What would Happen? Adda Motor

[bjk896]

I’m an old bloke (81 yo) picking up model aircraft activity with a build of a C130 Hercules that was intended to be a display model. It will now be a flying model  because as the build progressed, some things needed to be done along the way or else it could never happen. Its 1600 mm wingspan and in the 3-4Kg weight range built of depron.

 

So a great learning curve got started and rolled on and things are now  to the power train stage with a lot of sums to be done.

 

In the course of getting there “someone” asked the rhetorical question “A Herc has four engines but could you run it on two electrics  and 2 dummies?” Whilst I doubt that will happen it is an interesting concept and DID raise some questions in my mind about the things that happen when one makes a propeller, or propellers, spin.

 

If a given electric motor with 7 x 5   prop rotates at “x” RPM the craft has “y” thrust and an end  distance “z”  meters through the air.

If an additional engine/prop combo is added, what are the dynamics that occur? Will the  power(watts)  to  the two be halved, is the air distance  doubled or what relationships occur or change or remain the same?

 

I’d appreciate the discussion

 

[Denis Watkins]

It will take time for the lads on here to work the numbers bjk, but my twopenerth.

When building " to fly " a model of this size, I would be aiming for 2kg all up.

In old money, ballpark, if building to fly a 5 foot depron electric model, aim would be 3lb - 4lb.

Lots of discussion to come.

Edited August 21, 2023 by Denis Watkins

[David perry 1]

Short answer to the half power etc etc is ..depends.  series or parallel fed?  Same battery or twice as big /one each?   Apply logic.

 

Two airscrews won't pull the model twice as far... a 9 inch pitch is a 9 inch pitch however many props there are doing it.  They might do it faster or more reliably (ie without slip) or pull more mass through that 9 inches, but 9 inches it will be 

 

The real answer you want is that yes, you can run the four engined model on two motors and two dummies and most builders probably would.  

 

Sounds a fun.project and a few pics would be nice to see.

[Outrunner]

Not done any sums but 3 - 4 kilo sounds awfully heavy for a 1600mm span model. Do you mean 3 - 4 lb?

I would try it on two motors first and add another two if required.

[MattyB]

9 hours ago, bjk896 said:

It will now be a flying model  because as the build progressed, some things needed to be done along the way or else it could never happen. Its 1600 mm wingspan and in the 3-4Kg weight range built of depron.

I have read and re-read the first sentence above , but I still can’t work out what it means, sorry… What led you to change your mind from this being a static model to a flyable one, and is that 3-4kg AUW really correct? It sounds hugely heavy for a Depron model, even at 1.6m span.

[Eric Robson]

My foamboard and depron Sunderland is just over 1800mm weight about 5.5lb ready to fly, it would fly on two motors as it is way over scale speed at full throttle. The outer motors are 2212 1000kv with 9x6 props not sure on the inner, they came from a Hobbyking B25 and have 9x4 props battery power is 3s 3000 x2 one for the outers and one for the inners. 7 minutes flight leaves about 20 to 30% despite being different motors and props  consumption is similar. 

[Simon Chaddock]

bjk896

If you think about it the Herc has four engines because it needed that amount of power to carry theintended payload and there wasn't at the time two big engines of suitable power.

For RC model electric there are motors avaiabel of almost any power so you could make a Herc fly quite happliy on two or even one.

There is a question of do you use dummy props. They create drag even if they are modeled as fully feathered.

Any chance of a picture of progress so far?

 

As others have mentioned 3-4kg is pretty heavy for a 1.6m span plane, particularly if using Depron foam. It is likely to have to fly, and land, rather fast. Far from ideal if this is your first RC plane.  

    

[bjk896]

Fellas,   Thanks for the interest so far 

MattyB    A translation is that at 81 the choices are do something or sit on the backside so Plan A was do something and a Herc seemed like a good idea at the time. As I began getting things together, friends commented about where, when, I might fly it. It evolved from those comments that if a flying machine needed a radio, radio installation, servo installation, power, linking bits etc etc they couldnt be added when it was finished as a display model - so do it along the way. That decision took 3 months or so. Thats also why the weight is a bit of a guess.  I have no idea what it will weigh when complete.

 

Chris There are no photos of significance now as I lost my phone pics but attached is one early on when I took it inside to use the smoother less cluttered table to assess levels etc and before dihedral brace was made for wing.. It has progressed far beyond that with fuselage painted and looking a bit more complete   I shall take one tomorrow and post it

 

This might seem like a casual approach but that is what it is. Hence the sums needed are to actually work it all out never having had the experience and finally use 6.5 x 4 props that are scale for it.

[bjk896]

Eric

The Sunderland  has me totally jealous. Looks fantastic but your numbers are the real interest for me because it is the whole story and a lot  of reading I have done never has the total picture for a new fella to get some confidence about the subject.

I shall try to understand what your numbers mean and thank you

[Eric Robson]

HI bjk896, this is the same motor that is in the Sunderland outers as you can see it is quite small, the 1000kv is the revs per volt so with 12 volts that is 12000 rpm 300kv would be 3600 rpm but it would turn a much bigger prop. Feel free to ask whatever you need to know. 

[MattyB]

3 hours ago, bjk896 said:

MattyB    A translation is that at 81 the choices are do something or sit on the backside so Plan A was do something and a Herc seemed like a good idea at the time. As I began getting things together, friends commented about where, when, I might fly it. It evolved from those comments that if a flying machine needed a radio, radio installation, servo installation, power, linking bits etc etc they couldn't be added when it was finished as a display model - so do it along the way. That decision took 3 months or so. That's also why the weight is a bit of a guess.  I have no idea what it will weigh when complete.

 

OK fair enough. Based on that photo I doubt it will weigh anything like 4kg, so that is good, but we do have to give you a reality check - that will be no beginners model.

 

If you do want to fly it yourself you are going to have to learn on a much simpler and more forgiving trainer first, and there is at least one and probably two more models needed between that and you being able to fly the Herc with confidence. Of course an alternative you could just get another experienced pilot to fly it for you. Sorry if that is a bit disappointing,  but trust us that if you went out and tried to fly that as a complete beginner, it would not last long! 

[Simon Chaddock]

bjk896

That looks a very competant build.

Can you weight it as it stands now along with a current picture.

The weight will be important as it largely determines how much power you will need to fly satisfctorily that  in turn will deermine the size of the motor to be used and thus the size and weight of the battery required.

Just to give you an idea this is the Avios Hercules

Span 1600mm

Weight 2400g

4x2627 1000kV motors

18A speed controllers

Scale props

It shows it can be done but unfortunately it is no longer in production. 

 

[bjk896]

The Plan I used is an oldie I was given and was a control line plan However its numbers are close to the Avios and I an only hope my weight guesstimate is way too high.

Time will tell.   I have 4 props purported to be same as Avios and I got those because they were scale but that is probably the basis for my whole quest.

That is having the props, can I get reliable methodology to work for calculating all the bits in the power train. As part of that I need to understand it fully

 

Sorry Simon I haven't weighed it as I have no scales but Ebay promises to fix that in two weeks and maybe then I will have a better picture

 

Mattyb  I have no fear of learning to fly straight off regardless of consequences. That said, I very much appreciate your comment. I am a qualified drone pilot and for years sailed A class model yachts so I'd think I'm not starting as a complete dud. As well I decided early on that simulator, simulator simulator and carefully plan the steps on the path to leaving the ground.  I live in a rural part of Australia so my choices are limited. However it will happen !!

 

Three tries at loading a recent photo have failed so that'll come later

[Don Fry]

Trouble is mate, after you choose to leave the ground, you are obliged to land it. If you are in rural Australia, if it is legal to fly, (advise  insurance), then your drone licence may be good enough to find a safe site for the experiment.

But a first build, 4 motors,  from a control line plan, altered to radio control is a big learning curve, a lot of time, and a wad of dosh. 
Now if your quest is to see it rise, and fly, and that is the end of the quest, good luck, and so be it. If you want to build it, to prove you can, great. 
But if you want to take it home, not the model for you yet. 
I too have a commercial drone licence, acquired by accident basicly. It a French licence, and of no use for flying model aircraft whatsoever, but the safety exam covered site risk assessment to a reasonable standard.

Otherwise, get/build a cheap tough trainer, and go from there. Build, crash, repair, replace. It’s more fun than it sounds, it’s as I did it 60 odd years ago.
A motor glider is a good start point. Or a rudder elevator free flight conversion to RC. 

 

[Peter Jenkins]

5 hours ago, bjk896 said:

I am a qualified drone pilot and for years sailed A class model yachts so I'd think I'm not starting as a complete dud. As well I decided early on that simulator, simulator simulator and carefully plan the steps on the path to leaving the ground.  I live in a rural part of Australia so my choices are limited. However it will happen !!

 

Hi bjk896

 

When you say you are a qualified drone pilot is that a commercial drone which has an autopilot flying it with your inputs just telling it where to go or is it a hobby drone that you have to fly yourself with limited stability provided?   If the latter, then you stand a fighting chance but if the former then I think 10 secs from take off is the average time for the first flight when on your own.

[Geoff S]

14 minutes ago, Peter Jenkins said:

Hi bjk896

 

When you say you are a qualified drone pilot is that a commercial drone which has an autopilot flying it with your inputs just telling it where to go or is it a hobby drone that you have to fly yourself with limited stability provided?   If the latter, then you stand a fighting chance but if the former then I think 10 secs from take off is the average time for the first flight when on your own.

 

That isn't necessarily the case, though not unlikely.  The adult son of one of our members who'd been flying helicopters brought along an Extra with an OS52 engine to the field he'd bought on eBay.  He started it after checking range and controls, took off, did a few circuits, a roll and a loop before landing with a bit of a bounce but zero damage.  It was the first time he'd flown a fixed wing in real life other than on a simulator!  He's one of those annoying people who are naturals at everything they attempt - and even more annoying he's a very pleasant chap 🙂

[Peter Jenkins]

I think if you can fly a helicopter, which is a lot less stable than a fixed wing, flying fixed wing is no big deal.  That was why I asked what sort of drone he flew.  If he's capable of flying a drone with all the stability aids turned off, not always possible, then he might be like the chap you mention.  However, flying an aircraft that has already been flown takes out many of the unknowns such as CG position, control rates etc.

You are saying what I said Geoff.

[bjk896]

I'm having so much trouble answering previous posts its not funny. This isnt a contribution but rather an attempt to see of my post is successfull bjk

 

[bjk896]

Guys, This is getting a bit off track. I notice this unfortunately happens on every forum I have ever  visited in my learning path.  It is not particular to RC flying either.

Add to that my attempts at previous replies have been thwarted by the foul up fairy or a close relative. Here goes again

 

I do not have RC fixed wing experience. I'll wear the consequences of that.

If I lose it I'm in a pretty big club with about equal number of experts and novices walking away with a few bits in their hands on a first flight.. I will try to mitigate  that with learning, simulator time, sound advice and reasoning.

 

I do very much appreciate the things experienced people are telling me and the concern for my inexperience but please appreciate that this is what I want to do.

 

Now, please, I'd like to move on and get back to my question which may have been a bit round about but I repeat it below..

 

Beginning with four props that I wish to use because they fit the original intention of this as a  display aircraft, what sequence of calculations are needed to drive them, perhaps even in what order, and get hardware to do just that. Yes I may have problems along the way but it is what I want to do., I would really appreciate your guidance to that end.  Thanks

 

PS  I tried three times to load a photo and each time got a "Code 200"   This attempt No 4 of the Herc as of last week

The really observant may spot the camera slot in front mid windscreen

 

 

 

[Simon Chaddock]

bjk896

That is a very impressive piece of work. Certainly worthy as a display model.

 

If you are using the same scale props as the Avios C130 you could simply use the same motors, ESCs and battery unless your C130 is goig to be significantly heavier.

Indeed the exact same motor was carried by Hobby King as a replacement for those in the Avios C130 but at the moment is out of stock with no expected delivery.

https://hobbyking.com/en_us/avios-c-130-v2-replacement-2627-1000kv-brushless-motor-w-x-mount-screws.html

If the same motor is not available it should be possible to get one that is close to the same specification.

As an example this would have similar power of the 2627 on a 3s battery..

https://www.banggood.com/SURPASS-HOBBY-C28-Series-V2-C2826-1000KV-or-1200KV-or-1350KV-or-1900KV-Outrunner-Brushless-Motor-2-3S-for-RC-Airplane-p-1992712.html?utm_source=googleshopping&utm_medium=cpc_organic&gmcCountry=GB&utm_content=minha&utm_campaign=aceng-pmax-gb-en-pc&currency=GBP&cur_warehouse=CN&createTmp=1&ID=47991&utm_source=googleshopping&utm_medium=cpc_pt&utm_content=meruem&utm_campaign=aceng-pmax-uk-HCLT-230705&ad_id=&gclid=CjwKCAjwxaanBhBQEiwA84TVXLGih-iMYE7iwN9LCyvo0Azf_LYCHg_Xo9S_fYBEkSsF616yP3rZHhoCGcYQAvD_BwE

 

There is aot to be said for copying a set up that is known to work for a particular plane sixe and weight.  

[bjk896]

Thanks for that Simon

I have parked those details away to have a look at.

 

I had earlier looked at Avios specs and wondered if I could copy them off for my Herc and thought that -

(1)  I wouldnt learn anything if it worked and that was still a long way down the track of the build

(2) A month or so ago, I'd put Avios numbers thru one of the US Calculators and was bewildered when it reported it wouldnt fly !!!

(3) If my Herc's weight was agonisingly different, what would I have to change to make it fly and I wouldnt get a clue about that till I was at heaven's door.

 

Hence that really was why I started this thread - to better understand the progression of calculations to get a more certain or less risky outcome.

 

PS  the Ebay scales haven't arrived yet

[Don Fry]

I copied this from somewhere when I started designing electric setups. I found it good.

 

Magic numbers for modelers...

 

Schoolboys (and girls) know Watts, Ohms and Amperes. Modelers speak of props, lipos and BESC's. Not to forget the mysterious ‘KV’ and the famous ‘C’, which is not the speed of light... But what hides behind these cabbalistic concepts? And how do they relate to the everyday business of flying RC machines? Follow the magic numbers...

 

Today's pilots understand that you get more from a good electric setup than an average IC engine. Cheap sources of equipment have dramatically changed the price tag on brushless motors, ESC's and batteries. But it is still something akin to the dark arts to select the right combination of these three items in order to fly well. The best way to success is to follow the secret recipe of electrical gurus, based on kilometers of burned windings, and the third law of universal common sense. Enter the hidden side of real-life quantum physics, the one that mixes weight and mass, translates temperature in 'seconds-of-finger-on-the-motor-bell' and flying times in burned amperes... Who cares for the Science, as long as we can punch holes in the sky 

 

 

Buy your watts by the kilo (or Pound)

The first magical number tells you how much watts you need to fly your plane. Of course, it works only for decently matched systems. A GWS parkflyer won't fly with a 300gr motor,

however powerful it is...

 

Foamie, motorglider, Piper Cub: 100watt per kilogram (2lbs)

Trainer: 150 watts per kilo

Warbird, 'sport' aerobat: 200 watts per kilo

Racer, 3D: 300 watts per kilo

EDF Jet: 400 watts per kilo

 

Examples: a 3kg (6lbs) 150cm (60") Hurricane will fly on a 600watts setup. A 2.5kg Calmato will require 375 watts, etc.

 

Watt is pushing us forward?

The second magical number gives an idea of how much static thrust you can expect from a good setup. Once again, this is only true for a propulsion system that is performing normally.

These values give a good indication of what is possible... and what is not.

 

Brushless outrunner: 4gr per watt

EDF: 2gr per watt

Brushless 'inline': 2gr per watt

Brushless 'inline' with gearbox: 5gr per watt

 

Examples: A warbird with a 1000 watt brushless outrunner will have 4kg static thrust. An EDF jet having a 600 watts power system gives 1200gr thrust on the ground.

 

Powerful horses...

The third magic number is in fact a magic formula, one that most of us forgot after school...

 

Watts = Volts x Amperes

Volts = Watts / Amperes

Amperes = Watts / Volts

 

How does that relate to horses? Easy: you can convert watts to horsepower with the following rule: 1000 watts = 1.34 HP or 1HP = 750 watts.

Example: a Trainer aircraft with a 12 volt battery delivering 40Amps gives 480 watts (or 0.65HP). Note that the same plane having the same performance in IC would use a .40ci engine providing 1HP, which is 750watts... This is because electrics have a better efficiency, with more power at lower rpms. A similar phenomenon applies to diesel vs. petrol cars. The diesel drives better even if both cars have the same 95HP.

 

 

One Hot Minute!

E=Mc2 and the planet is warming up, everyone knows that. Electric motors also get warm. To know how much too warm the windings should not glow, here is a rule of thumb that is nothing short of magical... 

 

Prop aircraft: motor weight in grams x 3 = max. watts.

EDF: motor weight in grams x 5 = max. watts.

 

Example: a 235gr brushless outrunner can dissipate 705 watts for a minute without meltdown.

A 200gr inrunner on an EDF will not die even at 1000watts.

Of course, this is assuming the motor is correctly used and cooled by adequate airflow.

This rule is only true for brushless motors. Old 'can-style' brushed motors like the Speed 600 don't survive more than their weight in watts...

 

 

 

Resistance is useless...

Gold is a fantastic metal when it comes to moving currents. Unfortunately it is also very heavy. That is the main reason for us to use copper in electrical wires. But then copper transforms some of the current into heat. Not only does it fuel global warming, but it reduces the available in-flight power, which is a real catastrophe!

To avoid this dramatic event, one should always use large enough wires:

 

Up to 25A: 1.5mm² wire section (15 AWG)

Up to 60A: 2.5mm² wire section (13 AWG)

Up to 100A: 4mm² wire section (11AWG)

 

Not only wires, but connectors and soldering must be able to handle the current. In this field like in others, bigger is also better...

 

Round and round

You always wanted to know what the famous 'KV' stands for? This indicates the number of revolutions per volt provided by an electrical motor. It gives us the 'nominal' rpm of a motor on a plane.

 

rpm = KV x volts x 3/4

 

Examples: a 1200KV brushless outrunner connected to a 10 volts source will turn at 9000rpm. A 4200KV inrunner on 10 volts will spin at 31500rpm.

 

Full or empty, that is the question...

The voltage of NiMh cells is said to be 1.2 volts and lipos are sold for 3.7 volts. These 'nominal' values are confusing at best. The real figures depend on what you need. For instance, to know the wattage of a power system, you need to take into account the voltage of the battery at full throttle. But when you need to know if a battery is full, you measure the 'idle' voltage. The values written here give you an idea of typical 'real life' cell voltage.

 

Lipo in flight (motor full power): 3,3 volts

Lipo fully charged (idle): 4.1 volts

Lipo empty (idle): 3.7 volts

 

NiMh in flight (motor full power): 1.1 volts

NiMh fully charged (idle): 1.4 volts

NiMh empty (idle): 1.2 volts

 

 

Example: In order to get 300watts from a power system, you will need a 3-cell LiPo or a 9-cell NiMh battery and a motor loaded to about 30A.

Here are the (rounded) 'in flight' voltages of typical lipos:

2S = 7 volts, 3S = 10 volts, 4S = 13 volts, 6S = 20 volts, 10S = 33 volts.

 

Need for speed? Get some serious pitch!

Chosing a prop is not easy. Most people select the right diameter so that the motor doesn't soak too much current . But the pich is often disregarded. Nothing replaces the test flight, but here are some magic numbers to guide you when choosing the pitch of a prop.

 

Airspeed in kph = pitch (in inches) x rpm / 800

Airspeed in kph = pitch (in cm) x rpm / 2.000 

 

Example: On a big trainer aircraft, a large 14x4" prop spinning at 8000 rpm will get you 40 kph of speed, which is marginal.But a 11x8" at 11000 rpm gives 110 kph which you don't need. The best choice will probably be a 13x6" spinning at 9600 rpm and providing a top speed of 72 kph. This is true for all planes, not only electrics.

 

 

Masters of the 'C'

The label on your brand new lipos reads '15-20C', but there is also a '1C' somewhere else on the sticker... WTH???

The '1C' in small letters means the maximum charge current is 1 time the cell's capacity (all lipos charge at '1C'). On the other hand, the '15-20C' note promises you can discharge the battery at 15 times the capacity and even push it briefly to 20 times the capacity without damage. The truth is that most manufacturers are too optimistic, so forget the second number and try to keep the 'peak' discharge current under the first number. A 'realistic' discharge current can be calculated like this:

 

Max discharge current on the ground = (first number) C x capacity / 1250

Max discharge current during 1 minute = (first number) C x capacity / 1500

Max continuous discharge = (first number) C x capacity / 2000

 

Example: A 3000mah '20/30C' battery should be able to discharge at 60A during a few seconds. It will survive a take-off at 48A. A whole flight alternating slow passes and full throttle at 40A will be OK. And it could be discharged at 30A continuous without degrading.

Whatever the 'C', remember to provide adequate airflow to cool the battery.

 

 

The heat is on!

To cool down an IC engine, you just cut some holes in the motor cowl. For an electric aircraft, you also have to provide cooling for the ESC and batteries. The warm air has to find it's way out of the plane so there have to be additional holes at the rear... But what size of holes do you need to drill?

 

Air entry surface (cm²) = number of watts / 40

Air exit surface (cm²) = number of watts / 30

 

Example: a warbird using 1000 watts needs 1000 / 40 = 25cm² of cooling air intake and 33cm² of opening behind the battery to let the warm air exit. The exit MUST be larger than the entry to avoid warm air stagnation which is even worse than too small an air intake. 

 

 

Check the internal resistance

Modern batteries provide tremendous performance thanks to a very low internal resistance ('Ri'). But all batteries are not equal. To compare two brands or to know if an older pack is still fit-to-fly, you must measure the Ri. All you need is a voltmeter and an (cl)amp meter (or a wattmeter that combines both functions).

 

Measure the voltage 'V1' during a discharge at a current 'A1' corresponding to ±1C

Measure the voltage 'V2' during a discharge at a current 'A2' corresponding to ±10C

 

Ri = (V1 - V2) / (A2 - A1)

 

Example: on a brand new 3-cell 2200mAh lipo you measure 11.4 volts at 2.2A discharge and 10.5 volts at 22A discharge. The Ri of the pack is (11.4 - 10.5) / (22 - 2.2) = 0.045Ω. This means a single cell Ri of 0.015Ω.

Several month later, your plane doesn't fly like it used to do. You measure Ri again with 11.2 volts at 2.2A and 9.5 volts at 22A, which gives 0,086Ω. This means that the battery has lost half its performance...

To be meaningful, Ri must be measured in 'standard' conditions. Ambient temperature, cells temperature and state of discharge have a direct impact on the results. The easiest is to always measure Ri on a freshly charged pack at ambient temp.

 

 

What goes up...

...Must come down. But when? Follow these magic formulas to estimate how long you can fly using a specific battery:

 

Contest or 'full throttle': Seconds = capacity (mAh) x 4.2 / max current on the ground

Aerobatics: Seconds = capacity (mAh) x 7 / max current on the ground

'No-stress' flight: Seconds = capacity (mAh) x 11 / max current on the ground

 

Examples:

FunJet race using a 2.400mAh battery discharging at 42A Max: 2400 x 4.2 / 42 = 240 seconds, or 4 minutes.

F3A aerobatics using a 4100mAh battery discharging at 52A Max: 4100 x 7 / 52 = 552 seconds, or 9 minutes.

Piper Cub flight using a 3000mAh pack at 34A Max: 3000 x 11 / 34 = 970 seconds, or 16 minutes.

 

 

Fly longer: add a cell!

The last magical number gives you an estimate of how much energy a battery stores:

 

E = capacity (in Ah) x voltage

 

For instance, did you know you can fly longer with a 3S 1000mAh lipo than with a 2S 1300mAh...? Indeed, to get the same flying style, the 2S at 7.4volts needs to discharge at 13.5A for 100 watts of power. The 3S needs giving only 9A for the same power. Using the time formula, we get a 'No Stress' flying time of 20 minutes for the 3S vs 18 minutes for the 2S. As a bonus, the lower discharge 'C' rate on the 3S battery means it will last longer.

The magic number tells the same story:

 

Energy in the 2S: 1.3 x 7.4 = 9.62

Energy in the 3S: 1 x 11.1 = 11.1

 

Some will say that a lower voltage usually means a larger prop and better efficiency. True, but the higher 'C' discharge and current on the motor cause losses that cancel the expected benefits.

 

 

Demonstration on my P-40 Svenson (170cm span, 4kg AUW, Motor HXT50-55)

The motor uses 51A Max current on a 6S lipo. The voltage magic number predicts ±20 volts so we can estimate the power: 20v x 51A = 1020watts or 1.36HP. This plane has more than 250 watts per kilogram, it is powerful and climbs vertically, just like the magic formula says: 4gr x 1020 = 4080gr thrust. But beware of the excess heat buildup because the motor weights only 320gr! In theory, it should not be used above 320 x 3 = 960watts. However, on this plane the 26 cm² air intake and 34 cm² air exit provide optimal cooling.

2.5mm² power cables are used for efficient c urrent transfer. The motor has a KV of 500, it runs at 20 x 500 x 3/4 = ±7500 rpm. The prop is a 15x8", which gives a max speed of 8 x 7500 / 800 = 75kph, which is ideal for this warbird. I use a 4400mAh battery, So I can fly for 4.400mAh x 11 / 51A = 949 seconds or about 16 minutes of cruising 'No Stress' performance.

the battery is sold for '20/30C' and could deliver a maximum of 20 x 4400 / 1250 = 70.4A peak and 20 x 4400 / 1500 = 58A during one minute. I must avoid flying continuously at full throttle because I would discharge the pack above its safety limit: 2

[Torsten Spitzner]

I too have the 'Magic numbers for modelers ' save on my computer. When I did more electric flying, I found it to be remarkably accurate when compared to logged data.

[Simon Chaddock]

bjk896

I think you can see from Don fry's magic number post the calculations have many variables. Made more complex as one effects the others so arriving at a workable solution is quite complex.

I started in RC electric planes 12 years ago (I was 65) and I had no idea of what was required so I bought a 'ready to fly' foam trainer where everything required was provided in the box. It did fly.

From there it was a matter of reading posts on web sites like this to determine what was likely to be required, along with a bit of my own experimentation, to power each of my own designed planes.

Over the years I have learned what all the 'magic numbers' mean and how to use tham however it was a good few years before I felt confident enough to try a four engine one.

     

[bjk896]

Don, 

That is an epistle to frighten a budding builder/pilot but with  my first read through, I saw that it was written to help not to frighten.

My first read also said it was an enormous mouthful to chew which is OK by me. I shall put it into the place between my ears in stages and see where it takes me.

 

Thank you, I'm an old data techo from wayback so the electrons and smoke aren't a mystery but the sequencing and variations are and will be. I might be old but the big writing (font) wasn't necessary but probably helpful !!

 

Simon, to you too, I am indebted because you took a long  and wide view of things which reminds me that a bloke called Electriflier on this forum built a Herc a few years ago. I recall your comments there about cooling and airflow and maybe trying to place either heatsinking or electronics on exposed surfaces. More there later for me to consider I'm sure

 

I shall see where it all takes me

 

Thanks to all

 

Brian