As the title says my weight is 59.2 GW Flaps 15 vref is 148kts but on my Flap Maneuvre Speed for the 800 is F15 Vref 40 + 20 = 153

 

I'm on approach at F15 gear down all that good stuff at command speed of 153 kts. So why does it drop 5 kts. I know its adding wind cor of +5, but shouldn't the speed be like on my chart 153kts for that weight and also the green bug weight on my speed tape which is 153 for F15. So why not vref 153 + wind cor

 

Regards

 

 

So why not vref 153 + wind cor

 

Because wind cor is already being applied in the FMC calc. Look at the bottom right of the FMC Approach Ref page - what does it say?

Hi kyle, yes i understand its adding wind cor. But how come my performance flap maneuvre speed for the 800 is showing for a GW of 58.9 is 153 kts ? 

Hi kyle, yes i understand its adding wind cor. But how come my performance flap maneuvre speed for the 800 is showing for a GW of 58.9 is 153 kts ? 

 

Not quite understanding the question here.

 

Flap maneuver speeds are based off of VREF. It seems you understand this. The FMC automatically adds in the base 5 knot wind correction, unless you change it. What are you not understanding, or what do you find to be odd?

as you can see my FMC is showing for F15 vref is 148 kts and command speed is 153kts (well 154 i've set,so just ignore that lol) because plus 5 wind cor.

 

2nd picture is flap maneuvre speed,my weight is 59t so that gives me for F15 vref 40 + 20 is 153

 

Do you see it now or am i not clicking on to something , just need a little bit of help here lol why isn't my FMC showing 153 for my vref because my table is - 153 kts

 

 

 

 

 

 

 

 

 

 

 

 

 

 

:blink:

No sure what you mean.

 

If you selected flaps15  you get  148+5=153 VREF?

 

Looks like you have selected in both 2 and 3 flaps 30/141 edited to 30/140 

 

pic 3 shows flaps 15@ 154, what is the problem Vernon? did you want to see 153 are we talking about 1 snot? (I know )

 

If you really are talking about 1 snot it might be down to fractions .5= the greater number .4 rounded down.

 

also it that chart for the 800 and are you flying a 800WL?

 

Also if we are being really picky the marker is not on flaps 15 its a little above. The green line looks like it would =153

 

 

Also if we are being really picky the marker is not on flaps 15 its a little above. The green line looks like it would =153

 

Like i said above, i had my command speed set to 154 and it should be 153, but thats not the problem. The problem is the chart for my weight for flaps 15 is 153 kts but my FMC is 148 plus 5 153, so how come my chart is saying 153? yeh 800W but that shouldn't affect it? or should it? sorry but i'm not a performance engineer.

Like i said above, i had my command speed set to 154 and it should be 153, but thats not the problem. The problem is the chart for my weight for flaps 15 is 153 kts but my FMC is 148 plus 5 153, so how come my chart is saying 153? yeh 800W but that shouldn't affect it? or should it? sorry but i'm not a performance engineer.

 

Where did the chart come from?

This is the one in the FCOM

[Copyrighted material removed]

 

Vernon what do you want/expect to see in the FMC?

 

 

Where did the chart come from?

 

I got it from a link from xplane.

 

 

 

Vernon what do you want/expect to see in the FMC?

 

Hold on david, look you still don't get the point i'm trying to get across. I'll try to explain the best i can to make you understand - On the chart that i posted above is the speeds for flap maneuvre speed depending on weight. so what i done is, set up a test and loaded my 737 800W to 59t with me so ?????????? so if you look at my chart above, find my weight 59t and use that line (58.9) is closest ok with me so far ???? next go along that line you will see various speeds for those flaps F0 F1 F2 F5 F10 F15 F25

 

Now for flaps 15 you can see the speed is 153 kts for my weight at 59t and you can see on my other picture of my PFD with my plane at flaps 15 command speed set at 154 well it should be 153, but lets say i did set it at 153.

 

Now look at my FMC for flaps 15 at 59t gives me 148kts why is there a difference in my chart and the FMC?

 

I would also would like to say this chart isn't WRONG because how can it be when for a given weight 59t and the speeds that show on the speed tape for flaps 15 is 153 kts and even flaps up speed is the same as the chart 203 kts.

 

 

I got it from a link from xplane.

 

Try a more solid source. My bet is someone made that in Excel. Who knows how accurate it is. Moreover, someone could've just run through a whole bunch of weight values on our FMC, which would explain why the +05 is already in there.

I think I see the question.

 

The difference is that the Flap 15 speed in the table (Vref40 + 20) is based off Vref40.

 

The Flap 15 speed in the FMC is not based off Vref40. It is Vref15, which is a different equation (1.3 x Vs1g with Flap 15 set).

 

You're comparing apples and oranges.

 

 

Try a more solid source. My bet is someone made that in Excel. Who knows how accurate it is

 

kyle you still haven't clicked onto what i'm trying to explain. read my text thoroughly. How can this chart be wrong when i done tests with my NGX at weights matching the chart weight and my flaps up speed on my NGX match that of the chart and so does flaps 1 flaps 2 flaps 5 and so....

 

 

I think I see the question.
 
The difference is that the Flap 15 speed in the table (Vref40 + 20) is based off Vref40.
 
The Flap 15 speed in the FMC is not based off Vref40. It is Vref15, which is a different equation (1.3 x Vs1g with Flap 15 set).
 
You're comparing apples and oranges.

 

Thankyou simon, you understand do you see where i'm coming from and why i got confused lol

 

 

kyle you still haven't clicked onto what i'm trying to explain. read my text thoroughly. How can this chart be wrong when i done tests with my NGX at weights matching the chart weight and my flaps up speed on my NGX match that of the chart and so does flaps 1 flaps 2 flaps 5 and so....

 

No. Re-read what I'm saying here:

 

If you're going to draw things into question, cite official references. A chart from a link from X-Plane is questionable. It doesn't matter that things match at some point. If I'm plotting a line of best fit, it might hit a couple of my data points, but if it actually doesn't cover the data accurately, then it isn't an accurate line.

 

If you were quoting from the Boeing charts, then we'd have a discussion. As it stands, though, you're drawing a simulation into question based on some random chart, from some random link, that could have been put together by someone's 12 year old brother.

No problem! It's important to remember that Vrefxx is the base for the speed schedule: the speeds on the APPROACH REF page are not the flap manoeuvre speeds as displayed on the speedtape, they are Vref speeds (i.e. changing the base from which the speed schedule is derived) for each configuration.

 

As I say, 1.3 x Vs1g in each configuration does not necessarily yield the same result as 1.3 x Vs1g(Flap40) + 10/20/30/40.

 

Kyle -- I'm not sure Vernon's questioning the accuracy of the simulation, just trying to understand why the speeds on the APP REF page are different to the speeds on the speedtape.