How do certain flight instruments work?

[Brian Jackson]

Hello again to everyone.

I'm still (and will probably/hopefully always be) in my aircraft learning mode. Thinking nine steps ahead in my GyroBee build, I have a question about instruments.

I understand certain instruments like VAS and Altimeters work on barometric pressure, and airspeed indicators (standard type) require a pitot tube & static port. But many others confuse me as to what they need to work. A perfect example is a Verical Card Compass. From what I gather they contain a precision geared gyroscope that is air-driven, thus requires a ducted venturi to spin its gyro to keep it pointing the right way.

Can a "vertical" card compass be mounted at an angle in a gyrpolane panel and still be accurate?

I've also hear the term "gimbal lock" mentioned a bit... From what I gather this is a condition where the attitude of the aircraft exceeds an instrument's ability to track? I'm guessing this is such for an artificial horizon, which a gyro has no need for.

Do any "standard instruments" require electrical power? And if not, how is it that various engine sensors can provide information to EGT & CHT instruments?

Sorry for all the questions, but they're interrelated. If certain instruments require a battery, that could help determine if we're aiming for a Part 103 machine or Experimental. It all sort-of coalesces...

Respectfully,
Brian Jackson

[pwendell]

Brian,

I think you are confusing a vertical card compass with an with an Automatic Direction Finder (ADF). An ADF is a gyroscopic instrument. A compass, vertical or not, is simply magnetic. EGT and CHT gauges, as far as know, do require a very small amount of electricity.

[Mike Jackson]

Hi Brian,

If you have a chance, I'd recommend getting a book by the late Tony Bingelis called Sortplane Construction Techniques . It is a builder's handbook and has a good chapter on basic VFR instrumentation. It is available thru the EAA (Experimental Aircraft Association) and can be ordered thru

eaa.org.

Having said that, IMHO, a vertical compass is probably overkill for a Bee and too much weight and cost. Thru creative mounting you could mount any number of mag compasses found in any automotive supply places. I saw several at Mentone this year. Effective, light and simple.

Mike

[barnstorm2]

Brain,

I know you are a gaget guy like myself.. so I am going to put my 2cents in.

On my 447 gyro I use my GPS's compass. Many GPS and palm pilot/computer GPS combos can reproduce most of the aircrafts traditional instraments with less weight and cost with more accuracy. Pardon the spelling I just woke up...

[Alan Coats]

Brian

The CHT and EGT sensors are thermocouples. Heating them causes them to generate electricity, at the millivolt level. The amount gnerated varies with the amount of heat. That electricity then passes through an electromagnet in the instrument. This is attached to the pointer, and causes it to move in proportion the the amount of electricity generated.

So, the temperature gauges provide their own power.

Alan

[Caribean_gyro]

I once had a talked with Ken brock about instrument. He said " why you need them? airspeed is what you need. I started talking about all gadgets he said "ah!! more weight not good. sat I am rying to say is that we can have every thing the penalty is weight and distraction. the EDI current generated by the thermocuple is feed to a coil in the meter that will delect the needle forward or backward depending in designed.

ADF is a n AUtomatic direction finder and is an equipment that received an AM signal sample it and feed it to the radio out of phase with the original signal the strenght is compare and creates a novement in the adf compas pointing to whrer the radio sation is. what you want is to know what is happening to your engine, the speed and altitude and if you want a taxy light then you need battery.

ChuckP

[pwendell]

Chuck,

Doh! When I said I ADF, I was thinking Heading Indicator, which is gyroscopic. Thanks for the correction.

[Udi]

So, the temperature gauges provide their own power.
Not always. The coolant temp probe is usually an RTD - resistance temperature device. RTD gauges require external power.

Another instrument that is often found in gyros and requires power is capacitance fuel gauge.

I support keeping the gyro light and simple. Lighter gyros fly best. I would get ASI, ALT, RPM, RRPM and EGTs. You need a compass only if you are going to register the gyro as Experimental or fly cross-country flights.

Udi

[Caribean_gyro]

and I will add to Udi. You need instrument if you are going to use them.

Chuck