# Air routes around a “hurricane eye” on a tidally locked planet

On a tidally locked Earth-like planet a big part of long distance air routes would have to approach the hurricane eye and some may even benefit from it.

On Earth aircraft are able to save time and fuel by going along a jetstream. Realistically that mechanism should also work there. The question is what would be the limiting factor in using such routes? (Or maybe it's not worthy and going directly would be the best idea?)

How much speed should I realistically add to an aircraft because of flying along such jetstreams around "eye" on tidally locked planet and what would be the main limiting factor?

• speed of the wind?
• endurance of aircraft?
• endurance of passengers? (sickness bags)
• very hard to use reserve airports? (after all they are all built in area with permanently bad weather...)
• other?

EDIT: The planet circulates a dim red dwarf, one year is 9 days long.

• What's the period of orbit for your planet? To get an indication how strong air currents are and to what extent the coreolis effect works we need to know how fast your planet spins. – Hyfnae May 11 '17 at 11:36
• The main limiting factor would be a lack of an atmosphere. It has to be a super dim red dwarf (brown dwarf) - what is the dimmest star possible? If someone could research that ... I don't think this is possible. The atmosphere has to be long gone. The gamma radiation alone .. I think this isn't thought through 100%. – Raditz_35 May 11 '17 at 13:09
• I read up on this, but don't know enough to give a legit answer. Check out these posts on Aviation.SE: aviation.stackexchange.com/questions/19271/…, aviation.stackexchange.com/questions/27574/…. There is evidently a lot that goes into calculating these values. I would consider asking there about how V-speeds ($V_A$ and $V_B$ in particular) and turbulent airspeeds work, I can't explain them well enough to post an answer. – kingledion May 11 '17 at 13:41
• Since the rotational nature of hurricanes/typhoons is predicated on the Earth's rapid rotation, ISTM that a tidally locked planet cannot have such tightly spinning storms. – RonJohn May 16 '17 at 20:26
• worldbuilding.stackexchange.com/questions/4850/… Also, "one year is 9 days long" is unrealistic. From the referenced question, "Their orbital periods are short (15 - 40 days)". – RonJohn May 16 '17 at 20:36

## 2 Answers

A tidally locked planet does not rotate (well, it does, once every year), and its temperature gradients should be symmetrical facing its Sun.

So there isn't a mechanism to trigger a Earth-like hurricane; Coriolis force for example would be negligible, as the relevant distance would be that from near the axis of the Sun, not that of the planet.

There will be reasonably stable convection cells, though, with hot air being generated Sunward, cooling and precipitating beyond the terminator. All sorts of cyclical patterns are possible.

Pressure gradients would be caused by the underlying geography - perhaps a high mountain range with a deep chasm would cause a permanent localized outflow, and that could give rise to a "tornado alley" through vortex shedding.

Locally, one could surely use such currents for travel: rise high, ride the outgoing hot jetstream to go nightward, or the lower cold current going the other way. For all intents and purposes you get a reasonably predictable, continuous pattern of trade winds.

I could go into a physics based answer, but I'll chose a more down to Earth approach.

The maximum airspeed of a 747 is somewhere around Mach 0.92 or 1,100km/hr (705 miles per hour). Your cruise speed is around 920km/hr (570 mph) (https://en.wikipedia.org/wiki/Boeing_747).

Your category five cyclone comes in at usually just over 251 km/hr (74 miles per hour) (https://en.wikipedia.org/wiki/Tropical_cyclone_scales). Even multiplying this by four, it still just compares to the awesome speed of a 747. And even still, the maximum airspeed of a 747 is still only a few hundred km/hr above what the cruising speed is. The fortification to increase this would add weight, and reduce this further.

So for a practical answer, the max speed you could add is the maximum airspeed less your standard cruising speed, plus maybe 60mph for "science fiction" added fortifications increasing max airspeed. The reason why I haven't just added your cyclone speed to your cruising speed, is if you were to suddenly exit the jetstream, you could now be over speed (although this value is still coincidentally similar to the speed of a category 5, so little risk there). So the |maximum| is somewhere around 280km/hr with minimal fuel cost assuming a massive high power category 5 cyclone.

However, you not only decrease safety, but the speed increase in reality is negligible for the fuel costs you may save (vs the price spent fortifying an aircraft). It wouldn't be unthinkable that this could actually decrease your aircraft speed.

The only benifit could be fuel costs, but those are negated by safety.

If this is science fiction, you could work in gliders that run on minimal power, and focus on the fuel saving aspect rather than the speed benefit aspect. We already have conventional aircraft that travel unimaginably fast, with very little risk.

But

Enter the "AirPlane". It's not for travel, but it builds a thriving tourism industry! How?

Use the cyclone to whisk people around in a dome, like a theme park ride. You're tethered to the ground, and it's perfectly "safe", and people pay tons for the experience of riding the cyclone. Then re-invest the money in super sea cruisers and non-cyclone based aircraft.

• The maximum speed of an airplane is relative to the air it's flying in. An airplane doesn't have a maximum ground speed (while cruising). So you can just add the speed of the jet stream to the normal cruising speed of the airplane. – Swier May 17 '17 at 12:14
• May you explain, why you expect that the maximum gain would be tops 60mph, while on Atlantic Ocean routes, 100mph is common gain, while recent record for passenger jet included around additional 250mph? telegraph.co.uk/news/worldnews/northamerica/usa/11337617/… – Shadow1024 May 17 '17 at 13:20
• @Swier, how I meant to say it was, if the air moving relative to you is 250kmph faster, then your max airspeed increases by 250kmph. Then, you'd probably increase your cruising speed by 250kmph too, as you wouldn't stray too close to your maximum airspeed. But yeah, you're totally right! – Liam Daly May 17 '17 at 21:27
• And @Shadow1024 I meant 60mph for additional fortifications on top of the cruising speed difference, and then 250km/hr for the actual airspeed difference (Somewhere around 250km/hr with minimal fuel cost). Will edit to make this more clear. – Liam Daly May 17 '17 at 21:27
• Keep in mind that Mach 0.92 is the maximum operating dive speed of the 747 -- it's been flight tested past that, to Mach 0.99. (And the main thing you need to worry about fortifying against to go faster is flutter, not a lack of raw structural strength, so I'd expect the impact on weight from the upgrades to be far less than anticipated) – Shalvenay May 18 '17 at 16:11