Sub 115Kg

rogerburge · Post by **rogerburge** » Thu Mar 06, 2008 11:44 am

Just a quick question,
"Empty weight is the weight of the aircraft without pilot or FUEL, and need not include items carried at the discretion of the pilot on a flight-by-flight basis e.g. hand-held radios, extra seat cushions etc."
Does fuel include Batteries if the power plant is electric?

Nick Allen · Post by **Nick Allen** » Thu Mar 06, 2008 11:51 am

Does fuel include Batteries if the power plant is electric?

...or just the mass of the electrons...?

Oh, I can see many happy hours of legalistic argument here...

PB · Post by PB » Thu Mar 06, 2008 8:13 pm

On the assumption that the battery gains weight when it is charged (e=mc^2) the answer is simple. The weighing needs to be done with a discharged battery.

I'm not sure that the man from the CAA has any scales that accurate.

Perhaps more seriously, if it were fitted with a fuel cell then I'm sure that the weight could be obtained with no fuel in the cell.

Pete · Post by **Pete** » Fri Mar 07, 2008 2:20 pm

how much does a cockpit full of wishful thinking weigh ?

Nick Allen · Post by **Nick Allen** » Fri Mar 07, 2008 3:57 pm

how much does a cockpit full of wishful thinking weigh ?

I think it's given by the (weight of daydreams)/[(income)squared]

Paul Dewhurst · Post by **Paul Dewhurst** » Fri Mar 07, 2008 6:58 pm

The ANO says its weight without its pilot and fuel must be below 115kg. There has in the past been a lot of speculation about what empty weight means and interpretation has been offered that it excludes everything not necessary for flight - so things like wheel spats etc etc need not be counted. the ANO wording neatly avoids the term empty weight and makes itself quite clear I reckon - those wheel spats do count in the empty weight!

As for batteries counting as fuel I reckon they should(otherwise a fuelled internal combustion engined craft could have a far higher MTOW, which doesnt make any sense). I have officially asked CAA this (I was on the BMAA negotiating team for deregulation), and had one reply where they offered a range of opinions from a number of the technical staff, also raising some questions.they didnt say no - but they didnt say definitely yes! We responded answering their questions, which we felt then proved the case, and putting an offcial BMAA view that batteries should be counted for weight purposes as fuel. They didnt respond, and the man in charge that we were corresponding with has since I believe left CAA for EASA, and the exemption has now been replaced by the ANO change. So we may not get an answer unless we ask again, or could take their silence as acceptance! It may be that now the exemption has ended and the class is not regulated by CAA they might not want to offer a definitive opinion...

Paul

rogerburge · Post by **rogerburge** » Fri Mar 07, 2008 9:28 pm

Perfectly reasonable to carry batteries on board, just as I carry fuel to the airfield now so I would take batteries home to charge! The only difference is I would strap them in rather than poor.

Dave Hall · Post by **Dave Hall** » Fri Mar 07, 2008 9:49 pm

But Welshman, won't the buoyancy effect of displaced air be more on a cold day than a warm one, which would affect all the volume taken up by the aircraft, not just the air trapped in the structure.

On the other hand, I did once (well, enough times to be sure I was right) weigh a hot copper calorimeter on a very accurate balance, and it always weighed less than it did once cool again, so there might be something in your belief. I never tried it with a sealed container, or a solid block so am not sure of the mechanism.