Synchronised crashes -- coincidence or not?

[Allan Bennett]

Yesterday after two uneventful 10-minute flights my Multiplex Twinstar suddendly went out of control and crashed about a minute into its third flight of the day.  Shortly after I had taken off for that flight another club member had launched his Bixler (clone, I think) which, like my Twinstar, has had many successful flights.  Being busy trying to recover control before my crash I didn't realise that the Bixler was experiencing the same problem, and crashed, at exactly the same time as I had until other club members told me when I was picking up my pieces.

 

I was using FrSky radio equipment and the Bixler had Spektrum.  We were the only two models in the sky at the time.  What's the chance of this being coincidence?  If not, what could be the cause and how can we guard against it?  In the old 35MHz days we used to have a scanner to detect unwanted transmissions -- is there an equivalent to detect 2.4GHz interference?

[leccyflyer]

Might be worth checking that there were no Radio Frequency Jamming Trails notifications for your area, active yesterday, IIRC there were some jamming trials notified last week, which were in Mid Wales, but not sure which frequency bands were likely to be affected.

[EvilC57]

Sometimes coincidences happen. Over the years we’ve found that mid-air collisions have happened most often when there are only two models in the air. Other times, when we’ve had four or five flying, it’s been proven to happen less often - against all the increased chances of two models being in the same place at the same time.

[John Lee]

Impossible to say if it was, or was not, coincidence or interference or another cause without more information. This is where telemetry comes into its own.

 

Various FrSky & Spektrum equipment are able to log round trip signal quality/fades/holds and Rx voltage. That should be the first thing to look at.

[Allan Bennett]

There's no suggestion it was a collision, EvilC57; the models was well separated and heading different directions. 

 

We're in North Hertfordshire, and I can't see any notice of jamming trials there.  The closest seems to be Scotland over a month ago.  As for telemetry, there were no low signal or lost signal warnings on my FrSky system during flight, and failsafe is configured to shut the motors on loss of signal, not throw the model all over the sky as it did just before crashing.  But I don't have logging so can't prove it one way or the other.

Edited November 4 by Allan Bennett

[Martin Harris - Moderator]

I wasn’t flying yesterday but we’re also in North Herts.  I haven’t heard of any incidents at our field between Hitchin and Luton though but I’ll keep an ear open.  
 

Was anyone operating airborne video perhaps?  Are you close to industrial or domestic properties?  Any unusual events taking place locally?

 

While coincidence is a possibility, it seems unlikely.  Could there be another factor such as the other pilot being distracted by your loss of control?
 

 

 

[Allan Bennett]

No airborne video that we know of.  Unlikely that the other pilot was distracted by my loss of control -- according to onlookers his model hit the ground the same time as mine (I didn't hear the noise of his crash), so was probably just as busy with his own model as I was with mine!

[Brian Cooper]

There is always the possibility of someone being somewhat naughty with some jamming equipment. 

 

We used to have similar problems back in the days of CB radio. 

When the CB people discovered they affected R/C aircraft, a few of them deliberately went looking for model flying fields to cause as much disruption as they could. 

Basically, they liked to watch models crash. 

 

Time will tell if the radio problems were deliberate or not. 

[Geoff S]

When I was flying with the RR(Hucknall)MAC at the RR airfield (Now built on) There was a known problem on one 35MHz channel (I think 2 models were lost) and use of the channel was banned.  It eventually turned out that someone was using a bait boat for fishing in a nearby pond (hidden by trees) which was illegally using that 35Mhz channel.  I suspect it was ignorance rather than malice but the effect was the same.

 

Both my mid-airs have happened when few were flying - on one occasion just two of us.  I think when there's a lot flying you tend to fly circuits but with just one other you tend to fly as if alone - it doesn't always work!   If there are few of us at the field we tend to take it in turns to fly and I prefer that - or we agree to fly in different bits of sky.

[Martin Harris - Moderator]

Do you have a rough idea of the time Allan?

[Konrad]

This has always been a problem with our RC aircraft. It is difficult to make a filtering system that is light, low cost and small enough for our aircraft. On top of that, as the aircraft gains altitude it is exposed to more and more RF signals from other transmitting sources.

 

With the floor of 2.4 gHz band getting so noisy, with so many 2.4gHz transmitters. Most of us are moving to dual band equipment. FrSky has the Tandem (2.4gHz and 900 mHz) they also have the Twin system (dual 2.4 gHz).  

Edited November 4 by Konrad

[Kim Taylor]

4 hours ago, Allan Bennett said:

 In the old 35MHz days we used to have a scanner to detect unwanted transmissions -- is there an equivalent to detect 2.4GHz interference?

Many current gen OpenTX and EdgeTX transmitters have a 2.4GHz scanner function. Taranis 2019 tx's and Radiomaster TX16S Mk11 certainly do - I have both. 

Kim 

[Allan Bennett]

6 hours ago, Martin Harris - Moderator said:

Do you have a rough idea of the time Allan?

 

It must have been around 3:30pm on Sunday -- I didn't make a note.

 

5 hours ago, Kim Taylor said:

Many current gen OpenTX and EdgeTX transmitters have a 2.4GHz scanner function. Taranis 2019 tx's and Radiomaster TX16S Mk11 certainly do - I have both. 

Kim 

 

That's interesting.  I was flying with my Taranis X9D 2019 transmitter.  I'll have to check out its scanning capability.

[leccyflyer]

6 hours ago, Konrad said:

This has always been a problem with our RC aircraft. It is difficult to make a filtering system that is light, low cost and small enough for our aircraft. On top of that, as the aircraft gains altitude it is exposed to more and more RF signals from other transmitting sources.

 

With the floor of 2.4 gHz band getting so noisy, with so many 2.4gHz transmitters. Most of us are moving to dual band equipment. FrSky has the Tandem (2.4gHz and 900 mHz) they also have the Twin system (dual 2.4 gHz).  

Where are you getting the information from that "Most of Us are moving to Dual Band equipment"?

[Martin Harris - Moderator]

No real link then Allan. Apparently, one of our members had a massive flurry of activity from all surfaces while readying a model, resulting in (or caused by?) a servo with a stripped gear train - but it was sometime just before midday. 

[Kim Taylor]

12 hours ago, leccyflyer said:

Where are you getting the information from that "Most of Us are moving to Dual Band equipment"?

Maybe where Konrad operates, which seems to be in the USA, most of his peers are moving towards dual band equipment.

I know that my (in southern UK) next tx purchase will be dual band, unless ELRS becomes predominant in the next 12 months.

Kim

[GrumpyGnome]

Do Spektrum do Dual Band ? That seems to be THE most popular brand in the US from the comments on US/Canada based forums.........

[Andy Stephenson]

They used to, it was called DSM2.

[Kim Taylor]

55 minutes ago, GrumpyGnome said:

Do Spektrum do Dual Band ? That seems to be THE most popular brand in the US from the comments on US/Canada based forums.........

Not sure, I don't think so.

I'm going to get one of the FrSky X series tx's which run 2.4GHz/900MHz rf modules simultaneously. 

Jeti do something similar, as do other, mainly higher end, manufacturers. 

Can't afford them, though 😐

Kim 

Edited November 5 by Kim Taylor

[Kim Taylor]

Getting back to the original question, let me relate a recent experience:

I was flying my Kyosho Calmato Sport (so a fairly weighty balsa plane) when I suddenly felt that the model was doing 'odd' stuff, just not responding to the controls as I was expecting. 

Suspecting some kind of radio issue, I landed immediately, and only then noticed a filthy black cloud (like something out of a Harry Potter film) churning it's way across the field, closely followed by really strong, squally winds. 

Checked out on the ground, the model was flown later with no problems. 

So, is it possible that wind shear could cause the simultaneous events?

Kim

[Konrad]

Good questions.

Yikes I see we have to cover a bit more ground than I thought!

2 hours ago, Andy Stephenson said:

They used to, it was called DSM2.

DSM2 as in Spektrum's antiquated RF protocol? This was a fixed 2 frequency 2.4 gHz protocol. Yes, all modulated RF is a band but let's not quibble over a few kHz. All modern 2.4 gHz protocols are frequency hoping across the full allowed spectrum (band).

 

Dual band RF schemes are using 2 allocated bands  usually called 900mHz and 2.4gHz. Yes there are schemes that split the 2.4 gHz band into two regions and focus their RF distribution between these two. 

 

I don't have access to any sales data. I make the statement that dual band transmitters are the direction of the TX market based on what I'm seeing across the 5 RC clubs I'm a member of, across 2 regions of the United States (the West Coast [San Francisco] and the Rocky Mountains [Denver]).

 

Spektrum still accounts for over 50% of the radios one will see on the flight line. But of the new sales (say in the last 3 years) most of what I've seen have been FrSky with the X-18 and X-20. Yes I see a lot of new Power Box and Jeti TX's. 

 

To be clear I moved from Spektrum to FrSky in 2014, not out of concern for the RF link . But rather the TX programing architecture of OPENTX as it was similar to what I had with my Multiplex profi 4000. I hated the master/slave concept of Futaba and Jr. I really liked the object based mixer focused concept of programing.

 

At one of the flying fields I fly at we are requested to map our crashes. As you might expect the distribution of crashes does not follow the Montecarlo distribution. Most crashes are at the ends of the runway (stall, spins). But over time we see a very strong indication of a 15 meter wide band of crashes that extend 1Km a way from our field. We have not isolated the cause of this but it is in the data so it is real.

 

I've had two Tandem crashes at the field. One was a power management issue. I took off with a half discharged battery pack. The other was a CG issue.

FYI; There are no Tandem crashes reported in that band.

Edited November 5 by Konrad

[Don Fry]

1 hour ago, Kim Taylor said:

Getting back to the original question, let me relate a recent experience:

I was flying my Kyosho Calmato Sport (so a fairly weighty balsa plane) when I suddenly felt that the model was doing 'odd' stuff, just not responding to the controls as I was expecting. 

Suspecting some kind of radio issue, I landed immediately, and only then noticed a filthy black cloud (like something out of a Harry Potter film) churning it's way across the field, closely followed by really strong, squally winds. 

Checked out on the ground, the model was flown later with no problems. 

So, is it possible that wind shear could cause the simultaneous events?

Kim

Wind shear does odd things. My flight line has woodland about 60 meters behind. Not a problem, until an east wind blows, and you want to land.  About the hight stuff crosses the threshhold of the landing area, about 1 to 2 meters up, the airframe hits a wind swirl, with a bit of drop.  Not a problem if expected, but it catches the unwary, or memory light.  It looked like aileron servos cycling to a starboard. 
But in the OPs case, no report of weather, turbance, and in fairness, my memories of a bixler is if in trouble and out of ideas, you let go and ignore it until it sorts itself out.

 

11 minutes ago, Konrad said:

 

Edited November 5 by Don Fry

[Konrad]

Get over what?

 

It was a legitimate question, or so I thought. What was I basing my comment on, about sale of dual band equipment?

Edited November 5 by Konrad

[Andy Stephenson]

52 minutes ago, Konrad said:

Good questions.

Yikes I see we have to cover a bit more ground than I thought!

DSM2 as in Spektrum's antiquated RF protocol? This was a fixed 2 frequency 2.4 gHz protocol. Yes, all modulated RF is a band but let's not quibble over a few kHz. All modern 2.4 gHz protocols are frequency hoping across the full allowed spectrum (band).

 

Dual band RF schemes are using 2 allocated bands  usually called 900mHz and 2.4gHz. Yes there are schemes that split the 2.4 gHz band into two regions and focus their RF distribution between these two...

Yeah, I know, it was a remark made tongue-in-cheek. Should'a used an emoji with that one.

[Chris Walby]

Apologies to digress and it should only take a quick reply.

Dual band 900 mHz and 2.4 gHz TX's (looking at the internet its not clear to me) are they transmitting control commands from the TX to the RX simultaneously on both frequencies? Or is the TX transmitting on 2.4 and utilising the 900 mHz for telemetry only?

 

One of the flying sites I frequent  there has been discussions of poor signal strength at times. One flyer said that if he flew back and forth across the flying field he would be notified of low signal strength alarms. By tracking along the field he could visualise a line where the signal was good either side, but poor along the line. One suggestion was that a nearby radio mast my have a micro wave dish (for emergency use) and that they test it occasionally. Its quite a rural location so unless the local farm has something there it not a lot to cause interference.