Several questions about a 4" FWFG build.

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Sailorbill

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I am planning to build a 4" FWFG version of a PML Endeavour with a 75mm motor mount. I have a 3 grain CTI case I plan to use. I have been running some sims in RocSim but not having final weights limits their accuracy.

Parts I have in house.
60"X4" Rocketry Warehouse FWFG tube.
4"X8" MadCow FWFG Electronics bay.
75mm PML Phenolic Motor Mount tube. Will this be strong enough or should I go with FG?
75mm Slimline Retainer.
Various G10 centering rings.
MadCow Tail Cone. Why you may ask, because I like the look. The 6" Endeavour I built for my L3 has one.
Need to purchase.
Fins I need advise on fin thickness, I was thinking 0.093 would be thick enough but I can get 0.125 from PML and I can get them beveled.
Nosecone. Finding a 4 inch 4:1 ogive in Fiberglass is limited. I also plan on using it for my tracker and adding weight as necessary.
This will be my first all fiber glass rocket.
All suggestions, questions and ridicule will be gladly accepted.
 
All my Wildman 4X3 (or 98x75 for those who prefer metric) kits came with 3/16" fiberglass fins. An AT 75/3840 case with a L1520T really rips off the pad. I'd be afraid of flutter with anything thinner.
 
I am planning to build a 4" FWFG version of a PML Endeavour with a 75mm motor mount. I have a 3 grain CTI case I plan to use. I have been running some sims in RocSim but not having final weights limits their accuracy.

Parts I have in house.
60"X4" Rocketry Warehouse FWFG tube.
4"X8" MadCow FWFG Electronics bay.
75mm PML Phenolic Motor Mount tube. Will this be strong enough or should I go with FG?
75mm Slimline Retainer.
Various G10 centering rings.
MadCow Tail Cone. Why you may ask, because I like the look. The 6" Endeavour I built for my L3 has one.
Need to purchase.
Fins I need advise on fin thickness, I was thinking 0.093 would be thick enough but I can get 0.125 from PML and I can get them beveled.
Nosecone. Finding a 4 inch 4:1 ogive in Fiberglass is limited. I also plan on using it for my tracker and adding weight as necessary.
This will be my first all fiber glass rocket.
All suggestions, questions and ridicule will be gladly accepted.

The PML phenolic motor mount tube is just fine. In most cases a motor retainer couples the thrust of the motor to the aft centering ring where it then is transmitted to the fin tabs and body tube so the motor mount tube really doesn’t have to withstand thrust, but there are a lot of rockets out there without retainers, but which have phenolic motor mount tubes that withstand a ton of thrust.


Steve Shannon
 
The only question you asked in your entire post was "Will this be strong enough or should I go with FG?" I agree with Steve's answer.
 
The only question you asked in your entire post was "Will this be strong enough or should I go with FG?" I agree with Steve's answer.

While not phrased as a question, he also asked for advice on fin thickness.

I would definitely go with .125" or even a composite sandwich fin if you plan to go fast.
 
As the others have said PML MMT is fine
.125 fins, if you're really going to hammer it then go .1875

Also if this is your first foray with fiberglass, make sure you pre-clean thoroughly, surface prep properly and use a good grade epoxy
 
Sorry for the meandering post. It is hard to concentrate when my three year old great granddaughter is competing for my attention.:wink:
Thanks for the replies. They allayed some concerns I had and gave me some ideas.
Motor retention is with a Giant Leap Slimline.
I think my best option for the fins is to purchase 0.125" G-10 fins already beveled from PML. Price is reasonable and it saves me a bunch of time.
Hope to have it done in time for Airfest along with several other rockets. Just need to have the weather warm up. No epoxy in the house, my wife got really bad headaches when I have tried it before.
 
Definitely .125 for fins. If you want to reduce 'floppiness' of fins, since your scratch building, cut the size down about 20%. will look the same, no one will notice, and makes for a better flier!

I did that on my 6 in. Endeavor.

BUT ...with a 75mm hole, if you plan on flying any big motors [ Large L-s & M's] 3/16 fins are a must.
 
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John Thanks for the reminder on cleaning every thing before assembly.
 
Thanks Jim
I didn't think about reducing the size of the fins. I might have to look into that. I also have some carbon cloth I could cover the G-10 fins in to add stiffness.
When I built my 6" Endeavour I used 1/8" Fiberglass/Honeycomb Sandwich Panels from ACP Composites. They were inexpensive back then but not now.
 
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