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AOA indicators in general aviation a/c

I have done a marathon session merging half a dozen “AOA” threads

The Q which has often been asked, but rarely has anyone attempted to answer it, is the one in Noe’s post above i.e. how do you actually use the device.

Administrator
Shoreham EGKA, United Kingdom

From my POH:

Norman
United Kingdom

Peter wrote:

The Q which has often been asked, but rarely has anyone attempted to answer it, is the one in Noe’s post above i.e. how do you actually use the device.

Ok fair point which I didnt address. I use mine for every landing and most climbs.

Since the winglets were fitted the plane’s wings “generate more lift”. As a result, the POH speed calculate by the FMS for landing is too high by about 5 knots. My airspeed tape has a green doughnut for Vref (regardless of configuration) and an indexer on the glareshield. On final I will bring the speed back to Vref using the airspeed tape and when i am short final I can see with the indexer if i am fast or slow. The indexer has coloured lights – a green circle for on speed and a red chevron for slow and an amber chevron for fast.

It is also (assuming the sensor is correctly calibrated) always right ie doesn’t depend on weight or configuration.

In the climb I can also now climb slower as the plane is faster to accelerate at the top so i can if I need best rate, fly the plane in pitch mode keeping a constant AoA of .35 on the dial. Pre winglets this would have you too slow at the top of climb and it would be hard to accelerate. Now it will easily accelerate so you can maintain best rate all the way to the top. It naturally requires vigilance as your speed gets close to 1.3x stall (the green doughnut) near the ceiling.

So those are the two ways I use mine.

EGTK Oxford

@JasonC wrote:

In the climb I can also now climb slower as the plane is faster to accelerate at the top so i can if I need best rate, fly the plane in pitch mode keeping a constant AoA of .35 on the dial.

Jason, while keeping AoA at .35, can you tell us how the pitch and the indicated speed move, during the climb up to the ceiling ?

Thanks Jason. I had planned to go flying and take some better pictures (and have a better looked at it) but the weather wasn’t good yesterday.

I googled different terms (added “using”) and found some better documents, e.g. here

Numbers seem to coincide with Jason’s post, pointer a 3 oclock (0.6) for approach. The advantage is that it’s intependent of weight / flaps configuration.

[ local copy ]

PetitCessnaVoyageur wrote:

Jason, while keeping AoA at .35, can you tell us how the pitch and the indicated speed move, during the climb up to the ceiling ?

Mine is probably not terribly relevant to lighter GA. But let’s say starting at 10,000 feet, would be a 20 degree nose up (it will go up fast like that) coming down to 5 degrees. My IAS will gradually drop from 220 to say 145 if I flew it all the way to the ceiling.

Last Edited by JasonC at 30 Jul 09:54
EGTK Oxford

As I posted here a long time ago, I looked at installing one of these to hopefully make it easier to climb to the operating ceiling, but none of the manufacturers were willing to discuss high altitude operation or indeed whether it works usefully at all.

The calibration is done at low levels and there seems to be no barometric input. The AoA is derived indirectly so I wonder whether this works.

The AoA sensor on a jet like Jason’s is normally a rotating vane which reads the airflow angle directly.

Administrator
Shoreham EGKA, United Kingdom

Let’s look at these AOA sensors from a different angle.

The TB20 TKS system has an unheated stall warner. The certification route for replacing this with a heated one is likely to be complex. I wonder if a heated AOA sensor would work well enough? Taking the FAA (I am N-reg) concessions for AOA sensor installation, and assuming the heater wiring is a Minor Alteration (it should be), this ought to work.

One issue I see is that, as per my various previous posts, I was never able to establish whether any of these products actually work at high altitude. The AOA sensors on jets use a physical rotating vane (heated) which will obviously work, but all the “GA” sensors measure AOA indirectly by sensing the pressure difference between two holes. The manufacturers I contacted would not discuss this topic.

Has anyone here installed an AOA sensor?

Administrator
Shoreham EGKA, United Kingdom

Peter wrote:

Has anyone here installed an AOA sensor?

I have the Aspen one and it works well at high or low altitude. However, it indicates from an algorythm based on static&dynamic pressure (IAS) plus acceleration as measured in its AHRS and GS from the GPS , so it is rather theoretical (but so is attitude, at least partially, on the Aspen). It is probably just a derivation from the algorythm it uses for attitude. It still needs your pitot and static ports to be working, I think it might also work on an iced up wing but have not tested it.

The ones measuring pressure differential should work as well, but I would not worry so much about altitude as about different IAS (ie very wide weight ranges and accelerated stalls, on which the Aspen seems to do fine).

As you say the vane ones are the most accurate as they indicate either the relative wind angle (high-end version) or the position of the stagnation point on the wing (which is also a measure of the same). Were it not for the TKS panels, perhaps it would be possible for you to install a secondary advisory heated AOA vane on your leading edge as a minor mod, as long as you do not eliminate the OEM one.

Antonio
LESB, Spain
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