Help with VS on take off and proper mode engagement.

[alexzar14 5]

I fly this aircraft once in a while, somewhat less often than (little bit less then) NGX, 777 and Airbus-X because Douglass (MD-11 or MD-88) are a bit more complicated.

In the past month I've been flying double-time the Coolsky MD-80 and that has been figured via videos, questions and etc. Now I need to catch on with MD-11.

Ok with prelude. The systems, start-up, FMS and Autopilot I do understand and that is ok. I have a problem on take off though:

So far, I managed the VS rate manually until I was in a stable climb and heading at like 3000 ft (same with NAV). Understanding that's not the right way even compared to ways I fly the NGX and 777 (I engage LNAV/VNAV early after take off, things are fine with those two).

Today I took the FedEx MD-11, LAX-JFK, set it up for take off ok with no messages/alerts displayed, and decided I should do it the right way with LNAV and VNAV (PROF) engaged right away at 1500 as per the tutorial included with documents. The PROF engaged, the speed was reset but the nose pitch remained as is (VS was 2700fpm), it didn't lower the nose. The speed was 210-220kts at the time of PROF engagement, then started to drop, down-down-down to 165knts. At that point I went to manual VS and lowered the rate down to 2000 which helped acceleration, then reengaged the PROF again.

 

So this didn't kill the flight, but a very unpleasant experience, I hate when things don't go right. Please explain why this happened and how to prevent it, what to take into account. 

If there is a good video of takeoff and climb on utube, please suggest.

[pschlute 37]

First, do not think about VS. You climb the aircraft using a thrust setting and a target speed.

 

Second, there is no "right" way. A good sim pilot should be able to take off and climb using no autopilot or PROF/NAV settings just as well as using the electronic magic.

 

It sounds like you allowed the aircraft to accelerate beyond V2+10 (you say 210-220 knots) before you reached acceleration altitude, so if you engage A/P and PROF below acceleration altitude the aircraft will want to maintain V2+10.

 

PROF and NAV can be armed before takeoff. Either way, whether using PROF or not, autopilot or not, you initially climb at V2+10 until you reach acceleration altitude. Then you (or the AP lower the nose and accelerate to 250 knots or intermediate speed if one is required by the departure procedure.

[alexzar14 5]

ok I will practice it tonight. Take off was always the difficult part (landing you just steer the ac down the runway). Things happen very fast, speed sometimes doesn't want to stay constant (V2+10), you raise the nose per FD, something distracts your attention and the speed grows, or the nose pitches up more than needed, engage the AP like I did and the speed starts to drop.

[Don t moderate me this way 882]

Do you derate the takeoff thrust? Derating will slow things down considerably (that is a lower acceleration rate during the takeoff run and less "surplus" power during the initial climb).

 

Should be easier to rotate the aircraft then and to pitch manually for the appropriate speed.

[alexzar14 5]

I used less power than called for by N1 bugs.

V2 was high about 180 (2/3 freight cargo and 140000 lb fuel), rotation and take-off itself were beautiful and realistic, and so was the climb to 1000 at about constant speed initially, then grew up a to 220 which I believed was fine (I preset it to 220). The speed didn't grow, I thought all is well but the nose was too high perhaps. I engaged AP/PROF expecting it to lower the nose but it didn't. I was a bit confused and just watched what happens, the nose was still high so the speed started to drop. Only as it dropped to 165 I said it is time to take it manually (it took 5 seconds to go from 220 to 165).

 

Guys please share with me the exact (scientific as you call it) procedure for derated take off, I am basically familiar with normal procedures only, as described in tutorials or seen on videos on utube.

[Don t moderate me this way 882]

The MD 11 has no fixed derates; it's all handled via assumed temperatures in a pretty standard way.

 

Reading your very precise description, derate, rotation and initial handflying don't seem to be any problem at all.

Not sure, though, whether you are aware of the "default" acceleration altitude in the MD11: It's significantly higher than what you can expect in a B737 or an A320. Maybe you were under the impression that the MD11 would have to accelerate on PROF already, while it was actually still below ACC ALT?

[Imanual 0]

Enable Autoflight prior to departure when engines are on. When above 400 feet, hit autoflight again and then either control parameters by right-clicking or push the buttons beneath the rotaries and let the plane do it. I will be putting up a youtube video soon with such details from flight I took to anchorage.

[alexzar14 5]

Ok I tried some takeoffs, almost a dozen times. I saved the flight so I could repeat it with FMS programmed and all ready for take off.

I worked it out, nice and smooth. Initial speed on ND was 189 (V2(179)+10). Most of the times I accelerated to 191-192 (it's hard to stay on FD-pitch but that is a good result I believe), engaged the FMS SPD and that decelerated me to 189. Pretty neat. All takeoffs were from one location however - LAX 25L SID-JEDDD1, I hope my next flight with take off from a new/different location will be just as good.

Enable Autoflight prior to departure when engines are on. When above 400 feet, hit autoflight again and then either control parameters by right-clicking or push the buttons beneath the rotaries and let the plane do it. I will be putting up a youtube video soon with such details from flight I took to anchorage.

 

I did it both ways and didn't notice a difference (except the disappearance of highlighted area of PFD), technically was the same thing. What difference is it in enabling the AP before take off? Will wait for the video...

[pschlute 37]

You cannot enable autopilot when on the ground. Before takeoff you press the AUTOFLIGHT button to ARM the autothrottle.

 

You can also ARM the PROF and NAV while on the ground , so that when you have taken of (above 400 feet), you press AUTOFLIGHT again and the autopilot will engage in PROF and NAV modes..... Or,  if you dont engage autopilot in the air , the FD will be giving you pitch and roll cues from PROF and NAV.

[alexzar14 5]

You cannot enable autopilot when on the ground. Before takeoff you press the AUTOFLIGHT button to ARM the autothrottle.

 

That sounds like an unnecessary step because you have to press on Autoflight anyway. Necessary with Boeings because AT is separated from AP, but here we have one button doing both.

 

I had another question on "speed hold" at V2+10, I've never seen that on Boeing and Airbus, the VNAV on those will right away take you to 250kts unless a waypoint has a restriction.

 

[pschlute 37]

That sounds like an unnecessary step because you have to press on Autoflight anyway. Necessary with Boeings because AT is separated from AP, but here we have one button doing both.

 

 

I do not understand your point here. What step is unnecessary? 

 

The AUTOFLIGHT button on the ground will only arm the autothrottle.  Pressing it after take off will engage the autopilot. 

 

 

I had another question on "speed hold" at V2+10, I've never seen that on Boeing and Airbus, the VNAV on those will right away take you to 250kts unless a waypoint has a restriction

 

Immediately after takeoff, BEFORE you reach acceleration height the MD-11 FD or autopilot will command V2+10. At acceleration height it will command climb speed (usually 250 knots). This works the same on Airbus and Boeing, although the margin over V2 may vary .... +15 for example on some aircraft.

 

If you have not noticed this, it is probably because the default acceleration height on the MD-11 is 3000 feet, which is higher than most aircraft FMCs

[alexzar14 5]

I got it, thanks.

[alexzar14 5]

Guys I posed a question in pmdg-General forum regarding another subject, would like to hear your thoughts/suggestions.

I trust you most.