Legacy Build

[Tim Wescott]

There's a couple of hard-to-photograph spots where TE sheeting dips down about 20 mils.  That seems a lot to take off from 1/16 inch.

[Tim Wescott]

Filler?      It looks like some sandpaper will do the job. Why add weight?

How thin would you let things get in that area, on that big a plane?

[john e. holliday]

Yeah, 100grit will make short work.

[Randy Cuberly]

Hey Tim...
At this stage it doesn't look like it would be too much trouble to replace that piece of sheeting with 3/32 and then sand that down to blend with the other sheeting and the Trailing edge sheeting.  That's what I would do.  I don't think filling it with fillet material or anythin else suitable will be easy and will probably never look quite right...at least that's been my experience with trying to do something like that in the past.

As for sanding the trailing edge sheeting I doubt you'll get it to blend with the rest of the trailing properly.  There will be a dip at the point it starts getting thinner even if it is gradual.

Just my two cents!

UUUhhhhhh....I just reread what you said above and guess I'm not clear on what is thinner the trailing edge sheeting or the center sheeting.  What I said above obviously applies to the center sheeting being thinner.  If it is the other way around then I would agree with Paul...just sand the center sheeting to blend with the trailing edge.  No real loss of strength there.  The spars are the real load carriers.
Besides,  you did put verticle grain supports in the front edge of the trailing edge sheeting...Right?...

Randy Cuberly

[Tim Wescott]

I think at this point I'm just going to do my best with filler and move on.  That's not the best solution, but I'd like to have this plane done before the end of the 2015 competition season and even if it turns out a bit ragged it's certainly going to be better than the Twister that I'm flying now.

It would be nice to know how to avoid this problem in the future -- the only really positive way I can think of, barring making a miniature set of tongue & groove routers, is to put a bit of 1/32" sheeting behind the TE (and LE, too, probably) sheeting to maintain the same level.  Either that or I just had a slightly too-tight fit on the sheeting and it kinda dragged the other sheeting along with it.

[Paul Walker]

I think at this point I'm just going to do my best with filler and move on.  That's not the best solution, but I'd like to have this plane done before the end of the 2015 competition season and even if it turns out a bit ragged it's certainly going to be better than the Twister that I'm flying now.

It would be nice to know how to avoid this problem in the future -- the only really positive way I can think of, barring making a miniature set of tongue & groove routers, is to put a bit of 1/32" sheeting behind the TE (and LE, too, probably) sheeting to maintain the same level.  Either that or I just had a slightly too-tight fit on the sheeting and it kinda dragged the other sheeting along with it.

One problem I have found is that no two pieces of balsa are "exactly" the same thickness. That could be your problem. The center sheeting might be thicker than the TE piece. I make an effort to pick all my sheets and make sure they are the same. I have a planer to deal with the sheets that are too thick!

[Tim Wescott]

One problem I have found is that no two pieces of balsa are "exactly" the same thickness. That could be your problem. The center sheeting might be thicker than the TE piece. I make an effort to pick all my sheets and make sure they are the same. I have a planer to deal with the sheets that are too thick!

I have that issue, too -- this isn't it.  What I'm complaining about is a spot where the TE sheeting sags a bit between a pair of ribs (Mike Haverly is going to get on and ding me for not putting shear webs on the TE in the center section -- he's right).

[Mike Haverly]

AAAhhh, yeah!

[Tim Wescott]

If I remember the next time I build a wing I'm going to get some nice soft balsa and I'm going to put the shear webs for the TE in before I put on the sheeting.  I might even make up one continuous web for each side with deep notches, and matching notches in the ribs.  I'll design the whole thing to stand a bit proud of the ribs (hence the soft balsa), and then sand it down to match the ribs before putting on flawless -- flawless -- TE sheeting.

If I succeed at that, knowing me, there will be something else in the plane to be totally atrocious.  My building seems to operate on a principle that the aggregate severity of screwups is conserved -- I only get to move them around, not make them go away entirely.

[Randy Cuberly]

If I remember the next time I build a wing I'm going to get some nice soft balsa and I'm going to put the shear webs for the TE in before I put on the sheeting.  I might even make up one continuous web for each side with deep notches, and matching notches in the ribs.  I'll design the whole thing to stand a bit proud of the ribs (hence the soft balsa), and then sand it down to match the ribs before putting on flawless -- flawless -- TE sheeting.

If I succeed at that, knowing me, there will be something else in the plane to be totally atrocious.  My building seems to operate on a principle that the aggregate severity of screwups is conserved -- I only get to move them around, not make them go away entirely.

The way you've described is maybe the best but not really necessary unless you intend to finish the wing in transparent covering.
Look at the picture of the Nobler wing I put in my post above.  cutting the cross grain sheeting a little shy of the outside edges of the trailing edge and simply glueing it to the inside edges with CA actually works about as well structurally.  I've done it both ways and never had a problem with either.  I would say that it's very easy to screw up the sanding operation you describe and get things out of kilter on the ribs if the task isn't done very carefully.  The method shown in the post is much easier to do!

Randy Cuberly

[Tim Wescott]

The way you've described is maybe the best but not really necessary unless you intend to finish the wing in transparent covering.
Look at the picture of the Nobler wing I put in my post above.  cutting the cross grain sheeting a little shy of the outside edges of the trailing edge and simply glueing it to the inside edges with CA actually works about as well structurally.  I've done it both ways and never had a problem with either.  I would say that it's very easy to screw up the sanding operation you describe and get things out of kilter on the ribs if the task isn't done very carefully.  The method shown in the post is much easier to do!

It occurs to me that if I cut the webs just a hair smaller than they'd need to fit inside the TE, I may not have perfect control of how deep they set inside but they'll still do their intended job.  I'll probably go back and do the TE right before I get too much farther along.

I was able to slit the TE sheeting and pull it up in a couple of places.  This alleviates the wow, but still leaves a bit to be desired.  Oh well -- this is better than what I'm flying now, and the next one should be better yet.

[john e. holliday]

If you watch any of Bobby Hunts videos you may have seen how he does it.   He made a jig to cut the web pieces and then fits each on. Just did that on my latest stunt fun machine.  Sure makes for a stiff trailing edge.

[Tim Wescott]

Spinning off into wackiness for a moment, here's the ongoing effort to add an electronics bay to the wing.  This is for a TUT, which at a minimum will be used to record flights, and if things work out, may add some helpful engine-control features.

I should have done all of this before the top sheeting went in -- the reason I didn't was primarily due to forgetfulness!  Late is better than never.  Hopefully I'm not adding too much weight.  The extra hole you see in the front of the wing is because the first time I drilled everything I was not correctly visualizing where the bellcrank was.  Asking the bellcrank to pass through a piece of balsa is Not Good.  The actual conduit location is above the bellcrank; it's well out of the way, and having a conduit means that there won't be any dangling wires to get entangled with the bellcrank.

The electronics bay is in the last sheeted bay on the outside of the wing, and communicates with the tank compartment of the stunter with a conduit that's formed from 1/32" balsa, molded around a carved former.  The conduit should be just big enough to let me slide a connector in from the outside.

[Tim Wescott]

More fun with the electronics bay.  I've used up something like 72 square inches of lite ply to get a hatch cover that uses about 18 -- the rest are all false starts, screwups, and the like.

But, I now have all the electronic bits I need to support a TUT all tucked away into the outboard wing where they'll be out of the way of the control system and where the weight might do some good.  Much of the agony was trying to make a super-duper one size fits all box that would attach with the hatch cover and hold TUT, battery, and regulator.  I finally ended up with a hatch cover that holds the TUT (something needs to hold the TUT rigidly, or the accelerometer and gyro readings won't make sense), and I just stuffed the rest of the electronics in between the wing ribs.  Which is what I should have done from the start...

I did find a nifty way to make a hatch cover that you don't have to pry out with your fingernails.  The hatch cover will need to come off any time the TUT is being talked to, or when I need to take the battery out for recharging; I didn't want to mar up my finish.  So I put a magnet on the TUT carrier and a magnet in the hatch cover, oriented so they oppose one another.  As long as the hatch cover isn't stuck it floats right out of the hole.

The last picture in the series shows the magnets being glued in.  I routed holes in the two bits of plywood, and epoxied the magnets in.  I always get magnets and such backwards from how I want, so I was careful in how I jigged this up.  I started with a magnet underneath the TUT carrier.  That forced the magnet in the TUT carrier to orient with the first magnet, and held it at the bottom of its hole.  It's embedded in epoxy.  Then there was a piece of waxed paper, with the plywood for the hatch cover laid out upside down on top.  This means that the magnet in the hatch cover will attract when the hatch cover is upside down -- and repel when it's right side up.  Finally, I topped the whole thing off with more waxed paper, a scrap of wood, and a magnet to hold the wood down and give me a nice flat surface.

If you're flying in the Pacific Northwest late this year, you'll know my plane -- it'll be the one with a dot of iron filings on the outboard wing, just outside of the fuselage.

[Howard Rush]

I suggest you seal the conduit with tape or something: 1) to keep oil out and 2) to keep the hatch from blowing off.

Edit: Oh, now I see how you used the magnets.  Sorry, Tim.  Once again I underestimated your cleverness and weirdness.  Couldn't you have achieved the same repulsive force with less mass with a foam peanut?

[Dennis Moritz]

Will the magnets scramble something in the electronics? Over time.

[Tim Wescott]

I suggest you seal the conduit with tape or something: 1) to keep oil out and 2) to keep the hatch from blowing off.

Thank you.  I'll have to think about how that might be accomplished without weighing a ton.  There'll be wires going through it, so just tape won't seal much at all.

Will the magnets scramble something in the electronics? Over time.

There's nothing in the TUT that's sensitive to magnetic fields, at least that I know of.  Strong magnets and hard drives, or strong magnets and credit cards, don't go together well -- but I think I'll be fine.

[Randy Powell]

Clever hatch. Not sure about the path, but hey, if it's crazy and it works, it's not crazy.

[Tim Wescott]

Clever hatch. Not sure about the path, but hey, if it's crazy and it works, it's not crazy.

I will be advancing science, if nothing else.  Next up in the build is to design the circuit board to make a micro servo into an Auntie servo so that I can record elevator deflection in flight.  Test Pig #3 has an Auntie servo but it's an old full size Royal that I used because it let cobble together a circuit by hand -- to get the size & weight down I need to have a board made that'll use surface-mount components.

[Tim Wescott]

I got Auntie Servo mounted in the wing, I need to get the linkage to the thing in and pictures taken.

The absolute latest work was getting Auntie Servo's schematic into CAD and getting a PC board made and shipped off.  The first Auntie Servo was cobbled together from through-hole parts, but that won't fit into a miniature servo -- the one for which parts are on order will be 9mm x 12mm, and will fit nicely inside a "9gm" micro servo.

[Tim Wescott]

Auntie Servo, waiting on linkage.  This is the top of the wing, so I need to get everything sorted before I start messing with the fuselage.  There'll be a rod from Auntie Servo back to the outside flap control horn; that plus some hand calibration should tell me all I need to know about where the controls are on any given flight.

Edit:  Things always work better when you actually remember to include the pictures.

[Tim Wescott]

Linkage installed and working.  Auntie Servo will be doing her job.

Everything is just taped together at the moment -- I'm about to go back out and apply some epoxy to the joints.  I'm usually very leery of metal-to-plastic bonds, but there's practically no force on these.

[Tim Wescott]

Back to normal CL stunt stuff.  Making the flap pockets.  The Brodak kit has you glue a piece made out of 1/8" plywood to the end-grain of your flap.  I didn't feel that was going to be strong enough, so I made up some bits out of 1/16" balsa and inlaid them into the ends of the flaps, then glued 1/16" plywood end caps on.  It's probably overkill, but it should be enough to tweak the flaps with, which means that it's more than enough to hold things together in the air.

The inlaid pieces are put in with gap-filling CA, the end plates are epoxied with 30-minute.  It should all be stout enough.

[Tim Wescott]

Except that now I have to wait for the epoxy to cure.  If I had some of this http://www.masterbond.com/newsrelease/led401 then I'd be on to the next step!!!

[Robby Hunt]

Pretty cool!

[Tim Wescott]

Update on the flap pockets: in retrospect, I should have glued the plates in with some sort of spacer in the hole, to make sure they were spaced correctly.  I didn't, and I ended up filing the ends of my flap horns a bit so they'd slip into the boxes.  Next time.  If I remember.

[Tim Wescott]

At the Tune Up this past weekend Paul pulled me aside to discuss my flap mechanics.  It turns out the pockets & whatnot are both overkill and insufficient.  But I've figured out what to do, Paul has approved, and next time it'll be WAY EASIER.

In the mean time, here are Aunty Servo's brains, courtesy of the Atomic Zombie Workshop.

[Tim Wescott]

Tips tips tips.

The plans tell you to make the tips, then carve a slot in the inboard tip for the leadouts.  I decided that since the thing is built up from all the right sizes of wood, I'd build the slot into the tip and carve around it.  The middle lamination for the tip is 1/4" and I like a 1/8" slot, so I just whacked a hunk out of the middle, marked where the remaining bits landed on the two outer plates, and made a pair of 1/16" thick plywood rub plates.  Then I glued the plywood bits to the wood, and then I laminated up my stack -- viola, I had a tip plate blank with a nice hard-faced leadout slot.

The final picture is the two tips (the outer is glued to the wing already, the inner has the leadout guide shoved in the slot so that I will not forget to install it before the tip goes on.  Most of the tools I used are there, too -- a utility knife, two sanding boards (different grits), a home-made gouge, and a home-made whittling knife.

[Tim Wescott]

Got the leadouts finished.  I used 1/16" copper tubing for the ends rather than eyelets -- it makes a very clean termination, and I was able to get the leadout lengths matched to within my eyeball's ability to estimate the flap horn being flat.

The leadout guide is mounted on some scrap pieces of lite-ply, because just putting it on a rib seemed inadequate.  The leadout terminations are done using 1/16" copper tubing (K&S, bought from Amazon).  Using soft tubing allowed me to do a very tidy job of terminating the leadouts, and let me get them matched in length to well within my eyeball's ability to tell that the flap horn was at neutral.

The leadout assembly is done more or less to a method that Igor Burger showed on a European forum (I think it was Polish -- all I can remember for sure is that it's not Slovak, but on questioning Igor told me that if you can speak one Slavic language then you can read them all, so people just post in their native languages and everyone else reads their posts just fine).

The procedure was to mark the extreme "in" extent of the leadouts using masking tape, then to install one tube on one leadout.  Having done that, getting the other tube located was just a matter of putting it on, matching it's end to the end of the already-installed leadout, then giving the thing a light crimp, just enough to hold onto the leadout until it's bent.

I used round-nose pliers to do all the bending, per Igor's tutorial.  I wish that I had gotten a pair ages ago; I've wasted 40 years trying to make nice bends in wire with just about everything but round-nose pliers.

[Tim Wescott]

At the Tune Up this past weekend Paul Walker mentioned that with the split flap horn, you need to nail down the flap horn travel from side to side.  He'll undoubtedly have the right way to do it in his article; after coming up with several Really Complicated ways of doing this, I realized that I could just stuff some plywood and bass strips down the slots to narrow them up.

Which I did.

[Tim Wescott]

I put the flaps on and noticed that the top of the left (inside) wingtip tapers down horrendously.  The other tip tapers up, but less bad and on the bottom.  I think this has something to do with being a right-handed wingtip carver.

It needed a lot of filling, so I chose to use wood.  The method I use is to sand the patch and the piece to fit -- in this case I sanded flats into the tip -- then glue the piece on, carve & sand when the glue is hard, and repeat as necessary.

In the past I've used just about every glue for this except epoxy, and the best has been Ambroid or SigMent -- but even that has left a discernible ridge.  This time around I had some Ambroid handy that's been thinned half & half with acetone.  I painted it on with an acid brush (double glued -- if you just apply Ambroid and stick things together the glue soaks into the wood and leaves nothing for the joint.  Doubly so for thinned.  So you apply glue, let it dry, then do it again). It worked great.  The pictures tell the story, except for the final carving & sanding.

[Tim Wescott]

Not fixing mistakes, not TUT weirdness, but real forward progress (however small): got the landing gear leg blocks finished.

The Legacy kit puts the jig hole right through the LG block so if you're using the jig you can't put in the LG blocks when called for.  So I just put them in, and will drill the holes soon.  Then I'll cuss because the holes aren't quite right, but I know how to cope with that.

[Tim Wescott]

LG blocks drilled, and LG legs inspected closely.  Why didn't I scratch build this one?  I either use these and have visions of the leg snapping right where it turns to go into the wing, or I take the time to bend up new ones.

Woe is me, etc., etc.

[Tim Wescott]

LG bent (more) correctly.  There are guidelines for bending structural members -- bending it over something sharp is not generally in the guidelines.

Kit LG is to the right, new LG is to the left.  The only fault in the newly bent stuff is that, because of the bender I'm using, the bend kind of trails off to the bottom instead of starting and stopping promptly -- you need to think about where that's more acceptable as you bend stuff.

(The bender is basically a home-built copy of a Biso Bender arbor, without any handle-thingie: I just bend wire around it with my hands.)

[Howard Rush]

Maybe the stress man would sign off the kinked one.

[Tim Wescott]

Last little bit (I think) on the wing.  Weight box is done.  Simple, straightforward construction is best.  I wish I could manage it.

[Tim Wescott]

Finally finished doing this & that to the wing and set it aside, cleaned up my bench, reached into the kit box for the engine bearers, and found -- this.

@#$%

Kits!

Fortunately I have replacement wood that is whole and straight-grained.

[Randy Cuberly]

Finally finished doing this & that to the wing and set it aside, cleaned up my bench, reached into the kit box for the engine bearers, and found -- this.

@#$%

Kits!

Fortunately I have replacement wood that is whole and straight-grained.

Wow, hard to beloeve that anyone would select wood like that for engine bearers!!!
It's common to find some that isn't very straight, but that has to be the worst I've seen for wood grain direction.

Randy Cuberly

[Randy Cuberly]

Tim,
I don't know your plans for building the Fuselage, but I would strongly reccommend building a crutch first by perparing the individual bearers with aluminum facing with the bearers relieved about 1/8 inch behind the engine (makes locating the tank easier), then drilling the engine mounting holes in the individual bearers and bolting the engine to them.  This aligns each bearer to the engine mounting surfaces.  Then cut 3/8 cross grain balsa and epoxy it between the bearers with everything clamped gently to a flat surface (I use glass covered with wax paper as shown in the pictures).  I also strongly reccommend a Jig something like the one shown in the photo.  I think Tom Morris makes something like this...but not sure about that.  I used to make some like the one shown in the photo.  Not hard to do but does require a good table saw to get everything square.  The whole thing needs to be very stiff also.  The one shown is reinforced with steel angle on the bottom (lengthwise).
The advantage to all this is that it allows the Fuse to be built pretty stress free because the engine itself determines the angular position of the mounting surfaces.  No twisting or bending when the engine is tightened down.  This makes for far less stress and vibration cracking in the fuselage over the years of usage.

Randy Cuberly

[Tim Wescott]

Wow, hard to beloeve that anyone would select wood like that for engine bearers!!!
It's common to find some that isn't very straight, but that has to be the worst I've seen for wood grain direction.

If you look closely you'll see that the grain is fairly straight at the right of the picture, then curves.  I think it was just sawn from wood that had curvy grain, and then got by QC somehow.

I don't know your plans for building the Fuselage, but I would strongly reccommend building a crutch first by perparing the individual bearers with aluminum facing with the bearers  <snip>

That's more or less what I was planning on doing: getting the crutch built with the aluminum bearers, etc.  My flying buddy has a jig that I'm planning on borrowing.  He used assembly triangles that cost $2 each at Horror Freight, on a heavy board of some sort.

I'm planning on making the aluminum motor mounts 3/16", and bolting the motor to them, then bolting the mounts to the bearers.  This isn't just to spread the force from the motor -- I'm also anticipating engine swaps, so I'm trying to make the thing so that I can easily change out an engine just by changing bearers.

[Randy Cuberly]

If you look closely you'll see that the grain is fairly straight at the right of the picture, then curves.  I think it was just sawn from wood that had curvy grain, and then got by QC somehow.

That's more or less what I was planning on doing: getting the crutch built with the aluminum bearers, etc.  My flying buddy has a jig that I'm planning on borrowing.  He used assembly triangles that cost $2 each at Horror Freight, on a heavy board of some sort.

I'm planning on making the aluminum motor mounts 3/16", and bolting the motor to them, then bolting the mounts to the bearers.  This isn't just to spread the force from the motor -- I'm also anticipating engine swaps, so I'm trying to make the thing so that I can easily change out an engine just by changing bearers.

I don't know what you're using for an engine but most of the PA's, ROJetts, and european engines all have the same mounting holes etc.

3/16 in aluminum is a lot of weight and unnecessary unless you plan to use tapped holes in it, in which case it's marginally not thick enough!

Randy Cuberly

Sorry about having to constantly correct typing errors...I stuck a finger in Burt Brokaws 22,000 RPM prop a few days ago and the bandage makes typing very clumsy!   

[Howard Rush]

Looking at one of your pictures I see a "crankcase cooling vent".  Crankcases typically run cooler than ambient.

[Randy Cuberly]

Looking at one of your pictures I see a "crankcase cooling vent".  Crankcases typically run cooler than ambient.

Hi Howard,
Was that comment directed to me or to Tim.  The only time I've used what could be construed as a "crankcase cooling vent" was on my GeoXL and it was actually a small vent to the venturi for the long shaft Belko that has the intake located 180 degrees from where most engines have them.  In an inverted position for the engine the intake is on the top, which is a pretty static area for air flow on that particular airplane hence the "scoop style" vent for the intake.

If the comment was aimed at Tim, then...Never Mind!

Randy Cuberly

[Tim Wescott]

Was that comment directed to me or to Tim.

The Legacy plans call out a crankcase cooling vent.  Howard is being -- Howard.

[Randy Cuberly]

The Legacy plans call out a crankcase cooling vent.  Howard is being -- Howard.

Huh...Howard are you wearing that Clown Suit again?   

Randy Cuberly

[Randy Powell]

Howard never leaves home without it.

[Tim Wescott]

I got out the stuff to do the stab -- none of the sticks are less than 8lb/cu ft, and one is at least 13 (I mistook it for motor mount stock!)  Moreover, they're all bent to some degree or another.

So -- off the deep end!  This thing is getting a foam-cored stab.  I have enough wood that's contest weight or nearly so; if I can be sparing enough with the glue I should be able to do a stab that's not too much worse than the kit one for weight, and a heck of a lot straighter.

Yesterday was spent cutting lots and lots of foam, to get a few pieces that will be good enough for cores, and even then only after I sand to size.  Bob Hunt I'm not.

This may not end up being the best kit build ever, but I think it'll rank up there with the most whined about.

[Randy Cuberly]

I got out the stuff to do the stab -- none of the sticks are less than 8lb/cu ft, and one is at least 13 (I mistook it for motor mount stock!)  Moreover, they're all bent to some degree or another.

So -- off the deep end!  This thing is getting a foam-cored stab.  I have enough wood that's contest weight or nearly so; if I can be sparing enough with the glue I should be able to do a stab that's not too much worse than the kit one for weight, and a heck of a lot straighter.

Yesterday was spent cutting lots and lots of foam, to get a few pieces that will be good enough for cores, and even then only after I sand to size.  Bob Hunt I'm not.

This may not end up being the best kit build ever, but I think it'll rank up there with the most whined about.

Hi Tim,
This question may be a bit ot of order and you may even have answered it before but I'm curious to know what engine you are planning to use in this Legacy?

Randy Cuberly

[Tim Wescott]

What, you're considering all the weight I must be adding, and thinking I'll need a small-block Chevy?

I plan on putting a Byron Barker Magnum 52 in it.  I'm also planning on making the motor mounts such that I can swap in a different engine at need, since I've heard contradictory stories about the suitability of that engine for that airframe.

[Randy Powell]

Gee Tim, mine is in silkspan. You need to move it along.