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Speed Vs Altitude LearJet!!!

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Speed Vs Altitude LearJet!!!

Old 26th Jun 2011, 05:58
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Speed Vs Altitude LearJet!!!

Alright sooooo we got a discussion going here between myself and some fellow Lear 60 Pilots and would see if anyone else got some inputs.

In the Lear 60 manual the recommended climb-speeds are 250kts until reaching Mach .70 then .70 til cruise (Normal Climb)

275kts til .70 then .70 til cruise (High Speed Climb)

These are the book values and the values most used between us. Some though believe that we should fly the 60 as the airlines do, doing 310kts from 10.000ft. till cruise. Their thought of mind is that by flying that much faster we will cover more distance hence saving time. On the other hand they understand that by gaining altitude first we would save more fuel but they believe that the more distance covered is worth more in $$ then the fuel saved.

Myself personally normally do the things written in the book, i do believe that the numbers recommended by the factory are the correct numbers and when i do compare the time saved flying at 310kts compared to 250kts is negligent and hardly not there. As i climb faster my TAS increases, my fuel goes down and i do believe that there is hardly no difference in the time saved. But i will be able to reach FL410 10 min faster then the highspeed.

Anyways hope someone got some inputs :-).

Thanks
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Old 26th Jun 2011, 07:06
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Book figures are a good guide. However in certain latitudes if you climb at the book figures you wont make it into the colder air. Eg., if you are in temperatures of say ISA + 18 until FL330 or FL350 the book values may not get you high enough to get into the colder air. Therefore a lower ias/ mac no would be more beneficial, to achieve a reasonable R of C. At FL400 you then maybe at ISA. Yes you will loose a few minutes, so it is a trade off.

This does not only apply to LJ's
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Old 26th Jun 2011, 08:03
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Sure depending on the ISA you might have to reduce the rate of climb used if you are using the book numbers.

But if we take a regular standard day standard temperature. Would it be more beneficial to climb using non recommended high speeds or the recommended climb speeds? That is the real question i guess as some of the guys say that whom ever made the book didnt know what they were talking about!!!! Bombardier i am pretty sure do know what they are doing so thats why i had this discussion with them!!! Hence the reason why i stay with the numbers in the book "depending on temperature"

BUT for me also, i've always learned a JET performs best at high altitude and specially in a LEAR that climb's as a bad out of hell i would think getting high fast would be more beneficial then flying fast and climbing slow!!!
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Old 26th Jun 2011, 08:16
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Point taken.

The idea to climb an aircraft is to get it to its optimum altitude as quickly as possible to get the most economical cruise performance. Climbing at 300knots + ind is producing a lot of drag, therefore fuel burn. It's all about the best lift/drag ratio up to a point IIRC.

Yes BB built the aircraft, therefore if you want the most out of the aircraft I would suggest use their book values.
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Old 26th Jun 2011, 09:18
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Hmmm...I don´t fly the 60, we do climb our Sovereign faster (by about 30-50 KIAS/.06-.08) than the book says. (250KIAS/.64 for all conditions)
2 reasons:
1) the ROC is roughly up to FL300 more or less the same, some times I belive its even better. Above that the airplane loses som ROC (300-500fpm roughly) Still we climb better than most others.
2) when heavy and one climbs directly to a high level, it takes ages to accelerate when arriving at .64. We accelerate at MCT, which produces roughly 300 lbs/hr more fuel flow than CRU. So we hit, say FL400, climbing at .72, we can throttle back at least 10 minutes earlier than at .64 (have no idea about the 'push' the 60 has at altitude, but the Sov is not exactly underpowered.

2) is particularly true, when the atmosphere is warm Few days ago we returned from Kasachstan, departed the place at MTOW and climbed to 430 directly. It was ISA +12 and using standard climb we probably would still be accelerating.

I think - and thats pure speculation - that the manufactures don´t waste to much time in calculating/validating these figures.

Regarding the drag, its my feeling that using standard climb figures (again, talking sov here) produces way more drag than zooming along close to redline.
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Old 26th Jun 2011, 12:37
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Hi Dude

It seems I'm on the wrong end of the drag curve.

If that SOV of yours can end up producing less drag (form, parasite, skin friction etc.,) by doing 300 kts, rather than 250kts, then Cessna are onto a winner!
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Old 26th Jun 2011, 13:02
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I am pretty sure that the most books that publish a recommended climb speed are basing their numbers on the best lift/drag ration. If not i do not see any need for the speeds in the books!!!!
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Old 26th Jun 2011, 13:30
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If that SOV of yours can end up producing less drag (form, parasite, skin friction etc.,) by doing 300 kts, rather than 250kts, then Cessna are onto a winner!
You´re right of course, should have added that smiley.

I can´t say that I did a climb, landed back, refilled to same weight than before and then tried an alternate climb method to check the differences, still I think they are ROC wise not big...

I am pretty sure that the most books that publish a recommended climb speed are basing their numbers on the best lift/drag ration.
I´m sure you´re right there, still I think that these curves are - in certain cases - pretty flat, so one ends up with small differences in ROC´s, but big differences in forward speed.
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Old 26th Jun 2011, 14:40
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Why don't you just try climbing by the book once and the next time with your high-speed profile? See how long it takes to get to altitude, what your fuel burn is and how far down range you are when you're level and compare. Your FMS will show you "air miles" flown so a few turns won't make a difference.

Of course weight and temp will vary but we all have flights that depart at similar weight and temp.

Sure, you might have to make an ATC level off here or there but after a few tries you should have your answer. Might not be exact but you will see the trend.
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Old 26th Jun 2011, 17:39
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HD

NetJets USA did a study on their 680's, they were struggling making coast to coast at certain times of the year, they reckoned book figures were good for an extra 400lbs at destination and made it SOP shortly thereafter.

I fly the book figures after that..... or take 39 for as little while if its really warm
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Old 26th Jun 2011, 18:15
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G-Spot, thanks for that info. Do you know how they determined that? Real "testflying", like parallel flights?

Reg.390...we thought about that as well, using our flight planning prog it looks like the differences at least in fuel used aren`t real big.(100-200lbs when climbing to 430 aften an hour) Having said that, for the flight in question I could NOT have used 390 (actually 381 for the metric system over there). We landed with 80 lbs over minimum diversion, 60 lbs more than predicted...

@theaviator2005: sorry for the thread drift...
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Old 26th Jun 2011, 19:42
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250? wrong, you should use 275 or .73 on LVL change or pitch mode, but never 250
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Old 26th Jun 2011, 19:47
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"Lear60fellow" Where ever you get your information from i do not know, but if you have a look at the book RECOMMENDED NORMAL CLIMB is 250kts RECOMMENDED HIGHSPEED is 275kts. So yes you most certainly should use 250kts, perhaps you needa hit the books again ;-) hehe
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Old 27th Jun 2011, 04:56
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I am pretty sure that the most books that publish a recommended climb speed are basing their numbers on the best lift/drag ration. If not i do not see any need for the speeds in the books!!!!
Incorrect. recommended climb speed will be faster than best L/D ration.
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Old 27th Jun 2011, 06:28
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Being as aircraft manufacturers always want to publish the best performance figures they can possibly get away with to entice sales, and the guy's and girl's that come up with these figures have forgotten far more than I will ever know, I would be very surprised if they have got it wrong.
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Old 27th Jun 2011, 10:37
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Yes, sure, in the middle east? if you fly the LJ60 as all the americans I know over there then I understand why you use 250kts.... use 275 .73M and you will make it faster to FL390, books also say range on the LJ60 is 2.800 miles and FL510, have you ever been close to those figures? I do not and I have a bunch of hours on the 60, of course in europe....
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Old 27th Jun 2011, 12:21
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I got Plenty of time in the 60 flying in Europe/Middle East/ USA and China.

Aircraft perform well doing 250kts both in Europe and the Middle East, the question is what is most beneficial. Climbing fast to cruise or flying fast taking you longer to reach cruise altitude.

And yes to correct myself ofcause the speed is faster then the lift/drag curve for recommended climb. But it is alot closer to the lift/drag flying at the recommended speed's then flying at speeds +50 to 60kts faster.

As of the calculations i have done, climbing to my altitude of Fl. 41/43 at recommended 250kts. Gets me to altitude almost 8-10 min quicker then doing 300-310kts. ISA standard or ISA +10

On a 2.5hr leg the time difference on arrival (varies with wind) but will be not much more then 5 minutes, where of the fuel burn is much more different.

I think the Aviation Industry have a tendency to have a lot of pilots thinking they know the way much better then others and always better then the manufacture, what i am asking is that if someone wants to move outside the recommended speed-range with more then 50-60kts please by all means do so but show me on paper where it would benefit me more.

Anyways thats all ;-)
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Old 27th Jun 2011, 18:41
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His dudeness wrote G-Spot, thanks for that info. Do you know how they determined that? Real "testflying", like parallel flights?
Yep same routing, same departure times. Got it from a NJUS crew at MCO on a renewal
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Old 28th Jun 2011, 08:28
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I have been told by our charter sales team that extra fuel burn is almost irrelevant in our biz jet operations. The greatest proportion of cost is spent on flight time. They have told the owner that they can expect to make X amount of profit on a flight, every extra minute of flight erodes that profit far more than extra lbs of fuel.

So, as long as specific range is not a concern they want us to fly as fast as possible, even on ferry flights. Therefore we climb at 300kts, if not too heavy etc.

Don't tell the Greens
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Old 28th Jun 2011, 19:24
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We usually use 275/.73 for climb. That numbers gives on average day (ISA-+some and weights at 22ish) 15mins to TOC. Reasonable fuel burn is also a benefit. But I like to think, that you can save much more fuel, if you can be until 75 miles on level and then make a continous descent to final. The fuel burn difference between 3.0' decent and 4.5' decent is quite remarkable. To meet our dispach expectations about fuel burn, we fly - 275/.73 on climb, .77 on cruise and leave the decent as late as possible (excluding VKO and London airports). And dispatch got their fuel burn numbers from the flight manual...


And remark about altitudes.

Also, I have been once in F470 (weight mid18s, ISA-9, empty leg), and it was pain to get there (last 200 ft the roc was ~40ft per minute) . It seemed impossible to get higher, but it was quite stable at .75 on altitude, disregarding the 'humming' from the wings.
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