Alternative Power Systems

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Trevor Lyons
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Alternative Power Systems

Post by Trevor Lyons » Wed Apr 07, 2010 12:09 pm

On another thread, Simon Clifton wrote:Let's start a thread on electric motor development.
Brian Hope wrote:Major feature on alternative power systems coming up in the next couple of issues of LA.
Here's that thread! Where to start? The known quantity is the internal combustion engine, whether diesel and spark-ignition, piston or rotary, 2 stroke, 4 stroke & (even) 6-stroke. So, if one is to look for an alternative, one has to identify what is the ideal power source for an aircraft, and to identify the characteristics of what's on offer. I suggest the ideal aero-engine is: compact, lightweight, powerful, smooth, economical and reliable. How do existing motors match up?

4-stroke diesel piston: very economical & reliable, but heavy, bulky and prone to vibration. If based on a car-engine, it needs to be modified to accept Avtur rather than road diesel. All diesels need to be turbocharged for optimum power.

2-stroke diesel piston: as above, but lighter, more powerful and still economical; purpose-made for aviation, so may be expensive.

2-stroke petrol piston: light, cheap, compact, powerful, if rather thirsty and unreliable. Oil-injection is better than pre-mix; and the use of reed-valves, disc-valves, and exhaust power-valves (all common on motorbikes) improve the power characteristics. Direct fuel injection into the chamber after the ports have closed eliminates unburnt fuel in the exhaust, giving better economy and reducing emissions. However, almost all current aviation 2-strokes are still as basic as can be, which is why only microlights use them.

4-stroke petrol piston: the mainstay of GA. Expensive to buy, very reliable, heavy, not compact, and a poor power-to-weight ratio. Modern engines are more economical than the thirsty American dinosaurs.

Wankel rotary: very smooth, small, lightweight & powerful. Reasonably economical but some doubts on reliability; uncommon and unknown to most engineers. However, they can spin at high revs without damage (if the bearings & tips can cope); they are not sensitive to fuel quality and can run on Avtur as a spark ignition engine. They almost never seize as the "crankcase" expand more than do the rotors.

Reduction gear or Direct Drive? Direct drive is simple and reliable; but a gearbox allows a smaller, lighter engine to run faster and deliver peak power.

Electric motors: compact, lightweight, smooth, powerful, and reliable. Almost perfect! Economical? There's the rub. Batteries are still heavy. No doubt Simon Clifton will expand on this. Fuel cells? Over to you, Simon!

A good compromise might be a hybrid aircraft, with a small bank of batteries powering a geared electric motor driving a feathering VP prop. Batteries would be charged while on the ground from the mains, and in the air by a small Wankel industrial engine and by an array of solar panels on the wings. To save fuel and weight, the aircraft would be able to be winch-launched, which means that we're considering a lightweight aircraft with only one or two seats. Imagine that: a winch launch to 1500 feet; then run on the batteries, relying on sunshine to keep you flying; and then start the charging engine only when the volts start to drop!
formerly "arriviste" (ARV-ist!)

Simon Clifton
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Post by Simon Clifton » Thu Apr 08, 2010 1:10 pm

Trevor said...
Electric motors: compact, lightweight, smooth, powerful, and reliable. Almost perfect!
Trevor - agreed. Electric motors are almost perfect, although I am sure some 'aviation specific' minor adaptations could help with the last few percentage points towards total perfection (whatever that might be).

In particular, installations that are difficult with legacy engines (e.g. twins, ducted fans, pushers that need long prop shaft) all become very much easier indeed.

Even better, feeding power to the motors is easier and inherently safer, and modern power electronics means very efficient and lightweight controllers. No more vapour-lock or bleed systems required. Because nothing is burning in the motor, there are no exhaust systems, and reduced risk to other systems from very hot things. Because there is no carburation, there are no mixture controls, chokes, primers or anything other than a faster/slower lever needed.

Trevor then said (more or less)
'the rub is in energy storage'
Yep, dead right. This is what is holding the world back, and has been true since the invention of the battery and the electric motor in the mid 1800's (well before the infernal combustion engine).

It is a fairly universal truth that aviation motive power has always slightly lagged the automotive world (except the jet, which is the other way around - but I am not considering jets really viable for LAA types!).

The same will be true for electric aeroplanes - we're gonna have real options once the automotive world has got to generation 2 or 3 or mainstream electric road vehicles (say in 5-years). I believe both GM and Nissan will have Gen 1 all-electric cars for general sale in the UK in 2010. Honda have backed the hydrogen fuel-cell ticket, but the distribution of hydrogen is virtually nowhere, and extremely tricky to do effectively.
It is in the automotive world that the battle between batteries and fuel-cells will be fought and won, and that will be the time for a simple technology transfer to aeroplanes.

My own guess is that batteries will win because they can still be developed a lot. Improving battery energy density by about 10-fold will see electric vehicles directly competing with current engines, and that will be the almost instant end of the combustion engine in new cars.

Making, transporting and storing hydrogen for a fuel cell really is tricky, and can't be made easier by development, I can't see it really happening.

And then Trevor said
A good compromise might be a hybrid aircraft
Actually, this is where the automotive world is at right now. Its okay(ish) to carry around both power systems in a car because weight and complexity is not such a big deal when you have wheels. It is a big deal in an aeroplane, and I see this option more as a 'worst of both worlds' than as a way forward at the moment for 'planes.

I'd like to know the position of the authorites on this one. If I wanted to put in an electric motor and some batteries in my aeroplane instead of my 912, which design code do I follow?

There are a few early electic 'planes about today - who can tell me what the main technical issues are with those? (other than range which is obvious).

There are lots more points and questions I am sure, but thats' enough for now!

Simon C
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Nick Allen
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Post by Nick Allen » Fri Apr 09, 2010 2:57 pm

The technical specification for the new Chinese electric plane, the E430 (see http://yuneeccouk.site.securepod.com/Ai ... ation.html),
gives an engine+controller weight of 24 kg, and a 10-pack of batteries (for 2.5 hours flying) as 130 kg. For the power, I reckon that's getting on for double the weight of an equivalent petrol engine plus fuel...but not bad for a "first attempt"!
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Simon Clifton
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Post by Simon Clifton » Fri Apr 09, 2010 3:25 pm

The Yuneec proposition is very interesting indeed. It breaks the 'develop a new power plant in an established airframe, or vice versa' old rule by being a new airframe and motive power system. It is also interesting to see what seems like a home-grown Chinese organisation doing development and not just series large-scale manufacturing.

If Mr. Yuneec brought one to the UK, what would the LAA be able to do to help get it legal to fly?

Would Francis just jump in and give us a report in the mag?

There seems to be a bit of momentum on electric planes at Aero 2010 this wekend...

Cheers

Simon C
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Ian Melville
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Post by Ian Melville » Fri Apr 09, 2010 7:56 pm

I am very sure that in the long term electric will be the way to go. Battery technology still has some way to go before it can offer a system as a direct replacement.

Electric motors do not need a reduction gearbox as Trevor mentioned. Out-runner motors can be made for any RPM/Torque you wish. VP prop would be the icing on the cake. Since the prop will not have to face ignition pulses, in theory it can be made lighter than current models. Motors will be the cheap part.

The area that needs work is the controllers, which at the power and efficency needed, cannot be knocked up in five minutes. Hence will be expensive.

One concept that I would like to explore is ganging several large model Electric motors together with a common shaft, each with thier own controller. Easy to do with electric motors, but not IC engines. This would build in redundancy, despite using (relative to GA)low cost conponments.
Three of these would exceed the E430 power unit.
http://www.hacker-motor-shop.com/e-vend ... &c=36&p=36
Still not cheap for these low volume items.

I too would like to see a design code. I would also like to see battery/fuel cell weight taken into consideration when writing legislation.

I have been flying electric model aircraft since the 80's so look forward to an electric future in the air.

cardiffrob
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Post by cardiffrob » Sat Apr 10, 2010 5:53 am

How about electric power plus an in-flight top-up from one of those mini jet engines for model aircraft tied to an alternator. Aren't they efficient at high rpm and altitude?
Rob Thomas
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Ian Melville
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Post by Ian Melville » Sat Apr 10, 2010 11:12 pm

Rob, I don't think it would get to high enough altitutude. A small model jet will burn fuel at 0.3 litre per minute, or more, so not too efficient.
Anyway I doubt its contribution would make much difference.
A better choice would be a piston engine to drive the alternator. Even better skip the alternator and just fit a prop on the engine. Now that may work :D

Bill McCarthy
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Post by Bill McCarthy » Sun Apr 11, 2010 2:38 pm

The advantage of the ICE powering an electric motor is that the aircraft can be balanced with the lightweight high revving engine aft perhaps.

Trevor Lyons
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Location: Staffordshire

Post by Trevor Lyons » Sun Apr 11, 2010 2:58 pm

Simon Clifton wrote: I see this (hybrid aircraft) option more as a 'worst of both worlds' than as a way forward at the moment
If and when batteries become significantly lighter and more powerful, then electric aircraft will really take-off (pun intended). Until then, the hybrid has a lot to offer; and it should be possible to design one with a minimal weight penalty. Also, there is a safety benefit: even if the charging engine fails, the aircraft ought to be able to land safely using residual battery power and solar power.

Of course, a further way to maximise efficiency is to adopt the canard layout, since both pairs of wings provide lift, whereas a conventional tailplane produces only parasitic downforce. My hybrid canard would not need a pusher prop, as do the Rutan designs (for C-of-G reasons); but following the Rutan custom, the nose wheel would retract out of the propwash, even if the main gear remained fixed.
formerly "arriviste" (ARV-ist!)

G.Dawes
Posts: 279
Joined: Wed Jan 02, 2008 11:00 am

Electric planes

Post by G.Dawes » Sun Apr 11, 2010 9:11 pm

I am most the way to having one, except for the battery and motor, Why is that? I have a Moni up and ready to go but never to fly as powers will not let me use my engine. That airframe is the same as the electric flyer in the States. The idea of of battery powered one would send someone into orbit. Think of all the unknown caculations that would be needed to invented. What section would it need to be certified under, how much cable would be needed for the backup power supply from the mains, would it need two of everything?

Brian Hope
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Post by Brian Hope » Mon Apr 12, 2010 2:44 am

Graham, it's becoming legend how many times you can manage to bring up your angst about the Moni. As I recall you are being asked to show that the firewall/engine mount is strong enough for the non standard engine you wish to fit - something many others have managed to do in the past but you seem to think shouldn't apply to you. I was only talking to somebody yesterday about a project they are working on fitting a four cylinder Jab engine into an ARV, they have designed, built and tested an engine mount and received approval for it. No complaints there about Enginering being obstructive, they just did what was reasonably asked of them and will soon have the aircraft up and running with its new engine.
Some while ago it was announced in the magazine that Engineering would waive project registration fees etc on the first electric LAA aircraft, that offer still stands as I do not believe we yet have had any takers.
With 2500 aircraft of umpteen configurations, standard aircraft and non aircraft engines and systems etc etc, your implied argument that Engineering is not willing to accept new ideas is patently unfounded. I have no doubt that when somebody decides to use electric power, Engineering will be more than happy and willing to assist them.

G.Dawes
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Post by G.Dawes » Mon Apr 12, 2010 8:24 pm

Many times is correct, but there has been a lot of negativity about the moni,
one of the engineers even wanted an alloy frame to hold the engine together from back to the front not the mount. I was assisted a lot by Jeremy Harris who did a lot of work only to be discounted by engineering, he thought there was another agenda. I set up a jig to test the front end and to a degree about five times any possible loading but that wasnt good enough. Never mind I cant fly anyway.

Simon Clifton
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Post by Simon Clifton » Tue Apr 13, 2010 11:53 am

Just to stop a bit of thread drift, and add my own thread drift instead...

Last weeks Flight International mag carried some interesting articles on electric GA stuff, did any one else see it?

The reason I am posting this now is that the Printers/Post office messed up the FI mailing, so it only arrived at the weekend. And maybe that will make Brian feel a bit better for a while.

Cheers

Simon C
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Ian Melville
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Post by Ian Melville » Tue Apr 13, 2010 6:40 pm

This may interest a few of you
The Royal Aeronautical Society is pleased to invite you to a General Aviation Evening Lecture …


The Technical Barriers and Progress Towards Electric Powered Small Aircraft

Ian Tadd, Philippine Aviation

**Free to Attend** Simply RSVP!

Thursday 27 May 2010 – 18:00pm

No.4 Hamilton Place, London, W1J 7BQ, UK

After a brief review of current electric aircraft projects, Ian Tadd will discuss the requirements for an alternative power plant to replace IC engines now used in light aircraft. To keep development costs down, major components from other applications are considered. Fuel is replaced by batteries or other energy sources and the piston engine by standard electric vehicle motors. The potential gains are considerable and Ian will explain what these are and how they may be optimised. Where figures can be estimated Ian will indicate potential capital and operating costs.

Serious challenges remain despite the huge advances and Ian will discuss these and promising research. Legislation, energy storage and the Governments need to maintain fuel tax revenues will be touched on. The aim is to inspire others to pursue this exciting new development in small aircraft.


RSVP is appreciated- Please contact the Conference & Events Department at [email protected] or telephone +44 (0)20 7670 4345


Time – Commencing at 18:00hrs, refreshments served from 17:30hrs.

Free – There is no cost to attend RAeS Lectures and they are open to members and non-members alike

IanTadd
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Post by IanTadd » Mon Nov 22, 2010 9:11 am

For those interested I'm repeating the RAeS presentation to the Gloucester Strut on December the 13th.

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