# Would it be possible to put wind turbines alongside runways that are driven by the exhaust of planes?

The only thing somewhat similar that I could find is research from students to use air vents from factories. This is of course a much lower force to deal with.

I'm curious if someone could give some advice or could tell me why it would or wouldn't work.

• @Fred Larson: From that article "Natural wind speed normally does not exceed several miles an hour." They sure don't live around here, where it's quite commonplace for winds to be strong enough to flip semis: carsonnow.org/story/06/09/2021/… I've often thought a line of wind turbines along that highway would be quite useful. Nov 30, 2021 at 18:13
• The list of things that are possible, yet are not good ideas, is virtually infinite. Dec 1, 2021 at 1:34
• Yeah, make them really high, too! Dec 1, 2021 at 6:24
• Electricity generated per day: \$0.02 worth. Cost of recovering from a fully loaded 747 hitting a wind turbine: \$xx,000,000 Dec 1, 2021 at 8:05
• Hey, we could find a way to harness the kinetic energy of everyone typing on keyboards, just think of how energy is produced just through typing. I think I read it only takes 100 novels to heat a cup of tea. There are a lot of these ideas that sound good, but don't work out in reality. Placing wind turbines in optimal areas would produce far more electricity than an occasional increase in wind from several planes taking off every hour. Dec 1, 2021 at 15:22

## 5 Answers

No, there's no practical benefit to putting wind turbines alongside runways and plenty of drawbacks. Airplane engines and propellers direct their thrust straight back, so the only logical place to put a turbine for energy reclamation would be directly behind the runway threshold to catch the wind from engines as they are spooled up for takeoff.

In order to successfully catch energy behind a departing airplane wind turbines would have to be very close to the engines. There are several problems with that:

1. Safety: remember that almost all airstrips are used both directions depending on wind, and many runways have an overshoot area past the threshold on the other end which is used in emergencies. Putting wind turbines at the thresholds places an obstacle between a landing airplane and the overshoot area which would be a serious safety risk. The only way this would work is if the turbines are retractable
2. Turbine Design: wind turbine blades have to be pitched correctly in order to efficiently produce power, the profile of the wind they would capture is a brief, powerful burst which then tails off. A simple turbine with fixed blades would need to be optimized for that brief burst, if you want to catch more of the energy as the airplane rolls away you'd have to have a much more complex variable pitch system. Complexity adds cost
3. Economics: a wind turbine right behind the threshold would get a few seconds of wind every time. Let's be generous and say each takeoff will produce 10 seconds of wind for power generation, and it's a relatively busy airport with 500 takeoffs per day. That's 5000 seconds of power per day, or about 83 minutes per day. It's doubtful you would be able to make any wind turbine profitable on 83 minutes of wind per day, especially since you'd need these to be retractable and you'd need 2 sets - one for each end of the strip

As for putting turbines to the sides of the runway you would catch very limited amounts of energy, at the same time you'd be installing obstacles and increasing risks. Turbines also cause turbulence which would make crosswind takeoffs more risky.

• Two other constraints: All obstacles along the runway must be frangible. and interferences created by blades on VOR and ILS.
– mins
Nov 30, 2021 at 11:25
• To add a few other numbers, say an average twin-engined jet has 60MW of total engine capacity and let's say you could capture even 10% of that, which is absurdly generous, for those 83 minutes. At a typical market rate of \$17 per MWh you would be making about \$141 per day. More likely you'd be lucky to capture 1% of that energy for a whopping revenue of about fifteen bucks a day.
– J...
Dec 1, 2021 at 1:38
• @J 0.1%? 0.01%? Dec 1, 2021 at 6:25
• @Peter-ReinstateMonica Yeah, floor's the limit. I said lucky, after all ;)
– J...
Dec 1, 2021 at 12:09
• ... so, mount the turbine onto the tail of the plane, where it can continuously recapture the output of the engines and use it to recharge batteries to extend range... (only kidding! :) ) Dec 1, 2021 at 23:46

Safety would be a big issue. The runways are where planes take off - and land. Large windmills next to the runway would not be a good thimg.

There is quite some energy expelled from the engines, and catching all of it on a busy airport would be worth looking at were it not for:

• The main jetstreams are flowing along the runway itself, where there may not be any windmills!
• The exhaust flow is close to the ground, which decelerates it.

A better set-up for reducing TO and landing energy would be to imitate aircraft carrier launch & arrest, in a gentler, more comfortable way of course. Airbus made a case for this some time ago, as mentioned in this answer.

• Daft as it may seem... airteamimages.com/pics/250/250521_800.jpg Nov 30, 2021 at 17:43
• Energy is expelled on the ground for only a brief period, vs. in-flight. Dec 1, 2021 at 0:01
• Maybe it would be better for efficiency to install reflectors to redirect the aircraft's exhaust back at the aircraft, giving it an extra push. Dec 1, 2021 at 14:51

I had many thoughts in the past on how to recover part of the energy dissipated by a landing aircraft. The best idea I came up with is to install on runways an arresting gear (like the ones used in aircraft carriers) connected to a power generating turbine.

Of course there should be some sort of construction standards that all (heavy) aircraft should implement, but the idea is to let the arresting gear to brake the landing aircraft until it comes to a stop; this device could be used in place of air-brakes, gear-brakes, and thrust reversals.

• Yeah arresting gear would help,at what cost though? A lot of financial investment, safety may not be impacted, and we’re catching the plane at its lowest airborne energy state. Dec 1, 2021 at 20:55
• @Koyovis it doesn't look a massive investment to me; true, it's the lowest energy state, but still a 737-800 (170 tons landing at 140kts) has 500MJ of kinetic energy that can spin an alternator long enough until the next landing in a busy airport. With a landing every 5 minutes you can produce (ideally) ~150MW, like a mid-size hydroelectric power plant. To me it's definitely worth a serious study
– Jack
Dec 2, 2021 at 8:04
• @Jack This has been discussed here: Why don't airports use arresting gears to recover energy from landing passenger planes? Also, a 737-800 for sure does not land at 170 t (MTOW is only 79 t, MLW probably lower). Dec 2, 2021 at 12:15
• Thanks @Bianfable
– Jack
Dec 2, 2021 at 17:38

Turbochargers are the practical implementation of this idea.

A turbocharger uses the exhaust gases to spin the turbine which then forces more air into your car's engine and increases the engine's power.' According to the law of thermodynamics; 'energy can neither be created nor destroyed, only altered in form

In the case of planes, already, most of the energy from the fuel is converted into useful mechanical energy used to fly it. The idea is to get the maximum energy in the desirable form, i.e. electrical or mechanical energy. So, essentially, one might think of the turbocharger as the wind turbine installed on the vehicle itself. Specifically in cars with turbochargers, it uses the exhaust as well as the car's air intake as well to increase its power.

• That's not the same thing! If you extract more kinetic energy from a jet engine exhaust, you reduce the thrust. But the airplane needs the thrust for takeoff. Placing wind turbines on the ground would recover some of the energy without reducing thrust. Dec 1, 2021 at 9:05
• @Bianfable - It's actually rather comparable. Both solutions improve thrust in their own way. Turbochargers make the engine smaller/lighter at the same maximum thrust, thus improving fuel economy. The turbine on the ground creates a horizontal ground effect, thus improving thrust. Unfortunately, only for the short while its blade stands directly behind the engine. That's why turbochargers are more popular than the wind turbines. Dec 1, 2021 at 20:28
• Turnochargers are used in piston engines, not in turbine engines like a turbofan. Dec 1, 2021 at 20:58
• A turbofan is, for all intents and purposes, already turbocharged. That is what the "turbo" means. The exhaust drives the turbine, which via a driveshaft drives the compressor. Dec 2, 2021 at 4:36

Other people have explained a lot of the issues with this system, but assuming you could finally build a system that works with all these restrictions in place and manages to produce power...

You would produce orders of magnitude more power, cheaper and more efficiently, simply by directly burning the kerosene that these planes use to take off and fly and using the generated energy to power a generator. It would probably also be better for the environment.

• That may be true, but the kerosene is being burned already. This question is asking about whether that energy (which is already being used) can be reclaimed. Nov 30, 2021 at 21:00
• @randomhead I'm sorry, but that wasn't obvious for me. At best it was implied. Dec 1, 2021 at 8:10
• “by directly burning the kerosene that these planes use to take off and fly and using the generated energy to power a generator”: But then the planes wouldn't fly! :)
– DaG
Dec 1, 2021 at 9:53