I decided to write a post about the first decade of the R-1820 “Cyclone” development (up to the R-1820-60 version, i.e. 1940). This engine was used in many designs from 1930s, and you can find the references to its various models in many technical specifications. However, sometimes it is difficult to determine how such a referenced version looked like! The early models of the “Cyclone” were produced in small batches, so there is less historical photos. Sometimes even the specialists from the museums are misguided: in one of them, you can find a SBD-3 fitted with the engine and the propeller from the SBD-5. My query, which resulted in this article, started with comparison of the R-1820-60 (used in the SBD-5) and the R-1820-52 (used in the SBD-3 and -4). I have found so many differences, that I started to wonder about the engine used in the pre-war SBD-1 and SBD-2. (They used the earlier “Cyclone” version: R-1820-32). The results presented below may be interesting to the modelers who recreate aircraft from this period (for example – the Curtiss “Hawk”, or the Grumman F3F-2 “Flying Barrel”).
Let’s start from the beginning: below you can see the first model of the R-1820 family, designed in 1931 (Figure 90‑1):
Frankly speaking, there is only a general resemblance to the later “Cyclone” versions. Note the small crankcase front section and the “archaic” cylinder heads. (They have different shape, and their fins are much shorter and widely spaced: these are indicators of a simpler casting technology). Another strange feature is the exhaust, which could be also mounted in the reversed (i.e. forward) direction. (Some of the aircraft from this era used front exhaust collectors). This engine used large spark plugs, mounted horizontally (in parallel to the centerline). It was rated at 575hp on takeoff, and used in some contemporary designs, like the Curtiss “Hawk” biplane.
Before introducing the next “Cyclone” version, let’s try to decode its symbol. It seems that there are two parallel conventions: one used by the engine vendor (Wright Aeronautical), and another used by the US Air Corps and the Navy.
Wright designated this engine as R-1820E. The “R” stands for “radial”, “1820” is the displacement (in cubic inch), and the “E” denotes the model. There were also other, 7-cylinder “Cyclones” produced by Wright during 1920s, as well as smaller 9-cylinder “Cyclone” (R-1750) produced before 1931. About 100 of these “Cyclones” were sold for the Navy flying boats. Technically, this “E” model, featuring 1820 in3, was an advancement.
For the US military purposes, there was a similar convention, in which this engine was referred as the R-1820-1. The “R” stands for “radial”, “1820” is the displacement (in cubic inch), and the “-1” is the sequential version number. (I suppose, that this “sequential” suffix applies to the purchasing chronology, not to the engine development).
Wright offered simultaneously two variants of the same engine: direct drive and geared. (“Direct drive” means that there was no reduction gear). The “geared” models had the “G” prefix: for example GR-1820E. According the “military” convention, each of these “parallel” versions could have a different sequential number (depending on the date of the first purchase?).
The next development stage was the R-1820F. It featured larger cylinder heads (because of the deeper and closer cooling fins), simple supercharger, forged (and then machined) main crankcase, and many other important improvements. It was difficult to find a decent photos of this model. Finally I identified one (military designation: R-1820-19) in National Museum of the USAF. It was mounted in the only preserved Martin B-10 (Figure 90‑2):
This particular airplane was built in 1938 for Argentina, as the export model Martin 139W. (In 1970 this only survived B-10 in the world was given to the US as a donation from the Government of Argentina. It was later restored by the National Museum of the United States Air Force). It seems that Martin used in this aircraft the R-1820-19 engines (rated at 665hp). It was the same “Cyclone” model as in the original US Army versions (YB-10 and B-10, delivered in 1934).
Looking for the decent photos of the “F” model, I finally found a few pictures of the Soviet M-25 engine. (In 1933 the Soviet Union bought a license for one of the R-1820F variants. First Soviet “Cyclones” were built in 1934 from kits delivered by Wright Aeronautical. After conversion to the metric system, from 1935 they were produced in thousands by a dedicated factory in Perm). Below you can see photos of this engine (Figure 90‑3):
Wright licensed to the USSR the direct drive version named R-1820F3.
The last digit in this symbol (“3”) could indicate the blower (i.e. supercharger) gear ratio. Wright offered several variants of this engine, optimized for various flight altitudes. Each of these variants had different supercharger gear ratio. The suffix “2” means ratio of 7:1, “3” – 8.31:1, “4” – 10:1, “6” – 8.83:1. Similar engine was used in the DC-1, but its symbol had an additional “SG” prefix: SGR-1820F3. This “S” probably stands for an external supercharger, and “G” for the reduction gear.
The direct drive versions of the “Cyclone” had much shorter crankcase front section than the geared models (compare Figure 90‑3 and Figure 90‑2). Their oil sump also lacked the “L”-shaped forward pipe. (I suppose that it was not needed in the much shorter crankcase, without the reduction gear inside). The deflectors, attached to the cylinder heads on the photo above, have circular shape. (They differ from the rectangular deflectors mounted in R-1820-19. I will come back to this issue in a moment, discussing the “G” model). It seems that they removed corresponding side deflectors from this museum exhibit. On the crankcase front section there is a small base for the governor of a variable-pitch propeller. The rocker covers differ from the “E” model, and Wright engineers added small attachment points at their ends. (These points were useful for mounting the large NACA cowlings). Note that most of the cooling fins concentrate around the exhaust valve. There are only few of them around the intake valve.
The “F” model of the “Cyclone” was a commercial success, powering many aircraft in the first half of the 1930s (for example – the Douglas DC-2 airliner). The later versions of this engine had two-digit numerical suffixes, like “F52” or “F62”. (It seems that these middle “5” or “6” indicate an improved version). They were rated at about 745 – 785hp. The GR-1820-F52 reached 890hp for takeoff, but it was the upper limit of this design. (The F52 model had the lowest blower ratio: 7:1, and it was rated at 725hp at sea level and 775hp at 5800 ft.
The next “Cyclone” model was the R-1820G. It had larger cylinder heads than the “F” version (as explained in this article, to get higher power from a cylinder, you need the larger area of its cooling fins). I have found some detailed pictures of an early, direct-drive “G” versions in the F3F-2s restored at Chino Planes of Fame. Comparing to the original photos, it seems that this is not the R-1820G5 (R-1820-22), but another “Cyclone” version. However, it seems to be nearly identical with the original engine (Figure 90‑4):
It is not clearly visible on these photos, but the intake duct in the heads is set at about 45⁰ to the centerline, as in the blueprints of my R-1820-60 version. (In the “E” and “F” models it was parallel to the centerline, as the exhaust duct). The intake valve is finally covered by short fins. The spark plugs are thinner, and placed in a less asymmetric way than in the “F” model (in fact, this head looks similar to the version that I recreated in the previous post). The top rocker covers received the new shape and four bolts around their rims. On the left photo you can see the attachment points on the rocker covers, introduced in the “F” version (they are more visible here than on the previous picture). The higher pressure produced in the combustion chambers of this engine increased the number of attaching bolts to 16 per cylinder (there were 12 in the “E” and “F” versions). On the left photo you can see the details of the “rectangular” deflectors. Note their elastic tips – I think that this brown material is the rubber (or leather?). The original R-1820-22 (GR-1820G5) engine, used in the F3F-2, was rated at 950hp for takeoff. (The same engine was used in the F2A-1 Buffalo, and the export version of this fighter, Brewster 239, delivered to Finland).
Figure 90‑5 shows the later, geared version of the “Cyclone” (it was rated at 930hp at 2200 rpm for takeoff):
Note that its front crankcase section is larger than in the geared “F” model (Figure 90‑2). Wright referred to these more powerful series as “Cyclone” GR-1820-G100. I studied many historical pictures of these “G” engines. It seems that in certain versions Wright placed the ignition harness in the front of the valve pushrods, while in the other versions – behind these pushrods. The semi-circular deflectors occur together with the latter variant of the ignition harness. In such a configuration every second cable goes between the cylinders to the rear spark plugs.
The “rectangular” deflectors usually occurs in the engines withe ignition harness placed in the front of the pushrods. (Figure 90‑6):
In such a configuration the cables go to the rear spark plug around the cylinder head (and across its deflector – as you can see in Figure 90‑6). The picture above shows the later “Cyclone” G100 model, most probably one of the R-1820-5x series (I am not able to precisely determine this version). It is nearly identical with the R-1820-52 (used in the SBD-3 and -4). This photo also show us detailed fragment of the angular main crankcase section. (It was built from two symmetric, forged and machined aluminum parts). Similar crankcases appear in the “F” family. In this later model the base for the propeller governor was even more elevated than in the R-1820-45 (compare this photo with the previous illustration). I do not think that the engine from Figure 90‑6 uses a different version of the deflectors. I rather suppose that this particular museum exhibit uses their standard “rectangular” model with the flexible tips removed.
I have just a few pictures of the engines used in the earlier Dauntless versions (SBD-1 .. -4). Below you can see two of them (unfortunately, both are in low resolution):
The engine depicted in Figure 90‑7a) belongs to a restored SBD-1 (BuNo 1612). (When you can see the original wreck, you can be at least sure that this is the original piece). The engine in Figure 90‑7b) was attached to the SBD-4, restored in Chino. It seems that there are no external differences between these two engines (at least as viewed from the front). The “-32” is missing the ignition harness, but you can see in the attached miniature that the restored version of this harness is identical to the “-52” on the right. Both engines have the standard, “rectangular” deflectors with flexible tips. Note how Douglass engineers make use of these auxiliary attachment points on the valve covers (Figure 90‑7b). The cowling flaps bow was supported by the rear row of these points, while the supports of the NACA cowling use the forward attachments.
Why the R-1820-45 differs a little from the R-1820-52 (see Figure 90‑5), while the R-1820-32 seems to be identical? There are two possibilities: 1. the military symbols do not correspond to the development chronology; 2. Wright run in parallel several development lines of this engine;
Both engines – R-1820-32 and R-1820-52 – were rated at 1000hp for takeoff. I have no information if there were any differences in their blower or gear ratio. The most powerful “Cyclones” G were rated at 1200hp for takeoff (the geared R-1820G5E).
The next “Cyclone” generation was a result of significant reengineering. Wright referred them as the GR-1820-G200 series (or, skipping the “G” suffix, as the R-1820-G200, because there were no direct drive versions in this family). It seems that the first of these models had military symbol R-1820-56. One of them is the R-1820-60 (the version that I already have recreated) and the R-1820-66 (version used in the SBD-6, presented in Figure 90‑8):
Frankly speaking, Wright has redesigned most of this engine, so it is easier to point out the elements that did not change between the G100 and G200 series: spark plugs and propeller governor (these two items were delivered by the third party vendors). While preserving the overall dimensions and mounting points, all of their external details are different. In the G200 the enlarged front section of the crankcase housed even bigger reduction gear and more efficient auxiliary shafts for the propeller governor. The pushrods became slightly shorter, thanks to the enlarged diameter of the front crankshaft. The cylinder heads grew bigger, because of the longer fins. (It was another increase of the cooling area – thus the shape of these heads is slightly different than in the G100 series). The deflectors are all-metal, without the flexible tips, and have different mounts among the cylinders. The cylinders are prepared for the high-octane fuel which means higher pressures, thus their bases feature 20 bolts (instead of 16 bolts in the G100 series). What is not visible on this photo, the main crankshaft section (under the cylinders) is a steel cast of gently curved shape.
In this engine you can see different auxiliary attachment points: double bolts on each intake rocker cover (the exhaust rocker covers have none). (This “bolted” mount already appeared in the late G100s models, but not in the engines used in the SBD-1 ..-4).
The R-1820-60 was rated at 1200hp for takeoff. It was also used in the B-17C, D, E, and F. The R-1820-66 was rated ever higher: at 1350hp for takeoff. (Similar R-1820 version was used in the B-17G).
Finally, to increase the overall confusion (hopefully of the Axis spies 🙂 ), at the beginning of 1940s Wright Aeronautical altered its naming convention. Since this time:
- The R-1820G and GR-1820G series are referred as “Cyclone” 9GA (shortcut: C9GA);
- The R-1820-G100 series are referred as “Cyclone” 9GB (shortcut: C9GB);
- The R-1820-G200 series are referred as “Cyclone” 9GC (shortcut: C9GC);
Thus you can find in various source documents and the books three different symbols for the same engine. For example – the full title of my Wright service manual from 1943 is: “Overhaul Manual/Wright Aircraft Engines Cyclone 9 GC”. This means that it applies to the R-1820-G200 series. In particular, this group includes the models named in the U.S. Army and Navy documents as the R-1820-60 and the R-1820-66.
Well, all in all this means that I have to recreate another engine: R-1820-52 (late G100 series) for my earlier Dauntless models: SBD-1, SBD-2, SBD-3 and SBD-4. There are too many differences to adapt the R-1820-60 model that I have already created. I describe shortly this “subproject” in the two next posts.
- “Parts Catalog for Wright Cyclone Aircraft Engines Series GR-1820G-200”. Wright Aeronautical Corporation, 1940;
- “Wright Cyclone 9 Aircraft Engine, series C9-GC: Installation, Operation, and Service Maintenance”. Wright Aeronautical Corporation, 1942;
- “Overhaul Manual Wright Aircraft Engines Cyclone 9 GC”, Third Edition. Wright Aeronautical Corporation, 1943;
- “Operation and Service Manual: Wright Cyclone 9 Aircraft Engines Series C9GA, C9GB, C9GC”, First Edition. Wright Aeronautical Corporation, 1943;
- Francis H. Dean “America’s Hundred Thousand: The US Production Fighter Aircraft of World War II”, Schiffer Publishing, 1997 (ISBN: 0-7643-0072-5);
- Francis H. Dean, Dan Hagedron “Curtiss Fighter Aircraft – a Photographic History 1917-1948”, Schiffer Publishing, 2007 (ISBN: 978-0-7643-2580-9);
- Wawrzyniec Markowski “Boeing B-17 Flying Fortress”, parts 1 and 2, AJ-Press 2004, (ISBNs: 83-7237-143-1 and 83-7237-152-0);
- Barret Tillman “The Dauntless Dive Bomber of World War Two”, Naval Institute Press, 2006 (ISBN: 1-59114-867-7);
- Bert Kinzey “SBD Dauntless”, Detail & Scale, 2016 (ISBN: 978-0-9860677-5-4)
- Robert Pęczkowski “Douglas SBD Dauntless”, Stratus, 2007, (ISBN: 978-8389450-39-5);
- Kimble D. McCutcheon “Wright R-1820 ‘Cyclone’”. Aircraft Engine Historical Society, www.enginehistory.org, 1999, revised: 2014;
- Поршневой авиационный двигатель М-25 (Wright «Cyclone» R-1820 F3) (in Russian). Accessed 2018-07-10;
- The Wright R-1820 “Cyclone” Engine. Acessed 2018-07-02;
- Martin B-10. Accessed 2018-07-12;
Photo collections of:
- National Museum of the USAF, Riverside;
- Muzey V. P. Chkalova (Музей В.П.Чкалова), Chkalovsk;
- Planes of Fame, Chino;
- National Naval Aviation Museum, Pensacola;
- Yanks Air Museum, Chino;
- Jimmy Doolittle Air & Space Museum, Travis AFB;
- “Life” magazine