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John Deakin |
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| About the Author ... |
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John Deakin is a 35,000-hour pilot who worked his way up the aviation food chain
via charter, corporate, and cargo flying; spent five years in Southeast Asia
with Air America; 33 years with Japan Airlines, mostly as a 747 captain; and
now flies the Gulfstream IV for a West Coast operator.
He also flies his own
V35 Bonanza (N1BE) and is very active in the warbird and vintage aircraft
scene, flying the C-46, M-404, DC-3, F8F Bearcat, Constellation, B-29, and
others. He is also a National Designated Pilot Examiner (NDPER), able to give
type ratings and check rides on 43 different aircraft types.
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We've
now beaten the technical issues to death, let's go fly!
If you haven't read any of the prior material on this, please don't fail to
see "Those
Fire-Breathing Turbos (Part 3)."
This column is highly specific to the "turbonormalizer" systems
as installed on Teledyne Continental Motors (TCM) "big bore" engines
like the IO-520 and IO-550, most notably the "Whirlwind" system by
Tornado Alley Turbo, in Ada, Okla. However, the general principles apply
across a broad spectrum of engines, with and without turbos. If you have read
prior columns, and understand them, you should be able to sort out the
specifics from the generalities. I am deliberately avoiding Lycoming engines
here, as I have little recent experience with any Lycomings with decent
instrumentation. Try these techniques with your Lycoming if you wish, but if
they don't work, go buy a TCM!
Seriously, I can throw bricks at TCM for some things they've done very
poorly, but their basic engine is very well-done, and usually runs much
smoother than most Lycomings. A well tricked-out TCM IO-550, preferably with
Millennium cylinders, a JPI engine monitor and GAMIjectors, is a fine, fine
powerplant. A turbonormalizer makes it even better. Much is made of modern
automotive engines, but they really are not very good, or efficient. They are
optimized for minimum emissions, at considerable cost to efficiency.
If anyone consistently has trouble starting any of these flat TCM engines (turbo'd
or not) when they are cold, they are either doing something seriously wrong,
or something in the engine is not right. Throttle cracked, mixture rich, a
shot of boost (or prime) until the fuel pressure steadies, or about five
seconds, and the engine should start and run on the first turn of the prop.
Hot starts are equally easy.
Yup, that's what I said, there's NO difference between a cold start and a
hot start, PROVIDED you do it using science, not folklore. In fact, hot starts
are easier. Everyone has a favorite method, and some of them even work on some
airplanes, some of the time. Most often, you will hear of flooding the engine
deliberately, then cranking with some combination of throttle and mixture
settings until the engine starts. Generally, that's NOT a good idea, because
most methods of doing this end up with copious quantities of raw fuel in
various unknown locations, creating a fire hazard. Fuel on the ground can
catch fire and cause the loss of the airplane, fuel in the exhaust manifold
can "torch" and sear the paint above the exhaust pipes, and fuel in
the induction manifold can do great damage to the tubing, much of which is not
metal. Yes, many get away with doing this, some for years. But I've seen all
three results, and in each case the pilots whined, "I did it the way I
always do it!"
There is a bit more science involved with hot starts, because the heat
developed by an engine that has just been shut down can have an undesirable
effect. The key here is to understand that with the engine running just before
shutdown, cool fuel is circulating through all the fuel lines and the
engine-driven fuel pump, effectively keeping the plumbing AND THE PUMP cool
from the inside. There is also some cooling airflow, blowing hot air out of
the accessory compartment. Once you shut down and trap fuel in the lines, the
large thermal mass of the engine transmits the heat throughout all metal parts
of the engine and the engine compartment. This "cooks" the fuel in
the lines, and more importantly, the heat from the engine "soaks"
into the engine-driven fuel pump, warming that fuel. Since there is no cooling
airflow to partially cool the outside of the fuel pump, the temperature of
that metal assembly will actually rise after shutdown. The fuel trapped in the
fuel pump heats up, slowly develops bubbles, and the engine-driven fuel pump
becomes full of them after about 15 minutes.
One thing every new pilot on the old radials learned was that engine-driven
fuel pumps don't work very well with mixed air (vapor) and fuel, they cavitate.
On the other hand, electric boost pumps are quite happy to pump either fuel or
air, or both. The two complement each other, with the additional benefit of
having a backup if the engine-driven pump takes a break.
If you prime the hot engine, and turn the boost pump off, you'll probably
get some fuel and air bubbles through to the cylinders. The fuel you injected
into the engine is enough to make it cough to life, perhaps even run for a
second or two. But as soon as that fuel and the little bit of fuel in the
injector lines is used up, the engine-driven fuel pump is simply spinning its
wheels in vapor, unable to move the needed fuel, and the engine dies. Repeat
that, and the same cycle occurs until the battery goes dead.
Yes, you can run the electric boost pump for the start, but it's so good at
moving fuel (and air), even with bubbles in it, it's very hard to control the
actual flow, and the mixture will probably become too rich to run. Some master
the trick of running the boost pump, and slowly moving the mixture control or
the throttle until a viable mixture exists, but it's a difficult trick, and
different for every engine. Some push the throttle in and run the boost pump
before hitting the starter, but this pumps raw fuel into the engine, and
possibly overboard, creating a very real risk of fire. Just because you've
never seen one, don't think this cannot happen! Even if you get the engine
started, the fire can do damage, scorching paint at best, and burning up the
airplane at worst.
A better starting method is needed, and there is one, at least for the TCM
engines. We haven't had much chance to try it on the Lycomings.
For starts within the first 10 or 15 minutes after shut-down, just put the
mixture rich, crack the throttle, DON'T prime, or just a tiny shot, and go. If
that fizzles once, don't run your battery down with further attempts, just go
right into a hot start.
Simply leave the mixture in full lean ("idle cutoff"), and run
the electric boost for one full minute. Sixty seconds. Time it, by the clock.
More won't hurt a bit, but less may well not be enough. A full 60 seconds, not
a second less. The first few times you do it, it will seem interminable, but
there's no reason you have to just sit there. When you know you're going to
use this procedure, flip the pump on early, hit the stopwatch, and go ahead
and do your cockpit setup, or study the instrument departure, or brief your
passengers (you DO brief passengers, don't you?)
This little trick uses the ELECTRIC pump to pressurize the lines to the
engine pump and the chamber inside the pump case itself. Since that fuel can't
go beyond the fuel control with the mixture shut off, the only way out is
through the rather small "vapor vent return" line. This is the exact
purpose for which this line is provided.
Once this "cooling" step is done, the start is identical to the
cold start, and just as easy. At the end of the sixty seconds, let the
electric pump continue to run while you push the mixture in until the fuel
flow stabilizes (as for the cold start), flip the boost off, and hit the
starter. Instant gratification. Well, sixty-second gratification, anyway. In
effect, this procedure converts a hot start into a cold start. (Actually, it
may be better than a cold start, because the engine is warm, and the fuel will
vaporize better.)
What's the magic behind 60 seconds? Well, if you lay your hand on the fuel
pump of a recently shutdown engine — ouch, you'll burn yourself. Run the
boost pump, and you still won't be able to touch the fuel pump until about 60
seconds have gone by, and then you'll actually feel the case cool off from the
fuel running through it. There isn't a lot of fuel passing through it, because
the vapor vent return line is fairly small. But new, cool fuel IS coming in,
and it IS driving out those nasty little air bubbles, and it is cooling the
pump from the inside out. Patience, take the full 60 seconds. Works great.
I have heard people complain that this longish use of the boost pump will
run the battery down. Maybe, but so will repeated attempts to start a hot
engine using any other way, and the starter is a LOT more load than the
electric boost pump! Also, your battery is an important reserve of electrical
power, and if it cannot perform this function briskly, then I think the
airplane is unsafe for any flight beyond a simple hop around the pattern in
good weather. Remember, the engine is hot, implying a very recent flight, and
that battery should be fully charged.
You may have your own way of doing the hot start. It may work for you, in
your airplane, most of the time. That's fine, use it. But the method above
works in ALL these TCM fuel-injected, flat-engined airplanes, ALL the time. It
has the advantage of leaving the engine in a known condition, fully equivalent
to the cold engine. I may not have seen all the methods out there, but I'll
bet I haven't missed many. I like this one best of all, for it uses science
instead of oaths and imprecations. Credit George Braly with this one, not me.
Why not? Hey, if you want to foul your plugs and worse, by all means, go
ahead, be lazy, and leave the mixture full rich for ground operations. There
are also rumors that this is a stunt invented by cheap airline captains,
trying to save a little fuel, but I discount that. On the other hand, I'm a
post-60 co-pilot now, and I'd believe anything about those dreadful captains! I
never realized how bad they were when I was one. Terrible people. Just
terrible.
Remember, idle mixtures are universally set up for easy starting, and are
universally richer than necessary for any RPM below roughly 1200 to 1500 RPM.
If the engine is set up for sea-level airports, then the idle mixture will get
REALLY rich at higher elevation airports. On the other hand, if an engine is
set up at Crede, Colorado (9,000 feet MSL), and then flown to a low-elevation
airport, it will be hard to start from a mixture that is much too lean.
You can prove this to yourself by leaning the engine after you start it,
and watching the RPM very closely. You should, with considerable leaning at
1,000 RPM, see a definite RPM rise and peak, as the mixture goes from
"too rich" to "just right." If you lean for maximum RPM at
this point (on the ground), you're actually setting a "best power"
mixture at that throttle setting. It is impossible to hurt the engine by doing
this. Remember, TCM says any mixture setting is okay below about 65% of rated
power, and Lycoming says 75%. Ground running is a LOT less than 65% power,
unless you're trying to taxi to the ramp after landing gear up, when all your
power is converted to noise.
The real danger here is forgetting the leaned mixture, and attempting to
take off with it leaned. THAT could be bad news! To prevent this from
happening, EITHER leave the mixture full rich (and pay the price in fouled
plugs), OR lean it so brutally that you can't even get runup RPM without the
engine wheezing for air, and quitting. (No, this won't hurt it either.) Don't
ever put the mixture in some indeterminate position, in between "full
rich" and "brutally lean." So many pilots will grab the mixture
levers and just pull 'em back by feel, figuring that improves things, and it's
"good enough." IT ISN'T. I don't care how good your checklist is,
and how religiously you use it. If you do this, sooner or later, you'll try a
takeoff set that way.
Can you run up while leaned? Sure, why not? Even a runup is well under 65%,
isn't it? If the mixture is so lean you can't get your runup RPM (as it should
be), you may need to bump the mixture up a little, or even go full rich for
the runup, if you feel better with that. One advantage of doing a leaned mag
check is that it is a much more demanding test of the ignition system, and may
well reveal faults that the normal runup won't! I like that. If you have an
all-cylinder engine monitor (and you should), monitor the graphic display
during the mag check, rather than worrying so much about the RPM. The RPM drop
on one mag will be MUCH greater when leaned (200 RPM is common), and that's
perfectly normal WHEN LEANED BRUTALLY. You should see all EGTs RISE during
single-mag operation, because with only one plug per cylinder firing, it takes
longer for the mixture to burn, and it will be much hotter when it leaves the
combustion chamber. So when you select one mag, you should see all the EGT
bars jump up. Switch back to "both," and see them drop back, then
repeat for the other mag. If you see one or more EGTs fall during single-mag
operation, SOMETHING IS WRONG. That plug is NOT firing properly, and
combustion is not developing fully before the exhaust valve opens.
There is a tendency by many pilots to spend only a second or less on one
mag during this check. Sometimes I wonder if they've checked all six plugs on
that mag, they're so quick! Please, leave it there for several seconds. On the
old engines, 30 seconds or more on one mag was recommended for a really good
mag check, monitoring for the usual "fast drop" in a second or two,
followed by an abnormal "slow drop" over a longer period of time.
Excessive "fast drop" meant bad plugs or ignition, while any further
"slow drop" might mean bad timing, or improperly adjusted valves.
There is no need to do such a long mag check on every flight, but it's not a
bad idea before and after maintenance, and there's no need to be quite so
quick on the everyday mag check, either. Remember, you're LOOKING for an
abnormal condition, here! Give it a few seconds to show itself, and a few
seconds to see the normal EGT response.
On the other hand, excessive ground time and runup time can be harmful in
the long term, because the engine temperatures do build up in many engines
without the cooling airflow of flight. Even if the CHT doesn't show this,
"hot spots" can develop, which are not measured by normal
instrumentation. On the normal runup, get the RPM up to APPROXIMATELY the
figure called for, but anywhere within 100 RPM, or even 200 RPM is just fine.
DON'T sit there and twiddle with the throttle, trying to get exactly 1700 RPM,
or whatever. Get it up into the approximate range, do a quick prop check, do
your mag check with a few seconds on each mag, note the engine instruments are
all in the proper range, and pull it back to normal ground RPM (usually
1,000). With practice, this whole procedure shouldn't take more than about 20
seconds from the time you leave 1,000 RPM, to the time you return to it.
Properly done, there isn't enough time for the CHTs to rise much, and that's
good.
DON'T INVENT POWER SETTINGS, unless you have the data and the knowledge to
back it up! Please, do your engine a favor, and USE the specified MP and RPM!
In general, if you have a power setting for takeoff, and another power setting
for "maximum continuous" or "climb," the engine has not
been tested much at the in-between settings. In MANY engines, by reducing the
throttle, you also lean the mixture, and this is NOT recommended, and usually
NOT tested. Additionally, less than full takeoff power increases the time it
takes to get to an airspeed that will properly cool the engine. In the
single-engine airplanes, it leaves you lower longer, and in the twin, it will
immensely complicate your problems if an engine fails.
In theory, given enough MP, all these engines can produce the same power
for takeoff when lean of peak, and with cooler cylinder temperatures, too.
Some of us have experimented with this, but it is not for the faint of heart,
and you risk very serious and immediate damage if you make a mistake. In the
future, special systems may make this the preferred method, and there is even
talk of a "Full Time Lean Run" engine (FTLR) that will do it
automatically. No, I'm not talking about TCM or Lycoming. For now, the
risk-reward ratio is not good enough for most pilots.
Tornado Alley installs a two-speed electric boost on all their
turbonormalizer systems, and they recommend its use in the "Low"
position for takeoff and climb. On mine, turning it on at low power while
entering the runway will make the engine run a bit rough from a too-rich
mixture, so I generally wait until I've got full throttle, then I flip it to
low. DO NOT use "High" for takeoff, and if you have only a single-speed
pump, DO NOT use it for takeoff either, unless you have a failure of the
engine driven pump.
As on all takeoffs, you should take a quick peek at the engine instruments
right after setting full power. Fuel flow is especially important, but look at
RPM and MP, too. Next, take a quick glance at the engine monitor, to see what
the graphical bars are doing. Very early on, you should develop awareness of
what "pattern" you should see at takeoff power, so that you can
recognize abnormalities when they occur.
During this instrument check on takeoff with the turbonormalizer, you will
probably see a slight overboost on the MP if the engine oil temperature has
not yet come up to full normal operating temperature. This is perfectly
normal, very common on these engines, and an inch or two over redline MP won't
hurt a thing. If it goes above that, go ahead and reduce the MP to
approximately redline, but not below. As the oil warms, you'll need to add
throttle again, to maintain that redline MP.
In summary, for takeoffs, full throttle, full redline RPM, and full redline
fuel flow.
Unless you want to be a test pilot with your very expensive engine, climb
should be at the power setting recommended by the manufacturer. That's
generally a full rich mixture, and some specific MP and RPM. On any engine, if
the manufacturer approves or permits full throttle, USE IT, all the way to
cruise altitude. You won't hurt a thing, and it is probably better for your
engine than some lesser power setting. If the manufacturer approves or permits
full RPM, use that, too. Just like takeoff, resist the temptation to invent
your own power settings.
With the Tornado Alley Turbo (TATurbo), more refined testing has been done
on heavily instrumented engines for FAA certification, and a few minor
exceptions result. During certification tests, in order to keep the CHTs down
at altitudes around 15,000 feet, the fuel flow at the full rich position had
to be set up so high that it is somewhat too rich at the lower altitudes. The
result is that a little leaning at low altitudes is a good thing, as it will
give you full rated power and a cleaner mixture, without getting too hot. I
cannot tell you if other systems react the same way.
TATurbo has done a lot of research, and has developed what they believe to
be the best way to operate the turbonormalized IO-520/550 engines in climb.
I've found it works very well.
First, set the throttle to wide open for takeoff. You don't have to tease
it in, and you don't have to baby it, just a nice, steady push, taking perhaps
three to five seconds from idle to full power. Once fully open, LEAVE it there
for the entire flight until time to control the speed during descent, or until
time to reduce to traffic pattern speeds. Simple. Just forget the throttle.
Experienced pilots find this VERY difficult! One very senior pilot has flown
my airplane a number of times now, and he knows I want full throttle, full
RPM, and full rich mixture on takeoff. Instinctively, his hand will sneak
towards that throttle at about 1,000 feet AGL, and he'll start backing it out,
heading for the classic 25 inches. When I rap his knuckles, he'll say,
"Yeah, yeah, I understand, but MAN, that's hard to get used to." He
probably never will, the habit is so ingrained.
In addition to the wide-open throttle (WOT), use full RPM (generally 2700)
for all takeoffs, and all climbs. Do your engine a favor, and check the
tachometer for accuracy. If nothing else, use the strobe effect from the ramp
lights at many airports. They flicker at 60 Hz, so you will see the prop
"stop" at night from this effect at common multiples of this speed
(check it at 2,400, for example). Or borrow a cheap optical RPM checker. If
you're not an airline captain, heck, BUY one as a backup. Once you know what
your tach is really reporting, have your mechanic adjust your maximum RPM on
successive flights until it's as close to the redline value as you can get it.
Certainly within 25 RPM. Go on, test his patience, it's good for building
character.
In a Bonanza, I like to climb at about 120 knots IAS, for cooling. I like
to do a gentle climb AND a gentle acceleration right from liftoff, while
accelerating to 120. If you want to climb at lower speeds, be my guest, but I
don't think it's worth it. And yes, I've heard all the arguments in favor of
clawing for altitude, so you can turn back to the runway. Hogwash, most of it.
By heating up your engine with a slow speed climb, you increase the chances of
an engine failure at some time in the future, in my opinion. But that's just
my opinion.
TATurbo says, for climb, rich of peak EGT (ROP), with their turbo installation, use the
mixture, and:
- Below 10,000 feet MSL, adjust the Turbine Inlet Temperature (TIT) to
about 1290°F.
- Above 10,000 feet MSL, adjust the TIT to about 1270°F.
- Above 17,000 feet MSL, adjust the TIT to about 1250°F.
In my opinion, those are GENERAL recommendations. There are variations
between engines, so you will need to watch CHTs closely for a few times, to
get a "feel" for what YOUR engine needs. In my airplane, those TITs
put me pretty close to the self-imposed 380-400°F "limit," so I'll
probably aim for a few degrees on the low side.
Notice the pattern? 1290, 1270, 1250. Five or ten degrees off the target
probably won't matter, but 15 degrees off the target EGT can put your CHTs
well over the limit. You may need to tweak the mixture a couple times during
the climb, but basically, it's a very simple operation, and pretty easy to
remember. Put a little Post-It note somewhere on your panel, until this is
imprinted in your wetware.
In fact, I suspect that pilots could just use 1250°F during ROP climbs,
with very little "cost." The higher the TIT you choose, the closer
attention you'll have to pay to CHT. The lower the target TIT, the more you
can relax. Experiment with yours, determine a number, and use it thereafter.
This concept of a "Target TIT" works very well in a very wide
variety of turbocharged engines, not just the normalized versions. The
"Target TIT" will be a bit higher in lower compression engines, as
found in factory installations of the TSIO (turbosupercharged injected opposed) variety. There are at least three
very beneficial results in using "Target TIT":
- First, the "Target TIT" will remain constant over a very wide
range of outside air temperatures.
- Second, TIT reacts very quickly, allowing very positive control, and
immediate detection of problems and abnormalities.
- Third, bubbles in the fuel from vaporization will show up immediately as
a fast-rising, very much out-of-place TIT from the effective leaning (more
air, less fuel). This vaporization is not abnormal, you'll see it a lot
when operating these fire-breathers, and correcting for it is a perfectly
normal, straightforward procedure. Fuel can get quite hot while an
airplane bakes in the summer sun on the ramp, and if you climb to 18,000
feet, you're cutting the ambient pressure in half. Also, the climb rates
are so much faster with turbos, the fuel doesn't have as much time to
cool.
There's an exception. IF you have an all-cylinder monitor that shows CHT in
one-degree increments, you MAY prefer to monitor the hottest CHT, instead.
Pick a number, and try to maintain it somewhere near that number. Some might
like the hottest CHT at 360, some might prefer to "push it" to 380
or even 390, for max performance. The JPI EDM-700 will show CHT in one-degree
increments, and it reacts very quickly to mixture changes. I've tried both
methods, and I think I prefer the CHT method myself. But without that
one-degree capability, the "Target TIT" method is clearly superior.
Take a peek at the CHTs once in awhile, to make sure they're normal.
With ROP climbs and my IO-550 (TN), I find that I need a fair amount of
manual leaning (still ROP!) during the early climb at low altitude (or even
during takeoff), and then I have to slowly enrich during the climb, ending up
at or near full rich at 15,000, in order to keep the CHTs where they should be
(380). I may need to have my "maximum full rich fuel flow" tweaked a
little, to give me some additional fuel flow at the full rich position. That
will mean a little bit more leaning on the takeoff and early climb.
(Remember the mantra, "rich of peak (ROP), richer is cooler but lean of peak (LOP), richer is
hotter.")
If cooling requirements permit, you can get a better rate of climb above
about 15,000 feet by reducing that 120-knot climb speed a little at a time,
eventually dropping to around 105 at very high altitudes. It's not necessary
to memorize numbers, just realize that when you see the performance (climb
rate) drop off, reducing the IAS a bit will help. This can be a subtle balance
of climb needs and engine cooling. If CHTs are a problem up there, you may
need to increase airspeed for cooling, and take the "hit" on climb
rate.
At those TITs, you should never see a problem with CHT, unless there is a
serious problem with the engine, but some problems can cause changes in the
CHT, so don't fail to monitor that parameter.
If you're concerned about the performance for a short-field operation, you
can lean it during takeoff just a bit more for maximum HP, to about 1310 to
1380. This will result in a fuel flow of as little as 24 GPH on a hot day
(less power), to 30 GPH on a cold day (more power). Once performance is not a
concern, you can return to the 1290, 1270, 1250 settings, as soon as you can,
because CHTs will be rising slowly. If you leave the mixture set there, you'll
eventually see more than 400°F.
At no time should you EVER allow any CHT to go above 400°F, and this makes
380°F a good "target." If your engine monitor has alarms (and it
should!), then set it to reach out and hit your knee with a hammer if the CHT
goes over 400°F. While climbing with the TIT showing, it wouldn't hurt to
note the hottest CHT, and check that from time to time. Don't depend on the
"missing bar," as it is NOT RELIABLE for showing the value of CHT,
at least on the JPI! It will show the hottest cylinder, in my experience, but
it also wouldn't hurt to do a quick scan of all digital CHTs, just to be sure
you know which is the hottest. On some engines, the TIT may not be as accurate
as you might like, and checking the CHTs will prevent this from causing a
problem.
If you should happen to see one or more CHTs creeping up over 380, don't
panic, don't flinch, and don't scare your passengers with your reaction, but
quietly DO SOMETHING about it! Open the cowl flaps more if you can, or
increase the airspeed as necessary for cooling. If this fails to keep the CHT
below 380, your fuel flow is not sufficient, and needs to be adjusted. If this
happens consistently, and you have trouble keeping it down, it needs adjusting
by a mechanic. Many/most of these engines absolutely require redline fuel
flow, and many knowledgeable people, even at the factory, will quietly suggest
just a tiny smidgeon more. Some engines will run nice and cool for the early
climb, but you'll see CHTs go up at some point on the way to cruise altitude.
Engines with the TATurbo are usually the exception, they'll be properly set up
with a bit too much fuel flow at sea level, and a little leaning is usually
beneficial.
If CHTs still persist above 380°F, with the mixture full rich, cowl flaps
open, and airspeed higher than the normal climb speed, then as a final resort,
go to first LOW boost (if it's not already on from takeoff), and see what
happens. Obviously, if you have only a one-speed electric boost pump, use that
speed. If that doesn't do it, then try HIGH on the electric boost, while
remaining very alert to what the engine is telling you. High boost and full
rich can flood the engine with too much fuel, and in some cases, can make you
think you've lost the engine. Not good, at low altitude, so save this trick
for well after takeoff.
Think about this "High" position, just in case you ever do need
it. If despite your best efforts you're "too hot" on the rich side
of peak EGT, AND flipping the electric boost from LOW to HIGH gives you
"too much" fuel, then the only remaining thing you can do is leave
the boost pump on, but manually lean the mixture to the point where the engine
does run properly, without getting too hot. In the end, the only thing that
matters is how much fuel you are getting into the engine, and it matters not
at all how it gets there.
By using TATurbo's "Target TIT" method, you will see fairly large
variations in fuel flow, depending on the OAT. On very cold days, you'll see
high fuel flow, perhaps as much as 35 GPH, on very hot days as little as 24
GPH. This is quite normal, a BENEFIT of using the target TIT method. On cold
days, your engine will produce more power, which needs more fuel. On hot days,
the reverse is true. This technique handles both, without thinking about it.
In summary, for climb, full throttle, full RPM (or maybe 200 less, but no
less than that!), and mixture adjusted to 1290, 1270 and 1250.
Now, it's true, you may have heard of some of us who will climb to some low
altitude (1,000 feet agl is common), and then do "The Big Pull," or
the "Big Mixture Pull " (BMP), drastically reducing the mixture to a
setting very lean of peak EGT, and climbing to altitude that way. Again, this
is not for the faint of heart, for it puts us in the test pilot category. More
than any other phase of flight, you really, really need to know exactly what
you're doing, have the instrumentation to do it, and pay close attention, for
this procedure operates much closer to the edge. In the future, this may
become a common procedure, but it's still too new, with too many unknowns, to
recommend it for the average user.
So, in summary, climb at WOT, ROP, full RPM, and leaned slightly to a TIT
of 1290, 1270, and 1250 (or what YOUR engine likes), cowl flaps open, and keep
an eye on the CHTs. DO NOT use partial throttle settings, unless there is a
serious overboost, and then only until it goes away. You will almost certainly
need to tweak the mixture a few times during the climb to maintain these
values. In general, there are very few cases where precise temperature control
really makes much difference, but TIT during climb is important. Only 15 or 20
degrees of error may produce CHTs in the danger zone, over 400°F. With a
little practice, monitoring the TIT during climb will become very natural, and
remember, you no longer have to worry about anything else! If you have a
monitor with an alarm set to warn you of anything over 390 or 400, you need
only watch the TIT. If there is no warning, I suggest you set fuel flow by the
TIT, but continuously monitor the hottest CHT at all other times.
Remember too, this climb is ROP, where "leaner is hotter, richer is
cooler." Later, we will get into LOP operation, where "Leaner is
cooler, richer is hotter." For most pilots, this is a very new concept,
and very alien!
How does all this look when the data is charted?
Here is the data from a flight I did on September 9, from Camarillo,
Calif., to Santa Barbara, cruising at 1,500 feet. This is "Go REALLY
Fast" mode!
Click for higher-resolution image.
For a less complex chart, I have plotted the AVERAGE EGT and the TIT
(Turbine Inlet Temperature) against the scale on the left side of the chart. I
have also plotted the AVERAGE CHT against the scale on the RIGHT side. I have
multiplied the fuel flow by 10, in order to make it much more obvious, and I
have plotted it against the scale on the right. OAT (Outside Air Temperature)
and oil temperature are also plotted against the scale on the right. Data was
recorded at six-second intervals.
Note this plotting exaggerates the CHT trace a bit, but even so, it shows a
nice, steady, smooth rise, leveling out at an AVERAGE of about 360 or 370. The
hottest CHT (#4 on my engine) was right at 390, and stable after the BMP (Big
Mixture Pull). What you are looking at here is my engine run at the absolute
maximum power I'll run it, WOTLOPSOP (Wide Open Throttle, Lean Of Peak,
Standard Operating Procedure). Multiplying the fuel flow (18.0 GPH) by 14.9
(the constant for this engine), we know this is 268 HP, or a whopping 89%.
Indicated airspeed was in the 180 knot range, but the flight was too short to
nail it down.
In the lower left corner we start the engine, cold. The spike to about 6
GPH is with the throttle cracked, mixture full rich, and high boost for a few
seconds. The boost was turned off, and the fuel flow drops to zero. The engine
starts at the 1:00 (one minute) point, and the EGT and TIT rise quickly to
normal ground operating temperatures of just over 1,000°F. CHT starts up much
more slowly, as it takes time to heat the mass of the engine. The
"bump" in the fuel flow at the five-minute point is the runup, also
shown by TIT and EGT spikes.
The sudden steep rise at about six minutes is the takeoff, rising quickly
to about 38 GPH.
The little "jaggie" at the halfway point is interesting. Test
data has a way of showing pilot screw-ups, and this was a minor one. We were
on the runup pad and called "ready." The tower controller came back
with "I have a Cessna on a one-mile final, if you can take off without
delay, absolutely without any delay, you're cleared for takeoff."
I was crossing the yaller lines about sixty degrees to the runway heading,
when he said "absolutely," with the power coming up hard, and
realized maybe I ought to back off just a little, or I'd have a tough time
staying on the runway. The "jaggie" is the result. As soon as it
felt "better," I shoved it in all the way, the airplane drifted in a
big arc to nearly the far side of the runway, and away we went.
I held that full-bore power setting to gear up, then leaned to about 1290
TIT for the short climb to 1,500 feet. I leveled out, closed the cowl flaps,
let the speed build (to over 180 knots), and then did the BMP, as shown, right
back to roughly 16 GPH. I cycled the JPI to show the hottest CHT, and #4
showed about 360, and falling. Here's where that one-degree resolution is so
neat, it shows the trend instantly! So I enriched to almost 18 GPH, and the
CHT started tick, tick, ticking up towards my target of 380. In the final
stage of this short flight, #4 was right around 380 to 390, which is
"close enough."
It is also impressive how solid the Bonanza feels at 180 knots indicated!
After landing at SBA and dropping my passenger, I did a special
data-gathering flight. While we are not suggesting LOP climbs, I do them
routinely myself, so this was my first experience at doing a ROP climb. I find
the resulting data absolutely fascinating from many standpoints, and I hope
you do, too.
Click for higher-resolution image.
The time across the bottom of this one is actual time, with the hour
dropped. I meant to convert that to start from zero and show elapsed time, but
by the time I'd done the chart and realized that omission, I was out of time.
The chart actually starts at 17:43:18, and runs to 18:10:30.
The takeoff is at the extreme left, and shows the initial flow of 34 GPH,
somewhat too rich. Right after liftoff, I leaned to 1290 TIT for the ROP
climb. Rate of climb was within a second or two of 1,000 feet every minute, so
the time across the bottom can also be read as altitude. 120 knots IAS for the
entire climb, except after 16,000 feet.
Right around 10,000 feet, EGT and TIT started rising abnormally. It was a
hot day on the ground, and the fuel in my tanks was quite warm, so I'm
theorizing that with the drop in pressure at 10,000 feet, the fuel was
beginning to develop tiny bubbles. Tiny bubbles in champagne make the nose
itch, and tiny bubbles in avgas makes the engine's nose itch, too. More
precisely, the fuel and bubbles don't change the indication of fuel flow
nearly as much as the bubbles effectively lean the mixture. Air is air, no
matter how it gets to the combustion chamber. It took me almost two minutes to
catch on to this, and I finally hit the boost pump at about 53:42.
As you can see, the effect of the additional fuel flow (or "more fuel,
less bubbles") was immediate. EGT/TIT dropped instantly, and CHT started
ticking right back down again. In fact, low boost resulted in too much fuel,
so I had to lean it out some more with the mixture control.
At 58:30, I momentarily turned the boost off to see what would happen, and
didn't like it. EGT/TIT instantly started up, and I discovered that by this
time I was getting very close to full rich on the mixture control, with no
further control left. With the boost on, mixture full rich, the fuel flow
continued to drop off with altitude due to the altitude compensating fuel pump
(I think), and the CHTs started a slow rise that I could not control without
changing airspeed. Cowl flaps were fully open, at this point.
For the purposes of this test, I let it go until the hottest CHT (good old
#4) was 421, and that was all the testing I was interested in subjecting my
engine to, thank you very much. There IS a limit on what I'll do for my
readers! I pushed the nose over to 140 knots, and the CHT came right back
down, average 380, hottest just over 400, while I continued the climb to
17,500.
Once stabilized at 17,500, I did the BMP, and monkeyed around with it for a
time to show the effects. Note the EGTs go much higher, with the TIT higher
still. This is probably because the TIT probe is seeing the full heat all the
time, and is not seeing the hot, cold, hot that the EGT sees for each
cylinder, as the exhaust valves open and close. At about 05:42, I got it
really lean, about 14 GPH (196 HP, or 65%).
Next column, we'll get into cruise and descents, including a neat method
for descending at 2500 FPM, without shock cooling the engine, and without
speed brakes. Sorry, I don't like speed brakes.
Be careful up there!
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