Attitude Indicator/Artificial Horizon

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ratty
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Attitude Indicator/Artificial Horizon

Post by ratty »

I've got questions about the attitude indicator. It erects when you turn on the battery switch, and topples if you turn off the battery and generator in flight, so I guess it's electric rather than vacuum driven. In that case, what's the suction for, just the HSI?
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Skycat
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Re: Attitude Indicator/Artificial Horizon

Post by Skycat »

It should be part of suction system.

AAF Manual 51-127-5, Pilot Training Manual For The P-51 Mustang (15 Aug 45), states: "Vacuum System Instruments. These are operated by a vacuum pump driven off the engine and include:
-- the flight indicator,
-- the bank-and-turn indicator,
-- the directional gyro, and
-- the suction gage.
The suction gage shows whether the vacuum pump is providing proper vacuum for the system. If this gage reads more than 4.25 or less than 3.75, you know that the vacuum instruments are not functioning properly and are not giving reliable readings. Normal suction reading is 4.00."

The AAF Pilot's Information File dated 1944 states: "The Suction System. Gyro instruments are operated normally by suction, supplied by a vacuum pump driven by the airplane engine. Actually each gyro instrument works on the same principle as a turbo. A gate is provided to indicate amount of suction. On modern single-engine airplanes there is no alternate source of suction." The Suction System section of the PIF continues with this description of the Gyro-Horizon Indicator: "This instrument indicates realistically the attitude of the airplane. After starting engines allow at least 5 minutes at sufficient rpm before takeoff for the instrument to obtain proper speed. Be sure before takeoff the horizon bar has settled into its proper 3-point position. This may be speeded up by caging and uncaging the instrument after engines are started. This is the only time the instrument should be caged while on the ground. Leave it uncaged at all times except in maneuvers which exceed its upset limits..."

For comparison, the DCS World P-51D manual states: "Vacuum System Instruments Vacuum system instruments are operated by a vacuum pump driven by the engine and include the Flight Indicator, Bank and Turn Indicator, Directional Gyro, and Suction Gauge. Flight Indicator The AN5736 Flight Indicator (Gyro Horizon Indicator) indicates a miniature plane and a gyro-actuated horizon bar. This instrument is used during instrument flying to indicate the longitudinal and lateral attitude of the aircraft. The horizon bar will indicate pitch up to 60° and bank up to 100°. The top needle of the instrument indicates the angle of bank on the bank scale, graduated from 0° to 90° and scaled to 30°. The cage knob is used to cage the instrument. To operate the cage knob, left-click on it to pull the knob out and roll the mouse wheel to turn it clockwise to the caged position. To uncage the instrument, roll the mouse wheel over the knob to turn it counter-clockwise. The horizon knob is used to adjust the horizon level. To operate the horizon knob, place the mouse over the knob and roll the mouse wheel to set the horizon higher or lower."
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Skycat
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Re: Attitude Indicator/Artificial Horizon

Post by Skycat »

I just tested this in the Military version and the Gyro Horizon Indicator/Artificial Horizon rises and levels only when the engine is running. Simply switching on the battery if the engine is not operating does not affect the indicator. Shutting off the engine causes the horizon bar to drop.

I do not have the civilian P-51.
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ratty
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Re: Attitude Indicator/Artificial Horizon

Post by ratty »

All the planes I flew in real life had artificial horizons that were vacuum driven, and turn coordinators that were electrically driven, the rationale being that you could lose one system and still fly on instruments with the other. Apparently there are such things as electrically driven AIs, so I assume that's what's in the Civ.
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Tomas Linnet
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Re: Attitude Indicator/Artificial Horizon

Post by Tomas Linnet »

I believe this was confirmed by :a2a: not to long ago. The AI is electric in the P-51 Civilian
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Tomas

Sim: FSX SE
Accu-Sim aircraft in my hangar:
C172, C182, P51 Civ, P51 Mil, B17, Spitfire, P47, B377 COTS,
J3 Cub, T6, Connie, P-40, V35B
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ratty
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Re: Attitude Indicator/Artificial Horizon

Post by ratty »

Tomas Linnet wrote: 12 Mar 2020, 14:03 I believe this was confirmed by :a2a: not to long ago. The AI is electric in the P-51 Civilian
Oh. That was easy. Thanks!
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Tomas Linnet
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Re: Attitude Indicator/Artificial Horizon

Post by Tomas Linnet »

Kind Regards
Tomas

Sim: FSX SE
Accu-Sim aircraft in my hangar:
C172, C182, P51 Civ, P51 Mil, B17, Spitfire, P47, B377 COTS,
J3 Cub, T6, Connie, P-40, V35B
A2A Accu-Sim Avro Lancaster Loading:............0.000003% complete, please wait.

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