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In the same theme as the topic I posted related to reestablishment of manufacturing competence, I think reestablishment of national defense competence is of equal importance. As strange as this concept may seem to some people, a credible national defense procurement and force structure strategy for a nation with limited defense funding does not automatically mean that their military forces are significantly less combat capable than a nation such as the United States of America, which has a functionally unlimited ability to spend money on its national defense. In many ways, unlimited budgets invite highly questionable procurement strategies because one functional knowledge domain which has consistently proven to be a weak point across virtually all military services is development and refinement of realistic Concept of Operations (CONOPS) for execution of fighting doctrine and usage of defense assets and personnel.
Bright shining examples of this include employment of autonomous systems and beyond visual range (BVR) guided missile intercepts of enemy bombers, fighters, and missiles, many decades before any technology was mostly ready to do this with a better that 50/50 chance of success when all training and operational procedures were followed. An entire fighting doctrine was built around the false belief that all air combat would be conducted at extended ranges and dogfighting was therefore irrelevant because it would never happen. At the start, appropriate training to employ this then-new fighting doctrine in a realistic manner was never provided. The problem was so acute that fighter weapon schools were established to teach employment of weapon systems to both air and ground crews. The first missiles using tube-based electronics were so delicate that normal handling caused operational issues, to the point that a pilot squeezing the trigger was not even guaranteed to see the missile leap off the launch rail, much less guide to the target, or the warhead detonate when passing within lethal distance. Initial work began in the 1940s, but until the solid state electronics and improved seekers of the 1980s, merely having a chance at a successful engagement was almost entirely a result of the pilot positioning his aircraft and only taking missile shots from a near-ideal positions for the missiles to execute the intercept.
Needless to say, all these significant limitations did not describe typical positional advantage achievable during mock fighting, much less actual combat. In real air combat, prior to the improved generation of weapons fielded in the 1980s, all BVR missile shots had less than a 10% chance of intercepting their targets. All military forces which employed BVR radar-guided missiles in air combat quickly learned that it was a very expensive luxury capability, truly fantastic when it worked, which was not very often, but in no way could it assure the outcome of air combat engagements. An aware target would generally defeat BVR missiles fired at them, whether from the ground or other aircraft. Hundreds of billions of dollars were devoted to this technology across dozens of nations using fighter jets and air defense systems using air search radars and radar-guided BVR missiles. It took 40 years of development work before the odds of a successful intercept were better than a coin toss, because the tech simply wasn't ready to meet conceptual expectations of how it would be used. Worse than that, far too little realistic training and testing was conducted to "know" that what the military wanted to achieve wasn't even possible, let alone practical, absent dramatic improvements to computers, sensors, and institutionalized knowledge from continuous training for development and refinement of air combat fighting doctrine. There was either a refusal to accept the limitations or a lack of general awareness amongst people in development and procurement regarding realistic expectations for the weapon systems they were purchasing, with the anticipation of acquiring all-weather BVR radar-guided air intercept capabilities. In other words, everyone was heavily relying upon something to "just work as intended" that was in no way ready to do so.
We see AI-enhanced combat drones showing the same technological readiness limitations today. They look brilliant for a few moments, then do something completely ridiculous that requires human operator intervention, else they crash or otherwise fail to complete their assigned missions. While everyone is breathlessly proclaiming that combat drones are "the future of all warfare", we should probably use all historical military experience with development and employment of BVR radar-guided missiles as a very pointed "warning order" related to how relevant and effectual these AI-enhanced combat drones truly would be, if any nation relies upon them to "deliver victory" in the short term. In another 10 to 20 years, they'll probably complete missions successfully more often than not. Everything I've seen indicates they're a very promising future technology, but in no way ready for combat against a peer level adversary. A shrewd national defense strategist with a budget to adhere to would continue earnest AI combat drone and weapons development while refraining from making any large purchase orders for technologies that simply are not ready for combat.
Any budget-limited nation which wants to retain competitive military capabilities must be very shrewd about when and where it chooses to purchase or outsource procurement of systems with substantial acquisition and sustainment costs. There's no faster way to handicap your military than to spend large sums of money on doctrinally-disconnected "new capabilities" that you cannot capitalize on. The US military has proven highly susceptible to this problem. Most people would view purchase of a BVR radar guided missile without airframes equipped with powerful air search radars as a pointless waste of money, for example. AI-enhanced combat drones using today's tech would be similarly encumbered.
We'll first highlight what I consider to be non-negotiable defense systems, then explain how the associated core combat capabilities represented by those systems, or functionally equivalent capabilities, can be acquired without bankrupting a modern industrialized nation.
I. Artillery
This can include anything from 105mm or 155mm gun-launched shells, to artillery rockets, to ballistic missiles, to long range loitering munitions like the Iranian Shahed-136 drones. Modern 155mm gun-based artillery systems have become so expensive to purchase and maintain that it might be cheaper to build drones to carry those 155mm artillery shell-sized warheads to their targets. The difference is in marginal cost per successful engagement, which will be higher with a drone or rocket-based artillery systems than it is with gun-based artillery systems. The support infrastructure for drones vs cannons is also different, not eliminated. Drones and rockets / missile artillery require physically larger and more expensive vehicles to deploy and maintain them.
M777 towed howitzers have an initial purchase price of about $5M. The cost to fire the unguided / unassisted shells is fairly low, at around $3K per shell. If your loitering munitions cost around $25K per weapon to mass produce, then you can procure around 200 munitions for the same cost as the howitzer itself. Howitzer crews don't materialize out of thin air, either, which means an entire training and logistics pipeline is required to continue to have trained artillery operators and serviceable guns. As of today, drones still require operators and maintainers. If the total number of required attacks is low and the chance of success is high, there will be some kind of inflection point where beyond a certain number of munitions fired off to attack the enemy, conventional artillery makes more economic sense than drones / loitering munitions or artillery rockets / guided missiles. At the same time, long range drones like Shahed can provide the range to conduct deep strikes that far more expensive missile-based artillery systems would otherwise be required to execute. Shaheds are much slower than missile-based systems, but the number of attack opportunities is much greater because per-unit cost is far lower than that of ballistic weapons.
II. Integrated Air Defense Systems
The core of any modern integrated air defense system is a networked system of surveillance / tracking / missile mid-course guidance radars. These long range / high power radars are inevitably expensive, but vital to air defense. If there is no awareness of threats posed by incoming enemy missiles and aircraft, then there is no possibility of intercepting them.
There are 4 categories of air defense interceptor missiles:
hypersonic / ballistic missile and nuclear warhead threats - THAAD / SM3
long range high capability radar guided interceptors - Patriot / SM6
medium range radar guided - ESSM / NASAMS
short range infrared guided - Sidewinder / IRIS / MICA derivatives
man portable air defense systems - Stinger / Starstreak / Mistral
There are 3 categories of air defense guns:
35-76mm autocannons (some of these now have data-linked self-guided shells as ammo options)
20-30mm caliber autocannons (close-in weapon systems used to put a "Wall of Lead" in front of missiles or drones)
12.7-15mm heavy machine guns (typically used to kill drones and helicopters)
It's unreasonable to expect most nations to have the resources to locally design and produce their own version of THAAD or Patriot. As sophisticated as medium range radar guided missiles have become, even those may be a bridge too far. If you cannot produce your own IR guided missiles and autocannons, then you need to fix that.
The inability to purchase the components to create active radar guided missiles does not mean BVR radar-directed intercepts are impossible to effect. A missile's mid-course guidance is still provided by its launching platform, which means greatly improved modern IR seekers can still be used for terminal guidance to targets without indigenous or even acquired miniaturized onboard missile radars and guidance computers. Against stealthy targets, IR seekers typically out-range onboard missile radars, often by a considerable margin. The radar and guidance computer technology items represent a disproportionate percentage of a BVR radar-guided missile's total cost. A drastically lower cost option is use of modern IR seekers, which are also nearly impossible to distract or confuse because they cannot as easily be "jammed", unlike radar-based systems.
III. Off-Road Mobile Armored Transport Vehicles
The ability to effectively transport soldiers, food, water, equipment, fuel, and weapon systems around the battlefield has been a military requirement since armies existed. While the means of transport have varied greatly over time, all modern armies use motorized vehicles. Parts of civil vehicles can be adapted to battlefield use, or at least benefit from a domestic automotive industry that nominally makes vehicles for civil on-road and off-road use. Significant procurement cost increases tend to be driven by bespoke vs off-the-shelf solutions where the technology item in question is not shared with any civil motorized vehicle.
Tank engines used to be then-common automotive engines with bespoke transmissions / gearboxes. When there was no difference at all between a tank engine and a semi truck engine, the cost of the engine development and procurement was nominal. It's not written in stone anywhere that a tank absolutely requires a bespoke engine design which is not shared with any other civil vehicle. Unsustainable weight increases created the requirement for specialized tank engines. Advanced armor materials and uncrewed turrets with autoloaders will help return armored vehicle weights to the realm of sanity, as will resisting the temptation to load up every armored vehicle with "some of everything". A tank was originally intended to provide direct fire support to infantry assaults using a large caliber highly mobile cannon. We've since added anti-tank missiles, surface-to-air missiles, anti-drone machine guns or light cannons, active protection systems, lasers, and an array of sensors that would make Cold War era fighter pilots jealous.
It's still possible to cap vehicle weights at 40t (the GVWR of a fully loaded semi-truck) by using single crew compartment tank designs (uncrewed turrets) with adequate 360 degree protection to assure crew survival while accepting vehicle losses from modern anti-tank weapons. Even if all those other systems are added to armored vehicles, increasing their weight and cost to impractical figures, losses to enemy anti-tank weapons remain inevitable. There is still no active protection system against anti-tank mines, for example. That doesn't mean we should attempt to add one to the tank, either. There's no point to "gold plating" a direct fire artillery piece which immediately becomes the target of choice for everyone else on the battlefield. Save the crew and sacrifice the vehicle. You're going to do that irrespective of how many additional expensive protection systems you burden the tank with. If losing a tank or other armored fighting vehicle was not a multi-million dollar loss involving a collection of difficult-to-replace systems-based capabilities, then your military can afford to "eat" the vehicle loss and make more replacement vehicles. If you still require those other weapons and sensors, then put them in separate specialist vehicles instead of attempting to transform every armored vehicle into the land-based equivalent of a tactical fighter jet.
Combined arms maneuver warfare provides complementary protection of disparate forces by mixing the capabilities of tanks, artillery, other armored fighting vehicles armed with autocannons and missiles, infantry, air defense systems, and aircraft to achieve outcomes not possible using any specific type of weapon system alone. As important as establishing air superiority is to successful combat operations, aircraft alone cannot take ground from the enemy and hold it. Coordination of movements and sharing of positional data is far more effective than trying to use singular assets to operate in a vacuum.
Armored off-road capable motorized vehicles is the one category with the widest possible array of affordable, practical, and survivable solutions. It's also not clear that one vehicle type provides any kind of insurmountable technological advantage over another type. There is such a thing as appropriateness to task, but that's as far as it goes.
IV. Air Forces and Air Assault Vehicles
There's a persistent yet false interpretation of what turbine engines actually permitted military aircraft to do. Achieving faster flight speeds is the colloquially stated reason for their development, and turbine powered aircraft typically fly faster than piston engine aircraft. It seems obvious, and is in fact used that way by most aircraft designers, but that explanation is wrong from an engineering perspective. Simply put, turbine engines offered aircraft designers greater payload-to-distance by reducing the engine mass to deliver a given amount of thrust. Delivering more power per unit of engine weight allowed aircraft designers to design aircraft to choose between faster flight speeds or pushing more payload through the air. For military purposes, this significant design advantage was most frequently used to make aircraft fly faster.
Unfortunately, the instant you demand that an aircraft to fly at high subsonic speeds or faster, you run into a basic flight physics challenge. There's a very steep rise in aerodynamic drag which dictates airframe shaping and minimum wing loading to minimize lift-induced drag at higher flight speeds. In turn, wing loading dictates minimum takeoff and landing speeds. There's a very narrow range of reasonably efficient cruise flight speeds for turbofan and turbojet engines, coupled with an extreme cost increase.
It would be fair to say that manufacturing and maintaining turboprop and turboshaft engines, which are the least expensive types of turbine aircraft engines, are at least ten times more costly than equivalently powerful piston engines. Turbofan and turbojet engines are significantly more costly to make and operate than equivalently powerful turboprop engines. If you're not flying at high subsonic speeds at altitudes above 20,000ft or so, then even high-bypass turbofan engines tend to be horrendously inefficient, relative to piston engines, for the power generated. Propellers are more efficient "wings" than the much smaller fan blade "wings" in a turbofan or turbojet engine, until you reach a certain speed at higher altitudes. You're not "free" to travel at higher speeds and altitudes, you're effectively limited to exclusively operating in that narrowly defined flight regime because any deviation severely affects range, speed, and acceleration performance.
A modern computer-controlled 550hp spark-ignited and liquid-cooled automotive piston engine will cost about $25,000. A 550hp PT-6A turboprop engine costs around $1M, so it's 40 times more expensive for the same power generated. The PT-6A is about half the weight of the automotive engine, but it's fuel burn rate is significantly greater than the piston engine, especially at lower altitudes. Inside of 4 hours of flight time using onboard fuel, and perhaps as little as 2 hours at lower altitudes, the turbine engine's apparent weight advantage over the piston engine is gone. It does not matter to flight physics at all whether an airframe must carry additional fuel weight or engine weight to remain airborne. However, a significant change in fuel burn rate will at least partially dictate cost per flight hour. At 33,000ft, the PT-6A is only generating roughly 1/3rd of its sea level power output because its compressor section operates on ambient atmospheric pressure and must be driven by hot gas expansion through the expansion section. An appropriately turbocharged and intercooled piston engine, on the other hand, can maintain 100% of sea level power output at altitudes up to 36,000ft, which was achieved during WWII.
Early avionics, sensors, and weapons were very large and heavy because their electronics were large and heavy. 2025 electronics have been miniaturized to the point that a smart phone has more than sufficient computing power to operate every system and sensor aboard combat aircraft. The precision of modern missiles almost entirely negates the requirement for a massive warhead to eliminate a target. Modern composite airframe materials are meaningfully lighter than Aluminum or steel for the same strength and stiffness provided. The net effect has been to dramatically reduce the mass of sensors and weapons required to find, fix, and eliminate a target, thus the airframe they're attached to. It would be fair to say that piston engine aircraft could carry most of the sensors and weapon systems in a practical manner, at greatly reduced cost relative to any turbine engine aircraft, while flying at the same speeds that are typical of "best maneuvering speeds" for fighter jets.
Whenever fighter jets slow down to turn well enough to evade incoming missiles, best maneuvering speeds range between 350 and 550mph, with most tactical fighter jets exhibiting best maneuvering characteristics between 400 and 500mph. Oddly enough, we developed piston engine aircraft that could cruise between 400 and 450mph, at the same altitudes where modern fighter jets typically operate at (25,000 to 35,000ft), during WWII. The significant increase in cruising speeds of fighter jets does not alter flight physics to enable them to turn better at high subsonic or supersonic speeds, nor "get away with" cruising at high subsonic speeds without burning fuel at a much faster rate. The closest approximation to how modern tactical fighter jets actually operate is by economically cruising at speeds functionally unattainable by piston engine fighters, only to revert back to WWII flight speeds during evasive maneuvers. Even if some fighter jets are technically or functionally capable of out-running a missile, in actual practice air intercept missiles are at least twice as fast as the fighter jets they're fired at. In simple terms, you're never out-running a rocket engine missile in either a turbine or piston engine fighter, but if you can maneuver well, then you can use their speed against them by turning inside of them with a correctly timed evasive maneuver.
If you no longer require enormous carrying capacity provided by more powerful but drastically more expensive and difficult to produce turbine engines, per unit of engine weight, and you'll always need to evade inbound missiles and occasionally dogfight with other fighter type aircraft at flight speeds functionally identical to WWII era piston engine aircraft, is there still an insurmountable advantage offered by turbine engine aircraft and higher flight speeds?
If your air force can affordably field multiple squadrons of piston engine aircraft with identical sensor and weapons capabilities as any other modern tactical fighter jet, can a military that exclusively operates far fewer numbers of turbine engine fighter jets ever win a war of attrition, or do they get to shoot down a handful of your far less costly piston engine fighters, and then still lose the war on the first day after your remaining piston engine fighters bomb all of their much fancier fighter jets on the ground?
The F-15 is a fine flying and fighting machine, clearly much more capable than the P-51s that came before it, but it's also a $100M machine that cannot physically be in 100 different places at the same time. If we pit 100 P-51s against 1 F-15, then the P-51s still win every time, even if they loose 100% of their dogfights against F-15s. The F-15 still requires weapons, which means it still has to land somewhere to rearm. Let's assert that our lone F-15 can shoot down an entire squadron of P-51s. He'll be an "ace" for every bit of a half day, because the remaining 7 squadrons of P-51s will then proceed to strafe or bomb his F-15 on the ground. It no longer matters how individually capable the F-15 is. The problem it's run into is purely a numbers game, and the F-15 loses that fight every single time.
The US Air Force ran an entire series of war games under the moniker "Project J-CATCH" during the 1970s and 1980s using F-4s / F-15s / A-7s / A-10s to intercept helicopter gunships which could fly no faster than 200mph. Using BVR missile shots, the kill ratio in favor of the F-15s was 2.9:1. F-4s attempted to merge with and dogfight the gunships, using Sidewinders and Vulcan autocannons. At that point, both the F-4s and later the F-15s were killed as often or more often than they killed the gunships. WVR dogfights managed 0.7:1 to as high as 1:1 kill ratios in some instances. More maneuverable A-10s carrying minimal air-to-ground ordnance only achieved 1.3:1. The gunships were vulnerable to BVR missile shots because they initially had no radar warning receivers to let them know when they were being attacked. The most frequent problem reported by the fighter pilots who flew against the gunships was that gunships were difficult to find on radar and EO / IR sensors due to ground clutter. They were also much smaller than fighter jets, especially Huey Cobras, therefore difficult to visually acquire. The recommendation regarding combat tactics was that fighter jets should never attempt to dogfight a slower but more maneuverable opponents, because all the thrust and speed their engines could provide was insufficient to avoid 1:1 kill ratios, and to only engage them using BVR missiles when absolutely necessary. The conclusion reached was that fighter jets should use superior speed to avoid them altogether. This only works to a point. When those same opponents resolve to attack your airfield, then what?
MiG-19s are very maneuverable as fighter jets go, and able to turn inside a F-16 in a rate-fight, which is not easy to do. Several MiG-19s were lost attempting to shoot down A-1 Skyraiders during the Viet Nam War using IR guided missiles and cannon fire. The A-1s involved were laden with ordnance for use against ground targets, but had little difficulty turning inside the MiG-19s and hosing them down with 20mm cannon fire. The Vietnamese pilots attempted both high speed passes and maneuvering for positional advantage. Neither tactic proved effective against the A-1s when they were aware that they were being attacked. If A-1s were fabricated from composites to further reduce weight and increase maneuvering limits, and equipped with modern miniaturized air search radars, radar warning receivers, plus Sidewinder or Peregrine missiles, then attacking them using F-15s or F-16s or similar tactical fighter jets would most likely result in 1:1 kill/loss ratios at best. The problem, of course, is that a single F-15 or F-16 costs more than a squadron of A-1s, and a F-15 burns about as much fuel per hour as a squadron of A-1s.
During WWII, several nations made more piston engine fighters per month than the total number of modern fighter jets in existence. Fighter jets are awesome, and the little boy inside me still loves them to pieces, but my more rational adult brain tells me that they still cannot be in more places than we have flyable physical copies of them to fight with. Most of the time half of any given fighter jet squadron is down for maintenance. We don't have 100+ maintainers who work on 4-12 jets in a squadron because they work perfectly all of the time. You fly a fighter jet, something on it inevitably breaks, and then the rest of the day is spent diagnosing and fixing it. This is understood and accepted by people who have actually served in fighter squadrons in any capacity. If the jets are on the ground, then the maintainers are fixing whatever broke the last time they flew. There's also a major difference between flyable vs fully mission capable.
Many people remain completely convinced that speed alone confers an insurmountable technical advantage to turbojet / turbofan engine aircraft, despite all evidence to the contrary from actual and mock air combat engagements. The conclusion I reached is the one supported by my personal knowledge of flight physics from actually flying piston engine aircraft, my time spent supporting a carrier based squadron and air wing that flew combat missions over Afghanistan, and all available evidence collected over the decades on air combat tactics development to evaluate the limitations of jet powered tactical fighters flown against dissimilar adversaries. Speed matters when getting to a target area. Maneuverability then determines whether or not you come home alive. There are no free lunches in aeronautical engineering, so if you design an airframe and engine combination to deliver fantastic speed then you necessarily give up some maneuverability. Balance is what we should strive for. If you already know that all real world fighting will occur at flight speeds readily achievable using piston engines, then truck loads of money can be saved on engines and airframes, then redirected towards more capable sensors and weapons. The sensors do the finding and the weapons do the killing, not the aircraft itself, unless we're talking about kamikazes.
You can spend unlimited money on faster airframes and more powerful engines, but doing so doesn't change fundamental flight physics related to economical cruise flight speeds nor the ability to maneuver well enough to evade incoming missiles or gain positional advantage. You can't engage a turbine powered aircraft in a vertical fight using a piston powered aircraft but that's about it. In the real world you still fight using the strengths of your aircraft. If you pair modern lightweight / compact sensors and weapons with modern high-output automotive piston engines and composite materials for airframes, then you'll be able to manufacture and maintain several squadrons worth of aircraft for the same cost as a single tactical fighter jet. You do not need to bankrupt your nation's air forces with bespoke turbine power plants and functionally unusable speed due to fuel burn rates.
The individual piston engine aircraft are less capable than a singular turbofan powered aircraft, but collectively they deliver vastly more usable combat capability by virtue of at least some of them being fully mission capable and by sheer numbers allowing them to overwhelm enemy air defenses.
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Sounds like piston aircraft work for defense, turbines for attack from a distance (need the speed)?
Another area where piston aircraft should be viable is close air support / counter insurgency. Jet powered aircraft are used currently, but the speeds aren't above what you say piston engines can do.
Use what is abundant and build to last
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Terraformer,
The Proper Role of Turbine Powered Military Aviation Assets
There's a militarily justifiable argument for launching stealthy turbine powered cruise missiles to attack the enemy's network of integrated air defense system sensors and to destroy their tactical fighter jets on the ground. After that work is done, all further work should be accomplished using dramatically more cost-effective piston engine aircraft.
What makes a military aviation asset "modern"?
If we had a time machine and could send A-1 Skyraiders back to Viet Nam, re-equipped with the radar from the XQ-58A (a Super Hornet equivalent radar that only weighs 100lbs), an ample supply of AIM-9X and AIM-120D missiles, and tasked them with wiping out all American and North Vietnamese aircraft flying over Viet Nam, then within a month or two the only aircraft to be found in the skies over Viet Nam would be A-1s. I don't care if every American and Vietnamese pilot was a Top Gun valedictorian. There is only one possible result. Modern military aircraft aren't "modern" on the basis of engine type or cruising speeds. Their avionics, sensors, and weapons are what make them "modern" (and lethal). The speed is nice to have, but there are vanishingly few opportunities to exploit it to any significant degree.
Pure Speed vs Unsustainable Fuel Burn Rates, Cost Unimportant
During the actual Viet Nam War, not one American plane designed to achieve Mach 2 or faster, ever hit Mach 1.4. During 10 years of fighting, the highest achieved speed during a combat mission was Mach 1.3. The reason was quite simple. From Mach 0.95 to about Mach 3, the rise in aerodynamic drag is so sharp that your fuel burn rate increases so fast that your effective combat radius drops to less than 150 miles or so. At lower altitudes you can burn through all internal and external fuel in minutes. That's why every F-4 over Viet Nam was equipped with at least 2X 370 gallon wing tanks, and usually a centerline 600 gallon external tank as well.
Presume you came screaming in on the deck in your Phabulous Phantom, full 'burner, "flying under the radar", such as it were.
Let's do some fighter pilot math to illustrate how fast you'll run out of fuel:
While the example used here is America's Cold War Era "heavy fighter", the F-4E Phantom II, it's applicable to essentially every turbojet and turbofan engine powered fighter type aircraft ever made.
12,961lbs of internal fuel
5,032lbs for both 370 gallon wing tanks
4,080lbs for the 600 gallon centerline tank
You have 22,073lbs of total onboard fuel for your combat configured tactical fighter.
17,845lbf of thrust per GE J79 engine in full afterburner, so 35,690lbf from both engines
35,690lbf * 1.965lbs/lbf/hr (TSFC) = 70,130.85lbs of fuel burned per hour
70,130.85lbs / 60 minutes = 1,168.8475lbs of fuel burned per minute
22,073lbs / 1,168.8475lbs/min = 18.88 minutes
You're out of fuel in less than 20 minutes. You can meaningfully extend your time-of-flight by flying at 30,000ft vs sea level, but the additional flight time you get is less than you'd think. Flying at high altitudes in a non-stealthy aircraft also comes with significant tradeoffs in a combat zone.
A totally clean F-4 with no external anything (no fuel tanks, ordnance, or even pylons) could achieve 900mph at sea level. If you're carrying anything at all, especially those giant external fuel tanks, then you will never hit 900mph, but let's pretend to illustrate how utterly ridiculous its Mach 2.2 "top speed" truly is.
900mph = 15 miles per minute
15 miles per minute * 18.88 minutes = 283.2 miles
That's exactly how far your F-4 can travel at sea level in afterburner before it's completely out of fuel. You'd be lucky to achieve 200 miles if you had anything at all hung off the wings, especially those giant drag-inducing external fuel tanks. Regardless, you're going to have a very short flight if you stay in burner for very long.
Let's briefly pretend our Phantom was re-engined with very modern GE F414 engines, so 44,000lbf for both engines.
44,000lbf * 1.85lbs/lbf/hr (TSFC) = 81,400lbs of fuel burned per hour
81,400lbs / 60 minutes = 1,356.6667lbs of fuel burned per minute
22,073lbs / 1.356.6667 = 16.27 minutes
That means you're out of fuel even faster by using modern afterburning turbofan vs turbojet tactical fighter jet engines. Yes, you clearly get more thrust at all power settings and even low-bypass fighter jet turbofans burn a bit less fuel than turbojets, but at the end of the day making more thrust means burning more fuel, period. End of story. There never was any other story.
The Irrelevance of "Supercruise" to Air Combat
The F-22 has a meaningfully higher thrust-to-weight ratio than the F-4, so it can actually fly faster than Mach 1 without using afterburner, but that doesn't mean its fuel load lasts significantly longer when you try to "max out" flight speed at mil power or burner, because F-119s are still very thirsty engines which only generate a lot more thrust by burning a lot more fuel. TSFCs in afterburner for the F414 (a modern turbofan representing a J79-sized engine equivalent) are 1.85lbs/lbf/hr vs 1.965lbs/lbf/hr for "old smokey" (J79). Even without going into burner, J79 mil power TSFC was 0.81lbs/lbf/hr vs 0.84lbs/lbf/hr for the F414. That means fuel consumption to make more power is worse, not better. The primary benefit to the F414 is that you get as much mil power as a J79 produces in full burner, in an engine that weighs 2/3rds as much as the J79. At no throttle setting does a F414 actually burn less fuel than the J79, and the J79 was a gas guzzler.
If you try to fly just as fast as you can, then you still don't get much more air time, even if the F414 would allow the F-4 to "supercruise" above Mach 1 like the F-22. Older engines like the J79 also frequently had "burner time limits" of 15 minutes or so, but let's be completely honest with ourselves here, you're not going to fly much farther after 15 minutes in burner anyway. If you spend any significant time in burner or even at mil power, then you'd better have a tanker directly in front of you or a suitable landing spot picked out.
The Yankee Station Example: Closer to "The Action" than any Modern Forward Air Base
Yankee Station was located approximately 100 miles off the coast of Viet Nam, so 100 miles to "feet dry", and then another 100 miles back to the boat.
Do you plan on making it back to the boat after a mission that takes you 100+ miles inland?
If so, then you're going to be really stingy with the afterburner, and likely have second thoughts about moving the throttle up to the mil power setting after climb-out. You definitely won't want to "get low" unless forced to do so. You'll want to stay between 25,000 and 35,000ft whenever possible. Most of the time you're going to cruise around at 500mph in combat configuration, because that's what you must do to conserve enough gas to fight someone or evade missiles if you have to, and still make it back to Yankee Station. Best maneuvering speed in the F-4 is also around 500mph. By the time you're moving at Mach 1, an Iowa class battleship moving at 30 knots has a tighter turn radius than the F-4. F-4s moving at 500mph could turn inside SA-2 missiles fired at them. F-4s moving at Mach 1 couldn't turn inside of a ZIP code.
The Multi-Billion Dollar Question
Are we starting to understand why nobody ever went faster than Mach 1.3 during the entire Viet Nam War, despite the fact that we flew tens of thousands of sorties in Mach 2 capable tactical fighters like the F-4, F-8, F-105, and F-111?
Every time I hear someone tell me about how fast their fighter jet is, relative to someone else's fighter jet, my eyes roll harder than the A-4 with its rate limiter removed.
Even in "Fantasy Land", Speed Still Kills Life-Saving Evasive Maneuvering
If you were dropped into the cockpit of a combat jet so fuel efficient that you could economically fly faster than Mach 1, if you don't slow down in a hurry after someone launches a missile at you, you're probably going to D-I-E. You can pull hard enough to rip the wings off, but when you're flying much faster than 600mph (well below Mach 1), you still can't turn inside of an 80g capable heat seeker like the AIM-9X. This best maneuvering speed limit is dictated by both flight physics for a 9g capable combat jet and human physiology. Highly trained and conditioned humans can withstand 10g for very short periods of time, but not much more than that, and nearly all high time fighter pilots who routinely perform such maneuvers end up with severe spinal injuries later in life.
Max power output for a combat jet is therefore reserved for 3 events:
1. Short field takeoffs
2. Rapidly ascending to cruising altitude
3. Recovering energy (speed) following hard maneuvering
Throw a Nickel on the Grass
In fighter pilot training, they teach you to do the fuel math in your head, because if you can't then you're probably not making it home. Yes, modern fighter jets have fuel totalizers to do the math for you. If that nifty gadget ever breaks, then what? I trust my fuel flow rate meter and my ability to do math in my head. When the fuel totalizer gadget works, it's great. If not, I'm still not going to have my mother read my obituary because I can't do basic math. You can think of flight in a modern combat jet as "minutes of life remaining before you run out of fuel, crash, and die", because that is very close to the truth.
Parting Thoughts as to Why Speed Alone isn't a "Determining Factor"
Yes, I absolutely did have to spill that much ink to explain to a non-pilot why the impressive "paper speeds" of fighter jets aren't all that impressive to anyone who actually uses aircraft as weapons. You are not going to chase down an enemy bomber 500 miles away, which has 10X more fuel onboard than your fighter jet, simply because you're in a Mach 2.5 capable fighter jet, or any similar cockamamie nonsense. They're either coming to you, in which case you don't need to chase them down, or you're going to launch your own cruise missiles at their air base, because then you still don't need to chase them down. That is how real world air intercept and attack works. You send missiles after enemy aircraft, not fighter jets. The fighter jet is a mobile launch platform.
I think that horse is now well and truly "dead", although one can never be too sure.
Military Aircraft Applications for Modern Automotive Engines
Now let's talk about modern automotive piston engines, which are approximately twice as fuel efficient as a tactical fighter's turbojet or low-bypass turbofan engines across a much wider power output range, while still delivering enough power to "cruise" between 400 and 500mph at altitude, although 350mph is a better cruising speed for fuel economy, and quite similar to the actual cruising speed of a combat loaded A-10. For comparison, the V-22 Osprey tops out at 350mph and the A-1 Skyraider's top speed was 325mph.
Modern Big Block Automotive Engines as Military Aircraft Engines
Modern so-called "big block" pushrod V8 automotive engines with electronic fuel injection and electronic ignition can deliver 1,000hp, naturally aspirated. When equipped with a modern supercharger and intercooler located atop the lifter valley, they can continuously deliver 800hp. RPM kills piston engines, primarily because the pistons come apart. For extended duration piston life, 4,000fpm is about as fast as you want the piston to move an Aluminum piston. The most modern high performance heavy duty diesel truck pistons are high strength steel forgings, rather than Aluminum forgings, and do not have the same piston speed limitations. That said, for a spark-ignited big block, if you keep the RPM to about 4,500 or less, then the engine can run continuously, even using forged Aluminum pistons.
Big Block Definition
I define "big blocks" as V8s that can be configured to total displacement of over 500 cubic inches. Chrysler, Ford, and General Motors all made "big block" V8 engines. Ford and GM still offer updated versions of these block designs. Modern big blocks, whether factory-built or aftermarket, are substantially stronger than the blocks that rolled off the assembly lines in Detroit during America's "muscle car" era.
With a 4.5 inch bore and 4.5 inch stroke, you have a 572 cubic inch V8 engine, a so-called "square" (bore and stroke are the same) engine. That's a good configuration for fairly high-RPM operation. Over-square engines (bore larger than stroke) are better for higher-RPM operation, common in racing applications. Under-square engines (stroke longer than bore diameter), are better for lower-RPM operation, which is why nearly all diesels are under-square designs.
Hot Rod Magazine:
572-Inch Blown Big-Block Chevy Engine Makes 1,013 HP on the Dyno!
Notice from the dyno chart that the engine is making 1,000hp at 6,000rpm, and 800hp at 4,400rpm.
The engine in question has 8:1 compression and runs on 91 Octane motor gasoline using carbs, so no special AVGAS containing toxic Tetra-Ethyl-Lead is required. Removing TEL from the fuel greatly reduces spark plug fouling and doesn't plate-out on valve seats. Single vs dual plug ignition is acceptable. Larger bore engines like the Merlin engine, as well as the slightly newer air-cooled engines from Continental and Lycoming, use dual plugs in part because their bores are so large that the flame front would take longer to reach across the bore. This has not been an issue for American big block V8s.
The blower configuration used on the newer LS series engines, as found in the Cadillac V series and Corvette, can deliver more boost at lower temperatures, from far less blower displacement than the monster blower shown on the engine from the Hot Rod Magazine article. Harrop's TVS2650 blower can deliver up to 1,200hp on a big block. An EFI / EI motor could run 9:1 compression on 93 Octane motor gasoline, so the RPM of the engine could then be lowered to something very similar to the operating RPM range of the geared Continentals and Lycomings, which have even longer strokes. At that point, the big block is operating like a "real aircraft engine" (the air-cooled magneto-fired dinosaurs that Continental and Lycoming still produce).
Piston Tech, The Real Power Limiter
2618 is the Aluminum alloy of choice, which hasn't changed since it was first used for Merlin engine pistons by Rolls-Royce during WWII. The best steels for this application produce pistons that are very slightly lighter than 2618 for equal strength at room temperature, but much better strength than any Aluminum alloy at max operating temperature. Delivering enough splash lubrication to the bottom of the steel piston for adequate cooling is the only issue. Steel pistons require more cooling oil than Aluminum. Ceramic thermal barrier coatings on the piston crown help reflect heat back into the combustion chamber. This sort of tech simply didn't exist when the Merlin and Meteor engines were being developed by Rolls-Royce. For high-boost engines, thermal barrier coatings are piston savers. Modern motor oils that can completely remove Carbon deposits from piston ring lands have only existed for the past 10 years or so.
WWII Merlin / Meteor Engine Comparison
The 27 liter Rolls-Royce Meteor tank engine, effectively a Merlin without the supercharger, had a dry weight of 1,841lbs and a power output of made about 550-810hp between 2,600 and 2,800rpm. The 572 Big Block Chevy with an Iron block and cylinder heads, plus the supercharger and all accessories, weighs less than half as much as a Meteor, which was not equipped with the two-speed supercharger for high-altitude max effort power output. What is less obvious from looking at pictures is that even with a gearbox attached, the 572 Chevy is less than half the size of the Meteor and Merlin engines for roughly the same power output without boosting it to the moon the way they did the Merlin to produce 1,750 to 2,000hp. Merlin engines were famous for lifting heads and in war time use would see as little as 50 hours of operation before tear-down inspection and overhaul of select components. Modern automotive engines, even when used in aircraft applications, do not require nearly as much maintenance.
General Motors Engine Testing
General Motors is famous for running their LS series modern small block engines for over a month at wide-open throttle as part of their testing process. This manner of engine operation would cause any type-certificated air-cooled boxer-layout "real aircraft engine" from Continental or Lycoming to self-destruct, which is why max output for takeoff is limited to 5 minutes. You will typically find this admonishment in the POH (Pilot's Operating Handbook). A "throttle slam" (idle to max power as fast as you can jam the throttle into the firewall), is a better than average way to shear a crankshaft on a Continental or Lycoming. Maybe you can do it and get away with it, but if I'm flying the plane we're not doing that. This practice is accepted as "normal operation" for automotive V8 engines like the big block and small block V8 engines.
PSRU Reduction Gearbox Tech Improvements
Modern gearboxes can benefit from Austempered Ductile Iron gears which have a bit of "give" to them to help absorb the torque pulses from the engine. CAD-enhanced snouts to absorb thrust loads from the props or prop shafts. Torsional vibration evaluation and testing, which was a "black art" during WWII, is now something that can be readily evaluated almost entirely within a computer program. The design of the gearbox casings is also enhanced by CNC machining that can accurately machine Aluminum billets or castings. Substantial weight reduction relative to WWII era designs, for a given torque and rpm input range, is now possible.
Modern Piston Engine Military Aircraft Roles
All of these relatively new-ish but now exhaustively tested and proven technologies add up to the possibility of 1,000hp modified automotive engines for miniature versions of WWII style fighters / close air support / multi-engine bombers, enhanced with modern composite airframe materials, exceptionally powerful and capable miniaturized radars, and exceptionally precise guided munitions. WWII era aircraft ended the war with 2,000-ish horsepower engines because every bit of the tech from that era was less than half as capable as modern equivalents. Modern sensors and guided munitions are most certainly incomparably more advanced. We have self-guided 3 inch cannon shells now, which have shot down cruise missiles and drones at ranges of over 25 miles, for example. No such animal existed during WWII. CLGPs for artillery and tanks were 1970s tech, roughly speaking, but now quite practical / reliable / cost-effective. Palm-sized imaging sensors that can distinguish between two outwardly identical vehicles were the stuff of fantasy.
WWII bomber raids involved dozens of planes, dropping up to 10,000lbs worth of dumb bombs, because their accuracy was almost nonexistent and their sensors were barely adequate to find something resembling the target. A modernized 4 piston engine bomber equivalent would only need to launch 1 or 2 JSOW glide bombs or cruise missiles from a safe distance to inflict similar damage. It wouldn't carry 4 to 6 gunners, even if it was equipped with gun turrets for self-defense. Most likely, a tail turret with 2 to 4 rear-firing Peregrine missiles would be sufficient discourage pursuit.
For "gunship" missions we could replace the bombs or cruise missiles with a 50mm XM913 cannon turret or 40mm CTAS turret that the British use. The APFSDS rounds fired from the 40 or 50mm would go right through a MBT's turret, and possibly exit through the bottom of the vehicle. MBT turret top and hull bottom armor are very minimal. It'll stop 20mm most of the time. Armored vehicles engaged this way are very dead, for minimal cost. If that's too close for comfort, then it could also carry some Brimstone or Hellfire or Griffin missiles to plink at enemy vehicles from modest standoff ranges. Anduril is now making Brimstone / Hellfire weight and cost class miniature cruise missiles that can be fired at targets from 100+ miles away. That would put a low altitude piston engine "gunship" / "bomber" below the radar horizon, which means any effective defense against them would virtually require air assets. If the enemy has no IADS, then these are low-risk missions that don't require enormously expensive turbine powered gunships.
Even if this 4 engine bomber / gunship was "lost" in the fight, the weapons it's carrying are probably worth more than the plane itself. Aircrew are always expensive to lose, but a modern take on the WWII 4-engine strategic bomber won't risk losing 10 aircrew per aircraft. It will have at least 1 and possibly 2 crew members for most missions. We could have 1 human pilot and 9 Optimus robots if we decided that we absolutely had to replicate every last detail of the WWII model by assigning 10 aircrew per bomber, but even that doesn't make much sense these days.
When we can afford to put several squadrons worth of planes in the sky for every tactical fighter jet our enemies field, with better sensors and weapons, they're going to get massacred. Yes, we will lose some of these lower-capability planes in the process, and that's unfortunate. The difference will be that when all the shooting is over with, since we spent more of our money on better sensors and weapons instead of engines and heavier airframes, our planes will be the only planes still flying, because that's how attritional warfare works. We can afford to "eat" the losses, as painful as they may be. Our enemies won't be able to produce enough tactical fighter jets and well-trained pilots to offset their losses. We can "spam" tens of thousands of these things at our enemies, and eventually most of them won't even have human crew members aboard, only Optimus robots.
Suppose there was a surprise cruise and ballistic missile attack on one of our forward air bases. Do you want to lose 4 automotive engines and a bit of fiberglass, or an $85M F-35 that we only produce at the rate of 156 per year?
Think about how much money you're willing to risk by placing so much of it in so few tactical fighter jet "baskets". The US military currently has about 12,000 total aircraft across all types. Every nation involved in WWII typically made more aircraft of a single type than our entire aviation asset inventory. The US lost about 10,000 aircraft during the Viet Nam War, mostly rotary wing assets, but also a very significant number of tactical fighters. That would be an unrecoverable loss with today's turbine powered military aircraft costs. In WWII, we would call such losses "a bad quarter". Quantity still has a quality of its own.
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