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1507 Help And Questions

A

Alexis Mikhailovich

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5
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sweden
Hi, I'm hoping someone here can help me.

I've read through Roy's great Thrust vs Altitude document and also sifted through various threads here discussing the 1502, 1503, 1504, 1506 and 1507 turbine tables.

I understand that in 1506 there are two choices one has, to zero out 1507 and use net thrust in 1506, or to draw up a ram drag table in 1507 and use that in conjunction with 1506.

Now what I don't understand about table 1507 is how the numbers in columns 2 and 3 get calculated from the Mach number and CN1 value in column 1. As I understand it, in 1506 columns 2 and 3 represent a percentage of static thrust at the relative CN1 value in column 1, meaning that if your static thrust in the aircraft.cfg is defined as 15000 lbs and a CN1 value of 75 yields 12000 lbs at 0.9 M, then the value in column 3 would be 12000/15000=0.8. If I apply the same methodology in 1507 for a ram drag value of 3000 lbs, then the factor would be 0.2 in relation to my 15000 lbs static thrust. The numbers in Roy's document are all in the double digits, and don't seem to correlate with the way that 1506 seems to be calculated. Could someone kindly explain how exactly columns 2 and 3 in table 1507 are calculated for the corresponding CN1 and Mach value?

Thanks in advance for assistance with this.

Alexi
 
Read part 3 of Roy's paper again. The values were derived iteratively from a comparison between EngineSim and AirWrench.
 
Hi Björn,

Thanks for your reply and btw thanks also for all your great Razbam Metroliner mods :)

I think perhaps you mean part 4 and I have been through all parts of that paper several times. Both EngineSim and AirWrench output ram drag in pounds (lbs), yet the number in table 1507 is not that lbs value and I'm unable to find out how the 1507 table value correlates to the actual lbs ram drag value I get from EngineSim and AirWrench.

Roy's paper also says:

Having established values for gross thrust (with 1507 all zeros) the next step was to put values in for 1507 using stock data. AirWrench then gave net thrust and by subtracting that from the established gross thrust the results were compared with EngineSim values for ram drag.

What stock data is being referred to?

Finding net thrust, gross thrust and ram drag in EngineSim seems fairly straight forward. My main question is how do I enter the ram drag lbs value from EngineSim into table 1507, does it need to be divided by delta2 or theta or any other formula, what is it a factor of? If you understand how this works, please share your knowledge.

Thanks and regards,

Alexi
 
Alexi,
Stock data meant the 1507 table from a stock MS airplane. For example the MS Airbus and 737 have identical values in 1507.
I entered the correct values by noting the lbs of ram drag in EngineSim (which was what I took as correct) then compared the value given by AirWrench (which calculates the same way as the sim.) It was then simply a question of adjusting the stock values to give the correct result in AirWrench. If ram drag was 10% greater in EngineSim than in AirWrench then the 1507 table value was increased by 10% for that CN1 and, perhaps, then a small correction was made to get best agreement. So the only entry tweaked was the 1507 table value
As the paper said :
Ram Drag = (V/g)* Intake Area * [TBL 1507] * delta2/sqrt(theta2) where V is Mach number in ft/sec and g is 32.174 ft/sec/sec.
Note that the 1507 Mach=0 and Mach=1.0 values are the same above 90% CN1.

The intake area is from the aircraft.cfg and is also used in EngineSim to scale the engine for sea level static thrust.

I could have explained it a bit better in the paper.
Roy
 
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