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View Full Version : Setting N1 thrust on final


jetjockey696
1st Sep 2007, 09:36
Hi Guys

I am line training right now, my friend has this new instructor he decided a new way of setting N1 thrust for target speed when he DESELECT SPEED to him.

What he does is to take ground speed and divide it into two and add/substract (can;t thin which is which) 5 from it...this gives you a number around thrust N1 you need to start with.

Has anyone heard of this technique?

Please feel free to expand and fine tune this technique.

tQ

JJ696

sebxl
1st Sep 2007, 10:23
It has nothing to do with groundspeed and if you approach at 140 kts and you divide by 2 that is 70% - 5% it will give 65%.But it is more something around 55% like on any other jet.
Tell your instructor to have a seat in the cockpit and actually fly the aircraft, maybe he'll learn the real thing.

robin747
1st Sep 2007, 11:35
Quite true, all Bull----.... instead try the QRH 'Flt with unreliable ASI' and check the N1 readout for that config/wt/conditions, thats more close to actual then all this boomerang...:ugh:

ITCZ
1st Sep 2007, 12:49
The above were helpful in telling you it was BS but they didn't tell you why it was BS. I think you might be confusing two rules of thumb.

Your target speed on final will be a function of your weight. Robin747 is close to the mark - take a look in your QRH or POH and look at airspeed suspect/erratic checklists and tables.

You may be able to come up with a quick calculation that gives an approximate N1 setting for your weight (not speed). We had one in the BAe146-300, it was something like "landing weight plus three take two." Eg, landing weight 36 tonnes. Add "three". 66. Take "two." 64. So set 64%N1 as target for a normal landing at 36 tonnes.

Take a look at your aircraft's tables and see if you can spot a similar relationship.

As for your factoring in groundspeed for your N1 -- don't know why you would be interested in doing this. The aim of a stabilised final approach is to put the aircraft in a steady state condition, and your Vref is a fixed proportion above your Vs for the landing config and weight. You are still airborne and your flight condition is based on your progress through the air, not the ground. The only adjustment you should make for groundspeed is to adjust your vertical speed, your descent rate, to maintain the glidepath.

Pub User
1st Sep 2007, 13:24
The groundspeed is a factor. If you have a strong headwind you will require a lower rate of descent to maintain the approach angle, thus needing more power.

RYR-738-JOCKEY
1st Sep 2007, 14:52
I think what he was talking about is: For a NPA GS/2=req V/S
So if your gs is 150, you'll need about 750 V/S. Works a treat.

Capn Bloggs
1st Sep 2007, 15:02
groundspeed is a factor
Absolutely. A strong headwind will require significantly more power than normal down final.
We use 82% N2 (as it is far easier to set/adjust than N1, since it responds much quicker to thrust lever movements) as a base and then if it's not right, change > check > adjust to come up with the power required on the day. Just like basic IF technique.

bushbolox
3rd Sep 2007, 00:44
FFs. Another thread of theoretical general aviation bolox. If you want to know your vs look at the plate under speed/vs for the published slope. OR
If you need to know your thrust setting in advance look at the qrh. or develop a memory:ok:

Even better as the bloke above alludes to learn to fly and not analyse., if not admit apptitude defeat and join a bank.

I cant believe how many threads are springing up having long winded discussions about stuff that wouldnt be an issue if there was some requirement for flying skill in this job these days.

taperlok
4th Sep 2007, 14:15
never flew B727/737.
from war stories int he pub. On older 737 you used fuel flow to set up speed on finals. ball park figures of course.

john_tullamarine
4th Sep 2007, 23:06
.. learn to fly and not analyse ..

Interestingly, though, it has been my observation that those pilots who think about things a bit and develop (or pinch) useful aides memoire somehow seem to be far more flexible and effective pilots .. I would even go so far as to suggest that "learning to fly" and "not analyse" are mutually exclusive ?

As those in the bridge community will appreciate, a bit like Goren (I think it was) when he observed "the more I practise, the luckier I get ..." It seems pretty much a lemma that such an observation applies to most skilled activities ...

I can only presume that bushbolox, claiming to be an experienced pilot, is stirring the pot a tad ... ?

fireflybob
5th Sep 2007, 01:53
Although target thrust settings for approach are useful I find I hardly ever look at the N1 on the approach these days - with practice it's really thrust lever position thats more useful adjusting as necessary for speed control.

This assumes normal 2 eng operation - in the event of an engine out I find I look at the N1 a bit more often!

Tight Slot
5th Sep 2007, 02:06
Wish I could remember the Airbus ground speed mini maths!!!

PK-KAR
5th Sep 2007, 11:25
With a working ASI, thrust selection really can't be simpler after deselecting A/T... Use last setting, and adjust to get your target speed, and speed trends... *too obvious, I think you guys are talking about something else then*

PK-KAR

RAT 5
5th Sep 2007, 18:06
JJ696.

Flying jets is easier if you are in control of the a/c and ahead of it, rather than letting it fly you and chasing it. When making pitch & power adjustments it is easier to do so +/- a datum using small changes. Thus, knowing dautms and setting them to achieve a given task helps a great deal. You are giving energy to the a/c and asking it to behave as you would want. If you give it the correct amount of energy (datum), and see how it is feeling today, you have a chance of coaxing it into submission, gently. A little more or less, or even find you have chosen correctly, will win the day. Guessing in the dark and pumping the thrust levers is handing control to the a/c and will bring you a troublesome workload. Fly the automatics and watch what they do. The next time you want to do the same thing manually, copy the auto-settings. B737 for level flight in the circuit 6 & 60% works as a starting datum. More drag will require a little more thrust. On finals, trying to keep things simpel and easy to remember I use F30 = 53% F40 = 64% F15 SE = 75%. There are 3's & 3's, 4's & 4's & 5's & 5's. If level on SE add 10% to the 2 engine settings. On finals these numbers work for headwinds of 10kts and normal landing weights. It will take quite a few tonnes to changes these by much, but greater changes are needed for wind effect. i.e. higher Vfly for head wind will need more N1% than a couple of extra tonnes. Tailwinds will require less. This also allows you to sense the wind when noticing the required N1%.
If you set these datums in advance, and watch the a/c's behaviour, then make small adjustments to find 'today's' datum you will be controlling the a/c and not the other way round. Chasing the speed down finals is hard work and not recommended.

FCS Explorer
6th Sep 2007, 07:24
you're not supposed to calculate the plane; YOU ARE THERE TO FLY IT

one hand on the throttle, one on the wheel.

mustafagander
6th Sep 2007, 08:03
Come on guys, there are rules of thumb to make life easier - it's not meant to be secret mens business.

I recall that the B767 had "the numbers" for an approach. No, sorry, I've forgotten!!

AFAIK it's all about getting close quickly, then fine tuning. We fly by performance, not numbers.

Airbusalltheway
6th Sep 2007, 10:32
Avro RJ, typical weather, light headwind +-37t 60%
our 'magic nr' is 60%
all the rest is basic flying skills, your speed drops(steady on the glide), you need power, and vice versa....