Fail Safe

[ChrisB]

Safety is of course number 1 priority,with no drive,the blades whether held at positive or negative will slow very quickly,then you have a heli doing an impression of a brick,zero pitch will hold some headspeed,you still have time to shout a warning,the heli is losing energy during the process and hopefully control can be regained with some inertia left in the blades,if it does go in and the blades are still turning so what,the main thing is to have no drive to them.

I agree that there is no right or wrong way you could have an instance where a heli is travelling towards a car or something and it goes into failsafe,pitch is held at its current position and the heli quickly loses lift and falls hitting the car where as if it was at zero pitch it would sort of float along and go over the car missing it.

You could easily reverse this situation where it floats on and hits the car instead of falling short and missing it.

I will continue to use both PPM and PCM,i think we all do our best to minimise problems,modern radios are very reliable,i only use JR Rx`s with my JR Tx,i make sure my radio is in as good a condition as possible and try to ensure that good frequency control is practiced at the flying field,if a hit happens be it with PPM or PCM the answer is to land asap and find the cause..

[jimbob]

with some inertia left in the blades,if it does go in and the blades are still turning so what,the main thing is to have no drive to them.

Have to disagree with you there slightly...

Scenario a) man throws non head-rotating heli at you as hard as he can...

Scenario b) man gently tosses 2000rpm heli to you...

Choose....

You say 'the blades are still turning... so what' well the 'what' is the amount of inertia (energy) still in those turning blades. I'd rather a heli pile into the ground next to me with the engine at full but no head speed than visa-versa...

[Ade_Law]

he has a point actually....

chris, remember jon mann's heli that you walked into at idle? <doh>

Ade

[ChrisB]

Jimbob,

I was referring to the amount of damage the model would sustain itself in that instance,i meant i have put them in at full power and seen them destroyed as opposed to little or no headspeed,i dont intend to put any of my models in near a person or their property,if i did i would sell the lot of them.


Ade..

I still have the scar ,that reminds me why i dont like black blades,now i tend to let the rotor speed decay naturally as opposed to leaning in and pressing down on headbutton,as with most things in life we learn by ours or others mistakes,i have an awful lot of respect for them blades

[jimbob]

Didnt mean to suggest you would do anything untoward Raptor50, just making the point about the energy stored in a rotating head.

Regards leaning over black blades, I made my flying mate put some stripes on the ends of his Carbon 90s before I would help him with it anymore . You just could not see the disk spinning, and got a shin brushed when stopping it one time - that was close enough I reckoned and I've got long arms!!

[ChrisB]

I just re read my post and i didnt make it very clear what i meant...

I had an NHP whallop my shin...bled for 15 mins...ouch

[mchristyuk]

Probably a bit late to this discussion but a few pointers from past experience...

Many years ago I was running a stock Xcell 60 with a wrap through magna pipe that was all the rage in the early 90's. During some hovering practise the model failsafed owing to the exhaust chaffing against the aerial tube and through to the wire. The model was setup to centre the sticks and 0 degree pitch.

The way the model moved was shocking. Consider your model normally hovers at around 6 degrees.. going to 0 is around 50% of your positive pitch changing in a split second. The model shot earthwards very fast and luckily the sturdy tuff strut undercarriage stopped any serious damage.. either way an alarming situation!

If you were to put your pitch to maximum positive or negative then the rate of acceleration would be huge. If a 60 size model can hover for around 4 seconds at the bottom of an auto then the inertia is enough to cause the model to travel a long distance in a short amount of time. A model at hovering head speed on the ground can easily take off and fly quite a distance with out the engine powering the blades...

When you are flying around you are generally loading the rotor system in some way with either some positive or negative pitch. Therefore I always set the engine to idle and the controls to hold their last position just like Ade says. This means there is a load on the disc and no engine power to slow the rotor RPM.. but crucially (see my 1st paragraph) the model makes no sudden lunges one way or another.. when these things happen you are generally suprised and have maybe a maximum of a couple of seconds to notify people.. so the more predictable you can make the model the better in my opinion...

Cheers

Mark

[Raptorite]

I agree with Mark and Ade on this, I too was of the opinion that a good failsafe setup is pitch to 0 degrees, cyclics and tail to neutral, governor off and engine to idle.

However, my opinion of this changed last year when I experienced a lockout on my 90, fortunately it was right at the end of a tank of fuel and was only hovering about 3 foot off the ground when the crystal failed. The model went into failsafe, and as Mark has said it was a very startling event, the model simply plummeted to the ground at a terrific rate of speed. So much so that it broke the skid set, but did manage to avoid any other damage.

I am now of the opinion that a good fail safe setup is engine to idle, governor off and all other controls to maintain last position. Unfortunately this was proved to be successful earlier this year when the predator turbine locked out on me in flight.

I was at the end of a circuit, just banking it round a left hand turn to bring the model back across the field when it locked out. The turbine was set to shut down, which it did straight away, displaying the tale tale puff of smoke which they all do to signify a flame out. As the model was banked over to the left, it carried on going on its last course, continuing around the bank. The nose of the model slowly dropped to a nose down attitude, as I was obviously unable to maintain up elevator to keep its nose up. As the model was only 50 or so foot up at the time it didn't take long to impact with terra firma, which was an inevitable consequence of the lockout. Even so there was a good 2 or 3 seconds between the time I first noticed the lockout to the time it impacted the ground, which I would consider enough time to make other people aware of the situation had there been anyone around at the time.

So I suppose you could say I have tried and tested both schools of thought as far as failsafe settings go, by far and away the best one in my view is the engine to idle and all other controls to hold last positions.

Cheers,
Pete.

[ChrisB]

All my Rx`s are JR ZPCM i could only set a fail position or hold for all channels and i did not want to hold all including throttle


SPCM allows individual channel selection so holding all controls apart from throttle would seem to make sense having given it some thought..