DEECs and powerplant management

[CaptainSpaz]

holy smokes!

Are you familiar with the acronym, RTFM?

Indeed. It is rather ridiculous this thread has gone on this long. Just read the dang AFM, for the love of God! :smash:

Edit: Also try the POH or Crew Reference Guide if you have one of thise.

 

[svcta]

I have read the AFM. If you have noticed the point is that when our thrust levers are placed in the CLB position we are not getting anywhere close to max climb. This question came about when a friend of mine(operating a different dash # of 731) said that his company was told to never try to out think their DEECs, just to make sure they weren't over temping the motors and let 'em rip.

My AFM only says that max climb ITT MAY be used anytime you want(in the climb or while accelerating). That's as far as IAI took it. I think we all know that there are many finer points that are often left outside of the AFM to discover.

Regarding this "mythical chart" in the G100/Astra......where does this come from? I can't find anything so far in my stuff about that #(900 degrees). I just walked in to this operation a few months ago, so this A/C is new to me.

 

[LJ45]

If you have not flown the -20 , -40 or -60, you might not realize the engines are different then the other earlier 731. These engines have a large ITT range that is not normally limiting like earlier 731. They are different and the DEEC performs like FADEC except with a hydro-mechanical back up. The DEEC on this series are NOT like the N1 DEECs on the earlier engine. I have many hours behind the 731-20BR, 731-20AR, 731-2.

 

[Lead Sled]

Sorry that I'm arriving late to the party. As for the -40's on the SPX/G100 the DEECs will get you close in the power department, but you have to remember, they are not FADECs. Anyone who who sets climb and/or cruise power settings based on temp settings alone has not read or does not understand the manual. Sure, you can use the "flats" for climb, but don't expect the resulting N1s to be the max allowable - that's why they give you climb charts.

From some of the comments, it's probably time for a little Power Setting 101...

N1 is the ONLY indication of thrust output. PERIOD, end of discussion.

N2 tells you the internal speed of the engine.

ITT or EGT essentially 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 also exchanged e-mails. I any of you are interested, I kept copies of our correspondence and can forward them to you - just pm me.

More Power Setting 101...

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. Takeoff 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 - remember the turboprop comparison.

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" 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

 

[LJ45]

I digress, The DEEC in the Lear 45 must be more sophisticated then the Astra. We have a MCT (max continuous thrust detent and the DEEC sets the correct power unless it is broken). The AFM says put it in the MCT detent and let it rip as long as the ITT limits are not exceeded.

 

[TurboAWD]

Anyone know of a "users guide" (like the link above to Honeywell) for the GE CF-34 series (dash 3).

Thanks,
Turbo

 

[Lead Sled]

I digress, The DEEC in the Lear 45 must be more sophisticated then the Astra. We have a MCT (max continuous thrust detent and the DEEC sets the correct power unless it is broken). The AFM says put it in the MCT detent and let it rip as long as the ITT limits are not exceeded.

I have no experience with the Lear 45, but his question was specific to the -40R in the Astra SPX/G100 - those, do know something about.

LS