Centaurus
11th May 2012, 09:15
I am not sure whether this question should be posed on the Military Aircrew Forum or Tech Log. But here goes anyway..
Pilots flying in the era of Canberra bombers, Sabres, Mirages and a host of these post war jet types were taught to use the bleeding airspeed approach technique.
For example, RAF Pilot's Notes for Vampire F1 A.P 4099A published by the Air Ministry in January 1947 stated: "Approach and Landing" At a weight of 7,808 lb (full ammunition, half fuel remaining) the recommended final* approach speeds in knots IAS are:
Flaps down.....87 knots.
Flaps up.........104-108 knots.
* This is the speed at which the boundary is crossed.
Note -Except in the case of the "flapless" landing, the initial straight approach should be made at a speed some 18-22 knots above these figures.
The Lincoln bomber engine assisted approach and landing speed was 95 Knots at maximum landing weight and according its Pilot's Notes the initial straight approach should be made at a speed some 10-15 knots above that figure.
The Bristol Beaufighter recommended final approach speed was 100 knots with the recommendation that the initial straight approach should be at 15 knots above that figure.
In each case the recommended approach technique consisted of bleeding off the airspeed on final to be at the correct speed over the fence.
On the other hand manufacturer's manuals for today's jet transports recommend a fixed airspeed approach after landing flap is selected, with additives for meteorological conditions.
I am sure there is a good technical reason for the fixed airspeed approach in jet transports versus a bleeding airspeed technique used in years past. Stable approach criteria calls for approach parameters to be stabilised by a certain minimum height, while the bleeding airspeed technique does not address this. Some jet transport manuals do recommend a bleeding off of additives approaching touch down.
One example of this technique is found in the Boeing 737 FCOM under the heading of Adverse Weather Approach and Landing. If ice formations are observed on the airplane surfaces, (wings, windshield wipers, window frames etc) an additional 10 knots is added to Vref. However, a note states "To prevent increased landing distance due to high airspeed, bleed off airspeed in excess of Vref + 5 knots= gust correction when below 200 ft."
So clearly from the above Boeing statement there is no handling problem with a bleeding airspeed technique - although I would have thought that 200 ft agl is a bit late to start bleeding away airspeed.
Flying a fixed airspeed approach with landing flap down requires in general a fixed thrust setting. It could be argued that a bleeding airspeed approach makes less noise and thus less fuel consumption.
Informed comments appreciated.
Pilots flying in the era of Canberra bombers, Sabres, Mirages and a host of these post war jet types were taught to use the bleeding airspeed approach technique.
For example, RAF Pilot's Notes for Vampire F1 A.P 4099A published by the Air Ministry in January 1947 stated: "Approach and Landing" At a weight of 7,808 lb (full ammunition, half fuel remaining) the recommended final* approach speeds in knots IAS are:
Flaps down.....87 knots.
Flaps up.........104-108 knots.
* This is the speed at which the boundary is crossed.
Note -Except in the case of the "flapless" landing, the initial straight approach should be made at a speed some 18-22 knots above these figures.
The Lincoln bomber engine assisted approach and landing speed was 95 Knots at maximum landing weight and according its Pilot's Notes the initial straight approach should be made at a speed some 10-15 knots above that figure.
The Bristol Beaufighter recommended final approach speed was 100 knots with the recommendation that the initial straight approach should be at 15 knots above that figure.
In each case the recommended approach technique consisted of bleeding off the airspeed on final to be at the correct speed over the fence.
On the other hand manufacturer's manuals for today's jet transports recommend a fixed airspeed approach after landing flap is selected, with additives for meteorological conditions.
I am sure there is a good technical reason for the fixed airspeed approach in jet transports versus a bleeding airspeed technique used in years past. Stable approach criteria calls for approach parameters to be stabilised by a certain minimum height, while the bleeding airspeed technique does not address this. Some jet transport manuals do recommend a bleeding off of additives approaching touch down.
One example of this technique is found in the Boeing 737 FCOM under the heading of Adverse Weather Approach and Landing. If ice formations are observed on the airplane surfaces, (wings, windshield wipers, window frames etc) an additional 10 knots is added to Vref. However, a note states "To prevent increased landing distance due to high airspeed, bleed off airspeed in excess of Vref + 5 knots= gust correction when below 200 ft."
So clearly from the above Boeing statement there is no handling problem with a bleeding airspeed technique - although I would have thought that 200 ft agl is a bit late to start bleeding away airspeed.
Flying a fixed airspeed approach with landing flap down requires in general a fixed thrust setting. It could be argued that a bleeding airspeed approach makes less noise and thus less fuel consumption.
Informed comments appreciated.