When big is TOO BIG?

[Le TVR]

Looks a bit like destructive flutter? Either way that's 100kg of model coming down as shrapnel

https://www.youtube.com/watch?v=8yf_QTbDeWM

[BIRMA]

Incredible model, just before the mid air disintegration I was thinking how much his public liability insurance must cost, but then if you are wealthy enough to build something like that you can afford to insure it. Great pity and I wonder how much they were able to salvage.

[dr_gn]

Le TVR said:

Looks a bit like destructive flutter? Either way that's 100kg of model coming down as shrapnel

https://www.youtube.com/watch?v=8yf_QTbDeWM

Looks like the fin couldn't take the load from the rudder deflection, and that put it into an attitude that shagged the wings.

[Mansells Tash]

Perfect excuse to build something else!

I guess these models are not built to do much aerobatic work?

[jamieduff1981]

It makes a good case for the existence of Engineers.

[Le TVR]

jamieduff1981 said:

It makes a good case for the existence of Engineers.

My thoughts exactly! It's not that difficult to build something that big but understanding the structural issues is something else....

[dr_gn]

Le TVR said:

jamieduff1981 said:

It makes a good case for the existence of Engineers.

My thoughts exactly! It's not that difficult to build something that big but understanding the structural issues is something else....

Some commercial aircraft have been lost in recent times due to fin failure caused by excessive rudder deflections or some catastrophic event like explosive decompression.

[CaptainSlow]

Those sneaky Germans and their secret rearmament plans.


Good to see the 4x4 Emergency Response chap was there ready.

[Le TVR]

dr_gn said:

Some commercial aircraft have been lost in recent times due to fin failure caused by excessive rudder deflections or some catastrophic event like explosive decompression.

Got to agree, It appeared that the fin failed just when he applied rudder to compensate for the knife-edge attitude of the jet. Aircraft had a curent airworthyness examination (due to the weight).

[jamieduff1981]

Le TVR said:

dr_gn said:

Some commercial aircraft have been lost in recent times due to fin failure caused by excessive rudder deflections or some catastrophic event like explosive decompression.

Got to agree, It appeared that the fin failed just when he applied rudder to compensate for the knife-edge attitude of the jet. Aircraft had a curent airworthyness examination (due to the weight).

There are a number of ways this could have been initiated. The Airbus tail separation was caused by aggressive use of rudder.

On models, control flutter is a common way in which structural failures are initiated. R/C model builders are typically aware of control flutter, but they often don't fully understand what causes it. They have moved to short, stiff carbon rod control linkages between the servo and control surface which does help, but the residual causes of flutter is often a lack of stiffness in the aerodynamic surfaces, or lack of mass balancing of the surface. The linkage can be nice and stiff and the bottom of the rudder could be held still be the control rod, but if the rudder isn't torsionally stiff it can twist along its hinge line and still flutter badly.

A fluttering control surface can rapidly build up large reactionary forces which can greatly exceed the static force on the structure which is the part that most people can visualise / account for. On fullsize aeroplanes, flutter can be low enough frequency to observe, but on models it's usually only an audible buzz for about a second at most followed by a bang.

[Zombie]

You've got to feel for the owner. He looks resigned and devastated at the same time.