already reported Mosquito's artificial horizon fails on shutdown

[ssn]

Artifical horizon drifts on shutdown and newer corrects itself neither stationary on the ground with engine running nor in a level flight.

mosquito-gyro-broken-on-shutdown.trk

[NineLine]

On 11/9/2024 at 12:05 PM, ssn said:

Artifical horizon drifts on shutdown and newer corrects itself neither stationary on the ground with engine running nor in a level flight.

mosquito-gyro-broken-on-shutdown.trk 8.46 MB · 1 download

Hi, thanks for the report, it is already reported that there are errors in the AH where there shouldn't be, it's not a Mossie issue but more of an issue in many modules. I will bump it internally but it is reported. thanks!

[Q3ark]

I hope this can be addressed quickly, I did a cold start flight on the Normandy map from Tangmere, south to Cherbourg, east to Caen and Le Havre and back to Tangmere, at no point in the entire flight did the artificial horizon show the correct attitude. 

[Bozon]

On 4/17/2025 at 2:44 PM, Q3ark said:

 addressed quickly

[grafspee]

I haven't seen any news from ww2 team for a long time. Does anyone know are they alive ?

[Q3ark]

1 hour ago, grafspee said:

I haven't seen any news from ww2 team for a long time. Does anyone know are they alive ?

Can someone throw some bread and water into their cell and ask them to do some work?

Edited April 19 by Q3ark

[-0303-]

On 11/9/2024 at 9:05 PM, ssn said:

Artifical horizon drifts on shutdown and newer corrects itself neither stationary on the ground with engine running nor in a level flight.

mosquito-gyro-broken-on-shutdown.trk 8.46 MB · 2 downloads

This bug is documented for at least 12 years (by June 1 2025). It affects every "old" plane up to and including the F-5 without exception AFAIK. I personally made tracks for Spitfire, Bf 109, P-51 & F-86 back in 2021.

Drift on shutdown might be a real thing (I dunno), though it generally shouldn't because the instruments are deliberately made slightly bottom heavy. The real bug is they never self correct.

Shutting engine on/off a few times is the quickest, most convenient way to get the Artificial Horizon (AH) "wrong" so one can rev up and confirm it doesn't self correct as it should. More convenient than flying around half an hour...

This is not  a minor bug. It makes the AH completely useless. It always drifts while flying. The AH is one of the "sixpack", the six basic flight instruments , not a peripheral instrument.

When they fix this (as promised ca October 2024), they must include the "tumbling". Old AH will tumble whenever pitch exceeds typically 60 degrees or roll exceeds 110 degrees. Source Pilot training film (timestamp 2:53). Reason is mechanical stops protecting the instruments. Of course the angles can vary from plane to plane but I won't be a stickler if every plane tumbles at the same angles. I'll be quiet for at least a year before start whining about the Bf 109 tumbling the same degrees as the Spitfire. (maybe it does, maybe it should tumble 10 degree different)...

There are (more modern) instruments that only tumble on pitch. I imagine once the basic tumble algorithm is in place, it'll be easy to just insert different angles following plane documentation. In many cases it's easy, Spitfire, Hurricane, Mosquito all use the same AH...

Nor does the tumbling need be physically perfect. I'm fine if it's somewhat randomized, though watching real Spitfire tumble video I get the sense the tumble mostly go maximum wrong, taking maximum time to self correct. Makes sense instrument being blocked at a full roll or a full looping at internal mechanical stops and remaining there after leveling out until self corrected.

Hmm, second thought. If rolling until just 10 degrees beyond internal mechanical stops and then aborting and rolling back again would the error be just 10 degrees? As opposed a complete roll when the error would be the stops limit (110 degrees)? Assuming it tumbles 180 when it tumbles (and my thinking is correct). If that's true, the algorithm would be "simple" making the post-tumble error "correct".

AH tumble Spitfire video. Tumbles a lot. Instrument easy to see.

AH Spitfire startup self correction video.

Another Spifire AH tumble video. First tumble at 17:01. Unfortunately a film cut at 18:05 but watching from 18:05 (AH shows 90 degrees wrong in level flight at 18:15) there's non cut film until finally self corrected at about 26:30. Tumbles at 17:01, 17:18, 17:29, 17:41 (more times I tired of counting), 27:15, 31:40, 32:40, 37:50, 38:47, 39:08, 39:40.

Notice, first and last films, the AH tumbles whenever the instrument hit the stops regardless if the Spitfire is actually close to level. The instrument only cares about it's internal position. A correct algorithm  would act like this.

Caveat, I don't think AH maintenance is a priority on veteran planes only flying VFR. Perhaps a "good" up to specs Spitfire AH self corrects faster than ~9 minutes.

Edited May 16 by -0303-