PCM Lockout question
 

Hi guys,

Two questions...

1. If a jet does a full pcm lockout snap roll at say, 150 mph[X(], how slow (in mph) do you guys/gals think the airplane will begin it's flutter down?.... 60 mph, 50mph, 40 mph??

2. If a jet was falling out of the sky at say, 20-30mph, and struck the earth at this same rate, do you guys think that the turbine, assiociated electronics and radio would mostly survive?

I'm just playing around with ideas...

When I say mostly, I mean not completely destroyed!:D, ie do you think the ecu/reciever/turbine/ maybe a servo or two would need minimal (Is $500 minimal?:)) costs to get back in flying shape.

I'm sure the airframe would be toast, but I'd like to know your opinion on these numbers.....

Thanks, I got my pen and pad out!

Raf

RE: PCM Lockout question
 

I don't know that situation #1 is even possible... According to my understanding of PCM, it will either hold the last good frame of data in the transmission, or it will travel to some predefined servo location upon losing the signal. To go into a full on snap roll in fail safe, either the surfaces would need to be preprogrammed to do so by the pilot (which may be dangerous, and very unlikely), or the user would command it to do a snap roll at 150 mph just before the lockout occurred (which is also pretty unlikely)... It sounds like you're assuming a PCM system will react to a glitch like an FM unit will, with random fluctuations at times. Someone will surely correct me if I'm wrong, but I don't believe the system will react like this.

Kelly

RE: PCM Lockout question
 

When it goes into full PCM lockout the servos will go to preprogrammed failsafe positions, ie. snap roll.

RE: PCM Lockout question
 

Another problem is that many jets won't even do a proper snap roll or spin, just a spiral.

RE: PCM Lockout question
 

I have always programmed my PCM to give me

1: throttle shutdown
2: Up Elevator
3: slight left aileron
4: gear up

in the case of a total lockout

RE: PCM Lockout question
 

KellyW,

It seems that most folks think that preprogramming a jet to go to "snap roll" deflections is the safest way to burn speed in the event of a pcm lock out, HOPEFULLY, decreasing the danger to onlookers and the pilot. See the rather large discussion regarding the recent deaths in europe...

Causeitflies,

So you don't think a jet could slow down to say 60 or 50 mph with those inputs?

Shok,

I hope you can't answer this, but....Have you had your jet go to these deflections upon lock out? And if you did, how much did your jet slow down? If you went to full left aileron instead of slight, do you think it might slow down more? What about a jet with an airbrake set to deploy upon failsafe?

Thanks again for the responses!

Raf

RE: PCM Lockout question
 

The problem with the "snap roll" failsafe settings is that you could well end up with a brief lockout that causes the plane to veer violently, perhaps towards bystanders (due tot he elevator/aileron settings) before control is restored -- which means the controls will now be at neutral and the plane will stop snapping and start travelling in a straight line again..

How many of us have the reflexes to then regain control and steer away before encountering the ground or an object on it?

Remember -- one second the model will be flying normally, the next it will have snapped to some wild angle/orentation. Your brain will have to determine the heading and apply the necessary inputs to correct it. I believe the average reaction time of even a good pilot will be significant fraction of a second under ideal conditions -- how far can a jet (even after some fraction of a snap roll) travel in that time?

There's no "best" setting for failsafe that will cope ideally with all possible scenarios and it's been my experience that momentary lockouts are a lot more common than total, long-lasting ones. If that's true elsewhere then the snap-roll failsafe setting could me even more dangerous than "last position hold".

RE: PCM Lockout question
 

I think it would slow down, but not as dramaticly as say my big aerobatic plane, which would slow to probably 10 to 20 MPH very suddenly and violently and rapidly decelerate to 0 even at a hight of 50ft.
Gear down, full flaps, speed brake out, and full deflections should slow a jet but depending on the plane I couldn't guess the final speed or how fast it would decelerate.

RE: PCM Lockout question
 

Xjet,

Have you read the posts regarding the 2 deaths in europe? I've had PCM radios since they came out and I have never (knock on wood!:)) had a lock out. And I am ok if this continues to be the case! I've only heard accounts of people having lock outs....

I am not trying to start a "whats the best way to set your failsafe" debate, I just want to get folks opinion regarding how much a model flying "fast" will slow down with this full deflection setting. I know many people are strongly opinionated and that is OK, I just want folks input on my question!:)

Mark,

Thanks. No guess to what speed? Think about how fast your jet is traveling when you land. (I think it is safe to assume most jets land in the 25-40mph range?) Do you think a jet would slow down to a landing speed?

Thanks again,

Raf

RE: PCM Lockout question
 

Mark, Silly question. Once the rx. goes into failsafe can it come back out? And if it does how long would it take?

RE: PCM Lockout question
 

As soon as a good signal is received it should come out.
I think the problem is that the PCM RX sees bad frames and copes with it very well until it just can't process it any more. At that point it goes into failsafe and usually doesn't come out because it no longer has those few good frames to fall back on. This is in layman's terms as that is what I am:D. At least with a PPM RX you should get some warning before it goes into failsafe.

RE: PCM Lockout question
 

Wow, sorry to have excited things... Yes, I'm well aware of the other thread. I guess I just misinterpreted what you were asking.

Not that I'm trying to start a 'best lockout option' debate either, but the only pre-programmed control surface deflections I use, and the guys I tend to fly with, is to deploy the speed brake and lower the gear. The rest of the servos hold the last known position. Its just my own preference to have the jet not change its trajectory unless I command it to do so. My reasoning is that if it were locked into failsafe indefinitely, it finds a way to increase the drag and lower the energy state of the model, while the model stays on a consistent vector such that any onlookers can easily predict its path. In a short burst of PCM lockout, it gives me a visual clue of the occurrence, since I may not think to have a look at the glitch counter in my ECU.

Unfortunately its just one of those situations where one can analyze every possible failure mode and never find a 'one size fits all' solution.

Kelly

RE: PCM Lockout question
 

Kelly,

No excitement here!:D

Any thoughts on how much a jet would slow down with those deflections? Please try to use numbers (ie mph, model weight, etc....) I know, I'm sorry, it may alot to ask, but it doesn't hurt to ask!

Raf

RE: PCM Lockout question
 

Anyone’s guess really...

Aside from the fact that virtually every jet will behave differently, you could try asking someone with an Eagle Tree Seagull system to mimic exactly the setup they use in failsafe, except manually operate the controls in the same manner. The only assumption is that an engine at idle would closely simulate an engine that's shut down since most guys would avoid shutting down the motor while in 100% control of the model. The seagull system would read out exactly what the velocity, g-loading, and altitude behavior would be in real time... (along with logging the change in trajectory via GPS if you wish!) That would produce some very interesting and valuable data, which I'd like to see if anyone feels like trying it.

Kelly

RE: PCM Lockout question
 

Darn good point!!

RE: PCM Lockout question
 

well not saying i do it a lot
but i get some repairs here and then from crashes but must say that most of them have no critical damages.
the worst i always seen when it was on fire then mostly you can trow everything away.
normal damages i encounter are:
exhaust bend , starter damaged , compressor damaged
most of these repairs are somewhere around 500-600 usd
here is a fire example:

RE: PCM Lockout question
 

I have flown Futaba 1024 PCM since it started and would fly nothing else.

A PCM receiver WILL return to normal once good data is received.

Test it on the ground...turn off the TX...failsafe engages...turn it back on ...it works again.

If it dosnt then you have another issue.

In flight when signal is lost the RX will drop failsafe much faster than the ground test of switchig of TX and back on again.
This because in that test the TX has to re-boot.
A better test is to have the model on the ground and have somone else stand along side with the same frequency.
When they switch on, failsafe engages, when they switch off conrol is restored instantly.

My preference is Throttle to low..all other controls hold. This is also the recomondation of the UK JMA.


Paul

RE: PCM Lockout question
 

How much the airplane slows down would be dependent upon the size, total amount of surface deflection, and aerodynamic characteristics of the aircraft. Each one would be different.

Take note: I believe the snap-roll fail-safe setting is the best choice scenario in the case of a fly-a-way full lockup R/F link failure, per how the majority of our model aircraft are equipped today!

Thinking about the tragedy that occurred most recently. Understand a snap-roll fail-safe setting... precludes the availability (some day) of some sort of on board parachute deployment safety system.... similar to some that are available for full scale aircraft today! I believe the parachute auto deployment system would be the best of all worlds. It could react within one second of R/F link failure and conceivably be the best and safest system!

There is nothing new about REQUIRING a fail-safe setup, as it was required for many, many years by the AMA for all Experimental Class aircraft. The snap-roll idea is not how slow the aircraft will be going when it hits the ground... but rather that it WILL NOT wander off out of the (safe flight area) and hit someone! The aircraft is going to hit the ground ASAP! Minimum wander time, if you will.

Yes, there are several other R/F link failure scenario's, examples might be short one or two second failures, intermittent and shorter... ect., ect. The one scenario that is all of our nightmare, and is the one we should program for is the total loss fly-a-way! You must understand that is the scenario that can most likely put people in harms-way! To heck with all of the MY MODEL comes first folks.

The snap-roll fail-safe setting has little to do with how well the aircraft survives the crash... rather that the model aircraft crashes quickly.... out in the safe flight zone!
Lee H. DeMary
AMA 36099

RE: PCM Lockout question
 

Actually no I have never been in a full PCM lockout before, knock on wood.

RE: PCM Lockout question
 

Yep, under ideal conditions it will come right back but usually when there is interference conditions aren't ideal. A good test is with two radios as you said.

RE: PCM Lockout question
 

I have actually seen the snap-roll fail-safe work very well.. in fact it was several years ago while our flight demonstration team was flying the noon show at a full scale Airshow. My airplane luckily was not involved and because of that fact, I got a good look at how it all came out.

At the time of the lockup we had three airplanes doing circuit fly-bys and mixed septate aerobatic maneuvers. All of a sudden one of them did in fact began a continous snap-roll while climbing out turning downwind. We knew imediately the pilot had lost control! Within no more than 7 or 8 seconds the airplane screwed itself in out in the grass/dirt. We never did find out what caused the fail-safe condition.. but clearly we all became convinced this was the safest way to configure airplanes flying in flight demo's. Mind you this had to of been 12 years ago if it's been a day!

Today I am convinced this is still the safest possible configuration...state of our technology being what it is...the only problem.... and it's a BIG PROBLEM is that at least 75 to 80% of the radios flying today can't be set safely to fly with the snap-roll configuration!

A requirement of the radio is that it's software will allow a 1 second delay or HOLD condition before going to the snap-roll condition. JR's earlier 10 channel radios had a fail-safe feature that would allow the user to set the time delay before surface activation. The later 10X radio transmitting to an S-mode receiver does not have a delay feature. In fact there is NO time delay before activation. Can you see why no one with this type radio wants to hear anything about fail-safe settings other than HOLD...

In fact my two turbine aircraft are controlled using Futaba radios just for this reason! Futaba has for years built-in a 1 second time delay before activation. This means the interference has to last 1 second or more! In providing this delay feature Futaba has thoughtfully allowed the use and setting of a full snap-roll safety system.... or for that matter the safe setting of virtually any fail-safe seting. Caution: do not set fail-safe surface deflection if your radio does not have the time delay feature!

As I have mentioned several times before the reason the turbine manufactures have a time delay feature within the ECU is to allow a shutdown fail-safe setting required by AMA for turbine use! Yep, the most widely used radio the JR 10X would not be usable.... in the turbine world if the turbine ECU did not have the time delay feature included within it's software.
Lee H. DeMary
AMA 36099

RE: PCM Lockout question
 

Lee, Wow that is something I did not know. You explained that very well. Something to think about when buying a new radio.

What are you views on a parachute system deployed with a fail safe system?

RE: PCM Lockout question
 

Air mail rcu,
I believe the parachute system could be the best of all worlds... If the AMA were to decide to again require fail-safes to be activated.... for say all aircraft weighing over 20lbs for starters....the technology could be worked out and I believe the parachute technology would be an easier pill for everyone to swallow.

Actually the full snap-roll setting seems a little scary, but when implemented correctly is very much a confidence builder and I believe a vast improvement over all safety.

In fact the range checking and correcting required to ensure a solid R/F link, the heighten diligence in all aspects of operation, i.e. double checking possible impound problems, scanning for outside interference especially at unknown fields all contribute to safer flying. Another hidden benefit is that it makes you more conscious of sustained flight directions, sensitizes your perception of distances from ramp / spectator no-fly zones, and last but not least improves awareness of the designated flight area itself. The biggest drawback to a wider acceptance is that it does require a radio with time delay feature in the radios fail-safe software.

Again with good engineering the parachute system could certainly be a very effective fail-safe system. I could see the chute system with it's own built-in time delay allowing one or two seconds of motor kill and speed reduction before deployment. I could see the chute fully deployed within 3 seconds of R/F failure if designed properly.
Lee H. DeMary
AMA 30699

RE: PCM Lockout question
 

Lee, I couldn't agree with you more. Thank you for such a great explanation.

RE: PCM Lockout question
 

Lee,

When you saw that airplane snap to the ground, it sounds like you think a parachute would have saved it. Is this true? Did it slow down enough that a parachute would likely slow it's descend to earth vs tearing the model to shreds because of the high speed?

Thanks for sharing!! I also am a futaba guy!

Raf