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Guest Ron Freimuth

Fuel Management Systems

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Hi, I'm trying to design a fuel management system for older aircraft with many tanks (primarily the B-707/KC-135 and DC-8 aircraft). Part of this is being able to realistically control how the airplane consumes fuel from its tanks. The big problem I run into is being able to burn or transfer fuel from the center tanks into the wings before burning off the wing tanks. If you don't do this in these aircraft, you will encounter a sigificant reduction in range as the Center of Gravity moves too far forward and you are using a substantial amount of up trim to keep the nose in position since the fuel makes the nose want to go down. Now, the idea I've had is to devise a system using fuel selector gauges that have only and on and off position to simulate the boost pumps in each tank and that there is one for each tank (instead of the multiple that really exist to account for the simulator's deficiencies). So baiscally I'm wondering if I can create 8-10 fuel selectors within FS2002 and also if I can create selectors such as I suggested or if there's another way. I don't want to be putting the wing tanks in the center of the plane in place of the center tanks so they'll burn first because that's cheating and is confusing to other people who might use a panel with this system or this addon for panels.Your thoughts and Ideas are appreciated.

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Hello Chris, I am about to start a similar project for Concorde. The fuel panel consists of 11 fuel tanks. Fuel is being moved around the aircraft all the time on Concorde, the flight engineer is working constantly throughout the flight! "If you don't do this in these aircraft, you will encounter a significant reduction in range as the Centre of Gravity moves too far forward and you are using a substantial amount of up trim to keep the nose in position since the fuel makes the nose want to go down."This applies to Concorde also. On routes between London - New York, the fuel is pumped around the tanks to avoid this. On the London - Barbados route, which is 3900nm (200nm over the aircrafts max range) a full fuel load is required. On a number of flights, tank 11 (the rear tank) has become full, which then restricts the amount of fuel which can be pumped back, the CG then deviates from its correct position - and you get into the situation which you have described above. http://ftp.avsim.com/dcforum/User_files/3dda226d048cd562.jpgThis image shows the fuel panel on Concorde. The four main collector tanks can be seen in the centre of the image (tanks 1,2,3,4) - as well as the boost pump switches. Wing tanks are shown on the left/right (tanks 5,6,7,8). Above this the forward tanks (5A, 7A, 9,10). The rear tank (tank 11) is show in the center of the photo below tanks 1-4. I believe this setup is the similar to that used on the 707/DC8 etc? So far, the only K: events I know, which may be of use are: - Used to move fuel around the tanks, although rather limitedSET_FUEL_TRANSFER_FORWARDSET_FUEL_TRANSFER_AFTSET_FUEL_TRANSFER_AUTOSET_FUEL_TRANSFER_OFFThe following are used to select which tanks to feed from: E.g. Only Tanks 1,2,3,4

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I try with 10 tanks in my C-141 but the L/R tip tanks was not usable. I put the fuel selector for this tanks and the engine shutdown. In other forum say me. "the fs2002 has a bug" those tanks aren

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I'm not personally doing the coding (not my area), but am working on the bitmap and gauge layout with Michael Verlin over at HJG for this project. He and I were wondering if my idea would work. What you're wanting to do Andrew is close. Let me make an example of how I want to be able to do this-In the RC-135W (a plane the requires a LOT of fuel management) has 9 fuel tanks-Fwd BodyCtr WingAft Body#1 Reserve#1 Main#2 Main#3 Main#4 Main#4 ReserveUsual fuel consumption schedule is to be feeding the engines from the 4 main wing tanks while at the same time transferring fuel from the Center tanks (Fwd Body then Aft Body then Center Wing) to those tanks to keep them topped off. With the normal fuel transfer system, you can't do that. Finally, the Wings would be drained to 1,500 LBS each before the #1 and #4 reserve tanks would be used to feed the 4 mains, then the final 1500 LBS would be burned. With the current system, you can't do that. It's not a matter of moving the fuel forward or aft, it's a matter of moving it out of the Center tank(s) into the wings.On another note- even the 737 is the same way. You burn out of the Wings and feed the center into the wings to keep them topped. Most aircraft with 2 or 4 engines are setup this way since the Center tanks are technically "auxiliary" tanks since they are not required to have fuel in them to feed an engine since the rule of thumb is that you have 1 tank that feeds directly to each engine on the plane.Any ideas?

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Due to this "buggyness" and limitations in the FS fuel system, the only thing I can suggest is using a simplistic tank system in the menu, and then build a complete fuel system using gauges only. I don't believe it is possible to influence the CG position though, but any fuel mismanagement can be "punished" by cutting the fuel lines with i.e. the event (K:TOGGLE_FUEL_VALVE_ENG1).This works for me. I will "punish" with an engine shutdown (fuel valve turned off) if an attempt is made on crossfeeding from a dead engine (since the fuel pump is no longer running). Not using the mains makes sure crossfeeding actually works. This is on a Cessna 421B though, dunno how things would work out on a jet.

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Actually, having flown several extreme range flights with the RC-135W I can attest that the CG is indeed affected by poor fuel management in FS2002, just as it was in FS2000. I believe the problem with most aircraft not seeming to be affected is very simple- poor placement of the CG and Fuel tanks in releation to the CG in the model. I have found several models, incluing Kevin Trinkle and Gary Carlson's models where the plane will sit WAY aft if you mis-load the fuel system. Try filling the wings and putting nothing in the center tank and then taking off. You'll get an extremely premature rotation and have to use a TON of down trim to keep the plane flying right. In the real world, such a fuel mis-load would have ended up in the plane being on it's tail just sitting there, but that's an FS2002 limitation on the static state of the airplanes.Also, if you put too uch fuel forward or too much weight forward, you'll find that you can also break the nose gear on most planes too. I've done this on several occasions when not paying attention to how I was setting up the fuel and weight loadings on aircraft.

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Oh, I ment I don't think it is possible to affect CG shift as an xml means of transferring fuel amonst the tanks by code. Haven't tried the events for fuel transfer though, so I'm not sure they even work in xml. There are some events that doesn't work.Anyway, due to the limitations in the system, you most likely will have to compromise.

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You can check the CG position during the flight with the AFSD aplication. This program display you several data via FSUIPC. You can download and check it.Jose

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There are some CG variables available directly from xml variables, but I haven't checked their operation fully yet. If these work, there is nothing stopping you from doing "nasty" stuff :D

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>Hi, I'm trying to design a fuel management system for older >aircraft with many tanks (primarily the B-707/KC-135 and >DC-8 aircraft). Part of this is being able to realistically >control how the airplane consumes fuel from its tanks. The >big problem I run into is being able to burn or transfer >fuel from the center tanks into the wings before burning off >the wing tanks. If you don't do this in these aircraft, you >will encounter a sigificant reduction in range as the Center >of Gravity moves too far forward and you are using a >substantial amount of up trim to keep the nose in position >since the fuel makes the nose want to go down. In FS2K and FS2K2, trim has no effect on drag. Thus, a forward CG has no effect on drag and range. This is because the MSFS trim does not generate a 'Lift' component -- only a Pitching moment. A real elevator or H. Stab trim generates lift and moment. In a real AC, aft CG requires Down elevator (or H. Stab). That adds some lift so the Wing CL is reduced. Thus, Wing Induced drag is reduced with Up elevator, but not with Up trim in FS2K+. If one really trims the elevator (by using a trim control on a JS that changes the Elevator deflection), then range will change. Another shortcomming of MSFS. I think FS98 allowed 'elevator trim', but the MS flight dynamics amateurs often mess up good elements in the flight model code they purchased. Rather than fixing or improving it. MSFS unrealistic tank drainage is another example of them not understanding real AC. Ron

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Thanks for the great info. I do want my CoG to be placed correctly in the model. And I can report that getting it just a little bit off can produce spectacular behavoir in the aircraft! My first adjustment the plane would just do endless ever widening and lowering loops until it hit the ground.I have a question for the experts. A website for a pusher observation aircraft said the following:"The Seeker gives a remarkably smooth ride; one is seated forward of the Centre of Gravity, so the heave of the aeroplane in turbulence is offset (so far as the occupants are concerned) by the accompanying pitch, with the result that the effects of turbulence are greatly reduced, by comparison with an aeroplane of conventional layout."AND"A pusher layout does have one peculiarity to bear in mind, however; a burst of power in an undershoot situation gives no additional lift - so one cannot "pick it up by the bootstrap" if one gets too low, too slow."Does FS model this behavoir?Steve

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>Thanks for the great info. I do want my CoG to be placed >correctly in the model. And I can report that getting it >just a little bit off can produce spectacular behavoir in >the aircraft! My first adjustment the plane would just do >endless ever widening and lowering loops until it hit the >ground. I think Herve' Sors just UL'ed the new, AFSD v1.30 to the avsim library. AFSD shows CG and now 'distance from FS_Reference'. Also, current weight, fuel, and more other parameters than you want to see. :) I always work to get the FS AC so CG is 25% MAC (assuming that is correct for the AC) with full fuel and payload. Normally, CG changes as fuel is burned. Often the fuel tanks are a bit aft of the 25% MAC and as fuel is burned, the CG moves forward slightly. This corrects for the lower flight weight and little change in pitch trim occurs. A typical CG range is 15% to 35% MAC. But, since the Mean Aerodynamic Chord is only 5 ft or so for SEL's, that is only +/- 6 inches. The Lear 45 in FS has a CG range that is forward typical. I think the CoL for the Wing is set behind the MAC/4 and the virtual wing set forward. So the CG variable gives a balanced flight model when it shows something like 10% to 25%. I generally do not set the wing parameters in aircraft.cfg to the real wing. Rather, I set the virtual wing: a rectangle with the LE MAC/4 ahead of the CG. I don't know just how FSEdit calculates the changes in the AIR file from info in aircraft.cfg, but I do know some of it is bad! I haven't seen see much effect on flight as the CG changes, other than pitch trim. Unless the CG is at something like 50% MAC. Which would be half way back along the wing. However, I do think a forward CG does make the static pitch more stable. I just noticed a graph for the phugoid oscillation vs CG for a Cherokee, maybe I'll check the DF Archer some time to see if the phugoid changes anything like the graph. >I have a question for the experts. A website for a pusher >observation aircraft said the following: >>"The Seeker gives a remarkably smooth ride; one is seated >forward of the Centre of Gravity, so the heave of the >aeroplane in turbulence is offset (so far as the occupants >are concerned) by the accompanying pitch, with the result >that the effects of turbulence are greatly reduced, by >comparison with an aeroplane of conventional layout." >AND FS should model that, but you don't feel the difference. The location of the VIEW is what counts. If it is in the middle of a tranport AC you won't see the runway correctly. Especially when pitch changes during landing. One should see the effect of turbulence when he is some distance from the CG in an FS AC. Since AC pitch, etc. correctly from the spot view.>"A pusher layout does have one peculiarity to bear in mind, >however; a burst of power in an undershoot situation gives >no additional lift - so one cannot "pick it up by the >bootstrap" if one gets too low, too slow." >>Does FS model this behavoir? >Steve FS can model many things. Usually the limit is the designer, not the FS 'flight model'. We are currently looking at prop effects in the AIR file. However, MS killed the 'Prop effect on H. Stab' in FS2K2. Another bug they don't plan to fix for FS2K2. I did a pusher prop RQ-1 Predator flight model and it flies nicely. I reversed one of the 'stability deriviatives' to account for the inverted 'V' tail under the fuselage. However, I don't think the parameter was large enough to see the effect in turns. I think the public specs on the Predator are undertated. Based on basic aeronautics my model could stay up 40 hours at 65-70 kts. I think it can carry 300 gallons of fuel and the 100 HP Rotex powerplant normally is running at about 35%. The high aspect ratio of the wing helps. We have a research and development Forum on MS AIR files at: , it's linked from a pull down menu at the top. Ron

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> We have a research and development Forum on MS AIR files >at: >> , it's linked from a pull down >menu at the top. >> Ron Hmm, doesn't seem to work (pulldown menu doesn't exist, apparently anyway) with my version of Opera.I've been looking for this place in the past, no wonder I could never find the forum :DJust thought I'd let you know.

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>> We have a research and development Forum on MS AIR files >>at: >>>> , it's linked from a pull down >>menu at the top. >>>> Ron >>Hmm, doesn't seem to work (pulldown menu doesn't exist, >apparently anyway) with my version of Opera. It seems to take a while to load. I just got there again by clicking on the link above and see 'Message Boards'. The direct URL to the AIR file Forum was listed twice in my Aired.ini. At the top of the file and in Info for REC 1101. But, it changed more than once and I'm not sure what is shown in the aired.ini linked from one of the recent messages right here.Ron>>I've been looking for this place in the past, no wonder I >could never find the forum :D >>Just thought I'd let you know.

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Hi Ron,The aired.ini on http://www.avhistory.org/ seems dated and optimized to CFS compared to the one I got directly from you. Has it been updated to account for all the known/unknown issues for fs2002.I also downloaded and installed the CFS3 avsdk.msi. It seems to give some new details for MOI I had not seen before. Its in the Aircraft Container Overview.doc, p.7. It must be what FS2002 Aircraft Editor uses since they refer designers to FSAE to build the aero.

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>Hi Ron, >>The aired.ini on http://www.avhistory.org/ seems dated and >optimized to CFS compared to the one I got directly from >you. Has it been updated to account for all the >known/unknown issues for fs2002. There was a problem with the link to my Aired.ini at the top of the AIR file Forum, that may have been fixed. I checked the version when set the correct link and it was recent. Howver, you probably have a more recent version. The one attached to a message here was dated the 13'th. I keep making changes, sometimes just in nomenclature. The main stuff in the AIR file is pretty stable.>I also downloaded and installed the CFS3 avsdk.msi. It >seems to give some new details for MOI I had not seen >before. Its in the Aircraft Container Overview.doc, p.7. >It must be what FS2002 Aircraft Editor uses since they refer >designers to FSAE to build the aero. Is that the CFS3 SDK released recently? That requires G-Max to be installed? There are ways to calculate the MoI's from the AC weight and dimensions. In fact, Greg P. at avhistory wrote a VB app that lets you enter the AC weight, span, length, and type and it does the work for you. I've also found tables of AC MoI's and other data at various sites on the WEB. It appears that Roll MoI and Pitch MoI need to be quite different or an AC can be difficult to get out of a spin. I just noted that in an aerodynamics text I have. Ron

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Seems I've sparked an interesting thread here.For those of you who are interested in how much the fuel can effect the CoG of an aircraft, load up one of these planes-B-727 (Series)B-747 (Series)MD-80 (Series)DC-9 (SeriesMD-90 (Series)These aircraft all have VERY sensitive CoGs.Now for the CG exercise- Load up the plane with the fuel like thisB-727, MD-80, DC-9, MD-90 - Full Wings and Empty Center (or 1&3 full, 2 empty)B-747 - #1 & #4 Main and Reserves filledIn each case, with no other payload (i.e. empty plane), the aircraft should promptly rotate back on its tail. If it doesn't, then either the Fuel Tanks are mis-located, the Main Gear contact points are mislocated, the engines are not located and weighted correctly, or the static CoG is improperly placed. I know that Mike Stone's B727 is setup wrong (don't know which of the factors). I can actually fly the plane without problem with an empty center tank, which in real life would be impossible. I haven't tested POSKY or MelJet's 747s yet for this to see about them, nor have I tested the default MD-88 or other aircraft listed, I just know that this is what they do in real life.From your friendly ASIG Aircraft fueler,

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>For those of you who are interested in how much the fuel can >effect the CoG of an aircraft, load up one of these planes- >>B-727 (Series) >B-747 (Series) >MD-80 (Series) >DC-9 (Series >MD-90 (Series) >>Now for the CG exercise- Load up the plane with the fuel >like this >>B-727, MD-80, DC-9, MD-90 - Full Wings and Empty Center (or >1&3 full, 2 empty) >B-747 - #1 & #4 Main and Reserves filled >In each case, with no other payload (i.e. empty plane), the >aircraft should promptly rotate back on its tail. If it >doesn't, then either the Fuel Tanks are mis-located, the >Main Gear contact points are mislocated, the engines are not >located and weighted correctly, or the static CoG is >improperly placed. Yes, most FS AC are set up incorrectly (in just about every way possible). I check the FAA TCDS file for CG range and make sure my AC don't tip on their tails with full aft payload. At least for the SEL's. I did see a picture of a jet transport that had tipped on its tail when unloaded incorrectly. Main LG location is critical, too far aft and an AC will be hard to rotate on TO. Too far forward and it can tip on its tail. Further, nose wheel steering is weak if there isn't enough weight on it. FS simulates this quite well, but one has to set up the AC correctly. From drawings, jet transports generally have the MG half the MAC lenght behind the 1/4 MAC CoL. So, if CG moves back to 75% MAC the AC would tip on its tail. However, the Empty CG may not be at 25% MAC, and the payload and/or fuel tanks generally are located to bring it close to 25% MAC -- at least after some fuel has burned off. TO is easier with an aft CG, since it takes less UP trim to get good rotation. Ron

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> From drawings, jet transports generally have the MG half >the MAC lenght behind the 1/4 MAC CoL. So, if CG moves back >to 75% MAC the AC would tip on its tail. However, the Empty >CG may not be at 25% MAC, and the payload and/or fuel tanks >generally are located to bring it close to 25% MAC -- at >least after some fuel has burned off. TO is easier with an >aft CG, since it takes less UP trim to get good rotation. Just FYI- Most planes I work around are loaded with a FORWARD CoG for departure. FedEX and UPS especially won't let their aircraft depart if the CoG is too far aft of "normal" loaded CoG. When I look at the final load plan screen at both UPS and FedEX after I'm done fueling the plane and they've got all the info in, usually the CoG is around the 30-40% CoG (with 0% being the forward CoG limit and 100% being the aft CoG limit) They try to keep it balanced perfectly, but usually you end up being a bit forward loaded. I know most pilots (including myself) prefer a forward CoG over an AFT one. It does take more up trim on departure, but it also makes the plane less likely to stall on departure from having the CoG too far back or risking a weight shift on departure from having all that weight back there.

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Hi Ron,Yes, I believe you need GMAX 1.2 installed, which I have, since it provides the gamepack modules for GMAX. It also provides five Word documents. Why they needed to incorporate those into the gamepack, I don't know.There is also a mission SDK available. Neither require CFS3 to be installed. Again I don't understand why they put them in an installer package format. The mission SDK is just a Word document.BTW, I was using Herv'e Sors latest AFSD! Very nice program. His updates are tremendous. I am trying to redo the 717-200 aero. It immediately pointed out my errors, talk about aft CoG. Probably 30yds behind the aircraft!!!:-lolThe CFS3 files are available at: http://microsoftgamesinsider.com/CFSInsider/default.htm

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>>least after some fuel has burned off. TO is easier with an >>aft CG, since it takes less UP trim to get good rotation. >>>Just FYI- Most planes I work around are loaded with a >FORWARD CoG for departure. FedEX and UPS especially won't >let their aircraft depart if the CoG is too far aft of >"normal" loaded CoG.>forward loaded. I know most pilots (including myself) >prefer a forward CoG over an AFT one. It does take more up >trim on departure, but it also makes the plane less likely >to stall on departure from having the CoG too far back or >risking a weight shift on departure from having all that >weight back there. That's true also. Forward CG is more stable. More recent jets have stability enhancment systems and move the CG rearward during cruise to reduce 'trim drag'. The 747-400 has fuel tanks in the three tail surfaces. I modified the FS2K2 747 a bit and noted CG is at 36% MAC (or more) when tanks are full and payload brings it to 875,000 lb. Probably the empty CG or payload should be changed to bring it within the aft limit. Ron

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>Hi Ron, >>Yes, I believe you need GMAX 1.2 installed, which I have, >since it provides the gamepack modules for GMAX. It also >provides five Word documents. Does the document on the 'aircraft container' have any better information that provided for FS2K2?>BTW, I was using Herv'e Sors latest AFSD! Very nice >program. His updates are tremendous. I am trying to redo >the 717-200 aero. It immediately pointed out my errors, >talk about aft CoG. Probably 30yds behind the >aircraft!!!:-lol Getting the CG to read correctly can be a problem. I have more than one AC that appears to fly well with CG way off. I suspect it isn't, and the CG variable reads incorrectly due to the settings in aircraft.cfg. However, I do get the CG to come out at 25.0% when I calculate all the moments and set the payload for 25% balance. Also setting the wing parameters in aircraft.cfg to a 'rectangular wing' and the LE 1/4 the length of the MAC ahead of the desired CG. In these cases, I set the 'root_chord' to the length of the MAC and the taper and sweep to zero. I had suggested to Herve' that a Balance number be calculated consistent with the 'load moment' shown in many SEL PoH's. He may do that in AFSD Pro. Which should be able to log flight data. I also suggested many other things. This version will be so arcane that he doesn't expect to UL it -- but it will be available for those who can use whatever it displays. BTW, if you watch the AFSD Aerodynamics Window flying the MS 747-400 you will see the "Mach Drag", Cdm go negative at cruise speeds. Just one stupid thing set by MS. Of course, 'Mach Drag' should start increasing at about Mach 0.80 and normally peaks at 1.0. Ron

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