The trouble with the basement dwellers

Discuss the F-35 Lightning II
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charlielima223

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Unread post28 Feb 2016, 12:48

les_paul59 wrote:Russia Today just quoted Dave Majumdar's most recent "how to kill a F-35" article, isn't that the definition of credibility right there lol.....


Jesus they will call any critic of an F-35 an "expert" wont they? But they'll never speak to actual experts... pilots to get their opinion will they? Instead they'll talk to any tard with ZERO flight or combat experience and quickly label them an "expert" because it falls inline with their views.
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endre

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Unread post28 Feb 2016, 12:49

Had another interesting discovery last week ref: what does the DOT&E-report actually tell us. A Norwegian critic sent out this newsletter where he tried to ridicule the F-35 for having to "wave its skirts around" all the time, referencing the comment in the DOT&E-report about the 10 minute limitation on closed weapons bays at certain altitudes and at certain speeds. So I started digging and asking around - and the answer surprised me.

First of all - the reason for this limitation is not found in the design of the F-35, as many would have you think. What is really the case is that certain components belonging to the avionics, that have been installed in the weapons bays for ease of maintenance, have not been qualified at the required temperatures. Until these components are re-qualified, their temperature limitations by definition become the temperature limitations of the weapons bay as a whole, and anything above that becomes "excessive." So while the contents of the report on this area are factually correct, it in no way tells the whole story, and creates the impression that an isolated issue is indicative of an issue with the aircraft as a whole.

Also, the real tactical implications of this are quite limited. Our pilots at Luke report that they have not once had to adapt any of their plans to work around this issue, nor have any of those that have flown the aircraft a lot more aggressively than our guys have so far.

Not that this rational explanation will have an impression on anyone who has already decided what to think about the issue...
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Unread post28 Feb 2016, 13:13

Thanks 'Endre' I was just reading the 'English' translation of that but found some difficulty in understanding some of the 'translated' English. Would it be possible to have a more formal translation than the one Google provides please?
Some comments on the new allegations of F-35 by CLEVER MORTEN :mrgreen:
25 Feb 2016 Morten Klever

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Unread post29 Feb 2016, 10:27

Thank you Endre, that's what I also suspected. I also find if very likely to have about zero impact in real life. IMO, F-35s would likely very seldom need to fly fast and low for extended periods of time (over 10 minutes). In real combat, I doubt anyone would give much thought about breaking that rule if really needed. Of course if it really was potentially fatal, then sure, but this 10 minute restriction sounds very much like peace time rule erring on the side of safety. So, F-35 is being targeted by surprise S-400 and to avoid that they have to fly fast and low and they have flown for 9 minutes and 55 seconds. Is the pilot going to suddenly pull back the throttle and/or gain altitude? I somehow doubt that...
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element1loop

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Unread post29 Feb 2016, 11:20

Perhaps someone can enlighten here, as this quote seems to contradict the suggestion there remains a cooling or heating issue, since about June 2015.

Next-Generation Us Fighter Engines Technology

Towards Tomorrow's United States Fighter Engine

June 2015

Richard Vander Meulen

[Page 75]

"... There is no doubt about this. During its original ground-testing effort for the F135, P&W ran an unimproved engine at thrust levels of up to 51,000lb in uninstalled configuration (ie without any accessory gearboxes or drives drawing power from the engine). This suggested that, even on an installed basis, the F135 had several thousand pounds of additional thrust available if necessary, if run at high temperatures.

Kenyon [Jim Kenyon, Pratt & Whitney’s Director of Advanced Programmes and Technologies] pointed out that, although the F-35 airframe has had heat-retention issues, "right now, there are no thermal restrictions with the engine". In-service F135s are operating within the specifications required by the JPO and presumably could be operated at a higher maximum temperature as long as the F-35 airframe could withstand and dump the additional heat burden. ..."


Source: https://www.scribd.com/doc/269303020/AIR-US-NG

As I understood it, the thermal restriction with the engine was imposed due to thermal retention issues within the airframe, i.e. the engine was limited in output, such as throttle at low altitude (higher ambient air temps), to reduce heating of the aircraft in hotter air at low altitude. But Mr Kenyon is implicitly stating the prior airframe conditions that caused the retention of heat, and thus thermal restrictions of the engine at low altitude, no longer exist, as there are no restrictions in place, at all of about 8 months now.

There was also this comment in 2014:
bumtish

viewtopic.php?f=55&t=25735&start=75

August 13th, 2014, 8:08 pm

The F-35's propulsion and avionics are running at higher temperatures than expected. To compensate, more bleed air from the Pratt & Whitney F135 engine is used for cooling, but this reduced propulsion efficiency and shortened range by 19.3km, according to sources familiar with the design issues.

http://www.flightglobal.com/news/articl ... ll-356581/


I had supposed (to myself) that this thermal issue had been dealt with, probably as a part of the removal and retrofit of new engine parts (post fire) which as I understand it has now been completed for all of the existing F135 engines.
F135 Fix Nears Completion As Production Ramps Up

Apr 6, 2015

HARTFORD, Connecticut—Pratt & Whitney is ramping up retrofits to operational F135 engines with a fix to the problem that led to a catastrophic engine fire last year in the F-35A Joint Strike Fighter, and aims to modify the entire fleet by the first quarter of 2016.


Source: http://aviationweek.com/defense/f135-fi ... tion-ramps

So is there an existing thermal restriction, or not?

And if there is, why is P&W's Jim Kenyon saying there isn't, and that the jet is meeting JPO requirements, as of June 2015, with respect to the prior engine thermal restriction?
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Dragon029

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Unread post29 Feb 2016, 12:49

I'm a bit confused, but from my understanding "there are no thermal restrictions with the engine" means that the engine itself is fine operating at the current temperatures (the turbines aren't deforming or cracking prematurely from normal operating temperatures), but regardless, the heat output from the engine (and avionics) was more than expected, meaning that the airframe heat retention issues persist in certain circumstances. The increased bypass air being used for cooling would be about reducing the net heat transfer between the engine and airframe.
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element1loop

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Unread post29 Feb 2016, 13:28

Dragon029 wrote:I'm a bit confused, but from my understanding "there are no thermal restrictions with the engine" means that the engine itself is fine operating at the current temperatures (the turbines aren't deforming or cracking prematurely from normal operating temperatures), but regardless, the heat output from the engine (and avionics) was more than expected, meaning that the airframe heat retention issues persist in certain circumstances. The increased bypass air being used for cooling would be about reducing the net heat transfer between the engine and airframe.


I presumed the engine testing regime would have found thermal longevity issues with turbine cracking or coatings most of a decade ago, and that the restrictions were never related to the engine itself, which given is capable of 51,000lb sustained is operating with substantial turbine thermal and longevity buffer.

So I take that to mean this is purely about the airframe and possibly a change to bypass ducting and venting, when the engines were removed for retrofit. The same article says there is a substantial blow-by of the main fan (not bypass) as not all the air that comes into the intakes can actually fit into the engine. So presumably this air passes between engine and airframe and around burner and nozzle facets to cool them. And that they changed the channeling of that air, while the engines were out, to improve the thermal insulation and cooling between engine and airframe, thus eliminating the problem and providing some thermal overhead that previously did not exist.

Thus Kenyon went as far as to suggest that there's now some room to extend standard thrust with the existing (retrofitted) standard engine, and that some of the performance increase can be obtained with that engine, before a Block-1 upgrade occurs.

Plus P&W just finished pushing five F135 engines past 5,000 hours, one out to 5,400 hours and another to 5,260. So there's room there to use some of that margin for performance boosting right now, given 400hr per year is a decent number of hours flown, which means an engine of ~5,000 hr life is good for about 10 to 12 years. But P&W say they're proposing to JPO to go to a Block-1 level engine from 2018 to 2020 time frame, and that Block-2 may be ready from 2020 to 2022 window. So why not trade some of that excellent engine life for more thrust in the interim 2 to 4 years, until Block-1 upgrade is performed?

That effectively is what P&W's Kenyon was saying is an option, a significant thrust increase "right now", in his words, with the standard F135 engine.

Either way, I'm fairly confident the thermal issue never was with the engine, and is now gone from the airframe as well, unless there is some other thermal issue that someone else knows of.
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Unread post01 Mar 2016, 05:24

I recall or wild dementia?... there was a problem with low fuel and sitting at idle for a period of time, this was fixed with more bypass/flow? the fuel is used as a heat sink and they were going to use a chiller to got it colder to start with? latest talk is it's not too hot to start the engine. it didn't address the heat sink properties.
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Unread post01 Mar 2016, 05:42

My 'demented' [non TOTAL] recall (with a load of references in this forum that can be searched) suggests that - for example - the 'fuel truck issue' was one dreamt up by a well meaning refueller, anticipating a problem that does not exist. Sure there are limits to heat for all aircraft when refuelling on the ground but these are not likely to be encountered. The F-35 operates in at least two desert environments - not noted for mild day time temperatures - whilst the F-35B was tested under extreme hot/cold conditions last year in the climate chamber with success.

As I recall there was a minimum fuel for aircraft under certain circumstances but I do not recall how this was resolved. There would be info on this in this forum from some years back. Probably DOT&Es from a year or two ago report on it.
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Unread post01 Mar 2016, 07:11

optimist wrote:I recall or wild dementia?... there was a problem with low fuel and sitting at idle for a period of time, this was fixed with more bypass/flow? the fuel is used as a heat sink and they were going to use a chiller to got it colder to start with? latest talk is it's not too hot to start the engine. it didn't address the heat sink properties.


I've personally not heard of turbines having a problem with starting with pre-heated fuel. I can't see why that would be a problem. I have heard it occurring to reciprocating engines, where excessive engine bay temps (during a refuel stop) causes bubbles in 100LL fuel lines (i.e. the fuel boils and vaporizes if pressures are low enough for it in the lines) which is resolved via priming to clear the lines of the hot fuel and gasses replacing it with freshly primed cooler fuel from the tanks. i.e. the hot fuel is simply dumped back into the wing,s or a header tank, and the engine starts per normal after that.

But bubbles in pressurized kerosene lines? Not likely, but not impossible. But could be remedied easily in the same way.
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Unread post01 Mar 2016, 08:32

"The F-35 in a dogfight - what have I learned so far?" First Norwegian pilot shares his insights (in English even...!)
http://nettsteder.regjeringen.no/kampfl ... ed-so-far/

BD meltdown in 3, 2, 1.....
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Unread post01 Mar 2016, 09:07

endre wrote:"The F-35 in a dogfight - what have I learned so far?" First Norwegian pilot shares his insights (in English even...!)
http://nettsteder.regjeringen.no/kampfl ... ed-so-far/

BD meltdown in 3, 2, 1.....



THANKs Endre!!!!!

:applause:

I found this part to be interesting

The overall experience of flying the F-35 in aerial combat is different from what I’m used to with the F-16. One obvious difference is that the F-35 shakes quite a bit at high g-loadings and at high angles of attack, while the F-16 hardly shakes at all. The professional terminology is «buffeting», which I also described in an earlier blog post (English version available). This buffeting serves as useful feedback, but it can also be a disadvantage. Because the buffeting only begins at moderate angles of attack, it provides me an intuitive feel for how much I am demanding from the aircraft; what is happening to my overall energy state? On the other hand, several pilots have had trouble reading the information which is displayed on the helmet visor, due to the buffeting. Most of the pilots here at Luke fly with the second-generation helmet. I fly with the third-generation helmet, and I have not found this to be a real issue.


Seems like those 3rd gens resolve what I remember pilots having a larger issue (reading the screen on the HMD).

He pretty much covers every complaint that was in the AOA test complaints list, so that will be interesting to see the anti F-35 crowd counter. For the most part his word pretty much confirm what others on the forum have believed for awhile, in BFM the F-35 performs like a F/A-18 but with better acceleration/energy. :thumb:
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Unread post01 Mar 2016, 09:39

There are a few threads with the AXEd Doggie Fite Reveal - this is one of them now with 'endre' link also: Read TRIMBLE story and on to 'endre' link below:

Test pilot admits the F35 cant dogfight viewtopic.php?f=55&t=27497&p=316751&hilit=Trimble#p316751
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rheonomic

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Unread post01 Mar 2016, 14:33

geforcerfx wrote: For the most part his word pretty much confirm what others on the forum have believed for awhile, in BFM the F-35 performs like a F/A-18 but with better acceleration/energy. :thumb:


I had the opportunity to speak with a USAF Lightning driver that had also flown Hornets as an exchange officer, and that's pretty much exactly what he said, so there's another data point.
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cosmicdwarf

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Unread post01 Mar 2016, 15:12

rheonomic wrote:
geforcerfx wrote: For the most part his word pretty much confirm what others on the forum have believed for awhile, in BFM the F-35 performs like a F/A-18 but with better acceleration/energy. :thumb:


I had the opportunity to speak with a USAF Lightning driver that had also flown Hornets as an exchange officer, and that's pretty much exactly what he said, so there's another data point.

Which makes it a good point for countries that operate the Hornet already.

There will obviously be some training, but they'll be used to the style already.
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