Instruments for Home Built

[wmgeorge]

Right now I studying to get my Student Certificate and passing the written test. So learning about flight instruments and just wondering Altimeters are $400 - $2000 and need to be set correctly before every flight. Since I already own a very nice GPS that when locked on can give readings including altitude to within 12 feet why the need for a barometric altimeter?

Don't know if I am going to buy or build but Light Sport is my first goal and perhaps all.

[rwanttaja]

Right now I studying to get my Student Certificate and passing the written test. So learning about flight instruments and just wondering Altimeters are $400 - $2000 and need to be set correctly before every flight. Since I already own a very nice GPS that when locked on can give readings including altitude to within 12 feet why the need for a barometric altimeter?
Because all the guidance and rules about altitudes are based on barometric altitude, not GPS altitude. You may bust through the bottom of Class B airspace if you use GPS for your altitude reference. And being hundreds of feet off the pattern altitude won't endear you to other folks in the same pattern.

Buying individual instruments is SOOOOOO old school. An Electronic Flight Information System (EFIS) will give all the needed data on a single screen, for less than new individual instruments would total.

http://dynonstore.com/#!/EFIS-D6-System/p/52526463/category=13788228

Ron Wanttaja

[wmgeorge]

I would think a GPS altitude would be more accurate to real ground location than a barometric. So a little online research shows that since everyone else is using barometric pressure they are all going to be off by the same number of feet. But really the GPS is a more true reading of where the ground level is actually at.

The Electronic Flight Information System (EFIS)is nice, but how many air craft actually have them installed?

[Auburntsts]

GPS altitude might become the standard one day, but I don’t think it will be anytime soon. Until it does, the difference is significant enough (I typically see a difference of hundreds of feet) that you’ll have to stick with barometric simply because it’s the current standard and as Ron pointed out, all of the current rules and procedures are based on that standard.

[wmgeorge]

I am wondering how Chris got permission to sail to the new world with those 3 ships equipped with those new style compasses.

So even if the GPS system is good enough for air force bombers and missiles to complete their missions, its not good enough for modern aviation. I was in the USAF mid 60s and our aircraft electrical shop was right next to the instrument shop. Now I wished I paid more attention to what they were doing!!

[rwanttaja]

I am wondering how Chris got permission to sail to the new world with those 3 ships equipped with those new style compasses.

So even if the GPS system is good enough for air force bombers and missiles to complete their missions, its not good enough for modern aviation. I was in the USAF mid 60s and our aircraft electrical shop was right next to the instrument shop. Now I wished I paid more attention to what they were doing!!
If you look on the panel of today's USAF aircraft, you'll see an EFIS with a readout of barometric altitude.

Physical height above the ground is good to avoid contact with said ground, but it's of little worth during actual navigation. My airport is at 57 feet in altitude, one about 80 miles away is at 1500 feet. Between us is a mountain range running to 6000 feet or so. Imagine trying to fly that distance with constant altitude. Your way, I'd be hauling back and forth on the stick to keep the same distance from the rising and falling terrain. With barometric altitude, it's easy to maintain a constant altitude.

Imagine, also, that I'm over a area with ~500 feet ground level near some hills to 1500 feet. Another plane is over that 1500-foot range. If I report I'm at 2000 feet (above the 500 foot ground) and the other pilot is at 1000 feet (above the 1500 foot ground), WE'RE ACTUALLY AT THE SAME PHYSICAL HEIGHT. But if I tell him I'm at 2,000 feet, and he says he's at 1000 feet...it sounds like we're well clear of each other.

Again, the ABSOLUTE altitude isn't important air traffic coordination...nor for normal operations, other that keeping the height in the positive range. What's important is a common altitude standard that all aircraft in the area can comply with. And that's where the barometric altitude comes in.

I'm guessing you aren't a pilot?

Ron Wanttaja

[Auburntsts]

I don’t understand your angst with barometric altimetry. It’s just not that big a deal. You do realize that besides not using GPS for altitude you’ll need to learn to navigate without GPS too (ground based radio Nav aids, ded reckoning, pilotage)?

[wmgeorge]

So for navigation and proper air space between air craft the standard barometric altimeter is used, but for true how far above the ground am I for sure, the GPS comes in handy. Got it. Thanks guys.

[Gary.Sobek]

I have an IFR Approach Certified GPS in my airplane and have more more than a decade. One thing I can tell you about GPS altitude is the it is never correct. There have been many times that I am sitting on the ground adjusting my altimeter only to have my IFR Approached Certified GPS tell me that I am over 200-feet below ground level.

[Auburntsts]

So for navigation and proper air space between air craft the standard barometric altimeter is used, but for true how far above the ground am I for sure, the GPS comes in handy. Got it. Thanks guys.

That's not really true either. GPS height is based upon a flat reference ellipsoid modeled to approximate the geodetic mean sea level. The GPS receiver uses this theoretical sea level estimated by the World Geodetic System (WGS84) reference ellipsoid in conjunction with the GPS constellation to establish its height above the ellipsoid model, not the actual ground. In simple terms, the reason for this is the model and Earth don't match because the Earth doesn't have a geometrically perfect shape.

[wmgeorge]

Apparently there has been some old discussion about this and it seems current software has been corrected to make it more accurate, Just one link http://www.gpspassion.com/forumsen/topic.asp?TOPIC_ID=10915 last post in 2012.

[Auburntsts]

Apparently there has been some old discussion about this and it seems current software has been corrected to make it more accurate, Just one link http://www.gpspassion.com/forumsen/topic.asp?TOPIC_ID=10915 last post in 2012.


I can tell you from experience that the error is still very real. However, the bottom line is to fly, you have to do it the FAA way regardless of how you personally feel about it. If you really have to know your AGL altitude, invest in a radar altimeter (I'm kidding). Otherwise, my advice is save the philosophical debates for later and focus on learning what you need to obtain your ticket. There will be plenty of time after that to figure out how to implement the better mouse trap. Good luck!

[wmgeorge]

I can tell you from experience that the error is still very real. However, the bottom line is to fly, you have to do it the FAA way regardless of how you personally feel about it. If you really have to know your AGL altitude, invest in a radar altimeter (I'm kidding). Otherwise, my advice is save the philosophical debates for later and focus on learning what you need to obtain your ticket. There will be plenty of time after that to figure out how to implement the better mouse trap. Good luck!

Thanks for the help and elightment. Frankly I thought the altitude was calculated from the GPS Horizonal position and was referenced back to topographical satellite mapping? I still like the standard altimeter. :)

[stinsoner]

About the only time actual height above ground is referenced is when flying a precision approach; i.e. an ILS or RNAV/GPS approach with LPV(Localizer Performance) minimums. The Decision Height (DH), typically 200', would be referenced on the radar altimeter, but the minimums on the approach are still referenced to the altimeter and are designated as Decision Altitude (DA). When flying in the low altitude airway structure in the U.S., the altimeter is changed along the route from station to station generally within 100 miles of an aircraft's position. This altimeter setting is called QNH and ensures that all aircraft in your vicinity will be flying the same barometric reference. When the airplane lands, you should read field elevation on the altimeter. Some countries might reference QFE altimeter settings(Russia?), so that when the airplane lands the altimeter reads zero. When aircraft are flying in the high altitude structure in the U.S., altimeters are set to "Standard", which is 29.92" or 1013.2 hPa(hectoPaschals)(millibars) when climbing though 18,000'. Aircraft are now flying in the Flight Levels. This altimetry reference is called QNE. In different parts of the world this transition altitude may be much lower; say 5000'. This is probably way more information than you care about; but at any rate, the GPS altitude is useless data and I don't bother to display it on my iFly 740 GPS.

Dennis Crenshaw Stinson 108-3

[Mike M]

Light sport? Experimental? https://www.ebay.com/itm/SB-400-ALTIMETER/182860067437?epid=1800413814&hash=item2a934f326d:g:KywAAOSwPyRa23RW

[wmgeorge]

No, all information and help is appreciated. I realize being over 70 is a little late to start but I have always been up to date on computers and technology. Being retired and with a nice home machine shop, a couple laser engraving machines and CNC router I never lack for something to do! Just finishing up on a kitchen remodel so I have a little time on my hands.

[FlyingRon]

You're off on your computation of accuracy as well. WAAS GPS vertical accuracy is on the order of 10 meters (32+ feet) and as RonW points out, the GPS altitude is NOT the same as the barometric reason for two reasons:

1. GPS altitude is determined based on a stylized model of the shape of the earth. IFR vertical guidance is predicated on the fact that the individual approach in the database has the GPS altitude in it as well (and still you have to tell the GPS about the baro correction).

2. Everybody else (as Ron W says) is using baro altitude, which may not be accurate but ATC has told them what the common altimeter setting everybody should be using is.

[Frank Giger]

And GPS can play games as well.

This morning's flight, as recorded using GPS data, had my aircraft hovering fifty feet above the ground during landing and while putting her back in the hangar.

:)

[wmgeorge]

Went out to our local airport flying service this morning to pick up a sectional map, and a young pilot was standing there. Turns out he was CFI and he said there a big changes coming from the FAA in the next few years regarding GPS and navigation in general and not to believe everything you read online.

[Auburntsts]

Went out to our local airport flying service this morning to pick up a sectional map, and a young pilot was standing there. Turns out he was CFI and he said there a big changes coming from the FAA in the next few years regarding GPS and navigation in general and not to believe everything you read online.

Sigh. Yeah NEXGEN will save us all. Meanwhile I’ll just keep motoring along. The thing of it is I navigate 99% by IFR GPS but I have the skills to navigate without it and I do practice those skills. I also fly behind a 100% glass instrument panel and use an iPad based EFB for all my charts and pubs.

Best to learn how to fly in today’s airspace using today’s equipment and procedures and not put a lot of stock into what iffing the future. If you end up building then you can worry about that kind of stuff once you get to the point where you are ready to purchase avionics.

[wmgeorge]

Sigh. Yeah NEXGEN will save us all. Meanwhile I’ll just keep motoring along. The thing of it is I navigate 99% by IFR GPS but I have the skills to navigate without it and I do practice those skills. I also fly behind a 100% glass instrument panel and use an iPad based EFB for all my charts and pubs.

Best to learn how to fly in today’s airspace using today’s equipment and procedures and not put a lot of stock into what iffing the future. If you end up building then you can worry about that kind of stuff once you get to the point where you are ready to purchase avionics.

Trust me, I am learning the old way to navigate. I may someday get my IPad app but I do Not plan to do before I get the basics under my belt.

[Sam Buchanan]

Went out to our local airport flying service this morning to pick up a sectional map, and a young pilot was standing there. Turns out he was CFI and he said there a big changes coming from the FAA in the next few years regarding GPS and navigation in general and not to believe everything you read online.

Not only don't believe everything you read online, but don't believe everything a CFI tells you!

[Auburntsts]

Nothing wrong with going paperless from the get go in my book. The beauty of using a EFB (ForeFlight, GarminPilot, etc) is you can have all the charts, supplements and flight planning tools right at your fingertips and not have to work to keep them all current. I will never go back to paper.

[wmgeorge]

So the "new" system will be using GPS location and altitude? Looks interesting > https://www.amazon.com/gp/product/B071HMQY19/ref=ox_sc_act_title_1?smid=A3TXMSIFSSB0X&psc=1


Wow, and did you read the Reviews on Amazon? Seems GPS Is good enough for the FAA.

[rwanttaja]

Not only don't believe everything you read online, but don't believe everything a CFI tells you!
I don't believe that. :-)

Ron "Murphy was right" Wanttaja

[Auburntsts]

So the "new" system will be using GPS location and altitude? Looks interesting > https://www.amazon.com/gp/product/B071HMQY19/ref=ox_sc_act_title_1?smid=A3TXMSIFSSB0X&psc=1

Thats not really new. The 2020 mandate for ADS-B “out” has been published for years. I installed both ADS-B out and in on my plane as part of its build. Folks have been using Stratux like ADS-B in receivers for cockpit traffic and weather for years now too.

[wmgeorge]

BTW you did a beautiful job on your build!!

[Frank Giger]

He really did.

I'm of the mind that students should be taught to navigate using Ye Olde Sectional, including both flight planning and in-air navigation. It's not that one shouldn't use modern technology, it's that the principles and ideas that drive those tools should be fully understood.

Much like the E6B, it's not that pilots are truly expected to use them routinely, but we learn it to understand relationships between different factors of flight.*

* Feel free to now tell me how you use the whiz wheel all the time, including during flight, to calculate everything from fuel burn to crosswind components - and I'll laugh, as you'd be a severe outlier in aviation.

[wmgeorge]

Frank I agree 100%, I am 74 years old and I have learned things a bit more complicated than flying a plane in my life. And after semi retiring I went on to teach and head a program at our local community college. It may take me a bit longer to learn these days but so what? I can use a computer better than my grand daughters, design in Fusion 360, run my CNC machines and 3D printer build stuff in my home machine/fab shop and so on. Not ready for the retirement village yet! Yet I did just sell my off road dune buggy, making room for maybe a air craft build??

[mmarien]

I think the right answer is that everybody is using indicated altitude adjusted for barometric pressure. Unlike true altitude which is adjusted for both temperature and pressure. So if you want to fly at the same altitude as other aircraft, the best thing is to use the same type of altitude measurement as they are.

Lots of misconceptions about GPS altitude. As noted above it is the distance above a spheroid (mathematical model of the earth). It differs from ground elevation which is based on a geoid, the lumps and bumps on the earth caused by masses (mountains) and lack or masses (valleys). When you setup your spirit level next to a mountain, the mass of the mountain pulls the bubble off level. Same phenomena happens next to a large valley. Not to worry, the government knows about this and elevations shown on the airport diagram are based on this geoid. So if your GPS elevation differs from what the sign at the airport says it's could be the difference between the geoid (lumpy) and the spheroid (perfect), plus a little error in the GPS measurements. If you have a WAAS signal, the errors are probably less than five feet.

So when you set your altimeter to the barometric pressure broadcast at the airport you should see the elevation of the airport. Keep in mind the elevation is based on the geoid.

[wmgeorge]

What some folks tend to forget is the GPS readout is based on computer software and it can change... unlike the satellites in orbit. ;) So when the FAA implements the GPS system we know Is coming, will it need be calibrated to agree with the barometric altimeters? Its going to be interesting.

[robert l]

Got my P/L in 1974 and all we had was paper charts and they worked good. Also, we didn't have head sets, the only thing in the 150 was a hand held mic and what ever volume you could get from the radio speaker ! Damn, and we survived !
Bob

[Frank Giger]

Well, Robert, it's true, but the advent of cheap handhelds that hook to a headset, GPS tracking, and other modern advances like flaps sure have made things easier.

It's kind of like a conversation I had about WWI pilots, the finicky airplanes and the lack of training or aids to help them out:

"How did they manage?"
"Well, actually, they crashed a lot."

[conodeuce]

Having once gotten myself into a very tight corner, exacerbated by my GPS device deciding to cease functioning at the absolutely worst moment, I'll never be without a back up, old-tech, solution.

[Frank Giger]

Having once gotten myself into a very tight corner, exacerbated by my GPS device deciding to cease functioning at the absolutely worst moment, I'll never be without a back up, old-tech, solution.

Someone asked me why I still carry a sectional on a kneeboard when I have a perfectly good GPS enabled tablet on the other leg. That's why.

[martymayes]

Got my P/L in 1974 and all we had was paper charts and they worked good. Also, we didn't have head sets, the only thing in the 150 was a hand held mic and what ever volume you could get from the radio speaker ! Damn, and we survived !
Bob

Bob, same era but I flew a light plane with an iPad and moving map (sectional chart scale) for the very first time earlier this month. I was blown away, lol. Penty of room in my fight bag to store those paper charts......IF I need them.

Also bought my son a ANR headset as a high school graduation gift last yr and by golly, I'm thinking about buying one for myself! I might embrace this technology stuff after all!!

[Auburntsts]

Someone asked me why I still carry a sectional on a kneeboard when I have a perfectly good GPS enabled tablet on the other leg. That's why.

Meh. I ditched paper years ago and will never go back. I have a triple redundant system: EFIS, tablet, and phone with all the US Sectionals, Terminal charts, IFR low enroute charts, approach charts, and chart supplements not to mention misc pubs plus redundant avionics. If all you fly is local VFR, then having a sectional as a backup isn’t an issue. I fly a lot of IFR X/C and having paper backups just isn’t practical for me. YMMV....

[wmgeorge]

Paradigm shift. I wonder how many crashes or ran out of fuel stories there were when the pilot got lost using charts? If it saves lives, and least of all just saves time and fuel why not use GPS? This is a guy who owned a Garmin before everyone had one for car travel, and there have been some major advances in the software over the past 20 years.

My son used my newest one when he went snowmobiling up in Gods country, Northern Wisconsin and the UP of Michigan. Yes I needed to load in the purchased maps for the trails. but when you get up there all the trees looked the same,it gets dark early and you can make one wrong turn and your camping out in the snow for the night and no gas to get back.

Yes I know it can not be used for flying.

[WLIU]

I now fly with two GPS in the aircraft. My Samsung tablet running Naviator and an old Garmin 196. No paper charts. That said, I have flown coast-to-coast and from Canada to the Gulf with paper charts. And I will suggest that running out of gas has nothing to do with the type of charts on board.

I also carry a big power brick to keep the tablet going on the days when I am in the air for 6 or 8 hours on a trip. The Garmin gets ships power.

I never trust my life or my situational awareness to a single electrical device. They fail. These days a second unit, even if it is just your phone, is very cheap insurance.

Best of luck,

Wes

[rwanttaja]

Paradigm shift. I wonder how many crashes or ran out of fuel stories there were when the pilot got lost using charts?

Well...severe consequences for bad navigation have never been limited to aviation. The other side of the coin is what is referred to as "Children of the Magenta Line": Those who are slavishly devoted to the product of automation they cannot detect when things were wrong, and get in, perhaps, even worse trouble than the paper-chart guys.

Ran into this situation this very afternoon. Went to a destination I hadn't been to for 15 years. In my car, fortunately. I entered the address into the built-in Nav function and let Betty tell me how to get there.

However, about two miles shy of the destination, we hit a weird intersection.... a hard left turn, then a three-way intersection following. With two left turns and one right one. Betty told me to turn left, and I did. Into the wrong road.

In the past, I would have traced my route on a paper map first, and noticed the weird intersection. Last trip (15 years ago), I would have called up an online map before departure and found the weird spot.

Failing THAT, I just would have followed the signs on the road and taken the RIGHT turn at the 3-way intersection. It was the main road into the town, and I would have quickly found the intersecting road to the destination. Betty was saving me a mile or so by taking some side streets.

I'm not quite the luddite I pretend to be. I do own a GPS*, and do use it when I'm flying to places without direct, clearly visible ground references. But I do monitor where I'm at, and how the GPS is taking me there. I don't just follow the magenta line.

* Garmin Etrex 30. A hiking GPS

Ron "How do you change the line color?" Wanttaja

[mmarien]

My son used my newest one when he went snowmobiling up in Gods country, For a minute there I thought he came to Canada. GPS works here unless you go too far north. The far north has never been charted. You have to rely on GLONASS. ;)

[FlyingRon]

And make sure it isn't too cold for it to work. Gus McLeod found his LCD screen in the GPS was useless up in the great white north (of course, he was flying open cockpit, yes, Gus is a bit crazy).