Reliability of WW2 fighters.

[renrich]

I would bet that of all US fighters in WW2 the Hellcat would have the best servicability record. It had a reliable engine and most Grumman products were known in those days to be designed for ruggedness and reliability. The R2800 did have many problems during it's development. In the book, "Whistling Death" by Boone Guyton which was the story of the design and development of the Corsair there were many mentions of engine and to a lesser extent prop problems. In fact, the lengthy development time the Corsair required was to some extent caused by the fact that the Corsair was designed for and was one of the first AC to use the R2800 and a new Hamilton Standard prop.

 

[davparlr]

Not to be picky but FOD means foriegn object debris as opposed to damage

FOD has become its own word meaning both foriegn object damage and foriegn object debris. I was in the aerospace industry for about 35 years both in the Air Force and in industry and I don't every remember the term foriegn object debris used in any of the endless lectures on the subject (FOD was always defined as foreign object damage and the debris was always just called FOD).

 

[Crumpp]

I would bet that of all US fighters in WW2 the Hellcat would have the best servicability record.

I would bet it is not much different than any other airplane of similar type.

All the best,

Crumpp

 

[Crumpp]

You can see by examing this document that the R-2800 offered no advantage in number of maintenance hours over any other aircraft engine.

http://afhra.maxwell.af.mil/aafsd/aafsd_pdf/t114and115.pdf

 

[renrich]

During the 1944 Pax river fighter conference when voting on the engine that inspired the most confidence, 79% of the pilots voted for the R2800.

 

[AL Schlageter]

You can see by examing this document that the R-2800 offered no advantage in number of maintenance hours over any other aircraft engine.

http://afhra.maxwell.af.mil/aafsd/aafsd_pdf/t114and115.pdf

That is for average man-hours per major overhaul at depots.

 

[renrich]

From what I understand the original engines in the F14, the P&W engine, was not designed or suited for a lot of abrupt throttle changes and inputs. In other words, the usage occurring in an ACM context. When the GE engines were substituted, most of the engine problems ceased. The F14 technology as far as electrical circuits was concerned was 1960s and 70s vintage and the AC began to have a lot of problems with the miles and miles of electrical wiring which made the AC a maintenance hog. I forget the exact number but it was a lot of hours maintenance for one hour flight time. In addition many of the AC were beginning to be risks because of metal fatigue. I believe many F14s were severely G limited near the end. I had an F14D driver tell me one time that the Tomcats that were taken to Top Gun school almost invariably came back "bent out of shape" and would never fly right again. Sounds nutty but maybe plausible. Having said that I still believe a newly manufactured strike Tomcat would have been a better purchase than the F18E-F.

 

[Crumpp]

That is for average man-hours per major overhaul at depots.

Yes it is and do you understand what that means?

I don't think you do if your intent is to call into question the fact it is a representation of maintenance hours.

 

[Crumpp]

During the 1944 Pax river fighter conference when voting on the engine that inspired the most confidence, 79% of the pilots voted for the R2800.

Yeah, there is nothing like the feeling of that big radial thumping up in front of you to inspire confidence.

There is also the mistaken belief that aircooled engines are more reliable than water cooled. Air cooled engines are simpler and require less parts.

All in all, they are about the same due to the fact all airplanes engines are designed with the physics of flight in mind.

All the Best,

Crumpp

 

[Crumpp]

You might get a kick out of this one and some insight into aircraft engines:


View: https://www.youtube.com/watch?v=EkcX0KGIBwk

 

[AL Schlageter]

Yes it is and do you understand what that means?

I don't think you do if your intent is to call into question the fact it is a representation of maintenance hours.

Do you?

 

[renrich]

I think the notion that air cooled engines are more reliable than liquid cooled is based somewhat that they are more resistant to battle damage. That is the reason the US Navy ruled out liquid engines prior to WW2.

 

[davparlr]

You can see by examing this document that the R-2800 offered no advantage in number of maintenance hours over any other aircraft engine.

http://afhra.maxwell.af.mil/aafsd/aafsd_pdf/t114and115.pdf

I am not sure this tells us anything about the availability of aircraft at the squadron level but only tells us how long it takes to overhall the engine at depot. I am not too knowledgeable but I suspect that depot overhall manhours starts with the engine out of the aircraft and probably does not include the cooling system on the liquid cooled engines. As such, the hours are similar for work accomplished, 11.8 hr./cylinder for the V-1710 to 13.4 hr/cyl for the R-2800 (average, 1945).

The real importance to warplane availability is things like mean time between failure (MTBF), mean time between scheduled maintenance (MTBSM) (like engine overhall), mean time between unscheduled maintenance (MTBUM), mean time to repair (MTTR), etc. These are what planners must use to determine how many of 100 aircraft assigned will be available for combat at any given time. Improvements in these numbers at the weapon system (aircraft) level are force multipliers.

Since we don't have these numbers for the engine systems, predicting weapons system reliability is difficult. However, as a rule of thumb, these numbers are proportional to complexity. As such, when you calculate in the liquid cooling system reliability, it seems the air cooled engine should have fewer failures, thus more reliability. Also, it must be noted that the 18 cylinder R-2800 engine in itself is pretty complex (note that the overhall number for the R-2800 is higher than the smaller cylindered stablemates).

 

[Crumpp]

but only tells us how long it takes to overhall the engine

That is a very good indicator of maintenance guys. Why do you think Bill, another aircraft owner, thought it was such a good find?

Here is why it is a very good indicator of maintenance requirements:

There are several levels of "major overhaul".

Service limit - Parts are checked to ensure they fall within service limits.
This overhaul has little chance of reaching TBO as the standard is the minimum service limits. If a part is allowed a service limit of .010 and it is at .009 when checked the part continues life. It does not need to be replaced in a service limit overhaul. These are the least expensive overhaul because generally, there is less disassembly involved. Parts are replaced as needed.

New Limit Overhaul - Parts are checked to ensure they fall within new part tolerances. Engine time is zeroed and reset. This is the overhaul the US Military most commonly does as it has it's own mechanics to perform the work. The engine logbook continues life. Parts are replaced as needed

Re-manufactured limits - Performed at the factory by the factory being the major difference between a "New Limit" major overhaul and "re-manufactured Limits". Engine time is zeroed and reset. Factory issues new warranty and new logbooks. Parts are replaced as needed.

The common theme with all of the overhauls is, "Parts are replaced as needed.".

Therefore we can examine the document and see that in 1943, the R-2800 required considerably more time to overhaul than it did in 1945. Why? The engine became more reliable. The parts were made stronger or the points of stress reduced and the overhauls did not need as many parts replaced.

Partial disassembly and checking tolerances is one thing. Complete disassembly and reinstallation of a new part is quite another.

You can now see that the R-2800 developed into a reliable aircraft engine and that all aircraft engines are very similar in their maintenance.

All the best,

Crumpp

 

[Crumpp]

Understand too that crank tolerences on most aircooled engines can be checked by removing the barrels while leaving the corncob on the mounts.

Liquid cooled inlines require removal of the engine and disassembly of the case to check the crank. So pick your poison, both engines take about the same amount of time to overhaul. Do you want more barrels to overhaul or do you want to remove the engine?

All the best,

Crumpp

 

[drgondog]

That is a very good indicator of maintenance guys. Why do you think Bill, another aircraft owner, thought it was such a good find?

Here is why it is a very good indicator of maintenance requirements:

There are several levels of "major overhaul".

Service limit - Parts are checked to ensure they fall within service limits.
This overhaul has little chance of reaching TBO as the standard is the minimum service limits. If a part is allowed a service limit of .010 and it is at .009 when checked the part continues life. It does not need to be replaced in a service limit overhaul. These are the least expensive overhaul because generally, there is less disassembly involved. Parts are replaced as needed.

New Limit Overhaul - Parts are checked to ensure they falls within new part tolerances. Engine time is zeroed and reset. This is the overhaul the US Military most commonly does as it has it's own mechanics to perform the work. The engine logbook continues life. Parts are replaced as needed

Re-manufactured limits - Performed at the factory by the factory being the major difference between a "New Limit" major overhaul and "re-manufactured Limits". Engine time is zeroed and reset. Factory issues new warranty and new logbooks. Parts are replaced as needed.

The common theme with all of the overhauls is, "Parts are replaced as needed.".

Therefore we can examine the document and see that in 1943, the R-2800 required considerably more time to overhaul than it did in 1945. Why? The engine became more reliable. The parts were made stronger or the points of stress reduced and the overhauls did not need as many parts replaced.

Partial disassembly and checking tolerances is one thing. Complete disassembly and reinstallation of a new part is quite another.

You can now see that the R-2800 developed into a reliable aircraft engine and that all aircraft engines are very similar in their maintenance.

All the best,

Crumpp

Gene - slightly off on a tangent but still in the strike zone. While I no longer fly or own my own ship 'the dreaded engine overhaul' to New Limit OR Re-manufactured Limit was by far the worst sound - then and now.

I have a close friend with both a Gulfstream IV and Challenger at Hayward who is having turbine blade replacements for a cool Million and a Half on the Challenger - approximately 20% of the total value of the entire ship.

Has anyone priced out a Re-manufacured Limit $$ for either the R2800 or 1650-7 lately?

This is why Mustangs get sold.. The previous owner got one 25 years ago, flew it very little but one day the dreaded day comes.

Of course the stuff that Crump and his guys do on rebuilding an Fw 190 ranging from inspection of spars (and repair/re-manufacture) of 60 year old combat airframes (and engine parts) is unbelieveably expensive and doesn't even fit in the discussion.

 

[Crumpp]

This is why Mustangs get sold..

You are so right, Bill. The cost of airplanes is staggering.

> The following is a shameless plea for donations!

We live off donations and are non-profit. One of the reasons I am out posting on these types of boards is to help keep up the interest in WWII aircraft and get the word out on the WWII Aircraft Foundation.

Buy some Christmas gifts from our shop, make a donation, or become a member. We need your support and only through that support can these airplanes continue to grace blue skies.

All of you are more than welcome to visit the Museum and the Restoration Shop.

WWII Fighter Aircraft Foundation

All the best,

Crumpp

 

[Crumpp]

Hi davparlr,

There is no mystery to solve. Failure predictions give us the maintenance time schedule. This schedule is posted in the appropriate pubs on the type. Keep in mind too, that as an aircraft, our margins are much smaller than we would find on any other form of transportation.

The real importance to warplane availability is things like mean time between failure (MTBF),

Time Between Overhauls is a function of time between failures. Most aircraft engines have a TBO of around 2000hrs. For example, both the R-2800 and the BMW801D2 both had 2000hrs TBO's.

mean time between scheduled maintenance (MTBSM) (like engine overhall),

All engines have a recommended regular maintained schedule. This schedule is dictated by probable failures of subcomponents. These schedules are very similar in scope and frequency by the fact physics limits our design choices.

The schedule is posted in the engines manuals.

mean time between unscheduled maintenance (MTBUM),

Impossible to quantify and has little bearing IMHO. Everyone works to reduce this portion. Given a reasonable passage of time, both operators and design teams will reduce this to the point that once again, all aircraft engines are similar.

All the best,

Crumpp

 

[davparlr]

Hi davparlr,

There is no mystery to solve. Failure predictions give us the maintenance time schedule. This schedule is posted in the appropriate pubs on the type. Keep in mind too, that as an aircraft, our margins are much smaller than we would find on any other form of transportation.

I still do not think that rebuild time tells us anything about reliability of the engine. In a way it corresponds in that a more complex engine typically takes more time to rebuild and a also has a lower MTBF. However, an engine may be very difficult to rebuild but be built to such standards as to be very reliable. In fact, in designing equipment and installation on modern aircraft, this is a criteria. If the part is difficult to repair or is hard to get to, reliability must be built into the component. Still rebuild time is high but reliability is up.

Impossible to quantify and has little bearing IMHO.

Actually, operationally this is of major concern since all aircraft related aborts are due to unscheduled maintenance (if it could have been scheduled, it would have been). As you mentioned, operationally, this can indeed be quanitified over time and incorporated in aircraft availability planning and corrective action implemented.

On newly developed engines, it is a large impact, but, as time goes by, fixing these are part of the maturing process and equipment get more reliable. For comparing reliability of engines, only mature designs should considered and MTBUM should indeed have little bearing.

 

[Crumpp]

On newly developed engines, it is a large impact, but, as time goes by, fixing these are part of the maturing process and equipment get more reliable. For comparing reliability of engines, only mature designs should considered and MTBUM should indeed have little bearing.

Over a fixed and finite time period such as determining the reliability of WWII aircraft engines it is impossible to only consider mature designs.

Hence my statement that MTBUM has little bearing in the context of comparing WWII engines.

In a way it corresponds in that a more complex engine typically takes more time to rebuild and a also has a lower MTBF. However, an engine may be very difficult to rebuild but be built to such standards as to be very reliable.

An engine with a 1500hour TBO has a shorter MTBF than an engine with a 2000hour TBO.

A 2000hour TBO is a 2000hour TBO whether it is on a 4 cylinder engine or a 28 cylinder radial. FYI a Lycoming IO-360 4 Cylinder air-cooled engine, PW R-2800 series, and the BMW801 series all have a TBO of 2000hours. The MTBF of these engines is comparable and the TBO is a function of that MTBF.

Certainly the more complex engines designer worked to increase the MTBF and that workload was higher than the team that worked on a simpler engine.

The complexity of the engine is irrelevant if both engines last 2000hours and we are looking to compare reliability.

If we want to compare reliability as a function of complexity then your point is valid. The R-2800 required much more development time than the Lycoming IO-360.

If the engine we are comparing are reliable and shows little or consistent wear, then the Overhaul Man-Hours will remain consistent as well.

If the engine is not reliable, then we will see a large reduction in overhaul man-hours as that reliability is increased by the designers as well as end user's input.

All the best,

Crumpp