Yes, N1 is important (it is the "propellor" if you like generating most of the thrust) but it doesn't tell the whole story of the thrust output, which EPR does (EPR is the ratio of the input air pressure to the output air pressure).http://www.grc.nasa....rplane/epr.htmlhttp://www.grc.nasa....lane/thsum.htmlRemember that the higher N1 value is in thinner air, compared to the lower N1 at lower altitude, in thicker air. The net thrust is probably the same but without measuring it it is very hard to tell, yet is very important in this discussion.Best regards,Robin.

Forgetting the N1 value, the value that counts is N2, or core RPM. This is what keeps the engine running and must not fall below a minimum value otherwise it becomes unstable. It is fairly consistent at each altitude compared with N1:N2 vs. N1:* 65.3% vs. 44.2% (FL360)* 63.8% vs. 35.2% (FL200)* 64.1% vs. 32.6% (10000 ft)

That's all well and good and my Kroes and McKinley Turbine Powerplant books would agree. But where are the N1 numbers coming from? I don't mean how does an engine work?, I mean is that 44.2% realistic? I'm saying it's high. I could be wrong, but I've seen less than that at TOD.

I just checked and confirm the exact N1 value at fl360, but I must do the test again because I forgot to use clear skies and there was (a pretty costant) tail wind.

Wind will not affect the rate of deceleration, only the distance, which is easily computed if you know what the wind is. :)Time is more important!! In 60 seconds you lost 33 kts at FL360, and 39 kts at 10000 ft.The whole "x kts per nm" is useless anyway. For a start your GS is higher at FL410 than 5000 ft so right there the figure is screwed, and that doesn't allow for any wind (e.g. you could have a 140 kts tail wind or head wind if you are in the jetstream at the moment you decide to decelerate).If you have a speed/altitude restriction, descend first, then level off and decelerate. You may need the higher speed to get down. If you decelerate first, you may not have the distance to make the altitude restriction before crossing thanks to the reduced rate of descent.A good ball park is 3x your altitude in thousands of feet to lose, to start your descent. If you need to decel add 10 nm to this to allow deceleration. In 1 minute at 300 kts you travel 5 nm. so if you need to lose 15000 ft, Start down 45 nm back. If you need to decel start down 55 nm back, and you should be good.Best regards,Robin.

As told the winds were pretty costant (25kts in the first 2 test, 22 in the last) but if there was a change in wind direction/force during the deceleration, it surely affected the results.

As far as slowing, down low I expect approximately 1nm to slow 10knots.

The whole "x kts per nm" is useless anyway. For a start your GS is higher at FL410 than 5000 ft so right there the figure is screwed, and that doesn't allow for any wind (e.g. you could have a 140 kts tail wind or head wind if you are in the jetstream at the moment you decide to decelerate).

"Down low" meaning on vectors for the approach. "Approximately" meaning it's a rule of thumb, not a galactic constant.

@Spin737: I didn't even see your post. With him being concerned about deceleration rate with respect to distance it seemed he had this rule of x kts per y nm in his head at the time, which is not very useful for this particular discussion.

But where are the N1 numbers coming from?

In the sim, N1 vs. N2 vs. Mach tables IIRC, unless the figure we see on the display is computed by PMDG and totally seperated from what FSX is ultimately doing (which I hope is the case as FSX leaves a lot to be desired in just about anything to do with physics of flight).Best regards,Robin.

Engine data on the NGX is a totally custom routine, we are not using the FSX turbine/N1 model.To the OP in this thread - yes the drag characteristics are correct. This addon was tested and commented on extensively by about a dozen real world NG pilots during development. We ran extensive testing in a real level D simulator as well. In fact, one of our tester pilots, Jack Colwill, post a video a while back on descent techniques - he was able to do exactly what he does in the real airplane in the NGX. Simmers are used to addons that have very unrealistic drag characteristics where the spoilers are these magic things that can slow you down while in a 2500fpm decent. That's completely wrong, ask any real pilot.Everything in this product is based on actual Boeing performance data that we paid a lot of money for - it's within 5% or so of those tables, which is as good as we could do given some FSX FDE limitations - you can't 100% replace everything in the sim with custom routines unfortunately. (and I mean 5% of the predicted values in the tables, not 5% N1 - it's a very small difference if there is one)If you want something that slows easier, get the 600/700 addon - the 700 has different characteristics because of its lower weight and shape. It's the best flying one of the four of them if you're looking for the ability to slow down easier.

During testing I flew the SEAVU arrival into KLAX (which I fly almost every trip in the real plane) numerous times and compared it to what I see in the real plane as far as descent rates and deceleration NGX is very accurate in it's performance. I used the same techniques I use in the real plane and saw the same results. The 737 is just very difficult to slow and get down at the same time.

I used the same techniques

Can you tell us what techniques you operate to land safely or maybe if you already done that what link you describe the process.Here there is an interesting video maybe there are other technique.http://vimeo.com/27673259

Edited February 9, 201214 yr by simbio

The main thing I do to slow the plane is level it out when I want to decelerate. I try not to extend the flaps too close to their max speeds but they help with the drag so I extemnd them when I can. My technique usually takes me above the VNAV path but I raraely have too much trouble getting back down to it before the final approach fix. If it is looking close I will extend the gear for additional drag. Of course I hand fly that arrival which makes it easier to make the plane do what I want that trying to get the autopilot to do it.

3-2-1-Now, on 08 February 2012 - 04:08 PM, said:Go down or slow down. Pick one. :)That sums it up. My friend, a 737-400 captain, says you can descend in a 737, and you can slow down. But you can't do both.

Zach, I hope you don't think Robin is a 737 400 captain. he's not! :( Trust me!

Edited February 10, 201214 yr by martin-w

@Spin737: I didn't even see your post.

Cool beans.