Molded 40mm FAI Airframes

The Rocketry Forum

Help Support The Rocketry Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

TheAviator

Well-Known Member
Joined
Jan 18, 2009
Messages
935
Reaction score
121
A couple of months ago, a member of the US Spacemodeling team showed me a 40mm model he bought from a Russian manufacturer. It had an immaculate surface finish indicative of a internally molded process. I recently came by some scrap 1" thick acrylic stock, so I am taking a pass at making my own 40mm airframe molds.

These are two halves of a complete mold machined on a ShopBot type router. They're hot off the presses today, and the next step is to polish the molds with increasingly fine grit sandpaper. First, I need to polish the mold cavity and resin channel, then knock down the extra material around the cavity and polish the parting plane. More info as more work is done! Time for some elbow grease...

20160627_165710.jpg

20160628_201330.jpg
 
Super cool.

For a long time I've wanted to make airfoiled fins in a two part mold. A ShopBot was discussed, but with MDF mold material. The acrylic is a really cool idea.

Subscribed!
 
Very impressive, Brian! Please keep us updated as you progress with this project.

James
 
Super cool!

Can you explain a bit about the molds? We're they made made by you or by a third party?

My recent bladder mold was a ton of work and probably not much cheaper than an aluminum one.
 
Super cool!

Can you explain a bit about the molds? We're they made made by you or by a third party?

My recent bladder mold was a ton of work and probably not much cheaper than an aluminum one.
Scott- 2nd party and an FAI team member. I provided the coords and general mold parameters and he turned it out. With CNC aluminum molds, polishing of the mold surface is required after receipt. 500 grit sandpaper to start and then working up to 0.25 micron diamond polish is mandatory for a mirror like finish on the mold and then on your finished model.
 
A couple of months ago, a member of the US Spacemodeling team showed me a 40mm model he bought from a Russian manufacturer. It had an immaculate surface finish indicative of a internally molded process. I recently came by some scrap 1" thick acrylic stock, so I am taking a pass at making my own 40mm airframe molds.

These are two halves of a complete mold machined on a ShopBot type router. They're hot off the presses today, and the next step is to polish the molds with increasingly fine grit sandpaper. First, I need to polish the mold cavity and resin channel, then knock down the extra material around the cavity and polish the parting plane. More info as more work is done! Time for some elbow grease...

View attachment 295456

View attachment 295457
Fantastic. Good Luck!
 
Super cool.

For a long time I've wanted to make airfoiled fins in a two part mold. A ShopBot was discussed, but with MDF mold material. The acrylic is a really cool idea.

Subscribed!
I've had aluminum molds made for thin fins via a UK Fai modeler. With small thickness fins and a razor sharp TE, when removing from the mold, they can distort, slightly and unfortunately. This will cause squirrely trajectories! Composite, tiny thickness fins that have a good molded airfoil is something to endeavor.

Best so far is true C-grain balsa, contest grade with Japanese tissue on top and vac'd down. Flat, and can be attached to the body using a jig. With flat fins and attached accurately, there is minimal spin on boost. Though I have been imparting a very small angle so that the model does spin slightly on boost and because of head winds aloft. So a tiny spin on boost is desirable - 2-3 rotations before apogee.

Kooch
 
are these molded for 10 or 13mm motors? Will they be available to the general public to purchase?
Shockie- Show up for a contest using and I can supply you with models! They are molded 10mm, but a simple cut at the aft and you can add on a 13mm tube. I have no desire to get into the rocketry kit biz, unfortunately, if you are thinking. Too much going on with my career.
 
Shockie- Show up for a contest using and I can supply you with models! They are molded 10mm, but a simple cut at the aft and you can add on a 13mm tube. I have no desire to get into the rocketry kit biz, unfortunately, if you are thinking. Too much going on with my career.
What does this mean?

Show up for a contest using and I can supply you with models!
 
ched to the body using a jig. With flat fins and attached accurately, there is minimal spin on boost. Though I have been imparting a very small angle so that the model does spin slightly on boost and because of head winds aloft. So a tiny spin on boost is desirable - 2-3 rotations before apogee

What method do you use to make that happen? I would think that imparting that little spin would take a precision that my N years old (N = large positive integer) eyes can no longer support, even with glasses. . . .
 
What method do you use to make that happen? I would think that imparting that little spin would take a precision that my N years old (N = large positive integer) eyes can no longer support, even with glasses. . . .

A jig would relatively easy to print,
 
Now would be a good time for someone to figure out how to mass-produce 40mm airframes, as the USA just won the bid to host the 2023 FAI World Championships for Space Models.

July 1-8, 2023, Austin metro area. Go ahead and produce them with 13mm motor mounts, because the tube events will be using Estes motors exclusively.

James
 
Now would be a good time for someone to figure out how to mass-produce 40mm airframes, as the USA just won the bid to host the 2023 FAI World Championships for Space Models.

July 1-8, 2023, Austin metro area. Go ahead and produce them with 13mm motor mounts, because the tube events will be using Estes motors exclusively.

James
How did you manage to restrict FAI World championships to Estes 13mm motors? I thought they were always open to whatever the contestants submitted, down to 10mm, and contest certified on site. Also, will Estes be producing special motors for the FAI competition?
 
How did you manage to restrict FAI World championships to Estes 13mm motors? I thought they were always open to whatever the contestants submitted, down to 10mm, and contest certified on site. Also, will Estes be producing special motors for the FAI competition?

This event will be a NAR event run under NAR insurance at a US launch site. Therefore we will be using only motors certified for use, sale, and transport in the US. In short, NAR Certified motors.

The bid was clear on this point, and was accepted by the FAI. The plan is to use the same motors that can be purchased by anyone from any hobby supplier in the US. 13mm motors will be used for 40mm tube events, while other events can use 13mm, 18mm, 24mm, and 29mm NAR contest certified motors, just like a NARAM.

Estes may produce some unique delays for the tube events, but that decision will not be made for some time. (I have not yet asked them to make any special motors for the Championships. If special motors are made, they will be available to every competitor in the event. No competitor will have the benefit of using motors that are not available to all other competitors.)

Also: a TARC-like event will be elevated to World Championship status for this contest for both Juniors and Seniors. Single egg, 300 meter target altitude, 60 second target duration, three flights. Look up the S2/P event in the FAI Sporting Code.

https://www.fai.org/sites/default/files/ciam/sc4_vol_s_space_21.pdf
James
 
What method do you use to make that happen? I would think that imparting that little spin would take a precision that my N years old (N = large positive integer) eyes can no longer support, even with glasses. . . .
A jig would relatively easy to print,

If you're using a Rose-style jig, a small wedge between the plate and fin would impart a repeatable amount of cant. Alternatively, I've sanded a single-sided (read: flat-bottomed) airfoil into a piece of 1/16" (1.6 mm) balsa. Put the flat side on the jig and you get an effective cant in your fin, and the spin is slow enough that I can watch it go up. A very rough calculation says that you need 0.5 to 1.0 degrees of cant to get 1 roll per 50 m on a typical FAI model.

I have some not-laminar flow plugs that I can pull molds from. I gave up on the acrylic mold a while ago, but mostly because I got bored with it. I was able to pull some pretty good S1 upper stages from a smaller mold a while ago, I'll try some larger ones this summer. I'd be willing to send a mold to potential US team members for cost of supplies and time. @kkooch If you want to send me a set of points for your laminar flow airframes, I'd be interested in taking a look. Did you use CFD or a momentum-integral method for your shape determination?
 
If you want to send me a set of points for your laminar flow airframes, I'd be interested in taking a look. Did you use CFD or a momentum-integral method for your shape determination?
Sure, I can send them, but don't want them posted for public viewing and for obvious reasons with WSMC's coming up. Send me a private message on this forum with your email.

The shaping formulas are 5 degree polynomials with 8 parameters and are Navy torpedo formulas. The CFD program is MTFLOW and then the altitude program is one that I wrote that integrates the varying Cd's output by MTFLOW over the entire flight velocity (Re) profile. Began the process in 2012 and it has evolved!
 
Back
Top