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Thread: ITT as reference in formation flying?

  1. #11
    74th vTS Pilot El_Roto's Avatar
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    Using the GS readout on the TAD is best used for judging closing speed with the hooked a/c, though if you're using the contracts you already know what the reference speed is.
    “Get the nosewheel on the ****ing centerline.” - Al Hawley, my first IP

    [SIGPIC][/SIGPIC]

  2. #12
    GOMER 2 Noodle's Avatar
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    Mostly covered by others, but I'll try and fill in a few gaps. But first, a disclaimer: I left work at 0100, its presently 0330, and I have to be up at 0600 to go back to work...so if I make some spelling or grammatical mistakes while typing on my phone from bed with one eye open, you'll forgive me if I dont spend a lot of time correcting them. Please and thank you.

    ITT and FF are control instruments. The FAA has a definition of control instruments versus performance instruments. Google it for the specifics, but the gist is that you set or adjust a control instrument, then observe a change in aircraft state on one or more performance instruments. In our case, set ITT then observe a change in airspeed on the airspeed indicator.

    ITT is a good control instrument in the A-10 because at low altitude and airspeed, the TF34 is temperature limited. That means that when you push the throttles to MAX, at some point the engine encounters the max temperature limitation, and the ITT amplifiers must "trim" the fuel flow in order to prevent the engine from exceeding 865C ITT. So even though the engine is capable of obtaining a higher fuel flow and correspondingly higher core RPM, it is hydromechanically prevented from doing so.

    The benefit to using ITT is that it provides a (generally) fixed reference: at MAX thrust everyone in the flight is going to get 865 ITT regardless of altitude and therefore, for any particular ITT setting, each flight member will have very similar thrust. In contrast, at MAX thrust, core and fan RPM vary according to altitude (OAT), making it difficult to use as a reference.

    A little more about ITT: when you move the Fuel Flow switches to Override, the ITT amplifiers are bypassed and engine RPM is mechanically controlled directly by throttle lever position. In the event of an ITT amplifier failure or malfunction, this will allow you to achieve rated ITT (and beyond). In an emergency, it will allow you to exceed the ITT limits to extract maximum thrust from the engine. Think of an engine failure during takeoff. But depending on the duration and peak ITT attained, the engine can be damaged severely enough to fail.

    Fuel flow is also a good control, especially when you want to have a predictable endurance. In the A-10, perhaps you need to cover a particular vul period, or you want to maximize time on station for CSAR or FAC mission requirements. Preplanned fuel flows are also a good crutch for obtaining max range AoA, specifically when you need to calculate a bingo fuel for diversion purposes. For instance, 2000pph (1000pph/engine) at 15k is a good ROT when diverting. I think I got the altitude right...it might be 10k...

    The point of all of this is that unless you're adhering to a contract airspeed, striving for a TOT/ARCT, or using "dead reckoning" for LATN in a high threat environment, you generally accept the airspeed that results from the thrust reference you've chosen.

    As far as using SADL and TAD to maintain position, that's a non-starter. First, the SA in SADL means its there to help build SA, not become a crutch or replacement for airmanship. It's great for flying and Instrument Trail Departure (ITD) when your primary duties include staring at the instrument panel. But in tactical formation, every second you spend looking at the TAD is a second you're not clearing FL's six.

    99% of all difficulties can be avoided by thoroughly briefing the planned/desired tactical formation and power settings. Armed with this knowledge, the wingman is able to anticipate where he needs to be and how to get there. Remember, fix fore/aft position errors first, then fix spacing, then fix altitude stack. Also, wingmen should stack 1 to 2k high so that they can use the vertical to regain fore/aft position without adnusting throttle if they fall behind.

    It's a visual excercise, don't rely on sensors to do the job for you.

    Ok, post quality is decli ing. Sleepy time...

  3. The Following 12 Users Say Thank You to Noodle For This Useful Post:

    Baxter (03Jan15), Coolhand (03Jan15), Dojo (03Jan15), Eddie (03Jan15), El_Roto (04Jan15), Howie (03Jan15), IronHog (06Jan15), JayPee (03Jan15), Kimi (10Aug15), Stuka (03Jan15), Trigger (03Jan15), Vitormoura (19Jul17)

  4. #13
    Member Dojo's Avatar
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    While we're on the subject, a slight tangent: How accurate is the ITT gauge in DCS compared to the real thing? I can't achieve 800 ITT; slightly less than in fact, and this has always stuck in my craw as per the Instrument Trail Departure contract: we're suppose to be MAX at roll to 200, and then "setting" 800 ITT to maintain 200 during climb. This of course gives the impression the ITT can be "pulled back" from MAX to 800. So presently I just stay MAX and pitch to 200.

    If this is just another "DCS-ism", so be it, but if I'm thinking about it incorrectly, I'd like to know. It's no big deal, as lots of things stick in my craw, and since I'm not terribly certain where my craw is (though I suspect it's in the nether regions), I suppose I don't mind something else being "there".

    Stop getting turned on, Howie.

    Geez... this guy.

  5. #14
    Member JayPee's Avatar
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    Wow guys.. Again, the added value of a dedicated community is proven in this thread. Thanks for the detailed explanations, and especially Noodle for the additional insight in 'how it should be done'. For the time being I'll go and find me a random online FL/wingman to practice the proper technique. As pointed out once more, without the proper planning and contracts it'll soon become a confusing mess up in the air.. unfortunately such planning is almost impossible to do with random online players, since most don't take the sim as serious as it should be taken.

    I have the 10C dash 1 so I'll take a look at the graphs, thinks for pointing that out Snoopy. Don't know why I didn't think of that myself.
    Last edited by JayPee; 03Jan15 at 13:12.

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  7. #15

    Da FAC?


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    Quote Originally Posted by Dojo View Post
    While we're on the subject, a slight tangent: How accurate is the ITT gauge in DCS compared to the real thing? I can't achieve 800 ITT; slightly less than in fact, and this has always stuck in my craw as per the Instrument Trail Departure contract: we're suppose to be MAX at roll to 200, and then "setting" 800 ITT to maintain 200 during climb. This of course gives the impression the ITT can be "pulled back" from MAX to 800. So presently I just stay MAX and pitch to 200.

    If this is just another "DCS-ism", so be it, but if I'm thinking about it incorrectly, I'd like to know. It's no big deal, as lots of things stick in my craw, and since I'm not terribly certain where my craw is (though I suspect it's in the nether regions), I suppose I don't mind something else being "there".

    Stop getting turned on, Howie.

    Geez... this guy.
    Correct, the DCS A-10C can not do 800 ITT, I think it's limited to about 780 or so.
    The nr in the OI's is reflecting RL operations. We'll update it once.

    Providing CAS when you're all out of HUA!

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    Dojo (03Jan15)

  9. #16
    Thought the OIs had already been adjusted, obviously not. In meantime use 750 ITT in place of 800 across the board.

  10. The Following User Says Thank You to Eddie For This Useful Post:

    Dojo (03Jan15)

  11. #17

    KOVIC


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    Sounds like a good big report stuka. They'll ignore it because I know I mentioned it and believe noodle did too when he was a tester.

    Added 476-01 OI updated with DCS A-10C ITT limitation.

  12. #18
    GOMER 2 Noodle's Avatar
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    Sorry. I meant to discuss the differences between DCS and the real world, but in my stupor I simply forgot.

    DCS modeling of the turbofan engine is inaccurate in places. The inability to attain rated ITT is one of the most obvious flaws. Fuel Flow gets jumpy at 750 ITT, there's a lack of compressor stalls/surging/roll-backs/flameouts beyond stall AoA, there's no stagnation at high altitude, and heat soak back after shutdown is excessive. There's ancilliary issues too, like hydraulics that don't lose pressure after the loss of an engine-driven pump, slats not extending upon loss of the right hyd system, etc...

    All of these things have been reported to ED, in some cases years ago. But ED is a lot like a honey badger: it don't give a shit!

    So no, you can't pull the power back from MAX to 800 like you should. I use 750 instead to achieve similar effect.

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    Eddie (04Jan15), El_Roto (04Jan15), JayPee (04Jan15), Snoopy (04Jan15)

  14. #19

    KOVIC


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    I remember all this reports noodle as well as Eddie and I asking repeatedly before we left on a status.

  15. #20
    Senior Member PFunk's Avatar
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    Here's a question.

    Does this ITT limit compared to the real A-10 mean that the DCS A-10 never reaches correct rated thrust output, or that the DCS A-10 reaches rated or similar thrust output to the real one at a lower ITT?

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