GPS altitude vs altimeter altitude

Chris W wrote:
There is still the possibility that something goes wrong with the
autopilot and sends the plane down the wrong side of the highway at 3
feet off the ground. To virtually eliminate this type of situation, I
plan on having a completely independent system that will kill the engine
and put the plane in a slow flight configuration should the altitude
drop below a given amount. Granted that could also fail but the chances
of both the autopilot and that system failing is very remote, that "fail
safe" system would be pretty small and light and could be made redundant
and possibly include a the deployment of a parachute. All this said I
am open to other ideas to make it safer.

What is the purpose of the project? Why couldn't it be done in a way
where the model remains within sight at all times - say by flying a
pre-established figure-8 course or something similar, and having a
manual override capability if it's observed to stray from the planned
course? Your current plan certainly appears to violate the model
airplane safety guidelines which state that "10. The operator of a
radio-controlled model aircraft
shall control it during the entire flight, maintaining visual contact
without enhancement
other than by corrective lenses that are prescribed for the pilot. No
model aircraft shall be
equipped with devices which allow it to be flown to a selected location
which is beyond
the visual range of the pilot."
http://www.modelaircraft.org/PDF-files/105.PDF

I lived in Tulsa and OKC and have now been in Kansas over 25
years. Your proposed altitudes are above the MEA on
airways. Done properly, with reserved airspace [you can get
approval to use the MOAs] what you want to do is safe. But
if you just want to launch and depend on luck to avoid
killing somebody you're being reckless.
A quick Google returned this...
Drone aircraft may prowl US skies | CNET News.com Drone
aircraft may prowl US skies | Can unmanned aerial vehicles
doing ... the FAA says it's created a UAV "program office"
to come up with new rules of the ...
news.com.com/Drone+aircraft+may+prowl+U.
S.+skies/2100-11746_3-6055658.html - 54k - Cached - Similar
pages


Unmanned Aerial Vehicles (UAVs) and the National Airspace
System This process has aided the FAA, other government
agencies, and the UAV manufacturers ... except for those
flown under the AMA Experimental Aircraft Rules; ...
www.house.gov/transportation/
aviation/03-29-06/03-29-06memo.html - 16k - Cached - Similar
pages


AOPA Online - Regulatory Brief -- Unmanned Aircraft Systems
Unmanned aircraft (UA) operate without an on-board pilot or
crew. ... The FAA is in the process of drafting rules that
establish regulatory guidance for UAS ...
www.aopa.org/whatsnew/regulatory/unmanned.html - 29k -
Cached - Similar pages


Use of Pilotless Planes May Be on the Rise Last year, the
FAA allowed two unmanned aircraft to be tested for
commercial use. ... The Fine Print: WPNI Rules for Posting
Content | Privacy Policy ...
www.washingtonpost.com/wp-dyn/
content/article/2006/03/29/AR2006032901814.html - Similar
pages


Federal Aviation Administration - Unmanned Aerial Vehicles
(UAVs) Unmanned Aerial Vehicles (UAVs) – sometimes called
“unmanned aircraft systems,” ... The FAA’s main concern
about UAV operations in civil airspace is safety. ...
www.faa.gov/news/news_story.cfm?type=fact_
sheet&year=2005&date=092005 - 8k - Cached - Similar pages


Section 5. Potential Flight Hazards 7-5-1. Accident Cause
Factors ... However, some time may pass before the FAA is
notified of these outages, ... 7-5-5. Unmanned Aircraft. a.
Unmanned aircraft (UA), commonly referred to as ...
www.faa.gov/ATpubs/AIM/Chap7/aim0705.html - 57k -
Cached - Similar pages
[ More results from www.faa.gov ]




I see on your website that your name is Woodhouse and you
sell wishes. Does your planned UAV that will fly up to
6,000 feet for many miles [you said you early test would be
20 miles] make up a "wish" for a customer?
Since you're in OKC, why not visit the Feds and learn what
is legal and how to do it safely?

--
James H. Macklin
ATP,CFI,A&P


--
The people think the Constitution protects their rights;
But government sees it as an obstacle to be overcome.
some support
http://www.usdoj.gov/olc/secondamendment2.htm
See http://www.fija.org/ more about your rights and duties.



"Chris W" wrote in message
news:TpF0g.942$9c6.755@dukeread11...
| Morgans wrote:
|
| Most likely, nothing bad would happen. Is that
something you want to
| gamble your like on? Is it worth it?
|
|
| I'm guessing that you either live east of the Mississippi
or on/near the
| west coast, and not in Oklahoma. RC airplanes can and
have killed
| people. However, generally this happens from a much
larger plane than I
| plan on using, and the chances of someone getting injured
is reduced
| significantly when the engine isn't running. With this in
mind these
| are the situations I foresee potential for serious injury.
The only way
| I see this coming in contact with someone on the ground is
if the engine
| is not running. Therefore, the biggest danger to someone
or something
| on the ground is gone. So for the plane to impact a
person while the
| engine was running it would have to be an impact with a
real plane. If
| the difference in heading of the real plane and the model
were between
| greater than 0 and less than 90, then the prop wold be
history before it
| penetrated the cabin and would the now dead engine would
loose most of
| it's energy before in impacted someone in the plane, most
of the rest of
| the plane would never enter the cabin. If the difference
between the
| heading of the real plane and the model were between 90
and 180, that's
| big a problem. I'm not sure how feasible it would be to
have some kind
| of sensor to detect such an impending collision and do
something about
| it. Other than avoiding busy airspace, I'm not sure what
to do about
| it. Keep in mind that the class C around KOKC which is
with in 3 miles
| of my house and I plan on staying away from, really isn't
very busy at
| all. There is still the possibility that something goes
wrong with the
| autopilot and sends the plane down the wrong side of the
highway at 3
| feet off the ground. To virtually eliminate this type of
situation, I
| plan on having a completely independent system that will
kill the engine
| and put the plane in a slow flight configuration should
the altitude
| drop below a given amount. Granted that could also fail
but the chances
| of both the autopilot and that system failing is very
remote, that "fail
| safe" system would be pretty small and light and could be
made redundant
| and possibly include a the deployment of a parachute. All
this said I
| am open to other ideas to make it safer.
|
| --
| Chris W
| KE5GIX
|
| Gift Giving Made Easy
| Get the gifts you want &
| give the gifts they want
| One stop wish list for any gift,
| from anywhere, for any occasion!
| http://thewishzone.com

In article .com,
says...


To respond to the original posters question. I have often asked the
same thing. My observations are this. My plane is sitting in the hangar
at 6412.37 msl. The airport was just recently surveyed so I am sure
this is a real close number.


They just surveyed the airport, and they put the datum point in your
hangar?

The airport elevation is the highest spot on a runway, not
the ramps or taxiways. Depending on the local terrain,
there can be more than 50 feet difference on the runways.


--
James H. Macklin
ATP,CFI,A&P

--
The people think the Constitution protects their rights;
But government sees it as an obstacle to be overcome.
some support
http://www.usdoj.gov/olc/secondamendment2.htm
See http://www.fija.org/ more about your rights and duties.


"Greg Farris" wrote in message
...
| In article
.com,
| says...
|
|
| To respond to the original posters question. I have often
asked the
| same thing. My observations are this. My plane is sitting
in the hangar
| at 6412.37 msl. The airport was just recently surveyed so
I am sure
| this is a real close number.
|
|
| They just surveyed the airport, and they put the datum
point in your
| hangar?
|

On Sun, 16 Apr 2006 14:37:53 -0500, Chris W wrote:

It is my understanding that even if a GPS is reading perfectly and your
standard altimeter is reading perfectly even on a standard day that the
2 values will not be the same

Mine generally read within 50-100 feet of one another. However, I
rarely fly above 3,500 feet. (Altimeter is 60 years old, assuming same
age as airplane.)


-- all the best, Dan Ford

email: usenet AT danford DOT net

Warbird's Forum: www.warbirdforum.com
Piper Cub Forum: www.pipercubforum.com
In Search of Lost Time: www.readingproust.com

Does your old Cub have a sensitive altimeter or just a
standard?



--
James H. Macklin
ATP,CFI,A&P

--
The people think the Constitution protects their rights;
But government sees it as an obstacle to be overcome.
some support
http://www.usdoj.gov/olc/secondamendment2.htm
See http://www.fija.org/ more about your rights and duties.


"Cub Driver" usenet AT danford DOT net wrote in message
...
| On Sun, 16 Apr 2006 14:37:53 -0500, Chris W
wrote:
|
| It is my understanding that even if a GPS is reading
perfectly and your
| standard altimeter is reading perfectly even on a
standard day that the
| 2 values will not be the same
|
| Mine generally read within 50-100 feet of one another.
However, I
| rarely fly above 3,500 feet. (Altimeter is 60 years old,
assuming same
| age as airplane.)
|
|
| -- all the best, Dan Ford
|
| email: usenet AT danford DOT net
|
| Warbird's Forum: www.warbirdforum.com
| Piper Cub Forum: www.pipercubforum.com
| In Search of Lost Time: www.readingproust.com

On 16 Apr 2006 22:42:05 -0700, "peter" wrote:

"10. The operator of a
radio-controlled model aircraft
shall control it during the entire flight, maintaining visual contact
without enhancement
other than by corrective lenses that are prescribed for the pilot. No
model aircraft shall be
equipped with devices which allow it to be flown to a selected location
which is beyond
the visual range of the pilot."

What about the guys who flew the RC plane to Ireland?

(Gotta love that bit about corrective lenses!... "My glasses! Where
did I put my glasses?")



-- all the best, Dan Ford

email: usenet AT danford DOT net

Warbird's Forum: www.warbirdforum.com
Piper Cub Forum: www.pipercubforum.com
In Search of Lost Time: www.readingproust.com

It wasn't radio controlled, but a robot. It was also out of
US airspace over the ocean and well below any Atlantic
aircraft traffic and above the ships. It may have had a
chase airplane until it was off-shore and it may have been
met at the other end. It wasn't a secret, they had to have
all the paperwork in order to get the record.

Maybe the guy is wanting to build a cheap cruise missile?



--
James H. Macklin
ATP,CFI,A&P

--
The people think the Constitution protects their rights;
But government sees it as an obstacle to be overcome.
some support
http://www.usdoj.gov/olc/secondamendment2.htm
See http://www.fija.org/ more about your rights and duties.


"Cub Driver" usenet AT danford DOT net wrote in message
...
| On 16 Apr 2006 22:42:05 -0700, "peter"
wrote:
|
| "10. The operator of a
| radio-controlled model aircraft
| shall control it during the entire flight, maintaining
visual contact
| without enhancement
| other than by corrective lenses that are prescribed for
the pilot. No
| model aircraft shall be
| equipped with devices which allow it to be flown to a
selected location
| which is beyond
| the visual range of the pilot."
|
| What about the guys who flew the RC plane to Ireland?
|
| (Gotta love that bit about corrective lenses!... "My
glasses! Where
| did I put my glasses?")
|
|
|
| -- all the best, Dan Ford
|
| email: usenet AT danford DOT net
|
| Warbird's Forum: www.warbirdforum.com
| Piper Cub Forum: www.pipercubforum.com
| In Search of Lost Time: www.readingproust.com

On Sun, 16 Apr 2006 19:58:19 -0500, Chris W wrote:

It seems as though those who actually read what I was really asking
didn't think it was important to find or know the answer so let me get a
little more specific. I am going to launch a remote control airplane
that has an autopilot. The autopilot has an altitude hold function that
is based on barometric pressure sensor. I will also have a GPS used for
guidance. The data from that GPS will be transmitted using APRS on
144.39 mhz to any amateur station listening. Once the autopilot is
turned on it will hold the pressure altitude it is at, so as it flies
along it's route (maybe as many as a few hundred miles) and the
barometric pressure changes the plane will climb and descend to maintain
the same pressure altitude. However the only data I will be getting
back is the GPS altitude. I need a way to do a reality check so if I
see the plane is descending or climbing I will know it is because of
changes in the barometric pressure and not the something that has gone
wrong. The plan is to get the latest METAR data from the closest
observation point to the current position of the plane and then do the
math compared to what it was where and when it launched so I will know
about what the GPS altitude should be reading as that is all I will be
able to see. For those who want to know why I don't just have it
transmit the pressure altitude back, I have four good reasons; cost,
weight, size, complexity. My first flights will be only 20 miles or
so. For safety I will be sure it steers clear of any class B, C, and D
air space. I'm not sure what pressure altitude I will have it fly at
.... probably somewhere between 1500' and 6000' AGL depending on the
distance for it to cover.

I do not believe there is any formulaic method to convert from GPS altitude
to pressure altitude.

GPS altitude may be more akin to true altitude, with variations based on
the precise geographic location that could be placed into a table.

But if altitude is varying with pressure altitude, bearing in mind that the
pressure altitude sensor is also sensitive to temperature, I think you have
your work cut out for yourself.

Perhaps you could graph the METAR derived data and compare it with the GPS
derived altitude, and if the trend (direction of change) is the same, be
satisfied that the aircraft is performing as designed.

If you had the lookup table to derive geographic position vs GPS altitude
error; and also something like a SKEW-T plot to look at temperatures aloft;
and also the METAR data, perhaps you could develop something to convert
true altitude (from your corrected GPS output) to assumed pressure altitude
reading on your altimeter) and draw some conclusions that way.

It sounds like an interesting problem.


Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)

DUH ......Any given survey uses multiple elevations to show contour
lines. It just happens the apron right infront of my hangar was a
reference spot for one of those data points. I will just lurk here and
watch the chaos run rampant....... G