As promised, this should be all the performance data needed from the Pilot's Information Manual for the 1979 Cessna 172N Skyhawk:

Perf. Data File

The data is all in PDF form, and should be relatively self-explanatory, however, in the next couple days I will do a quick run-through of each chart and table and go over how to do a weight and balance calculation and performance calculations.

Also, here is an example of a Navigation Log that you would use to write all the information you need for a flight.  I can go over this in the next couple of days also, but this is what most of this flight planning is for.

Yeah, after I spent so much time on it, I actually wanted to fly it, but it was for my IR checkride, so we didn't get all the way there.

Might be useful to put this in a separate forum section...

Basicall... we're talkin GA here right?

If any of you guys need hints on Yak-18 and An-2 instruments and engine management i can write a small section about that

Sorry it's been so long, I had some school and medical issues that I had to deal with, but almost everything is in order now, so I'm going to explain the performance data information that I posted HERE.  To get the charts and information, you need to download the "Perf. Data file" in the post by clicking it and choosing "save as" or "save to disk", then you can open the files with Adobe Reader.  If you don't have Adobe Reader, you can download the free version HERE.

An important thing to remember about all these charts are that they are only estimates, they are not the exact performance you will get.  That is why we will be using the most conservative estimates with each calculation and why there are minimum fuel requirements for VFR and IFR flight.  Also, all altitudes are indicated altitudes MSL not AGL unless it says they are.

Alright, on to the good stuff...

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Climb Performance Chart

This chart will give you the time to climb from one altitude to another, the fuel used during this climb, and the distance traveled along the ground during the climb in nautical miles.  Above the chart are some important things to note before using the chart.  This chart assumes that the climb is made with no flaps deployed and with full throttle, in a standard atmosphere (density altitude = pressure altitude).  Also, it's important to note that for fuel consumption calculations, you must add 1.1 gallons of fuel for engine start, taxi, and take-off.  The chart also assumes that above an altitude of 3000 ft, the engine is leaned for maximum performance (however, I've been taught to make all climbs with the mixture fully rich, at the altitudes that the 172 normally flies, the density will usually be within 80% of sea level density).  Also, the values of the chart can be adjusted by 10% for every 10°C above standard temperature and the values of distance during the climb assume that there is no wind, but these can be adjusted if you know the wind.  Also, the chart assumes an aircraft weight of 2300 lb (maximum take-off weight), which is a good assumption because it will always give you a conservative estimate for the values in the chart.

Now, to read the chart, you find your altitude and the altitude you plan to climb to, then read the values of the temperature, climb speed, and rate of climb for each altitude.  I usually average these values to get an estimate of what my airspeed will be, the average temperature, and my average climb rate.  These values aren't terribly important, as the rest of the chart will tell you the performance data you'll most likely need.  For the three columns on the right side of the table, you subtract the values for the altitude you plan to climb to from the values for the altitude you are at to get your time for the climb, fuel used during the climb, and the distance you travel during the climb.

So, as an example, say I'm flying at 3000 ft, and want to climb to 6000 ft.  Using the first three columns, I can find my average OAT (outside air temperature) will be approximately 6°C, I'll want to climb at approximately 71 kts, and my climb rate will be around 550 fpm.  Then, using the three columns on the right, my time to climb will be 10 min - 4 min = 6 minutes, the fuel used during the climb will be 1.9 gal - 0.9 gal = 1 gallon of fuel, and I will travel 12 nm - 5 nm = 7 nm.

Now, if the actual temperature were 12°C instead of the 6°C I found with the chart I could use the rule in the notes section of the chart.  Since 12°C is 6°C above standard temperature, we know there must be some correction, so as a conservative estimate we will just assume 10% above the values in the chart.  So, from before, our time was 6 min, so we will add 0.6 min, which will give approximately 6.6 min for the climb, and our fuel was 1 gallons, so we will add 0.1 gallon for 1.1 gallons used, and our distance was 7 nm, so we will add 0.7 nm for 7.7 nm traveled during the climb. 

So, if we had taken off at 3000 ft and climbed to 6000 ft, our values would all be the same, but we would add 1.1 gallons of fuel for start-up, taxi, and take-off, for a total of 2.2 gallons of fuel used in the whole first portion of the flight.

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Rate of Climb Table

This table is similar to the climb performance table.  Again, it is assumed you use full throttle and no flaps in the climb, and the mixture is leaned above 3000 feet.

To read this table, all you do is find the altitude that you are at (or close to, or if you are between altitudes, you might want to average the nearest values, but this isn't really necessary), then just read over to find your climb speed, and your rate of climb according to the nearest value for the OAT.

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Cruise Performance

This table looks a little complicated, but it is very similar to the rate of climb table from before.

To read this table all you do is find your altitude (or if you are between altitudes, you can round up for a conservative estimate), then find your engine RPM using the tachometer, and read over to find your engine power setting in % brake horsepower (BHP), or percentage of the maximum engine output, the airspeed this setting will give you in knots true airspeed, and your fuel burn rate in gallons per hour at these settings.

For example, you are flying at 4000 feet, with the engine at 2400 RPM in a standard atmosphere.  This will give you 64% of the engine power output, and a cruise speed of 110 ktas, and a fuel burn of 7.1 gallons per hour.

Again, if your altitude or temperature falls between the values given in the table, you can either interpolate to find something in between, or you can round up for a conservative estimate (usually the safer method).

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Take-off Distance

A little out of order, but it will work.

The take-off and landing distance tables that are given in the information manual are for short-field operations, so they can be used to find the minimum distances required for landing and take-off.  If you aren't sure you can land your aircraft in a regular configuration, you can use the short-field data and procedures for landing so you can be sure.

For this table, it's very important to take note of the conditions and notes at the top of the chart.  For the short-field take-off, the chart assumes you are using no flaps, however, as I was taught, and as Brett outlines HERE, 10° of flaps are usually used on short- and soft-field take-offs.  Also, the chart assumes you taxi to the runway and apply the brakes before applying full power so you don't have to wait for the engine to reach full power output after applying full throttle.  For the values in the chart, the table assumes a flat, dry, paved runway, and no wind, which might not always be the case, however, there are some corrections that can be made if this isn't the case.

Next, the notes sections details the corrections that can be made to the values in the chart if the conditions aren't the same as the chart assumes.  The chart assumes a short-field take-off technique is used, as Brett explained HERE, and that the mixture is leaned above 3000 ft for maximum RPM.  The next two corrections are very important.  Since it is a very rare day when there is no wind, the wind correction is extremely important.  First, you must use a crosswind component calculator, like THIS ONE, to determine your headwind component on take-off, then use the correction in note #3 to adjust the value you find in the table.  Also, if you are flying from a grass runway, you must increase the ground roll by 15% because of the increased friction.

To find your take-off roll, you find your pressure altitude in the third column, then read over to the temperature that is the next highest above the actual temperature (if it's 8°C, use the 10°C column, or if it's 14°C, use the 20°C column for conservative estimates), and find your ground roll, and the distance required to clear a 50 ft obstacle that is in your flight path (trees, buildings, power lines, etc...).  Also, it's important to note that the chart assumes a 2300 lb total weight, and that you lift-off at 50 KIAS, and climb at Vx (59 KIAS in the 172).

Next, make any corrections for wind speed or runway conditions that are necessary.

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Landing Distance

The landing distance table is almost exactly the same as the take-off distance table, except it assumes you are landing with full (40°) flaps, no power, and that you use maximum braking on landing.  Now, this is somewhat off, because to get these values, test pilots land in as short a distance as possible.  This means they slam the airplane down and jump on the brakes to come to a screeching halt (or something like it).  This is something you won't want to be doing on a regular basis, and since you will need a little extra distance for landing, you'll probably want to add a bit on to the value you read in the table. 

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Next post will discuss the weight and balance charts...

In this post we'll discuss the weight and balance calculations to determine whether it is safe to fly the aircraft.

It's extremely important in flying to determine the how heavy the aircraft will be when you're fully loaded and the location of the center of gravity (CG).  An aircraft in-flight is a lot like a teeter-totter, with the center of pressure (where the lift force is applied) as the center of the teeter-totter, the CG is on one end of the teeter-totter, and the lift force from the tail is on the other end of the teeter-totter, as shown in the picture below.  In the picture, the blue arrow is the lift force generated by the wings, acting at the center of pressure, and the front red arrow is the weight of the aircraft and passengers, acting at the center of gravity, and the back red arrow is the lift being generated by the tail.  Notice that when the center of gravity is in front of the center of pressure, the tail actually produces a lift force downwards, opposite the lift generated by the wings.  This is a desirable situation because if, for some reason, the tail wasn't producing any lift and the center of gravity was behind the center of pressure (opposite the picture), the aircraft would want to pitch up on it's own, and would eventually stall and be uncontrollable.  If the CG is in front of the center of pressure, the aircraft will want to pitch down, and the airflow over the control surfaces allow some degree of controllability.



Now, if the center of gravity is too far forward or too far backward, the lift forces generated by the horizontal stabilizer will not be enough to allow the pilot to keep the aircraft level, and the aircraft will either never get off the ground (too far forward), or the aircraft will pitch up too soon (too far backward), and stall on take-off and fall back to the runway.  Because of this, it is extremely important to calculate where the CG will be, and whether or not it is within the limits for your aircraft.

One important concept to understand is that of a torque, or a moment.  Using the teeter-totter again, imagine that you have a very fat man, sitting very close to the center of the teeter-totter.  You could balance him out by having another very fat man sit very close to the teeter-totter, or you could have a skinny man sit very far from the center of the teeter-totter.  The torque results when you have the force from the weight of the man acting at a distance from the center of the teeter-totter.  So increasing the force applied increases the torque and increasing the distance from the center increases the torque.  THIS might be a better explanation of torques and moments.

The following charts will allow you to easily calculate the important values for only the 1979 Cessna 172N we're talking about.

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Weight and Balance Sample and Loading Graph

This table is a handy way to calculate how everything will affect the weight and balance of the aircraft.  We'll use the values that are used in the sample problem in the left columns.  The "weight" column is the column where the weights of the aircraft, fuel, passengers, and luggage are input, and the "moment" column are where the torques, or moments are calculated.

The very first thing that must be done is to calculate the weight of everything going into the aircraft except for the fuel.  This includes the pilot, passengers, and luggage.  This value is added to the weight of the aircraft to determine how much fuel can be carried.  In the sample problem everything (minus the fuel) weighs 2060 lb.  Since the maximum take-off weight is 2300 lb, that means that 240 lb of fuel can be added without going over the maximum weight.  At 6 lb of fuel per gallon, this is 40 gallons of fuel, and at approximately 8 gallons per hour in flight, this is about 4.5 hours of flight time with VFR reserves.

Now, starting with the first row, the weight of the aircraft with no fuel and full oil is 1454 lb.  The moment arm for the weight is already calculated, and fixed for this aircraft, so the moment that results is 57,600 lb-in (note that the values in the second 'moment' column are divided by 1000).

Next, the fuel required was calculated before, and is 240 lb.  The moment arm for the fuel is calculated using the "Loading Graph".  To use the loading graph, read up the left side to the weight you need, then go across the graph to the line for whatever you are looking for (in this case, the "Fuel" line), and read down to the bottom of the graph to find the moment that results.  In this case the resulting moment is 11.5 in-lb (x1000).  Input that in to the table. 

Next, using the weight of the front seat pilot and passenger, the rear passengers, and the baggage, us the loading graph to find the moment for each.

Then, the total weight and moments can be added together to find the total ramp weight and moment.  In the sample, they assume that 7 lb of fuel are used for startup and taxi so the total take-off weight and moment are 2300 lb and 103.6 in-lb.

Next, use the remaining two charts to determine if these values are within the limits specified.

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COG Moment Envelope/COG Limits

These charts will both tell you whether or not you are within the limits for your aircraft.

To read the COG Moment Envelope chart, you find the weight of the aircraft on the left side of the chart, and the moment you calculated on the bottom of the chart, and see if the point where these two intersect are within the outlined area.  If they are, you are safe to fly.  If they aren't, you'll have to adjust the loading of the aircraft until they lie within the limits.

To read the COG Limits chart, you use the same method as the COG Moment Envelope chart, except you have to divide the moment you found by the weight to get the moment arm.  You then find this value on the bottom of the chart and read up to the weight of the aircraft to see if you are within the outlined envelope.

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Now, most of this is different from the data Brett used earlier for the demo flight, but it should give you an idea of what must be done for a flight to be safely conducted.  But, I don't know of any pilot who does all this work on each an every flight they go on.  If you fly by yourself, or with one or two other passengers who you know won't put you over the maximum weight, and you don't fly on quarter full tanks to an airport 100 miles away, you will most likely be quite safe in doing so.  However, it's important to know this data, and be quire familiar with it in case something happens (you get stuck above the clouds, passengers freak out, etc...), you don't want to be up there trying to remember all this data while you're flying.  So, if you're ever (ever, ever, ever) in doubt, just do the calculations quick.  It shouldn't take more than five or ten minutes if you're familiar with them.

You got it !  (I'm not checking your math, but I'm sure it's correct) 

Now.. couple that endurance (1.8 hours) to your ground speed (adjusting for winds aloft), and you've got your maximum range..

Point of wording and accuracy:

You said: Quote:



TAS (true airpseed) is not the same as ground speed. I know, you know this.. but I'm compelled to point it out for others who might stumble in.

For the record:  True airspeed is indicated airspeed adjusted for density altitude. (there's another step in there called calibrated airspeed, but the difference is insignificant in planes traveling at these speeds and at these altitudes)... Ground speed is true airspeed adjusted for the winds aloft.