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Vref not updating as fuel decreases


Leo Sten

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Hi!

I'm loving CRJ, but as some other I find it very "floaty". I'm not intending to start another topic on the floating, but rather made an to me interesting observation. The approach speed vref in the EFB doesn't seem to update during the flight. At start it seems to be set in the performance page like all takeoff speeds but then never changes. To me this feels like the vref for landing gets a bit to high considering that weights are above max landing weight at the start of the trip.

 

The last trip I made gave me a landing vref of 138 knots. From what I can find online from the real thing vref at max landing weight should be 135. I also made a try with a couple of circuits where fuel didn't differ that much from takeoff to landing and it felt easier to land...

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Yep, I have also noticed this in the past and it can have quite an impact. I believe I looked but could not find anything in the manuals or videos discussing doing any recalculations in the EFB for reference speed and the EFB does not know the trip fuel so it only gives the Vref for current weight. You'd have to load the fuel from the aircraft again into the EFB but I don't recall if this by itself recalculates the Vref or if you then have to load the EFB values into the sim again as well.

 

It is roughly 2kts per 1000kg of fuel burned so you definitely start to notice it on flights of say 1h20-1h30 or longer.

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Thanks for the reply and tip!

 

Is it correct to extend that reasoning to any weight below MLW and not specifically fuel? Meaning if I have a landing weight of 28 400 kgs, 2000 kgs below MLW that should give me a vref of 131 and not the 134 kts the EFB suggested... For my last flights doing this felt better, less "floaty".

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10 hours ago, Leo Sten said:

Thanks for the reply and tip!

 

Is it correct to extend that reasoning to any weight below MLW and not specifically fuel? Meaning if I have a landing weight of 28 400 kgs, 2000 kgs below MLW that should give me a vref of 131 and not the 134 kts the EFB suggested... For my last flights doing this felt better, less "floaty".

 

Yeah. The speed tables in the CRJ700 QRH on average go about 2kts per 1000kg lighter below MLW. This does not account for quite a few variables such as wind, or pressure altitude and such, just a quick generic performance guideline. 

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