Hi! I have the Problem that RPM (N2) and Exhaust Temp is going low in high Altitude! Is there a way to fix that in the Airfile? The thing is that this 2 Instruments should stay at a constant level, no matter which altitude I have! Any Ideas?
Post by Tom Goodrick on Apr 16, 2011 11:34:13 GMT -5
RPM (N2) should stay constant as set as long as throttle stays in the normal cruise range. But I don't know about Exhaust Temp. The inlet temp goes down significantly with altitude. What aircraft are you flying in FS and what aircraft do you fly in real life? I don't usually look at exhaust temp.
I flew a short test in the Beech KA350. I cruised at FL280 at 71.90% power and at FL200 at 71.68% power (I tried to set the same power but there was a slight long-term oscillation and I didn't want to wait for it to stabilize.
At FL280, Power 71.90%, 75.6% TQ, 586C ITT, 408 pph/e, 1501 RPM (as set), 222 KIAS, 337 KTAS.
AT FL200, Power 71.68%, 77.4% TQ, 613C ITT, 418 pph/e, 1501 RPM (did not change prop lever setting), 225 KIAS, 300 KTAS.
What was it you were keeping constant between the different altitude levels?
Hi Tom! I also took a ride on the Beech KA350! On ground with full Power I have 100% RPM, on FL 260 with full throttle only 90% RPM. I dont know about this Machine, but this difference is automatically hydro-mechanical corrected on a Jet Engine in real!
The reason for the difference is the atmospheric pressure, so I am looking for a curve or something in the Airfile to correct this, that the RPM stays more or less constant at the same RPM level.
My Bird has on Ground 8460 RPM and a exhaust Temp. of 700°. At FL 400 only 8000 RPM and 560° exhaust. A Former Pilot told me that no matter on which FL you are, the RPM stays constant +- 50 RPM and also the Exhaust Temp. +- 20°. It would be great if there would be a way to correct this.
Post by Tom Goodrick on Apr 17, 2011 7:55:34 GMT -5
I have checked the atmosphere in FS2004 at all levels to 70,000 ft against standard tables and it is pretty good. This is the atmosphere you see in FS2004 when you set Clear Weather. I have several sets of atmosphere tables. I used to work for NASA abd specialized in the flight mechanics and aerodynamics of shuttle=type spacecraft entering the atmosphere and flying to a landing at the surface. The density, temperature and pressure profiles in FS2004 are very similar to the tables I used with NASA. Of course you can get arguments about what is "standard". We used to separate them into East Coast or West Coast or Summer or Winter, etc. Somebody set one as Standard in 1958, another as Standard in 1962, the 1976 and there are probably some new ones I haven't seen. But suffice to say the Clear Weather profiles are very reasonable and the variations you find with Real Weather are determined using scientific principles.
The effects on aircraft flight are properly determined in FS2004 - true airspeed relates to density allowing faster flight at altitude. The speed of sound is properly computed from temperature at altitude so that Mach number can be properly determined.
If you set Real Weather, then the atmosphere is different as it is in real life. To compare the atmosphere on any given day and altitude with a standard atmosphere profile, real pilots use the corrected outside temperature. In FS we can see this by reading OAT in degrees C. That is corrected for motion. I have made such a gauge. The temperature gauge many people use from the Bell helicopter is bad because it heats up as you gain airspeed. This should not happen with a properly designed stagnation temperature probe. So turboprop pilots often use the ratio of temp C to standard C. Performance tables for the turboprop often include curves for that ratio.
I don't think you have to change anything in FS2004 nor can you change what may be needed. Atmospheric pressure and temperature do change correctly with altitude in FS2004. The case you mention of flight at FL400 is well above the legal ceiling for the Beech 350. There should be a decrease in power!
I had to check the accuracy of the atmosphere in FS95 in order to use FS to demonstrate flight mechanics problems with some NASA projects I worked on. There were some problems with it so I had to keep the altitude low. I complained to Microsoft and so did others. FS98 came out with many improvements.
I cannot attest to all aspects of the accuracy of the turboprop propulsion in FS2004. I have compared FS experience to real flight test reports published in reputable magazines. There is also some variation in engine management related to company policies and to different engine control computer software in the Real World.
By the way, the only aircraft I know of in the Real World that commonly set power using exhaust gas temperature are flying Garrett engines like the Rockwell Turbo Commanders. The EGT gauge is not used in the Beech 350 default panel, nor is it used by Real World Beech King Air pilots as far as I can determine from test reports. What panel are you using to see an EGT? I am not sure there is an EGT parameter for a turbine engine in FS. (I don't have the panel SDK on this computer.)
Let me see if I remember the entire thread. Tom's responses are mostly right on. A few points tho: The KA is going to reach an altitude where power, shown on the torque gauge, reduces at max throttle. I'm sure this occurs well below FL400. At the beginning you did mention N2, but later, the use of "RPM" could be confusing, as you should be using the expression N2 rather than RPM. "RPM" as stated refers to the prop. Note specifically that SAT and TAT are two different measurements, and TAT increases as speed increases. ITT or any other temp can be critical on take-off/ climb, although at cruise, it should be okay if initial cruise is okay- but occassional glances are to be expected. In this case,also remember, you are talking about two different engines, therefore the two gauges will shown different readings at the same torque setting. Not often modelled in FS. To re-state, how the engine itself reacts to climbing depends on the engine type and variation- some engines the power levers must be pushed forward, within parameters of course, as alitude increases. I think that covers anything I wondered at in the posts. However, the modeling in FS is suspect, depending on who did the actual modeling. Some gauges are actually quite good, the DF727 is the best, but you'd have to have been a 727 driver to appreciate what they did. That also includes "flight dynamics". I've seen other gauges that are way off. Unfortunately, MS does a poor job in modeling the actual operation of the PT6A (eg King Air type engines), which to the best I've been able to figure is an FS limitation. lr.
Post by Tom Goodrick on Apr 17, 2011 17:03:24 GMT -5
Thanks for your input Lou. I use N2 and RPM interchangeably because, at least in FS, in flight they are proportional to each other by the gear ratio between the 2nd fan and the prop.
Our friend may be the victim of a faulty gauge design. He is using at least one custom gauge.
I can make faulty gauges too. I just made a corrected version of my power gauge for turboprops that is handy for setting power. As you know well, a variety of methods are used in turboprops to manage the power. This gauge shows the actual percent power being developed regardless of the method used. It uses the product of the percent N2 and the percent torque so it is independent of the particular engine. Send me an email if you'd like a copy of the gauge.
In order to clarify what I think I understand, FS does not typically use the correct parameters to indicate power on turbo-props as torque, so you are using the parameters that actually show real power. So if I install your gauge, it will read what it would actually read in the real airplane, not an incorrect value. Do I have that correct? lou.
Post by Tom Goodrick on Apr 18, 2011 22:48:03 GMT -5
Essentially right. My gauge gives the correct power. (I had the corrected gauge available and operating in one aircraft but named as a test gauge while the gauge in general use used the old, less accurate method.) The parameters are there that could be used to indicate the power but they may not be in the form you are accustomed to. I have assumed that Beech signed off on the representation of the King Air panel as having the essential elements - torque, interstage turbine temperature (not sure that works right), fan rpm and prop rpm. Some turboprops use EGT and some use EPR (I think, not sure, example Dash 7).
As you have pointed out there are some details of the engine operation that are not correct. As I understand it this applies to some transitory situations, not to basic cruise and climb conditions. I have good engineering data on the Beech King Airs that indicates they perform properly and that the parameters a real pilot would use can be used in the sim to give proper performance. I will give an example of a report on the Beech 350 by Edward H Phillips in Aviation Week and will describe a table for setting cruise power in the Beech B200 King Air that appeared in a text book on flight mechanics.
Post by Tom Goodrick on Apr 19, 2011 10:19:35 GMT -5
To see the process for a typical turboprop flight, follow this procedure with the King Air 350 described by Edward H Phillips in Aviation Week, Sept 30, 1991. Phillips is writing in the first person. He's the "I" in this text.
"I activated the starter for the right engine and moved the condition lever from cutoff to the low idle gate as the gas generator speed (Ng) exceeded 12% minimum. (I don't know if this is N1 or N2). After recharging the battery, I repeated the procedure to start the left engine. With 3600 lb of fuel on board, the airplane weighed 13,400 lb as I taxied to Runway 5 at Salisbury. The manual nosewheel steering was positive, and visibility from the cockpit was good. During taxi, I lifted the power levers up and aft of flight idle gate into the ground fine range, which reduced blade angle and virtually eliminated brake application to control speed. (We can do that. That seems to be the same as starting reverse blade thrust. Note the end of the flight when reverse thrust is applied.)
After completing the checklist, Sullivan (Beech rep in copilot's seat) calculated a takeoff decision speed (V1) of 104 kt (KIAS), rotation speed (Vr) of 106 kt and a takeoff safety speed (V2) of 113 kts. (On jet panels I have a routine that calculates and displays V2 based on weights. I don't do it on turboprops because the fuel weights are small enough that the speeds don't change a large amount.)
I aligned the aircraft with the runway centerline and advanced the power levers. The propellers came into governing range at about 50% TQ as Sullivan monitored and set takeoff power at 90% TQ. There was no tendency for the propellers to surge as in the model 300, and directional control was good as the aircraft accelerated.
After a takeoff roll of 3,700 ft, the aircraft reached Vr and I rotated the 350 to about a 10 degree nose-up pitch attitude. The rotation force was lower than I expected and lower than that of other King Airs thanks to a heavier bobweight that improves longitudinal (dynamic) stability and expands the center of gravity range.
With a positive rate of climb established, I retracted the gear. Flaps were retracted after passing the 125 kt blueline for single-engine best rate of climb speed. Cockpit noise level was surprisingly low.
Climbing at 170 kt, we were cleared to Flight Level 280. Climb power was set at 98% Ng, 70% TQ with interstage turbine temperatures indicating 780 C. Propeller speed was set at 1500 RPM and fuel flow showed 360 pph/hr per engine. ....
Climb airspeed was decreased to 160 kt from 10,000 to 15,000 ft, then to 130 kt as we passed through 25,000 ft. (This indicates effective power has decreased with altitude.) It took 18 minutes to reach FL280 with a rate of climb indicating 800 ft/min at that height. ATC cleared us to our planned altitude of 31,000 ft. The pleasant flying qualities of the 350 convinced me to continue hand-flying the aircraft throughout the trip.
I made the transition from climb to cruise flight (at 31,000 ft), with Ng remaining at 98%,
TQ indicating 48%, and fuel flow was 225 pph per engine. True airspeed worked out to nearly 270 kt. Cabin altitude was a comfortable 9800 ft.
(They cruised for about 1 hour over the Atlantic until they began taking vectors for a descent into the New York Terminal Area, heading for Farmingdale on Long Island.)
For most of the descent I maintained 190 kt indicated (KIAS) and found the 350 mixed easily with the abundant jet traffic. It responded quickly to power and airspeed changes needed to maintain ATC flow into the New York Terminal Control Area. Sullivan and I completed the prelanding checklist as we entered the traffic pattern at Farmingdale for landing on Runway 19. The landing gear was extended when airspeed fell below the 184 KIAS maximum limit, and approach flaps had already been deployed during the final phase of descent when airspeed decreased below the 202 KIAS limit.
Cleared to land I selected full flaps on final approach, trimmed the aircraft to relieve control pressure and maintained a reference speed of 102 KIAS. Over the runway threshold I reduced power to flight idle and initiated the flare.
The 350's main landing gear settled on the runway with a gentle thud, followed quickly by the nose gear. I raised the power levers and moved them aft into ground fine range and applied moderate braking to make the intersection turnoff."
This piece is a little unusual in the way kt is used in the first part instead of KIAS. In the last part they use KIAS. It is important to note that true airspeed is only used when talking about cruise speed and bears, when combined with wind speed, on the time it takes to get to the destination. KIAS is used to keep the airplane out of trouble (keep it flying and keep from breaking the gear and flaps).
Power can be set by any combination of measurements singularly related to torque and to prop rpm. Different companies select different gauges in this relationship and provide guidance to the pilots in their Pilot Operating Manual.
In addition to being published in an issue of Aviation Week and Space Technology (a publication mainly for professional pilots and engineers), this article was published in a book entitled "BUSINESS & GENERAL AVIATION AIRCRAFT PILOT REPORTS" (McGraw-Hill, New York, 1996). Other aircraft discussed in this book include several business jets, turboprops and a few singles. Commercial airline aircraft are covered in another, similar book. The publication here is justified under the "Fair Use Clause" of the copyright law because one purpose we try to serve here is aeronautical education.
(Sorry about the formatting. This was written offline in Notepad and copied in. Then I went through and corrected all messed up line endings I found in this forum's editor. Then it displayed the text with new formatting problems!)
Hi! I checked your gauges, tanks a lot! I used the Digital N2 xml on my Jet (not Prop) to see what happen. The thing what I got is, that I have now on ground N2 = 99.9% at FL 400 N2 = 106.0%. This is exactly the oposit I had befor. In this example I got 6% more N2 at a high Flightlevel than on Ground. But what I need is that on Ground and at FL 400 N2 should be 100% +-.
I have no Idea how it is in real with a Prop Machine, but what I know for sure is, that the Former Testpilot said, that on Ground and at FL 400, you always have moreless 8460 RPM/N2 what ever with full Throttle. (hydro-mechanical corrected).
Thats why I came up at the beginnig with this strange Idea to find something in the Airfile.
My Bird has on Ground 8460 RPM and a exhaust Temp. of 700°. At FL 400 only 8000 RPM and 560° exhaust. A Former Pilot told me that no matter on which FL you are, the RPM stays constant +- 50 RPM and also the Exhaust Temp. +- 20°.
Hi Tom! This is what I posted in my second Posting! Fakt is, that in real you have +-50 RPM, Exhaust Temp +- 20° with full Throttle (this is moreless hehe). Thats why I was wondering that everything was concerned to Props here...
Okay. We are talking here about the KingAir xxx, whereas I flew the Beech 99. However they both have the PT6a-xx engines. The newer versions have had some changes. He said he moved the condition lever forward at 12%, although as I remember the figure was like 20%, but I could be wrong. However, it appears to me that he made a serious error in his take-off procedure. The way I understand it he: rotated at Vr (106), positive rate gear UP (), didn't raise flaps until he reached 125. Could be okay for some, or many a/c, but you want positive rate- gear UP, flaps UP--- IF you are using flaps for take-off, which is not customary in that a/c. Typical T.O. is no flaps. Apparently he is confused about "V2" and "blue line". Or, they have changed the definitions of the words, and nothing I've seen anywhere indicates that. If I remember correctly N2 in the PT6A engines is the gauge indicated. He said the props were not in the governing range until 50% torque. I take issue with that, however, he is not a KA pilot, was probably quite busy mentally, if not overwhelmed, the "co-pilot" had to set power, so he was probably not aware of the actual setting where, the props, ummmm, wait a minute... Something is wrong there. Below a specific torque level (torque, or, ), prop pitch is governed directly by the position of the power levers. Once torque increases to a certain level (well below 50%), (or is it ...), prop RPM is controlled by the prop lever. If in actuality they had 50% torque and the props weren't being governed, the Beech check pilot would have aborted. Later, he said he was cruising at 48%, so ...
His IAS would definitely be dropping off before FL250, which is why he needs to be using mach vs. IAS, which is, essentially, useless at that altitude. This a/c is not an Electra or Metroliner. It has a Pratt-n-Whitney PT6A engine, so the expressions "flight idle gate" and "ground fine range" explain what he's trying to say, but what he did was to move the power levers from idle into reverse. Wrong terminology is okay (for the TV shows), but it is misleading and leads to incorrect ideas to those who don't know or a person who wants to understand the operation. In fact, he (should have) started the engines with the power levers at idle position and props feathered, then after start, moved the prop levers to full forward and pushed the power levers up then back to idle when he wanted to begin taxiing. Moving the power levers from idle to a bit forward controls taxi speed by changing prop pitch, but not engine RPM. To come to a normal stop, lift the levers over the gate and barely into reverse and the props reverse, but by just moving into reverese position engine RPM does not increase. During the entire taxi portion as you work the power levers, N2 remains constant. It would be common, to increase taxi speed some or prevent the a/c from slowing, to see the pilot push the power levers way forward then immediately back to idle- and note that turbine RPM remains constant, but you can hear the props changing pitch (as does the RPM).
Now a thought comes to mind. Be aware who is writing the article, as well as who is doing the flying. Some "well known" and "reputable" aviation magazine had an article about flying the DC3 some time back. I think maybe it was written by a light plane pilot, a woman, with no DC3 experience. I knew some DC3 pilots, and her article was at odds with many things they talked about. I contacted a pilot who had flown them and he said she didn't know what she was talking about. They have a program here in MX called "Aviation Disasters". The pilot actors are the"3 Stooges" wanna be's, the dialogs are changed, the sounds must come from Hollywood FX, turboprops have sounds from piston engines, facts given are limited, etc. Well. lou.
Post by Tom Goodrick on Apr 19, 2011 16:57:36 GMT -5
Lou, remember the Beech rep was in the right seat and was there to make sure the author-pilot handled the Beech correctly. You don't think you can cruise at 48% torque at 31000 ft? This magazine is far more "reputable" than FLYING which is the one you are referring to. But you should note that one of those females was an experienced FAA examiner in the DC-3. This author, Mr Phillips, normally writes on piston aircraft. But he impressed me as a careful person who studied an aircraft thoroughly before writing about it, If his technique was as bad as you say, I think Aviation Week would have been buried in letters complaining of incompetance and Beech would have required a correction.
48%. No problem with the figure, but he says at take-off the props weren't governed until 50%, but he is cruising at 48%. There is a contradiction there. Beech check pilot. The person writing the article was not being checked out in the KA. He hadn't gone thru the ground training program. He was flying it as a demo flight. He is probably an experienced GA pilot, including twins, but he was not a KA pilot at the time. I'm sure with a safety pilot on board, he could basically manage the airplane. First time for everybody. I personally knew a pilot at the Beech company in Wichita. In fact he was a "test pilot". He'd spent years flying in the military. Only met three " pilots" in my life who were not competent in any way and should never have been flying. Two were student pilots- one quit flying at about 25 hrs. and the other quit after he busted his private check ride. The third one was a test pilot at Beech. After the military he went into civil flying with a company and the FAA immediately (almost) removed his authority as a designated check pilot; finally the company "let him go"; he went to Beech as a test pilot. Had a friend who was a check pilot for Cessna Citations. He'd tell me stories about clients and potential clients he'd put thru the check-out program and he'd laugh- I didn't know whether to laugh or cry at some of the stories. He likes to use the phrase, "You'll read about him some day in 'Cause and Circumstance". Some of these people could push the butons at the right time, but totally out-classed by the airplane. I had a friend who was an instructor at UAL. Part of his job was to check out Captains from other airlines in different equipment or upgrading from F/O to Capt. 12 hours sim time was programed. 15 was more-or-less common. A lot of these pilots were foreigners. Let's see if I remember where they are from... how can I be "politically correct here"? Well, I'm not going to say, however, he would never fly on airlines based on that continent south of Europe. He'd consistenly give 25 hrs of time, go to his manager at UA to explain the guy wasn't ready yet, and the response was, "This is a business. Sign him off (check him out and sign the papers)." So I'm not saying anything against the Beech check pilot. He's not going to let the other guy buy the farm or otherwise hurt the airplane. They were FAA check pilots? Want to hear a (good) joke? "Good afternoon. I'm from the FAA. I'm here to help you." Okay. One step forward is that unlike an ealier time, at least now FAA check pilots have to be certified in the airplane. That's a step forward. I'll take info from a line pilot over an FAA inspector any time there is a discrepency. I don't remember the specific statements made by the author, but some were definitely wrong. Typically, companies do not require corrections concerning aviation media. They don't have time. The papers are full of statements that are no where near the truth. TV and news programs too. I could give a book of examples. So I'm not questioning the check pilot, nor the author. Certain points are suspect at best. The fact that a person has a position doesn't necessarily mean he is competent. "Our pilots exceed government requirements." Remember the Comair thing on approach a few years back? lou.