Cessna 150 - Fuel rule of thumbs

[Ian_Wannabe]

Hey guys 'n girls!

Just a quick question. Here's the situation:

A Cessna 150 when on a cross country flight, Sherburn - East Midlands - Humberside - Sherburn.

Say we leave with full tanks, 5hrs endurance and we're burning at 5g/phr

If I get to east midlands and check the tanks visually - I see that they're half full..... what kind of endurance hrs wise does that give me as a rule of thumb?

So say -

full to the tabs = 5hrs
Three quarters = ??
Half = ??
Quarter = ??

etc...

I'd just like to get a second opinion and see if anyone else uses a rule of thumb for this aircraft, I hope that this may improve my judgment when considering picking up extra fuel whilst on my cross country flights. Don't wanna run outta juice!

I'm not a PPL just yet - about to embark on my QXC (well i've been saying that for months... damn weather!) So i'm trying to learn as many tips to keep me and others safe.

Thanks in advance

Ian :ok:

[S-Works]

Does this 150 have long range fuel tanks? if it does then if you fill them full there is no "we" on this trip.

My cessna holds 88litres of fuel with standard tanks and burns 23lph unleaned in the cruise which at absolute best will give you a 4hr duration. it burns 33lph in the climb which averaging it all out gives you an effective range of 3:30 with no reserves.

I always allow a 30min diversion time when VFR and 45mins when IFR subject to the closest airports on track being within this flying time.

So in a nutshell my rule of thum is for planning purposes 6GPH gives me 3hrs useable and the rest for reserve.

I have very accurate fuel consumption figures for my aircraft based on a FS450 fuel computer linked to a GNS430 and several hundred hours of practice.

In your scenario I would probably be refueling twice for sanitys sake. If I got to East Mids with half tanks then I would be concerned at making Humberside without a refuel. And I would probably refuel at Humberside as well.

[LowNSlow]

Given the innaccuracies in standard Cessna fuel gauges you could do worse than buy a dipstick.

It'll at least let you know how much juice is really in the tanks after you've make your first landing. This will avoid the awful buttock clenching, sweat inducing moment when the gauges lurch toward empty even though you "know" there's another 1.5 hours worth in the tanks......

I'd agree with bose-x and plan on 6gph not 5. It always worked on my old Aerobat after I'd had the moment described above. (I DID have well over an hour's fuel left by the way :ok: ).

[Ian_Wannabe]

Sure that makes sense thanks - They're standard tanks bose-x

The reason for my question was that when I did this route with my instructor we landed at east mids and he kinda said "hmmm I wasnt going to but I guess we'll fuel up here to be safe"

But yeah, for sanitys sake your advice is great - thanks

[aiglon]

Ian,

The only absolutely known quantity here (assuming you don't drain the tanks) is how long it took you to get to East Midlands. Even with a dipstick, you are only estimating the fuel left and your 5gph is also, presumably, an estimate.

So, estimate how much fuel you used to get there, divide by time and that gives you a revised estimated fuel burn. Assuming you did not do/will not do anything unusual - eg extra long taxi/hold, lengthy full power climb - that will do as a reasonable estimate . Now, take the estimated fuel remaining and divide by the revised estimated fuel flow and you have your revised estimated endurance.

Remember, though, this is a total endurance figure and does not have any reserve built in. Also, it is an estimate :D

Safe flying :ok:

Aiglon

[Ian_Wannabe]

Great advice - thanks :ok:

[IO540]

I think one can get an accurate enough figure for the fuel flow, if one starts with a full tank, does two flights, identical in profile except one has a longer cruise period than the other, and fills up to the top (at a pump that is regularly checked by Weights & Measures) after each one.

From that one can work it out, because the climb/descend part will be constant.

Obviously this will be true only for a particular power setting and only for a particular aircraft. But this is how one calibrates the proper flowmeters: against a pump - I get mine within 1-2% and it gets re-checked at every fill-up. Much better than a dipstick.

I would also do this at the full-rich mixture setting; then anything one does with the mixture lever will be a bonus.

The range of a C150 is such that one must be really really careful, especially re the reserve for weather diversions.