10 Posts

Eventually I will probably manage to drive the calculations using the C-172 POH into my thick head but I am struggling; math is my weakness. Does anyone know of either a computerised process for calculating these numbers (there's no such category in Sporty's E6B for iPhone) or a really good step-by-step explanation, online or in a document, for the mathematically challenged? I am struggling a bit with the process. Many thanks.

4 Replies

12 Posts

ForeFlight! they have a student discount. download it to your iPad and iPhone (I think it works on android too) spend an hour or two getting familiar with it on their Youtube channel and you'll be all set. It will calculate performance, fuel burn, time, and distance and all that jazz. HOWEVER you will need to learn the E6B (in my humble opinion) because technology can and will fail. It will do so at the most inconvenient time when your least prepared. Its why I keep an old aluminum E6B in my flight bag. you just never know when your going to have your Apollo 13 moment.

Some good rules of thumb for roughing numbers in your mind (but you really should get as precise as you can as a general rule)

in a C-172 Plan your decent at 500 fpm and you can easily calculate out you decent in your brain! every 2min your defending a 1000 feet. this makes it pretty easy to figure out when you need to start your planned decent. Some folks use distance away from the airport I generally use time because its easier. For example, if I need to descend 3000 feet I know that I need about 6min to do that.

Climb to assigned altitude is a bit more challenging because of performance factors like density altitude, weight and power settings. But you can rough that in as well if you know that you will get at least "x" climb rate per minute as indicated on your vertical speed indicator. then you just multiply that by however many minutes to get that much altitude gain.

Fuel burn is pretty easy if you look at it in time and not distance. generally speaking you should know what your C172's hourly burn rate is! Mine for example is 8gph and I have a 38 gallon tank. 38 divided by 8 gives me time aloft of 4.75 which amounts to 4hrs and 45 minutes. you could also do the reverse. your planning your flight and it's going to be a 2hr flight. well you know that you are using roughly 16gal of fuel (add a gallon or two for taxi, takeoff & landing).

this is how I do the rough math in my head in the scenarios above. I mostly use foreflight but will bust out my E6B just to keep the cobwebs off. Hope this helped

Some good rules of thumb for roughing numbers in your mind (but you really should get as precise as you can as a general rule)

in a C-172 Plan your decent at 500 fpm and you can easily calculate out you decent in your brain! every 2min your defending a 1000 feet. this makes it pretty easy to figure out when you need to start your planned decent. Some folks use distance away from the airport I generally use time because its easier. For example, if I need to descend 3000 feet I know that I need about 6min to do that.

Climb to assigned altitude is a bit more challenging because of performance factors like density altitude, weight and power settings. But you can rough that in as well if you know that you will get at least "x" climb rate per minute as indicated on your vertical speed indicator. then you just multiply that by however many minutes to get that much altitude gain.

Fuel burn is pretty easy if you look at it in time and not distance. generally speaking you should know what your C172's hourly burn rate is! Mine for example is 8gph and I have a 38 gallon tank. 38 divided by 8 gives me time aloft of 4.75 which amounts to 4hrs and 45 minutes. you could also do the reverse. your planning your flight and it's going to be a 2hr flight. well you know that you are using roughly 16gal of fuel (add a gallon or two for taxi, takeoff & landing).

this is how I do the rough math in my head in the scenarios above. I mostly use foreflight but will bust out my E6B just to keep the cobwebs off. Hope this helped

1522 Posts

If you get Foreflight, you can use 12/8.5/7 gph for climb/cruise/descent for the O-300/320 engines, and 14/10/8 for the 180 HP O-360's.

17 Posts

Barry,

i agree with the rule of thumb approach for our small aircraft. The POH gives a good starting point and you should seek to understand why your result differs. You don’t need to be constantly entering stuff in a calculator. I have a C-182. I know it takes about 5 miles to loose 1000 feet at a normal 500 ft/min. I simply adjust the rate a little more or less to arrive at the place and altitude I want. I flight plan my airplane for 14 gph using the foreflight enroute time. I usually lean to get in the 12 gph area. Get in the habit of dip sticking your tanks to know if your factors are about right. It also helps you get confidence in the fuel gauge accuracy. If you have a fuel totalizer, it is probably the best fuel gauge you have. For max range, use flight time and a 10% greater fuel burn than you normally get. In other words, make conservative but reasonable estimates and keep it simple!

i agree with the rule of thumb approach for our small aircraft. The POH gives a good starting point and you should seek to understand why your result differs. You don’t need to be constantly entering stuff in a calculator. I have a C-182. I know it takes about 5 miles to loose 1000 feet at a normal 500 ft/min. I simply adjust the rate a little more or less to arrive at the place and altitude I want. I flight plan my airplane for 14 gph using the foreflight enroute time. I usually lean to get in the 12 gph area. Get in the habit of dip sticking your tanks to know if your factors are about right. It also helps you get confidence in the fuel gauge accuracy. If you have a fuel totalizer, it is probably the best fuel gauge you have. For max range, use flight time and a 10% greater fuel burn than you normally get. In other words, make conservative but reasonable estimates and keep it simple!