Least resource intensive/easy to maintain aircraft of WW2?

nDaca

Recruit
4
3
Sep 19, 2022
I can't see any other threads about this, and thought it might be an interesting subject
Whilst characteristics like combat capability, engines and armament are more often talked about, I feel like the quality-of-life factors of an aircraft are often underrated.
Which WW2 aircraft gained a reputation from their crews and mechanics for being easy to work on and maintain, and requiring few resources to field/being logistically uncomplicated?
This is regardless of nationality, though I suppose later on in the war, the Axis nations would start to appreciate their more economical aircraft more, wouldn't they?
This is talking about how easy they are to repair, and how much resources they use up, not how durable their airframes are during combat, though I suppose that could factor into it.
Examples would be appreciated for each of the following roles:

Observational
Multi-role
Fighter
Light Bomber
Medium Bomber
Heavy Bomber
 

jimh

Senior Airman
375
326
Feb 6, 2009
Ohio
community.webshots.com
Interesting question. We operated the P-51, B-25, B-24, and B-17 on tour 300 days a year, 38 states, and 110 cities on average. Although we weren't arming them and flying at altitude, we put a lot of cycles on the gear and engines. Even 80 years on, they performed remarkably well. The Wings of Freedom tour existed for 30 years, during that time we had a handle on what parts were prone to failure or were limited life span. We also had the knowledge gleaned from the 4-5 years of WWII combat service. If it helps, I've broken down the maintenance issues for each. We didn't meet too many WWII mechanics on the tour, mostly gunners and essential flight crew members. BUT, the mechanics we did meet could immediately relate to our issues, particularly the B-24 and it's electric prop governors. Combat damaged sheet metal damage seemed miniscule when compared to running the engines hard.

P-51 Tour Average 500 hours per year. Spark Plugs and tires were the major maintenance items. The radiator is considered a consumable and would last around 2 seasons. The heaviest maintenance were the 25, 50 and 100 hour inspections. Other than wing jacks, all the tools necessary to perform these tasks fit in to a couple average sized tool bags and took less than a day to perform. We never did an hour of maintenance to an hour of flight comparison because it rarely broke...it just ran solid.

B-24 Tour Average 250-300 hours per year. The B-24 is maintenance intensive in certain areas and not so much in others. Chasing pushrod tube leaks is never ending although manageable. The hydraulic system rarely needed maintenance, considering it is an open center 1000psi system, gear, flaps, bombay doors, and brakes, it was incredibly reliable. The prop governors are the Achilles Heel of the B-24, they are electric and extremely fragile. The were prone to failure at anytime. We averaged 10 governors per year and always had them in an overhaul rotation. The only specialty tools are used in changing an engine or a cylinder. The inspections required large wing jacks and we averaged 2-3 days to do the main airframe inspections. Each engine is on a progressive inspection program per the WWII manuals and Pratt & Whitney so that saved time on the airframe inspections. The wheels and brakes were changed about every 100 hours depending on who was flying it and required at a minimum a bottle jack shored up with heavy lumber under the gear leg. The tools required to keep it running fit in to two large tool bags, but most of our mechanics broke their bags down in to specialty bags for the prop governors, cylinders, etc.. Engine or prop issues required a fork lift and took around 3-4 days to complete. QEC's keep the down time to a minimum.

B-17 Tour Average 500 hours per year. The B-17 was old reliable. Everything was cable, from the prop governors to the flight controls. The hydraulic system for the brakes and cowl flaps rarely leaked. The electric motors for the gear, even 80 years old were solid. The gear was limited to 2 cycles per hour due to heating the retract jack screw. This had to diligently enforced. Not letting the jack screw cool down would cause it to 'skip' in the threads and lead to stripping. Again, following the military inspection program, everything could be carried in 1-2 average sized tool bags and 2-3 days depending on weather conditions. The 1820 is also prone to pushrod tube leaks, but that goes for any radial. The wheels and brakes are identical to the B-24, so the same tools and procedures for changing were identical. There is a large socket and breaker bar for removing the main wheel nut, but they are universal for both the 24 and 17.

B-25 Tour Average Hours 250. The B-25 is incredibly simple and easy to maintain. Chasing pushrod tube leaks and servicing the nose wheel shimmy dampener were the only real squawks. An average tool bag was carried and the majority of tasks could be performed easily. Wing jacks for gear swings and a forklift for engine or prop issues is standard. It's a North American product, and it just runs reliably as long as it's kept up on.


Radial engines are prone to a couple operational issues that give mechanics nightmares. Reverse loading the engine is the biggest issue, when the prop is turning the crankshaft rather than vice-versa. The 1830 book indicates that 2 incidences of Reverse loading is a mandatory engine change. The 1830 and 2600 aren't as bad, but it does the engine bearings and nose case gears no favors. I can imagine in WWII this was closely monitored due to the stresses they were imposing. Now days it's just expensive. The other issue is shock cooling the cylinders. When letting down from altitude you really have to keep your eyes on the Cylinder Head Temps and vary the cowl flaps for each engine. The cylinders take very little nudging to split...it's like throwing hot water on a frozen windshield. Changing a cylinder could take anywhere from 1-3 days depending if it was a cylinder next to the oil sump. But again, an average tool bag will do the job.

Overall the US equipment was unbelievably simple to work on, there is still a fair amount of cussing, but very few issues that weren't thoroughly thought out by the manufacturers.

Hope this helps

Jim
 

BiffF15

Tech Sergeant
1,770
2,810
Aug 15, 2010
Florida
Interesting question. We operated the P-51, B-25, B-24, and B-17 on tour 300 days a year, 38 states, and 110 cities on average. Although we weren't arming them and flying at altitude, we put a lot of cycles on the gear and engines. Even 80 years on, they performed remarkably well. The Wings of Freedom tour existed for 30 years, during that time we had a handle on what parts were prone to failure or were limited life span. We also had the knowledge gleaned from the 4-5 years of WWII combat service. If it helps, I've broken down the maintenance issues for each. We didn't meet too many WWII mechanics on the tour, mostly gunners and essential flight crew members. BUT, the mechanics we did meet could immediately relate to our issues, particularly the B-24 and it's electric prop governors. Combat damaged sheet metal damage seemed miniscule when compared to running the engines hard.

P-51 Tour Average 500 hours per year. Spark Plugs and tires were the major maintenance items. The radiator is considered a consumable and would last around 2 seasons. The heaviest maintenance were the 25, 50 and 100 hour inspections. Other than wing jacks, all the tools necessary to perform these tasks fit in to a couple average sized tool bags and took less than a day to perform. We never did an hour of maintenance to an hour of flight comparison because it rarely broke...it just ran solid.

B-24 Tour Average 250-300 hours per year. The B-24 is maintenance intensive in certain areas and not so much in others. Chasing pushrod tube leaks is never ending although manageable. The hydraulic system rarely needed maintenance, considering it is an open center 1000psi system, gear, flaps, bombay doors, and brakes, it was incredibly reliable. The prop governors are the Achilles Heel of the B-24, they are electric and extremely fragile. The were prone to failure at anytime. We averaged 10 governors per year and always had them in an overhaul rotation. The only specialty tools are used in changing an engine or a cylinder. The inspections required large wing jacks and we averaged 2-3 days to do the main airframe inspections. Each engine is on a progressive inspection program per the WWII manuals and Pratt & Whitney so that saved time on the airframe inspections. The wheels and brakes were changed about every 100 hours depending on who was flying it and required at a minimum a bottle jack shored up with heavy lumber under the gear leg. The tools required to keep it running fit in to two large tool bags, but most of our mechanics broke their bags down in to specialty bags for the prop governors, cylinders, etc.. Engine or prop issues required a fork lift and took around 3-4 days to complete. QEC's keep the down time to a minimum.

B-17 Tour Average 500 hours per year. The B-17 was old reliable. Everything was cable, from the prop governors to the flight controls. The hydraulic system for the brakes and cowl flaps rarely leaked. The electric motors for the gear, even 80 years old were solid. The gear was limited to 2 cycles per hour due to heating the retract jack screw. This had to diligently enforced. Not letting the jack screw cool down would cause it to 'skip' in the threads and lead to stripping. Again, following the military inspection program, everything could be carried in 1-2 average sized tool bags and 2-3 days depending on weather conditions. The 1820 is also prone to pushrod tube leaks, but that goes for any radial. The wheels and brakes are identical to the B-24, so the same tools and procedures for changing were identical. There is a large socket and breaker bar for removing the main wheel nut, but they are universal for both the 24 and 17.

B-25 Tour Average Hours 250. The B-25 is incredibly simple and easy to maintain. Chasing pushrod tube leaks and servicing the nose wheel shimmy dampener were the only real squawks. An average tool bag was carried and the majority of tasks could be performed easily. Wing jacks for gear swings and a forklift for engine or prop issues is standard. It's a North American product, and it just runs reliably as long as it's kept up on.


Radial engines are prone to a couple operational issues that give mechanics nightmares. Reverse loading the engine is the biggest issue, when the prop is turning the crankshaft rather than vice-versa. The 1830 book indicates that 2 incidences of Reverse loading is a mandatory engine change. The 1830 and 2600 aren't as bad, but it does the engine bearings and nose case gears no favors. I can imagine in WWII this was closely monitored due to the stresses they were imposing. Now days it's just expensive. The other issue is shock cooling the cylinders. When letting down from altitude you really have to keep your eyes on the Cylinder Head Temps and vary the cowl flaps for each engine. The cylinders take very little nudging to split...it's like throwing hot water on a frozen windshield. Changing a cylinder could take anywhere from 1-3 days depending if it was a cylinder next to the oil sump. But again, an average tool bag will do the job.

Overall the US equipment was unbelievably simple to work on, there is still a fair amount of cussing, but very few issues that weren't thoroughly thought out by the manufacturers.

Hope this helps

Jim
Jim,

What is a “open hydraulic system“ as mentioned in your B24 synopsis? I plumbed the DC8 many moons ago and it’s hydraulic system had minimal separation between “heavy use items” and would isolate during malfunctions. Does the B24 operate in a similar fashion?

Cheers,
Biff
 

nDaca

Recruit
4
3
Sep 19, 2022
Interesting question. We operated the P-51, B-25, B-24, and B-17 on tour 300 days a year, 38 states, and 110 cities on average. Although we weren't arming them and flying at altitude, we put a lot of cycles on the gear and engines. Even 80 years on, they performed remarkably well. The Wings of Freedom tour existed for 30 years, during that time we had a handle on what parts were prone to failure or were limited life span. We also had the knowledge gleaned from the 4-5 years of WWII combat service. If it helps, I've broken down the maintenance issues for each. We didn't meet too many WWII mechanics on the tour, mostly gunners and essential flight crew members. BUT, the mechanics we did meet could immediately relate to our issues, particularly the B-24 and it's electric prop governors. Combat damaged sheet metal damage seemed miniscule when compared to running the engines hard.

P-51 Tour Average 500 hours per year. Spark Plugs and tires were the major maintenance items. The radiator is considered a consumable and would last around 2 seasons. The heaviest maintenance were the 25, 50 and 100 hour inspections. Other than wing jacks, all the tools necessary to perform these tasks fit in to a couple average sized tool bags and took less than a day to perform. We never did an hour of maintenance to an hour of flight comparison because it rarely broke...it just ran solid.

B-24 Tour Average 250-300 hours per year. The B-24 is maintenance intensive in certain areas and not so much in others. Chasing pushrod tube leaks is never ending although manageable. The hydraulic system rarely needed maintenance, considering it is an open center 1000psi system, gear, flaps, bombay doors, and brakes, it was incredibly reliable. The prop governors are the Achilles Heel of the B-24, they are electric and extremely fragile. The were prone to failure at anytime. We averaged 10 governors per year and always had them in an overhaul rotation. The only specialty tools are used in changing an engine or a cylinder. The inspections required large wing jacks and we averaged 2-3 days to do the main airframe inspections. Each engine is on a progressive inspection program per the WWII manuals and Pratt & Whitney so that saved time on the airframe inspections. The wheels and brakes were changed about every 100 hours depending on who was flying it and required at a minimum a bottle jack shored up with heavy lumber under the gear leg. The tools required to keep it running fit in to two large tool bags, but most of our mechanics broke their bags down in to specialty bags for the prop governors, cylinders, etc.. Engine or prop issues required a fork lift and took around 3-4 days to complete. QEC's keep the down time to a minimum.

B-17 Tour Average 500 hours per year. The B-17 was old reliable. Everything was cable, from the prop governors to the flight controls. The hydraulic system for the brakes and cowl flaps rarely leaked. The electric motors for the gear, even 80 years old were solid. The gear was limited to 2 cycles per hour due to heating the retract jack screw. This had to diligently enforced. Not letting the jack screw cool down would cause it to 'skip' in the threads and lead to stripping. Again, following the military inspection program, everything could be carried in 1-2 average sized tool bags and 2-3 days depending on weather conditions. The 1820 is also prone to pushrod tube leaks, but that goes for any radial. The wheels and brakes are identical to the B-24, so the same tools and procedures for changing were identical. There is a large socket and breaker bar for removing the main wheel nut, but they are universal for both the 24 and 17.

B-25 Tour Average Hours 250. The B-25 is incredibly simple and easy to maintain. Chasing pushrod tube leaks and servicing the nose wheel shimmy dampener were the only real squawks. An average tool bag was carried and the majority of tasks could be performed easily. Wing jacks for gear swings and a forklift for engine or prop issues is standard. It's a North American product, and it just runs reliably as long as it's kept up on.


Radial engines are prone to a couple operational issues that give mechanics nightmares. Reverse loading the engine is the biggest issue, when the prop is turning the crankshaft rather than vice-versa. The 1830 book indicates that 2 incidences of Reverse loading is a mandatory engine change. The 1830 and 2600 aren't as bad, but it does the engine bearings and nose case gears no favors. I can imagine in WWII this was closely monitored due to the stresses they were imposing. Now days it's just expensive. The other issue is shock cooling the cylinders. When letting down from altitude you really have to keep your eyes on the Cylinder Head Temps and vary the cowl flaps for each engine. The cylinders take very little nudging to split...it's like throwing hot water on a frozen windshield. Changing a cylinder could take anywhere from 1-3 days depending if it was a cylinder next to the oil sump. But again, an average tool bag will do the job.

Overall the US equipment was unbelievably simple to work on, there is still a fair amount of cussing, but very few issues that weren't thoroughly thought out by the manufacturers.

Hope this helps

Jim
Thanks Jim, that was very informative.

Considering you've worked on these planes before, was there any additional information you could give about the electrical systems in particular, the turrets in the B-25 and B-17? I've heard neat things about them, and I've always found it rather interesting, the B-17 ball turrets in particular.

Regards,
Dustin
 

jimh

Senior Airman
375
326
Feb 6, 2009
Ohio
community.webshots.com
Jim,

What is a “open hydraulic system“ as mentioned in your B24 synopsis? I plumbed the DC8 many moons ago and it’s hydraulic system had minimal separation between “heavy use items” and would isolate during malfunctions. Does the B24 operate in a similar fashion?

Cheers,
Biff

Hey Biff, sure. The open system means fluid is running through the system at 1000psi until a component is selected. When you drop the gear, fluid is directed toward that system and so on. You don’t want to run more than one system at a time. Each selector for the flaps, gear, and Bombay doors has a neutral position. The gear handle automatically pops in to neutral once the up and down cycle is complete. When you drop or raise the flaps you watch the gauge to the desired setting then select the neutral detent. The Bombay door handle operates the same way, but in combat that’s the only hydraulic system that you would need. It sure makes the brakes touchy since there is no debooster in the system.

Jim
 

jimh

Senior Airman
375
326
Feb 6, 2009
Ohio
community.webshots.com
Thanks Jim, that was very informative.

Considering you've worked on these planes before, was there any additional information you could give about the electrical systems in particular, the turrets in the B-25 and B-17? I've heard neat things about them, and I've always found it rather interesting, the B-17 ball turrets in particular.

Regards,
Dustin
Hey Dustin,
We managed to get the B-24 tail turret fully operational and the B-17 ball turret working. They are both a combination of hydraulic and electric motion. They are completely isolated from the overall aircraft flight control systems, but share the same electrical power source. They are both controlled by pistol grip handles that function like a rheostat. The farther you move the handles, the faster the turrets move. And they zipped around at full deflection!

Jim
 

nuuumannn

Major
9,749
8,320
Oct 12, 2011
Nelson
the B-17 ball turrets in particular.

I'll let Jim chime in with the details, but a little of what I have learned. The Briggs-Sperry ball turrets were based on the electro-hydraulic workings supplied by British power turret manufacturer Boulton Paul. The turret and its workings were entirely self-contained, in the Boulton Paul turrets they did not have to rely on the aircraft's hydraulic system for actuation. Two hydraulic pumps were driven by a constant-speed electric motor, the pumps supplying fluid to actuate the turret in rotation and elevation, controlled by hand grips, with the amount of pressure applied determining the speed of movement. firing the guns was done by pedals at the gunner's feet. The turret also relied on the solenoid system that shut power off to the guns when bits of the aircraft got in the gunner's line of sight, which was designed by Boulton Paul. Unfortunately, the hydraulic system had a tendency to leak into the turret, which wasn't a good thing for the poor guy inside.

The Sperry Model A-1 turret fitted to B-17Es and 'Fs also worked by the same methods as the ball turret, being an electro-hydraulic unit based on the Boulton Paul electro-hydraulic system. Sperry had studied the BP Type T turret sent to the USA for study and externally they both look remarkably similar, betraying the US turret's origins.
 

nDaca

Recruit
4
3
Sep 19, 2022
Hey Dustin,
We managed to get the B-24 tail turret fully operational and the B-17 ball turret working. They are both a combination of hydraulic and electric motion. They are completely isolated from the overall aircraft flight control systems, but share the same electrical power source. They are both controlled by pistol grip handles that function like a rheostat. The farther you move the handles, the faster the turrets move. And they zipped around at full deflection!

Jim
Thanks for that, I've always sort of wondered about them, but finding resources is tricky.

Dustin
 

nuuumannn

Major
9,749
8,320
Oct 12, 2011
Nelson
The open system means fluid is running through the system at 1000psi until a component is selected. When you drop the gear, fluid is directed toward that system and so on. You don’t want to run more than one system at a time.

This is a common system for modern large aircraft, to have more than one system, but within an open circuit. Modern aircraft hydraulic systems have an auxiliary motor that provides added pressure to the system when high demand is expected of the system. In the aircraft I worked on this was called the Power Transfer Unit and we used to rely on the PTU when we had the aircraft on jacks in the hangar and were working with an external hydraulic rig when doing gear retracts. The PTU was used when flaps were lowered and raised in the hangar as well, it just helps the system a little when the engines are not on, and the system's relying on the standby pumps (SPU) and not being driven by the EDPs. The SPUs don't work at full hydraulic pressure of 3,000 psi so the PTU comes in handy when doing maintenance stuff.
 

jimh

Senior Airman
375
326
Feb 6, 2009
Ohio
community.webshots.com
I'll let Jim chime in with the details, but a little of what I have learned. The Briggs-Sperry ball turrets were based on the electro-hydraulic workings supplied by British power turret manufacturer Boulton Paul. The turret and its workings were entirely self-contained, in the Boulton Paul turrets they did not have to rely on the aircraft's hydraulic system for actuation. Two hydraulic pumps were driven by a constant-speed electric motor, the pumps supplying fluid to actuate the turret in rotation and elevation, controlled by hand grips, with the amount of pressure applied determining the speed of movement. firing the guns was done by pedals at the gunner's feet. The turret also relied on the solenoid system that shut power off to the guns when bits of the aircraft got in the gunner's line of sight, which was designed by Boulton Paul. Unfortunately, the hydraulic system had a tendency to leak into the turret, which wasn't a good thing for the poor guy inside.

The Sperry Model A-1 turret fitted to B-17Es and 'Fs also worked by the same methods as the ball turret, being an electro-hydraulic unit based on the Boulton Paul electro-hydraulic system. Sperry had studied the BP Type T turret sent to the USA for study and externally they both look remarkably similar, betraying the US turret's origins.
You nailed it!
 

SplitRz

Airman 1st Class
124
187
Feb 6, 2021
I would imagine that looking to nations which were comparatively low-tech in terms of access to exotic materials and skilled labour might feed some interesting examples into this thread. I'd also imagine that aircraft selected for use in adverse conditions - be they desert or extreme cold / salt water might be inherently engineered to be more rugged and reliable if complex maintenance (and or skills) were going to be an inherent challenge?

I know the Fairey Swordfish was famed for the simplicity and reliability of its systems and the rugged and dependable nature of its Bristol Pegasus engine (which out of interest, also served aircraft requiring a reliable engine which wasn't going to receive much servicing in a purpose build hangar when it was stationed on a 'Woolworth' carrier. I'd imagine it would be a pretty good example.

What about some of the Russian front line aircraft?
 

Dimlee

Staff Sergeant
1,448
3,391
Feb 18, 2018
I would imagine that looking to nations which were comparatively low-tech in terms of access to exotic materials and skilled labour might feed some interesting examples into this thread. I'd also imagine that aircraft selected for use in adverse conditions - be they desert or extreme cold / salt water might be inherently engineered to be more rugged and reliable if complex maintenance (and or skills) were going to be an inherent challenge?

I know the Fairey Swordfish was famed for the simplicity and reliability of its systems and the rugged and dependable nature of its Bristol Pegasus engine (which out of interest, also served aircraft requiring a reliable engine which wasn't going to receive much servicing in a purpose build hangar when it was stationed on a 'Woolworth' carrier. I'd imagine it would be a pretty good example.

What about some of the Russian front line aircraft?
USSR...
I don't remember hours (or man-hours) numbers, but lend-leased equipment was usually more "user-friendly" for ground crews. Il-4 was considered much more difficult to serve than A-20 and B-25. PBY Catalina was probably the most reliable and the easiest to maintain among all Soviet flying boats. Earlier Yak models were easier than LaGGs and MiGs in 1941-1942. Il-10 became a nightmare for ground crews who worked with Il-2 before.
 

GregP

Captain
8,535
4,813
Jul 28, 2003
Chino, California, U.S.A.
At Yanks Air Museum, we are currently restoring a couple of Erco 250 teardrop turrets, right and left. We are just assembling the first one and will restore the second one now that we are familiar with it. Then we will come back and restore the first one.

To date, my partner and I have made up three ribs and stringers and replaced the skin opposite the entry door where it was dropped from the PB4Y2 when it was converted to a fire bomber, have just managed to get the seat in it, and will now begin working on getting the armor and spent shell canisters installed.

The Hydraulics is an open system, and it looks like we will have to "invent" the cables as we go along. Most of the documentation (not much, to tell the truth) isn't very helpful. But, at SOME point, we hope to reinstall them into our PB4Y2 Privateer.

Anyone around Southern California (Chino Airport), come by and see us on Tuesdays and Thursdays, ask for Greg or Phil.

Cheers! :)
 

Admiral Beez

1st Lieutenant
6,350
6,298
Oct 21, 2019
Toronto, Canada
I would think anything running an interwar-designed, mass-produced air cooled inline engine in a low stress application would be very low maintenance. A trainer thus equipped, like the de Havilland Tiger Moth must run for hundreds of hours before a wrench is needed for anything beyond spark plugs.

As for high performance engines, skip sleeve valves and anything Bristol made (too many grease nipples). I’d want a single Packard Merlin.
 

FLYBOYJ

"THE GREAT GAZOO"
Staff
Mod
28,097
8,668
Apr 9, 2005
Colorado, USA
I would think anything running an interwar-designed, mass-produced air cooled inline engine in a low stress application would be very low maintenance. A trainer thus equipped, like the de Havilland Tiger Moth must run for hundreds of hours before a wrench is needed for anything beyond spark plugs.

Absolutely not!

Although a simple aircraft, pulleys, cables and bellcranks need to be lubricated, the airframe itself needs to be periodically inspected, especially if one is performing aerobatics. Read about the maintenance of fabric aircraft and what goes into them, lastly we have some wood in the structure, very labor intensive depending on the environment where the aircraft is being operated. Are you getting the picture? I haven't even gotten into the engine! Engine oil - 25 to 50 hour changes. Inspections - 50 to 100 hour. I believe a few of our members have actually turned wrenches on the Moth so I know they'll chime in.

No - even the simplest of aircraft cannot go for "hundreds of hours" without some kind of maintenance!
 

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