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HighlyCritical
04-17-2012, 08:21 AM
This discussion is also going on in another "Steam Games" thread, but I thought I'd bring it here.

I haven't bought anything yet, and I'm kind of waiting to see if the altimeter issue I'm having is an isolated bug. I know a few other people have had it.

I have two issues:

1) Right after take off, I'll already be a few thousand feet off ground the ground when I know I'm only a few hundred, and

2) I was playing a sight-seeing job in the Stearman. I looked at the altimeter to ensure I was climbing (I was also doing work in the background) and it said I was, but when I looked up, I was actually only about 100ft from the ground and slowly descending.

So... any idea why it's so wrong? The game is great, but before I dump cash into it, it's gotta work. Anyone else having problems?

bastila13091
04-17-2012, 08:28 AM
1) This is Hawaii. It is not level. There are airports on it that are a few thousand feet above sealevel. Altimeters start at sealevel, not groundlevel. There usually is a difference.

2) Once again, Hawaii is not level. There are mountains there. When you fly level at a mountain, it seems like you're descending.

HighlyCritical
04-17-2012, 08:35 AM
1) This is Hawaii. It is not level. There are airports on it that are a few thousand feet above sealevel. Altimeters start at sealevel, not groundlevel. There usually is a difference.

2) Once again, Hawaii is not level. There are mountains there. When you fly level at a mountain, it seems like you're descending.


Okay on #1. But #2... I was looking at the ground, flying (almost!) straight towards it, but climbing, according to altimeter. You're telling me that's correct? :|

bastila13091
04-17-2012, 08:43 AM
Okay on #1. But #2... I was looking at the ground, flying (almost!) straight towards it, but climbing, according to altimeter. You're telling me that's correct? :|

Check the horizon more. Instruments can lie, but the eyesight cannot. Unless you're like blind or crosseyed or something.

HighFlyerXX
04-17-2012, 10:49 AM
If you are climbing at say 500 ft/min but the elevation is increasing by 1,000 ft in the same distance travelled, you are going to crash eventually if you're low enough even though your instruments say you are climbing. I would guess that for your second scenario that the ground elevation was increasing faster than your climb rate.

BASys_ODG
04-17-2012, 12:35 PM
Hi Folks

Check the horizon more.
Instruments can lie, but the eyesight cannot.
Not true, see below. ;)

Okay on #1.
But #2...
I was looking at the ground, flying (almost!) straight towards it,
but climbing, according to altimeter.
You're telling me that's correct? :|
Yes.
Its partly an optical illusion / lack of situational awareness.

Hawaii is a shield volcano.
What appears to be flat & level ground,
is actually a massive slope.

See the Mauna Kea inset in this cross section (http://xkcd.com/1040/).

HTH
ATB
Paul

bastila13091
04-17-2012, 01:26 PM
Hi Folks


Not true, see below. ;)


Yes.
Its partly an optical illusion / lack of situational awareness.

Hawaii is a shield volcano.
What appears to be flat & level ground,
is actually a massive slope.

See the Mauna Kea inset in this cross section (http://xkcd.com/1040/).

HTH
ATB
Paul

I was meaning to one side, not straight ahead.

BASys_ODG
04-17-2012, 02:32 PM
Hi Folks

bastila -
Understand now.
Sorry about that.

ATB
Paul

bastila13091
04-17-2012, 02:34 PM
Hi Folks

bastila -
Understand now.
Sorry about that.

ATB
Paul

Its fine, but thats typically what you wanna do is look to the side. Thats the whole point of that artificial horizon gauge.

Fabe_ca
04-20-2012, 05:41 PM
Is perfect level flight even possible or will we always be climbing/descending even over the ocean?

wlayton27
04-20-2012, 05:53 PM
Is perfect level flight even possible or will we always be climbing/descending even over the ocean?

It's very possible. You finish your climb, set your pitch trim somewhere below neutral (it doesn't have to be on any exact setting), set your prop RPM low (somewhere like 70-75% Np), and use the pitch control to stabilize your airspeed as high as you can get it for your aircraft (higher speeds allow more stability for neutral rudder and aileron to maintain level flight and a constant heading), then try to maintain that speed while managing your vertical speed as close to neutral as possible. It shouldn't take long before you'll be flying nice and level hands-off.

It's much easier to get there in the RV-6A or Maule M-7 because those aircraft actually have VSIs (Vertical Speed Indicators) and variable speed prop control.

RoboRay
04-21-2012, 05:15 AM
And once you get very close to the level trimmed airspeed, you may need to make a slight prop adjustment to help zero it in. It is normal for the vertical (and horizontal) speeds to oscillate slightly as you settle in. (Plane descends slightly and picks up a little speed, producing a little more lift. Plane gradually climbs from extra lift and slows a little, loosing the extra lift. Repeat a few times.) Don't try to chase every little change with an adjustment. So long as each oscillation of vertical speed is smaller than the last, you'll eventually settle out pretty close to your desired altitude. If you're within 200' of the desired altitude, just leave it be. That's close enough. Trying to hold an exact altitude perfectly will drive you crazy.

Note that you will still drift off from level flight, due simply to variable wind conditions. Even trimmed out as perfectly as you can get it, you do need to watch your altitude and periodically adjust your controls. This is what makes Altitude Hold on an autopilot so desirable.

sub7th
04-28-2012, 02:57 PM
@ the OP
Hehe, yeah according to my altimeter I just hit a tree at 1700 feet.
This is the first time it's happened though. All of my flights have been pretty bug free up till now.
I hit the tree on purpose just to see if the altimeter would correct, no luck.

wlayton27
04-28-2012, 04:20 PM
@ the OP
Hehe, yeah according to my altimeter I just hit a tree at 1700 feet.
This is the first time it's happened though. All of my flights have been pretty bug free up till now.
I hit the tree on purpose just to see if the altimeter would correct, no luck.

There's no fault with the altimeter. It's a barometric altimeter, and it gives your altitude relative to sea level on a normal day.

Standard atmospheric pressure at sea level is 29.92 inches of mercury, and the altimeter has a dial that you can rotate to change the baseline pressure (default is 29.92 in. Hg and always gives a 0 foot indication at sea level altitude).

If we had an ATIS signal, we could get the local pressure of an airfield that we intend to land on (e.g 29.45 inHg), set our altimeter to that pressure, and get an indication of our altitude relative to the runway. You can set this altitude manually as long as you're parked on the runway by rotating the knob until the altimeter reads zero and noting the pressure baseline.

Perhaps I'll go into the game and get the pressure baselines for each of the airfields and list them here...

bastila13091
04-28-2012, 04:25 PM
@ the OP
Hehe, yeah according to my altimeter I just hit a tree at 1700 feet.
This is the first time it's happened though. All of my flights have been pretty bug free up till now.
I hit the tree on purpose just to see if the altimeter would correct, no luck.

Trees are possible at 1700 feet. Heck denver is known as the mile high city and there are trees there and the altimeter there will read 5280 feet if its exactlty a mile above sealevel. If you think it should be otherwise think about this, if you take off from denver with your altimeter set at 0 and land in, for instance, houston, your altimeter would read zero/negative, so you would have absolutely no idea how high up you are, heavily increasing the chances of damages or the injury.

wlayton27
04-28-2012, 04:39 PM
Continuing from my last post:

No need to read the elevations at all the airfields. Just did Kona International:

Kona Intl at Keahole (PHKO)
ILS: 109.7 MHz (IKOA)
ATIS: 127.4 MHz
Elevation
Listed: 47 ASL
Read: 51 ASL
Absolute Pressure: 29.87 in. HG

From this information, you should be able to notice that each thousandth of an inch of mercury equates to a foot of altitude. Absolute pressure at sea level was 29.92 in. HG, and the airfield's elevation was listed as 47 feet (about 50). Take fifty thousandths (0.050) from 29.92, and you get 29.87 in. HG.

You should be able to do the same with any airfield up to an altitude of 1920 feet above sea level. Bradshaw AAF for instance has a listed altitude of 6190 feet ASL which is a pressure difference of 6.19 inches of mercury ... so its absolute pressure should be right about 23.68 in. HG. Unfortunately, the altimeter's dial only goes down as far as 28.00 in. HG, so there's no way to set it to zero feet while resting on Bradshaw's tarmac.

sub7th
04-28-2012, 07:37 PM
Trees are possible at 1700 feet. Heck denver is known as the mile high city and there are trees there and the altimeter there will read 5280 feet if its exactlty a mile above sealevel. If you think it should be otherwise think about this, if you take off from denver with your altimeter set at 0 and land in, for instance, houston, your altimeter would read zero/negative, so you would have absolutely no idea how high up you are, heavily increasing the chances of damages or the injury.

So the altimeter shows how high I am above sea level but not the actual ground?
Makes perfect sense now. Thanks.

bastila13091
04-28-2012, 07:50 PM
So the altimeter shows how high I am above sea level but not the actual ground?
I think I understand... zero from the point of take off but not necessarily the ground where you might be well after take off?

Not even zero from the point of takeoff. Not even if you're in a seaplane. There you should still be a few feet up just because the altimeter is not sitting at the bottom of the plane. Sure some planes can simulate that if they have a digital altimeter but not the ones we have now.

wlayton27
04-28-2012, 07:58 PM
The aircraft I'm used to flying in have two altimeters, a barometric altimeter and a radar altimeter. Barometric altimeters are useful as a backup and also serve to provide pilots with ASL ("above sea level" or flight level) pressure altitude, which is also used during engine performance tests. The radar altimeter's only purpose is to ping the ground and provide a distance estimate between the aircraft and the ground directly below. You could still crash with a reading of a few hundred feet on a radar altimeter if you're flying up a steep slope (flying into a mountain) or if you strike a tree or antenna.

sub7th
04-28-2012, 08:06 PM
Ah, cool. That explains why some other flight sims I've played have shown my relation to the ground in the altimeter.
Seems like a pretty useful feature especially when conducting barrel rolls and Immelmans and split S's. :cool: