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Author Topic: Minislick -Build-  (Read 11914 times)
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Alan Cohen
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« on: March 30, 2010, 06:59:27 AM »

It's time for a new ministick. I need a fresh one for Kent. Seems I say that every year. I think I have 4 stuck up in the lights there by now. So I'm clearing the building board, pulling out that old plan and rummaging through the balsa supply. I thought I'd post the build, highlighting a few of the main processes and techniques. I think there is a better copy of the plan in the Plan Gallery.
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lemuel
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« Reply #1 on: March 30, 2010, 07:27:05 AM »

Cool, I hope to learn much from you on this build Alan. I have made a micro version of this model that I fly in my house. What sort of times have you had with previous versions of this model?

regards
Matthew
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Alan Cohen
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« Reply #2 on: March 30, 2010, 08:42:34 AM »

I have a micro version as well. Mine is a 5" span. Flies just as well as its "big" brother.

The Minislick has done 15:30 at Lakehurst under a 200' ceiling where it was designed for. Most of my practice with this model was trying to get it to the ceiling there. Skinny rubber, lower pitch prop etc. Consequently, I have struggled under lower ceilings. I think I approached 12 minutes under a 50' ceiling at Kent. I need a lot more practice to match prop and rubber for lower ceilings. I am trying something different with this one to try and help: Previous versions have been very stable flyers with very quick recoveries when banging into the ceiling or fixtures. That is not a desirable trait for a ministick under a low ceiling. Ideally, you would like to model to climb not too aggressively to the ceiling, bounce once and do a tail slide all the way to the floor and then climb back up again. Of course I'm exaggerating, but you get the idea. A 20' drop effectively raises a 50' ceiling to 70'. A longer cruise and less climb is also necessary for low ceilings. All I need is a clone to go out and practice while I'm handling the rest of life.
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Alan Cohen
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« Reply #3 on: March 30, 2010, 08:50:24 AM »

I always start with the motorstick for indoor models. I can't seem to find old my 3/32" prop blank wood, so I went to the pile for a fresh piece. I picked a very stiff piece of 6.5# wood and checked it for grain consistency. I cut off 6" and reweighed it. This blank is a little light at 6.2# density, but I'll go with it since it is very stiff. I do not like a ministick motorstick to bend at all under full load. It's hard enough getting a repeatable launch.

I first cut the .148" motorstick using the full LE of the 5% simplex template. For the tailboom (pic #4), the LE of the template is actually the rearmost part of the model and where the stab mounts. After cutting it is turned upside down. How much of the LE of the simplex airfoil is utilized will determine the amount of negative incidence on the stab. I normally slide the template over to the left 1-3/4". For this one I'm sliding over 2-1/4" for less negative incidence. I'm hoping for less decalage and less stability.

In the last pic you can see the general layout.
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« Last Edit: March 30, 2010, 09:00:29 AM by Alan Cohen » Logged

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« Reply #4 on: March 30, 2010, 09:09:19 AM »

This motorstick blank is a little thick at .108". I like it more around .094". I need to plane off a bit. I used to sand my indoor motorsticks to weight and dimension until I was scolded passionately. Now, only a razor plane touches them. OK, I do a tiny bit of cosmetic sanding, but don't tell.

The tailboom also needs to be tapered. Three stepped passes with the razor plane on both sides gets the job done. Weight before hooks is 160mg. Funny, I used to have these target weights burned into my brain. I seemed to have misplaced them Huh Looking back at my plan I see my fuselage all up weight was 185mg so I think I'm OK.

Now to cut a groove at the rear of the motorstick to accept the rear hook. Then a poke with some .010mw and then inserting the hook. I little Duco and plenty of time to completely dry before handling.

Off to make a pigtail bearing. Haven't done one of these is a while. This should be interesting!
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Art356A
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« Reply #5 on: March 30, 2010, 09:16:37 AM »

Are you using two different weights for the front and back of the stick and scarfing them together? Or is that an optical illusion?

My last one came out only 40% heavier than yours, big improvement from the one before that. The highest ceiling in SoFla is 26' so our problems are different.

Art.
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« Reply #6 on: March 30, 2010, 10:05:47 AM »

Actually, I just had an epiphany, Art. I had been using the same 6.5+# wood for the motorstick and tailboom previously. I just made a management decision to go lighter on the boom. I think that might be where I'm getting my stability issues. With a heavy boom I would need more decalage to keep the nose up, yes? I think my previous versions were in the neighbor of 5-6* decalage. I'm trying for 3* on this one and lets see what happens. Gotta keep the tail light. I found a really primo piece of 4.5# wood and made a new boom and motorstick. I went taller on the MS to compensate for the lighter density. The old boom weighed 50mg, the new one is 40. The MS is the same. And it's still stiffer than I will need. Here's a pic of the first and second ones.
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« Reply #7 on: March 30, 2010, 12:17:58 PM »

Nice stuff so far Alan.

Out of curiosity (and ignorance on my part), but what about reducing the stab area to reduce some of the Static Margin of Stability? You'd also get a lighter stab, less stress on the boom and lower overall drag.

Just thinking as I watch along with our build....

Tony
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« Reply #8 on: March 30, 2010, 12:20:44 PM »

Got the bearing done. It wasn't too bad after a few years of not making one. I made a video of the process and will post it when it's done simmering at YouTube.

Make a pigtail bearing video: http://www.youtube.com/watch?v=IAnm1gXUyx4

Here's a pic of slicing the motor stick and installing the bearing. You need a straight piece of .010mw in place to get the alignment close. I usually use no down thrust, but I'm putting in 1º this time. The glue holding the bearing in is easily loosened with MEK and the final adjustments will be made with the prop installed.

So far I'm a little light at 162mg.
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« Reply #9 on: March 30, 2010, 01:37:52 PM »

Nice stuff so far Alan.
Out of curiosity (and ignorance on my part), but what about reducing the stab area to reduce some of the Static Margin of Stability? You'd also get a lighter stab, less stress on the boom and lower overall drag.
Just thinking as I watch along with our build....

That's a very good question, Tony. There is something about indoor guys and larger stabs and them generating more lift. I never got it. I always felt that the lift came only from the wing and the stabilizer did just that... stabilize. That said I'll probably just build a lighter stab this time and keep the size the same. Mostly because I don't feel like making new forms. <Bling> A light just came on. I do have the forms for my micro stick. It would be interesting to see the effect. Don't take much to unglue one and slap on the other.

Here's the forms for building both the Minislick and Microslick. I'll definitely build the smaller stab and see what happens. If it turns out to be a winner, I'll give you half my winnings, Tony.

Wing wood dimensions as per plan. .030" wide x .040" high, c-grain on top. I first stripped the .040" dimension off a very stiff, 6-7# density sheet of 1/8" balsa and then restripped the same piece to the .030" dimension. I made several so I could pick out the best one (and have back ups if necessary). It will not be easy to bend even wet. No soaking required, just a brush full of water at the radiuses. It's important to maintain tension as the wing spar is bent around the radii to avoid kinking. Not that a kink would affect performance, it's just bad form. I use a magnet to gently pinch the spar against the form and then glide the magnet and spar together around the curve.

Double glued the ribs and added the pre-cut TE. Ribs are the same dimensions and the spars.
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« Reply #10 on: March 30, 2010, 05:30:48 PM »

Cool!

So what are the forms made from Alan? They look like card stock. Is that right?

I was thinking something like a 20 to 25% smaller stab, the micro looks like it's half the area? Should be interesting.

Quick question: How do you make the wing posts round? Is there an easy method?

Tony
-waiting for the cheque from the winnings... Grin
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« Reply #11 on: March 30, 2010, 05:36:39 PM »

Cool!
So what are the forms made from Alan? They look like card stock. Is that right?

I was thinking something like a 20 to 25% smaller stab, the micro looks like it's half the area?
Should be interesting.

The forms are .040" thick styrene sheet. It gives a smoother edge than card stock or matt board...better to release the outline.

Wing outline is done. Dry weight looks good. I want 90mg covered.
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lemuel
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« Reply #12 on: March 30, 2010, 07:18:31 PM »

Here is a Video of my micro minislick...

http://upload.youtube.com/my_videos_upload?feature=mhw4

regards
Matthew
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« Reply #13 on: March 30, 2010, 10:03:14 PM »

Try this:

http://www.youtube.com/watch?v=xtwEeEfP37M

I like how you talk to your planes as they fly! I've noticed a lot of people do the same.

Rey
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Alan Cohen
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« Reply #14 on: March 31, 2010, 07:42:34 AM »

Here is a Video of my micro minislick...

Most excellent Matt. Does yours have the same uncanny way of seeking the most hazardous places to land. Mine loves bicycle spokes. I built my micro more as a test of the design. Anything that can fly that well with a 5" span will certainly do better at 7".
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« Reply #15 on: March 31, 2010, 07:58:41 AM »

As a matter of fact, we have a hole in our glass cabinet about 1" x 2" and it did manage to fly into that SOMEHOW?Huh We also have a picture rail in the lounge room that it lands on frequently. I must make one of your ministicks. I think I might go for a stupidly light version. Then I will have two!! Yay.

regards
matthew
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Alan Cohen
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« Reply #16 on: March 31, 2010, 11:30:29 AM »

I think I might go for a stupidly light version. Then I will have two!! Yay.

Ministicks are overbuilt at 430mg. I built a "stupid light version" a while ago. It was 179mg sans rubber. It flew on a single strand of .009" rubber and looked like a tiny F1D in flight. It just floated around my LR. I will build another one day. I think we officially dubbed them T.U.M.S, or, The Ultimate Mini Stick.
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« Reply #17 on: March 31, 2010, 03:42:05 PM »

With a heavy boom I would need more decalage to keep the nose up, yes? I think my previous versions were in the neighbor of 5-6* decalage. I'm trying for 3* on this one and lets see what happens.

Nope. Rearward CG uses less decalage. Rearward CG also reduces static stability. Plug the numbers into Bernie Hunt's spreadsheet if you want to see the effects without spending flying time doing it.
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« Reply #18 on: March 31, 2010, 03:46:18 PM »

Nope. Rearward CG uses less decalage. Rearward CG also reduces static stability. Plug the numbers into Bernie Hunt's spreadsheet if you want to see the effects without spending flying time doing it.

D'oh!!! Of course Bill. What the heck was I thinking? Obviously, not much! I knew there was a reason I used the same 6.9# wood for both motorstick and tailboom. It helped with that nice nose-up attitude. Now I need to make a new tailboom...basswood I'm thinkin'. Wink
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« Reply #19 on: March 31, 2010, 06:00:55 PM »

Nope. Rearward CG uses less decalage. Rearward CG also reduces static stability.

Yep, I agree. What about just moving the wing forward to move the CG back?

Declage and CG are entwined as we all know.

Tony
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« Reply #20 on: March 31, 2010, 06:33:36 PM »

Yep, I agree. What about just moving the wing forward to move the CG back?

I currently mount the wing about 1/4" forward of where you see it on the plan. Can't go much farther without the prop hitting the the LE, especially with 3º left thrust.

This time I think I will go with as light a prop as possible. I've made them as low as 50mg. 70mg is the right number to keep it relatively sturdy. This should help move the CG rearward. I usually fly it with CG at the rear wing post. I'll shoot for 105-110% wing chord this time.

The good news is this one is coming in maybe 50mg light of the 430mg minimum. I can stick the ballast anywhere I want to play with the CG.
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« Reply #21 on: April 03, 2010, 09:34:25 AM »

OK, I stole a little time this morning to cover the flying surfaces.

First, to build the sub-rudder, by far the most important part of this design, I use one end of the stab form to get the curve.

Then add the straight pieces.

Now for the covering. Pic 3 shows the equipment. I like to use a spongy foam surface to roll out some OS Film. Yes, you can use PPP or some of the heavier films equally well on a ministick, but since I am the procurer and guardian of the main roll of OS Film, why not use it. The foam serves to keep the film from moving around while handling. I simply roll out the length I need, place a lipgloss coated frame on top (lipgloss side down of course), cut it free from the roll with an electric cautery and turn it over. Because the lipgloss is not a permanent adhesive, it allows for manipulating the film to remove, or at least even out, the wrinkles. To tight is not good; the balsa outlines cannot handle tension. I normally crinkle the film to help with this, but to be honest, I haven't done this in so long, I just plain forgot.

After a nice even, semi-taught surface is achieved, the outlines are lightly misted with Super 77 spray adhesive and and gently placed on the film. I run a finger all around the outline ensure good adhesion because the worse thing that can happen is the film releasing from the outline after it is trimmed. There is just no getting it back on.

Now, the fun part. Cutting the outlines free from the frame. There is just no way around this, an electric cautery is the way to go. When I first started, I used a piece of .010 music wire, repeatedly heating it over a flame and cutting film. You can cut about an inch or two at a time this way, but the edges of the film get blackened and if you get greedy and go for that extra 1/4" around a corner and the wire cools...yank...you're starting over again.

All surfaces are now free and ready for dihedrals. Later...
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« Reply #22 on: April 03, 2010, 09:40:31 AM »

278mg so far. Too light. With 70-75 target weight for the prop, plus tissue tubes, wing posts and a little more glue to hold everything together, I'm thinking I'll be around 375mg all done. That will leave me 55mg of ballast to help manipulate the CG a bit. More than I wanted, but better too light than too heavy.
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« Reply #23 on: April 03, 2010, 11:50:32 AM »

I made a little video on covering with light mylar film. It might be still brewing at YouTube.

http://www.youtube.com/watch?v=wTLIsItvwJk
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« Reply #24 on: April 03, 2010, 07:30:43 PM »

Time to do the dihedrals. First, a small slice about halfway through the LE and TEs just outside the dihedral ribs. Then crack each slice trying not to separate the spars. Dip an .010-.015 piece of wire into a small drop of full non-diluted aliphatic wood glue and slide it into the joint. Then prop up the wingtips making sure everything is flat, square and the wingspan does not exceed the prescribed 7". Let dry completely while cutting wingposts and preparing for the propeller. Lastly, run a saliva soaked paint brush just outside the dihedral rib to remove the slack in the wingtip film.

Everyone that sees these little beasties for the first time always asks, after the obligatory "where can I buy one?", "how long did it take to make it"? I answer, "a couple of days", "But it took a couple of years to learn how."
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