The Demise of Autorotation

[Rotor Rooter]

The Comanche RAH-66 helicopter's flight control system is fly-by-wire with triple redundancy for safety. It can be assumed that this electrical triple redundant system meets and probably exceeds the reliability of conventional mechanical control systems. This being the case, it appears that a triple redundant fly-by-wire of only the collective portion of the flight control system should have a reliability that equals or exceeds that of the much more complex one in the Comanche.

Helicopters with two or three engines have a significantly reduced probability of utilizing autorotation. In fact, the twin-rotor Osprey V-22 is incapable of safe autorotation. It is claimed that electrical motors have a reliability that exceeds that of internal combustion engines. Therefore, it appears that a triple redundancy in the power system of a helicopter that utilizes electric motors, will meet and probably exceed the reliability of multiple internal combustion engines. In addition, the power from helicopters with two or three motors comes together in a single gearbox to drive the rotor(s), where as a 'slow-turning motor does not require a gearbox.

The stored electrical energy reduces as this energy is consumed. By reading this reduction, the control system is able to advise the pilot of the impending 'brownout' and then shortly thereafter force the pilot to the ground by automatically reducing the available energy. Before the flare the pilot will activate small ultra-capacitors on each circuit that will provide full power for the actual landing.

__________________

Without the need for autorotation, the size of the rotor-disk(s) can now be downsized to suit the requirements of a simple but responsive, weight-shifting, absolutely rigid, rotor system, while maintaining a reasonably disk-loading. In other word, an electric version of Frans Schoeffman's helicopter that can safely go as high and as far as the pilot wants and the batteries will allow.

The forgoing is in support of the belief that recreational rotorcraft have a bright future.

[brett s]

The V-22 isn't a great example to make your point with, it was supposed to be capable of doing so - when it became obvious that it couldn't they just quietly dropped the spec. A combat rotorcraft in particular that can't autorotate is insane, over a large part of it's flight envelope a dual engine failure is fatal. Like where it's most likely to be shot at in the first place, in helicopter mode when arriving or departing an LZ...

I'm personally not interested in a civilian rotorcraft of any sort that can't either, while the odds of all the holes in the Swiss cheese lining up might be very high it'll happen sooner or later (I'd suggest in a recreational rotorcraft built by amateurs it'll be far more likely than in a certified ship too) - and unlike an airplane, you don't have wings to glide with when it gets quiet. BRS will help in some parts but it needs altitude, it's not a cure-all here either.

[Rotor Rooter]

Brett,

Your points are very valid. However, there is no vehicle that is 'absolutely' safe. The objective of the above is to provide a VTOL craft that is significantly safer than any existing, or currently contemplated, rotorcraft.

R/C motors and Electronic Speed Controllers exist now that can provide triple redundancy, and "When Ni-Cd batteries approach the end of their charge, voltage falls drastically and quickly. The 'future-l series' detects this and reduces the power to the motor automatically. This should leave sufficient energy to bring your model safely back home."

Electric motors are being developed for in-hub automotive applications, which eliminate the need for power transmission components. And, this eliminates the major S92 problem ~ 30 minutes operation without oil.


IMHO, 'Thou must have Autorotation' was never cast in stone. It is a belief that has existed because until now there has never been a meaningful life-saving alternative.


Dave

[brett s]

Stuff happens - even modern multi-engined transport category jets can lose all engine power in flight. It's happened more than once...and not just from running out of fuel.

When the alternative is turning into a tumbling brick with no hope of survival, I'm not giving up autorotation.

I can't think of any other certified or military aircraft where a total power loss within much of the normal flight envelope would result in a uncontrollable/unsurvivable event (other than the V-22 in helicopter mode!) that doesn't have a crew ejection system of some sort.

[StanFoster]

If my rotorcraft wont auto....I am going to stay on the ground in my auto!


Stan

[Rotor Rooter]

Originally Posted by brett s

I can't think of any other certified or military aircraft where a total power loss within much of the normal flight envelope would result in a uncontrollable/unsurvivable event (other than the V-22 in helicopter mode!) that doesn't have a crew ejection system of some sort.

Here is one from earlier this year. Sikorsky S-92, 17 dead.



Brett and Stan,

Remember that the bar in rotorcraft safety is not exceptionally high.

You will become believers.


Dave

[brett s]

The S-92 event was a catastrophic transmission failure, not engine failures - something generally not survivable in any helicopter no matter why it happens, and only occurred here because the pilots disregarded the RFM procedures after losing oil pressure. That was a fatal assumption...

Which you already know if you read that thread...no other helicopter designs would fare any better with a similar failure, including yours.

[Rotor Rooter]

Originally Posted by brett s

The S-92 event was a catastrophic transmission failure, not engine failures - something generally not survivable in any helicopter no matter why it happens, and only occurred here because the pilots disregarded the RFM procedures after losing oil pressure. That was a fatal assumption...

Which you already know if you read that thread...no other helicopter designs would fare any better with a similar failure, including yours.

Brett,

I politely beg to disagree.

Previous to the crash, I read the PPRuNe threads on the subject of S-92, the regulation, and its 'adjustment', that related to the allowable flight time after losing oil pressure. Following the accident, I read the earlier portions of the two long threads. One of which is linked to above. There was much discussion among the pilots on this subject, however I have no desire to get close the legal situations that may arise from this incident.

On the subject of autorotation, perhaps the lead post in this tread did not emphasize strongly enough "a slow-turning motor does not require a gearbox." The presumptuous objective of this thread is that of eventually antiquating the subject of 'autorotation', IF, it can be assured that VTOL craft have sufficient stored energy onboard and that they have an extremely reliable means of transforming this stored energy into controled aerodynamic thrust.

IMHO, a reduction in the 'part' count and an increase in the reliability [Deconstruction] should 'theoretically' be a route to safer rotorcraft.

Dave

[brett s]

S-92 RFM says "land immediately" if oil pressure hits zero, which it did.

Not ambiguous at all, unlike the FAA certification requirements or Sikorsky marketing material that the pilots may have thought meant they had 30 minutes dry run time.

A "slow turning motor" must still be connected in some manner to the rotors - maybe less gears, but there's always something there that could potentially break. Unless you mean for the motor shaft to be the actual rotor shaft, but even then you still have to allow for what happens if the motor seizes. Ever see a brushless motor throw a magnet & lock up? I have...

[Rotor Rooter]

Brett,

Unless you mean for the motor shaft to be the actual rotor shaft

Basically, yes. The objective is to have the 'so-called mast' be part of the motor's stator and be stationary. The motor's rotor will be directly coupled to, or be in integral part of, the blade's rotor. This is the reason that I am contesting Sikorsky's patent application.

but even then you still have to allow for what happens if the motor seizes. Ever see a brushless motor throw a magnet & lock up? I have...

There is no argument with your comments. The positive is that retention of the permanent magnets is probably the weakest link in the system and knowing this allows for an extremely high safety factor to be applied. For example; The permanent magnet will consist of a Halbach Array and with no need for a steel backing it should be possible to embed the magnets, complete with their tabs, in a strong composite constructed containment ring.

Dave

[EI-GYRO]

And sure if the electronics dont notice the impending brownout,
you'll do a 'brownout' of your own when it all goes quiet.

[Rotor Rooter]

EI-GYRO

No sh.it.


Don't laugh, I'm serious. This is all covered in the operating manual.

The pilot actually farts. At the same time, he grabs the Bic lighter off of the dashboard, takes it down below his seat and ...... jet assisted landing.


Tomorrow's project is that of electronically maintaining synchronization of two Intermeshing Rotors.


Dave

[Rotor Rooter]

Brett,

Your constructive criticism is much appreciated, particularly your last post that questions the adhesion of permanent magnets.

The initial prototype of the Electrotor Project was intending to use two, or possibly three, large model electric motors to drive through a mechanical transmission. There was no intention to add to the complexity by including overrunning clutches.

The likelihood of one of these motors failing is quite high, and with three motors it is up to three time as likely. The time and monetary loss of an accident while under remote control, and, the human danger of being tempted to man the craft for a flight within the envelope used by Frans Schoeffman are too high.

The objectives of the project will continue to be pursued, but at a more methodical rate.


Thanks again.

Dave

[StanFoster]

Dave- I find this thread interesting..so please dont take my comment about staying on the ground in my auto personal. Even though I wouldnt want to fly without the capability of an auto, watching others go through the thought processes, then the mechanical processes of doing such.....then trusting all that....is fun to watch. The fact that there is that video of someone flying one of those makes it fun to watch him achieving his goal. Watching is about as daring as I will get.

Keep on thinking and posting...these threads get a lot of hits.


Stan

[Rotor Rooter]

Stan,

Your comment is not taken personally. Even the funny ones are allowed to convey a subtle message.

As for the elimination of autorotation ~ this is one of the objectives.
It has jokingly been said been said that; "A helicopters is 10,000 moving parts all trying to kill you at the same time". It must be possible with new technologies to reduce the large part count (etcetera) to the point where the increased reliability results in the safety exceeding that of existing craft, even with their ability to autorotate.


(etcetera) is intended to also include reducing the piloting demands.
Wasn't it the automatic transmission that allowed women to drive?



Dave