Douglas
DC-6B CB16 MiniTutorial
(adapted
from the DC-7C minitutorial)
by FSAviator
Real
world DC6B target performance at max gross / nil wind / ISA / sea level calls
for the aircraft to be 10 metres above the runway 4500
feet after brake release. Few airline pilots would actually have achieved this
at every attempt. The updated FS9 FD will deliver that possibility to within
the usual error % present in any MSFS flight dynamics which must also deliver
many other cases. At 25C and at 2000 feet QNH that distance becomes 5000 feet.
Any FS9 flight dynamics are likely to be a little 'long' for one case and a
little 'short' for another.
Some
users may have unrealistic expectations that the take off distance for a DC6B
should be less.
At max
gross with FLAP 2 deployed at around 115 KIAS a DC6B needs a very substantial
angle of attack to fly at all. The rotation (at 115 KIAS at max gross) must be
very positive, but not excessive.
In DC6B
terms 115 KIAS is not a lot of airflow. The elevators are not fully effective
and a large aft yoke movement is necessary to achieve a large angle of elevator
deflection to achieve + 8 pitch quickly. We don't need to be nearly as
aggressive when flaring for the landing from a similar IAS because we have full
flap deployed and developing much more lift.
Once we unstick with very positive rotation the problem is then not
lack of climb performance but preventing excessive climb rates. Rate of climb
must quickly be restrained to almost nothing until the drag reaches 130 KIAS.
****************************
Take Off
(with water/meth injection):
APPLY
BRAKES
MIXTURE
- AUTO in realism screen
CARB
HEAT - COLD
TRIM + 4
degrees
FLAP =
STAGE 2
PROPS =
MAX RPM
IF
ADI/AF desired/required: ADI & AF ON
Invokes
water/meth injection giving 59.5" MAP @FT
WET
departure/AF is MANDATORY > 92,200lbs
*DRY
TAKE OFF SET MAP = 53"
COWL
FLAPS = 4 degrees
Check
CHT < 260C
CALL for
TOGA POWER (2400hp WET)
RELEASE
BRAKES
Slowly
apply FULL THROTTLE or 53" DRY
ROTATE
at 115 KIAS (@ 103800lbs)
Establish
positive rate of climb
GEAR UP
ACCELERATE
> 130 KIAS @ <= 500 ft/min
CLIMB
300 feet AGL
FLAP =
STAGE 1
ACCELERATE
140 KIAS @ <= 500 ft/min
FLAP =
UP
Establish
500 VSI
CALL for
METO Power (1800hp)
**********************************
Note
that we should hold the aircraft below 300 AGL until 130 KIAS is achieved.
Climb rate should be very low. This post unstick
phase is all about using the only briefly available TOGA power to accelerate
the aircraft to the 'right side' of the drag curve as fast as possible. It is
not about climbing.
Once we
have achieved 140 KIAS about 300 feet above the runway elevation we get rid of
the drag of the flaps and stop thrashing the engines to death and reduce to
METO power.
**********************************
METO
Power (1800hp x 4):
48
inches MAP
2600 RPM
160 KIAS
ADI
& AF OFF
COWL
FLAPS = 4 degrees
Check
CHT < 260C
Above
all obstacles:
VSI =
500
ACCELERATE
> 180 KIAS
CALL for
climb power
***********************************
We have
just shifted up from first gear to second. All propliners
have manual shift gear boxes. One gear shift lever for each airscrew. In an aeroplane we call the gear shift levers rpm levers. In a
car with manual shift we need to select first gear for pulling away from the kerb. The engine must be revved hard even at very low speed
to get things rolling.
Once we
are rolling and have developed enough speed we must select second gear. Staying
in first gear would be wrong and shifting straight up to third would be wrong.
In first the rpm would be too high and in third too low. When we are about to
climb a hill in a car we must make the gear ratio (rpm) match both the
steepness of the hill and the speed we approach the bottom of the hill. Aeroplanes are no different. We have to shift up (reduce
rpm) manually in a piston propliner, as we
accelerate, whether or not we are going up hill.
In the
DC6B first gear = 2800 rpm is great for pulling away from a standing start and
getting things rolling, but now we have reached 140 KIAS and we intend to
steepen the gradient of the climb to 500 VSI. We must shift up to second gear
(2600rpm). We cannot accelerate a car with a manual shift gear box to
economical cruising speed in first gear and it doesn't work in aeroplanes either.
The
principle reason that users of the DC6B fail to climb the hill after take off without stalling is that they try to climb a steep
hill at 500 VSI before building up speed to 140 KIAS and also try to do it in
the wrong gear. We have to both build up speed and select the correct gear
(rpm) before tackling a hill climb. In an aeroplane
we choose when and at what speed to tackle a climb. Much of the Propliner Tutorial is about how and when to even try.
Once the
DC6B is in the correct gear ratio (2600rpm when throttle = 48 inches of MAP) it
will accelerate to 160 KIAS even whilst climbing a hill. If we try to tackle a
hill that steep with the speed below 150 at the bottom of the hill, or in the
wrong gear for that gradient at that entry speed, it just won't make it up the
hill.
We are
now accelerating up hill in second gear (2600rpm at 48 inches). When we get the
speed up to 160 second gear is too low even though we have no intention of
changing the climb rate from 500 VSI. We shift up to third by selecting 39
inches and 2400rpm.
**********************************
Climb
Power (1400 hp x 4):
39
inches MAP
2400 RPM
170 KIAS
COWL
FLAPS = 4 degrees
Check
CHT < 232C
IF
UNABLE to maintain 500 VSI @ 170 KIAS
(or use
Initial Alt value on Notepad)
REQUEST
LEVEL OFF from ATC
ACCELERATE
> 180 KIAS
***********************************
Each
time our increased speed allows us to shift up we reduce the load on the engine
(reduce its rpm) and extend its useful life (time between overhauls). Once we
are at a really decent speed we can get into gears that allow as to continue
acceleration (up hill), with less and less power,
burning less and less fuel, so we choose to do just that. High gears (low rpm)
are more efficient, but they are incompatible with climbing hills at low speed.
We can only shift up as speed increases, but we must shift up (reduce rpm) at
the right time and make sure we choose the correct climb rate for the current
speed and gear selected.
The
handling notes explain how steep a climb we can handle, what speed we have to
be when we arrive at the bottom, what power we need to supply with the
throttles, and what gear we need to select using the rpm levers.
After
the take off phase is over international law requires us to climb at not less
than 500 VSI. If our virtual airline or military employer wants us to climb
faster they supply handling notes that explain the throttle and rpm values
required for the higher target VSI or they specify constant IAS with varying
VSI.
Of
course when we are ready to cruise (reach operational ceiling) we shift up
again from third to fourth.
***********************************
High
Weight/Speed Cruise (1100hp x 4):
>89,000
lbs: High Wt. Econ Cruise
<89,000
lbs: High Speed Cruise
UAL
Standard Cruise Power
MAP = 34
inches
RPM =
2100
****************************
In a
DC6B we just shift up (reduce to 2100 rpm). When we are running lighter we take
the opportunity to shift up to fifth (overdrive = 1850rpm).
****************************
Econ
Cruise (1000hp x 4):
Use only
<= 89,000lbs
MAP = 32
inches
RPM =
1850
****************************
Just
don't try climbing steep hills from a low speed at the bottom in overdrive.
When we hit the built up area and the traffic near our destination we need to
slow down and shift down again (to higher rpm).
****************************
Approach
and Circuit:
Cross
FAF = 140 KIAS & FLAP 2 deployed
2400 RPM
MAP
=> 24 inches
COWL
FLAPS = 2 degrees
***************************
If we
need to go around we must select full throttle and first gear because we will
be about to climb a steep hill from very low speed,
***************************
Baulked
Landing:
CALL for
EMERGENCY POWER
PROPS
FULL FINE
FULL
THROTTLE
***************************
Maybe
this is all more apparent to Europeans who nearly always drive cars with manual
shift, but I suspect that failure to climb the DC6B without much difficulty is
the result of not fully understanding the above even though it was always
promulgated in the handling notes.
Although
not strictly relevant at this point note that the flight planning fuel flow
values in the DC6B handling notes are per engine which is anomalous compared to
my other handling notes which promulgate the total for all engines.
Finally
Part 4 of the Propliner Tutorial explains how to make
the departure phase more realistic and uses the Sebago departure from KIZG as
the worked example. That worked example in the tutorial talks about the DC7B rather
than the DC6B so I have abridged it here with specific relevance to the DC6B.
Climb
Stage 1 is for obstacle clearance. The obstacle can be a mountain, a mast, a
gunnery range, another airfield's holding pattern, a nature reserve, or just
noise abatement at a sensitive site such as a hospital. The departure
procedures for the runway will not usually tell us why we must proceed to a
given fix after take off and cross that fix at a
minimum altitude, but we must.
When we
receive, (issue to ourselves), the realistic ATC clearance, 'cross Sebago 3500
or above' we must bear in mind that Sebago is a fixed distance from KIZG. Climb
rate is unimportant. We must instead target a good climb gradient. We achieve a
better climb gradient (per mile) by restricting IAS even if we climb at the
same rate (per minute).
Remember
this is just an example. A DC6B would need to be very light and have a favourable headwind to depart KIZG at all.
The DC6B
handling notes cannot cover the details of all real departure procedures
everywhere. We have to adapt them to each specific case during flight planning.
In this case we will not terminate stage 1 climb until we have complied with
the realistic local clearance 'cross Sebago (at an ALTITUDE of) 3500 QNH or
above'. We will substitute this specific local restriction for the generic
handling note noise abatement restriction which is climb 2000 feet QFE (agl).
**********************************
METO
Power (1800hp x 4):
48
inches MAP
2600 RPM
160 KIAS
ADI
& AF OFF
COWL
FLAPS = 4 degrees
Check
CHT < 260C
Above
all obstacles:
VSI =
500
ACCELERATE
> 175 KIAS
CALL for
climb power
***********************************
Departing
KIZG in a DC6B we will climb in METO power towards Sebago at 160 KIAS until
passing 3500 QNH. The generic requirements of the handling notes must be
translated into the specific requirements of the departure phase from each
particular runway. We will not begin acceleration to 175 KIAS until we have
achieved the cross above restriction of the departure clearance and we will not
exit METO power until we have achieved our final stage 1 climb operating target
of 175 KIAS, which we only attempt after clearing all obstacles.
Or to
put it the other way round. We must climb at only 160 KIAS (Vx),
using exactly METO power = 48/2600, achieving much more than 500 VSI, until we
are clear of all obstacles, but once we are clear of all obstacles we will
accelerate to 175 KIAS (Vy) at only 500 VSI. Only
when we have achieved 175 KIAS at 500 VSI can we proceed to climb stage 2.
During
each departure we decide when we are clear of all obstacles, ideally using the
real airfield departure procedure downloaded from the web site of the real
federal authority, else we must decide what altitude is adequate by other means
and on passing the altitude we decided upon in our flight plan begin
acceleration from Vx (best climb gradient) to Vy (normal climb).
If that
is not making much sense or you are thinking of obstacles as things the size of
trees and buildings near the runway try departing Los Angeles eastbound and
turn direct for New York in good visibility. Those mountains are the obstacles
to be avoided during this departure. Handling notes are not a check list. They
explain the targets to be achieved and the captaincy decisions to be made. If
we do not download the real procedures with the real departure route and the
real cross above restrictions we must determine by visual reference to the
surface when it is safe to exit stage 1 climb airframe configuration, IAS, MAP
and rpm criteria and begin stage 2 climb. Just like cruising level the correct
solution varies day by day, even on the same route, towards the same obstacles,
at the same weight, because it varies with the weather, especially headwind
vector.
The
handling notes for the DC6B have always reflected the fact that it has a poor
post take off climb gradient at Vy = 170 KIAS and it
has to target a lower IAS = Vx = 160 until all obstables have been cleared.
The phase
by phase on screen handling notes tell us the targets which we must achieve one
at a time, in exactly the sequence specified, before we can move to the next
phase of the flight. Doing things in a different sequence is not an option.
Moving on without achieving all the targets is not an option. The exception is
transition from climb to cruise.
In
general when we cannot sustain 500 VSI at constant Vy
using the correct throttle and rpm setting for the correct and current climb
phase we have reached operational ceiling and must transition to cruise. As I
have explained in another thread that would normally be triggered by less than
500 fpm at 160 KIAS in a DC6B. We may also need to exit climb for cruise if max
specified engine temperatures are reached during climb.
Big
complex aeroplanes are designed to be flown by the
numbers. The input numbers such as Trim %, FLAP stage, MAP and rpm and the
output targets such as IAS and VSI. Hit all the numbers in the correct sequence
and they handle nicely. Miss them, or even achieve them in the wrong order, and
they may handle like pigs.
FSAviator
12/06