High weight cruise altitude capability

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canuck
Airman
Posts: 37
Joined: 06 Aug 2008, 23:53
Location: Vancouver, BC, Canada

High weight cruise altitude capability

Post by canuck »

Hi to all, first post in a long time.. Hope I don't screw it up :D ..
Attempting a very an old KLM schedule from 1957, LPAZ to SVMI.. flight plan is 12:06 with full tanks.. Loaded up, and gross weight is 88,900.. Power settings (pg 138) indicates that I should be able to climb to FL140 at this weight.. I tried @ FL90 and FL70, and was unable to maintain airspeed unless I used power settings from 'constant power schedule' (pg 140) @ 2300/145.. I was finally able to find reasonable cruise at FL50 with the following power settings.. 1840/145 which gave me a fuel flow of 530lbs/hr/eng and 180kts, OAT was +7C.. 'Power setting' page indicated for FL50; 1840/141 475lbs/hr/eng and 188~190kts.. Is there a 'Weight/Altitude/Temperature' chart that will highlight altitude capability? Am I seeing proper results for 'high weight' cruise performance?

Glenn
Propliners Rule !!..

flapman
Staff Sergeant
Posts: 457
Joined: 10 Oct 2013, 21:35

Re: High weight cruise altitude capability

Post by flapman »

I had a think about it, and your scenario sounds a lot like an encounter with icing. Can you describe the weather conditions during the climb?

canuck
Airman
Posts: 37
Joined: 06 Aug 2008, 23:53
Location: Vancouver, BC, Canada

Re: High weight cruise altitude capability

Post by canuck »

OAT at FL50 was +7C, route was over water, and there light scattered cumulus in the vicinity.. I'm pretty sure there was no icing issue..
Propliners Rule !!..

flapman
Staff Sergeant
Posts: 457
Joined: 10 Oct 2013, 21:35

Re: High weight cruise altitude capability

Post by flapman »

Hmmm....

FL090-FL050=4,000ft. At 2°C/1000ft that's a drop of 4x2°=8°. 7°-8° = -1°C at FL090. Assuming a standard temperature lapse rate. Below freezing. At 7,000ft it's 3°C. Above, but not by much. Scattered Cumulus you say?

Well, it's one possibility. But it doesn't sound right either way. My experience is you should be getting above at least FL100-FL120 no problem, even at max weight. Having to drop all the way down to FL050 doesn't seem right.. unless the air there was warm enough to shed the ice.

Your statements support that the engines were at least making sufficient power for the flight. Ice on the propellers could explain the reduced thrust with that power, I'm not sure what else could cause a loss of thrust with those RPM/BMEP values.
The next place to look is drag. The obvious culprit would be cowl flaps. Was Larry manning the panel back there?

What type of speed are you stating here? Indicated, True, or Ground?
What was your speed in the climb?

TreeTops
Master Sergeant
Posts: 1086
Joined: 07 Apr 2010, 06:13

Re: High weight cruise altitude capability

Post by TreeTops »

Also, are you using a weather program?
Cheers
Trev

canuck
Airman
Posts: 37
Joined: 06 Aug 2008, 23:53
Location: Vancouver, BC, Canada

Re: High weight cruise altitude capability

Post by canuck »

Well thanks for all the questions, made me realize that I needed to do a real second pass at the problem.. For all my flights which reinact schedules of the past, I would always 'save' the flight at the destination, then 'load' from the saved flight for the next leg.. So for my second pass, I started from scratch, selected the aircraft, departure airport, gate, time of day and date.. Long and short of it, climbed FL130, departing with a gross weight off 88300.. Other than starting from scratch, I did not load a program I have called 'Little Nav Map' at the start of the flight, and I exercised the props a few timebefore starting the takeoff.. My weather program is AS16.. I recorded all the specifics, but as all went well, don't want to bore you guys with them.. At TOC, set power 2040 rpm and BMEP 130 (vs 127), fiel flow 565lbs and MP 26.5 inches.. Airspeed slowly decayed from 180 to 169KIAS.. Increased power to 136 BMEP and 560lbs/eng, and speed slowly inceased to 175~179kts which gave a TAS of 217kts with an OAT of -3C.. I then started up Liitle Nav Map and everything continued perfectly.. After 2 hours 32 minute in flight I was indicating 179 kts and the power had crept up to 138 BMEP and 580 lbs/eng..

Basically it would appear that with the L049 I need to start each leg from scratch rather than loading from a saved flight..

Thank you to all who replied, your questions lead me down the right path.. :D
Propliners Rule !!..

TreeTops
Master Sergeant
Posts: 1086
Joined: 07 Apr 2010, 06:13

Re: High weight cruise altitude capability

Post by TreeTops »

Starting from scratch is always the first thing to try with the A2A planes. Glad things are sorted for you.
Cheers
Trev

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