Static and Dynamic Response of a Design of Differential ... - aerade

3-$ calibres behind the nose in accordance nith the recommendations or
reference 3, and arranged as a circumferential ring of 12 equally spaced
holes. Tests were carried out to see to what extent the pressures recorded
at incidence differed from the lrnown stagnation and static pressures.
The variation of pitot pressure with incidence is shown in fig.6,
non-dimensionalised in terms of ps. It was found by plotting
Ppit
Ps
i.e.
PO
p against
for constant incidence, 8 , that o - 6 is proportional to
cp PS >
the constant of proportionality being given closely by set
This variation is also shown in fig.6. It is of interest that
equation 4 is found to predict very closely indeed the pressure distribution
over the whole of the hemisphere, and to collapse 2 great deal of existing
pressure data obtained over a wide range of supersonic speeds.
pe static pressers at M = 1.4 as recorded at the holes in the
cylindrical body are shonn in fig.?, non-dimensionslised again with
respect to the true free stream static pressure. 'Thesg pressures are .
noticeably dependent on the incidence, the value at 17 being only 72$ of
that at zero angle. Certain modifications to the size, shape snd number
of holes were tried, but they effected no significant improvement. It is
thought unlikely that an accurate measurement of static pressure will be
obtained with this type of instrument where the pressure holes are subject
to the influence of the vortices shed from the body of the instrument at
incidence.
3.5 Determination of incidence, roll angle and D&zch No. from flight
records
In the application of this instrument to flight test work the
requirement will in general be to derive the angles e and $5 inpolar
axes, or a and P in Cartesian axes, together with Mach No., from a
knowledge of three pressure ratios, viz.
AP,
p,'
AP9
;
Ps
m& Ppit
ps
the statio
pressure, psy having been determined independently. This can be done by
a tedious, purely iterative process from the curves given in figs.2 to 6,
but the labour can be reduced, or eliminated depending upon the accuraay
required, by several methods.
Firstly, if the incidence range is small, say less than IO’, then
the non-linesrities may be disregarded and the parsmeters evaluated as
follows:-
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S