An air heater for an air inlet of an electronic system
TECHNICAL FIELD
This invention relates generally to airborne electronic systems and more
particularly to an air heater for a cooling system of the electronic system of a
radar antenna mounted on an aircraft.
BACKGROUND ART
During the use of the radar antennas, the components in the electronic
system of the radar antenna heats up and must be cooled not to be
overheated. Electronic systems of radar antennas mounted on the body of an
aircraft are, during flight, cooled by the airflow from the surrounding air. The
electronic system is arranged within a housing, wherein the airflow is lead
into the components of the electronic system through an air inlet and an air
pipe. The electronic system of the radar antenna is thereby exposed to varied
temperatures, wherein the lowest temperatures are below -55°C.
Due to the very low temperature caused by airflow, special designed
components are used in the electronic system of the radar antenna. The
special designed components can withstand lower temperatures than
conventional industrial components; this makes the electronic system of the
radar antenna more insensitive to low temperatures. For industrial
components used today the critical temperature is normally at -40°C. The
special designed components are supplied by just a few suppliers and are
much more expensive than conventional components.
The electronic systems must not just be designed to be able to stand low
temperatures; the same system is subjected to high temperatures, essentially
because of the heating effect of the system itself. For electronic system with
soldered components, the temperature can not be allowed to be raised
above the critical temperature +85°C, because the soldered seems can start
to degrade.
DESCRIPTION
It is therefore an object of the invention to provide a device which facilitates
the use of sensitive industrial components in an electronic system of a radar
antenna mounted on a body of an aircraft.
The present invention is directed to solve the aforementioned problems of the
prior art. In accordance with criteria used for the application of devices for
airborne operation any system must be low cost, light weight, small in volume
and consume a minimum amount of power.
The air heater according to the invention is located between an air inlet and
an electronic system of a radar antenna, said electronic system is mounted
on the body of an aircraft. The electronic system is enclosed in a housing
with at least one air inlet, that is adapted to provide outside air for cooling of
the electronic system, further, an air pipe is located between the air inlet and
the electronic system.
To achieve a raised temperature of outside air taken in by the air inlet, it
seems attractive to just increase the speed of the aircraft, whereby the
aerodynamic heating would increase. However, the aerodynamic heating
would in fact not be enough in the present case. The aerodynamic heating
would not be sufficient to raise the temperature of the air taken in above the
critical temperature for the industrial components.
Thereby, a conventional heater, for heating the outside air flowing into the air
inlet could seem interesting. Because of the high speed of the aircraft, the
heater must heat huge volumes of air. Accordingly, the heater would get high
energy consumption. As long as the heater is the only major electric energy
consumer in the aircraft, this would not be a problem. But, when the
electronic system, i.e. the radar system, or parts of it, is in operation at the
same time as the heater, the generator of the aircraft won't be able to supply
both the heater and the electronic system with the power needed.
Hence, just placing a conventional air heater in the air inlet and/or air pipe
would not solve the problem with satisfactory results.
The invention rests upon the findings, that when the air is warm, i.e. up to
+30°C, the airflow through the electronic system can be restricted, and the
desired cooling effect on the components of the electronic system would still
sufficient, when the radar antenna is in use. Further, a restricted airflow of
outside air with a temperature beiow a critical temperature can be heated to
temperatures above the critical temperature, with less energy consumption
than if the airflow was not restricted.
An air heater according to the preamble of claim 1 is therefore suggested,
wherein the inventive air heater is mounted in the air pipe between the air
inlet and the electronic system and comprises heating means and regulating
means. When the aircraft is in the air, the regulating means is arranged to
restrict an airflow which arises through the air pipe. The regulating means is
invariable, such that it just can restrict the air flow stationary, not varying it.
The heating means is arranged and dimensioned to heat the restricted
airflow such, that the temperature of the restricted airflow after it has passed
the heating means is maintained above a first predetermined threshold value.
Further, the cooling effect of the restricted airflow, on the electronic system,
is maintained above a second predetermined threshold value, when the
temperature is below a third predetermined threshold value.
The first predetermined threshold value is lower than the third predetermined
threshold value, and the first, the second and the third predetermined
threshold values are dependent on material properties of the components in
the electronic system.
The first predetermined threshold value is essentially -40°C, as limited by the
temperature limit for the industrial components in the electronic system. The
second predetermined threshold value for the cooling effect is essentially 20
k , preferably essentially 25 kW and more preferably essentially 35 k .
These are the cooling effects needed to keep the temperature of the
electronic components of the electronic system below the critical temperature
+85°C, during operation of the radar antenna and its electronic system. The
cooling effect is thereby, the heat removed from the electronic system, by the
airflow. With a higher cooling effect, a more efficient cooling of the electronic
system and a greater margin to the critical temperature is maintained. The
third predetermined threshold value is essentially +30°C, as limited by the
operating temperatures of the radar antenna and the components in the
electronic system. Obviously, through progress within the field of electronic
components, these threshold values can change over time.
In situations where no heating of the air is necessary, i.e. when the
temperature of the air taken in by the air inlet is -40°C or above, the heating
means can be turned off.
The regulating means is dimensioned such, that when the air has a
temperature of essentially +30°C, i.e. the third predetermined value, the
restricted airflow still maintains a cooling effect of at least 20 kW, preferably
25 kW and more preferably 35 kW, i.e. above the second predetermined
threshold value. This cooling effect is sufficient to keep the temperature of
the components in the electronic system below +85°C, during use of the
electronic system.
Due to the regulating means, the restricted airflow becomes a lower flow rate,
and thereby can the temperature of the air be raised with a heating means
with less effect, than if the airflow wasn't restricted by the regulating means.
The flow rate is important for calculating the effect needed to heat the air and
to determine the cooling effect of the airflow. The flow rate is determined of
the air pressure, viscosity of the air and the speed of the air craft. To
calculate the flow rate is an Equivalent Air Speed (EAS) used for the
calculations of the cooling effect. The EAS is the speed at sea level which
gives the same dynamic pressure as the speed of the aircraft relative the
surrounding mass of air, i.e. the True Air Speed (TAS).
Two worst case scenarios are to be considered. First, the cold case; when
the temperature of the air is -55°C at a height corresponding to 7 00 meters
above sea level and an EAS of 90 m/s. Second, the warm case; when the
temperature of the air is +30°C, on a height corresponding to 2120 meters
above sea level and an EAS of 80 m/s.
The inventive air heater with its regulating means and heating means
achieves a lower energy consumption of the heater, since less air must be
heated, to heat air below the first predetermined threshold value and reach
the desired air temperature of at least -40°C, which is the first predetermined
threshold value. When the flow rate of the airflow passing through the
electronic system is decreased, the cooling effect of the airflow will also
decrease. Thereby it is of important for the invention, that the regulating
means is adapted such, that the flow rate of the airflow passing the regulating
means is sufficient to coo! the electronics as the air temperature is +30°C, i.e.
the third predetermined threshold value. Thereby, the airflow must maintain a
cooling effect on the eiectronic system of at least the second predetermined
threshold value, essentially 20 kW, preferably essentially 25 kW and more
preferably essentially 35 kW. This especially important for the warm case, i.e.
air temperatures of +30°C and an EAS of the aircraft of 90 m/s at a height
corresponding to 7 00 meters above sea level.
By restricting the airflow, heating means with a lower effect can be used to
secure, that the temperature of the components in the electronic system is
kept at a temperature above -40°C, i.e. above the first predetermined
threshold value, relative if the airflow was not restricted. However, the cooling
effect of the restricted airflow, at air temperatures about the third
predetermined threshold value, i.e. +30°C, is maintained sufficient to coo! the
electronic system during use in these conditions.
A preferred heating means is an electronic heater. For safety reasons it is
suggested that the electronic heater automatically switches off, if the
temperature of the heating means exceeds a predetermined value.
In the air heater according to the invention, it is preferred that the heating
means and the regulating means restricts the airflow such that, when the
temperature of the airflow is below the first predetermined threshold value;
-40°C, and especially when the temperature is essentially -55°C, the
maximum heating effect required to heat the restricted airflow to at least the
first predetermined threshold value; -40°C, is less than 20 kW, preferably less
than 15 kW.
With an effect lower than 20 kW it want be a problem to activate the
electronic system, i.e. radar system, at the same time as the heating means
is activated. An even greater margin is achieved with an effect lower than 5
kW. The generator of the aircraft can manage to supply both consumers with
the energy required.
Further, the regulating means restricts the airflow such that, when
temperature of the airflow is below the third predetermined threshold value,
the cooling effect of the restricted airflow, at a height corresponding to
essentially 2120 meters above sea level, is at least essentially 20 kW,
preferably at least essentially 25 kW and more preferably at least essentially
35 kW.
To achieve this cooling effect, and stiil reduce the flow rate of the airflow in
the air pipe, there are several ways of design and construct the regulating
means. Independent of its construction, the regulating means restricts the
flow rate of the airflow with 40 - 50 %, especially essentially 46%, during all
the below listed conditions:
- When the air temperature is -55°C, the aircraft is flying at a height
equivalent to 7100 m above sea level and the speed of the aircraft is
80 m/s EAS.
- When the air temperature is +30"C, the aircraft is flying at a height
equivalent to 2120 meters above sea level and the speed of the
aircraft is 90 m/s EAS.
- When the air temperature is -55°C, the aircraft is flying at a height
equivalent to 9141 meters above sea level ant the speed of the aircraft
is 80 m/s EAS.
To cool the electronic system, i.e. the radar system, when the aircraft is not in
operation, an external cooling system which forces air to flow through the
housing, is connected to the air inlet it is therefore preferable, that the
inventive air heater is attached to the housing with detachable attachment
means. The air heater can thereby be demounted, when the aircraft is
standing on the ground. The detachable attachment means, can be screw,
bolts, click attachment means or other suitable detachable attachment
means.
It is preferable, that the regulating means is mounted in the air pipe, closer to
the air inlet than the heating means. Further, that the air heater additionally
comprises an impact protection means also located in closer to the air inlet
than the heating means. The impact protection means is protecting the
heating means and the electronic components of the electronic system, such
that if a bird or another foreign object collides with the housing and enters the
air inlet, it does not damage these parts. To exchange a damaged protection
means is much cheaper than if parts of the whole electronic system must be
exchanged because of the impact with the foreign object.
To reduce the impact force on the heating means and the surrounding
structure, the impact protection means is adapted to deform, if the regulating
means is hit by a foreign object. Hence, the impact protection means is
adapted such, that it has a deformation zone.
It is especially provided, that the impact protection means is integrated with
the regulating means. The surface of the regulator means has thereby, a
convex shape, when looking at the regulating means (6) from the air inlet
such, that a deformation zone is created by the convex shape. The convex
shape is a construction of the deformation zone which is easy to produce and
which allows the impact protection means/regulating means to deform, such
that the impact of the collision is reduced.
A construction of the regulating means, which is easy to produce and which
in addition can be used as an impact protection means, is a plate placed in
the airflow. Said plate must have at least one through opening. The at least
one through opening in the plate restricts the flow rate of the air flowing
through the air pipe. This particular regulating means can also be
manufactured to a low price.
An alternative construction of the impact protection means is bars or a wire
netting located in the airflow before the heating means. Also this impact
protection means are preferably adapted to have a shape allowing it to
reduce the impact with a foreign object.
In an alternative embodiment of the inventive air heater is the heating means
and the regulating means integrally formed in one unit. Hence, either heating
means additionally functions as the regulating means, i.e. restricting the air
flow, or the regulating means additionally functions as the heating means, i.e.
heating. Obviously the impact protection means can also be integrally formed
in the same unit as the heating means and the regulating means.
The inventive air heater is preferably insulated attached to the housing of the
electronic system. Due to the insulation, no energy is lead away from the
heating means, and thereby lost. Further, the material of the housing may
thereby be in a material sensitive for higher temperatures, like plastic of
composite.
A preferred insulation material between the air heater and the housing is
ceramic which possesses very good insulating qualities.
The inventive air heater is supposed to be used for an electronic system, and
more specifically a radar system, mounted on or in the body of an aircraft.
The electronic system is enclosed in a housing with at least one air inlet
through which air for cooling of the electronic system can be provided, and
wherein an air pipe is located between the air inlet and the electronic system.
The inventive air heater is thereby mounted in the air pipe between the air
inlet and the electronic system.
An electronic system with the inventive air heater mounted in its air pipe
between the air inlet and the electronics, is able to operate in conditions from
-55°C and up to +30°C and still keep the temperatures of the electronics
components within the desired temperature range.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 shows an aircraft with a radar system mounted on its back.
Fig. 2a shows explode drawing of an inventive air heater.
Fig. 2b shows an inventive air heater in a perspective view.
Fig. 3 shows a cross section through a housing of a radar system.
DETAILED DESCRIPTION
Ail the figures 1 - 4 are schematically illustrated. The inventive air heater 1 is
to be used in electronic systems, i.e. a radar system, mounted in or on an
aircraft 2 as shown in fig. 1. The radar system 11 is arranged within a
housing 3, wherein the housing 3 has an air inlet 4 to allow air flowing
through the housing 3 . The purpose of the airflow 9 is to cool the electronic
components 10 of the radar system 11, such that they not get over heated
during use of the electronic system. Still, to allow the use of industrial
components in the radar system, the airflow 9 must be heated when the
temperature of the air is below the first predetermined threshold values, i.e.
40°C.
Fig. 2a shows an explode drawing of the inventive air heater 1 with heating
means 5 and regulating means 6. in the example shown, the regulating
means comprises a piate 6 with a plurality of openings 7. The plate is
mounted with screws 12 in a frame 13 of the air heater 1. As can be seen in
both figure 2a and 2b, the plate 6 has a shape, such that its surface has a
convex form, if looking at the plate 6 from the air iniet 4. Due to the convex
shape, the plate 6 becomes a deformation zone. If the air heater 1 collides
with a foreign object, the deformation zone reduces the impact on the air
heater 1 and the surrounding structure, i.e. the housing 3 . The deformation
zone further creates a distance to the heating means 5 which thereby don't
get hit if a foreign object collides with the air heater 1.
The openings 7 in plate 6 , as seen in figure 2a and b, is adapted such that
they restrict the air flowing through the air pipe 8 shown in fig. 3 . Obviously,
the heating means 5 also contribute to the reduction of the flow rate of the air
flowing through the air heater 1. However, in the embodiment shown in the
figures, the heating means 5 is constructed such that its contribution to the
reduction of the flow rate of the airflow 9 is minimal.
In an embodiment of the inventive air heater 1 the heating means 5 and the
regulating means 6 is integrally formed, such that the same unit achieves the
result of both the regulating means 6 and the heating means 5. For example,
the in figure 2 shown heating means 5 could be integrated in the regulating
means 6, such that the heating means 6 can heat the airflow through the air
heater 1 by itself.
The air heater 1 is mounted in the housing 3 of the radar system, with screws
or bolts 14. Between the screws/bolts 14 and the frame 3 is insulating
means 5, 16 arranged. Thereby, won't it be any heat transferred from the air
heater 1 to the housing 3 .
The air heater 1 is mounted in the housing 3 with screws/bolts 14 such, that
the air heater can be removed if the radar system is going to be operated
when the aircraft 2 is stationary on the ground.
As illustrated in figure 3, the air heater 1 can be mounted in different
positions A , B, C in the air pipe 8. A first position A is located close to the air
inlet 4; the position A facilitates an easy removal of the air heater 1. The two
alternative positions B, C of the air heater 1 is closer to the electronic
components 10 of the radar system 1.
As can be seen in figure 3, it is preferred that the regulating means 6 is
mounted before the heating means 5 in the airflow 9.

CLAIMS
1. An air heater (1) arranged in an air pipe (8) of an electronic system ( 0) of
a radar antenna, wherein the electronic system (10) is mounted on the body
of an aircraft (2) and the electronic system ( 10) is enclosed in a housing (3)
with at least one air iniet (4), that is adapted to provide outside air for cooling
of the electronic system ( 0), wherein the air pipe is located between the air
inlet (4) and the electronic system (10), characterised in,
that the air heater (1) is mounted in the air pipe (8) between the air iniet (4)
and the electronic system (10), and wherein the air heater ( 1) comprises
heating means (5) and regulating means (6), wherein the regulating means
(6) is invariable and is arranged to restrict an airflow through the air pipe (8),
and
- the heating means (5) is arranged and dimensioned to heat the
restricted airflow (9) such, that the temperature of the restricted airflow
(9), after it has passed the heating means (5), is maintained above a
first predetermined threshold value, and wherein
- the cooling effect of the restricted airflow (9) on the electronic system
is maintained above a second predetermined threshold value when
the temperature of the restricted airflow (9) is below a third
predetermined threshold value, wherein
the first predetermined threshold value is lower than the third predetermined
threshold vaiue, and the first, the second and the third predetermined
threshold values are dependent on material properties of components
arranged in the electronic system (10).
2. An air heater (1) according to claim 1, wherein the first predetermined
threshold value is -40°C, and the second predetermined threshold vaiue is
essentiaily 20 kW, preferably essentially 25 kW and more preferably
essentially 35 kW and the third predetermined threshold value is +30°C.
3 . Air heater according to claim 1 or 2, wherein the regulating means (6) is
arranged to restrict the airflow such that, when the temperature of the airflow,
before the heating means (5), is below the first predetermined threshold
value, and especially is -55°C, the maximum heating effect required to heat
the restricted airflow (9) to above the first predetermined threshold value, is
less than essentially 20 W, and preferably less than essentially 5 kW.
4. Air heater (1) according to any of the preceding claims, wherein, the
regulating means (6) is arranged to restrict the airflow such that, when the
temperature of the restricted airflow (9) is below the third predetermined
threshold value, the cooling effect of the restricted airflow (9), at a height
corresponding to essentially 2120 meters above sea lever, is at least
essentially 20 kW, preferably at least essentially 25 kW and more preferably
at least essentially 35 kW.
5 . Air heater (1) according to any of the preceding claims, wherein, the
regulating means (6) is adapted to restrict the airflow with 40 to 50 % at a
height equivalent to 7 100 meters above sea level, a speed of the aircraft (2)
of 80 m/s Equivalent Air Speed, wherein the air temperature is - 55°C.
6. Air heater (1) according to any of the preceding claims, wherein the air
heater (1) is attached to the housing (3) with detachable attachment means
(16), such that the air heater (1) can be fully demounted.
7. Air heater (1) according to any of the preceding claims, wherein the
regulating means (6) is mounted in the air pipe (8), closer to the air inlet (4)
than the heating means (5) and that the air heater (1) further comprises
impact protection means (6) also located closer to the air inlet than the
heating means (5).
8. Air heater according to claim 7, wherein the impact protection means (6) is
integrated with the regulating means (6), wherein the regulating means (6) is
adapted to deform, if the regulating means is hit by a foreign object, and
thereby reduce the impact force on the air heater (1) and the surrounding
structure.
9. Air heater ( 1) according to any of the preceding claims, wherein a surface
of the regulating means (6) has a convex shape, when looking at the
regulating means (6) from the air inlet, such that a deformation zone is
created by the convex shape.
10. Air heater (1) according to claim 9 , wherein the regulating means
comprises a plate (6) placed in the airflow, said plate (6) having at least one
through opening (7).
1. Air heater (1) according to any of the claims 1 - 9, wherein the impact
protection means consists of bars or plates (6) or a wire netting located in the
airflow before the heating means (5).
12. Air heater (1) according to any of the preceding claims, wherein the
heating means (5) and regulating means (6) is integrally formed in one unit.
13. Air heater (1) according to any of the preceding claims, wherein the air
heater (5) is insulated attached to the housing (3) of the electronic system.
14. Atr heater (1) according to any of the preceding claims, wherein the
insulation between the air heater (1) and the housing (3) is ceramic bushings
( 15 , 16).
15. Electronic system ( 0) of a radar antenna, wherein the electronic system
(10) is mounted on or inside the body (2) of an aircraft and the electronic
system (10) is enclosed in a housing (3) with at least one air inlet (4), that is
adapted to provide outside air for cooling of the electronic system ( 1 0), and
wherein an air pipe (8) is located between the air inlet (4) and the electronic
system (10), characterised in,
that an air heater (1) according to any of the claims 1 to 14 is mounted in the
air pipe (8) between the air inlet (4) and the electronic system ( 1 0).