Angle of Attack when landing.

[Nigel H-J]

Not sure where to put this question so chose CNB as this relates to different a/c. Also there must be summat wrong with me as flown FS for many, many years and it has taken me up til now to become really aware of this phenomenon!!

The angle of attack when flying the Trident on approach to land is a slight nose up attitude which Peter once described as being normal so no problem there however, my question is does this relate to all a/c such as business jets and pax aircraft?

The reason for this question is that some of the approaches I fly the nose from external view when replaying the landing on say the 737, Twin Otter, Just Flight Bis Jet and Piper Carenado BAC1-11 appears high, I have fiddled around with the C of G and found that by moving it forward the angle of attack appears to be much better in the sense of either slightly nose down or near enough level which means the nose is not raised overly high during the flare.

I know when I used to fly light a/c the angle of attack on approach was of a nose down attitude but just wonder what it should be for passenger and business jets.

OK, now to confuse me even more I'll just wait until someone comes along and tells me it all depends on the type of a/c, loading, weight etc.

Unfortunately I won't be back until Saturday so no hurry.

Many thanks in advance.

Nigel.

[Garry Russell]

Some aircraft needed to be landed a flat as possible like the Viscount. It had micro switches on the main gear which put the props into ground fine which is like slamming on the brakes. The trick was as soon as the mains touched you got the nose on the ground. Too high an angle could mean the engine braking happening with the nose gear in the air causing it to slam down and in some cases, collapse.

Other types on short field landings hold the nose well up to aid braking

Probably a set of figures for the particular type

With the One-Eleven it was a greaser on a long runway but on short fields it was the normal to stick it down almost flat and very firm to get all the wheels and weight on the runway along with reverse ASAP

A few types do this the reason for the 'Hard landings' seen on YT which is nothing more than a firm touchdown due to shorter runways or a need to clear the runway at the earliest turn off, which is a bit like doing a short field landing on a long runway which is busy.

[Dev One]

I think the Trident is the only aircraft on your list that has 'true' slats, which I think will change the aircraft attitude in the opposite direction to flaps, (not sure about kreuger leading edge flaps) which will normally give a pitch down attitude, but if the aircraft is designed properly, once on a 3° glide slope will keep the aircraft datum parallel with the ground, so allowing one to round out with a bit of pitch up, although as Garry says a 3 pointer carrier type 'crash' landing (much hated by Ozzy driven Ryan Air passengers!) gets it able to stop quicker!
Keith

[MALTBY D]

Hi Nigel

The 'normal' attitude is only going to be seen if you fly a normal approach at the correct airspeed for the weight.

Flying below ideal speed will cause the nose to be higher than normal. Above ideal speed the nose will be lower than normal.

Generally (unless it's a weird one), if you're very nose up on the glide slope you're going too slow.
Weird would be something like a TriStar, where very nose up is normal. Or a Concorde which should have it's nose down.

DM

[Chris Trott]

There are three factors which affect the deck angle / pitch during approach. On all the airplanes, the AoA is actually nearly identical as your 'ideal' approach speed is 1.3 Vso (or 1.3x the stall speed), but because of these factors, the deck angle can be quite different.

1) Wing Sweep. The Trident & Citation X have wing sweeps of 35*. The 737 and BAC 1-11 is 20*, and the DHC-6 is 0*. The higher the wing sweep, the higher the pitch when a given AoA is reached due to the higher apparent chord of the wing.

2) Lift Devices. The Trident and Citation X use both leading edge slats and trailing edge flaps. The 737 uses a combination of leading edge flaps and slats and trailing edge flaps. The Twin Otter and BAC 1-11 use only trailing edge flaps. Trailing edge flaps increase the apparent AoA, leading edge flaps/slats decrease the apparent AoA. Thus, on an aircraft that has both, the increase in apparent AoA is less, requiring more pitch to achieve a given AoA versus an airplane without leading edge devices. Thus, the DHC-6 and BAC 1-11 would have lower pitch angles on approach than the other 3.

3) Wing Angle of Incidence. This is the difference in the angle of the wing versus the fuselage. On the Trident, 737, and Citation, it's ~1*. On the BAC 1-11 and DHC-6, it's 3*. The higher AoI further reduces the increase in pitch required for a given AoA. Slower cruising aircraft (like the DHC-6 and most propliners) had an increased AoI not to reduce deck angle on approach, but to keep the plane nearly level during cruise, but it had a resulting reduction in pitch during approach as well.

It's interesting to note that the A300/310 also have an angle of incidence of 3* which is shown in pictures of those aircraft on approach being much "flatter" than the similarly sized 767.

(edit: Fixed the Vso factor)

[Dev One]

Talking of incidence....I presume the quoted values are taken at the root chord or on the centreline of the aircraft. Between all those aircraft quoted above there must be big differences in the airfoil section & the amount of twist given out towards the tips. It always amazes me on the difference in profile of the wing near the root - it looks as if its upside down, but I suppose its designed to reduce wing/fuse interference in the cruise.
The bendy 787, must be very cleverly designed structurally so as not to change this twist as the wing flexes.
Keith

[adysmith]

I have to say I have a few issues with some of the comments above.

Conventional wisdom is 1.3 * Vso to give an adequate margin above stall speed.
Vso (Stall speed with gear extended and land flap) is dependant on weight (lift is proportional to speed squared) hence approach/touchdown speed is related to total aircraft weight.

That round thing towards the front of the aeroplane with tyre(s) on it is NOT part of the LANDING gear.
LAND on that and you are asking for trouble.
Tricycle gear aircraft should be landed on the main gear.

I see far too many aircraft (light aircraft particularly) which get landed on pretty much all three wheels, indicating the aircraft is way too fast.

I should add my qualifications for stating the above.
Commercial Pilot's licence, Flying instructor and examiner. I teach people to become flying instructors.
I have been assessed by some of the best in the UK CAA.

[Chris Trott]

I have to say I have a few issues with some of the comments above.

Other than my error in the Vso multiplier (thank you for correcting me), what issues do you have? No one was advocating landing on the nose wheel. "As flat as possible" doesn't mean 3-point. It just means you don't want more than a few degrees of pitch to avoid slamming the nose down when the props went into BETA on touchdown. This is true of many turboprop airplanes as an excessive pitch (above 5 degrees on landing) can result in much more damage to the landing gear and the airplane than accidentally touching the nose at the same time as the mains. It also doesn't always mean you're too fast. Of the airplanes mentioned, only 2 (the 737 and Citation X) are modern jet aircraft with modern supercritical airfoils. The Trident, Viscount, and BAC 1-11 were designed in a much different time with vastly different theories on how a plane should be flown. Take the B377 for example, it too had a high angle of incidence on the wing and it wasn't unusual for the nose to touch first, even with some of the most experienced pilots of the time at the helm. It was the nature of the beast.

Talking of incidence....I presume the quoted values are taken at the root chord or on the centreline of the aircraft.

The AoI values I quoted are as published by several sources via a Google Search, so I'm not sure where it was taken from, but as the values all seem to be fairly consistent, I'm guessing that it's an average for the entire wing. However, I would also note that with the exception of the Citaiton X, all the wings were designed prior to 1970, so the utilization of wing twist wasn't as predominant anyway.

[dfarrow]

Gents , just a reminder , the angle of attack is the angle the airflow makes to the wing as the a/c flies . Most civil a/c do not have an angle of attack indicator ... Dash 7 is the only one I know of . Military a/c often do , especially Naval carrier a/c .
Any a/c with an artificial horizon will show its Pitch Attitude to the pilot . Generally the more flap that is used [ at the correct speed ] the more nose down the a/c ... from Cherokees to Boeings . A 737 landing with Flap 40 is about 1/2 - 1 degree more nose down than with Flap 30 [ variable flap landings are allowed ]. PA 28 Flap 0 is more nose up than Flap 40 !.....
Slats / Droops when deployed generally pitch the a/c nose up ... Back in the day watching British Midland DC9s ... Model 30s had slats and would approach in a nose up attitude , and thus easily land on mainwheels first . Earlier models like the -10 , -15 did not have slats , and would approach with the nose slightly down , if fast or the flare incomplete , a WheelBarrow would be seen , with the a/c landing on its nosewheel first ! Very directionally unstable I imagine .
The BAC 11 never had slats or droops , so its approach attitude is flatter than the Trident , drooped or slatted .
Tristar was a little different in normal operation , a bit like a glider in that you came down the approach with the speedbrakes partly out .... if you got low and thus pulled the stick back the a/c pitch attitude did not change ! The speedbrakes retracted and the a/c floated back up to the glideslope .Converesly if high on the glideslope , stick pushed forward , pitch angle did not change ... speedbrakes opened further and a/c sank back towards the gideslope ...... Got used to it quite quickly . 'Tho converting back to a Boeing was a b****r , especially with the pitch and power couple ..... get slow put on power , a/c pitches up ...... get fast , reduce power a/c pitches down ..... you can imagine a light 744 with 4 x 60000lbs of thrust ! All due to the engines being underslung and thus one of the reasons why lightly loaded a/c are more difficult to handle than an heavy a/c .

Brgds dave f.

[Chris Trott]

Gents , just a reminder , the angle of attack is the angle the airflow makes to the wing as the a/c flies . Most civil a/c do not have an angle of attack indicator ... Dash 7 is the only one I know of . Military a/c often do , especially Naval carrier a/c .

Thankfully, this isn't true anymore. More and more of them have an AoA display either as part of the PFD or available on a sub screen selection on one of the MFDs. After Air France 447 once again showed how important having an AoA display was in the cockpit, Airbus finally conceeded and sent software updates to enable AoA display on their cockpit systems, something that other manufacturers had available for almost 15 years prior. Both Boeing and McDonnell Douglas began putting AoA on their displays back with the MD-80 and 737-300, while Bombardier and Embraer have always had it as an option. Many biz jets have AoA displays as well, especially those using Honeywell or Garmin products as they have been at the forefront of exposing that information on their displays.