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## Specific Gravity and Echo Conversions

• FlyingThereAndBack
• Topic Author

### FlyingThereAndBack created the topic: Specific Gravity and Echo Conversions

Just trying to clear things up here. The differences give very little variation in the answering of questions, but you don't need much variation when it comes to CASA.

The specific gravity of AVGAS is now 0.72

When converting USG to Kg do we use 2.72 or 2.69 for Echo for the most accurate answer? I have seen 2.69 around a lot.

Thanks.

• Posts: 1962

### bobtait replied the topic: Re: Specific Gravity and Echo Conversions

.72 and 2.72 are the CASA official conversions according to ERSA.

• FlyingThereAndBack
• Topic Author

### FlyingThereAndBack replied the topic: Re: Specific Gravity and Echo Conversions

Ok, all though they do go through the effort to state 0.71 on the Charlie Loading sheet in the Day VFR Workbook. I had been told by a TAFE lecturer to use 0.72 for all except for Charlie which is 0.71 for reasons only CASA will ever know and to use 2.69 for Echo. I will take your word for it though, just though I'd share, seems to be a bit of confusion. Thanks for advice.

• Posts: 1962

### bobtait replied the topic: Re: Specific Gravity and Echo Conversions

In any case, there is no point getting too excited about fine detail here. Specific gravity relates volume to mass. Since the volume of a given mass of fuel varies with temperature the specific gravity varies also. When fuel gets hot, it expands like any other substance, so a kilo of fuel only has a particular volume at a particular temperature. There is no way you would have an exam question that is going to require you to use a specific gravity value to an accuracy of the second decimal place. I grew up with .71 SG for AVGAS 100/130 and .72 for AVGAS 80/87 [no longer available but it was the equivalent of LL].

Show me a dip stick that is calibrated to the second decimal place of a litre!! What's the use of going crazy over SG when you cannot measure the actual number of litres with any thing like that accuracy.

I'm going to have another rum and coke.................

• FlyingThereAndBack
• Topic Author

### FlyingThereAndBack replied the topic: Re: Specific Gravity and Echo Conversions

LOL Okay thanks, you enjoy that rum and coke

I am waiting for the footy to start so I can put this Performance book down and enjoy a few beers myself, well deserved I think.

I did have ONE other question for when you get a chance, If a scenario was given where an Echo was out of balance, and you were given the loading, which produced a ZFW out of balance as well as a TOW out of balance, and a Landing wieght out of balance, would I be right in presuming you would pick the one which is farthest from the COG limit and work with that weight etc. as fixing the worst one would bring the other weights in.

No rush, enjoy that rum, 2 hours and it's beer o'clock over here

• Posts: 1962

### bobtait replied the topic: Re: Specific Gravity and Echo Conversions

The CAR says that the pilot must check that the CofG is within limits both at ZFW and at take-off.

If you are carrying a lot of cargo, it would usually be smart to check at ZFW first and, if it is out add, subtract or shift weight to correct it. It will always be the aft limit if there is a problem at ZFW because that is the way the aircraft is disigned. Note that, except for the nose locker and row 1, all of the places where you can put weight in the ECHO are well behind the aft limit of 2680 mm. This is the case with all GA aircraft.

As long as you are on or near the aft limit at ZFW, you can always be confident that the fuel can be added without any further problem. This is because, as long as you fill the tanks in the order specified [mains first], the fuel will always move the CofG forward.

The only other problem occurs when you are carrying no cargo or passengers but full fuel, such as a long ferry flight. In that case, it is possible to be out of the forward limit in some aircraft, so you may need to add ballast to put the CofG onto the forward limit. You would then be safe because, as long as you burn the fuel in the order specified [aux first], burning fuel can only move the CofG aft.