eroc144

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I drew, built, flew and crashed a modified .074 Pacer this past year and really liked how it handled and flew (in spite of its unfortunate demise). I've been wanting to get into somewhat larger stuff and have decided to redo the Pacer for a Magnum .15 engine and thought I'd share the build process with all of you. The overall goal is to have something that can hover, and is stable, precise, light and nimble enough to do IMAC / 3D stuff. So I guess no machine guns on this one...

I'm starting with the .074 Pacer plans, which originated from Super Pacer plans I downloaded from Dave Fritzke's site last year. I've added a few modifications to the design so that it meets my aesthetic needs: Fore & aft taper on wing, larger rudder & stabilizer, removed the canopy & upper fuselage ridge, NACA 18 rib profile,and a few other minor things. I'd really like to do retracts & flaps, but I'm not sure I want to burden this plane with the extra weight and may wait for a .25 build later this year.

Specifications:
Span = 40in
Length = 31.5in
Wing Area = 275 sq in
Target wt = 21 - 23 oz.
Wing loading = 11 - 12 oz/sq ft
Covering = fiberglass on fuselage & sheeted areas, polyspan on wing & open areas
Finish = Nelson's hobby paint or Dope

I did an initial moment balance and am expecting the plane to be nose-heavy, so the plans indicate the battery and servos in a hatch behind the wing. I'll finalize that after the pieces are built and I can do a dry run of the actual balance.

Here are the plans and a few pix of the progress to date. When cutting the ribs, I rubber cement 2 pieces of 1/16" balsa together then rubber cement the rib plan to the top. Cut once, get two ribs, then peel everything apart.

EG

combatpigg

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Alright! Muscle planes! I'll be tuned in with interest, Erok. [8D]

eroc144

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I like that - a muscle plane! Guess I'll have to use carbon fiber somewhere, either that or name it Nova, SS, Charger, etc!

More progress and pix tomorrow.

EG

BTerry

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Looks great! I love seeing creative projects like this.

I notice your shear webs have the grain running spanwise instead of vertical. It might just be the picture, but if not you should rotate the shear webs 90*. I have seen too many planes fall apart when the shear webs split (including many ARFS).

Other than that I can't wait to see what the finished plane looks like!

soarrich

My Feedback: (98)

that's a common misconception. The load is diagonal across the shear web. This is a pdf showing how to cut shear webs, notice the grain, it was designed by Mark Drela PHD at MIT, he's really good. http://www.charlesriverrc.org/articl...webcutting.pdf

eroc144

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Made some more progress on the wing last night and today.

I had originally cut lightening holes in the ribs to save some weight, but they're too flimsy and I've snapped several just with routine handling. Oddly enough, I still had the donut holes (or would that be munchkins?) so I was able to scab the center sections back in place while still achieving some weight savings. I normally don't bother with wing tips but they feel right on this plane. I've used 1/2 of the rib pattern from the last rib as the shape, and built it up from a few pieces of 1/16" balsa. I stubbed a 1" piece of the trailing edge end to support the wingtip, and then a little sanding to smooth things out.

Next the trailing edges are glued to the center section and the torque rods are installed using the vaseline / epoxy tube technique. I'm not sure I used enough vaseline this time and they're a little stiff. May need to try and work some WD40 or similar into the end of the torque rod. With the torque rods in place it's time to hinge the ailerons. This is done pretty quickly and the hinges are recessed in the aileron to minimize the gap. Last task is to putty up the trailing edge joint and the other areas on the wing. I hate sanding but I hate looking at gouges even more so this is a necessary evil.

BTerry - Common wisdom is that the shear webs should go vertical, and there are a number of folks who say "at this scale it doesn't matter" as well as some who say "they should really be at 45 degrees." I'm going to do some more reading and may just glue vertical pieces on the front and leave the ones on the back. Muscle planes need strong wings!

EG

SGC

Rich , if you look again at that PDF you'll see the last picture showing the cuts for the shear webs, and the grain WILL be vertical

Andrew

EG -

Nice idea using threaded couplers on your aileron linkage - I'll tuck that one away for future use.

build light

True indeed! Good eye!

Another possibility is to use half thickness shear webbbing an make a 2 ply, one with the grain in each direction. The down side of this is the increased complexity of building and the extra glue weight. Carefully managed this could please everyone including yourself!

Robert

combatpigg

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It's looking real, real good!
Shear webs are a very personal subject so I will keep my personal thoughts about them to myself...

rainedave

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This is a very cool project. Sort of half-way between the Pacer and Super Pacer; a nice size. I like the fat naca 0018. I'll be watching.

BTW, I'll be starting my Super Pacer thread in the classic pattern forum soon. I re-drew the plans and had my parts cut for me. I guess I'm getting lazy because I actually like cutting out ribs.

David

RocketRob

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Looks great!
I'll be curious how it flys with that fat airfoil, Hope it doesn't give up speed or get pitch funny at speed.....

WEDJ

I agree

eroc144

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Hey folks - Thanks for all the thoughts and input. I love these build threads because I always pick up at least one or two new tidbits of wisdom, and Andrew I'm glad that I've finally helped you out as you've given me much valuable info over the years.

CP - Keeping your thoughts to yourself? Wow...

RD - I can never do anything off-the-shelf. It's a significant personality flaw, but I manage to cope! (not so much for the people around me) In this case I'd heard so many good things about the SP, but wanted the plane to look the way I wanted it to look and since I have Turbo CAD... I'm looking forward to your SP thread. Your build threads are always interesting and informative - you're a real artisan in this medium. Please send me a PM with info on your laser cutter. I'm curious about general prices and volume.

On weekdays I only get to build during my morning coffee and after the kids go to bed, so not too much to share this morning. I've started on the stabilizer and am going to build it up into an airfoil shape rather than going with the simpler 1/8" flat slab. On my .074 Pacer I actually cut stab ribs, but that didn't work very well at this scale and this time I'm going to use 1/4" spars and contour it using a razor plane, then sheet it with 1/32" stock. This will give me good aerodynamics and strength at a reasonable weight, and will look cool to boot. I've also decided to deviate from my originally planned deviation by installing a 1/8x1/4" hardwood spar across the center of the stab. My HOB P-47 / Magnum .15 experiment demonstrated some significant stab flutter and since this is a muscle plane... I'm leaving the center section unsheeted so it slides right into the stab slot in the fuselage. Hopefully this will make getting everything square and level much easier. Couple of pics of the stab build so far.

EG

PS - After a lot of reading on shear webs, including some very old structural beam design books from my days at PSU, I've decided that I will install vertical grain shear webs across the middle third of each wing half. I'll leave the existing webs and put the new ones on the front of the spar. Hope this makes everyone happy!

Andrew

There's something wrong with you, boy.

Guess I'll have to get over to the classic pattern forum to watch the build - .15 sized planes are just about my favorite sized model.

combatpigg

My Feedback: (3)

EROK, since you insist on knowing what my thoughts are on shear webbing, I guess you've pried it out of me.

Many moons ago when Morris Hobbies introduced their .40 sized 3D SuDoKoi, it was the first kit of it's kind I ever built. No wasted wood anywhere. This plane is engineered to take anything that a piped Rossi .45 can dish out. All they use for shear webbing is 1/4" wide x 1/16" thick strips of balsa glued vertically at each rib / spar junction.
If you can keep the ribs from buckling on our typical sport flyers, that's all it takes.
Spar doublers that run spanwise to the first rib out are a good thing, too.

BTW, I wouldn't worry about your wing, it looks plenty strong from here.

eroc144

My Feedback: (1)

Well CP, it sure was hard prying it out of you! I may regret writing this, but don't ever hold back on my account - I value the discussion. Do you have any pictures of the SuDoku you could post? Highly engineered things appeal to my meticulous nature.

Of course all of this info & research brings out the worst of my obsessive compulsive tendencies, and the weight savings from a 1/4 x 1/16" shear web is intriguing. Maybe with some cyanoacrylate thinner I could pry the current shear webs off and...

EG

rainedave

My Feedback: (1)

This is interesting. I have always thought of shear webs as functioning to produce a "C" beam (or, "I" beam if centered between the spars). cp, your description as a means to prevent ribs from folding is a function I hadn't really thought about. But then, I always try to use C-grain (quartersawn) balsa for ribs. It resists splitting lengthwise. A-grain is the worst wood to use for ribs, IMO.

David

combatpigg

My Feedback: (3)

EROK, just for you, I tore the covering off so you could see inside. It has been sitting in the attic for [quite] a few years, the starboard flaperon is fuel soaked.
I see what we have here made a liar out of me, the inner bays are almost completely webbed, but maybe that was my idea, not the kit designer's? The outer bays just have a vertical strip to strengthen the rib / spar junction, so my memory isn't totally full of it.

What a great plane this was, I think the designer's name is Tom Stryker?

As you can see it uses similar dimension wood to 1/2A and .15 designs.

rainedave

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Didn't he design the Wild Thing?

combatpigg

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David, you're right. He might have been into that early competition fun fly stuff, too.

What I like most about this Pacer project is that it has been on my mental back burner for years and now I won't have to build it....or maybe I will? Same goes for the Mach None, it needs more punch than a .049 can dish out.

eroc144

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The ribs on the Sudoku and the Super Pacer are pretty linear on the trailing side of the main spar - what's the rib profile?

I'd be happy to email the plans to anyone who wants them. That is after I fix all the issues I find during the build!

EG

combatpigg

My Feedback: (3)

It's just a straight line from the spars to the TE on the SuDoKoi. This way, you build the wing flat on the table, upside down and come away with a straight wing that was easy to build. Real airfoils on these toy planes are highly over rated.

eroc144

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Well I made slow but steady progress this week but I didn't have time to post so here goes.

The stabilizer sheeting is done, and I've done an initial sanding on the edges. My plans call for a 1/" dowel to connect the elevator halves, but this detail always struck me as flimsy and I've had a few elevators split during rough landings. So instead I used 1/16" C - shaped metal rod to connect the halves. The bent ends of the rod will be buried in the elevator giving me good strength and solid response. I built the elevator using 1/16" balsa sheeting, and cut out around the C rod so that it's embedded in the elevator. The tunnel got filled with epoxy and then the final pieces glues on top. It's a little heavier than a dowel, but I need tail weight anyway and this is not going to come apart easily.

Next up is the rudder and I followed the same process as stab. Blah blah blah. Sand sand sand. Glue glue glue. Finished pix attached!

Now to the fuselage. I'm pretty sure that all of my planes have something wrong with the fuselage. Someday I'll get or build one of those really cool fuse jigs, but for now I've improvised with epoxy bottles, pins and similar. After cutting out the formers I bevel the edges to try and get a more natural curve over the fuse. Next I glue 3/8" triangle stock to the outside edges of all of the straight edges. I drop down to a 1/8" square spar around the stabilizer as the fuse tapers down to 1/8" at the tail. I'll leave the areas around the wing alone for now. The formers and fuse sides go over the plans, and the epoxy bottles and pins start holding things in place. The dry run looks good and after some minor trimming and fixing in a few places I'm ready to start gluing. The fore & aft wing formers go in fine, as does the firewall, and then finally I glue up the tail. Everything looks straight and square and I can't help myself - I have to put all the pieces together to see how it looks. I've got a lot of work left to do on the fuse - supports for the formers and firewall, cross-grain sheeting above the wing, pushrod supports, a battery cubby, but this will do for now.

More tomorrow!

EG

OzMo

My Feedback: (3)

I understqand the strongest application for shear webs is front AND back of spar. Although I have not seen it in a kit or plan I have seen evey other one front or back with doubles in the center few bays. Always vertical grain.

If yours are already glued in a layer of paper glued to each one would likely bring the strength up to par.