Approach Vertical speed fluctuations

[BigBadStato 1]

Captains,

When I disconnect the autopilot to handfly my approach I get big variations in vertical speed and can not get it to hold a steady descent profile....I'm aware of the fbw trim indicator and I have it positioned for my approach speed but no matter what I do it wont sit steady...it'll drop the nose and all of a sudden im descending at 1500fpm so I intervene and pull the nose up a little and it then reduces the sink rate to the point where i end up high..so basically i end up wallowing up and down the glideslope...anyone have a similar issue? Do i have a bug..need a fresh install? 

Just for comparison, I have no problem in hand flying and getting good steady descent profiles in the 737 and MD-11 

Thanks in advance

John Davis 

[downscc 1,327]

 

 

Do i have a bug..need a fresh install?

 

Funny how many think this will make the simulator straighten up and fly right.  No, but you need to watch your speed and don't chase the IVSI (instantaneous vertical speed indicator), it's not a primary flight instrument.  You didn't mention type approach or when disconnect A/P and if you are using A/T.  The T7 flies like a big Cessna in many respects.

[skelsey 765]

I don't have the T7, and I don't want to cast aspersions on your hand-flying ability, but this sounds rather like PIO to me.

 

I know that when I moved from the LDS 767 to the PMDG 744 I found the extra weight and inertia took a bit of getting used to. Small, smooth corrections are the order of the day: I would agree with Dan that it's best not to chase the IVSI. Move the controls, hold the input, wait for the aircraft to respond. It sounds to me like you're overcontrolling.

 

As I said in another post on a similar topic, it's best to learn the datums for the aircraft and aim for them, with just small corrections. To give you an example, the Jumbo at 250 tonnes likes to fly down a 3 degree glide slope at Vref+5 with the pitch reference square just sitting on top of the 2.5 degree pitch line and 1.15 EPR with flap 25: with flap 30 the pitch square sits more or less underneath the 2.5 degree line with 1.20 EPR. If you fly those numbers, with just very small corrections (no more than a degree or two up or down on the pitch, and little if any thrust lever movement), you'll generally have a consistent, stable approach on speed and on the glidepath. I imagine somebody else would be able to provide you with the equivalent numbers for the 777, or alternatively let the autopilot fly an approach and landing and make a note of the appropriate values.

[BigBadStato 1]

Gentlemen, 

Whilst I didn't want to hear it, I think you were both right. Not so much over controlling but more so incorrect use of the trim...I was in the middle of typing my rebuke when I thought I better go and do some testing before I argue with you. I have found what I was doing is rather than progressively trimming as the airspeed bled off, I was simply trimming too much...ammature mistake, thanks for helping me realize what I was doing...a bit too used to the MD-11.

Sim pilot since 2008, always learning....I need to go and have a good hard look at myself...

Cheers

John