motor/prop info,for the scratch builder - RC Groups
Shop our Airplanes Products Drone Products Sales
Thread Tools
Sep 07, 2006, 03:34 AM
Registered User
Discussion

motor/prop info,for the scratch builder


does anyone know of any data sheets available for the scratch builder to help with choice of motor size and correct prop?Could really use that kind of info when designing planes.thnx John.
Sign up now
to remove ads between posts
Sep 07, 2006, 03:57 AM
Registered User
vintage1's Avatar
Watts per lb is the staring pount really, with an idea of model weight and wing loading the rest pops out.

..after some hefty maths and Motocalc (www.motocalc.com) seswsions.

The principle Iuse is braodly this.

1/. Decide what model and what size.

2/. Estimate wight from experience.

3/. Set up a simulation in motocalc.

4/. decide on performance level required..slow WWI bipes will fly onm 30W/lb but 50 ius safer..warbirds need 60-100W/lb.

5/. Armed with power requiremenst, ssettle on a pack size and wight..that usually dominates the equation...

6/. If its scale, that sets the prop diameter. Otherwise about 1/3rd span for WWI, and a lot less for sporty non scale stuff..maybe 1/6 to 1/4.

7/. use motocalc to translate that diameter into teh right power and pitch speed - that sets RPM and pitch speed.

8/. find a motor gearbox combo that will produce that on the selectd pack.

These days its easier because I 'know' roughly where to start from.
Sep 07, 2006, 04:56 AM
Registered User
thnx for the info,,,will come in handy.My problem is this,and you could probably help,I want to build a slow flying cabin style plane.Rudder,elevators,throttle,stick and tissue{coz I know it well}To keep it low cost i'm looking at a geared 400,with standard servoes,size is no option.got some plans and wondering how big to make it and get it to fly.
Sep 07, 2006, 05:15 AM
Xtreme Nut
With a geared system your 400 sized motor can turn a SF prop of up to about 11x6 or 12x6 even. Try not to use standard servos, its heavy, for cheap and good go with the GWS Naro/Pico servos

I would say for an easy flying plane the likes of a Cub (a lot of wing area) you can get something in the 40" w/span range with AUW of about say up to 30 oz.
Sep 07, 2006, 05:23 PM
Registered User
vintage1's Avatar
Quote:
Originally Posted by cymraeg54
thnx for the info,,,will come in handy.My problem is this,and you could probably help,I want to build a slow flying cabin style plane.Rudder,elevators,throttle,stick and tissue{coz I know it well}To keep it low cost i'm looking at a geared 400,with standard servoes,size is no option.got some plans and wondering how big to make it and get it to fly.

Ah. Right up my street.

Want some free plans? I redid this one in CAD..have a look in the vintage forum and search on 'challenger'

24oz AUW, speed 400 geared 4:1, 10x7 prop, 3s 1200 LIPO pack, 49" wing, 400 square inches. Its a 1943 design and flies like a Slow stick

In general 40-50" span built of stick and tissue will be fine. Aim for 17-24oz.

In fact the vintage forum is where you need to hang out..loads of old timers get recycled for electric power..loads of old plans too. I've got a vic smeed 'Tomboy' courtesy of 'Chas' somewhere that needs a redraw.
Sep 07, 2006, 05:40 PM
Registered User
vintage1's Avatar
Quote:
Originally Posted by tIANcI
With a geared system your 400 sized motor can turn a SF prop of up to about 11x6 or 12x6 even. Try not to use standard servos, its heavy, for cheap and good go with the GWS Naro/Pico servos

I would say for an easy flying plane the likes of a Cub (a lot of wing area) you can get something in the 40" w/span range with AUW of about say up to 30 oz.

Altho you can turn a 12" on a 400, the pitch speed is a bit low. They run best on 3s LIPO - the 6v ones anyway..and for general sport use I don't gear deeper than 4:1. Thats suits a 10" prop and gives a pitch pseed of about 26mph, which suits a low wing loading model.

Ive used 3.5:1 on 9x6, 3:1 on 8x6 and 2.33:1 on 7x5 - all APC 'E' props. All work well weith the models getting progressively faster..

I tend to use a lightweight RX and a pair of HS55 9gm servos. More than enough.

Here are some of the ones that flew
Sep 08, 2006, 03:26 AM
Registered User
thnx guys,,,JUST what i'm after.have this idea to build a Frog Redwing originally 18"was gunna try three times that.Good looking bird.thanks again
Sep 08, 2006, 03:29 AM
Registered User
vintage1's Avatar
Quote:
Originally Posted by cymraeg54
thnx guys,,,JUST what i'm after.have this idea to build a Frog Redwing originally 18"was gunna try three times that.Good looking bird.thanks again
Build it light, gear 4:1 and use a 10x7 and 3s LIPO.

I've seen a 42" rubber conversion running off a 12mm geared brushless at around 12oz...but I would expect you to end up around 17-18oz.


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
max motor/prop combo for qualcomm batts freeflight Parkflyers 3 Sep 21, 2002 08:30 AM
Question re: motor / prop / battery for Apache Tempest Sport Planes 7 Aug 08, 2002 01:03 AM
Best Motor/prop/battery for high altitude WickedFunRC Foamies (Kits) 5 Jul 12, 2002 12:32 AM
a good battery/motor/prop-pack for Zagi lothlean Foamies (Kits) 2 May 05, 2002 01:44 PM
Hottest Motor/Prop/Battery for Push-E Cat? ScottChase Foamies (Kits) 0 Feb 06, 2002 10:46 PM