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big saab gripen crash

Old 09-16-2016, 03:41 PM
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hmjets
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Default big saab gripen crash

Sadness!
Rudder-fin failed?
Crashed at jet power 2016.

http://www.youtube.com/watch?v=e7EZ6...e_gdata_player

Last edited by hmjets; 09-18-2016 at 05:59 AM.
Old 09-16-2016, 04:11 PM
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raron455
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Ouch, show center,,,that sucks..hate to see that
Old 09-16-2016, 04:40 PM
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NEWSFLASH: Jets crashed before and will crash in future!
Old 09-16-2016, 05:48 PM
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Geez... that went bad quick!!
Old 09-16-2016, 05:57 PM
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1/2 scale jet made of wood with a huge 40+ kg turbine. Hhhmmmmmm?
Old 09-16-2016, 06:09 PM
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Sad.

But isn't it a bit ironic that the commentator talked about how it had passed an aviation certificate (I'm assuming for air worthiness) right before it disintegrated in mid air?
Old 09-16-2016, 06:40 PM
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rhklenke
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Originally Posted by luge_racer View Post
Sad.

But isn't it a bit ironic that the commentator talked about how it had passed an aviation certificate (I'm assuming for air worthiness) right before it disintegrated in mid air?
Yep, and lots of the "large model rules" talk about things like servo power, but not many of them (maybe not any of them?) talk about load testing the actual structure.

And yet, failures of the structure itself are what we see most...

Bob
Old 09-16-2016, 07:08 PM
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Airforce7
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Damn was that thing made out of paper????? Incredible out it disintegrated so easily.
Old 09-16-2016, 07:13 PM
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Originally Posted by luge_racer View Post
Sad.

But isn't it a bit ironic that the commentator talked about how it had passed an aviation certificate (I'm assuming for air worthiness) right before it disintegrated in mid air?
I was thinking the same exact thing. Couldn't have made it any more "prophetic" than that.

looked to me like flutter turned to structural failure in rapid progression.

PaulD
Old 09-16-2016, 08:13 PM
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The Germans have been in a war over the last 5 yrs seeing who can make the biggest RC jet out of wood? As per another link i posted here is a 1 to 1 scale BD-5 with two turbines.

http://www.rc-network.de/forum/showt...Richter/page9?


On one hand i have to admit the workmanship is awesome, yet the stupidity is in a league of its own. Biggest model crashing at the biggest jet event.

Regards,
Old 09-16-2016, 10:01 PM
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I don't think it is rudder flutter.
The pilot comes in at full power for a knife edge pass. Kicks the rudder in full travel.
The fin separates due to excessive aerodynamic loads. As the plane is not full knife edge pass yet, this creates an increase of the AOA and left roll in a split of a second. The lift generated induces the structural failure of both wings ( one can actually see that the spars went through the structure and are sitll in position after the wings separated ). The nose section separates due to the AOA now being 90 degrees and still high velocity.
The rear section yaws in inverted and inflates from the front opening. It self destroys before reaching the ground. The only thing that reaches the ground relatively intact is the nose section.

Bottom line:
1. A 1/2 scale airplane IS an airplane. Proper structural design and analysis must be conducted for public presentation. This was not the case.
2. A presentation pilot must know the limitations of its plane. Proper flight test must be conducted before putting a plane to its limits in a meeting.

What I mean by this is progressive opening of the flight domain.
The first flights must be done to only test the takeoff and landing flap configurations and stall speeds ( gear remains down ) as well as CG position in this configuration.
When all the stall speeds are confirmed, flights with gear up can be conducted.
Only then can the clean configuration stall be tested. This typically takes 4 to 6 flights.
Then the CG position can be fine tuned in clean configuration.
Once this is done, clean configuration top speed can be gradually extended.
Once maneuvering speed is reached, the first aerobatics maneuvers can be tested.

All of this implies a thorough inspection after each flight and maintaining a flight log with a snag list.

I have the full description of proper test flights and pre-maiden procedures on my blog.

http://www.ultimate-jets.net/blogs/f...ols-on-rc-jets

Last edited by olnico; 09-16-2016 at 11:50 PM.
Old 09-16-2016, 10:23 PM
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Originally Posted by olnico View Post
i don't think it is rudder flutter.
The pilot comes in at full power for a knife edge pass. Kicks the rudder in full travel.
The fin separates due to structural failure. As the plane is not ful knife edge pass yet, this creates an increase of the AOA in a split of a second. The lift generated induces the structural failure of both wings. The the nose section separates due to the AOA now being 90 degrees and still high velocity. The rear section yaws in inverted and self destroys before reaching the ground. The only thing that reaches the ground relatively intact is the nose section.

Bottom line:
1. A 1/2 scale airplane IS an airplane. Proper structural design and analysis must be conducted for public presentation. This was not the case.
2. A presentation pilot must know the limitations of its plane. Proper flight test must be conducted before putting a plane to its limits in a meeting.
What I mean by this is progressive opening of the flight domain.
The first flights must be done to only test the takeoff and landing flap configurations and stall speeds ( gear remains down ) as well as CG position in this configuration.
When all the stall speeds are confirmed, flights with gear up can be conducted.
Only then can the clean configuration stall be tested. This typically takes 4 to 6 flights.
Then the CG positioin can be fine tuned in clean configuration.
Once this is done, clean configuration top speed can be gradually extended.
Once maneuvering speed is reached, the first aerobatics maneuvers can be tested.

All of this implies a thorough inspection after each flight and maintaining a flight log with a snag list.

I have the full description of proper test flights and pre-maiden procedures on my blog.
100% agree to this observation. There are rumors that the plane did not have a German testing / passing. I wonder why the plane was allowed to fly without that. If my memory serves right foreign models over 25kg were not allowed to take off in previous years at JetPower, which caused a lot of upset. How everything played out and as reported about the building and testing of this plane on rc-network it seems that everything was rushed in order to present the model at JetPower.

I also think that this strange trend in Germany, to build the biggest and heaviest jets is somewhat awkward.

Hi Res Video:

https://www.youtube.com/watch?v=8yf_...ature=youtu.be

Last edited by Tuggs; 09-16-2016 at 10:26 PM.
Old 09-17-2016, 03:48 AM
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Originally Posted by Halcyon66 View Post
1/2 scale jet made of wood with a huge 40+ kg turbine. Hhhmmmmmm?
Nothing wrong with wood - remember the fullsize Mosquito - 2 Merlin engines and the Vampire also "made of wood".

The Heinkel 162 fastest 1st generation jet aircraft ( https://en.wikipedia.org/wiki/Heinkel_He_162 )-
was - like this model "badly made of wood"! However the Germans had an excuse - the glue factory that they had intended to source from was bombed and the substitute glue was inappropriate resulting in structural failures - including one that seems to be a carbon copy of this one "On 9 November 1945 during a demonstration flight from RAE Farnborough one of the fin and rudder assemblies broke off at the start of a low-level roll causing the aircraft to crash into Oudenarde Barracks, Aldershot killing Marks and a soldier on the ground.[SUP][21]")[/SUP]

Last edited by cmp3cantrj; 09-17-2016 at 04:57 AM.
Old 09-17-2016, 04:20 AM
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Watched the sad ending to that beautiful Gripen then found this L-39 claiming to be the 'world's biggest RC scale model'......anyone 'over the pond' see this one up close and personal and if so how's it compare to the ill-fated Gripen?

https://www.youtube.com/watch?v=wK7n....be#t=67.77019
Old 09-17-2016, 04:25 AM
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Originally Posted by olnico View Post
I don't think it is rudder flutter.
The pilot comes in at full power for a knife edge pass. Kicks the rudder in full travel.
The fin separates due to excessive aerodynamic loads. As the plane is not full knife edge pass yet, this creates an increase of the AOA and left roll in a split of a second. The lift generated induces the structural failure of both wings ( one can actually see that the spars went through the structure and are sitll in position after the wings separated ). The nose section separates due to the AOA now being 90 degrees and still high velocity.
The rear section yaws in inverted and inflates from the front opening. It self destroys before reaching the ground. The only thing that reaches the ground relatively intact is the nose section.

Bottom line:
1. A 1/2 scale airplane IS an airplane. Proper structural design and analysis must be conducted for public presentation. This was not the case.
2. A presentation pilot must know the limitations of its plane. Proper flight test must be conducted before putting a plane to its limits in a meeting.

What I mean by this is progressive opening of the flight domain.
The first flights must be done to only test the takeoff and landing flap configurations and stall speeds ( gear remains down ) as well as CG position in this configuration.
When all the stall speeds are confirmed, flights with gear up can be conducted.
Only then can the clean configuration stall be tested. This typically takes 4 to 6 flights.
Then the CG position can be fine tuned in clean configuration.
Once this is done, clean configuration top speed can be gradually extended.
Once maneuvering speed is reached, the first aerobatics maneuvers can be tested.

All of this implies a thorough inspection after each flight and maintaining a flight log with a snag list.

I have the full description of proper test flights and pre-maiden procedures on my blog.

http://www.ultimate-jets.net/blogs/f...ols-on-rc-jets
Exactly!!! Been at Jetpower 8 times. Two years ago pilots were not allowed to fly over 25kg. Not sure if this jet was under 25Kg. Doubt it, but maybe wrong.

In my opinion yet again Jetpower organisers bending rules as they please. If somebody got killed who would be to blame? What is the German rules on this?

Rgds
Old 09-17-2016, 08:10 AM
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Mods hat off.

Like others I think that model came apart too easily.

Somebody needs to look at the construction and materials used to make sure that this is not repeated.

The UK Large Model Association has an excellent certification process for large models which starts by an experienced examiner looking at the plans and materials to be used and there are furtherr inspections as construction proceeds.
Old 09-17-2016, 08:43 AM
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Paper Mache is a perfectly acceptable medium for building jets, HA!
Old 09-17-2016, 09:19 AM
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4.40 minute https://youtu.be/X4xqimAEsug

Knife edge performed faultlessly
Old 09-17-2016, 03:24 PM
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Originally Posted by Halcyon66 View Post
1/2 scale jet made of wood with a huge 40+ kg turbine. Hhhmmmmmm?
Actually you will find that most really large (one off) models are made of wood. The reasons are simple. The kind of professional facilities necessary to build large composite structures are not economic to use for a one-off. Also the expertise to build and verify large wooden structures exists within the modelling community. See J Duncker's comment above.

It is actually much more difficult to verify the soundness of large composite structures without professional resources. There is a tendency to believe that simply because you are using carbon fibre (or whatever) you have a better structure - but this isn't true - composite structures have very particular properties and are quite easy to get wrong (FEJ anyone?).

I am more inclined to believe that the sheer size of this model is the issue here. Most really big models tend to be models of large aircraft (eg the Vulcan) and hence are relatively low stressed. A similar size model of a highly aerobatic fighter is much more of an issue.
Old 09-17-2016, 04:20 PM
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That's exactly what it looked like. The rudder started to fluttr which took out the fin and thent he top of the fuse.
Old 09-17-2016, 04:59 PM
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Yes there were many aircraft made from wood over the years and since they actually have a human in them they are built accordingly. And again as they have a human in then they have G limitations which is a major design factor.


Model jets of this size built by guys in a garage may not have the skill set to do FOS on components and design. Some very large german composite models have had 100's of kgs placed on wings etc while on the ground to massively over stress various parts of the air frame and in some cases done CFD work to additionally test. They are from established manufacturers who have some idea what they are doing. The big 1/4 f-16 and Tomahawks L-39 monsters are good examples and little issues, and even these models cannot be guaranteed incident free.


So wood is fine to build with if you can guarantee no week spots, two strips of wood one can be a strong as steel and the other brakes in a second, same could be said for carbon yet i know which one I build in.


cmp3cantrj makes a valid statement in regards to the tooling needed to make one of these out of composite which would be considerate, yet that is no reason to make something this big with a huge powerplant/aerobatic out of wood. Just because you cannot afford to made a large model from serious materials does not mean you should go down a rung. On the other hand Ali had the massive 1/3 scale ME 262 in wood and that has had 100's of flights so what's the answer.

Also in some instances you have model aircraft inspectors who have never seen this size of model and yet need to be able to clarify its structural integrity. Home build aircraft have inspections along the way so each section is signed off. Seeing a finished fuse does not allow you to determine the internal structure.


This monster could have broken up over spectators or caused considerable damage.


Regards,
Old 09-17-2016, 06:10 PM
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makes one reconsider the idea of a 1/10 XB-70 valkyrie they are designing....
Old 09-18-2016, 12:39 AM
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So far in this debate no one has mentioned what is the probable cause of failure which is to build the plane as light as possible to fall under 100KG. There are a number off master builders in Germany making large balsa models. One of the most expert is the guy that built this one. As the commentary on the video said it had passed the relevant German large model inspections presumably including weight testing. As this is an aerobatic model it would have been stress tested to a higher G force than if it were a bomber. Even though this was a very light model it was powered by a hugely powerful engine of 784 N thrust and with ancillaries weighs 11 Kg.
The German thread details the testing that went on and see shots of the balsa clad model http://www.rc-network.de/forum/showt...t-wieder-aktiv
The first flight had 10 KG of lead in the nose, but this was cut back as flight testing proceeded. Plenty of tests were conducted on servo power and current draw and things were done as carefully as they could. It had been flown in public twice before including at Pampa jets. Difficult to see how things could have been done more carefully.

A comparison with the Mosquito is not really a good one. This had a balsa core sandwiched between 2 ply sheets and was a composite structure.http://www.mosquitorestoration.com/gallery02.shtml The resulting fuselage half was a bit like a moulded canoe had great strength and did not need a large number of formers to stiffen it. Also look at the shot of the rear bulkhead with the fin attached. Similar construction was used on several WW2 German jet aircraft with ply skins on a light core.

Typical model construction is to design the plane with a lot of very closely spaced light formers and to plank the outside and finish with fibreglass to add to the surface strength.

John
Old 09-18-2016, 03:15 AM
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What protocols were used to certified this Jet on Jet power 2016 ?

jose
Old 09-18-2016, 06:41 AM
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Originally Posted by Jgwright View Post
As the commentary on the video said it had passed the relevant German large model inspections presumably including weight testing.
Sorry, this is not what the commentary said. He said that it is imperative to conduct those tests on models of that size, not that they have been conducted on this particular model. Rumors have it that the model only had a french certificate, not a german one.

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