Capabilities

[JimP]

What are you trying to protect against with backup engine monitoring?

If the engine instruments go down, land. You shouldn’t need to push the engine limits to cruise to an airport and land, right? If you do have backups, how would that change your handling of a failure of the primaries?

Don’t add the weight and complexity unless they are necessary.

[dirkverdonck]

Hi,
I did my Onex instrument panel like this, see pic and created more space between the tank and the panel by installing the panel at the edge of the glareshield and added an extra extension on top which is removable and conceals a hole made in the original glareshield to have easy access to the back. The whole front is removable as well.
I installed a TRIG transponder TT21,mode S and radio TY91, both have only controllers in the panel, the electronic boxes are installed in front of the main spar. These controllers are very small and fit very well in the confined space and leave ample room for cabling.
The EFIS is a MGL Discovery Lite 7" which deals with flight instrumentation and engine monitoring. For regulatory reasons and peace of mind, I added two steam gauges, airspeed and altitude.
Another mod to ease installation and create more space behind the panel is removing the upward bent lip and replace is by one that is bent downward.

[dtibbo]

What are you trying to protect against with backup engine monitoring?

If the engine instruments go down, land. You shouldn’t need to push the engine limits to cruise to an airport and land, right? If you do have backups, how would that change your handling of a failure of the primaries?

Don’t add the weight and complexity unless they are necessary.

In an ideal world, I'd fly with one EFIS screen and nothing else but a few switches. No backups. If the screen fails with nothing else, yeah, land.

With backups I'm still VFR legal in a dark screen; I could continue that flight. Or return home from a cross country.

[NWade]

With backups I'm still VFR legal in a dark screen; I could continue that flight. Or return home from a cross country.

I get the urge to make improvements, I really do! However, its important to think through these kinds of trade-offs in a comprehensive manner.

What % of the time are you expecting to have your primary instruments fail? (I'd argue its a single-digit percentage...)

Mounting an entirely separate set of backup instrumentation means spending 100% of the time flying around with a bunch of extra wires and probes and electronics and display equipment. That means every flight you're carrying extra weight, dealing with extra current-draw, you have extra maintenance, and every flight is undertaken with extra failure modes.

Don't discount that last one. FMEA is not just for things as complex as the Space Shuttle! What happens when one wire comes loose and flops against something else inside your engine compartment? What happens when you add extra components that then rub against each other during flight? What happens when that added fastener or clamp comes loose? The engine compartment of an aircraft is a hot, wet, oily, dirty, noisy, high-vibration environment - something is bound to wear out, wear through, or come loose at some point!

Just like twin engine aircraft aren't automatically safer than a single, more instruments and wiring are not automatically better than a simple, reliable, well-engineered setup.

I'd argue that - if you perform a risk analysis - the time and money would be far better spent on training. Most of the Sonex accidents we see are not due to instrument failure, or due to some issue that a second set of instruments would've caught. I've been reading Sonex accident reports for over a decade now, and the main serious accident causes are (like most of the E-AB fleet) loss of engine power or the classic stall/spin issue. Therefore you are far more likely to get value and added safety by learning to land slowly and softly (without a stall/spin entry) in an emergency.

BTW, I personally think that training in gliders - especially modern gliders - is veru useful in learning how to deal with engine-out situations and slow-flight.

Lastly, remember that Sonex aircraft don't have incredibly long legs. Even with an aux tank you're not likely to be more than ~400-500 miles from home at maximum. In an emergency where you have to land and leave the aircraft somewhere remote, you're still less than 1 day's drive from home. And again, what % of your flights will be venturing that far afield? Most pilots in most airplanes stick within ~100 miles of home for the vast majority of their flights - meaning a "land out" due to a dark panel (or any other nuisance failure) means a 1-2 hour drive.

I'd take that minor inconvenience once every several years in return for saving money, weight, and complexity in my airplane!

--Noel

[dtibbo]

Noel,

I think you just epitomized why people seem to love this community.

I'm very new to the design and construction of my own aircraft, and I'm listening for as much advice as I can gather. Thinking about it now, even if I flew cross-continent, the return airline trip is about the same cost as one backup instrument....

Thank you for an in-depth explanation!

[JimP]

Noel,

I think you just epitomized why people seem to love this community.

I'm very new to the design and construction of my own aircraft, and I'm listening for as much advice as I can gather. Thinking about it now, even if I flew cross-continent, the return airline trip is about the same cost as one backup instrument....

Thank you for an in-depth explanation!

Yes. Very good explanation. Much longer than my question, but the point is the same.

Weight and complexity in return for non-essential backup instruments. That’s why I asked. The extra instruments can also increase the pilot workload by being in the way and distracting form important things. And you have to spend some time using them to be able to if you ever need them.

If your EFIS dies, you land. More important to know why it died than to continue on somewhere. And if you do continue, your now have no backup for your airspeed and altimeter, which you do need. It could also be the first step in a failure cascade. If something breaks, until you know why, you don’t know what else could be affected.

It’s always legal to land. :-)

What would the extra instruments do for you even if they were free, 100% reliable, and weighed nothing? At most, you might learn a temp was high somewhere? You can’t land (successfully) any faster when you learn that. You don’t need a tach to land. When would those extra instruments safe your life, or even save airplane damage? If you can’t come up with a good answer to that, the time, money, effort, weight, etc... is better spent elsewhere.

The bigger picture is to always ask what can go wrong, and to make sure you have a plan to safely recover from that. What can go wrong mechanically, electrically, comms, fuel feed, ignition, weather, with the pilot, and on and on and on. Paul Dye has written a bunch of articles along these lines in the Kitplanes magazine that you can read online if you are a subscriber. I highly recommend them. It is definitely a mindset that you have to learn to always be looking for failure modes and risks to guard against (and to evaluate those and possible mitigations realistically in light of their probability and their impact to your mission).

Looking at the FAA/NTSB crash data, training should definitely be at the top of people’s lists.

[NWade]

Thank you for an in-depth explanation!

You're welcome, and thanks for the compliment! :-)

Hope things go well with your design & build. Holler anytime you have more questions - that's what this forum is for!

--Noel

[EdW]

Back when I learned to fly (a decade before we went to the moon) one of the most important things I learned from my instructor was to listen to the airplane...what does it sound like at climb power, cruise power, in slow flight? What sight picture is there for the same conditions? Listen, learn, and practice a bit. Learn what your airplane looks and sounds like, and if/when one of those fancy (or not so fancy) instruments takes a nap you will still have a healthy picture of your true condition. Just like practicing partial panel flight, try melding with the machine occasionally. It just might ave your butt some day.

Ed
Onex 209 t/d tail finished, wings in work
Too many prospective names too early in the build

Just east of Graceland

[GordonTurner]

One more data point:

For Amater Built Experimental, no instruments are required for day VFR. None.

FAR91.205 only comes into play for night or IFR.

[DCASonex]

I have a 2-1/4' old steam gauge air speed indicator in addition to my GRT EFIS. The EFIS's digital display of airspeed changes too slowly and could fool one into thinking all is okay when actually rapidly slowing or losing head wind and approaching stall. I use the steam gauge "backup" for landing. Sonex change speed very rapidly.

The EFIS has a small arrow moves rapidly to show actual current air speed, but is is small and one's eye tends to see only the much larger digital display when making quick glance at panel. Better to glance at the the steam gauge than the EFIS.

I have also recently fitted a DIY lift reserve indicator (another steam gauge) and that is positioned directly above the steam gauge air speed.

David A. Sonex TD, CAMit 3300.