I just got in my first shipment of Brodak 40 engines, with more on back order. Since there has been a lot posted already on its performance, I thought I would give a few observations on other details.
The engine on the outside bears a lot of similarity to the Double Starr 40 (made in the same factory), but that is about where the similarity ends. It has the same Fox 35-ish 3-bolt back plate, but this is not a “bored out” Fox 35. The bolt pattern, in fact, is made to fit the OS 35S, 40H, 35/40 FP, 40/46 LA pattern. That means you can mount this engine where you had previously mounted (or intended to mount) an OS engine of similar size...except…it matches the 35S shaft length, but the shaft length is slightly shorter than the FP or LA. Thus, with a slight change in needle location, it is a drop in replacement for the OS 35S and a great choice for a classic size airplane.
The muffler mounting arrangement is similar to a Fox 40, but the bolt spacing is just slightly wider. This is one thing I have never quite understood with manufacturers. If the bolt spacing were made just slightly narrower, which could easily have been done without changing the size of the opening, it would allow the interchanging of other mufflers that were already available. As it is, I have had to put in for some custom-made tongue mufflers just to fit the Brodak 40 engines.
The muffler that comes with the engine is also unique. Whereas the previous Double Starr 40 used a muffler that was “Strangely similar” to “Big Art’s” tube muffler in design, this muffler is very similar in construction to the RC version of the OS. The weight, however, is considerably less. Actual weight of the engine (on my gram scale) is 191 grams or 6.74 ounces. Weight of the muffler with screws is 50 grams or 1.76 ounces, for a total weight of engine plus muffler of 8.5 ounces. And with the tongue mufflers that we will shortly have, it would bring the total weight to just over 7 ounces.
I might add that the “stinger” on the muffler is slightly small by my standards (as was the OS) and the engine would probably benefit with an after market muffler that is slightly less restrictive. Perhaps this is a running change that could be made in later models. Yes, it would “bark” a little louder with a little larger diameter stinger on the muffler. But it would still provide ample muffling and the power to be gained would be worth it.
All in all, however, it looks quite good for a modern Schnurle engine, designed from the ground up as a stunt motor, with proper timing, AAC construction, and the aforementioned light weight.
The venturi that comes with the engine is quite tall—1.325 inches above the mount at the front end, which means it will clear the cowl quite admirably on most cowled installations, making for easy choking. The bore of the venturi is .302, which is pretty much in line with this type of engine and its timing, considering the 1.57 diameter of the Double Starr needle assembly with which it is equipped. This was a flaw of the Double Starr 40 which came with a venturi of the same bore as the Fox 35, but with a spray bar that was 30 thousandths wider.
While mentioning the Double Starr needle assembly, it uses two holes opposite one another similar to the Fox 35 (but with an ST type needle with much finer threads). The holes in the spray bar, as on some of the Fox 35 engines, are just slightly off center, meaning care must be taken if removing the needle to turn it around for a profile installation to make sure that the two holes are pointing slightly down, not slightly up. Although this was probably by design, the venturi cross hole is slightly off center as well, meaning it fits in the case one way, but not the other. It would thus be best not to remove the venturi, or, if one had to, to make sure that it was replaced in its proper orientation.
This goes for the back plate as well. Although the three mounting lugs are evenly spaced around the perimeter, they are cast in a way that it fits properly only with one lug faced down. This is obvious when one examines it carefully, but could be missed by the careless “tinkerer”.
The engine uses a cast case and machined parts everywhere else. Even the piston and rod are machined from bar stock, not cast as on the later OS engines. It uses true AAC construction (aluminum sleeve, chromed, with an aluminum piston) and the sleeve is a reasonable, for its size, .070 thick (compared to .085 for the Nelson made PA .61). The head is hemi shaped with a narrow squish band. Even a glow plug is furnished which is unusual in engines these days.
The porting in the case and the sleeve jump out at you as being different. The “standard” for Schnurle engines these days is to have two by pass ports in the case, one on each side of the exhaust, and one “boost” port opposite the exhaust. On this engine the case has two huge bypass ports that wrap around from each side of the exhaust and almost meet at the back side. There are then two boost ports cut into the sleeve which are fed by the same ports in the case that feed the adjacent by pass.
On the “normal” Schnurle engine the boost port is cut lower in the sleeve and designed to boost the high rpm of the engine. It is common practice of the engine reworkers to grind these ports at an angle so that they meet the height of the side by pass ports. This has already been done on the Brodak 40, but it leaves me to wonder why it wasn’t just cut square to match the side ports. Perhaps the thought was that the fuel would shoot up in a more turbulent fashion, but once this port opens, it opens, and the angle really makes no difference. Of course, if there is no help, there is also no hurt.
Over all, the engine appears to be of very good quality and workmanship, and worth every bit the $99.95 retail price on the engine. Given the early performance reports, it would give much less reason to buy an old 35S of Fox 35 for that classic ship. What you have here is an engine of the same size and weight, but with much improved quality and greater power, while being timed for the classic 4-2 break. Even the instruction sheet that comes with it is quite complete, although the translation from Russian to English wasn’t all that great. I found it amusing that the recommended fuel is at least 22% oil of 50% castor, 50% synthetic and 10% nitro, and then on the spec sheet it gives performance using a fuel of 80% methanol and 20% oil (less than the recommended) with no nitro. This is probably the fuel more readily available at the factory.
Do I have gripes? Oh, we would all always like to change something. I would much prefer having a 4 bolt back plate and see no reason to have copied the Fox 3-bolt as used on the previous Double Starr 40. I would also wish that the muffler bolt spacing had matched the Fox 40 for simplification of after market mufflers, and that the venturi size would match something like the venturi on the FP (here it is slightly larger in diameter with a cross hole that is slightly lower) None of these affect the run or the quality of the engine, however, and once these are made in quantity, I would expect a ready acceptance by the control line crowd.
For those who might be considering the engine, the recommended prop is a 4 or 5 inch pitch of 10 or 11 inch diameter, and it is recommended for planes up to about 44 ounces in weight.
Leonard Neumann
