Quantcast

Fun project on the bench

The Rocketry Forum

Help Support The Rocketry Forum:

Theory

Well-Known Member
Joined
Nov 30, 2018
Messages
797
Reaction score
521
Having some fun with this one, a 4inch “DER Red Max”

Built around a 4”Estes airframe and nose cone with a 38mm motor mount w/ an aero pack retainer, fins cut from 1/4” ply, and recovery by LOC.

You can see my daughters next to mine. As with hers, the decals will be from Stickershock23 though a different theme.

Not going to do a full build thread but wanted to share.

Aiming for a completed weight of just under 3 pounds to have her be a class 1 flyer, though I’m really looking forward to H and I motors.

BC197792-78AD-459D-9AD5-18C7E1602DEB.jpeg
 

Theory

Well-Known Member
Joined
Nov 30, 2018
Messages
797
Reaction score
521
making some progress, the motor mount is complete and in, and the Kevlar harness is secured to the forward centering ring.

something i keep going back and forth over is the fins. they are large and very heavy. had an idea to drill a well planned series of 1/2" and 3/4" holes in each, then skin them in 1/16" balsa. concern is that i am not sure if i will really end up saving much and will surely compromise strength.

will absolutely be drilling a few 1/2" holes in the fin tab. figure i can shave off about an ounce there.

thrust curve SIMs show decent performance on H and I motors. looking to get a little lighter so as to have better performance on a G or maybe even an F50 or F67 at the local field.

thoughts?
 

mo2872

Well-Known Member
Joined
Jun 22, 2020
Messages
431
Reaction score
364
Location
NE OK
Currently have this same project going, but I went with a 29mm mount. Also went with the RocketryWorks fins. https://www.rocketryworks.com/mega-der-red-max-plywood-fin-upgrade-set-of-3/

I also chopped the end of the nose cone off, and added a bulk plate and eyebolt. I’m at about 2 pounds without the chute or motor. I went emerald green metallic Duplicolor on the body, but haven’t decided a theme yet.
 

Attachments

Last edited:

Nytrunner

Pop lugs, not drugs
TRF Supporter
Joined
Oct 15, 2016
Messages
7,751
Reaction score
3,377
Location
Huntsville AL
something i keep going back and forth over is the fins. they are large and very heavy. had an idea to drill a well planned series of 1/2" and 3/4" holes in each, then skin them in 1/16" balsa. concern is that i am not sure if i will really end up saving much and will surely compromise strength.
@rharshberger and others have done similar for large area scale fin upscales. They'll cut out geometric sections, replace that with balsa or honeycomb that's lighter weight, then skin over the top with glass/carbon/thin wood
 

Theory

Well-Known Member
Joined
Nov 30, 2018
Messages
797
Reaction score
521
cool, thanks all.

@mo2872 no doubt the 1/8" fins you are using are much lighter than mine.
 

mooffle

Well-Known Member
TRF Supporter
Joined
Apr 20, 2020
Messages
282
Reaction score
174
something i keep going back and forth over is the fins. they are large and very heavy. had an idea to drill a well planned series of 1/2" and 3/4" holes in each, then skin them in 1/16" balsa. concern is that i am not sure if i will really end up saving much and will surely compromise strength.
Risky idea but: drill/cut holes and balsa skin it, then do an airfoil. The balsa would be much easier to shape and the plywood edges would be all that need to be sanded.
 

mo2872

Well-Known Member
Joined
Jun 22, 2020
Messages
431
Reaction score
364
Location
NE OK
cool, thanks all.

@mo2872 no doubt the 1/8" fins you are using are much lighter than mine.
Yeah, but yours look more appropriately "chunky". I was torn on whether to skin mine with some balsa just for the look, but ultimately decided I didn't want to take the time. I may regret that on the first landing......LOL.
 

Theory

Well-Known Member
Joined
Nov 30, 2018
Messages
797
Reaction score
521
Yeah, but yours look more appropriately "chunky". I was torn on whether to skin mine with some balsa just for the look, but ultimately decided I didn't want to take the time. I may regret that on the first landing......LOL.
It’s a trade off to be sure

going to drill the tabs, then weigh it all. If I’m under 42oz before paint I’ll be happy
 

Theory

Well-Known Member
Joined
Nov 30, 2018
Messages
797
Reaction score
521
Drilled the fin tabs. Saved just about an ounce. Not sure it was worth the trouble, but an ounce off the aft end is an ounce off the aft end...

tacked the fins in place with rocketpoxy and then moved on to the fillets. Something a little different for me here. More out of necessity than anything as I’m out of rocketpoxy. These are 30min BSI thickened with silica.

I taped them off, plopped down the thickened epoxy, worked it in to the joint, then pulled with a finely calibrated tongue depresser. I then pulled the tape and smoothed them out with gloved finger dipped in alcohol.

E45F21F9-8695-46CF-8434-88C73A11C557.jpeg
A5DDECC7-F8EE-4430-850B-6F61DB5AA0E1.jpeg


Came out ok. If it were a performance build I would have played with them more, however, as this has the aerodynamic properties of a fridge, I’m not going to worry too much.

should get to the second set later this evening. Will likely be out of BSI 30 at that point, so the last set will probably be with T88.

thinking it’s time to buy more epoxy...
 

Theory

Well-Known Member
Joined
Nov 30, 2018
Messages
797
Reaction score
521
I want to see this aerodynamic fridge
lolz. That’s the point. Blunt nose cone, huge blocky fins... going to take some umph to get her through the air. Happy I went with the 38mm
 

Theory

Well-Known Member
Joined
Nov 30, 2018
Messages
797
Reaction score
521
T88 and the silica thickener works ok but thins out REALLY fast with the ol’ gloves alcohol finger... chased more than a few drips
 

Theory

Well-Known Member
Joined
Nov 30, 2018
Messages
797
Reaction score
521
The pictures are less than good as the lighting was poor. Wanted to get some shots outside before the next round of snow
 

mo2872

Well-Known Member
Joined
Jun 22, 2020
Messages
431
Reaction score
364
Location
NE OK
Looks great! Still pondering my “theme” with my jewel green paint on mine.
 

Latest posts

Top