Ratio of Hobbs to Tach for instruction w/tower

Let's say someone (not me!!) is crazy enough to buy a Cessna 152 or 172
and instruct in it at a towered airport. What sort of ratio of Hobbs
to tach time would you expect?

The value (I've played with .85 up to 1.0) has a surprisingly large
effect on how much you have to charge for the plane.

--
Ben Jackson

http://www.ben.com/

I don't think it makes a lot of difference whether the airport is towered or
not. Why not just put a Hobbs meter in the plane?

"C J Campbell" wrote in message
...
I don't think it makes a lot of difference whether the airport is towered or
not. Why not just put a Hobbs meter in the plane?


Or look at your watch? Write down engine start time, then engine shutdown time.
That's how we did it when towing banners. Cub's don't have electrical systems
or hobbs meters, and when you're flying along at 1900 rpm's, the tach time isn't
exactly accurate either.

Or look at your watch? Write down engine start time, then engine shutdown time.
That's how we did it when towing banners. Cub's don't have electrical systems
or hobbs meters, and when you're flying along at 1900 rpm's, the tach time isn't
exactly accurate either.

That's the way I do it today, with my watch, though by the puzzled
looks I get when I'm converting minutes to decimals, I think most
everybody else must use the tach.

My first flight instructor used watch time, and as with so many
things, the way you learned it when you were green is the way you keep
doing it.

all the best -- Dan Ford
email:

see the Warbird's Forum at www.warbirdforum.com
and the Piper Cub Forum at www.pipercubforum.com

In article ,
C J Campbell wrote:
I don't think it makes a lot of difference whether the airport is towered or
not. Why not just put a Hobbs meter in the plane?

It does have a Hobbs meter. But plane costs are mostly in units of Tach
time. At a towered airport you (probably?) spend more time taxiing and
therefore accumulate more Hobbs time per unit Tach.

So if you charge $66/hr wet hobbs and tach time is accumulating at 85%
as fast as the hobbs you have about $7765 of revenue per hundred tach
hours.

--
Ben Jackson

http://www.ben.com/

On Sat, 03 Jan 2004 22:41:13 +0000, Ben Jackson wrote:

It does have a Hobbs meter. But plane costs are mostly in units of Tach
time. At a towered airport you (probably?) spend more time taxiing and
therefore accumulate more Hobbs time per unit Tach.

I assume you mean maintenance since that's about all done with tach time,
where rentals are usually based on Hobbs time, if the plane has one of
those. The reason is that the rental makes more money since the Hobbs
will indicate a higher number than the tach. This is a benefit when it
comes to paying for your maintenance.

I've almost never rented a plane based on tach time unless the Hobbs was
not working right, but then most of the planes I rent have a Hobbs meter
and you can see why they'd want to use it's figure.

You're correct in that at towered airports you'll log more Hobbs time than
tach time, but those have been the breaks for me. I know of no planes
around here that use the tach for anything beyond maintenance.

Out of curiosity, why are you trying to figure the ratio anyhow? It
varies at each airport depending on how far from the hangar to the ramp or
runway you are, how long you warm it up, etc.

Based on your website, are you planning on getting back into flying, or is
your site just not updated, kinda like how I do mine?

In article . net,
Matthew P. Cummings wrote:
On Sat, 03 Jan 2004 22:41:13 +0000, Ben Jackson wrote:
I assume you mean maintenance since that's about all done with tach time,

Scheduled maintenance (100hr inspections, possible 50hr inspections),
oil changes, oil consumption, fuel consumption, engine life, airframe
life, etc all scale with tach time.

If you then charge by Hobbs time there's a 'slop' factor in there
because Hobbs Tach. My question is: what is that factor? I was
hoping someone who had been involved in renting airplanes had an
estimate.

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
towards your fixed expenses. In that case you might break even around
600 hours, assuming about $5000/yr fixed expenses.

Since the margins are small, the factor makes a big difference.

Based on your website, are you planning on getting back into flying, or is
your site just not updated, kinda like how I do mine?

Oh, I just never update my website. I bought a 1965 Comanche 260 last
August and I'm about 2/3rds of the way to my instrument rating (checkride
on Feb 7 if the weather lets up enough to get the rest of my hours).

--
Ben Jackson

http://www.ben.com/

Ben Jackson wrote:

If you then charge by Hobbs time there's a 'slop' factor in there
because Hobbs Tach. My question is: what is that factor? I was
hoping someone who had been involved in renting airplanes had an
estimate.

The FBO at the uncontrolled field at which I got my PPC used to use a factor of
1.2 times the tach in a Cessna 150. The aircraft had Hobbs meters, and we usually
paid according to the Hobbs, but sometimes one of the meters went TU.

George Patterson
Great discoveries are not announced with "Eureka!". What's usually said is
"Hummmmm... That's interesting...."

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.

"Ben Jackson" wrote in message news:BJFJb.49560

. What sort of ratio of Hobbs
to tach time would you expect?

I've recall a figure of about .8 for planes used at flight schools. Of
course, that's going to vary widely depending on the nature of usage and
location, but on average, .8 or a little higher. All you could use the
figure for would be an approximate anticipated figure, anyway. Your real
figures could only be determined after-the-fact.

JG