nucleus
Well-Known Member
This is speculative, as the motor that is the best fit (read low weight & high output at 2700 RPM) is an EMREX 268 which is not yet readily available. With the EMREX you don't have to have have a redrive, but you will need to engineer a prop hub/stem.
One should easily save 180 pounds on the electric motor FWF install vs. a Lycoming engine. These 180 pounds, plus 216 for the 36 gallons of fuel you will never use, make for an airframe & fuel weight savings of 396 pounds. If you are willing to live with a reduced payload of 450 pounds (probably necessary in this application), then you can bump your empty weight up by 250 pounds to 1300. This makes 646 pounds available for batteries, our battery weight budget so to speak.
So lets talk batteries. The clear leader as far as energy density are the panasonic 18650 cells that Tesla uses. You could build your own pack, or a better solution is to buy used ones. EVWest sells 42 pound 3KwH packs for $990. 15 modules meet our battery weight budget, and put us at 42 kWh of energy storage which is the best we will do for the weight.
The downside to the Tesla/Panasonic packs is that they don't have good power density, and the low runaway temperature (read fire-prone) of their lithium-cobalt-manganese-nickel-aluminum chemistry means they require liquid cooling which adds weight. The also don't have as flat of a voltage discharge curve as my preferred chemistry (LiFeP04), so the voltage will sag a lot more, decreasing available power even when only partially discharged.
The snappier, less saggy and more power-dense Lithium Iron Phosphate chemistry appeals to me for its lack of voltage sag AND high runaway temperature (read NOT fire-prone). EVTV sells 80 Ah CALB CAM cells that are 4.2 pounds, so we could do 150 within our weight budget. This gives 38.4 kWh, but no cooling needed, and much less sag.
I have been scratching my head on how many pattern circuits this would give you in an RV-9. In a small car you might get 120 miles range with 38 kWh of energy.
My RV-6A would get about 7.2 GPH at 172 knots LOP (27 MPG). I suspect this is around .4 BSFC, very efficient for a gas engine. An electric motor will at least twice as efficient.
Gasoline is 33.7 kWh, so with at 2.2 times the efficiency, our 34 kWh of usable battery energy would be about equivalent to about 2.2 gallons of fuel. :suprised:
So if you are only averaging 85 knots in the pattern, this would mean about 1/4 the energy usage vs. a 172 knot cruise - the climbs average out the descents, so about so 7.2/4 = 1.8 GPH lets round to 2, so our 2.2 gallons worth of battery power should let us fly the RV-9 for about an hour at 90 MPH with a 10% reserve.
Or 15 minutes at 172 knots...
Electric plane reality is short jaunts! I love the fuel bill though...
One should easily save 180 pounds on the electric motor FWF install vs. a Lycoming engine. These 180 pounds, plus 216 for the 36 gallons of fuel you will never use, make for an airframe & fuel weight savings of 396 pounds. If you are willing to live with a reduced payload of 450 pounds (probably necessary in this application), then you can bump your empty weight up by 250 pounds to 1300. This makes 646 pounds available for batteries, our battery weight budget so to speak.
So lets talk batteries. The clear leader as far as energy density are the panasonic 18650 cells that Tesla uses. You could build your own pack, or a better solution is to buy used ones. EVWest sells 42 pound 3KwH packs for $990. 15 modules meet our battery weight budget, and put us at 42 kWh of energy storage which is the best we will do for the weight.
The downside to the Tesla/Panasonic packs is that they don't have good power density, and the low runaway temperature (read fire-prone) of their lithium-cobalt-manganese-nickel-aluminum chemistry means they require liquid cooling which adds weight. The also don't have as flat of a voltage discharge curve as my preferred chemistry (LiFeP04), so the voltage will sag a lot more, decreasing available power even when only partially discharged.
The snappier, less saggy and more power-dense Lithium Iron Phosphate chemistry appeals to me for its lack of voltage sag AND high runaway temperature (read NOT fire-prone). EVTV sells 80 Ah CALB CAM cells that are 4.2 pounds, so we could do 150 within our weight budget. This gives 38.4 kWh, but no cooling needed, and much less sag.
I have been scratching my head on how many pattern circuits this would give you in an RV-9. In a small car you might get 120 miles range with 38 kWh of energy.
My RV-6A would get about 7.2 GPH at 172 knots LOP (27 MPG). I suspect this is around .4 BSFC, very efficient for a gas engine. An electric motor will at least twice as efficient.
Gasoline is 33.7 kWh, so with at 2.2 times the efficiency, our 34 kWh of usable battery energy would be about equivalent to about 2.2 gallons of fuel. :suprised:
So if you are only averaging 85 knots in the pattern, this would mean about 1/4 the energy usage vs. a 172 knot cruise - the climbs average out the descents, so about so 7.2/4 = 1.8 GPH lets round to 2, so our 2.2 gallons worth of battery power should let us fly the RV-9 for about an hour at 90 MPH with a 10% reserve.
Or 15 minutes at 172 knots...
Electric plane reality is short jaunts! I love the fuel bill though...
