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Post by jimhalinda on Dec 2, 2009 18:06:02 GMT
I did a short flight yesterday in the HJG DC-8-72.
I took off from Miami around 10:30 PM local time. OAT was around +10 degrees (using FS9's real weather).
I was climbing to 25000 feet with a 25% fuel load, so I was pretty light.
Once settled into the climb with flaps fully retracted, I noticed that the EGTs were in the reds (above 750 degrees), so I reduced thrust until the temp was back around 750. This brought N1 down to the low-mid 80s if I recall correctly.
At this EGT (and OAT was still around +10 degrees) I had to reduce my climb rate to below 1000 fpm just to maintain 250 knots indicated.
Is that realistic behaviour for the CFM-56s? I don't fly the -70 series much, but I thought the CFMs would make it climb like a rocket. By keeping EGT to 750 degrees that was certainly not the case for me last night.
Any comments welcome.
Regards,
Jim
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Post by aerofoto - HJG Admin on Dec 2, 2009 18:42:29 GMT
I honestly don't know Jim. Those DC8-70's FDE's were all prepared for us by "John D" .... whom seems to have disappeared right off the face of the planet , so, I don't know if there's going to be any further advice coming from that quarter now I can't make any comparison between your observation versus mine .... at the moment .... and due to other commitments. The new DC8 FDE may address this .... but again .... I can't progress it as quickly as I'd like and because of these "other commitments" For what it's worth .... I think I recall John previously advising that a typical DC8-70 T/O N1 value was around 95-97% .... reducing to around 92% after clean-up. I don't recall there previously being an EGT issue with our DC9-70's .... other than they might have been a wee bit low. Climb performance will of course be subject to load and OAT .... as you already appreciate .... but .... I think 1,000 FPM is really low .... unless you were both really overweight and it was very hot. I recall John stating that ROC for a typical DC8-70 load in normal operating conditions could be anything between 2,000-4,000 FPM .... and .... that he'd even seen 6,000 FPM on some very rare occasions. If I get time to do so I'll try'n compare your stated performance to my own .... and report accordingly. Mark C AKL/NZ
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Post by jimhalinda on Dec 2, 2009 19:14:05 GMT
Thanks Mark. I started with N1 up around 95% and it did indeed climb like a rocket - until I noticed the EGT and had to back off on the thrust.
That's a shame if Mr. Detrick is no longer around, we have all benefitted from his generous sharing of his real world experience!
I'm hoping maybe Skyking could comment on real world CFM-56 settings, as he of course flew -71s for UAL.....
I will try another -72 flight as soon as I get a chance, and will update this thread accordingly.
Regards,
Jim
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Post by aerofoto - HJG Admin on Dec 2, 2009 19:17:24 GMT
I'm sure "SKYKING" would love to help out .... and .... I'm sure he'll drop-in .... in due course !
Mark C AKL/NZ
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Post by skyking on Dec 2, 2009 19:52:10 GMT
Ya.....I'm here, Mark. Couple of comments. 1st, I flew the -71, not the -72. [Did fly the -62, however: loved THAT airplane]. -72 should perform pretty close to the -71 I would think. He said the OAT was +10. If we can assume the RAT to be the same [it would be a bit higher actually], N1 limit would be 94.6 [Temp Limit]. At SL, 5T, 10T, 15T, 20T, N1 Limit would be, 85.6, 88.4, 90.6, 92.5, and 94.3. These values are for Max Climb Thrust. When N1 is limited by both temp and alt, use the lesser value. I doubt HJG has factored in different engine bleed settings, so we'll assume all bleeds are normal. He stated he only had a 25% fuel load but did not state the GW. While the aircraft will have a fairly impressive climb initially, it will decrease with altitude as all aircraft will do. Our climb schedule had us climb at 300 kts [above 10T] to .7 MACH, then at .7 to cruise altitude. So.....only thing I can think of at this stage is his GW might've been too high. But even then, he should've been able to get to FL250 without too much trouble. To be honest, in the sim I don't pay too much attention to the engine instruments. That's what the FE was for !!! ;D
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Post by jimhalinda on Dec 2, 2009 21:39:43 GMT
Thanks Skyking, regarding my GW, I selected the -72 with HJG's default weights and then reduced fuel to 25%. Although I don't remember the final number I know it was WAY below MTOW. I don't meddle with the payload values, I just try to set fuel for the distance I intend to travel (in this case only around 200 NM).
I don't quite understand your terminology. When you say "N1 limit would be 94.6 [Temp Limit]", do you mean use 94.6% N1 unless that exceeds EGT limits? Because in my case the EGT was in the red zone (but not over the red line). To get out of the reds I had to pull N1 back to the low 80s.
If you just set your N1 and ignore EGT, then I will too. I was just wondering, as I know HJG strive to calibrate all of the instruments realistically. So I wasn't sure if I was "allowed" to have EGT in the red zone.
Regards,
Jim
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Post by skyking on Dec 2, 2009 23:27:53 GMT
The HJG 'default' weight might be at or near Gross. It's no big deal to adjust the weight and fuel to 'simulate' whatever flight you're trying to 'simulate'. Keep in mind also your max landing weight, 240,000lbs. Another reason to check your payload/fuel.
I just took a -71 up to see what was going on. I took off at 270M lbs vs 325M max. I had 60M lbs of fuel vs 115M max. OAT was around +15. Takeoff N1 was ~89, 90, somewhere near there. After leaving 10T and accelerating to 300 KAIS, climb settled in around 2000 - 2500 FPM. Transition to Mach [.7] was around 24,500'.
Remember now, you have to continually adjust N1 [increase it] as you continue to climb. Again, not exceeding the values given. At no time during my 'test hop' did I get close to the Red Band on the EGT Gauge. In fact, I remained at the bottom end of the Yellow Band most of the way up.
The Temp Limits I listed are just that: RAT Temperature. There is also an Altitude restriction. If both are limiting, you use the lesser value.
Your "low 80s" N1 values were probably pretty close to normal for whatever altitude you were at. Again; you have to keep adusting the N1 upward as you climb.
I was able to climb above FL250 at .7 Mach at 2500FPM with no trouble.
I didn't mean to imply to IGNORE your gauges. It's good that you want to do it as realistic as possible, and I think you'll be able to if you check your weight. It's just that I did this stuff for real for so long, I don't feel as though I have to be so "accurate". I leave that up to my "SIMULATED FLIGHT ENGINEER" !! I think HJG has come as close to the 'real thing' as any flight simulator aircraft I have ever seen/flown compared to its' real-life counterpart that I have flown.
Another thing: you can't normally just firewall the throttles [excuse me, thrust levers] on takeoff either or you WILL over temp these engines.
Standard day at sea level Limit N1 is about 90.4%. Can't figure Normal N1 without the Gross Weight pages in order to figure 'assumed' temperature. Limit N1 is the maximum thrust available. Some other things that don't need mentioning. Normal N1 is the thrust required under normal conditions and reduces engine wear. In other words, it's like a reduced takeoff setting. That of course depends on weight, temp, runway, etc. I don't think you want to be bothered with that in this simulator.
Hope the above helps a little. Remember, the main thing is to have FUN. The only person giving you a 'check ride' is yourself.
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Post by jimhalinda on Dec 3, 2009 5:22:43 GMT
YELLOW band!?!
On my monitor it looks more like a dark orange, and so I assumed the whole band was red. That must be my problem! (The band starts at 750 degrees and then goes up to the actual 'red line').
So is it OK to have the EGT in the yellow for the duration of climb (assuming N1 is set to a reasonable value)? If so then there is plenty of power of course!
I do try to be realistic, and so I don't firewall the thrust levers. On aircraft I have the appropriate data for, I try to fly by the numbers. But I don't have N1 tables for the -70 series. So I takeoff with N1 at about 95% and then power back to around 85%. And then I check all engine instruments to be sure nothing is in the red.
(I once read about how Chuck Yeager didn't believe in 'reduced power' takeoffs. On takeoff he couldn't understand why you wouldn't want to use all the power that was safely available. A 'military' attitude I suppose but I must admit it has its appeal!)
Then I adjust during the climb, as you say, finding that I slowly move the thrust levers forward as altitude increases and temperature drops. Rate of climb of course slowly reduces.
Thanks again for your input, SkyKing. My favourite aircraft are stretch 8s, and it is always a treat to hear from people who flew them for real! I was a passenger on one once as a kid, Air Canada, I know it was a stretch 8 but don't know if it was a -61 or a -63. Even got to visit the flight deck during cruise.
Regards,
Jim
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Post by aerofoto - HJG Admin on Dec 3, 2009 7:18:48 GMT
Jim .... and everyone else out there too .... you're in good hands there with "SKYKING" "SKYKING" .... thanks for your invaluable input ! Mark C AKL/NZ
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Post by skyking on Dec 3, 2009 12:36:50 GMT
Hey, no problem Mark. Enjoy it. But, remember it's been nearly 20 years now since I had my hands on these things, so don't hold me to everything !! ;D
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Post by skyking on Dec 3, 2009 12:39:05 GMT
OK.....EGT gauge: Red Line - 870 [ÂșC] = Max Takeoff with a time limit of 5 minutes.
Then you should see on your gauge [assuming your colors are normal] a little Yellow band from 870 down to about 750. Max Continuous EGT for Climb or Cruise is 835. I guess the Yellow band is there just to let you know you're getting close to the limit. Another limitation is 725 during engine start. And if the EGT ever exceeds 930 you're supposed to shut it down.
I never liked reduced power takeoffs either. I would use them with plenty of runway but was always aware that more thrust was available as I had a good grip on the throttles !!
Sounds/reads like you're doing just fine with what I consider to be the finest jet transport ever built [DC-8 60 and 70 Series. -50s were ok too]
Enjoy.
EDIT: I just had a closer look at the EGT gauge on the HJG panel and noticed that their Red Line is at 800 and the Yellow Band goes from ~750 to 800. Not sure where they got their figures from, but I guess you could "feel free" to use the numbers I gave you, which happend to be out of my manual. Maybe with their next update, that gauge will be adjusted.
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Post by aerofoto - HJG Admin on Dec 3, 2009 18:39:36 GMT
That data came from "John D" .... I believe.
One thing we must always be conscious of here is that the calibration of some instrument readings in FS (engine parameters in particular) are often a delicate balance between fact an fiction. What tends to happen here is that if we get one parameter more-or-less correct then this achievement alone can sometime influence another parameter elsewhere. Due to the limitations the FS program itself we do sometimes need to make compromises.
Our next DC8 related update will be in respect of FDE only .... and which will, inevitably, influence engine parameters, but, at this stage (due to my commitments with other projects behind the scenes here) I can't say .... or even hazard guess .... to what extent .... other than to say that the turbojet engines should all spool more slowly, the fanjet engines a bit faster, and the turbofan versions a wee bit faster again (as is evident with our B707/72o range) .... all DC9 engine types certainly spooling slower than they currently do.
Mark C AKL/NZ
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Post by skyking on Dec 3, 2009 18:55:57 GMT
That 'nit-pickin' of mine was NOT meant as a complaint, just a comment. I had never noticed it before. As I said earlier, I very rarely even look at the engine instruments on FS jet aircraft. I do, however, monitor piston-engine FS aircraft engine gauges. Whether you can adjust those DC-8 gauges or not, I don't think will really make much difference to anyone except the "purists" that are out there. Like I said, just ignore the Red Line and use the values I supplied.
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Post by aerofoto - HJG Admin on Dec 3, 2009 19:13:51 GMT
YEAH .... I realize that "SKYKING" .... and "NO PROBLEM" at all BTW ;D I was really just trying to explain, only for the benefit of those whom don't understand, that in FS certain compromises do sometimes need being made in respect panel/gauge programming .... and other things too .... because, believe it or not, there's some folk out there whom are under the erroneous illusion that FS, with its finite limit of editable parameters, represents absolute realworld fidelity .... and which simply isn't so or even possible of course. I/we all .... appreciate your valuable technical feedback 20 years or not .... keep it all coming .... and maybe I'll find a job here for you yet ! Mark C AKL/NZ
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Post by skyking on Dec 3, 2009 19:18:12 GMT
Uh.....P L E A S E.....do NOT go looking for a job for me. Thanks just the same. That is unless the pay is good.....like in the six-figure range. ;D ;D
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