First off, I want to say that this product is so freakin amazing and has renewed my passion for FS realism.

 

There is one thing, however, that is bothering me with this otherwise polished product.

 

I was experimenting with the effect of different flap settings in straight and level flight, at constant speeds just to see how much lift and drag they create, so I could know what kind of forces to expect when hand flying.  I was flying with the -800WL model, straight and level at 4000' at flap1 speed with flap1 extended (164kts, I was fairly light). I was interested in how much lift and drag would be created if i went to flaps5 and kept constant speed and altitude. When selecting flaps5, there was no change in lift, and no spool up from the engines to maintain speed while on autothrottle. Then, a few seconds after the flaps had already completed their travel to flaps5, I started seeing the effects. A small jump in VS, airspeed starting to drop, and the autothrottle compensating for it. I did this back and forth several times from flaps 5-1, 1-5, watching the flap position indicator, and the flaps on the wings themselves.  The indicator and the external visuals seem to match up, but the effect from the flaps seems to lag a few solid seconds behind for some reason. Just wondering if this has been noticed by anyone else, and if this is something to be looked at for SP2.

 

Other than that, it's awesome!

 

Then, a few seconds after the flaps had already completed their travel to flaps5, I started seeing the effects.

 

It takes a while for the flaps to travel from 1-5.  Chances are, in order to keep from completely hosing end-user computers, they just told it to understand the lift/drag values of the flaps at 1 and at 5, but spared the computer from calculating everything in between.

 

Just a thought.

I understand all of that. But what I am saying is that after all of the flap traveling has happened, it still takes a few extra seconds afterward for the effects to kick in.

 

Then, a few seconds after the flaps had already completed their travel to flaps5, I started seeing the effects. A small jump in VS, airspeed starting to drop, and the autothrottle compensating for it. I did this back and forth several times from flaps 5-1, 1-5, watching the flap position indicator, and the flaps on the wings themselves. 

 

Hi William,

From what I recall from the RW guys, the 737NG is a very slippery girl and the a/c takes a bit to slow down due to being very drag efficient. Looking through the FCTM, confirms it may take several seconds before speed changes when a flap setting is established.

 

"•flap retraction and extension schedules provide speeds that are close to minimum drag, ....In level flight they provide a relatively constant pitch attitude and require little change in thrust at different flap settings."

 

and when planning for approach....section 4.21 climb, cruise descent and holding..."Losing airspeed can be difficult and may require a level flight segment. For planning purposes, it requires approximately 25 seconds and 2 NM to decelerate from 280 to 250 knots in level flight without speedbrakes. It requires an additional 35 seconds and 3 NM to decelerate to flaps up maneuvering speed at average gross weights. Using speedbrakes to aid in deceleration reduces these times and distances by approximately 50%."

 

So, maybe the PMDG guys got it correct, it takes several seconds after a flap selected setting to cause a corresponding airspeed reduction/increase due to the aircraft lack of drag. The aircraft is very heavy, so its inertia combined with being very slippery means any added drag has to overcome this inertia, which take time. Anyway, my view. 

 

Regards

yeah, i know all about the slipperiness (is that a word?) of the aircraft. I don't have any problems flying the aircraft and slowing down like some others here have. I just find it odd that after the flaps have reached their setting, there is still a delay of a few seconds, and then all of a sudden the effects of the extra drag/lift (which actually lift=drag too) take effect.

It's just an odd quirk in my eyes, if it is even a quirk. Not detrimental by any means.

 

by the way, I am not trying to sound like a know-it-all.  It's just that I've followed these forums for years, and only just recently purchased the NGX. However, I've been reading all the feedback about the product and all the user "complaints" about how the product flies, when it's really just the way their flying it that's the problem. I just haven't see anyone post about this quirk that I have experienced.

Yeah, I recall seeing a comment about wing flex and it seemed to be pretty flat at take off and then when some metres off the ground, the wing lift would happen. I suppose difficult to actually program a gradual incline with ground speed increase. Maybe the same issue with flap/speed/action response. While PMDG say this bird is as real as it gets,I guess we have to give them some leeway. Still, I think she aint too bad.

 

Regards 

As far as I can tell, wingflex is triggerred by actual lift, and lift does actually increase pretty massively at rotation, that might be the reason why you feel it happens only few meters off ground.

 

As for flaps effect "lag", consider inertia and reaction lag of the computers (A/T and AP)

 

I was interested in how much lift and drag would be created if i went to flaps5 and kept constant speed and altitude. When selecting flaps5, there was no change in lift, and no spool up from the engines to maintain speed while on autothrottle. Then, a few seconds after the flaps had already completed their travel to flaps5, I started seeing the effects. A small jump in VS, airspeed starting to drop, and the autothrottle compensating for it.

The only way to see what you wanted to see is to do the same test hands free, with AP and A/T off.  Use them to trim the aircraft out at Flap 1, then disengage them.  Now if you select flap 5 you will see the aircraft begin to respond before flaps reach 5.  By using AP and A/T to maintain speed and altitude they are masking the effects of the flaps.

The only way to see what you wanted to see is to do the same test hands free, with AP and A/T off. Use them to trim the aircraft out at Flap 1, then disengage them. Now if you select flap 5 you will see the aircraft begin to respond before flaps reach 5. By using AP and A/T to maintain speed and altitude they are masking the effects of the flaps.

Yeah, already ahead of you on that one my good man. I tried it that way, and there was still almost a 3 second delay between the new flap setting being completely set and completing movement, and the effect that the flaps had on the airplane. It is just odd is all. I'll take a 737 pilot's or PMDG's researchers' word for it if that is the case in real life. It is just not what I am expecting considering my real world flying experience (no airliners.....yet lol) and when I logically think about the physics of the situation.

Still love the plane!

Yeah, already ahead of you on that one my good man. I tried it that way, and there was still almost a 3 second delay between the new flap setting being completely set and completing movement, and the effect that the flaps had on the airplane. It is just odd is all. I'll take a 737 pilot's or PMDG's researchers' word for it if that is the case in real life. It is just not what I am expecting considering my real world flying experience (no airliners.....yet lol) and when I logically think about the physics of the situation.

Still love the plane!

Glad you got there before my post.  The fact is there will be a delay between the flaps reaching their final position and the full effect of that position being felt in attitude changes.  Rather like if you slowly ramp in a small wheel input it takes time for the roll rate to build up to the final value.  You won't reach peak roll rate until after the final wheel position is reached.  This delay is partly due to inertia, partly to aerodynamic damping.

 

You can see the NGX beginning to pitch while the flaps are in transit, so clearly the effects begin as the flap is moving, not when it reaches the final position.