Comet Power for Approach and Landing

[walterleo]

Hi friends:

Some points for further development:

Davids manual proposes for Landing:

Once 20 degrees flaps are selected, adjust engine power to between 6,500 and 6,700 RPM, depending on your expected landing speed (VAT roughly between 115 kts to 125 kts). You can keep the same engine power all the way down, using the flaps to lower your speed. As a rough guide flaps 20 dig = 175 kts, 30 deg = 150 kts, 40 deg = 140 kts, 60 deg = 130 kts, 80 deg = 120 kts.

For me with a Comet IVC at 104.000 pounds for 116 kts at threshold the power setting is too low even when already descending on the ILS. 6800/ 6900 RPM works better. Flaps 80 selected at 100 ft AGL.

Kind regards

Walter

[aerofoto - HJG Admin]

"For COMET IV only" (not the -IVB or IVC) .... and flying with maximum payload only as well .... I've calculated TO/climb, cruise, decent, and approach to landing performance and handling to be as quoted below and per "SECTION 5.00" of our own current forum based manual ....
tonymadgehjg.proboards.com/thread/9974/dh106-comet-manual

REMEMBER .... the FDE currently supporting the COMET's (and ONE-ELEVEN's also) is still the last version DMFS data and "NOT" that I've been re-working and which isn't quite complete.

REMEMBER ALSO .... due to their simulated weights (as currently compiled by DMFS) the performance and handling for each these COMET simulations "DOES" vary .... and as should be the case. This variance will mostly be noticeable per the power settings required in order to maintain a specific performance.

What we offer later .... FDE-wise .... will/should somewhat further improve performances .... including other aspects of performance not yet commented by Walter

In the meantime .... on final approach, with a full payload but not more than 20% total fuel remaining, and subject to the influences/drag of both flap (per increments) and landing gear extension also, I've recorded that throughout the approach to landing power will need to be varied from RPM 6400 (at FLAP 20) to RPM 7000 (at FLAP 80/FULL FLAPS) in order to acquire a VAT airspeed of 117/118 KTS. Power settings "are not" constant and do need to be manipulated/adjusted (increased/decreased slightly .... as required) throughout the approach to landing.

My experience and observations are mostly in line/agree with Walter's .... except I find myself using slightly more power during the last stages/s of the approach to landing.

5.00: "RECOMMENDED MGW LOADING/TO/CLIMB/CRUISE/DESCENT/APPROACH TO LANDING PROCEDURES".

DH106 COMET IV

4X RR AVON Mk 524 turbo-jet engines rated at 10,500 lbs thrust each.

MTOW 152,000 LBS

FUEL & PAYLOAD ADJUSTMENT (for MGW departure) ....

Default Overload = 346 LBS

LEFT = 100 %
CENTER = 97.8 %
RIGHT = 100 %

No payload adjustment .... results in 16 LBS overload

PANEL = "DMFS COMET"

TRIM = 4 units
SLAT/FLAP SETTING = 20* (1 notches)
MAX T/O THRUST = RPM 100 %
V1 = 117
VR = 127
V2 = 139
VAT = 138
INITIAL ROC = 2,000 FPM
FLAPS RETRACT = 220 KTS .... increase ROC to 2,500 FPM
TARGET AIRSPEED BELOW 10,000 FT = 250 KTS.

Maintain 2,000 FPM ROC after Gear and Flaps retraction (by 3,000 FT) .... reduce engine thrust to RPM 7,500 then assume the following ROC climb and airspeed/power adjustment schedule .....

- 10,000 FT reduce ROC to 2,000 FPM @ RPM 7,450
- 15,000 FT reduce ROC to 1,800 FPM @ RPM 7,450
- 20,000 FT reduce ROC to 1,500 FPM @ RPM 7,450
- 22,000 FT reduce ROC to 1,200 FPM @ RPM 7,450
- 24,000 FT reduce ROC to 1,000 FPM @ RPM 7,400
- 26,000 FT reduce ROC to 800 FPM @ RPM 7,350
- 28,000 FT reduce ROC to 500 FPM @ RPM 7,250
- 30,000 FT reduce ROC to 200 FPM @ RPM 7,200
- 31,000 ALT CAPTURE @ RPM/ 7,150

FL310 MACH 0.79 CRUISE PERFORMANCE ....

IAS = 300
GS = 465
TAS = 492 (300 X 1.64 = 492)
MACH = 0.79
RPM = 7,150
F/F = 1,075 KG per engine (4,300 KG total)
AI = +1*


5.01: "RECOMMENDED MAX PAYLOAD DESCENT & APPROACH TO LANDING PROCEDURES".


DH106 COMET IV COMET IV

Descending from FL310 ....

- 110 DME from destination airport .... reduce airspeed to 290 KTS (RPM 7,000) .... maintain level flight to aid airspeed reduction to less than 300 KTS prior to commencing descent.

- 100 DME from destination airport .... commence 2,000 FPM ROD (RPM 6,500).

- 17,500 FT .... adjust QNH 2991/1012 (RPM 6,450).

- 10,000 FT .... reduce ROD to 1,000 FMP .... and reduce airspeed to 250 KTS (RPM 6,400).

- "DO NOT" commence approach to landing with in excess of 20% total fuel remaining.

- Commencing the approach to landing from 18.5 DME is most advantageous for these recommended approach to landing procedures.

- Downwind legue = 250 KTS reducing to 220 KTS (RPM 6,500).

- Base Legue = 220 KTS reducing to 200 KTS (RPM 6,350).

- Engage Auto-approach (select AP "BEAM" mode).

- FINAL APPROACH = 200 KTS reducing to 180 KTS (RPM 6,300).

- Yaw Damper = OFF".

- Select FLAPS 20 = 200 KTS.

- ILS/GS intercept = 180 KTS

- Select gear down = 180 KTS

- Select FLAPS 30 = 175 KTS.

- Reduce airspeed toward 118/117 KTS.

- Select FLAPS 40 = 155 KTS.

- Select FLAPS 60 = 145 KTS.

- Select FLAPS 80 = 135 KTS.

- Approach to landing airspeed (full flaps) = 118/117 KTS (VAT).

- Touchdown airspeed = 108/107 KTS.

- Manually deploy Wing Spoilers.

- Engage reverse thrust at idle RPM (reverse is available on engines #1 and #4 only).

- 80-60 KTS = cancel reverse thrust .... retract wing Spoilers and Flaps.

- Taxi to gate/stand.

Mark C
AKL/NZ