Electrifying free plan models

[kc]

Would anyone care to suggest suitable motors and LiPo for any of the free plan models designed by Peter Miller recently such as


48 inch Lil Mustang          468sq in   4lb 0oz
51 inch Miss Lizzy            490sq in   4lb 1 oz
53inch CAP21                   477sq in   4lb 3oz
52 inch Werewolf              520 sq in  4lb 5 oz
48 inch Midget Mustang    475 sq in  4lb 12oz
56inch Bootlace                 510sq in   5lb 0oz

All RCME designs over the last few years except Lil Mustang which is from RCMW.  All the weights are Peter Millers own prototype models and he says they are as light as possible, but of course they are built for glow engines at this weight.  So maybe just a little scope for lightening..

I would be interested to know what motors could be used from those currently available from GiantCod, Overlander etc

[Steve Hargreaves - Moderator]

Well...they are all 4-5lbs so 4-500 watts should fly them very nicely...in fact one "set up" (motor/ESC/Battery) would probably be suitable for all of them depending on how you wanted them to fly....for example you might want a small fast prop on the pylon racers & a bigger slower one on the CAP as an aerobatic machine!!!

 

Without being specific then I would look at a 500watt motor with a kv around 1000, 60A ESC & a 3300-3700 3S Lipo or for a 4S set up a kv of 8-900 & perhaps a slightly smaller LIPO....you might even get away with a slightly smaller ESC.

 

Obviously you would need to check the available space in each for a suitable battery.....

 

Homework time kc...why don't you size up a few motors & post your thoughts back here for "marking" ....then we can see if its off to Matron for another bit of tuck or a trip to see the Headmaster with a copy of Tiger Tims Weekly down the back of your shorts as padding....

 

Remember to include your working/sums as extra points can be gained or taken away.....

[kc]

Steve,

I have already done some homework ( plus extracted the data from the old mags for extra marks) but I was hoping for other peoples ideas.  In fact I wanted to use the same 3S2200 Lipo also to be used for another model ( vintage style ). Standardising on these common LIPos.  This seems far away from your suggestions

A fellow club member has a 50 inch Extra and a Sukoi running on some 3S2200 packs with great success. The Extra & Sukoi are ARTF and highly fretted out liteply for the chunky fuselages.  I am looking for a slimmer all balsa plan built model to give similar flights.  ie smooth aerobatic flights of short duration, 4 or 5 minutes is quite OK

 

Whats Tiger Tims Weekly?  When I was at school we read Practical Wireless or Hobbies Weekly!

 

[Richard Wood]

Hi KC

Are you planning on paralleling up two 3S 2200 packs in these to

give you a 4400?

A single 2200 pack in a 4.5 - 5lb model isn't really big enough.

Look at 1000KV & over for a motor on 3S

I've a 3.5 lb sport model using a 540W/1250kV motor which goes well

on a 9x6 at 400W or so. A 10x6 would up the power quite a bit.

GCod has them for £13 or so.

 This one

That Midget Mustang looks like an interesting one.I've got the plan

& was thinking of using a 4S for 600W or so.

 

Edited By Richard Wood on 19/10/2010 13:11:11

[Erfolg]

I have now motorised a number of small traditional builds.

 

My largest to date is 40" span. Gliders up to 3.5m, but that is a different tale.

 

I will emphasize that one of my prioritise is to keep weight down. I also work on 100-200 w/lb. I keep the Kv low, but care is needed that you do not end up with needing a large dia. propeller. I am not interested in out and out speed, as stick with 4-6" pitch speed, to date I have found  this to be adequate.

 

There is a balance between revs obtained and pitch, which is also influenced by Kv, volts supplied. All constrained by max amperage the motor is capable off accepting.

 

My advice on motor selection is to pour over comments by users of a particular motor, what they used it for, their set up and what data they may or may not post.

 

I also do what you are doing, and ask for comment/advice for a specific model.

 

I have used the data sheets from distributor/web site. I have not found these to be as reliable as I would have thought. Still view them. though.

 

I also in some cases have visited web sites where results from tested motors have been tested , by such people as Dr Kiwi.

 

All in all it takes longer than IC, as there are more variables, which alter the characteristics of the system. There is no one answer, as there tends to be with IC.

 

I will also concur with Steve, regarding space for Lipo. I keep the centre area clear, I put aileron servos, in the wing. I will need a location in the nose area for the ESC, yet may need the Lipo in that area or possibly well to the rear. I use lightweight servos for elevator and rudder (if used). These are fitted behind the CG normally, along with the Rx. A lot of this is iterative, as i assemble the basic airframe with motor and Lipo to judge the best most flexible layout for equipment, before finishing.

[Steve Hargreaves - Moderator]

Hi kc...yes I understand what you mean...indeed I have a Seagul Extra(42") running 400watts from a 3S 2200 pack & its just lovely. It does mean I'm pulling 40+ amps from the pack at full chat ie 20C so I'm pushing things very hard (& only getting 3 minutes at full throttle) & this really isn't adviseable if you want a long life from yer batteries.

 

I often fly the Extra with 2 x 2200 packs in parallel so a 3S2P pack effectively.... 4400mAh capacity. You can "feel" the extra weight but I'm only pushing my batteries to 10C & get a much longer flight.....so it depends what you want to achieve. Such short flights might be OK for some people but not for others......up to you really ....

 

Probably worth noting that the Extra only weighs around 2 & a bit pounds so I don't need much power to fly it around & it would certainly fly well on less power. The 4lb & up models will need more throttle, more of the time to keep them aloft.

 

Personally I try to keep my batteries around the 10-12C mark at WOT & look forward to 8-10 minute flights....I agree with Richard...a 2200 3S pack is a bit small for a 4lb model. You could maybe look at a 4S 2200 pack which would need to provide 28 - 35A for a 4-500watt set up which is 12 - 16C so 4-5 mins of WOT or about 7 mins in the air....

[Erfolg]

I have just realised I do fly a sports model which is 58" span model (which I fly each week).

 

 

This flies with a Tower pro A2409/12T star wind 1570kv. It is interesting that this motor costs £27 UK and £9 from HK (made me think).

 

Propped to provide 200w at a all up weight of 1kg.

 

This was a case where I had to keep increasing the dia of the prop to get the watts, the data sheet being conservative. Conversely I have a Tower Pro A22176T 1500kv at 250w, where the data sheet was overly optimistic on the current drawn on the specified propeller.

 

 

[kc]

One of the problems with electric is the motors are rarely marked so they can be identified afterwards.  So its difficult to find out exactly what is in the models that fly well.  The owners know the supplier but not the exact model!  And things change so rapidly.

I know from watching my clubmates that these Extra's etc are a reasonable size and fly well on a 3S2200.  They just used the motor recommended. 

One member has flown one many times almost every week for the last year or more.  So it is practical.   Exactly what these models weigh is not known but they are light but not extremely light.  Somewhere between 3 to 4 pounds probably.

To me they seem to fly well, on a small motor & Lipo, because there is plenty of wing area not because they are extremely lightweight.  

So I am looking for a similar but slimmer model to build from plans.  All balsa no carbon etc.  I was hoping that someone would have built one of these free plan designs for electric and state what they used.

 

My understanding is that putting two 3S2200 in parallel will only give longer flights and slightly less performance due to twice the battery weight.  So nothing would be gained as I am content with short flights.

 

I thought the point of using a higher voltage ( 4S instead of 3S ) was to reduce the amps drawn with the same motor.  But recent comments seem to say this is wrong?

[Steve Hargreaves - Moderator]

Its all about matching the powertrain to the model & to your requirements...remember short flights equals high battery drain equals short battery life!!!

 

My Seagull Extra (2.5lbs) flys well on a 2200mAh battery. At 40A current it's pushing the battery but this is my choice...I could prop down, draw less current or I can use two batteries in parallel & fly longer...true... this set up would fly a 4lb model but you would need a higher throttle setting more of the time & probably need to replace your batteries more often.....as I say...its up to you!!!

 

Yes two 2200 in parallel will give more duration because you now have 4400mAh on board & yes it will weigh a bit more because you have two batteries....you could fly longer & your batteries would be happier as they aren't being pushed so hard.

 

Yes you are right...using a 4S set up for the same power will draw less current than a 3S set up but you would either need a lower kv motor for the same prop or a smaller prop on the same motor.....keeping the same motor & prop & substituting a 4S for a 3S battery would see the current shoot up as the motor would try & turn the prop much faster....

 

As with most things in life...its all about compromise....

[Erfolg]

You are correct in thinking identification can be an issue.

 

Although it sometimes appears that there are thousands of motors out there, you can probably reduce by a factor of at least 5. Many of these household names are sold under many different "Badges".

 

I personally always print the details of the motor, write on the printed sheet, which model it has gone into and then file it in my model file.

 

In my model file I keep details of motors, ESC's, together with my Radio Manuals.

 

I note your comments on power. A lot depends on how you want to fly. although obvious, if you want to prop hang, have unlimited vertical performance, high level speed, you need power.

 

If however you want a more scale type performance, for many models, lower power per kg will suffice.

 

Dependant on source, many motors of high power can be quite cheap as can Esc's

 

 

[kc]

Most aeromodellers seem to like building and flying but mostly dont want to experiment.  We just want a simple formula that works well!

If anything is holding electric back it is the lack of 'instant solutions' like there is in glow powered models ( i.e. any experienced modeller can tell you what to fit in a 4.5 pound Wot4 --fit a modern 40 2 stroke with 10x 6 to 11x 7 it will fly well, fit a Merco 35 it will be marginal, ballistic with any 60 etc. )

But for all those published models I mentioned there is little in the way of hard fact on what to use!  (  excluding the helpful comments on this thread )

 

Perhaps we need a special thread with just details of what worked ( or didnt ) for each published design that people  tried with electric power. ( Just the basic facts )

[Erfolg]

Kc

 

I do believe that modellers do experiment, all the time. There are many levels of experiment, many examples are found on this web site.

 

Specifics relating to electric flying are easily found by examination of the comments posted on the GC & HK product appendages. Information regarding the model flown, details of the power train, with respect to the product. The only reason the data exists is that investigations and results have been undertaken.

 

I rely heavily on the work of others.

 

My only criticism or despondency is that as a hobby we mostly just mentally deliberate and then do. We seldom if ever sit down and record what we are investigating, why, what we wish to achieve, what success is for us as an individual, the process and results. In short, if we design an experiment, it is seldom recorded. Timbo is amongst the most disciplined on the site, in this respect.

 

We do experiment, just record poorly report our specific documented findings. We trade in generalisations, including myself.

 

Yet we have so much to learn from one and other.

[Steve Hargreaves - Moderator]

Different strokes I suppose but one of the things I like about electric is the "experimental" nature of it.....there are just so many variables you need to keep your wits about you or face disaster!!!! I call it "extremely flexible" where as othes might see it as £difficult to get right"

 

But maybe thats just me!!!!

 

& yes I agree with Erfolg too....we are all standing on the shoulders of giants really (isn't that right?? I heard Timbo was pretty tall...) in that we all learn from the works & indeed mistakes of others.....

[Richard Wood]

That's the thing with electric - the odd variable or three to make it

confusing. It's also a very handy thing - the opportunity to fiddle with

different parameters to tailor a configuration.

Even if you make a mistake it's often possible to change something

else, such as prop size, to get round the prob.

 

A useful rule of thumb with any setup is to over-rate by 20%.

As Steve says, Lipos reward a little TLC with longer life.

Don't discharge them to LVC or charge them to max capacity & try

to use them well within their C ratings.

Makers claimed C ratings used to be a big discussion point......

 

I've a couple of lipos which were worked hard for a few flights & are

now pretty much goosed for anything but a light, low current application.

Going for lowest weight with a small battery is laudable but there is a

compromise.

 

As is often stated,data sheets & power calculators should be treated

with caution.

I once put together a setup using calculator data for a manageable 48A,

but in practice the thing was drawing over 60A!

This sort of discrepancy does nowt to help.

 

Sites like Giantcod have useful user product reviews.

These can help greatly with motor selection.

 

Cheers

 

 

[kc]

Well perhaps I should re-phrase my comment " most aeromodellers" .....by that I was referring to the majority of people who do lots of flying!   In my experience most of my fellow club members did not experiment much, maybe on a few occasions trying different props on glow engines etc.   Perhaps I have just belonged to the clubs where flying is the main thing not experimenting!   ( living in a suburban area where flying is done in public parks and therfore flying in a very disciplined way may inhibit experimentation and therefore affect the club  ethos )

I think the fact that ARTF models are so popular proves that most model fliers dont experiment much (but of course they are not actually aeromodellers anyway! )

So even though I think they are a small minority we rely heavily on those who experiment!  

 

So far lots of helpful comments on electrifying but nobody has said that they have built these free plan planes for electric.   Maybe it is not worth doing, maybe a puprose built electric model is easier.  If so which  plans built model?  My requirement is a smooth aerobatic flier about 50 inch span and built from balsa, not made from unobtainium.

[Marc Humphries]

Posted by kc on 19/10/2010 11:51:36:
Would anyone care to suggest suitable motors and LiPo for any of the free plan models designed by Peter Miller recently such as


48 inch Lil Mustang          468sq in   4lb 0oz
51 inch Miss Lizzy            490sq in   4lb 1 oz
53inch CAP21                   477sq in   4lb 3oz
52 inch Werewolf              520 sq in  4lb 5 oz
48 inch Midget Mustang    475 sq in  4lb 12oz
56inch Bootlace                 510sq in   5lb 0oz

All RCME designs over the last few years except Lil Mustang which is from RCMW.  All the weights are Peter Millers own prototype models and he says they are as light as possible, but of course they are built for glow engines at this weight.  So maybe just a little scope for lightening..

I would be interested to know what motors could be used from those currently available from GiantCod, Overlander etc

 

These are all good designs.  But most of them are built like the proverbial brick **** house.

 

My guess is that you could trim lots of weight off these.  There are some good threads around that deal with electrifying the Flair kits.  Someone mnaged to save over 10 ounces on the Atilla - which for a 46 span model is significant.  Swapping lite play ribs for balsa, minimising ply doublers, building up tail surfaces etc.

 

 

[IanN]

Methinks the mods may be making a low strafing pass over those asterisks, Marc - you of course meant to say brick lavatory house

 

I can't agree that these designs are majorly over engineered. They are after all i.c. models for the average clubman which in many cases will be flown from, or over (and sometimes into) pretty rough ground. I'll bet they all survive relatively unscathed from dings that would reduce the front end of your average artf to matchsticks.

 

They are all also said - in the build articles, backed up by forum members who fly them - to fly very well at the designed wing loading so there ain't too much wrong there

 

That said there is of course always scope to reduce weight somewhere, and I'm as guilty as the next man of doing that, on any model. Can you build up a cowl rather than carve it from 3/8 and 1/2 sheet, e.g, or could I use 1/8 there instead of 1/4 sheet, etc etc. Your examples of building up tail (assuming you can compensate elsewhere in the airframe to maintain balance) is a good example.

 

 

Edited By IanN on 20/10/2010 12:11:14

Edited By IanN on 20/10/2010 12:32:35

[Erfolg]

A recurring theme in this discussion is that of weight.

 

We have all tended to gloss over, possibly taking it as unspoken given, that is "Duty".

 

PR designs have been used as the bench mark, which are IC designs.

 

Discussing duty and drawing comparisons, I wish to consider competition conventional build gliders 2m, 100s, Open. Ignoring glass moulded models, even though the same arguments pertain.

 

Competition towline, winch launched gliders had tremendously strong spars. In the past many would contain Duraluminum spars of approx 1" dia, with as many as 3 per panel, stepped in length. The rest of the model would follow similar considerations, capable of absorbing the massive stresses of launch. The penalty was weight, but the extra height gained in launch was of greater benefit.

 

Now consider the electric thermal competition gliders, Hyper Glide, Bubble Dancer and even moulded composite models. Ultimate strength is not as necessary. The weight is significantly lower, even with all the electric bits.

 

I have converted many of old competition gliders have been converted to electric flight. The wings in particular are much heavier than necessary for the conditions which we typically fly in. Where as modern electric gliders, have generally better performance for most conditions due to weight.

 

The same is true of many IC scale type designs, the duty is much different. The build in all respects can be much lighter with benefit, with regard to electric models. Look at many electric kits, say Great Planes, they are the product of a "virtuous circle" as weight is lost, more of the airframe can be beneficially lightened whilst maintaining the service duty capability.

 

So when it is suggested that PM and other designs could be beneficially lightened for electric flight, I would tend to agree it can be doable. This not to criticise the original design, just reflects the change of duty. 

[Richard Wood]

KC,

I think the Midget Mustang for one would make an excellent e-conversion.

I have this plan & it's on the 'to do' list.

The power available from electric equals or exceeds glow these days

so lightening ic designs for that particular reason isn't really necessary.

Just build to the original design & you won't go far wrong..

 

Lightweight leccy models were essential back in the days of brushed

can motors & Nicads.

TBH I've never bothered changing the construction of any ic conversion.

You could of course shave off an ounce or two if you wish.

 

 

 

[kc]

Peter Miller stated in a thread about the RV3 that all these designs were built by him to the lowest weight practical ( for glow of course ).  Looking at the plans I accept Peters comment  & strongly disagree with the 'outhouse' comment.  But its to some extent a matter of opinion.

For electric I expect that the typical 1/4  birch ply engine former normally used for IC could be reduced to 1/8 and would be smaller too because further forward.  Also the 1/32 ply doubler could be reduced in height or eliminated because the main weight ( LIpo ) will perhaps be further back than the than the heavy lump of glow engine.  The built up balsa cowls might be lightened but would be more work, which could be unnecessary if any lead is needed up front.  The wing sheeting might be reduced in extent but not much. Built up tailplanes could be used.   Peters undercarriage design seems minimal for metal and only carbon fibre would be lighter perhaps.

A 3S220 Lipo plus ESC plus electric motor weighs around 10 ounces compared to 12 ounces for an OS 40 FP etc.  Maybe another ounce for tank and fuel proofing.

So really only a few ounces could be saved, perhaps 4 oz, for electric..

[Marc Humphries]

Hi folks,

 

Maybe I've got it wrong.  But a 48 inch span Midget Mustang nudging the scales at nearly 5 lbs does seem heavy to me for any model.

 

Perhaps I've been spoilt so far by my light weight models.  Absolutely no critcism of the original PM designs - just my experience.

[Erfolg]

Regarding the scope for weight reduction, commensurate with strength for duty. I may have an indicator

 

I have built the PM Cassutts for electric. this weights in at

 

1025 grm, 2200 Rhino, +200w motor

 

Motor XYH35-36 1300kv rather than linked model.

 

I am not sure what the PM model came in at.

 

A Swedish modeller Tommy? I think managed even lower weight..

Edited By Erfolg on 20/10/2010 14:44:14

[Peter Miller]

I have read the comments with interest. I can't say that I disagree with anything in principle. 

 

I think that I would like to clarify a few things.

 

First, The Midget Mustang was heavier than I wanted. I will say that it was not my own choice. I was asked to design it and not allowed to do my normal stretching a slimming so it is much more scale.

 

Yes, I do try and build lightly consistent with reasonable strength for normal club flying. Examples of this would be the fact that I use 3/32" sheet sides and 1/32" ply doublers. Most equivalent designs use 1/8" sheet and 1/16" ply.

 

I use 1/4" ply for F-1 for a very simple reason. I use blind nuts for the bolts that hold the engine mount on. these will protrude through 1/8" ply so I just make it from 1/4"

 

I use medium grade 1/4" sheet for the tail components because I usually need to add a little lead in the tail. I never seem to have to add lead in the nose.

 

There is a lot of talk of weights. Weight is a single dimension. The real figure that is important is wing loading.

 

Not if you look at the wing loading figures you will see that most of the models have wing loadings of between 20 and 22 ounces per square foot.

 

My new RV-3 came out at 26.5 ounces per square foot which is well over most of my designs.

 

Now engines produce quite a lot pf vibration and a structure has to absorb that and resist fatigue cracks so it has to be a bit stronger. The structure also has to absorb the rough and tumble of normal club flying on sometimes less than perfect fields and pilots.

 

If you want to look at extreme weight saving look an any ARTF with its components fretted away to extremes. These structures are not designed to take any thumps because the fretted ply is only strong along the length of the grain but no strength in any of the diagonals or uprights. To see a drawing oof this may I sugget you look at "Miller's Tales" in the current issue of AMI where I illustrate this very point.

 

I don't even pretend to know about the structural requirements for electric power but I could suggest that a sheet fuselage side could be built as a Warren Girder built with 3/16" or 1/4" sq. but these would need to be hard balsa longerons and medium for the diagonals.

 

With regard to ply parts, these could have lightening holes in them. What is not commonly known is that a sheet such as a doubler has most of the stress and loads round the edges so the holes would not weaken them significantly.

 

I hope that this may help with anyone converting my plans.

 

[Steve Hargreaves - Moderator]

KC I reckon you'd do a lot worse than the Seagul EP range......a bit smaller than your nominated 50" span...(they are about 40") but beautifully built & fly very well.....sadly you can't get the Extra anymore but the Edge or X-Ray or even the Decathlon might tick your boxes!!!

 

[kc]

Steve,

The planes you recommend are ARTF I think.   I believe that ARTF can only  be produced by paying people only 'slave' wages.  Anyone who has built a model knows the number of hours it takes.  Divide that into the cost and it is obvious the actual builder was paid very little after the dealers have had a cut.  Even with mass production it must surely be a mainly hand made item.  So it is completely against my principles to buy an ARTF!

The pleasure in aeromodelling is building the model ones self and then flying it!  Anything less is not aeromodelling!