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1/7 Scale Blackburn Buccaneer All Composite Scratch Build

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1/7 Scale Blackburn Buccaneer All Composite Scratch Build

Old 10-22-2021, 12:25 PM
  #676  
JSF-TC
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Thomas,

Luckily it seems that all of the systems survived. At least they look undamaged - I have not powered anything up yet for a functional check though.

I lost the fuel tanks and one exhaust pipe. One engine tailcone has a small dent in it, plus both engine mounts are bent.

Not bad after being dropped from 300ft!


Paul
Old 10-22-2021, 01:32 PM
  #677  
alasdair
 
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Paul,
I am so sorry to hear about your unfortunate crash. It must be immensely disappointing.
You are right about the skin to framework glue. It has not contacted the skin over quite a large area.
Years ago I bought a *camera on a snake for checking internals. I've never really used it, but I will in future, having seen the problems that can lurk unnoticed..
I hope you get over your shock and disappointment and build a third model. After all that effort you deserve to end up with a great model.
(* endoscopic camera)

Last edited by alasdair; 10-23-2021 at 06:21 AM.
Old 10-22-2021, 02:14 PM
  #678  
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Sorry for your loss. Prototyping and testing, is a tough business.
I have built a few Airex sandwich wings, after learning from a very good Slovakian guy. He stressed two things; sanding and priming. Never be happy with the peel ply surface alone, but sand it. Prime the edges of the shear webs, and the contact area of the wing skin, preferably with a low viscosity epoxy. Small gaps, and a good fit, is mandatory, but the primed surfaces will shake hands with your glue bead, even if it barely touches.
I hope you find the inspiration to go on. The aircraft looked so good in the air!

Lars
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Ron S (10-22-2021)
Old 10-22-2021, 04:28 PM
  #679  
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Paul, nothing I can say can take away the gut punch I'm sure you feel after the loss of #2. At least there are some clues for the possible cause. I just want you to know how much you have taught and encouraged us mere mortals seeing you bring this model to life using engineering, inovation and new technology. I hope you will continue. It is an awesome project.
Gary
Old 10-22-2021, 07:37 PM
  #680  
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I know a lot of people use the Hysol yet the Plexus range of methacrylic's is far superior. Even if your your bonding surface is not 100% it actually eats into the material being bonded, any failures will always be material not the actual bond.

Yes in this case it may not have helped yet the MA 300 and 320 are the way to go.

Only downside is it can leave dimples if your using thin layups.

It is a pity she has gone in, very interesting model choice and great attention to detail.

Regards,

Old 10-23-2021, 01:23 AM
  #681  
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Originally Posted by JSF-TC View Post
it is really hard to check the closed structure once the top skin is down.
Sorry for your loss, it's really a pity.
One thing you can do to help with this issue is invest in a cheap endoscopic camera, for 20 bucks or so.
I inspect all new planes this way as I don't trust any ARF company out there. I found ribs glued to just one side in multiple planes from different brands. Went as far as drilling an inspection hole in the tail booms of one of my planes that didn't have any accessible inspections before building it for this very reason. If you find any issue on the ground, you can stick some hysol in there and apply some pressure to fix the issue. Troublesome, but a lot better than inflight failure/flutter
The camera can also help inspecting a plane after it suffers a hard landing or minor crash, or just at the beginning of a season for peace of mind!
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Old 10-28-2021, 04:03 PM
  #682  
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Originally Posted by JSF-TC View Post
Spent the morning stripping the wreckage and looking for clues, especially in regards to some form of structural failure.

All control surfaces were still attached and linkages intact and able to move freely. Servos felt smooth, but have not been powered to check if they still work.The rear fuselage bulkhead that holds the elevator servo had fractured in multiple places and allowed the elevator servo to come loose, but I suspect that was a result of the impact.

Both flaperons and the left inner flap are undamaged. The tailplane has one minor crack in the upper fairing, but is otherwise undamaged.

The left wing was virtually undamaged, with just the loss of the last 1" on the trailing edge at the wing tip. No structural damage was observed. After loosening the retaining screws, it slid off the wing joiners easily at the crash site so that we could get it in the car.

The right wing showed significant damage, and it had separated along with a section of the fuselage, which was easily removed at the wing joiners. The upper and lower skins were cracked in multiple places. On initial inspection it was not possible to tell if the damage was caused in-flight or by the impact.

Further checking of the right wing showed that the upper skin was loose and could easily be removed. As I peeled back the skin it became apparent that it was not bonded to the internal structure. The Hysol on the structure showed very little contact with the skin.











De-skinning the left wing showed that it was firmly attached and in contact in all areas, although the tolerances could be tightened up to reduce the glue thickness.


I feel confident that this lack of upper skin bonding to the internal structure resulted in a loss of torsional rigidity of the right wing. With the 3deg washout, there will be significant torsion acting on the outer wing and this is likely to have caused the right outer wing to fail, probably in a nose down direction, leading to the snap/ spin.

I'm currently not sure if I made an error in generating the internal structure in CAD, or if the built-up wing plugs caused a variation in wing thickness. Probably a combination of both, but it allowed at least a 1.5mm gap between the top of the structure and the upper skin across most of the structure, both ribs and spars. I had bonded the structure to the lower skin first and confirmed it was seated correctly, but it is really hard to check the closed structure once the top skin is down.

No one to blame apart from myself.......

Paul
I do wonder if, tap testing would detect a disbond or if even going as far as injecting foam would help?
Old 10-28-2021, 05:51 PM
  #683  
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Hang in there and get back on the horse. This is a great looking jet and you have learned from both. The 3rd times the charm!
Old 10-28-2021, 11:53 PM
  #684  
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Really saddened for your loss, Paul, really tragic. Lets hope you can resurrect the project.
Its always risky to speculate on the cause of a crash but that said, heres my take on the evidence you have shown.
If the right wing upper skin was not bonded it would likely have balloned, increasing camber and lift , so producing a roll and maybe spin to the LEFT not right.
Now, take a look of the last still ( just above the railway line) with the model spinning and look carefully, enlarged, at the RIGHT leading edge. That leading edge is not straight as is the left, something is protruding forward for the outboard half of that wing section. Skin separation, failure of the leading edge, resulting in an upward twist and stall of that section of wing ?

To. me that suggests the skin has separated at the le, resulting in a huge loss of lift and increase of drag, perfect conditions for autorotation, spinning.

Maybe, just maybe, but possible.

Anyway, a succesful first flight proves the model is certainly perfectly flyable, so lets hope #3 is a huge success.


Look at outboard section of right wing le.

Last edited by David Gladwin; 10-29-2021 at 04:13 AM.
Old 10-29-2021, 08:18 AM
  #685  
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Th company Micro Mark has a camera system w/ an 8mm camera end w/ a 9+ft cord....Product #90063 ...cost is 129.99$......beautiful airplane BTW!
Old 10-29-2021, 08:36 AM
  #686  
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Amazon Amazon

Most of these will do!
Old 10-29-2021, 02:24 PM
  #687  
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Originally Posted by mauryr View Post
Check carefully, they are not compatible with iphones or older model Samsung phones.

Easiest way to tell is simply plug them in, if the LED lights on the camera light up you
should be good to go after downloading the included app. If they do work they work great.
Old 10-29-2021, 04:52 PM
  #688  
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Wow David, the pic you’re showing above almost looks like a RH wing outer panel that has partially folded… 😮 or maybe it’s just my eyes…

Talking to Paul, I suspect there will be a Bucc #3 - with further improvements...
🙂👍
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Old 10-29-2021, 05:01 PM
  #689  
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Totally looks like a buckled wing in the photo....meaning the last half of the wing has collapsed...and split apart enough to fail
Old 10-29-2021, 06:52 PM
  #690  
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Thanks all for all the comments and support.

Confirming that there will be a Bucc #3. Just catching up on some deferred maintenance on my other planes before starting back on the Bucc.

David G - thanks - I had done the same, resampling the original photo and zooming in to get a full screen view of that last photo before impact. There are some very strange aberrations in the image, such as the radome appears short and blunt and there is an obvious kink in the LEFT wing trailing edge, which is most definitely not there as both flaperons survived the crash intact and are fully usable again. These aberrations make interpreting the image difficult, but there is clearly something different between the 2 wings. Based on all the evidence, I am confident that the RIGHT wing failed due to lack of a bond between the upper skin and the internal structure. That resulted in a loss of torsional strength, which likely led to a leading edge bond failure and the skin tears. Loss of the model was inevitable.

I have used the surviving structure to accurately measure the required offset to contact the skins and have already generated the updated CAD for the new structure. I have not found the 'smoking gun' as to what went wrong with the previous design, but both wings are very similar - I must have used slightly more glue on the left wing that resulted in it bridging the gap. I will also re-introduce a lap-joint across the leading edge to ensure a wider glue joint and not just rely on the thickness of the skins butt-joined together. I used this on the first Bucc, but omitted them from #2.



Paul

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Old 10-29-2021, 10:42 PM
  #691  
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Glad to hear there will be a third Buc!

what i have been doing for my leading edge seam joints is CA gluing a piece of 1/16” balsa strip or scrap airex( about 1/4 to 3/8” wide ) roughly 1/8” aft of the leading edge with it standing vertically. This creates a splooge “Dam”. Splooge is generously applied along the leading edge and up against the Dam prior to closing up the mold halves

this ends up being slightly heavier, but its near impossible to open up the LE seam.
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