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Author Topic: Miller "Little Gem" build for FAC Goodyear mass launch  (Read 13247 times)
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MKelly
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« on: May 15, 2017, 12:25:14 PM »

I've really been enjoying time with the Flying Aces Club since I got back into free flight last year.  I've got a slim hope of attending the non-nats this July, so I've decided to put together a peanut Goodyear racer in hopes of joining another event should I be able to attend.

I picked up a Shorty's Basement short kit of the Miller "Little Gem" for a song last fall, so that has become my candidate for the build.  Lasercutting on the kit is beautiful, but the wood is pretty heavy - the two sheets of 1/8" parts are 11.5 lb/ft3, and the 1/32" sheet isn't much better!  I grabbed some lighter balsa from the pile and re-cut the ribs and tip plates, saving almost 1.5g.  I am using the kit's TE as the wood is stiff and straight.

Hoping to make this a fairly quick build, as I'd like to build a Thompson racer before the non-nats as well.

Cheers,

Mike
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MKelly
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« Reply #1 on: May 17, 2017, 12:37:46 PM »

Wings and stab assembled.  I'm a little nervous about the wing joint - plan shows the wing butt-joined to a 1/16" plate in the fuselage frame.  Trying to decide whether I should incorporate some sort of reinforcement here...
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FLYACE1946
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« Reply #2 on: May 18, 2017, 07:55:59 PM »

Really looking great so far. Wish my work bench was that neat.
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OZPAF
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« Reply #3 on: May 18, 2017, 08:06:31 PM »

it's probably ok for a Pnut Mike, but I understand your concern. perhaps just taking the stub ends of the spar and TE into the I/16 plate would help without adding much weight.

John
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« Reply #4 on: May 18, 2017, 08:39:16 PM »

Mike,
My feelings about the wing fuselage joint are similar to ozpaf john but I can't tell from the picture of the plan exactly what is involved. I suspect the fuselage to root rib joint will be good(probably too good!) but the load will be on the main spars, particularly in the inner bays.  I think gusseting the spars to the root rib would be good and perhaps a 1/32nd web between the spars in the inner bay.
John
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MKelly
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« Reply #5 on: May 19, 2017, 10:45:43 AM »

Thanks for the thoughts, guys.  Hopefully the attached plan pictures will explain my concerns clearly.  The wing is built with the LE, TE and spars ending flush at the edge of the 1/16" innermost rib.  A 1/8" root rib is glued to that.  The wing then gets glued to a 1/16" plate embedded in the fuselage side structure.

This gives me two concerns:  first, that the 1/8" root rib is a weak point, likely to split between the wing and fuselage upon hard landings because there is nothing crossing the grain to prevent cracks from starting.  Second, there is no structure inside the fuselage to reinforce the wing attach plate, so any bending moments are resisted only by the 1/16" plate and 1/16" square uprights - easy to collapse the fuselage sides.

My thoughts for corrective action are to carry the LE and spars through the root rib and into the fuselage about 3/16", and put some reinforcing gussets inside the fuselage at the LE, TE and spar intersections to spread loads down the sides of the fuselage into the crossmembers.

Can't carry the wing structure across the fuselage because it would interfere with the motor.

Thoughts?

Meanwhile, I built the fin and cut/sanded replacement wheel pant parts from lighter wood using the hard kit parts as templates.  The new pants save 2.5g over the kit parts (before sanding to shape).

Cheers,

Mike
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OZPAF
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« Reply #6 on: May 19, 2017, 08:03:28 PM »

That should work a little better Mike. The reinforcement plates picking up the LE, spar and TE extensions would add a fair bit of strength if cross grain to the 1/16 plate which is what I imagine you mean.

John
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MKelly
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« Reply #7 on: May 22, 2017, 11:36:14 AM »

John,

Yes, that's what I was planning, small vertical reinforcements that would run cross-grain to the wing attach plate. and reinforce the uprights below the wing attach plate.

That said, I built the fuselage sides this weekend.  I used fairly stout 1/16" square stock for the uprights that attach to the wing plates and the resulting structure seems pretty sturdy.  I think with the reinforcements it will be satisfactory.  Pic shows the fuselage sides, and the 1/8" root ribs being glued to the wings after notching them to allow the spars and LE to carry across into the fuselage.  Information on this plan is pretty sparse, but after comparing this one to the Walt Mooney Little Gem plan I see why the 1/8" root ribs are necessary - the fuselage curves a bit so the 1/8" ribs get trimmed to allow a flush fit the full length of the root chord.

Next step is to drill holes in the attach plate for the spars and LE, then get on with assembling the fuselage.

Cheers,

Mike
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MKelly
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« Reply #8 on: May 23, 2017, 10:31:10 PM »

Fun with magnets!  This is the first fuselage I've built on the magnet board.  Overall it's going pretty smooth, although I think I want to embed smaller magnets in some of my poplar blocks.  The big rectangular magnets have a fair amount of power, and can either push the other magnets (and your parts) around or crush wood between magnets if you're not careful.  I've got a lot of the small round magnets - looks like I'll finally have a use for the Forstner bits I bought.

I cut some foam blocks for the two center bays to help keep the fuselage square throughout assembly.  I cut the corners off them to keep from gluing them in place when adding the crossmembers.  I also bent the landing gear wire, glued up the wire/former sandwich and glued that assembly into the fuselage.

I love these little metal Zona L-squares - perfect for aligning components, and with a magnet you can stick them anywhere you need them and they'll stay put.

Mike




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« Reply #9 on: May 23, 2017, 11:54:02 PM »

I generally like building with magnets, it's dead flat and easy to jig stuff, but they do present their own challenges do.  Polarity can be tricky.
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MKelly
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« Reply #10 on: May 24, 2017, 03:42:25 PM »

Got the fuselage crossmembers installed and added the lower formers and stringer while everything was jigged up on the board..

I added 1/16x1/8" doublers from light balsa to the uprights at formers 3 and 4 (basically front and rear of the cockpit.  This made the fuselage sides very rigid - should be sufficient to handle loads coming in from the wings.

Fuselage frame as shown weighs 2.8g.  Still have to add all the upper structure.

Mike
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MKelly
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« Reply #11 on: May 26, 2017, 03:36:51 PM »

Installed the upper fuselage formers.  I replaced the kit parts with lightweight 1/16" sheet.  The turtledeck formers are cut from sheet spliced together on a diagonal, excess cut out from the middle, and sanded down to about 1/32" thickness.  Replacing these parts saved about half a gram.

For the forward sheeting, I made a paper template, cut the balsa, test-fit it and trimmed the right edge to fit as good as I could get it, then glued the right edge to the framework.  After that set, I glued the sheeting most of the way across the formers, wetting it to make it easier to wrap, and leaving the last 1/8" unglued on the formers.  After again waiting for that glue to set, I trimmed and sanded the left edge to fit, then glued and taped that.

While that dried I put in the turtledeck stringers, stripped 1/20th" wide from 1/32" sheet.

Through all that I only managed to put my fingers through one longeron...twice.  Fortunately it's at the nose, where there will be carved balsa for the lower cowl.

Cheers,

Mike
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MKelly
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« Reply #12 on: May 31, 2017, 04:28:15 PM »

Not much progress this week due to other commitments.

I haven't had much luck finding documentation on this airplane via the internet - just a few relatively small black and white pictures and an OK multi-view drawing. Yesterday I received in the mail a copy of the 1968-71 air racing annuals by Reed Kinert - this had several pictures of Ole Tiger which helped me understand the shape of the lower cowling and showed the instrument panel.  Lots of other interesting airplanes in there as well, along with some fascinating descriptions of the modifications racers were making to try and get a competitive edge.  I see several potential projects in this book...

Hope to get back to building this evening.

Mike
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« Reply #13 on: June 01, 2017, 06:23:33 AM »

That's a handy way of doing the turtle deck formers with opposing diagonal grain. Probably a better way to do all curved formers to keep them strong - especially after they are notched for stringers.
Also a practical way to approach the nose sheeting - I suppose it's a very old method but it's new for me.

John
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« Reply #14 on: June 02, 2017, 12:13:23 AM »

John,

Can't take any credit for the former approach - I stole it from Jim Longstreth's Sweet Patootie plan (2001 Flying Models article).  It's light, and it works well where the formers sit on crossmembers.

Glued the cheek blocks on last night and squeaked in an hour of whittling and sanding this evening.  Assembled the noseblock and used a length of tubing to set in some down and right thrust.  The plans are silent on thrust angles, so this is my TLAR approach...

Mike
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MKelly
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« Reply #15 on: June 04, 2017, 12:30:35 AM »

Spent some time today working on the "canoe" that makes up the lower cowl.  The plan just says to carve blocks of foam and glue it to the provided balsa keel, without giving any outlines or templates for what the cross-section or plan view looks like.  The pictures I've found help some, but they are all black and white, and the details of the shape don't show clearly, especially how the carb air scoop fairs into the canoe.  Best I can tell, the canoe has nearly-vertical sides and a slightly convex bottom that rides up the sides of the carb air scoop.

Armed with vague info and suppositions, I made a paper template for the plan view of the canoe, cut 1/8" and 1/4" sheet using the template, fit that against the lower fuselage and keel, trimming and sanding until it all fit together reasonably well, then glued it together.  Next I made another template and used it to cut sheeting for the sides of the canoe from soft 1/16" balsa, trimmed the sheets and glued them to the 1/8" and 1/4" top and bottom plates.  I purposely did not glue any of this to the fuselage yet, which allowed me to sand the assembly without having to work around the gear legs or worry about crushing sticks or sheet on the fuselage.  After sanding till it looked about right I cut away almost all of the 1/8" plate, gouged out a good bit of the inside of the 1/4" plate and cut away as much of the keel piece as I dared.  Final weight on the canoe assembly as glued onto the fuselage is 1.15g.

I also cut out replacement parts for the cheeks from lightweight balsa.  The kit cheek parts were almost 5 grams - replacements are about 2.5g.  A lot of this will get sanded off, but the fuselage is pretty nose-heavy already and the bare airframe is pushing 10g, so it seemed worthwhile.

Mike
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MKelly
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« Reply #16 on: June 11, 2017, 12:44:55 AM »

Another slow week on Ole Tiger.  Carved, sanded, fitted and hollowed the cheek blocks.  Reduced their weight to 1.4g.  Still need to trim them for where the wing will run through.

I'm starting to feel rather weight-obsessed with this model, as it seems really heavy for a peanut (13.5g structure  weight at the moment including the wheel pant blanks).  Lots of sanding still to do.

Regarding the cheeks, I'm thinking through whether to add them before or after covering the fuselage.  Seems like it might look better in the end if they are added before covering, but that seems like it would make covering the fuselage a lot harder.  I also think a little sheeting at the lower intersection of the cheeks and fuselage will be necessary if the cheeks are added before covering, to give a good surface for attaching the tissue.

Kinda losing steam on this build...

Mike
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« Reply #17 on: June 11, 2017, 04:31:55 AM »

Love these little racers....must build one myself next winter. Keep at the nice work Mike, we are curious how she fly's.

Personally I would fit the cheeks before covering. It might be just my opinion, but stuck on later always looks like that, stuck on, not integral part of the frame.

Myself I would open up the nose block former, maybe to diamond shape. These models are already small and the bigger the hole in the front former, the better access you have to change motors, use a blast tube etc. Just my 2-cent's worth  Wink

Urs

PS: the diagonal cut formers will be part of my future builds, thanks for that!

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« Reply #18 on: June 12, 2017, 03:47:16 AM »

I think Urs idea of adding the cheeks to the structure before covering will be neater.

Would it be possible to add a thin light flange to the cowl as a tissue anchor where there is no balsa on the main fus structure?

Happy building.

John
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« Reply #19 on: June 12, 2017, 05:58:02 PM »

John, Urs,

Agree that the model will look better if the cheeks go on first.  I added some light sheet to either side of the fuselage to form a "tissue anchor" as John suggested.  Will mount the cheeks after mocking up the wings and trimming for the wing-cheek intersection.

Rearranged the building area this week to make the room work better for the family.  The work table ended up against a wall, so I added a magnetic whiteboard above the building board.  Makes a good place to hang the plans for quick reference, and also gets the magnets off the building surface when not needed.

Mike
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« Reply #20 on: June 12, 2017, 07:45:57 PM »

it's a complicated little model in the nose area Mike. Pity you couldn't just add a composite FG nose cowl, cheek cowls intakes etc. Smiley
The cheek cowls attachment will be stronger with your additional inlaid sheeting, better than my idea of flanging the cowls.

John
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« Reply #21 on: June 12, 2017, 09:54:43 PM »

Yep, up front it's starting to look like a lumberyard after a tornado.  We'll see if it finishes up as more of a Tiger tank than 'Ole Tiger...

Cheers,

Mike
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« Reply #22 on: June 13, 2017, 10:25:58 AM »

Mike this project is moving forward, seems like you just made a huge positive turn getting past the hard part. You will finish in fine fashion.  I am looking forward to the flights ahead for this racer.
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« Reply #23 on: June 13, 2017, 11:59:10 PM »

Thanks Allen,  I'll get this thing done yet.

Got the wings sanded and fitted today.  The root rib is very long, and because of the way the fuselage sides curve the root ribs have to be trimmed to match that curve.  This has to be done on an angle to allow the wing to sit flush at the plan-specified dihedral (3/4" root-tip).  To facilitate this, a 1/16" root rib is installed using a dihedral gage, an additional 1/8" root rib is glued in, then the 1/8" root rib is trimmed to match the fuselage sides.

When I built the fuselage sides I marked and match-drilled holes for the spars and leading edge.  On the wings, I left the LE and spars long at the root so that they could carry through the fuselage sides.  I cut the 1/8" root rib oversize, trimmed it to fit inside the spars and LE, then sanded the wing to bring the root rib profile parallel with the rest of the wing top and bottom surfaces.

With the fuselage and wing panels assembled and sanded, I used a square needle file to open up the holes in the fuselage just enough to pass the spar and LE into the fuselage sides.  After checking that the spars were perpendicular to the fuselage centerline from a top view, I used a divider to scribe the fuselage profile onto the root rib.  The wings were then taken off the fuselage and jigged onto the building board with the tip raised 3/4" for dihedral.  I carved almost to the profile line, then used a right angle sanding block to sand to the profile line.  A couple of iterations of fitting and sanding got the wings to match the fuselage sides pretty well with the right dihedral.  A little bit more fill is needed at the TE - I've glued a couple of short lengths of soft 3/32" sheet to the root at the TE and will trim that tomorrow.

Once that's done it's on to trimming the cheeks to clear the wings...

Mike
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« Reply #24 on: June 15, 2017, 06:13:25 AM »

Good solution Mike. I like the way you carefully broke the problem down into achievable solutions.

John
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