Simviation Forums

Hello again. I been flying jets and I am interested in understanding the relationship between targeted cruise speed and auto throttle. I notice on many of my flights, it's a struggle to get to the cruise speed I set in the "hold speed" section of the autopilot. For example I was flying a 747 and had the speed set to 315. But the plane seemed to be dragging it's tail at 31,000ft and could barely make it over 270-280. The GS is around 370 and can rarely make it over 400. I would try trimming the nose down a little to increase the speed but then it goes back to dragging it's tale and the speed reduces again.
Only once traveling from Northern Cal. to Galapagos Islands did I get a gs of 611. I have no idea how I got the plane to travel at that speed. My theory is that I had the wind with me on that flight. Am I right?

From another thread I know this whole airspeed thing is complex. I know to realize the difference between indicated airspeed, and ground speed. I also understand that wind and altitude plays a role also.

I just want to understand the principles of getting the most speed out of a jet (or any aircraft) and what are the major factors in speed getting from point A to B.

You've kinda answered the question.. It's all about true vs indicated airspeed. Ground-speed has a wind factor to it.

280 knots indicated, at 31,000msl could be as high as 500 knots true airspeed (temperature and atmospheric pressure affect it).

Now, in zero wind; true airspeed and ground-speed are the same. At 31,000msl, 70 knot winds are not uncommon. If that 70 is a tailwind; your 280 knots on the airspeed indicator will be upwards of 570 knot ground-speed.. And of course a 70 knot headwind could make 280 indicated into 430 across the ground.

To keep everyone on the same page, just use Mach-numbers, instead of airspeed, at high altitudes.

OOps.. to answer the question (sorta).. it struggles at 280 indicated at FL310, because that's about all it can do, with a load, at that altitude.

The IAS VS TAS is important to grasp and yes you are not suppose to have speed set to knots but Mach at that altitude.

Pretty much the same principle as setting the altimeter to STD (Standard) above 18 000 feet (US Standard)

You need to adjust your rate of climb. Climbing at 1800 f/m in a loaded heavy at that altitude is suicide. You will end up with more then a dragging tail.

Infact the flight director will increase the pitch to try and make up for engine power loss increasing the magnitude of the problem.

Should you use real weather a head-wind could result in a stall as your rate of climb already nearly exceed the aircraft's ability to climb.

Looks like you need some time in the 152

For clarification..  the airplane doesn't "know" if there's any wind at all.. head, tail or otherwise.

Now if there is a CHANGE in wind direction or velocity, then it "knows"..  Like, if a 50 knot headwind decreases to a 20 knot headwind.. that (to the airplane) is sudden, 30 knot tail wind..  you'll lose 30 knots of airspeed.. and THAT can be a problem if you're on the edge of a stall.

But if the wind is constant... the only thing effected is ground-speed. To the airplane, there is no wind at all.

Thanks for the replies. I think it's my climbing that I have to work on. I will look into that. I did assume that maybe I pushed to get to a high altitude too quickly without adjusting the pitch and throttle properly along the way. Am I right?

Also what's the best way to check wind conditions along a flight using real weather. I only use real weather btw.

to check wind conditions, speed, heading, altitude, GPS Coordinates inside FS (not the gps map, but the N45* 43.45' , W12* 94.32' coordinates), as well as FPS - frames per second....

hold down SHIFT and press Z - 3 times.  See picture for detail.


What does all of this mean?????
GPS Coordinates / ALTitude 20,037 FT Mean Sea Level / Heading 229 / 435 Knots Indicated Airspeed / Wind Direction 356 @ 0 Magnitude (no wind comming from heading 356) / FPS=10.6 / +1.0 Gravity / Fuel Quantity on board 68%


The information i just gave you is from this picture that I took.

Thank you Capt.Propwash. That hole look like it may get filled up one day with all that water. Unless it's a bottomless pit.

nope, its not bottomless..... it does indeed have a bottom, ive been down there, but i am not going to say what is down there.  8-)