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Old 10th Jul 2017, 15:14
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Centaurus
 
Join Date: Jun 2000
Location: Australia
Posts: 3,847
Short Field Landing Airspeed Conundrum

The Short field Landing Conundrum.

The July 2017 revision of the CASA Flight Examiners Handbook requires the applicant demonstrate a short field landing for the following flight tests: RPL A, PPL A, CPL A, SEA Class.

Early post war standard operating procedures at flying schools included short field approach and landings that were based upon normal landing speeds for the type minus ten knots as an approximate figure. For example the Pilots Notes for Tiger Moth aircraft (RAAF Publication No. 416 dated February 1944) showed 58 knots for glide and engine assisted approaches. For Precautionary Approach and Landing the correct speed was 48 knots which was assumed at 250 feet. You were really hanging on the prop

Pilot’s Notes Chipmunk T10 (A.P. 4308A-P.N) recommended over the fence at 55-60 knots. The precautionary approach crossed the fence at 50 knots. Note the term Precautionary Approach is nowadays called Short Field landing.

Pilot’s Notes for Sea Fury (A.P. 4018A-P.N) displayed final approach speed at max landing weight as 125 knots and for a carrier deck landing the recommended speed is 90-92 knots with the caveat that it is necessary to pull the control column well back to effect a three-point touchdown. In current parlance that is around 1.1VS in the landing configuration.

In contrast the Cessna 172N POH recommends a normal airspeed on approach with flaps as desired (ie flaps up to Flaps 40) as between 55-65 knots. Published short field full flap landing approach is 59 knots until flare.

A major difference between a true short field or precautionary approach and landing and a normal landing (see RAAF Pilots Notes above) is with the precautionary landing there is more drag on approach, a lower approach speed and thus a shorter float and ground roll.

RAAF Pilot’s Notes do not include landing distance information whereas the Cessna POH includes a table based upon 59 knots at 50 feet. The airspeed is based on approximately 1.3Vs in the landing configuration. The landing distance and associated airspeed at 50 feet is a characteristic of American aircraft POH.

Having observed many flying school pre-flight briefings on so called “short landings” versus normal landings, the majority of instructors talk about lack of float in short field landings. That was correct in the old days where speeds for a short field or precautionary landing were roughly 10 knots slower than normal. Nowadays that doesn’t happen anymore, simply because current landing speeds in typical light aircraft POH are based upon 1.3VS. After all, for a true short field landing it is desirable to touch down with practically no float to enable a shorter landing roll. In a tricycle landing gear type which means the majority of today’s aircraft, it is unwise to force the aircraft on the landing surface while it still has flying speed where the danger is damaging the nose-wheel if it hits first. So a float is necessary to dissipate over the fence speed to actual safe touch down speed which should be at the point of stall.

Large transport aircraft have published approach speeds of approximately 1.3Vs in the landing configuration. These are not called short field landings. They are normal landings. Why then is the same principle not applied to the everyday landing in a typical Cessna, Piper or Beech light single that use 1.3Vs ie normal landing as against the use of the term “short field.

It could be argued it is reckless flying to approach deliberately below the POH published 1.3Vs figure. In days of yore and because of the exigencies of the Service, military aircraft could often be required to land in fields of unknown dimensions and unknown surface. A slower speed than normal would be therefore needed to ensure minimum ground roll. In fact, it was not long ago that CASA changed the title of short field landing to minimum ground roll landing. Now the Flight Examiners Handbook has discarded minimum ground roll and for some reason has gone back to short field. Some would argue this is a retrograde step.

Summary: Instructor training schools should ensure briefings on short field landings delete reference to alleged minimum float characteristics when approaching at 1.3Vs. The accent on short field landings should be on accurate touch down point and associated minimum ground roll. The approach speed for so called short field landing and normal landing is the same at 1.3Vs. There is no landing airspeed differentiation with larger aircraft between a limiting runway length and one with excess landing distance available. However in large aircraft the ground roll distance is highly dependent on stopping aids such as ground and flight spoilers, reverse thrust, and anti-skid devices.

A recent US Flyer magazine reader’s contribution about how to fly a short field landing will probably raise a few eyebrows among PPRuNe readers. Quote:
“Since the approach speed is likely only a few knots above stall, it is critical to fly accurately. MacNichol challenges her students to stay within 0 knots below and 1 knot above the target speed to enable the shortest landing possible while minimizing the risks.” Unquote.

And guess what? That’s exactly what we did on Tiger Moths, Wirraways and even venerable Austers in days of yore..
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