Anwar,

You sure passed the jinx on!! Two mishaps in two days..

Saturday :

Landed my Yak and it cleared me and I turned to the right to see my friend waving a car away from the runway... Ran into him and the wing hit him on his leg... Lucky the plane was slow at the time.. Even then, I broke the carbon fiber wing tube and also the fuse part where the wing sits!!

Sunday :

The jinx continued!! Let me say that it was a spectacular crash (and really dangerous as well)!! My Funstar is now resting in pieces.. One of the other flyers (flying a Pitts on PCM) had a lockout and nose dived from more than 50 feet height!! I also had a lockout whien flying my Funstar at full throttle at the same spot!! My plane turned towards the runway and came straight at me at full throttle.. Nothing worked on my radio and I started shouting for the crowd around me to run!! It crashed onto the tarmac on the opposite side of the runway and one part of the wing disintegrated there.. The fuselage came like a torpedo scaled the whole breadth of the runway (must be atleast 20 meters), missed me by a few inches and went under my car, came out through the other side and travelled another 15 to 20 meters before resting!! The fuselage was in almost 3 pieces, one portion of the wing disintegrated, the engine (a brand new ASP .52) had taken quite a beating but would live to see some more flights, the Rx was intact, the Lipo (though hit) survived, the BEC is totally ruined and the servos survived!!  Dumped the plane on the field itself!!

I was real lucky that it did not hit anyone!! Gave me quite a jolt to think of the impact on a person or someone else's car!! The fuse travelled like a torpedo and sailed under my car!! It went so fast that I was not even able to see it!! 

And let me tell you guys.. I fly Futaba 2.4 Ghz.. First time I am having a lockout issue with 2.4Ghz!! And I had taken all the precautions against heating and antenna orientation.. Moreover, the Lipo voltage after the crash was more than 12.5V!!

Time to do some investigation!!

- Chan

Chan,
  Regarding the YAK, how come the CF tube broke? Does this plane have CF tubes as wing joiners? Then it makes sense that it would have broken through the balsa structure.

Reg. the Funstar - that was a great looking plane - in the photos posted on IndiaRC. But isn't that a lot of useful scrap balsa thrown away    Which can be useful for at least repairs of other planes. I've never thrown away balsa - especially when you consider the local price

Anyway, the analysis of this lockout should be pretty intersting. Planning to get a 2.4 system myself, so interested in knowing what fails these systems!!

Sorry to hear that   

Are you sure you had no control over any of the surfaces ?  Did you have failsafe set ?

Most importantly, how much of "plugging in" do you do (for example, if you move receivers around) ?  Loose contacts/connectors is something overlooked easily.

How many people were on the field ?  How many 2.4 systems ?  Did you establish why the 72Mhz guy crashed, was there a true frequency conflict with another flyer ?

I can understand Shabir having a crash  as he was on the good old radio  like mine  .
But  lock out on 2.4G guys its not supposed to happen 
I understand Meenakshi also had a problem of the throttle moving to max when he lost contact with his Futaba twice before , this is scary , I would assume if the receiver were to reset the throttle should not get onto full 

Sai

Throttle position on receiver losing contact with the TX for whatever reason is a function of setting failsafe (or default failsafe). "Failsafe" itself is a topic for another thread.

Unless we know it is a 2.4 lockout, we are speculating. The chances for a 2.4 lockout are pretty rare, but not impossible.

Oww.. sorry for your loss.

Looks like there is too much of RF activity in Sholavaram that even 2.4G is no good!. Its ironic that I have never felt a glitch when I flew in Sholavaram. I was using my good old 72MHz 8UAF (Ch 54).

Ya. the sight of an ariplane ploughing directly to you & your car should be terrifying. I remember when one of the flyer at sholavaram lost orientation flying directly into the sun. The next moment he realized that the model has turned some how and is directly descending on to the run way where the cars were parked. At that moment, I was enjoying my red spitfire and was not looking at this charging missile.  All I heard was a nice engine doppler sound and sound of the aircraft's wing tearing the wind... at that moment i knew something is wrong but have no time to react!... Next second is a loud impact and I could see shards of balsa busting off on impact - just 15 to 20 feet from where I stood.!!.. Man, that was scary!.

-Ismail

Nope, the sight of a 50size (or larger) heli coming towards you with those 600+mm blades going 2100rpm is better  

Ask me how I know ?   

in both cases it is $$$$$$$ in the air I guess Anwar is right the sight in the case of the heli would be more terrifying  or satisfying depends on the way you look at it for obvious reasons 

Its always a delight looking other people's carnage!!..   

Sorry to hear about the crash .. It is a matter for worry for everyone, since this occured with your new 10C .. Now i have the same, and we are planning to use it wit hthe gasser .. So need to really test out the Rx/Radio with cheaper models before installing them into these $$$$$ laden airplanes.
-Gaurav

It will not prevent your model crashing, and will not surely make you less sad if that happens.... but for the record, I fly fully loaded Trex 500 and 600 helis using 2.4 

And couple of months back, I test flew a co-fliers Vario Bell turbine scale heli (1.7meters) on a Futaba 2.4 system.  That is like 12x the cost of what I fly   There was no throttle range control, just pitch to control the ascent/descent.  And my friends were making fun of me saying you should start logging your hours on turbines, like the real pilots do !

The CF Tube is the wing joiner as you have correctly infered.  Yeah.. but I have too much of useless balsa with me and I didnt want to junk up my place any more.. Asked if anyone wanted the scrap, then threw it off!!


It was definitely a 2.4 lockout since I did not have any control over the surfaces.. Failsafe was programmed correctly and it also did not kick in!!  Failsafe was set to 20% of throttle and the crash happened at full throttle.. First thing I did after the lockout was switch on the throttle cut swithc!! Still no cut in engine!! My Rx Lipo was fully charged and was checked even after the crash!! But shoud do a detailed research onto how and why this happened!!

- Chan

To me that seems like there was loss of power. You BEC should be the suspect. If it was loss of signal, then failsafe should have kicked in.

That brings up an interesting point. Do you use a separate BEC, or you use a builtin one in your ESC ?

If you use a separate one, most of them are rated for 2s lipos, and it looks like you were using a 3s pack.  Wonder if that is a factor.

And most importantly, I see every where people not trusting 2.4 because of "rare unexplained crashes", while they conveniently ignore that non-2.4 crashes happen all the time (many times on the same day at the same field) due to a variety of reasons (lock out, frequency clashes etc etc).  Isn't it logical to conclude that even in the worst case 2.4 is at least as safe as non-2.4, and in the best case it is many times safer ?

Maybe yes... but if it happened once I would have accepted your comment!! But 3 times on the same field on 2.4 Ghz cannot be attributed to power loss (there were other incidents too)... And why did it happen at exactly the same place where the PCM locked out?? I have used this BEC with the Lipo for close to 7 months without any problems...I have also found that 2.4Ghz is susceptible to mucrowave interference and this has also happened in Bangalore to 2.4 Ghz flyers too!!




I use a separate BEC.. This is compatible for 2s to 6s!! And moreover I have been using this on 3s for almost 7 months!! I would never say that 2.4 is unsafe!! This is the first time it has happened to me though I had taken all the precautions!! I knew about this technology quite a bit and hence it is not the regular "Voltage was low" / "Heat issues"!! There was something else yesterday which created a mess out of my transmission and I would have to do some research into what that might be!!

That Bermuda triangle in our field has existed for a long time now and mine is the 7th or 8th plane to go down at the same spot!!  Though mine is the only 2.4 plane that went down!!

- Chan

May be it is the temperature affecting the  FASST as mentioned in this article  posted earlier by Saju reposting it for immediate reference .
The article also says it has not been addressed by Futaba.
May be this explains the problems with FASST that have been experienced here .
Sai

Yeah heat is definitely an issue with 2.4 Ghz.  But it is mostly in cases of planes with clear canopies!!  The Rx gets heated up in the sun!! I take care of mounting my Rx in a cool spot in the fuse and I take extra special care not to park my model in the sun because I was aware of the heating probs!!  My bet is still on the microwave transmissions!!

I would also go to the extent of saying the other 2 Futaba 2.4 lockouts might be because of heat issues because the Rx was wrapped up in foam which is a big NO-NO!! That totally cuts off heat dissipation! But mine was free from all that!

But still, if not the microwaves, then my next suspect would be the BEC failing!!

- Chan

Chan

I think Saihe nail has hit the nail on the head. The problem as described in the article occurs at  or near 120deg F i.e 48 deg C. With temperatures here (at Sholavaram ) going close to 38 to 39 deg C, and taking into consideration the heating up of the individual transistor in the receiver by itself when powering servos, it is but anutural feasibility that this is the cause of your problem... This is then inspite of the fact that you have taken due precautions to shield the receiver from the Sun as well as provide a cleared up space around the receiver ( no wrapping in foam!). The article also mentions that some individual users have taken to providing a cooling fan on the receiver to avoid this issue. Maybe, what you have to do is to see that there is sufficient  cool air-flow directly onto the position on the reciever that heats up (where the hot individual transistor is located).

Saju

I find it hard to attribute it to heat.  The chip in question that has the heat tolerance issue is rated for 60C.  I can't imagine Sholavaram temperatures plus the ambient heat due to heated air inside the canopy together going over that, as Chan flies earlier in the day.

Here is Futaba's best practice instructions on this :

http://2.4gigahertz.com/features/receiver-tips.html#air

Anwar

I believe you have mis-understood me... What I am saying is that the power draw by the servos could heat up the power device used in the receiver. Since it is placed in an enclosed space, the heat does not dissipate off easily. In the article (I am attaching a pdf form of the same article for your benefit) under the heading "How to Get the Best Performance from Your 2.4GHz FASST™ Vehicle Receivers", it is mentioned as quoted below:

"  We also recommend that you mount the receiver to the far inner wall of the radio box, opposite of the engine. Mount the receiver on its side. This allows air to flow over the top and bottom of the receiver. Secure the receiver using Velcro® or gel tape.
Tip: To improve the cooling airflow in your radio box, try drilling a few air holes. You must have at least two holes so air can escape as quickly as it enters. Position the holes where they create the maximum air movement over your receiver."


It clearly shows that air flow over the max'm area of the rx is recommended. This may not have been the case with Chan's model and could have resulted in the crash

Saju

Saju -

The same portion you quoted is in the link I posted above too    I did take what you suggested into account, and still feel that heat is most likely not the culprit. 

Waiting for Chan to confirm the time of the day when this happened.  If it is in the morning, I just feel it is highly unlikely a heat issue.

BTW, we are just investigating something together, and this is just a open discussion.  I value your input with the utmost regard/respect.

I think there could be different reasons affecting the 2.4GHz and 72MHz.

Heat: Doesn't explain why the 72MHz rx were hit.

Interference: I don't find the interference theory convincing. It is unlikely that there is wideband interference over the whole range from 72Mhz to 2.4GHz. If the signal is very very strong it is possible (though highly unlikely) that the pcb traces inside the rx is picking up inteference and is affecting baseband directly. If there is such a strong interfering signal, it should be easy to detect it on ground where the glitches occurred. The reason I think it should be observable at ground and not just up in the air is that the 72MHz rx (where there is virtually no reboot time) should have recovered as soon as it was out of the interference region. Since the planes didn't recover all the way to ground, it should be detectable at ground. It'd be more believable that the 72MHz went down because of interference and 2.4 because of other reasons.

BEC: Doesn't explain the glitches on planes without BEC.

And I never heard of 2.4GHz interference in Bangalore. Where did you see that ? I know the corona MHz range receivers and hitec receivers have been hit at specific locations. I have never come across any interference using Futaba PCM and FM receivers.

Anwar

With all due respect... Let me explain my experience in an unrelated topic on similar lines. For this I have to bring my work experience into play:

We manufacture hydraulically operated injection moulding machines. The hydraulics is based on very sophisticated electronically controlled axial piston variable displacement pumps with integral electronics. The pump is driven by an induction motor (size of motors range from 11kw to 74 kw). This induction motor has a fan which also shuffles air over the pump. The electronics is capable of handling 80deg C on the surface of the case. Thereafter it shuts itself down automatically. Suffice to say that in one size of pump (140 cc - 37kw), the temperature in hot climes even with air blowing from the fan of the main motor was not sufficient to cool down the electronics. Investigation showed that the electronics by itself heats up far higher than the oil temperature and the rest of the pump, because of the load of actuation of the swash plate of the pump. We found that we could run the machine if we had air separately channelled to it from the outside by a separate blower. So this is the case which involved a number of experiences of this sort of failure from all over the world, especially during the hottest summer months. We also found that if we enclose the unit separately, the heat generated was too stupendous and failure was almost immediate. If we used cold water, it introduced another element of failure namely condensation of moisture on the electronics which is even more dangerous. Sorry for the digression but this memory is too deeply burnt in me and I couldn't help but relate it here.

Lesson learnt was that enclosing a heating body (in our case the rx) in a separate chamber only builds up the heat. After all this what we learn by the term 'entropy'. So it is not only necessary to enclose the heating body in a separate chamber, but also to see that there is adequate means of removing the heat. In this case it would be by way of convection with sufficient airflow... The airflow could be induced by natural convection or forced. It is accepted that the rx device is heating up on its own, therefore we should see to it that the heat is dissipated.

And another fact is that the temperature at which instability is reported is 48 degC. With Chennai temperatures at about 10.00am in an open space like Sholavaram (with a tarred tarmac radiating heat directly below) and the Sun up and shining, I expect the surrounding ambient temperature to be somewhere near 38 deg C. Only 10 deg C from the unstable value... with a heat source in an enclosed space with no airflow... it is inevitable.

Saju

thanks saju uncle (heard a lot about you from sai uncle) a lot i will ensure i make necessary intakes and exhaust vents in the vtol - osprey.


subbu

The key is that the failure does not happen at 48C, it happens much closer to 60C.  Futaba rates their recievers to 60C (you can look up the manual for the FASST receivers to confirm this).  The 48C (or 50C) number comes from the same explanation you gave earlier. So if the temperature of the day is close to 50 and the heat generated in the enclosed device pushes it up by 10C, the total approaches 60C which may result in failures. Sholavaram ambient temperatures at 50C sounds way overboard for the time of the incident.

I feel you are misled a little bit with the 48C number.  When a company like Futaba says it is safe to use the receiver up to 60C, they have to be pretty close; otherwise class action lawsuits will follow as some really expensive aircraft are trusted to be flown with this