Removable Fins For Traveling. Fillets?

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K'Tesh

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Ok... I'm returning to the US this July, and I'm planning on picking up a Binder Design Excel. I'm thinking that I can make it with removable fins to allow for easier packing and travel. So, to that end, I'm planning on making internal walls that are mounted to a removable motor mount section that are drilled to allow the fins to be screwed in place, or removed. Aesthetically, I like the look of fillets, and I know that they reduce drag. However, it is not my intention to build the highest flying Excel, ever made, just one that can do the job (Go up, and come down safely).

There are three ideas when it comes to fillets.

  1. Forget them altogether.
  2. Fillets attached to the fins, but not to the airframe.
  3. Fillets attached to the airframe, but not to the fins.

Clearly, forgetting about them is the easiest, but is it the wisest? Option 2 is the one I'm leaning towards. Using a nonstick surface (wax paper) attached to the airframe, construct the fillets on the fins while the fins are attached to the body tube. Option 3 is the same as option 2, except the fins are wax papered instead of the airframe.

If I went with them, I think option 2 would be easiest to repair should the need arise (think banging around in a suitcase), would be stronger, and would look better overall (no weird line/shadow) on the fin above the joint. Also it would be easier to pack.

Thoughts?
 
Internal fillets holding pockets. The toe of the fintab goes in first, then the heel. A pin or screw goes pocket-heel-pocket, and Bob's your uncle.
 
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Personally I'd omit them all together. Matter of fact, my latest build does not have them at all and I actually like the way it looks better. It's cleaner looking. Like you, I am not concerned with max performance so what ever drag is created by the fin/tube joint is irrelevant. I decided to forgo fillets because I really want to eliminate epoxy in my builds. I tried to use the trim mold stuff but it shrank to the point you couldn't tell it was there. So no more fillets for me.
 
Internal fillets holding pockets. The toe of the fintab goes in first, then the heel. A pin or screw goes pocket-heel-pocjet, and Bob's your uncle.

Yes, it's going to have internal fillets... I'm talking about aerodynamic/aesthetic external fillets....

[Edit] Oh... you're talking about losing the removable motor mount. However, external fillets on the fins would prevent that.[/EDIT]
 
Sweet looking rocket. Since I'm a BAR I had to look it up. I'm thinking forget the fillets.

You could always add them at a later date. Then you could establish a baseline of with / without from a performance perspective.

It would be interesting see the: performance without fillets, performance with fillets.

Binder Design - Excel Rocket.jpg
 
You could always order it with a Max Q fin can - I'm sure Mike could cut some custom Excel-shaped fins. It would add considerably to the cost, but it would be pretty cool.

Are you around long enough to attend a launch, or are you heading right back to China?
 
You could always order it with a Max Q fin can - I'm sure Mike could cut some custom Excel-shaped fins. It would add considerably to the cost, but it would be pretty cool.

Are you around long enough to attend a launch, or are you heading right back to China?

I think I'll pass on the MAX Q fin can... Harder to get through customs without lots of questions.

I'll be in the PDX area from the 1st of July through the 10th or 11th, then down to Southern Oregon until shortly before I return on the 23rd. I'm planning on attending the OROC meeting on the 5th.

Sweet looking rocket. Since I'm a BAR I had to look it up. I'm thinking forget the fillets.

You could always add them at a later date. Then you could establish a baseline of with / without from a performance perspective.

It would be interesting see the: performance without fillets, performance with fillets.

I'm seeing possibilities here, except that I like having fillets.

BTW: You've got the wrong variant... I'm looking at the Dual Deploy version.

Excel1.jpg


I've been thinking more about screw the fins in through the back... That might work if I were to notch the fins to allow them to drop in, then slide forward to get the "toe" hooked.
 
Look up Steve Lubliner's L3 rocket adventure. (it was in the NAR magazine.....a year (and a half?) ago.

In order to build his rocket in America, pack it in a box, ship it to Australia, and certify at Thunder Down-under, he made tight fin pockets on the mmt and cut slots for 3(or4) heavy duty (wide) zip ties. He shipped it in a compact box, strapped on the fins, and flew successfully.

~A
 
BTW: You've got the wrong variant... I'm looking at the Dual Deploy version.

The stretch model... even better! Good looking rocket. The decals on the fins are a nice touch.

Reminiscent of a DIMPS III Sopwith Camel..

Dimps III Sopwith Camel F1.jpg

Dimps III Sopwith Camel F1 Decal Set.jpg
 
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Look up Steve Lubliner's L3 rocket adventure. (it was in the NAR magazine.....a year (and a half?) ago.

In order to build his rocket in America, pack it in a box, ship it to Australia, and certify at Thunder Down-under, he made tight fin pockets on the mmt and cut slots for 3(or4) heavy duty (wide) zip ties. He shipped it in a compact box, strapped on the fins, and flew successfully.

~A

I don't have that issue of Sports Rocketry... When my former employer turned out to be a dud, I didn't have the cash to re-up with the foreign rate. Any chance you could scan that and send it to me? My idea is similar, as is the location.
 
Fin pockets, like dhbarr suggested. They’re done frequently for surfboards, but you’d want something lighter. I wouldn’t worry about fillets on the fins, but if you do them, do them on the fins, not the body tube. Nice thing about removable fins is that you can replace the fins if you want to try something else.
 
Your original plan sounds good do me. When forming the fillets, in order to avoid a gap between the fillet and the body tube later, be sure to add a spacer to the edge of the tab so that the fin sits away from its final position by the thickness of the wax paper. Yes, it's pretty near insignificant, but since you're doing this for aesthetics you really don't want any line at all. Maybe even double the space (two pieces of wax paper) on the tab so that the fin has to be pushed hard against the body tube when installed for flight.
 
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