Support Specifications
 for the Dave Bitzer modified aircraft.cfg

14th February 2004

 

 

 

 Several un-graphed specs from the Quebec Air Regulations documents are copied to a table below, and compared with data collected using the modified aircraft.cfg. The QAR specs are in statute miles and Imperial gallons, so some adjustments were made to present the comparison using Knots and US gallons.

 

 

  

 

 

 

 

 

 

 

These are comments on the "to meet specs" notation in the aircraft.cfg file changes.

 

 This note shows some of the DC3 specs referenced in explanation of the changes in the aircraft.cfg file from the stock file.  Many of the specs had to be "interpreted", so let's start there.  All specifications are for the vintage 1939 DC-3 with the r-1830 S1C3-G  P&W Engines.

 

 Fig 1 is a specification that comes from Pratt and Whitney, and shows, in US Gallons, what the aircraft requires in gallons per hour vs. horsepower, and what the MP setting should be.  All values are for the autolean position.  It is the density altitude that is important, so you need to check the OAT to determine the altitude. The measured data on the modified aircraft is within 5% of the fuel burn spec, for altitudes up to 13,000 ft.

 

Fig.1

 

 Figure 2, is a spec. from the MAAM CD WW2 Manuals section. It shows the relationship between HP and mph at 24K lbs. Gross Weight.  Don't be misled, these specs are for the Standard 1200 HP P&W engines.  Note that you need to use figure 1 to set the horsepower, and you need to convert Knots to mph and convert TAS to IAS to be compatible with the DC3 Airspeed Indicator.

 

 Fig.2

Figure 3 is a companion to figure 2, but the Gross Weight is 20 K lbs.

 

Fig.3

 

 Figure 4 presents the data in a different form, in a hard to read chart that comes from Quebec Air Regulations.  It shows power control similar to Figure 1, and cruise numbers similar to Figures 2 and 3.  It presents fuel in Imperial gallons per hour, and speeds in statute miles (not NM), so it needs to be converted to see the similarity in the specs. (They are very similar).

 

Fig.4

Figure 5 plots the figure 4 data for the "more than 23K GW" table, arranged in a way to display speed, MP, and altitude on the same chart.

 

Fig.5

 Figure 6 is the companion data from figure 4 for the "less than 23K GW" table, described in Figure 5 above.

 

Fig.6

The Stock (default) aircraft was then flown at various power settings, and altitudes, at both 20K lbs. and 25K GW to measure fuel flow and TAS.  The data collected is plotted in the same format as figures 5 and 6.  The stock data is figures 7 and 8. To eliminate the ambiguity of how lean to set the mixture, the game's automixture control was enabled for all the tests. Note in figure 8 that the 13,000 ft performance is not good, and the speed does not increase with altitude at the lower altitudes as much as it should. Please note that in figure 7 that I could not get the stock plane to maintain 13,000 ft altitude at 2050 RPM, and that it straightened out at 2150 RPM.

 

Fig.7

 Fig.8

Then the modified aircraft.cfg file is substituted in the aircraft, and more data was collected.  It is presented in figures 9 and 10.  Note that the high altitude performance is much better. The data for figures 9 and 10 was taken with the Beaumont and Bitzer auto-lean gauge enabled, rather than using the automixture setting used on the stock aircraft.

 

Fig.9

Fig.10

Comparing figures 7 and 9, or 8 and 10, you may see the differences in performance between the stock and the modified flight dynamics, and compare them with the specs in figures 5 and 6.

 

 Figure 11 shows the differences between the stock vs the modified aircraft.cfg  on the plane pitch. This is data at 2050 RPM, at 4100 ft. It shows the comparison at two different Gross Weights. There is also variability as a function of altitude that is not shown. I didn't see anything significant up to 13,000 ft, but didn't take careful data and plot it. Note that the "heavy" plane data is dead on the stock plane's characteristics, while at 20K GW our plane is a bit (0.2 degrees) nose down, compared to the stock plane. I have been unable to find any specifications for what the pitch on a real dc-3 is, as a function of speed, altitude, and GW.

 

Fig.11

Dave Bitzer

bitzer7@comcast.net