Overview:

Over the past few months, the team at Pioneer Aero has spent some of their time working on engine bay components. They have continued to use the forward fuselage of RA-24B Banshee 42-54593, a US Army Air Force’s variant of the Dauntless, as scaffolding for trial-fitting various firewall-forward components—as discussed in previous articles. [As some may remember, this Banshee was once used as a wind machine at the MGM film studios in Hollywood, California.] Some of the more recent work has involved refabricating engine linkages, plumbing and cowling-related items. This article will fill in some of the details regarding those efforts.

A view of the A-24's forward fuselage from back in the spring of 2024 during the trial-fitting of Dauntless engine cowlings. Newly-refurbished parts for the SBD's engine bay are now being trial-fitted to this same section of forward fuselage. (image via Pioneer Aero Ltd.)
A view of the A-24's forward fuselage from back in the spring of 2024 during the trial-fitting of Dauntless engine cowlings. Newly-refurbished parts for the SBD's engine bay are now being trial-fitted to this same section of forward fuselage. (image via Pioneer Aero Ltd.)

Control Linkages and Cowl Mounts:

Pioneer’s Les Wilson has worked on a range of engine-related components. Amongst other tasks, he has fabricated new engine control linkages and restored the components which hold the engine cowlings in place. Many of these items are made from steel, thus needing to be sent away for cadmium plating to enhance their corrosion resistance; a few have also required sending off for heat treating to increase their material strength too.

A wide range of steel engine-related components are on view here. The push rods and end fittings are part of the engine control systems. The welded tube with the square cross-section seen in the middle holds the lower gearbox for the oil cooler door control system. The two rectangular and two semicircular brackets to its left are the mounting clamps which attach it to the engine bearer. The brackets at the top middle are part of the control lock system, whilst the two tubular fittings with flanges on their ends are the inlet and outlet for the engine oil system. At the time this image was captured, all of these parts were due to be sent away for cadmium plating. (image via Pioneer Aero Ltd.)
A wide range of steel engine-related components are on view here. The push rods and end fittings are part of the engine control systems. The welded tube with the square cross-section seen in the middle holds the lower gearbox for the oil cooler door control system. The two rectangular and two semicircular brackets to its left are the mounting clamps which attach it to the engine bearer. The brackets at the top middle are part of the control lock system, whilst the two tubular fittings with flanges on their ends are the inlet and outlet for the engine oil system. At the time this image was captured, all of these parts were due to be sent away for cadmium plating. (image via Pioneer Aero Ltd.)

A range of steel components have been restored or refabricated for the Dauntless, with some of them seen here in this image. While the curved sector at the top is actually the locking index from the arrestor hook control located in the pilot's cockpit, the other parts are engine bay-related. The two bell-cranks and five push rods are part of the system which connects the cowl flaps to the hydraulic cowl flap ram which adjust their position. They are located just aft of the diaphragm behind the engine. All of these parts have had to be sent away for heat treatment and cadmium plating—the former for strengthening the metal, and the latter adding corrosion protection. (image via Pioneer Aero Ltd.)

The steel pieces seen here are components for the mounts which hold the main engine cowlings away from the engine. There are nine of them, one for each engine cylinder (to which they attach). At the time this image was captured they were due to be sent away for cadmium plating. (image via Pioneer Aero Ltd.)

There are several engine-related components seen here. The two long push rods and components immediately below them will form part of the engine throttle and mixture controls. The bracket at the top is one of the mounts for the propellor governor control system. At the time this image was captured these parts were due to be sent away for cadmium plating. (image via Pioneer Aero Ltd.)

Plumbing Work:

For a while now, the non-airworthy engine—or mule— has been fitted to the Banshee’s forward fuselage, serving as a scaffold for trial-fitting various firewall-forward components to ensure that they will be ready for attaching to the Dauntless fuselage once it is complete. In addition to the engine, an original oil tank has been trial-fitted to the engine bearer; regular readers will remember the restoration of this fascinating component, as discussed in Update No.5 back in March 2023.

In recent weeks, Pioneer’s Les Wilson has spent time using the mule to trial-fit engine bay-related parts for the oil system, hydraulics, and powerplant controls. Engine oil and hydraulic fluid lines have been partially fabricated and held in place with temporary pieces of tube and rolled cardboard. The ends of these lines will be terminated once all of the various system components have been fitted too. The engine control mounts and related bell-cranks have been temporarily fitted to the firewall and the engine bearer, which then allowed the related push rods to be fabricated.

A lefthand view of the Banshee forward fuselage with the mule engine fitted. Note the large green component at the top of the image in front of the firewall is a fully-restored, original SBD oil tank. Les Wilson has been mocking up the oil system, hydraulic system, and various controls in the engine bay. Fluid lines (oil and hydraulics) have been partially fabricated and held in place with temporary pieces of tube and rolled cardboard. Control mounts and bell-cranks (shown partially completed earlier in this article) have also been temporarily fitted to the firewall and the engine bearer. (image via Pioneer Aero Ltd.)
A lefthand view of the Banshee forward fuselage with the mule engine fitted. Note the large green component at the top of the image in front of the firewall is a fully-restored, original SBD oil tank. Les Wilson has been mocking up the oil system, hydraulic system, and various controls in the engine bay. Fluid lines (oil and hydraulics) have been partially fabricated and held in place with temporary pieces of tube and rolled cardboard. Control mounts and bell-cranks (shown partially completed earlier in this article) have also been temporarily fitted to the firewall and the engine bearer. (image via Pioneer Aero Ltd.)

A closeup of the engine bay from the lefthand side showing the oil tank, the lefthand magneto and lower aft portion of the carburetor (above the magneto) on the mule engine. Here the oil lines which run down the front side of the oil tank have been fabricated. Note: an unserviceable check valve has been temporarily fitted into the tank sump to allow the fabrication of the line which runs from it. (image via Pioneer Aero Ltd.)

Another closeup view of the engine bay from the lefthand side showing the oil tank, the lefthand opening for the air intake (grey oval at image left) and upper aft portion of the carburetor on the mule engine. Here we can see the oil lines which run down the front side of the oil tank have been fabricated and trial-fitted. (image via Pioneer Aero Ltd.)

Another closeup of the engine bay from the lefthand side, this time showing the as-yet unrestored oil cooler, and lower portion of the firewall. The ‘vernatherm’ (oil cooler bypass valve) mounted to the top of the oil cooler is fully-restored, however, as are the oil cooler mounts. Mounted to the firewall above the cooler is the presently-unrestored hydraulic filter. The oil lines seen here running to/from the vernatherm are newly-fabricated, as are the hydraulic lines running to/from the filter. The straight, cadmium plated (silver) torque tube seen crossing over the cooler is the oil intake door control rod which runs between the two gearboxes in the system. (image via Pioneer Aero Ltd.)

A slightly wider angle view of the engine bay systems depicted in the previous image. The engine-driven oil pump is the bluish-gray unit to the upper left of the image. Beside it is a gloss black unit, which is the engine-driven hydraulic pump. The oil drain "Y" valve is seen mounted to the engine bearer towards the lower middle of the image. In the background, strapped between two engine bearer arms, we can see the silver-tinted, square cross-section tube which will mount the lower gearbox for the oil intake door control system. An image of this mount is seen earlier in the article, prior to its cadmium plating. (image via Pioneer Aero Ltd.)

A view of the engine bay showing the lefthand side of the oil cooler and lower portion of the firewall. The engine-driven oil pump is the blue-gray unit to the left of the image. At the upper right corner of this image, we can just see the hydraulic filter mounted to the firewall, above the cooler. The oil drain "Y" valve is attached to the engine bearer at the lower right corner of the image. We can also see the newly-fabricated oil lines which run to/from the vernatherm and the newly-fabricated lines which run to/from the hydraulic filter. (image via Pioneer Aero Ltd.)

The righthand face of the oil tank (in green) is seen here, along with the righthand air intake opening (the grey oval just above the carburetor at the upper right quadrant of this image). Note the two newly-fabricated, aluminum oil lines running down the front side of the oil tank. (image via Pioneer Aero Ltd.)
The righthand face of the oil tank (in green) is seen here, along with the righthand air intake opening (the grey oval just above the carburetor at the upper right quadrant of this image). Note the two newly-fabricated, aluminum oil lines running down the front side of the oil tank. (image via Pioneer Aero Ltd.)

A closeup view of the lefthand side of the engine bay showing the carburetor (gloss black) at the middle top of the image. We can see the bell-cranks and mount for the throttle and mixture controls and, behind the bearer arm, the pushrods which attach to the carburetor. (image via Pioneer Aero Ltd.)

A view in the engine bay looking towards the rear of the engine accessory housing from the lefthand side. Here the bell-cranks and mount for the throttle and mixture controls are visible at image center. The pushrods linking the carburetor to the opposite side of the bellcrank can also be seen. The two pushrods coming towards the camera run through the firewall. (image via Pioneer Aero Ltd.)

A view of the engine bay from the righthand side showing the oil cooler, and lower portion of the firewall. Along the righthand edge of the image, we can see the engine-driven oil pump (blue-gray) and the engine-driven hydraulic pump (gloss black). We also have a clearer perspective of the hydraulic filter (the small, medium grey cylinder mounted to the firewall above the oil cooler). Note that the black-hued line running between this filter and the hydraulic pump on the back of the engine accessory casing is not a rigid aluminum tube, but rather a flexible hose—while this is a temporary fitting, it’s replacement will be of the same ‘rubberized’ material. The large, light-grey pressure vessel at image left is a hydraulic accumulator for the propeller pitch control mechanism. Although non-airworthy, it has been temporarily fitted to permit fabrication of the connecting fluid lines for that part of the system. The image also provides a different view of the newly-fabricated oil lines which run to/from the vernatherm as well. (image via Pioneer Aero Ltd.)

The righthand face of the oil tank (in green) is seen here, along with the righthand air intake opening (the grey oval just above the carburetor at the upper right quadrant of this image). Note the two newly-fabricated, aluminum oil lines running down the front side of the oil tank. (image via Pioneer Aero Ltd.)

A righthand closeup of the engine accessory section (at image right) and the oil tank (upper left). The engine-driven oil pump is the blue-gray unit in the background at image center middle of the photo. Closer to the camera, the gloss black, engine-driven hydraulic pump (note the two openings with orange plastic caps sealing their entry/exit ports). Above that pump is the righthand magneto (non-airworthy) and above that is the ignition harness. (image via Pioneer Aero Ltd.)

A similar shot to the previous image, albeit from a lower perspective with a clearer view of the newly-fabricated engine oil lines running to/from the vernatherm and the the oil pump. Hydraulic fluid lines running to from the pump have also been cut to size and shaped, but were still awaiting the addition of their connectors at the pump end. (image via Pioneer Aero Ltd.)

More recently, Wilson added in the vacuum and instrument indicating systems to the engine bay, continuing with the plan of partially fabricating the lines and holding them in place with temporary pieces of tube and rolled cardboard. This will allow the lines to be adjusted (as more and more components are positioned) to ensure proper clearances are maintained. While this may feel like an odd way of doing things, it has become a necessity since the available manufacturing drawings provide only vague references regarding the precise routing of fluid lines and cabling—often without referencing the other systems which need to fit within the same general area. Bizarrely, this technique is essential for fitting out many other WWII aircraft types as well, demonstrating yet another significant challenge in their restoration.

The engine accessory section, as viewed from righthand side showing several newly-fabricated lines for the vacuum system. Straddling the two engine bearers in the foreground, we can see a non-flightworthy air/oil separator, temporarily installed to allow the fabrication of new tubing for the vacuum-driven instruments in the cockpit. The tube exiting the top side of the separator is for the “air overboard” line, while the lower tube is the oil return line to the engine. As for the line entering the side of the device, this comes from the vacuum pump, whilst the line coming from near the top of the firewall—and traveling past the oil tank—is heading to the pump. (image via Pioneer Aero Ltd.)
The engine accessory section, as viewed from righthand side showing several newly-fabricated lines for the vacuum system. Straddling the two engine bearers in the foreground, we can see a non-flightworthy air/oil separator, temporarily installed to allow the fabrication of new tubing for the vacuum-driven instruments in the cockpit. The tube exiting the top side of the separator is for the “air overboard” line, while the lower tube is the oil return line to the engine. As for the line entering the side of the device, this comes from the vacuum pump, whilst the line coming from near the top of the firewall—and traveling past the oil tank—is heading to the pump. (image via Pioneer Aero Ltd.)

A closeup of the air/oil separator for the vacuum system. The line exiting the bottom of the separator, heading right, is the oil return to the engine. The vacuum pump itself is visible in the lower right quadrant of the image with the two lines running vertically to/from it, one going to the separator and the other coming from the instruments. (image via Pioneer Aero Ltd.)

Another view of the air/oil separator attached to the engine bearers, this time with a different perspective on where the various, newly-manufactured vacuum lines flow to or from the device. (image via Pioneer Aero Ltd.)

Another view of the air/oil separator attached to the engine bearers, this time from a higher perspective showing where the various, newly-manufactured vacuum lines flow to or from the device. The line from the side of the separator is from the vacuum pump, whilst that flowing from the top of the firewall is heading towards the pump. In the middle of the firewall, just above the oil tank, we can see a group of small lines which clearly penetrate the bulkhead. These lines transfer engine oil, manifold, and fuel pressure levels from the engine to the associated cockpit instruments. (image via Pioneer Aero Ltd.)

A closeup view of the engine accessory section from the righthand side. It is starting to get congested here as various systems are mocked up. The device with pealing black paint in the middle is one of the two magnetos, with the other just being visible behind it. We can see the gloss black vacuum pump below them in the foreground (with the two vertical lines feeding too/from its side). As described in previous images, the blue-grey painted device is the oil pump, while the gloss black device at the bottom is the hydraulic pump (with the two orange blanks holding the lines). To the far right, with orange tape wrapped around one of its junctions, we see the fuel pump. (image via Pioneer Aero Ltd.)
A closeup view of the engine accessory section from the righthand side. It is starting to get congested here as various systems are mocked up. The device with pealing black paint in the middle is one of the two magnetos, with the other just being visible behind it. We can see the gloss black vacuum pump below them in the foreground (with the two vertical lines feeding too/from its side). As described in previous images, the blue-grey painted device is the oil pump, while the gloss black device at the bottom is the hydraulic pump (with the two orange blanks holding the lines). To the far right, with orange tape wrapped around one of its junctions, we see the fuel pump. (image via Pioneer Aero Ltd.)

The is a view of the fuel filter attached to its mounting bracket on the firewall. While overhauled, and technically airworthy, it just needs to be painted before final assembly. The thin, bare aluminum tube we see running to the right is one of the hydraulic lines which goes to the cowl flap actuator. (image via Pioneer Aero Ltd.)

A closeup of the lower, lefthand side of the firewall. Looking down past the engine bearer we can see the fuel filter, one of its ports capped in orange tape. The two thin bare aluminum tubes are the hydraulic lines which go to the cowl flap actuator; one line runs up each side of the engine to each end of the actuator. (image via Pioneer Aero Ltd.)

A closeup view of the lower, righthand side of the firewall. The thin, bare aluminum tube emerging from the block mounted to the firewall near the upper middle of the image is one of the hydraulic lines for the cowl flap actuator. The thicker, Z-shaped bare aluminum tube and the black, flexible hose running just above it both run to/from the hydraulic pump. The bare aluminum tube running vertically and flush with the firewall is the air overboard line for the vacuum system. (image via Pioneer Aero Ltd.)

A closeup of the engine accessory section looking towards the diaphragm from the lefthand side. The thin, bare aluminum tube running parallel to the lower engine bearer is one of the hydraulic lines for the cowl flap actuator. We can just see the end of this line poking out from behind the upper engine bearer. A bulkhead fitting will be used here to attach another section of the line which will continue up to the actuator. (image via Pioneer Aero Ltd.)

Cowl Flaps:

Aircraft with air-cooled piston engines usually feature adjustable cowl flaps right behind the powerplant to help regulate airflow over the engine's cooling fins, and thus the engine's operating temperature. Cowl flaps resemble the gills on a fish, which is why they are sometimes referred to as cooling gills. The Dauntless features three cowl flaps on either side of the engine (as depicted in the wartime image below), and the team at Pioneer Aero has been working on both the hydraulic system which actuates the flaps, and the structure for attaching them to the airframe, the latter being referred to as Support Ring or Cowling Hoop. This hoop also attaches to the engine cylinders and helps support the forward engine cowling panels.

A wartime image of an SBD-3 Dauntless taking off from a US Navy aircraft carrier. Note that the aircraft's cowl flaps are in the "open" position to provide extra cooling for the engine in the hot conditions which carrier pilots often found themselves in when serving in the Pacific Theatre during WWII. Note that the -5 and -6 variants of the Dauntless replaced the 3-section cowl flap units with a single gill (as the following image will reveal).
A wartime image of an SBD-3 Dauntless taking off from a US Navy aircraft carrier. Note that the aircraft's cowl flaps are in the "open" position to provide extra cooling for the engine in the hot conditions which carrier pilots often found themselves in when serving in the Pacific Theatre during WWII. Note that the -5 and -6 variants of the Dauntless replaced the 3-section cowl flap units with a single gill (as the following image will reveal).
A U.S. Navy Douglas SBD-5 Dauntless belonging to VB-16 aboard USS Lexington (CV 16) seen here passing Dublon and Eten Island en route to strike Japanese installations at Truk circa mid-February 1944. Note that the Dauntless has its cowl flaps open. Earlier variants of the SBD had three cowl flaps either side, whereas the -5 and -6 Dauntlesses replaced these with a single flap unit. This difference is subtle clue for determining what variant is depicted in a given image. Another clue is that the later variants also moved the carburetor air intakes between the engine cylinders inside the cowling, whereas the -3 and -4 featured theirs in the upper lip of the nose cowling. (US Navy image)
A U.S. Navy Douglas SBD-5 Dauntless belonging to VB-16 aboard USS Lexington (CV 16) seen here passing Dublon and Eten Island en route to strike Japanese installations at Truk circa mid-February 1944. Note that the Dauntless has its cowl flaps open. Earlier variants of the SBD had three cowl flaps either side, whereas the -5 and -6 Dauntlesses replaced these with a single flap unit. This difference is subtle clue for determining what variant is depicted in a given image. Another clue is that the later variants also moved the carburetor air intakes between the engine cylinders inside the cowling, whereas the -3 and -4 featured theirs in the upper lip of the nose cowling. (US Navy image)

A depiction of the cowl flap support ring arrangement for the SBD-5 and -6. Earlier variants had a significantly different setup featuring 3 flaps each side. Pioneer Aero has begun remanufacturing the support ring for the Museum's Dauntless. Image from page 497 of the SBD/A-24 Illustrated Parts Manual.

As a way of contrasting the difference between the cowl flap arrangement which the SBD-5 and -6 Dauntless airframes fielded, this drawing shows the earlier version which featured 3 cowl flap gills each side of the fuselage. By necessity, the support ring was quite different too. This image is from page 447 of the Dauntless Illustrated Parts Manual.

Cowling Hoop Replacement Begins:

In one of the very early updates it was mentioned that the cowl hoop required major repair work to be become airworthy. Since that time it was decided that a replacement cowl hoop as the best option. Now we have received the replacement sections. For ease of manufacture that have been fabricated in four sections rather than the original two sections. This month Les Wilson has begun the joining them together, and drilling all the mounting holes in them. Firstly a template was created using the original hoop and known dimensions. From there the individual sections were placed on the template and the required hole and end positions marked out. With the four sections mounted on the template the joiner, hinge and other bracket mounting holes could be marked and drilled.

A view of the sections which will form the replacement engine cowl hoop laid atop one another in the approximate position which the four sections will sit relative to each other after being trimmed to the correct size. The parts were fabricated with extra material at each end to allow the exact join position to be finalized during assembly. (image via Pioneer Aero Ltd.)

The replacement engine cowl hoop during fabrication; its four sections have been trimmed to the correct length, with the joiner holes having been drilled in them too. They are seen here attached to the template board. Note the sections of the original hoop are also on the template, being used as a reference for marking out the next set of mounting holes. The original was a two-piece assembly, but one of them is broken which was a significant factor in the decision to replace them. (image via Pioneer Aero Ltd.)
The replacement engine cowl hoop during fabrication; its four sections have been trimmed to the correct length, with the joiner holes having been drilled in them too. They are seen here attached to the template board. Note the sections of the original hoop are also on the template, being used as a reference for marking out the next set of mounting holes. The original was a two-piece assembly, but one of them is broken which was a significant factor in the decision to replace them. (image via Pioneer Aero Ltd.)
Les Wilson is seen here using the original cowl hoop as reference for marking out the next set of mounting holes. In this particular instance, he is working on a set of holes for a bracket which mounts one of the cowl flap hinges to the hoop. (image via Pioneer Aero Ltd.)
Les Wilson is seen here using the original cowl hoop as reference for marking out the next set of mounting holes. In this particular instance, he is working on a set of holes for a bracket which mounts one of the cowl flap hinges to the hoop. (image via Pioneer Aero Ltd.)