Freight vs Passengers?

[mikeandpatty]

Freighter versions often have higher "Zero Fuel Weights" and maximum landing weights - makes a big difference in what you can carry. Passenger versions typically have lower Zero Fuel Weights - the maximum internal weight allowed, the rest of the weight up to maximum takeoff weight must all be fuel.

Consequently. a freighter might be able to take off with lots of internal weight and less fuel, still land without being required to burn a lot of fuel, etc - much more flexible. Jet pax and cargo planes are really affected by these factors because they carry a lot of fuel, and need to burn a lot between maximum takeoff weight and maximum landing weight.

A good way to get smart on all this is to look at different airplanes by searching the web for a certain plane and see if you can find:

-empty weight
-zero fuel weight
-maximum ramp (max taxi) weight
-max takeoff weight (slightly less than max ramp weight)
-maximum landing weight

You also must remember that a 747-400 or 747-400F (for instance) can come with three different manufacturer's engines - GE, P&W and Rolls Royce; and, within those manufacturers, different versions of the same basic engine. Usually the total thrust difference across all these combinations may only be 4000 lbs thrust per engine, but it does change some weight limits in some cases.

It is not unusual to find some differences in these numbers given by different sources; this is usually do to the fact that the reference source is using data for a version upgrade of some type or other; there are MANY of these upgrades on many types of airplanes in use today.

In spite of all this, a pax or freighter version with the same total thrust and similar weight will handle pretty much the same way, and have the same or similar airspeed limits such as max Mach number, best cruise speed, stall speeds, etc.

The FAA certifies these design limits - it's not the builder or user who makes the decisions.

[mbish01]

I live close to CYHM (Hamilton, ON) which is Canada's busiest freight airport. Purolator flies converted 727's and DC10's in and out all the time, as does Cargojet (727 & 757) and DHL (mostly A300, I think). Most movement is at night, unfortunately, but the noise at takeoff from rwy 11 is only for aircraft enthusiasts!!!
Mike

[jomni]

Freight can sometimes be more fragile than humans. They won't complain but they will break if the pilot is not careful.

[clayton6221]

"It is not unusual to find some differences in these numbers given by different sources; this is usually do to the fact that the reference source is using data for a version upgrade of some type or other; there are MANY of these upgrades on many types of airplanes in use today."


Add that you can always turn up or turn down the engine thrust, depending upon what you want. AKA: Power or longevity...
Our version of the CF6-80C2's can be turned up to a rating of 60,000 Lbs, but are normally operated by the user at a thrust rating of 50,000 Lbs to save on airframe wear and tear. The airframe will take the thrust, but will use those hours up at a faster rate than the customer wishes.


"The FAA certifies these design limits - it's not the builder or user who makes the decisions."

The airframe manufacturer certifies and turns this data over to the FAA to gain the type certification for review, thru both flight test and the engineering departments. FAA does not have the resources to go into that kind of detail for each plane submitted for certification. They might have a representative observing, but they do not do the actual certification work, that is the work of the airframe manufacturer.
FAA is a regulatory oversight agency, not an engineering or design company, and thankfully they do not build airframes either...

Clay