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The current setting i'm working on plays in an alternate timeline to our own in the late 1920's, with one of the key differences being that the helicopter had already been invented in the late 1880's through a number of convenient (basically hand-waved) breakthroughs in technology, essentially predating the first, recognized, motorized airplane flights of our world by nearly two decades. Even though calling these first helicopters "rudimentary" would be a compliment, they still were able to hover and fly very short distances, bouncing over the surface of the earth like the first motorized flight-attempts of our own world, and would grow to resemble rotorcraft like the Flettner Fl 282 in the coming decades.

My question would be, if these helicopters had already existed decades before the invention of the fixed-wing aircraft, would they still have been invented?

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    $\begingroup$ Helicopters are slow and lift capacity and flight range is inferior to fixed wing aircraft. The VTOL/ hovering ability of helicopters are really what makes them useful. $\endgroup$
    – Gillgamesh
    Jul 26, 2023 at 18:16
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    $\begingroup$ Helicopters are grossly inefficient compared to fixed-wing aircraft. They use a lot more fuel, they are slow, their carrying capacity is small, and they are very much less safe. Their ability to hover and to take off and land vertically makes them useful in a handful of niche applications. In the vast majority of applications, fixed-wing aircraft are far superior. $\endgroup$
    – AlexP
    Jul 26, 2023 at 18:32
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    $\begingroup$ And loud. You'll go deaf if you fly one often without ear protection. Very unpleasant. $\endgroup$
    – Nelson
    Jul 27, 2023 at 2:48
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    $\begingroup$ Helicopters were (arguably) invented before airplanes. $\endgroup$
    – bracco23
    Jul 27, 2023 at 13:18
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    $\begingroup$ @bracco23 That's a facetious argument. Go back far enough and history and you can find a drawing or description of pretty much anything in the modern era. An idea is not an invention. $\endgroup$
    – Ian Kemp
    Jul 28, 2023 at 7:16

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Fixed-wing aircraft would be invented by the 50s at the latest, likely in the 30s

The other answers have covered the ways in which an airplane is superior to a helicopter. But we only know this with hindsight, having invented both.

We must ask ourselves: what would encourage the aviation industry to abandon the local maximum (helicopter) in favor of seeking a global maximum if they didn't know for sure that there was a better option out there?

The answer is: missiles.

Amateur historians of war talk a lot about the tank rewriting the rules of warfare in WWII, but in the sky and the seas, the rules were changed again by the rapid developments of rocketry. Compared to cannons, a missile has far greater range and destructive potential. Post-war air and naval development revolved entirely around leveraging or defending from this new weapon.

A helicopter-focused airforce would find itself blown out of the sky by even unguided WWI era rockets, never mind guided missiles. The ability to hover, while operationally useful, would be a death sentence on the battlefield. Combat between rocket-armed copters would be fast and brutal, encouraging engineers to develop maneuverable craft able to bring rockets to bear against enemy air power, while being safe themselves.

Your first planes would be rocket interceptors

Your alternate timeline branches off too late to prevent the invention of kites and gliders. So it would be a form factor known to your engineers. OTL, liquid-fuel rocket planes were conceptualized as early as 1902, and developed primarily by the Axis powers during WWII. They were essentially a glider with a big rocket attached: the pilot would blitz through enemy formations on one or two attack runs, moving too fast to react to, and then glide home when the fuel ran out.

In our timeline they remained marginal due to their drawbacks compared to conventional airplanes (due to high rate of fuel consumption, the Komet's range was 80km and the Ohka's was half that) and were made obsolete by the invention of the jet engine.

But facing helicopter forces (the Flettner had a measly 170km range compared to the 820km range of a MiG-3 or 2,100 km range of a P-38), rocket interceptors would be much more effective, and their speed would make them untouchable. Even armed with cannons, they could close distance too quickly for a helicopter air wing to react, blast them at close range, and retreat before they could be retaliated against (although it's hard to say whether anything would survive the attack to strike back). The retreating rocket planes would simply outrace or evade any fire coming their way (the Komet's maximum velocity was in excess of 1000km/h, carrying it out of a rocket's practical range in under 60 seconds).

Of course, engineers would quickly follow the same logic as in our timeline, and develop jets as a far better engine type to put on these new "powered gliders", leading to a Cold War period that looks very similar to ours, with jet aircraft as the primary combat type.

Silly Wunderwaffle opportunity: Airships and parasite craft

Since the rocket planes would still have short range, and be untested technology besides, your story's armed forces might be tempted to combine them with something more familiar to them. OTL, all major powers experimented with parasite aircraft during the war, putting small planes on big planes to extend their range. The Japanese even put rocket planes on conventional planes. So there is an opportunity for you to field large rotary aircraft with a few parasite fighters slung under the body (the V-12 could have taken off with the weight of up to 10 fully loaded Komets, and even late 50s designs like the Mil-6 would have been able to carry two or three).

This "helicarrier" would act much like aircraft carriers do in naval engagements, launching its air wing in an over-the-horizon strike on an enemy formation while remaining at a safe distance from retaliation. If the helicopter carried sufficient fuel, it would even be possible to refuel the interceptors for multiple sorties.

Since helicopters are slow and have relatively low flight ceilings, another type of aircraft becomes viable (for countries with large helium reserves): the venerable airship. OTL, they were vulnerable to patrolling fighters, but even 1917 airship designs could fly at 2x the altitude of the 1942 Flettner. In addition to taking over the high-altitude bomber role normally done by strategic bombers, airships could also be used as a carrier platform for these parasite rocket planes.

However, as in OTL, these would merely be a stopgap measure until it became clear that the exceptional operational range of jet planes renders the parasite concept unnecessary.

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    $\begingroup$ This is exactly the kind of answer i was looking for. Something focused about if or how the airplane would still existed when faced with the existing monopoly that helicopters already had in that setting. thank you! $\endgroup$
    – NimRad
    Jul 27, 2023 at 15:11
  • $\begingroup$ Good answer, @SPavel. This is an example of a frame challenge, defined simply, "the premise of your idea doesn't work because of X, but it would work if you think about Y." $\endgroup$
    – JBH
    Jul 27, 2023 at 15:29
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    $\begingroup$ I'm not sure I would consider it a frame challenge - the question is "would planes be invented" and the answer is "yes, eventually." $\endgroup$
    – SPavel
    Jul 27, 2023 at 15:44
  • $\begingroup$ Actually, I remember (but can't find) an article on how the USAF staged a series of exercises pitting airplanes against helicopters, with the conclusion of "an airplane should never try to get involved in a fight against an helicopter, except launching missiles from far, far away". The low profile and high-maneveurability at low speeds of the helicopter made a dogfight between helicopters and airplanes a very bad proposition for the latter. $\endgroup$
    – Rekesoft
    Jul 28, 2023 at 7:48
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    $\begingroup$ @Rekesoft But I assume the helicopters had missiles in these tests right? That's not a fair comparison if the helicopters are allowed to use their missiles but the airplanes are not allowed to use theirs. $\endgroup$
    – DKNguyen
    Jul 28, 2023 at 18:56
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Absolutely. Helicopters are one of the least efficient modes of transport. Wikipedia has a good run-down on the power efficiencies of various modes of transport, and a Stack Exchange (Aviation) answer sums it up very nicely. We're still talking about using blimps for air transport because they're more energy efficient, and that consideration never goes away.

Also, helicopters can't move as fast as airplanes. The limiter here is the forward spinning rotor speed. If you add the linear velocity of the helicopter to the velocity of the main rotor as it's rotating forward, you really, really don't want to break the speed of sound. This limits the top speed of a helicopter to around 400mph, whereas the cruising speed of an airliner is around 575mph.

Plus, there's a size issue. If you remove its wings, you can fit the largest ever built helicopter inside the largest ever built airplane, and carry it for more than four times the helicopter's maximum range.

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    $\begingroup$ In fact, if I understand the mechanics correctly, there comes a rotor velocity where cavitation is caused and the helicopter drops to the ground like a lead brick. $\endgroup$
    – JBH
    Jul 26, 2023 at 22:44
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    $\begingroup$ @JBH: To add to that - when a helicopter falters, it does drop - when a plane fails, it can usually glide (Barring a stall). Or as one person I recall said on Twitter (I don't have the reference on hand) - "A Plane wants to fly; a Helicopter wants to crash.". $\endgroup$ Jul 26, 2023 at 22:51
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    $\begingroup$ @AlexanderThe1st, an airplane tricks the air into letting it fly. A helicopter beats the air into submission. $\endgroup$
    – Mark
    Jul 27, 2023 at 2:50
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    $\begingroup$ (helicopter crash landings are often survivable thanks to a very scary trick called autorotation) $\endgroup$ Jul 27, 2023 at 9:17
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    $\begingroup$ Funny thing -- Helicopters actually have a better (fatal) accident rate than general aviation (.63 vs .94 per 100k hrs). They attribute this to the lower altitudes and speeds. However, 25% of helicopter accidents are due to mechanical failure, compared to around 8% for airplanes. $\endgroup$ Jul 27, 2023 at 15:34
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Have a look at the autogyro. This was invented in 1923. It is not a helicopter: the rotor can turn but it is not powered. This gives it a lower stall speed than a fixed wing. It cannot hover in still air, but it would stay motionless in a light wind. It behaves like a very light conventional aircraft with a short take-off and landing.

Autogyros did not stop the development of regular aircraft. As aircraft engines got more powerful, and people used maintained runways rather than handy fields, the low stall speed was no longer the safety factor it once was. A fast autogyro would have increased air resistance from the forward travelling rotor arm. There were some applications such as submarine spotting, where the autogyro's slow speed and ability to stay in the air for long times were just what was wanted. They look fun, too. But they did not compete with fixed-wing aircraft.

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  • $\begingroup$ what if the evolution was heli/quadcopters morphing into VTOL planes which can tilt rotors for faster flight. Is it possible long runways & large airports never became common? $\endgroup$ Jul 27, 2023 at 14:56
  • $\begingroup$ Possibly the closest we came was the Fairey Rotodyne in the 1950's. This was a helicopter with a jet engine on the tip of each rotor. The PanAm building in NY had a landing pad big enough for these on the roof. $\endgroup$ Jul 27, 2023 at 17:59
  • $\begingroup$ @BeniCherniavsky-Paskin I imagine cost-cutting would come into play rather quickly and someone would quickly cost optimize away the tilt rotors and turn it into a normal airplane. Remember, not all fixed wing airplanes need long runways or large airports. $\endgroup$
    – DKNguyen
    Jul 28, 2023 at 18:59
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Helicopters are very maintenance intensive. They need an "A" check every 125 hours of flight and it is a very long procedure. Many helicopters also require various service actions every 25 hours of flight. In comparison, fixed-wing aircraft can go up to 600 hours before needing an "A" check and inspection usually takes less time.

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    $\begingroup$ The old joke defintion of Helicopter is "10,000 moving parts, flying in loose formation." $\endgroup$
    – T.E.D.
    Jul 27, 2023 at 14:52
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Airplane case 1: Crossing an ocean

Really fancy military helicopters today have a max range around 1200mi. Most helicopters have vastly smaller ranges (250-400mi). Airliners can cross the Pacific Ocean or Asia non-stop.

Airplane case 2: Crossing big mountains

Modern helicopters have a max altitude around 25,000ft. This is not sufficient for parts of the Himalayas, and may be uncomfortably close for lower mountains. Airliners cruise around 40,000ft. Something like a Concorde or SR-71 could go even higher.

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Absolutely.

Both fixed- and rotary-wing aircraft work by the principle of lift, and it's far simpler - both in terms of conception and construction - to build a fixed-wing aircraft than a rotary-wing one. This is because the simplest functional fixed-wing aircraft doesn't even need a propulsion system other than the pilot:

https://upload.wikimedia.org/wikipedia/commons/3/3e/Lilienthal_in_flight.jpg

This is not true of rotary-wing aircraft; they require their wings to spin at a relatively high speed to generate enough lift to get the aircraft off the ground, and a pilot isn't capable of providing enough power, consistently enough, to accomplish this.

Essentially, basic physics ensures it's incredibly unlikely to invent rotary-wing aircraft without inventing fixed-wing ones first.

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