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Unread postPosted: 15 Aug 2011, 21:07
by battleshipagincourt
wrightwing wrote:It's all in how the size of the fighter is scaled, as to whether there'll be significant performance degradation. Internal bays are more costly, which is why the majority of legacy fighters were designed with the compromise of draggy combat configurations.


Actually they seriously considered having internal bays for the Eurofighter, but preferred external stores due to the physical limitations weapon bays present in terms of war load. The F-22 is an unfortunate example of this, as it can't carry 2k-class weapons internally. And I marvel at how elegantly they designed the weapon bays of the F-35, making it possible to mount JDAM's and AMRAAM's without constricting the deployment of either kind of weapon. If I were able to redesign the F-22 (say this was the year 1995) I would definitely have extended the bays to allow AIM-120's in the sides and 2k-class weapons in the central compartment. This could have made it a lot more useful.

Otherwise I believe the other primary advantage to using external weapons was in terms of not constricting the kinds of ordinance a fighter could carry. Aircraft like the F-4, F-14, Tornado, Eurofighter, and Rafale compromised with semi-recessed weapons, which allowed a less significant drag penalty than hanging things off pylons.

Unread postPosted: 15 Aug 2011, 22:02
by lamoey
grinner68 wrote:
SpudmanWP wrote:
grinner68 wrote:At some point the cost of the aircraft will exceed it's capabilities.
The F-35 may have hit that mile post before it's even entered service.


At FRP the F-35A will cost about 15% more than current 4th gen US jets (F/A-18E). If you think that 6xF-15As can do more and survive longer than 7xF/A-18Es, then it is worth it.


How many F-16's have we lost from 2001-2011?
How many F-16 flight hours were flown during those years.
Now how many F-35's will you need to fly those same flight hours and how much would it cost to purchase those airframes, fly, arm and support them?
I'm thinking it would cost less to fly the F-16's.


One thing to keep in mind that for the F-35 there is no two seater for training, so the training that previously was done in a two seater may be done in the simulator now, so that will reduce total hours flown compared to the F-16. Nor will there be any other forms of backseat rides for anybody else, but this is probably a very small percentage anyway.

I have not seen any estimates for this, but I would expect attrition to be similar to current/older design. Others may be able to add to this but I would expect the more modern engine design to be more reliable than older designs and the flight control system may be smarter in the way it avoids hitting stationary objects in the absence of input from the pilot.

Unread postPosted: 15 Aug 2011, 22:13
by spazsinbad
There is a lot of information about the 'health monitoring' that will help ensure not so many preventable losses. Here is one example:

http://www.globalsecurity.org/military/ ... design.htm

"Autonomic Logistics (AL)
Because logistics support accounts for two-thirds of an aircraft's life cycle cost, the F-35 will achieve unprecedented levels of reliability and maintainability, combined with a highly responsive support and training system linked with the latest in information technology. The aircraft will be ready to fight anytime and anyplace. Autonomic Logistics (AL) is a seamless, embedded solution that integrates current performance, operational parameters, current configuration, scheduled upgrades and maintenance, component history, predictive diagnostics (prognostics) and health management, and service support for the F-35. Essentially, AL does invaluable and efficient behind-the-scenes monitoring, maintenance and prognostics to support the aircraft and ensure its continued good health.

The F-35 is designed to reduce operational and support costs significantly by increasing reliability and reducing required maintenance. Such high reliability will enable rapid deployment with minimum support equipment. The cost to operate and maintain the F-35 is expected to be 50 percent less than that for the aircraft it is designed to replace. For decades, the concept of repairing new aircraft came only after the aircraft was built. Then, it had to conform to an existing logistics structure. But the F-35's logistics system has to be up and running before the first aircraft is flown.

The autonomic logistics system, as the F-35 system is called, will monitor the health of the aircraft systems in flight; downlink that information to the ground; and trigger personnel, equipment, and parts to be pre-positioned for quick turnaround of the aircraft. Ultimately, this automated approach will result in higher sortie-generation rates. Autonomic logistics is also something of a mind reader. Through a system called prognostics and health management, computers use accumulated data to keep track of when a part is predicted to fail. With this aid, maintainers can fix or replace a part before it fails and keep the aircraft ready to fly. Like the rest of the program, the autonomic logistics system is on a fast track. It has to be available to support the air vehicle during operational test and evaluation."

Unread postPosted: 15 Aug 2011, 22:41
by outlaw162
With this aid, maintainers can fix or replace a part before it fails and keep the aircraft ready to fly.


Does this include the IPP?

(From experience, pilots have always been able to figure out a way to break an airplane.)

Unread postPosted: 15 Aug 2011, 22:55
by spazsinbad
outlaw162 said: "From experience, pilots have always been able to figure out a way to break an airplane." Yep agree. I can show pictures. Took a year to fix it. :D I guess the data about failed valve in IPP has gone into the database for future reference?

Unread postPosted: 15 Aug 2011, 23:11
by outlaw162
A year? :D

I was able to put one out of commission permanently.

I assume this "AL" means the ejection system will no longer be required.

That weight savings may solve the 12 NM range shortfall. :D

OL

Unread postPosted: 15 Aug 2011, 23:20
by andreas77
lamoey wrote:...
The NG and all other 4th generation fighters use external tanks because they have to, not because they want to. Otherwise many of them would not be able to defend anything but their own runway.
...


They do not always have to, but they have more options since they can choose between fuel and weapons to a much greater extent. The high fuel fraction of the F-35 and the impact the huge fuselage seems to have on the flight characteristics when hanging external stores under the wings is kind of limiting. What about those situations where 6 tons of fuel would be enough, then the F-35 still flies around with that huge internal fuel tank which adds extra drag (and weight) that other fighters would avoid by just not adding that extra fuel tank.



lamoey wrote:...
The advantages the F-35 brings to support and operational folks was further highlighted in another thread where the flexibility of not having to have two or three different configurations prepared on the line at all times, reducing the number of fighters that needs to be ready at all times, or makes more fighters ready for whatever happens.
...


I am not really sure what you mean here, but I agree to some extent since the high fuel fraction and limited useful external stores reduces the number of payload configurations, but how is that a good thing?

Unread postPosted: 16 Aug 2011, 00:34
by sewerrat
andreas77 wrote:
lamoey wrote:

the F-35 still flies around with that huge internal fuel tank which adds extra drag (and weight) that other fighters would avoid by just not adding that extra fuel tank.
lamoey wrote:



Of course there ain't no such thing as a free lunch, and the volumetric size of the F-35 is much greater than the F-16. But, no Falcon's go to war naked; they go dirty full of external tanks, missiles, sensors.

The price you pay in drag is much higher when dirty as compared to clean, which is what the -35 will do. Load 'em the same, 2 sidewinders, 4 amraam, and give the -16 a centerline tank for good measure of range. I doubt the -16s performance (whatever parameters you want to look at) will be as good as the -35s. Certainly the -35s "aerodynamics" will be superior to a "real world" F-16 loaded for a CAP sortie.

Unread postPosted: 16 Aug 2011, 01:18
by spazsinbad
outlaw162, an interesting point about possibility of flying without an ejection seat. :D Here is one example of 'when things don't work as predicted'.

Test Flying The Joint Strike Fighter Talk by Graham Tomlinson 9th Feb 2011

http://myweb.tiscali.co.uk/hawkerassoci ... ghter.html

"...In the unlikely event of the lift fan failing catastrophically the aircraft would pitch inverted in 0.6 seconds, and the pilot is protected by auto-ejection signalled by pitch rate and attitude (derived from the YAK 38 & 141 systems)...."

Full article also found on this thread: Many F-35B landings won’t be vertical
http://www.f-16.net/f-16_forum_viewtopi ... t-105.html

Unread postPosted: 16 Aug 2011, 01:38
by spazsinbad
outlaw mentioned in passing.... :D "A year? :D I was able to put one out of commission permanently." I'm guessing by the smileyface that all was OK?

Mine was just [my own night deck landing] incompetence. Broke it once 'elsewhere' trying to land at night on a bobbing runway and then broke it twice during the full stop landing on a permanent runway but the second landing was deemed cool by onlookers. :D At night empty droptanks substituted for broken undercarriage during arrest with large flames from fuel vapour in empty drop tanks providing some fireworks - no fire though. Fuselage permanently bent from first landing with many popped rivets from both landings and of course lots of other stuff broken. sigh.

Unread postPosted: 16 Aug 2011, 02:34
by outlaw162
All's well that ends well. We're still here to post. :D

I can hear the F-35 driver talking on the radio to MX control after landing:

"Tell the 'Autonomic Logistics' guy to meet me at MX debrief. The "Check Engine" light is on."

:D

OL

Unread postPosted: 16 Aug 2011, 02:42
by delvo
battleshipagincourt wrote:The F-22 is an unfortunate example of this, as it can't carry 2k-class weapons internally... I would definitely have extended the bays to allow AIM-120's in the sides and 2k-class weapons in the central compartment.
I've been wondering lately what makes these classes what they are and what makes a given plane able or unable to carry them.

Wikipedia tells me we have two different JDAMs in the 2000-pound class: the 2039-pound Mark 84 (129" long, 18" diameter) and the 1927-pound BLU-109 (95" by 14.6"). The difference in weight isn't much, but in size, the BLU-109 is closer to a 1000-pound JDAM (119.49" by 14.06") than it is to a Mark 84. It's actually almost 25% shorter than the lighter bomb, and thicker by hardly over half of an inch. So when we're told that a plane's internal bays can't carry a 2000-pound weapon but can carry a 1000-pounder, we're apparently being told that either the weight made the difference, or the half-inch did. (...Unless the comments excluding the use of a 2000-pounder referred only to Mark 84, neglecting BLU-109 for whatever reason, as if its size put it in the 1000-pound "class" despite its weight.)

So, why a 1000-pound bomb but not a BLU-109... did they really design F-22's bays in a way that could fit a 14.06" diameter in there but not a 14.6" one, thus refusing to budge a half-inch in order to carry twice as heavy of a bomb?.. and then do the same thing, to the same level of precision, to F-35B but somehow not A or C? That seems unlikely enough to indicate that the issue was weight. But both planes can certainly carry more weight in total, so that indicates that we're dealing with not total load weight but apparently a matter of structural reinforcement of the hardpoint and the area of the plane's frame that the hardpoint hangs from. So, given that they could have built in a hardpoint that could hold 2000 pounds, why did they choose not to? Does that save money and weight in airframe materials, and if so, how much?

Or am I barking up the wrong tree by looking at sizes and weights in the first place because these weapon classes are actually defined by something else?

Unread postPosted: 16 Aug 2011, 03:01
by spazsinbad
outlaw162 said: "All's well that ends well. We're still here to post." Who knew? :D Very Shakespearian.

Unread postPosted: 16 Aug 2011, 05:35
by sirsapo
So, given that they could have built in a hardpoint that could hold 2000 pounds, why did they choose not to? Does that save money and weight in airframe materials, and if so, how much?


As people have said before, everything in aircraft design is a tradeoff, and any small change can ripple throughout the entire design. Its probable that by the time they finalized the design there was no requirement for 2000 pound weapons carriage. You have to take into account that not only does the pylon have to support 2000 lbs, but it also has to support that weight at whatever load factor you want to rate the airplane to (ie 12,000 lbs @ 6g). That extra 1000lbs of capability might end up costing you too much in airframe weight to offset the benefit of the larger weapon.

The short answer is that traditional fighter aircraft cost is pretty much directly related to aircraft weight, so any saving in weight will most likely save you money in the long run.

Unread postPosted: 16 Aug 2011, 05:52
by wrightwing
andreas77 wrote:
lamoey wrote:...
The NG and all other 4th generation fighters use external tanks because they have to, not because they want to. Otherwise many of them would not be able to defend anything but their own runway.
...


They do not always have to, but they have more options since they can choose between fuel and weapons to a much greater extent. The high fuel fraction of the F-35 and the impact the huge fuselage seems to have on the flight characteristics when hanging external stores under the wings is kind of limiting. What about those situations where 6 tons of fuel would be enough, then the F-35 still flies around with that huge internal fuel tank which adds extra drag (and weight) that other fighters would avoid by just not adding that extra fuel tank.



lamoey wrote:...
The advantages the F-35 brings to support and operational folks was further highlighted in another thread where the flexibility of not having to have two or three different configurations prepared on the line at all times, reducing the number of fighters that needs to be ready at all times, or makes more fighters ready for whatever happens.
...


I am not really sure what you mean here, but I agree to some extent since the high fuel fraction and limited useful external stores reduces the number of payload configurations, but how is that a good thing?


So I suppose having a large internal volume of fuel is a design flaw in the Flanker too? I've only seen one source claim an 8% increase in range, with EFTs, so I'll take that claim with a grain of salt. I have on the other hand seen other charts showing a combat radius for the F-35C, with EFTs, at 900+nm.