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Topic: Operating Costs Between Aircraft On A Given Route
Posted 2012-12-19 19:32:58 and read 4638 times.

Manufacturers all have their published estimates for how their aircraft's operational costs compare to the industry or even specific aircraft. Is there a tool out there or an empirical method for comparing operational costs on a given route between Equipment A and B to include input for variables such as Origin and Destination altitude?

I would like to get a better idea of how the Q400 compares to other aircraft in the mountains on routes such as DEN - SLC.
I understand there are many variables in play. Bombardier sites 30-50% better fuel efficiency. Does that estimate still hold true if the origin is above 5,000 ft and the jet has to clear a mountain during winter weather?

Topic: RE: Operating Costs Between Aircraft On A Given Route
Posted 2012-12-20 08:47:25 and read 4537 times.

 Quoting frequentfryer (Thread starter): Is there a tool out there or an empirical method for comparing operational costs on a given route between Equipment A and B to include input for variables such as Origin and Destination altitude?

There are very good tools for calculating fuel burn...this is what almost all airline dispatchers use to determine required fuel loads. These are extremely accurate (better than 1%).

There are no tools to do total operating cost comparisson on a rigorous basis because that's hyper airline specific (crew cost, maintenance cost, overhead cost, etc.). The OEM estimates all have to use baseline assumptions.

 Quoting frequentfryer (Thread starter):Bombardier sites 30-50% better fuel efficiency. Does that estimate still hold true if the origin is above 5,000 ft and the jet has to clear a mountain during winter weather?

It should still hold true. There's very little of operating cost will change with altitude or weather. Payload may change but that's on the revenue side, not the cost.

Tom.

Topic: RE: Operating Costs Between Aircraft On A Given Route
Posted 2012-12-20 11:43:56 and read 4483 times.

Thanks! My understanding was that the you push the engine harder at wheels to take advantage of denser air and build momentum that carry the aircraft through the rest of the clime to cruising altitude.

The thought was that starting at 5,000 ft would mean the engines have to work harder to get the same traction in thinner air, thus burning more fuel. A steeper climb to clear the terrain and potentially freezing temperatures at ground level also have an effect do they not?

I've been told that this is a real challenge for the CRJ2 for example. That the number of PAX would be limited in certain conditions to ensure that they could clear terrain and get to altitude with enough in the tank to complete a medium length flight.

Am I just making this up? Isn't this a scenario where the Q4 really shines?

Topic: RE: Operating Costs Between Aircraft On A Given Route
Posted 2012-12-20 13:54:16 and read 4447 times.

 Quoting frequentfryer (Reply 2): The thought was that starting at 5,000 ft would mean the engines have to work harder to get the same traction in thinner air, thus burning more fuel. A steeper climb to clear the terrain and potentially freezing temperatures at ground level also have an effect do they not?

The software in engines varies the fuel to get optimal performance. In thinner air, the engine is capable of producing less thrust, but also burns less fuel. The result is a longer runway needed, or not derating the takeoff as much (at sea level most airplanes takeoff with less than maximum power to save fuel and this is known as derating).

 Quoting frequentfryer (Reply 2): I've been told that this is a real challenge for the CRJ2 for example. That the number of PAX would be limited in certain conditions to ensure that they could clear terrain and get to altitude with enough in the tank to complete a medium length flight.

I think you are referring to density altitude and its affect on the CRJ. All airplanes produce less lift and have less thrust in high altitude airports. The ERJ and CRJ do not have the same takeoff performance as a Q400. The result is that in high altitude operations or during hot weather, the useable payload on the CRJ and ERJ drops dramatically to the point where they cannot take a full load of passengers.

 Quoting frequentfryer (Reply 2): Am I just making this up? Isn't this a scenario where the Q4 really shines?

The Q400 has better short field performance and is not as affected, but also does not have as much range either. One benefit for the Q400 is that it is rarely scheduled for flights over 500 miles.

Each manufacturer publishes ACAPs on their website. Take a look at them as they will show you airplane performance charts.

Topic: RE: Operating Costs Between Aircraft On A Given Route
Posted 2012-12-20 14:22:06 and read 4438 times.

 Quoting Roseflyer (Reply 3):The ERJ and CRJ do not have the same takeoff performance as a Q400.

Indeed. In general, most turboprops have wings that are designed with minimal wingsweep, if any at all. This offers a huge increase in performance during takeoff and landing, but hinders the aircraft as far as range and maximum speed. A good example to look at is the 328Jet, which is where they took some turbofan engines and hung them where turboprops used to be. While the plane could go faster than its turboprop counterpart, it was very slow compared to other turbofan aircraft, and its range was not much better than its turboprop counterpart---not to mention that it burned fuel at nearly twice the rate.

Topic: RE: Operating Costs Between Aircraft On A Given Route
Posted 2012-12-21 11:24:53 and read 4282 times.

 Quoting frequentfryer (Reply 2):My understanding was that the you push the engine harder at wheels to take advantage of denser air and build momentum that carry the aircraft through the rest of the clime to cruising altitude.

Most aircraft climb at constant speed, so they're not using momentum to carry them through the climb. Climb comes from excess thrust, not excess speed. There is a special case of using excess speed during the takeoff roll to get better climb gradient very early in the climbout but that can only be used when you have more runway than you otherwise need.

 Quoting frequentfryer (Reply 2):The thought was that starting at 5,000 ft would mean the engines have to work harder to get the same traction in thinner air, thus burning more fuel.

They can't work harder; in fact, it's the opposite. They can't work as hard so they produce less thrust and burn less fuel. This is why you need a longer runway at high altitude.

 Quoting frequentfryer (Reply 2):A steeper climb to clear the terrain and potentially freezing temperatures at ground level also have an effect do they not?

Freezing temperatures are actually good for performance (jet engines are happier when it's cold). Terrain clearance can be an issue but, for any two aircraft, they're going to have equivalent issues at the same altitude.

 Quoting frequentfryer (Reply 2):I've been told that this is a real challenge for the CRJ2 for example. That the number of PAX would be limited in certain conditions to ensure that they could clear terrain and get to altitude with enough in the tank to complete a medium length flight. Am I just making this up? Isn't this a scenario where the Q4 really shines?

You're not making it up but I think you're mis-allocating the difference...as others mentioned, it's a fundamental difference in takeoff performance between the two aircraft. It doesn't really impact the operating cost in any meaningful way. It does have a huge impact on revenue because aircraft with poor takeoff performance will take a bigger hit at high altitude airports and not be able to carry as many revenue-generating passengers or cargo.

Tom.

Topic: RE: Operating Costs Between Aircraft On A Given Route
Posted 2012-12-21 12:56:10 and read 4256 times.

 Quoting Goldenshield (Reply 4): In general, most turboprops have wings that are designed with minimal wingsweep, if any at all. This offers a huge increase in performance during takeoff and landing
 Quoting tdscanuck (Reply 5):It doesn't really impact the operating cost in any meaningful way. It does have a huge impact on revenue because aircraft with poor takeoff performance will take a bigger hit at high altitude airports and not be able to carry as many revenue-generating passengers or cargo.

This is fascinating.. so fuel burn is not increased to compensate for thinner air. The jet aircraft can't burn the same amount of fuel in thinner air, meaning less thrust is generated which is why the aircraft needs more runway to get up to speed.
So at altitude, runway length determines takeoff weight? I never would have suspected this. Very interesting indeed.

Then if we were to compare a turboprop such as the Q4 with a lower cruising altitude(say 25,000 ft) and better takeoff performance, to another jet aircraft such as a CRJ or an E190 (40,000 ft) on a 400 mile route in and out of terrain, that route for the jet is actually longer because the jet has to travel to 40,000 ft and then back down again with less time at cruze altitude, whereas the Q4 flies a straight line once it hits 20-25000 ft, correct? So in this case, a gain in fuel efficiency comes from the difference in actual distance traveled.

Topic: RE: Operating Costs Between Aircraft On A Given Route
Posted 2012-12-21 13:30:12 and read 4246 times.

 Quoting frequentfryer (Reply 6):This is fascinating.. so fuel burn is not increased to compensate for thinner air. The jet aircraft can't burn the same amount of fuel in thinner air, meaning less thrust is generated which is why the aircraft needs more runway to get up to speed. So at altitude, runway length determines takeoff weight? I never would have suspected this. Very interesting indeed.

Altitude is a reason, not the only reason. Take off performance is determined by:
- Altitude.
- Temperature. Colder is better as colder air is more dense.
- Humidity (though the effect is not that great). Dry is better as dryer air is more dense.
- Relative wind. Headwind is better.
- Runway surface.
- Runway slope.

The higher the altitude, the more runway is needed because thinner air means:
- Higher speed needed for the same lift.
- Less dense air entering engines, meaning less air, meaning less fuel can be used, meaning less thrust. (The same holds true for pistons.)

 Quoting frequentfryer (Reply 6):Then if we were to compare a turboprop such as the Q4 with a lower cruising altitude(say 25,000 ft) and better takeoff performance, to another jet aircraft such as a CRJ or an E190 (40,000 ft) on a 400 mile route in and out of terrain, that route for the jet is actually longer because the jet has to travel to 40,000 ft and then back down again with less time at cruze altitude, whereas the Q4 flies a straight line once it hits 20-25000 ft, correct?

Sure, but the extra distance is negligible. The extra 15000 feet is only a bit under 3 miles, so a small fraction of the total distance. The extra fuel burn comes about from the need to haul all that weight up an extra 25000. The cruise fuel savings will more than make up for it.

Topic: RE: Operating Costs Between Aircraft On A Given Route
Posted 2012-12-21 14:58:03 and read 4230 times.

 Quoting frequentfryer (Reply 6): Then if we were to compare a turboprop such as the Q4 with a lower cruising altitude(say 25,000 ft) and better takeoff performance, to another jet aircraft such as a CRJ or an E190 (40,000 ft) on a 400 mile route in and out of terrain, that route for the jet is actually longer because the jet has to travel to 40,000 ft and then back down again with less time at cruze altitude, whereas the Q4 flies a straight line once it hits 20-25000 ft, correct? So in this case, a gain in fuel efficiency comes from the difference in actual distance traveled.

The distance in climb is negligible. Airplanes almost never fly direct between two destinations. They fly point to point and through a pattern for landing. Turboprops and jets don't always fly in the same airways. Turboprops are more exposed to weather which means they have to go around more storms, however jets have to fly in more crowded airspace and don't always get as direct routings due to traffic.

Topic: RE: Operating Costs Between Aircraft On A Given Route
Posted 2012-12-21 21:02:43 and read 4189 times.

 Quoting frequentfryer (Reply 6):So at altitude, runway length determines takeoff weight? I never would have suspected this. Very interesting indeed.

All other things being equal, yes. As Starlionblue said, there are a lot of other factors too. Runway length can be the performance limit at any altitude but it becomes more of a factor at high altitude. But very high altitudes tend to be a problem because there is a practical upper limit to runway length in most places and you start to run into the tire speed limit.

With small aircraft like a CRJ or Q-400 that are designed for relatively short airfields, it's rare for them to have a runway length issue at "normal" airports because those airports were sized for larger jets that need more runway. However, especially the CRJs tend to have relatively un-complicated high-lift systems compared to the larger jets so their performance drops off badly with altitude and temperature.

 Quoting frequentfryer (Reply 6):Then if we were to compare a turboprop such as the Q4 with a lower cruising altitude(say 25,000 ft) and better takeoff performance, to another jet aircraft such as a CRJ or an E190 (40,000 ft) on a 400 mile route in and out of terrain, that route for the jet is actually longer because the jet has to travel to 40,000 ft and then back down again with less time at cruze altitude, whereas the Q4 flies a straight line once it hits 20-25000 ft, correct?

Yes. But...

 Quoting frequentfryer (Reply 6):So in this case, a gain in fuel efficiency comes from the difference in actual distance traveled.

No. The difference in actual distance traveled is very small, and the fuel burn on the different segments is extremely asymmetric...the jet has to climb farther but also spends a lot more distance on descent where the engines are at or near idle. The increased burn to get up higher is countered by less fuel required to cruise at higher altitude. The drop in drag from thinner air more than counters the drop in engine thrust due to falling density.

Tom.

Topic: RE: Operating Costs Between Aircraft On A Given Route