Hello everyone, I need your expertise to help me sort out my problems. I recently bought fsx (been using fs9 for years). Anyway I have a few problems with the default 737 and 747. With the 737 I waste WAY too much fuel and the engine runs at 80 percent N1 at FL 300 and above not sure if that's normal. The 747 feels even worse. Upon takeoff I can barely lift the plane up only past 205 kts while it's designed to rotate at 180 kts or even less. I get to FL360 it pitched to 6 degrees and ran at 90 percent N1 during cruise which in my opinion seems like I'm doing something wrong. If anyone has some answers I'd appreciate it.

Sounds like you've got too much fuel on board; basically you need to determine the distance of your flight, figure out how much fuel that will take, then throw in enough additional fuel for another 45 minutes flying time to allow for diversions and hold procedures. You can get flight planners which will do that, both free and payware ones, or if you fancy doing a bit of test pilot work, you can find out the fuel burn in gallons/lbs/kgs per hour from a short test flight at a light fuel load using a watch or clock, and then use that as your baseline for calculations. If you can't be arsed working all that out, then a very rough guide to it can be worked out by simply knowing the maximum range of your aircraft, then dividing its range into four, each of those distances will then need about 25 percent of the fuel tank capacity, although if you use that rough guide, then be sure to err on the side of caution, because there is nothing more useless in aviation, than fuel which you left in the tanker on the ground.

 

Where the B747 is concerned, it can cruise at around 43,000 feet, but it can't make it up there straight away, it has to burn off some fuel before it is able to do so, since it will be far too heavy when carrying a full fuel load, and you will be wasting that fuel too, because you'll have to burn a lot of it just to be able to lift it off the ground, in fact, full fuel on a Boeing 747 actually weighs more than the aeroplane itself does when it is empty.

 

Thus a long 747 flight across the ocean is usually made in 'step climbs'. For example, the crew will request clearance up to maybe 31,000 feet, and then as the fuel burns off, they may ask for an increase up a few thousand feet, and then do so again when they get a bit lighter still. The trick is to not be wallowing along with the engines having to put out a lot of power to hold you up there, but rather to only go up there when you are light enough to be able to do so on a lower thrust setting. Keep in mind too that if you can get up higher sooner, then you will use even less fuel, and you'll use considerably less when coming down of course, since even a big heavy airliner can glide for about sixty miles from cruise altitude with the engines completely shut down, so with minimal throttle settings, most airliners can in fact go a very long way using far less fuel than they do in the cruise when not trying to maintain height.

 

Al

This may not be accurate to the nth decimal place but then, I don't suppose the default aircraft model fuel consumption very well either.

 

http://fuel.aerotexas.com/

 

It works pretty well with the PMDG 737NGX, although I'd check whether you have a headwind or a convoluted approach to handle and add bit more fuel to be on the safe side.

Welcome to the AVSIM Forums.

 

"With the 737 I waste WAY too much fuel and the engine runs at 80 percent N1 at FL 300 and above not sure if that's normal."

 

Alan has given you good advice, but to add: at FL300, 80% N1 sounds fine, depending upon your total weight. Make sure you are carrying the required amount of fuel for the trip (as suggested by the default flight plan) plus extra for emergencies (I carry up to 10000 lbs extra, for the B744, for long hauls).

"Upon take off I can barely lift the plane up only past 205 kts while it's designed to rotate at 180 kts or even less."

 

The three things you need to do prior to take off is: determine your take off speed, flap setting, and stabilizer trim. These calculations are based mainly on your aircraft take off weight, runway length, and wind conditions. For example, if your weight is 775,000 lbs on a runway length of 11,000 ft, with minimal wind conditions, I would use 94% thrust (N1), 10 degrees flaps, and 8 units of stabilizer trim. Your aircraft should commence rotation at around 175 knots. During climb and if you are still in control of the aircraft (ie. not on autopilot), you can adjust your stab. trim accordingly. Once autopilot is in command, it will adjust the trim automatically.

 

"I get to FL360 it pitched to 6 degrees and ran at 90 percent N1 during cruise which in my opinion seems like I'm doing something wrong."

 

It sounds that you are still too heavy to be at FL360. Maybe FL320 would be more appropriate for your weight. After your AOA drops to about 4 degrees, then you could request a further altitude increase to FL340. Also, it's good practice to keep your N2 under 90% (ie. below redline, even though I've seen actual flight videos showing pilots cruising up to 95% N2!).

 

Hope this helps and keep on practising. Also, for each airport you take off from, keep a running list of the above calculations (ie. what flap, trim and thrust setting worked well for the given runway length and aircraft weight). This will make it easier for future take offs and remove some of the guesswork.

 

Chris David

Thanks a lot to everyone that answered. I hope to get my issues solved soon, and if anyone has similar questions they can refer to this useful thread. But I do have one question. How do I handle the stab trim and to what degree would I have to adjust it to upon 175 kts for takeoff?

Hi Vlad,

 

The Stabilizer Trim control on the B744 is located to the left of the Throttle levers. The best way to view it and to control it, is to scroll down to it while in the VC mode and zoom in to see it more clearly. You can either click on the bottom of the control to gain more positive trim (ie. to trim the elevators up), or use the appropriate key (Elevator Trim, Up/Down). I use the keyboard to trim as it is quicker and easier. When you see the Trim control, it is probably already set to 7.5 units (default). The ACES team has probably deemed this an ideal setting for most take offs, since the B744 is so heavy, it generally needs a lot of trim for take off and for cruising.

 

In regards to your other question: as mentioned in my other response, you need to know other factors that affect an aircraft's take off profile, such as, runway length, aircraft weight and wind direction and speed. Using my example given previously, I would use 8 units of Trim to start rotation at 175 to 180 kts. You can try 8.5 units and see if you can achieve rotation at 175 kts or less. But for realistic planning and flying, you need to ascertain the other factors. So basically, if you are on a long runway (over 12000 ft) and flying light (under 675,000 lbs), you may need only 7 or 7.5 units of Trim. Whereas on a short runway (under 9000 ft) and a heavy aircraft (under 875,000 lbs), you may have to trim up to 9 units. Remember, that your Flap and Thrust settings are also vital in achieving your rotation speed.

 

Regards,

Chris David

Ok thanks a lot. After a couple of medium range flights on the 737 and one pond hop on the 747 I see a big difference. I should've been more aware of all the factors that were mentioned in this thread. And thanks to the advice fsx jets fly more realistic. Still have more practice to do though XD