Large RC Saab Gripen crash

[Dr. David]

Seems most of you chaps do not feel safe, so why bother attending these air show in the first place? Just let the people enjoy their hobby, this is enough of a nanny state these days anyway.

I was doing flying shows in the late 50's, now that would have made your hair curl.

At full size shows, we would all line the runway, even sitting on the edge of the tarmac.

[Peter Beeney]

Leaving aside the safety implications of this incident for a moment, I started tinkering around with the video and I managed to grab these screen shots. They are a bit hazy, probably due in part to my ineptitude, but they are simply just as taken.

Interestingly, (to me), that as the model rolled to the right and the pilot used left hand top rudder to hold the nose up, I’d have thought that the weight would have been forcing the fin to the right; but it would seem from the photos that might not quite be the case and in fact the fin actually broke off, and in the event apparently quite violently, to the left. So was was there something else going on as well, such as maybe a side slip which was actually having a stronger and overriding effect?

Once the fin had gone I suspect that the resultant violent pitch up at the nose may have caused the cockpit coaming and canopy to depart, this then started the chain reaction which as BEB rightly said, very rapidly sealed it’s fate! I too guess it all happened sequentially, but because our human perception is relatively quite slow it seems to be instantaneous.

However, at the end of the day it seems that catastrophic structural failure was indeed the reason for the breakup; but I’m sure that by now the flying team will have carefully analysed the video frame by frame and drawn their own conclusions. Let’s hope the next one may be built to a better specification, as I’m sure it will.

PB

[Phil 9]

Posted by David Wilson 5 on 25/09/2016 00:17:46:

Seems most of you chaps do not feel safe, so why bother attending these air show in the first place? Just let the people enjoy their hobby, this is enough of a nanny state these days anyway.

I was doing flying shows in the late 50's, now that would have made your hair curl.

At full size shows, we would all line the runway, even sitting on the edge of the tarmac.

I don't think past errors forgive modern ones. spectators uses to line the roads of car rally's until many fatal accidents proved this was a stupid idea

[Peter Beeney]

This picture perhaps shows rather better the moment the fin starts breaking away and leaning over to the left, which I guess can only be caused by the back end moving to the right?

PB

[bouncebounce crunch]

Horrible to lose any model.

in defense of the risks, we try to reduce them no doubt, but as with full size aeroplanes they do crash whether from structural fatigue, pilot error or other anomalies.

full size airshows are littered with crashes and casualties, so the possibility of a smaller scale disaster within aeromodelling is a reality. we just have to try our best to reduce the knowns.

[Bob Cotsford]

Josip, I'm not convinced that you can compare 4-5lb models that have been structurally proved over many years with a 100lb+(?) model that has demonstrated that it was structurally unsound.

Peter, interesting photos and if you think about it it is logical. Left rudder pushes the fin hingeline to the right (or if you prefer causes a lift component to the right) and induces in the airframe a yaw to the left so the airflow would indeed be hitting the fin from the right and pushing it that way. I guess this demonstrates how the forces on the fin and rudder can be in opposition causing torsional forces in the structure.

In any spectator sport the ideal is to represent an element of risk in order to get the Ooohs and Aaahs while minimising the actual risk. The subject of this thread certainly accomplished that - at great cost to the owner! It might have been a different matter if the failure had occurred during the turn back onto the flightline while it was still pointing towards the spectators - how far can an uncontained turbine travel?

[KiwiKid]

There were apparently six incidents at the JetPower 2016 event. This comment from one attendee: "This [the Gripen] was not the worst incident at the show IMO. As we arrived early Friday we were watching a sports jet fly, when it lost half of its wing. With amazing control, the pilot somehow managed to complete 3/4 of a circuit and "land" the model on the runway. There was nothing left of the airframe, so I could not actually identify the model type. Whilst the pilot could get full marks for skill, he scores zero for intelligence. He had acres of grass to safely dump the model on, and had a softer landing. But personally I would have grounded the guy because he was flying a barely controlled, high speed model, at one point directly towards the crowd. No imagination! Clearly the safety of the public and other pilots was less important than this guys ego."

[Martin Harris - Moderator]

Posted by David Wilson 5 on 25/09/2016 00:17:46:

Seems most of you chaps do not feel safe, so why bother attending these air show in the first place? Just let the people enjoy their hobby, this is enough of a nanny state these days anyway.

There's a massive difference between being aware of risk and letting it get in the way of enjoyment. Whilst I might think very hard before taking my granddaughter to a model show, I have enjoyed many displays since the occasion I mentioned.

[The real Ron Truth]

A big problem we have in this hobby is the lack of testing done , esp with regards bigger models. Most full size designers can either calculate stress loads or conduct destructive testing of a design to ensure it meets specific wing loading limits or g ratings.etc One off unique designs like the Grippen are probably built using sound model building ideas but do not get the same level of performance scrutiny. Did the pilot have any idea of its limits ? Was it G rated ? Did he know of any traits of the full size that would explain the accident?

Its not until its flown that we see if it works . Many bigger models only get flown at such events so you are therefore seeing a design being put hroughi its early flights in reality. Steve Carrs recent crash at Blackbushe was the same , if I recall.

Id prefer to see all large models over 20kg subject to a tough series of flight schedules away from the public. Not perfect but at least this crash would have been away from the public.

[Martin Harris - Moderator]

Whether it's sufficient may be open to debate given the sort of incident you mentioned, but I understand that the LMA (acting on behalf of the CAA who I'm sure monitor its effectiveness) require demonstration and test flights under closely supervised and controlled conditions before clearing models for public displays or general operation.

Edited By Martin Harris on 26/09/2016 12:02:41

[ChrisB]

As other have said, there are stringent regulations laid down by the CAA and administered by the LMA for all models weighing over 20kg. This includes the construction and private flight testing. Similar schemes are also in operation in many other countries including France and Germany.

Visit the link to read more on how it actually happens here rather than supposition and rumour.

**LINK**

Edited By ChrisB on 26/09/2016 12:20:26

Edited By ChrisB on 26/09/2016 12:21:45

[The real Ron Truth]

Chris,

Im well aware of the CAA rules and reciprocal schemes in Europe, but in this case they failed.

Someone didn't do there job or the model in question wasn't designed properly.

[Dr. David]

I really think we have heard enough about the testing/lack of, etc.etc.

In case you have not noticed there have been many catastrophic failures on full size aircraft that have abviously been thoroughly designed/tested.

Accidents happen, get over it!

[Jon H]

I dont think we can really 'get over' this one. I mean i understand what you are saying and agree that in many respects accidents these days are over analysed, but this was (i believe) the first model if this type/size and for it to come to such an end it could, and perhaps should,be argued that procedures need to be investigated. Say for example the fin detached but the wings did not. The model could have gone wherever it wanted and that could have been nasty. Sure there is a good deal of 'if' and 'could have' in that statement, but its worth looking at even if no changes are deemed necessary.

As has been mentioned already on the thread, full size aircraft have limits on them in terms of loading and, in general, models dont. Even if you really went for it you would struggle to tear the wings off an acrowot for example. You might loose the tail through flutter, but it would be really hard to break most models (not gliders or piper cubs or something like that) through pure G loading.

From looking at the video it appears to me that he was attempting a knife edge and the fin was obviously not up to the task. That said, i dont often see full size aircraft of this type do any pure knife edging with the sort of rudder deflection/nose up angle used here so its possible not even the full size aircraft could do this type of manoeuver.

[Rich too]

Posted by Dr. David on 26/09/2016 13:34:57:

I really think we have heard enough about the testing/lack of, etc.etc.

In case you have not noticed there have been many catastrophic failures on full size aircraft that have abviously been thoroughly designed/tested.

Accidents happen, get over it!

+ 1

I am sure that the necessary crash investigation will take place.

Edited By Rich2 on 26/09/2016 14:16:56

[Nigel R]

Posted by Dr. David on 26/09/2016 13:34:57:

In case you have not noticed there have been many catastrophic failures on full size aircraft that have abviously been thoroughly designed/tested.

Accidents happen, get over it!

I think I'm on reasonably safe ground when stating that one thing the full size industry certainly doesn't do is "get over it" when a catastrophic accident occurs. A vast amount of effort goes into ensuring "it", whatever "it" was, doesn't happen again. It's thanks to that attitude that the accident rate in full size is as safe as it is.

Or perhaps I'm misunderstanding, and you're only referring to these unimportant little bits of foam and wood that get flown around by RC guys.

Except that at 100kg this is as big as a small fixed wing microlight - fine, nobody gets on board, etc. But 100kg is still a big old whack of stuff to lose control of because it hasn't been built strong enough. If this passed the inspection procedures, the inspection procedures aren't good enough. Feel free to disagree.

[MattyB]

Posted by Dr. David on 26/09/2016 13:34:57:

I really think we have heard enough about the testing/lack of, etc.etc.

In case you have not noticed there have been many catastrophic failures on full size aircraft that have abviously been thoroughly designed/tested.

Accidents happen, get over it!

Yes, accidents do occur to full size aircraft too. But how many accidents like this do you know of where a full size aircraft broke up spontaneously in flight whilst being flown well within it's flight envelope and structural tolerances? I'm sure there are some, but they are VERY rare compared to the instances caused by another factor (pilot error, icing, bird strike causing unexpected loss of power etc). Why is that? Because they undergo rigorous structural modelling and destructive testing before they are allowed to fly.

Now let's look at the model in question, which was being flown very gently at the time of the accident. If constructed correctly it should have been able to withstand the manoeuvre in question easily, but it didn't. Why? Well the real thing weighs ~6800kg and is stressed to +9g, yet this half sized variant only tips the scales at 100kg. 100kg is only ~1.5% of the real thing, yet it's 50% scale! I understand the builders desire to hit a low weight to get decent performance (it clearly wasn't overpowered even at 100kg), but surely it should have been obvious to both him and the inspectors that such a low weight for the size was going to lead to serious compromises in structural integrity.

So how do we answer the questions re: "How big is too big for a model?" posed in this and the other thread? It would seem that the answer (if vague and unhelpful!) is that anything requiring full scale structural analysis and destructive testing to be certain it can be operated safely within it's targeted flight envelope is too big. I am not qualified to say where that line is, but I suspect it would be difficult to put a weight on it - clearly 100kg was too light for a 1/2 scale single seat jet fighter, but the LMA Vulcan at 1/5 scale and ~140kg is well proven in operation with it's more sedate flying style. Not an easy question to answer.

[Jez Harris 1]

Hi all.

Sad to see such a lovely model lost.

Geoff mentioned Ian Redshaws Hp42 being tested in Germany prior to being allowed to fly in a public display..It was at euroflugtag in 2012. They took various measurements of the model and calculated what the wingloading should be.
They then proceeded to suspend the model and actually added the weight using sandbags along the flying surfaces. The scrutineers checked the amount of distortion/deflection.
I remember the look on Ians face as they gradually added a couple of hundred kilos to the wings...priceless!!

Far more rigorous than the LMA testing carried out here in the UK.

Jez

[Colin Leighfield]

If very large models(? Define) are going to be flow in public displays, as I want them to continue to be, simple static loading based on agreed criteria is a simple and sensible thing to do. It should only need to be done once and then a certificate could be issued, perhaps with the proviso that a precautionary re-test should be done in the event of crash damage repair. Jez describes how it can be done.

[john stones 1 - Moderator]

Posted by ChrisB on 26/09/2016 12:17:51:

As other have said, there are stringent regulations laid down by the CAA and administered by the LMA for all models weighing over 20kg. This includes the construction and private flight testing. Similar schemes are also in operation in many other countries including France and Germany.

Visit the link to read more on how it actually happens here rather than supposition and rumour.

**LINK**

Edited By ChrisB on 26/09/2016 12:20:26

Edited By ChrisB on 26/09/2016 12:21:45

Interesting reading, cheers Chris

[Tony Richardson]

Could this landing have contributed to the break up?

[ChrisB]

Posted by The real Ron Truth on 26/09/2016 11:48:31:

A big problem we have in this hobby is the lack of testing done , esp with regards bigger models. Most full size designers can either calculate stress loads or conduct destructive testing of a design to ensure it meets specific wing loading limits or g ratings.etc One off unique designs like the Grippen are probably built using sound model building ideas but do not get the same level of performance scrutiny. Did the pilot have any idea of its limits ? Was it G rated ? Did he know of any traits of the full size that would explain the accident?

Its not until its flown that we see if it works . Many bigger models only get flown at such events so you are therefore seeing a design being put hroughi its early flights in reality. Steve Carrs recent crash at Blackbushe was the same , if I recall.

Id prefer to see all large models over 20kg subject to a tough series of flight schedules away from the public. Not perfect but at least this crash would have been away from the public.

 

 

Ron, in your earlier post above you make several statements that suggest that you aren't fully aware of the processes.

Who is to say that on this occasion the tests weren't stringent? Failures happen and that is a fact, no amount of testing or design will ever remove them, only reduce them.

No worries John, hope the article shed some light on the situation.

Edited By ChrisB on 26/09/2016 20:13:10