How is cost determined from a Hobbs Meter

[JP1]

Hi,

Can someone be kind enough to answer a question about Hobbs meters.

I have never really understood how charging works when based on a Hobbs meter. Or more accurately how to compare rental costs when one is based on brakes on/off and the other on a Hobbs meter.

Googling I found this on wikipedia:-

It (Hobbs meter) can be activated by oil pressure running into a pressure switch and therefore only runs while the engine is running. Many rental aircraft use this method to preclude the possibility of flying with the master switch off to improperly reduce Hobbs time.

If this is true for most rentals based on Hobbs meter, then effectively the charge is based on engine on to engine off. But if you spend 10 minutes with the engine on waiting for it to warm up, carrying out pre-flight check etc, then you are at a disadvantage to a club that charges brakes on/off. And if the Hobbs meter really does register from master on, then you are at even more of a disadvantage!

So how can you compare costs from different clubs? Is the hobbs rate usually lower to cover the fact there may be 10 minutes before brakes off?

Finally it seems to go against flight safety when charging from engine on/off. It's human nature to rush checks, not wait for the engine to warm up etc for the sake of maybe 5, 10 minutes of non-charged time for those individuals that may be dishonest. (Hobbs could always be used to verify the nominal time. If the Hobbs meter indicates 2 hours and only 1 was logged then obviously questions would be asked)

So if a club charges £100 per hobbs hour(meter) what is the opinion of ppruners of the equivalent cost per hour based on brakes on/off. Yes I know some people will do checks quicker, but factoring by 10 minutes (1.17) does that seem reasonable. So the equivilant cost would be £117 for brakes on/off

Is my understanding of how charging works (for comparison purposes) broadly correct.

Looking forward to the replies.

JP1

[englishal]

Our group uses the Hobbs, and yes you find that a one hour cross country flight (start, taxy, run up, take off, land, taxy to parking, shutdown) costs about 1.3 on the hobbs due to the ground time, and this is quite normal at many places I have flown. However on long flights the differential between hobbs and flight time (or tach time) gets less, so if you did a 3 hr leg, the hobbs would read 3.3 hrs.

We could of course charge "flight time", but if we did we'd have to up the hourly rate from about £65 per hour Hobbs to £80 per hour flight time. Swings and roundabouts really, the little bit extra in the pot left over from charging Hobbs time helps keep the aircraft account healthy and the "hourly costs" down.

[A and C]

I rent aircraft and won't use the hobbs as I think it encourages people to not take the proper time over checks and in the winter walming the engine.

The probem is that the dishonest can cheat me because I only charge from take off to landing, the balance is that the aircraft usualy get treated better.

The way flying clubs charge is a minefield when it comes to calculating the real cost per hour and I have no other advice but to steer clear of clubs that quote a low price and then hit you with "add ons" as these are usualy used to hide a high price.

I may soon fit the flight GPS loggers that the glider pilots use to my aircraft, this will solve the problem of the dishonest pilots and may even save the honest pilots a little money by reducing my costs, the result would be that the honest guys would not be subsidizing the dishonest guys.

[S-Works]

I am with A an C on this one, Hobbs just makes people rush the checks and mistreat the aircraft. I had a friend who used to rent a twin out on Hobbs time, led to a lot of cracked cylinders from people mistreating it. When it moved to airborne timed people took much better care of the aircraft.

[englishal]

Hobbs just makes people rush the checks and mistreat the aircraft

Should read

Hobbs MAY MAKE people rush the checks and mistreat the aircraft ;)

I don't take any notice of it where the checks are concerned but must admit I'd prefer flight time so as not to penalize people stuck on the ground for any length of time - maybe we'll change it soon. Our 496 records each flight with dep / dest and time spent over 30kts (i.e. flight time) which can be downloaded and analysed using the Garmin logbook software which makes charging very easy.

[Keygrip]

Most of the US based Piper aircraft that I find have the Hobbs working through the battery master switch - so you can be paying $220 plus fuel surcharges per hour for doing the walk around on a Seminole, never mind the engine run-up.

Best system I've found is either an airspeed operated hobbs meter, a squat switch hobbs meter with a weight on wheels switch or, the more common in the UK, charged on Tacho time with or without adjustments.

Tacho duration plus ten minutes is popular for short training flights. Tacho time multiplied by 1.2 is often used, too.

[IO540]

Also, there is no standard "hobbs meter".

Some of these hour meters run on oil pressure and count time all the time the engine is running.

Some of these hour meters run on oil pressure and count time all the time the oil pressure is above a certain level.

Some of these hour meters run on aircraft power and count time all the time the Master switch is ON (the renters sometimes fly with the Master off; no radio etc but it cheats the owner allright).

Some of these hour meters run on aircraft power and count time all the time the engine RPM is above a certain value (mine work that way; counts precise hours when above 1200rpm).

Some of these hour meters run on engine revs and count time based on the engine running at 2300rpm or whatever.

Any other offers? :)

The school has to decide how much to charge to get the total cost recovery they are after, and accept that some people will find ways to cheat the system.

A lot of schools (ALL where I've been based) charge for brakes off to brakes on, which causes all kinds of bizzare behaviour.

The fair way is to charge for airborne time only (aircraft maintenance is anyway based on this) and charge for fuel separately (i.e. rent DRY) but this has problems too (e.g. the renter can tamper with the fuel recording system) unless the plane is always returned with the tanks full (which can be highly inconvenient).

[englishal]

Charge dry and someone will lean in all the way out just to save a bit on fuel!

Actually this "cheating" must be a UK thing, because it has never every crossed my mind to speed up checks, or turn off the Master in flight just to save a few $$...Mind you, I suppose if you're paying £300 per hour + VAT I can see the temptation. When you pay $65 per hour for a WET 172 in the USA, there really is no point....

[Flyluke]

To charge Hobbs time is probably a rip-off, and leads to pilot frustration.

At today's prices, any time spent taxying or (especially somewhere like Biggin on a fine weekend) waiting in a queue to get aloft is wasted, expensive time.
And with the engine at, say, 1200 rpm, and no stresses acting on the airframe due to flight, the costs to the operater are simply not those on an aircraft in flight.

Time between maintenance is also not based on Hobbs time, but upon flying time.

It doesnt't seem to be value for the customer to charge on Hobbs in a rental scenario.

If it's how a group wants to operate, where one is looking at costs rather than margins, that may be different.

[englishal]

Well as I said earlier, it is swings and roundabouts.

Would you pay £100 per hour* for a C172 Hobbs, or £130 per hour flight time? If doing a long flight, then the £100 per hour is going to be cheaper, if doing small hops for your £100 burger then you will pay more for the flight time.

Whatever way it is done, one thing is sure that the operator won't lose out. If a club charging £100 per hour is forced to charge flight time, then you'll end up paying £130 per hour anyway.

What you have to watch is the club that charges £130 per hour hobbs when compared to one charging £130 per hour tach.

*NB: Made up prices, I have no idea what it costs to rent a 172 these days.

[BackPacker]

To charge Hobbs time is probably a rip-off, and leads to pilot frustration.

What you will find is that in the long run, an aircraft owner/operator will simply tally up all costs for fuel, maintenance, hangarage, insurance and everything, and divide that amount by whatever amount the hobbs/tacho/whatever racked up in that period. That, plus an uplift for the owner, is your rental fee per hobbs/tacho hour.

So it's true that on a typical one-hour flight your hobbs will show 1.1. or 1.2 while the tacho shows 1.0. But at the same time, all else being equal, the price per hobbs hour will be 10 to 20% lower than the price based on tacho hours.

Unless the owner is using your ignorance to rip you off of course.

The reality is that there is no easy, tamperproof and accurate way to charge fair rental prices. After all, insurance and hangarage are typically a fixed amount annually, tires only wear out from landings, taxiing and take-offs but not from airtime, fuel is both used to taxi and to fly, 50-hour checks are based on airtime only and depreciation is outside your control whatsoever. So to do this properly your rental fee should include the miles you taxi, the airtime you have, the power/leaning setting you used while flying, the amount of landings you made and a few other factors. Simply not doable. So most owners go for tamperproof, easy and more-or-less-accurate.

At my club, most rental fees are based on tacho. But the Seminole twin and the Thielert-equipped planes (DA40 and DR400) are based on hobbs. In our rental fee overview the last ones are clearly marked as such, and the hourly hobbs fee, all else being equal, is 10% lower than the hourly tacho fee. Precisely because the hobbs, in a typical flight, will show 10% more than the tacho would.

[Cows getting bigger]

At my club we charge by Hobbs but log aircraft (ie 50hr checks etc) by tacho. historical data tells me that the tacho hour is about 70% of the Hobbs hour. Not exactly 'cricket' but, unfortunately, you can't rely on people being honest about their logbook time.

[Jim59]

Some aircraft I fly have an hourmeter airspeed switch. This is powered by an internal battery and connected to its own pitot. It only runs when the airspeed exceeds about 25 kts.

Benefits:

Charged on flying time only.
50 hour checks etc. done when needed - not early if based on tacho.Disadvantage:

In motor gliders you get charged when the engine is off!

[IO540]

Yeah, some people will cheat. I've already written on this so won't do it again but I had some bad cases when I used to rent; the worst being an instructor (who also had a fake ATPL but that's another story).

It is possible to charge for airborne time and fuel separately, and catch the cheats (you compare the data downloaded from an engine monitor such as an EDM700 with the declared flight times, etc) but most rental planes don't have that equipment, and few firms will have the inclination to do it.

So we will continue to see people rev the thing up, engine cold, right in front of the hangar, and then taxi like crazy to the departure point.

[Pace]

Larger aircraft twins or corporate jets are usually charged take off to touchdown.

It does seem a real cheat if you are charged for sitting there with the engine ticking over in a line of aircraft going no where fast.

One point especially in these hard times is that non negotiable usually is so at least try to negotiate a rate and method of charging which suits you.

Pace

[B2N2]

To charge Hobbs time is probably a rip-off, and leads to pilot frustration.
Excuse me?
You pay for the use of the aircraft, not per hour flight time.
You don't pay per mile driven on a rental either now do you?
You get charged per day or portion of a day that you have the car in your posession, why would it need to be different for an aircraft?
You still pay for the rental car even if you've been stuck in traffic all day right? You don't go argue at the AVIS desk that you've only driven 30 miles in 3 days because of traffic jams?
For commercial enterprises eg flight schools the aircraft is a source of revenue.
For a small group (4-5) you may decide to charge on tach time.
Hobbs time usually ends up being 1.2 tach or 1.3 tach if the aircraft is flown correctly. You can always tell if somebody has flown it on "rental" power :}
So your choice:
$100/hr for Hobbs time
$125/hr for Tach time
The chicken or the egg my friend....

[ExSp33db1rd]

My personal syndicate charge Hobbs time less 0.1 for every full stop landing. This encourages people to do a proper warm up, and not rush a back track for the next take-off.

My Coastguard Unit charge Hobbs as is, 'cos we want re-imbursement from a grateful public, but only log Hobbs less 0.1 per full stop for the maintenance log - ( this is legal ) cos we have to pay the engineering bills.

You can charge, or log, whichever you wish, organise it to suit yourself.

If only charging and logging airborne time, then an airspeed switch attached to the Hobbs it the way to go. Fair to all, then.

[tmmorris]

You pay for the use of the aircraft, not per hour flight time.

Not if you want my custom, you don't. I'm not paying for time while the aircraft sits on the ground and I eat lunch. It's not (significantly*) costing the owner, so why should it cost me? I know it's how car hire works, but I don't think many of us are renting an aircraft as a means of transport, if we are truthful.

As a happy customer of A and C I greatly appreciated his charging T/O to T/D (though he does add 10 minutes to that for the C152s used for intensive training, presumably because of the arithmetic of lots of short sorties). He's right that there is room for dishonesty but as actual flight time is used for maintenance purposes it is the clearest and most honest approach; plus it means as he says that I don't mind sitting warming the thing up, or programming the GPS after startup rather than before, or holding for 15 minutes waiting for the latest 5-ship Puma formation to get off the ground...

Tim

*yes, I know insurance, hangarage, and 'opportunity cost' of someone else not renting it at that time continue to mount up, but they are minor compared to fuel and maintenance

[Pace]

B2N2

You get charged per day or portion of a day that you have the car in your posession, why would it need to be different for an aircraft?

Quite true you get charged a price for the day and in most unlimited mileage rentals they dont care whether you do 1 mile or 600 miles in that day.

Wish the same was true with aircraft :rolleyes: I would love to go touring for the day around france with just fuel to pay and as many miles as I could cram in :)

Pace

[A and C]

It is not me who gets the extra ten minutes per sector on the C152 but the club! as I charge take off to landing for all my aircraft.

It was found that the students take so long to get the aircraft into the air , (it can take up to 15 minutes) that the club was makng a loss on the fuel.

This seemed to be the best way to solve the problem without overcharging those who do longer flights.

[tmmorris]

Of course - sorry, I was forgetting your charge was dry.

Good not to rush students into the air, though.

Tim

[B2N2]

I'm not paying for time while the aircraft sits on the ground and I eat lunch
Who is then? I'll tell you who,the owner or operator.
Hobbs time = you paying for the time you are operating the aircraft.
If that makes you skip a proper run-up you are a poorly trained pilot with a lousy attitude.

[tmmorris]

B2N2,

I'm not rising to that. Can I suggest, though, a holiday in the UK with lots of flying at $200/hr in a SEP thrown in? I'm sure any of us would welcome you to rent from our clubs.

Last time I flew in the US (about three years ago) I was paying less than half what I pay here. It's easy to be smug when it's costing peanuts.

Tim

[B2N2]

Sorry TM, I got a little agitated.
I just feel that engine run time (oil pressure activated Hobbs) is the fairest way of charging a customer.
As far as wait times at the hold line; that's all part of the game, inherent to flying. Half the time you do and half the time you don't have to wait.
Sometimes you have a tail wind sometimes a head wind; sometimes downwind is on your (approaching) side of the field sometimes you'll have to fly around.

C'est la vie, nothing we can do about it.
Even though the official definition of flight time (USA) is "all time the aircraft is moving under it's own power with the intention of flight" the FAA has ruled that Hobbs time is an acceptable way of logging, so at the end you pay for what you log.
As far as prices in the UK (and the rest of Europe) go; I feel for you but that is not the operators fault it's your government with their ludicrous taxes and fees.

OK we can get back to being buddies...:ok: