Post by volkerboehme on Mar 30, 2010 12:06:35 GMT -5
Hi,
The answer to your question is mostly a function of the the American aviation
fraternity 'belief and practice', (Europeans say mythology), that aero engines
should not be run 'under square' with MAP less than RPM divided by 100; but let's
recap the basics of DC-6B operation first.
Every DC-6B flight has a descent from cruise phase whose operating targets are
greatly simplified thus in my handling notes;
*****************************
Descent:
ABOVE FL170 DO NOT EXCEED Mno = 220 KIAS
DO NOT EXCEED Vno = 251 KIAS
COWL FLAPS = CLOSED
RPM = 2000 <<<<<<<<<<<<<<
REDUCE MAP in stages of 3 inches (per minute)
MINIMUM 20 INCHES MAP <<<<<<<<<<<<<<
See CARB HEAT below
*****************************
2000 RPM is correct during descent from cruise and 2000 RPM are retained for any
subsequent holding, (slowly going nowhere).
We must TIME our descent so that we achieve the holding and approach compliance
criteria for the DC-6B. The handling notes explain exactly what the DC-6B
compliance criteria are as we approach the Initial Approach Fix (IAF) and then after
the IAF;
*****************************
Terminal Holding:
Approaching IAF / Hold <<<<<<<<<
COWL FLAPS = 1 degree
2000 RPM
REDUCE < 160 KIAS
FLAP = STAGE 1
REDUCE < 150 KIAS
Crossing IAF entering Hold <<<<<<<<<<
FLAP = STAGE 2
MAINTAIN 140 KIAS
Check CHT < 232C
Plan 2100 PPH
****************************
We must achieve < 150 KIAS with FLAP 1 deployed *before* we reach the Initial
Approach Fix (IAF) of our destination airfield. As we cross that fix we deploy FLAP
2 and reduce to 140 KIAS. These targets are not just a sequence, they must be
achieved before, or delayed until, we reach a defined fix in our flight plan. The
IAF is usually the last radio beacon in the plan.
A DC-6B always cruises with more than 150 KIAS of profile drag applied. So whether
or not we need to hold at the IAF to meet our more onerous DC-6B Final Approach Fix
(FAF) compliance criteria, we need to reduce our profile drag significantly as we
descend towards the IAF. To do that we must reduce power very significantly.
Americans believe that they should not reduce to 20 MAP (to slow down) unless they
also reduce to 2000 RPM and that drove how Americans operated the R-2800 in the
DC-6B whether or not their beliefs concerning such equivalence are logical.
The supplied handling notes greatly simplify the operating practice of UAL in
particular and their handling notes not surprisingly complied with 'US practice'.
The operating manual of a 'foreign' airline might well have specified different
engine handling criteria. I addressed the same issue here about a year ago in
relation to TWA and Air France L1649A approach RPM and MAP criteria.
Whether or not we need to enter a holding pattern to achieve the DC-6B Final
Approach Fix (FAF) compliance criteria on a particular flight, we are not free to
ignore the higher and earlier IAF compliance criteria. In a DC-6B we must achieve
150 KIAS with FLAP 1 deployed *before* we cross the IAF and 140 KIAS with FLAP 2
deployed *before* (or potentially just as) we cross the FAF.
Until they commenced the approach from the FAF UAL crews always applied both low MAP
and low RPM so they could slow down to meet those sequential compliance criteria.
However neither value may be reduced so low that engine lubrication suffers or
electrical and hydraulic systems are not driven to adequate voltage / pressure.
Whether or not 'equivalence' has any real utility there are real limits and the UAL
specific criteria are within the more logical P&W specified engine limits which use
different criteria that are also used outside the U.S.
After we have achieved 140 KIAS and FLAP 2 we are allowed to exit any holding
pattern, which we may have needed to employ to achieve those FAF compliance
criteria, and only then begin an approach.
The RPM and MAP UAL employed to slow rapidly to 140 KIAS with less than FLAP 2
applied are much lower than are needed to later sustain 140 KIAS with FLAP 2
applied. So after we achieve the DC-6B FAF compliance criteria we must increase
power, and Americans believe they must increase MAP at least 'equally to RPM' so the
(UAL specific) operating criteria become 2400 RPM and not less than 24 MAP after the
FAF.
****************************
Approach and Circuit:
Cross FAF = 140 KIAS & FLAP 2 deployed <<<<<<<<<
COWL FLAPS = 2 degrees
2400 RPM <<<<<<<<<<<<<<<<<<<<<<<
MAP => 24 inches <<<<<<<<<<<<<<<<<<<<<<<
etcetera
****************************
During the approach from the FAF our IAS targets reduce much further. High RPM must
be applied before we do so, mostly to ensure adequate screw traction efficiency at
ever lower IAS, and partly so that the engines will spool up rapidly to even higher
RPM for a go around if required.
<<Also, how much lower is V1 than Vr?>>
V1 has no meaning at all inside MSFS and no agreed meaning in the real world.
en.wikipedia.org/wiki/V_speeds#V1_definitions
However it is defined locally in the jurisdiction you are operating the DC-6B in
today, inside MSFS there is no way to calculate it and graph it for all the
necessary criteria of any varying and local real world definition. The only option
you have is to evaluate your own skill to stop the aeroplane under different
conditions of altitude and weather on different runway types of different surface
friction and create tables or graphs relating to your own skill.
Remember you must interrogate the bgl code every time you attempt a take off, before
using any tables you create, because the friction data is not stored in a bitmap.
You may be lining up on a gravel (bitmap) runway which has been encoded by an 'AFCAD
author' to have tarmac friction. Any data from real world documents is useless
partly because MSFS and real runway friction do not match, and because the real
world runway slope is absent in MSFS. My advice is forget V1 altogether inside
MSFS. Whatever V1 criteria you 'graph' they won't work most of the time inside MSFS,
which is why I never supply them.
Even the belief that FS9 can replicate V2 criteria is very optimistic and my DC-6B
FD won't comply across all relevant altitude densities. It's simply no good just
pretending MSFS can do all sorts of things that have always prevented it from
achieving real world aircrew simulator training authorisation.
FSAviator.
The answer to your question is mostly a function of the the American aviation
fraternity 'belief and practice', (Europeans say mythology), that aero engines
should not be run 'under square' with MAP less than RPM divided by 100; but let's
recap the basics of DC-6B operation first.
Every DC-6B flight has a descent from cruise phase whose operating targets are
greatly simplified thus in my handling notes;
*****************************
Descent:
ABOVE FL170 DO NOT EXCEED Mno = 220 KIAS
DO NOT EXCEED Vno = 251 KIAS
COWL FLAPS = CLOSED
RPM = 2000 <<<<<<<<<<<<<<
REDUCE MAP in stages of 3 inches (per minute)
MINIMUM 20 INCHES MAP <<<<<<<<<<<<<<
See CARB HEAT below
*****************************
2000 RPM is correct during descent from cruise and 2000 RPM are retained for any
subsequent holding, (slowly going nowhere).
We must TIME our descent so that we achieve the holding and approach compliance
criteria for the DC-6B. The handling notes explain exactly what the DC-6B
compliance criteria are as we approach the Initial Approach Fix (IAF) and then after
the IAF;
*****************************
Terminal Holding:
Approaching IAF / Hold <<<<<<<<<
COWL FLAPS = 1 degree
2000 RPM
REDUCE < 160 KIAS
FLAP = STAGE 1
REDUCE < 150 KIAS
Crossing IAF entering Hold <<<<<<<<<<
FLAP = STAGE 2
MAINTAIN 140 KIAS
Check CHT < 232C
Plan 2100 PPH
****************************
We must achieve < 150 KIAS with FLAP 1 deployed *before* we reach the Initial
Approach Fix (IAF) of our destination airfield. As we cross that fix we deploy FLAP
2 and reduce to 140 KIAS. These targets are not just a sequence, they must be
achieved before, or delayed until, we reach a defined fix in our flight plan. The
IAF is usually the last radio beacon in the plan.
A DC-6B always cruises with more than 150 KIAS of profile drag applied. So whether
or not we need to hold at the IAF to meet our more onerous DC-6B Final Approach Fix
(FAF) compliance criteria, we need to reduce our profile drag significantly as we
descend towards the IAF. To do that we must reduce power very significantly.
Americans believe that they should not reduce to 20 MAP (to slow down) unless they
also reduce to 2000 RPM and that drove how Americans operated the R-2800 in the
DC-6B whether or not their beliefs concerning such equivalence are logical.
The supplied handling notes greatly simplify the operating practice of UAL in
particular and their handling notes not surprisingly complied with 'US practice'.
The operating manual of a 'foreign' airline might well have specified different
engine handling criteria. I addressed the same issue here about a year ago in
relation to TWA and Air France L1649A approach RPM and MAP criteria.
Whether or not we need to enter a holding pattern to achieve the DC-6B Final
Approach Fix (FAF) compliance criteria on a particular flight, we are not free to
ignore the higher and earlier IAF compliance criteria. In a DC-6B we must achieve
150 KIAS with FLAP 1 deployed *before* we cross the IAF and 140 KIAS with FLAP 2
deployed *before* (or potentially just as) we cross the FAF.
Until they commenced the approach from the FAF UAL crews always applied both low MAP
and low RPM so they could slow down to meet those sequential compliance criteria.
However neither value may be reduced so low that engine lubrication suffers or
electrical and hydraulic systems are not driven to adequate voltage / pressure.
Whether or not 'equivalence' has any real utility there are real limits and the UAL
specific criteria are within the more logical P&W specified engine limits which use
different criteria that are also used outside the U.S.
After we have achieved 140 KIAS and FLAP 2 we are allowed to exit any holding
pattern, which we may have needed to employ to achieve those FAF compliance
criteria, and only then begin an approach.
The RPM and MAP UAL employed to slow rapidly to 140 KIAS with less than FLAP 2
applied are much lower than are needed to later sustain 140 KIAS with FLAP 2
applied. So after we achieve the DC-6B FAF compliance criteria we must increase
power, and Americans believe they must increase MAP at least 'equally to RPM' so the
(UAL specific) operating criteria become 2400 RPM and not less than 24 MAP after the
FAF.
****************************
Approach and Circuit:
Cross FAF = 140 KIAS & FLAP 2 deployed <<<<<<<<<
COWL FLAPS = 2 degrees
2400 RPM <<<<<<<<<<<<<<<<<<<<<<<
MAP => 24 inches <<<<<<<<<<<<<<<<<<<<<<<
etcetera
****************************
During the approach from the FAF our IAS targets reduce much further. High RPM must
be applied before we do so, mostly to ensure adequate screw traction efficiency at
ever lower IAS, and partly so that the engines will spool up rapidly to even higher
RPM for a go around if required.
<<Also, how much lower is V1 than Vr?>>
V1 has no meaning at all inside MSFS and no agreed meaning in the real world.
en.wikipedia.org/wiki/V_speeds#V1_definitions
However it is defined locally in the jurisdiction you are operating the DC-6B in
today, inside MSFS there is no way to calculate it and graph it for all the
necessary criteria of any varying and local real world definition. The only option
you have is to evaluate your own skill to stop the aeroplane under different
conditions of altitude and weather on different runway types of different surface
friction and create tables or graphs relating to your own skill.
Remember you must interrogate the bgl code every time you attempt a take off, before
using any tables you create, because the friction data is not stored in a bitmap.
You may be lining up on a gravel (bitmap) runway which has been encoded by an 'AFCAD
author' to have tarmac friction. Any data from real world documents is useless
partly because MSFS and real runway friction do not match, and because the real
world runway slope is absent in MSFS. My advice is forget V1 altogether inside
MSFS. Whatever V1 criteria you 'graph' they won't work most of the time inside MSFS,
which is why I never supply them.
Even the belief that FS9 can replicate V2 criteria is very optimistic and my DC-6B
FD won't comply across all relevant altitude densities. It's simply no good just
pretending MSFS can do all sorts of things that have always prevented it from
achieving real world aircrew simulator training authorisation.
FSAviator.