Q about 'idle decents' with iFDG 757 V2 and PIC panel

[Guest]

Hello,After flying the new iFDG 757 version 2 (which is such a perfect visual model by the way, sheesh), I'm not able to accomplish decents at idle power as seems to have been mentioned by the flight dynamics' file author. For example, decending from 35,000ft at a cruising speed of M .80, I dial in 10,000ft in the MCP window and select FL CHANGE with a decent profile speed initially selected at M .78 I expected the autothrottles to retard to flight idle and decend at .78M until reaching 295 IAS with a 'comfortable' decent rate of 1200-2000 fpm. I found however that the aircraft had to dive at around 6000fpm and add copious amounts of power to maintain .78M initially. Am I doing something wrong? (yes my flaps, gear and spoilers are retracted and all the windows are down, lol).767PIC doesn't model realworld drag coefficients at altitude but this is a well known limitation. 767PIC is programmed to add power to 'simulate' the actual drag values on decent from cruise altitude. I had thought from what I read on the threads here that the new iDFG 757 flight dynamics actually was able to model proper drag effects and accomplish realistic idle power decents from cruise altitude. My experience so far is that iFDG's V2 757 is as draggy on decent as 767PIC, so much so that I was certain that I was somehow managing to be using the 767PIC .air file with the new 757 :) I checked and rechecked though and I'm definitely using the .air and aircraft.cfg files that were uploaded here at AVSIM with the new 757 packages :) I'm just not experiences the 'slippery' idle decents that everyone is raving about, lolI do love the idle taxiing and the smoothness of the new iDFG 757 though!!!!!!!!! It's wonderful, very stable and easy to hand fly, a very beautiful job of programming altogether from such talented group of people, my gosh. It's so much fun to fly and to just look at! :(

[crvm]

Hummmm. I would not have a idea using FL CH from that alt, seems a bit odd seeing that you would not want to use FL CH for descent above 10000' seeing that you would get fired mighty quick for all the wasted fuel. Best Wishes,Randy J. [email protected]" A little learning is a dangerous thing"AMD XP2100 |MUNCHKIN512 DDR RAM |ECS[/b ]K7S5A MB |[b]GF364 MEG |WIN XP PRO

[Guest Iz]

Hello Suzanne, thanks for the compliments!There does seem to be something wrong during your descent but I don't understand your story completely as you tell it. First of all, check your throttle on your joystick to be at idle and make sure that the joystick throttle is switched off during autothrottle modes in the PIC preferences. But still, during the descent with FLCH, the thrust mode will switch to THR HOLD, which means you get back control over your throttle so you can vary the descent rate a bit.With the throttles at idle, you should get somewhere between 2500-3500 fpm descent, depending on weight, winds, atmosphere and such. However, during the first part when you're holding mach, the nose will drop more to keep the Mach (and IAS increases) so your descent rate may be significantly higher.It is not uncommon to see descent rates at high alts of 4-5000 fpm or even more.Drag coefficients are only in the FDE file, the panel doesn't do anything with that. Still, you might see a little power used during a VNAV descent, I don't have any influence on what type of path the 767PIC FMC calculates.Hope that helps.Iz

[Guest]

Hi Iz,Thank you so much for taking the time to reply. You really did such a wonderful job with the FDE's for the 757's and I'm enjoying them so much as I'm sure so many other people are :)I just don't know what's going on with the idle decent thing in my case. Do you real pilots initially hold mach in a decent from cruise altitude (i.e., would you bring power to idle and pitch down to maintain .78m until reaching 295 kts IAS, ect?) If so, would you initially see the 5000fpm decent you mentioned in your previous reply? Thank you for taking the time to answer my questions Iz, you are so nice for taking the time to put so much effort into this :)

[Guest]

I will definitely check on my joystick throttle settings Iz, thanks!

[Guest Iz]

Hi Suzanne,Well I'm on standby duty today, which means I'm sitting at home and can't go anywhere in case the phone rings and I have to do a flight. My girl flies for KLM so I just waste my time scouring the Avsim forums :)Anyway, since for climbs and descents, the pitch mode controls the airspeed in FLCH or VNAV, we do track Mach and then IAS during the descent. The most economic way is to stay high as long as possible and make a descent all the way to the approach at idle thrust. So if you start at FL420 where your IAS is only 230 knots @ M.800, you actually have to accelerate all the way to 312 knots that we use for descent. High descent rates may be a direct result, but as long as it happens smoothly, it's no big deal.Glad you're enjoying the 75.Iz

[Guest]

Hi Iz,Cool picture! Wow, you guys were way on up there! I was going to ask about your latest reply where you described having to accelerate to 309 kts IAS or so for decent. In the situation illustrated by your picture then, a typical decent would be (if I understand correctly), bring power back to flight idle, pitching down to maintain .80M and holding this attitude until reacing 309 kts IAS at a lower altitude? If you are decending at 5000 fpm at .80M this isn't uncomfortable for the passengers as long as the decent is intitiated in a smooth way?Thanks again as always, I learn so much from talking to real pilots about all this stuff! :)

[Guest Iz]

Hello Suzanne,As you can see, with M.800 = 230 kts @ FL420 to M.800 = 310 @ FL320 (or thereabouts), it means the aircraft has to accelerate with respect to IAS (indicated airspeed). IAS is the main value which affects all aerodynamic characteristics for the aircraft. You need a specific pitch attitude to maintain level flight at a certain speed (and a certain AoA, angle of attack). So whether it's 240KIAS (knots IAS) at high altitude and you're doing M.800 or it's 240KIAS at low altitude and you're only doing M.400, it's the same pitch attitude.So even though we're maintaining, we have to accelerate about 1 knot for every 130 feet we descend. So 1000 ft lower, we need to be about 7-8 knots faster to still be at M.800. And since we need to keep accelerating all the way to 312KIAS, it means we'll be lowering the nose the whole time (this is quite subtle) until we reach 312KIAS, at which point we'll maintain pitch to maintain the 312KIAS. The nose down pitching moment also causes quite rapid descent rates.So while we're accelerating, we might be at a tad less than 1.0 g. This is not so drastic that your stomach is in your throat. It does happen sometimes that the down pitching is a little much and you do get a bit of a rollercoaster feeling but it's not spectacular.Iz

[Guest MB327]

Iz,I just want to add my thanks for your contributions here, not only with the iFDG 757, but your help here on the Forum too. Keep in mind that a lot of the "I am having this problem" stuff is relayed by people just like me who are trying to get use to the new aircraft and learn how to use it.Nice work man - Thanks!edited kaus I kant tipe are spel

[Guest crashing_pilot]

i second that mate,great work,to help us PIC junkies out!!!!have a good one