Back-up or prime attitude instrument.
The TruTrak may be (may be?) a suitable last chance back-up. I have not flown one but from what I understand and what is written above it's a derived "Attitude" from other data.
A
true GYRO (like the VAC unit you mention) is totally internal, does not use air pressure or BARO, does not use acceleration (intentionally) or GPS to show an attitude (pitch/bank). It only uses the principle of "
rigidity of gyroscopic forces" to maintain its postion (attitude) which gives us the display. Gyros are not perfect either; they do have "precision errors" and are affected by acceleration, which can cause erroneous indications.
TruTrak is not using gyroscopic forces but is using software to detect, acceleration, air pressure and a GPS signal, to interpret and display bank and pitch. If you know vertical acceleration and BARO you can display IVSI or instantaneous vertical speed, from chance in pressure and acceleration. You can fly pretty level with IVSI, so it makes a good approx of pitch. If your VSI is ZERO and does not change you are level (kind of, your in level flight but not level attitude necessarily).
LEVEL flight path is not LEVEL attitude. However for little planes we really only care about level flight path, which pretty much correlates to level attitude. For example, in slow flight your attitude is nose high but you can be in level flight. At high speed in level flight, not climbing or descending, you are at a different and lower attitude than slow flight.
A Gyro will display attitude and indirectly tells you if you are climbing or descending. You need to look at airspeed, VSI or altitude to know if you are climbing or descending.
So TruTrak is using are you climbing/descending info (vert acceleration and BARO) to display approx pitch attitude. This clearly could get you into a little trouble in turbulence? It all depends on how good the they tuned the software and how good you are at flying with it.
I wounder what it would do in an unusual attitude?
Frankly the hardest thing to do IMC is keep the wings level. There is nothing that will give you wings level other than a Gyro or Gyro type device. At least with pitch we have airspeed, altimeter and VSI to determine if we are going up or down, which is a clue to our pitch attitude. Bank? You need a gyro.
Again TruTrak derives or approximates bank on acceleration and heading change (from the GPS). All good things but only related to bank, not absolute. BANK ANGLE can only be displayed by a GYRO device. Heading change and acceleration are approximate indication of bank.
Truth be told all the new EFIS Gyros are really derived or approx using acceleration in some form to determine attitude. They are more sophisticated with all 6 degrees of freedom, X, Y, Z and rotation in those three Axis measured. THe BMA and Dynon do use airspeed and may be Baro to "tune" the attitude. Airspeed is used to tune out acceleration error in the horizontal plane which can indicate a pitch up or pitch down. Even mechanical gyros suffer a little from this. Also some use a GPS signal to help in resolve bank as well. Dynon of course does not use GPS, but I think BMA does. Now REAL electronic gyros are totally independant of BARO, Pitot (airspeed) and GPS signal to work, but they cost $250,000.
The Honeywell Laser Ring Gyro (all solid state) used in a Boeing is more sophisticated than most of what we are using in experimental planes. Both are trying to do the same thing however, measure the acceleration in all three axis and three rotations, with software turning that into an attitude. The lower end units get HELP to resolve errors with the helpers, baro, airspeed and GPS heading. The high end units are so precise they don't have the same errors and thus are TRUE INTERNAL Reference units, not relying on anything else, like a mechanical gyro.
Bottom line is unless you have a spinning mass you are using some form of "inertial refrence system" or IRS you are making an educated guess at attitude. The TruTrak is a simple unit, apparently added by barometric info (pitch) and GPS (heading), assisting in deriving attitude. There are limitations to using BARO for attitude or GPS heading for bank.
It appears from the above post the TruTrak does an OK job. The fact is the trutrak is an experimental device. It may work as a last chance back-up but not as a primary instrument. Also practice and currency is key to using it.
I suspect the manufacture TruTrak has some legal words and disclaimers about using it (not using it) for IFR flight. With that said we are flying an experimental aircraft and if you trust a "derived" attitude for a back up than that is your choice.
If you have an electric T&B / TC gyro for bank (really rate of yaw) plus the "pitch instruments", airspeed, altimeter and VSI, you should be able to fly partial panel. However I think the TruTrak is a nice thing to have. I would much prefer to also have the TruTrak AI, but as a sole back-up? That is an individual choice. On the other hand if you rely on "Needle, Ball and Airspeed" only you need to practice that as well.
I don't think anyone would put the TruTrak front and center as the prime attitude instrument, at least I would not. If you want TRUE attitude you want a GYRO. The Sportys back up gyro is a contender. However remember its all electric and if you get a lightning strike you may blow everything out, glass or not. I agree Vac is undesirable, especially for an experimental. However it is truly independent because it uses a differnt kind of power, but vacuum sucks for a reason.
