Solicitating Fin Suggestions

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11bravo

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Attached is a RS file of an upscale that I am ready to start on the fins.
The original has a plastic fin can that has fins that are all of about 1/20th of an inch thick.
A not very good picture of it can be seen here-
https://pg.photos.yahoo.com/ph/gps_greg/detail?.dir=2fbe&.dnm=803b.jpg&.src=ph

This is VERY close to a 2.5x upscale which would yeild fins of 1/8" thickness.
But, when I looked at plywood that thick (or should I say "thin") I was way worried that it would not survive landings as the fins will almost certainly hit first.
3/16" didn't impress me with it's robustness much either.
And since they will be TTW mounted, a broken fin will pretty much equal a totaled rocket.
I currently have the rocket designed with 1/4" fins that I'm pretty sure will take the hit and it seems to fly just fine, but what do you guys think?
Good to go?
Too Thick?

Thanks,

Greg
 
There WAS an attached file before I previewed, must have been stripped off then.
Here it is.
I hope.

Greg
 
hokkyokusei-
I could I guess, but this one I wanted to keep as simple as possible (read into this, don't have experience with fancy stuff) with stuff pretty much locally available.

Greg
 
That's fair enough, but really, glassing a fin is pretty easy. A good intro to fibreglassing, actually.
 
I could look into it, have looked into FGing actually for other apps.
I've also wondered why a guy couldn't use something like an old bed sheet smeared and smoothed with epoxy or resin.
That I have available.

Greg
 
Get some really light fiberglass cloth (SIG make 0.5oz./yd) in the R/C airplane section of most hobby shops.

It's really cheap too.
 
unglassed 1/4" ply would certainly be sturdy enough. although, it's a bit heavy, but that seems OK for what you're doing here.
 
Originally posted by 11Bravo
I could look into it, have looked into FGing actually for other apps.
I've also wondered why a guy couldn't use something like an old bed sheet smeared and smoothed with epoxy or resin.
That I have available.

It's the glass that adds the strength really, rather than the resin.
 
Originally posted by sandman
Get some really light fiberglass cloth (SIG make 0.5oz./yd) in the R/C airplane section of most hobby shops.

It's really cheap too.

That the rub.
Only decent hobby shop with in about 70 miles closed sometime ago and the new one caters only to RC wheeled vehicles and boats and the boats seem to just be a nod to others.
But seriously, I wonder about a this piece of sheet or rip-stop.

Greg

I'd really like to continue this near real-time conversation (they are my favorite way to message), but call wave says I have to make a phone call, thanks for the replies and I hope to see more.

Thanks,

Greg
 
Originally posted by 11Bravo
I'd really like to continue this near real-time conversation (they are my favorite way to message), but call wave says I have to make a phone call, thanks for the replies and I hope to see more.

Sometimes the best plan is to take it to the chat room, and come back here with a conclusion ;)
 
Originally posted by 11Bravo
Attached is a RS file of an upscale that I am ready to start on the fins.
The original has a plastic fin can that has fins that are all of about 1/20th of an inch thick.
A not very good picture of it can be seen here-
https://pg.photos.yahoo.com/ph/gps_greg/detail?.dir=2fbe&.dnm=803b.jpg&.src=ph

This is VERY close to a 2.5x upscale which would yeild fins of 1/8" thickness.
But, when I looked at plywood that thick (or should I say "thin") I was way worried that it would not survive landings as the fins will almost certainly hit first.
3/16" didn't impress me with it's robustness much either.
And since they will be TTW mounted, a broken fin will pretty much equal a totaled rocket.
I currently have the rocket designed with 1/4" fins that I'm pretty sure will take the hit and it seems to fly just fine, but what do you guys think?
Good to go?
Too Thick?

Thanks,

Greg

I'm not so sure you need to worry about this.

Both the big bird on the left (2.5 lbs) and the upscale on the right (14 oz.) have 1/8" basswood fins.

The one of the left nose darted and demolished everything up to the transition. The fins are TTW. One of them got a stress fracture along the edge of the fillet, and that's all.

The upscale on the right is surface mount. It always lands on its fins, including the two times it did so without a parachute. No damage.

If you feel you need protection, rather than covering the fin (which is more for flutter and shear strength) how about gluing half-round dowel to the edges? You've got your streamlining, you've got your harder surface, and you've got essentially a composite, because the edges will go wood, glue, other wood (and glue on the surface if you want, for more protection). I really doubt 1/8" ply would break, but it could chip and fray, and this would prevent that.
 
Now that sounds like the idea I need.
I will look hard into it.
Friday to do list-
Buy dowels.

Thanks,

Greg
 
Don't get me wrong, that idea is a good one.
I am just presenting a few others---

You could sand or cut a notch into the leading edge, tip, and trailing edge, and use a full-diameter piece of bamboo skewer (they are used for shishkebabs and come in sizes like 1/16th up to 1/4 inch in the home/kitchen sections of stores like W-world, and others)

You could glue a piece of bamboo skewer to just the tip so that there is a short length projecting aft of the fin trailing edge (a sacrificial piece to take 'the beating')

You could leave your basic balsa fin edges square and laminate the leading edge, tip, and trailing edge with a square piece of spruce (available at your local RC/model airplane hobby shop)

You could use a piece of thin music wire bent to the shape of your fin planform and glued to the perimeter of your balsa fin shape

You could just soak the trailing edge/tip area with CA

You could glue a length of 1/4 x 1/4 spruce to the aft body tube so that the rear tip projects below the fins and is the first part to hit the ground (this was called a 'bang stick' and was from some club's newsletter from about 15 or 20 years ago)

Last but not least: you could use an external tether point so the rocket hangs sideways (or even a teeny bit nose-down) during descent and takes ALL the beating off of the fin trailing edges
 
I think 1/8" Midwest Aircraft Ply will be just fine. You can get it at Micheals, or Hobby People or just about any hobby shop, maybe even a hardware store. I used it for my upscale Photon Disruptor and it works great. No need to worry about reinforcing, the TTW method is good enough, and use plenty of epoxy.You wanted to keep it simple, right?
 
Forgot to get dowels! hhmmpphh.
Bad day at work. Way bad.
powderburner-
I not sure about your comment
You could leave your basic balsa fin edges square.....
meaning I could use balsa or if you misunderstood (or I miscommunicated) that I was using balsa; I'm using plywood (at this time anyway).
What I have now is 1/4" stuff that I got at Hobby Lobby; its about 6 inches by 12 inches; nice and purdy on both sides.
What I intended my question to mean was: a) would thinner work OK or would the 1/4" be better?; b) would the 1/4" look too big, its twice as thick as the upscale calls for?
I like the ideas you've presented me, I think the easiest way with the tools I have would be the dowels.
I have copied your ideas to a text file in my Rockets folder for future use, thanks for them.

Hey, thanks everyone for the ideas, they're great.
Out of paranoia mostly, I think right now that I'll go with the dowel idea on 1/4" (maybe 3/16" uuuggghhh, still can't really make up the mind!).
As this is an upscale for the fact of having it more than flying it, and it will likely only fly at most a handful of times, the thinner would probably work just fine.
But I don't want it on display broken.

Thanks again all.
Have a great New Year's!

Greg
 
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