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Author Topic: Comet Sparky for P-30  (Read 4469 times)
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Zeiss Ikon
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« Reply #75 on: April 26, 2011, 07:13:10 AM »

I realized, on looking back at this this morning, that I didn't mention the material of the DT cover -- I cut it from the foam lid of an 18-pack egg carton. Grin
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« Reply #76 on: April 26, 2011, 10:22:25 AM »

Zeiss Ikon,

If you buy from Gizmo Geezer, they are already corrected, and since they're commercially available, they are legal.

Looking at your reply #61, "fast" builders usually are working on all the airplane parts at once. If you get yourself 3-4 building boards, and build one part on each one (can put the tail pieces on one board), you have something to do when you're waiting on the other pieces to dry. If you stack longerons and build both fuselage sides at once, then cut apart after they're dry, it goes much quicker. I also find it useful to spend one evening making all the parts; i.e. "kitting" the model first. Then the parts are ready to assemble. It speeds me up. I've also find that if I spend 15 minutes before I leave for work, I can get a significant amount done. I'm not as fast as a week, but I can build quickly without CA glue. If you made the same model a number of times, and made templates for the wing ribs, and fuselage parts, doing the "kitting" doesn't take that much time, either. For models like the Sparky, you only need a center and wingtip template, then add 2 pieces of balsa for each rib "pair" between them. The ribs can be sanded to shape, and the a final sanding to match the pairs, and you have all the ribs without much time. Once you've done the templates, you can make ribs pretty quickly this way.

BTW, I gave up on using rubber bands to hold balsa - too much breakage. You might want to try thin strips of masking tape, say, 1/8" wide. The adhesive will usually hold it in place well enough (you can wrap around longerons a bit to help), and you can control the amount of "clamping" going on.

Justin
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Zeiss Ikon
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« Reply #77 on: April 26, 2011, 05:12:49 PM »

I can see how working on one part while another is drying can speed things up in terms of final finish date -- and kitting the parts, use of templates, building both side frames at once, are all old standards (and useful independent of building speed because they also make for more accurate construction). Of course, the other question is what use I'd possibly have for fifty or so Sparkies at the end of a year... Roll Eyes

I thought about using tape, but didn't think it would be strong enough to (for instance) hold the final bend in the stringers at the nose. It certainly would have done the job holding the side frames in place on the nose former, though -- I'll have to put a roll on my building table.
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Zeiss Ikon
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« Reply #78 on: April 26, 2011, 09:57:58 PM »

Okay, this is getting scary...

But let me back up a little. I searched high and low for a thrust button; I have one smallish hardwood button in my Sterling Piper PA-18 Cub kit, an even smaller hardwood one in an Easy Built Piper Cub dimer, and a still smaller plastic one in a Peck Peanut Andreasen BA-4B kit -- and one installed in my Fat Lancer, but not a single loose one anywhere. No time to order one, even if I had money before payday, but I'm not beat.

First: find a dowel of a suitable size (never, ever throw anything away unless it's actual trash). Chuck it in the lathe (never mind it's a metal cutting lathe, this isn't going to require a tool rest and set of chisels) -- see photo 1. Use a couple lathe bits already mounted in the tool holder to chamfer and cut the neck (eyeballed size on both), take one of the "dull" razor blades and "catch the center" to make a starting point, then "peck drill" a 1/16" hole with a bit in a pin vise. Clean up and smooth the button with a set of "Grit Stix" -- quarter inch wide sanding belts on spring tensioned carriers that taper to a chisel point. Part the button most of the way off the stick with a utility knife held against the underside of the part (so it's pulling, not pushing -- this is slightly hazardous, in that a bound blade could fly in a random direction, so take care not to bind); see photo 2. Finish parting off by rolling the stick with a razor blade in the knife cut; a few turns and off it comes, as neat as anything sold in 1950s vintage kits, took about ten minutes from looking for a dowel to finishing off (not counting dusting off the lathe). Assemble the nose block parts from the sheet wood, carefully trim out the center hole to fit the button (which, by luck or good eye, or both, came out to exactly a 1/4" hole). Carve the nose block insert to fit the hole in the fuselage nose, dope the block -- see photo 3. Everything is ready in photo 4 -- so I went ahead and put together the nose block and propeller (I'm not going to have time to build the spinner this week, I can always cut the prop shaft and retrofit).

Now the scary part -- I weighed the complete airplane, with tail surfaces glued in place, wing held with a single rubber band, and propeller unit -- it's still under 35 g (reads 30 on my diet scale, but I'm not sure where the rounding is). I'll add another two or three grams with the DT timer and rigging, and another gram or so for the windshield and side windows, but it looks as if, unless I need a lot of clay to balance the model, I'll need to add a few grams of ballast to bring the model up to P-30 minimum weight. This is a completely new experience to me; building underweight, I mean... Huh
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Re: Comet Sparky for P-30
Re: Comet Sparky for P-30
Re: Comet Sparky for P-30
Re: Comet Sparky for P-30
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« Reply #79 on: April 27, 2011, 05:51:58 AM »

Nice nose button!  I've done similar and have also given Comet/Guillow's/Whosis wood buttons a fair chance at life by adding a brass tube bushing for an exact slip fit to the wire.

(Aside:  I need a lathe, milling machine - ALL CNC, of course... Roll Eyes)
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Zeiss Ikon
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« Reply #80 on: April 27, 2011, 07:27:06 AM »

Thanks, Pete! A few years ago, I spent a little over $300 for this lathe (a Chinese made 7x10; they're back up around $500 now), then another $250 or so for a second chuck, tool bits, center drills, tailstock drill chuck, etc.; at the time, I wanted to use it for minor gunsmithing and to build small steam engines and the like. Unfortunately, I've never found the time and haven't had the money for materials for much of the intervening period, though I have used it for a lot of "off label" stuff (like cutting down 120 film for 127, 828, and 16 mm camera reloads) and quick jobs like this one. Unlike my bandsaw and sander, this tool does what I expect without problems (kind of ironic, since it's a type of lathe that has a largely undeserved reputation for poor quality and accuracy).

I should mention that one doesn't really need $500+ worth of lathe and tooling to get this job done; at the cost of a little more material waste (due to having to cut the dowel short) and time, I could have done the same job with a drill press or even a hand held drill motor (as long as it has a 1/2" chuck to hold a large enough dowel) and a few sanding sticks (though it's hard to get the taper out of the neck with a sanding tool, it can be done).
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Zeiss Ikon
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« Reply #81 on: April 27, 2011, 09:49:42 PM »

Tonight I got the DT timer built for the Sparky. It's a pretty straight up Silly Putty timer, but I made what I consider a couple minor improvements over the last one. The first photo shows the assembled core -- wire drive arm, extended tube to keep the thread from slipping over the end, holes (cut with a Dremel cutoff wheel, same as last time), roughed up surface, and Silly Putty oozing out of the holes. The change here is that instead of a haphazard method of building up a bearing and seal collar from thread or super glue, I just used the intermediate tube size (in this case, 1/8", the timer uses a 3/32" core and 5/32" outer tube, plus a little piece of 1/16" to accept the 1/32" wire); it's a perfect fit in the larger tube, as designed. The second photo shows the other change; instead of a time consuming and effortful process of swaging down the end of the 5/32" outer tube to accept a plug made from 3 mm bamboo skewer, I made up a plug from nested tube and wire -- 1/32" wire, 1/16", 3/32", and 1/8" tube, to completely fill the end of the 5/32" tube. This neater than the bamboo, I think, and certainly less work to cut a few short pieces of tube than to swage down the end of the unit. The third photo is the complete unit, ready to mount on the model.

I also got the side windows installed (along with all the glazing on the Fat Lancer), using Formula 560 and the plastic wrap from a couple packs of my girlfriend's cigarettes. The windshield on the Sparky will require heavier material, because it's curved and more exposed (and larger), so I'll use the piece of clear material that came in the Lancer kit; I hope to get that done tomorrow night, along with rigging the DT and putting a retaining key on the nose block. I also need to install a shim under the wing -- I got the retaining dowel a little high relative to the wing saddle, but I think a 1/32" shim over the entire saddle will raise the wing enough to avoid rocking without changing the incidence/decalage. That won't take long. Then Friday evening I'll make up the motors for the fun fly and repack my flight box.
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Re: Comet Sparky for P-30
Re: Comet Sparky for P-30
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« Reply #82 on: April 28, 2011, 07:37:34 AM »

I liked your solution to the thrust button problem, ZI. Its typical of your never say can't approach.
I bet you're looking forward to seeing this fly.
have fun
John
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Zeiss Ikon
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« Reply #83 on: April 28, 2011, 07:33:34 PM »

I bet you're looking forward to seeing this fly.

You bet I am. The only time I've ever flown a model that was close to class weight was my Limited Penny, which I recall finishing up at around 3.5 grams (class weight is 3.1). It's looking very much as if my 94% Sparky will be as close to class weight as my scales will allow -- which means has the potential to out perform the One Night 28 I built long ago (it's prettier, too). This is, of course, if I manage to get it trimmed without smashing anything, but I seem to recall that the lighter a model is, the less damage it tends to take when it hits something, because it'll fly slower and there's less mass to stop.

I am a little worried about Saturday, though -- if this flies as well as I think it might, I'm liable to get a bad case of sunburned gums...
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Dave Andreski
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« Reply #84 on: April 28, 2011, 08:23:59 PM »

Zeiss,
I hope the rubber I've sent arrives in time for the weekend flying session.

Dave Andreski
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Zeiss Ikon
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« Reply #85 on: April 28, 2011, 10:10:21 PM »

Well, with the windows all on and DT fully rigged except one .025" wire peg for the deployment band (sorry, no photos -- window installation is hard to photograph, and there isn't much to see on the DT rigging), the Sparky weighs, as nearly as I can figure it, barely below 35 g, so I'll need just over 5 g of ballast to make 40 g without rubber. Compared to most of the models I've built in the past, this is going to be like flying a soap bubble; definitely one in which to use a cruise-climb motor.

I'm going to try like heck to get some video of these two models in flight at the fun fly -- plenty of space on my phone's memory card, so I should be able to manage something.
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« Reply #86 on: April 29, 2011, 07:57:56 AM »

Under 35 grams? Good job, Zeiss!  Grin
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Zeiss Ikon
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« Reply #87 on: April 29, 2011, 06:01:34 PM »

Thanks! Now if it'll just fly... Roll Eyes
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Zeiss Ikon
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« Reply #88 on: April 29, 2011, 10:34:33 PM »

I figured out that my diet scale doesn't really round, it reads the last full increment. That is, if I put 4.5 g on the pan, it still reads zero, but if I have 5.0, it reads 5 (and continues to do so until the weight reaches 10.0). At least, that's the intent; it also, however, tends to "lighten up" if I leave it standing for a minute. So...

I put the Sparky (fully assembled, with motor peg and that last piece of wire, wing held with a single band, and both DT drive and deployment bands in place) on the scale, and started adding clay to the pan until it read 40 and stayed there. Before the last increment of clay, I could blow gently downward on the wing and watch the display flip back and forth from 35 to 40 and back; after adding the last bit, it went to 40 and stayed that way. In the end, I wound up with about a one inch ball of modeling clay which, assuming a density similar to water, ought to be close to 6 g. While I was at it, I also checked the balance -- as it stands, without any ballast or rubber, the model balances about 3/8" behind the rear spar, which I'm pretty certain is too far back. Though there isn't a CG mark on the plan, I'd expect a similar balance point to the Lancer, since they have similar setups in terms of airfoils on wing and stab, similar stab ratio, and similar moment arms -- and the Lancer is supposed to balance at the trailing edge of the tips, which looks like about 80% of the wing area. A similar balance point for the Sparky would be about halfway between the two spars; looks like I'll need to put most of that 6 g of ballast in the nose, just inside the forward bulkhead, when I have a 10 g motor installed, with around two thirds of the motor length behind the intended CG location. Once I have the balance, I can pull the clay out and replace it with lead, if I can find the two film cans full of #6 shot I used to have; otherwise, I can use some tin-lead solder I have on hand.

I've got three motors made up with nice new FAI SS Tan (thanks again, Dave!), ready to lube, break in and wind. Nice rubber; it's got a good bit more stretch than the Peck rubber I have left from the '80s. I made a new version of my old stuffer stick that vanished in one of my moves -- a bent wire rubber holder mounted on a dowel with Beacon 527 and a wrap of heavy thread, the ends of the wire butted against the bottoms of slots cut in the dowel to receive them (and thus hidden from the rubber that they might otherwise snag). This isn't suitable for loading a wound motor, but it'll work fine for getting a braided motor into the model with a minimum of hassle. Hopefully I can use someone's stooge at the fun fly; I haven't had time to make my own yet (it'll take an hour or two, but I think I have all the materials I need; should easily have it ready for the contest in two weeks).
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« Reply #89 on: April 30, 2011, 03:35:06 AM »

Hope you get a chance to do a maiden flight before the contest.
John
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« Reply #90 on: April 30, 2011, 07:52:45 PM »

Hope you get a chance to do a maiden flight before the contest./quote]

Oh, today's fun fly wasn't a contest, just a group getting together to fly, most of whom, like myself, treated it as a tune-up for the actual contest coming in two weeks. And yes, I got a maiden flight; in fact, I got several flights, and found out that, far from needing all that ballast in the nose, I had to put a little of it (guesstimate, about half a gram) on the tail as well as adding 1/32" incidence shim under the leading edge of the wing (still need to add about 1/32" to 1/16" right thrust shim -- glide turn is good, but it's too straight during climb). One of the test flights was 45+ seconds, though (once I got the glide sorted), and, at 650 turns, that was still not full winds on the motor. I wound up using six strands of 1/8", which came out about two and a half inches longer than the hook-to-hook, though now that I have the model climbing and gliding well I may try remounting the motor as four much longer strands -- slower climb, longer run, likely will produce a longer flight.

Also, I note that, despite its low weight, this Sparky is not excessively fragile. In addition to taking the tension of that 650 turns on 6 strands, on a couple flights before I had things working well it landed at a very steep descent angle (propeller stopped instead of freewheeling, so not a full-on dive, at least) -- with zero damage.The last flight of the day landed about six or seven feet high in a tree, then tumbled to the ground -- again, zero damage.

If you can't tell, I'm stoked. Smiley This Sparky promises to be one of if not the best flying model I've ever built; I'm sure being light has much to do with that, as well as the huge improvement in covering quality since I discovered wet tissue.
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« Reply #91 on: May 01, 2011, 01:24:05 AM »

It looks like all your effort was well worth while. Its a very pretty model that flies as well as it looks.
Happy flying
John
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« Reply #92 on: May 01, 2011, 03:36:48 AM »

A good looking airplane.
Fly and enjoy.
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« Reply #93 on: May 01, 2011, 04:41:00 PM »

I definitely approve of the color scheme. See my Moths pic for why.    Grin
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« Reply #94 on: May 01, 2011, 05:20:18 PM »

Wait until you wind it up!
6 strands of 1/8" (10 grams) should give you well over 1000 turns, maybe 1200 or more depending on the batch. 4 strands can get over 2000 turns!

Nice model!

Tony
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« Reply #95 on: May 02, 2011, 07:06:06 AM »

2000 on four strands of 1/8th @ 10 grams!  I REALlY need to practice my winding techniques Embarrassed!  I've been chickening out at ~1250 (probably not stretching enough yet), but anything more would put my planes - the Cloud Tramp, no P-30's yet - in the next county!
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« Reply #96 on: May 02, 2011, 07:28:53 AM »

Wait until you wind it up!
6 strands of 1/8" (10 grams) should give you well over 1000 turns, maybe 1200 or more depending on the batch. 4 strands can get over 2000 turns!

Nice model!

Well, assuming the model still climbs reasonably well on the 4 strand motor (it should, given it weighs just barely 40 grams without the rubber), I should get a motor run of a minute or more... Shocked Kawabunga!!

Thanks for all the kind words, everyone -- if I'd had this kind of support group back in the 1980s, I might never have gone away from free flight. Smiley
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