On Sun, 04 Jan 2004 00:22:11 +0000, Ben Jackson wrote:

For example, let's say it costs exactly $45/hr wet Tach to operate a
Cessna 152. If you charge $45/hr wet Hobbs and the ratio is 1:1, you
will never break even (pay your fixed costs of insurance, storage, and
interest on the loan above and beyond hourly expenses). However if the
ratio is .85 Tach hours per Hobbs hour, then you will get about $8/hr

Others have said this and it's true, it varies depending on your location
and can only be determined accurately for your situation. However, in my
plane the difference is more like .1 per hour since my hangar is not that
far from the runway and I don't spend time screwing around. In other
words I'm not like a Bonanza guy I saw recently who spent 30 minutes
warming up his engine prior to flight, I'll not comment beyond saying his
ratio is going to be much larger than mine as will his operating expenses.

Looking at the logs prior to my getting the plane, and it used to be based
at a big airport the time difference was closer to .4 difference. He must
have either spent a long time in line or had a long taxi.

But, you're going about it the wrong way. If you have a hobbs meter you
charge hobbs time and don't worry about the fact it will not be quite
accurate because you'll make more money on it. Don't feel like you're
cheating the renter, he can log the time the hobbs says as long as he
intends to fly the plane. You couldn't log it for example if you just
spent an hour driving around the ramp...

What you do is first figure out what it costs to fly based on tach time,
figure what it'll take to make enough money to keep it going, and then
charge based on Hobbs. The hobbs will of course show more time than the
tach unless you've got a dishonest renter. If you insist on making
exactly $? per hour on your rental then you will need to figure the
hobbs/tach ratio for YOUR usage. If you want to guess, use .2 as it's
close enough as .8 tach is pretty close to 1.0 hobbs at many airports.

I give you the above based on my usage of a plane as a renter, and as an
owner. I know what my plane does now, and I know what it did before I got
it, thanks to good logs. What is the ratio in your plane? I forgot to
add one more thing, the Hobbs ratio can change in the Winter due to cold
and the mechanical nature of the meter. In a Cessna it's a very cheap
clock mechanism that gums up a bit over time and slows down during cold
weather due to that fact. I've been asked to log tach time for paying for
flights in the Winter.