It seems the F-35 has run into another problem. It won’t run on warm fuel – such as might be available in desert environments where the airplane is expected to be used. The solution? Well, they’re going to fix the airplane of course!
Oh, wait… They’re not. The solution to the warm fuel problem is to paint all of the fuel trucks to keep the fuel cooler. :smack:
Lockheed-Martin might have had a good idea, using the fuel as a heat sink for the cooling system; but someone didn’t think the issue all the way through.
The notable issue with the SR-71 was that it leaked like a sieve. The joints were loose at normal temperatures, but became tight as the metal expanded at high speed.
Forgive me for my failure to understand the physics properly; I transferred out of physics half-way through my junior year in high school because it was too mathematical.
But if you’re transferring the heat from the cooling system to the fuel system – which is losing fuel due to usage as flight time progresses – aren’t you effectively increasing the amount of heat that the fuel system (tanks) is absorbing/sustaining?
How is it that this warbird hasn’t just dropped out of the sky in mid- test-flight when the fuel temperature passed its usable threshold? They haven’t been doing endurance testing on the engines yet? If you just chain it out on the tarmac and let it run at medium speed, will it run out of fuel, or overheat the fuel and ‘choke’ first?
–G?!?
Out along the edge
Is always where I burn to be
The further on the edge
The hotter the intensity
…–Kenny Loggins
…Danger Zone
…Top Gun Soundtrack
As much as I would like to take a college Physics series, I have to work for a living; and in this state it is assumed that if you are going to school you’re 18 years old and living at home. But as I understand it, based on this:
It’s not so much that the engines won’t run on hot fuel; it’s that it can’t absorb enough heat to cool the avionics when the aircraft is on the ground. Presumably, this is not a problem at altitude or with sufficient airflow.
So what happens when the aircraft is slowing down with little fuel while lining up for a landing?
Seriously, was the F-35 program actually some sort of giant psychological experiment to see how much money people are willing to spend on something that is totally worthless?
It all depends on how the fuel is acting as a heat sink. I’ve flown aircraft that run fuel through the oil cooler. The fuel cools the oil and the oil warms the fuel, both a good thing. It didn’t matter how empty the fuel tanks were because the fuel was on its way to the engine, it wasn’t using fuel sitting in the wings as a heat sink. So there are reasonable ways to use fuel for cooling and without knowing the specifics of the F-35 it’s impossible to say whether it is a reasonable design or not.
The SR-71 did indeed use fuel as a heat sink and as hydraulic fluid. The fuel had a very high flash point, a classic example was dropping a match in a bucket of the what they called JP-7 and nothing happened. It required an exotic boron compound to light it up (which the term escapes me right now, but burns on contact with air.)
When large planes are at cruise altitude and speed, what % of their maximum thrust is used? I realize that this will vary from plane to plane, I am asking for data points drawn from your experience.
The only time they weren’t on was in the 30 minutes or so prior to start for taxi and take-off and after shutting down after landing.
I don’t know as a percentage but it is close to maximum. The higher you fly the closer the engines have to run to their limits to put out enough thrust/power to achieve the required air speed. Max operating altitude is pretty much defined as the altitude where you no longer have any excess thrust.
The type I’m thinking of with the fuel / oil heat exchanger is a Dash 8 turbo prop by the way.
No, that was the Strategic Defense Initiative and the B-2 bomber programs, which aptly demonstrated that, in fact, Congress was willing to spend giant dumptrucks of money on something that either couldn’t physically work as promised and/or was obsolete before it ever left the drawing board. The F-35 program was purely an effort by Lockheed Martin to sell the aerospace equivalent of chocolate-covered cotton balls as part of their decades-long history of utter non-performance on major aerospace contracts.
“But I make a profit of three and a quarter cents an egg by selling them for four and a quarter cents an egg to the people in Malta I buy them from for seven cents an egg. Of course, I don’t make the profit. The syndicate makes the profit. And everybody has a share.”
[INDENT][INDENT][INDENT][INDENT][INDENT][INDENT][INDENT][INDENT][INDENT]-- Milo Minderbender, Catch-22[/INDENT][/INDENT][/INDENT][/INDENT][/INDENT][/INDENT][/INDENT][/INDENT][/INDENT]
Augustine’s Law Law Number XVI: In the year 2054, the entire defense budget will purchase just one aircraft. This aircraft will have to be shared by the Air Force and Navy 3-1/2 days each per week except for leap year, when it will be made available to the Marines for the extra day.
(Semi-log plot validating the law.)
Seriously, when the DoD decided to curtail procurement of the F-22 ‘Raptor’ because of cost, a lot of additional mission and functional requirements were levied upon the F-35, which then predictably became just as expensive as the F-22. This, combined with the reality is that the F-35 was supposed to be able to leverage off of the supply chain management, technology development, and other ‘economies of scale’ of the F-22, but instead ended up bearing a lot of the additional costs, in addition to the typical mismanagement that is unfortunately too common with large aerospace and defense projects. Subsequent curtailing of F-35 procurement also meant that the per-unit costs increased to absorb the non-recurring engineering, manufacturing, and testing costs. And all of this for an aircraft that will be obsolete before the end of the decade in comparison to more capable UAVs.
Your tax dollars at work. Meanwhile, we still can’t get any significant pull on a space-based asteroid detection and deflection system, development of alternative transportation fuel infrastructure, or even upgrading the electrical distribution network to avoid the potential wide-scale damage that could occur from a Carrington-type event as independently assessed by both the JASON Group and the Lloyd’s/AER report. Go figure.
I think it was more “how much money people are willing to spend to appease the Marines.” If they hadn’t wanted the mediocre STOVL version they could have at least fixed some of the problems.
From what I’ve read, this was the main cost overrun driver. Had it just been a carrier-capable fixed-wing plane, it would have been much simpler. But the USMC insisted on the STOVL version, which was both hugely expensive, and had costly side-effects that carried into the other versions of the plan.
Using the fuel tankage as a heat sink is common in fighter or transport aircraft. It’s bog-standard aero engineering practice. The F35 just pushed the envelope a bunch harder than everybody else did/does.
At any reasonable altitude, even a few thousand feet, the ambient temperature is low enough to keep the fuel cool to cold. So the waste avionic & hydraulic heat is just offsetting that ambient cooling. It’s NOT a matter of simply pumping ever more heat in without any compensation until the fuel eventually boils. Or at least that’s not how it *should *be designed.
Clearly the F35 is a mix of A) out past the bleeding edge of technology; and B) poorly implemented due to some combo of greed and incompetence; and C) a victim of DoD dithering, spec changing, and budget cutting.
I hear a lot of totally uninformed people who say something like this and it is easily dismissed for simple ignorance. But you are extremely well informed on aerospace matters, so a higher standard applies: that statement is total and complete BS.
There is no UAV in the works that is anywhere near as capable as an F-35. I’m not talking about just in the next ten years; I’m saying that there is no UAV in any stage of development that is even as capable as a fourth generation fighter or strike aircraft.
I’m dying to know what, specifically, you are thinking of. UCLASS? That program could well be cancelled, and it is more or less a stealthy Predator that can fly off a carrier. Doesn’t even have a radar on it. Both the Air Force and Navy are starting to look at 6th generation fighters, which could be unmanned, but probably won’t be, and in any case won’t likely be fielded for another 20 plus years. I can’t think of a single other program out there that you could even claim pertains to your statement in the least.
