Autopilot

[Bubblehead]

I've been using the Flight Planner provision of the FS9 and I have a question. When on autopilot, how do you maintain airpeed. I see a Speed Switch, a MACH switch, the speed gauge and the Autothrottle switch. Here's what I have been unable to do. When at cruising altitude, I want to go on Autopilot. I know how to set the altitude and the course ut not the speed. Any help?

Bubblehead

[Brett_Henderson]

It depends on the the A/P and how the A/P is confifured in the aircraft.cfg file.

If it's one of the default, big jets (737 747 777) you need to have the auto-throttle engaged AND either the speed or mach turned on. Then it will hold the speed/mach-number you have dialed in.

[simonmd]

Yes, you should see a three figure guage just like the HDG and NAV readouts with IAS/MACH on it. All the default AC also require you to turn on or arm the auto throttle as well. If you can't find an Auto Throttle switch on a different AC it may simply not have one and is armed automaticaly once the IAS or MACH button is pressed. I've done this pic from the default 737 to make it clearer;



Remember, the autothrottle works independantly from the AutoPilot even though it is on the same panel. To operate, set the cruising speed required in the IAS/MACH window. Press the IAS button, it should light up. When you are ready to engage, press the A/T ARM switch and the set speed will be maintained.

One point to note. Many people don't understand why there is a Mach Hold function on a subsonic aircraft like the 737. This is beacause Mach is a measurement of speed relative to the ground and therefore, remains constant no matter what the altitude. However, IAS is just the Indicated Air Speed. The higher you go, the thinner the air is so the IAS will apear to drop even though you are travelling at the same speed in reality. 300 kts at 30,000ft is a hell of a lot faster than 300kts at ground level! Therefore, when travelling to high altitudes, it's easier to set the Mach speed to keep the AC at a constant speed by pressing the MACH button under the speed you've set. This will change the readout to the current speed as a Mach number, eg. 250kts at 20,000ft is Mach 0.54, with a ground speed of 330. If you climb to 30,000ft your speed will stay the same if set to Mach but would increase if you left it set on IAS.

Hope some of you find this usefull. My brain hurts now!

[Bubblehead]

Got the picture. One more thing. Any suggestion on the best way for the approach, that is, how far before descending from a cruising altitude (let's say, 30K feet). Is there anything in the FS9 on how to make the approach. Presently I just do visual but often times I lose sight of the airport.

Bubblehead

[simonmd]

I'd suggest making a flightplan and flying it useing FS9's ATC. They will give you instructions as to when to decend and to what level, etc. and you can gauge from these flights roughly when it is apropriate to decend. Personaly I usualy like to be down to a max of 8000ft by the time i'm 60-70 mls out or so. Of course, in the real world each airport is different with some allowing a 'shallow' aproach but some will have a min height restriction until you are very near, an airport in or near a city for example.

There is an excellent tutorial on here as to how to make an ILS approach.

[Jakemaster]

I would say use IFR flight when flying something more complex.  When I fly my DC-3, I just use VFR and follow a GPS flightplan.  But in a plane like my PMDG B1900C, I just listen to what ATC says in a filed IFR plan

[Brett_Henderson]

Mach is a lot like airspeed.. more like true airspeed ... even though the speed of sound actually goes DOWN as altitude increases.. It's not a speed realtive to the ground though. In theory, you could fly at mach 0.8 into a 600 knot headwind at 3,000 feet and not be going anywhere across the ground. It's just that at higher altitudes, true airspeed and indicated airspeed differ so much that mach numbers are more uniform... . Kind of the same reason that above 18,000 feet you disregard atmospheric pressure and just set your altimeter to 29.92.

In both cases.. it just puts everybody on the same page.

[Brett_Henderson]

Oh.. and the best rule for descending from high altitude is the old "3 to 1"..

Three 3 miles for every 1,000 feet of altitude..

At 30,000 feet start your descent from 90 miles out.. But that's just a guideline, because you'll start pretty shallow and steepen it as you get closer... shallowing again for final.

[Marlin]

Bubblehead,

Check out these links, they are just PACKED full of info.

http://stoenworks.com/Tutorials/

and

http://www.navfltsm.addr.com/index.htm