Safe To Fly Again???

[tfrielin]

I flew my new Der Big Red Max twice over Easter weekend and the second time it came back with a fin with the top third chopped off---photos attached.

Question: Do you think it is safe to fly it again with this damaged fin? It seems to me that there's enough left to provide proper stability. It certainly is firmly attached at the root to the body tube.

Will probably use another F-16-6 blackpowder engine.

Probably safe? Or don't launch when children or pets present?

 

[Art Upton]

Any Idea what that fin hit to take it out? Did it launch going thru a tree ?

 

[tfrielin]

Any Idea what that fin hit to take it out? Did it launch going thru a tree ?

I'm pretty sure the fin was chopped by the nose cone impinging on it at parachute deploy.

I don't think it was areodynamic forces shredding it or else it would have ripped off at the root and neither other fin showed any damage.

But, having said that, I was a little skeptical when building it of just how thin the fins were for an F-powered engine. Not to mention the fins were built up from multiple parts---Just asking for failure, or so I thought. And I guess so.

Anybody else experience fin failures on Der Big Red Max flights???

 

[Back_at_it]

I would think that it would fly fine. I've certainly seen much worse.

I also agree with your thought that the nose cone took that out when it deployed. I'd check for red paint on the cone.

As for fin failures. When I took mine out of the box I Immediately set it aside as I wasn't going to build it with those stock flimsy multi piece fins. They might stand up to Estes F motors but I figured there would be no way they would live with a composite F. I was also concerned with their ability to survive any kind of landing.

Today, I might chance it as I've learned a lot more about papering fins with card stock and epoxy. Using this method, I'm thinking they MIGHT be ok.

 

[lr64]

Just how hard would it be to fix it?

 

[tfrielin]

I would think that it would fly fine. I've certainly seen much worse.

I also agree with your thought that the nose cone took that out when it deployed. I'd check for red paint on the cone.

As for fin failures. When I took mine out of the box I Immediately set it aside as I wasn't going to build it with those stock flimsy multi piece fins. They might stand up to Estes F motors but I figured there would be no way they would live with a composite F. I was also concerned with their ability to survive any kind of landing.

Today, I might chance it as I've learned a lot more about papering fins with card stock and epoxy. Using this method, I'm thinking they MIGHT be ok.

Yes---there is a definite smudge of red on the nose cone---Has to be the culprit.

 

[mikec]

Sorry to be a hard*ss but if I were an RSO I would not let you fly it that way, and if this had been a cert flight, I'd have failed it. But it would probably fly OK.

Snapback of the nose cone is a *very* common cause of damage. I'd use a longer shock cord for sure.

 

[OzHybrid]

Fix the fin.
Check your cord lengths to make sure that under full chute your nosecone is not able to hit your fins. Generally I have nosecone, short cord, parachute, long cord to body tube. If you put a lot of slip-knot bundles in your cordage, it absorbs the ejection energy as the nosecone reaches the end, rather than the nosecone getting all that energy ready for a spring back into the fins. This keeps nosecone well away from fins.
Here's how to tie one. Don't put the tail through the last one and as you pull the series of slipknots will come apart absorbing a little bit of energy with each knot coming undone. You want to get a balance between tight enough and loose enough. You should feel a slight pop as each knot comes undone.

https://www.animatedknots.com/chain-sinnet-knot

Good luck with your repair. Everything is fixable. You could always resim it in OR with the broken fin to see if it's safe as is.....