The contentious issue of the use of the Carburettor Heat

[crazy_aviator]

That's a good thing - I would be worried if most of the people
who you saw tried to start airplanes were homeless people, drunks,
plumbers or hairdressers.

Well, good one , but i was meaning pilots as compared to AME s starting the engines,,

Hmm, where did i say that i knew it all ? I am not an instructor nor do i teach pilots to start A/C engines

Why would I care what you think?

Well, im not concerned with your concern about what you think of me , i was just pointing out some facts and the fact that pilots in general , dont score too highly in the minds of AME s as they try to rewrite the book on doing things like starting engines,

You do seem rather self assured and proud of all your accomplishments but short on accepting constructive criticism !!!

There is a saying and it goes something like this " The most dangerous thing is a pilot that knows a LITTLE about maintaining and troubleshooting a plane " ! ( remember the heavy airplane that ran out of fuel while the pilots played Mr. fix-it and tried to diagnose/troubleshoot a gear warning light? They were just smart enough to pull light bulbs out of sockets but too stupid to manage the whole situation and fly the plane !!!)

[Hedley]

I am not an instructor nor do i teach pilots to start A/C engines

Why not?

P.S. I actually have a lot of respect for Michael - anyone
that has survived 30 years of flying weird old airplanes
must know a thing or two worth learning.

But it's precisely because of his knowledge and experience
that I am so hard on him - I expect an awful lot from him,
far more than I would from some young instructor that's
only been flying a couple of years and only has experience
on a couple of types of gentle, certified light training aircraft.

The students that are the most capable are the ones
that I drive the hardest, because they have the ability
to achieve the most, if they develop the personal
motivation to aspire to excellence.

[AntiNakedMan]

Out of the three BN2s I have flown, I have always found that the left engine tends to get carb ice before the right engine. Never figured that one out...

It's perhaps the water distribution in the fuel tanks and whether you kept the ball in the middle on the climb out
Perhaps the problem was associated with the fuel source?
Which tank was fueled first and which tank was fueled second, which tank picked up the water from the bottom of the reservoir or drum?

There is also the possibility that there was a mixture problem and that by applying the carb heat you brought the mixture back into the proper range...

When problems occur to an engine we often look at one thing, and perhaps what we do is cure the problem by doing something like apply carb heat while that is not the real problem.
If it's a lean mixture problem then this could be cured with hot air... Therefore it's not necessarily carb icing you are curing!

I look at the exhaust pipes to see how my mixture is doing, am I leaning too much or too little?
There's a lot to tell from the exhausts...

I like how I manage to refute a statement about never seeing carb ice on a Lycoming and I get told I don't know how to keep the ball in the center, how to fuel from a non-contaminated fuel source, or how to properly set the mixtures....

[MichaelP]

I like how I manage to refute a statement about never seeing carb ice on a Lycoming and I get told I don't know how to keep the ball in the center, how to fuel from a non-contaminated fuel source, or how to properly set the mixtures....

"It's perhaps ..."

I'm not accusing you of anything... I'm just looking for other possible causes.
You wrote that it was only the left engine so I look for reasons that might precipitate this icing problem.

What did you conclude was the reason for the one engine icing while the other didn't?

This thread is about thinking about what we do. So give us your thoughts.

I realise that pilots are sensitive creatures, I do not mean to criticise anyone. I apologise for offending people at times.
I do want to stimulate thought however...

I have to say though that most pilots I have flown with in Cessna 172's have used more fuel from the left side when the cock is set to 'Both' than the right side. Even though we keep the ball in the middle most of the time there are obvious lapses as is evident in the fuel levels.

So I accept these lapses we all do it.
When the DA40's tanks are full you can lose fuel from the right tanks on the climb out, so I recommend we use the right tank for takeoff and climb in this aeroplane when they are full.
Likewise, when the tanks are half or below, I recommend we use the left tank because the right tank fuel might not flow so easy.

The Piper Tripacer book recommended taking off on the left tank when the fuel was lower for the same reason.

Fuel sourced at less frequented airfields could be contaminated with water and that is why we drain it into the test cup. But we might not catch it all.
I am always concerned when there are bladder tanks. I'm not sure if the BN2 has bladder tanks but these are not always flat and so water could accumulate in the bottom away from the drain to be sloshed into the system.
We check for large amounts of water, the teaspoon of water we sometimes find in the cup probably would not lead to more than a 'pfft' from the engine.
At idle the teaspoon of water might form ice, but at takeoff power I believe it will just go straight through. Correct me if I'm wrong, but icing is a lot less likely with the throttle fully open and even then will not accumulate quickly unless you are flying in near freezing rain...
Personally, no one can convince me to fly in freezing rain

How often do we check for water in the car's fuel tank?
Like all tanks there must be water getting in there from time to time.

I thought this was interesting from a 1964 Cessna 172 POH:

[iflyforpie]

Islanders are also bad for water in the tanks because of the fuel panels on top of the wings and the stringers and ribs in the wings keeping water from reaching the fuel drains.

However the British must be used to water in the tanks. One particular Islander I worked on still ran before I drained nearly 5 gallons of water out of the fuel tanks.

[AntiNakedMan]

MichaelP - Thanks, sometimes its hard to read attitude. FYI, BN2s don't have bladders, but wet wings.

ifly - For a plane built in a damp country with lots of rainfall, I cannot fathom why hollow rivets were used in the roof. 5 gal of water is amazing out of a tank, the worst I have ever seen is just a few strainer fulls, but I could see it happening.

[iflyforpie]

The plane was an ex-Sonic Blue machine and had been sitting on our ramp in YCW for a winter (rain is measured in feet in the Lower Mainland). Ran it up to do an annual. Wasn't going flying, so didn't bother checking the tanks until I started pulling lids off.

P.S. Thank you for reminding me about all those monel pop rivets!

I still have a few in my tool box to remind me of drilling those suckers out (spin spin spin) and the cramping hands after popping them with a hand squeeze (no pneumatic).

F****** Brits! (JK MichaelP).

[KHills]

Plug fouling and bad mag drops are typically from long periods of idling and improper mixture adjustment. Another thing the Cessna POH doesn't say (or Pipers, which are usually worse in spite of having many of the same enignes ) is to lean the mixture for taxi. Since I have put this into practice, the plugs have been coming out clean during inspection rather than filled nearly to the top with lead deposits.

Temperature dew-point spread is an important consideration when dealing with carb icing. But localized conditions (think fog) can change the RH from what the weather station is reporting.

In a properly adjusted and operated engine, putting carb heat on at low power settings shouldn't be an issue. Think of it like pitot-heat. You most likely aren't going to need it, but it is sure nice to have it already on if you do!

not to hijack the thread...but will the engine always backfire when applying full power with lead deposits on the plugs? enough lead to decrease engine power by 100-200 rpm?

[iflyforpie]

It is nothing I've ever noticed before. Mind you, I am not in the habit of advancing the throttle to full power after having a bad mag drop.

For there to be a backfire, there would have to be two intermittent or weak plugs on the same cylinder (or cylinders) that allow the fuel to accumulate, and then ignite.

This isn't a situation to even contemplate a takeoff.

Sometimes for maintenance, I will get a bad plug and I will run it on the bad mag to find which cylinder it is in (using the plastic screwdriver on the exhaust trick). Never at high RPM, cause even at low RPM there are some large burps when the errant plug decides to fire.

[Hedley]

Just to clarify: backfiring is a greatly over/mis-used term.

IMHO, backfiring is incorrect combustion that
back through the instake manifold, out either
the carburetor or fuel injection throttle body.

I have seen orange flames a couple feet long
emitted out the air intake during a difficult
start. I think what may happen is that an
excessively rich mixture is burning much
too slowly, and is still burning in the cylinder
when the intake valve opens. This is generally
pretty harmless, except that it can result in
an intake fire if there is pooled gas anywhere
around the intake system. This is no big deal,
generally, as long as the engine is kept running -
the fire is sucked into the engine.

Contrast this with "afterfiring" which is
when combustion occurs in the exhaust
manifold. This is often very violent, and
can be seen during 1700 rpm runup when a
student erroneously selects "off" mags briefly,
which results in unburned air and gas being
pumped into the exhaust manifold.

When the student turns a mag on again, the
next time an exhaust valve opens, it
ignites the combustible mixture in the
exhaust manifold, easily damaging it.

Backfiring and afterfiring are completely
different phenomena, even though everyone
treats them the same.

[KHills]

thanks headley for the clarification...i do believe backfiring is the correct term i am after.

now, is it possible for a proper mag drop and still have lead deposits on spark plugs (say equal number of spark plugs per mag) to reduce available power on take-off?

[MichaelP]

You might get it to backfire if you pump the throttle on start up
The Continental O-200 engine will backfire if you prime it when it is warm and either the starter doesn't crank it fast enough or there's a wooden propeller fitted (not enough momentum).

Be careful priming a warm engine.

Back firing is also pre-ignition where the mixture is ignited before the inlet valve has closed.
This might be a timing issue which probably means the mechanics need to time it properly, or the impulse coupling is not working.
More commonly it is coke in the cylinders due to running too rich and this glows and ignites the mixture before the official
spark(s) from the plug(s)... This condition sometimes leads to the engine running on after the mags have been turned off.

In the winter the non impulse mag may ignite the mixture too soon as it will work better at cold temperatures. (Better conductivity at low temps).
This is what causes carburettor fires in the winter.
In many aircraft the impulse mag is the left mag, and the engine should be started only on this one as the implulse coupling retards the ignition (delays the spark).
But with oil at low temps the arms can stick and not cause the impulse to work, and in this situation the timing is advanced (early spark 20 - 25 degrees before top dead centre).

You can also get the engine to backfire in flight by over leaning it. There were stories of pilots doing this deliberately during the war to rid the induction system of ice!

Plugs.

If you have a bad enough mag drop that you return to maintenance rather than fly, remember someone landed with that, and that person might have had to go around!
With that in mind, it is important we learn to lean the mixture properly and avoid the problem.

[Hedley]

re: fouled spark plugs

learn to lean the mixture properly and avoid the problem

Absolutely! I lean the mixture ALL THE TIME on the ground -
immediately after startup, it comes out one inch, and during
the landing rollout (I know, I know), it comes out one inch.

This coming from the guy who cleans and gaps the spark
plugs in FOURTEEN aircraft.

What is disappointing, Michael, is how few FTU checklists -
even though they are lengthy enough to operate an eight-engine
bomber - do not mention this important item, esp in the summer,
when the hotter temps yield higher density altitudes and
resulting richer mixtures and more fouling.

You CANNOT hurt an engine, leaning it at idle - if you lean
it too far - beyond max RPM - it simply quits. It isn't hot
enough to hurt the metal.

Lean the mixture on the ground at all times. Lean the
mixture in cruise at all times. Lean the mixture in descent.
And when above 3000 foot density altitude, lean the mixture
for takeoff and climb.

Even if you don't care about fouling the plugs, and you aren't
paying for the gas, an extra couple gallons in the tanks at the
end of the trip will, sooner or later, make the difference between
you making the front page of the newspaper or not. Trust me.

But, what would I know compared to the red-hot keyboard
jockeys here, in their pajamas in their parent's basements?


Next nit that really bugs me: people using excessive throttle
and riding the brakes during taxi. I know, you don't care
about premature brake wear - it all costs the same to you -
but sometime, in the winter, you're in for a nasty surprise.

Get your godd*amned heels on the floor, and toes off the
brakes, and control the speed while taxiiing FIRST with
the throttle, then with the brakes.

[MichaelP]

riding the brakes during taxi

This is a bit of a problem with the Katana, and a serious one with the DA20-C1 Eclipse in which you can't do anything about it.
The aeroplane free wheels at idle because:

1. the engine is too heavy so:
2. they put a light weight toothpick prop on the front to bring the CG back a bit so:
3. there's no momentum and with a strong tailwind at idle the prop will stop and so:
4. the idle is set at a minimum 950 RPM which produces enough thrust to accelerate the aeroplane along at 'brake' neck speed.

The Katana's 80hp Rotax has a bigger prop than the 125hp -C1, and its a CSU as opposed to the coarse fixed C1's propeller.

The Katana's engine is always properly leaned, Rotax made sure us inaccurate pilots have nothing to do with it!
Of course you can burn unleaded petrol in it too we use Shell V Power.

[Shiny Side Up]

What is disappointing, Michael, is how few FTU checklists -
even though they are lengthy enough to operate an eight-engine
bomber - do not mention this important item, esp in the summer,
when the hotter temps yield higher density altitudes and
resulting richer mixtures and more fouling.

Unfortunately if you modify a checklist in such a way, the next time someone from TC sees it they'll stomp all over you, been there, done that. In fact to do so, I'd have to consult several AMEs and the people from the manufacturer themselves. Such stuff must remain at the discretion of the instructor to add in any bits of sense in how to operate the machine properly. Its tough though to explain why to a new pilot they must use a checklist, but then deviate from it in certain places.

Next nit that really bugs me: people using excessive throttle
and riding the brakes during taxi. I know, you don't care
about premature brake wear - it all costs the same to you -
but sometime, in the winter, you're in for a nasty surprise

A little off topic, but you'd be suprised how many people drive their cars two footed out there with a foot on the brake and one on the throttle. For some reason the idea that the two shouldn't be used simultaeneously is a difficult concept for your average human being. Since it would seem that many haven't figured out that hot brakes in the snow or cold isn't a good idea (not to mention the application of the park brake to make matters worse isn't a good idea) I got a bar around here ideally suited to the task of chipping ice away and prying frozen brake pads apart. Like my ground power unit, it gets used far too often in the six months of the year we have winter.

[iflyforpie]

Next nit that really bugs me: people using excessive throttle
and riding the brakes during taxi. I know, you don't care
about premature brake wear - it all costs the same to you -
but sometime, in the winter, you're in for a nasty surprise

I do this all the time. Got to wear in new brake linings somehow!