Help estimating altitude without altimeter?

On Oct 25, 9:30*pm, Darryl Ramm wrote:
On Oct 25, 8:51*pm, tstock wrote:



Hi, as a beginner I am still a little rough at this. *I've done 3
successful patterns with no altimeter, but today I failed one
miserably with my instructor. * There were two issues which threw me
off. 1) *we towed higher than the past attempts, and 2) instead of
entering the pattern at a familiar entry point, he had me circle
directly over the airport which made judging the angle a bit
difficult.

While we did eventually land safely, I failed miserably at setting up
the first pattern (way too high) and was forced to land on the
opposite runway (which left me way too low). *A little scary but a
good learning experience... one I do not care to repeat anytime soon.

I know I should be looking for the landing strip to be about 30
degrees below the horizon. *But how can I do this when circling
directly over the field looking down at it?

I made a second attempt and moved my circle so that the outermost edge
of the circle was where I would enter the downwind.. I succeeded this
time. *Unfortunately we also only towed to 1500' AGL which left me
with a much smaller chance of messing things up... so I can't say I am
completely confident despite the success.

Are there any easy methods for estimating the angle from the horizon?
For example a fist at arms length is 10 degrees, but obviously I can't
hold my first at arms length through the canopy. * The method I've
used is to wait until my aim point aligns with the outer most edge of
the air brakes. *To measure 45 degrees I look directly over the top of
my shoulder... *is there a better method?

Thanks
-tom

But but but...

You were flying with an instructor. Was this not addressed to your
satisfaction in the post-flight debrief? Its fresh in your mind then
and that's the time to get answers. Sorry but I cringe at these "where
was the instructor" questions on r.a.s.

If you are circling overhead you can use sized of common things (cars,
gliders, runway width (if known), runway markings, etc.) to judge
height. I think I saw some good slides on that once that Cindy
Brickner had.

But...You don't transition from just circling overhead to rolling out
on the runway. At some time you transition from that circle overhead
to picking up an the downwind or base or whatever leg and a relatively
steady state angle to the runway. Even if the whole approach is curved
your sight picture needs to transition from looking down to across at
that 30-45 degree picture. At that point if you look too high you
should be doing something about it, extend the leg, get on the
spoilers, slip, or all the above.

So you have at least two things to go over with the instructor.
Judging height from overhead and being on-top of altitude correction
in the pattern.

Darryl

BTW you can't use the horizon. It is hard to know where the true
horizon often is. What if you are in mountainous areas. In smoke or
haze etc. (which will cause enough problems with depth/distance
perception as is). Same reason you don't want to set up behind the tow
plane based on where the horizon looks. Even if you knew the location
of the true horizon you would not be able to estimate your altitude
from that to anything like a useful accuracy.

Darryl

On Oct 25, 10:00*pm, Darryl Ramm wrote:
On Oct 25, 9:30*pm, Darryl Ramm wrote:





On Oct 25, 8:51*pm, tstock wrote:

Hi, as a beginner I am still a little rough at this. *I've done 3
successful patterns with no altimeter, but today I failed one
miserably with my instructor. * There were two issues which threw me
off. 1) *we towed higher than the past attempts, and 2) instead of
entering the pattern at a familiar entry point, he had me circle
directly over the airport which made judging the angle a bit
difficult.

While we did eventually land safely, I failed miserably at setting up
the first pattern (way too high) and was forced to land on the
opposite runway (which left me way too low). *A little scary but a
good learning experience... one I do not care to repeat anytime soon.

I know I should be looking for the landing strip to be about 30
degrees below the horizon. *But how can I do this when circling
directly over the field looking down at it?

I made a second attempt and moved my circle so that the outermost edge
of the circle was where I would enter the downwind.. I succeeded this
time. *Unfortunately we also only towed to 1500' AGL which left me
with a much smaller chance of messing things up... so I can't say I am
completely confident despite the success.

Are there any easy methods for estimating the angle from the horizon?
For example a fist at arms length is 10 degrees, but obviously I can't
hold my first at arms length through the canopy. * The method I've
used is to wait until my aim point aligns with the outer most edge of
the air brakes. *To measure 45 degrees I look directly over the top of
my shoulder... *is there a better method?

Thanks
-tom

But but but...

You were flying with an instructor. Was this not addressed to your
satisfaction in the post-flight debrief? Its fresh in your mind then
and that's the time to get answers. Sorry but I cringe at these "where
was the instructor" questions on r.a.s.

If you are circling overhead you can use sized of common things (cars,
gliders, runway width (if known), runway markings, etc.) to judge
height. I think I saw some good slides on that once that Cindy
Brickner had.

But...You don't transition from just circling overhead to rolling out
on the runway. At some time you transition from that circle overhead
to picking up an the downwind or base or whatever leg and a relatively
steady state angle to the runway. Even if the whole approach is curved
your sight picture needs to transition from looking down to across at
that 30-45 degree picture. At that point if you look too high you
should be doing something about it, extend the leg, get on the
spoilers, slip, or all the above.

So you have at least two things to go over with the instructor.
Judging height from overhead and being on-top of altitude correction
in the pattern.

Darryl

BTW you can't use the horizon. It is hard to know where the true
horizon often is. What if you are in mountainous areas. In smoke or
haze etc. (which will cause enough problems with depth/distance
perception as is). Same reason you don't want to set up behind the tow
plane based on where the horizon looks. Even if you knew the location
of the true horizon you would not be able to estimate your altitude
from that to anything like a useful accuracy.

Darryl

I agree with Darryl - angle below the horizon only tells you the angle
to the runway, not your height. You can be at the right height 2,000
feet laterally from the runway or 3x the right height a nautical mile
from the runway and the angles will be the same. You really need to
judge height by looking at the angle between two points a known
distance apart on the ground. This can be the wingspan of an airplane,
the distance between phone poles the width or length of a runway,
circular crop fields - whatever works. Try guessing your height 20
times over the course of a flight - especially when you are between
1,000 and 2,500 feet AGL. You will build a pretty good sense faster
than you think.

9B

Andy wrote:
angle below the horizon only tells you the angle
to the runway, not your height. You can be at the right height 2,000
feet laterally from the runway or 3x the right height a nautical mile
from the runway and the angles will be the same.

The vertical angle is all you need to know. Gliders tend to glide at an
angle.

On Oct 26, 2:04*am, John Smith wrote:

The vertical angle is all you need to know. Gliders tend to glide at an
angle.

It helps when you are in the pattern, but the issue here is what to do
when you are away from the pattern. Also, I wouldn't necessarily
recommend that a student focus solely on the angle. I would not
consider it equally good piloting to enter the pattern at 3,000' AGL a
mile abeam of the runway as at 1,000' 1/3 mile abeam of the runway.

For the circling over the airport problem you can get some indication
of altitude by looking at the path the wingtip traces on the ground
from a known bank angle. Above a certain height the path will be
counter to the turning direction, below that height it will be in the
same direction. Do the math to convince yourself. (Note: This is one
cue that creates problems as it tends to make skidding turns down low
seem "normal". A pilot will over-rudder to make the wingtip move
backward -- don't do this). You also get altitude cues from the rate
that objects on the ground change angle in straight ahead flight at a
known airspeed. The least precise cue except at very low altitudes (or
for very big objects) is the included angle from one end of a ground
object to another. Use the length of the ramp, not the length of a
car.

Another big issue is gaining the experience to know when you need to
"head for home" from 10-20 miles away to hit a point that's 1,000' AGL
for pattern entry. The angle for most gliders is very flat but looks
flatter and flatter the farther away you get because the glide
terminates well above the ground. For instance, if your glider can go
7 miles for every 1,000' (L/D= 37) the angle will "look" roughly half
as steep from 20 miles as from 5 miles away. Fortunately this builds
in some conservatism in the pilot's judgement rather than the other
way around.

Try some of these techniques from different altitudes the next few
times you fly. Eventually it becomes (almost) second nature. Also read
Tom Knauff's fine text or one of the many others on the subject. They
are written by professionals.

9B

On Oct 28, 3:13*am, Andy wrote:
For the circling over the airport problem you can get some indication
of altitude by looking at the path the wingtip traces on the ground
from a known bank angle. *Above a certain height the path will be
counter to the turning direction, below that height it will be in the
same direction. Do the math to convince yourself.

I guess you didn't do the math yourself :-)

The height at which the change from wingtip-goes-backwards to wingtip-
goes-forwards occurs is too low to be used for normal circuit entry.
At 40 knots it's only 140 ft, and at 60 knots it is about 320 ft. If
you want to use this to judge a 700 ft circuit entry then you'll have
to be flying at 90 knots.

On Oct 27, 7:47*pm, Bruce Hoult wrote:
On Oct 28, 3:13*am, Andy wrote:

For the circling over the airport problem you can get some indication
of altitude by looking at the path the wingtip traces on the ground
from a known bank angle. *Above a certain height the path will be
counter to the turning direction, below that height it will be in the
same direction. Do the math to convince yourself.

I guess you didn't do the math yourself :-)

The height at which the change from wingtip-goes-backwards to wingtip-
goes-forwards occurs is too low to be used for normal circuit entry.
At 40 knots it's only 140 ft, and at 60 knots it is about 320 ft. If
you want to use this to judge a 700 ft circuit entry then you'll have
to be flying at 90 knots.

Glad you mentioned this. I did think of this myself also, and tried it
on a simulator many many times before reading these posts and in every
case the wingtip appeared to move backwards over the terrain. Decided
it would not work.

On Oct 27, 4:47*pm, Bruce Hoult wrote:
On Oct 28, 3:13*am, Andy wrote:

For the circling over the airport problem you can get some indication
of altitude by looking at the path the wingtip traces on the ground
from a known bank angle. *Above a certain height the path will be
counter to the turning direction, below that height it will be in the
same direction. Do the math to convince yourself.

I guess you didn't do the math yourself :-)

The height at which the change from wingtip-goes-backwards to wingtip-
goes-forwards occurs is too low to be used for normal circuit entry.
At 40 knots it's only 140 ft, and at 60 knots it is about 320 ft. If
you want to use this to judge a 700 ft circuit entry then you'll have
to be flying at 90 knots.

On Oct 27, 4:47*pm, Bruce Hoult wrote:
On Oct 28, 3:13*am, Andy wrote:

For the circling over the airport problem you can get some indication
of altitude by looking at the path the wingtip traces on the ground
from a known bank angle. *Above a certain height the path will be
counter to the turning direction, below that height it will be in the
same direction. Do the math to convince yourself.

I guess you didn't do the math yourself :-)

The height at which the change from wingtip-goes-backwards to wingtip-
goes-forwards occurs is too low to be used for normal circuit entry.
At 40 knots it's only 140 ft, and at 60 knots it is about 320 ft. If
you want to use this to judge a 700 ft circuit entry then you'll have
to be flying at 90 knots.

Thanks - I didn't do the math. I usually do the math but was feeling
lazy. :-(

I would argue that pattern traced by the wingtip changes even if it
doesn't reverse direction at higher elevations - the reverse circle
gets bigger and bigger as you go higher.

I generally enter the pattern at about 75-80 knots. You could
certainly do a circle at 90 knots if you really needed to see the
wingtip rotate the other way and had no idea how high you were - at
that speed your energy would take you back up to 1000' AGL.

The general point is that all the angular rates versus ground
references change as you get closer to the ground and you should be
aware of them. Turning flight likely gives you more cues than flying
straight ahead.

9B