electric gauges vs vaccum instruments.

[speed]

I have read about serveral builders using 100% electrial guages with proper back-up system.

Are the electrical gauges better than the vaccum ?

complexity? I see them equally as complex, once you have the sytem set up its just understanding the gauages, because they both can fail and I would still have to get the plane to the ground. ( safely )

operational? I dont think I can say that vaccum are more reliable than electric, cause if the system is designed properly it should as fail-safe as the vaccuum system.

Cost effective? Do electrical gauges cost more than vaccum gauages?

The reason I am exploring electric gauges is because if I have to have an electrical system to drive my comm/nav/gps instrumentation for VFR & IFR, why not go 100% electrical or full glass cockpit.

[gmcjetpilot]

Vacuum pumps have got a bad reputation, which is deserved, but that is all we had. Electric mechanical gyros are expensive and still are $2000 each. With the advent of low cost EFIS or glass cockpits for the experimental market, the trend is towards these all electric powered "glass" instruments. Lets face it a colorful digital display with all kinds of superimposed info, flight, Nav and system info looks good, gives more info and is reliability. Mechanical vacuum pumps and gyros wear out. But what about back-up to the all electric instrument panel.

One new vacuum gyro and a new vacuum pump might set you back $1,200. You can buy a Dynon EFIS for $2,195 and get:

Attitude Indicator
Airspeed Indicator
Altimeter
Vertical Speed Indicator
Gyro-Stabilized Compass Heading
Turn Coordinator/Ball
Turn Rate
Clock/Timer
G-Meter
Voltmeter
Angle-of-Attack (with optional Dynon AOA pitot)
Serial altitude encoder output to your transponder

Back in the day, the Vacuum instruments were backed up with an electrical instrument, usually just one electric T&B. Of course when the pilot lost the vacuum pump, loosing the attitude and directional gyro, flying partial panel in IMC, "needle-ball-and-airspeed" was not fun IFR and often not successful. Today 100% electrical powered instruments with the EFIS displays and electronic engine monitors is common, and in many cases even the altimeter, VSI and airspeed have been all replaced and have no pitot-static back-up. Many RVs with 100% electric panels fly IFR. What about back-up?

What builders are doing to back-up their all glass cockpits is adding an extra alternator or extra battery or both to assure uninterrupted electrical power. This is still cheaper than a $400 vacuum pump and an $800 mechanical vacuum gyro, plus regulator and filter. When you are done you could almost buy a second Dynon for the price of one vac gyro.

However I still think the a vacuum gyro, totally independent of the electrical system, could be a good choice for a back up, but the vacuum pump still is the same expensive limited life piece of equipment. What about the good old Venturi tube? They are cheap, light and work well if up to flying speed. The down side is drag and looks. As the EFIS gets more capability and cheaper you will see vacuum instruments disappear. Unfortunately for the Cessna and Pipers they can't use the "cheap" EFIS and must still use the old gyro technology. There are certified EFIS for General Aviation, but the cost is still high. The Chelton EFIS is over $20,000. (Hard to tell price because they don't publish it. Got to wonder, must be expensive if they only give "quotes".)

Cheers George

[N916K]

Speed

I have the Dynon D10 with an electric T&B (Navaid) and an ASI and an altimeter. Personally I don't see a reason why you need a vacuum system or some fancy double electrical system when you have a reliable EFIS with a backup set of steam gauges.

Good luck and have a blast bulding and flying.

Cam

[GRANT ED]

I am an aircraft avionics engineer and have seen heaps of intruments both air and electric. Our workshop has a gyro overhaul section in which I have overhauled many gyros. Here is what I have noticed.
Note I am only talking gyro instruments here.
Usually a gyro instrument has failed because one or more of its bearings have failed.
In air intruments the number one cause for failure is bearing contamination due to a dirty air supply. Piper chieftan's have a pressure air system. When the pump fails it pushes bits of carbon into all the gyro instruments. 9 times out of 10 if this happens all the gyro instruments will need to be overhauled. I have lost count of how many times this has happened to a customers plane. We tell them to clean the lines and filters. We then overhaul the instruments, send them back where they refit them. A month later we get all the gyros back with a request for repair under warranty. After inspecting the instruments we see they have been contaminated with carbon. After talking to the customer we find they did not clean the lines because they thought it would take too long.
The number 2 cause of failure is handling damage.
Gyroscopic instruments have very high quality bearings in them. They also have a lot of weight hanginging off these bearings. A small knock can dent the bearings to the point the intrument will not operate correctly.
One of the gyro manuals states that if you place a gyro instrument on a hard surface then pick up one end 1/2 and inch off the surface and let it go. The impact will damage all the bearings to the point the instument must not be used till all the bearings have been replace. We never place a gyroscopic instrument on a bench without sitting it on a piece of foam.
So for everyone with air gyros make sure the air supply is clean. This means having good filters.
If you remove your instrument be very careful with it. A firm knock against the dash when installing it can damage the bearings.
For electric gyros the same conditions for handling care exist.
For the most part the electric side of things is very reliable.

Which one is more reliable???

I would say that electric is more reliable. Having said that if you can be sure the air supply is good an air driven gyro will last a very long time.
My boss has an RV-6. He used electric gyro's in his plane.

As far as other instruments such as mechanical airspeed and altimeters etc.
I would say the airspeed indicator is the most reliable instrument in the average aircraft. I have never seen one fail.

[RV7ator]

Speed,

Go all-electric. Plumbing is non-existant. Two wires to each gyro and you're done. I've experienced multiple vac pump failures in different aircraft, and the outcome can be very expensive, so much so as to completely offset the initial higher system costs of electric AH and DG (or EFIS if that tickles your fancy). Also, properly designed electrical system architecture is very failure resistant, and paves the way for dual electronic ignition. If your vac system goes down, you loose both gyros.

My personal belief is that vac systems continue to exist only to service and prop up the certificated market, which has glacial resistance to change because of the huge cost of any change. (Ah, the joys of experimental!)

[dan]

Opinions are free and worth even less. Come to your own conclusions. But...do yourself a favor and read the AeroElectric Connection by Bob Nuckolls. It's a great read and reference that will help guide you through designing a safe and reliable electrical system regardless of the instrumentation you choose.

And...it will probably push you toward the all-electric side of the fence if you're teetering.

http://www.aeroelectric.com

Bob holds seminars here and there. I used just the book, but lots of builders swear by his seminars. He definitely has an intelligent, modern way of approaching your amateur-built aircraft electrical system.

)_( Dan
RV-7 N714D
http://www.rvproject.com