Flight endurance - maximising efficiency
 

My first "modern" RC plane was a RTF ans a rather basic one at that.
https://cimg4.ibsrv.net/gimg/www.rcu...4f5f6782d1.jpg
The Artech Wing Dragon. Even in 2009 it was an obsolete design using a NiMh battery and a brushed 480 motor! It did fly well enough but not for that long on each flight.
To my mind using four 9g servo was unnecessary weight along with long snakes for the rudder and elevator
By setting the ailerons to have differential movement I judged just three 3.7g servos it would be OK with bank and yank along elevator servo servo in the tail so no snakes.
Flown hand launch/belly land (no undercarriage) overall these changes saved 45g or nearly 10% of the AUW with a resulting significant improvement in performance.
The solid foam wing was next..Using 3mm Depron i fabricated a new wing.


https://cimg5.ibsrv.net/gimg/www.rcu...c7edea4a4c.jpg
https://cimg0.ibsrv.net/gimg/www.rcu...a23132e7d2.jpg
Being basically hollow the new wing was lighter by 20g) had a similar strength and lkely better aerodynamics. Still more performance.
At tis point I decided to go properly modern with brushless and LiPo. This proved to be a real eye opener saving a further75g alnog with more battery capacity and more thrust.
The performance was remarkable but by far the biggest improvement was it endurance. At a cruise power it could fly for 30 minutes rather than the 5 maximum of the original.
As so much weight had been saved a new tapered wing was built with added flaps and a V tail.
https://cimg3.ibsrv.net/gimg/www.rcu...dab8c6c47b.jpg
The performance was now noting like the original and could be really thrown about.
This then posed the question "how much longer could a similar sized plane fly if it was specifically designed for endurance?"
A lightweight aerodynamic air frame, efficient motor and prop and a big capacity battery.
With a slow programme of improvement I eventually got this plane to fly for 1 hour with a 1000mA 2s but at the same time carrying ballast to match a 5000mAh battery. In other words a theoretic endurance of 5 hours.
https://cimg2.ibsrv.net/gimg/www.rcu...eaacfe96a2.jpg
It was flying on just 1A. On a 2s that is 7.5W. As it weighs 436g or 1ib that's a remarkable 7.5W/lb average power..
The final twist is it has over 10 times that available at full power so it is even modestly aerobatic too!.
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I have never actually flown it for its full 5 hours as after 2 hours I decided that was my limit even if the plane could go on for longer! .
I still fly it occasionally.