plus control line models to fly them in (provided your local circle does not have noise restrictions). The second is a pdf document in book form by Fredrik Westburg. It explains the principles and practice of pulse jet operation, and shows some innovative ways Fredrik has conceived to risk life and limb. I'd go so far as to say his report is an outstanding example of the "good" of the Internet: providing a vehicle for a person or group who are passionate and knowledgable on a topic to make their knowledge available to anyone with curiosity and a computer.

A Tank Driver

...or fuel tank from a screwdriver handle, it you prefer. This is one smart idea from Bert Striegler. The plastic used for the handles of inexpensive, hardware store screwdrivers makes a great fuel tank plastic. It's resistant to petrol, glow and diesel fuel, turns easily, and looks like the "real thing", being colored to emulate age-yellowed plastics ('though many tanks were dyed yellow amongst other colors, from the factory). Just thought I'd pop this photo in to fill out space and give you ideas. I'll take photos and give procedures for doing this in a future construction series--maybe the Battiwallah...