My first micro downscale

Well decided to try my hand at 1/8 a sd. I am a total rookie so i figure the best way to go is a downscale from one of my favorite manufacturers Fliskits. I ordered everything from fliskits including a cougar 660 that i am planning on using for parachute duration. I am downscaling by a factor of .56 roughly.

gagreen said:

Well decided to try my hand at 1/8 a sd. I am a total rookie so i figure the best way to go is a downscale from one of my favorite manufacturers Fliskits. I ordered everything from fliskits including a cougar 660 that i am planning on using for parachute duration. I am downscaling by a factor of .56 roughly.

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gagreen:
Are you building a fun flying 1/8A-SD or for a contest?
For a fun fly or gentle competition a micor cougar 660 should be a great start at micro downscaling and super fun to flying.

If your working toward a real contest you my want to look into lighter vehicle body materials like tracing vellium and Pratt Hobbies Vacuum formed ultra light weight styrene Nosecones 10.5, 13, 18 and even 24mm.

Micro "Paper Tigers", "Taper Papers" and Double Taper Papers are a terror on the field LOL.... As large a diameter as BT-20 and up to 12" long with only 2.1 to 3.5 grams of total vehicle mass.....leaving lots of room for steamer mass for total lift off mass under 10 grams
Biggest challange is deciding how much streamer is needed with your group & field...to get a Return. Piston or tower launchers are also a necessary evil.

Good luck either way, We'll be watching to see how your MM Cougar comes out and how it does SD wise

Im just doing it for fun. I haven't been to a competition flight before so this first one coming up later this month will be more of a learning experience for me. I plan on going both days so i didn't want to show empty handed lol. The cougar 660 downscale and the actual kit that i got are going to be my first attempts at the competition part of the hobby. being i don't have a whole lot of time to test new building techniques and materials it seemed like the best set for me to start and have fun with. I am sure its like any other part of this hobby, once i start getting into it ill get into more "exotic" builds.


anyways i was thinking about going to kinkos and having them just half scale the pattern sheet for me... but what is the fun in that? I broke out the protractor and got to making my own tail cone and fin templates. It all came out pretty good just need to clean up the edges then install them.

Sounds like a great project! Can't wait to see more.

Lookin good so far!
Keep Up the good work.

fins are on... but im not really that happy with the end result a few degrees of from perfect spacing due to my shaky hands so i am making a jig of sorts to make them perfect. But this is a scratch and everything else went pretty good. I used a 1/32 drill bit to bore a very small hole near the cg, i am running the shock cord up along the side of the bt then into it that way i get a sideways recovery. attached a pic of the rocket as it sits but i will have to redo 2 of the fins before i call it good to go.

For my duration models, I use Kevlar thread for the shock cord. I cut a small notch in the root edge of one of the fins and run the Kevlar through that hole after the fin is attached. The thread is imbedded in the fillet, half on one side aft of the hole and the other half forward of the hole. I then use silver mylar tape to tape the thread at the balance point so the model hangs sideways from the thread. To fly, I run attach the other end to the nose cone, which has a small notch running the length of its shoulder. The streamer or chute is attached to a loop on the nose cone and inserted into the body above the wadding. The thread runs up the body and inside at the notch. I've found that the small amount of drag that the outside shock cord induces is more than offset by putting a larger streamer or chute inside that has a clear path out. After that, the key is finding the thermals and letting them hold up your rocket.

I like the finhole idea. the way i used sounds kind of similar to that only my hole is through the body and the kevlar thread is held to the body by a knot on the inside of the tube. I cant find my camera's usb cable so i cant get a good macro shot of it. I also slotted my nc shoulder to let the ejection charge to freely pop the streamer out.

I added a picture of its balance test, i may end up needing to move the hole further up. I put it a little back to account for the weight of a spent engine.

the fin fiasco is fixed now. It really amazes me how only 2 degrees off is so exaggerated on mmx aesthetics.

I attach kevlar thread Shocklines as Greg suggests also. It really is the best way for most SD and PD models for that matter regardless of thrust level or motor size.
Adjusting for horizontal body hang with the Kevlar embedded in the fin fillet is easy with a single wrap of very thin & light weight mylar tape. I've often used silver Trim monokote for this purpose though it is a bit on the thick side.

Something to keep in mind about fin placement & alignment: I assume the couple degree error your talking about is that one of your three fins isn't exactly on the 120° seperation line. If that understanding is correct the fact that one fin is not perfectly spaced is really NOT a big deal IF the fins are on absolutely in-line with the bodytube centerline (direction of travel). While it may not look as nice as perfectly spaced fins those couple degrees have very little to do with achieved altitude. Inducing any spin at all however does.... Dead on alignment is vary important, degrees of seperation not so much

Hope that helps.

The few degrees of separation was just to noticeable for me to leave alone. I kind of copied one of you fin alignment jigs i had the body strapped to a block and leveled and allowed the fin to rest level on the block while the glue dried.

gagreen said:

The few degrees of separation was just to noticeable for me to leave alone. I kind of copied one of you fin alignment jigs i had the body strapped to a block and leveled and allowed the fin to rest level on the block while the glue dried.

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That great! just didn't want you (or others) obsessing over a few degress of seperation when it's the alignment that's most important. I know I did for a lot of years before a couple of the International flyers clued me in
Do your best at setting everything perfect, keeping in mind NOTHING in or on this earth is perfect, make the important parts of the whatever the objective.

Neat project here. Especially so since I am working on a Cougar 330 idea for competition. I will be most interested in how yours works and what you will use for a streamer (material and size).

As for optimization for weight and launch speed (like using pistons), 1/8A-SD is one such contest event that won't really benefit all that much... Since there is only one motor available with a fixed delay charge (which is way too short for things like this), designing a rocket that can hit 200 feet doesn't do much when the ejection charge is going to fire 125 feet up...

Unless the piston launch gets the rocket up higher before the short ejection charge goes off :blush:

In any event, it's a lot of work to make such a small piston..

jflis said:

Neat project here. Especially so since I am working on a Cougar 330 idea for competition. I will be most interested in how yours works and what you will use for a streamer (material and size).

As for optimization for weight and launch speed (like using pistons), 1/8A-SD is one such contest event that won't really benefit all that much... Since there is only one motor available with a fixed delay charge (which is way too short for things like this), designing a rocket that can hit 200 feet doesn't do much when the ejection charge is going to fire 125 feet up...

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I am not real sure about streamer materials or size, so far with it ive basically just downscaled the important parts from the 660. I really need to go get some more motors so i can do some tests before the actual event comes up. I will use the 660's comp streamer as template for starting out and depending on what other papers i can find ill modify according to how its flying and falling. I have my spring break this week and i just got the music wire to build my launch pad so ill get some results and mats up asap.

I have never used a piston launcher before that may be something i build this summer to mess around with for now ill stick to the less exotic till i have time to really invest in learning how they work.

hhhmmmmm, just realized... I'm going to have to work out a design for a micro pop-lug... man, that one's going to keep me up nights... LOL

jflis said:

hhhmmmmm, just realized... I'm going to have to work out a design for a micro pop-lug... man, that one's going to keep me up nights... LOL

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Shouldn't keep you up long Jim:
It's already been done and shown over the the MicroMaxRockets Yahoo Group. They work quite well but no where near as well as a micro piston or better yet micro floating head piston.

Pistons by the way Pat don't need to be turned on a lathe to be very effective and accurate.
As you mention pistons do in fact get our 200ft + models to altitude before the ejection pops. That's why the current altitude records for both 1/8A Altitude and 2x1/8A cluster altitude are both 82m (269feet). All on the current MMX-II motor. So designing for optimum mass is just as important with micros as it is with any other motor class cometition model.

Pistons by the way Pat don't need to be turned on a lathe to be very effective and accurate.

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They don't abosolutely need to be, but it's the better way to do it. The clearance between the piston and piston tube is important and requires accuracy to do it properly.

The choice of materials is important too. Materials such as fiberglass and carbon fiber are more stable than cardboard with temperature and humidity changes and make the best outer piston tubes so that the proper clearances can be maintained in changing weather.

Pat_B said:

They don't abosolutely need to be, but it's the better way to do it. The clearance between the piston and piston tube is important and requires accuracy to do it properly.

The choice of materials is important too. Materials such as fiberglass and carbon fiber are more stable than cardboard with temperature and humidity changes and make the best outer piston tubes so that the proper clearances can be maintained in changing weather.

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Your correct the clearance between support tube and piston tube are something to think about but it's the Piston or head stop clearance that's critical. Use of standard thin wall brass tubing provides both excellant precision in draw and somewhat self-lubricating traits that lend itself to the process. Additionally a very slight taper too the top isn't a bad thing either expecially with floating heads which can be easily provided by chucking the tubes in a handdrill and polish sanding with light sandpapers between the fingers. Lets not try to scare new contest flyers away from building quick and easy launch aids like pistons and towers.
While FG & CF may be somewhat more stable to temp and humidity they also add greatly to cost without real proven advantage. They are fine if you have the stuff already but the basic NAR contest flyer neither needs degree of precison or is it required to blow the majority of competitiors away. I'd pit my piston against anything produced on a lathe without the slightest hesitation. Over processing is almost as bad as over building.... particularly on things with as much fudge factor as our mr motors and the luck of the weather.

Show up at an FAI contest sometime and see whose design is being used; especially at a Spacemodeling Championship. You'll find hundreds of machined pistons and no cardboard tubes.

I agree that simpler cardboard pistons are satifactory for NAR contests, but that doesn't make them better. As soon as the humidty changes then you'll see plenty of failures where the piston sticks or where the entire assembly just isn't giving the rocket any additional boost.

The rocket also has to lift the weight of the outer piston tube, so lightweight construction is critical there.

Pat_B said:

Show up at an FAI contest sometime and see whose design is being used; especially at a Spacemodeling Championship. You'll find hundreds of machined pistons and no cardboard tubes.

I agree that simpler cardboard pistons are satifactory for NAR contests, but that doesn't make them better. As soon as the humidty changes then you'll see plenty of failures where the piston sticks or where the entire assembly just isn't giving the rocket any additional boost.

The rocket also has to lift the weight of the outer piston tube, so lightweight construction is critical there.

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Really don't have to Pat:
I have several of the current FAI flyer in our club, Didn't say it was better, my stuff has proven to be more then competitive. Particularly in the motor class we are talking about. No brag just fact, lets keep the discussion on the process at hand shell we.