Author: dale

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Trying out the steam box

The other night I finished up the steam box and made a set of little standoffs for the bottom.  I wanted to keep the wood off the bottom of the box to allow air circulation, but also allow water to run back to the low point at the rear.   I got a little lazy and didn’t put in dowels like most plans show.

Tonight I loaded it up with eight cap strips and let it run for 45 minutes while I went out and hung some outdoor lights on the deck.  When I came back I found that the door had developed a pretty good curl — concave from the outside – and was venting a lot of the steam past the door seal.  The spruce inside was fairly pliable, so I clamped three pieces in my bending form and put four more in the rib jigs.  They would only fit partway down in the jigs, since the wood is swollen.  While the wood cooled down I got all of the geodetic braces ready to install.  I’ll glue these two ribs up tomorrow night.

I did email System 3 about their epoxy.  Some of the ribs were assembled with the capstrips not pre-bent.  They’re fine, but the wood will spring out of shape if it gets hot enough for the epoxy to soften.  I don’t want that to happen. so I was thinking about clamping them in their current shape and steaming them to relieve some of the stress in the capstrip.  Of course that will soften the epoxy, and I wanted to know what that would do.  Their answer is that T-88 will begin to soften at around 120 degrees, but once returned to room temperature will be at full strength.  That’s great news.

I’m definitely not in love with the geodetic rib bracing design.  24 braces, no two alike, and I’m having to hand-fit them all.  It takes for-freaking-ever.  I have to wonder how much heavier 3/32 plywood would be with suitable lightening holes.  A guy could pop sets of them out on a CNC router in no time, save a ton of time and effort on the ribs, and probably end up with much stronger ribs too.   But, I don’t think I’m going to re-engineer the ribs right now.

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Built a steam box

Last night I built a steam box out of 1×6 boards.  All that remains to be done is to put some foam weatherstrip on the door and run a few dowels through it to get the wood off of the bottom of the box for steam circulation.  The steam generator arrived a few days ago, so once I get the box finished up it will be ready to go.  I found that the Wagner steamer hose will mate with 1/4″ pipe fittings.  I spent a little extra for brass rather than galvanized iron.  I also re-worked my bending form with a gentler curve, providing a fairly close match for the rib shape.  It won’t give me a perfect fit, but will get the capstrip close to the curvature needed.

 

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Finally — two more!

Glued up two more ribs tonight, at last.  I had dry fit the parts a couple of nights ago.  I really need to break down and build a steam box.  I ordered a Wagner 715 steamer, and will start on the box while I wait for delivery.

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More geodetic stock prepped

Last night I ran another 20 sticks of geodetic capstrip stock through the sander.  I had to adjust one of the guide boards for thickness; due to temperature and humidity changes it was too close to the drum by about .014 or so.  So, 20 more down, a hundred or so to go.  Sounds like a lot, but if I can do 20 in a night it’s another week before they’re all done.  Then it’s just measuring, marking, and cutting them in stacks on the bandsaw.  Over lunch today, in fact, I ran another ten through the process.  It took about 40 minutes start to finish.

I can totally understand why people like plywood ribs.  I could be knocking out plywood pieces, or more traditional braces for “normal” non-geodetic ribs.  Would it be less work?  Probably not.  I’d still have to make precise cuts and no two pieces in a rib would be identical.  There might be fewer of them, but with this method at least I have a very small amount of leeway on the exact length and angles.  If a piece is 1/64″ or 1/32″ longer or shorter than the next, I can adjust the angle or position to make it fit without causing problems.  I think wing ribs are just going to be a lot of repetitious work no matter how you do it.  My only regret here is not calling Wicks or ACS on the phone to see if they would custom cut my capstrip to 1/32″, that would have saved a lot of work and waste.

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Sensor scored!

An update on the oil pressure sending unit.  I had found exactly one of the correct sending units for sale, a NOS Honeywell part that was listed on eBay for a couple hundred bucks.  I didn’t buy it, but I was watching the listing.  They dropped the price, I made a lower offer and they accepted.  I ended up paying roughly what a normal oil pressure sending unit would have cost from a source like Aircraft Spruce.  And, it’s got the exact output that the Westach quad gauge needs.  Now I won’t have to build a conversion unit but can just wire this one up directly.  These transducers are no longer in production, and if you can find one you’ll pay 8-10 times what I got this one for.  If it ever fails, I’ll probably replace it with a cheap one and a converter board — now that I have that figured out.

Update 5/4/17:  Transducer arrived, NOS as advertised with a nice sealed electrical connector.  This thing will likely outlive me.

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Not entirely dormant

I haven’t posted any updates to speak of this month.  I did get out to the garage and spend a couple of hours sanding down rib geodetic stock..  What a pain in the ass.  I really wish I’d gone a different route than I did on this stuff.  I just don’t know what that route would have been.  Anyway, today I started taping stacks of geodetic strips together and cutting braces.  I’ll do as many as I can before starting to build ribs again, so hopefully when I can return to building I can get some momentum going.

I have to be honest…  I look at some of the single-seat parasols and think, “Hey, I could be building half as many wings…”  But I just need to stick t this.  It will be worth it in the end.  I’m working on an idea to semi-automate the sanding of the geodetic stock, I just need to fabricate a couple of guides and use a stepper motor to feed the stock through my sanding rig.  That could increase throughput and give more consistent results, while I get other things done.

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Pause button

I haven’t had much opportunity to do any construction for a few weeks now.  The garage is a disaster with a remodel project going on, and I’ve been busy selling my side business.  Hopefully in another week or so I’ll be able to get back to it.  The first order of business will be to try out the steamer to soften up capstrip for the ribs.

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Some advance planning

A while ago, I picked up a used Westach quad gauge.  it looked like a great deal…  oil temperature, oil pressure, CHT & EGT in one round gauge.  What I found was that it’s an older gauge, though in excellent condition — almost like brand new.  The only problem is, it’s designed to use an oil pressure transducer that is no longer produced.  0 to 100 PSI, with an output of 0 to 50 mV.  You can get transducers like that, but they cost a few hundred bucks.

Fortunately, there are other transducers that are dirt cheap ($20 and below)   that can be adapted to work with the Westach gauge.  I found some that have a 0-5V output, and looking at the spec sheet they actually output 0.5 to 4.5V.  They also require a 5V supply, and I think the gauge supplies 12V nominal.  So…  we have two tasks.  Supply the transducer with 5V regulated DC, and convert the 5V ouptut to 50mV.  Easy!

Below is a schematic for a little interface board to do the job.  A common 78L05 regulator supplies power to the transducer.  A simple resistive voltage divider does the 100:1 voltage conversion.  I used a 100K Ohm fixed resistor, and a 2K Ohm trimmer.  That way you can calibrate the divider to account for resistor tolerances.  Apply 2.5V to the transducer side, and adjust the gauge side for 25 mV.  There will be some non-linearity near the high and low ends of the scale, but that’s OK in this case.  We don’t need an absolutely accurate oil pressure indication, more of a relatively good indication within a reasonable range.  once you get very low or very high, the exact numbers aren’t really important.

Really, it was a great deal.  A new similar gauge would cost over $800.  Individual small gauges to do the same jobs would cost several hundred and take up a lot more panel space.  I’m pretty happy with this one.

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Fixin’ and cookin’ ribs

Last night I glued the two separated ribs back together.  I cleaned off/out all of the old epoxy, sanded everything clean, mixed up some new T-88 and brought them in overnight.  Just to be extra sure of a good glue cure I’ve got them warming up under a heating pad.  I took one of the others to the EAA chapter meeting, no one seemed to see anything wrong with it…  although the reaction varied from “Wow, that’s cool” to something closer to “You’re nuts, why would anyone do that?”

It’s cold, I’m not looking forward to the next session of shaving down geodetics for the next batch of ribs.  I’ll have to go out tomorrow and do it though.

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Second guessing

Not me.  I made my choice and I’m happy with it.  But I swear I have not had this much well-intentioned second guessing since I announced my engagement to the woman I’ve been married to for nearly four decades.

“You should build a Hatz.”  No, I love the look of the Hatz but it’s not LSA.  “Oh, a Hatz Bantam.”  Nope, sorry.  I’m tired of aluminum, it’s got a welded fuselage (which I did not want to build) and at the time I was looking was designed ONLY for a Jabiru engine, nothing else.  “Oh, you should build a Murphy Renegade.”  Ummm, nope.  Two-strokes are simply not an option  for me.  And on and on, with every non-LSA, or steel fuselage, all aluminum or single seat variation on the planet mentioned.

“Oh, just go find someone’s abandoned project.”  No thanks, I think I can do fine at creating my own problems, no need to try to find what someone else did wrong or “different” along the way.  I’m not traveling the country inspecting half-built (or wrecked) airframes to see if they’re suitable.  And would YOU buy that plane that was built but has been sitting for a few years, and has never flown?  Maybe there is a reason it’s never been given an airworthiness certificate.

Holy crap.  Can’t a guy pick an airplane and build it without everybody on the planet having a better idea?  No matter.  I’m building on.  I learned my lesson the first time around.  It’s really easy to get wrapped up in so much well meaning advice that you spend a few thousand hours on something like this, and never finish it.