Abstract:
The design of a model helicopter rotor blade incorporating a
swept tip is described. The swept tip is chosen to provide a coupling
between the lift at the tip and the blade twist thus achieving a
variation of blade tvist both with azimuth and with forward speed. The
design is the first stop in an investigation of aeroelastic tailoring
as a means of reducing helicopter vibration and increasing rotor
performance.
The first prototype blade encountered stability problems and
further designs were evaluated using a new modes/stability computer
program developed within RAE. Comparisons are made between the
stresses measured on a second stable swept tip blade and a dynamically
similar rectangular blade. The results show that a beneficial twisting
of the swept tip blade is achieved which enhances rotor perforawtnee
and reduces the flatvise bending and torsional moments. Comparisons
are made between the experimental results and those predicted by the
RAE/VOL coupled modes analysis. The predictions are. reasonably
accurate for the flatwise moments but a more representative model of
the hub is needed to produce acceptable predictions of the torsional
moments.
The design of a further set of blades is discussed, the aim
being to investigate the effects of introducing a strong coupling
between the flap and torsion notions of the blade by sweeping back the
shear centre. An analysis of-the results shows that there are large
gains in blade stability with no severe adverse effects on blade
loads.
A theoretical investigation has been undertaken to observe the
effects of tip sweep on the performance of a full size rotor. The
results show that aft tip sweep can reduce control loads and rotor
power for a rotor with a cambered aerofoil, section.
