Thanks, and I'll give this a try ASAP.

Michael

I have downloaded your B727-200 mod package, but I have a question. I compared the data in the current aircraft.cfg file and the one you propose. I notice that you have reduced the weights (max, empty and max_zf to nearly the same values as the -100. Is that necessary? Does that represent the real -200?

In the first place, what drew me to your post in the forum were the problems I am having with controlling this aircraft, which is new to me. I was trying to do a flight from Toronto (CYYZ) to Montreal (CYUL), about a 1-hour flight. My payload was as follows:

•      155 passengers at 180 lbs = 27,900 lbs
•      4 3,000 lbs containers (2 front, 2 aft) = 12,000 lbs.
•      Crew = 510 lbs
•      Total payload = 40,410 lbs

I loaded 18,500 lbs of fuel, spread equally amongst the 3 tanks.

The problems I encountered are:

•      Climbing beyond 25,000 ft. was very difficult. I managed to reach only 31,000ft in about 18 minutes from takeoff.
•      Once in the cruise portion, I tried to maintain a constant speed of M0.8, but the speed kept changing up and down, so I constantly had to adjust the throttle. I was on real weather, but the winds were pretty constant. I never have such variations in other planes (C-130X, B-52).
•      When descending, I found it hard to slow the airplane and had to use the speed brakes to reduce the speed once I got below 10,000 ft. (Incidentally, the speed brake lever does not work. I had to use a keystroke. Is that a known bug?)
•      In the turn from the base leg onto final, it slowed down very rapidly from 150 Kts and I lost it; it stalled and crashed. My flaps were at 15° when I was at 150 Kts.

Is this the normal behaviour for this plane? Or am I doing something wrong? Or is it something that your mod would fix?

GDex wrote on Feb 11^th, 2011 at 3:50am:


All of the information I used comes from Boeing and airline manuals for the real aircraft, and some material taken from the engine manuals as well.  As for the weights, they are accurate.  The 727 200 Advanced had a significantly higher maximum weight, but that is not the aircraft I modeled. See page 5 of the following document from Boeing as to weights:

http://www.boeing.com/commercial/airports/acaps/727sec2.pdf

Your total weight was 194,000 lbs which was more than 20,000 lbs in excess of the maximum takeoff weight.  In the readme I noted that it quite easy to overload the basic 200 model and that you should check to see that you haven't done so in the FSX fuel and payload dialog.

I don't have detailed climb performance charts for the 200 with JT8D-9 engines, but I do for the 100 and for a 727-100 starting at 170,000 lbs with JT8D-7s, the climb to FL310 is 21 minutes at standard temperatures, so I am not sure why you perceive your results to be a problem.   If anything the climb performance may be too good based on your figure, although I wonder if you used more than maximum climb power since you perceived the performance as deficient?

My figures are from a Boeing performance manual.  Climb above 25,000 feet is only going to be around 1000' feet per minute.  That is the performance of the real aircraft.

As for the cruise behaviour, there is nothing in the flight model that could cause varying speed with a constant power setting.  And I have yet to experience "pretty constant" winds aloft with any of the weather programs I have tried.  Try again with "clear" weather, which has no wind at all, to see if in fact you really have a problem with this.

I can't use the mouse to operate the speed brake lever either -- I have to either use a key or a joystick slider, but I haven't done anything to cause that problem.

I don't find that I need speedbrakes to slow down. I start descending at 2,500 fpm at 290 knots at 55% N1 (which is the desired behaviour). I set the autopilot for that rate of descent and reduce it to about 2000 fpm at 20,000 feet and 1,500 fpm at 15,000 and then 1000 fpm under 10,000.  You will not need speed brakes if you do that.

With flaps 15 in level flight you need a fair amount of power.  I have two unreliable airspeed charts for the 727-200.  The one says you need an N1 of 74 and 7' of pitch at 150 kias at a typical weight.  The other chart is more detailed and shows for a weight of 160,00 lbs:  EPR of 1.43/N1 of 74 and 7' pitch at 160 kias.  I have tweaked my flight model to approximate these figures.  And of course if you are turning with a lot of bank angle you are going to have to increase your power from those figures in the turn.

So I think that yes, you are doing something wrong.

Michael

Looking again at the Boeing chart you supplied, I see the CS numbers match the highest numbers provided in it (rightmost column). So I withdraw my comment in the last paragraph about their choice of weights.

Mark, Michael

As I indicated earlier, it seems that CS chose to model the Advanced version of the -200. So since I wanted to use the heavier version and the CS ACE, I decided to keep the original CS files, but modified the aircraft.cfg file as suggested by Mark. However Michael’s comments on engine settings, speeds and FPMs were still very useful, and I performed the flight successfully. Now, the aircraft climbed as it was supposed to.  It took me just under 20 minutes to reach FL310 from the time I started the takeoff roll.

As Michael suggested, I did the flight in clear weather. There was not as much variation in speed (in cruise) as when I was in real weather, but it still varied more than it does in other aircraft. This may have to do with a lack of precise control in my joystick throttle paddle, and the fact that those old jet engines were slow to react to any change in throttle input.

Mark, I do have a question on EPR and N1 values. Prior to making the change you suggested, the EPR could go as high as 2.3. Now I notice that with the new value, the maximum EPR I can reach, with throttles to the wall and N1 at 100%, is 1.98. Is that normal? I also noticed that after a few minutes, the EPR went down to 1.82, while N1 was still at 100%, and the throttle still all the way forward. Why the change? Is it Pt2 that goes up or Pt7 that goes down?

I also have a question on the EPR gauge. The manual explains that the Engine Pressure Ratio Setting Knob (13-15) sets “the reference index and the digital indicator to the preselected EPR value when the knob is pulled out to the manual position”. It also explains what it does if the button is pushed into the automatic mode. First of all, when I push on it, it always stays in manual mode; possibly the automatic function was not modelled? More importantly, when setting it manually to some value, I see the bug moves up to that value and the value is also shown digitally. Is that only to act as a reminder of some value we want to reach, or does it actually limit the EPR to the value selected?

Now all I need to do is to practice, practice, practice, particularly the takeoff and initial climb, so that my vertical path will somehow resemble the prescribed speed and climb rate numbers! In particular, I have trouble when switching from manual  control to the autopilot: as soon as I activate the AP, the aircraft pitches down into a descent! Not a good deal!

Thanks to both of you for all the help.

There is no auto-function for the EPR bugs modelled.  The EPR bug is just to remind you of what power is needed for whatever phase of flight you are in.  You should use it for takeoff, climb and cruise and also for go around power on your approach. In climb, the EPR needed will change quite a bit as you climb, but you will not have to move the throttles much as the EPR will rise on its own to some degree with a constant throttle setting as you climb.  The bug does not in any way set power -- you do that manually with the throttles.

The EPR gauge is my mod is modelled to show EPR as a function of corrected N1.  What you see on the gauge is just N1, so on the gauges you see, the relationship between N1 and EPR will vary with ram air temperature and thus with outside air temperature, altitude and Mach, all of which will change a lot over the course of a flight.  The end result is accurate. The Captain Sim epr gauge does not give meaningful values for any engine variant if that is what you are using.

My flight model will only perform properly with the air file and and all aircraft.cfg changes and to be able to fly realistically you also need to install the EPR gauge use the thrust charts. If you pick and choose bits of it will not function as intended or accurately.

If you want to model an advanced version I suppose you can change the thrust and weights, but you then need thrust setting charts for JT8D-17s or whatever it is your modelling and my EPR gauge and turbine tables in the air file may very well not give the desired results because they were made to model a different engine variant.

By the way Asanal has sent me an email indicating that he has discovered his trim problems are connected to his yoke trim calibration and possibly third party software he is using to load the aircraft. It's nothing to do my flight model modification.

When you turn off the autopilot, the aircraft should stay in trim.  As I stated in another thread, none of my modifications do anything to affect trim or the autopilot operation.  And you can use the MAC gauge included in the package to ensure you your weight distribution is within reason.

Mark,

When installed Michael  727-200 EPR Mod, It did not function as 727-100.
I went through MOD  installation  item by item and I found like you I did-not insert new air file. After Air File replaced. EPR function was PERFECT.
Sanal