HighBypass

Sky Simulations MD-11 V2.0 stabiliser angle "fix"?...

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I know there's not many of us about, but there are hopefully other owners of this IMHO nice, if slightly overpriced MD-11 who have noticed this "anomaly" :blush:

When she is cruising at altitude (FL370 to FL410) at the usual speed of M0.84 the Sky Sim MD exhibits a nose up attitude which to my eyes appears a little exaggerated. I know most airliners fly in the cruise with a slight nose up attitude, but please hear me out if you would.

This visual nose up attitude is compounded by the horizontal stabiliser pointing several degrees down at its leading edge. I believe I've mentioned in another post that the synoptic displays where stabiliser angle is displayed seems rather high at cruise which backs up the visual image (a setting of around 6 Aircraft Nose Up). One usually sees such stabiliser attitude when the plane is on approach with flaps out and gear down..

MD111.jpg

The Sky Sim MD exhibits this behaviour whether she is carrying a hefty payload (120000 lb) YET with most of her fuel burned off, or maxed out on gross weight with a full load of pax & fuel (default start of flight when selecting the plane)

Most image of PMDG's benchmark MD-11 and real MDs 've seen have much less stabiliser attitude when in the cruise. Again this appears to be backed up by in cockpit videos which show the stab between 1 and 2 ANU.

lufthansacargomd-11cruising-lufthansacar

I've played around with the aircraft.cfg file and have managed to get a more "correct" visual attitude and synoptic display by altering the htail_incidence to 0. It was set to 2. I have also altered the cruise_lift_scalar to 2. It was at 1.1

I don't yet know if I'll have to alter the flap lift, but I'll find that out when I land in Dakar :biggrin:.

 I have not tried flying her on empty with next to no payload, but again that would probably be quite unrealistic unless one was ferrying her to a boneyard I guess.

Any thoughts please?

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Well, it seems that with flaps deployed she adopts a serious nose down attitude like a STOL plane on approach. I had completely destroyed her characteristics for landing.. :wacko::wacko:Oh well. I'll revert back to the original aircraft.cfg and await a more knowledgeable fix for the visuals .:blush:

If only Sky Simulations followed these forums and or replied to my other questions... fat chance I guess..

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For $50 I would expect the basics to function. The autopilot on this aircraft is a mess; the alteration to the cfg is required to establish a positive rate on takeoff, otherwise, it nose dives when engaging the AP. It’s ability to track an ILS and maintain a consistent speed are also highly questionable. Ironically, V1 had the same issues.  Visually it’s not terrible, but it lacks basic functionality.  We’ll have to see if SP 2 addresses our issues, HF 

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I agree that I'm waiting for a service pack 2, and a response to my support questions .. yet overall...

I must be doing something different, but I've not noticed a nose dive upon engaging the AP. OK well I did before finding a "workaround". I mean I've never had issues with getting her off the deck - I've input an amount of stab trim depending upon weight, and I've done some max weight takeoffs..

Prior to takeoff I've dialled in the speed (say 250kt), heading and alt with desired V/S. Once I've got the gear up (and got a positive rate of climb and nicely trimmed) I've clicked on AUTOFLIGHT. THEN I've clicked the knobs to engage speed heading and altitude. The plane then follows the AP commands, but I agree that there is some hunting around - it does not have the fastest responding AP yet changing heading is quite responsive.

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For the horizontal stabiliser try increasing the elevator trim effectiveness in the aircraft cfg.

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I have noticed huge hirizontal stab deflection in the cruise as well.

But my main problem with SkySim MD11 is the autopilot which is simply unpredictable... does anyone experiance significant loss of altitude on low altitude/ low speed turns, on approach for example? The aircraft starts to decent immediatelly after HDG or NAV turn is initiated.

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I've experienced some loss of altitude, but the AP compensates. I do have a bunch of flap dialled in on those low speed turns, say about 175kt and at least flaps 28. It is not as responsive as some APs out there. I guess because it is using the stab movement for pitch and not elevator too.

I'll have a look at the elevator trim effectiveness. Would this make the horizontal stabiliser more efficient so that it takes less incidence to have the jet fly level, thus making the stab position look more realistic?

I have gained a couple of degrees of ANU by making sure the MD-11 is loaded with an aft c of g, especially if I'm not at MTOW. I've seen less than 5 ANU as opposed to above 6.

I begin with zero fuel weight then input the amount of payload I'd like to drag into the sky given the range consideration. Then input the required fuel. I've not had a c of g limit warning for the past few flights. Then again I've been recreating real world flights. Maybe not the exact routes, but the payload and fuel numbers.

It is the best MD-11 options for me for FSX:SE and I want to like it more. I just wish Sky Sim would at least try and reply to any support emails... especially from a customer who likes the product!

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Interesting, my VS hits even -1800 ft per minute at 220kts flaps 10...

I am using Topcat MD11 profile to build loadsheet i am using then to load fuel and pax. Also ending with CG alert.

 

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Kris I'll monitor my approaches more. How long a duration of -1800 are you seeing? Is it just a momentary "blip" or long enough to have to disconnect the AP and take over?

I'm only using the default fuel and payload menu within FSX:SE. I don't fly the pax versions, so I zero out all the stations apart from the 600 lbs for crew. I then usually split the total load evenly between the two tourist class stations, ignoring the first class. I may put a few thousand pounds in the aft cargo too. I obtained some real world figures for freighter loading (not sure which operator) in my post in Hangar Chat - a maximum of 3400kg in the aft belly cargo area on a freighter, 25400kg in the forward belly, and 70760kg in the main area. These max load limits exceed the max payload of the MD-11 (90 tons or so), but it enables the c of g to be shifted even when at that max payload.

It appears that Sky Sim's forward and aft belly cargo stations are not the same as a real freighter. For example Sky Sim has 11050 lbs in rear cargo, yet real world is 7496 lb (3400kg).

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I need to disengage AP to recover from dive. I am thinking that this may be caused by ISG integration i use, as you dont experiance such problem. Or, maybe the stab deflection may be to be blame.

Will work on the CG and if i manage to get proper trimming will check the AP behaviour again.

Other than that, this bird is promissing, especially with TSS sound, hoping SS will fix mayor issues.

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Wel.. Stuff it. I've altered the htail incidence to 0 (it was 2) . The horizontal stab looks better now compared to the real plane. I'll leave the nose up attitude alone for now :wacko:. Messing with cruise lift scalar can ruin your entire day lol.

I believe elevator trim effectiveness alters how sensitive any applications of pitch trim are; too large a number and the aircraft will just climb or dive by one click of the button.. 

 

Tell me Kris.. Does the TSS sound deal with the engine sounds only? I'd rather it didn't mess with bitchin betty and other cockpit call outs - I quite like those!

Thank you for the comments so far gents!

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You will have all your GPWS and bitchin betty sounds untouched as they seat in the Gauges folder while with TSS you replace Sound folder in Simobjects/ SkySim Md11 directory only.

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On today's flight I monitored the localiser and glideslope captures more closely.. This was going in to Bogota with a light fuel load (22 tonnes a bit excessive for the trip from Quito but still a "light" load) and payload (10 tonnes) Prior to capturing the localiser, I'd already slowed her down to about 180 with flaps 28. She overshot and had to correct but I was far enough away and the correction was done in time. When it came time for glideslope capture I already had gear down and flaps 35. She dropped her nose to just over 1000 fpm for initial descent to capture then just bobbed up and down slightly - no scary nose dives. I then had to disconnect the AP due to the circle-to-land approach. I'll keep an eye out on future approaches.

 

UPDATE EDIT...  I found an article in Airways magazine where KLM crew and engineers were remembering (fondly!) the MD-11.

https://airwaysmag.com/best-of-airways/twilight-md-11/

I quote

Quote

“The triple-seven is the airplane I like, but the MD-11 is the airplane I love,” said Marije, a KLM senior flight attendant. “I enjoyed spending time with my colleagues in the rear galley, which was so large we could have thrown parties, danced and even jumped if we had wanted to,” she noted. “However, pushing a cart from the rear to the front while the airplane cruised was quite the workout!” she explained, making reference to the noticeable pitch-up attitude the MD-11 was known for during its cruise setting.

 

So, the nose up attitude may be not as bad as I thought! The artificial horizon reads less than 5 degrees nose up, maybe 2 to 3 so that's good enough I reckon. 

Edited by HighBypass
reference

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What angle did you approach the localizer? Did you have to make a low speed, high angle turn like 45-180 degree?

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I'm trying to remember I think it was no more than 45 degrees, whatever the stock FSX ATC vectors you for intercept.:blush:

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