As extreme heat bakes the West, emergency helicopters struggle to fly | Hacker News Reader

As extreme heat bakes the West, emergency helicopters struggle to fly

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35 pointscainxinth25 comments

Heat has two problems for helicopters and airplanes that combined cause much reduced performance.

Simplified: Hot air is less dense meaning we get less lift at the same power/speed. And hot air reduces engine performance, making it harder to get enough power.

Helicopters can land at airports with much higher weight (or less power) than the limits for hovering and vertical takeoff. Because forward speed when taking off from a runway creates additional lift.

Emergency helicopters, like commercial transport, will also consider the risks of engine failure. You don't want to put the helicopter in a position where engine failure is unrecoverable, it's too high risk. Just like (commercial) airplanes don't take off from runways too short to safely handle an engine failure.

Thanks for explaining all this and saving an article click!

I seem to recall Phoenix closing Sky Harbor when the temperature went above (IIRC) 117 F. Fixed-wing planes generate less lift, too. (Or was that because the asphalt runways were softening? I think it was lift, but I'm not 100% sure.)

Some airplanes just aren't certified for high temps too.

There's no certification for heat per se; it's more that there's just a point where the aircraft can't take off safely from a given runway. Increased air temperature means increased takeoff distances for a given weight.

These are set by the manufacturer, and can be revisited as appropriate.

Not a certification limit, but you need valid performance data to be allowed to take off. So if the data is only provided up to 50 C / 122 F, then you can't take off legally at 128 F.

Sky Harbor hit 118F last Friday and Monday. It's supposed to be 117F today and tomorrow.

That's a lot of closures.

Phoenix didn't close Sky Harbor due to high temperatures. Some airlines canceled flights years ago when temperatures exceed 118 °F but those limits have since been raised.

https://www.azcentral.com/story/news/local/phoenix-weather/2...

I stand corrected.

I'm very skeptical that helicopters can't safely operate at this temperature. It's likely a certification thing capped at the highest temperature they can actually test.

While there are plenty of certifications for aircraft maintenance and testing, this is legitimately a capacity issue. The air density issue is huge for aircraft. It caps maximum operating ceilings (as in the aircraft literally can't go any higher), it affects engine power (hence why things like intercoolers are an issue for performance engines), and it affects takeoff distance.

Ironically, it can increase the overall airspeed, since less dense air is easier to move through.

https://journals.ametsoc.org/view/journals/wcas/13/1/WCAS-D-... for more

Hot air also makes air cooling across the cylinders (EDIT: for piston aircraft) less effective, causing the pilot to have to use lower power settings to keep CHTs and oil temps in line with the airplane manufacturer's guidance. I blow through 400F regularly on takeoff on hot summer days, while I can consistently keep CHTs below that in the winter.

I don't think any emergency medical helicopters in the Western US still have cylinders. They switched to turbine engine models years ago. But of course your general point about engine cooling still applies.

how are turbines cooled? genuine question, no idea how they are supposed to work.

IIRC, the cooling is mostly achieved as a byproduct of continuously pulling in outside air and using a portion of it to cool the rest of the turbine.

https://aerospaceengineeringblog.com/turbine-cooling/

Thank you, the article didn't explain any of this nearly so succinctly.

The article alludes to two technical problems. One is density altitude; hot air is remarkably less dense than normal air. Redding is at 500', when it's 120°F out that's like 4400'. Not impossible for an ordinary helicopter but as the pilot says, you can't lift as much. The other problem is the electronics overheat.

Both seem like fixable problems: bigger engines and more heat-resistant electronics (possibly with active cooling). But you have to build for that. It's only going to keep getting worse.

(There may be a third problem with engine performance, I don't know about that.)

El Paso is at ~3800' elevation. It should reach 98F-100F for the next week. That's still only like 3800', right?

At 98F at 3800' elevation, the density altitude would be 7,268' (assuming standard pressure). https://e6bx.com/density-altitude/

Bigger engines won't help overcome lower air density.

First, bigger engines mean more weight, which will mean more power required to lift the base weight of the aircraft. Second, the problem isn't (ironically enough) pushing the blades through the air, it's the limit of each blade's ability to generate lift. Third, they can't just spin the blades faster, since they're approaching the speed of sound at the tips as it is. Breaking that speed causes a whole new set of issues to design around.

It's a balancing act, and the weight/lift/capacity/payload balance has already been struck in many cases. Will we see new designs? Perhaps, as they become economical due to climate change.

https://journals.ametsoc.org/view/journals/wcas/13/1/WCAS-D-... <- From someone with more smarts than me.

There is a term used in aviation called “hot and high” that describes an air field that is situated at a high altitude as well as having a warm ambient temperature. Hot air is less dense than cold air and higher elevation further reduces the density. It’s two lines on a performance graph that must be checked prior to takeoff.

For fixed wing aircraft, this means that your V2 speed (speed where you generate enough lift to begin climbing) is affected and you have to go faster in these conditions. This is overcome during cruise speeds because less air density is required for lift.

The story changes for helicopters, however. Because they generate lift via the rotary wings (rotors) only, they need to spin faster to get more air to hit the blade and thus produce lift. There is an upper RPM that it cannot pass due to physical limitations of the rotors assembly, engine, or both. If it gets hot enough, it can literally spin up to full speed and not move.

Helicopters freak me out. Fixed wing aircraft degrade to a glider should all power be lost, a helicopter becomes dead weight with deader occupants.

Helicopters also glide, it’s called auto rotation. Helicopters can also land in much more confined spaces than airplanes, even with an auto rotation. As we helicopter pilots like to say, if an airplane engine quits, you just know you’re going to die for a long time unless you’re near an airport. All I need in a helicopter is a small area to set it down in. Source: I fly helicopters

https://www.washingtonpost.com/climate-environment/2024/07/1... | https://archive.today/SFR8v

In the good news column, California has a long history of being a thought leader on climate law and policy. This goes back at least to the 1960s and even further if you count them hashing out water law and being the birthplace of many patents related to water development.

So maybe someone there will do something and solutions will result.

Perhaps they could embrace passive solar design as one element of a solution package instead of running the AC more, thereby making the problem worse.

[dupe]

Some more discussion: https://news.ycombinator.com/item?id=40895816

Reply on news.ycombinator.com