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martin-w

Short Field Package VREF sppeds - Service pack one ?

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Currently, the 737NGX FMC does not calculate the reduced VREF speeds with the SFP package. I would be interested to know, if in the first service pack, PMDG will be implementing the lower VREF speeds. From what I can gather from the Flight Crew Training Manual, and other sources, VREF speeds are lower with two tail skids. And thus, with a lower VREF, angle of attack is increased, pitch is therefore 3.5 degrees up on approach. If the SFP VREF reduction isn't going to be coded into the FMC for the first service pack, what is the reduction in VREF associated with the SFP so I can determine this myself?

Two-position tailskid that extends an extra 127mm (5ins) for landing protection. This allows greater angles of attack to be safely flown thereby reducing Vref and hence landing distance. http://www.b737.org....ncement_Program
Martin Wilby

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Most likely not - certain aspects of this system require changes to the air file and a whole separate model etc - probably not going to be doing that.

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Yeah I would be interested to know that too. Is it visual only or does it actually work but at the same vrefs as the normal equipment. Does having the Short Field Package Equipment with the Skids and Higher Deflection Spoilers have any affect on the rate that you slow down?

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Expected reduce in VREF is supposed to be around 5 knots I been told. Normally you'd add 5 knots to what the FMC says, so in the SFP's case, just set the actual VREF for that flap setting, and you should be alright.

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Most likely not - certain aspects of this system require changes to the air file and a whole separate model etc - probably not going to be doing that.
Thanks Ryan, no problem. I guess it's better not to mess with the coding and risk introducing further bugs. Upon testing though, I have come up with a workaround. VREF reduction to generate the same pitch as per the manuals for SFP... At flap 30, reducing VREF by -10 knots provides the same SFP pitch as per the manuals. [3.5 up]At flap 40 reducing VREF by -5 knots provides the same degree of pitch increase. Ignoring the current pitch inaccuracy in the add-on that some percieve.... At flap 30, reduce VREF by -5 knots.At flap 40 reduce VREF by -2 knots. If someone could test this, in case i've messed up it would help. Rather than relying on pitch as a guide, It would help if there was a VREF chart somewhere for the Short Field Package. Apologies If I've missed it. Martin Wilby

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Yeah I would be interested to know that too. Is it visual only or does it actually work but at the same vrefs as the normal equipment. Does having the Short Field Package Equipment with the Skids and Higher Deflection Spoilers have any affect on the rate that you slow down?
I haven't tested stopping distances, but it appears to work. I know i can land effectively on short runways. So I think it's just the VREF that's too high. I may be wrong though, as I say, I haven't tested.. I have to say, given that VREF speeds are calculated 5-10 knots too high with the SFP, it would explain why some are saying they are coming in too hot, and floating. Idea.gif Martin Wilby

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So Ryan... There seems to be some confusion here. Can you tell us what effect choosing the SFP option has in regard to the add-on? Does it have any aerodynamic affect at all? Or is it just visual, for example skids? Martin Wilby

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Expected reduce in VREF is supposed to be around 5 knots I been told. Normally you'd add 5 knots to what the FMC says, so in the SFP's case, just set the actual VREF for that flap setting, and you should be alright.
I'm using this same workaround with the normal -800 model, to account for it's pitch on finals bug where PMDG acknowledges they are using performance figures (unreliable speed table) that result in the FMC VREF giving VRef +5 speeds that are really in effect VREF + 10. That being said, if I'm subtracting 5 kts from the VREF for the normal model, you would want to subtract 10 kts from VREF for the SFP, right?

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That being said, if I'm subtracting 5 kts from the VREF for the normal model, you would want to subtract 10 kts from VREF for the SFP, right?
Not exactly... I don't think the issue is the FMC speeds. I checked them against the manual and they are correct. The issue is that the unreliable airspeed table has mistakenly been used to determine pitch on approach, and obviously because the table is based on VREF+10, the pitch has thus been set too low. Reducing VREF by 10 knots will give you the correct pitch, with SFP as per the real aircraft. [but 5 slower than the aircraft should be flying] Reducing your VREF by 5 knots will give you the correct SFP speed reduction, but of course the pitch will still be too low due to the bug. The real fix it to adjust the lift scalar to correct the inacurate pitch. And then to reduce VREF by 5 knots to comply with the correct SFP speed requirement. But of course I am not encouraging anyone to do that, just trying to explain the issue clearly. Martin Wilby

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Well, no reply, so I tested the short field package. Absolutely no difference. The SFP in the add-on is a visual enhancement only, no reduction in landing distance at all. The only reduction in landing distance you will get, is if you reduce the FMC generated VREF, to what it really should be with the SFP. Martin Wilby

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Well, no reply, so I tested the short field package. Absolutely no difference. The SFP in the add-on is a visual enhancement only, no reduction in landing distance at all. The only reduction in landing distance you will get, is if you reduce the FMC generated VREF, to what it really should be with the SFP. Martin Wilby
I wonder why they even bothered to add it if its a visual ehancement only.
The SFP is not a visual enhancement only!Shame%20On%20You.gifhttp://www.facebook.com/note.php?note_id=229349443771514

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I know, I tested it see this topic... http://forum.avsim.n...ge/page__st__25

Gary...I have tested again. I was wrong!I tested at EGJJ' date=' both with the SFP and without. All parameters identical.As far as I'm concerned, the SFP DOES reduce landing distance, and thats with the same VREF, with and without SFP.[/quote'] You must keep up with the program my boy! Shame%20On%20You.gif We can't have slackers around here. Martin Wilby

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I have tested again. I was wrong!I tested at EGJJ, both with the SFP and without. All parameters identical.As far as I'm concerned, the SFP DOES reduce landing distance, and thats with the same VREF, with and without SFP.
Well that is good to know. I was begining to think it was a visual enhancement only. But now that we know it actually works I will be using is as part of my equipment again on the 800 series. I think it already standard on the 900 series.

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Well that is good to know. I was begining to think it was a visual enhancement only. But now that we know it actually works I will be using is as part of my equipment again on the 800 series. I think it already standard on the 900 series.
I think it is indeed standard on the 900ER, not the normal one, but I stand to be corrected!

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Well that is good to know. I was beginning to think it was a visual enhancement only. But now that we know it actually works I will be using is as part of my equipment again on the 800 series. I think it already standard on the 900 series.
Yep, certainly works as advertised. I tested no less than six times. I think that's correct in regard to the 900, SFP is indeed standard equipment. I read that somewhere the other day. Good news that PMDG are fixing the attitude on approach issue too.

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