This is so incredible I just had to share it with you guys. PL
Ray Clegg wrote:
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Vance, Scott, Marks and everyone else
It is not possible for me to detail everything we have had to do to satisfy
PFA but I will summarise and then maybe answer any specific questions you
have.
1. Fuselage carry through spar
Martin Hollman admits his calculations were incorrect regarding
shear loads between the two main spar bolts and suggested 8 additional glass
plies to the rear face. PFA thought the figure should be 12 plies aft and 4
plies forward but wrapped onto the upper and lower spar webs. They still
believe this area is 'marginal' and have reduced the MAX ZERO FUEL WEIGHT to
2000lb
2. Wing spar
Because I had closed the wing it would have been impossible
without destroying it to reinforce the spar. PFA have accepted it as it is.
3. Additional fuel tanks
I have installed additional fuel tanks behind the spar and have
a total capacity of 110 imperial gallons. Because PFA were concerned about
lower skin adhesion to the ribs they made me put double flanges on each rib
to reduce the risk of peel forces. I had to test the torsional stiffness of
the wing by bolting it to a steel spar on the workshop wall and twisting it.
>From the formula provided by PFA a Vcf (critical flutter) of 630 knots was
calculated - that will be sufficient for me.
4. Fuselage, tailplane, fin and control surface load tests
The fuselage was mounted on trestles under the main gear and the
engine mount chained to the floor. The tailplane was loaded to 990lbs which
gave a load on the engine mount of 1594lbs.
Fin loaded to 350 lbs
Elevator 336
Aileron 168
Flap 392
Rudder - test not required as construction similar to elevator
What a coincidence. This is about the load I came up with on our rotary engine
motor mounts. PL
5. Control system load testing
The control system is expected to take a greater load than would
normally be applied via the control surface. It is assumed that in a
situation where a control system or surface jams, a pilot and passenger
would apply a combined force to the stick or pedals of 1.5 x the figures
Scott quotes:-
aileron 90 lb
elevator 225 lb
rudder 292 lb
Those were the loads we had to achieve - and did. The only damage being to
the one weld.
The question of control stops does not apply in this case as the control may
jam in a neutral position.
Certain modifications were required by PFA prior to testing.
The yoke at each end of the interstick link was considered at risk of
twisting and had to be reinforced. Gussets had to be welded to the elevator
horn to reinforce it. The idler between the two elevator tubes was
calculated as 'under strength' and had to be remade.
The one piece rear elevator tube was calculated as being at risk
from buckling but as we had already divided it into two with an intermediate
idler that problem did not arise.
We have used a complete Cessna rudder pedal asembly so PFA dared
not fault it (or risk grounding 50% of the worlds single engine aircraft!!)
We (not PFA) were concerned regarding the load on the bulkhead where the
rudder idler was attached and reinforced the area.
The flap torque tube wall at 0.065" was calculated as being
insufficient to resist shear so was reinforced at the centre and both ends
with an inner tube rosette welded in place. The centre torque arm bolts
(3/16") were calculated as being under strength. They were replaced with
1/4" bolts which necessitated making a new arm as there was insufficient
material to take the large bolts. We (not PFA) were concerned about the
thickness of material of the outer torque arms where the bolts pass through
(less than 1/8") so we made new arms and used 1/4" bolts. The flap arms were
loaded upwards using hydraulic jacks to 288 lbs each (576 lbs to the centre
arm, the Cessna flap motor screw jack, and the mounting of the motor to the
fuselage floor)
All these modifications plus the luxuries we have built into the
aircraft gives a total weight of 1498 lbs. It is now down at the airfield.
The engine runs beautifully. Only the PFA is preventing it from flying
Ray
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