L60 idle N1 please

[learsimmer]

Would some kind soul tell me the typical idle N1 before taxi for a Learjet 60, and the N1 reading during a Normal Descent?

Many thanks
Nick

[transilvana]

idle is 52% on ground, around 62%-65% on descend, you may get lower as you go down, when you get below 60% then for engine syncro you have to use N2 instead of N1.

[learsimmer]

idle is 52% on ground, around 68 to 73 on descend

Wow! I would have expected figures like that from N2 but not from N1!

Regards
Nick

[learsimmer]

Flight Safety teaches the following 'rules-of-thumb' regarding idle values on the ground for this engine ...

2-5-5-2 ...

Many thanks, PPPMember, that is most useful.

Nick

[transilvana]

Sorry, I was wrong with the numbers, too much flying and my head is stuck. I checked it yesterday on flight, 23% N1 on ground, around 200Lb/h per engine and in flight you may start with 68% and go down as you descend.
Typical cruise fuel flow full load is 1600lb/h at high speed M.79 and 95-96%N1 and lower N1 is 92% when not heavy. If you check the QRH the numbers are ok, max range 2.200nm

[learsimmer]

First hour - including start-up, taxi and climb - 1800 lbs total used
Second hour - 1700 lbs
Third hour - 1600 lbs
Next hours - 1500 lbs

Interesting. Do you have a figure for approach and landing or is that included in the above?

And is 1800+1294=3094 the minimum fuel you would load for any flight under an hour?

Regards
Nick

[learsimmer]

Sorry, I was wrong with the numbers, too much flying and my head is stuck. I checked it yesterday on flight, 23% N1 on ground, around 200Lb/h per engine and in flight you may start with 68% and go down as you descend.

Thanks, Transilvana, for that confirmation. With regard to the descent, P-33 of the Crew Checklist and QRH implies an initial rate of -1500 to -2000 fpm, peaking at -6667 through FL290 and reducing to -2500 by 5000ft. Do you follow this? If so, what autopilot modes would you use to achieve it - SPD, VS or LVL CHG?

Regards
Nick

[transilvana]

On descend depends, some use Vnav, other VS, other speed..the good thing is that you can choose any. Normally I input the VNAV at 2000fpm to check my descend point, then I use VS or VNAV. For a smooth transition for the pax to start descend throttle back to 85% and at the same time trim slowly to 300fpm, then choose VS and lower it to 2000fpm.
About Minimum fuel I would say 3.500lbs, but would have 4.500, itīs not big difference in performance and you have the extra one, on cheap fuel places top it up calculated for Max landing weigth. On routes above 4 hours go to 7.800 no doubt. If you fly to Russia Top it up, you may encounter long delays on approach a low level.

[Lear Jockey]

yep, 2-5-5-2...that is correct, I can hear some of our FI at FSI ATL telling us that ;-)

To make a stabilized approach with flaps 20° and gear up, I recommend maybe 180 kts to 6 NM and ~55% N1. Then start to configure with gear down, no chnage in pwr setting and soon at 3-4 NM full flaps from 165 kts and slowing to Vapp and then Vref with a slight increase to 58-60% N1 depending on your weight and conditions. Typically I find the 60 to be flying much better at Vref+5 kts or even Vapp until 1 NM from touch down. Vref is quite slow, you don't fly the 60 quite a well as with a bit of extra speed. Of course fly it all the time and for a short rwy aim for Vref+2 to 5 max and don't flare too much, at 139kts Vref it bleed rapidely the rwy ahead!

Have fun!

[transilvana]

thatīs right, fly it quick on approach,as soon as you retard the engines the speed will go down fast. Yo can fly the 60 without wings, those two rockets on the back do the rest

[learsimmer]

To make a stabilized approach with flaps 20° and gear up, I recommend maybe 180 kts to 6 NM and ~55% N1.

Thanks, LearJockey, for that useful information

Regards
Nick

[learsimmer]

For a smooth transition for the pax to start descend throttle back to 85% and at the same time trim slowly to 300fpm, then choose VS and lower it to 2000fpm.

If you use VS for the whole of the descent, Transilvana, will you be adjusting the selected vertical speed to follow the descent profile described on P-33 of the Crew Checklist and QRH which means, as I read it, dialling it to -6000fpm around FL290?

Regards
Nick

[60JC]

6000 fpm is dropping like a rock! Very uncomfortable for the people writing the check. 2500fpm is about the max that I will do unless we get a late crossing restriction. Even then, more than 4000 fpm is screaming down.

I don't have my manual in front of me to reference what you are describing, sorry.

[learsimmer]

6000 fpm is dropping like a rock! Very uncomfortable for the people writing the check.

Well, exactly, 60JC, yet it seems to be what the book requires!

2500fpm is about the max that I will do unless we get a late crossing restriction.

Assuming that -6000 is needed to maintain M0.76 if you are at idle approaching FL290, and that maintaining -2500 fpm AND M0.76 requires the thrust to be greater than idle, my question was, and remains, how much greater? Transilvana appears to be saying around 68% N1 reducing as necessary to maintain -2500fpm at M0.76 to FL280; at 300KIAS to 10,000ft and at 250KIAS below that. This implies using VS at a fixed -2500, continually adjusting thrust to maintain the target speeds.

Also, since the distance covered will be greater than that given in the descent table on P-33 of the Crew Checklist and QRH this table cannot be used to calculate TOD. I am left wondering why it is there and why it is called "Normal Descent"! :-)

Regards
Nick

[transilvana]

Well, donīt count on the QRH, most of the time you will not be able to do a descend as the book. On my experience use max 2.500fpm, is much better for the pax. Of course you can do 6.000fpm down and 10.000fpm up, but will your pax take it?

[60JC]

I guess I didn't understand what you meant by normal descent. Typically, for me, around 2000-2500 fpm @ approx 70% N1 is normal. Then adjust as necessary when transitioning to IAS to maintain approx 300 kts. I don't really pay attention to what the book says, just do what is comfortable for the pax and complies with ATC.

[transilvana]

In any case the 60 is a wonderful plane to fly, the more you fly the more you like.

[learsimmer]

Thanks for all your help, guys, it was all useful.

Regards
Nick

[balaton]

Your question is similar to my one posted a couple of months ago. In essence: If you follow the descent tables in the QRH you will run in descent rates more than 5000 fpm. It is simply not realistic for every day ops. Therfore the data given by Learjet is completely useless. You can not calculate distances/time/fuel based on them. (The same can be applied to LR35/31 series). I really don't know why Learjet even publish that.
You could find more problem areas in the performance section:
- No N1 given in the cruise tables.
- The autopilot has two climb modes (LVL CHG) norrnal (250KIAS/.70M) and high speed (275/.73M) but you are provided only with the normal climb tables in the Pilot's Manual. Again you can not calculate time/fuel/dist for the hi spd climb. (Altough it is frequntly used in day-to-day ops especially at light weights.)
So the the performace section is not the best in the industry, to my opinion.
If you would like to study a really good one, it is the CL604 "Cruise Control Manual". It is absolutelly detailed and contains all data required.
Be carefull with those tiny main wheel tyres,
balaton

[learsimmer]

In essence: If you follow the descent tables in the QRH you will run in descent rates more than 5000 fpm. It is simply not realistic for every day ops.

Thanks, Balaton, for that input. I assume no-one minds climbing at 5000fpm or more?

Oh, and does anyone have a view as to the accuracy of the fuel consumption given by the QRH in the climb tables?

Regards
Nick