The Anonymous Widower

Distributed Propulsion ‘Maybe The Only Means’ For Small Electric Flight Progress

The title of this post, is the same as that of this article on the Institute of Mechanical Engineers web site.

If you want to fly again, then this article offers pointers to how you might do it.

The E-Fan X Airliner

It gives this latest information on the E-Fa X airliner being tested by Rolls-Royce and Airbus.

Amid the strain of the Covid-19 pandemic, Rolls-Royce and Airbus cancelled flight tests of their E-Fan X airliner, a promising project that could have provided vital data on issues such as thrust management and electric systems at altitude.

Does that mean cancelled or scrapped?

2.5 MW From A Beer Keg-Sized Generator

This paragraph could be important.

“Among the many great achievements from E-Fan X has been the generator – about the same size as a beer keg – but producing a staggering 2.5MW,” said Vittadini’s Rolls-Royce counterpart Paul Stein. “That’s enough power to supply 2,500 homes and fully represents the pioneering spirit on this project.”

This picture shows a Class 66 locomotive.

The locomotive has a 2,460 kW diesel engine and an electric transmission.

I just wonder, if Rolls Royce’s high-powered small generator could replace the large, noisy and smelly diesel engines in these locomotives.

If the technology worked there are 455 of the noisy locomotives.

Snowballing Improvements

The article has a section with this title and it talks about how electric power may lead to other advantages.

Conclusion

Electric aircraft are more promising, than many think!

 

July 17, 2020 Posted by | Energy, Transport | , , , , | 1 Comment

Can A Green Revolution Really Save Britain’s Crisis-Stricken Aerospace Industry?

The title of this post, is the same as that of this article on the Telegraph.

This is the sub-title.

The Prime Minister has set a challenging target of green flights within a generation, but is it a sustainable plan?

I have read the whole article, which is mainly about Velocys and their project at Immingham to create aviation biofuel from household rubbish.

They say the main problem is scaling up the process to get enough jet fuel. When I was working at ICI in the early 1970s, modelling chemical processes, scale-up always loomed-large as a problem.

Nothing changes!

I think we’ll get to our carbon-neutral objective, for aviation, but it will be a mixture of things.

  • Aviation biofuel.
  • All-electric airports.
  • Efficient aerodynamics and engines.
  • Electric short-haul aircraft.
  • Rail substitution for short flights.

Traditional aerospace must reform itself or die!

As to Velocys, they must solve their scaleup problem, so that all suitable household and industrial rubbish ends up doing something more useful, than beinmg incinerated or nuried in landfill.

July 5, 2020 Posted by | Energy, Transport | , , , , , | 1 Comment

James Bond Stunt Pilot’s Electrifying Flight

The title of this post, is the same as that of this article in The Times.

This is the introductory paragraph.

A James Bond stunt pilot has completed the first electric-powered flights from a UK airport in an aircraft capable of carrying passengers.

The aircraft was a modified Piper Malibu.

  • They can carry a pilot and five passengers.
  • They are single-engined.
  • Some are powered by piston engines and some by turboprops.
  • Over 1,200 of different variants have been produced and the aircraft is still in production.

Tragicilly, the footballer; Emiliano Sala, died in a Piper Malibu.

Zeroavia, the company, who seem to be behind this flight, in my view seem to be on the right track. The Zeroavia Hyflyer, has its own section in the Wikipedia entry for the Piper Malibu. This is the first sentence.

ZeroAvia, a Cranfield University partner, is a U.S./UK startup developing a Hydrogen fuel cell power train targeting to halve a turbine operating costs.

Roei Ganzarsky, who is CEO of magniX, who are a company, who make efficient electric motors for aviation, appears to very much believe that electric aircraft will be cheaper to run.

June 23, 2020 Posted by | Transport | , , | 6 Comments

Honeywell Launches Lightweight Cooling System For Electric Aircraft

The title of this post is the same as that of this article on Flight Global.

This is the introductory paragraph.

Honeywell Aerospace has unveiled a lightweight, low-maintenance cooling system for developers of urban air mobility (UAM) and electric aircraft, and has named the Eviation Alice as launch platform for the energy-efficient feature.

I particularly like the comment of Eviation’s founder Omer Bay-Yohay’s comment of “Every ounce counts!”.

But although weight is important in an electric aircraft, like the Eviation Alice, it is also important in other forms of transport from a family runabout to a high-speed train. Especially, if the vehicle is powered by batteries.

It should also be noted, that Honeywell are setting up a specialist business unit to provide equipment for and help the builders of electric aircraft.

Conclusion

Other companies will follow Honeywell’s lead and produce lightweight equipment for the automotive and rail industries.

June 21, 2020 Posted by | Transport | , , , , | Leave a comment

MagniX Electric Aircraft Engines Take To The Skies

The title of this post, is the same as that of this article on pv magazine Australia.

This is the introductory paragraph.

No emissions, low-cost regional flights with just eight other sanitised folk and a disinfected pilot… Yes, Covid-19 is warping our view of the future, but the successful electrically powered maiden flight last week of a Cessna Caravan aircraft, offers the potential for new models of travel supporting wider distribution of commerce in Australia.

The article goes on to discuss Roei Ganzarski’s vision of what zero-emission electrically-powered aviation could do.

Economics

This is a paragraph from the article.

Its successful half-hour, 160km test flight used less than US$6 worth of electricity, compared to a Cessna Caravan powered by conventional combustion engine which would have sucked up some US$300-400 worth of fuel. And Ganzarski points out that, as in electric vehicles, the motor requires very little maintenance compared to its gas-guzzling cousins.

That is impressive.

The Market

This is a sentence from the article.

MagniX says 45% of all airline flights cover less than 800 km, while 5% of flights are sub-160 km, and it’s likely that commercial electric flights powered by magniX motors will first be offered in the UK, US or Europe.

I didn’t believe that the proportion of short flights was so high.

I could see all flights below 160 km (100 miles) will be flown by electric aircraft and a large proportion of those below (800 km (500 miles) going in the same direction.

The Vision

This is a paragraph from the article.

You could have phenomenal factories or businesses in these places that can’t currently sell their goods or can’t receive goods because the 4.5 to 6-hour truck drive that happens maybe once a week is just operatively prohibitive. If you could have an aircraft do that in 20, 40, 60 minutes and do it with zero emissions at a really low cost, and suddenly you’re really connecting these communities…

As it was given in quotes, I would assume it was spoken by Roei Ganzarski.

What would that do for high-quality agricultural products and seafood produced on remote islands.

This statement is in the Wikipedia entry for Loganair.

Loganair is planning to introduce electric aircraft to the Orkney Islands by 2021 due to the short distance between the islands that would make such flights possible.

They seem to be following a parallel path, with their involvement in Project Fresson. But as that development of a Britten-Norman Islander, is not planned to fly until 2022, could Loganair be a possible launch customer for an electric Cessna Caravan?

  • Loganair have the ideal short routes.
  • The electric Caravan won’t be the most difficult aircraft to certify for flying with a Supplemental Type Certificate, as several other Caravan variants with a change of powerplant, are flown this way.
  • The environmental profile fits some of Loganair’s routes in Scotland.
  • According to Roei Ganzarski, the economics would be ideal for Loganair’s routes.
  • Roei Ganzarski gave a long sales promotion-style interview on the BBC. Who was he targetting?

But the biggest factor is that Roei Ganzarski appears to be a showman in the mould of those great Victorian engineer/entrepreneurs, who defined and built much of the world we admire. What better stage is there to showcase his electric aircraft, but the remote airports served by Loganair?

The Specification

The Wikipedia entry for the Cessna Caravan now has s section for the electric Caravan, where this is said.

The eCaravan is an electric aircraft modification of the 208B built by AeroTEC and magniX powered by a 750 hp (560 kW) motor and a 1 t (2,200 lb), 750V lithium-ion battery. Its 30 min first flight happened from Grant County International Airport in Moses Lake, Washington, on May 28, 2020, consuming $6 worth of electricity, needing 30-40 min of charging. The Magni500-powered variant can fly 100 mi (160 km) with 4-5 passengers while keeping reserve power, and aims for a certification by the end of 2021, hoping to operate 100-mile flights with a full load of nine passengers with better batteries.

The pv magazine Australia article says the flight was for 160 km (100 miles), so that would cover a lot of short routes.

Suppose with reserves, that the plane should have a one hour endurance. my experience of piloting aircraft leads me to estimate that the average power setting would be less than fifty percent of full power for a real flight, as cruise and descent, need a lot less power than climb.

This would mean, that the aircraft needs to take-off with around 280 kWh of fuel, which would be enough to power the motor at half-power for an hour.

In Sparking A Revolution, I comment on an article of the same name in Issue 898 of Rail Magazine, which talks about Hitachi’s plans for battery-electric trains.

This is an insert in the Rail Magazine article, which will apply to all applications with traction batteries. Including aviation!

This is said.

The costs of batteries are expected to halve in the next five years, before dropping further again by 2030.

Hitachi cites research by Bloomberg New Energy Finance (BNEF) which expects costs to fall from £135/kWh at the pack level today to £67/kWh in 2025 and £47/kWh in 2030.

United Kingdom Research and Innovation (UKRI)  is also predicting that battery energy density will double in the next 15 years, from 700 Wh/l to 1,400 Wh/l in 2035, while power density (fast charging) is likely to increase four times in the same period from 3 kW/kg now to 12 kW/kg in 2035.

This page on the Clean Energy institute at the University of Washington is entitled Lithium-Ion Battery.

This is a sentence from the page.

Compared to the other high-quality rechargeable battery technologies (nickel-cadmium or nickel-metal-hydride), Li-ion batteries have a number of advantages. They have one of the highest energy densities of any battery technology today (100-265 Wh/kg or 250-670 Wh/L).

The highest figure of 670 Wh/l would appear to fit the Hitachi extract, where 700 Wh/l is quoted.

If I use the Wh/kg figure, it would appear that a one tonne battery could hold between 100 kWh and 265 kWh.

I suspect, that the higher figure would be enough to perform the 160 km. test flight, which I estimated could need 280 kWh.

But battery development in the next few years will be on the side of Roei Ganzarski’s vision.

Conclusion

Electric aircraft are not a politically correct mad idea, but a serious proposition to make the world a better place.

The article is a must-read!

June 1, 2020 Posted by | Transport | , , , , , | Leave a comment

MagniX and AeroTEC Put All-Electric Cessna Airplane Into The Air For First Time

The title of this post is the same as that of this article on GeekWire.

This is the introductory paragraph.

An all-electric version of one of the world’s best-known small utility airplanes hummed through its first flight today at Moses Lake in central Washington state.

This is a picture of another Cessna Caravan, that I took, as I boarded it in Kenya for a flight to the Maasai Mara.

 

The aircraft are very much a Ford Transit or Mercedes  Vito of the skies.

  • 2,600 have been built.
  • It is still in production.
  • The passenger version can carry nine passengers.
  • Total flight hours are over twenty million.
  • FedEx operates 239 of the type.

It must surely, be an ideal aircraft to convert to electric power.

This is a video of the first flight on YouTube.

The guy behind the project;Roei Ganzarski has just given a very optimistic interview on BBC Breakfast.

He emphasised the various environmental and financial advantages of the aircraft and if you can catch it on the iPlayer, it outlines a possible future for aviation.

I can see electric Cessna Caravans flying around the UK within the next couple of years.

Designing And Building An Electric Aircraft

Three of the designs for commercial electric aircraft under development are conversions of existing designs.

This must make certification of the aircraft simpler, as you’ve just replaced one type of engine with a battery and electric motor of similar size.

The difficult parts of the design; the aerodynamics and structure are probably almost unchanged.

As MagniX are involved in the first two of these projects, I would suspect that they have come up with an electric motor, that fits what is needed for aviation very well.

But then electric motor design is changing, probably driven by the needs of electric transport from bicycles through cars and vans to buses, planes, ships, trains and trucks.

It should also be noted, that the Beaver, Caravan and Islander are all simple aircraft, with a long history of successful operation and a vast knowledge base amongst pilots, engineers and operators of how to use these aircraft safely and in a financially viable way.

Will we see other aircraft conversions from to electric power in the next few years?

This page on Flying Magazine discusses conversion of Cessna 172 to electric power.

 

May 29, 2020 Posted by | Transport | , , , , | Leave a comment

Watch First Electric Caravan Fly

The title of this post, is the same as that of this article on AOPA.

As AOPA is the Aircraft Owners And Pilots Association, the caravan is a Cessna C208B Grand Caravan, which has been converted to electric power.

I have flown in a Cessna Caravan in Kenya, where it took me from Nairobi Airport to the Maasai Mara.

It is a typical workhorse all over the world carrying up to nine or thirteen passengers or freight.

  • They have a single turboprop engine.
  • The undercarriage is fixed and very sturdy.
  • Around 2,600 had been built by 2017.
  • It is used by a variety of operators.

I would certainly be happy to fly in one at any time, unlike some aircraft I could mention.

This paragraph from the article details how the maker of the electric motor;magniX is involved in electric flight.

The Grand Caravan is to be the largest, but not the first commercial aircraft magniX has converted to fly with 100 percent electric power. Roei Ganzarski, CEO of magniX, wrote in an email exchange that the de Havilland DHC–2 Beaver first flown in December continues its test flight program in Canada. Harbour Air, a short-haul air carrier with a fleet of seaplanes, is working with magniX to convert its fleet to all-electric power, and the same 750-hp electric motor that will power the upcoming Grand Caravan flight has been performing well in test flights over British Columbia.

Ganzarski is quoted as saying he is pleased with results to date.

The aircraft is lined up to make its first flight on May 28th, which hopefully will be shown on the Internet.

My flight in Kenya was only about half-an-hour and despite the Caravan having a range of nearly 2,000 kilometres, I suspect that many flights in the aircraft are of similar duration.

A Quick Battery Size Estimate

  • 750 hp is 560 kW.
  • So a half-hour flight on full power will use 280 kWh plus whatever is needed for aircraft systems like avionics, heating and air conditioning.
  • The Eviation Alice electric aircraft seats nine passengers and has a 900 kWh battery according to Wikipedia.

I  would suspect a 900 kWh battery should allow the Electric Caravan to do two half-hour trips.

The Future Of Electric Aviation

It is interesting to note, that four of the projects in designing and building a viable electric aircraft are in this nine-seater segment.

Note.

  • All except Eviation Alice, are conversions of proven high-wing aircraft with a fixed undercarriage.
  • Moderately large fleets available for conversion. – Beaver (1,600 plus built), Caravan (2,600) and Islander (700)
  • Conversion only needs a Supplemental Type Certificate, rather than full certification.
  • The DHC-2 Beaver prototype first flew on the day I was born, so it can’t be all bad.

A detailed insight into the reasons and the economics of converting an existing fleet of aircraft are given in a sub-section called Development in the Wikipedia entry for Project Fresson.

  • Scottish Airline Loganair appears to be the launch airline and will use the plane for their short flights around the Orkneys.
  • Several companies are involved in the development.
  • First flight is aimed for 2021.
  • Conversion kits could be available in 2022-2023.
  • It is hoped that operators would get a return on their money for the kit in 2-3 years.

Once they get the design right, there is talk of a nineteen-seat electric airliner.

I can see hundreds of converted electric Caravans and Islanders flying short routes by 2030.

 

May 21, 2020 Posted by | Transport | , , , , , , | 2 Comments

Airbus On Electric Flight

This page on the Airbus web site is all about electric flight.

This paragraph greets you.

Today, zero-emission flight is closer to reality than ever. Electric and hybrid-electric propulsion is rapidly revolutionising mobility technologies across industries, from automotive to marine. And the aviation industry is no exception. Airbus is committed to developing, building and testing electric and hybrid-electric future technology that will enable the aviation industry to significantly reduce the CO2 emissions of commercial aircraft.

A read of the whole section is recommended.

A lot of technology will need to be improved even to get say a 60-seat airliner, with a 500 mile range.

  • Design-changing efficient aerodynamics.
  • Lightweight, strong structures.
  • Efficient zero-carbon propulsion systems.
  • Batteries with a much higher energy capacity per kilogram of battery weight.

It’s a tough ask, but I believe it is possible!

We might even see some very unusual ideas. And some proven ones.

Catapults

Naval fighters are usually literally thrown into the air from aircraft carriers using aircraft catapults, which traditionally were steam-powered. Gliders are often towed into the air using a rope.

So could something similar be used to accelerate the aircraft to flying speed?

Taxiing And Take-Off Using A Tug

All taxiing would use a battery-electric or hybrid-hydrogen-electric tug to minimise use of energy from the plane’s batteries.

Could the tug be combined with charging and a vehicle to handle the catapult launch?

  • A fully-charged tug would meet incoming aircraft and tow them to the terminal.
  • The aircraft would use the tug for power, if it was low.
  • At the terminal, the tug and aircraft would be charged, during passenger unloading and loading.
  • On the taxi to the runway, all power would be provided by the tug.
  • The catapult system, would attach to the tug on take-off.
  • Once take-off speed was achieved, the aircraft would disconnect and climb away under its own power.

All the power for acceleration to take-off speed would be provided on the ground and the aircraft wouldn’t have to carry it.

Energy Calculations For An Airbus 220-100

The smallest Airbus aircraft is the A220-100, which has the following specification.

  • Passengers – 135
  • Maximum Take-Off Weight – 63.1 tonnes
  • Cruise speed – 871 kph
  • Take-off speed – 220 kph (estimated)
  • Ceiling – 41,000 ft.

Note that the design cruise speed of the nine-seat electric Eviation Alice is 482 kph at 10,000 ft.

Using Omni’s Kinetic Energy Calculator, the following values are obtained.

  • 220 kph – 32.7 kWh
  • 482 kph – 157 kWh
  • 981 kph – 513 kWh

As the kinetic energy is proportional to the square of the speed, I would expect that a small electric airliner would have a cruise speed slower than current airliners.

I would expect that Alice’s cruise at 482 kph and 10,000 ft., could have been chosen to get a decent range for the maximum size of battery.

The aircraft will also have to be given potential energy in the climb.

Using Omni’s Potential Energy Calculator, the following values are obtained.

  • 5,000 ft. – 262 kWh
  • 10,000 ft. – 524 kWh
  • 41,000 ft. – 2148 kWh

I would expect a small electric airliner  would fly a lot lower.

A 135-seat electric airliner, which is the same weight as an Airbus 220-100 and cruising at 482 kph and 10,000 feet would need the following energy to establish itself in the cruise.

  • Kinetic energy – 157 kWh
  • Potential energy – 524 kWh
  • Take-off energy at 220 kph – 32.7 kWh

Which gives a total of 681 kWh.

It should be noted that both the kinetic and potential energies are proportional to the maximum take-off weight. Assuming that take-off weight would be proportional to the number of passengers, rough estimates for the battery size needed.

  • 25 – 126 kWh
  • 50 – 252 kWh
  • 75 – 378 kWh

As Wikipedia says the smaller nine-seater Eviation Alice has a 900 kWh battery, I feel that at least a fifty passenger electric airliner is possible.

Very Efficient Aerodynamics

One of the biggest losses of energy will be due to less-than-perfect aerodynamics, with vortices, eddies and skin friction wasting precious energy.

Look at the pictures on the Internet of the Eviation Alice and you’ll see a strange aircraft.

  • A very pointed nose.
  • Two propellers at the wing-tips.
  • A third propeller at the tail.
  • I suspect, all the propellers are placed to get the most out of the power.

When Alice is cruising, her energy consumption will be minimal, so that the maximum range for a given battery size can be obtained.

Any electric airliner will draw on all the aerodynamic tricks in the book.

Efficient Flight Profiles

The longest flight, that I ever did in my Cessna 340A was from Southend to Naples.

  • Before take-off at Southend, the fuel bowser followed me to the end of the runway to give me a last-second top-up.
  • I travelled across France on a beautifully-clear day and the accommodating Lyon ATC allowed me to fly at 19,500 feet all the way to French Coast at Nice.
  • The French then decided that, as I was happy at that height, they would hand me over to the Italians without a change of level.
  • So I flew down the Italian coast past Genoa and Rome at 180 knots, with spectacular views all the way.
  • The Italians, then used radar to vector me on to final approach at Naples.

I reckon, I had flown nearly a thousand miles in if I remember correctly about six hours.

But it was a very efficient flight profile to get the range.

  • I took the maximum about of fuel, I could carry.
  • I climbed as fast as possible to an efficient cruising level.
  • I cruised at an efficient speed.
  • I used very little fuel on the descent and landing into Naples.

I certainly was pleased, that I had about another hour’s fuel left, when I arrived in Naples.

Electric aircraft will probably always fly efficient profiles, to get the maximum range. But they will all be calculated by the plane’s computer system.

Most Aircraft Are Heaviest At Take-Off

This is because they burn fuel in the engines, as they fly along.

But a full battery weighs the same as an empty one, so the electric aircraft will have the same flying characteristics in all stages of the flight.

This could have design and operational advantages.

Hybrid Propulsion

Some electric aircraft designs are hybrid, with both battery and turboprop power.

It still cuts carbon emissions and may give better performance.

Fuel created from biomass can also be used.

Conclusion

I expect to fly in an Aubus battery-electric short-haul plane between London and Geneva by 2030.

But I’m certain, I’ll fly before that in an electric aircraft.

 

 

 

 

 

May 20, 2020 Posted by | Transport | , , , , | 4 Comments

GKN Aerospace Joins Eviation Alice Electric Plane Project As Work Continues After Fire

The title of this post, is the same as that of this article filed under Engineering News on the IMechE web site.

This is the interlocutory paragraph.

Electric plane pioneer Eviation has signed a collaboration agreement with GKN Aerospace for the design and manufacture of wing, tail assembly and electrical wiring interconnection systems for its Alice aircraft.

It is very matter of fact, but does the tie up signal good news and progress, after the prototype Eviation Alice was destroyed in a fire?

As a disruptive innovator and one-time pilot, I like the Alice.

  • The performance, in terms or passenger capacity, speed and range match a market, where money could be made.
  • The propulsion system makes the most of up-and-coming technology.
  • I suspect that the unusual shape allows some efficient aerodynamics to work.
  • Some people might put their money down on a ride in space. A ride in an electric aeroplane would satisfy me.

I think, the Alice could be the first electric plane I ride in.

And the tie up with GKN, makes my dream more likely.

May 19, 2020 Posted by | Transport | , , | Leave a comment

Flying Taxi Start-Up Raises $240m From Existing Investors Led By Tencent

The title of this post, is the same as that as this article on the Financial Times.

This is the introductory paragraph.

Lilium, a German flying taxi start-up, has raised $240m from existing investors led by Chinese technology group Tencent to fund the next stage of its growth.

The article has a picture of the Lilium Jet, which looks to be an interesting design.

  • It is an electric VTOL aircraft.
  • Power comes from no less than thirty-six electric motors driving ducted fans.
  • The fans will tilt for take-off and landing.
  • Maximum speed will be 190 mph, with a cruise of 170 mph.
  • Range will be 300 kilometres or 186 miles
  • Total installed power is 320 kW.
  • Less than 150 kW will be needed for cruise.
  • A MW (?) battery will be fitted according to Wikipedia. Do they mean MWh?
  • It can carry two passengers with five from 2025.
  • Empty weight is 440 Kg.
  • Maximum take-off is 640 Kg.
  • Initially, it will have a pilot, but the aim is for a completely autonomous aircraft.

Lilium aims to run a city-to-city taxi service starting in 2025.

I have a few thoughts.

Aerodynamics

There have been a lot of developments in aerodynamics in the last few years and the Lilium Jet and other electric aircraft like the Eviation Alice take full advantage of the developments.

So don’t expect electric aircraft to look convectional, unless perhaps they are an electric-engined conversion of an existing conventional aircraft!

Structure

The structure of aircraft is getting lighter and Airbus and Boeing with the 787 Dreamliner are showing what is possible.

Will an empty weight of 440 Kg be possible? Especially, if that includes the battery.

The Wikipedia figures allow a payload of 200 Kg. That must be only two passengers.

Power

Wikipedia talks about a one MW battery, but I suspect they mean one MWh, as this is the unit of battery capacity.

In Sparking A Revolution, I quoted Hitachi’s predictions and suggested that they could have a five-tonne battery, that held 15 MWh by 2035.

This would mean that a one MWh battery would weigh 333 Kg.

This must be near to the target weight of the battery needed to power a Lilium Jet.

But a one MWh battery that weighs just 333 Kg. would be a tough ask given the limitations of today’s battery chemistry.

Fire

Wikipedia says this about a fire.

The first prototype was destroyed by fire during maintenance on 27 February 2020.

As the Eviation Alice also suffered a fire, are these aircraft pushing batteries too hard.

Conclusion

I am sceptical about some of the figures quoted for the Lilium Jet in Wikipedia.

When I see the following.

  • A Lilium Jet in the air, taking-off and landing.
  • Two passengers flying in the aircraft.
  • A Lilium Jet on a set of scales.

I’ll revise my opinion.

There is this video.

Obviously, I’m doing something wrong in my calculations.

March 23, 2020 Posted by | Transport | , , | 2 Comments