Post by Tom Goodrick on Dec 18, 2009 20:29:58 GMT -5
I just finished the penecillan yesterday. I feel pretty good but not perfect. I did use a bit of honey when I had a sore throat. (Honey in vanilla ice cream works well.) But before I get a relapse, I'll stock up on Apricot Brandy. Sounds like a winner. With high blood pressure, most of the over-the-counter cold medications cannot be used.
I just did a little algebraeic hen scratching that shows to minimize both time and fuel, you need to maximize KTAS squared over gph. Time for some flight tests.
Post by Bill Von Sennet on Dec 19, 2009 12:59:15 GMT -5
I always fly the DC-3 in cruise with 30" map and 2050 rpm. Fuel flow is 90gph.
Tom in the rally I flew with the dynamics you provide Charlie Woods fo some of the flights, but had trouble generating enough power for the high altitude flights so I switched to the dynamics that come with Norm Homan's DC-3 panel set.
There was one flight early on that I had difficulty with for the first third of the flight, with symptoms that indicated icing. During that portion of the flight I flew with increaded power and fuel flow.
Trevor Morson is something of an enthusiast on the DC-3, and long legs from the site home page
Like Bill I used 2050 at 30 for the cruise. One issue with using any one airlines settings is likely to be the difference between engines fitted, and the point in the engine life at which the airline was operating it. As the Rally progressed my settings seemed to drift ever further away from the average, which I suspect may have at least in part been an indication that the average moved as people adjusted their settings - particularly those who were running over-rich to start with.
As DCA put such great store in averages, perhaps we should be hailing Bill as the winner with the average position in a table of 120! (Apologies to John and Zlogg.)
Each to their own, I'm afraid that I struggled to understand the logic in the scoring system. So I did not actually check my scores for the last few flights, preferring to fly with settings that I was comfortable with and enjoy the nav practise over some interesting routes.
Of course that might explain why I slid down the table against my position last year.
The effort that went into finding and preparing the routes certainly puts the feeble features that I throw together in the shade!
Maybe there is something to be said for the GAAR "fly against yourself" philosophy for a consistent scoring system all the same. Always assuming it doesn't change this year of course.
By the way, the arbitrary comparison with a moving average is exactly the system to be used in the UK Carbon Reduction Commitment Energy Efficiency Scheme (snappy eh?) which is to be inflicted on thousands of UK businesses in a year or so.
Businesses are less than happy with the whole scheme, but I'd better say no more in a public forum.
Post by Tom Goodrick on Dec 19, 2009 22:27:51 GMT -5
Bill, as for the high altitude performance, I was under the impression that DC-3 Airways flew passengers. In such a case they should never fly above 12,000 ft. On this Rally I never flew higher than 13,000 ft. I had no trouble operating the aircraft and thought it would go higher if I wanted to. But in each case where they specified higher altitudes, they went out of their way to go where higher altitude was required. There were better routes in all cases that kept the altitude within reason. I thought that was a major flaw in the rally. The only way a DC-3 does that stuff is with inert cargo in back and the crew on oxygen.
I have heard from people who have flown different radial engines that there is a level of inherent supercharging in the radial engine due to ram induction. The mention using inflated MAP values. I don't know how to model this properly though it could be done if we had data on the high-altitude speeds and power settings. On some FD I have tried setting a level of turbocharging. But there are problems with this. In FS9 turbocharging works best as done with inline engines where automixture is set. This means there is no leaning. When leaning is allowed with slight to moderate turbocharging as some people have done, the performance is a bit erratic. I have not looked into this in a couple years. I think I had supercharging and automixture in the DC-6 and a few other pressurized airliners.
OK, I stand corrected. "My FD" has a low level of turbocharging to allow the high MAP levels generally expected with the radial engine. But the critical altitude is only 5000 ft so I was not intending to simulate fully supercharged engines. The automixture is not ON so you do need to lean for best power at any altitude. I checked the web site Alan refers to and noted that they used an "Auto Lean" feature. I would not put much stock in his 2050 rpm and 30 inches setting although it is not too far below 50% power. I am sure that applies only to the creaky old beast he was flying around Oshkosh. I am sure a healthy DC-3 in its day would fly a bit faster. The Piedmont Manual was dated 1954 when the DC-3's could be maintained in good condition.
I was in the Navy Reserve in the 1960-1962 and was in training to be an aircraft mechanic. There were several aircraft with radial engines in use and our hangars always had several engines torn down. I know they were starting to baby those engines in those days. I have seen several radials torn down at airshows in recent years with several gray-headed mechanics hanging around twiddling with various parts. I am sure that today, any radial engine is treated very carefully.
But I think FS should show the aircraft performance expected when the aircraft was young. After all, we pilots are all young in our minds!
I'll check the high-altitude performance of my FD so it can be flown high on cargo missions.
Post by Tom Goodrick on Dec 20, 2009 10:32:08 GMT -5
Having cleared some of the cobwebs from my memory, I think that the portions of the aircraft.cfg file that pertain to turbocharging were carried over from the "default" FS9 DC-3. I have been checking the result of increasing the critical altitude from 5000 ft to 10,000 ft and that looks good for a moderate improvement in altitude. Here are the lines in the aircraft.cfg file that pertain:
turbocharged= 1 //Is it turbocharged? 0=FALSE, 1=TRUE max_design_mp= 47 //Max design manifold pressure, (inHg) min_design_mp= 10 //Min design manifold pressure, (inHg) critical_altitude= 10000 //Altitude to which the turbocharger will provide max design manifold pressure (feet)
I saw 48% power at 2050 rpm and 30 inches. The speed was a little low showing 135 KIAS.
It seems the DC-3 needs a little kick to get it "on the step" at cruise speed. There really is no "step" but it can seem like there is because of the very low acceleration once you reach cruise altitude if you just go to the chosen power setting for cruise. This is a function of what I'll call the "speed stability dynamics." The stability due to the combination of horizontal stabilizer design, pitch trim and elevator setting causes a non-zero moment when too slow or too high in airspeed that drives the aircraft toward a particular speed. This is made more complex by a pilot or autopilot who tries to keep the aircraft flying level while the speed changes. To get to the proper "trim speed," it is best to get above it a slight amount and then set the cruise power so the aircraft slowly decelerates to the cruise speed. Otherwise you can easily spend half your cruise time at a lower speed and mileage. Some adjustments in the air file can improve speed stability dynamics so this is where we need input from real DC-3 pilots about how fast the DC-3 should get to its cruise speed if you don't use high power initially. Any comments about this phase of flight would help.
Post by Tom Goodrick on Dec 20, 2009 22:33:57 GMT -5
With the critical altitude set at 10,000 ft, I climbed to 16,000 ft where the rate of climb was 203 fpm at 59.3% power. I was manually adjusting mixture for max power. I switched to auto mixture and then set the critical altitude at 15,000 ft. I climbed to 18,000 ft but the climb rate was low, about 160 fpm. At 18,000 ft I leveled off and saw (eventually) 92 KIAS and 123 KTAS using 70% power. But holding airspeed was difficult. After some adjustment I was able to get the airspeed steady at 94.57 KIAS, 126 KTAS on 66.3% power. The fuel flow was 2x55.9 gph for a mileage of 1.12 nmpg. There certainly is no benefit to being up there except the height itself. I can't think of anyplace in the world where you would need that altitude. Any place where a ridge is that I you should be able to go around it or find a pass.
I don't know why the performance is so poor. Propulsion is not my specialty. I'll go back to flying the DC-3 down low and leaving high altitude flight to pressurized aircraft with engines designed for the job.
Hi Tom I found two PDF files, 1 from pratt & whitney time 1946 ( dc3engine.pdf ) #2 is a flight manual for Quebecair ( dc3operatinglimitations.pdf )
If you do a Google for those file names it will take you to a place to download them.
Ho there small 1 mb and 297 kb
I see critical altitude is not a fix number, mixture, pressure alt, rpm,and outher thing all play a part in it. Like at 2000 rpm will lower than 2700. It will be interesting to see how you model critical altitude
Post by Tom Goodrick on Dec 21, 2009 15:09:13 GMT -5
Richard, thanks very much for those references. I downloaded both of them. They do shed light on these apsects of operation we have been discussing.
The P&W paper mentions 4 critical altitudes not because you can have any you want but because they are commonly available, depending on the installation. Each installation - particular aircraft operated by a company - will have only one critical altitude. The choices are 4800 ft, 7000 ft and 10000 ft. Based on the tests I ran yesterday, I think I will choose 10000 ft. That seems in agreement with the info from QBA for its aircraft. It should be good for flight to 16,000 ft. Again, only cargo flights should go above 12,000 ft.
From the charts in the P&W paper, cruise power settings seem to be recommended at 2000 or 2200 rpm and at power settings from 43% to 51%. If you use my power meter, you can set either of these rpm values and then adjust the throttle for the power desired. MAP and GPH will come out right. They like 2050 rpm as do the folks at QBA. Why not 2000 rpm? 2100 or 2200 should be fine as well with power adjusted for the range to 51%.
Here's the summary of the QBA specs for cruise: (note these are independent of altitude)
(Flow corrected from Imperial Gal to US Gal/hr) Power__GPH 43.8%__85.2 45.8%__87.6 47.9%__90.0 50.0%__93.6 52.1%__96.0 54.2%__98.4
Speed will vary with altitude. Note that in physics, power is defined as the rate of doing work. Burning a gallon of fuel is doing work so GPH is a rate of doing work. Thus fuel flow is constant for constant power. But see notes below regarding speed.
I like 50% power. It seems a good compromise. The specs seem to indicate two possible settings: 2000 rpm and 30.6 in or 2200 rpm and 29.0 in. The original data showed a descrepency of about 10 gph compared to the other two reports. The answer is the Canadian report uses Imperial gallons per hour while the US reports give US gallons per hour. The difference is a factor of 1.20.
One aspect remains to be checked out: Should we use Auto Mixture? The specs all indicate the aircraft is normally operated with Auto Mixture ON in real life - either auto lean or auto rich. Auto rich is used for lower altitudes. I'll have to do some testing to see whether our Auto Mixture is suitable and whether it is close to lean or rich. I know many people love to fiddle with the mixture to get their personal settings. But it seems unnecessary.
Post by Allen Peterson on Dec 21, 2009 16:53:36 GMT -5
Tom, when looking over the pilots shoulders back in the 50s, I seem to remember seeing a placard saying something like: Don't operate engines continuously at xxxxRPMs I don't remember the exact RPM, I think it was a vibration issue and it probably referred to cruise settings. I looked around in Alan's DC-3 link, above, but couldn't find anything. Maybe some of the other guys have heard about particular RPM restrictions. We were flying R4D-6s, I don't remember what make the engines were.
Post by Tom Goodrick on Dec 21, 2009 17:16:33 GMT -5
Yes, indeed. The number for the DC-3 is 2550 rpm. This is the max continuous rate for use in climb. 2700 is for one minute. There is another intermediate level but 2550 is the one to remember.
I just found the cause of the seeming descrepency between QBA and Piedmont fuel rates: Imperial gallons were used by QBA. So those flow rates should be multiplied by 1.2 to get US gal per hour. This makes the 78 IG/Hr by QBA become 93.6 gph as reorted by Piedmont.
Post by Tom Goodrick on Dec 21, 2009 23:25:31 GMT -5
MORE TESTING - MORE QUESTIONS!!
I compared Auto Mixture ON with Auto Mixture OFF. The difference, at 5500 ft for "50% power at 2200 and 2000 rpm, is very slight, just about 2.5 gph reduction in fuel flow using Auto Mixture ON. I would be tempted to use Auto Mixture ON and adjust the air file to increase the fuel flow so it agrees with the specs.
But there was a big surprise when comparing two different rpm at the same power level. The higher rpm gave a higher airspeed by about 12 knots! (Of course, the MAP was adjusted to get the same power as shown on my power gauge.) That agrees with what we have all been saying. I was using a higher rpm but the same power level in the Rally and was getting higher airspeeds than those using 2050 rpm. (I was generally using 2200 to 2300 which is still within the performance charts.)
This seems to be a bug in FS related to radial engines. As long as the same power is developed, the airspeed should be close to the same value whether you spin the props fast or slow. The drag from the engines may change a little bit but I would not expect it to change very much. I compared the results for the DC-3 to two aircraft with inline engines at about the same speeds and altitude. For the same 2000 rpm change, they showed airspeed changes of about 1 knot. (Note the A36 has no turbo charging while the Cessna 340 is turbocharged.)
HI all I run two climb test flight out LAMBERT. Default DC-3 C the only one I fly now. #1 at 2350 and 36 critical altitude came at 12100. ( def DC-3 C climb setings ) #2 at 2050 and 31 as per P&W pg16 pdf file. critical altitude would beleve came at 15300. P&W pdf file call for critical altitude at 10000 at that point I moved prop to max RPM, there was NO change in MP. Should have gone up.
So is there a way to coax the flight sim into using RPM in the control of MP. I don't see how one could set up a true flight model with out the RPM input
well that my 2 cents worth Richard
BTW I always thought the tach made a better airspeed ind, and that a subject I would like to persue
Post by Tom Goodrick on Dec 22, 2009 10:43:22 GMT -5
Except at very low taxi power, RPM should be controlled by the prop levers and MP by the throttle, shouldn't it? How does your "critical altitude" as tested agree with the value in the aircraft.cfg file? The PDF file does NOT say all their aircraft have a critical altitude of 10,000 ft. Some do but others have a critical altitude of about 15,000 ft. Some in their fleet have a much lower critical altitude.
I ran a test on the DC-4 to see if speed changed at the same power value with different rpm (but adjusted mp). It showed a constant speed - essentially. The test was done at 5500 ft in standard conditions. 70% power was set, first using 2451 rpm and 27.21 inches and then using 2248 rpm and 29.13 inches. The power gauge shows these give 69.89% and 70.06%, respectively. The airspeeds were 202.8 KIAS and 203.1 KIAS, respectively. The DC-3 remains unique in its speed deficit with rpm.
Post by Tom Goodrick on Dec 23, 2009 10:07:11 GMT -5
I goofed in a way that relates to the accuracy of my Power Gauge for the DC-3. Several years ago, I was using a factor for fuel flow rate as an indication of power. I made several Power Gauges for various aircraft based on that principle. It is valid to a large extent. But it depends on the accuracy of the fuel flow rate set in the aircraft.cfg file.
Later I began using Power Gauges that read the actual power as determined within the sim. The gauge then divides that by the max power specified for the engine. This is an accurate measure if the engine dimensional specs are accurate in the aircraft.cfg file. I converted most of the Power Gauges to this new method. But I forgot about the radial engine aircraft. The DC-3 and DC-4 gauges were still using the old method until I caught the mistake yesterday.
In testing the DC-3, I found no difference at the higher rpm settings. I also changed the FD for the DC-3 to use Auto Mixture ON and then boosted the fuel flow by a factor of 1.06 to agree with the data for manually leaned settings.
Now I see the following at moderate weight: (4500 ft) Powr____RPM___MAP___GPH/e___lb Thr___KTAS 50.17%__2207__28.65__45.14___987____156 50.19%__1999__30.81__45.15___940____151
To get the thrust I used the Power Panel I developed some time ago that shows many power-related parameters. You can download this small pop-up panel from my web site. It comes with instructions for use when testing aircraft.
I'll make the new Power Gauge available to any who request it and will send one to those who presently have the old one. (Please use Email to request one.)