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Post by Tom Goodrick on May 16, 2010 9:44:14 GMT -5
I decided to put this here even though it is actual a problem encountered in FS2002 because it is typical of so many problems encountered over the years. You might think developers have learned to do better. But I don't think so. It is just that I went looking for a neat plane and found one that had a small enough zip file that I could download in a reasonable time (under an hour). I have not looked for such a plane in FS2004 because all developers now go crazy with detail so the files are 4x and 5x the size of this file.
This aircraft, the Douglas C-124C, looks beautiful in its gleaming silver skin with markings painted on for the Utah Air National Guard. It's a big double decker cargo ship from the era of the Korean War and the early Cold War. It was intended to move troops and their support vehicles to a remote battle theater. After my junior year in high school, I considered joining either the Naval Air Reserve or the Air National Guard, both based at minneapolis. The ANG flew C-124's and the job I considered trying for was a loadmaster on a C-124. I chose the Navy where my squadron flew attack planes (AD-5's, later called AE-1's). I probably would have gotten very sick on the C-124 so it is just as well.
The problems are:
1) The FD gives it a cruise of 325 knots when the proper value is 200 knots.
2) On landing the aircraft has an extreme nose-high attitude (about 40 degrees), far more than any real plane could tolerate.
3) The panel, created by a guy who some think is a master of the craft, is ridiculous with various gauges from the Extra, the Hughes Jet Ranger, and the Cessna 182. This for 3850 hp P&W radialks!
4) There were so many gauges you could not read any of them clearly enough to fly with them. Even if they could help you fly!
5) The weight values are suspiciously low. The text say that FD from a C-97 was adapted. I think it was simply plugged in and used.
I spent this morning working on the lift problems. Yesterday I solved the drag and most panel problems. I dumped the gauges that did not pertain at all like the turboprop engine gauge from the Jet Ranger. I am trying to find better engine gauges (preferably from Microsoft) for the 4x4 bank of engine gauges. I put in the digital flow gauge from the Mooney which is the only gauge that presently makes it possible to fly the plane.
After this I will go on line to look for weight data (such as to USAF Museum, etc).
There were two problems with the lift data. I have not been able to double check the wing area. That may be a large part of the problem. The CL vs aplpha data chowed a peak CL of 2.4 for the bare wing - no wing would ever exceed 1.6. When I set in 1.6, the plane would not lift off without stalling imediately. I set 2.0 and increased the flap lift so I use half flaps for a gross weight takeoff. Also the peak came at too high an angle of attack. I reduced that range. Then I had pitch stability problems on takeoff. Solved that by an adjustment of the Cm Vs Alpha table.
I have something that will fly with a cruise speed of 200 knots and looks reasonable during takeoffs and landings though it still has a high pitch attitude.
Now to check all the numbers. This falls in a crack between WWII aircraft and modern aircraft in my library.
~~~~ OK I checked the numbers on line.
What a mess. The max gross weight is somewhere between 175,000 lbs and 216,000 lbs. They all beat the 130000 lbs this model had. Range is somewhere between 1200 miles and 4000 miles. Nobody lists the fuel capacity. I saw the span (consitent at 174 ft) but not the wing area. I'll guess an aspect ratio of 10 and calculate the area.
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Post by Tom Goodrick on May 16, 2010 19:42:31 GMT -5
OK. I never found all the answrs so I mad up some. Here's what I did to get a reasonable model of the C-124 up and flying.
The most common Gross Weight was 195,000 lbs with 216,000 lbs also mentioned by two sources. But I felt the 216,000 figure comes from the military's standard use of an extra 10% in gross weight in emergiencies - the kind that become SOP. So I had 195,000 for max gross, with 26,375 lb being the payload that can be carried with full fuel for 4000 mi (3500 nm). It seemed like 100 gph per engine was a reasonable long-range cruise flow rate and that would give a cruise at 200 knots. That gives a long-range mileage of 0.5 nmpg. So to go 3500 nm you'd need 7000 gal fuel. That weighs 42000 lbs (gasoline). Now we can estimate a BOW as 195000 -26375 - 42000 = 126625. that's about 65% gross which is reasonable. Now what about the stated max payload of 74000 lbs? That can only be carried if you allow use of the enhanced capability 216000 gross weight. But that may be okay.
I set those numbers in for the model in FS2002 and found reasonable performance. It even managed a no flaps takeoff at 195000 lbs. It makes a good aircraft. I have good flaps on it so a takeoff with flaps is even better and safer.
I distributed the 7000 gal fuel between a center tank (1000 gal' and both a main (2000 gal) and an aux (1000 gal) in each wing. It seems reasonable.
Now it flies great. I made several takeoffs and flew extended circuits that seemed pretty good. But they each ended in a fatal crash. For some reason, when i put down some flaps and go to about half cruise power to slow for the approach in level flight, the plane slows gradually and then suddenly stalls and falls out of the sky.
Oh well. A little more work may be needed!
If anybody knows about the weights and fuel capacity of the C-124, please let me know!
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Post by flaminghotsauce on May 17, 2010 5:03:11 GMT -5
I found a post on a discussion forum that called the capacity 11,100 gallons. The weight is all over the place.
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Post by Tom Goodrick on May 17, 2010 9:06:18 GMT -5
Thanks but that would weigh 66,600 lbs and would eliminate any payload on a max range flight. I'll stick with my estimates.
I added a little nose-down moment with the flaps and that solved the problem of extreme nose-high approaches. Now the approach with gear and 2 notches of flaps out is flown level at cruise power (100 gph.e) and down hill on final with full flaps at 80 gph/e to maintain airspeed. The nose is raised slightly to flare for a gentle touch at about 90 KIAS.
Let me know if you want a copy of the model.
My panel seems to work pretty good although the rpms do not work quite right. It likes to fly with a max rpm of about 1600. I just leave that alone. It also does not like to start. That was noted by the designer. I am happy to start any other plane (even a lowly Cessna) and then switch to the C-124. There is an FS9 version of the C-124 that has very big files that I once tried flying and it would not start either. (I dumped that model).
This model is now fun and interesting to fly if you like big slow planes (200 knot cruise). I think it has a pressurized crew compartment (5-man cockpit, galley, lounge and bunk space for a second crew). I have flown it at 15,000 ft (again 200 KTAS at 100 gph/e). During the 1960's routine flights were made non-stop from Travis AFB near San Francisco to Ton Sonute AFB in Viet Nam. That's about the 3500 nm limit with a 26,000 lb payload.
I just checked and found the distance from Travis to Danang is 6500 nm. The C-124 flew that trip regularly with w round trip time of 97 hours. BUT I think they stoped somewhere. I knew a lady that made that flight and she said the first leg was 18 hours. Perhaps a rest/fuel stop was made at Guam or Japan.
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Post by louross on May 17, 2010 15:57:46 GMT -5
Found empty weight at 101,160 lbs. Add crew + the usual and maybe another 2000-2500 lbs for BOW of +/- 103,000. Add load of 77,000 you got 180,000 lbs. Leaves 36,000 lbs for fuel using the operational weight of 216. With full fuel still leaves 48.0 for payload. lr.
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Post by Tom Goodrick on May 17, 2010 20:03:33 GMT -5
Thanks for that info. It does make the 74,000 lb payload more reasonable. If the 216,000 lb max gross can be believed, then it would mean a lot more fuel is available for max range of 4000 miles (3500 nm). My estimate of empty weight is 23000 lbs more.
Then the max fuel for the long range flihgt of 3500 nm would be 216000 - 26375 - 103000 = 86625 lbs. That's 14437 gallons.
If we just use 195000 lb for max gross, that still would leave 195000 - 26375 - 103000 = 65625 lbs or 10937 gallons. That is close to the 11000 gals mentioned by Flaming.
Then if we carry a payload of 74000 lbs, the 195000 lb gross weight allows 18000 lbs for fuel or 3000 gallons. That would be reasonable.
The two references that list 216000 lbs were Air Force - USAF Museum and SAC. But they might list that if it was the emergency rating - 10% overage.
The source i tend to give the highest credibility to is Jane's. But they give two values for gross weight - 175000 lbs in their 1958 edition and 194500 in their Encyclopedia of Aviation.
Boeing, the current owner of the C-124, is the least credible. They list 185,000 lbs gross weight, 304 mph (264 knot) cruising speed and a range of 1200 miles.
It's confusing. I think I'll go with the empty weight of 103000 lbs. Then the fuel capacity of 11000 gallons also makes sense. The gross weight of 194500 lbs for normal operations and 216000 lbs for emergency operations can work. I am not sure if I can get it off the ground from a 10,000 ft runway at such a high weight. I think Travis has a longer runway than that. I'll check and use that runway as a guide to the setup.
Part of the confusion here may be due to the Air Force being careful when publishing numbers like payload and range for transports. I am sure this stuff was classified in the 1960's. The aircraft was in use by Air National Guard units as late as 1974.
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Post by Tom Goodrick on May 18, 2010 9:05:04 GMT -5
OK. This flies nicely.
EW 103000 lbs Fuel 11000 gals MGW 216000 lbs MLW 195000 lbs
I had to boost the poer by 10% and the prop thrust by 20%. I think the props were not done well. They seemed too small.
It lifted off in 9000 ft with no flaps, 7500 ft with 40% flaps (2 notches). It lands fine when you burn off enough fuel to get down to 195000 lbs. I pust the fuel in lef main, right main center1 at 3000 gal each, left aux and right aux at 1000 gal each. With empty aux tanks and 50% in center, you are close to MLW.
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n7rg
Member
Going Home to Alaska
Posts: 62
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Post by n7rg on May 18, 2010 10:52:32 GMT -5
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Post by Tom Goodrick on May 18, 2010 22:02:42 GMT -5
Thanks for the info. I have seen all those specs before but the comentary by the flight engineer was very interesting.
I get the feeling my estimate of fuel flow per engine is lower than it should be. I estimate 100 gph at cruise power. We now know that normal cruise was 170 knots. I guess the 200 knots I saw in several sources is a little optimistic.
Does anybody have a handle on this fuel flow?
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n7rg
Member
Going Home to Alaska
Posts: 62
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Post by n7rg on May 19, 2010 0:33:13 GMT -5
modelenginenews.org/ed.2008.08.html ( just for fun ) www.456fis.org/PRATT_&_WHITNEY_4360_WASP_MAJOR.htmBore: 5.75 in. 146 mm Stroke: 6.00 152 mm Displacement: 4.363 cu.in. 71.5 lit Compression ratio: 6.7:1 6.7:1 Length: (engine only) 96.5 in. 2 451 mm Diameter: 55.0 1 397 mm Frontal area: 16.5 sq.ft. 1.35 m² Weight: (engine only) 3,670 lb. 1 665 kg Weight/Horsepower: 1.05 lb./h.p. 0.48 kg/hp Fuel Consumption: (cr.) 0.43 lb./h.p./hr. 195 g/hp/hr Oil consumption: (cr.) 0.015 lb.h.p./hr. 11 g/hp/hr Gasoline Grade: 115/145 grade 115/145 Oil Viscosity: 100 S.U. secs. 20.5 cs Output/Displacement: 0.80 h.p./cu.in. 49.0 hp/lit Output/Piston Area: 4.81 h.p./sq.in. 0.75 hp/cm² Piston Speed: (max) 2,700 ft./min. 13.t m/sec. B.m.e.p.: (max) 235 lb./sq.in. 16.5 kg/cm² Rating: (take off, wet)..3.500 h.p./2,700 r.p.m./60.o in. (1 524 mm)+15.0 lb. Rating: (take off dry)...3250 h.p./2,700 r.p.m./60.0 in. (1 524 mm)+15.0 lb. Rating: (normal)...2,650 h.p./2,550 r.p.m. /5,500 ft. (1 680m) Rating: (max. cruising)...2,800 h.p./2550 r.p.m./3,500 ft. (1 070 m) www.aviastar.org/air/usa/douglas_globemaster.phpfuel capacity of the "A" models was 11,100 gallons of 115/145 ( Fuel system by Serial number ) books.google.com/books?id=tsceumd-VS8C&pg=PA45&lpg=PA45&dq=C-124+Globemaster+II++fuel&source=bl&ots=Gguro1VFBJ&sig=b-lfBZQED_DGVsrh4n8lydiI7u4&hl=en&ei=tXLzS4_8AYrKMe_F_YkO&sa=X&oi=book_result&ct=result&resnum=3&ved=0CBoQ6AEwAjge#v=onepage&q=C-124%20Globemaster%20II%20%20fuel&f=falseuscockpits.com/Cargo/Cargo%20Aircraft.html#C124 ( Cockpit Photos )
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Post by Tom Goodrick on May 19, 2010 9:43:05 GMT -5
Thanks very much. There is some new information there. To get fuel consumption in cruise we still have to guess the percent power setting. I'll guess 60% for now. That gives 150 gph per engine.
All 11000 gal of fuel goes into three tanks in each wing. We can do that (main, aux and tip tanks).
The most helpful bit of info is the wing area of 2508. That means there is an aspect ratio of 12. I had guessed 10 which gave me a bigger wing area. I'll plug in the correct one.
If anyone still flies in FS2002, I can send you a copy of the FD files in a few days. I don't think it would be much fun converting this to FS2004 with all the CG and incidence issues.
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Post by louross on May 19, 2010 10:06:09 GMT -5
Was talking wiith a former Air Force pilot awhile back and the C124 came up. He said the pilots he knew didn't want to fly the plane because it was limited to 10,000 msl because it wasn't pressurized. His point was "who wants to bounce around in hot wx at 10 thou all day long..." 10,000 msl is also (has the FAR) changed?) the max altitude permissible with paying pax on board. As a note on some of the technique here, I find it difficult to believe that a no flap take-off would be done in an a/c of that weight, on the other hand, I'm not a heavy prop pilot. That's RW, however; have seen some people do strange things in FS- like select the default 737NG (FSX), loaded to the gills, no flaps, take-off and climb directly to FL340!!! lr.
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Post by Tom Goodrick on May 19, 2010 23:51:07 GMT -5
I am sure you are correct on both counts. I had thought maybe the crew compartment was pressurized. But it is not, according to that flight engineer who wrote the note. The Air Force has a history of expecting crew members to use oxygen masks at their duty stations but in this plane, the five extra crewmen have a lounge, galley and bunk area. Using oxygen certainly would be a bother - especially for the engineer or mechanic who has to go out in the wing to check the engines periodically. Most specs say the ceiling is above 30,000 ft but I bet there were very few flights above 10,000 ft.
This bird definitely needs flaps for takeoff. While makeing various adjustments on the plane i have had configurations that did lift off without flaps though they took more runway. As I get closer to realistic weights and wing design, it is clear you need the extra lift of flaps. I always try to make my FD files as realistic as possible.
That's why I'm asking all these questions. usually I don't start work on a plane without a lot of documentation on the plane, mostly from my own library. That includes full specs, anecdotal notes from pilots and pilot test reports. This is an exception.
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Post by Tom Goodrick on May 23, 2010 9:21:06 GMT -5
The model came with notches of flap every 10 degrees and I have left it that way. I take off with 20 degrees of flap or 2 notches. I had pumped up the power and prop thrust to get good takeoffs with a gross weight of 216000 lbs. Though we have indocations it often flew with less weight, we can't ignore official USAF reports that max gross is 216000 lbs. I have since bee reducing the extra power and thrust until I can just get it off the ground in about 9.000 ft at low elevation on a normal day. I use HSV which is at 640 ft msl. Yesterday I rantests with hot temperatures up to 100 F at sea level, The takeoff distance extended close to 9500 ft at HSV. Then, because my plane is marked for the Utah Air National Guard, I put it at Hill AFB where the runway is at 4700 ft msl and the length is 13500 ft. I was able to land and take off there without much difficulty. But you do have to use care.
I made a flight from Nellis AFB in Nevada to Hill. Cruise was at about 230 knots and 150 gph/e. The computer said the minimum altitude should be 15500 ft but I flew at 11000 ft and only had to deviate mildly a couple times as ridges looked like they might come a bit close. In IMC you'd have to fly higher to be safe. That would force the crew to use oxygen masks. It would rule out passenger operations with this aircraft. I wonder if the Utah ANG ever actually used this aircraft, I understand the normal use is cargo and for that the crew can use oxygen. So use in Utah is possible where going anywhere means leaping over ridges with peaks near 12000 ft.
Because the aircraft has a low wing, the effect of flap on pitching moment would be slightly nose-down if flaps are not deployed at an excessive speed. Thus I have been able to tame the attitide on approach. I also assigned it a 4.0 degree wing incidence angle. With the normal CG position, it is level in cruise. When slowing to about 140 knots with gear and flaps up, the aircraft does take a moderate nose-up attitude. But with gear and first flaps this becomes lower and goes to nearly level when you start going down the standard glide slope. At full flaps it is slightly nose down while descending on the glide slope. I watched them land as a kid from some distance away. I don't remember seeing a nose-up attitude on approach until they flared over the runway. That's what this plane does.
I punch up the seat one notch to see the general area of the airport over the nose when first slowing to 140 KIAS. That becomes unnecessary about halfway down but it does help you see the centerline during the flare.
I welcome all comments.
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Post by flaminghotsauce on May 23, 2010 18:54:12 GMT -5
Sounds like you just about have it nailed, Tom. I think I found the same one you've been working on, it's 2.3 mb download size? If you could send me the FD's I'd like to give it a shot. I don't normally fly such beasts.
I just finished this morning finally setting up all the controls in FS2002 for my yoke, throttle etc. It's funny how the defaults are so bad! Also, none of my fancy-schmancy panels work with 2002, so I have to set up flaps, gear, etc, buttons.
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