The Reeves 3.4 cc Diesel
by Adrian Duncan
Click on images to view larger picture.
Once more into the breach, dear friends! Yet again we find ourselves taking as our subject one of the least documented British model engine lines of the early post-WW2 era—the Reeves range from Shropshire, England.
Our justification for indulging in another masochistic exercise in the art of scantily documented, but lovely old model engines is that interest will only be sustained after all of us old retreads are gone (and the engines' long-term preservation assured) if their history is documented—no-one's going to collect or even take an interest in a class of items about which there's little or no recorded history. Recording that history will never get any easier than it is now since the window of opportunity for the recovery of any first-hand information about these more obscure ranges is now all but closed, so if we don't get it done now, it may never get done at all.
As always in these cases in which little information appears on the record, we are painfully aware of the fact that we are at best able to present the bare outlines of the story. If any reader knows something that we don't, or experiences a stirring of the an old memory upon reading our efforts, please get in touch and share what you know while the opportunity exists! All contributions openly and gratefully acknowledged, and the more the merrier.
The Reeves engines were never made in large numbers and are consequently very rare today. I looked for years before acquiring my first engine from this manufacturer—a near-mint example of the 3.4 cc diesel model which is our main subject—and many others are still looking. I subsequently had a second and less perfect example more or less dropped into my lap, but my joy was a little tempered by the fact that it was a duplicate of the one that I already had, albeit incomplete! Still, this did have the great advantage that I was able to replicate the missing parts very exactly using my original example as the prototype. Another Reeves faithfully restored!
At the time when this article was first published, we had only one Reeves model available for first-hand examination—the 3.4 cc model which was Reeves' first diesel design. However, by way of compensation we had two examples of that model and so are in a position to subject this engine to a very searching examination both in the shop and on the test bench, but before we do so, let's set out what we know about the history of the Reeves model engine range.
A Brief History of the Reeves Range
The Reeves model aero engines were manufactured on a relatively small scale in Shifnal, Shropshire, a small town which lies a little to the south-east of Telford between Wolverhampton and Shrewsbury. The company traded under the name of E Reeves, Model and Precision Engineers from an address on Church Street. Later they traded as Reeves Model Power Units from an address on Victoria Road, now part of the A464 and so constitutes one of the main thoroughfares passing through the community. No street address was ever given for either location, so it is impossible today to identify the former sites with any precision. In any case, the town has changed considerably since the war and the two sites have almost certainly been re-developed in consequence.
The company appears to have started in 1946 as one of the many small-scale "cottage industry" model engine manufacturing concerns which sprang into existence in Britain during the years immediately following WW2. In fact, given the rural small-town address, it may well have been located in a cottage! The rarity of surviving examples suggests that production was very small, suggesting a one or two-man "garden shed" operation in keeping with the location.
As far as I've been able to discover, the first Reeves advertisement appeared in the "Trade" section of the Classified Advertisement feature in the June 1946 issue of "Aeromodeller" magazine. This advertisement offered castings, blueprints and pre-machined components for a spark ignition engine which was available in both 5 cc and 6 cc displacements. A limited number of completed and tested engines were also reportedly available to first-comers. A 10 cc model was said to be in preparation, but there's currently no evidence that this design ever materialized.
The initial advertisement was repeated with minor variations in several subsequent issues of "Aeromodeller". These advertisements were placed in the name of E. Reeves, Model and Precision Engineers, at the Church Street address. All that is known of this individual is that his name was Edward Reeves, as confirmed by the address on a surviving box which was used to return a 6 cc petrol engine to the maker for service in 1947. The date is confirmed by a piece of newspaper dated July 4th, 1947 which was used to line the box and is still in it (with thanks to Kevin Richards for supplying this valuable piece of evidence).
The manufacturer's initial address simply given as was Church Street in Shifnal. No street address was used, presumably because (in typical British small-town fashion) Edward Reeves was sufficiently well known as a resident of Church Street to ensure correct delivery without a number. The move to nearby Victoria Road must have come at some later point in time, certainly by 1949.
Like the majority of the small post-war British engine manufacturing firms having a similar genesis, the Reeves company appears never to have expanded beyond its small-scale beginnings. Grass-roots manufacturing concerns of this type generally followed one of three routes—one, they grew by merging with a competitor (for example, Allbon merging with Davies-Charlton Ltd); two, they established themselves in a competition market niche based on performance and quality along with the ability to charge accordingly (like Oliver and ETA); or three (and most commonly), they faded relatively quickly from the scene or moved on to other work.
Reeves never took advantage of the first possibility, and the second possibility was precluded by the fact that their products were never targeted towards the "performance" market, being very much in the nature of sports engines. Despite this, Reeves Model Power Units actually ended up lasting longer than most of the other small-scale independents, staying the course for over 6 years.
Despite advertising nationally from time to time in the British modelling media, Reeves never achieved the production volumes which would have been required to establish a real presence on the national scene and thus compete with the larger volume manufacturers such as International Model Aircraft (Frog), Davies-Charlton/Allbon and E.D. Consequently the range always remained on the fringes and never attracted much attention from contemporary commentators. Even in their hey-day, such as it was, the Reeves engines constituted something of a "cult" range.
The company began in 1946 with the first of two successive variants of a 6 cc crankshaft front rotary valve (FRV) spark ignition design—the 5 cc variant mentioned in the initial advertisements seems to have faded into the background fairly quickly and the 10 cc model never made an appearance for the record. Distinguishing features of this engine included the updraft intake beneath the main bearing, the tall steel cylinder with integrally-machined cooling fins and the bolt-on bypass passage cover. In his October 1952 test report of the later Reeves Goblin diesel, Peter Chinn recalled this model from his personal experience as "a sound and likeable spark ignition engine".
As with all Reeves engines, the emphasis in this design was on internal fits rather than external finish. Consequently, despite their somewhat utilitarian appearance the engines quickly acquired a solid reputation for being well-made and dependable—Chinn's evaluation was typical. Reeves were to maintain this "care where it counts" philosophy throughout the production life of the range.
The successive variants of the Reeves 6 cc sparker enjoyed a two-year production run, selling steadily enough that the small workshop in which they were made was obviously kept quite sufficiently busy to justify continued production and further product development. By 1948 the diesel engine was well and truly in the ascendant in Britain and the appearance of the glow-plug in America had already heralded the beginning of the end for the spark ignition engine. Reeves clearly recognized this, and it was in 1948 that they took a significant step towards the future by ending production of the trusty 6 cc sparker in favour of their first diesel design, the 3.4 cc model which is the main subject of this article.
Although production of the spark-ignition version of the Reeves 6 cc model seems to have ended at this point, it does appear certain that a few examples were produced in glow-plug form. An incomplete and severely battered example of this variant was recently offered on eBay. Although the engine was very incomplete, itís an indisputable fact that there was no provision for a timer, proving the engineís glow-plug heritage.
The Reeves 3.4 cc diesel had a broadly similar layout to its spark-ignition predecessor, with a tall steel cylinder and FRV induction through an updraft carburettor. However, the bolt-on bypass cover had gone, being replaced by a soldered-on component. In addition, the integrally-machined cooling fins had been supplanted by a conventional screw-on cooling jacket of light alloy.
As usual with Reeves, the appearance of the engine was lacking in sophistication, with the initial visual impression being that it lay somewhere between the crude side of good and the good side of crude!! However, this impression was quickly dispelled when one handled an example—the internal fits and finishes were beyond reproach. Indeed, it was this model which was the subject of Reeves' remarkable guarantee to the effect that if one of these engines failed to hold its compression at top dead centre for a minimum of one hour, the buyer could retain it free of charge!! I can only report that both of my examples still pass this test today, even after an unknown amount of running.
The Reeves 3.4 cc diesel was a dependable if unspectacular sports performer by the standards of its day and was quite successful in the sense that the company was apparently able to sell all of its relatively small production. The engine was mentioned in quite favourable terms by Col. C. E. Bowden in the 1949 second edition of his book Diesel Model Engines, which can't have hurt the cause. It was also included in the technical data tables which formed appendices to Ron Warring's 1949 book Miniature Aero Motors.
The Reeves 3.4 cc model was still being advertised in late 1949—an advertisement appeared at that time in the 1949 Aeromodeller Annual in which the price of the engine was quoted as a quite reasonable £3 7s 6d. This price apparently included the provision of a glow-plug conversion kit—a common practise among British manufacturers of the day. Castings were said to be available as well, and reference was made to "other engines" in the range, although exactly what these other models were was not made clear.
One other model from this period about which we do know a little was a 4 cc version of the 3.4 which was generally quite similar but was "prettied up" a little and utilized a bolt-on cylinder assembly in place of the former screw-in system. This very rare engine cannot have been made in large numbers—it is almost never encountered today, although examples do exist.
The Reeves H.18 was introduced in the latter half of 1950. This was a disc-valve plain bearing 1.67 cc engine of relatively sophisticated design. It was tested by Lawrence Sparey, the report being published in the March 1951 issue of Aeromodeller. Sparey measured an output of 0.1034 BHP @11,700 rpm. He had little but praise for the engine's design and construction, commenting particularly upon the outstanding piston-cylinder fit.
The H.18 remained in production for some time and was still being advertised in Aeromodeller in November of 1951. However, by January of 1952 the company was no longer advertising a specific model but was instead hinting at new models to come. By 1952, these hints had become reality in the form of the 2.5 cc Goblin diesel, a plain-bearing disc-valve model once again which evidently replaced the H.18.
Unfortunately, the Goblin got off to the worst possible start by failing to complete its test in the hands of the resident Model Aircraft tester, almost certainly Peter Chinn. As noted in the published test report which appeared in the magazine's October 1952 issue, the engine broke its crankshaft during the course of the test, and Chinn also reported that he had been unable to establish contact with the manufacturers to discuss the issue, nor was he able to obtain a second example for comparison purposes.
Although Chinn exercised his usual professional restraint, this report must have done much to seal the fate of the engine in the marketplace. You had to look hard to find a Reeves engine to buy at the best of times, and it would appear that after reading this test report people stopped looking.
This was a pity, because the Goblin was an interesting design and was in many ways a quite attractive unit. The fact that a limited number of them still survive intact today indicates that they didn't all suffer the fate of Chinn's example—indeed, Chinn himself was of the opinion that he had simply got a flawed example of the engine since the basic design seemed sturdy enough. The engine's light weight of only 4.1 ounces was a point in its favour, and the implied power curve obtained by Chinn prior to the crankshaft failure indicated a peak of around 0.17 BHP at 11,000 rpm, a quite acceptable figure for a lightweight plain-bearing 2.5 cc diesel in 1952. In his 1977 Collector's Guide to model Aero Engines, OFW Fisher recalled using the Goblin to power a three-engined helicopter! Seemingly, he at least got the engines to work OK!
The fact that Chinn could not establish contact with them in connection with his test of the Goblin implies that the makers may have already been in the process of winding up their affairs at this time. They must have had some already-manufactured engines still to liquidate, because they continued to advertise sporadically, the final advertisement appearing in the December 1952 issue of Aeromodeller, still promoting the Goblin. This was the last that was to be heard of the Reeves model engine line.
There has been speculation in the past that there might have been some kind of connection between Reeves Model Power Units and the well-known model engineering supply firm of A. J. Reeves & Co., who started just after WW2 at Moseley Road in Birmingham at more or less the same time as Reeves Model Power Units became established in Shifnal. However, no less an authority than the late Ron Moulton assured us from his own first-hand knowledge that no such connection existed.
Having provided a capsule history of the activities of the Reeves model engine manufacturing concern during its 6-year existence, let's now have a look at a sample of their work in the form of the 3.4 cc model with which Reeves entered the model diesel field.
The Reeves 3.4 cc Diesel in the Modelling Media
The Reeves 3.4 cc diesel was never the subject of a published test in the British modelling media. Indeed, its sole appearance in descriptive terms was its aforementioned inclusion in the 1949 second edition of Col. Bowden's book Diesel Model Engines. Here's what the gallant Colonel had to say about the engine:
"The "Reeves" 3.4 cc has a crankshaft rotary valve, and is suitable for planes from 2 ft. 6 in. span control line to medium size free flight. The bore is 0.570 in., stroke 0.760 in., weight approx 6-1/2 oz. The cut out is of the positive valve type, and the tank is located at the rear of the crankcase. This motor has a good speed range. See Fig. 44."
Figure 44 provided a good general view of the engine, with the caption: "The Reeves diesel of 3.4 cc has a rotary crankshaft valve and a good speed range from 2,000 to 7,000 rpm."
The technical tables in Ron Warring's Miniature Aero Motors confirm the above measurements in every respect and provide details of the engine's material specification which are again confirmed by direct observation. However, there are a few apparent anomalies! The displacement given by Warring is 3.4 cc (0.208 cu. in.), exactly as indicated in the engine's name, and Warring also confirms the bore and stroke figures quoted by Col. Bowden. My own direct measurements of two examples confirm those figures almost exactly, and I also come up with a weight of precisely 6.5 ounces.
So far so good, but my pesky calculator keeps on converting those confirmed bore and stroke figures of 0.570 in. (14.48 mm) and 0.760 in. (19.30 mm) into an actual displacement of 3.18 cc (0.194 cu. in.) rather than the 3.4 cc of the engine's name! I really have no explanation for this—I can only say that both of my examples check out more or less identically at the stated figures. So it appears that we are dealing here with an engine having a true displacement of only 3.18 cc, whatever the makers may have claimed!
The other seeming anomaly in Warring's table centres upon the airscrew recommendations. Warring generally used manufacturer's recommendations as a guide, and it's possible that this is what he was doing here. He recorded 13x6 as the recommended airscrew for free flight and 11x8 as the recommended control-line prop. Based on my own tests (see below), the suggested control-line prop isn't too far off base but the stated free flight size pulls the engine's speed way down below its optimum operating range. We'll comment further in the test section of this article.
So much for the treatment of the engine in the contemporary modelling media. The only later comment that I can find that has any relevance is O. F. W. Fisher's note on page 40 of his 1977 Collector's Guide to Model Aero Engines to the effect that he had used the Reeves 3.4 cc engine (incorrectly identified as the Reeves 3.5 cc) in both a 5 foot span sports free-flight model and the prototype Eclipse Mk II twin-engined control line stunt model. Clearly, Fisher had found the engine to be perfectly satisfactory in actual service. He also noted that his example too passed the Reeves "one hour compression test"! I suspect that most of them did.
The Reeves 3.4 cc Diesel—Description
One's first impression of the Reeves 3.4 cc diesel is that it has a distinctly "old-fashioned" and "home-made" look, even by the standards of 1948. This is mainly due to the very tall cylinder coupled with the seeming lack of attention to the external finish of the unit. There's no denying the fact that the engine has a rather "agricultural" look about it!
However, when one actually gets to grips with the engine and starts turning it over, these initial impressions immediately cease to hold centre stage. The engine is outstandingly well-fitted throughout—neither of my two examples exhibits the slightest trace of play anywhere in the power train, and compression seal is absolutely perfect without there being the slightest trace of binding at any point in the stroke. I can honestly say that I have never encountered better-fitted pistons in a lapped engine—the engines feel positively "silky" when turned over. Both of my examples easily pass the Reeves "1 hour compression test" after who knows how much running.
The construction of the engine is about as simple as it could possibly be. No screws are used apart from the tank retaining screw—all major components are of the screw-in variety. The engine is built around a very solidly-proportioned gravity die-cast aluminium alloy crankcase. An internally-threaded recess at the top of this casting accommodates the base of the screw-in steel cylinder. A gasket is used to ensure a good seal at this point. The engine bears no serial number, the sole identification being the letters R M P U cast rather indistinctly in low relief in small font just below the right-hand mounting lug (looking forward in the direction of flight). You actually have to look carefully to notice these letters!
The steel cylinder is of basically tubular form, with two opposed exhaust ports of roughly oval shape. A ledge just above the exhaust ports locates the screw-on cast aluminium alloy cooling jacket. A chamfered expansion is incorporated near the cylinder base, and this expansion serves the dual purposes of carrying the external male assembly threads and providing for the inclusion of an annular internal channel inside the cylinder at its base. This channel surrounds the lower piston skirt at bottom dead centre and ensures access of transfer gas to the bypass passage regardless of the radial position in which the cylinder may end up when securely tightened.
The bypass passage itself is formed by the space between the outer cylinder wall and a thin channel of brass sheet which is soldered onto the exterior of the cylinder, rather akin to the system used on the E.D. 2 cc and 2.5 cc "stovepipe" models. The bypass passage formed in this way is fed from the crankcase by three holes drilled through the chamfered upper face of the lower cylinder expansion into the bypass passage itself. I had to remove the cover to repair a bad dent on my second example, allowing me the opportunity to secure the attached images for clarity.
The upper end of the bypass passage communicates with the cylinder through three drilled holes which together constitute the actual transfer ports. These three holes are located between the twin exhaust ports in such a position that they overlap the exhaust to a significant degree. They are drilled diametrically through the cylinder wall rather than being drilled at an upward angle, which might have helped to direct the incoming charge into the upper cylinder. As it is, the incoming gas is discharged more or less directly into the escape path of the exhaust gasses, and considerable losses of incoming mixture through the exhaust ports may be expected.
At the top end, the contra piston is of hardened steel, which is a problematic choice of material in that a steel contra-piston has an aggravating tendency to stick in a steel bore when the engine warms up. The cooling jacket is another casting in aluminium alloy which is internally threaded and screws onto the threaded upper cylinder in conventional fashion. The single-armed compression screw is carried in this component, and the range of available compression settings is limited by the inclusion of a wire stop in the manner adopted later by makers such as Davies-Charlton. This stop was presumably staked in place in the head after the engine's test run had established the correct running settings. My second example is missing this pin, presumably because the range of operating settings on this example crosses the stop pin location for some reason.
Looking now at the working components, the hardened steel piston is an extremely substantial item which displays no signs of any attempt to lighten it through appropriate machining operations. It communicates with the crankshaft through an equally substantial connecting rod made of bronze alloy. The gudgeon pin is of 0.140 (9/64) in. diameter and is pressed into the piston bosses. The reciprocating components (piston, gudgeon pin, con-rod) together weigh all of 19 gm. (0.67 oz.)!! High revs need not apply!
The con rod big end has an oil hole drilled in it for lubrication. It runs on a crankpin having a diameter of 0.218 (7/32) inches. The one-piece steel crankshaft features a disc crankweb with two cut-aways on the crankpin side for counterbalance. It has a journal diameter of 0.345 (11/32) inches. The internal gas passage has a diameter of 0.218 (7/32) inches, yielding a wall thickness of 0.062 (1/16) inches. This gas passage is supplied with mixture through a circular induction port which registers with an updraft intake cast integrally with the main bearing. A conventional brass spraybar is used in conjunction with a needle carried in a split brass thimble for retention of settings.
The die-cast aluminium alloy prop driver is a very close press-fit on a squared-off section of the shaft forward of the main journal. The shaft assembly is completed on both of my examples by a conventional nut and washer, although some examples have a turned aluminium alloy spinner nut. It's possible that both styles were used.
The main bearing is relatively long—a good feature for stability and wearing qualities. A steel bushing is incorporated and the fit of the journal in this bushing is as close as the fits in the rest of the engine. Overall, I'd expect this motor to run forever as long as it was well handled and supplied with good fuel!
The screw-in aluminium alloy backplate is again machined from a casting. A gasket is used to ensure a good seal. The tank is a stamping from soft aluminium alloy and is attached to the backplate with a single screw. It is unusually short, but the backplate recess adds considerably to its internal volume and the resulting capacity is more than adequate for free flight purposes. The tank incorporates a threaded filler hole which is stopped with a screw-in plug—a somewhat unusual feature. The fuel supply spigot at the base is threaded into the material of the tank.
However, the most individualistic feature of this tank is the cut-out! This is more easily illustrated than described, and we hope that the attached images will suffice to clarify the design. In simple terms, a thick wire plunger enters the tank at the top. It carries a compression spring which tries to force it downwards, and is bent in the middle to clear the tank retaining screw. At its lower end it features a ground tapered point which engages with the inner end of the screw-in brass fuel supply spigot to which the fuel tubing is attached.
When the plunger is left free, the spring naturally forces the tapered point downward into the end of the fuel spigot, theoretically shutting off the supply of fuel. To open the fuel supply, it's necessary to pull the plunger upwards partially out of the nipple and hold it there for as long as the engine is required to run. But how to do this?
The solution is actually both simple and elegant. The outer end of the plunger is bent into a "hook" shape in such a way that when it is pulled up it can be swung around through 90 degrees and the end of the "hook" can be allowed to rest on the top of the tank, keeping the plunger in its open position. To activate the cut-out, all that is required is to pull the outer tip of the "hook" towards the rear so that the end of the "hook" slips off the tank and the spring returns the plunger to its closed position.
In a strictly mechanical sense, this arrangement works perfectly. It will be appreciated from the geometry of the situation that in order to swing the "hook" off the tank to activate the cut-out, one actually has to pull the plunger a little further out, and the system naturally resists this. Consequently, the system remains in the "open" position very securely while the engine is running, showing no signs of working towards the "shut" position due to vibration.
Despite this, the word on the street regarding this unit is that it didn't work, plain and simple. How true is this condemnation? There's only one way to find out—let's set these engines up on the bench and give them a try!
The Reeves 3.4 cc Diesel On Test
Being mindful of the recommendations in Ron Warring's tables as well as recalling the long stroke and high reciprocating mass, I elected to begin testing on somewhat larger airscrews than I might otherwise have employed for an engine of this displacement. After thinking it over, I decided to start off with an 11x7 wood prop which I had on hand. This was actually less prop than the 11x8 recommended by Warring for control-line use, but I still thought that it was too much prop for a 3.2 cc engine. However, time would tell.
The first engine tested was my earlier example which was complete and original in all respects. Here however I encountered a problem—the contra piston was well and truly frozen in the bore! It seems that this had occurred with the engine at running settings, because I was actually able to get it started at the setting in question. However, even after a few heat cycles the contra piston remained immobile, no matter what I did. So I put this one away for a future re-test after un-sticking the contra-piston in my home workshop.
The other example which I had restored using replica components faithfully copied from its partner was far easier to manage and could readily be adjusted. It did however exhibit the previously-mentioned tendency for the steel contra-piston to freeze in the steel bore upon warming up. However, the contra-piston invariably freed up quite quickly after the engine had stopped. Hence, settings were always manageable, although it was occasionally necessary to stop the engine to make a needed correction.
This issue was of little consequence in any practical sense, because the engine was found to start and run at the same compression setting once this had been established for a given load. It was found best to open the needle slightly for cold starting, but otherwise the engine could be left alone as long as neither the fuel nor the prop were changed.
The other starting characteristic of the engine was one that is typical of engines fitted with updraft intakes when run in an upright position. Finger-choking is of little use with such engines—the fuel simply drips by gravity out of the intake rather than being absorbed by the engine. A prime is thus more or less essential for reliable starting. However, the fact that the engine seems to have excellent suction ensures that it picks up very quickly on a prime, and I'd rate the engine overall as being very easy indeed to start once the settings have been established.
In view of the problems with the first engine's contra-piston, I elected not to take any test figures on the initial session because the whole point of having two examples to test was to reduce the possibility that a given engine was either a "good" or "bad" one—there's a lot of value in reproducibility of testing! So I contented myself with giving the engines a little running time to settle themselves down. Even this amount of running was enough to indicate that this was no world-beater in performance terms! Low-speed torque rather than top end power were clearly its strong suit.
Returning another day after sorting the problem of the sticky contra-piston, I was in a position to test both engines. One of the two examples proved to be very slightly faster than the other on a given load, but the difference (only a matter of 100 rpm or so) was well within the expected range of variation between different examples of the same series-produced design with perhaps different amounts of running time. I therefore elected to report the results for the slightly faster example, with the caveat that both examples exhibited pretty much identical performance potential and handling characteristics.
The engines both started equally easily and ran very steadily under all loads. The establishment of optimum settings for both the compression and needle valve proved to be quite easy since both controls were very effective without being unduly sensitive. The engines were relatively impervious to artificially-induced changes in the fuel tank level, indicating that suction was pretty good. Vibration levels were on the high side, as one would expect given the very heavy reciprocating mass involved, but at the speeds of which the engine proved capable this did not become a really major issue.
The slightly better of the two engines managed to drag the 11x7 test prop around at a reasonably respectable rate (for a 3.2 cc engine) of 5,100 rpm and seemed quite happy doing so—running was remarkably steady and smooth. This is right in the middle of Col. Bowden's "good" speed range of 2,000 to 7,000 rpm. I tried an APC 12x6, which was turned at a rock-steady speed of 4,600 rpm. The engine is clearly quite happy at these very low speeds, and being a diesel the ignition timing can of course be set to accommodate such speeds with no excessive loads on the working parts.
Being anxious to test the upper regions of the quoted range, I then proceeded to test a series of progressively lighter airscrews. The results obtained are summarized in the table below, with the BHP figures being those implied from known or derived power coefficients for the airscrews involved.
None of the tested props apart from the 12x6 and the 11x7 bore any resemblance to those recommended in Warring's tables! And even the 10x4 didn't quite allow the engine to reach the 7,000 rpm upper limit noted by the good Colonel. I didn't feel inclined to test the engine past that point in any case given the vibration levels experienced plus the clear indications that power was falling off at that speed anyway. Although running remained absolutely smooth throughout, vibration was now becoming quite noticeable, even in the test stand.
My conclusion was that the engine probably peaks in the region of 5700 rpm or so at perhaps 0.102 BHP and there's little point in pushing it much further. This is undeniably a rather dismal performance for a 3.2 cc engine, even in a 1948 context—a 2 cc K Kestrel tested at more or less the same time handily beat this power figure, albeit at a significantly higher speed! However, it's true that the Reeves delivers its power at a very usable speed for sport free-flight use and the engine's docile handling characteristics and excellent flexibility might well have been viewed as useful assets in that context. The low power would have been far more of a limitation for control-line applications.
As far as I can tell, the limiting factors are probably the rather high vibration levels resulting from the overweight reciprocating components coupled with poor scavenging arising from the somewhat convoluted bypass arrangements and relatively inefficient transfer porting. As noted earlier, the diametrically-drilled holes provide little in the way of direction to the incoming transfer gas flow, and a fair proportion of the fuel mixture supplied seems to leave unburned via the exhaust ports—a well-trained nose can easily detect this while the engine is running.
With these results in hand, the prop recommendation given by Warring for control-line use actually makes a certain amount of sense. An 11x8 prop would likely slow the engine to around 4,700 rpm or so on the ground but would probably approach the peak in the air. Using the time-honoured formula:
Airspeed = RPM x Pitch (inches) 1320
we find that one might expect an airspeed of around 35 mph with the engine running at its peak of 5,700 rpm on an 8 in. pitch prop. For my part, I'd be tempted to try something like a suitably-trimmed 10x10, which might get the airspeed up to somewhere in the neighbourhood of 44 mph. These speed figures may be a little on the low side - the above formula incorporates a 20% allowance for prop slippage, and the large props about which we're speaking here might do a little better than this.
All well and good, but the 13x6 recommended for free flight would unquestionably bring the engine to its knees. Based on my own testing, I'd probably opt for the recommended 11x8 for control line, or perhaps a 10x10 to get higher airspeed at these low revs. An 11x6 or 11x7 would likely be ideal for free flight. The suggested 13x6 would kill the engine for that purpose.
The back tank supplied with the engine is of course quite unsuitable for control line applications and would doubtless be removed in such cases. However, it does appear entirely suitable for free flight use. On the test 10x8 prop using a leaned-out setting, the back tank gives an approximately 2 min 20 sec run including warm-up. This is more than adequate for free flight, the one limitation being that the non-translucent nature of the tank makes it impossible to see the fuel level for the purpose of timing the powered portion of the flight.
So—enter the cut-out!! Question is—does it work? I naturally took a close interest in this question, and the answer is that the cut-out works perfectly when the engine is running in a leaned-out condition—the engine stops in around one second every time. However, if the engine is set rich, activating the cut-out speeds the engine up by leaning the mixture, but doesn't always stop it. This suggests a) that the engine has pretty good suction and b) that that the seal between the plunger tip and the fuel orifice is perhaps less than perfect in the tested examples. I'd guess that this was probably typical.
The problem with a cut-out of this nature is that its effectiveness is entirely dependent upon the closeness of the fit between the tapered end of the plunger and the opening of the fuel spigot. The tests that I undertook show that if that fit is even reasonably close, the cut-out works quite well enough for practical purposes. Furthermore, the fact that the fuel spigot can be unscrewed from the tank for attention means that any irregularities which might prevent a good seal between the plunger and the orifice can easily be corrected.
A Further Variant
Following the initial publication of this article, we were delighted to hear from Graham Podd, who is well known both to collectors and engine builders. Graham advises that he has an example of the Reeves 3.4 cc diesel which is fitted with soldered-on exhaust stacks similar to those seen on many of the contemporary ED 2 cc Mk. II engines. These stacks are clearly original since both they and the rest of the cylinder are cadmium-plated.
Graham tells us that this is the only stack-equipped example of this engine that he has ever seen. It seems likely that this was a special-order modification and that very few engines were produced in this form. Our sincere thanks to Graham for making us aware of this seemingly super-rare variant!
It's clear from the above discussion that we're talking here about an engine that is all about torque rather than horsepower. There's no doubt at all that it's an extremely well-made and dependable power unit which is very easy to handle and should give indefinite service in sports model applications. However, there was no way in which it could compete in either visual or performance terms with the new generation of 3.5 cc diesels such as the Amco 3.5 and the E.D. Mk IV which began appearing in 1949. Viewed in this context, its early departure was inevitable.
Still, an interesting example of the work of the unknown makers of the Reeves model engines. We hope that you've enjoyed our attempt to draw the veil aside a little!
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