Shredder - Estes Pro Series on a K535

[pathtouch]

Well this started a joke facebook post, turned into a thought experiment, and then finally an actual build.
Could you stuff a 54mm motor into an Estes Pro Series 2.5" kit and have it survive, with no composites?

It seemed silly until I made a sim, and the forces aren't that unreasonable. We wanted to use a DMS motor incase we never got this back and settled on the K535 from Aerotech.
28.5Gs and assuming a 5oz nose cone is only 9ish lbs of force. Do I think I could stack a 10lb weight on a 2" section of unreinforced cardboard tube... sure.




So I set off looking for a Pro Series 2.5" Kit I liked and ended up actually buying one from Bad Boy Rocketry on Ebay. It shipped with two lengths of 2.5" tube, a coupler, 29mm motor mount, and wonderfully cut 1/8" fins and centering rings.



I wanted to go traditional dual deploy since this sims to like 8k. LOC 54mm Motor Mount Tube (MMT) was a little small but sleaving that with some mailing tube brought it up to the perfect diameter. I epoxied them together and had to add a little sliver for the right circumference. Used Electrical tape to keep it all tight during the cure.




Shot a coat of primer and started filling spirals.


The motor mount used the same 54mm LOC tube and more mailing tube as centering rings. I also epoxied on some Kevlar for a recovery harness. Note I left the centering rings gaped to pass over tnuts for the rail buttons.





Got the AV Bay put together and vent holes and static ports all drilled in.

 

[pathtouch]

I also wanted to address that sloped nose cone and get a tracker in there. We all know about the deployment issues with the Big Daddy so I normally cut the slope off and put a flat bulkhead there. I got a little lazy here and slapped a bulkhead in the bottom but this should help act like a piston for the nose cone.





Also made some stepped bulkheads for the AV bay.



Then after updating the sim with some actual weights with epoxied components I designed a fin shape that maintained 2 calibers of stability as this will go super sonic. Also the 1/8" fins in the kit were upgrade to 1/4" after I did a fin flutter analysis. This shape and thickness should give me some margin against flutter.






I'll probably coat these with epoxy then attach them later this week.

 

[pathtouch]

Coated the fins with a layer of epoxy and stacked them under a battery to smooth them out. This may add a small amount of strength but with no fiberglass it’s probably minimal. Also learned the hard way wax paper is only waxy on one side and will boned to epoxy…



Wrapped up the AV bay. Gonna direct wire initiators to the altimeter. .40 brass for charge wells, holds about a gram. Finally, motors came in!

 

[Handeman]

Use parchment paper for baking. Should work with both sides.

 

[cerving]

I like your optimism... you bought TWO motors.

 

[pathtouch]

Use parchment paper for baking. Should work with both sides.

You know I started with a sheet of that and thought to myself, this feels like it would stick to epoxy and changed to the wax paper. I’ll try that next time.

 

[Hobie1dog]

 

[pathtouch]

Steady progress. Filled most the space between the body and motor mount with thickened epoxy and tacked the fins on. Gonna make some healthy 1” diameter fillets on this pig over the weekend.



Love those payloadbay.com printed fin jigs.

 

[CoyoteNumber2]

I like your style.

 

[ljwilley]

Keep us posted!

 

[pathtouch]

Got the last of the external fillets done tonight. (oh hey is that a 98mm motor tube and 60" long 6" fiberglass airframe in the background )



So previously I had assumed max forces on the unstiffened Estes tube would be related to max acceleration and the weight of the nose cone. I think I sort of missed the aerodynamic component completely there. So I did some quick Open Rocket checks. First found out where maxQ was and what velocity and drag force was associated with that. Came out to about Match 1.36 and 72 lbf.


So I then did a component analysis at that Mach Number and found the nose cone and upper payload body tube were about 10% of the total drag. So I'm still only looking at 7lb due to drag. Everything below that is a super stiff av bay, then basically LOC 54mm Motor Mount Tube.


This doesn't occur at max acceleration, in fact acceleration at maxQ is like near zero Gs (makes sense I guess). I'm still thinking this is very possible. I will probably strategically wrap some chrome vinyl around the unreinforced areas to help with strength, and also help with visual tracking.

 

[pathtouch]

This is still alive just taking a back seat to an L3 project. It’s pretty much done, just needs some paint and recovery harnesses finalized.

I decided I wanted about a bit of nose weight and epoxied two .50 cal musket balls in there. Did the typical epoxy and wood skewer method to retain them.



The I went to pack my 30” recon chute in the payload and realized I have seriously underestimated the size requirements. So I ordered a thin mil 30” from Top Flight. That thing packs down to nothing! Side by side comparison.



I’ve got some leftover 3/8 Kevlar I might use to attach the fincan. Super overkill but free. Main chute harness will probably be some Emma Kites Kevlar.

More to come later.