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.

http://www.unicopter.com/Austrian_Coaxial_Propellers.jpg


The forgoing is in support of the belief that recreational rotorcraft have a bright future.
http://www.unicopter.com/lightbulb%20idea.gif

[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]

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. (http://www.pprune.org/rotorheads/365720-helicopter-crash-off-coast-newfoundland-18-aboard.html) Sikorsky S-92, 17 dead.



Brett and Stan,

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

You will become believers. :D


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]

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 (http://www.rotaryforum.com/forum/showthread.php?t=21649&highlight=Patent). 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 (http://www.unicopter.com/1530.html) 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. :yo:


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

[brett s]

I freely admit I'm a chicken & am pretty picky about what I'll choose to fly these days, was different 20 years ago :)

Making helicopters safer, reducing parts count & complexity is great - why is eliminating autorotation a major goal though? It's just another tool that might come in handy someday since there will never be a 100% reliable powerplant.

I'll take a total power failure in a helicopter over anything else flying, no matter what I've got to land it on.

[EI-GYRO]

A possible compromise might be to have two pitch settings available, much like
the A&S 18-A. Arrange the rotor drive to apply positive pitch for powered operation,
and default to a lower pitch for autorotation in the event of power failure.
In my view (blinkered) all helicopters should automatically de-pitch the blades
in the event of power loss. At least a few helicopters have been lost through failure to drop the collective quickly enough.

You want to simplify choppers, fair enough, but you dont actually WANT to eliminate
autorotation. You want to eliminate its complexity, which is a different thing.

A helicopter is made of anti-social parts, all trying to leave the scene of the accident.

The more I learn about helicopters, the more I love autogyros.

[brett s]

There are times when reducing the collective in a power failure isn't the right thing to do & will guarantee a crash - like when hovering in ground effect.

There are times in fwd flight where you might not reduce it immediately, or not very fast - high speed/low level comes to mind (to keep from either whacking the tail or contacting the ground before you get it slowed down), you'll trade some speed for altitude & use that energy to maintain rpm as well. You can delay dropping the collective several seconds that way, energy is your friend.

[StanFoster]

Brett- I liked your explanation of high speed /low altitude use of the collective. That of course is the bottom area of the grey area in the height/velocity curve to minimize activities in. I had asked my instructor several times about doing such....trading speed for altitude..but never had your input.

Thanks

Stan

[EI-GYRO]

Points taken, Brett, but my thoughts related to preserving the pilot rather than the machine.
Either way, it would be better then no autorotation available, which was the proposed
alternative.
I dont think the Feds would ever approve a passenger-carrying aircraft with no glide
capability, for civilian use, so the point is probably moot, anyway.

[BEN S]

looses its ability to fly they don't glide so well or autorotate, but they are approved for civilian transport.
Ben S

[EI-GYRO]

I was wondering if some smartass would come up with that, but decided to leave it open
anyway. Well done.

[brett s]

The difference is a blimp also doesn't lose it's ability to fly when the engines quit, just like an airplane or helicopter. You just can't choose exactly where you're going at that point, it won't plummet out of the sky.

If it has an envelope failure that's the equivalent of a major structural failure in a plane or helicopter, with about the same results.

[Rotor Rooter]

OK, you guys are ganging-up so it's time for a little confession. The objective of the Electrotor is not that of eliminating auto-rotation. The objective is to eliminate the need for autorotation.

The objective is to develop a recreational rotorcraft that significantly exceeds the attributes of existing recreational helicopters, by;
~ being much easier to fly,
~ having a reduced complexity, weight and cost,
~ requiring less maintenance,
~ being easy to transport,
~ and of course, being safer to fly.

A primary means of doing this is to reduce the large number of "anti-social parts". To reduce this friction between parts, the Electrotor-SloMo may have only three parts that wear.

~ One large 4-point ball bearing takes the forces and moments of the CW rotorhub AND the integrated rotor of the electric motor.
~ One identical bearing does the same for the CCW rotor & motor.
~ One spherical rod-end bearing hangs the fuselage from the rotor assemblage.
That's it for mechanical friction and wear.


A simple 2-position pitch, which automatically operates by a torque-pitch coupling, is being considered, however the objective is to make it superfluous by eliminating the ability to loose all primary power.

The rotors are to be relatively small, light and extremely rigid so the simplistic and logical action of weight shifting allows the pilot to get quick responses to his actions. However, these rotors will be unable to store any rotational inertial for use during landing.

Here is the proposed solution to the above two auto-rotation concerns;

Loss of power at altitude: ~ Upon loss of all power the 2-position collective will automatically drop to the autorotation position, due to a torque-pitch coupling. The throttle will be located in the 'LOW' position. Just before landing he will flip the Emergency Power Switch to 'ON', which will then allow him to provide emergency power for lift to decrease his descent rate, flare and touchdown.

Loss of power near ground level: ~ When setting up for a conventional landing the pilot will also flip the Emergency Power Switch to 'ON'. This will allow the emergency power to automatically come in to effect, at the current setting of the throttle, plus an announcement warning alarm to sound, if the primary batteries fail.
The above two lines suggest that the Emergency Power Switch should be 'ON' whenever the craft is < xx ft AGL and off when > xx ft.


Dave

[Rotor Rooter]

This is the drawing of the rotorhead that was described in the preceding post.

The only moving parts are;
~ the 2 counter-rotating rotors (c/w the rotating portion of their motors), and
~ the gimbal to the weight-shifting fuselage.

Simplicity = Low weight & High reliability & Low cost & Low maintenance & Easy piloting = High safety. http://www.unicopter.com/Pray.gif


http://www.unicopter.com/1031WithChanges.gif

[Rotor Rooter]

Safety;- When too much results in too little. http://www.youtube.com/user/itw2931

:eek: