setting climb power in TFE 731

[Raskal]

The different numbers for the 731's are interesting, in the hawker 700's its max cont at 885, the climb profile is 865 until 25000 then let it creep up to 885 max.

 

[OUPilot]

In the 35 with deecs at our company, it is normally full forward for takeoff, pull back to about 90 n1 for noise abatement till about 4000 agl, then set in about 800 itt. At 10,000 you can set n1 from the chart and let the deecs do the rest. Once level, let the thing speed up and then set 795 itt.

 

[HawkerF/O]

At 10,000 you can set n1 from the chart and let the deecs do the rest. Once level, let the thing speed up and then set 795 itt.

Exactly what is it that you think the DEECs are doing at this point? DEECs (N1) just keep the N1 from exceeding the manufacture's operational limts, typically when the power levers are full forward, but not always. What exactly is it that the DEECs are doing when you set the N1s then you say 'let the DEECs do the rest'? There's nothing for them to do. With N1 DEECs, your concern should be temperature, not N1. The DEECs are keeping the N1 in check, but they do nothing for the ITT. If you're operating by setting the N1s, then thinking the DEECs are doing something, you have not read the included documentation of the DEECs and/or you have been improperly trained and do not understand how the DEECs operate.

 

[OUPilot]

"The DEECs are keeping the N1 in check"

ok so when i said let the deecs do the rest...you are right, i should have said let the deecs keep the n1 in check. same thing. in the climb, make sure the itt is under it's limits, and check the chart every once in a while to make sure that the deecs are exactly keeping n1 where it should be. how's that? i guess i sorta assumed people know to keep the itt under limits.

 

[pettylear]

N1 deecs or not your still limited to the max N1 for climb chart in the AFM. 832 is your max ITT (period). There is no max N1 for cruise for the LR35/36. If you push it up automatically to 832 in the climb odds are 50% of the time your exceeding the max N1 for climb numbers. Ive found that setting 795 in cruise will ALMOST always keep you under the max N1 number. Once in cruise you can then fly 832 all day if you want (795 recommended after 30 minutes) - all this is goes off the same principles of a constant speed prop. *note* the max N1 for climb chart is also dependant on using the climb schedule 250 to .7, any faster then the max N1 chart isnt valid. Also just pushing the thrust levers to the stops to set takeoff power and let the deecs figure it out is a risky way to do things. Although the N1 deecs are much better they will still over shoot the N1 setting and re-adjust on the take off roll.

 

[HawkerF/O]

Also just pushing the thrust levers to the stops to set takeoff power and let the deecs figure it out is a risky way to do things.

What are you talking about?????? It's not risky at all. It's proper operation and exactly how the system was designed to be operated. The increase is due to RamRise and there is nothing anyone can do about that. If you hold the brakes and set 94% then start the take off roll, you are going to get an increase, DEEC or EEC. Letting the DEECs control it is much more accurate than any human. DEECs are designed to allow the pilot to push the power levers to the stops, then essentially forget about them, except for confirming the settings are close to what the QRH says. If you are not pushing the levers to the stops, but trying to set the power, then I hope you are not teaching others to do that. Unless there in an ENG COMP light illuminated or flashing, you are not going to be as accurate as the DEECs, but you can't go with a computer light on anyway, so that arguement holds no water anyway. Plain and simple. If you ever had an issue on the take off roll and told the FEDS, "Well, even though we have DEECs, I set the power to less than what the DEECS thought the power should be, blah blah blah", then you are going to have some tough questions to answer. Just push the power levels to the stops, confirm N1 is in the ballpark, and let the engines to their thing. Pulling power off, thus reducing T/O thrust, because you think are you are more accurate than the functioning engine computer is just ignorant.

From an AMT Article:
Positioning the power lever to the maximum stop (fuel control at 120-122 degrees) results in maximum N1 RPM automatically adjusted for air temperature and altitude.

Although the N1 deecs are much better they will still over shoot the N1 setting and re-adjust on the take off roll.

The Tattle-tales built into the DEECs will show the engine manufacture that the N1 was over for a 1/10 of a second and they will be able to see that it happened during the start of the takeoff roll, so it'll be a moot point in terms of MSP fixing any engine problem. They'll know it was from RamRise and not pilot abuse.

 

[Lead Sled]

As is usually the case, I've got a pretty strong opinion on this. (Actually, it is one of my aeronautical pet peeves.) This very question resurfaces with every new pilot generation. I think HMR said it well...

You guys who set power based on temps instead of using N1 on the 731's, where did you learn this? It wasn't from Garrett and I doubt it was from the aircraft manufacturer. How do you flight plan? How do you know what fuel burns you'll have on a transcon trip? I haven't seen charts in any jet I've ever flown that say "Fuel Flow @ 800 Degrees".

For you new guys, here a little TFE731 Class 101: N1 is the ONLY indication of thrust output. PERIOD, end of discussion. When it comes to the various engine indications, N1 tells you how much power the engine is generating; N2 tells you the internal speed of the engine; and ITT or EGT tells you the health of the engine. A "fresh" engine will be able to achieve its rated thrust at a lower ITT or EGT than an engine with some time on it. As an engine wears, the internal tolerances open up and it takes more heat energy (fuel flow) to generate the same amount of thrust. More fuel into the engine results in higher temperatures. A new engine will have a greater margin than older engines.

In a way, it's comparable to a turboprop engine where N1 is comparable to % Torque. With turboprop engines you advance the power levers until you hit the maximum torque. You continue to advance the power levers to maintain that torque until you reach the maximum ITT or EGT. The concept is the same.

Several years ago, we had this very same discussion within our flight department. We had a pilot who came up through the freighter ranks and believed that the only real limitations on the engines were the N1 RPM red line, the N2 RPM red line, and the ITT red line. He simply pushed the power levers up to whatever red line happened to occur that particular day without regard to the N1 that the engine was operating at. Takeoff, climb, cruise - it was all the same. Later on, when we got airplanes with -40 (DEEC) engines, his thoughts were that he could simply push everything to stops and keep it there because the DEECs would keep the engines from exceeding any parameters.

Back then, Allied Signal manufactured the engines and I spoke at length to one of their representatives regarding how to operate their engines. We exchanged e-mails. TransMach hit the nail on the head when he said...

The real problem is that a lot of folks simply set thrust according to ITT. The 731-2-2B engine on the Learjet 35/35A/36/36A has a max continuous ITT of 832C and the manufacturer recommends that you reduce to 795C after 30 minutes. The correct method of setting climb thrust is setting maximum continuous RPM, at a temperature at or below 832C, or 795C after 30 minutes. If you depart a low altitude airport in the winter, i.e. Chicago in January, you will see ITT temps of around 730-750 at takeoff thrust. Now, if you push it up to 795C you have just exceeded max RPM for takeoff thrust let alone max continuous.

Well said, and it just doesn't apply to the -2 engines in the Lear, but to the -3,-4,-5, and -40's as well. The specific temperatures will vary according to the specific engine, but the technique is the same.

As long as we're talking power settings. Here are some more basics - the takeoff power charts will give you a specific N1 required to achieved the required takeoff performance. Garrett/Allied Signal/Honeywell looks upon that number as a "minimum" number. Take of is one area where if you get a little more that what the book says, you're fine. Many aircraft AFMs, allow you to advance the power levers to the stops on takeoff regardless of whether the engines are EEC, DEEC, or FADEC, and allow the fuel computers to do their thing to keep the engine parameters in line. (There is also a time limit in this type of operation - 5 minutes.) After takeoff, you need to transition into the climb power charts. Climb (and cruise) charts are based on specific N1 settings and should be used. The temperature limits are the maximum allowable for the specific N1.

HMR talked about cruise power settings, and he was spot on. I've flown coast-to-coast over 1000 times in 731 powered aircraft. I've seen every possible method used to set power. In a -3 or -40 powered Astra, the difference between "balls to the wall" (885C) and a charted "Max Cruise" power setting is a very consistent 1.5 to 2 minutes and 200 pounds per 500 mile increment. In other words, balls to the wall on a 2000 mile trip will get you there 6 to 8 minutes quicker, but it will also burn 800 pounds more fuel. Personally, the extra time is meaningless - a series of vectors at either end of the trip can easily chew up that much time. I'd much rather have the extra 800 pounds of fuel - often it's the difference between being able to make the trip non-stop or having to make an otherwise unnecessary fuel stop. I've flown with guys who end up sweating over their fuel reserves unnecessarily - all that they'd had to have done was just go to the charts and pull the power back a bit. If you want book performance you've got to fly it by the book. The problem is most of us are lazy and we don't want to take the time to go to the charts. We also don't normally fly the airplane out to the edges of its performance envelope where these types of sloppy habits and techniques start to take their toll.

LS

 

[HawkerF/O]

Well said. Lots of good info there. I will say that you will find Hawker drivers using temp for climb settings, as that is one of the items on the "climb checklist".

Here is what I remember from the 800A AFM


Climb

Below FL250 890° C. Above FL250 924° C or 98.7% N1 MAX (use lower of the 2)​

Allow N1 to drift, as long as 924° C or 100% N1 is not exceeded​

Crusie
Set N1 per the Chart, but ITT & N2 can be limiting: 908° C and/or 100% N2 MAX

As is usually the case, I've got a pretty strong opinion on this. (Actually, it is one of my aeronautical pet peeves.) This very question resurfaces with every new pilot generation. I think HMR said it well...



For you new guys, here a little TFE731 Class 101: N1 is the ONLY indication of thrust output. PERIOD, end of discussion. When it comes to the various engine indications, N1 tells you how much power the engine is generating; N2 tells you the internal speed of the engine; and ITT or EGT tells you the health of the engine. A "fresh" engine will be able to achieve its rated thrust at a lower ITT or EGT than an engine with some time on it. As an engine wears, the internal tolerances open up and it takes more heat energy (fuel flow) to generate the same amount of thrust. More fuel into the engine results in higher temperatures. A new engine will have a greater margin than older engines.

In a way, it's comparable to a turboprop engine where N1 is comparable to % Torque. With turboprop engines you advance the power levers until you hit the maximum torque. You continue to advance the power levers to maintain that torque until you reach the maximum ITT or EGT. The concept is the same.

Several years ago, we had this very same discussion within our flight department. We had a pilot who came up through the freighter ranks and believed that the only real limitations on the engines were the N1 RPM red line, the N2 RPM red line, and the ITT red line. He simply pushed the power levers up to whatever red line happened to occur that particular day without regard to the N1 that the engine was operating at. Takeoff, climb, cruise - it was all the same. Later on, when we got airplanes with -40 (DEEC) engines, his thoughts were that he could simply push everything to stops and keep it there because the DEECs would keep the engines from exceeding any parameters.

Back then, Allied Signal manufactured the engines and I spoke at length to one of their representatives regarding how to operate their engines. We exchanged e-mails. TransMach hit the nail on the head when he said...
Well said, and it just doesn't apply to the -2 engines in the Lear, but to the -3,-4,-5, and -40's as well. The specific temperatures will vary according to the specific engine, but the technique is the same.

As long as we're talking power settings. Here are some more basics - the takeoff power charts will give you a specific N1 required to achieved the required takeoff performance. Garrett/Allied Signal/Honeywell looks upon that number as a "minimum" number. Take of is one area where if you get a little more that what the book says, you're fine. Many aircraft AFMs, allow you to advance the power levers to the stops on takeoff regardless of whether the engines are EEC, DEEC, or FADEC, and allow the fuel computers to do their thing to keep the engine parameters in line. (There is also a time limit in this type of operation - 5 minutes.) After takeoff, you need to transition into the climb power charts. Climb (and cruise) charts are based on specific N1 settings and should be used. The temperature limits are the maximum allowable for the specific N1.

HMR talked about cruise power settings, and he was spot on. I've flown coast-to-coast over 1000 times in 731 powered aircraft. I've seen every possible method used to set power. In a -3 or -40 powered Astra, the difference between "balls to the wall" (885C) and a charted "Max Cruise" power setting is a very consistent 1.5 to 2 minutes and 200 pounds per 500 mile increment. In other words, balls to the wall on a 2000 mile trip will get you there 6 to 8 minutes quicker, but it will also burn 800 pounds more fuel. Personally, the extra time is meaningless - a series of vectors at either end of the trip can easily chew up that much time. I'd much rather have the extra 800 pounds of fuel - often it's the difference between being able to make the trip non-stop or having to make an otherwise unnecessary fuel stop. I've flown with guys who end up sweating over their fuel reserves unnecessarily - all that they'd had to have done was just go to the charts and pull the power back a bit. If you want book performance you've got to fly it by the book. The problem is most of us are lazy and we don't want to take the time to go to the charts. We also don't normally fly the airplane out to the edges of its performance envelope where these types of sloppy habits and techniques start to take their toll.

LS

 

[FO4life]

On the LJ-55, I get the max con N1 out of 15,000 ft. note the ITT and hold that ITT (about 845 usually) all the way up until FL360 when you can set 870 ITT not to exceed 885 for the rest of the climb. This method keeps within +/- .5% of the charted max N1. Just my 2 cents.

 

[Lead Sled]

On the LJ-55, I get the max con N1 out of 15,000 ft. note the ITT and hold that ITT (about 845 usually) all the way up until FL360 when you can set 870 ITT not to exceed 885 for the rest of the climb. This method keeps within +/- .5% of the charted max N1. Just my 2 cents.

The Astra AFM lists a similar procedure as well. And it too works well as long as the engines aren't too tired. In my original post, I was talking about guys who set power without regard to the N1s being achieved.

I've got a lot of time in -40 (DEEC) powered Astra SPXes and G-100s. Honeywell/Allied Signal has made it easy - all you have to do is out the power levers into the climb range on the throttle quadrant and the power will "take care of itself". Well not really. N1 will actually fall into an area comfortably below the charted maximum for climb. If you want more power you can get it, but you're going to have to go to the chart to figure out what it should be. Something that most of us are too lazy to do.

Personally, from my dealings with them over the years, I believe that they have done this on purpose - most of us are too lazy to dig into the charts to find the appropriate N1 limits. Excess heat takes a toll on engines and increases maintenance costs. Engines on MSP esentially are on fixed cost per hour maintenance plans and it's to Honeywell's best interest to do what ever they can to keep the costs down - it increases their profit margin.

LS

 

[pettylear]

What are you talking about?????? It's not risky at all. It's proper operation and exactly how the system was designed to be operated. If you ever had an issue on the take off roll and told the FEDS, "Well, even though we have DEECs, I set the power to less than what the DEECS thought the power should be, blah blah blah", then you are going to have some tough questions to answer. Just push the power levels to the stops, confirm N1 is in the ballpark, and let the engines to their thing. Pulling power off, thus reducing T/O thrust, because you think are you are more accurate than the functioning engine computer is just ignorant.

Learjet AFM Performance page 5-24 reads:
From the applicable Takeoff Thrust (N1) Chart, determine the Fan Speed (N1) setting for temperature and altitude. Move thrust lever until Fan Speed (N1) indicator aligns with chart value.

I missed the part where it says push it to the stops and let the Deecs figure it out? Ignorance is going against the AFM and airplane manufactures procedures. I recognize that the Deecs schedule fuel much better than I do but that doesn’t elevate the pilot’s responsibility to set the proper take-off power.

 

[Lead Sled]

Learjet AFM Performance page 5-24 reads:
From the applicable Takeoff Thrust (N1) Chart, determine the Fan Speed (N1) setting for temperature and altitude. Move thrust lever until Fan Speed (N1) indicator aligns with chart value.

I missed the part where it says push it to the stops and let the Deecs figure it out? Ignorance is going against the AFM and airplane manufactures procedures. I recognize that the Deecs schedule fuel much better than I do but that doesn’t elevate the pilot’s responsibility to set the proper take-off power.

FWIW, Garrett/Allied Signal/Honeywell procedures allow for the pilot to simply push the power levers to the stops and let the fuel computers (all of them - EECs, DEECs, or FADEC) to do their thing. (This assumes that your fuel computers are properly set - ours are.) Of course, the airframe manufacturer can chose to allow that or not - many do and some do not.

Personally, I have a hard time understanding why you would want to spend a lot of time screwing around with the power levers trying to set just exactly the precise power setting that will insure that you have the minimum amount required to achieve the required takeoff performance. (While the co-pilot is concentrating on trimming the throttles, s/he's also blowing past some V-speeds as well.) I'm not advocating going against the AFM, but if you happen to get a little more N1 than the charts call for, I'm not going to be too concerned with pulling power while I'm screaming down the runway.

LS

 

[typeratedjet]

I fly 35's and 55's. I have asked this specific question of Simuflite (where we train) and the answer was N1 for takeoff (not to exceed itt limits) then climb out at 865 (55). The n1 chart has never been pointed out in our training. Then I met a Learjet test pilot and asked him the same question. His response was "the ITT limits are in the limitation section. We fly by ITT limits. The N1 chart is included in the AFM because it is provided by the manufacturer. But it is for reference and not a limitation." So that's how we do it.

I do reference the N1 power chart for "anti ice on" climb power.

PS. Deecs do not allow you to go to the stops. You should still be setting N1 on takeoff.

 

[festus89]

I would do whatever your "chief" tells you to.

 

[cyork25]

i hear your cp is a real toolbox