Speed of Heat

[vlado]

Is there a rule of thumb for 'speed of heat'? Meaning the speed in
knots where ice will not form on the leading edges of a wing. For
example, the Saberliner had no de-ice or anti-ice system, just speeding
up would remove or prevent ice build up.
Thanks.

[Mike Rapoport]

I don't know the formula but Saberliners are too slow to offer reliable
deicing from speed alone although, like anything else, they change temp with
velocity. I recall reading that you need 400kt indicated for complete
protection.

Mike
MU-2


"vlado" > wrote in message
ups.com...
> Is there a rule of thumb for 'speed of heat'? Meaning the speed in
> knots where ice will not form on the leading edges of a wing. For
> example, the Saberliner had no de-ice or anti-ice system, just speeding
> up would remove or prevent ice build up.
> Thanks.
>

[Robert M. Gary]

In the Citation the temp difference is about 4 degrees. I think it goes
up exponentially as you approach the speed of sound. You have to get
pretty close to the speed of sounds before you get much difference (I
think).
-Robert

[TripFarmer]

Don't you eventually have to slow down? :o)


Trip



In article . net>, says...
>
>I don't know the formula but Saberliners are too slow to offer reliable
>deicing from speed alone although, like anything else, they change temp with
>velocity. I recall reading that you need 400kt indicated for complete
>protection.
>
>Mike
>MU-2
>
>
>"vlado" > wrote in message
ups.com...
>> Is there a rule of thumb for 'speed of heat'? Meaning the speed in
>> knots where ice will not form on the leading edges of a wing. For
>> example, the Saberliner had no de-ice or anti-ice system, just speeding
>> up would remove or prevent ice build up.
>> Thanks.
>>
>
>

[Don Hammer]

On 14 Mar 2005 21:23:47 -0800, "vlado" > wrote:

>Is there a rule of thumb for 'speed of heat'?

I don't have a CR-2 with me, but it seems like the ram rise at M.82 is
about 7 deg C.

Icing conditions don't occur at flight levels for cruise anyway, so a
jet aircraft will only ice during climb, decent, or holding. If the
old gray matter serves me, I think Rockwell proved the aircraft could
fly acceptably with any ice load it was expected to encounter. The
type certificate for the military versions show them as VFR only when
operating in the civil system. I doubt seriously it could pass the
testing now required for certification. I seem to remember some de-ice
mods to later versions, but I'm not sure. They did de-ice the engines
and the windscreens are heated. Most of these aircraft are in the
scrap yard by now I would imagine.

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[Kurt R. Todoroff]

In article >,
Don Hammer > wrote:

> On 14 Mar 2005 21:23:47 -0800, "vlado" > wrote:
>
> >Is there a rule of thumb for 'speed of heat'?
>
> I don't have a CR-2 with me, but it seems like the ram rise at M.82 is
> about 7 deg C.

The Mach heating temperature rise ratio (T_t / T_s) at M0.82 is .13348
referenced to absolute temperature regardless of altitude and other
atmospheric conditions. For example, if the static air temperature
(T_s) is -40F, then the total temperature (T_t) is +16F. The Mach
heating formula is:

TAU = T_t / T_s = 1 + ((gamma-1)/2)M^2

For a typical atmospheric gamma value of 1.4, the equation reduces to:

T_t / T_s = 1 + .2M^2

Converting -40F to absolute:

-40 + 459 = 419R

Insert temperature and Mach into the formula:

T_t / T_s = 1 + .2 * .82^2 = 1.13448

And:

T_t = T_s * 1.13448 = 419 * 1.13448 = 475R = 16F

So, if the outside air temperature is -40F ambient (zero velocity), then
at M0.82 the total temperature would be +16F.

>
> Icing conditions don't occur at flight levels for cruise anyway, so a
> jet aircraft will only ice during climb, decent, or holding.

This is not correct. Icing conditions can and do occur at any altitude
in which visible moisture is present.

If the
> old gray matter serves me, I think Rockwell proved the aircraft could
> fly acceptably with any ice load it was expected to encounter. The
> type certificate for the military versions show them as VFR only when
> operating in the civil system. I doubt seriously it could pass the
> testing now required for certification. I seem to remember some de-ice
> mods to later versions, but I'm not sure. They did de-ice the engines
> and the windscreens are heated. Most of these aircraft are in the
> scrap yard by now I would imagine.
>
> Posted Via Usenet.com Premium Usenet Newsgroup Services
> ----------------------------------------------------------
> ** SPEED ** RETENTION ** COMPLETION ** ANONYMITY **
> ----------------------------------------------------------
> http://www.usenet.com

--

Kurt Todoroff


Markets, not mandates and mob rule.
Consent, not compulsion.

[Kurt R. Todoroff]

In article >,
(TripFarmer) wrote:

> Don't you eventually have to slow down? :o)
>
>
> Trip
>
>
>
> In article . net>,
> says...
> >
> >I don't know the formula but Saberliners are too slow to offer reliable
> >deicing from speed alone although, like anything else, they change temp with
> >velocity. I recall reading that you need 400kt indicated for complete
> >protection.
> >
> >Mike
> >MU-2
> >
> >
> >"vlado" > wrote in message
> ups.com...
> >> Is there a rule of thumb for 'speed of heat'? Meaning the speed in
> >> knots where ice will not form on the leading edges of a wing. For
> >> example, the Saberliner had no de-ice or anti-ice system, just speeding
> >> up would remove or prevent ice build up.
> >> Thanks.
> >>
> >
> >

By the way, in the jet fighter business, we referred to the speed of
sound (Mach) as the "speed of heat".

--

Kurt Todoroff


Markets, not mandates and mob rule.
Consent, not compulsion.

[BTIZ]

All of the others talk of temperature rise do to compressibility based on
mach number, but no one really addressed the speed accounting for friction
of air molecules on the sheet metal which warms the aircraft. War story
time, low level over the plains of eastern Montana, near Conrad and Havre
Bomb Plots (Radar Bomb Scoring sites) and the outside air temp was
about -15F, however, we were moving along at about .88mach at 500ft AGL, and
the skin temperature was about 100F, not a worry about accumulating icing.

Some one else referred to "Speed of heat" as being Mach 1, because most
aircraft need after-burner or "heat" (reheat) as the Brits would say.. to
make Mach1. BTDT


BT

"vlado" > wrote in message
ups.com...
> Is there a rule of thumb for 'speed of heat'? Meaning the speed in
> knots where ice will not form on the leading edges of a wing. For
> example, the Saberliner had no de-ice or anti-ice system, just speeding
> up would remove or prevent ice build up.
> Thanks.
>

[Mike Rapoport]

I found this formula:

http://williams.best.vwh.net/avform.htm#Mach

Which shows a temp rise pretty close to what the MU-2 flight manual shows.

Mike
MU-2


"vlado" > wrote in message
ups.com...
> Is there a rule of thumb for 'speed of heat'? Meaning the speed in
> knots where ice will not form on the leading edges of a wing. For
> example, the Saberliner had no de-ice or anti-ice system, just speeding
> up would remove or prevent ice build up.
> Thanks.
>

[Kurt R. Todoroff]

In article <R5QZd.71896$Tt.15712@fed1read05>,
"BTIZ" > wrote:

> All of the others talk of temperature rise do to compressibility based on
> mach number, but no one really addressed the speed accounting for friction
> of air molecules on the sheet metal which warms the aircraft. War story
> time, low level over the plains of eastern Montana, near Conrad and Havre
> Bomb Plots (Radar Bomb Scoring sites) and the outside air temp was
> about -15F, however, we were moving along at about .88mach at 500ft AGL, and
> the skin temperature was about 100F, not a worry about accumulating icing.
>
> Some one else referred to "Speed of heat" as being Mach 1, because most
> aircraft need after-burner or "heat" (reheat) as the Brits would say.. to
> make Mach1. BTDT
>
>
> BT

Hi BT,

What were you flying? Most of my time is in the F-111D and the EF-111A.
I've also flown the F-15, C-130, C-141, KC-10, E-3. Did your aircraft
have a skin temperature indicator or a total temperature indicator?
Aircraft component heating is due to Mach compressibility, not skin
friction. I'm confident that your 100F value reflected total
temperature which is based on Mach compressibility.

The "speed of heat" received it's colloquial name because the speed of
sound is based only on the static temperature of the fluid medium, not
on pressure or density as is often mistakenly believed.

--

Kurt Todoroff


Markets, not mandates and mob rule.
Consent, not compulsion.

[BTIZ]

Kurt, you may be correct, as it was about 12 yrs ago, been retired a few
years now.. I believe it was total temp... B-1B

BT

> Hi BT,
>
> What were you flying? Most of my time is in the F-111D and the EF-111A.
> I've also flown the F-15, C-130, C-141, KC-10, E-3. Did your aircraft
> have a skin temperature indicator or a total temperature indicator?
> Aircraft component heating is due to Mach compressibility, not skin
> friction. I'm confident that your 100F value reflected total
> temperature which is based on Mach compressibility.
>
> The "speed of heat" received it's colloquial name because the speed of
> sound is based only on the static temperature of the fluid medium, not
> on pressure or density as is often mistakenly believed.
>
> --
>
> Kurt Todoroff
>
>
> Markets, not mandates and mob rule.
> Consent, not compulsion.

[Orval Fairbairn]

In article
>,
"Kurt R. Todoroff" > wrote:

> In article <R5QZd.71896$Tt.15712@fed1read05>,
> "BTIZ" > wrote:
>
> > All of the others talk of temperature rise do to compressibility based on
> > mach number, but no one really addressed the speed accounting for friction
> > of air molecules on the sheet metal which warms the aircraft. War story
> > time, low level over the plains of eastern Montana, near Conrad and Havre
> > Bomb Plots (Radar Bomb Scoring sites) and the outside air temp was
> > about -15F, however, we were moving along at about .88mach at 500ft AGL,
> > and
> > the skin temperature was about 100F, not a worry about accumulating icing.
> >
> > Some one else referred to "Speed of heat" as being Mach 1, because most
> > aircraft need after-burner or "heat" (reheat) as the Brits would say.. to
> > make Mach1. BTDT
> >
> >
> > BT
>
> Hi BT,
>
> What were you flying? Most of my time is in the F-111D and the EF-111A.
> I've also flown the F-15, C-130, C-141, KC-10, E-3. Did your aircraft
> have a skin temperature indicator or a total temperature indicator?
> Aircraft component heating is due to Mach compressibility, not skin
> friction. I'm confident that your 100F value reflected total
> temperature which is based on Mach compressibility.
>
> The "speed of heat" received it's colloquial name because the speed of
> sound is based only on the static temperature of the fluid medium, not
> on pressure or density as is often mistakenly believed.

Kurt is quite correct in this.

You can determine the temperature by taking the Mach number, finding the
local ambient temperature/total temperature ratio. (all temperatures are
absolute temperatures)
At Mach = 1.0, the ratio is 1.2;
at Mach = 1.5, it is 1.34;
at Mach = 2.0 it is 1.8;
at Mach = 3.0 it is 2.8.

Just add the OAT to 459.7 deg F or 273.2 deg C to get the absolute
temperature.

[Montblack]

("Orval Fairbairn" wrote)
> at Mach = 2.0 it is 1.8;
> at Mach = 3.0 it is 2.8.


That's-all-you-got? :-)


Montblack

[David CL Francis]

On Tue, 15 Mar 2005 at 22:10:56 in message
<R5QZd.71896$Tt.15712@fed1read05>, BTIZ >
wrote:
>All of the others talk of temperature rise do to compressibility based on
>mach number, but no one really addressed the speed accounting for friction
>of air molecules on the sheet metal which warms the aircraft. War story
>time, low level over the plains of eastern Montana, near Conrad and Havre
>Bomb Plots (Radar Bomb Scoring sites) and the outside air temp was
>about -15F, however, we were moving along at about .88mach at 500ft AGL, and
>the skin temperature was about 100F, not a worry about accumulating icing.
>
>Some one else referred to "Speed of heat" as being Mach 1, because most
>aircraft need after-burner or "heat" (reheat) as the Brits would say.. to
>make Mach1. BTDT
>
The stagnation temperature I recall is roughly given by the following:

Ts/T1 = (1 + (M^2)/5)

Where T1 is the absolute air temperature and Ts is the stagnation
temperature. So if the outside air temperature is -10C and the Mach
number is 0.5 then T1 = 263

Ts = 263*(1 + 0.25/5) = 263 *1.05 = +3.15 degrees

That is the _maximum_ temperature rise at the stagnation point.
Elsewhere it will be lower. The heat transfer through the ice and
aluminium and their thermal capacity will affect how long it takes.

The fact that it depends on the square of the mach number brings the
effect down markedly at lower speeds.
--
David CL Francis

[Mike Rapoport]

"David CL Francis" > wrote in message
...
> On Tue, 15 Mar 2005 at 22:10:56 in message
> <R5QZd.71896$Tt.15712@fed1read05>, BTIZ > wrote:
>>All of the others talk of temperature rise do to compressibility based on
>>mach number, but no one really addressed the speed accounting for friction
>>of air molecules on the sheet metal which warms the aircraft. War story
>>time, low level over the plains of eastern Montana, near Conrad and Havre
>>Bomb Plots (Radar Bomb Scoring sites) and the outside air temp was
>>about -15F, however, we were moving along at about .88mach at 500ft AGL,
>>and
>>the skin temperature was about 100F, not a worry about accumulating icing.
>>
>>Some one else referred to "Speed of heat" as being Mach 1, because most
>>aircraft need after-burner or "heat" (reheat) as the Brits would say.. to
>>make Mach1. BTDT
>>
> The stagnation temperature I recall is roughly given by the following:
>
> Ts/T1 = (1 + (M^2)/5)
>
> Where T1 is the absolute air temperature and Ts is the stagnation
> temperature. So if the outside air temperature is -10C and the Mach number
> is 0.5 then T1 = 263
>
> Ts = 263*(1 + 0.25/5) = 263 *1.05 = +3.15 degrees
>
> That is the _maximum_ temperature rise at the stagnation point. Elsewhere
> it will be lower. The heat transfer through the ice and aluminium and
> their thermal capacity will affect how long it takes.
>
> The fact that it depends on the square of the mach number brings the
> effect down markedly at lower speeds.
> --
> David CL Francis

I have flight manuals that give a correction for airspeed and altitude and
the numbers are much higher than 3C even though the speeds are below M0.5.
In the MU-2, the temp sensor is in the tail section where the cross section
of the fusilage is actually decreasing.. Is there both a compression and a
friction heating of surfaces due to airflow?

Mike
MU-2

[Julian Scarfe]

>> The stagnation temperature I recall is roughly given by the following:
>>
>> Ts/T1 = (1 + (M^2)/5)

"Mike Rapoport" > wrote in message
link.net...

> I have flight manuals that give a correction for airspeed and altitude and
> the numbers are much higher than 3C even though the speeds are below M0.5.
> In the MU-2, the temp sensor is in the tail section where the cross
> section of the fusilage is actually decreasing..

I think the problem is only with the numbers that got plugged in. At M =
0.5, you get
Ts/T1 = 1.05. In other words a 5% temp rise. 5% of about 273 K is about 13
K,
i.e. 13 degC.

> Is there both a compression and a friction heating of surfaces due to
> airflow?

It's the same phenomenon. The "friction" occurs because the air is brought
to stagnation in the boundary layer.

Julian Scarfe

[David CL Francis]

On Fri, 18 Mar 2005 at 23:27:50 in message
. net>, Mike Rapoport
> wrote:

>I have flight manuals that give a correction for airspeed and altitude and
>the numbers are much higher than 3C even though the speeds are below M0.5.
>In the MU-2, the temp sensor is in the tail section where the cross section
>of the fusilage is actually decreasing.. Is there both a compression and a
>friction heating of surfaces due to airflow?

Of course; but I don't think the driving temperature can get higher than
the stagnation temperature. Let's try it for Concorde:

At 55,000 ft the outside standard air temperature is 217 deg K

So Ts = To(1 + (2.05^2)/5) = 408 == 126 C

That is very close to the value quoted in Brian Trubshaw's book about
Concorde. The chart on page 34 shows the nose temperature at 127 C, the
leading edge of the wing at 105 C, pilots cockpit area skin temperature
at 97C decreasing towards the rear fuselage at 91 C. Mind the fuel in
the wings kept down their temperature from rising too high!

It does not show the fins or air intakes but I doubt they were much
higher than the forward fuselage section just behind the nose at 100 C.
--
David CL Francis