IFDG/PIC question

[Guest putput28]

This evening I was on VATSIM doing my first flight with the IFDG 757/PIC merge in Delta NNC. I was flying from PHL-TPA and climbing to my cruise altitude of FL390. As I began to pass FL240 I noticed that my speed began to decrease. It got bad enough that I had to stop the flight. I have tried using the PIC merge with the PIC Aircraft CFG and the original IFDG CFG modified to go with PIC but this still happenes. If you have any advice, suggestions, comments, they will be greatly appreciated. Thanks!Putput28 :-wave

[marcom]

A screenshot would really help in a case like this.-Were you using VNAV?-Speedbrakes down?-A/T on and @ max N1?Regards,Mark

[Guest putput28]

I checked to make sure the spoilers were not down and the gear was not down. Nothing seemed to be wrong. I had a/t on and the engines were at max (103% N1) trying to maintain speed. I did not have VNAV on...just LNAV. I was at about a 30 degree angle of attack tryig to climb and hold 200IAS but I could not go any higher. The speed kept going down so I gave up. I tried leveling off but it did not help either.Putput28 :-wave

[crvm]

Yes I had one hell of a time getting up high myself. Are you heavy? Try burning some fuel first then resume your climb. Best Wishes,Randy J. [email protected]" A little learning is a dangerous thing"AMD XP 2100 |MUNCHKIN 512 DDR RAM |ECS[/b ] K7S5A MB |[b]GF3 64 MEG |WIN XP PRO |MITSUBISHI DIAMOND PLUS 91 19"

[Guest putput28]

Actually I was not that heavy. 20% in the left/right fuel tanks and 40 in the middle. I think my total weight was in the low to mid 200,000.Putput28 :-wave

[marcom]

Were you using Vertical Speed?That can be very dangerous and Boeing also recommends never to use V/S in climb.Three reasons:a) You have absolutely no stall protection. Should your speed become too low, (engine failure, windshear etc) then the plane will stall itself, with the trim full aft. You'll have one hell of a time getting out of that mess. VNAV and FLCH both have stall protection.:( Overspeed. If your set V/S is too low, you can easily overspeed the aircraft. Again, VNAV and FLCH both have overspeed protection, even for flap and gear settings.c) Induced drag. Should you become too slow (but not quite a stall yet), you might end up not being able to accelerate anymore, like in a situation you describe. This is the induced drag. It grows as airspeed decreases. Its important to stay above induced drag curve. Acclerating from the induced drag airspeed can be very difficult. You might have to descend! Again, FLCH and VNAV maintain a constant A/S.You can use V/S in a descent, but shouldn't use it in climb.Now, if you were using FLCH, then disregard the entire thing ;-)

[Guest putput28]

I just have one problem with your explination. When ever I do not use VNAV on PIC, this never happenes. I think that it is more of a CFG/FDE type thing, or maybe I merged it wrong. I am not saying that what you said could not happen, It just has never happened in all the times I have ever flown PIC.Putput28 :-wave

[Guest RyHoffman113]

I've had similar problems in the climb, but not as extreme as Putput's. Earlier today, I was flying LAS-DTW in a 5 with the new PW FDE. Around 35000lbs of fuel, haven't changed any weights in the FDE. Climb performance with VNAV under 10k was a bit over 3000fpm with full climb thrust maintaining 306kias, maybe just a bit below realistic. Climbing thru FL280 or so, v/s decreased to 500fpm and stayed there for the remainder of the climb to 370, but around FL300-310 the airspeed started decaying and continued to do so, still climbing at 500fpm. Airspeed kept decaying all the way up to FL370, climbing at 500fpm the whole time. I checked and the airplane was in a clean config, no flaps no gear no speedbrakes, even made sure the doors were closed. I know that a 5 must climb better than this. What might my problem be?????Ryan Hoffman

[Guest Van]

IFDG modeled the P&W 2037's with only 36,600lbs of thrust, which is quite a bit less powerful then the RR variant, but there are three series of P&W 2000's that power the 757. There is also the 2040's (40,100lbs thrust) and the 2043's (over 43,000lbs thrust)I changed the thrust ratings in my .air file and aircraft cfg to match the 2040's thrust as I find the 2040's to be a happy medium and the power is pretty much the same as the RR variant. So for people not happy with that slow climb, simply bump up the thrust to match either of the two more powerful P&W 2000's and you'll be all set.I also remember Iz saying that the FDE for the RR and P&W models were identical other then the thrust ratings so bumping the thrust up won't have any adverse affect on the FDE other then more power.Regards,Van LatendresseYeoDesigns Panel/FDE Designer

[teropa]

Van,It's really not a question of the 2037s being not powerful enough, but them being not as powerful as they should. The 757 is the most overpowered western passenger aircraft and this goes also for the 2037 version, although the RRs, 2040 and the 2043 indeed are more powerful. There's something wrong with the 2037 climb performance, and I just can't simply change the numbers to meet my liking. I'd like to know the reason to this problem, and it also raises the question if the RRs themselves are equally not as powerful as their real-life counterparts. People just don't think about it, because they are powerful enough not to make one alarmed. It would be nice if someone had tested the RR against real-life figures to see if there are similar problems in the RR model after all.rgdsTero

[Guest Van]

I think another thing to look at is the inlet_area = 55.000thats in the TurbineEngineData portion of the aircraft cfg. I believe 55 square feet may be too large for a P&W 2000 series engine. The higher the inlet area the less power you get. I remember seeing FDE's for a 737-200 that had the correct thrust rating for the P&W jt8d9's (14,500lbs thrust) but the inlet area was left at 19.6 which was a correct inlet area for the newer CFM56 engines, but way off for the old jt8d9's which has a much smaller inlet area of about 9.8. Once the appropriate inlet area was entered into the turbine engine data section the plane would finally climb and perform like it should. Now I'm not saying that 55.0 is definately wrong, but worth a look. I know I've seen many FDE's for the 767-300 with an inlet area of 48.0 and we all know that a 767-300's engines are quite a bit larger then a 757's. I also remember Iz saying that he created the FDE with the RR variation that he flies in real life in mind and simply changed the thrust rating for the P&W model and nothing more.Food for thought.Regards,Van LatendresseYeoDesigns Panel/FDE Designer

[Guest RyHoffman113]

Just taking a look at the FDE that came with the PIC package, I notice that the inlet area for the engines is 61, yet the static thrust rating is 61200, more than 24000lbs more than the PW2037. On another note, according to the Pratt & Whitney website, the PW2037 is rated at 38400lbs of thrust at sea level. Now if the "at sea level" part makes a difference, I don't know. But Boeing's site DOES show the 2037 as having a rating of 36600lbs. So which is right? NWA flies PW2037-powered 757-200s, so perhaps BBall can clear this up for us. I do believe he wrote awhile ago that the 2037s were rated at 38200lbs of thrust, awfully close to what the P&W site says.Ryan Hoffman

[Guest]

Mabey you have something. I have looked in the aircraft cfg of AIR TRANSAT that i have and the inlet area is 24.000 and i tell you this is a rocket.I have seen many times 6000ft per minute.