By Lisa Turner, EAA 509911
Previously printed in September 2018 EAA Sport Aviation.
Looking at my cross-country trip plan, I
was due for a stop in North Carolina. I made my calls and entered the pattern.
After hours of piloting, I had trouble slowing down on downwind. If you’ve been
on the interstate going 80 mph and gotten off after a long time at the wheel,
speed can be deceptive. This seemed to be happening to me now. I was behind the
curve. I put in half flaps on downwind across from the numbers. Full flaps on
base. Turning to final, I evaluated my situation. Still hot. I could slip a
little, or I could go around. At an airport I’d never been to before, on a long
cross-country, as a low-time pilot, I was straining to make this a safe landing.
Those of you who have trained in Pipers
and Cessnas know they can handle a lot of student error on the gear. Moving on
to light-sport aircraft has an entirely different feel — much lighter — but
that also means there is a lot less room for error.
I had these thoughts as I crossed the
threshold for Runway 16. Flying down the runway, I seemed to lose my ability to
locate the ground. Suddenly there it was. The pavement seemed to shift upward
by about 3 feet, and I’d done it. A hard three-point landing with a small bonus
bounce.
The Pulsar has a fiberglass main gear and
a steel nosewheel leg. Both are considered delicate by the builders. The rule is
to be very disciplined and never, ever drop it in or fly it into the runway. I
had somehow done both at the same time.
A violent shimmy took over the whole
airplane as if someone was shaking it. I braced for the gear to separate or
collapse as I rolled down the runway. I gingerly applied some brake and turned
off on a taxiway. I applied just enough power to get to the FBO. Fear welled
up. Now I’d done it.
I let the Rotax 912 idle for a moment and then shut down. I took a deep breath. I pushed the canopy forward and slid up and out of the tight cockpit, afraid of what I would find. No one was observing as I dropped to my knees and crawled under the aircraft.
Those Little Wheels
Here are the top trouble areas with
lightplane nose wheels. Tail wheels have their own set of problems, and I’ll
cover them in a future article. A problem with your nose wheel or your tail wheel
can send you into the runway signage or into the ditch. Understanding some of
the things that can go wrong, plus some attention to maintenance and inspection,
can keep you tracking safely down the centerline.
I’ll need to be very careful about how I
talk about nose wheels and tail wheels. We all know the controversy surrounding
tricycle-gear pilots and conventional-gear (tailwheel) pilots. There is no
doubt that tailwheel pilots are taught to fly the airplane to the runway and
then all the way to a stop, while nosewheel pilots may get a little lax right
after landing. Another way to say this is that once a tricycle-gear aircraft
has all wheels on the ground the brain disconnects. On tailwheel aircraft, the
brain disconnects when the aircraft discontinues all of its forward motion. I’ll
leave this to your next chapter meeting for the expanded discussion.
Most light-sport aircraft kits — E-LSA (experimental
light-sport) and E-AB (experimental amateur-built) — with tricycle gear have a
simple steel nose leg and a strut with a mechanical damper spring in the engine
mount area and a castering joint at the wheel fork. You steer the airplane with
judicious use of power and brake until enough speed provides rudder control. A
few kits, including some versions of the Lancair, employ a lightweight oleo-pneumatic
(oleo) type strut with internal viscous damping along with a castering wheel
assembly. Van’s RV nose gear design is also a very durable castering design.
The single-place Merlin PSA features an all-composite U spring and piston
assembly with a non-castering, steerable (rudder linkage) nose gear that looks
like it would survive anything. Some of the early designs for experimental aircraft,
including the Pulsar, had very light gear to save weight.
When you did your pilot training, it
might have been in a Cessna 150 series or a Piper Cherokee series. Since these
aircraft are heavier than your typical light-sport aircraft, they almost
exclusively employ oleo strut design into the nose gear along with a steering
mechanism and a shimmy damper. Think this prevents nose gear problems? Nope.
From the most simple of gear assemblies to the most complex, problems can and
do appear at any time.
This discussion is confined to the
lightplane spring-loaded strut and castering nose wheel, since that is what
most of the LSA and E-AB aircraft have. Although this system is much simpler
than the steerable oleo strut design many of us used in training, it offers its
own set of troubles because of its light weight. Following these tips should help
you troubleshoot and correct problems.
The top three nose wheel issues are shimmy, shimmy, and shimmy. Ok, kidding. Other problems besides shimmy, such as tracking and hardware assembly issues, can cause you to take out the runway lights, but shimmy is in first place. And fixing a shimmy problem may also fix other problems you thought you had. Here’s what to do.
Shimmy
Tire
air pressure. Check the tire pressure cold. Overinflation will amplify
every bump, and underinflation will allow too much flex in the tire and gear.
Either one could contribute to shimmy. Keeping the pressure on the lower side
of the recommended range reduces shimmy because it adds a little more
flexibility.
Wheel
balance. Unload the gear (raise the front of the airplane) and rotate the
wheel on the axle and observe what it does. A little bit of vertical out of
round on the tire is normal, but severe variation is not. Any flat spots from a
hard-braking landing? Tire damage? Unusual wear? Look at lateral movement. You
should not see or feel any wobble side to side. Check for play in the axle and
readjust per your manual.
Bearings.
When you rotate the wheel what do you hear? Hopefully nothing. If you hear
something, then disassemble the wheel from the fork and inspect the bearings,
including the spacers. Does the hardware match what is in the assembly manual?
Brakes.
Does the wheel only shimmy when you apply brake? Check the brake assembly and
pads.
The
castering joint. Check torque settings on all of the hardware, and in
particular, check the breakout force on the castering joint. This is the amount
of force that the wheel requires to pivot. It is typical for the joint to
loosen in the early life of the airplane. Follow the procedure your
manufacturer recommends and use a spring force scale if required in the
procedure. For lighter gear, pushing on the rear of the wheelpant provides a
quick check during the preflight.
Tracking
The primary cause of poor tracking is an
error on the assembly and installation of the nose gear leg and/or shock strut.
Depending on the sophistication of your particular kit or plans, an error on
the rigging can mean the leg leans to one side or the other and/or does not
track straight. This places stress on one side of the wheel axle, and at the
very least, your tire will wear more on one side. In the worst case, it will be
difficult to keep the airplane going in a straight line on the ground.
Check rigging by finding two center
points on your aircraft, fore and aft, and dropping a plumb bob from each one.
Run a chalk line or tape between the two points on the hangar floor and run it
up to the nose wheel. Then take a couple of straight boards — 2-by-4s work well
— space them equally from your line, and see where the nose wheel sits in
relationship to the centerline.
If your nose gear is not on the
centerline, you may be able to make adjustments in the hardware spacing and in
the attach points. In addition to consulting the assembly manual, you may want
to call the kit manufacturer and the builders group for advice.
Noises/Hardware Assembly
The primary cause of noises — grinding,
bumping, thuds, and squeaks — is hardware that is too tight or too loose, worn,
damaged or missing, or installed incorrectly.
With the nose gear off the ground, grab
the gear strut and try to move it sideways and up and down. Look at attach
points and observe any movement. This will show you where hardware might be
loose or even missing. Pay particular attention to the castering joint, which
is likely to have several cupped Belleville spring washers top and bottom. I’ve
seen these installed upside down — make sure you follow the plans exactly.
Finally, look carefully at the shock
strut — a spring and/or doughnut assembly that attaches to a mount under the
engine and dampens load and variation from the nose gear leg. Make sure the
spacers and hardware match what is on the plans or in the assembly manual. Look
for cracks in the gear and examine the upper attach bolts. Check torque values.
Using torque seal on all of these areas will make your preflight much easier.
All Clear
On my hands and knees, I crawled under the
wing and examined the main gear carefully. Everything looked fine. I crawled up
to the nose gear and pressed the aft part of the wheelpant down lightly. It
wobbled. I crawled back out and retrieved my toolkit from the cockpit. I
removed the pant as sightseers gathered around the Pulsar.
“What is this?” one man asked in
surprise, as if an alien ship had landed in front of the FBO.
“Pulsar,” I said as I looked at the fork
joint assembly with the Bellville washers, which were clearly too loose. “Aha!”
I said.
“A what?” the man asked.
“A Pulsar. A Pulsar XP.”
“Never heard of it.”
My mood brightened considerably when I
tightened the bottom of the castering joint just enough to remove the loose
condition. Then I put the wheelpant back on and checked the force at the back
of the pant. Good.
“It’s just a little experimental airplane,”
I said as I placed the toolkit behind the seats and closed the canopy. “There
aren’t a lot of them.” After a rest break and a detailed and lengthy preflight,
I slipped into the cockpit and was off on the third leg of my cross-country as
my newfound friends waved goodbye.
Lisa Turner, EAA 509911, is a manufacturing engineer, A&P, technical counselor, flight advisor, and former DAR. She built and flew a Pulsar XP and Kolb Mark III, and is currently restoring a Waco UPF-7 with her husband. Lisa is a member of the EAA Homebuilt Aircraft Council and Women in Aviation International. For more from Lisa, check out her Airworthy column every month in EAA Sport Aviation.