How high?

I'd like to get input on opinions on the "best" VFR altitude for a route.

It seems to me it's largely based on distance, winds aloft and comfort
level. Do you have a "rule of thumb" trading off altitude (and therefore
safety margin) to avoid headwinds? Or, if winds aloft are to your
advantage, how high would someone go in a 172 class aircraft before returns
diminish?

In a previous article, "John Harlow" said:
I'd like to get input on opinions on the "best" VFR altitude for a route.

It seems to me it's largely based on distance, winds aloft and comfort
level. Do you have a "rule of thumb" trading off altitude (and therefore
safety margin) to avoid headwinds? Or, if winds aloft are to your
advantage, how high would someone go in a 172 class aircraft before returns
diminish?

I want to be at least 4,000 feet, because it's quieter up there - there's
very little VFR traffic, and the airliners are only passing through. If
there is a few-to-scattered layer, I want to be above it because the air
is smoother. Before I was instrument rated, I'd have to be careful it
didn't turn into a broken layer when I wasn't paying attention. I don't
like to fly above 10,000 because of the lack of oxygen, although I got up
to 12,500 looking for a way though the storms coming back from Oshkosh.
So generally I end up at 6,000 (or 6,500 if VFR) going west and 9,000 (or
9,500 if VFR) going east.


--
Paul Tomblin http://xcski.com/blogs/pt/
I'm just waiting for the day that someone decides that "ignorant moron" is
an ethnic group, and thus cannot be discriminated against.
-- Christian Wagner

In article ,
"John Harlow" wrote:

I'd like to get input on opinions on the "best" VFR altitude for a route.

It seems to me it's largely based on distance, winds aloft and comfort
level. Do you have a "rule of thumb" trading off altitude (and therefore
safety margin) to avoid headwinds? Or, if winds aloft are to your
advantage, how high would someone go in a 172 class aircraft before returns
diminish?

Some rules of thumb:

A normally aspirated (i.e. no supercharger) engine such as found in a
172 will be running at about 65% power at 7000 density altitude with
wide open throttle. Above that, you will have less power as you climb
higher. Thus, there's usually not a lot of reason to fly much higher
than 7500 MSL, unless terrain forces you higher.

Below 3000 AGL, there tends to be lots of random traffic: people
practicing maneuvers or instrument approaches, and flights entering or
departing traffic patterns. Staying above 3000 AGL keeps you out of the
worst of that. Below 3000, you also run into Class D airspaces, and
there tends to be more turbulence (especially over rough terrain).
Thus, there's usually not a lot of reason to cruise below 3000 AGL.

It's usually not worth spending more than 1/3 of the trip time climbing.

Consider radar and radio coverage. Below 3000 AGL, both tend to be
spotty if you're not within about 10-20 miles of the charted boundary of
a Class B or C airspace (or TRSA).

Our plane (Cherokee 235 -- normally aspirated 6-cylinder O-540) runs best
(highest speed, lowest, most even EGTs and CHTs, with lowest fuel burn)
between 4500 and 6500 feet.

These altitudes work fine here in the Midwest.

We also like it there because it's usually smoother, and there is far less
traffic. We're well above the guys working the pattern, and well below the
"big boys" in the airliners.
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"
"John Harlow" wrote in message
...
I'd like to get input on opinions on the "best" VFR altitude for a route.

It seems to me it's largely based on distance, winds aloft and comfort
level. Do you have a "rule of thumb" trading off altitude (and therefore
safety margin) to avoid headwinds? Or, if winds aloft are to your
advantage, how high would someone go in a 172 class aircraft before
returns
diminish?

John Harlow wrote:

I'd like to get input on opinions on the "best" VFR altitude for a route.

It seems to me it's largely based on distance, winds aloft and comfort
level. Do you have a "rule of thumb" trading off altitude (and therefore
safety margin) to avoid headwinds? Or, if winds aloft are to your
advantage, how high would someone go in a 172 class aircraft before returns
diminish?

A lot depends on whether I'm alone or not. It's also the case that the various
airspace restrictions around here do a lot more to determine my enroute altitude
than anything else until I get south of the DC mess.

If I'm alone and have strong headwinds, I'll stay down as low as 600' AGL to make
time. If my wife is in the plane, I will go as high as is necessary to eliminate
turbulence (if this is possible). I will go as high as 9,500' to make the best use
of a tailwind, but I do not like to fly much higher than that, since flying higher
makes me drowsy and leaves me with a headache. I have gone as high as 11,500 to
get over a class-B.

All my flying is done in the eastern half of the country without oxygen on board.
If I had to deal with mountains higher than the Appalachians, it would be a
different story.

George Patterson
Love, n.: A form of temporary insanity afflicting the young. It is curable
either by marriage or by removal of the afflicted from the circumstances
under which he incurred the condition. It is sometimes fatal, but more
often to the physician than to the patient.

"John Harlow" wrote in message
...
I'd like to get input on opinions on the "best" VFR altitude for a route.

It depends on a variety of factors.

As has been pointed out, you get the most power with the least drag at
around 7000' MSL or so. So for a normally aspirated engine, that's a nice
target.

But for short flights, it may be a waste of time to climb that high. For
flights starting at high altitude, you may find 7000' is too low to keep you
out of local traffic and away from terrain. If there are strong winds going
in your direction, you may want to fly higher. If there are strong winds
going opposite your direction, you may want to fly lower. If it's a hot,
sunny day you may find it's bumpy down low and will want a higher cruise
altitude. If it's a windy, turbulent day, you may find the air smoother at
the middle altitudes.

You get the idea. Each flight is different. Rules of thumb are nice, but
you need to be considering all the factors anew each flight.

I have a turbocharged aircraft, so generally speaking, higher is better.
However, I still have to deal with headwinds and turbulence. But the winds
aloft forecast isn't reliable enough to use it to pick a cruising altitude.
So typically what I do is choose a cruising altitude independent of the
winds aloft forecast. Then I just see how things are in flight. I gain
about a knot in true airpspeed for every 1000' I climb, so that gives me a
guideline for how much the winds need to change for it to be worth picking a
new cruising altitude. Of course, if the ride is bumpy, I generally opt for
a slower but smoother flight.

For this sort of "wait and see" approach, it certainly helps to have good
climb rates at pretty much any altitude (I'm still getting 500-600 fpm at
16,000' or so, and much better lower...when I'm flying at 10,000' +/- a few
thousand, it only takes a few minutes to change altitude to a new,
significantly different altitude). It would be less practical with a
normally aspirated engine.

Pete

Except in high winds aloft or bad turbulence, I have found that flying
low (safety permitting) generally results in the most optimum
solution. Climbing higher for better tailwind doesn't buy more than a
few minutes. Of course, the ratio of climb time to cruise time has a
big effect too. There are too many variable to make a rule of thumb.
What I do is try a few altitudes on DUATs flight planner and pick the
lowest altitude that seems reasonable.



"John Harlow" wrote in message ...
I'd like to get input on opinions on the "best" VFR altitude for a route.

It seems to me it's largely based on distance, winds aloft and comfort
level. Do you have a "rule of thumb" trading off altitude (and therefore
safety margin) to avoid headwinds? Or, if winds aloft are to your
advantage, how high would someone go in a 172 class aircraft before returns
diminish?

If I am flying a long trip (several hours), I will go up 2000' and see
if I get an improvement in groundspeed. If I do, I stay up there and
my try another 2000'. Don't forget you burn less gas per mile up high,
so even if you just go the same speed, you are ahead. Sometimes I call
Fligh****ch and ask them for the winds aloft forecasts so I can plan
my altitude. In the summer, if I go up high enough, sometimes I can
get above the turbulence. But then you may slow down so you have the
age old turbulence vs airspeed tradeoff question.

If I am going west, leave in the morning, come back in the evening
will get me less headwind west and more tailwind east as winds
increase as the day goes on, statistically. Going east, leave late in
the day and come back the next day, if possible.

I do believe I have "outflown" the wind, that is, I have had more
tailwinds than headwinds due to being able to pick times and altitudes
flown.

Although there is software that calculates best solutions, I don't
have it. Might be interesting if the GPS mfgs put that function in
their GPS's. Could be done, I suppose.

ON long flights I don't have anything else to do, so might as well
mess around with trying to make time and saving fuel.


(Andrew Sarangan) wrote in message . com...
Except in high winds aloft or bad turbulence, I have found that flying
low (safety permitting) generally results in the most optimum
solution. Climbing higher for better tailwind doesn't buy more than a
few minutes. Of course, the ratio of climb time to cruise time has a
big effect too. There are too many variable to make a rule of thumb.
What I do is try a few altitudes on DUATs flight planner and pick the
lowest altitude that seems reasonable.



"John Harlow" wrote in message ...
I'd like to get input on opinions on the "best" VFR altitude for a route.

It seems to me it's largely based on distance, winds aloft and comfort
level. Do you have a "rule of thumb" trading off altitude (and therefore
safety margin) to avoid headwinds? Or, if winds aloft are to your
advantage, how high would someone go in a 172 class aircraft before returns
diminish?

In article ,
"G.R. Patterson III" wrote:

John Harlow wrote:

I'd like to get input on opinions on the "best" VFR altitude for a route.

It seems to me it's largely based on distance, winds aloft and comfort
level. Do you have a "rule of thumb" trading off altitude (and therefore
safety margin) to avoid headwinds? Or, if winds aloft are to your
advantage, how high would someone go in a 172 class aircraft before returns
diminish?

A lot depends on whether I'm alone or not. It's also the case that the
various
airspace restrictions around here do a lot more to determine my enroute
altitude
than anything else until I get south of the DC mess.

If I'm alone and have strong headwinds, I'll stay down as low as 600' AGL to
make
time. If my wife is in the plane, I will go as high as is necessary to

600 feet AGL for cruise? Not a lot of think/plan time if your engine
fails!

"John Harlow" wrote in message ...
I'd like to get input on opinions on the "best" VFR altitude for a route.

It seems to me it's largely based on distance, winds aloft and comfort
level. Do you have a "rule of thumb" trading off altitude (and therefore
safety margin) to avoid headwinds? Or, if winds aloft are to your
advantage, how high would someone go in a 172 class aircraft before returns
diminish?

First, I think previous posters have said it well when they pointed
out all the variables involved and concluded that "the best altitude"
is different for each flight.

Second, a minor correction: An earlier poster said he gained about 1
kt TAS per 1000'. The rule of thumb is 2% per 1000' so I'd expect more
like 2-4 kt TAS gain per 1000', assuming your cruise speed is between
100 and 200 kts. That can offset a slight increase in head wind.

Third, no one so far has pointed out the added safety that higher
altitude buys in the event of an engine failure. From 7500' and
assuming a 10:1 glide ratio (about right in practice for most small GA
planes, with a small safety margin added on), you can glide 75,000' or
over 12 nm. From 3000' you can glide only 5 nm. In civilized areas,
airports are often close enough that the 7500' cruise would allow an
engine out landing at an airport, while the 3000' cruise would
probably not. Of course, you'd also have to practice side slips and
S-turns in order to dump any excess altitude as you approach the
runway. (Altitude becomes your fuel, but unlike a power plane, you
have to land with "zero fuel.")

I fly a motor glider and, in glider mode, must constantly think in
terms of altitude to make an airport. Even though the engine is there
and it's always started for me when I've needed it so far, the prudent
assumption is that it won't start. That thinking carries over to
engine on time too, but I'll admit that with a 50:1 glide ratio and a
turbo charged engine, I have it a bit easier than you power guys.

Even considering their reduced glide ratios, I think many power pilots
don't adquately consider their planes as potential gliders when they
lose an engine. From the few stories I've heard, it sounds like, no
matter how much the pilot has been taught that the engine doesn't make
the plane fly, a gut reaction often takes over when the engine quits
and tells the pilot the plane is going to fall like a rock. That's
probably why all pilots I know who are rated for both power and
gliders say that all pilots should do at least a few landings in a
glider. It helps get over that gut reaction.

Martin