Reenforcing surface mount fins

[Sooner Boomer]

I'm rebuilding one of my old models. The original design had through-the-wall tabs on the fins. I don't think I'll be able to do that with the new one. What's a good way to reenforce surface mounted fins? I'm thinking of useing Tyvek saturated in yellow glue.

 

[jmasterj]

Tip-to-tip FG for HPR, tip-to-tip paper for LPR.

 

[bjphoenix]

I'm thinking of using Tyvek saturated in yellow glue.

I had that idea a few years ago so I did some tests- Tyvek doesn't stick to yellow glue very well since Tyvek is mostly plastic.

 

[grapetang]

Folded paper strips at the fin/tube joint with white or yellow glue works well. White glue will have more flex whereas yellow may be more brittle.
What works for glueing Tyvek? Spray glue or contact cement? The Estes Tercel recommended medium CA but I've never tried this. I'd like to know too.

 

[modeltrains]

The original design had through-the-wall tabs on the fins. I don't think I'll be able to do that with the new one. What's a good way to reenforce surface mounted fins?

With that starting at talking about how fins were attached to rocket body and then using the phrase "reinforce fins" there is uncertainty whether the question is about reinforcing the fin-to-body joint, or reinforcing the aerodynamic surface of the fin.

 

[BrendanH69]

I had to go with surface mounted canards for the Starstreak Darts.
I surface mounted them onto the BT50 tubes with epoxy, then applied epoxy/filler fillets before doing two thin layers of tip to tip using very fine 98gms/sqm F/Glass.
As the plywood canards were bevelled at the leading and trailing edges, I cut the tip to tip to only reinforce the central span of the canards. I cut three pieces of tip to tip - The first two pieces were cut to run from their respective canard tips and meet in the middle of the body tube, with the final piece cut to form the top layer to bridge fully across both canards from tip to tip.
All have stood up to flight and landing rigours very well. Sorry, don't seem to have taken good photo of the process, but I would encourage this method for sure.

 

[OzHybrid]

I'm rebuilding one of my old models. The original design had through-the-wall tabs on the fins. I don't think I'll be able to do that with the new one. What's a good way to reenforce surface mounted fins? I'm thinking of useing Tyvek saturated in yellow glue.

Post an ork file so we don't have to guess what you're talking about.

 

[Sooner Boomer]

Post an ork file so we don't have to guess what you're talking about.

Here are pictures of the original...



its last flight

 

[Sooner Boomer]

Why not TTW fin tabs? I'd like to experiment with a motor mount built into a coupler. This way I can build different configurations: from a single 24 or 29mm motor, to an 8x18mm cluster, and everything in between. Using a coupler requires a clean and smooth inside to slide it in. But, what the heck, I might just build one more 7 motor cluster with tabbed TTW (plywood) fins.

 

[dhbarr]

It seems to me that one could wood glue the fin on with no fillet and add a folded strip of material hard creased down into the filletess joint.

Then add the fiillet from molding and trim glue, with the full material layer on top of that. The body tube should split before the fins come off.

 

[Sooner Boomer]

It seems to me that one could wood glue the fin on with no fillet and add a folded strip of material hard creased down into the filletess joint.

What would you use for the "folded material"? That's what I had intended to use the Tyvek for, except that glue might not stick to it...

The body tube should split before the fins come off.

Well, that's happened, too. Not with this design, but with another rocket. I think the first improvement will be by using good quality plywood for the fins instead of balsa.
When I first started building this planform (Fat Boy cluster), I hadn't considered the longevity of the rocket. It was sort of a one-off to see if it would work. It does. And it's kind of fun to see people's reaction. I'd kinda like to make it more resiliant, and keep flying it.

 

[lakeroadster]

Why not TTW fin tabs? I'd like to experiment with a motor mount built into a coupler. This way I can build different configurations: from a single 24 or 29mm motor, to an 8x18mm cluster, and everything in between. Using a coupler requires a clean and smooth inside to slide it in. But, what the heck, I might just build one more 7 motor cluster with tabbed TTW (plywood) fins.

There is no reason you couldn't do through the wall fins, with a double wall design, then slide the MM - coupler sub-ass'y inside the inner tube.

 

[prfesser]

Folded paper strips at the fin/tube joint with white or yellow glue works well. White glue will have more flex whereas yellow may be more brittle.
What works for glueing Tyvek? Spray glue or contact cement? The Estes Tercel recommended medium CA but I've never tried this. I'd like to know too.

Very few glues work with Tyvek. It's polyethylene fibers bonded together. As hard to glue securely as a blowmolded polypropylene nose cone...

 

[Sooner Boomer]

There is no reason you couldn't do through the wall fins, with a double wall design, then slide the MM - coupler sub-ass'y inside the inner tube.

Not enough room. The tabs on the previous rocket went into the gaps between the motor mount tubes, which gave them a "valley" to sit in. Seven motors will barely fit into a BT80 coupler (eight will fit into a BT80 tube - but an eight motor Fat Boy would just be silly!).

 

[lakeroadster]

Not enough room. The tabs on the previous rocket went into the gaps between the motor mount tubes, which gave them a "valley" to sit in. Seven motors will barely fit into a BT80 coupler (eight will fit into a BT80 tube - but an eight motor Fat Boy would just be silly!).

Why can't you:

• Take a dremel cutoff wheel and cut the old fin off flush with the body tube.
• Take the dremel and carefully remove the old TTW fin tab material.
• Glue in the new fin?

What am I / we missing?

 

[Sooner Boomer]

Why can't you take a dremel cutoff wheel and cut the old fin off flush with the body tube. Then take the dremel and carefully remove the old TTW fin material. Then glue in the new fin?

What am I / we missing?

The broken fin (tab) is where the three dots are. I cut the rocket open to get the kevlar harness. The motor tubes are pretty much toast as well. I think in one of the Apogee videos, Tim mentions how clusters can fry the aft if the rear bulkhead is recessed. He's right.

 

[Sooner Boomer]

Nothing to do with the problem at hand... I watched several youtube videos with clustered Fat Boys. Each seems to do the same thing. Because the clustered motors (and mounts) add weight to the aft, nose weight has to be added to keep the CG/CP relationship for a "stable" flight. Using what OR called for, I think it makes these short rockets a bit overstable. What I noticed is that the aft sort of wanders around in a circle; "coning" as the rocket is in flight.

 

[lakeroadster]

Wouldn't it be more cost effective, less complex, and lighter weight, to just use one or 2 motors that have more thrust... instead of 7 motors?

 

[Sooner Boomer]

Wouldn't it be more cost effective, less complex, and lighter weight, to just use one or 2 motors that have more thrust... instead of 7 motors?

Of course it would.

 

[tsmith1315]

Wouldn't it be more cost effective, less complex, and lighter weight, to just use one or 2 motors that have more thrust... instead of 7 motors?

See Calvin's response:

 

[lakeroadster]

Of course it would.

Do that then?

 

[lakeroadster]

Nothing to do with the problem at hand... I watched several youtube videos with clustered Fat Boys. Each seems to do the same thing. Because the clustered motors (and mounts) add weight to the aft, nose weight has to be added to keep the CG/CP relationship for a "stable" flight. Using what OR called for, I think it makes these short rockets a bit overstable. What I noticed is that the aft sort of wanders around in a circle; "coning" as the rocket is in flight.

If you use the base drag hack, which is needed for Fat Boy rockets, that will minimize the amount of nose weight.

Then if you make the nose weight adjustable, once the model is built you can swing test it to ensure the stability.

 

[Sooner Boomer]

Do that then?

Because then it wouldn't be a seven engine cluster.

This is actually a rocket in the memory of my friend, James Brazzel. Braz was the local "King of Clusters". See the picture up there ^? What color is the nosecone?

Nope it's "brass" (Braz). The rocket is named "Hey! Braz!"

 

[BigMacDaddy]

Why not TTW fin tabs? I'd like to experiment with a motor mount built into a coupler. This way I can build different configurations: from a single 24 or 29mm motor, to an 8x18mm cluster, and everything in between. Using a coupler requires a clean and smooth inside to slide it in. But, what the heck, I might just build one more 7 motor cluster with tabbed TTW (plywood) fins.

I have been playing with this but not yet with fin tabs...

 

[lakeroadster]

Not enough room. The tabs on the previous rocket went into the gaps between the motor mount tubes, which gave them a "valley" to sit in. Seven motors will barely fit into a BT80 coupler (eight will fit into a BT80 tube - but an eight motor Fat Boy would just be silly!).

Actually, there is enough room. But it would require thinking outside of the box.

I'll fire up the cad station and make a couple models to show you what I'm thinking about.

 

[DaHabes]

If you are flying D engines the use basswood in place of balsa and do epoxy fillets. For C engi es and lower, do T2T paper.

 

[DaHabes]

View attachment 517475
View attachment 517476

The broken fin (tab) is where the three dots are. I cut the rocket open to get the kevlar harness. The motor tubes are pretty much toast as well. I think in one of the Apogee videos, Tim mentions how clusters can fry the aft if the rear bulkhead is recessed. He's right.

It's why I paint all of my rear CRs and the exposed BT high high temp black spray paint....

 

[DaHabes]

Not enough room. The tabs on the previous rocket went into the gaps between the motor mount tubes, which gave them a "valley" to sit in. Seven motors will barely fit into a BT80 coupler (eight will fit into a BT80 tube - but an eight motor Fat Boy would just be silly!).

You don't have to put motors in every tube, just the number that provides symmetrical thrust...

 

[OzHybrid]

I have been playing with this but not yet with fin tabs...

View attachment 517499

Looks interesting. Is a download available?

 

[lakeroadster]

Here's the Removable Bolt-In Motor Mount With TTW Fins, fresh off the CAD station...