It isn’t a Flaw – its a Feature!

1/30 to 1/31 – 4 hours.

Laying out the flap actuation brackets (left and right) on a plate of 1/8″ 2024-T3 provided with the kit.  Notice that these are mirror images of each other.  Also, notice my crossed out lines.  This was due to an error in the plans.  Laying them out, the error was apparent.  The plans called for dropping 1 1/16 from the red line to the bottom of the bracket, but the angle so formed was visibly off.  The next crossed out set of lines were made by assuming the 1 1/16″ was meant to be measured from the upper black line, not the the red line.  Again, noticeable visual error.  Closer, but definitely no cigar!  Luckily, the plans are full size, so I just had to ignore the erroneous 1 1/16″ dimension on the drawing and draw what was shown in the plans.  Luckily, this also lines up perfectly with the flap where it is supposed to.

Cutting out the plate on the bandsaw.  There is no way the shear will go through this stock.

VERY rough band-sawed parts.  The cuts are to larger than needed dimensions, and so I’ll sand up to the lines.  Sanding aircraft aluminum is OK if you use aluminum oxide paper.  Many other abrasives are not OK, and can set up corrosion issues later on.

Here are the final rough parts.  Next, the angle gets cut into two separate spar mounts as seen below.  This is a complex cut, as there is a slight bevel across the face.

Here are the parts clamped together.

Match drilling the parts.  This is thick enough that a drill press is very wise.

Zinc Chromate (actually this is zinc phosphate – my zinc chromate is still on the way).  Now its time to drill up the hinge to fit the spar.

OOPS!  The plans call for cutting the hinges to 55 1/2″ long.  I cut them (BOTH) to 55.”  I drilled the hinge into place, and it ends 1/2″ too far outboard.  Since the inboard side of the flap is where the actuator is, this is the highest stress point of the hinge.  I don’t want to terminate it at the wrong spot.  I can choose to buy new hinges, piece in additional hinge material, shift the hinge inboard 1/2″, OR …

Note the plans that call for a AN257-P3 hinge.  They supplied an MS20257-3 hinge (which cost $2 a foot).  The MS part number superseded the AN, so no problem there.  I have more of the MS20257-3 hinge, but only 36″ lengths.  But I also have a short (24″) piece of MS20001-3 hinge ($11 a foot) on hand.  Check out the difference.  Dimensionally, they are the same.  However, the MS20001 hinge is extruded, and the MS20257-3 hinge is rolled.  Under load, the MS20257 hinge can unroll and separate.  The MS20001 hinge cannot.  I wasn’t thrilled that the flap was attached with the MS20257 hinge, but the safety track record demonstrated that it is good enough.  Except I screwed up and trimmed my weak flap hinge too short at the highest stress point.

Solution – I trimmed 3 more inches off the 1/2″ short MS20257 hinge, and add 3.5 inches or high quality MS20001 hinge.  I slid the pin out before I cut, so my pin is only 1/2 inch shorter than both pieces of hinge, and runs continuous through them.  I now have the better quality hinge at the high stress point (where the actuator works) and this will keep the flap hinge from peeling in the event of a slight overspeed.

The two hinge sections on the common pin.

Both hinges drilled and clecoed in place.  I like this better than the original, and I will do the same thing on the other side.  (I have to.  I cut them both short).

Remember the 1/2″ too short pin?  This, too, is a feature.  I centered the pin in the hinge, and drilled a tiny hole for a cotter pin – 1/4″ from each side.  This is about halfway across the end segment on each side.  I am drilling with a #55 bit.

Here is the (test) cotter pin neatly terminating my piano hinge pin.  This isn’t going to fall out.  All my piano hinge pins will be terminated similarly.  My flight instructor drilled it in to me to check these cotter pins on my Cessna Ailerons during preflight.  I have seen several flying airplanes without them.

Still more work to go on the flaps.  Now I need some 3/4″ by 3/4″ angle 1/16″ thick to finish the mounting brackets.  There are many lengths of this material in the kit box, but I am nervous about using the wrong length – one that is intended for the fuselage.  If I do that, I’ll have to replace an entire angle.  Since I have a piece of 1/8″ by 1″ 6061 T6 C-channel, I think I’ll just trim a 3/4″ by 3/4″ by 1/8″ angle out of that and use it instead.  This will add about 1 ounce to the airplane – I checked!

An extra ounce?  I know:  “take care of the ounces and the pounds will take care of themselves.”  However, this is budget building, and will require some compromise.  I also have to take care of the dollars, and the thousands will take care of themselves.

 

Flapping my Wings…

1/29/2018 – Right Wing Flap Construction – 4.5 hours

Here are the parts before beginning.  KW drilled the lower holes on the spar the flange, as well as the lightening holes and rib mounting holes.

Here are the spar and ribs set in place on the lower skin.  Note the upward fold at the rear of the lower skin.  I will be referring to this as the rear spar area.  The main spar is held in place with c-clamps.

A closeup view of rear spar area on the flap.  It has to be trimmed on both sides.  Here, I am drilling the relief hole to trim the 1 3/4″ off the inboard side.  The cuts are then made to the relief hole, and there is much less stress concentration on the finished part.

Once the rear spar are has been trimmed to length, all the ribs can be clamped into position.  The rib holes through the main spar are then transferred through the ribs, and these are clecoed into place.

Now the rib tails are drilled and clecoed to the rear spar extension.  The structure is starting to take shape, but it is very floppy at this stage.  The skin will lock it in position.

After the structure is set, the skin holes on the spar flange are match drilled through the skin.  The extra long drill bit is a big help here.

The positions of the ribs are drawn on the outside of the bottom skin, and skin holes are drilled into the skin and lower rib flanges.  Lots of clecos needed.  Did I mention that I love rivet fans?

Here you can see all the lower holes drilled through the skin into the ribs and spar.

Now the top skin is clamped into position.  Note that this wraps around the back of the spar and forms the trailing edge.

Not shown, I drilled the rear holes on each rib through the bottom skin, locking the skin in position on the flap.

Drawing the position of the spar flange onto the outside of the top skin.

Now, the top skin is drilled to the top spar flange.  At this point, the flap must be perfectly flat, because this is the point where it stops feeling like a dishrag, and starts feeling like a solid flap.  Notice that I still have not drilled the end of the inboard flap rib.  This area must be match drilled with the actuator hardware.

Apparently, I stopped tacking pictures at this point – but there isn’t much else that I did today except to draw the positions of the ribs on the top, and drill the rivet pattern into the top skin.  I am very impressed with the simplicity and solidity of the flap.

*All* I have left to do on the flap is to drill the skin to the top rivet flanges, drill the joint between the top and bottom skins on the bottom of the flap,  find and build the flap mounting hardware, drill the flap hinge, and then dissasemble, debur, dimple, countersink the hinge, zinc chromate the parts, and then rivet it all together again.  And then I have to build the second flap.

Happy with today’s progress.  Having a lot of fun, and hope it stays this way.  I think the secret is to build each part as a separate project – not to think of it as building an airplane, but as building airplane parts.  That way, there are many small completions.

 

Keeping Track of Cost

One of the reasons for tracking all of this is so that I can know what this project really costs.  I intend to keep a running total of expenditures here.

  • Used RV6 Kit, including Empenage, Wing, and Fuselage subkits.  – $6000.
  • Trip to go and get kit.  Includes fuel, motel, and supplies to load kit on trailer.  $353.78.
  • #40 drill bits for 1/4-20 angle drill.  qty 3.  $5.25.
  • 6 Rattle cans of Zinc Chromate Priner.  PilotsHQ.com.  $50.61 including shipping.  Ordered 1/30/2018.
  • Inboard and Outboard Aileron Nose Ribs.  $29.51 for the pair with shipping.
  • 1/2 inch galvanized pipe 48 inch long. (Aileron balance weight.)  $9.87.
  • Tube of Silicone Caulk – $2.18.
  • Quart Kit of Wing Tank Sealant from Vans – $57.95
  • 2 new fuel tank cap o-rings – $6
  • Sold MAC servo to offset expenses- $-125 net

Running Total – $6380.15.

Free Stuff (Bought in a lot, and sold enough to cover)

  • Bought used tools – $550 with shipping.  Not included in the total, because I sold the ones I didn’t need for the same amount.  WIN!
  • Hope to put other stuff in this category soon.

 

 

Near Future expenses.

  • Qty 3 linear servos.

Big Future Expenses

  • Finishing kit – About 8K.  Hope to find cheaper.
  • Lycoming O-320 – Hope to get a mid-time one for around 7K
  • Prop – hope to get a controllable pitch one, but I have to find it cheap.
  • Radio
  • Other Avionics.  Lots of options.  I hope to build a lot of these on my own.  One of the big reasons for this project is that I hope to experiment with making my own glass cockpit stuff.  I have spent the last few years teaching aviation digital electronics, so this isn’t as far out as it sounds – but it is still pretty far out.

Framing an Aileron Trim Tab

First real day of work – 5.5 hours.  ($5.25 spent on drill bits)

These are the ailerons as I got them.  As you can see from the one on the left, it is missing the nose ribs.  I started looking everywhere for them, and finally found them mounted inside the other aileron, along with 2 extra tail ribs on the outboard section.  I really mulled over why this happened and what to do about it until I remembered that KW had told me he was going to add aileron trim (just like me!)  He was beefing up the aileron to accept a servo and be strong enough to separate a trim tab.

While I was figuring out what became of the nose ribs, I looked up the cost to buy new ones from Vans.  In stock, $13 each.  Wow!  I’m used to Cessna prices – and I like this!  I am also missing the aileron counterbalance weight for the left aileron.  It cost $10 from Lowes – its a piece of 1/2 inch galvanized water pipe.

Anyhow, the aileron trim tab KW began is on the outboars side of the right aileron.  I was thinking inboard, but since he began on the outboard, I’ll go that route.  I want to frame up a trim tab not unlike the rudder trim tab as per the plans.

Rudder Trim tab as per Vans Plans

Existing framing.  The two inside nose ribs and tail ribs are extras added by KW.  He already drilled the skins to match the ribs, so I was committed.  Luckily, I already had a length of MS20257 hinge – the same hinge Vans calls out in the plans for the elevator trim.

Frame with hinge.

Fabricating a trim tab spar of 0.032 2024 T3.  Luckily, I had some scrap to do the job.

Folded end of spar clamped on inboard rib.  Outboard rib trimmed, folded, and temporarily clamped in place.  The spar is clecoed to the inboard rib, but the outboard can’t be drilled until the skins are fitted up.

Trimming up the middle rib.  This will also be drilled after the skin is clecoed back on.

Spar clamped in place with skin installed and clecoed.

Cutting off the skin aft of the spar.

Trim tab cutout.  Now I can drill and cleco the joints between the ribs and spar, as the final position of the ribs is set by the skin clecos.

Laying out rivet pattern for spar/hinge/skin joint.  Rivet fans are a great tool.  You can see stools in the background.  I am working in the SIU Aviation Technologies Sheet Metal lab, where I teach aviation sheet metal fabrication and repair.  This is how I just “happen” to have so much good stuff and access to so many nice tools.

Hinge clecoed in position.  Trimmed portions of ribs clecoed back onto the cut out portion which becomes the trim tab skin.

Using one of the rib ends to make a pattern for a new rib.  Don’t try a job like this without a caliper.  I’m old fashioned enough to like my dial version over the more modern (and less reliable) digital versions.

Rib form block cut out of scrap pine and radiused.

Drawing the rib blank.  I used 0.030 aluminum instead of the 0.025 of the other ribs.  That will add a couple grams.  We’ll have to check the balance before we fly!

Hand forming the flanges with a rubber hammer.  This will be followed up with a more precise sheet metal hammer.

My new rib alongside the outboard rib and the pine bending block.

Clamping the trim tab to a straight edge before drilling the new rib to the skin.

Not shown – forming the trim tab spar.

Trimming and folding up the rib to fit the spar.  I’ve cut the triangle forming block to length, and I’ll hammer the flange down.  Notice the relief holes in the corners.  This was done on the 2 outside ribs.  The center rib will not be riveted in to the spar, forming a stiffener instead of a rib.  The full aileron had stiffeners only in the center, not ribs.  My trim tab is fine with a stiffener instead of a rib.

Trim tab set in position.

Drilling the skin/spar/hinge joint.

Tim tab clecoed in place, shown slightly raised.  Raising the trim tab will push the aileron down, pushing the wing up – so the trim tab moves the same direction as the wing travels.

Bottom clecos removed to fit in the bending brake.  Lower skin bent as per elevator instructions.

Completed end view of formed trim tab.  Compare to end view of elevator tab below.  I need to get the servo before I finish the tab.  I have decided to use the Actuonix digital servos because they are light, low cost, and I can hook them to an autopilot as well as a simple trim system.  They are specifically intended to be controlled by Arduino, and that will probably be the brains on my trim computer and my autopilot system.

I’m very happy with the trim tab – it easily moves up and down through an appropriate range – about 15 degrees down, and as far up as I want.  I can control the precise stops when I add the servo.

Reminder of the elevator trim for comparison.

About me and my project

To the very rare person who stumbles on my RV6 Documentation Site:

I was fortunate enough to take over a partially complete RV6 project early this year (January 20th, 2018).  As a *competent* sheet metal mechanic, this seems like a good way for me to get the aircraft I want – something sleek and fast that is also  safe.  The RV6 seems to be a good candidate – and this kit that was partially built by KW is a great starting point.

The kit I bought was originally purchased in 1998 or thereabouts.  It was built before Vans began prepunching the kits.  It is for an straight RV6, which means it has *conventional* landing gear – or in other words it has a tailwheel.  The original buyer/builder largely completed the empenage kit, was about 1/2 to 2/3rds done with the wing, and did not begin on the fuselage.  Unfortunately for me and my budget, he did not purchase the finishing kit yet – so that will be an expense I will have to prepare for along with an engine, prop, and avionics and instruments.  He did, however, give me a fuselage jig that he and some friends constructed.  This jig has already produced a flying RV6 – so that is reassuring.  Hauling that jig 750 miles on the roof of the suburban made my fuel economy go from 14.8 mpg to 11.5 mpg.

Thus far, the build quality on the kit looks to be excellent.  KW is an A&P IA with incredible amounts of experience, and it shows.  I am an A&P IA with a little less experience, so I consider myself qualified to make this judgement.

Since I am not a competent tailwheel pilot and since I like to let other people land my airplane, I will have to convert this kit to an RV6A with a nose wheel.  I really don’t intend to deviate much from the aircraft kit, but I do want three axes of trim so that I can add full autopilot.   This means adding trim tabs to the rudder and ailerons – something that is not included in the plans.

For the purpose of documenting my 51%, this kit is far less complete than a modern quick-build kit.  The spars are complete, and the leading edges have been riveted together and partially riveted to the spars.  The fuel tanks are partially complete.  The rear ribs are riveted to the spars, and the rear spar is clecoed in place.  The other skins are clecoed in place as well.  Many of the holes have been dimpled.

The empenage is largely completed, although I will be making the aforementioned mods to the rudder.  There is still a good deal of trimming and fitting to be done around the edges and endcaps of the pieces.

The ailerons are partially drilled, but can be regarded as unstarted when compared to a modern pre-punched kit.  The flaps are completely unstarted.

And now I am ready to begin building.

Ailerons and Fiberglass Tips

Elevators, Vertical Stab, and Rudder.

Unstarted Fuselage Kit

Plans and Paperwork (a critical part of a kit.  Don’t buy a kit without the right documentation!)

Wings and Horizontal in a lovely rolling stand.  Thanks, Ken!

End view of Wings.