Forum: F-35 Lightning II

@Alloycowboy

Where'd ya get the F135 dry weight from?

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Wouldn't it make more sense to compare the F-18 engines to the F-16 engine? Or the F119 to the F135 if you wanted a modern comparison.

destroid.... The F-35 is pretty much a direct replacement for the F-18E which is why they both have ~28000 lbs of dry thrust at full military power and ~43000 lbs and 44000 lbs in Afterburner. As for doing a F119 vs F-135 engine comparison that isn't really a good idea as the F-119 is a supercruising engine where as the F-135 is designed to cruise at subsonic speeds. So even though they are sister engines they have different design points which affects their design.

@bumtish..... The Dry Weight for the F-135 came from wikipedia so take it with a grain of salt............ and some tequila!

SpudmanWP wrote:

But cost more to maintain.

That's an known unknown.

maus92 wrote:

SpudmanWP wrote:

But cost more to maintain.

That's an known unknown.

http://www.youtube.com/watch?v=3SED0Wh1iwQ LMAO

alloycowboy wrote:

destroid.... The F-35 is pretty much a direct replacement for the F-18E which is why they both have ~28000 lbs of dry thrust at full military power and ~43000 lbs and 44000 lbs in Afterburner. As for doing a F119 vs F-135 engine comparison that isn't really a good idea as the F-119 is a supercruising engine where as the F-135 is designed to cruise at subsonic speeds. So even though they are sister engines they have different design points which affects their design.

@bumtish..... The Dry Weight for the F-135 came from wikipedia so take it with a grain of salt............ and some tequila!

What I meant was, shouldn't we compare designs from a similar era? The F414 is an evolutionary design from the 70s where the F135 is a new engine. From wikipedia the F100 and F404 have similar performance. Engine diameter is another reason you might pick a twin arrangement to reduce the vertical size, but I don't know enough about aircraft design to say why that might be useful.

How would they compare in terms of maintenance manhours required?

popcorn wrote:

How would they compare in terms of maintenance manhours required?

You don't even need to know remotely close to the specifics to realize the F135 wins that hands-down. There's only one of them, so all else being equal, it requires half the maintenance manhours of two smaller engines. It has fewer moving parts than legacy engines too, so probably a bit easier to maintain than a single legacy engine. Add in the modern digital monitoring that was built into the engine from the absolute beginning (if you want to add that to a legacy engine, expect a huge development cost), and the engine will probably require less actual hands-on maintenance than a single legacy engine even without counting the fewer parts. So in total, it's a very safe bet that its maintenance manhours are somewhere between one-half that of a twin-legacy-engine fighter at the absolute worst case, and one-quarter. Probably closer to, though significantly better than, one-half.

river_otter wrote:

popcorn wrote:

How would they compare in terms of maintenance manhours required?

You don't even need to know remotely close to the specifics to realize the F135 wins that hands-down. There's only one of them, so all else being equal, it requires half the maintenance manhours of two smaller engines. It has fewer moving parts than legacy engines too, so probably a bit easier to maintain than a single legacy engine. Add in the modern digital monitoring that was built into the engine from the absolute beginning (if you want to add that to a legacy engine, expect a huge development cost), and the engine will probably require less actual hands-on maintenance than a single legacy engine even without counting the fewer parts. So in total, it's a very safe bet that its maintenance manhours are somewhere between one-half that of a twin-legacy-engine fighter at the absolute worst case, and one-quarter. Probably closer to, though significantly better than, one-half.

F414 has digital monitoring. But it makes sense on the surface that 2 engines require more maintenance man-hours, and fewer parts are generally advantageous, but we really don't have enough data to validate F135 maintenance requirements as of yet. How many have actually been built and flown? How many cumulative flight hours has the type amassed? F-35B has an additional lift fan system - what are the maintenance costs associated with that system? We do know that the F135 costs considerably more than two F414's, and adding a lift fan system for the -B adds even more cost. Bottom line is that it is not a simple calculation to determine propulsion system cost differences between single and twin engine tactical aircraft.

alloycowboy wrote:

destroid.... The F-35 is pretty much a direct replacement for the F-18E

F-35 is a replacement for F-18A/C, but is comparable to F-18E...

Forum: F-35 Lightning II

two engines F-35 model