Power Setup for Top Flite DC3

[funflyerColin]

Hi all, i would like a bit of advice with this power system have asked in another site but not really getting the answers that i am looking for. Firstly i bought this model built of ebay not quite what i expected when i collected it, i was told that it had flown on 2 52 four strokes then converted to electric and had several flights after questionable imho. It had 2 Ultrafly UF MTR F1810 motors in it along with 2 Mystery Pentium 80a opto esc's, when powered up with 4s 2200 as suggested it was only pulling 300 watts per motor = 600 total weight of plane was 9lb 7oz. Not enough ?.

Cannot afford to buy the E-Flight 32 motors that some of the others are powered with also am unable to find any amp watt data as to what they are pulling using the 10 x 7 3 blade that's also used.

So i bought 2 x EMAX GT2825/06 - 962watt 710Kv motors, Had to do some repairs to the craft as undercarriage had been ripped out and other repairs around it needed to be done once motors were installed i ran some tests weight now went up to 10lb 7oz.

on 4s watt meter readings are

16.72V.......15.09VM.......0.097AH........25.27AP.......387.8WP........1.5WH

So would i be right in thinking that i need about 1000watts total to power this plane or is that figure too much?.

I did a test with a 5s and that yielded just over 700 watts per motor possibly to much?.

I don't really want to go down the 5s route as don't have any myself.

Specs of the plane are

Wingspan: 82.5 in (2095 mm)
Wing Area: 750 in² (48.8 dm²
Weight: 8-10 lb (3630-4540 g)
Wing Loading: 24.6-30.7 oz/ft² (75-94 g/dm²
Fuselage Length: 55.5 in (1410 mm)

This is my first venture into the larger size aircraft that i usually fly, learned to fly back in the late 80's on nitro's now laerning a bit about lecky's now or trying to.

Sorry if this is a bit long winded but don't want to try and haul this of underpowered or way over powered.

Colin

[funflyerColin]

Her's a pic of her posing at the club waiting for me to decide weather she has enough power or not, i am using 10 x 7 3 bladed props but have thought about 11 x 8 2 blade our site i not very smooth rather bumpy atm so need all the clearance i can get.

[Dave Hopkin]

1400W should be ample to get her into the air with a decent power margin over and above whats needed for scale flight

 

The 800W you got from the 4S test run does sound very marginal to me

Looks like you either have to go for bigger props or 5S I am afraid

Edited By Dave Hopkin on 14/07/2015 06:55:21

[Cuban8]

Are you taking any static thrust figures in combination with the electrical measurements? As a rule of thumb for a scale model like your Dak, I'd be designing for a static thrust figure of about 75% of the models AUW for starters. Just relying on power measurements alone is not very helpful. So around 7.5 - 8lbs total - it's possible that you'll not need all that power, but it's much easier to lose power than to gain it.

This is a very useful tool, and I find I can get surprisingly accurate results from it.

**LINK**

[funflyerColin]

Hello guys thanks for the replies looks like i may have to try larger props was hoping to fly on 3 blade with counter rotating props but it looks like i will have to go with 2 bladed props rotating the same way.

I haven't done any static thrust tests. Just an idea if i got a set of digital scales and put them against a wall , then ran the motors up on the dc3 with it's nose against the scales would that be the way to get static thrust? would it be reasonably accurate?.

[eflightray]

Bit late coming to this one.

My closest twin motor model is a bit bigger, but similar weight, (so slightly lower wing loading), but also uses similar sized motors.

E-Power GT2826 710kv.

I run one 3s Lipo per motor. On 3s it allows me to use a bigger prop, It has flown with APCe 12x8, but currently uses 13x 6.5, on approx 300watts per motor.

You may be limited by ground clearance for the DC3, but the bigger the diameter prop the better is my opinion. They give very good thrust at relatively low speed for a more realistic scale looking flight.

By the way the model is my B-25, now 22 years old, and has flown on brushed motor with belt-drives and a whole load of Nicad/Nimh cells on 12x8 wood props. I only converted it to brushless and Lipo four years ago.

Ray.

[David P Williams]

Can't help with the electric setup, but mine had two Thunder tiger GP40 two strokes, and it flew like a pylon racer.

[funflyerColin]

Hello Ray and David, sorry at bit slow at getting back thanks for the info. I haven't ha chance to do some more tests on her yet, i now have a 11x8 APC prop which I'm hoping to run up and see what the results are and also to check the static thrust measurements. All info and help is gratefully welcome once again thanks guys.

Colin

[Model Monster]

No electric setup advice, but hope the prop size and rev's help.

It was lovely to build and is a great flyer. Powered by OS 40 FS's with 10 x 6 three bladers (Graupner), Max rev's approx. 9000 Rpm. Cruises on just over half throttle.

[Rob Dunn]

Hi for electric setup I can not help you as I am building the TF DC3 using 2 x ASP .46 2 stroke with 10x6 3 blade prop's

Rob

[Djay]

I use e-flite 32 motors running 11x7 3 blade props.I think I have either e-flite 60 or 80 amp ESC's cannot remember, Each motor is powered by a 4 cell lipo and the plane is excessively overpowered. It flies like a pattern plane with unlimited vertical so do not worry to much about the power output as it does not require much. Previously I had two ASP 52fs engines and it flew OK but not as good sd with electric.

Ensure you open the throttle very slowly on take off as the torque from electric motors can flip the plane or make it go vertical before it has flying speed.

Most of my flying is done at 1/3rd throttle as this is more to scale and it flies like a dream.

Darryl

[funflyerColin]

Happy new Year all,

A bit late again at responding sorry but Thanks guy's for the info i'm still not sure about my setup atm but input from guy's like yourselves will steer me in the right direction, hopefully will give her a maiden this year if the field gets smoothed down a bit.

All my modeling work as well as flying has stalled for a bit as other projects and life are getting in the way ,am trying to restore a 5' windmill that my father built some 25yrs ago quite different to model aircraft.

Colin

[John Emms 1]

In the early days I speced power systems for this model that flew on 10 cells (3S equivalent), and the projects were a success. The 400W per motor that you have is a sensible figure to be running at on 4S, and 800W for the 10.5lb in this type of model is a comfortable amount of power to have - enjoy!

[Trevor]

In case it's still of interest to anyone, the specs for my 16 year old electric version of this model are here:

http://www.bartonhewsons.uk/home/modelflying/scale/dc3keydata.html

I agree that 800w is comfortable and would say from experience that anything below 50w/lb will require a very careful climb out! In looking at my figures, especially cell count, remember that the motors are brushed and wired in series. However the power, prop size and rpm figures are still applicable to brushless setups.

Trevor

[Chris Freeman 3]

Great flying aircraft this, mine was 4.5 kg and I had a total of 700 watts power which flew it better than expected as I stay in Johannesburg and can have are density issues with the heat and altitude. Trevor helped me with his power suggestions and can confirm his suggestions are good. The flaps are essential on this aircraft.

[funflyerColin]

Hello John,Trevor and Chris thanks for the input very much appreciated. I haven't got her up in the air a yet as too many household duties have taken over . But i will get her in the air at some point and will post pics, so any info about your power systems is much welcomed. I still want to run some more tests on her and put the results back up here again for any other remarks good or bad they would be taken in an adjusted as required. So this project isn't dead just taking too long really, Thanks again for your interest and advice.

Colin

[Trevor]

Glad to hear the project is still alive - albeit in hibernation. I'll keep watching this space for news!

[Chris Walby]

Hi, I'll take a look at what you have and see if I can help out (only been flying 4 years, but an electrical engineer for 35 years!).

I have a TN DC3 on the building board & a couple Mosquitos + a load of prop testing data when trying to size other planes!

It sort of all depends on which motors you picked which on the face of it look okay (I picked a 370KV for a war bird and ended up with a windmill up front).

[funflyerColin]

Hello all, finally got her out again yesterday only to find that i had robbed the rx for another plane. Searched around but couldn't find another so another plane got robbed, must remember to get another rx. Anyway today got her all set up and ran some more tests . Results were very close to my first post on 4s using 3 blade MAS 10x7 cw and ccw props 389.8wp, i managed to do static thrust test at 5.6 lbs at 9100 rpm. Put 2 blade MAS 10x7 cw and ccw props on but the results were worse 366wp at 9100 rpm and 5.1 lbs. So i gather I've got to increase the pitch as I don't think i would have enough ground clearance with 11 inch diameter props, our field is quite rough.

5 1/2 lbs static thrust for a 10 lb model what do you guys think ?

[Trevor]

You should be fine on the three bladers. I use graupner 10 x 7 three bladers and, at 10lb AUW, anything over 8000rpm is enough for safe takeoff, over 9000rpm is a luxury!

Obviously you won't be able to climb out at 45 degrees but unless you have a tight patch surrounded by trees, a scale-like takeoff and gentle climbing circuit should be easy.

Good luck,

[funflyerColin]

Hello Trevor, thanks for the advice looks then that I'm good to go, not really used to this electric milarky but persevering with it. I keep trying to find reasons not to fly her now, this along with a couple of larger birds i now have in my squadron are larger than i would usually fly. Mostly around .40 size sport planes so large scale is a bit nerve racking, the other 2 large planes are a Great Planes PT19 and a Precedent Stampe but ic powered so i'm more at ease with the power used on them.

[funflyerColin]

Hi all just a quick update, i am at present tidying up the wiring and and other bits and giving her a good going over making sure everything is fixed. Getting more nervous by the day, the only large model that i have flown is my bro's Bird-Dog at 72". Being a high winger it was a pussy to fly and let him fly it great for a learner. The DC3 will need some careful input don't want to stall her as can be seen in a lot of the top flite DC3 U-tube videos. Here's Hopeing for some light winds straight down the bumpy runway and fair weather.

[funflyerColin]

Hello all went to the field today to fly the Dakota but the wind was in the wrong direction and i believed it not safe to attempt a take off. The field hadn't been cut either pity maybe another day, here's some pics my bro took of her at the site.

Edited By funflyerColin on 09/07/2017 22:40:52