Attached my story of a wee adventure enroute to/from Oshkosh ’95
The flight to Oshkosh was going well. Late morning found us at Scotts
seaplane base on Crane Lake, just south of the US-Canada border in
Minnesota and west of the Boundary Waters Wilderness Area. The trusty
old PA-12 with its upgraded 150hp engine had transported me from my
home in northern Manitoba about 500 miles to this point. The weather
was fine and US customs had been helpful and courteous.
The takeoff run to the north and east was a bit longer than I wanted –
likely just didn’t hit the sweet spot on the step just right. Made a
boat load of fishermen nervous as we headed in their direction. Climbed
out and turned to the SE for the next leg to Round Lake, Wisconsin.
Throttled back on reaching 4000 ft and the engine abruptly ran a mite
rough. Thought the temperature and altitude might be making things rich
and tried leaning the mixture. The engine settled down to its normal
rythym. As the mini-adrenalin rush ebbed away I tried to figure out
what was happening. It was a warm day by my northern standards, about
25 C, but within the summertime range I normally encountered with no
roughness. The humidity seemed higher in these southern parts. Maybe
temp + humidity + altitude was a condition I’d not seen before, one
requiring more aggressive leaning. The engine was running just fine
now; I slowly relaxed.
The leg to Round Lake went fine. Felt a bit tense flying over 15 miles
or so of Lake Superior, and landmarks were harder to find as we got
further south out of the heavy duty lake country. But Round L. showed
up on schedule and the ’12 settled gracefully onto the water. After
taking on fuel and chatting a while we taxied out of the lagoon and
lined up for takeoff. Seemed to take a long time to accelerate to
flying speed on the step. Hot and humid – yes, that always extends the
takeoff run. Finally we were off the water to the north and climbing
and turning for Oshkosh! Throttled back on reaching 3000 ft and the
engine ran a bit rough again. Not as bad as at Crane L., but definitely
not smooth. Leaning cleared the roughness up once more and I started to
lull myself into the notion that this novel southern environment just
took a little adjusting.
One farm looks like another to me, but nav was fairly easy on a SE
course. Just point the nose evenly between the N-S and E-W roads and
the heading is near perfect. The farms and forests of Wisconsin went
rolling by. Not long after the mini-mountain at Wausau the waters of
Lake Poygan came into view and we lined up to go north of the city and
get low over the water and avoid the Oshkosh airport traffic. Crossing
the shoreline of Lake Winnebago I was down to nearly 100 ft and turning
south to seek out Vette seaplane base through the haze. A few minutes
listening to the Osh approach control convinced me of the need to stay
low. Excitement grew as my dream trip neared a close.
As I neared Vette base I enriched the mixture in preperation for the
climb to make my circuit for landing. The engine coughed and ran rough
immediately the mixture control pushed in. A moment of near panic
passed as the engine smoothed out – once my frantic hand leaned the
mixture again. We started the climb with throttle open and mixture
lean. Soon we were in position and gliding for a bumpy landing in the
waves of the lake. The engine roughness was forgotten for a while in
the excitement of arriving, unloading, registering, and setting up
camp.
Once I’d gotten my bearings at Oshkosh and got over the initial rush
of "Oh Gosh" as a first time visitor to the convention, I returned to
worrying about the engine roughness. I found the building where
volunteers tried to sort out maintenance problems. Was introduced to a
helpful gentleman, their expert on engines. I related my story. He took
it all in. He said " The engine is getting too much fuel and the
mixture is too rich. It is possible that the density altitude required
a leaner mixture. If it is mechanical I can think of two things that
would cause the problem. Either your carburetor float is sinking or gas
is leaking past your primer. If the float is sinking you will notice
gas leaking from the carb when you have a look. Very soon it will have
sunk completely and you won’t be able to even start the engine." He
seemed very sure of himself.
I thanked him for his help and promised to check things out. I felt a
lot better having an expert opinion. I wished it was easier to get a
mechanic to check my aircraft, but at least I had a starting point. I
went out to the plane at its mooring and pumped the floats and gave the
engine compartment a good look. No leaking gas. Everything looked to be
in its place. Mixture cable still attached correctly. Ditto throttle
cable. Carb heat cable and flapper seemed to be Ok. I guess that leaves
the primer as the likely cause. Density altitude sounds lame given the
roughness at low level but might be a contributing factor.
As much as I enjoyed my week at Osh, thoughts of engine roughness still
troubled me. Considered asking a mechanic to come out to the sea base,
get the plane towed to the dock and have it given a once over. But I
feared all I would get is a big bill, maybe a rebuilt carb and several
days delay. And the problem might still be there! I decided to make a
test flight before making the decision to head home.
On Aug.2, the night before home time, I taxied the ’12 out of the
lagoon and prepared to take off. As the throttle opened the plane
reared back in response to the thrust and the back elevator and tried
to climb on the step. We ploughed along, unable to get on the step.
Once I was convinced that waiting would not help I tried leaning the
mixture. The rpms came up and we climbed on to the step, making an
otherwise normal takeoff. A quick circuit and we touched down once
more. I was frustrated and puzzled as we taxied back into the lagoon.
Opened the cowl and looked the engine over once more. No sign of
anything out of place or abnormal. Closed the cowl. Secured the plane
for the night at the dock and headed for bed. What to do? Problem seems
to be getting worse. Can’t find anything wrong. Seems to work fine when
leaned. Convention all but over now – how would I get a mech to check
it out? Would a mech have any better luck finding a problem? I *do*
want to head home tomorrow. If the engine sounds worse on the way I can
get help at Round Lake or Scotts. If I get all the way to Red Lake,
Ontario I’ll have my choice of seaplane maintenance bases. Guess I’ll
try it in the morning and see how it goes. Settled into an uneasy
sleep.
Thursday morning the weather was lousy. Thunderstorm went through.
Steady light rain, low ceilings. Maybe inproving by lunch. Conditions
better to the west and north. Hung on, biding my time, thinking of the
weather. And the engine. After lunch conditions were marginal but a bit
better. Decided to head out. Used leaning to get airborne, climbed
couple hundred feet and snuck past Wittman field and Oshkosh. North and
west of the city climbed to 500 ft and settled in for the ride. All
seemed well. Weather not great but doable, and hope for improvement in
a while.
Somewhere near Waupaca, maybe 50 miles from Osh, the engine instantly
went from smooth to rough. Tried more leaning. Maybe a wee bit better,
hard to say. Starting to lose altitude. Increase power, very slowly,
engine sounds like there is not much more to have. Just about full
thottle and just holding altitude. Getting rougher.
As things slid downhill we had turned north to a small lake, maybe a
couple miles away. As we got closer I could see buildings on the south
shore, one fairly big. Circled to the north and started descending.
Lake had lots of reeds so likely pretty shallow, no time to be choosy.
Hope we can get back out again. Will have to get a mech to drive out.
Major delay. Major expense. Darn! At least we’ve got somewhere to
land.
Set down OK, engine still running, and idled toward the shore and the
buildings. Couple and a wee dog coming down to the beach as we head in
near their dock. Apologize for "dropping in". Introductions. Explain
problem. Open the cowl. Nothing seems to be wrong. But I *know*
something is wrong, finally. Out of frustration I lay hold of the carb
air box and give it a wiggle. IT MOVES. I can wiggle the heat box and
carb bowl back and forth. I can see the safety wired screws in the top
of the carb wiggling with the bowl as it moves. WOW! The safety wire
prevented the bowl from coming right off the carb, but it did *not*
prevent the screws getting loose.
Was worried the screws might be stripped, but after cutting away the
wire found I was able to tighten the screws up just fine, all four of
them. Used snare wire from my survival kit to rewire the screws. Not
the greatest wire but I’ll be checking at every stop. Sure hope nothing
else is wrong. Thank my hosts for their harbour and their help. Fire up
and taxi out. Big question now is whether this lake will let me go.
It’s big enough if I have normal power, but I don’t know these waters
and could go aground. The folks said another cottage owner flew on
floats out of here so there is hope.
The engine snarls to full throttle and rpms are normal with the mixture
full rich! A quick run on the step and we’re off to the west and
climbing well. Circle and wag the wings for my new friends. Throttle
back to cruise with no problems. As if in approval the weather slowly
lifts and the return adventure starts to become fun. Round Lake, Crane
and Sandpoint Lake, Red Lake, Gunisao Lake, and home to Thompson,
Manitoba, all went well. A great trip, and VERY educational.
……………….
A lesson learned, I guess. Looking back I can see the evidence of a
problem accumulating, starting at Crane lake. A sluggish takeoff,
roughness at cruise. And it only got worse thereafter. I kept trying to
convince myself there was not a serious problem. I was reluctant to
hire a mech while away from base when the problem wasn’t well defined.
I was too eager to rely on the well meaning opinion of an expert who
had only my verbal describtion of the symptoms to go by. I failed to
learn from the last and loudest warning on the test flight the night
before leaving. Then I compounded the risk by heading home under a low
ceiling, giving me little altitude to play with if (when) things go
sour.
I was lucky that there was a useable lake nearby when the engine
threatened to give up on me. Further along I would have been forcing it
into a farmers field. Still further and I’d have been cutting down
trees with the old PA-12. Not a nice thought.
Still don’t know why a loose carb bowl will make the engine run rich.
Seems like the air leaking in above the bowl will disturb the venturi
flow and should make the mixture too lean if anything. Perhaps the air
leaking into the induction was atomizing fuel as it passed over the
bowl and thus enriched the mixture. Anyway, it was too rich. If the
bowl had gotten loose enough the engine would likely have stopped dead.
Cheerfull!
My mechanic had worked on the bowl at the last annual. When he safety
wired the screws he had not brought them tight enough, and may not have
had the right threading direction through the holes to maintain the
screws in their tight position. It is not easy to do working in cramped
spaces. When I got home I did it myself. And did it right.
A carb security check is part of my normal preflight now. It’s easy to
open the cowl on a ’12 and I do it anyway each day I fly. That’s one
gremlin that will never catch me again!
Hope this little story helps someone else avoid a bad experience.
Cheers, Phil