atc4ksaw

I've been doing some poking around on Microsoft's ESP Developer's center and found this: http://msdn.microsoft.com/en-us/library/cc707070.aspxIf you scroll down, you'll see some explanations to Tables 509, 1503, 1504, and 1508. The explanations for 1503 and 1504 are what we all already know. But for 509 and 1508, the explanations, to me, are a bit more interresting. This sample file doesn't exactly name the tables by name, but the descriptions closely compare to those in Aired.For 1508, it explains that this as a "N1 to shaft torque table" and the output (y-axis) is "percent maximum torque (corrected)". So could this be some correction for altitude, speed, to define the relationship in free turbine engines between the gas turbine and the turbine that turns the prop? Which would explain this tables' effect between N1 and N2?For 509, the ASP file explains this is RPM vs. Friction torque as explained in Aired. However, it further explains that the output from this table (y-axis) is Torque due to Friction expressed as a percentage of max torque. In tests, increasing this factor decreases torque so, thinking logically, this means this table introduces a loss of torque due to friction from the bearings in the engine itself as well as the friction in the gear box that drives the prop. One of the things that I find interresting is that, keeping in mind the definition above, the output from this table is in % of max torque that is defined in the .cfg and the default aircraft, as well as some of the payware I've peeked at (never copied but just looked at for comparrison) all have the same factors. At 100% RPM (another factor I find interresting that I'll explain in a bit) the torque due to friction is .80... or 80%?? According to the FAA's Airplane Flying Handbook, "The energy of the hot, high velocity gasses is converted to torque on the main shaft by the turbine rotors (TBL1508??). The reduction gear converts the high RPM-low torque of the main shaft to low RPM-high torque to drive the accessories and the propeller (TBL509??)The question comes back to: "OK, now how do we figure out how to set each of these tables?" It seems that, confirming Aired's description, that TBL1508 sets N2 by defining the low amount of torque produced by the process of the exhaust gasses producing a turning force on the prop turbine. It would then seem that we need to find some reference that can define appromixametly how much torque is produced by the gearbox and the process of the gas turbine turning the prop shaft in order to determine starting points for setting up a turboprop.The propblem reverts back to how to set the Gas Generator in Table 1503 to read accurately given throttle inputs. I can't seem to understand why I can't get any higher CN1 speeds than 101.5%.But in the end, I think it all comes down to the fact that, as long as you set up TBL1508 to give approximate N1/N2 relationships, you can adjust TBL509 to give proper torque at 100% prop RPM (which is what I think this table is referencing along the x-axis) as well as proper torque/HP at cruising prop RPM.I may go to the library and see if I can find some texts on turboprops.

Very true Herve on the N2/prop lever point.I'm one of those sticklers for trying to set things up according to the specs. But what I find that is important with these elusive turboprops is to get the torque output correct as well as Tables 511 and 512. Adjusting 509 and 1508 will set up the proper torque while 511 and 512 will give you proper propeller thrust. So I'm willing to settle for that in order to produce results that come close to reference videos and photos. I would just love to solve this TP mystery. :)I also have figured out the issue with the engines remaining spooled up. I touched on it in another thread, but I'll summarise it here again: I use the published data that I can find to set up the first line of tbl1503, which is static at sea level as you know (CN=N). For all the other lines, I use the formula CN=N/SQRT(Theta Total). This usually gives me pretty close N readings throughout the operating range for jets. However, for TPs, using this method, where the lines that assign CN2 at higher altitudes are higher than the first line in 1503, I will encounter this "hung" engine issue. Whenever I arbitrarilly lower the higher IAP lines, the problem goes away. I've looked at the default TPs as well as some payware and see that the numbers are lower as well in these lines. It's very curious.

Thank you Herve for the comment. it seems that no matter which table I change, the output stays at CN1: 101.5% and CN2: 100%. If I change TBL1503 to give, at 100% throttle, 117.7% at IAP 1.00 and Mach 0.00; I still only get CN1 of 101.5% and CN2 of 100.0%.If I lower the value in TBL1508, I can change the relationship between CN1 and CN2. CN1 stays the same, but CN2 will change up to a certain point. But after that point, torque will increase but CN2 will not.One other issue that has confused me for a year or two:At cruise and 100% throttle, I set the condition levers to the appropriate torque settings that I see in airliners.net photos. These are the references that I use to model the engines. However, after cruising for an hour or so, I pull the power levers back to start a descent and the engines stay spooled up for minutes. This usually ends up in an overspeed condition which is bad for users using FsP or wanting realism. Any thoughts? I compare my tables to the default king air and they are very similar with the exception of TBL1504. The king air numbers are much lower than what I've calculated these values should be.Thanks again, Herve

Hello everyone,I've read some threads that touch on this, but I'm hoping some guys like Herve or one of the other gurus can shed some light on this question.We can start by saying that jets are much more straight-forward than turboprops to model. Throttle position sets CN2 in TBL1503 and 1504; TBL1502 sets the relationship between CN2 and CN1; TBL1506 sets thrust; TBL1507 sets Ram Drag; TBL1505 sets the spooling of the engine. And I think we can say the .cfg entries are straight forward.We can now say that the relationships between the tables for a turboprop, at least for me, don't really follow the straight-forwardness of the jet. Here's an example:I'm modelling a PW124B for the ATR72-200F. The TCDS' for the aircraft and engines give the N-speeds as well as the actual RPMs of the engines. When I set up TBL1503 relate a 100% throttle position to produce a CN1 (usually CN2, but in turboprops this is CN1 as you guys know) of 102.7% engine RPM with a static aircraft at Sea Level, AFSD reports, under the engine parameters, reads 101.5. When I look at TBL1503 in AFSD, it reads: 100% throttle, 1.000 IAP and 105% CN1. This is confusing the heck out of me. I'm under the assumption that, in turboprops, throttle position in TBL1503 would set the gas turbine (CN1 in AFSD) engine speed accurately with a static aircraft at sea level. Why would this read erratically for me?Then I'm assuming, after reading the notes for TBL1508 in AFSD, that this will set the relationship between the high and low speed turbines, and in turn, torque.After that, I'm guessing that TBL509 can be used to fine-tune the torque by changing the Friction?Any help would be greatly appreciated because, after 3 years of tinkering, I can't get these relationships to coalesce into a linear process to be able to properly set up a turboprop. Trial-and-error takes a long time and produces much frustration.Thanks in advance.Scott

FIXED!!! Yea!!! I don't like to do this but I took the default King Air air file, renamed it, and put it in my B1900 folder and used it. The engines performed well. So I started to replace the engine sections in the .air file with mine until the engines started to screw up. The problem was TBL1504.The formula I found on one of the BBs someplace along the journey of learning was: CN = N / SQRT ( Theta Total). Where N = uncorrected Engine N rotation percent and Theta Total = Theta * (1 +.2 * M^2 ). Where Theta is the the standard temperature ratio between cruising altitude (I use max published altitude for the aircraft per TCDS) and Sea Level. This is in degrees Kelvin. M = Mach number. (for the tables I use max operating number or Mmo per TCDS). The formula to attain Theta Total is from Herve's AFSD.This generally led to having the high mach (TBL 1504) higher than the Low Mach TBL1503. Perhaps I was using the wrong formula for CN. Perhaps it is CN = N * SQRT. I'll give that a go and see what results I get. In comparrison, the origional tbl1503 that I calculated read the following at 100% throttle: IAP 1.000000 = 104.000000 IAP 2.700000 = 114.295777And TBL 1504 read the following at 100% throttle at .480000 Mach: IAP 1.000000 = 101.683594 IAP 2.700000 = 111.750052The King Air TBL 1504 read much less than mine. @ MACH .900000 IAP 1.000000 = 83.830000 IAP 4.237000 = 95.000000I am not familiar with the properties of a turbine engine's characteristics at altitude and high MACH numbers so I don't know if the engine would be capable of higher N percentages or not. I may have to see if I can ask some guys at Purdue for some insight or one of my friends who flies ERJs for American Eagle if he'd know.But at any rate, the question I had about tthe Propeller section still stands:What is prop_tc and what does it affect?Any help would be appreciated!

Thanks Anthony. It's difficult to try to briefly explain. :) And thanks to WarpD as well. That's good to know. A good deal of airliners are not simply trapezoidal wings, but double delta wings (the inboard wing section has a different taper ratio than the outboard portion) and the MAC just can't be placed using the simple formula for trapezoidal wings. Those two entries in the .air file really help to set the plane up correctly.

Ah! Thanks! Most of my work is in FS9 for now. So how does FSX calculate the MAC and it's position?

Thought I'd add this:.cfg[GeneralEngineData]engine_type = 5 Engine.0 = -15.809, -8.600, 0.570Engine.1 = -15.809, 8.600, 0.570fuel_flow_scalar= 0.75min_throttle_limit = -0.25[propeller]thrust_scalar = 1.00 propeller_type = 0 propeller_diameter = 9.167propeller_blades = 4propeller_moi = 57.461beta_max = 50.00beta_min = 4.90min_gov_rpm = 25520prop_tc = 0.004gear_reduction_ratio = 19.349fixed_pitch_beta = 0low_speed_theory_limit = 80prop_sync_available = 1prop_deice_available = 1prop_feathering_available= 1prop_auto_feathering_available= 1min_rpm_for_feather = 700beta_feather = 79.0power_absorbed_cf = 0.92defeathering_accumulators_available= 0 prop_reverse_available = 1minimum_on_ground_beta = 1.0minimum_reverse_beta = -14.5[TurbineEngineData]fuel_flow_gain = 0.017inlet_area = 1.0 rated_N2_rpm = 32894.00 static_thrust = 178[turboprop_engine]power_scalar = 1.0maximum_torque = 3950Also could anyone explain what the prop_tc is and what it does? I have no idea. LOL.Thanks again,Scott B.

Hi everyone. I'm trying to model a B1900D and I'm running into a common problem that I have. I'd like to figure this one out so it isn't as time consuming in the future. I have the TCDS info for the PT6A-67D as well as the prop data/weight. I set the .cfg entries the best I can as well as records 510, 511, 512, 1501-1507. They don't have any real great departure from the default King Air 350 besides using the data for the different engine: i.e.: max torque, prop diameter, beta angles and such. I'm not too familiar with the 509 and 1508 tables but I tweak to get the proper torque and HP.The problem is that as I'm cruising along at 25000', I need full power and set the condition levers to the proper RPM, just like I saw in a Airliners.net photo. However what happens is as I pull the power back to begin a descent, the engines keep spooled up for minutes even with the throttles pulled back to idle. It isn't bad if I don't use 100% throttle, the engines remain rather responsive.I've pulled up the .cfg and .air for the 1900 to the default king Air and there isn't anything that really stands out as being out of the ballpark. I'm using a Prop MOI of 57.461 which I calculated from the following equation: MOI=2/3 * prop weight (slugs) * prop radius^2. The prop weight (including HUB) acording to the TCDS (P10NE) is 132 lbs (or 4.10269 slugs).I'm not sure if it is a prop MOI mix-up on my part. Is the MOI .cfg entry fo the propeller section as a whole or just a blade (where it would multiply by the number of blades??)Could it also be in either the 509 TBL or 1508 TBL? It could be a friction problem, I suppose. But again, comparing my tbls with the King Air, it isn't too off. in the King Ait TBL509, @ x=100.0, y=.80. In mine, it is .685. And TBL 1508 are very similar.Any help would be greatly appreciated.Scott B.

Albiet it a bit late of a response, if you can find an airport planning document for the aircraft, it usually gives an exact location. :(

Oh, and once you start moving CG's around, I've never run into a aircraft that didn't become very unstable on the landing gear. So be ready for that! :(

In case you are not aware, the CG is measured along the Mean Aerodynamic Chord of the wing. That's pretty basic knowledge but I wanted to put that out there first. FS9 calculates the MAC from the information in the geometry section of the .CFG: Also pretty straight forward. There are also two entries in the .AIR file that will move the leading edge of the MAC: 1204 and 1515. I love these two entries because you can tweak the MAC to where it is supposed to be.First, you'll need to go to the TCDS for the FAA and figure out what the MAC should be. I'm pretty sure that all of the aircraft in the A319, A320, A321 family use the same wing. I'm guessing this because the data given in the TCDS has that information in the :Data pertinent to all models section. It reads: Reference Datum (where everything on the aircraft is measured from) is 100 inches in front of the fuselage nose. The MAC is located 700.85 inches aft of that point and it is 165.1 inches long.Next you can get a top-down three view drawing from the Airbus site: just look up the Airport Planning Documents for the aircraft. After you scale the photo (it's a little different after you print it out versus what the scale is depicted on the page), you can then measure out the MAC and find it on the wing.Fill out entries 1204 and 1515. The MAC leading edge position entry in 1515 is measured from the reference_datum_position in the .cfg. (positive aft of the reference point and negative ahead of it). I usually always set this reference_datum_position point at the nose unless I have hard data such as this case. It's a lot of work converting every other position in the .cfg but I like it. The aerodynamic center entry in 1204 is a very hard entry to find and compute. But as a general rule, most airfoils have this point between 25% and 28% of the chord. The true data is proprietary for Airbus and you'll never find out legally. It is important not to have it too far back or else the aircraft won't rotate properly without over-doing the elevator and horizontal tail entries in the 1101 section of the .air file. Those trim settings you have are great, but only will work if you have everything located in the correct place. Taper ratio, in case you don' tknow is simply the tip chord divided by the root chord. The .cfg entry that locates the main wing apex is also critical.I'm going into all of this because a lot of freeware I see isn't even close when it comes to the most important aspect: weight and balance. It seems some people just go for the trial-and-error to make the plane fly approach. There are a lot of good freeware out there, don't get me wrong, but this aspect of the aircraft is critical.Also critical, after locating the MAC and the wing apex in the correct place, is the empty weight CG location. This is the CG of the aircraft itself as it sits without passengers, bags, cargo and fuel. How you find this is darn near impossible as far as hard data goes. I personally research through Just Flight videos (sometimes you can catch a glimpse of the W/B charts. If you know what the loaded aircraft CG is, you can reverse engineer from there), Google, and even the friendly guys over at PPRUNE tech forums.Once you put everything in the proper place of where it goes, you should be able to get a good CG reading that makes sense. I once saw a freeware aircraft whose loaded CG was -55% but it flew stable. That should fly stable in real world ops. LOL.But please understand that having all the weight and balance correct in the .cfg and the .air entries will not ensure a well-behaved airplane. You must set the coefficients in the 1101 section correctly... specifically the lift and pitch sections. The pitch moment coefficient (the first entry) in the pitch section is the main wing pitching moment coefficient. This, along with the H. stabilizer, elevator, and even the pitch trim moment all come into play as far as what trim is necessary for each phase of flight. Typically, cruise trim is just a very minute positive trim which, in real life, would minimize drag. On take-off you need some help to rotate the aircraft; which is why you need a lot of positive trim.Personally, I set the main wing pitching moment first, then the h. stabilizer lift and moment, then the elevator lift and moment, then if I need to, tweak with the trim moment entry in the 1101 pitching section. To set the H. tail moment, I guess at a lift number and use the following equation from Dynamics of Flight by Etkin and Reid: Vh= ("l sub t" * "S sub t") / (MAC * S) Where "l sub t" is the distance between the main wing aerodynamic center and the H. tail aerodynamic center. "S sub t" is the H. tail area. MAC is the main wing aerodynamic chord. and S is the main wing area. Cm(tail) = -Vh*Clt+Clt*(St/S)*(h-hn) Where: Clt is the H. Tail lift (remember to divide what you put into 1101 by 2048). St is the h. tail area. S is the main wing area. (h-hn) is the distance between the empty weight CG and the Aerodynamic Center of the main wing. That's a good example of the research you need. It's a large undertaking to say the least. I"ve been at this for over 5 years now and I'm just getting a good understanding of how all of this works together. Any questions, just let me know.Scott B.

I was trying to find a good engineering approach to calculating MOIs as well. I bought USAF DATCOM and there was a entire section on how to calculate these figures. I've used them for several models and they work very well. It is a long and involved process so I made it part of my Excel spreadsheet. The big thing is calculating component weights for the aircraft (wing, V. Tail, H. Tail, Engines, etc). I found an interresting paper done at Stanford ( http://adg.stanford.edu/aa241/structures/componentweight.html ) to help out. But some of the constants have to be tweaked until you get ballpark figures for the Empty Weight. I'm thinking this is because the data was from older, mostly-aluminum aircraft where today's aircraft have more composites. But these two items together seem to get me into the right section of the ballpark. :)Scott B.

Hi guys.I've done a quick search for this but I didn't really find anything. If there's a older post someplace, just point it out and I'll go read.I'm trying to get some stuff straight in my research. Firstly, Pitching Coefficients: According to Etkin/Reid's Dynamics of Flight, Positively cambered airfoils create a negative (Nose Down) pitching moment and Negatively cambered ones, naturally create a positive (nose up) moment. So side question here: since REC1101 says + = Nose down, if I'm modeling a positively cambered airfoil (main wing), the moment coefficient in Real Life would be negative resulting in a nose down moment. So to correctly model this in REC1101, i should invert the sign and multiply by 2048 and enter that... correct?But the real question kind of relates to pitching moment. Acording to how I'm reading some other text books, if the CG is ahead of the AC, the H. Tail requires a lift vector downward (while, conversly, if the CG is behind the AC, the lift vector is upward on the H. Tail). Is that correct? Hypothetically saying that is correct, would I model that as a negative number in 1101:Cl_dh ?Then I have a question about the Cm_dt - Trim Moment entry, are there any formulas to calculate this, or is there some aspect of dynamics that I'm looking to adjust as I go trial-and-error on the entry?Thanks in advance and, like I said, if this is covered elsewhere, just point me in the right direction.Scott B.