Buck fifty range profile question

Am I reading this graph incorrectly?

http://img.photobucket.com/albums/v1...ofileChart.jpg

At the 45% power setting, the best range for a Cessna 150M would be
achieved by flying anywhere from sea level to a maximum of 1,800 feet?

At 75% power the gain is about 2.5 NM of range by flying at 7,000 feet vs.
1,000 feet.

This pretty much trashes my fundamental belief that higher altitudes give
greater range. What am I missing?



--
Dallas

"Dallas" wrote in message
...

Am I reading this graph incorrectly?

http://img.photobucket.com/albums/v1...ofileChart.jpg

At the 45% power setting, the best range for a Cessna 150M would be
achieved by flying anywhere from sea level to a maximum of 1,800 feet?

At 75% power the gain is about 2.5 NM of range by flying at 7,000 feet vs.
1,000 feet.

This pretty much trashes my fundamental belief that higher altitudes give
greater range. What am I missing?



--
Dallas

If you stay at 45%, the climb to altitude takes a looooong time, and you are
moving slowly, so the range suffers.

I think most CAFE folks have figured out the best thing to do is climb at
max power, get to a high altitude quickly, then throttle back at the high
altitude to get the max fuel economy. YMMV.

Regards,
John Severyn
KLVK

On Jun 8, 1:43 pm, "J. Severyn" wrote:
"Dallas" wrote in message

...







Am I reading this graph incorrectly?

http://img.photobucket.com/albums/v1...RangeProfileCh...

At the 45% power setting, the best range for a Cessna 150M would be
achieved by flying anywhere from sea level to a maximum of 1,800 feet?

At 75% power the gain is about 2.5 NM of range by flying at 7,000 feet vs.
1,000 feet.

This pretty much trashes my fundamental belief that higher altitudes give
greater range. What am I missing?

--
Dallas

If you stay at 45%, the climb to altitude takes a looooong time, and you are
moving slowly, so the range suffers.

I think most CAFE folks have figured out the best thing to do is climb at
max power, get to a high altitude quickly, then throttle back at the high
altitude to get the max fuel economy. YMMV.

Regards,
John Severyn
KLVK- Hide quoted text -

- Show quoted text -

Climb time is not built into that chart because there is no assumption
about field elevation. It is simply a cruise performance chart *after*
you have climbed to altitude. The reduction in range comes from
reduced propeller efficiency at higher altitudes for the same output
power.

"Andrew Sarangan" wrote in message
oups.com...
On Jun 8, 1:43 pm, "J. Severyn" wrote:
"Dallas" wrote in message

...







Am I reading this graph incorrectly?

http://img.photobucket.com/albums/v1...RangeProfileCh...

At the 45% power setting, the best range for a Cessna 150M would be
achieved by flying anywhere from sea level to a maximum of 1,800 feet?

At 75% power the gain is about 2.5 NM of range by flying at 7,000 feet
vs.
1,000 feet.

This pretty much trashes my fundamental belief that higher altitudes
give
greater range. What am I missing?

--
Dallas

If you stay at 45%, the climb to altitude takes a looooong time, and you
are
moving slowly, so the range suffers.

I think most CAFE folks have figured out the best thing to do is climb at
max power, get to a high altitude quickly, then throttle back at the high
altitude to get the max fuel economy. YMMV.

Regards,
John Severyn
KLVK- Hide quoted text -

- Show quoted text -

Climb time is not built into that chart because there is no assumption
about field elevation. It is simply a cruise performance chart *after*
you have climbed to altitude. The reduction in range comes from
reduced propeller efficiency at higher altitudes for the same output
power.


Climb time is built into the referenced chart. Note on the referenced photo
of the page from the POH: "This chart allows for the fuel used for engine
start, taxi, takeoff and climb, and the distance during climb as shown in
Figure 5-6."

J. Severyn

On Fri, 08 Jun 2007 17:26:26 GMT, Dallas
wrote:


Am I reading this graph incorrectly?

http://img.photobucket.com/albums/v1...ofileChart.jpg

At the 45% power setting, the best range for a Cessna 150M would be
achieved by flying anywhere from sea level to a maximum of 1,800 feet?

At 75% power the gain is about 2.5 NM of range by flying at 7,000 feet vs.
1,000 feet.

This pretty much trashes my fundamental belief that higher altitudes give
greater range. What am I missing?

nothing.
your range is not related to speed directly but by fuel use.
(not theoretically but in real flying)
your engine uses about 20 litres per hour. that is the reality.
the size of the fuel tank is what governs the time possible in the
air.

the other factor which plays with the distance achieved over the time
in the air, at the speeds we fly at, more than any other factor, is
the wind direction and strength.

climb settings built in the graph are almost irrelevant because what
you lose in the climb you typically make up in the descent.

your idea that higher altitudes are more efficient is bought undone by
two aspects of your aircraft. the propeller becomes less efficent with
less dense air flowing past it. the engine also becomes less efficient
with less dense air going into it. the reduction in density almost
exactly undoes the benefits of altitude.
turbo charging was developed to remove one of those deficiencies.

another thing that I have accidently tested is that the speed that you
fly at in our aircraft doesnt affect range. flying slower keeps you
aloft for longer but you cover less distance in the time. in my
experience the range is near identical at any speed.

so what the revelation shows you in the graph is that you should run
your engine at max continuous rpm and lean it periodically to max rpm
at the throttle setting and get on with enjoying the scenery.
none of it actually matters! ...except the wind.

what altitude you fly at is actually dictated by the temperature of
the day and the amount of humidity in the air. you climb until the air
cools almost beyond comfortable provided that the humidity of the day
provides clear vision.

have you ever realised that at 105knots your aircraft is *always*
flying into a 105knot headwind. :-)
move the parcel of air that you are flying through across the
landscape and sometimes it can help you. (oh we dream of those days)

welcome to the real world. it is a lovely, far simpler place than you
may have imagined :-)
Stealth Pilot

On Sat, 09 Jun 2007 04:31:13 +0800, Stealth Pilot wrote:

welcome to the real world. it is a lovely, far simpler place than you
may have imagined :-)

Thanks... I thoroughly enjoyed that piece.

:-)

--
Dallas

Stealth Pilot wrote:

your range is not related to speed directly but by fuel use. (not
theoretically but in real flying) your engine uses about 20 litres
per hour. that is the reality. the size of the fuel tank is what
governs the time possible in the air.

I'm not sure I can explain the OP's question, except to reiterate that
the climb IS factored in and at low power settings seems to have a
negative effect, but your statement above is just plain incorrect.

Speed has a HUGE affect on total range. The Breguet Range equation
states that the range will be greatest when flying at the Max L/D
speed (which generally tends to be a lot slower than most folks fly,
and which decreases as the GW lowers as we burn fuel). I've verified
with my fuel flow gauge, hooked into my GPS, that my MPG is far higher
at 100 mph (about best L/D for my COZY MKIV) than it is at 200 mph (my
normal cruise speed). It would take me a lot longer than I want to
get somewhere at that speed, but I'd use less gas getting there, and
my total range to "tanks dry" is far higher at 100 mph than it is at
200 mph. Like 40% higher - 1400 NM vs 1000 NM.

the other factor which plays with the distance achieved over the
time in the air, at the speeds we fly at, more than any other
factor, is the wind direction and strength.

Obviously. We're talking no wind here. Speed up in a headwind, and
slow down with a tailwind to maximize range.

climb settings built in the graph are almost irrelevant because
what you lose in the climb you typically make up in the descent.

Due to entropy, you NEVER make up in the descent what you lose in the
climb.

your idea that higher altitudes are more efficient is bought undone
by two aspects of your aircraft. the propeller becomes less
efficent with less dense air flowing past it. the engine also
becomes less efficient with less dense air going into it. the
reduction in density almost exactly undoes the benefits of
altitude.

I have no idea where you're getting these ideas. Do you have any
references? Propellers are designed for a given cruise condition -
mine was optimized for 8K ft. altitudes and about 200-210 mph cruise.
The engine is not less EFFICIENT at higher altitudes - it just puts
out less power. In fact, since I can run LOP when below 75% power at
altitude, I am far MORE efficient at altitude than I am down low.

For a non-turbocharged piston engine aircraft, you will get the most
efficiency when flying at the highest altitude at which your engine
can put out the amount of power you want to use. If you want to use
75% power, you want to fly at 7000-8000 ft. If you want to use 55%
power, you want to fly at 12K ft. Obviously, for short trips (for me,
anything less than an hour), it's not worth the climb, but for long
trips, you use far less fuel at higher altitudes.

If you take a look at aircraft such as the Voyager, and examine the
altitudes and speeds that were used to maximize the range (hence
efficiency), you'll see that these things are the case.

turbo charging was developed to remove one of those deficiencies.

Turbo charging increases the altitude at which a given power output
can be produced, therefore increasing speed.

another thing that I have accidently tested is that the speed that
you fly at in our aircraft doesnt affect range. flying slower keeps
you aloft for longer but you cover less distance in the time. in my
experience the range is near identical at any speed.

Then you haven't completed the experimentation. It most certainly
does NOT balance. Again, review the history of aircraft built for
range, and look at what speeds they fly at, and what altitudes they
fly at. Review the L/D curves for the aircraft in question, and the
speed to maximize range will jump out at you.

welcome to the real world. it is a lovely, far simpler place than
you may have imagined :-)

While lovely, it's only simple if you don't want to understand it :-).

--
Marc J. Zeitlin
http://www.cozybuilders.org/
Copyright (c) 2007

On Jun 8, 2:09 pm, "J. Severyn" wrote:
"Andrew Sarangan" wrote in message

oups.com...



On Jun 8, 1:43 pm, "J. Severyn" wrote:
"Dallas" wrote in message

. ..

Am I reading this graph incorrectly?

http://img.photobucket.com/albums/v1...RangeProfileCh...

At the 45% power setting, the best range for a Cessna 150M would be
achieved by flying anywhere from sea level to a maximum of 1,800 feet?

At 75% power the gain is about 2.5 NM of range by flying at 7,000 feet
vs.
1,000 feet.

This pretty much trashes my fundamental belief that higher altitudes
give
greater range. What am I missing?

--
Dallas

If you stay at 45%, the climb to altitude takes a looooong time, and you
are
moving slowly, so the range suffers.

I think most CAFE folks have figured out the best thing to do is climb at
max power, get to a high altitude quickly, then throttle back at the high
altitude to get the max fuel economy. YMMV.

Regards,
John Severyn
KLVK- Hide quoted text -

- Show quoted text -

Climb time is not built into that chart because there is no assumption
about field elevation. It is simply a cruise performance chart *after*
you have climbed to altitude. The reduction in range comes from
reduced propeller efficiency at higher altitudes for the same output
power.

Climb time is built into the referenced chart. Note on the referenced photo
of the page from the POH: "This chart allows for the fuel used for engine
start, taxi, takeoff and climb, and the distance during climb as shown in
Figure 5-6."

J. Severyn- Hide quoted text -

- Show quoted text -

You are correct; I missed that part. Fig 5-6 shows climb performance
for climbing from sealevel to the designated altitude. So how does one
figure out the range when departing from a high elevation airport?

"Dallas" wrote in message
...

Am I reading this graph incorrectly?

http://img.photobucket.com/albums/v1...ofileChart.jpg

At the 45% power setting, the best range for a Cessna 150M would be
achieved by flying anywhere from sea level to a maximum of 1,800 feet?

At 75% power the gain is about 2.5 NM of range by flying at 7,000 feet vs.
1,000 feet.

This pretty much trashes my fundamental belief that higher altitudes give
greater range. What am I missing?

Wind



--
Dallas