Westland Whirlwind... test 2.. another crash arriv

You guys are the MEN! I've NEVERr used a watt meter etc... I read all the specifications from the manufacturer and make my own decisions and calculations based on the weight & type of the 'plane and the performance I want from it... sport / slowfly etc. I've done a whole load of nitro-electric conversions etc as well as setting up over 40 'planes which have all flown well until pilot error crept in, they are all good for power, thrust etc. Please don't make the mistake of blaming my set up for
a) a lousy throw (Spit) &
b) not having enough throttle at launch. (Westy..)
But 'Ta' anyroadup....
Cpl. Jones

I feel the lads on here are only trying to help Ian. If they see a member crashing a few models, the obvious way to go is to prevent him crashing more models. The folks on here DO care, and will do all in their power to prevent more expense

Garry

Yes a watt meter is essential for ensuring the best power output.Its amazing how just changing props can make such a difference good luck

Hi Corp, granted that you didn't have enough throttle, but, running your numbers on the calculator gives you this


That pitch of prop is stalling at zero speed, and your power is 108W/lb. Also your ESC is being over driven (only 2amps I grant you) so your forecast of 550watts is way off.

Klippy - in deference of us with less than microscopic eyesight, could you please post the salient numbers again below the e-calc sheet. No matter how much I enlarge it, on my screen, until it breaks up into a blurry mess of pixels, I cannot see the results, (I'm using 64 bit Win 7)
Thanks!

I'm guessing that some definition is lost in the resizing.

I've chosen
Medium motor cooling, a Model weight of 2,000gm including the drive, field 50M AGL and air temperature of 15C
2100mAh Lipo, 35 to 50C, normal (average charge), 3S and it's going to weigh 59gm/cell
A 40A ESC weighing 50gm
A Turnigy motor SK3542-04, which is a 1250KV that will give us 650W for up to 15sec and weighs 142gm
The propeller will be an APC Electric E of 9.5 x 8 with 2 blades

Calculating our choices gives us

Battery Motor @ optimum efficiency Motor@Maximum Propeller Total Drive
Max C load 20.37 Current 25.33amp Current 42.77A Static thrust 2216gm Weight 406gm
Min volts 10.19 rpm 11,586 rpm 10,009 rpm 10,009 AUW 2,000gm
Flight time WOT 2.9min elec power 263.6W Elec power 424.8W Stall thrust 989gm Power/weight 108W/lb
Mixed 5.0min mech power 226.4W mech power 354.9W Pitch speed 82mph Thrust/weight 0.49:1
Weight 177gm Efficiency 85.9% Efficiency 83.5% Tip speed 283mph P(in) @ max 474.8W
Specific thrust 2.33gm/W P(out) @ max 354.9W
Efficiency @ max 74.7%

We have 2 motors so we can double the numbers in the Total drive section.
To my mind upping the KV to about 1750 and reducing the pitch to about 6 will help.

.....Technical selection there klip.... I like it...ta. Anyroadup..... retracts now set into nacelles. Nacelles beefed up with several layers of fibre glassing. n I've managed to get myself distracted with other projects like a 6ft Catalina......mmmm......nice... I feel it deserves a fresh thread. Also I've finally got round to putting a Ripmax P51 together that's been hanging about since December. I know it should've only taken an evening but I got all precious about painting the pilot and cockpit up etc. Also been trying to sell gear to finance new 'Wants'. A Dynam Cessna 310 would be nice... as well as one of those giant 7ft W/S B25 s from the 'Banana people'..... want want want....