1. Opening
up: You’ll remove all reasonable inspection ports, hatches, covers, and
fairings. This means lots of screws running around loose, and lots of
potential for damaging screws, screw holes, and covers. Use a separate
snack-sized baggie for each cover, and mark the baggie with the location.
Take your time, and pay special attention to the engagement between your
tools and the fasteners. Every screw that you don’t break, strip, or lose
saves you about 20 minutes in the overall removal/replacement process.
2. Cleaning
up: Use brushes, rags, and a vacuum cleaner to remove all dust, dirt, lint,
twigs, grass, and other foreign material from the areas you opened up.
It’s amazing how much of that stuff can accumulate over a season. It all adds weight, and it all has potential for interfering
with the aircraft systems.
In particular, you’ll want to be on the lookout
for mouse and bird droppings. They are corrosive, and indicate that there
may be beasties and whatnot distributed into places that you can’t see.
3. Inspection:
The inspection will basically consist of making sure that the aircraft
conforms to acceptable practices and is of a condition for safe operation.
Unfortunately, what’s acceptable can vary widely between mechanics and can
even vary situationally between aircraft. That’s one of the reasons that
many mechanics won’t do homebuilt inspections - they don’t have any
solid guides to go by. In my experience, most A&Ps will inspect a
homebuilt with an eye towards making sure that it meets up with what they
know of AC43.13. I suppose that some may want to look at the plans as well,
but I’ve never encountered such a situation.
Anyhow, for most HPs, these are some of the
things I pay special attention to, in no particular order:
·
In general, anything that’s supposed to move should be checked
for smooth motion, with no binding, interference, or stickiness. Anything
that should not move (like wings, structural components, and stabilizers)
should be checked for security and stiffness. The wings and stabilizers,
in particular, might have a bit of play, but excessive play should be
noted and addressed. I like the wings to have no more than about ¾"
of fore-aft play and an inch or so of vertical play at the tip. As I’ve
written before, the size and weight of the wings, and the relative limberness
of all of the glider parts, makes it difficult to get a good assessment
of wing play. For the stabilizers, I like to have no more than about 3/8"
of vertical (rather, diagonal) play, and about 1/8" of fore-aft play
at the tip.
·
Carefully inspect the ruddervator drive angles where they
go into the pockets on the ruddervator drivers (those things made with
½" square steel tubing). The drivers are steel, and the drive angles
are aluminum, so there’s potential there for galvanic corrosion. I like
to keep mine painted and greased, but I still look closely at them at
every opportunity.
·
Inspect the cotter pins on the clevis pins that the
ruddervator drivers pivot on. They are in a position that doesn’t allow
for much freedom of motion, and they tend to get beat up.
·
For the flap drive torque tube, also check the cotter pins
(if fitted). On the HP-18 in particular, the cotters get beat up like they
do on the ruddervator driver clevises.
·
In fact, make it a point to track down and inspect every
cotter pin in every clevis pin on the aircraft. Dick used a lot of clevis
pins in his designs, because it saves weight and parts, making things
lighter and simpler.
Going off on a tangent, on occasion there’s
been a bit of a philosophical debate about which direction clevis pins
should be installed. Some people say you should always install them
head-up so that gravity will tend to hold them in place in the unlikely
event that the cotter pin is omitted or breaks. But in my HP-11, almost
all of the clevis pins in the control system are installed head-down.
The reason that I like it better that way is that it makes it easier to
inspect the critical part of the connection. When you look at the head
of a clevis pin, you usually can’t tell whether or not there’s a
cotter pin through the hole at the other end. All you can tell is that
the head hasn’t broken off. And, c’mon, has anybody ever seen a
clevis pin with the head broken off? But when you’re looking at the
tail of a clevis pin, you can tell in an instant whether it’s cottered.
·
Inspect the stabilizer attach pins or bolts for security
and freedom from corrosion. For HPs with spring-loaded pins, make sure
that the pin is cross-bolted per the safety bulletin. If the pin is cross-pinned,
I strongly recommend that you replace the pin with an AN-3 bolt as described
in this bulletin.
·
Use a flashlight and inspection mirror to carefully inspect
the aft bulkhead to which the ¼" tailplate is bolted. That hefty-looking
plate is bolted to a fairly light formed bulkhead, and there have been
reports of cracking where the flange and web of the bulkhead meet. I’ve
only seen this in ships where an unsprung tailwheel was fitted. That’s
why I use the coil spring suspension on my HP-18, and the leaf spring
on my HP-11.
Anyhow, get right in there and take a critical look
at where the flange meets the web. If it’s dusty or dirty, clean it off
to get a good look. But if it’s painted, you probably shouldn’t go to
the length of stripping or rubbing the paint off. That would expose the
part to greater corrosion potential. Besides, if the part is painted and
it cracks, the paint will most likely crack as well.
·
Inspect the stabilizer fittings for looseness, corrosion, or
trauma.
·
Inspect the stabilizer and ruddervator exterior for
corrosion or damage.
On any bonded HP, you’d want to take a close look
at the ruddervator trailing edge for any signs of trauma, cracking, or
delamination along the bond line. You’d also want to make sure that
there are at least two rivets in each trailing edge, one at each end of
the bond line.
·
While you’re at it, go to the wings and check the flap and
aileron sections to the same criteria as the ruddervators. Be especially
mindful of the inboard flap sections, since they carry the entire
cumulative torsional loads of all of the flap sections on the wing. And
again, check for the presence of the anti-peel rivets at each end of the
trailing edge bond line.
·
Check the rivet joints between the ruddervator tip plate and
the ruddervator skin for cracks or trauma, especially on the underside
near the hinge axis.
·
Sight carefully up the aft fuselage to look for any sign of
wrinkles, loose rivets, or trauma.
·
At the wing carrythrough(s) on the fuselage, look carefully
at all pin holes for signs of excessive trauma. They will always look at
least a little bit beat up. However, there should be no signs of heavy
gouging or notching in the holes or at their faces.
·
On HP-18, use your inspection mirror and flashlight to check
the aluminum stiffener plates installed on the bottom surface of the wing
deck where AN4 bolts secure the five aluminum carrythroughs to the deck.
Look for cracks or signs of overtightening. Udo has suggested replacing
the plates with thicker aluminum or steel plates to better distribute lift
loads. If you are so inclined, be sure to inspect the underlying
fiberglass for trauma while the plates are removed.
·
On HP-18 and RS-15, check for binding between the parts of
the aileron and flap control system. On some ships, there may be an issue
where the aileron bellcranks or rod ends contact the transverse flap
torque tube before reaching the specified aileron travel. Look for
scratches on the transverse tube that indicate interference.
·
Carefully inspect all cable runs, and run a cloth over as
much of the cable as you can to look for broken strands. Wherever there
are any fairleads or rub points, carefully inspect the cable to make sure
that no single filament is worn more than 50% of the way through. There
are diagrams in AC 43.13 that show the characteristic "hourglass"
shape of a strand that is worn too far.
Be especially critical of areas where phenolic
material is used for a fairlead. Studies have shown that the grain of the
phenolic material tends to become embedded with abrasive particles, which
accelerates cable wear. In my HP-11, I’ve replaced all phenolic
fairleads with blocks of Teflon or Nylon-6. It wears faster than the
phenolic, but the expensive and hard-to-replace cables wear much more
slowly.
·
Carefully inspect all exposed push-pull tubes for excessive
wear, kinks, scratches, gouges, or wrinkles. If your ship tends to honk or
squeak on pitch or rudder inputs, consider removing and waxing the
push-pull tubes inside the aft fuselage. However, if you do that, be very
careful not to damage or disrupt any part of the control system while
removing or replacing the tubes. Be careful to replace them on the correct
sides, and with the correct end forward.
Getting off-topic, there’s always the possibility
of an inspection actually making an aircraft less safe than it was
before, by damaging or disrupting parts or systems that were happy and
functional before the inspection intruded upon them. So you must seek
balance between functional inspection and disruptive intrusion.
·
Also check the aileron P-P tubes that run up the flap coves
on the wing.
Make sure that the tube sections are securely
joined at the rivet joints. Check
that the Teflon or nylon parts of the guides are secure and not cracked or
broken.
·
Carefully inspect all electrical wires, liquid or gas
plumbing, and other secondary systems. For the most part, the criteria of
the inspection should correspond with the criticality of the system.
However, all such stuff must be inspected to make sure that it will not
interfere with, damage, or intrude upon any of the primary structural or
control systems. Wires and hoses should be confined to neat bundles that
are well supported away from moving parts. Urine drains should be
inspected for security, and to make sure that they don’t leak or spray
their corrosive payload into the aircraft. Copper oxygen plumbing should
be free of kinks, and should be insulated from aluminum structural members
to prevent chafing and galvanic reaction. Also, long runs of copper tubing
should contain at least one loop of tubing to absorb physical expansion
and contraction from temperature changes.
·
Run the gear slowly through a complete extension and
retraction cycle. Or better yet, get someone else to cycle the gear while
you watch. There should be no binding or rubbing, and especially no
potential for binding that prevents the wheel from extending. If there is
excessive friction to the system, find out why and fix it.
·
Check the landing gear door springs. If you have actual
steel springs, check that they can’t bind and block extension or
retraction. If you have chunks of bungee cord, check that there’s still
some bounce to them, and that they’re not rotten or mouse-eaten.
·
Check the wheel and tire for cracks, weathering, and
excessive wear. For HPs with the band-on-tire brake, check that the tire
isn’t worn too far through where the band touches it. Spin the tire and
eyeball it for flat spots, wobbles, or lack of balance. Glider tires
rarely wear out from normal use. Far more often, they get flat spotted
being parked on too long, cracked from sun exposure, or worn through from
touching down with the brakes locked.
·
Check the operation of the wheel brake. With the brake
applied, you should not be able to turn the wheel by hand. All actuation
cables, cable sheaths, or plumbing should be secure and in good condition.
For disk brakes, inspect the thickness of the pads as well as you can
without removing the caliper.
·
Carefully inspect the restraining cable that keeps the oleo
struts of the landing gear from exceeding its travel length, and replace
it if you find any broken strands or unusual wear. There has been at least
one incident where one of these has broken, caused the gear to come apart
and self-retract.
Most worrisome is the possibility that parts of the
unrestrained gear mechanism might get shoved through the forward bulkhead
of the landing gear well. That’s a very good reason to keep an eye on
the condition of the restraining cable, and also a good reason to always
wear a parachute for a little extra protection from flailing parts.
·
Inspect the landing gear well for mouse intrusion potential.
Any opening greater than about ¼" inch should be screened, shielded,
or blocked to keep mice out. Mice will chew up seats, wires, and plumbing,
can be a health hazard, can interfere with controls, and are generally
corrosive. Do what you can to keep them out, but be careful that your
mouse exclusion measures don’t interfere with any primary or secondary
structures or systems.
·
For HP-18, make sure that the universal joint for the side
stick P-P/torque tube is of the correct type as specified in this
safety bulletin.
If the joint has a fixed rubber shield around its working
parts, it’s probably the correct one. If it is of the open type where
you can see the yokes, spider, and pins, it’s probably the suspect J-50
joint, and should be replaced.
·
For HP-14, check the main wing fittings to make sure that
they are not of the hermaphroditic Slingsby type as per this
safety bulletin.
The Slingsby forgings are elegantly designed, nicely
shaped, well machined, and almost certain to crack. I believe that all
of the original Slingsby fittings have been removed from service, but
you should check your ship at least at the first inspection. What you
are looking for are big blocky fittings machined from aluminum bar stock,
with three knuckles on one wing, and two on the other wing. Those are
the good ones. The ones you don’t want are elegantly curved, have three
knuckles on all four fittings, and have steel bushings pressed into the
main pin bores. Here’s a picture of a pair
of the bad ones.
·
For HP-18, carefully inspect the rod ends at the forward
ends of the ruddervator P-P tubes. These are prone to abuse from slamming
the stick to the full up or full down stops, and there have been one or
two that popped open and shed the balls from the ball bearing unit.
Fortunately, the design of the mechanism is such that the rod end will
remain secure even if so damaged. For the retrofit center stick mechanism
I’ve been selling for the HP-18, I have the installer replace the
RE3M6-2N with a pair of spherical bearings that allow greater angles of
misalignment. But the center stick also has good pitch input stops to
protect the rod ends from excessive misaligmnent.
·
While you’re at it, inspect all of the rod ends that you
can get to; that should be every rod end in the ship except the ones
buried in the wing at the inboard end of the aileron. For the most part,
Dick used high-quality ball-bearing rod ends like the Fafnir RE3M6-2N.
I’m pretty sure that Dick got a great deal on these through WWII
surplus. But that means that now all of the rod ends in your aircraft are
about 45 years old, and they’ve never been greased since they were
manufactured. Fortunately, the original grease is extremely long-lasting
stuff. But you should start to think about a program to remove,
pressure-grease, and reinstall all of the rod ends. But again, there’s
that issue about balance and doing no harm. Maybe keep it in mind for the
annual next year.
·
Check all of the rod end installations to make sure that
there is adequate thread engagement between the rod end and whatever it is
threaded into. I like to have things set up so that all of the rod ends
have at least 6 threads of engagement, and preferably more like 8. When I
first got my HP-18, some of the rod ends had as few as 3 threads of
engagement, and that made me nervous (but not until I found out about it).
I’ve heard that engineering studies of threaded joints show that most of
the load is carried by the first thread and a half. That may be so, but I
like to have a several-x safety factor for such joints.
Going off on a tangent, let’s do the math for a typical
rod end thread engagement. The shank of the RE3M6-2N has ¾" of
threads at 24 threads per inch. That means that there are 24 x .75 =
18 threads on the shank. Some of the threads will be hidden by the AN316-6
jam nut, which is about 3/16" thick - 3/16 x 24 = 4.5 threads to
be exact; lets call it 5 threads. So when I am looking at an RE3M6-2N
installation, I like to be able to count no more than 7 threads remaining
on the shank - at least 6 threads are hidden by whatever the rod end
is attached to, and 5 threads are hidden by the jam nut. Any more than
7 threads, and I get nervous. In some cases, I’ve been able to adjust
the rod ends to get more engagement at one end, less engagement at the
other, and no overall change in the eye-to-eye length of the push-pull
tube. In other cases, I’ve made adapters or just fabricated longer P-P
tubes.
·
Also check all cable turnbuckles to make sure that they have
adequate thread engagement. There should be no more than three threads
exposed on the clevises or forks at either end of the barrel. Also check
the turnbuckles for secure safety wire wrapping.
·
For ships with canopy transparencies that are glued to aluminum
frames, check that the transparency is secure. I guess that a few glue
voids or spots of delamination would be OK. But anything over a couple
of inches drastically increases the potential for the transparency to
unzip and depart the aircraft. From reading Flight International, I learned
that in the UK they call those BFO Incidents, for "Bits Falling Off."
Dick recommended using layers of contact cement or
rubber cement for securing the transparencies. So far, I’ve had good
luck using plain old Liquid Nails. Of note, Dick didn’t recommend using
the EA9430 epoxy that the wings are bonded with. There’s no record that
he recommended against it, but I think that the fact that he had that glue
at hand and recommended something else is reason enough not to use it. I
suspect that the thermal coefficient difference between aluminum and
acrylic is such that a more pliable, less rigid adhesive is required.
I’ve heard that some HP operators have also
installed nylon screws at the corners of the transparency and frame as a
safety backup for the adhesive.
·
For bonded wings, set the wings up on sawhorses, with one
stand each at the root and tip of the wing panel. Tap around with a light
plastic screwdriver handle or other non-marring tool to look for areas of
delamination. Some delamination is okay, but it’s really hard to say how
much is too much. If there are areas of delamination, you’ll want to map
them on a sheet of graph paper so that you can monitor them for spread.
Flip the wing over to check the bottom surface - just getting under it and
looking up at it will show you a falsely optimistic picture of how tight
the skins are.
·
For riveted wings, check for loose rivets and other badness.
In general, the riveted HPs are entirely conventional in their wing
construction, and any mechanic familiar with Cherokees and Cessna 172s
should be comfortable with them.
·
Look carefully at the exposed parts of the wing spar for
corrosion, cracks, scratches, or notches. In particular, look for places
where the spar has gotten beat up from assembly or disassembly operations.
The 7075-T6 material used in the wing spars is very strong stuff, but it
does tend to be sensitive to notches that can become crack initiation
sites. Minor scratches or defects in the middle of a face are usually
inconsequential. But scratches or notches along corners and edges should
be addressed.
·
Check carefully for places where contact with trailer
fittings might have trapped moisture against the wing parts, causing
corrosion.
·
Check the wing tips for pedestrian impalement potential.
Sharp, jagged corners on skids or trailing edges should be dressed.
·
Check all interior areas for signs of water entry. Anywhere
that water can get in should be protected from the elements, and further,
there should be a way for the water to get out. On my HP-11, I have
drilled holes in the leading edge of the wings at the tip. During the
soaring season, I have these taped over with aluminum foil tape. During
the winter, I leave these open to let out any water that might leak into
the trailer and get into the wing. When any substantial amount of water
gets into a wing, and then freezes, it is bad news.
·
In the cockpit, check to make sure that all the paperwork is
in order. You should have some permutation of the ARROW documents:
Airworthiness certificate - No exceptions. You probably
have a pink Special Airworthiness Certificate issued for the purpose of
operating an amateur-built aircraft. It is somewhat a matter of pride
to me to have a white Special Airworthiness Certificate for the HP-11,
which means that the aircraft is enough of a veteran that the pink coloring
has faded completely away.
Registration certificate - Again, no exceptions.
The name on the certificate should be you or your corporate incarnation,
and the address should be valid.
Radio station license - You only need one of these
if you’re going to fly internationally. That probably means you don’t
need one.
Operating Limitations - For almost all homebuilt
gliders, the Special Airworthiness Certificate is only valid when
accompanied with a separate list of operating limitations issued by the
original inspector. I hope you didn’t lose that letter, or file it where
it couldn’t be found; you’re supposed to carry it in the glider. There
should also be a list of operating speeds and limits at hand, although I
think you can substitute appropriate markings on the airspeed indicator.
Weight and balance - There should be information at
hand about the weight and balance situation of the aircraft. For the HP-11
and the HP-18, I carry diagrams of the datum and empty CG, and the pilot
CG. I also carry placards that show the calculated minimum and maximum
pilot weights.
·
Check to make sure that there is an EXPERIMENTAL marking
with 2" letters, and also a passenger warning. You can find the appropriate
verbiage and placement info in 14 CFR 49 (what we mostly call the FARs).
Few inspectors are really picky about the placement, but it should at
least be close to conforming to the rules. If you’re lax on this one,
they may go looking specifically for other stuff to bust you on.
·
Inspect all of the pitot/static plumbing for security and
freedom from foreign matter. You might find that bugs have built nests
inside the tubing, but that they didn’t completely block the tube. Clean
out all such things that you find.
·
Check the release mechanism for binding or stickiness. Check
to make sure that, when deployed, it takes at least a couple pounds of
pressure to pull the retainer back far enough to get the tow ring into it.
It should be about as tight as it can be and still let the average
lineperson engage the tow ring.
·
If an oxygen system is fitted, check the oxygen cylinder for
the date of its last inspection. I believe that most of the aluminum and
steel cylinders common in glider service must be hydrostatically checked
every five years. That may
sound exotic and expensive, but it’s actually a cheap and common
inspection, and any welding supply shop can have it done for you. However,
note that such shops are rarely very good about returing to you the same
cylinder that you submitted. So if you care at all about getting back the
same cylinder you started with, be sure to paint your name and phone
number on the cylinder. You might also consider painting the cylinder an
odd blue or green color to distinguish it from all the others. Avoid red
or orange colors, so that nobody mistakes it for an acetylene cylinder and
blows themselves up.
4. Lubrication:
Carefully lubricate all pivot points. Take care not to put more oil onto the
pivots than capillary action will draw into the joint.
Excessive oil or grease will just attract and hold dust, and the dust
will accelerate abrasion and wear. Here are some tips about lubrication:
