RCM&E Pans

[Phil 9]

As timbo says "Trying to simply produce a chart to directly equate an electric motor with an IC motor is simply not feasible"    They just do not work in the same way. It would be very convenient if we had such a chart. EP is relatively new and many old plans were originally designed with IC power in mind. But now many people (me included) would like to add electric power to a scratch build from an old plan.

Tibo's double and zero rule looks good "and is a good rule of thumb"

[Phil 9]

Myron I think you are right I think it is slightly more critical. The balance between the amount of power required, motor size, and battery size (both power and physical size). If the balance is not right it is easy to end up drawing on the batteries leaving you with a ridiculously short flight time.

Timbo its simple physics that a physically large motor will need more power to spin fast than a small motor will. so if you prop is too small then you are working a motor outside its most efficient range.

My point being you need an efficient set up to keep the model in the air for a decent time and powered sufficiently.

[Tim Mackey]

Yes Indeed Phil, but thats not how you phrased it in your earlier post, and I quote 

"too small a prop the motor can not run fast enough".

To the beginner, this suggests that fitting too small a prop on a motor will not allow it to rev fast enough!

Obviously, quite the contrary will happen amd revs will be somewhat higher than with the larger prop, because as we know, Kv is not a fixed constant, and despite the principles involved, RPM does actually change with different sized props on the same V in. 

[Phil 9]

Well it just goes to show how electric power can seem complicated.  with IC power you can almost guess the engine size just by looking at the model    "stick a .40 in it"

However if you get the set up right electric power can have many advantages. But we get back to the original problem of how do you choose the right set up. getting this wrong can be expensive (trail and error method is not a good option with the cost of motors and batteries)

The points you outlined earlier are a good starting place

"1) Aim for 100 watts per Lb of AUW

2) Small props on high Kv inrunners -  Large props on Low Kv Outrunners

If you simply MUST try to convert - then use the "double up and zero" system below.

IC 20 size? - double up the 20 = 40   then add a zero = 400 ( watts ) motor

IC 50 size? - again..... 50 X 2= 100 add the zero = 1000 Watts."

[Phil 9]

some usefull EP info try this link

[A.A. Barry]

See, I have opened a can of worms, and after reading all of the above, and thanks to all, still no where as simple as IC...

Free flight..... .049 - 1.5cc up to 50"

C/L ..... .049 - 7cc up to 50"

R/C .... 25s 2st..... 30 to 40" 8.6 / 9x4 props.  40/46.... 40" to 50' 9x8 / 10x8, 50/ 61..... 11x8 to 12x6.

yes I know,what the next comment will be, "what about the weight", I am refering to "sunday flyers". there is so much indicisions with E.P. that I think that the only way to go is , stick the bigest E.P that will fit and give a go, if is too big at least you can throttle (is that the right word nowdays) back.

the Battery packs, AH yes, 7.4v/11.1/ 14.8 and so on, 2s/3sup to 6s, well how long brfore the fuel/ power runs out?????? in I.C the average 40/46 on a 8oz tank will last about 10mins.  Even before you get to the flying field you can tell who is flying leecy, if your late, they have all got their car bonnets up,charging thier Bat Packs, the 1st time I wittnessed this, on arrival, I mussed amoungst the guys, ....thinking... ummmm... their seeing who has the biggest engine.... any way I found out the reason for this and have not been too concerned since, BUT......nothing like taking along 2lts of liquid in a can for power. 

Myron, I stated that I  have increased the Hurrie by 22%, yes on the photocopier , a4 and then stuck in all together with tape, and the necessary formers and ribs can the be copied again, normal, and stuck onto the balsa, It comes out at 76" span and like you an RCV, would be great, but 90sp, a FS91 os will fit fine...... Barry 

[Tim Mackey]

Listen Barry, as I said, if you really cant be bothered to just learn a little bit about it  - such as how the CAPACITY of the battery is what affects duration ....in EXACTLY the same way as a large bottle will hold more fuel than a small one  - then just buy a ready to go model, or phone Puffin or BRC etc.

Please remember that due to the excellent VFM created by the HUGE interest in electric power, certain models have now become entirely feasible for modellers to own and enjoy - Ducted Fans being a classic example. Just go and compare the cost and complications involved in trying to get a good fast flying scale IC powered ducted fan model compared to the same thing using electric power. No contest Barry.

Same applies of course to the average Joe who want s to dabble in the sport, and fancies a little aeroplane / heli to try in the farmers field out back etc...... or even the living room

- try firing up the IC engines in the lounge and watch the reaction from er indoors

This thread has now gone way off topic, and I suggest if you really want to try and understand it all a little better, rather than just keep knocking it, then you start a new thread in the appropriate section and ask questions.  I / We will be happy to try and help, but I also ask two things in return........

1) Dont keep telling me how easy IC is compared to EP -  that's defeatist and counter productive

2) Ask one question at a time on a subject that that you really dont understand at all...when you get the answer, if it makes sense, then say so, and move on to the next question.

[A.A. Barry]

THanks, Timbo, for all of those kind remarks,

1.. I am all in favor of E.P

2...I am willing and want learn

3...I am not the only one who has problems understanding all of this new power supply

4...I am certaintly not a defeatest

5 ..I hope the rest of the day goes well for you..............  Barry

[A.A. Barry]

Guys, can anyone help me with this one, DH103 Hornet, from RCME, 108' plan.  I have purchased 2 x "EMGC A3720 650kv" motors, are these big enough to the job????????  Timbo.......Barry 

[Phil 9]

yes they are big enough. But with EP it the set up as a whole will dictate how well it will work. Here is the point and  the aim (of all the discussion) is trying to get an efficient set up to give you the flight time and performance.

you can go over kill and put a large mAh capacity battery on (mHh milliamps/hour dictates how long they will last) but as you will notice the larger the capacity the higher the cost and weight. so as with most things its a compromise.

So Barry you have 650kv motors but what prop and battery size are you planning

[A.A. Barry]

Thanks Phil, these are the Q's is what I have been asking about, I have the plans, I have the motors, and 80amp esc, WHAT do I need nextall up weight, should come under 8kgs, without dragging out the plan I think the I.C version is 91 4 st, could be wrong . I will check. The manufacter of the moters say 12 x 10 to 16 x 4 wood? dunno . anyway 7mm prop shaft  . so there is the problem.   Barry

[Phil 9]

Barry as for props. APC have a line for electrical flight APC (E) props

The difference being slightly lighter. ie wood will work but being heavier they will draw more power to turn at the same speed as a lighter prop draining the battery slightly faster ( as I said before it is a compromise)

stick to the prop size range recommended by the motor manufacturer. the smallest giving more duration the largest higher performance (but for a shorter period) So depends on how you want to fly it.    As props do not cost too much it may be worth experimenting with the different sizes.

[Tim Mackey]

Come on guys...this is Terence's thread about building from plans - I have asked nicely to start a discussion in the correct place.

It costs nowt to start a thread ya know

[Tim Mackey]

Barry Wetherell wrote (see)

THanks, Timbo, for all of those kind remarks,

1.. I am all in favor of E.P

2...I am willing and want learn

3...I am not the only one who has problems understanding all of this new power supply

4...I am certaintly not a defeatest

5 ..I hope the rest of the day goes well for you..............  Barry

I am not sure which way to take those comments Barry.

I did say ( and have proven to be so in the past ) that I / we will help those who really want to learn.

Please start a new thread to discuss the matter further if you wish.,,, as requested earlier.

[Phil 9]

sorry Terence (oops in trouble now)

[A.A. Barry]

ME too , I will put this uder Hornet, sorry Timbo/Terence.. Barry

[andy watson]

Well at the risk of getting this thread back on topic, I am looking to build a Stuka around a Saito 1.20.  The RCME one (labelled as a Ju88) is about 80".

The scale concept is difficult- simpy because there is no end point.  At some point you have to say enough is enough, and that is your own call.  It is interesting, however, to build a specific plane and have an insight into that plane and pilot as an individual- even if you don't apply water staining to the radiator!

[Chris Salomon]

I echo Terry's comments that opened this thread, the description/pics in the plans listing are quite poo tbh!  The other plan providers are little better if any.  These days it should be fairly simple, on the online version at least, to provide maybe a link to the relevant details with the listing?

How about this scenario for an ideal world, the link takes you to a pdf of the relvant RCM&E build article, now that would be the coolest ever (may lose some revenue from back issue sales though!).

It is asking a lot to part with our cash based on a thumbnail and one line of text!

Sorry to moan David, take it as constructive criticism!

[Bert]

I bought the latest plans catalogue and I was quite disappointed by the number of errors in it.  I don't know what's happened to it over the years. It used to be quite accurate regarding the names and descriptions, but quite a few years' ago it just seemed to go off.

I remember Aeromodeller doing a competition to find the most number of errors in the plans handbook!

I don't think it's as bad as it was then, but still a little disappointing. David - if you want someone to proof read the next one - send it to me!

Bert

[Myron Beaumont]

Or me !  BERT  I think we both started together but in different places ,thats all

 I have the latest plans catalogue too -brought back memories - I thought at least someone could maybe update engine sizes to what is available these days . (good old Boddo  Eh !) eg My old Merco 60 ( if I remember right )didn't have the whooomph of the average 30 fs these days !

Happy new year !   Myron   Lets hope there are a few more left Eh !