Series Hybrid into Plane, need help

14573 Views 39 Replies 8 Participants Last post by DaDeemster, Aug 8, 2013

DaDeemster

Discussion Starter · Jul 18, 2013

Hello all, after spending a decent bit of time polishing back up on my electrical knowledge i decided i'd finally move on to the public feedback stage of my plan, this is my first post On this awesome forum. I'm aware of this not being an airplane forum , but with this being the goto place for all things "electric vehicle" i figured it couldnt hurt

The objective of this build is try and find a clever way to shoehorn all the necessitys of a typical series hybrid into the plane without the plane tipping the scales, and cost effectively.

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Ok so the build is to be based in one of the following (its not important to have alot of plane backround knowledge) they are 20k and under planes with relatively a decent positive history

Sonex aircraft -http://www.sonexaircraft.com/
Pulsar Xp - http://pulsar-airplane.com/
Sonerai II - http://www.greatplainsas.com/sonerai_ii.html

**The Ac electric motors i'm leaning towards** are the Enstroj Emrax motor and the Hpevs ac51-76.
But since the Motors are comparable and the Emrax has a drastically better power to weight i'm gonna go with it (22lbs roughly) i was considering possible two so as not to stress the motor , unless new affordable alternatives have been released SO-

Emrax 228 - http://www.enstroj.si/Electric-products/emrax-motors.html

** Motor For Generator ideas** - (thinking compact, powerful (for when i need to bump the rpm's up to get the batterys some immediate juice

**This is the Dyno of a ICE motor that is slightly more powerful then it needs to be for the drive motor application -
http://www.aeroconversions.com/products/aerovee/
http://www.aeroconversions.com/images/products/HP-Torque_graph.jpg

-The motor im wanting to use to power the On Board Dc Generator is a ar741 rotary wankel motor from Uavenginesltd.com ( thier site is semi down)
i was able to find one on the internet
-i was also able to find a 30-40 horse sachs rotary motor, pull start
-i also found some running vintage snowmobiles that have the 38hp Sachs rotary motor

^^ will these motors suffice my generator power needs? direct Hp to Kw conversion wise they do even at peak torque range but is that all that matters?

Which brings me to my next dilemma, and this is where things start getting hazy- My Dc generator needs be able to directly convert as close to 100% of the rotary engine output power as possible but i dont know what dc generator make/size is best for matching it to the motors above. or if i need to run a reduction drive (i'm thinking not)

Secondly, is it really as simple as hooking the rotary to the generator and then finding a way to hold it at preset throttle positions for different charge rates
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Can it go straight from the Dc Generator to main battery terminals? and if not then what is the direct most way. Also does Generator need modifying

Also has anyone had any experience with foreign batteries? I've only heard non educated guess'. The deals are amazing and look well put together

-http://www.aliexpress.com/item/lifepo4-battery-pack-48v-55ah-electric-wheelchair-batteries-scooter-battery-with-bms-BOGO/898298740.html

-http://www.aliexpress.com/item/customized-lifepo4-60v-40Ah-Battery-pack-for-electric-vehicle-with-BMS-and-8A-faster-charger/708769853.html

And based off of someones post in this forum and the recommended voltage range for the motor i'm thinking the second battery link option would be best since its more voltage mediocre amp hourage , but since i will be so many batteries above the voltage i need to make it to run consistently so i can just enjoy the benefits of a big pack with so-so amp hours (around 180-220lbs)

Also i'd probably use the Medium- High Voltage motor controller options that they have available on thier site

But to stay in theme, if anyone has alternatives that i could use. and also thoughts on using one heavy duty controller for Dual Emrax motors. They said its not what they would recommend but i'd like to know more anyway. two motors sounds like less wear on each motor plus it would give me a instant additional power range without putting strain on a single motor. but i'm kinda confused on this . If im applying 20kw continuous from the controller to the motor will it perform the same with dual motors under the same 20kw contin' on dual motors? and if not what would be different besides more potential torque? Would i need 40kw from the motor controller to get the same desired rpms? or would the dual motors be suffice with same 20kw from the controller?

P.S i know i'm new and i pretty much wrote an article but feel free to take your guys time responding, i have a feeling i'm gonna be on this site for awhile lol

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jk1981

· #14 · Jul 23, 2013

Why?

As I see it you get much more weight, more potential for unreliability, more cost, more maintenance, lower efficiency and you're moving hazardous stuff into the cabin behind the firewall and out of the cooling airflow it will need. You're also likely to upset the CoG to the point where you're carrying ballast in the nose reducing performance further. Additionally you don't get the clean and silence of the electric solution nor the well understood simplicity and reliability of a small aero engine. The conversion inefficiencies and added weight mean you're very unlikely to see any gain in efficiency over a properly selected internal combustion unit driving the prop directly.

Sorry to be negative about this but unless you're certain of what you're doing this is waste of time and money, go one way or the other. Series hybrids really can be awesome... in locomotives and quarrying equipment but this seems like picking a solution then shoehorning it into a problem almost entirely created by the solution!

jk

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jk1981

· #17 · Jul 23, 2013

DaDeemster said:
" simplicity and reliability of a small aero engine" - ICE motors have alot of things that can "Just Happen". I love them as much as any gearhead but they arent perfect and teardowns are a pain and cost plenty of money and time

Don't get me wrong, I'm far from being anti electric or pro ICE for the sake of it. I just think that as a project at the moment it doesn't stack up. You're adding weight, cost and risk for no additional gain. You're effectively cramming 3 power plants (ICE plus 2x 3phase generator/motors), two energy sources and two high power inverters and a lot of bracketry to tie it all together in in place of one ICE... I know they can go pop unexpectedly but which of those two options sounds more likely to develop gremlins and realistically, which is going to be heavier

Personally speaking as as a glider pilot and an electronic engineer, given your stated goals I'd go for a nice standard 'off the shelf' self launching motorglider if it's the flying you're interested in. Second choice, with a much bigger budget and pretty well purely for the pleasure in the project and for quiet flight I'd go for an electric conversion on an existing self launching motorglider. Sell the ICE to pay for some bits. Seems like an expensive option to me but then I think the regulatory environment is a little different over there. A battery fire would be my main concern, pretty much every other powertrain failure in an SLMG you'll walk away from.

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jk1981

· #20 · Jul 24, 2013

DaDeemster said:
Since your a gliding pilot and engineer i was wondering what your thoughts were on the Xenos by sonex and the Europa Xp with Glider/Long Wings? they both get 40-45+mpg on their best "economy" behavior and both sport engine out landing abilities. They also seemingly stay in theme within your electric self launch motor glider params

I'm not familiar with them to be honest, I only fly pure gliders and nobody at my club has either aircraft type. Interestingly, and I wasn't aware of this before so thanks for piquing my interest, the Europa is made just up the road from where I live.

Looking at those fuel consumption figures and doing some back of an envelope calculations it looks like you'll need something like 25-30kWH of battery for a 100mi flight, less if you get into some lift, more if you get into trouble plus a bit in reserve of course however far you choose to fly.

That's going to be roughly 20x the weight of the equivalent petrol at 200+Kg for a 30kWH pack which is going to seriously impact on performance even if it doesn't take you out of limits for the airframe. You also may not achieve the stated airframe efficiency at the upper weight limit, you'll be a lot draggier. You could probably do it as a single seater but that doesn't sound like a compromise worth making to me.

I think to make touring practical you probably need to look at something slower still that can cruise at nearer 80mpg than 40. Of course the beauty of an SLMG is that in good conditions they will fly engine off but that's not a great deal of help if you don't get good gliding conditions or are not into that type of flying.

Discovery channel did a series on building a Europa a few years back: 'An Aircraft is Born' I think it was called. Might be of interest.

Good luck with it, whichever way you go but I do think you're going to find it very difficult to develop a satisfactory solution. A roughly 30kW + 30kW parallel hybrid looks to me to have the most promise of the 'electrical' solutions for a practical aircraft but being hard nosed about it the standard engine is the better choice.

jk

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jk1981

· #30 · Aug 6, 2013 (Edited)

DaDeemster said:
not even on a glider? - http://customflightcreations.com/sitebuildercontent/sitebuilderpictures/EUROPA285.JPG

A glider with the brakes out (regenerating via the prop in your case) drops like a stone to maintain airspeed, maybe 800'/minute as best I can estimate for what I fly without actually timing a descent. You may do a little better given air brakes also spoil the airflow but I'd not count on it.

Earlier on you mentioned the generator engine making more power because there isn't a high braking torque applied (propeller). Perhaps I misread you but if there's not a high braking torque applied it's not making high power, it's just freewheeling burning a little fuel to overcome internal friction and pumping losses, you get nothing for free. Your planned generator is still driving the prop (or the pack) albeit indirectly through a drive system that's a lot heavier and lossier than a simple reduction belt drive. Yes, you could with careful control manage the engine to maintain peak efficiency (which you'll need to determine for a variety of load/rpm/altitude conditions) but then you could also do that with a variable pitch prop. That's traded against the inefficiency of flying with a couple of degrees extra AOA to carry batteries and motors.

All the losses associated with hard driven propellers operating away from their optimum conditions while climbing or flying fast still exist with your hybrid drive, they're just multiplied up by the low system efficiency so you burn more fuel. You'll have a real challenge on your hands to rival the efficiency of a light engine in a light airframe (no batteries) belt driving a prop. Doing it safely and at a cost where you see any return on investment vs the standard engine would be a hell of an achievement.

A direct/belt driven alternator sized (and likely re-wound) for your generating requirements will be the simplest way to implement a generator, the control is simpler than for PMDC, the high voltages/currents are all handled by simple diodes, the controller is a low power device.

Doing it in a car is far easier, the added weight doesn't contribute to the losses or structural problems in anything like the same way. The pulsed power delivery is quite different too allowing undersized, overloaded parts cooling time. When it lets the smoke out you can walk away from it

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jk1981

· #34 · Aug 7, 2013 (Edited)

To stand any chance of operating with a system efficiency above that of a standard ICE (especially considering the additional drag caused by the system weight) you're going to have to operate your generator ICE at its peak efficiency. So far as I'm aware and I could be wrong on this that'll be around the peak torque (not peak power) RPM at full throttle for a gasoline engine. You dump power into the electrical system in bursts then shut it down rather than throttling back. The generator set is the brake maintaining sweet-spot engine speed so it needs to be controlled to give constant power out. In reality not there may not be much control needed, it'll depend to some degree on the shape of the ICE torque curve and the rate at which efficiency rolls off away from peak torque. A wound to suit PM generator and diode rectifier may be adequate so long as there's over-voltage protection provided to prevent overcharging. If active control is needed to maintain good ICE efficiency an alternator will be simpler and less costly/weighty to control. I doubt there's much efficiency difference between these two generator sets so long as they're properly optimized.

I'm afraid you lost me with the mpg(e) bit and 4x performance increase for electric conversions. I presume this comes form 25% efficiency chemical-mechanical for a thrashed ICE (and presumed 100% for electric, more likely in the 70-80% bracket).

The way I'd look at it is 1L of petrol contains ~35MJ of chemical energy, an ICE will turn maybe 10MJ of that into useful work. 10MJ is 2.8kWH

A gallon of petrol can be interchanged for 4.5*2.8= 12.6kWH of motor work which after losses comes from ~15kWH of battery work from an oversized battery (avoiding extremes of charge) of ~18.7kWH

These are rough numbers but we can see they're in the ballpark. Swapping from petrol drive to electrical drive is unlikely to yield an overall efficiency increase for the system (the aircraft) even if you can significantly boost the propeller efficiency. The added battery weight and associated higher AOA or speed will wipe out any gains you do make, cars don't suffer this loss so direct comparisons are fraught.

An aircraft that will go 45mi on a gallon of fuel will still only go around 45mi on 18.7kWH of battery or whatever equivalent mix of battery and fuel you choose as an energy source. Swapping to electrical drive is no way ever going to yield a 400% system efficiency increase.

The system you're proposing is effectively electrical gearing (as is used in trains/cranes etc) with mixed energy storage to allow a more efficient fan-prop to be utilised (do these actually exist at the moment?). For comparable reliability and a lot less weight would a small gearbox or a variable pitch prop not actually be a better solution yielding higher system efficiency? The electrical drive optimised fan-prop has to yield a huge efficiency gain to overcome the increased losses elsewhere if this thing is to justify itself financially over its lifetime. I just wonder if it can actually do that.

For what it's worth I *really* like the idea of electric flight and I don't doubt it's on the horizon for pleasure flying. The quiet efficiency of a glider combined with the flexibility and freedom of a light aircraft would be magical but at the moment the only way I see that happening where long flights are involved* is with what's basically an electrically boosted glider, maybe even one incapable of self launch with a few kWH onboard and a folding pod or prop for minimal drag when not under power.

A large modern glider with an L/D ratio in the mid 30s only needs ~3kW input (net after losses) to sustain level flight (calculated from l/d, speed and mass) at nearly 100kph. A mere 10kWH of battery now gets you toward 200km range in still air and level flight. I think this may point toward where we'll see electric flight going until energy density improves significantly.

*Ignoring the ultra low wing loading solar powered test aircraft that fly at jogging pace.

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