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P3D v2 Table 1507

Messages
16
Country
italy
Hello everybody, :)

I'm trying to set the table 1507 according the paper "FS Thrust vs Altitude calculation" but I need help because I don't understand the correct workflow to do.
The paper 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."

I used a table 1507 with all zeros and changhing the throttle by means AW I have back the gross thrust values obtained previously with Engine Sim (this because with table 1507 all zeros, the gross thrust is equal to net thrust).

Then, the paper says:
"After only three iterations I got ram drag agreement with EngineSim within 0.03% from sea level to 36100 ft."

...and here starts the problem. What do the paper intends with "three iterations"? Do I have to use AW and EngineSim in conjunction?

Could someone kindly help me?
Thanks!!
:)
 

Heretic

Resource contributor
Messages
6,830
Country
germany
Probably three iterations of reloading the aircraft, flying the test points and comparing the results and subsequently adjusting 1507.

I don't have Roy's paper ready, but his conclusion for table 1507 was something along the lines that the default values work rather well.
 

Roy Holmes

Resource contributor
Messages
1,803
Country
us-virginia
A few words about 1507. There are two important factors in determining ram drag, the actual value in 1507 and the intake area.
Although I put 1507 all to zeros to calculate Gross thrust, there is a much quicker way to achieve the same end. That is put the intake area to zero.
This works because the ram drag equation is:
(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.
Actually it is intake area that has the most obvious effect because ram drag is caused by the airflow into the engine being slowed to low values before entering the combustion chambers in the engine.
For a turbojet that is the whole area of the compressor inlet. It is smaller than what you would get by using the compressor diameter to calculate the area because there is a solid cone at the intake that reduces the actual area.
For by-pass engines the same holds good because some of the air passing through the intake bypasses the combustion area. This bypassed area has no contribution to ram drag, it actually is part of the generation of thrust. Large bypass engines gain more of their thrust from the N1 work done on the airflow that from the N2 side whose main function is to provide torque to drive N1. So, when you see that the stock Lear 45 has an intake area of 4.29 and gives just 3000 lbs you can tell that the designer probably scaled off the intake. That means that the sim Lear has ram drag where it should have thrust.

When you look at my paper you will see that I describe the iterative process used to get 1506 correct. I used initial values at different CN1 points until I had a match to engine sim. I used the same process for 1507 but it only took three iterations to come to an acceptable solution.

Since writing the paper I have switched to AirWiz, it is similar to AirWrench but allows direct input of parameters. I have been able to get a really good match (under 3% error across the envelope) for several airplanes using AirWiz and therfore only need flight test to verify results and the errors are usually easy to understand.

Also as described in the paper I used EngineSim to get the core thrust data and then got AW to match it.
Any more questions, fire away.
Roy
 
Messages
9
Country
argentina
A few words about 1507. There are two important factors in determining ram drag, the actual value in 1507 and the intake area.
Although I put 1507 all to zeros to calculate Gross thrust, there is a much quicker way to achieve the same end. That is put the intake area to zero.
This works because the ram drag equation is:
(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.
Actually it is intake area that has the most obvious effect because ram drag is caused by the airflow into the engine being slowed to low values before entering the combustion chambers in the engine.
For a turbojet that is the whole area of the compressor inlet. It is smaller than what you would get by using the compressor diameter to calculate the area because there is a solid cone at the intake that reduces the actual area.
For by-pass engines the same holds good because some of the air passing through the intake bypasses the combustion area. This bypassed area has no contribution to ram drag, it actually is part of the generation of thrust. Large bypass engines gain more of their thrust from the N1 work done on the airflow that from the N2 side whose main function is to provide torque to drive N1. So, when you see that the stock Lear 45 has an intake area of 4.29 and gives just 3000 lbs you can tell that the designer probably scaled off the intake. That means that the sim Lear has ram drag where it should have thrust.

When you look at my paper you will see that I describe the iterative process used to get 1506 correct. I used initial values at different CN1 points until I had a match to engine sim. I used the same process for 1507 but it only took three iterations to come to an acceptable solution.

Since writing the paper I have switched to AirWiz, it is similar to AirWrench but allows direct input of parameters. I have been able to get a really good match (under 3% error across the envelope) for several airplanes using AirWiz and therfore only need flight test to verify results and the errors are usually easy to understand.

Also as described in the paper I used EngineSim to get the core thrust data and then got AW to match it.
Any more questions, fire away.
Roy
Please, How I get AirWiz???. Is a payware tool??. Thanks in advance. Marcelo
 
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