Can't get above 32,000ft

[toady1]

Hi guys, has anyone encountered a problem with default and/or add on aircraft whereby fs2004 will not allow you to go above 32,000ft. When I try using autopilot the plane (regardless of model/make etc) just goes nose up into a stall and then drops out of the sky. I can recover by switching off autopilot but I can't get above 32,000ft. Suggestions??

[chomp_rock]

Check your fuel levels, if you have, let's say, 90% fuel chances are you are too heavy to fly at that alt. Also, you might want to try using de-icing. By the way, what speed are you cruising at in the different aircraft you experience this with?

[JRoc]

It could be a few factors, as Chomp mentioned, weight is one, and VS is another.  I had the same problem the first time I took the 747/777 out - I was way too heavy, climbing too fast at a high vertical speed - a big no-no.

Basically step climbing is what you have to do - if you've flown IFR you've noticed that ATC gives you a new altitude after you've reached the previous altitude ATC gave you, until you've reached your planned flight level.  This way you'll have burned off enough fuel, and you'll be able to attain your desired height.

My explanation is pretty crummy, and I left a ton out, but that's the gist of it.

I'm sure one of our experts such as Nexus can give you a proper answer.

[Nav]

toady1, I've deliberately simplified this - you can work out your own refinements later, when you've got more of the hang of things, by referring to the 'Flight Notes' in the Learning Centre for specific aeroplanes.  But this method will get you up and flying in any jetliner!

1.  As soon as you take off and get the gear and flaps retracted, set your desired altitude, set Indicated Air Speed to 250 knots, and set the rate of climb to 1,800 feet per minute.

2.  Watch the Mach speed.  At about 20,000 feet it will have reached Mach 0.65 or so.  At that point set the autopilot to maintain the Mach speed instead of IAS; and then gradually increase it to say Mach 0.7.

3.  Thereafter, watch 'N1' on the engine panel.  If it goes much above 75%, reduce the rate of climb until it gets back down to that.  The reasons for doing it that way, of course, are that first, as the air gets thinner, the wings give less lift, and the engines have to work harder to maintain a steep rate of climb; secondly, to maintain too steep a rate of climb, they drink fuel; and thirdly that, in extreme cases, too little power plus too little lift plus too steep a rate of climb can result in a stall (which I believe is what has been happening to you)

4.  That method should get you up to any reasonable height with no problems.  But you'll probably find that 35,000 feet is about the limit with a full fuel load - which will be shown by the fact that you've had to reduce the rate of climb to a very shallow angle to keep N1 down to sensible levels.  At that point I suggest that you level out, accelerate to cruising speed, and reduce the fuel load before you go higher.

Hope all that helps.

 

[toady1]

Thanks, I'll try all that's been suggested. it does seem to make sense as I never work out how much fuel I'll need for a flight and I have tended to have a steeper climb rate (usually 2000fpm and faster too). It probably explains why the navigation plan shows I've used more fuel during takeoff than planned. Can someone then give me an idiots guide on how to work out fuel loads, I know it varies from aircraft to aircraft but a rough idea would be helpful. Thanks  

[JRoc]

Well, in the navlog it gives you the estimated total fuel burn for the flight.  What I usually do is add say, 10% more than the estimate states, plus extra fuel to account for taxiing.

You'll probably want to add the extra fuel, as the estimates are just that: estimates.  If you watch the navlog in flight you'll see the difference between est. and act. burn, so the extra fuel will account for that.  Better safe than sorry, right?

[Nexus]

first of all...don't keep the engines at 75% N1, that's ridiculous. Rather have them at 95%.
No Airliner in the world climbs at 75% N1 so I don't see any reason why you should do it.

The N1 has to be high here since the fan generates most of the thrust, especially in climbs.

But lets' be more specific. A turbofan engine is as most efficient at high altitudes AND when their compressors are operating in high RPM's, approx 90-95%. You wont reach the engines optimal gas flow condition(=Best specific fuel consumption) with an N1 speed of 75%...

Yes the air gets thinner, but just gradually reduce the rate of climb, but it's important to spend as less time as possible in the climb, because the fuel consumpition actually DECREASES as higher you go, due to the higher propulsive efficiency of the engine. To top it off, a jet engine is optmized for high altitudes, in high speed conditions and high engine speed RPM.

And to switch to mach at 20.000ft is not really correct either.
There is no set altitude when to do the IAS/Mach switch over, when to do it usually depends on temperature.

An airliner has 2 speeds for a climb, one in IAS (like 290kts after 10.000ft) and another in Mach (0.78 for example)
So you will simply fly the 290kts until the the mach number reaches 0.78 (it will as the temp drops as you get higher up in the air), when the actual mach number is equal to the mach climb speed you just switch from IAS to Mach, simple huh

[toady1]

Looks like I've started a bit of a discussion here, but I would like to say that I took on board (forgive the pun) what Nav and Jroc advised me and hey presto I reached and maintained an altitude of 35,000ft. It seems pretty obvious now but the combination of weight, thrust and angle of ascent all have an effect and have to match in order to attain altitude. Anyway please let me thank all of you for the advice given and I will continue to experiment with different combinations as I'm pretty sure it must differ from aircraft to aircraft. Keep an eye out for my posts, no doubt I'll be calling on your expertise again.
Meanwhile it's been nice up here at 35,000, now if I could just get down........

[Midnight_LS1]

[quote]It could be a few factors, as Chomp mentioned, weight is one, and VS is another.

[Nexus]

Of course you will reach the assigned altitude, but it is not the prefered way of doing it  :)