Thread: Cessna electric
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Old 2nd Apr 2019, 07:01
  #9 (permalink)  
Join Date: Nov 2015
Location: Farnham, Surrey
Posts: 1,193
Originally Posted by Squawk7700 View Post
The Beaver reference is from an announcement s few days ago...

Seaplane Airline Going All Electric - AVweb flash Article
I saw that, but struggle with it. The DHC2 has an empty weight of 3,000lbs and a max all-up of 5,100lbs, leaving a useful load of 2,100lbs (call it 960kg). To this we could add the difference between their electric motor and the weight of the stock radial (say 180kg) giving a useful load of 1,140kg.

Assume to do anything at all beaver-like you'd want it to carry a pilot and five passengers - allowing 90Kg per person that's 540kgs (assume these are day-trips so no baggage apart from the odd fishing rod). That leaves just 600kgs for the battery which (at their claimed 200w/kg energy density) would be a 120kWh battery (ignoring the extra structure needed to sling this 600kg battery under the floor when the fuel tanks usually reside).

Cruise power settings for the DHC2 are 240bhp (53%) or 300bhp (66%), which become 180kW and 224kW in new money respectively. Even ignoring the higher power settings for take-off and climb that gives us a maximum no-reserves duration of 40mins at 53% or just 32mins at 66%. And of course this is with the aeroplane remaining at max AUW for the whole flight (no fuel-burn). Is an aeroplane with less than 40 minute no-reserves max endurance, after which it needs a few hours to recharge, actually useful for anything? What am I missing?

I suppose you could swap the batteries rather than recharge, but these are floatplanes, and removing/refitting a 600kg load up between the floats isn't a typical bit of dockside maintenance AFAICS!

Then remembering that these are not new-builds, but are conversions of ageing aircraft. Most oaircraft of their age are significantly heavier than the book empty weight due to mods, repairs, anti-det husbandry etc (all the more so for seaplanes). Are they looking to grow the max all-up weight?

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