Simviation Forum - Losing speed at 30000 ft

Jun 7^th, 2010 at 3:37pm

RC1977 Offline
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Hi there

Im having a problem that i never experience before Undecided

..

Evertime i use the 747-200 and when i get to 30000 ft i start to lose speed,the speed starts to drop dramatic and thats it the plane stalls and nose dive,can someone give a tip of what's going on with this because i have no idea.

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Reply #1 - Jun 7^th, 2010 at 3:48pm

SeanTK Ex Member

I can think of two things....

1. You are climbing too fast for your aircraft's weight. Climb slower to allow it to burn off more fuel before reaching your cruising altitude.

2. Your pitot tube(s) is/are iced over, and due to the erroneous readings from it, your autopilot tries to compensate and makes things worse. Pitot heat is your friend here.

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Reply #2 - Jun 7^th, 2010 at 4:13pm

Groundbound1 Offline
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I'll choose option #2. Sounds a lot like ice to me.

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Reply #3 - Jun 7^th, 2010 at 4:18pm

DaveSims Offline
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My question is, do you understand the relationship of indicated airspeed? 30000 feet is about the point where you start to see major reductions in indicated vs true airspeed, and have to really manage your speed (usually in Mach number, not airspeed).

Dave

www.flymcw.com

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Reply #4 - Jun 7^th, 2010 at 4:32pm

Groundbound1 Offline
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DaveSims wrote on Jun 7^th, 2010 at 4:18pm:

My question is, do you understand the relationship of indicated airspeed? 30000 feet is about the point where you start to see major reductions in indicated vs true airspeed, and have to really manage your speed (usually in Mach number, not airspeed).

Good point, but if the plane is stalling and diving.... Wink

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Reply #5 - Jun 7^th, 2010 at 4:41pm

RC1977 Offline
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DaveSims wrote on Jun 7^th, 2010 at 4:18pm:

My question is, do you understand the relationship of indicated airspeed? 30000 feet is about the point where you start to see major reductions in indicated vs true airspeed, and have to really manage your speed (usually in Mach number, not airspeed).

Not really Undecided

..so in Mach number what do i put when i reach 30000 feet?

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Reply #6 - Jun 7^th, 2010 at 4:49pm

aeroart Offline
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Sounds more like the airplane is too heavy for the altitude. Cruise at a lower altitude for a while, then try a higher altitude. You may have to do this at a couple of altitudes until you can operate at your highest cruising altitude. This is the way it works in the real world.

If you could find an operating manual for the airplane, you'll be able to find the applicable charts.

Arts

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Reply #7 - Jun 7^th, 2010 at 5:06pm

RC1977 Offline
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aeroart wrote on Jun 7^th, 2010 at 4:49pm:

Sounds more like the airplane is too heavy for the altitude. Cruise at a lower altitude for a while, then try a higher altitude. You may have to do this at a couple of altitudes until you can operate at your highest cruising altitude. This is the way it works in the real world.

If you could find an operating manual for the airplane, you'll be able to find the applicable charts.

Arts

Well thats exacly what i did and 50 min later i made up to 37000 feet.

Like i said before i never experience this problem before with any other plane,not even with the pmdg 747-400.

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Reply #8 - Jun 8^th, 2010 at 11:28am

microlight Offline
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Just make sure you're not overweight at take-off; checking on the fuel/payload options should tell you whether you are or not. Then you need to 'step' your ascent, depending on plane - 767s are notorious for it.

Wink

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Reply #9 - Jun 8^th, 2010 at 4:33pm

skoker Offline
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Yep climbing too much too young too fast.... Grin

I do it all the time and end up staying at 20k for an hour... Angry

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Reply #10 - Jun 8^th, 2010 at 5:21pm

Rocket_Bird Offline
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RC1977 wrote on Jun 7^th, 2010 at 5:06pm:

aeroart wrote on Jun 7^th, 2010 at 4:49pm:

Sounds more like the airplane is too heavy for the altitude. Cruise at a lower altitude for a while, then try a higher altitude. You may have to do this at a couple of altitudes until you can operate at your highest cruising altitude. This is the way it works in the real world.

If you could find an operating manual for the airplane, you'll be able to find the applicable charts.

Arts

Well thats exacly what i did and 50 min later i made up to 37000 feet.

Like i said before i never experience this problem before with any other plane,not even with the pmdg 747-400.

Unless your doing a couple hour flight with low fuel, 37000 feet is pretty high on a 742. Yeah, most commercial airliners plan their weight (mostly their fuel weight) to that which is just a little over required. I used to work for an airline, and having shadowed some load planners before, in most cases, they don't even fuel up the birds more than 10k lbs more than the required fuel load on a 737NG. On wide-bodies and long hauls, you'd want a bit more obviously.

So unless your doing a 12 hour flight, chop down on the fuel load a little. Ideally you'd want a chart for this, but for a 747, I'd say usually 40k more than your required burn is enough for most purposes.

Cheers,
RB

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Reply #11 - Jun 9^th, 2010 at 10:26am

Nav Offline
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RC1977 wrote on Jun 7^th, 2010 at 4:41pm:

DaveSims wrote on Jun 7^th, 2010 at 4:18pm:

My question is, do you understand the relationship of indicated airspeed? 30000 feet is about the point where you start to see major reductions in indicated vs true airspeed, and have to really manage your speed (usually in Mach number, not airspeed).

Not really Undecided

..so in Mach number what do i put when i reach 30000 feet?

Generally, in an 'ordinary' airliner, 0.75 to 0.82 is about the max.

In the climb, and in descent, 275 old-fashioned knots is about right. In the thin air at height, your actual airspeed will be up to double that - but that 'policy' tends to work right up to 35,000 feet and right down to 10,000. Below 10,000, in most parts of the world, 250 knots 'indicated' is the legal limit.

Best approach, IMO, is to stick to knots until you reach height, say 34,000 feet - then note the Mach. number shown (probably about Mach 0.80) and set that. Starting a descent, it's not a bad policy to set '250 knots indicated' as soon as you start down. My guess is that you'll find that that's plenty fast enough once you start the complicated business of 'lining up.'

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Reply #12 - Jun 9^th, 2010 at 11:59am

Fozzer Offline
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Nav wrote on Jun 9^th, 2010 at 10:26am:

RC1977 wrote on Jun 7^th, 2010 at 4:41pm:

DaveSims wrote on Jun 7^th, 2010 at 4:18pm:

My question is, do you understand the relationship of indicated airspeed? 30000 feet is about the point where you start to see major reductions in indicated vs true airspeed, and have to really manage your speed (usually in Mach number, not airspeed).

Not really Undecided

..so in Mach number what do i put when i reach 30000 feet?

Generally, in an 'ordinary' airliner, 0.75 to 0.82 is about the max.

In the climb, and in descent, 275 old-fashioned knots is about right. In the thin air at height, your actual airspeed will be up to double that - but that 'policy' tends to work right up to 35,000 feet and right down to 10,000. Below 10,000, in most parts of the world, 250 knots 'indicated' is the legal limit.

Best approach, IMO, is to stick to knots until you reach height, say 34,000 feet - then note the Mach. number shown (probably about Mach 0.80) and set that. Starting a descent, it's not a bad policy to set '250 knots indicated' as soon as you start down. My guess is that you'll find that that's plenty fast enough once you start the complicated business of 'lining up.'

I find that very interesting....
Something I learned very recently in the "Real Aviation Forum".

250 Knots max, is about the speed limit for most of my GA Piston/Turbine Prop Aircraft when flying at around 10,000 feet ASL, which means I am flying within the regulations.

Military Jets seem to be something totally different!

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Reply #13 - Jun 11^th, 2010 at 10:41am

garryrussell Offline
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When 747-200 were common I often heared the pilots ask for a higher lever say from 270 to 290 and the controller say he could have 310 but the reply was negative I'm too heavy at this time.

I remember at the time the 767 went into service it was said it was the first commercial jet airliner that could take off at max load and climb to service ceiling without having to nurse it up to the higher levels as weight came off............how true that is I can't say but it shows that earlier types were not able to do this.

Another type of clearence I would here is being to told clim to a higher level at a given time which could be 30,40, 50 minuetes ahead.

In this case I would go for overload but you can checj this.

Do as you have been doing and when you get the problem, paused the sim, reduce the load and see what happens.

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Reply #14 - Jun 11^th, 2010 at 11:04am

DaveSims Offline
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Clear Lake, Iowa

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garryrussell wrote on Jun 11^th, 2010 at 10:41am:

When 747-200 were common I often heared the pilots ask for a higher lever say from 270 to 290 and the controller say he could have 310 but the reply was negative I'm too heavy at this time.

I remember at the time the 767 went into service it was said it was the first commercial jet airliner that could take off at max load and climb to service ceiling without having to nurse it up to the higher levels as weight came off............how true that is I can't say but it shows that earlier types were not able to do this.

Another type of clearence I would here is being to told clim to a higher level at a given time which could be 30,40, 50 minuetes ahead.

In this case I would go for overload but you can checj this.

Do as you have been doing and when you get the problem, paused the sim, reduce the load and see what happens.

As airline aircraft have developed, the have more power to climb to the higher altitudes. 20 years ago, you would rarely see an airliner above FL350, while today it is common to find many all the way up to FL410.

Dave

www.flymcw.com

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