Knowing if you are ascending or descending without help of alt, VSI

LongRoadBob

LongRoadBob

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This has been something I couldn't put my finger on since starting flying...that bothered me.

Until starting flying lessons, it never occured to me that the horizon is always at the same place, two feet off the ground, or 2000 ft AGL. It's right THERE. Same apparent height, etc.

So...If the altimeter and VSI were broken, or covered over, it seems to me like other than the attitude of the plane, it could be very hard to know if you are descending or ascending.

One can look down, see if objects on the ground are getting larger but from a decent altitude, it might not be that apparent.

Can experienced pilots feel it, from the seat, or some other sense? Thinking if a gradual descent.

This started also with my trying to understand the dynamics of a steep turn. First 45 deg. bank I did (not very well) when the instructor was calling for more nose up, I realized my shallow banks hadn't prepared me for this, and that we were sinking a little but that it was still the stick to get that nose up that was required. But second question, it still is relative the horizon, but nose up also tightens the turn more correct? Does that also mean increase in airspeed?

edited: changed title, turns out it wasn't such a dumb question, or... I have asked dumber ones so..
 
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A gradual constant speed descent will be pretty much impossible to feel because it's unaccelerated, meaning you are experiencing 1G. Same with a slight ascent. However. If you know that at a given power setting and conditions your airspeed indicator should say, 115kts, and it shows 120kts, you may be in a descent.
 
You tend to learn the sight picture of your nose at certain speeds like cruise so you can kinda tell, but it can be subtle. More telling is that even a 100 fpm climb or decent will change your airspeed noticeably.


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Airspeed is the secondary indicator for climbing and diving (as taught for Instrument Flight). Engine RPM for a fixed prop can also be a clue. But a very gradual climb or descent? You probably can't tell. Altimeter is one of the very few required instruments for day VFR flight for a reason.
 
A long, long time ago. I was told "If possible, in an emergency or instrument failure, trim for a slight climb and a slight right turn. This will give you time to sort things out and put a plan in place."
I always wondered about that advice, especially if it's the altimeter, but I did it a couple of times and it worked out for me.
In the old days, here was always a possibility of climbing until hypoxia was and issue.
Now a days, flying the Cub, anorexia is probably more of an issue.
 
In a constant, unaccelerated flight there are no physical cues to go by except visual. If you are 10K AGL, your comment:
One can look down, see if objects on the ground are getting larger but from a decent altitude, it might not be that apparent.
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is very true.

@EdFred 's comment is true, too... You have to know your plane's performance numbers.

-Skip
 
You can sense a change (acceleration), but not a constant decent or ascent.

Especially in a glider, I can feel when I hit a thermal and the plane starts going up, but a constant slow decent is undetectable.

In an elevator you can feel the acceleration, but once it gets up to speed, you can’t tell you’re moving other than by the vibrations of the equipment - until you accelerate back to a stop at your destination floor.
 
Everything said so far, plus I would add to what Salty said. If you are in rising or descending air, a change in the rate that it's rising or descending can feel like you are climbing or sinking, but can just mean you are sinking or climbing slower than you were. Mostly relevant for glider pilots, but I've spent a fair bit of time circling in sink, when all that happened is the air went from 600fpm down to 200fpm down. In my hang glider, I can usually get a good sense if I'm descending, even at 10k agl, but it's only over a few minutes rather than instantaneous.
 
Hang 4 said:
Everything said so far, plus I would add to what Salty said. If you are in rising or descending air, a change in the rate that it's rising or descending can feel like you are climbing or sinking, but can just mean you are sinking or climbing slower than you were. Mostly relevant for glider pilots, but I've spent a fair bit of time circling in sink, when all that happened is the air went from 600fpm down to 200fpm down. In my hang glider, I can usually get a good sense if I'm descending, even at 10k agl, but it's only over a few minutes rather than instantaneous.
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Yep. That slow down at the top of the ascent in an elevator will feel exactly like the acceleration downward when you start back down, even though you are still going up, you’re doing it more slowly so it feels like you’re going down.

Acceleration is both when you go faster and when you go slower (change). But you can easily confuse it with speed because you can’t sense speed or direction of movement (well you can with other senses like hearing the wind get louder, or seeing the horizon or a landmark move).
 
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Even attitude is not a good tell. You could be nose high and losing altitude, as in a landing flare.
 
I've only been into the flight levels a few times, but I seem to recall that the horizon did look lower from way up there. Maybe some of the jet jockeys can weigh in? @Greg Bockelman?

Geometrically speaking, and assuming a perfectly spherical Earth and unlimited visibility, at 41,000 feet the distance to the horizon is 248 miles, or very close to 1% of the earth's circumference. That means the horizon would be about 3.6 degrees down from level, which should be perceptible.

Certainly not from the altitudes we're usually at, though...
 
I think that if objects in the distance appear they are rising to meet you, you are descending. If not, you are either maintaining altitude or climbing. In fact, when landing, you'll know you are on the proper glideslope if your aiming point appears to be rising to meet you. If it moves up in your windshield, you'll land short. If it's moving down, you'll land long, or not at all.
 
Most of today's portable GPS moving maps have GPS derived altitude displayed. My Garmin Aera 660 is panel mounted using an AirGizmo dock and uses ship's power. It has a "3-D Vision" page showing the altitude as a sliding vertical tape, and in the event of a ship's power failure, the GPS continues to function powered by its internal battery.

While GPS derived altitude isn't as accurate as an altimeter, it's certainly good enough to avoid terrain and get you safely on the ground.

Aera%20660%203D%20Vision%20Page_zps2dh7xorw.jpg
 
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LongRoadBob said:
This has been something I couldn't put my finger on since starting flying...that bothered me.

Until starting flying lessons, it never occured to me that the horizon is always at the same place, two feet off the ground, or 2000 ft AGL. It's right THERE. Same apparent height, etc.

So...If the altimeter and VSI were broken, or covered over, it seems to me like other than the attitude of the plane, it could be very hard to know if you are descending or ascending.

One can look down, see if objects on the ground are getting larger but from a decent altitude, it might not be that apparent.

Can experienced pilots feel it, from the seat, or some other sense? Thinking if a gradual descent.

This started also with my trying to understand the dynamics of a steep turn. First 45 deg. bank I did (not very well) when the instructor was calling for more nose up, I realized my shallow banks hadn't prepared me for this, and that we were sinking a little but that it was still the stick to get that nose up that was required. But second question, it still is relative the horizon, but nose up also tightens the turn more correct? Does that also mean increase in airspeed?

If nothing else we can use this to point to when someone says "there are no dumb questions" to end the argument once and for all.

I'm a little off today, and it has been way too long since my previous flight. Weather (#1 cause), plane grounded, lack of instructor that can take the booking with me, etc. all contributed to being the longest dry spell for me for a long time.
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It is power and pitch that determines performance. Except for the sense of pressure changes in your inner ear, I don't think you can tell whether you are climbing or descending without knowing the exact pitch/power/performance combination for your plane. Even then, weight and temperature will have a role in it as well. Good question. Not stupid at all.
 
If you think your question is stupid,wait to see some of the answers you relieve.
 
Like pretty much all performance, it's a combination of pitch and power and the view out the window. Not just the horizon in front of you but other telltale clues peripherally. It's a learned and developed sense, like mainiating your speed in a car in the highway without looking at the speedometer or hitting the right airspeed on final for landing with all the instruments covered (easier than people expect).

It's not perfect. Up and downdrafts make a difference and some people are just better at it than others.

In your hypothetical, you also have airspeed and VSI as instruments which also provide altitude information crosschecks.
 
midlifeflyer said:
In your hypothetical, you also have airspeed and VSI as instruments which also provide altitude information crosschecks.
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ORLY??

So...If the altimeter and VSI were broken, or covered over, it seems to me like other than the attitude of the plane, it could be very hard to know if you are descending or ascending.
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:D
 
I don't think it has been mentioned yet, but your ear can also be a good way to tell once you get used to the sounds of your airplane. If there is enough of a climb/descent you can possibly detect the change in sound coming from your engine/prop, as well as the change in the sound of the slipstream moving past your airplane.
 
texasclouds said:
Does your radio and transponder work? Call atc.
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Where does your transponder get its altitude information? Hint...if you've got a bad static system that's affecting your altimeter and vertical speed indicator, ATC is going to give you bad information as well.
 
MauleSkinner said:
Where does your transponder get its altitude information? Hint...if you've got a bad static system that's affecting your altimeter and vertical speed indicator, ATC is going to give you bad information as well.
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I thought a modern transponder got its altitude info from the GPS, which derived it from GPS satellites.
 
texasclouds said:
I thought a modern transponder got its altitude info from the GPS, which derived it from GPS satellites.
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GPS altitude is not corrected for air pressure. (as when ATC gives you local Altimeter setting)
 
texasclouds said:
I thought a modern transponder got its altitude info from the GPS, which derived it from GPS satellites.
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On the aircraft side, isn't both being sent out? i.e. pressure attitude from the static system via mode-C and GPS via ADS-B?
 
My instructor always told me to stay in the middle of the air. It is dangerous to be near the edges. I'm pretty good at knowing when I'm at 1000 feet AGL. Anything above that is middle of the air and I'm fine with that.
 
Not sure if someone mentioned it...the MP (Manifold Pressure). If you are not making any carb ice and the throttle is locked the MP will slowly decrease as you climb and increase and you descend.
 
Sinistar said:
Not sure if someone mentioned it...the MP (Manifold Pressure). If you are not making any carb ice and the throttle is locked the MP will slowly decrease as you climb and increase and you descend.
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...assuming you aren't moving through an atmospheric pressure change.
 
Sinistar said:
Not sure if someone mentioned it...the MP (Manifold Pressure). If you are not making any carb ice and the throttle is locked the MP will slowly decrease as you climb and increase and you descend.
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Not very sensitive and only works on naturally aspirated engines. My turbo engine shows 30” of MP from sea level to FL250
 
RudyP said:
Not very sensitive and only works on naturally aspirated engines. My turbo engine shows 30” of MP from sea level to FL250
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Agreed. Didn't realize the turbo was so different.

In our 182 you can see a 1000ft change but 200ft...you'd be thinking carb ice. So maybe its not the best instrument but it was the only other thing I could think of that is a instrument and is directly effected by altitude.
 
So grasping for anything...you might also be able to use outside air temp (OAT). But once again it doesn't change that much in 1000ft and trying to use it for 100' or 200' would really just be noise.
 
Mainly I was just trying to confirm or not whether I was right that this is the one VFR flight characteristic that one has to just read the altimeter or VSI to know. I was unsure if I was missing something about it.

When I started flying the biggest surprise to me was that I couldn’t totally sense what the airplane was doing just visually. It is good to confirm this. Thanks all.
 
LongRoadBob said:
Mainly I was just trying to confirm or not whether I was right that this is the one VFR flight characteristic that one has to just read the altimeter or VSI to know. I was unsure if I was missing something about it.

When I started flying the biggest surprise to me was that I couldn’t totally sense what the airplane was doing just visually. It is good to confirm this. Thanks all.
Click to expand...

Get 500+ hours in the same airplane and you'll know, to some extent. But no, not something that's easy to do.
 
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