Peter Rake 36” Sopwith pup conversion setup

[Hunter]

Hi All,

      It’s many many years since I built and flew ect electric powered aircraft, and with time on my side, I thought I would get back into it.

   But as expected, things change! Electronic and power system improved, and now I’m scratching my head trying to fathom out how to convert a speed 400 model into a brushless setup.

 I have a Peter rake plan from twenty years ago, of a 36” span, speed 400 motor via a graupner 2.33.1 gearbox, having built her, in her original design, which proved very successful, I would like to build her again, but convert to a brushless system.

  I’ve researched as best I can, asked many questions, and have been recommended the power train below 

 

Tornado Thumper V3 3536/08 1050KV SKU2979
Overlander XP2 30A Brushless ESC - RTF - SKU 2724 SKU2724
Supersport 2200mAh 3s 11.1v 35C with Deans SKU2567
APC 10x5 Thin Electric Propeller (E-LP10050E) APCLP10050E

 

  I would appreciate it, if someone could confirm that the suggested equipment would be suitable, or maybe some other combination.

  I look forward to your comments and input

  many thanks 

   Mark

[Alan Gorham_]

That setup is way way too much for a 3 foot Peter Rake bipe. It's in no way equivalent to a geared Speed 400 setup. You only need around 80W to fly your model, not 350 to 400.

 

[Hunter]

Thanks, as I said brushless systems baffle me, so please bring on suggestions thanks

mark 

[Shaun Walsh]

According to this build log the finished model will weigh about 1Lb

Build Log

Your proposed setup will give around 400 watts which will render it ballistic at full throttle, more whippet than pup.

You should be looking for a motor with a power output of 80-100 watts for a realistic performance with a bit to spare. 

The question is what size prop do you want to use? The bigger the prop, the lower the Kv rating of the motor you need. 

Also, the battery is overkill, a 1300mAh battery should be fine and a lot lighter. A 2S or 3S battery should be chosen to suit the motor/prop combination and an appropriate ESC to suit the current drawn plus a safety margin.

eCalc is available at low cost to calculate the effect motor/battery/esc/prop variations.

Hope this helps.

[Alan Gorham_]

Instead of just giving you a shopping list maybe a short explanation of the theory will enable you to understand how to size power systems? It's irrelevant whether they are brushed motors or brushless by the way so there is no need to be baffled. 

If we consider the old brushed power system that used a Speed 400 with 2.33:1 gearbox. I will assume that you used an 8 cell Nickel based battery and something like a 9 x 6 prop. 

Graupners Speed 400 7.2V variant has a kV figure of 1762 revs per volt. Assuming the old 8 cell pack maintained a terminal voltage of 9.2V at full throttle, that means the motor turns at 16210rpm, ignoring slip. 

The 2.33:1 gear ratio means the prop will turn at 6957rpm. Using an online pitch speed calculator gives a full throttle flying speed of 47mph, ignoring drag etc. That all sounds in the ballpark for a WW1 biplane. 

 

The recommended maximum current for a Speed 400 motor was around 9A so to see how much power was used to fly the model using the above system we do 9.2 x 9 = 82W.

Peter Rake designs commonly end up around 20oz AUW, so the power loading in the brushed case was 65W per lb. 

 

If you wanted to use a 2S Lipo and keep the same size prop, then you could go for a brushless motor capable of more than 82W and a kV rating that will turn the prop at a near equivalent speed to the geared 400. There are lots of around 100W outrunner motors with a kV of 1000 that will do the job. As an example look at 2212 size motors with the 1000kV rating. 

Edited September 10, 2022 by Alan Gorham_

[kc]

Interesting comments Alan but perhaps a 'shopping list' is what he asked for!

 

What do the forum members think of this motor/ESC/prop from 4Max Value range?    Do you think it would suit?

[Alan Gorham_]

But there are multiple ways to achieve a usable result in electric flight. One person's shopping list is not the definitive list. Imagine if 10 people give the OP a completely different list. That would be unusable and confusing so perhaps some knowledge may be able to allow the OP to make a more informed decision themselves.

Of course the easy answer is just to recommend ringing George at 4-max and ask him to put together a complete power system which he is happy to do as many members of this forum have done successfully in the past. 

[Alan Gorham_]

Just for interest I am a fan of Peter Rake's designs. 

Here is his Isaacs Fury that I built the prototype of and his Sopwith Camel that I have in build. 

[Outrunner]

I built and flew and regrettably sold a Peter Rake Currie Wot that was about the same same as the Pup. It flew on a cheap Chinese bell motor that don't seem be available any more but it probably didn't produce any more than about 60 Watts and it flew lovely. If I was building another I would fit  a 4Max Emax CF2805 like this one https://www.4-max.co.uk/emax-cf2805-motor.html.

 

A few years ago I cut myself out a "kit" for a Peter Rake Sopwith Camel, must glue it together as Peters design do fly really well and are a manageable size too and only need a small cheap motor and battery pack of about 1300mA.

[Hunter]

Hi,

     Thanks for all your very interesting remarks, I shall digest all! And take note, and thanks outrunner your suggestion of motor seems just about right, 

Not having a computer, I can’t download motocalc or any others to test setups, so your suggestions will be on what I go on.

  Many thanks

  mark 

[kc]

Well the motor that Outrunner suggested is 2805kv and uses a very small prop which might not project too far outside a radial cowl.  Depends on the cowl dia.    Alan suggested 1000kv which could use a larger prop.    

[PatMc]

IMO this motor would probably be the most suitable of the ones from 4-Max. It's heavier & capable of more power than needed but the model was designed around a geared 400 can that would have weighed around 80g so extra weight will most likely be needed in the nose anyway. Using a 2s battery with a suitable dia prop should provide about the right power level & this 20A ESC would cover the max current with plenty of leeway.

 

Edited September 10, 2022 by PatMc

[Outrunner]

2 hours ago, kc said:

Well the motor that Outrunner suggested is 2805kv and uses a very small prop which might not project too far outside a radial cowl.  Depends on the cowl dia.    Alan suggested 1000kv which could use a larger prop.    

Oops! As kc says it's rather a high kv at 2805, I have a similar motor but much lower kv. Airtek have a nice motor with a much lower kv at 1200 and should swing an 8x6 prop https://www.airtekhobbies.co.uk/product/airmax-2822-1200kv/ 

I've used quite a few Airmax motors and they have always been very good quality, Airtek also publish lots of useful information on thier website about each motor.

[Hunter]

Thanks PatMc,

that seems a good combination, and good explanation, makes a lot of sense, just need to sort 2s battery out, let alone charger ect! 
  Mark

[Hunter]

Hi Outrunner

         Thanks for reply, much appreciated with your suggestions, I shall take a look at the motor you suggest and read up on there site

cheers

mark 

[kc]

The same motor that PatMc suggested is available from 4Max with ESC,prop & prop adaptor +servos as a Value Power package - a worthwhile deal i think.

[Hunter]

Thanks Kc, would it swing a wood prop?

[kc]

 Electric props are made to a more efficient shape and are suitable for the revs used.   The holes ( to suit the prop adaptor) may be smaller than that used on i.c engine props.    You could buy a grey colour prop instead of orange.    You could try a wood prop and check with a wattmeter what amps are drawn to ensure it doesn't excede the ESC's maximum amps.   Matching the motors kv ( revs per volt ) and prop and Lipo size plus ESC rating  are they key factors - change one and you probably need to change other things. 

[Tim Hooper]

Having built several of the later Pete Rake's models in the past, and converted them to brushless power, my advice would be to keep all the hardware as far forwards as possible!

 

That old S400 motor weighed in at around 3oz, whereas your new, dinky outrunner will be somewhat less.  The same applies to a small 2S li-po battery when compared to an old 7 or 8 cell NiCad or NiMH pack.

 

To keep the specified CG, without adding redundant nose weight, I really would try and get the li-po into the cowl, and all of the radio gear right behind the front bulkhead.

 

Tim

[Hunter]

Thanks Tim, I’ve noted down what you said regarding weight as far forward, obviously I will need to redesign firewall which shouldn’t be to difficult to fit motor and incorporate thrust lines ect.

    Will make a start on construction once I locate a good supply of balsa, found some but to soft for my needs.

cheers

[Andy Gates]

Hunter,

 

Have you tried Balsa Cabin for balsa supplies? They are very good.

 

As for Tims comments regarding keepng weight well forwards, I was really lucky to be able to build a prototype of the laser cut Nieuport that Peter did.

Superb machine, I still have it but it needs some refurbishment.

I ran it on a 1050kv 2820 motor that is no longer available and 3S on a 9" x 6" APC slow fly propeller. All of the propulsion system sat in the cowl on the front of the firewall so the CoG was right without ballast, flies really well too.

 

Info can be found here

[Hunter]

Thanks Tim, I will try balsa cabin, if they can select the right grade that be good.

    I built and tested Peters eindecker many years ago, and was a joy to fly, was in FSM, alas the aircraft was damaged when a ceiling collapsed! And think that put a stop to my flying until now! Just having to start from scratch! New tranny ect ect it goes on n on!

cheers

[kc]

The advice from Andy & Tim seems exactly right, but I would suggest you should consider whether the Lipo you choose can be inserted across F1 engine bulkhead.    A  3S 1000 is only 72mm x 36mm x17mm and might be inserted across & from front of cowl.    ( a 3S2200 commonly used by many models is 105mm x 37x 22 )

Personally I think it's important for safety to be able to connect up the Lipo with fingers clear of the prop so some access hatch would be preferable behind the cowl - - and one is shown underneath on the plan (it's on Outerzone )    Therefore planning to fit motor and Lipo to F1 with suitable modifications to get connectors through and then building fuselage around it will be easier than performing 'keyhole surgery' to fuselage later!  

Balsa Cabin are very good balsa suppliers and their website offers a choice of hard, light or medium and also 'Contest' grade in a different section.   SLEC is also as good and I see that SLEC are attending the BMFA Builders Show 1st and 2nd October if you want to select your own balsa. 

Edited September 12, 2022 by kc

[Hunter]

Hi Kc,

          Thanks for the suggestion regarding battery location, yes I agree, placing battery in cowl on F1 below motor would be a good idea plenty of room in keep cg up front, and also agree on having battery connection behind F1 via hatch. I will get a battery either s2 or maybe s3, or both! although s2 seems ok,  eithet In front of F1 or maybe behind. See how it goes!

   Still would like to swing a wood prop, around 9*5 in that region,  and s2 seems ok, but please correct me if I’m wrong,  of course I will check current draw, if a no go I will revert to electric prop.

    Been on balsa cabin site, and I did notice you can select grade of wood which is handy

  many thanks again

 mark 

 

Edited September 12, 2022 by Hunter

[kc]

Electric props normally come with a selection of plastic inserts to exactly match the diameter of the prop adaptor shaft, so have an advantage over ic props.

The reason for preferring 3S over 2S is not so important in this low powered model but that the same Lipo could be used in other models.    3S is used in many models and the higher voltage keeps current down and allows use of cheaper ESC - ( high amp ESC cost lots more )    You probably need as many Lipos as the flights in a day, so the cost mounts up if each model has a different size Lipo.   Therefore many people standardise on 3S2200 and also a 4S 3000 (or more) for a range of models.   Most of my clubmates take 5 or 6 different models to each flying session!

Some people recharge at the field but it's not considered a good idea to use ones car battery.