Long endurance with electric?

What would you guys recommend for a high-endurance electric? Airframe, esc, motor, prop, battery?

I currently have an e-flite apprentice, which gets something like 20 minutes on a battery. I'm looking to move to a different airframe and I'm hoping to get at least an hour on a battery.

- Airframe-wise, I want something that's available in an easy-to-build format. What properties make airframes more efficient? I know gliders use high aspect wings... Are flying wings more efficient? What about canards?

- I understand most ESCs run at reduced efficiency below 100% throttle. Are there any that don't?

- As for motor and prop, what properties make them more efficient? Lower/higher RPM? Wider/narrower blades?

- Which batteries have the best Wh/kg?

You are spot-on in looking at gliders for efficiency. The higher AR wings essentially lowers your induced drag, which can make up a large part of your overall drag during low-speed flight. If you are more ambitious, look for wings with airfoils that have high L/D values or Cl^1.5/Cd values (for endurance). There are some software tools out there, like xflr5, which can help with analysis of airfoils and wings if you are familiar with the basic theory.

Flying wings/Blended-wing bodies can theoretically have very high efficiency, but in order to make the design stable, you generally have to 'add drag' with wing twist and/or reflex airfoils. The BWB advantage is the volumetric efficieny.

A purpose-built UAV would be your best bet, since you could optimize the design for your requirements and payloads. Seeing as you want an easy-to-build format, look for planes with high AR wings (i.e. gliders). Or get a plane like an easy star and make you own wing.

As for motor and prop, it depends on the conditions you are flying. Generally speaking, larger diameter props spinning at lower RPMs are more efficient. Matching the diameter and pitch to the flight profile you are looking for is the best bet.

As far as I know, lithium polymer (lipos) have by the best wh/kg ratio commercially available.

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Jonathan M December 17, 2011 at 11:56am

You are spot-on in looking at gliders for efficiency. The higher AR wings essentially lowers your induced drag, which can make up a large part of your overall drag during low-speed flight. If you are more ambitious, look for wings with airfoils that have high L/D values or Cl^1.5/Cd values (for endurance). There are some software tools out there, like xflr5, which can help with analysis of airfoils and wings if you are familiar with the basic theory.

Flying wings/Blended-wing bodies can theoretically have very high efficiency, but in order to make the design stable, you generally have to 'add drag' with wing twist and/or reflex airfoils. The BWB advantage is the volumetric efficieny.

A purpose-built UAV would be your best bet, since you could optimize the design for your requirements and payloads. Seeing as you want an easy-to-build format, look for planes with high AR wings (i.e. gliders). Or get a plane like an easy star and make you own wing.

As for motor and prop, it depends on the conditions you are flying. Generally speaking, larger diameter props spinning at lower RPMs are more efficient. Matching the diameter and pitch to the flight profile you are looking for is the best bet.

As far as I know, lithium polymer (lipos) have by the best wh/kg ratio commercially available.

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Long endurance with electric?

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