Electric Set Up for Ballerina

[kc]

Dave, another way might be to use a closed box or one of those 4Max mounts and put the 4S5000 Lipo in from the front underneath the motor mount. The hatch could be used just for connecting up the Lipo.  F1 would need a tunnel cut into it, but easy carpentry even in 6mm ply.  ( I am thinking here about the novice builders with no woodwork experience )

Having each Lipo secured to it's own ply tray which is secured with a wing bolt and a tongue works well for some people. Would work with a front inserted Lipo here.

Edited By kc on 03/12/2015 17:27:43

Edited By kc on 03/12/2015 17:34:19

[Graham R]

Is there a rule regarding prop size and aircraft size and can anybody explain how to calculate prop speed and the most efficient tip speed for a prop.

Thanks

Graham

[Erfolg]

I have been considering this build from the view point of my own experiences as a builder and a modeller taking the BMFA "A" test.

Although contrary to my own believes, I have found that I have more than a few models running on 4s and also a number of models where I use a "Y" power lead.

The first thing that has struck me that a 4s model can be unbelievably fast from the standpoint of a relative novice. A comment made at Greenacres about this rather slow looking model was "first it was here, then it was gone", "wow, that was fast". Then when be observed when practising for the "A" test, you are flying the schedule at the speed of a pylon racer".

On that basis, with 3s things tend to go wrong at a slower pace. I know that in theory you can throttle back, yet at take off, I always end up on full power until at height. I am just suggesting that high power needs managing. You will notice my 4s models seem to have typically a 4 oz ft-^2 increase in wing loading, compared with my 3s models. To be truthful, the higher wing loading of 24 oz. ft-^2 does not seem to matter other than potentially at take off, where the excess power works to your advantage.

I have also been thinking about the hatch for the Lipo. An example of a very large hatch is the Clean Sweep of TH. Without looking at the plan, I cannot remember how the plan indicates Tim indicated it could be done. In my example the bulkheads are a series of "U" shaped items. Once the exact position of the Lipo was known, those where there was no restrictions with removing and inserting a lipo, I simply strapped a beam across to close off the "U", becoming essentailly a "O".

I do not know about others, but I have tended to have issues with IC conversions, in that with the Lipo right up front, I still cannot get the CG spot on, without lead up front. The worst example was a VS Tomboy I built. I ended up lengthening the nose, by an amount. In many electric builds, I have lengthened the nose by 1/2-1" to mitigate the issue.

The other aspect that I have become rather passionate to worried, is that I like to cool the ESC, especially the $s set ups. I no longer shove the ESC where I can get it in. With gliders on less than 30s of power you can get away with this practise. Where a continuos current is drawn, you often do not, I know, i have had ESC issues.

As you probably guess, I do not worry to much about the plan details. An example I may not have the material size specified, or I make an mistake. Does it matter. If I compare a model with the real world of engineering, in the past I would have been a rich man, for every time a contractor phoned up, with a request to change a detail or material sizes, as well as the manufacturing errors. In the majority of instances, there wishes can be accommodated, errors fixed, without any material effect on the job. I feel it is the case with models, very little is terribly important to the point where you have a scrapped major assembly.

You may gather that I use "Y" power leads, this is nearly always as a means of getting two lipos into a space that is not ideal. Although I use them, they take up more space than you think, which may matter. You need a good heavy soldering iron, as the joints are heavy. Ideally i would preffer to avoid there use.

[kc]

What Erfolg is saying is that lighter models ( lower oz sq ft ) fly better! But it's not really to do with 3S or 4S it's the battery weight that makes the difference. A high capacity 3S may weigh more than a lower Milliamp hour 4S.

However ESC may be affected by 3S or 4S ..... using the same number of watts on 3S will draw more currrent than same watts on 4S needing a higher rated ESC or risking ESC failure.

So I feel my idea of using only 100 watt per pound will result in a better flying ( meaning easier flying )  model than BEB's using 150 watt per pound. ( for the same flying time ) although BEB might have more vertical performance ( or might not as the weight might prevent much change)     BEB will need a bigger capacity Lipo and of course that means heavier.   However if I need to use lead to get CG right then the overall weight might be the same as BEB's model!     We will see.......

My model will be cheaper though as bigger Lipos cost much more.

Edited By kc on 04/12/2015 13:41:47

Edited By kc on 04/12/2015 13:58:43

[Erfolg]

I think we agree, at least in principle.

I did need the power with the 109, it was apparent that on a 3s, there was not enough grunt. A 4s was then used, then more than enough grunt, but the weight has gone up, more I think than anticipated. The thick aerofoil is defiantly high in drag.

CG management for me is a big issue, I nearly always end up with a rearward CG. I have bust a gut, using cyno, going out of my way by to minimise weight at the back, to avoid lead. Very rarely manage it, to the extent, I cannot remember when i did.

I do not know the weight of a IC motor, but will look at a few to compare with a typical electric motor, (the type with 35-- in their designation) to decide if a modest increase in nose length could be beneficial. At the end of the day, this is one of the factors Peter will have considered in deciding nose length. Possibly saying 1 chord is what works. I have had nose lengths much longer, at 2 chords and not suffered obviously from inertia issues.

[Biggles' Elder Brother - Moderator]

In a word Graham - "no". There are no rules - there are just too many variables. You see you can have a set up that pulls say 500W with a given size of prop. Put another prop on there (the same size but a different make) and it might pull 600W. Such variations can occur because the two props have slightly different profiles or the materials they are made from have different stiffnesses and one is more "efficient" than the other. Props are VERY complex bits of kit to model - far, far more complex than a motor or an ESC, which are child's play by comparison.

You will see programs such as eCalc that claim they can work all ths out. But in my experience they provide little extra accuracy over what an experienced electric flyer could achieve with the sort of "back of a fag packet" calculations I've shown here. In fact on more than one occassion the rough calcs have provided more accurate results! (My conversion of the BH Chipmunk blogged on here being a case in point).

What most of us do in practice is a combination of two things. First for any given power level we have prior experience of the sort of prop size that has worked in the past. So 500W - sort of 12x6 territory. 350W around a 10x6. 1000W try a 14x7. etc. Secondly, the motor, when sold, often gives some indication of the prop sizes typically used with it - but they are only that, an indication. So based on those ideas we pick a starting value for a prop and then use the Watt meter to home in on an optimum prop.

BEB

[Biggles' Elder Brother - Moderator]

OK, let's hold on the speculation and do some weight calculations. Based on the 150W/lb scenario from page one:

the motor weighs in at 195g.

the ESC is 60g

a 3300mAh 4s weighs 467g.

This gives us a total weight for the 150W/lb electric power system of 722g. (the second 100W/lb system would be a little lighter - not much though)

Now if we compare that with say a OS FS40 Surpass installation:

the engine (with silencer) weighs 361g

a 9oz tank has 255g of fuel and lets say about 140g for the tank,clunk, fittings etc so that's 395g (you could opt for a smaller 6oz tank - but it won't make a very big difference in the wider picture)

So the total weight of the IC system would be around 756g.

Clearly these are only approximations (but they are based on actual data from spec sheets). What they show us is that there is likely to be little difference in AUW whether the model is electric or IC. This means of course that the wing loading is likley to be relatively unchanged.

There is likley to be slight rearward shift in the weight distribution of the power system, as the battery is slightly heavier than the fuel tank while the motor is slightly lighter than the engine. But frankly, provided reasonable steps are taken to get the battery as far forward as practical, I really don't see any significant CoG problems.

So I'm not envisaging any major weight, or weight distribution, challenges from the electric set up.

BEB

Edited By Biggles' Elder Brother - Moderator on 04/12/2015 15:00:13

[Biggles' Elder Brother - Moderator]

Posted by Erfolg on 04/12/2015 12:45:31:

I have been considering this build from the view point of my own experiences as a builder and a modeller taking the BMFA "A" test.

Although contrary to my own believes, I have found that I have more than a few models running on 4s and also a number of models where I use a "Y" power lead.

The first thing that has struck me that a 4s model can be unbelievably fast from the standpoint of a relative novice. A comment made at Greenacres about this rather slow looking model was "first it was here, then it was gone", "wow, that was fast". Then when be observed when practising for the "A" test, you are flying the schedule at the speed of a pylon racer".

On that basis, with 3s things tend to go wrong at a slower pace. I know that in theory you can throttle back, yet at take off, I always end up on full power until at height. I am just suggesting that high power needs managing. You will notice my 4s models seem to have typically a 4 oz ft-^2 increase in wing loading, compared with my 3s models. To be truthful, the higher wing loading of 24 oz. ft-^2 does not seem to matter other than potentially at take off, where the excess power works to your advantage.

I have also been thinking about the hatch for the Lipo. An example of a very large hatch is the Clean Sweep of TH. Without looking at the plan, I cannot remember how the plan indicates Tim indicated it could be done. In my example the bulkheads are a series of "U" shaped items. Once the exact position of the Lipo was known, those where there was no restrictions with removing and inserting a lipo, I simply strapped a beam across to close off the "U", becoming essentailly a "O".

I do not know about others, but I have tended to have issues with IC conversions, in that with the Lipo right up front, I still cannot get the CG spot on, without lead up front. The worst example was a VS Tomboy I built. I ended up lengthening the nose, by an amount. In many electric builds, I have lengthened the nose by 1/2-1" to mitigate the issue.

The other aspect that I have become rather passionate to worried, is that I like to cool the ESC, especially the $s set ups. I no longer shove the ESC where I can get it in. With gliders on less than 30s of power you can get away with this practise. Where a continuos current is drawn, you often do not, I know, i have had ESC issues.

As you probably guess, I do not worry to much about the plan details. An example I may not have the material size specified, or I make an mistake. Does it matter. If I compare a model with the real world of engineering, in the past I would have been a rich man, for every time a contractor phoned up, with a request to change a detail or material sizes, as well as the manufacturing errors. In the majority of instances, there wishes can be accommodated, errors fixed, without any material effect on the job. I feel it is the case with models, very little is terribly important to the point where you have a scrapped major assembly.

You may gather that I use "Y" power leads, this is nearly always as a means of getting two lipos into a space that is not ideal. Although I use them, they take up more space than you think, which may matter. You need a good heavy soldering iron, as the joints are heavy. Ideally i would preffer to avoid there use.

All I can say to that Erf is come flying with me one day. You can fly my 6s powered Cub that floats around like a gentle old lady - then you can fly my 3s powered Radjet - which bombs around like a demented wasp and rolls like a dentist's drill! Ain't no correlation between battery size and speed in my experience. Between wing loading and speed, yes! But that's not what we are discussing!

BEB

Edited By Biggles' Elder Brother - Moderator on 04/12/2015 14:58:22

[kc]

Well perhaps BEB's model will not be so different from mine, perhaps it's it's those like Dave Hopkin's that may use the heavier 4500MAH Lipo.

My setup will be the combo that I have used in a approx 67 ounce model for the last 18 months for 560 flights. Motor is a Turnigy 3536/9 910kv Lipo is a Zippy 4S3000 20C The ESC is 60amp and the prop an 11 by 5.5 'APC type' This setup shows 500watts at 33 amps and gives 6 minutes of full throttle flights. About 120 watts per pound.

It just works! That's all we want isn't it -a setup for the novice builders that we can state will definitely work with a model of that weight.

Edited By kc on 04/12/2015 15:36:19

[Erfolg]

I do get what you are saying BEB, my Pushycat is no slouch another 3s 2200.

In many ways my views are there is no one solution. What I am conscious of is that piling on the watts, inevitably leads to a heavier model, when you started of with a 3s.

I do think that if possible a lighter plane (wing loading) is more tolerant in many respects, as a concept.

You know from previous correspondence, I have in some cases been chasing duration at one time.

My general feelings are that almost anything will fly, within some limits, it is just what the model is optimised to do is different. For those who are learning or just want to fly about, there is no absolute reason why they should want power, for powers sake. I feel the same about building models, absolute adherence to detail is not necessary, there are many ways of achieving the same end result.

On the other hand, maintaining the same tailplane moment arm, the same general area relationships, have some significance, although even here, some lee way is possible. Having some potential impact, although a 1% change of many features do not matter a jot.

My message to new comers is do not overly worry, as long as you stick broadly to the general features.

Perhaps the biggest issues are what i would call "aperture compensations", the pressure vessel ASME code type of thing. Yet for many people, this type of issue and how to deal with it, is common sense and can be made to seem complicated and difficult. My general solution is to have as few apertures as possible, where i must have them, stick some extra material on to reinforce the aperture.

I have just one critical area and that is the spar, again a area where i know a lot of so called experts could do with a little structural engineering training. A mention of the parallel axis theorem, (McCauleys), without the calculous, the general ideas perhaps for a future article?

There is a irony, in that I am certainly not trying to say this is what you should do, or not. More a discussion, to be wary, that every action has benefits and penalties. For modelling, why worry, if you go wrong (for what you want to happen, so what!

[Glyn44]

Hi all,

I was hoping to enjoy this build, but I'm starting to feel somewhat scared!

When's wood kit coming out, I need it soon before I lose my nerve!!!

[Erfolg]

There is defiantly nothing to fear, other than fear itself.

[Biggles' Elder Brother - Moderator]

Hi Glynn,

just ignore the distracting stuff. Get the sort of set up me, kc or John have outlined and you'll be fine! All this stuff about wing loading in my opinion is completely irrelevant!

What can we say for sure?:

1. Buy a set up as defined in whichever of the systems you like - John S, mine or kc. Just don't mix them! Or use the calcs I've shown to select your own system and put it up here if you like and we will check it out and advise if we think its OK.

2. We know that whether you go IC or electric you're going to get a model of about the same weight and shouldn't have any CoG issues. Debates on wing loading are off topic - the wing loading will be more or less the same however you power it!

That is all you NEED to know! Don't panic.

BEB

PS And as for the parallel axes theorem - God save us!

Edited By Biggles' Elder Brother - Moderator on 04/12/2015 16:30:13

[kc]

Glyn, it will be a very straightforward build for anyone. The experts will explain what to use for an electric version. Dont worry about the calculations just stick to whatever motor/prop/Lipo/ ESC that BEB advises if you want an easy build.

Erfolg said " as long as you stick broadly to the general features" Well I think electric power is one area that contradicts that! It's necessary to stick to the motor/prop/ lipo/ESC details unless you want to experiment and risk wrecking ESC's. The motor Kv is critical ( often the last digit of the number changes to denote different kv -revs per volt )

[kc]

BEB, what do you think of an Overlander 4240/10 890kv as suitable motor for the novices? It's rated at 540 watts - a bit more than the Turnigy I am using and also more than the one you mentioned yesterday

There seems to be a very similar 4Max version

 

Edited By kc on 04/12/2015 16:54:55

[Steve McIntosh]

Posted by Glyn Calow on 04/12/2015 16:08:37:

Hi all,

I was hoping to enjoy this build, but I'm starting to feel somewhat scared!

When's wood kit coming out, I need it soon before I lose my nerve!!!

You and me both

[Swissflyer]

Fascinating thread, thanks to all. I have often thought about electrifying an IC model (including some of Peter’s) but only did it once. The in-flight results are fantastic; the Black Horse Twister (with a larger rudder for knife edge authority and an unintended 700Watts up front) has impressive authority and flies the book.

7-8 minute flights take about 1’600mAh from the 3’600 mAh 4S pack so I often squeeze two flights from one charge.

The undercarriage is a nice springy affair made of high quality carbon fibre, anyone have a good European source for those please? My two current builds both need them.

Would I do it again? Not so sure. With a 50:50 balsa:foamy fleet I have to say that as I modified the Twister I was constantly noticing weight saving possibilities.

Of course the strength (and weight) were there to handle an IC engine, however, my thoroughbred acrobatic foamies (is there such a thing?) just don’t have that weight penalty in the first place and show corresponding performance benefits.

So in conclusion I would say if you really want a particular model that is only available in an IC version, go for it (use our old schoolboy moments formula measured from the designers CG to calculate if the electric motor + battery moments will fit in the fuselage without major surgery)

If flight performance is your thing (it is my thing) a dedicated electric design would be my choice.

And as BEB comments in his post, three years later, the model is still clean.

So Glyn, I hope you jump in and enjoy it, it will certainly fly beautifully.

[john stones 1 - Moderator]

Posted by Steve McIntosh on 04/12/2015 16:50:23:

Posted by Glyn Calow on 04/12/2015 16:08:37:

Hi all,

I was hoping to enjoy this build, but I'm starting to feel somewhat scared!

When's wood kit coming out, I need it soon before I lose my nerve!!!

 

 

You and me both

I got bewildered when I started with lecky flying, the combinations of set ups are mind boggling. Put your faith in advice given by one of the posters, and get stuck in (when others start building there'll be even more combinations) . What we have is a plan for a pretty model that will fly well on a variety of set ups I.C or electric.

John

 

 

 

Edited By john stones 1 on 04/12/2015 20:55:13

[PatMc]

If I was building this model my preference would be for a 35-48 size motor weighing at least 150g & around 800kv. Anything lighter would not run as cool at the necessary power level also any extra weight this far forward is more helpful regarding the cg than using a heavier than needed battery that's located further back or having to resort to ballast.

The ESC needs to be rated at 50A min and have a switch mode BEC (unless a seperate SBEC or Rx battery is used), a higher current rated ESC would be fine.

Depending on space & cg position a 4s lipo from 2650mAH up should give sufficient power & duration for 8 - 10 minute of normal club aerobatic flying on an a prop giving a load that draws about 30A from (Probably around 11x6 - 12x6)

If I needed to buy a motor & ESC from scratch my choice would be from :

Motors in order of preference : this 840kv 3548 or this virtualy identical one (difference seems to be the shaft orientation) or this cheapo at 790kv.

ESCs, again in order of personal preference : this Plush 60 or this HK 60 or this HK 50 . My first choice is based on having used several of this particular ESC but neither of the other two.

I wouldn't buy the batteries until the model was near complete. When building I'd make the battery bay as roomy as possible in order to accomodate as big a battery as is needed to help with the cg.
My standard connector for this size model is the XT60 so I've listed four that have these already fitted & that I think would suit the model but this time they're not in any order of preference. The fact that all my choices are Zippys is merely because they were the first ones in the right size range fitted with XT60s that I looked at.

Some suitable batteries : Zippy Compact 3300 ; Zippy Flightmax 2650 ; Zippy Flightmax 3000 ; Zippy Flightmax 2800

Any combo of motor, ESC & battery from the above list should be suitable.

Hope this is some help to electric newbies.

[kc]

The " virtually identical one " one is a front mounted type which is not really suited for this model The others would seem OK but how will you mount them if using the lasercut parts with F1 set at 4 inches back from nose Pat?

[john stones 1 - Moderator]

The SK3 have a bolt on prop adaptor which makes them rear mounted as well as front mounted, nice motors.

John

[Geoff S]

One problem those not familiar with electric motors have to face is that different manufacturers describe their motors differently. Specs need to read carefully. With glow, it's much easier even though (say) 40 size engines still vary in performance it's not so marked except for a few very high performance ones.

For example, the motor I have in my Tiger Moth is an Emax Grand Turbo 3526/04 870 rpm/volt. I can only assume the 3526 refers to the rotor size because its outside dimensions are: diameter 44mm and length 52mm. It weighs in at 265 grams so its quite a substtanial size with a constant current rating of 55 amps (69 amps peak for 60 seconds). I'll be running it on 4S with probably a 13x4 prop. It's quite a big bigger than the apparently larger 3548 Pat mentions above.

It would help if motor size and other specifications and descriptions were standardised.

Geoff

[Biggles' Elder Brother - Moderator]

I can't say how Pat intends to do it - but I can comment on what I have in mind!

Firstly I don't plan to move F1 - I'll leave it where it is. Then to mount the motor I will create a stand-off using 5mm studing - something similar to this from my Chipmunk conversion:

I will actually open up the centre of F1 to allow the battery to pass through it and come up almost as far as the stand-off plate. True, thus will weaken F1 - but three factors come into play here to help us:

1. The former does not have to be so strong as would for an IC model as the vibration is very much less.

2. We can thicken the former a little if we want to get some of the strength back.

3. We can add some light-weight extra bracing with some extra triangular fillet or local doublers where the former meets the fuselage side.

I think that this solution has two advantages - firstly it is very finely adjustable for both stand-off distance (giving you a neat spinner/fuselage gap) and any side thrust you wish to add. Secondly it leaves the major components of Peter's design unaltered in terms of position and outline.

Note that you do not have to use a standoff plate - the main reason for doing so is to create enough space between the studing bars for the battery.

BEB

[PatMc]

Posted by kc on 04/12/2015 22:16:44:

The " virtually identical one " one is a front mounted type which is not really suited for this model The others would seem OK but how will you mount them if using the lasercut parts with F1 set at 4 inches back from nose Pat?

That's why the second choice is second choice.

But anyone who is unable to work out how to use either of these motors should probably stick to ARTF's.

[PatMc]

Geoff, I was being a bit lazy as it seemed most of the motors previously quoted to were some version of Turnigy that use the form of spec I assumed.
Perversely I mentioned the Emax 2826/06 motor in my Druine Akrobat in my previous post which is roughly a 3548 in Turnigy speak.

If I were to build the Ballerina I would use the Emax 2826 but it'll be easier to repair the Druine Akrobat which I think is pretty much in the same genre.