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Post by Klaus Hullermann on Nov 26, 2011 21:11:21 GMT
Hi guys!
Could somebody explain me how to use and read the EPR/RAT-gauge (both digital and analogue) of the DC-9 panels?
Klaus
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Post by aerofoto - HJG Admin on Nov 26, 2011 22:04:35 GMT
I'm not actually sure myself .... TBH .... but .... I think it's both elevation and OAT which determines the maximum limits according to the variable scales .... and which are determined automatically by FS
I think one of these scales determines absolute maximum safe limitations for an emergency/single engine situation .... as I recall.
Personally .... I never use it .... and instead opt to simply avoid exceeding the maximum EPR bug limits appearing on each of the EPR engine gauges.
Although our SL EPR bug settings are accurate for each engine type. EPR is something that, apparently, doesn't simulate very well in FS, so, one should, maybe, really be focusing on just the N1/N2 values .... if anything there at all .... and then adjusting ROC (in particular) and both speed and thrust settings so as to remain within/bugged limits.
That's how I fly all of the DC9's .... and virtually everyhing else we offer too.
At the end of the DC9 PANEL INSTALLATION & HANDLING NOTES I've provided "basic flying guides" for each DC9 aircraft/engine types .... which record the best settings (I feel) to use (on the basis of my own very extensive pre-release testing) .... and for the use/reference of anyone else whom wants to adopt similar flying procedures as my own.
These do work quite well within FS.
These "basic flying guides" should be more than sufficient to aid one.
Mark C
AKL/NZ
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Post by aerofoto - HJG Admin on Nov 27, 2011 2:37:06 GMT
I've just had a closer look at these EPR/RAT gauges in the DC9 panels .... and this's how I interpret both these gauges and the information displayed by them ....
There are 2 seperate types of EPR/RAT gauge used in these panels .... depending on the aircraft panel/engine type version in use.
The P&W JT8D-1 through D-11 aircraft panels each feature vertical scales for EPR limits and ambient/air temperature ..... with a selectable button at the bottom of this scale to rotate the readings on these scales between NORM1 and NORM2 mode indications.
P&W JT8D-15 and -17 panels each feature a digital push buttom type display with selectable TO/MAX TO/GA/MCT/CL/CR flight mode settings.
In both cases these indications should be activated on the ground.
In FS, and on the ground, by default the maximum displayed EPR value will always agree with that which appears bugged within each of the engine EPR gauges .... which is where one starts.
This maximum EPR limit will always be determined by ambient/air temperature value (usually a standard 15*C in FS) .... and which will change with altitude during the climb .... as will the displayed temperature values also.
More information is displayed by the JT8D-15 and D-17 panel EPR/RAT gauges for each of the available flight modes than is evident within the D-1 through D-11 panel vertical scale EPR/RAT gauges.
I think the idea is .... based on ambient/air temperature one's engine thrust settings should not ever exceed the limits indicated by the vertical scales or digital indications provided by these EPR/RAT gauges during any particular flight mode.
Keep an eye on these gauges .... and adjust the engine thrust setting during T/O, climb, and cruise .... so that it never exceeds the limits indicated by these EPR/RAT gauges. In FS this means one's ROC also needs to be monitored too .... in accorance with airspeed and indicated engine thrust .... which might even sometimes result in one climbing at a much shallower rate, late in any climb segment to altitude, and in order to mantain a decent speed, for engine thrust setting, whilst also remaining "within the indicated limits" as displayed by the EPR/RAT gauges.
Mark C
AKL/NZ
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Post by christrott on Nov 27, 2011 4:07:18 GMT
Mark, Your explanation couldn't have been better.  One note - EPR is only what you use to set power. It is not what it limited. The reason that the gauge is based on RAT is because the actual thing being controlled is engine temps. By setting the EPR listed for a given RAT, you ensure that you won't exceed the engine's temperature limitations. The reason when you look on the planning charts you find altitude in the mix is not for EPR, it's for all the other items. Altitude really doesn't figure into the equation with setting engine power because on a jet engine it doesn't play as much of a factor into the temperatures of the engines like it can with pistons. |
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Post by Klaus Hullermann on Nov 27, 2011 7:46:19 GMT
Thank you Mark for the explanation.
Klaus
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Post by acourt on Dec 4, 2011 4:52:53 GMT
Here's a detailed explanation for the "nuts and bolts" crowd... ;D The DC-9 had two separate systems available: the early mechanical RAT / EPR Indicator, and the later RAT / Thrust Rating System. First, a quick review to make sure we're on the same page. Ram Air Temperature (RAT) is the Static Air Temperature (SAT) corrected for compressibility and air friction at high speeds. It is the temperature that the engines and structure of the aircraft "feels," and is used for almost all performance calculations. Unless the airplane is stationary, RAT is always higher than SAT. Engine Pressure Ratio is a measurement of the difference in pressure between the intake and exhaust of a jet engine. It is one method of measuring the engine's power. So, on to the gauges. We'll start with the older RAT/EPR Indicator. Down the middle of the gauge, you'll see a white RAT scale with two mechanical pointers. On either side is a white EPR scale. At the bottom of the gauge, there is a three-position mode selector knob. To find the maximum EPR for a given condition, first rotate the mode selector to the appropriate position (NORM1 for Static Takeoff and Climb, NORM2 for Cruise and Climb, or EMERG for Go Around and Maximum Continuous). Now read up from the bottom of the temperature scale to the two white RAT pointers. Read across to either EPR scale to find the maximum EPR. Example: My DC-9-10 (JT8D-7) is sitting at ORD, approximately 700 feet above sea level. The static air temperature is 14C. I need to find my takeoff and initial climb power settings. I set the mode selector to NORM 1, noting that the EPR scales say "STA TO" and "MCL." I start at the bottom of the RAT scale and read up to the two pointers, which should be sitting right at 14C. I read left for a Static Takeoff EPR of 1.95, and right for a maximum climb EPR of 1.84. Voila! There's a caveat here. Let's knock the SAT down to -25C. Notice the RAT pointers jump way up the scale to -25C. The resulting EPRs in this case would be 2.22 for takeoff, and 2.14 for climb, both of which would blow your Pratt and Whitneys to pieces. (Boom  ) So, look carefully and you'll see a series of yellow numbers on the EPR scales. Those numbers are Pressure Altitude in thousands of feet. Let's look at the -25C example again. I set my altimeter to 29.92 to find my pressure altitude, in this case 680 ft. Now go over to the RAT/EPR Indicator. Start at the bottom of the temperature scale and read up to your STA TO pressure altitude, a little over halfway between the 0 and 1. Read left for a Static Takeoff EPR of 1.98. Do the same on the MCL side, and read right for a Maximum Climb EPR of 1.95. So the rule is, to find any EPR, read up from the bottom of the RAT scale to your pressure altitude or the RAT, whichever comes first. Read left or right for EPR. I normally set the mode selector to NORM1 for takeoff and climb, NORM2 for cruise, and EMERG for descent and landing. Now for the later RAT / TRS. There's two components involved with this system: the RAT Gauge / Thrust Rating Indicator on the panel, and the Thrust Rating Computer (the brains behind the whole system). There's the rub: the TRC automatically accounts for RAT and pressure altitude, displaying a usable number on the RAT/TRI. Below the TRI are six mode select buttons: TO (Takeoff) ALTN TO (Alternate Takeoff: a 5% reduction in takeoff power) GA (Go Around) MCT (Max Continuous Thrust) CL (Climb) CR (Cruise) Select the desired thrust mode by pushing the respective mode select button. An integral blue light comes on within the selected button. Set your EPR bugs as desired. A few notes... The Takeoff EPR settings are Static (i.e. stationary) settings. Expect indicated EPR to rise as much as 0.02 above the static setting by 60 knots or so. Always verify the power settings with N1. Takeoff EPRs should put the N1s nicely into the mid-90% range. Climb should be in the high 80% to mid 90% range. If you set the EPRs and the N1s seem wrong, something probably is wrong, and you aren't getting the thrust you hoped for. Abort! Careful with the ATLN TO setting on the TRI. That setting is designed to reduce engine wear at the expense of takeoff performance. In FS, we don't have any usable performance data as far as field length and obstruction clearance go. So unless you're sure you have enough runway and can clear the buildings at the far end, I'd use max thrust. Also note that this panel apparently has no way to adjust your V-speeds for ALTN TO. These two gauges are really quite well programed. And once you understand what they're telling you, they're really handy. I hope this helps! Al |
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Post by christrott on Dec 4, 2011 8:14:29 GMT
Al, having checked my DC-9 book, I don't see different V-speeds for alternate TO settings. The only time you'd have different V-speeds is if you're runway limited, in which case, I agree with you - you should've been using full power or hauling less weight. If you download the Matt Zagoren charts, they're not for all DC-9 and MD-80 variants, but they do give you good ballpark numbers for the others and it does include runway limiting. Additionally, if you go to the Boeing website, you can download the Detailed Technical Specifications for the DC-9 series which includes charts that show (in general terms) the runway requirements for a given weight that can be used for our purposes to determine the max safe weight since all default and most addon runways in FS are flat. |
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Post by Klaus Hullermann on Dec 4, 2011 10:31:59 GMT
Thank you Al for this detailed explanation of the EPR/RAT-gauge (analogue and digital).
I will read your posting more than once before I understand all this information to the full.
Klaus
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Post by walterleo on Dec 4, 2011 10:51:35 GMT
Hi:
The Richard Probst panel for the 737-200 ADV has an EPR computer which transfers the limit-value to the limit-bug of the EPR gauges.
The caveat expressed here to look to the other engine parameters also is quite true. This had to do with the Air-Florida crash at Washington (a 737). In that case a not activated heating element gave erroneous EPR values luring the crew not to use the available power to take off safely despite the snowcovered wings.
Walter
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Post by acourt on Dec 4, 2011 14:47:54 GMT
Chris, I've referenced the Boeing numbers and Matt's numbers, and they do work well. But in the absence of usable obstruction data, and no corrections for anti-ice, headwind and tailwind, and other aircraft and environmental conditions, I use those numbers only for general reference. Since I don't know for certain how much runway I'll use, or what type of climb gradient I'm guaranteed after takeoff, I just use max power. Personal preference ;D That's curious about the ALTN TO numbers. I unfortunately don't have any of those numbers, but I'll guarantee they're different. Using ALTN TO is no different than using any other reduced power setting, which always changes your V-speeds. Again, in the absence of usable data, I personally opt for max power. The funny thing about all this is that I'm splitting hairs. Here's an example... Let's assume a DC-9-14 with JT8D-1B engines. Under a given set of ambient conditions and aircraft configuration, my v-speeds are: V1 = 120 VR = 125 V2 = 134 For the same conditions, if I opt for operation at JT8D-5 power (a reduction in power, just like ALTN TO), my speeds are: V1 = 124 VR = 128 V2 = 134 A four knot change to V1, and a 3 knot change to VR. With the acceleration rates we're talking, even single engine, that's essentially no difference. Add to that the inaccuracies inherent in FS, and it's all a SWAG anyway. It all depends how anal you want to be!  Al |
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Post by George Carty - HJG on Dec 4, 2011 15:25:32 GMT
Hi: The Richard Probst panel for the 737-200 ADV has an EPR computer which transfers the limit-value to the limit-bug of the EPR gauges. I know - I used it to determine the correct values to display on my EPR computer for the JT8D-15s.  |
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Post by christrott on Dec 4, 2011 19:08:38 GMT
The funny thing about all this is that I'm splitting hairs. Here's an example... Let's assume a DC-9-14 with JT8D-1B engines. Under a given set of ambient conditions and aircraft configuration, my v-speeds are: V1 = 120 VR = 125 V2 = 134 For the same conditions, if I opt for operation at JT8D-5 power (a reduction in power, just like ALTN TO), my speeds are: V1 = 124 VR = 128 V2 = 134 A four knot change to V1, and a 3 knot change to VR. With the acceleration rates we're talking, even single engine, that's essentially no difference. Add to that the inaccuracies inherent in FS, and it's all a SWAG anyway. It all depends how anal you want to be! Al I don't understand why you'd have different V-Speeds for a different power setting at the exact same weight and aircraft as V-Speeds are determined by aerodynamic factors and braking effort, not by engine power. That's the FAA's requirements, not the manufacturers. V1 is the speed at which you must abort takeoff to stop safely by the end of the runway using braking alone. Thrust reversers aren't supposed to be included in the calculation. VR is the speed at which you rotate which is based upon your stall speed, not power or acceleration. V2 is based on controlability of the aircraft in case of a problem. Also, if think about it, if you did include acceleration as part of the V-Speed calculations, your V-speeds would go down, not up with less power being produced. BTW, I'll check again with the 737NG and 747-400 when I get a chance, but I'm pretty sure that setting TO-1 and TO-2 don't change the V-speeds on them either. They're the only two I've got real manuals for and a good FMC with thrust computer to cross-check. |
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Post by aerofoto - HJG Admin on Dec 4, 2011 20:03:52 GMT
Just quickly .... because I'm now rushing to wind-things-up for the year ....  There's only a 3 KT difference between your V-Speed calculations .... as you say .... and which will hardly make any difference at all within FS .... BUT .... the greater part of our effort with these DC9 simulations were employed in getting the "WEIGHT/LOADING" right for each aircraft/engine type combination .... The critical factor in all of this though is mating the right engine type/aircraft type panels with the correct engine type/aircraft type base packs .... Each aircraft panel features a weight calculator .... which calibrated differently so as to read up to the MGTOW for each DC9 type .... and which then has a direct relationship with the IAS/V-Speed alculations for each aircraft weight condition. These weight/speed calculations are also be influenced by Flap setting too .... and again in regard to airport altitude as well of course. "IF" .... the wrong panel version is ever used with the wrong aircraft type .... then one's definitely going to realize inaccurate data .... particularly in relation to the calculated V-Speed indications, or, if the weight calculator isn't set prior to setting clicking on the ASI to set the V-Speed bugs .... then this data is going to be "OUT" again. I'm not saying this is the reason for any apparent discrepency you feel you're realizing. All I'm saying "IS" .... it could be a conttributing factor .... and more-so because I seem to be getting V-Speed calculations (based on MGTOW) which vary from yours, but, which I feel are reasonably accurate and in-line with what I'd expect to see between the heavier DC9-10 JT8D-1 and the lighter DC9-10 JT8D-5 versions. Again .... care must be taken to ensure that both panels and aircraft base packs are correctly assigned. Personally .... I find this what we've currently got is pretty darned good (I've never said it's 100% authentic)  .... "FOR FS" Mark C AKL/NZ |
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Post by Dan K. Hansen on Dec 4, 2011 21:43:31 GMT
I suppose you mean 100% instead of 1005 |
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Post by aerofoto - HJG Admin on Dec 4, 2011 22:11:12 GMT
YES ! ;D Just "TIRED" Dan .... and hurrying too I'll correct that imedistely Mark C AKL/NZ |
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.... "FOR FS" 
