Today's fighter jets can carry a bigger payload than the heavy bombers of World War II
Posted by Advanced-Injury-7186@reddit | aviation | View on Reddit | 66 comments
And when you consider that today's bombs are far more accurate, you realize that one F-35 can do the work of several B-17s
Interesting_Day2277@reddit
The real mind bender is the A-4 skyhawk carrying more than the mighty B-17.
Advanced-Injury-7186@reddit (OP)
Just how is that possible? Is it because turbine engines are so much lighter than piston?
discombobulated38x@reddit
Gas turbines have about 10x the power to weight ratio of piston engines
Advanced-Injury-7186@reddit (OP)
If they were cheaper to make, cars would have turbine engines.
discombobulated38x@reddit
I don't think they would, for a couple of reasons:
Gas turbines contain enough rotational kinetic energy to caaue serious damage when discs/shafts fail. Even a 120N thrust hobby turbine is more dangerous than a hand grenade. You can't life ths parts to never fail without trashing the fuel efficiency, so you'd have to expect the average consumer to bring their engine in for a complete rebuild semi regularly. Probably mitigatable with the right nerf in performance.
Clutching a free power turbine is challenging - helicopter rotors/ propellers can idle, car wheels can't when stationary. Completely stalling the FPT might be achievable though.
Noise. Even the smallest gas turbine kicks out 120dB or more, so exhaust systems would have to be far more finicky than they are now.
As far as RDEs go, they look super interesting. I think we'll see them in military applications long before they replace a conventional combustor in a subsonic civilian application, though they may be one of the technologies used to make hydrogen more competitive on price.
huyvanbin@reddit
The main issue I think is a turbine engine can’t respond as fast as a piston engine, so you would have problems with acceleration (as in the Chrysler car) if you have a mechanical drivetrain. A series hybrid is possible but then you lose the weight advantage over a normal engine.
Advanced-Injury-7186@reddit (OP)
Lots of automakers, most famously Chrysler, took the idea of turbine power seriously, serious enough to actually put turbine engines in real cars for experimental purposes. None of the problems you list came up. The only real problem they had came from the fact that the power turbines were constantly being exposed to the heat of combustion. To fix it, they had to use superalloys that were prohibitively expensive for mass-market automobiles.
discombobulated38x@reddit
This would be at around the same time that lots of engine/aircraft makers were seriously considering the idea of nuclear powered aircraft in much the same way, to put the idea in context. What we know now suggests this is an absolute non-starter.
Noise absolutely was one of the contributing factors to it being unpopular.
So maintenance wasn't an issue, but a turbine failing because it was exposed to the environment a turbine is designed to be exposed to was an issue?
Maintenance was better than a piston engine for 1960. To put this in perspective: Cars at that time needed oil changing every 2000 miles, piston rings would need replacing, reliability was trash. Almost everything in an automotive piston engine is good for life these days.
Chrysler only tested their engines for an average of 20,000 miles each. That's nowhere near enough to expose any of the issues you'd begin to see at higher lives due to sulphidation attack from car emissions.
Safety wasn't a problem for chrysler in the 1960s because cars didn't need seatbelts, you could put chrome spikes on steering wheels etc. It absolutely would be a problem today.
I didn't mention fuel efficiency and emissions (both of those would suck too), and Chrysler found that their turbine sucked on both of these metrics for the 1960s.
Advanced-Injury-7186@reddit (OP)
"Almost everything in an automotive piston engine is good for life these days."
Umm... today's cars still need oil changes and spark replacements
discombobulated38x@reddit
Indeed.
And the occasional timing belt/chain.
You'll notice I used the word "almost", not "everything".
The vast majority of cars don't need valves, piston rings, bearings, oil pumps, anything made of latex rubber, carburettor nozzles, tappets, cams within their lifetime. They used to, multiple times for some engines.
Advanced-Injury-7186@reddit (OP)
Today's automotive engines reached their reliability thanks to great improvements in quality control. The same would apply to turbine engines. The difference is turbines have fewer parts that could fail, so they would be more reliable.
discombobulated38x@reddit
Yep. Gas turbines have been improving too, they're still less reliable.
What? A 500shp gas turbine has approaching 10x as many parts as a 500shp piston engine.
Advanced-Injury-7186@reddit (OP)
"What? A 500shp gas turbine has approaching 10x as many parts as a 500shp piston engine."
According to Chrysler, a gas turbine had 1/5th as many moving parts as a comparable piston engine. And this was back in 1979 when piston engines didn't have such complexities as fuel injection and had 2 valves per cylinder with fixed timing
discombobulated38x@reddit
You're saying that like gas turbines haven't gotten orders of magnitude more complex in over half a century of development.
Relevant-Machine4651@reddit
Chrysler developed the M1 Abrams tank with turbine engine.
discombobulated38x@reddit
Yes, that's a military gas turbine with a 1400 hour service interval, that's maye 50,000 miles between overhauls.
I don't think that has much relevance to mass consumer automotive engineering.
Relevant-Machine4651@reddit
No, of course not. The engine is the size of a sedan and much more expensive. Just a footnote that Chrysler eventually made a successful ground vehicle using a turbine engine. That tank is still awesome and it started development 53 years ago.
BankBackground2496@reddit
Ford put some thinking into making a nuclear car. https://en.m.wikipedia.org/wiki/Ford_Nucleon
teddie_moto@reddit
Other issues with turbines in cars:
slower throttle response
very narrow band of good efficiency
much more complex/gentle starting process (partly because of the above)
The CX-75 prototype was powered by micro-gas turbines in a series hybrid configuration which largely gets around these because the turbines will always run at an efficient point to charge the batteries.
But ultimately Jaguar decided to go with a conventional (albeit very highly boosted) piston engine. Before then scrapping the project due to lack of pre-orders/interest.
Some purported reasons for the switch:
much more difficult to make gas turbines that small than expected
reliability
fires
mig82au@reddit
Importantly, the good efficiency being only around maximum power, i.e. useless for a car that spends the vast majority of its life at low power.
Advanced-Injury-7186@reddit (OP)
Piston engines also see efficiency drop off at part load. Turbine designers managed to get around that problem with variable nozzles.
mig82au@reddit
Piston engine efficiency peaks well below max power, in a regime of low RPM but high pressure. That's not the same as gas turbines, which keep getting more efficient with increasing power, until they melt or burst from centripetal force. Gas turbines use a shit ton of fuel just to idle, unlike piston engines.
nalc@reddit
The standard helicopter architecture is an overrunning clutch so that the rotor can move faster than the power turbine, and it's fairly common to also have a rotor brake that is capable of holding the rotor stopped (so that the power turbine is stopped as well) for some amount of time. A typical use case is for shipboard operations where you don't want the rotor spinning around slowly enough that it's getting weird gust loads that are difficult to control because the electrics and hydraulics that power the flight control system aren't fully online at such a low rotor speed.
In those you can do a cold start with the brake engaged and bring the N1 turbine up to idle with the power turbine braked, then once you're ready to go you can release the brake and it will spin up quicker and get you through the danger zone. There may be some limits set by the engine manufacturer on how long it can be in this state though because you're not necessarily getting oil circulation through the power turbine bearings.
Happy_cactus@reddit
What do you mean by the rotor is moving faster than the power turbine?
nalc@reddit
The rotor is connected to the power turbine via a gearbox and there's an overrunning clutch that lets the rotor move faster than the power turbine (faster in relative percent terms, it's usually somewhere between a 50:1 to 100:1 ratio gearbox)
It's like a freewheel on your bicycle that lets the wheel spin even when you stop pedaling, which is basically what an autorotation is (when your engine power cuts out and you use the inertia and aerodynamic forces of the rotor to keep it spinning and land safely)
discombobulated38x@reddit
Interesting to know, thank you!
mcnabb100@reddit
It’s certainly possible, the Abrams tank is turbine driven. Jay Leno also has a turbine driven Cadillac concept car.
Certainly not practical for typical commuting though!
NotStoll@reddit
I think Chrysler made a turbine powered car in the 60s.
Advanced-Injury-7186@reddit (OP)
And they kept trying until 1979
quietflyr@reddit
Small gas turbines have terrible fuel efficiency, and this is a physics limitation, not a design issue. This is a big reason why there aren't many vehicles powered by turbines.
-burnr-@reddit
Douglas A-1 Sky Raider has a piston engine, just like the B-17
dr_b_chungus@reddit
In addition to what other commenters have said, the b-17 mounted its payload internally whereas the Skyhawk has external pylon mounts as well.
Interesting_Day2277@reddit
Lot of smaller things adding up, much greater engine power, better tyres/landing gear construction and yes much great power to weight.
Bluishdoor76@reddit
That and that's just how much more powerful that single turbojet engine was compared to the B-17s engines. The J-52 P-8A could produce over 8000 lb of thrust or the equivalent to 2000-3000 horsepower. This is half to 3/4 the total horse power produced by all 4 of the B-17s engines.
quietflyr@reddit
To be fair, the B-17's bomb load wasn't even particularly impressive in WWII. Contemporaries like the Lancaster, Halifax, and even B-24 carried significantly larger bomb loads.
Maleficent_Beyond_95@reddit
The B-17 didn't gain its reputation by carrying the bombs... It was known for getting the absolute SHIT beat out of it and still carrying the crew home.
Raid-Z3r0@reddit
They did not call that thing flying fortress for nothing. Here is an example
MXG_NinjaWaffle@reddit
My favorite part of this story is that a heroic Lt. Bragg piloted it and we could’ve renamed the fort in NC after him and not some random guy.
WetRocksManatee@reddit
The Army is going to name one of their installations after a bomber pilot, even if the pilot was part of the Army then.
Maleficent_Beyond_95@reddit
I have seen a picture of one with most of the vertical stab, a big chunk of the nose, and a fuselage you could see daylight through, that came in on three engines, and lost one more on final. The other two were getting overheated and might have made another few miles or so.
LordofSpheres@reddit
It doesn't. The heaviest payload capacity possible for the A-4 is 8500lbs and the heaviest payload I've seen in the manuals was 6,000 lbs. The B-17G could carry 12,800 internally.
12kVStr8tothenips@reddit
Yeah but the range is 3x on the B-17.
ace_maker@reddit
The sky raider has the same max payload weight as a b17
Merker6@reddit
And nearly joined the fleet during WWII. Pretty insane to consider. Then you had the B-36 only a few years after that
doubletaxed88@reddit
The P-47 could carry more than a B-17
LordofSpheres@reddit
No it fucking couldn't. The P-47 could carry a maximum payload of 2500lbs of bombs - the B-17's longest-ranged missions flew with 4,000 lbs of bombs, and the B-17G, the most produced model, could carry 12,800lbs of bombs internally. Where in the world did you hear that a P-47 was somehow capable of more than a B-17?
Advanced-Injury-7186@reddit (OP)
https://www.worldwariiaviation.org/aircraft/republic-p47-thunderbolt
Not according to this
"When fully armed, a P-47 Thunderbolt could deliver about half the payload of a B-17 Flying Fortress"
CuriousQuerent@reddit
I think the natural first reaction of anyone walking down a line of fighter jets for the first time is "wow they're big". The instinct is to assume they aren't because they only hold one or two people and are usually seen from further afield, but they're absolutely massive. They're also very dense, relatively speaking. Not much dead space, compensated for by a buttload of power and high TWR.
arborck@reddit
If I'm not mistaken, the Tomcat was about 3ft longer than the B-25
lawyerslawyer@reddit
https://www.militaryfactory.com/aircraft/compare-aircraft-results.php?form=form&aircraft1=63&aircraft2=81&Submit=COMPARE
Huh
Sound_Indifference@reddit
Holy shit 9 feet longer
Bluishdoor76@reddit
I mean, have you ever looked at an SU-27 or F-15 size in comparison to a B-17? The Flanker is bigger than a B-17, and the F-15 is about equal in length and chunkier than a B-17. So yeah, it's not at all surprising. It's like when you compare a modern cruise liner to the Tintanic, yeah, the Titanic was impressive during its time. But it's tiny in comparison to modern cruise liners, which are just floating city blocks. And let's not forget that even our current largest fighter jets look tiny when next to modern airliners and cargo planes and are also faster than the fastest bombers of the 40s to the 60s. Technology advancements are a thing of beauty.
on3day@reddit
Well.. if you ignore air resistance. And airflow within the engines
Bluishdoor76@reddit
well yes thats a given.... a GE90 engine is about half the entire size of the F-22, a single GE90 engine weighs about 18k lbs which is just under half the weight of an empty F-22
CerealSpiller22@reddit
To continue with the comparisons, the 747-400F, certified in 1989, has a payload of 274,000 lbs (MTOW over 900,000 lbs) and mach .92 airspeed limit. Talk about a strategic bomber in the WWII timeframe, cruising at 45K ft.
draftstone@reddit
This is one thing most people don't realize, fighter jets are big! People see them as single seater plane so they think they would fit in their driveway, but a plane like the F-15 is bigger than most people home! (Roughly 40 feet of wingspan and 60 feet long).
joesnopes@reddit
Reading the F-35 specs I was pulled up by the max takeoff weight - about 70,000lbs. The 70-seat, four-engined DC-4 (C-54) I flew in an earlier life grossed out the same - 73,000lbs.
1rustyoldman@reddit
Technology improved. Things got better.
MrScrith@reddit
The scary part? it carries more fuel (18,498lb) than the gross weight of the P38-Lightning (17,500lb)
Gilmere@reddit
Yep, and not just today's fighter / attack aircraft. The A-6E carried 18,000 lbs (24 bombs in total I think). Long ago, I watched one take off and drop ALL of its sticks at the end of the runway when an engine failed. Fortunately it was water at the end of the runway when it happened. Multiple skips as well.
BiggyShake@reddit
Does anyone have a photo of a B-17 with external bomb racks? I've never seen one before.
Relevant-Machine4651@reddit
No doubt, the engine is about the size of a sedan by itself and absurdly loud.
suhki_mahdiq@reddit
Also yesterday’s fighter planes, this has been true since fighters of the Vietnam war era, if not before.
Advanced-Injury-7186@reddit (OP)
And considering these planes are more often dropping bombs than doing dogfights, one wonders why we call them fighters at all.
34786t234890@reddit
You left out a couple of words. They're "air dominance fighters". They're not primarily designed for dogfights, they're designed to deny the use of airspace to to enemies.
BrewCityChaserV2@reddit
Yes, that is how the progression of technology usually works.