SEMROC Swift Failure

[doug_kosty]

I took another step up the learning curve today, but I'm not sure what I learned exactly.

I build a SEMROC swift and took it out to Fiesta Island for a launch. The first launch was somewhat comical on a 1/2A6-2. Barely got into the air and then did a faceplant recovery.

The second launch on a B6-2 (the other recommended motor) was .... interesting. About 25 feet in the air both wings shredded. On recovery of the fuselage, I discovered that my glue joint was just fine as there were little stubs of wing still attached.

So... what happened? As I was building the kit, I noted that the wing balsa seemed pretty soft - not having much knowledge of how it should be I simply forged ahead. Is this the probably root cause for the failure?

I'd like to learn from this experience, so any thoughts are welcome and appreciated.

BTW - The kit was a fun build, and it SHALL fly again. Just needs a little repair - you know, like a new wing....

 

[Gillard]

i've had a glider to two shred, where its the balsa thats gone and not the joints, here's what i've learnt over the years.
if the balsa is soft and weak don't fly above an A.
to toughen up balsa, then use a good quality sanding sealer, and sand most of it off, this does increase he strength of the balsa alot.
add a line of CA along the edges of the wings- thats there the shreding starts.
did the wings both shred or was it on one side, if it was on one side then it cold be that the wing was at an angle causeing more stress on one wing.
attached is a pic of a glider that had a few A flights under its belt and then was pushed to a B, i had not done any of the above to it.

View attachment shred glider.bmp

 

[doug_kosty]

It was a bilateral shred - quite impressive really.

I will try your suggestions during my rebuild, and I'll also seek out some more suitable A motors. All part of the fun of learning!

My kids couldn't understand why I wasn't upset after the launch - I pointed out that I have the opportunity to learn something new, and besides if everything went perfectly all the time it would not be nearly as interesting to watch!

 

[dave carver]

And rocketry is a hobby where you can learn more from a failure than a success.

Post crash analisys is a fine art.:hohoho:

 

[MarkII]

The wings may have split or cracked when it hit the ground in the first flight. If a crack or split doesn't go all the way through, it can be easy to miss during a casual inspection. Everything will look fine, but the part will be significantly weaker and it will break in the next launch. My guess is that the damage actually occurred as a result of that prang in your first flight.

BTW, have you tried to figure out why it crashed the first time up? Was it too heavy? Launched the wrong way in relation to the wind? Did the glider fail to release? I would spend more time doing that analysis.

MarkII

 

[doug_kosty]

The wings may have split or cracked when it hit the ground in the first flight. If a crack or split doesn't go all the way through, it can be easy to miss during a casual inspection. Everything will look fine, but the part will be significantly weaker and it will break in the next launch. My guess is that the damage actually occurred as a result of that prang in your first flight.

MarkII

That is a decent notion. I will admit that I did not do a detailed inspection between flights. The first flight came down with everything jumbled together - the pod had separated but the glider and streamer were tangled together. That was another things that I noted - the streamer is really long at 30 inches or so in length. It easily fits into the pod, but looks much longer than streamers I have seen on other "conventional" rockets. Wonder if this could be a contributing factor?

The glider was built very light - the only extravagance was that I did put a 1/8 inch wide band of epoxy at each of the wing dihedral joints. This was on the top surface only and was to compensate for my frankly cruddy job of sanding the angles into the wing. The weight added was pretty minimal and at least those joints were not the weak spot in my construction.

 

[doug_kosty]

Just a followup - after the crash, I asked SEMROC if they could send me a pattern so that I could fabricate a new wing. I was expecting a scan of the wing. What I got in the mail today is the parts for a new glider! This is exceptional customer service and I know that my experience is not unique in that regard.