Large RC Saab Gripen crash

[Tony F]

Anyone seen this ? This thing was huge and looks like he was attempting a knife edge ??

Edited By Tony F on 22/09/2016 22:12:50

[Matt Jones]

I feel sad for the team that lost such a nice model and it was being flown really well too but it just validates my concern about such big models. Look how quickly it came apart.

[Colin Leighfield]

It amazed me the way that it flew to pieces, it wasn't at high speed and the manoeuvre wasn't particularly violent. Looked like a serious structural weakness. Something of that size and engine power needs to be designed by someone with full-size design expertise, you do wonder sometimes If the level of competence is up to the task because it isn't just about looking the part. If someone gets seriously hurt or killed at a show with an incident like that some serious questions might be asked.

[Colin Leighfield]

Just had another look at it and you can see that the first thing is the fin coming off, instigating a sharp yaw that overloads the airframe and leads to disintegration.

[Jon H]

I saw this the other day and was pretty shocked by it. But I then thought that this 'model' is basically the same size as a folland Gnat and when you think how strong the Gnat airframe is i find it hard to believe that a model built using traditional methods would ever get close to that level of strength with a flying weight of 100kg.

Its fortunate no one was under the beast when it came down

[kc]

Doesn't it look as though the turbine lost a blade or something, cutting off the fin then eventually exploding and destroying the fuselage?

Frankly these models are far too big.

[cymaz]

It's a damn shame for the team. Poor chap with his hands on his head.

Maybe it could have been a hairline crack, un- noticed , that suddenly gave in ? It was a lovely model, popular at shows perhaps ,and had a busy season.

[Geoff S]

Posted by kc on 23/09/2016 00:17:44:

Doesn't it look as though the turbine lost a blade or something, cutting off the fin then eventually exploding and destroying the fuselage?

Frankly these models are far too big.

That's a possibility. At one time I was involved in fan blade containment tests on full size gas turbines but I guess, as there are no paying passengers to protect, it's not a feature on model engines. I don't think this could be described as a crash. The aircraft was in pieces before it ever reached the ground.

I agree with your last statement. It's one thing making relatively low performance large models in wood as Ian Turney-White has shown (some of his huge models have been flying successfully for many years) but quite another when it comes to big gas turbine high performance aircraft. After all many 'golden age' and even WW2 aircraft were built using materials and techniques very similar to our models.

Geoff

[Frank Skilbeck]

Don't forget that this model had been through the German large model inspection and certification scheme, which is required before you are allow to fly such models in Germany, so I would hope they are reviewing their approval scheme/procedures.

There's a similar system in the UK for models over 20kg administered by the LMA, I've heard that the UK system is more stringent requiring more flight testing before the model is allowed to be flown public.

But look on the positive side the display and flight line was arranged such that the model crashed well away from anybody. Also while it was big and heavy it was flying fairly slowly, remember energy is = 1/2 mass x velocity squared, so a small faster model can be more dangerous.

[Biggles' Elder Brother - Moderator]

Posted by Colin Leighfield on 22/09/2016 23:03:00:

Something of that size and engine power needs to be designed by someone with full-size design expertise,

I totally agree Colin.

With the greatest respect to all the people involved, and acknowledging their considerable experience at building model aircraft, I too wonder about their competance to work at this level. For a full size-aircraft critcial design calculations and features have to be signed off by a Chartered Engineer, that is not being done here - despite the fact that, size wise at least, we are in that territory. Here the approval from the appropriate body may be given by someone with no professional engineering qualifications what-so-ever. Its one thing doing that at 20Kg, at this level its something else entirely and that certainly gives me cause for some unease.

BEB

[perttime]

A German forum has "after" photos of the fin. Looks like the fin and its tube supports came off with ragged pieces of the poplar plywood formers. It still amazed me how quickly and thoroughly it disintegrated after losing the fin. The fin looks as if there wasn't much on top of the balsa structure. Perhaps the same is true of the rest of the airframe?

[Jon H]

got a link to those photos?

[Josip Vrandecic -Mes]

Hi Colin, I agree, because the quality and nice flying this size jet models requires compromises on all levels, but this time the structural part was critical and very, very dangerous.

Jo

[ken anderson.]

when i first watched the video--I thought someone had done a disappearing act with the wing structure....pause the video just before and just after the fin coming off and there is very little material as such...very flimsy construction that appeared to fail at the wrong time....also the flight performance ...looked underpowered to me...just as well as I don't think that the air frame would stand much stress....my opinion as an armchair investigator....good that no one hurt etc...just a couple of ego's and wallet's...

ken Anderson...ne..1 ........ armchair/air crash dept.

[Martyn K]

Just before the break up, it appears that the rudder had gone hard left - its not a huge rudder but it's also not visible in the still from the video. It could have been a servo/control fail that instigated the break up but the airframe should never have failed in that manner anyway.

Have a look at the model on the runway. It's almost transparent, you can see through the skin

As everyone has also pointed out, I am glad no-one was injured in this. I also agree with the sentiments that this model is also too large.. The great unwashed may like this sort of thing but TBH, I think they are a huge step too far.

1/3 scale is more than big enough and only for certain subjects

Martyn

[ken anderson.]

now there's a thing at 013 sec's pause the vid ...and you can see through the wing!...well spotted martyn......as you've mentioned I think they bit off more than they could chew.....

 

ken Anderson...ne...1 see through dept.

Edited By ken anderson. on 23/09/2016 10:28:35

[Geoff S]

Further to BEB's post re inspection by Chartered Engineers, I don't know if anyone here watched the BBC program The Great Flying Challenge when a team made and flew a replica of Harry Ferguson's (think tractors) 1909 aeroplane but this was closely checked by the CAA. One of the builder's was a boat builder who made a big error in slotting the main wingspar to accept the ribs rather the the ribs to fit the spar and that caused some concern from the CAA inspector.

The finished aircraft was of a similar size to the one in the YouTube video yet, because it was carrying a pilot, was subject to very close official scrutiny. In the event it eventually flew a few hundred yards at an altitude of about 20 feet and risked no-one's life except the valiant pilot.

I agree the event was very well set out with the model well clear of any bystanders and nobody was at risk but that may not always be the case. I witnessed the crash of the big B52 at the Nationals a few years ago and that ended up not very far from the farm. That was pilot error rather than structural but it was a very big (and to be honest) very impressive model of a similar size.

Geoff

[Colin Leighfield]

There's no doubt that in a properly managed flying display with key manoeuvres carried out parallel to the flight-line, the risk of a plane coming down in the crowd is minimised. However, if the manoeuvre causing the failure or resulting from it causes a diversion from track, then clearly the possibility of coming down in the crowd is increased. In this case the manoeuvre certainly was divergent because the structural failure was apparently caused by a sudden yaw induced moment beyond the (too low) airframe limits. Fortunately the fragmentation was instantaneous and debris seemed to continue on track, but a more progressive failure could well have induced a direction change and greatly increased the risk. I wonder what investigations are being carried out subsequent to this. In the UK a failure like this at a publically licensed event is likely to be seen as a notifiable incident and there could be consequences from that.

Edited By Colin Leighfield on 23/09/2016 11:44:40

[bigbubba]

I have studied and studied the video and I can't see through the wing!

It would be more apparent just after take off with the sky behind it and there is nothing.

I think you might be seeing the reflection?

[perttime]

Posted by Jon Harper - Laser Engines on 23/09/2016 09:22:51:

got a link to those photos?

The ones I saw are in the RC Networks thread on the JetPower event:

**LINK**

edit: There's a thread with some photos where you can see the wooden airframe. I didn't spot anything about the internal structure.

http://www.rc-network.de/forum/showthread.php/482007-Der-Balsagott-ist-wieder-aktiv

Edited By perttime on 23/09/2016 12:34:53

Edited By perttime on 23/09/2016 12:36:01

[Peter Christy]

[armchair investigator mode]/ON

Looks to me like the fin detached when the pilot applied top rudder during the roll. The rudder is a very powerful control on a swept wing aircraft. A full size airliner with a load of passengers on board crashed in New York (?) in very similar circumstances (fin detached) when a pilot tried to correct for wake turbulence with rudder rather than aileron. I wonder if this pilot encountered some turbulence from his previous pass, just as he applied the rudder?

Either way, that looks like a weak structure as the root cause.

[armchair investigator mode]/OFF

--

Pete

[Colin Leighfield]

Peter, the one you refer to was the Airbus (A319/320)? Just after 911, at Newark? At first people thought it was terrorist related, but it wasn't. I remember thinking at the time that if it had been a 737 the fin would have stayed on.

[Martin Harris - Moderator]

Looking at some of the (hopefully!) informed comments and pictures from Jon's links, it appears that much of the load bearing structure was "liteply" and I'm very open to the suggestions that it was a simple structural failure of the fin and massive over stressing of the wing leading to catastrophic failure. It would be interesting to hear from an LMA inspector whether such a construction would be allowable under their scheme? Looking at the splendid low speed handling and short take off and landing rolls, I wonder if it was built too lightly so that it could comply with model qualification rules?

Edited By Martin Harris on 23/09/2016 13:17:18

[Martyn K]

Another earlier video with a happier ending

[MattyB]

Posted by Frank Skilbeck on 23/09/2016 07:53:20:

Don't forget that this model had been through the German large model inspection and certification scheme, which is required before you are allow to fly such models in Germany, so I would hope they are reviewing their approval scheme/procedures.

There's a similar system in the UK for models over 20kg administered by the LMA, I've heard that the UK system is more stringent requiring more flight testing before the model is allowed to be flown public.

I can't provide a link and don't speak German myself, but I have heard from others who have read about this on German forums that that may not be the case. Apparently the aircraft was tested for compliance, but not by the German authority - apparently it was tested in France where the regimen is less rigorous.