Sign in to follow this  
Guest jan737

Simulating a APU EGT indicator with Fs bus

Recommended Posts

Hi,Is there anybody who knows,if and how I can simulate a APU exhaust gas temperature indicator in the fs bus CCC? When I start the APU with th e start switch the exhaust gas temp must rise, and go down when the APU is switched off.I'll use it to complete the 737 NG overhead panel .Kind regardsJan Geurtsen.

Share this post


Link to post
Share on other sites
Help AVSIM continue to serve you!
Please donate today!

You're probably going to have to calculate it yourself. There are 'blank' offsets in FSUIPC where you could park such a calculated value so as to be able to pass it to FSBUS, but since MSFS doesn't include an APU, I don't think there's any other way.Richard

Share this post


Link to post
Share on other sites

Thank you Richard,Can you give a example how to calculate?Kind regardsJan.

Share this post


Link to post
Share on other sites

Sorry, I really don't know enough about the 737's hardware to know how it works out. Generically, though, the EGT is probably going to be pretty much a direct correlation with outside air temp and fuel consumption. You'd need to decide how much fuel the APU is drawing, and calculate what that would mean in terms of EGT. Probably best bet is to ask a 'real' 737 pilot how they relate.Richard

Share this post


Link to post
Share on other sites

You could hack the AIR and Aircraft.cfg and add a third engine not producing thrust.You calibrate it to use as much gas as an apu.Then you can hook your indicator to this third engine EGT value, easily enough with fsuipc and fsbus own interface.

Share this post


Link to post
Share on other sites

Brilliant Idea!! This fixes a LOT of issues with APU modeling that I was trying to figure out.

Share this post


Link to post
Share on other sites

Be aware though. This would probably affect the modelling of the flight performance envelope. Also I don't think it is possibility to create an engine with no thrust, you have to have at least some thrust. But that's just a wild guess here. If it works it would be great!! :-)Cheers,

Share this post


Link to post
Share on other sites

"You could hack the AIR and Aircraft.cfg and add a third engine not producing thrust."Verrrrrryyyyyy clever Can you have a zero thrust engine though ?Richard

Share this post


Link to post
Share on other sites

Actually, it just occurred to me that the thrust from the APU won't be zero. It is, after all, a Jet engine with the exhaust going right out the back. While it's designed to use as much as possible of the energy internally, there must be some "left over" as thrust.How much it is, I don't know, but it won't be zero. This is a good thing anyway, as trying to use a zero thrust engine might give a bunch of zero divisor errors.Richard

Share this post


Link to post
Share on other sites

I didn't approach it, i just tought of it; so i don't really know if it is possible to make a 0 thrust engine.But if it is not, the problem may be shifted to your throttoles: if you assign your throttles to operate only engine 1 and 2, even if the APU has some thrust, it won't affect your envelope because it always stays in idle.

Share this post


Link to post
Share on other sites

Normally the APU is of after engine start up procedues. SO what is the problem if it produces thrust?As klong as the aircraft is not starting to roll after APU start.So do not connect the throttles with the apu.I am interested in this item, so please post the results of your experiments and perhaps the lines you enter in the aircrdat.cfg.RegardsNorbert

Share this post


Link to post
Share on other sites

Hi guys,A lot of interesting ideas. Is there anybody who knows how to hack a air file, i.e. that one from PMDG 737-700?Regards Jan

Share this post


Link to post
Share on other sites

>Actually, it just occurred to me that the thrust from the APU>won't be zero. It is, after all, a Jet engine with the exhaust>going right out the back. While it's designed to use as much"The APU 'thrust' moves the aircraft as much as the exaust pipe of a car moves the car"(yes, there have been some experiments with "thusting APUs", but it wasn't worth it)Manuel

Share this post


Link to post
Share on other sites

Manuel:"The APU 'thrust' moves the aircraft as much as the exaust pipe of a car moves the car"I didn't say it would generate enough thrust to move the aircraft, just that the thrust it generates wouldn't be zero.If you put in the Aircraft.cfg that the max thrust is 1lb, and then the program tries to calculate the thrust for 50% power, it will generate a meaningfull number - 1 divided by two is 0.5lb. If you put in zero as the max thrust though, 0 divided by 2 would give an arithmetic error.Richard

Share this post


Link to post
Share on other sites

Hi guys>it won't affect your envelope because it always stays in idle.Actually I was thinking about this idle thing. There is an increase in fuel consumption depending on the load. With the generator online it draws about 225 lbs/h, with 1 pack it's 280 lbs/h and with 2 packs it's 226 lbs/h. (Figures are for the NG APU)Here's the idea. What if you could somehow connect the packs, and generator switches to the throttle control of the APU. This way we could simulate different loads on the APU as well!Wadaya think?

Share this post


Link to post
Share on other sites

>increase in fuel consumption depending on the load. With the>generator online it draws about 225 lbs/h, with 1 pack it's>280 lbs/h and with 2 packs it's 226 lbs/h. (Figures are for>the NG APU)I think the figure for 2 packs is wrong :)Maybe 326lbs/h?>Here's the idea. What if you could somehow connect the packs,>and generator switches to the throttle control of the APU.>This way we could simulate different loads on the APU as>well!Hmm....I think it is possible, you can do it this way:assign your pack switches the function to increase throttle.Talking FSBUS, you simply assign eah swithc a double function (on ON and on OFF) to sum or detract a constant value to engine 3 throttle.These specific numerical values should be found experimentally, in order to give the best result.That way when you switch packs on, the throttle increases, and the fuel flow grows, and the reverse when you switch them off.What do you think?

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this