WW2-piston engine life
bob u
Especially fighter aircraft. assuming no bullet holes through the block,
how many hours were an engine good for before major work?
When an engine did need major work, was it done in the field or were
engines swapped out with fresh ones from a repair depot?
bob
Eunometic
There would be a number of ways to look at that"
MTBO Mean Time Between Overhaul
MTBMO Mean Time Between Major Overhaul
Engine cumulative life.
The DB605, used on the Me 109G/K is often noted as having 220 hours
life, with an overhaul occuring at around 100.
Merlin in fighter use I think 300 hours.
In civil life such engines often reached 1200 hours.
Many engines started out with lives as short as 25 hours (eg BWM801 or
PW R-2800) and grow to hundreds of hours, in the case of the PW R-2800
thousand or so.
The life is dependent on how hard the engine is worked and how WEP
(War Emergency Power) or (Noteleistung in German) is used. For
instance heavy use of over boosting with 'rich mixtures' of fuel that
dissolve of lubricants shorten life on top of the extra thermal and
mechanical stresses. The use of water injection (Sonder
Noteleistung , i.e. special emergency power in german) also reduces
life as the harsh cooling effect can crack alloy components and cause
corrosion. One German Fw 190D-9 (92 victory expert Oskar Romm I
think) pilot landed having forgotten to turn of his emergency power
setting: the result was that the exhaust stubs were red hot and
drooping.
Emergency power might be defined for only one to three mintues. In
many of the German engines the WEP was quite long 10-20 minutues
followed by a rest period of about 10-20 minutes.
An engine that has exceded its life could still be refurbished. Given
the short life of the total airframe it may not be worth building the
engine life to last too long, such methods often require speical
metals eg chromium plating.
Keith Willshaw
"bob u" <so...@inetnebr.com> wrote in message
news:icmk08$clj$1...@speranza.aioe.org...
ISTR that a RR Merlin would be pulled for a full inspection and
overhaul after 500 hours or so. The Allison V-1710-39 was
good for up to 1500 hours. The Wright R-3350 started out
at around 250 hours but they got it up to 700 hours
by the end of the war.
Keith
Eunometic
The early missions had the upper 5 rear cylinders replaced at 25 hours
due to inadaquet fuel distribution, cooling and exhaust manifolding
that created hot spots.
>
> Keith
As for the 220 hours TBMO of the DB605. At the end of these 220 hours
period, the powerplants were returned to the manufacturer, checked and
worn parts replaced. After five such inspections, the cylinders would
be re-bored. Some engines would make this trip 7-8 times.
It worth doing some stats... ie. take an 1-hour fighter sortie, and a
low 1% loss rate per sortie to see how much concern TBO is in real
life.
The Luftwaffe seemed to have a preference for dropping the entire
engine of the airframe to do maintainance. It was possible to swap
out an entire engine in under 30 minutes.
I haven't seen a primary source on Merlin TBOs (Packard ones from 1944
which show 110-180 hours), but secondary sources (real mechanics) give
240 hours between overhauls specified by RR.
Now let see if we can understand this "according to Rolls-Royce with
the Merlin, if 30% of engines were reaching overhaul life and, no
single cause made-up more than 30% of rejections, then it was time for
an increase of maximum engine life ( that is with 30% failures). "
In other words, the 240 hours TBO for the Merlin specified in some
cases and versions by RR in practice implicity means that 70% of the
engines will actually NOT reach this specified TBO time.
Keith Willshaw
"Eunometic" <euno...@yahoo.com.au> wrote in message
news:e76b9bae-42b1-40f2...@12g2000prq.googlegroups.com...
On Nov 26, 9:35 am, "Keith Willshaw" <keithnos...@demon.co.uk> wrote:
> "bob u" <so...@inetnebr.com> wrote in message
> Now let see if we can understand this "according to Rolls-Royce with
> the Merlin, if 30% of engines were reaching overhaul life and, no
> single cause made-up more than 30% of rejections, then it was time for
> an increase of maximum engine life ( that is with 30% failures). "
> In other words, the 240 hours TBO for the Merlin specified in some
> cases and versions by RR in practice implicity means that 70% of the
> engines will actually NOT reach this specified TBO time.
The actual life of an engine depended crtically on its operating
history. On a Spitfire during heavy fighting the pilot would
likely be operating at high levels of boost which shortens the
engine life. In extremis a pilot could select emergency boost
(War Emergency Power in US parlance). This would be obvious
to the mechanics as a thin wire was broken when this was done
and that usually required the engine being torn down for inspection
and proabable rebuild. More wear could occur in 5 minutes of
WEP that 200 hours of normal use.
On the other hand the Merlin on a Lancaster or York might
spend its entire life trundling along at most efficient cruising
power and be in good condition after 500 hours. The
improvements in fuel and lubricant formulations as the
war progressed also extended engine life. Anti wear additives
such as molybdenum disulphide were first used in
aircraft engines during WW2
Keith
manitobian
> ISTR that a RR Merlin would be pulled for a full inspection and
> overhaul after 500 hours or so. The Allison V-1710-39 was
> good for up to 1500 hours. The Wright R-3350 started out
> at around 250 hours but they got it up to 700 hours
> by the end of the war.
>
> Keith
Would there have been a "top overhaul"
as in some civilian aircraft?
Testing my memory again, but
I seem to remember photos of the engine in
The Grace Spitfire showing the pistons and rods
still attached to the crank but the cylinder block(s)
removed.
Found it! I hope it shows up!
Keith Willshaw
"manitobian" <rsve...@mts.net> wrote in message
news:f19426ab-e886-486a...@w2g2000yqb.googlegroups.com...
> http://www.ml407.co.uk/pages/gallery_engineering.html
Well its 40 years since as a young apprentice I worked with
the old boy who told me this stuff but I seem to recall his saying
that it depended on how worn the engine was when they pulled
it. Now he was serving as an engine fitter with a bomber squadron
where the wear pattern may have been very different from that
found in fighter aircraft.
I do recall his saying that one of the major problems with the
Merlin was that the starter didnt always disengage after the
engine started and could burst with the centrifugal forces
damaging wiring and fuel pipes !
Keith
Jim Wilkins
> ...>
> I do recall his saying that one of the major problems with the
> Merlin was that the starter didnt always disengage after the
> engine started and could burst with the centrifugal forces
> damaging wiring and fuel pipes !
>
> Keith
What does the shop manual say about it?
http://www.haynes.co.uk/webapp/wcs/stores/servlet/BookFeature_RAFHandbookView?new=Y&storeId=10001&catalogId=10001
jsw