Madcow Twitch and a couple questions

[crossfire]

See post #1

Ok I missed that.

 

[CoachSteve]

Still have to do the internal fillets - with the aluminum tail cone, the aft CR is just extra weight - I may leave it out

 

[Buckeye]

The tailcone has a strong influence in OR barrowman equations. Try RasAero. It is not as pessimistic.

 

[wsume99]

Another thing to not overlook, the motor will be positioned further aft with a tailcone retainer than it would be with a normal retainer. This will reduce your stability margin. I am lamenting moving the MMT 1/4" aft on a recent build because of the stability impact. If I had used a tailcone the effect would have been even greater.

Love the build BTW. Thanks for the build thread.

 

[CoachSteve]

Agreed - the tail cone hurt me for sure (but you cannot deny the cool factor) - And since I am not going for performance here (will be flown on 29mm RMS stuff until I go for my cert) -I will just add the necessary nose weight and take the altitude penalty.
This build does fall into the short rocket stature as well so I will be getting a good bit of base drag stabilization. Adding a truncated, zero mass cone at the tail of my Open Rocket sim approximates that I should be good with about 100g nose weight.

 

[CoachSteve]

Here is my first try at epoxy fillets - I think they came out pretty good.
I went with small radius fillets and no sanding after application.
30 min BSI with black pigment added:

Once I do some internal fillets it will be ready to fly

 

[Forever_Metal]

Coach,

Had the same weight issue with my MC Patriot... Even with a loaded AVX bay still needed 500+grams of nose weight to counter the 54mm mount and big-I/small j motor

With the fins drilled out like that maybe use 2 part foam to lock everything in?

fm

 

[Nytrunner]

I dunno, foam ends up being non negligible weight at the wrong end of the rocket

 

[CoachSteve]

plan will be to do some internal fillets with epoxy and add some nose weight - anybody know how much base drag these guys get - they do fall into the short fat rule. I know the tail cone removes some of it - following the advice from Apogee on short fat rockets with tail cones and adding a zero mass cone to the tail of your sim- the sim above shows I should be cool with about 100g up front

 

[AfterBurners]

Here is my first try at epoxy fillets - I think they came out pretty good.
I went with small radius fillets and no sanding after application.
30 min BSI with black pigment added:

Once I do some internal fillets it will be ready to fly

I see you like RC trucks too! Anyway I think you did a nice job on your epoxy fillets. I think for me the hardest part making epoxy fillets is the leading and trailing edges. Getting it to form properly without having the problems with the epoxy running. For me I switched to epoxy clay. It allows you 3 hours of work time and you can do the entire rocket. I still mask the fillets with tape, just so they stay uniform and then when I pull it up I just make sure the edges are nice and smooth by running my finger on them with denatured alcohol. After they dry they are solid like concrete. I come by with rubber grips and sand paper and shape them.

 

[tim cubbedge]

My actual altitudes have been pretty close to sims without zero mass cone. My Twitch has an 11:1 L to D ratio which is greater than what Apogee considers short fat rocket.

 

[CoachSteve]

So if the Twitch is 11:1 then I should not sim it with a drag cone - that means I need ~200g up front - I can do it but that makes the rocket around 1480g with a G76 in it.

 

[CoachSteve]

And yeah - I have way too many RC cars too
Vintage Tamiya Midnight pumpkin
Vintage Associated RC10T
Losi XX
Traxxas 1/16 revo
Full custom Axial Wraith
Custom built 1/8 super crawler
Wpl 1/18 Toyota
Losi micro crawler
ECX Doomsday Barrage
Bolink Digger
full 3D printed 1/32 ford raptor
I think I have a problem