How large scale electric can you go?

[Adrian Smith 1]

Having successfully migrated to flying 60cc equivalent electrics and been pleased with the performance, I thought I might study the logistics of a 100cc electric equivalent.

Leaving aside the costs involved, largely because if the technology is unreliable or weights too much then the cost is immaterial. Anyway here goes.

For example if we take a Turnigy CA120 150kv (100cc) motor the weight is 2.73kg

The Opto ESC being Turnigy FatBoy V2 300A which weighs chunky 4.06kg. So basic power plant comes in at a hefty 6.79kg. Using a 12S set up comprising 2 (6S) X 10amp lipos totals 2.5kg. This added to 6.79kg comes to a shade over 9kg!

Averaging the weight of three 100cc petrol engines (DA, GP and DLE) comes in around for an engine 2.6kg! Okay so say an ignition battery 0.2kg and for arguments sake, 2 x 6v 3300 mAh nimh batteries plus Powerbox unit, equates to around 1kg so lets say 1.2kg in total. Add that to the engine makes 3.8kg. I think you can see where I am going with this. The ignition unit doesn’t amount to much in weight. However, the one thing I have not included is the possible weight of the exhaust system/canisters. But based on the above numbers I can’t believe it would be anywhere near the 5kg weight differences between the two systems. Reading through a few forums in the USA the subject is a bit "Marmite". There those who have done this successfully and those who dislike the idea with no middle ground. Clearly, duration is an issue with expectations no more than 8 minutes. Is my logic flawed? If so do tell!

[Dwain Dibley.]

Check out some of the big Electric indoor stuff Adrian, it's amazing, I was watching a 10 ft 4 motor jobbie, and an 8 ft C-47 just yesterday. I know you are talking outdoors, but it's worth a look Mate.

D.D.

[Adrian Smith 1]

That's crazy Dwain! I am sure H&S would have a field day there. I would love to know the electric spec on those aircraft.

[Peter Miller]

Now that reminded me of something frommy past,Now what was it?

Oh yes!! Of course!! Control line flying and that would be a lot cheaper and just as much fun

[Kim Taylor]

Posted by Adrian Smith 1 on 28/04/2018 11:54:10:

Having successfully migrated to flying 60cc equivalent electrics and been pleased with the performance, I thought I might study the logistics of a 100cc electric equivalent.

Leaving aside the costs involved, largely because if the technology is unreliable or weights too much then the cost is immaterial. Anyway here goes.

For example if we take a Turnigy CA120 150kv (100cc) motor the weight is 2.73kg

The Opto ESC being Turnigy FatBoy V2 300A which weighs chunky 4.06kg. So basic power plant comes in at a hefty 6.79kg. Using a 12S set up comprising 2 (6S) X 10amp lipos totals 2.5kg. This added to 6.79kg comes to a shade over 9kg!

Averaging the weight of three 100cc petrol engines (DA, GP and DLE) comes in around for an engine 2.6kg! Okay so say an ignition battery 0.2kg and for arguments sake, 2 x 6v 3300 mAh nimh batteries plus Powerbox unit, equates to around 1kg so lets say 1.2kg in total. Add that to the engine makes 3.8kg. I think you can see where I am going with this. The ignition unit doesn’t amount to much in weight. However, the one thing I have not included is the possible weight of the exhaust system/canisters. But based on the above numbers I can’t believe it would be anywhere near the 5kg weight differences between the two systems. Reading through a few forums in the USA the subject is a bit "Marmite". There those who have done this successfully and those who dislike the idea with no middle ground. Clearly, duration is an issue with expectations no more than 8 minutes. Is my logic flawed? If so do tell!

I don't know how much fuel a 100cc motor may use, but the weight should be added to the above to give a true maximum.

Obviously at landing, it would be lighter!!

Kim

[Former Member]

[This posting has been removed]

[Adrian Smith 1]

A quick calculation on the back of a fag packet, Kim. 1 cc of petrol = .75 gram so say a 100 cc engine has a tank of 50cc say ( I stand corrected there, however) so fuel weight would be 50 x 0.75, say 37.5 gram or 0.4kg at the take off. Still a weight issue for electric I guess.

Great piece of film, David. All those batteries .........!

[Phil 9]

I am no expert here but having attended a few IMAC competitions as a spectator I think a electric 100cc size model is perfectly doable and could offer some advantages in competition flying over petrol. but the stumbling block for IMAC at least is the duration. At a good model weight there is not enough duration to complete the IMAC routines. Adding enough battery to give the duration makes the model to heavy. But this is working within IMAC competition rules whils trying to stay competitive. I think for the sport flyer cost is a limiting factor

[Adrian Smith 1]

Yes Phil, I agree for a competition flier it really is a no, no (I am not one by the way so less of an issue). But yes, cost is a big consideration particularly you go for more upmarket on motors like Hacker. Also I am not sure that a 100cc equivalent electric is much quieter than a 100cc petrol with decent quality canister exhaust on it. So I am not sure pure noise consideration would bring any benefit.

[Adrian Smith 1]

Wot a dope I am!!

The Turnigy FatBoy ESC is 406 grams which equates to under 0.5 kg not as I said at the beginning (4.06kg) . That puts different complexion on it making the motor + ESC around 3.25kg. A much more healthy figure.

[Geoff S]

I haven't researched the idea of a 100cc electric equivalent because a) it's too big for me and b) probably too expensive (the thought of a few thousand quid up there relying on my uncertain skills horrifies me ). However, I have a few successful glow to electric conversions under my belt and I've always found the weight issue to be that I need extra lead (or batteries) to get the CoG to where it should be and designed to be with a liquid fuelled power source. I'm surprised that the weight advantage disappears somewhere higher up the scale. Perhaps it's because there are fewer options? The biggest I've done is my quarter scale Mew Gull which flies well on its 6S 4AH LiPos but I haven't yet tested its duration to the limit but 7/8 minutes is OK.

Certainly duration is still an issue with electric models but not so much as formerly with brushed motors and NiCads as the energy store. A 10 minute flight is a lot for me and I usually look to land after about 8 minutes and all my conversions cope with that easily with energy to spare in the LiPos. Power isn't an issue. You can get as much power as you want from an electric set-up ( I sometimes travelled to school in an electrically powered double-decker which had phenominal acceleration but it's energy came down overhead wires).

Geoff

[Adrian Smith 1]

Geoff, I must admit I rarely fly for more than 7 minute per flight (suspect concentration I fear) , so duration would be less of an issue. So really it's just down to cost & noise considerations I guess. I have study that too.

[Former Member]

[This posting has been removed]

[Adrian Smith 1]

As a solo flyer I am lucky enough not to have the problem of queues, other than one full size light aircraft using the runway a couple of times a week.

[Biggles' Elder Brother - Moderator]

Posted by Adrian Smith 1 on 28/04/2018 14:03:04:

A quick calculation on the back of a fag packet, Kim. 1 cc of petrol = .75 gram so say a 100 cc engine has a tank of 50cc say ( I stand corrected there, however) so fuel weight would be 50 x 0.75, say 37.5 gram or 0.4kg at the take off. Still a weight issue for electric I guess.

Great piece of film, David. All those batteries .........!

Adrian, I'm afraid you're being very cavalier with your decimal points again!

No way would a 100cc engine have a tank of 50cc - that's only approx ten teaspoons of fuel!!! Tell's call it 500cc, that would be more like it! and yes that would weigh around 0.4Kg. Right answe - wrong route!

BEB

[Tom Gaskin 1]

Going back to your fuel statement, 50cc is about 2 ounces, wouldn't keep a 100cc motor running for very long...

Tom

[Biggles' Elder Brother - Moderator]

Posted by Geoff Sleath on 28/04/2018 14:35:04:

...I have a few successful glow to electric conversions under my belt and I've always found the weight issue to be that I need extra lead (or batteries) to get the CoG to where it should be and designed to be with a liquid fuelled power source. I'm surprised that the weight advantage disappears somewhere higher up the scale.

Geoff

I my experience at the 60-120 size range there is very little difference in weight between the IC and the electric versions. A few ounces at most. But, there is a very big difference in how the weight is distributed!

In an IC model 90% of the weight is in the engine/muffler and that is right up front, maximum distance (leverage) to the CoG.

In an electric model of this size, while the motor has a significant weight (maybe 25-30%), the heaviest single component is usually the battery - probably 70% of the weight of the power system. And what do we do with that? We put it on its back in the fuel tank space. In this arrangement its mass acts half way along its longest dimension, its length, and it is at a reduced distance from the CoG, so the leverage of our heaviest element is compromised. Generally I find its much better to grasp the nettle, do a bit of extra work to make a new hatch and battery chute and position the battery on its end (vertical) on either the front or back face of the firewall. That way there is a lot less need for lead!

BEB

[Denis Watkins]

Don't forget that we use most of that fuel up, so may start the flight 1lb heavier

The fuel is usually stored behind the firewall, but have seen a few models with tanks nearer the wing inside

In old money, the fuel in this sized model weighs nearly 1lb, and the model still flys

There is some leeway

[Geoff S]

Posted by Biggles' Elder Brother - Moderator on 28/04/2018 16:29:17:

Posted by Geoff Sleath on 28/04/2018 14:35:04:

...I have a few successful glow to electric conversions under my belt and I've always found the weight issue to be that I need extra lead (or batteries) to get the CoG to where it should be and designed to be with a liquid fuelled power source. I'm surprised that the weight advantage disappears somewhere higher up the scale.

Geoff

I my experience at the 60-120 size range there is very little difference in weight between the IC and the electric versions. A few ounces at most. But, there is a very big difference in how the weight is distributed!

In an IC model 90% of the weight is in the engine/muffler and that is right up front, maximum distance (leverage) to the CoG.

In an electric model of this size, while the motor has a significant weight (maybe 25-30%), the heaviest single component is usually the battery - probably 70% of the weight of the power system. And what do we do with that? We put it on its back in the fuel tank space. In this arrangement its mass acts half way along its longest dimension, its length, and it is at a reduced distance from the CoG, so the leverage of our heaviest element is compromised. Generally I find its much better to grasp the nettle, do a bit of extra work to make a new hatch and battery chute and position the battery on its end (vertical) on either the front or back face of the firewall. That way there is a lot less need for lead!

BEB

I suppose that's true of my Mew Gull. The battery is in the fuel tank space (and there's room for about 4 x 6S 4000 mAH LiPos ) and I find it balances OK without ballast. On my current, almost completed, build of a DB Cirrus Moth I've done what you suggest and the 4s battery is as far forward as possible - a lot of it beneath the motor so I'm hoping for zero lead. I haven't yet had the opportunity to check the CoG but very soon.

In any case, unless measures are taken to reduce weight at the tail, both glow and electric conversions have to weigh the same in order to get the CoG right. It's just that in my experience the electric version needs a bit a ballast to achieve the right weight distribution.

The idea of a 100cc electric equivalent is interesting. The noise from IMAC competition models is one of the reasons they were stopped from promoting competitions at Ashbourne but there are F3A aerobatic events a couple of times/year and they are now almost exclusively electric.

Geoff

[Adrian Smith 1]

More competition fliers seem to be going electric from what I see, Geoff. It is just I thought I would look at the pros & cons of 100 cc conversions. Whilst I accept some of the comments I have seen on other forums discussions over electrics & IC is one about folks not being able to tune petrol engines properly hence the move to electric. I don’t buy that argument for the UK, as clearly flying site noise is a big factor in migration to electric. For me the simplicity of electric set up is the appeal vs IC, but I accept the cost is an inhibiting factor.

[eflightray]

To me the possible big problem with many large electric powered IMAC type planes is, they have used a model designed and built for IC power. Most IMAC models seem to use composite fuselages.

If you design and build for electric power you can reduce the weight. For every ounce you save of the build you could use as extra battery capacity.

Ray.

My depron version of the TN 70" Spitfire, (mine is 72" ) , is half the quoted plan weigh for a balsa IC powered version.

 

Edited By eflightray on 28/04/2018 18:53:24

[Phil 9]

[Phil 9]

[Former Member]

[This posting has been removed]

[Adrian Smith 1]

Thanks for those clips, Phil. Very interesting indeed. The Yak seems quite smooth. My only worry is using 14S set up pushes the voltage over 50V which requires a qualified electrician in UK, as it's considered life threatening. that's why i would stick with 12S

Edited By Adrian Smith 1 on 28/04/2018 19:49:55