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Combined Gauge Variometer Usage


Leviathan667

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Hello,

 

I am new to the L-39C. I am learning to use the instruments and I need help in understanding how to make good use of the parts I circled in yellow and green on the variometer screenshot below?

 

Thanks

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Wishlist: Tornado ADV/IDS, Blackburn Buccaneer, Super Mystère B2, Saab J 35 Draken,

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The yellow circled aspect is a heading gyroscopic rate of change indicator. There is a difference between yaw and heading rates because the wings aren't always level. You can tell I guess by rolling 90 degrees and pulling and seeing if the needle moves or not. If it does its heading if it doesn't it's yaw.

 

In any case the markings are a sort of indirect bank indication. It doesn't actually show bank but it shows a gyroscopic rate which may be correlated with one under certain conditions. The correlation isn't perfect for example if you jam on the rudder in level flight to yaw the nose you generate a heading rate which will move the needle even if the airplane remains zero bank throughout.

 

But in coordinated flight the heading rate is indicative of a particular bank angle at a certain speed. This explains why there is a printed 350 km/h. That's where the indicated bank should equal the actual bank given a coordinated turn. If you are going faster than 350 km/h then for every bank marking you are actually at a larger bank than shown because it takes more bank at higher speed to get the same heading rate. Conversely when less than 350 actual bank is less than shown. Naturally these speeds are true airspeed.

 

You may ask why have a bank instrument when you have a perfectly good AGD-1 attitude indicator? It's a backup in case the AGD fails.

 

The green-circled item is a common inclinometer which is simply a curved glass tube with a weighted ball filled with a damping fluid. The ball will be between the two metal wire lines when the local acceleration is straight toward the floor of the airplane, i.e. a penny dropped will fall from the top center of the cabin to the bottom center of the cabin. It could be functionally replaced with a rock tied on a string. This is also a coordination instrument. Coordinated turns are turns where local acceleration is aligned with the vertical axis of the airplane. If the ball is outside of the lines the flight is not coordinated.

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Thank you for your comprehensive reply! :)

 

 

 

You may ask why have a bank instrument when you have a perfectly good AGD-1 attitude indicator? It's a backup in case the AGD fails.

 

I am not sure I am making the best possible use of the AGD but it seems to me, following your explanation that the variometer may help counteract drift due to crosswinds while AGD cannot since the variometer will show a non null rate of change for the heading?

Wishlist: Tornado ADV/IDS, Blackburn Buccaneer, Super Mystère B2, Saab J 35 Draken,

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The variometer is a barometric altitude rate component of the combined instrument. It gets confusing to call the entire three-in-one combined instrument by the name of only one of its parts. The combined instrument has three parts: variometer, turn needle, inclinometer. The variometer will only show altitude-related information.

 

As to the turn needle component it won't show anything special due to the wind. It shows heading rate of change and wind drift is unrelated. The AGD is the "attitude indicator" equivalent and shows pitch and bank gyroscopically. I guess if the airplane moves in yaw but not bank then the turn needle will deflect without the AGD showing bank but I don't know how that relates to wind. In case of AGD failure it will no longer show bank angle. The turn needle component of the triple instrument acts as a bank angle substitute because it measures heading rate and heading rate sort of equals bank angle.

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Thanks for the reply. I just tested a 55 min nav. flight from Mozdok to Maykop through two NDEs on the northern edge of the Caucasus. Wind drift pushed the plane to the left. I followed the turn and needle indicator and succesfully counteracted the drift induced by the wind.

 

On the downside of things, I had to continuously make micro-corrections on the stick, after triming the plane as precisely as I could (which only resulted in making the changes in pitch manageable with strick micro-corrections).

 

Is it how you do things? Do you know of another way?


Edited by Leviathan667

Wishlist: Tornado ADV/IDS, Blackburn Buccaneer, Super Mystère B2, Saab J 35 Draken,

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I'm not exactly sure what you mean by "NDE" (NDB?)

 

Point the nose (Heading) into the wind so that that the airplane flies on a straight ground track (Track) to the station. Aircraft heading should remain unchanged, and station position relative to aircraft heading (Called "Relative Bearing=RB") will remain unchanged.

But errors in station reception will make the station heading (RB) change, and as you get very close to the station the minute error in ground track will cause the station RB to change as well. When it moves too quickly for you to correct you can know you are about to pass over the station.

 

Instead of reacting to wind drift, adjust to counteract it before it has the chance to blow you off course. In modern aircraft with TVV/FPV this is easy to see, as the miniature airplane will drift left or right of the center of the HUD as the aircraft track drifts in that direction due to the wind.


Edited by randomTOTEN
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Thanks for the reply. I just tested a 55 min nav. flight from Mozdok to Maykop through two NDEs on the northern edge of the Caucasus. Wind drift pushed the plane to the left. I followed the turn and needle indicator and succesfully counteracted the drift induced by the wind.

 

On the downside of things, I had to continuously make micro-corrections on the stick, after triming the plane as precisely as I could (which only resulted in making the changes in pitch manageable with strick micro-corrections).

 

Is it how you do things? Do you know of another way?

 

Regarding pitch trim , trim as close as possible , then adjust throttle for perfect trim .

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  • 2 weeks later...

Thanks svs :)

 

Did that. I get a trim that remains stable for a few minutes before I have to make a slight adjustement up or down with the stick. Is this the outcome you get or do you really get a permanently stabvle trim (is this even possible given the fact thje plane burns oil and becomeds lighter?)

Wishlist: Tornado ADV/IDS, Blackburn Buccaneer, Super Mystère B2, Saab J 35 Draken,

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