Pitot heat

[Paul Mennen]

Just saw in this month's AOPA (Fall flights):

"Most pilots slumming around the pattern on a hot summer day
will probably not flip the pitot heat on, but certainly anytime
you're flying in or near moisture - at any air temperature - It's
safest to use pitot heat." - Editor in Chief, Thomas B. Haines.

Well that would cover at least half the time. Probably more if
one forgets to turn it off when the clouds finally slip out
of sight. Does this seem preposterous to anybody else?

Maybe its because my instructor covered up the airspeed indicator
of the J3 cub for an entire flight during my private training
just to make sure I wasn't becoming too dependent on it. Frankly
it didn't seem too hard to fly without it. Since the cub had no
stall warning system, I did use up more of the dirt patch next
to the runway than usual. (My instructor never actually let me
use the runway. He said that was too easy.) In the past 20 years
of flying my C185, I've flown without the airspeed indicator
several times. Twice it failed to work because of stuff in the
pitot tube. Once I just couldn't see it because there was no moon
and I had a total electrical system failure. (Actually I did have
a flashlight in my pocket, but I didn't see a great motivation
for getting it out. I just landed in the dark.) Twice I saw the
airspeed indicator rapidly head to zero because of icing conditions.
(My icing early warning system :) With constant power, pitch, and
altitude indications from the other instruments it never crossed
my mind to make any control inputs in response. Flipping the
pitot heater on restored the airspeed indicator within seconds.
(Well airspeed is at least a nice convenience.)

So Mr. Haines' suggestion seems somewhat radical to me. (Ok, I guess
I would use it in the cold soup when I'm already dealing with a loss
of vacuum system emergency.) Just think of all that power wasted.
And is really safer? Perhaps having it on so often would mean that it
would more likely be burnt out one of those few times it would be really
nice to have. And maybe it would snuff out that last 10 minutes of
battery capacity that you needed to complete your approach, because it
took you awhile to recognize that the alternator went belly up.

But he certainly has more experience than my meager 3000 hours,
so what do I know?

Reminds me of the instructions in the POH of my Decathlon that says I
should leave the electrical fuel pump on during takeoff because gravity
feed alone is not sufficient to produce takeoff power in the event the
engine driven fuel pump fails. Gosh, what are we - like the
monkeys on the early space missions. Can't we just turn on the
switch when we need it? (I've already replaced that very expensive
electrical pump twice because me or one of my partners forgot to turn
it off after climbout. It is not robust enough to run it continuously.
I've since given up on following the POH exactly.)

~Paul Mennen

[G.R. Patterson III]

Paul Mennen wrote:
>
> Does this seem preposterous to anybody else?

It does to me. The pitot heat on my aircraft has been on less than an hour in
over 500 hours.

George Patterson
If you're not part of the solution, you can make a lot of money prolonging
the problem.

[Ron Natalie]

"Paul Mennen" > wrote in message .com...

> Does this seem preposterous to anybody else?

Does what seem preposterous. You'd rather wait until it ices up?
Pitot heat is anti-ice, not de-ice. You'll never turn it on for fear you
will forget to turn it off?

> Reminds me of the instructions in the POH of my Decathlon that says I
> should leave the electrical fuel pump on during takeoff because gravity
> feed alone is not sufficient to produce takeoff power in the event the
> engine driven fuel pump fails. Gosh, what are we - like the
> monkeys on the early space missions. Can't we just turn on the
> switch when we need it?

Gosh, and you want to wait until the engine quits on takeoff to determine
you need to turn it on and wait for a restart while heading for the trees?
Takeoff is one of those times you are using full power and wish to retain
full power even in the event of a pump failure. At cruise, you have more
time to detect the failure and switch on the backup.

[Paul Mennen]

"Ron Natalie" wrote

> Gosh, and you want to wait until the engine quits on takeoff to determine
> you need to turn it on and wait for a restart while heading for the trees?

Well yes actually. For one I don't think the engine would quit since
you still have considerable fuel flow due to gravity feed. I have no
way to test that, but even if the engine quit, the prop would not stop.
(I've tried to stop the prop before after pulling the mixture. It takes
quite some time and one has to be flying very slowly.) So once turning
the fuel pump switch on, the engine would run almost immediately (at
least it would if I haven't burnt out the electric pump from over use :)

Another thing I might add, is that failure of the engine driven pump
is very rare. The chance that it would fail during the 20 seconds or so
of vulnerability (where the time it takes you to think of turning on
the switch really matters) seems to fall into the statistically
insignificant
range.

I think the engineer who thought to include the electric fuel
pump was thinking rationally. I think the person who wrote in
the POH that you should turn it on prophylactically was not.

~Paul

[Ron Natalie]

"Paul Mennen" > wrote in message m...

> Well yes actually. For one I don't think the engine would quit since
> you still have considerable fuel flow due to gravity feed. I have no
> way to test that, but even if the engine quit, the prop would not stop.
> (I've tried to stop the prop before after pulling the mixture. It takes
> quite some time and one has to be flying very slowly.) So once turning
> the fuel pump switch on, the engine would run almost immediately (at
> least it would if I haven't burnt out the electric pump from over use :)

If it died completely, you might think of that. What if the thing just dropped
to 25% power. Would the boost pump be the first thing you tried?

I fly a low wing, so using the boost on takeoffs is standard procedure. I've
never been tempted to forget to turn it off. The thing in my plane is pretty
noisy (it sits right under the right seat pilots feet).

[Russell Kent]

Ron Natalie wrote:

> I fly a low wing, so using the boost on takeoffs is standard procedure. I've
> never been tempted to forget to turn it off. The thing in my plane is pretty
> noisy (it sits right under the right seat pilots feet).

Must make it a challenge for Margy to work the rudder pedals... <vbg>

Russell Kent

[Doug]

Well water does not freeze until 0 degrees C at any pressure we pilots
will see. It is true that there is a problem getting an accurate
static temperature at speed and it is also true that you can have
pockets of lower pressure creating lower temperatures around the wing
etc, but I would say that you certainly don't have to worry about
freezing Pitot until 5 degrees C or if you want to be conservative 10
degrees C. It is not like carb ice where you can get freezing temps in
the carb at outside static temps of, well up to 25 degrees C or so. So
I agree, the guy, if he really did write that, is not really on the
ball here, you don't need pitot heat on a hot summer day, no way.

"Paul Mennen" > wrote in message >...
> Just saw in this month's AOPA (Fall flights):
>
> "Most pilots slumming around the pattern on a hot summer day
> will probably not flip the pitot heat on, but certainly anytime
> you're flying in or near moisture - at any air temperature - It's
> safest to use pitot heat." - Editor in Chief, Thomas B. Haines.
>
> Well that would cover at least half the time. Probably more if
> one forgets to turn it off when the clouds finally slip out
> of sight. Does this seem preposterous to anybody else?
>
> Maybe its because my instructor covered up the airspeed indicator
> of the J3 cub for an entire flight during my private training
> just to make sure I wasn't becoming too dependent on it. Frankly
> it didn't seem too hard to fly without it. Since the cub had no
> stall warning system, I did use up more of the dirt patch next
> to the runway than usual. (My instructor never actually let me
> use the runway. He said that was too easy.) In the past 20 years
> of flying my C185, I've flown without the airspeed indicator
> several times. Twice it failed to work because of stuff in the
> pitot tube. Once I just couldn't see it because there was no moon
> and I had a total electrical system failure. (Actually I did have
> a flashlight in my pocket, but I didn't see a great motivation
> for getting it out. I just landed in the dark.) Twice I saw the
> airspeed indicator rapidly head to zero because of icing conditions.
> (My icing early warning system :) With constant power, pitch, and
> altitude indications from the other instruments it never crossed
> my mind to make any control inputs in response. Flipping the
> pitot heater on restored the airspeed indicator within seconds.
> (Well airspeed is at least a nice convenience.)
>
> So Mr. Haines' suggestion seems somewhat radical to me. (Ok, I guess
> I would use it in the cold soup when I'm already dealing with a loss
> of vacuum system emergency.) Just think of all that power wasted.
> And is really safer? Perhaps having it on so often would mean that it
> would more likely be burnt out one of those few times it would be really
> nice to have. And maybe it would snuff out that last 10 minutes of
> battery capacity that you needed to complete your approach, because it
> took you awhile to recognize that the alternator went belly up.
>
> But he certainly has more experience than my meager 3000 hours,
> so what do I know?
>
> Reminds me of the instructions in the POH of my Decathlon that says I
> should leave the electrical fuel pump on during takeoff because gravity
> feed alone is not sufficient to produce takeoff power in the event the
> engine driven fuel pump fails. Gosh, what are we - like the
> monkeys on the early space missions. Can't we just turn on the
> switch when we need it? (I've already replaced that very expensive
> electrical pump twice because me or one of my partners forgot to turn
> it off after climbout. It is not robust enough to run it continuously.
> I've since given up on following the POH exactly.)
>
> ~Paul Mennen

[Newps]

Doug wrote:

> Well water does not freeze until 0 degrees C at any pressure we pilots
> will see.

And yet at 5000 feet you need to adjust how you bake because of the
different boiling point of water.

[Ron Natalie]

"Russell Kent" > wrote in message ...
> Ron Natalie wrote:
>
> > I fly a low wing, so using the boost on takeoffs is standard procedure. I've
> > never been tempted to forget to turn it off. The thing in my plane is pretty
> > noisy (it sits right under the right seat pilots feet).
>
> Must make it a challenge for Margy to work the rudder pedals... <vbg>
>
Nah, she just sits on the left side.

[Ron Natalie]

"Newps" > wrote in message news:86dqb.113533$Fm2.101588@attbi_s04...

>
> > Well water does not freeze until 0 degrees C at any pressure we pilots
> > will see.
>
> And yet at 5000 feet you need to adjust how you bake because of the
> different boiling point of water.
>
Freezing and boiling are different processes. Freezing is not much
affected by pressure. Boiling on the other hand is DEFINED in terms of
pressure. It's the point where atmospheric pressure equals the vapor pressure.
At 5000' (and altimieter setting 29.92), the boiling point is only 202 degrees
The liquid water never can get above the boiling point, so the temperature
of the food stays cooler and hence it takes LONGER to cook things that
are boiled.

However, the reason baking instructions change is only partially the boiling
point. In baking the food rises due to leavening (yeast, baking powder, etc...)
This process (amount of leavening used, temperatures, etc...) is generally
set for sea level pressures. At higher altitudes, these recipes tend to
over-rise. Adding addional flour or other adjustments to the recipe
compensate for this.

Freezing (of water) is affected by pressure, but to raise the freezing point requires
rather severe decrease in pressure. Between 0 and 5000 feet the frezing point
difference is less than a degree.

[Tom S.]

"Ron Natalie" > wrote in message
. ..
> > And yet at 5000 feet you need to adjust how you bake because of the
> > different boiling point of water.
> >
> Freezing and boiling are different processes. Freezing is not much
> affected by pressure. Boiling on the other hand is DEFINED in terms of
> pressure. It's the point where atmospheric pressure equals the vapor
pressure.
> At 5000' (and altimieter setting 29.92), the boiling point is only 202
degrees
> The liquid water never can get above the boiling point, so the temperature
> of the food stays cooler and hence it takes LONGER to cook things that
> are boiled.
>
> However, the reason baking instructions change is only partially the
boiling
> point. In baking the food rises due to leavening (yeast, baking powder,
etc...)
> This process (amount of leavening used, temperatures, etc...) is generally
> set for sea level pressures. At higher altitudes, these recipes tend to
> over-rise. Adding addional flour or other adjustments to the recipe
> compensate for this.
>
> Freezing (of water) is affected by pressure, but to raise the freezing
point requires
> rather severe decrease in pressure. Between 0 and 5000 feet the frezing
point
> difference is less than a degree.

Hey!! Take it to alt.baking.recipes you guys!! :~)

Tom -- I lost the recipe for ice cubes.