And pretty wrong.
I find that a slowish plane needs about 20W/lb to keep it flying. Actually at about 20mph you only need theoretically about 3W/lb for a clean airframe. However there are motor, and prop inefficiencies..
Thats a 15lb plane you have there..not sure a Telemaster is anything like that.
and each emoli cell
Yeah, but a bushed 40 is turning a matchstick 10x6 at 10K RPM. AND ist maxiumum outpoyt is usually quoted at an RPM that is way above what we us in flight - maybe 16-18K RPM. If you gear or use an outrunner, you get more like a thin blade 13x10 at 6K RPM. that takes about half the power for a start to give the same thrust and pitch speed.
And half throttle I have found to be about 1/4 the power of WOT.
The nearest thing I have is a 60" span black magic that flies at 3lb AUW. On 200W. On an 11x7 prop doing at most 6500 RPM. On a pretty inefficient can motor (60-70% over the throttle range). Flight times and what goes back into the pack suggest I average about 50W on that during a gentle flying around sort of thing. Thats precsiley *16W/lb* *average*.
Motocalc tells me it will stay up on a 2000mAh pack for half an hour. This is borne out in practice.
Power to stay up, as opposed to climb, is simply the models weight, times its speed, divided by its lift to drag ratio at that speed.
You can see that a low wing loading model - large and light, and therefore slow - with fairly clean aerodynamics , therefore high L/D..takes almost nothing to stay up really.
I originally built that plane to carry a camera, but its too nice to hack it about..
Now a senior telemaster I am fairly sure can be built at 6lb or so.
It probably needs 300W or more to get it to climb decently, but I doubt it needs more than 90W to stay there.
In general for floaty type vintage models, I find that 60W/lb gives a brisk climb of around 600 fpm, and if I target for a 6 minute flight time based on full throttle, on the ground, I get at least 30 minutes in the air.
So targetting 12 minutes WOT statuic will net over an hour.
On a 6lb model thats 360W. Lets say its running a 3s LIPO pack, thats
35amps..so I want a 3s 4000mAh pack roughly.Here's a suitable pack
AS for the motor..well an AX 2826/8 is ticking over and nicely efficient on a 12x8 on 3s LIPO. Thats $96 for the motor from a web site I googled.
Heres the Jeti 70A with built in BEC - so no need for receiver batteries
- for $130
Total weight of everything is 150g for the motor, thats about 5oz, and 224g for the pack. am 1.5 oz for the ESC. I make that a shade under a lb.
Remember that replaces the motor, tank, fuel, engine mount, throttle servo and receiver battery. So its actually pretty close to similar weights on a sport model.
Then we are just about on. However I assumed the $500 for for the bits that would break in a crash.
I made it $230 for quality gear.
At
350W brushed motors are almost as expensive unless you pick up Ebay bargains.There are a lot of 350W Chinese brushless at very keen prices tho. And cheapo ESC's are about as well. BUT whilst suitable for those who know what they are doing, I quoted branded gear that I know is reliable and will do the job.
Er. Three cells. Yor power calculations were way out.
No, they aren't. You just don't know how to calculate power requirements and where to buy LIPOS.
As I said, $500 for the smashable parts of the plane.
Anyway, the bit of the post I replied to originally was referring to the cost of the batteries alone. I simply said you could easily get batteries for under $500. In fact I found a suitable pack for about $75...