Finishing up the Flaps

2-29-18 – 3-8-18.  8.5 hours.

I have always known that keeping up posting on this blog would be tough – and it definitely is.  I see that it has been half a month.  That has been busy time for me, buying a wrecked RV7 for parts – more on this soon – as well as selling stuff out of the hangar to finance the RV6 and annualling a friend’s airplane.  Then there was spring break.  Overall, I guess I’m proud of the 8.5 hours I have managed to spend riveting up the flaps.  Not much in the way of pictures, but both flaps are now pretty much done.  That is the last of the control surfaces.  I definitely enjoyed the flaps the most.

The skeleton – drilled and dimpled.

Riveting the trailing edge “spar” to the ribs.

Everything clecoed in place.  I used huge numbers of clecos in ordre to make the dimples fit down tight and the hole thing “pop” into position.

After clecoing the flap together, the front spar is removed, and the rivets are bucked through the skin seam and ribs.

The most difficult part of the job was reaching the rivets “blocked off” by the flap actuator.  I don’t like “pop” rivets, so these are all solid on my plane.  Lots of creative bucking bar placements.

Nearing the end – the spar gets riveted in.  This involves bucking rivets in the top seam – here almost completed –

and squeezing the rivets through the spar, skin, and hinge on the bottom size.  Much quicker to squeeze than buck.

I thought about trying to use bucked rivets through the spar into the ribs, but decided that this would be overkill.  Note the three cherry-max rivets on the actuator and rib.  I used cherrymax here, as they are stronger than avex.

And here are the avex rivets as per plans on the other ribs.

At this point, I haven’t touched the plane for a week, and can’t wait to get back at it.  The control surfaces are mostly done, and it is time to get to those wings!


Finishing the Flap Actuator. One Flap Drilled, One to Go

2/1 – 2.5 hours.

So last time I was pondering what material to use for the final piece of the flap actuator – and I had persuaded myself to use a scrap of 1/8″ 6061 angle instead of the 1/16″ called for in the plans.  It would add an ounce.

This morning, I remembered an entire drawer of surplus aircraft mounting brackets.  I couldn’t bring myself to recycle these a few years ago when I was cleaning out the shop, and I forgot them in a cabinet I seldom open.  They are all shapes and sizes, and a huge quantity.  This pair is 2024-T4 and 1/16th inch thick!

Brackets before shaping into the part shown below on the plans.  Just a few minutes with the band saw and sander, and I have a left and right set – ready to go to work – and better than the plans call for.

All the actuator parts set in position on the flap.  I extended the angle about 3/4 inch past what is called for in the plans in order to catch the next rivet.  The entire actuator assembly is built in 3 pieces so that it can be EXACTLY fitted to the flap – but order is very important.

Here is another view of the 3 parts.  Thus far the only joint is clecoed between the angle and the plate.

Clamping the angle and plate in position against the spar.  The plate now is held in position, not touching any parts.  The angle is carefully drilled and clecoed to the spar, as the 3 outermost holes also go through the front of the inboard rib.

Here is the angle set in position as well.  It transfers the movement of the flap handle to the spar and the inboard flap rib.  Notice how the three layers (skin, rib, and angle) tend to separate when there are no clecos in position.

I clamped the angle against the plate to ensure a firm fit.  Now, the bottom skin/rib flange holes can be extended onto the bottom of the angle.  I loosened the clamp and reclamped between adding clecos to ensure that alignment is true as the aforementioned gap is closed.

Now with the angle clecoed in place along the rib bottom, I can draw in and drill the holes that mount the angle to the plate.  The fit is perfect because it was match drilled in position.

Here is the right flap, completely drilled and clecoed.  All that remains is to dissemble, debur, dimple, prime, and rivet.  And now I get to start over again on the left flap.  I expect it to go quicker, however.  THis is because I have already grappled with the order and because I already built the actuator bracket.

This brings me almost to the place I would be if I had bought a modern pre-drilled kit.  If you count your time as worth anything, don’t buy an old kit that wasn’t pre-drilled.  I am about 10 hours into the flap.  If I charged myself the $50 per hour for A&P work that I charge other people, I’d have another $500 in just this flap.  And don’t forget – KW did the flap spars!  However, I am not upset.  I knew what I was getting into when I signed up for this job – and I am actually having A blast.  Right now, I can’t wait to get at it each day.  I am sure that will wear off, however.

Here we go again!  Spar, ribs, and bottom skin drilled and clecoed before the end of today’s work.  I probably will not be adding many more photos until I come to something new.


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.