Cover

A cover provided for covering a bladed rotor during a testing operation. The cover has a face plate of solid sheet like material having a centrally positioned orifice through which air is drawn by the action of part of blade adjacent to orifice. The remaining part of the blades is in a stalled condition and therefore relatively unloaded. The power required to turn the rotor is therefore reduced in comparison to that required if the cover was not present making testing easier. The cover also acts as a safety shroud preventing personnel coming into contact with the blades as they rotate and containing the rotor in the event of its disintegration.

BACKGROUND OF INVENTION 
This invention relates to a cover for use in the testing of turbine 
equipment having a bladed rotor, in particular, in the testing of ram air 
turbines in situ on aircraft. 
Ram air turbines conventionally comprise a main body which is attached to 
an arm and deployed, when required, by an actuator. The main body includes 
a bladed rotor including at least two blades, and a hydraulic pump which 
in normal operating conditions is powered by the rotation of the bladed 
rotor. 
Conventionally such ram air turbines are ground tested by powering the 
hydraulic pump so that it acts as a hydraulic motor and thereby driving 
the bladed rotor. In order to appropriately test the ram air turbine it is 
necessary to drive it at its normal operational speed, typically in the 
region of 4000-6000 r.p.m. 
As civilian aircraft have developed and grown in size, the power 
requirement and therefore the size of the bladed rotor on the ram air 
turbine has correspondingly grown. The power input required to drive the 
ram air turbine under test is very large and has dramatically increased as 
the size of the ram air turbine has increased. 
It has now reached the stage where the power input requirement for ground 
testing has become a problem. 
The present invention is concerned with reducing the power input 
requirement under testing of turbine equipment having a bladed rotor. 
BRIEF SUMMARY OF THE INVENTION 
In its broadest aspect, the present invention comprises a cover for use in 
the testing of turbine equipment having a bladed rotor, which cover 
includes: 
a face plate positioned so that in use any air drawn by the bladed rotor 
during testing encounters the face plate prior to the bladed rotor; 
a solidly formed side wall which circumferentially surrounds the bladed 
rotor, adjacent to the blade tips, of the turbine equipment, and to which 
the face plate is connected; 
and a meshed back plate positioned on the other side of the bladed rotor to 
the face plate and which is connected to the side wall; 
wherein the face plate is designed so that during testing over part of the 
blade length no air flow exists resulting in this part of the length the 
blade experiencing stall characteristics, whilst over the remaining part 
of the blade length air flow exists enabling the turbine equipment to be 
accurately tested. 
A cover made in accordance with the present invention is suitable for use 
in testing any turbine equipment including a bladed rotor. However the 
cover was devised, and is particularly suited for use in testing ram air 
turbines on aeroplanes in situ, i.e. for use in ground testing. 
It has been previously proposed that with ram air turbines the bladed rotor 
should be enclosed in a fully meshed cage. The use of such a cage is for 
safety reasons only, that is (1) to prevent people from accidentally 
walking into an operating ram air turbine, and (2) in the case of a bladed 
rotor failure to catch what debris they could to reduce shrapnel damage. 
The use of these cages has no effect on the air flow characteristics of 
the bladed rotor. 
A cover made in accordance with the present invention includes the safety 
features associated with a simple cage, and has the advantage that the 
power input requirement to test the turbine equipment is significantly 
reduced, whilst the air flow across the bladed rotor is maintained 
sufficiently high to enable testing. 
The power input requirement of the turbine equipment to reach the required 
r.p.m. is reduced to a minimum when the bladed rotor of the turbine 
equipment is completely enclosed, and consequently no flow can be 
generated by the blades of the bladed rotor. As will be well appreciated 
by those in the aerospace industry in this condition no testing of the 
turbine can be effected. 
With the present invention a balance is achieved between the reduction in 
the power input requirement and air flow necessary to enable testing, this 
normally being achieved by the provision of at least one opening in the 
face plate to allow the flow of air into the cover. 
The actual amount by which the power input requirement is reduced is 
dependent upon the surface area of the blades of the bladed rotor 
subjected to stall conditions and the position of this surface area along 
the length of the blade. As will be well appreciated, for equivalent 
surface areas subjected to stall conditions the power input requirement 
will be reduced more for the surface area near the tips of the blades, 
than for the surface area close to the centre of rotation. This is a 
simple force balance situation. 
Preferably, the part of blade length over which no air flow is induced is 
in the vicinity of the blade tips. 
In one embodiment of the present invention, the opening in the face plate 
to allow for the flow of air about the blades of the turbine equipment 
under test is a centrally positioned orifice. In this case, the surface 
area of the blades subjected to stall conditions is in the vicinity of the 
blade tips. Therefore, maximum reduction power input requirement is 
achieved for minimum surface area subjected to stall conditions. 
Obviously, the actual amount by which the power input requirement can be 
reduced, whilst maintaining a valid test condition is dependent upon the 
actual turbine equipment (Ram Air Turbine) under test. The cover, in 
particular the face plate, can be designed to cater for most conditions 
that will be encountered. In one embodiment of the present invention the 
face plate is connected to one edge of the side wall and the back plate is 
connected to the other edge. 
In an alternative arrangement of the present invention, the face plate is 
positioned on the side wall slightly inward from the edge, which edge is 
connected to a meshed front piece which is provided to catch debris in the 
case of a rotor failure. In this case the face place acts as a form of 
baffle in order to produce the required flow effects. 
Under certain conditions, in addition to the face plate the cover is also 
provided with baffle plates and/or vanes to further enhance the no flow, 
and thereby stall, conditions. 
Preferably, the opening, or openings, is provided with contouring to 
enhance the air flow conditions into the cover.

DESCRIPTION OF PREFERRED EMBODIMENT 
Now referring to the drawings, a cover 1 is located about a ram air turbine 
2 having a turbine 3 with blades 4 so that the blades of the turbine 3 
will not come into contact with the cover 1. 
The ram air turbine 2 comprises: 
a main body section 5; 
the turbine 3 having two blades 4 diametrically opposing one another and 
which is attached to the main body section 5; 
a hydraulic pump/motor 8 housed within the main body section 5 which is 
provided with two hydraulic connections 6; 
an arm member 7 which has the main body section 5 mounted at one end 
thereof and which at the other end thereof is connected to an aircraft; 
a hydraulic actuator (not shown) which is used to deploy the ram air 
turbine when required; 
and two hydraulic pipes 9 which connect the hydraulic connections 6 and 
therefore the hydraulic pump/motor 8, with equipment which is to be 
powered by the hydraulic pump/motor 8. 
In normal operational conditions the hydraulic pump/motor 8 acts as a 
hydraulic pump. In this configuration the blade rotor is caused to rotate 
by air flow and this rotation is converted to hydraulic energy by the 
hydraulic pump. 
The cover 1 comprises: 
a face plate 10 of solid sheet like material having a centrally positioned 
orifice 11 the edges of which are contoured so as to regulate the flow of 
air entering the cover; 
a side wall 12 of solid sheet like material; 
and a meshed back plate 13. 
In order to effect ground testing of a ram air turbine using a cover as 
hereinbefore described, firstly the cover 1 is positioned over the turbine 
3 so that the blades 4 of the turbine 3 are not in contact with the cover 
1. 
In order to power the ram air turbine so as to enable ground testing, the 
hydraulic pump/motor 8 is hydraulically connected so that it acts as a 
hydraulic motor rather than a hydraulic pump, and causes the turbine to 
rotate. 
The rotation of the turbine causes air to be drawn into the cover via the 
orifice 11 in the face plate 10. The face plate 10 in effect limits the 
air flow into the cover and therefore to the blades 4 of the turbine 3. 
This means the blades 4 have two opposed flow conditions existing thereon, 
these are: 
a no air flow condition resulting in stall characteristics; 
and an air flow condition meaning the blades will behave normally. 
The presence of the no air flow condition over a part of the blade 4 means 
little resistance is met with respect to this part of the blade therefore 
the power input requirement to drive the bladed rotor at a particular 
speed (r.p.m.) is lower than would be expected without the presence of the 
air flow condition.