Masonite???

The Binder Design kit I have has Masonite centering rings and bulkheads instead of plywood. On the bright side, everything's doubled up (4 CR's and 2 bulkheads). I was thinking that I would space it so the front CR is about 1" from the front of the motor mount tube, the 2nd one would be just in front of the forward edge of the fin tab, the 3rd would be just in back of the rear edge of the fin tab and the 4th would be right at the back of the rocket. I plan on epoxying the 2 bulkheads together for strength as I plan on using zipperless recovery again for this rocket. Any problems with this setup and/or better solutions?

Sounds like a good idea to me. Masonite is a very strong product. BTW, what kit did you buy?

I bought the Sentinel. I have no idea exactly why it caught my eye, but it did. It was actually the first HPR kit I bought, but I decided to build the Black Brant X first.

Sounds like a good plan to me. The Sentinel looks to be a good kit.

The masonite rings have withstood flights up to L class motors. Not sure why they get a bum rap. We've even flown some rockets with double tempered masonite FINS past mach 1 to test the material. This testing is ongoing, and we hope to have a mach 2+ flight in September using this material for fins.

The only drawback to it is that if it land in water, it will swell. Therefore, we recommend coating the masonite rings with epoxy to seal them.

Enjoy your rocket!

Mike Fisher
Binder Design
https://binderdesign.com

Sorry Mike, my intention was not to enhance any bad rap that Masonite may have. I was speaking from pure lack of knowledge of it whatsoever, having only used cardboard, plastic and plywood.. Thanks for the advice regarding the epoxy, as water can be a consideration where I fly and I would have missed that. As long as you're here, though, could you let me know why the instructions specifically state to only sand an airfoil into the leading edge of the fin instead of all of the edges?

my intention was not to enhance any bad rap that Masonite may have.

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There isn't any bad rap really, just poor public perception that it will not be strong enough. That is why we are doing some ultimate stress testing using it for fins. It has been extensively tested for centering rings in thousands of rockets, and as far as I know, they have never failed in flight.

On your fin beveling, keep in mind that the original instructions for your kit were written in the mid 90's by Scott Binder. On most of these kits, it was only recommended to bevel the leading edge for some reason.

I personally like to bevel all of the leading and trailing edges, as the instructions to our newer kits will show. It really does help reduce drag. Eventually I will be updating all of the instructions to our older kits to reflect this.

I'd like to suggest one other thing with the Sentinel. Keep an eye on your CP/CG relationship. The fins don't have much span, so the CP is fairly far forward for a model of this length. Check it before flight and add nose weight if necessary to get your 1 to 1 1/2 calibers of stability. We list the CP data at our site.

Best of luck!

Mike Fisher
Binder Design
https://binderdesign.com

Thanks for the advice. I'm using a zipperless design on this which will bring the CG way forward, as the recovery (including an 8 oz. TransBeep locator) will all be in the forward section. I haven't modified it in RockSim to check it, but I don't foresee a problem.