Are GD jet engines better than props for small airframe fighters? Test results

[Joshua Happytree]

Test setup

• EAI enabled (current version) but AI is turned off. No other mods.
• All DLCs except GD and the game is patched to the current version
• Panama Props vs. Costa Rica Jets
• Both start with 2000 planes
• Jet design is about 10% cheaper than Prop so it's not an equal IC test
• Air region -- Western Canal Zone
• Ground crews enabled
• Both countries have maxed out radar (not to 1940 level but really maxed out)
• No air doctrines, MIOs, Chiefs of Airforce or High Command
• Both countries have a penalty of 56.3% due to planes lacking range

Plane designs

• Techs available by 1940 in general
• I aimed at a good range for fighting in Europe and matched both designs as close as possible.
• Improved Small Airframe
• 4 HMGs
• Jet
  • 2x Jet Engines, not Axial
  • Extra Fuel Tank
  • Self-Sealing Fuel Tank
  • Armor Plate
• Prop
  • 2x Engine IIIs
  • Drop Tank
  • Self-Sealing Fuel Tank
  • Armor Plate
• Extra Fuel Tank is used for Jets instead of Drop Tank because it has a meagre range otherwise. So Jets take a little hit in Air Defense due to this.

Plane Stats

• Both
  • Air Attack -- 54.0
  • Reliability -- 80%
• Jet
  • Air Defense -- 19.0
  • Agility -- 53.7
  • Speed -- 720.0 km/h
  • Range -- 682 km
  • IC -- 46.0
  • Fuel use -- 0.65
• Prop
  • Air Defense -- 21.0
  • Agility -- 51.0
  • Speed -- 585.0 km/h
  • Range -- 747 km
  • IC -- 50.0
  • Fuel use -- 0.37

Results

Conclusions

• Given equal numbers on both sides there's no difference between jets and props
• Jets are almost 10% cheaper than props but
  • To get them one has to make considerable investments
    • 12K CIC, that's more than the cost of 1.5 MIL.
    • A typical level 2 Air scientist (e.g. Turkey) needs 738 days to complete the project and each day will cost 4 Aluminum, 2 Steel and 12 Chromium.
  • 738 days to complete a special project means there's absolutely no point in switching MILs that already produce Props to Jets. Productivity hit will be enormous.
  • Jets eat twice as much fuel as props.
  • Due to severe jet range disadvantage props take much less of a hit in air defense stat if one needs to switch from ranges typical for combat in Europe to Barb or Pacific vastness.
• IMHO jets to be optimal need such a rare combination of a country situation and state of the war that they're hardly anything but toys to play around.

 

[Bailing_Out]

As Chuck Yeager said

They were not as good as thought when he did that in WWII. He shot it down while it was landing so not a dogfight and he never claimed it was.

 

[L-Histidine]

Pretty annoying that you pay 3 breakthroughs and years of special project time to get a chromium-hungry sidegrade to engine III, then 2 more breakthroughs and more years to get a sidegrade to engine IV, and then do that again for the actual prize (supersonic airframe)...

 

[Terracos]

IMHO the problem is, that the progression in the air doctrine does not follow the evolution of the air frames itself away from dogfights and high agility aircraft to hit and run tactics with high speed aircraft.

 

[Kanitatlan]

The original post also ignores the fact that the gold standard fighter is single engine and the reduced payload for Jet 1 is a further issue. The real problem is that it gives a bit of benefit but is hamstrung by reduced payload, reduced range and resource cost. Axial jets partially correct this but only to the point where they aren't as bad. As mentioned above, the real win is the supersonice airframe (which, rather disappointingly, won't take a non-jet engine which would have been funny)

 

[Demonthese]

Speed is probably undervalued as a stat in air combat. Mechanically what a speed advantage should probably do is provide a modest boost to casualties inflicted and give an increasing chance to not take a casualty to represent a fast plane being able to choose to leave a disadvantageous fight.

 

[maruta074]

Early jet aircraft struggled to achieve any performance advantage, and only the Germans were able to prove their worth in combat, and only in 1945. It can be said to be faithful to history.
However, it is well known that Hitler developed the bomber first, which delayed its development as a fighter. I understand the argument that jets should be better in a hypothetical world.

 

[KubiG37]

Jets weren't really developed to allow a higher powered aircraft, but because piston engines and propeller propulsion were both nearing their physical limitations (propellers first, pistons later) and top speed was far more important than agility and amount of guns (this is sadly grossly misrepresented by the current meta).

- Propeller is only effective at lower speeds, the faster the plane travels, the less efficient it is. More blades also reduce efficiency, increase weight, make balancing more difficult, and complex = expensive. You also can't just keep increasing its size and speed forever, because the tips of the blade start hitting the speed of sound barrier which creates immense drag, and even more engine HP wouldn't help there.
- Piston Engines were also nearing their peak HP performance and they just couldn't really go much higher without a disproportionate increase in weight/size.

Jet engine didn't have issue 2 at all, and issue 1 only mattered at much higher speed.

Supersonic airframe is an aerodynamic advancement (drag reduction), not a result of a better engine (more power). Ofc jets evolved as well, but their problems and limitations were of different nature than piston engines and propellers.

 

[Findell_HOI]

Jet Engine I's arent good enough

Jet Engine II's are good enough but the war is already going to be over by the time you get there unless you are playing an extended timeline thing.

 

[Joshua Happytree]

The original post also ignores the fact that the gold standard fighter is single engine

All I see is lower agility with single engine vs double, may be I miss something, would you care to explain?

 

[Vengirni]

Given how much time investment it takes to research jet engines, between gathering all those breakthrough points and the special project itself, it's more likely that jet engines are going to be ready closer to 1944, when they have to compete against engines IV. Any design that weighs between 26 and 30 can be carried by a single engine IV, while requiring two engines III or two basic jet engines. A single engine IV aircraft is going to be both cheaper than a dual-engined jet, and consume less fuel than a dual engine III.

 

[Stolen Rutters]

As mentioned above, the real win is the supersonice airframe (which, rather disappointingly, won't take a non-jet engine which would have been funny)

Don’t joke. A non jet engine is fundamentally incapable of supersonic flight. A supersonic airframe with a propeller engine would perform worse in basically every measure compared to the optimized propeller designs of the day, and you can’t achieve a supersonic max speed. Nobody (sane) would buy off on such a design. It would indeed be funny to watch, but the trade offs of such a vanity project would be harsh.

 

[Dimmie_Dumm]

Another thing which unfortunately gimps [early] jets yet more is that IRL despite requiring more fuel mass wise they could get away with using far more crude kerosene as compared to high-octane fuel for piston engines. Would be cool to have it somehow modelled, albeit I've got no idea what to propose myself. Maybe fuel usage just shouldn't jump that much - hey, we have light and heavy tanks running on same amount and the Earth hasn't yet collapsed.

 

[Kanitatlan]

Don’t joke. A non jet engine is fundamentally incapable of supersonic flight. A supersonic airframe with a propeller engine would perform worse in basically every measure compared to the optimized propeller designs of the day, and you can’t achieve a supersonic max speed. Nobody (sane) would buy off on such a design. It would indeed be funny to watch, but the trade offs of such a vanity project would be harsh.

I meant it would have been funny in being a typical HOI4 exploit.

 

[Stolen Rutters]

I meant it would have been funny in being a typical HOI4 exploit.

Haha, now I got it.
Thanks. Sometimes I’m just glad the game got it right in the abstraction.

 

[Tomnoddy]

I wonder if the OP is getting poor results on the jet due to lower air defence due to Extra Fuel Tanks instead of drop tanks ? Of course, range is very much an issue when switching to Jet power, unless you're on the defensive. Eg. France or UK trying to contest Benelux air zone during Fall Gelb with rushed jet fighters (I can confirm this messes with AI Germany pretty bad).

My other use case is heavy fighters with a token rocket rail module, to provide "Air Support" bonus. Their actual attack value is negligible, i just don't want them taking high losses. As medium airframes, they get more air defense, also as mediums , they have sufficient range despite the jets. And I'm pretty sure that bombers/CAS take significantly lower losses from enemy fighters, when they have a higher top speed than the thing trying to intercept them.

 

[Joshua Happytree]

I meant it would have been funny in being a typical HOI4 exploit.

And for the Mothership Special Project

 

[Joshua Happytree]

I wonder if the OP is getting poor results on the jet due to lower air defence due to Extra Fuel Tanks instead of drop tanks

1. I did the damage math first so I expected them to be poor. I did the test afterwards only because I couldn't believe my eyes that the current formula really dilutes speed advantage so much. This jet design is 23% faster than prop which "feels" like a lot. But numerator where all "attack" advantage is placed is multiplied by 0.01 whereas denominator gets defense in full.
2. I don't critisise, I'm happy and will adapt to whatever formula PDX will provide. I don't care what particular icons I should use in the plane designer. And I'm rather glad that at least the jet engine special project has not been made into a magic wand that kills outright all and every plane not using it.