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Viper thrust lever vs. fuel flow strange behavior. Could this be a bug?


Lanzfeld113

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Go ahead and takeoff in a viper, level off and get your altitude hold on at any altitude. Go full military power. Right up so the white stripe on the thrust lever is up against the notch or detent thing but no more. Don't go into afterburner. Now let the jets speed (and fuel flow) stabilize.

Now...

Slowly pull the thrust lever back 1 mm at a time and watch your fuel flow. IT GOES UP! In fact it keeps getting higher as you pull back the thrust lever for about 1 1/2 to 2 inches before fuel flow begins decreasing (looking at that white stripe on the thrust lever).

I have a top quality Virpil thrust lever that is smooth as butter with no spikes or jitters so I know it's not my throttle. 

A. Is it just me seeing this?

B. It this how the real viper works (I doubt it).

C. Is this a bug?

No track file here. Just strap on the jet and see for yourself.


Edited by Lanzfeld113
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  • Lanzfeld113 changed the title to Viper thrust lever vs. fuel flow strange behavior. Could this be a bug?

I am guessing you're still accelerating. The faster a jet goes the more air it will get, the more fuel it will spend to get a good flame.

Even though you're pulling back on the throttle. The reduction does not overcome the effect of the acceleration.

Without any further evidence:

A. No

B. Yes, and pretty much every other fast jet. 

C. No

 

Try it again in steady unaccelerated flight. In that state it will probably work as you described.

 

Edit misread you being speed and fuel flow stable. Tried it and did not see the effect you described. 


Edited by Sinclair_76
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So strange. It is very pronounced. The first 1.5 inches of thrust lever movement away from military power in the direction of idle increases the fuel flow. Not a ton. Just a few hundred PPH but still...

I cannot be the only one seeing this. Can anyone else please try my instructions (make sure you are stable) and tell me if you get same results? Use the white maker on the thrust lever as your guide. back off military power a few mm at a time. watch fuel flow.


Edited by Lanzfeld113
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vor 6 Stunden schrieb Lanzfeld113:

So strange. It is very pronounced. The first 1.5 inches of thrust lever movement away from military power in the direction of idle increases the fuel flow. Not a ton. Just a few hundred PPH but still...

I cannot be the only one seeing this. Can anyone else please try my instructions (make sure you are stable) and tell me if you get same results? Use the white maker on the thrust lever as your guide. back off military power a few mm at a time. watch fuel flow.

 

Yes, because speed and thus airflow changes and so does the fuel flow.

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You are all not really reading my post. I know about the fuel flow changing with speed. That is why I say STABILIZE.

My throttle has no issues. Completely smooth linear throw. This is happening. For the first 1.5 inches out of military power fuel flow increases. 

Is anyone actually testing this or just trying guess what is happening? I challenge you to test the exact way I describe in my first post and look at your fuel flow. I wish I knew how to post a short video here but I would have to take it through my Reverb G2 and post it hear and is that possible?

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Over time the fuel flow increases by itself without any change to altitude or  throttle input or change in speed. I have no idea if this is correct or not, I figured it might be related to increase in heat or something but I have no idea.


Edited by Blinky.ben
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Actually, if there's absolutely no change in throttle input, there will be a very slight change in speed. As the jet flies, it consumes fuel. Fuel has weight. As it flies, the jet is constantly becoming lighter, meaning a constant throttle setting will let the plane accelerate slightly. As you go ever so slightly faster, the engine gets more air, requiring more fuel to get the optimum performance. Incidentally, this makes you go even faster, although drag also goes up with speed, so there's no actual positive feedback loop, just speed and fuel flow slowly creeping up. The fuel flow gauge is much more precise than the ASI, so you don't see it on the latter.

It's not a factor in normal flight, since you will typically adjust the throttle every so often, anyway. 


Edited by Dragon1-1
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I’ve only seen this a few times and I can’t remember the conditions other than it was on our MP server. When you push the throttle from about 85% up to 100% (no AB) then there is an area around 90% throttle that the fuel flow indicator spikes and goes up before setting back down. 

Ill see if I can record down the environmental conditions next time I see it happening and provide a track file.
 

 

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