Thread: Build Log 100% scale, Electric Lazair
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Old Jun 23, 2011, 02:14 PM
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Electric Ultralight Weight Issue

I have come up with the below analysis of the weight issues regarding electric ultralights. I believe that anyone considering a project like mine should use this approach in determining their allowable component weights as no one has yet found a flaw in the analysis and its implications will allow electric ultralights to be developed with reasonable endurance using todays technology.

Here is my analysis:
I have read Part 103 and its advisory circular thoroughly and I believe that the electric Lazair, as I have constructed it, meets the definition and its interpretation as described in both documents.

The 254 pound weight limit is defined as empty weight without fuel and then, fuel is limited to 5 U.S. gallons.

A U.S. gallon is a measurement of volume, not weight. 5 gallons of diesel, Avgas and Jet A all have different weights and, without question, all three would be acceptable fuels for a Part 103 ultralight.

There is no mention or limitation as to the type of fuel that can be used. Lacking an FAA definition of fuel, I see that the Wikipedea definition of a fuel is any material that can release energy and electric Lipo cells certainly do that.

My fuel is the 384 Lipo cells, each with a volume of 2.9 cubic inches. My total fuel volume is 1114 in^3. 5 U.S. gallons is 1155 in^3.

My fuel volume is therefore less than 5 U.S. gallons and the regulation is met. In effect, the rule allows us to carry 1155 in^3 (5 U.S. gallons) of fuel regardless of its density.

As a practical matter, I submit that since it is difficult to physically remove only the fuel (384 Lipo cells) from my aircraft, my aircraft should be weighed with fuel (Lipo cells) and then the Lipo fuel weight should be subtracted to obtain its empty weight.

The 384 Lipo cells weigh 90 lbs.

Since my electric Lazair currently weighs 282 lbs with fuel, I believe that the empty weight without fuel is 282 - 90 lbs OR 192 lbs which is significantly below the Part 103 maximum empty weight of 254 lbs.

I would also like to point out that, under the 2011 NASA Green Challenge rules, these 384 Lipo cells only carry an energy equivalent of less than 1/4 of a gallon of auto fuel.
Dale Kramer
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Last edited by KiloOne; Jun 23, 2011 at 03:40 PM.
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