George, I am, I think, reasonably well experienced and able to understand the principles of electric flight powertrains and have contributed one or two items to that effect here and in the mag

 It was the reference to " I must increase the volts to 8C" which, as you correctly surmised ,that I did not understand. As I say, things can be confusing enough for beginners without mixing the terminology of capacity ratings and voltages.

That Should read *8S or about 29 volts

NS = number of cells in a battery pack eg: for Lipo at @ 3.8 VOLTS per cell for 8 CELLS in total would be 3.8 X 8 = 30.4 VOLTS. As the actual cell voltage will vary with its state of charge, it is easier to say(in the above example) 8S rather than a nominal voltage to avoid confusion.

We say S rather than C (for Cell) which would seem more obvious, because the letter C is used to indicate the discharge rate of a battery pack. (Dunno why they did'nt use D then!)

So as a working example: a  5000ma (5 AMP) PER HOUR ,20C ,8S lipo pack can  deliver up to 5000 X 20 = 100AMPS, obviously not for an hour (more like about 3-4 minutes if operated continuously.

I now have an eight S battery pack for the Mitchell. The motors will take this voltage, but the ESC was only good for 6S. The Turnigy 100A  HV 8S ESC,s have now been fitted

As you can see I have discarded the old tubular spacers (see below) in favour of an integrated motor and ESC mount. If I wish I can cut a ventilation hole in the bottom of the cowl and the ESC heatsink is going to benefit from this.

This was tho old (manufacturers) method)

The motors feel more solidly mounted on what is essentially a small box with an extension glued  on the bottom side for the ESC. (picture 2 shown with wing inverted)

We Have:

13 X 8 props APC electric 2 blade

This produced 1,254Watts PER MOTOR @ 46AMPS!!   Yikes! I could nearly take off on one.   

Realistically, I would expect to cruise at half that power and achieve a decent flight time. 

I still have a lot of further work to do regarding flaps, the springs in the retract legs need looking at, but I am nearer to flight test!

Peter said

"That Should read *8S or about 29 volts

NS = number of cells in a battery pack eg: for Lipo at @ 3.8 VOLTS per cell for 8 CELLS in total would be 3.8 X 8 = 30.4 VOLTS. As the actual cell voltage will vary with its state of charge, it is easier to say(in the above example) 8S rather than a nominal voltage to avoid confusion.

We say S rather than C (for Cell) which would seem more obvious, because the letter C is used to indicate the discharge rate of a battery pack. (Dunno why they did'nt use D then!)"

But that is my point - you DIDNT - you said 8C and this is the reason for my post.

All that was required was a simple correction statement saying " I meant to say 8S not 8C " and all the other drawn out explanations would have been un-necessary

As for using "D" to describe the packs capacity this is hardly necessary either....the designation "20C" for instance is simple enough to understand especially as we are all used to it - 20 x Capacity.

We say S rather than C (for Cell) which would seem more obvious, because the letter C is used to indicate the discharge rate of a battery pack. (Dunno why they did'nt use D then!)"

The reason for using S is that it denotes cells in SERIES. You will also see the letter P used to denote cells in PARALLEL. e.g 3S2P which I think means 6 cells arranged in 3 cells in series, in parallel with another, 3 cells in series. You can see why the short hand is so useful because a full explanation is very confusing.

OMG I give up !

I am obviously not getting my point across here  

Roy...thats rich - suggesting "time out" and "lets get on with the build" - then you stray way off topic and start talking about chinese ARTF instructions!  My postings ( however interpreted ) were in reponse to the O/Ps comments and are important - even if you dont think so - call me pedantic if you wish - many have done so before - however I feel it is important that people do not add to the already confusing world of electric flight terminology by making unclear statements about such things. There is no need to post what comes across as an arrogant message - at least my frustrations are tempered with a few smily icons etc. If you had bothered to read the whole thread you will see that I have been involved in many postings in it, right from the start.

Incidentally Peter, thats looking very nice - I like the new mount arrangement

It reminds of the old joke about the 'lone modeller'

He was castigated by some of his peers for always flying on his own (as being seen to be unfriendly)

The lone modeller retorted that he preferred, as did a few, others to the peace and quiet of his flying.

He rejected this slur upon his character and said that he would see to it that, as he put it,

US LONE MODELLERS MUST STICK TOGETHER AND RESIST THIS ATTACK UPON OUR WAY OF FLYING (a little light humour always calms the day!)

There are increasingly less & less obstacles in my way of a test flight LOL,LOL.

All those who want to start something, be at OW at a convenient date!! HeHeHe.

PS. I went flying today with my CAP232 Ran the batts dry. Hope y'all were working hard

When we refer to the C rating of a battery this is NOT capacity.

A battery's capacity is mearured as its nominal Ampere/hour rating. In our models its is ofren expressed as milliamperes. This is more properly milliamps/hour

The 'C' rating of a battery is is the multiplier over the nominal rating, at which current may safely be drawn without detriment to the battery.

Example 1:    a 5000ma battery with a 20 C genuine raing can deliver 100 AMPS (5 X 20)

Example 2:   a 2500ma battery with a 25C genuine rating can deliver 62 AMPS 2.5 X25)  

 Where the demands on the battery are greater than its nominal '1 C' rating then you will get less than the (theoretical) ! hour.

AT 2C it will be !/2 an hour. At 4C it will be 1/4 hour. 

You cant get something for nothing. The blessing is that with our very efficient electric motors combined with light batteries with high energy density, we can have electric flight times of 5-10 minutes or longer.

B25 MAIDEN FLIGHT!!

At 1430 hours today I roareddown the strip and UP UP & AWAAAAAAAY.

The book said use 1/2 flap on rough grass. Well maybe, if you have marginal power. I had loads it seemed, because it reared up of the ground a bit quick. I hastily got it sorted, wheels up, flap up, and into the first turn. A wide and quite steep turn, back up the top of the field and in for a low pass.

Wow that looks the biz     . I had set the timer for 4 minutes, so I started throttling back for a trial approach & overshoot on 1/2 flap. That big wing certainly has some lift. The plane just floated on down the runway at @ 50 feet. 

Now the timer is bleeping in my pocket, so I had better get this baby in circuit for landing. Wheels down, half flap and a nice long straight in approach. It wasn't sinking very much. I should click in some down trim next time. The first wheel touch was too fast and she bounced about 10 feet . Keep cooool and level and let the speed die a bit more. Now the second landing was better

Model was checked over. I found a tyre half off the rim, on the port main, and the nose leg retract block needed squeezing back as it had spread a bit.

The speed controllers were cold, and the batteries barely warm.

The flying performance of this plane in the air is very smooth- thats what you get with large models. They don't however, like rough landings. Things get bent all too easily.

The ground clearance with 13 inch props on grass means I have green stains up the flaps!

The field I fly on is used for Sunday Morning car boot . Its big, but a bit 'Agricultural' 

My Neibour, Andy, has the stills and video clips. Hope to get these posted in the next day or so.

It would seem that 36 volts( 8 S ) @ 5000ma is not going to get me very long flight  times. I may have to consider more efficient motors. There is not much more room in the 'bomb bay' for larger capacity batteries.

I am going to have a think about the new Turnigy SK Aerodrive range. I have one in a CAP 232 which is a very smooth performer.

Anyway its a RESULT

Now for a few Fosters!

The battery packs lie directly acros the C/G

Google Link:

link

Conclusions

It has been an interesting project. Electric flight has, after many years of flying glow & petrol

re -awakened my interest in model flying . It is not without its own problems. I have been in electronics all my life.and there are still always new thing to learn.

My 88 year old father, who was a full size glider pilot in his younger days, has a keen interest in electric R/C flight. His eyesight is not sharp enough for model flying. But he still builds them, and I get to do the flying. 50 years ago he was teaching me!

An Old Bold Pilot with his Tiger Moth

Congratulations Peter .

Looks good in the air and  none of that oily mess to clean off afterwards .

Fly Electric .

Kelvin

A Cautionary Tale

An old acquaintance of mine who lives in the next town, Mick Reeves, once said:

If your maiden flight is a success, then no matter how fine a day it may be, take it home there & then- in one piece- and go over everything again, screws, links, solder joints etc.

With his words ringing in my ears, I discovered the wing dowels were not glued in !! .

It will be a week or two of checking over I think