Simviation Forum - Airspeed Drops before service cieling???

Sep 29^th, 2003 at 7:42pm

Simviation2003 Offline
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IFR is the most demanding
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North West NSW Australia

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Hello Fellow Aviator's,

I haven't had time to check all my aircraft, but I notice the CRJ-200 and my Boeing 737-300 have a sevice ceiling around the FL 380.

I would like to set my cruise speed at 0.74 - 0.81 MACH (423 to 460Kias) at FL 33 to 360.

I can hold these speeds from transition level up to around FL240, then the KIAS starts to drop dramatically.

The best speed I can get at FL330 is 349 Knts.

Is this a common problem, or is there something I can do to rectify this.

Hoping to hear from some one soon.

Thanks in advance

SV2003

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Reply #1 - Sep 29^th, 2003 at 8:26pm

KnightHawk Offline
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Ontario, Canada

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I'm not sure of a solution on this but I have had the same problem with a boeing 737-200. As I get towards a high altitude I can't reach a high speed.

Hawk

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Reply #2 - Sep 29^th, 2003 at 11:50pm

emh8 Offline
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Minneapolis, Minnesota

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SimV2003,

Could you specify which model of 737-300 and CRJ-200 you are having trouble with?

With some add-ons there have been documented problems maintaining airspeed at the higher altitudes, so it's not unusual.

You might want to check your vertical speed setting. If you have it set initially to 1800-2000 fpm, you might have to reduce it to 1200 fpm or lower above FL240.

Good luck

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Reply #3 - Sep 30^th, 2003 at 2:46am

Simviation2003 Offline
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Thanks both of you

I will try decreasing the VS at or above FL 240, if it doesn't work, I will post the specs of the aircraft in question..

SV2003

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Reply #4 - Sep 30^th, 2003 at 7:46am

Nexus Offline
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Quote:

Hello Fellow Aviator's,

I haven't had time to check all my aircraft, but I notice the CRJ-200 and my Boeing 737-300 have a sevice ceiling around the FL 380.

I would like to set my cruise speed at 0.74 - 0.81 MACH (423 to 460Kias) at FL 33 to 360.

I can hold these speeds from transition level up to around FL240, then the KIAS starts to drop dramatically.

The best speed I can get at FL330 is 349 Knts.

Is this a common problem, or is there something I can do to rectify this.

Hoping to hear from some one soon.

Thanks in advance

SV2003

My speed at FL400 is mostly around mach 0.78.
Depending on windspeed this would be about 240KIAS. The groundspeed, however is 445kts.

So I'm guessing you have mixed up true airspeed and indicated airspeed. ???

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Reply #5 - Sep 30^th, 2003 at 9:14am

Saratoga Ex Member

Ya it sounds like he mixed them up. My suggestion is maintain 230-250 KIAS in a climb all the way up. Upon reaching cruising altitude, set 300KIAS below FL320 and 275 above FL320 and work it from there. G'Day! Wink

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Reply #6 - Sep 30^th, 2003 at 9:59am

Redwing Offline
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Quote:

I can hold these speeds from transition level up to around FL240, then the KIAS starts to drop dramatically.

Has to do with density altitude.....because air density decreases with an increase in altitude, your True Airspeed will be faster than your Indicated.

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Reply #7 - Sep 30^th, 2003 at 6:39pm

JerryH Offline
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Bellevue, WA USA

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SV2003,

There is no question that an airspeed of 423-460 knots at FL330 is actually Knots True AirSpeed (KTAS) and is not KIAS. At that altitude, 349 KIAS is at or near the maximum speed of the B737. As a pilot, you must use KIAS to fly the aircraft safely. KTAS doesn't matter to the pilot, except for calculating how long it will take to get to his destination (taking winds into account). The entire subject of KIAS vs. KTAS vs. Ground speed and wind speed, etc., is a difficult subject to address in these forums and usually ends up in a confusing mess. I'll try not to add any more to the confusion today.

As to your first question, if you are losing airspeed, you Must reduce the VSI setting. You should continually monitor airspeed during climb and gradually reduce the climb rate (VSI setting). It is just as easy to stall at high altitude as it is when close to the ground. Also, service ceiling can only be reached if the aircraft is at the correct airspeed at that point. Most FS literature never addresses these details.

The service ceiling of an aircraft is limited by the weight of the aircraft. If the service ceiling you are trying to reach is a number that came from some performance specs, did it also specify the aircraft weight that corresponds to that ceiling altitude? My guess is that you may be trying to reach the maximum service ceiling specified for a very light aircraft, while flying that aircraft at a very heavy weight. It won't ever happen.

One more suggestion. If you don't already have it, try to find the operational climb speed schedule for the aircraft you are flying. For example, the FS2002 default B737-400 above 10,000 ft should gradually accelerate from 250 KIAS to 310 KIAS. It should then maintain 310 KIAS until reaching Mach 0.75. At that point, maintain the Mach number at 0.75 by further reducing the VSI setting until you reach the point where you run out of climb rate. It may take an hour of climbing to truly reach the service ceiling, defined as the altitude where you can only maintain a climb rate of 100 fpm. A ceiling defined by a climb rate of 500 fpm or more may be a better target.

Hope some of this helps you.

Cheers,
JerryH

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Reply #8 - Sep 30^th, 2003 at 7:08pm

Simviation2003 Offline
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IFR is the most demanding
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North West NSW Australia

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Roger that fella's,

Thanks very much for your input.

I shall try reducing the VS rate.

How do I know what my weight of the aircraft is??
I have no PAX loader or nothing, I just put some fuel in it and off I go!!!!

Thanks again

SV2003

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Reply #9 - Sep 30^th, 2003 at 11:32pm

JerryH Offline
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Bellevue, WA USA

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SV2003,

For some reason, it takes some work to find the weight of an aircraft. At least I don't know of an easy way. To start the process, look in the aircraft.cfg file using a text editor like Notepad. Part way down the file is the (Weight_and_Balance) section.

Max_gross_weight=XXXXXX (This tells you nothing about the actual weight in the sim; only someone's idea of a maximum.)

Empty_weight=XXXXXX (This is the total weight of the aircraft with no fuel, PAX or cargo.)

Station_load.0=XXXX,0,0,0 (This gives you the weight and x, y and z CG location of all PAX, crew, payload, etc. There may be only one or many station_loads specified.)

Last, when you select the aircraft, click on the fuel selector to view the gallons and pounds of fuel in each tank. Fuel in each tank can be reduced, but it may cause an imbalance if not done correctly. Fuel status can also be checked enroute by going to the 'Aircraft' menu and selecting fuel.

The Total Gross Weight of the aircraft when the sim starts:

Gross Wgt = Empty_weight + Station_load.0 (+ load.1 + load.2, etc.) + Total fuel

There has to be an easier way. If anyone knows how, please let us know.

Cheers,
JerryH

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Reply #10 - Sep 30^th, 2003 at 11:45pm

PSW Offline
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Project SkyWorks - Just
Plane Better !
Canada

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Hello SimV,

I don't fly high altitudes because I fly short Air Canada,Air Canada JAZZ & Air Canada ZIP routes,I usually take an Airbus 319-100,Airbus 320-200,Boeing 767 (all models except 400) or Boeing 737-200 to the skies at no more than FL250.What I usually do is before takeoff,I put on my parking brakes and flaps and give it a full boost and let the jet engines run for a little while,then it should give a good acceleration speed so you dont lost much speed at climbing and hopefully,you don't have that airspeed drop problem again.Hope this helps !

PSW

James

[size=2]&&James Jaw&&President & Founder&&Project SkyWorks&&

&&&&

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Reply #11 - Oct 1^st, 2003 at 1:49pm

gilbates Offline
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Fly Hyperion
UK

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or it could be a setting somewhere thats got messed up for that plane

i had the same with a 737-500 as i climbed the airspeed indicator would drop , and i`m not on about FL330 sort of height it was more like 0 ft and upward as i climbed from takeoff

i even called an emergency once on-line at a german airport , thinking my undercarriage was hanging off or something ,

a re-install of the same plane cured the problem however Grin

did yiu konw taht aoccdrnig to rscheearch at an&&Elingsh uinervtisy, it deosn't mttaer in waht oredr&&the ltteers in a wrod are, the olny iprmoetnat tihng&&is taht the frist and lsat ltteer is in the rghit&&pclae. The rset can be a toatl mses and you can sitll&&raed it wouthit porbelm. Tihs is bcuseae we do not&&raed ervey lteter by it slef but the wrod as a wlohe.&&Cool eh?&&

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Reply #12 - Oct 2^nd, 2003 at 1:32am

Simviation2003 Offline
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IFR is the most demanding
challenge a man can face
North West NSW Australia

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Posts: 126

Thanks Fella's,

Atfer a little research, I have found a formula which I think a lot of you might want to take a look at.

Understanding that KIAS is differnet to KTAS at high altitudes due to the density of the air, Your KIAS will show an incorrect reading and will increase to do so the higher your altitude.

This formular is used to calculate your KTAS regardless of Head/Tail winds.

TAS = True Air Speed
IAS = Indicated Air speed

IAS x 2% x ALT/1,000ft + IAS = TAS

Example: If your KIAS is 300 and your altitude is 20,000 ft, you would calculate the following::::::

300 x 0.02 x 20 000 / 1000 + 300 = 420 kts TAS
^
( / ) Divide ----------^

It's funny how I asked the question in the first place, but when finding information that would help others, I'm the first to share.

Hope it helps, and thankyou all

SV2003

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