feel the aircraft load up and get to shuddering....
Sounds simple until you know what loads are being put on the rotor head at that stage. During the development of the Puma they were regularly flown beyond 200 kts and sustained operations at 300 Rrpm. The classic was VNE at max aft C of G and putting the yaw channel into open loop, wait two seconds and recover from the inverted. The stacks of discarded rotor heads and gearboxes in the Aerospatial hangar were the accepted casualties.
get out there and pull a few G's
The only limit I can remember was the early 330G manual that had 2.67G below 6400kgs. A sustained level turn at sixty degrees of bank is about 2Gs. To do this you have to have a light aircraft with a lot of reserve power flown at VBROC. Outside those parameters you are overstressing the head. That’s why they have bank limits at high AUWs.
Years ago a fellow pilot decided that the Whirlwind VNE wasn’t fast enough for him. He cranked the collective up to Max Con on the engine and accepted the speed. Being the only one up top nobody knew until he inadvertently passed his flight commander with his extra 15 knots. When the truth came out they had no choice but to change all the rotor heads on all the aircraft he had flown on the squadron.
Blade slaps on the pylon. It is a five-bladed propeller that is capable of pulling a five ton fixed wing along at 170kts. It is incredibly powerful, that’s why there are all those doubling plates on the Pumas pylon/boom joint which is not helped by pilots trying to twist the pylon off when they are taxiing it.
Helicopters are blind, that’s why they keep flying into mountains. As long as they are in balanced flight, correct Rrpm and reasonable positive G than they do not know which way up they are. Keeping within those parameters you can do most things except make it talk. It is when you go outside those parameters that the trouble starts.
The classic Torque Turn. You cannot do it with a governed turbine helicopter. That is the prerogative of a ungoverned piston version. Especially the Sycamore which had insufficient cyclic of yaw authority so cranking the throttle was the only choice. On turbines pilots tend do fly it like a fixed wing stall turn. Unfortunately there are at least two vastly different parameters. The first is the rate of which the airspeed decays. Fixed wing have a nice engine which is pulling them up, helicopters don’t, so that plus gravity means they airspeed drops like a stone. As it passes through 45kts you have about two seconds before it is zero. A bootfull of pedal turns it, great, but if you are not fast enough two seconds later it can falling at 45knots, sideways. A fixed wing doesn’t worry, the fin assembly can cope with this without stress. But on a Puma going to the right you have full pedal pushing the tail rotor towards the airframe and as you are outside the sideways flight limit of the aircraft, the blades bump off the pylon.
Helicopter fuel and hydraulic systems are not designed with aerobatics in mind. The Puma is not so bad as the engines use tanks that are continuously topped up. Other types are not the same. Taking the S76 at a low fuel state, vertical operations can cause the fuel to bank up against the wall of the tank and uncover the fuel feed. Turbine engines, glow plugs or not, do not like slugs of air and pointing vertically downwards at 300ft is not the best place to initiate an EOL. The same with hydraulics, especially large capacity systems like the Puma.
In any form of inverted flight it is obvious that under positive G the main rotor is assisting gravity and in a very short time you will have insufficient roll rate to return the aircraft upright before hitting the ground. Fixed wing can reduce or apply negative G to extend this time. Helicopters don’t like this, even more as the droop stops are out.
One must always remember that if you do horse about with a helicopter, without regard to the stresses, that when you sign it off as serviceable the subsequent pilots and passengers who get into it do so with the belief that it IS fully serviceable. Who knows, when something eventually breaks, it may well be you in it.
Sasless is right in one way. There is no point in being a pilot if you cannot throw it around a bit to get away from the mundane routine. I do it still, although I should be old enough to know better. There was no shortage of Chinese co-pilots who want to come along with me on an air test. The primary rule is that there should be NO signs of protest from the aircraft. With this in mind you can go ahead and if you are the main attraction in a ball of fire and pillar of smoke on the airfield you can be comforted in knowing that the aircraft was fully serviceable when it crashed.