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Turbine Powered 1/2 Scale R/C SAAB Gripen - In-Flight Breakup

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Winston

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All of that work gone in a fraction of a second.

[video=youtube;8yf_QTbDeWM]https://www.youtube.com/watch?v=8yf_QTbDeWM[/video]

The real thing, a cool looking plane.:

 

rstaff3

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Yikes! I wonder how much that cost and how long it took to build.
 

rstaff3

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Yep, lose one piece and everything goes to hell.
 

rharshberger

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The builder did an awesome job of scale building an inflight shred, unintentional,but realistic all the same.
 

Winston

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7.1m long, weighs 118 kg, 100 kg thrust. Estimate of cost found in video comments - $50k euros, approximately US$56k.

Frank Schroeder is the owner/builder of the plane. Note the name of the YouTube channel where the next two videos are found - Schroeder Ryan - possibly his son:

[video=youtube;HmIHLKrJv0Q]https://www.youtube.com/watch?v=HmIHLKrJv0Q[/video]

Its 80 kg of thrust is lower than the claimd 100 kg thrust for the plane. Maybe they were able to tweek it for more thrust?

The AMT Nike costs $27,000:

https://www.dreamworksrc.com/catalog/Amt-Nike

[video=youtube;riDp_PeaCus]https://www.youtube.com/watch?v=riDp_PeaCus[/video]

Some humorous comments found below the breakup video. I don't think poor Mr. Schroeder would appreciate them.

A little CA glue and it was up and flying in 10 minutes.

Take-off weight: 100 Kg
Length: 8m
Landing weight: 27 Kg
Length: 1.5m

First world problems.
 

Winston

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Build images:











This German thread linked to below is about it, but I see no photos of the plane being glassed up in that thread. In that thread, the first image shown above has the associated text "Robert Moosbauer hat ein neues Kunstwerk gefertigt" = "Robert Moosbauer has made a new artwork," so Frank Schroeder might not be the owner/builder, just the owner:

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

rstaff3

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Seeing the nekkid version is that much more impressive. His glassing skills may not have been as good as his woodworking ones.
 

georgegassaway

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Seeing the nekkid version is that much more impressive. His glassing skills may not have been as good as his woodworking ones.
You do not understand the physical root cause of the crash.

It banks to the right, and then the pilot gives HARD left rudder. This was likely either an attempt at a knife-edge maneuver (fly sideways with full rudder holding the fuselage at a high sideslip angle of attack to provide lift), or if it suddenly had banked right by itself for some reason and he was giving hard left to try to compensate (most likely a knife-edge attempt).

The vertical tail mount could not take the stress of this, so it broke off. From that moment the rest of the model was doomed. If the rest of the model structure was 100% graphite, it may not have shredded so easily in mid-air but it would have crashed hard and been destroyed regardless.

Even if the vertical tail itself was 100% graphite, it would have broken off if the structural attachment to the fuselage was not strong enough.

There is a an unfortunate real-world famous airline crash which occurred near NYC in 2001, that crashed due to the vertical tail breaking loose (link and partial quote farther down). The FAA pretty much faulted the co-pilot for over-controlling the rudder, to the point of structural failure. But it was NOT commonly known that it was even possible for "wagging the rudder" , or sideslip, to cause the vertical tail to break off. That is an Achilles Heel weak point that should not be THAT weak, and Airbus is the only commercial airliner known to have crashed for that reason. And ironically, it was COMPOSITE structure that failed

In any case , that Gripen model was an INCREDIBLE feat of craftsmanship as well as engineering except for the tail mount.



https://en.wikipedia.org/wiki/American_Airlines_Flight_587#Summary_of_the_accident

Data from the flight data recorder (FDR) showed that the events leading into the crash began at 9:15:36, when the aircraft hit wake turbulence from the JAL flight just in front of it. The first officer attempted to stabilize the aircraft with alternating aggressive rudder inputs from left to right. This continued for at least 20 seconds, until 9:15:56, when the stress of the first officer's repeated rudder movements caused the lugs that attached the vertical stabilizer and rudder to fail. The stabilizer separated from the aircraft and fell into Jamaica Bay, about one mile north of the main wreckage site. Eight seconds later, the stall warning sounded on the cockpit voice recorder. The FDR cut off at 9:16:00, and the CVR (cockpit voice recorder) cut off at 9:16:15.
At the moment the stabilizer separated from the aircraft, the plane pitched downwards, headed straight for Belle Harbor. As the pilots struggled to control the aircraft, it went into a flat spin. The resulting aerodynamic loads sheared both engines from the aircraft seconds before impact. The engines landed several blocks north and east of the main wreckage site.
BTW - as far as composite meaning stronger..... nope. Composite means composite, not necessarily stronger (the best use of composite for things that fly is to build LIGHTER than possible with other materials for the same strength specs). if not designed/built to be strong enough, it's going to fail regardless of what it is made of. Again while the failure was due to exceeding the structural design limits, interestingly the parts that failed first were composite, not the classic Aluminum or titanium parts.

The vertical stabilizer is connected to the fuselage with six attaching points. Each point has two sets of attachment lugs, one made of composite material, another of aluminum, all connected by a titanium bolt; damage analysis showed that the bolts and aluminum lugs were intact, but not the composite lugs.
 
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watheyak

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Another disadvantage of composite structures is that it is impossible to detect damage other than by destructive testing. They're making strides in this area, but it's still much easier to detect cracks and other problems in metal. Not so much when the damage is 50 composite layers deep.

The vertical stabilizer on that Airbus had been damaged years earlier in a hard landing incident and a contributing factor in that accident.
 

rstaff3

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I concede that I paid no attention to the maneuver he performed when it came appart. I assumed it could have been made stronger as there are tons of huge jets documented on YouTube. Maybe they all would have failed in that circumstance?
 

watheyak

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It was a simple and common maneuver by airshow pilots to fly past show center a little cross-controlled for a good photo opportunity. It presents the top of the plane to the crowd, rather than a profile view. Not a total "knife edge", but on the way.

In this case he would have had a little right aileron and a little left rudder. Normally an easy, low load-factor maneuver that this airplane should have been able to do without breaking a sweat. Or apart.

It makes me wonder if there wasn't some prior damage on this plane as well.
 
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Cabernut

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My first impression seeing how it was constructed was that going 1/2 scale doesn't mean you can just go from titanium to wood. :confused2:

I feel bad for him though. Seemed like LOTS of work. For someone spending $50-60k on an R/C plane, I don't think that losing the money hurt as much as the time and effort wasted.
 

Winston

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It makes me wonder if there wasn't some prior damage on this plane as well.
That's what I was thinking, too, with vertical stabilizer damage being hidden by glassing or whatever he used. It was flown a number of times prior to the breakup.
 

Winston

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Video with some shots of internal construction:

[video=youtube;X4xqimAEsug]https://www.youtube.com/watch?v=X4xqimAEsug[/video]

EDIT: Forgot to mention that he did the same knife-edge maneuver in this earlier flight that led to destruction in the later one.
 
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georgegassaway

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Sage advice, and one the most true of modeling true-isms by R/C flier Ben Roberto:

If you're gonna fly, you're gonna crash.
His philosophy, pretty much, you don't fly models to begin with if you're not prepared to handle the risks involved. Whether you're risking the time, the money, the emotional investment that went into it, everything.

It's not meant to be a fatalistic attitude, or a justification for doing something risky or stupid ("Hey Ya'll - watch this!").

I suspect the builder of this model realized the same things, to some extent.

I will say that it was VERY ironic, that moments after the announcer spoke in English about how the pilot and the model had been CERTIFIED for safe flight, that was when it did that maneuver and broke up. Whoever certified the model (as well as designer/builder), probably didn't consider the kind of forces that could be exerted on the vertical tail during a full rudder high-yaw angle.

Indeed, that happened so fast, I am starting to wonder if the model's rudder deflection angle was a lot more than the real Gripen's rudder deflection angle. It is possible that with "X" amount of hard left rudder, the yaw angle could be so severe that the model was no longer aerodynamically stable along the yaw axis, like a model rocket that is usually stable but goes unstable on a windy day. If that was the case then that could explain why it seemed to yaw so quickly, as though it might have yawed far more than it should have been able to if it was stable, which could have made the vertical tail break from extreme forces (Not saying the vertical tail or its mount was not weak, but the root cause could be different). The canopy sticks up somewhat, so on a model rocket that would be like adding a long but very shallow fin near the nose of the rocket.

Hmm, looked at it again a few more times, can't look frame by frame but was able to jump back about 1 second and see it cycle over and over. One frame I sometimes stopped the recycle at looks like the rudder/tail starts to break in one piece but then another frame I sometimes hit after that, it "explodes" into a bunch of pieces. So it does not seem to be just the base mount failing, it's shocking that the whole vertical tail would shred like that.
 

georgegassaway

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EDIT: Forgot to mention that he did the same knife-edge maneuver in this earlier flight that led to destruction in the later one.
Nice find of that other video. But the whole flight was with the gear down. With a quick scan I didn't see what seemed to be any high speed knife-edge pass, it is banking while turning but not flying horizontally trying to do a knife-edge high yaw angle flying on its side. Indeed with the gear down, even if it did do a knife-edge, it would not have been at the same speed it was doing on its last flight.

Indeed in the first video it seemed to be doing its fastest high-speed pass when they tried that maneuver and broke up. The video was edited so there are only a few seconds shown before the maneuver, but when it jumps from the left hand bank to the next segment, it seems like it was just pulling out of a shallow dive, then pitches up a bit (and seemed lower altitude than it was when banking left), indicating it may have dived to get in extra speed for a high speed pass.

"Hey Ya wird , passen Sie dieses!"

English translation: "Hey Ya'll, watch this!"
 
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James Duffy

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Hmm, looked at it again a few more times, can't look frame by frame but was able to jump back about 1 second and see it cycle over and over. One frame I sometimes stopped the recycle at looks like the rudder/tail starts to break in one piece but then another frame I sometimes hit after that, it "explodes" into a bunch of pieces. So it does not seem to be just the base mount failing, it's shocking that the whole vertical tail would shred like that.
You just described surface control flutter, one of the most destructive gremlins that can befall an aircraft, model or full size. Even small Cessnas and Pipers have small weights affixed to the control surfaces to prevent or delay the onset of flutter.

If it starts, game over.

James
 

mpitfield

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If you set the playback speed to .25 and the def to 1080P you can see the rudder to the left then the vertical stabilizer sheers at the base. When it get tossed into the air behind the wings it breaks apart a bit more, but if you follow it there a lot of stabilizer left over than what first appears to be total disintegration.

My take on this is that the flight profile surpassed the structural limits of the plane, or at least the base of the vertical stabilizer.

I get that the designer and builder made some choices when it comes to weight vs. strength, in order to maximize the performance. However obviously a bit more reinforcement in this area was required. That is if you wanted to fly it they way they were.

[video]https://youtu.be/8yf_QTbDeWM?t=109[/video]
 
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Winston

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If you set the playback speed to .25 and the def to 1080P you can see the rudder to the left then the vertical stabilizer sheers at the base and when it get tossed into the air behind the wings it breaks apart a bit more but if you follow it there appear to be a lot more splinters than what is actually left over.

My take on this is that the flight profile surpassed the structural limits of the plane, or at least the base of the vertical stabilizer.

I get that the designer and builder made some choices when it comes to weight vs. strength in order to maximize the performance. However obviously a bit more reinforcement in this area was required. That is if you wanted to fly it they way they were.

[video]https://youtu.be/8yf_QTbDeWM?t=109[/video]
I didn't do any extensive Google translations of the German forum discussing the plane's design and construction, but I'll bet it was more of a best guest from experience sort of structural design than one submitted to computer structural analysis.
 

GregGleason

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I am curious as to what aero loads were on the verticle stab before it went. I'm thinking that 3 aluminum tubes would have given it enough structural stiffness to keep it on the airframe. But I don't know if that's allowed for R/C aircraft.

Greg
 

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Another disadvantage of composite structures is that it is impossible to detect damage other than by destructive testing. They're making strides in this area, but it's still much easier to detect cracks and other problems in metal. Not so much when the damage is 50 composite layers deep.

The vertical stabilizer on that Airbus had been damaged years earlier in a hard landing incident and a contributing factor in that accident.
That's precisely why NASA has invested in an enormous CT scan machine at Marshall Space Flight Center. They are using it to check for flaws in composite and 3-D printed objects.

What George said above applies to rocketry as well. Don't fly what you can't afford to lose.
 

Winston

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I am curious as to what aero loads were on the verticle stab before it went. I'm thinking that 3 aluminum tubes would have given it enough structural stiffness to keep it on the airframe. But I don't know if that's allowed for R/C aircraft.

Greg
To my knowledge, that would be allowed. The weight limit for R/C aircraft in the US is 55 lbs. Beyond that, they're not in the special category of "model aircraft," a category that used to exempt them from any FAA intervention.

Special inspection and certification is apparently required in Germany for something as big as the 1/2 scale Grippen as was being discussed by the commentator in the video... just before it broke into pieces... that certification being what I would suspect something similar to the requirement for home-built manned aircraft in the US, but perhaps not as rigorous.

I think the metal component restrictions for NAR rules model rocketry have to due with possible shrapnel due to CATOs and the penetration repercussions during ballistic returns or unstable flights.
 

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Aluminum is allowed in construction; before carbon fiber became mainstream most wing tubes were aluminum. I know I've even seen at least one design that was built entirely of aluminum. Aluminum spinners are still common, and of course the engines are aluminum.
 

Winston

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Aluminum is allowed in construction; before carbon fiber became mainstream most wing tubes were aluminum. I know I've even seen at least one design that was built entirely of aluminum. Aluminum spinners are still common, and of course the engines are aluminum.
The only experience I've had has been with EPO foam kits with carbon fiber tubing spars and brushless electric motors. I've never done anything stick built and would die inside if I'd ever build anything remotely like that plane and have it smashed to bits... which is why I did the foamie thing. Love to watch other people do incredible stuff and risk flying it, though.
 
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