737 200 very long takeoff roll.

[rennman 4]

Hi. I can get her to nose up until 160 kts...even with flaps 5 and a light load.

I thought vr is supposed to be around 120 kts...any ideas?

[beechcaptain 105]

What settings did you have in the performance initialization pages of the fmc? what were your v speeds and trim setting?

Lots of items if not properly set up in configuring the a/c for takeoff could cause similar issues.

[Chock 17,769]

What airport are you at, and what is the weather? (specifically, the important things to note are the altitude of the airport and the outside air temperature). This is critical for a 200 series Boeing 737 equipped with  JT8D engines, since you need to ensure you have the correct EPR settings for take off. You can find those on the take off EPR setting charts. You do still use the N1 settings as a guide to having the correct thrust set, but not those alone, you use EPR too.

Older aeroplanes with low bypass turbojets such as the JT8D don't have any fancy FADEC systems to do all that correct fuel/air mixture stuff for you, which is why you have to consult the SOP manual charts for the correct throttle settings.

Beyond purely reasons of economy or noise reduction necessitating a reduced thrust take off, it's often the only way you'd get off the ground at some airports. At high OATs and/or high altitudes, the air is appreciably thinner, when this is the case, simply ramming the throttles to the stops can actually prevent the engines from developing the best thrust possible. This is because you'll have too much fuel going into the combustion chambers for the amount of air the engines can actually suck in, so the combustion will be inefficient.
In extreme cases, the unburned fuel can cause problems too; acting as a coolant, which will further inhibit combustion. So, you reduce the thrust settings to allow the engines to operate at their best rate for combustion in the thinner air.

It's also worth noting that in cases where the air is thinner owing to being at an airport at high altitude, or a particularly warm OAT, this will also mean the wings won't develop enough lift either until you are at quite a high speed. It is entirely possible that a particularly warm day at an airport which is up high, you wouldn't even get off the deck at all. For example, Mexico City (MMMX) is over 7,300 feet above sea level, which is almost up at the point where some people would need to start using supplementary oxygen. On a warm day, the air will be so thin there that you'd be lucky to get off the ground, which is one of the reasons why it has two runways which are nearly 13,000 feet long.

I don't have the Milviz 737-200, but since it is made by Milviz, I'm assuming it has a good simulation of the JT8D becuase their stuff is normally pretty 'pro'. If that is the case and their engine model simulates failures and such, another problem could be the following: When you throttle up the JT8D, you are supposed to make a check at 1.4 EPR. What you're looking for is a noticeable jump in the needles as a dump valve closes and more air suddenly comes through; specifically this occurs because at low power settings the low pressure compressor stage of a JT8D has more air than the high pressure stage needs, so a bleed valve dumps some of air off through surge bleed valves, but these valves close automatically as the throttle is increased so that the high pressure stage can get enough air at higher throttle settings. If the valves don't close, the high pressure compressor stage will stall from air starvation, which is obviously even more likely if the air is thinner already owing to the reasons mentioned above.

Edited August 24, 2018 by Chock

[rennman 4]

thank for replying...i dont think it's thin air or epr settings...she gets to up to 160 kts just fine...but just needing 160 kts with flaps 15 to nose up seems too much...the CS 737 noses up at 120 kts...all variables being equal...it's in the plane...so how do i know which one is right?

Edited September 3, 2018 by rennman

[rennman 4]

On 8/24/2018 at 4:43 PM, rennman said:

 can

*can't

[n4gix 4,947]

Try using more up trim.

[rennman 4]

If I trim up any more she will stall after takeoff...At this point I think the issue is in the flight dynamics...but what, why, and how?

[Milviz 919]

well...  that would make zero sense... cause others, including myself this morning, are able to get it into the air... pretty easily... no flaps and no trim....

[rennman 4]

I just got her to rotate at 120kts!

For the first time I used the milviz manager to enter the weights. (I was using FS passengers before.) The only thing I can think of is that the plane's weight was being read by Flightsim as fully maxed out.

Could that have been it?

Edited September 13, 2018 by rennman

[Milviz 919]

likely.  You MUST use the AMS to enter weights on this aircraft...

[rennman 4]

If we don't use the AMS, will the AC load fully loaded by default?

[Katoun 30]

No

[rennman 4]

I think I found the culprit. FS passengers was making my AC way heavier than what I put in the AMS, even with weights disabled in FS passengers.

I'll take it up at the FS passengers forum, but I consider the mystery solved!

Thank you to all who helped, and thank you to milviz for a beast of an airplane in the 737.

Edited September 14, 2018 by rennman