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Flight Dynamic problem

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jimos87 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jimos87 Quote  Post ReplyReply Direct Link To This Post Posted: 03 Dec 2017 at 11:09am
Support sent me a new config to try which seems to have fixed it so far, maybe they will release a new installer. I'm currently reinstalling all P3D related things to test it again. 
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ncooper View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ncooper Quote  Post ReplyReply Direct Link To This Post Posted: 04 Dec 2017 at 6:30pm
Hello,
For what it's worth and not being a rivet counter, I have solved the autopilot porpoising
(+2000 ft -2000 ft) by amending these two lines in the aircraft.cfg file.

pitch_stability=0.5
elevator_trim_effectiveness=7.0

Of course, it is none of my business to be doing this but it does seem to make the autopilot trim behaviour much less unpredictable.

I was finding that the aircraft was losing several thousand feet in a long turn and taking a very long time to settle back to the set altitude. Sometimes this ended in an autopilot controlled flight into terrain.

There also appeared to be a consequential effect on the autothrottle, each time the autopilot pitched up, the throttles opened and then when it pitched back down again, it throttled back.

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Delta558 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Delta558 Quote  Post ReplyReply Direct Link To This Post Posted: 04 Dec 2017 at 9:27pm
If that works for you and you are happier flying it like that, that's great - the main thing is that the end-user gets enjoyment from the product.

I will, however, just make a couple of points which I think should be borne in mind, particularly for others who may wish to make adjustments here:

Decreasing pitch stability will make hand-flying harder. It is currently set at a level where you should be able to leave it for a short time with no real adverse consequences (e.g. when you are looking down at the autopilot in the VC). The reduction in pitch stability will likely mean that it wanders much more easily, especially in wind or turbulence.

Increasing the elevator trim effectiveness will throw out all trim calculations - for take-off, trim should be set at some point in the white band on the trim gauge (dependant on CG). With the adjustment above, setting it to the lowest point on the band (4 units) results in a steep nose-up rotation once the aircraft is off the ground and the need for nearly full forward stick to prevent a stall.
If you set up for the approach at reasonable landing weights (7 units nose-up trim, 80%rpm roughly) unless you have full flap and are below 140kts the nose is again rotating upwards very rapidly.

And then the general handling - the combination of the two adjustments above will enable you to comfortably complete a 360 degree turn at 1000ft and 200kts within the boundary of Brize Norton airfield. I would have though that well out of the ability of even this sprightly old aircraft.

I'm not being deliberately negative here, the flight dynamics are not the problem though. For anybody who hand-flies this, I would suggest steering clear of such adjustments. If you spend all your time on the Autopilot, it may well be worth a try. The problem is with the way the default FS AP functions and interacts with an aircraft that has been set up with realistic levels in the fde. I'm still working on this around my real-world work, and hopefully will have a solution which suits all parties soon.

Cheers,
Paul.
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ncooper View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ncooper Quote  Post ReplyReply Direct Link To This Post Posted: 04 Dec 2017 at 9:51pm
Thank you for the very detailed reply.
Indeed I have observed some of the negative effects of my adjustment and would not commend it to anyone except for the positive effect that it has in eliminating the autopilot porpoising.
I am most certainly not a developer and I take my hat off to you.
Regards, Nick
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vanhelsing View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote vanhelsing Quote  Post ReplyReply Direct Link To This Post Posted: 10 Dec 2017 at 2:03pm
Hello
I have also problems with the flight Dynamic during the landing.
The effect of the stabilizer is to low. Following situation:
Landing approach with flaps 35 °, speed 130 kn, fuel 8000 kg, payload default after loading the VC 10. In the final the stabilizer is fully extended (13 °) and I have to pull on the elevator permanet. If I bring the joistick in the neutral position, the plane crashed. Can someone help me with this problem?

regrads
Chris
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jimos87 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jimos87 Quote  Post ReplyReply Direct Link To This Post Posted: 10 Dec 2017 at 5:24pm
So I have just re tested again with the config I was sent, my stability issue I fixed, but there are other things I am noticing. When I lowered the flaps the nose went up and the climb read 4000 fpm, little extreme, Also upon trying to use the ILS the first time nothing captured, The 2nd time it captured but when it was on the approach it randomly took a steep dive, I had very low visibility because of the snow ad if I hadn't have noticed and taken control we would have all died.

Also, it wouldn't let me trim back up during approach its stuck int he same position. I did manage to do a long landing with just enough runway left. I don't know whats causing these issue because of its only affecting some of us but its infuriating. 
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Delta558 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Delta558 Quote  Post ReplyReply Direct Link To This Post Posted: 11 Dec 2017 at 1:26am
Originally posted by vanhelsing vanhelsing wrote:

Hello
I have also problems with the flight Dynamic during the landing.
The effect of the stabilizer is to low. Following situation:
Landing approach with flaps 35 °, speed 130 kn, fuel 8000 kg, payload default after loading the VC 10. In the final the stabilizer is fully extended (13 °) and I have to pull on the elevator permanet. If I bring the joistick in the neutral position, the plane crashed. Can someone help me with this problem?

regrads
Chris


Hi Chris,

I have just attempted to replicate your situation, though I used full flap which should give more nose-down than the 35° you used so if anything should make your problem worse.

At the AUW / fuel you give, threshold speed is 126kts so an approach at 130 is reasonable. Generally, for setting up the approach, initial figures of +7 units trim and 82%rpm should put you in the ballpark and adjust from there. I found that a push FORWARDS on the stick was required and that by reducing trim to roughly +6 I was able to leave the stick in the neutral position.

I actually don't know what to suggest right now, as the behaviour is so far removed from what I am seeing. Perhaps try a re-install, see if that helps?

Cheers,
Paul.
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Delta558 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Delta558 Quote  Post ReplyReply Direct Link To This Post Posted: 11 Dec 2017 at 1:38am
Originally posted by jimos87 jimos87 wrote:

When I lowered the flaps the nose went up and the climb read 4000 fpm, little extreme


If you think that's bad, you should try the Canberra! Seriously, the pitching on the flaps is a known thing, you should be prepared for it and trim it out as it happens (over the 10 secs or so that the nose is moving upwards) and also be prepared for the reversal of trim that may well be required in the following 5 seconds of the first stage of flap selection. Further flap extension gives a strong nose-down, which again you need to trim out. It was all described thoroughly to me during testing by a VC10 pilot on the testing team and he was happy with the pitching effect. Expect it and fly the aircraft, don't let it fly you.



Originally posted by jimos87 jimos87 wrote:

Also upon trying to use the ILS the first time nothing captured, The 2nd time it captured but when it was on the approach it randomly took a steep dive, I had very low visibility because of the snow ad if I hadn't have noticed and taken control we would have all died.

Also, it wouldn't let me trim back up during approach its stuck int he same position. I did manage to do a long landing with just enough runway left. I don't know whats causing these issue because of its only affecting some of us but its infuriating. 


If you read back up the thread a bit, you'll see plenty of discussion on the AP - it is not working as well as it should because of the reliance of the default MSFS AP on elevator trim to control pitch, rather than the elevator itself. It's something that is still being looked at, not going to be a quick fix but neither is it going to be left as is. This is also the reason for your inability to 'trim back up' on approach - it is stuck where it is because the AP has taken control of it and you cannot override it.

Hope that helps,
Paul.
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Delta558 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Delta558 Quote  Post ReplyReply Direct Link To This Post Posted: 11 Dec 2017 at 3:27pm
Originally posted by Hriches2 Hriches2 wrote:

And for anyone new do I set the trim to 0 at climb and how would you trim the aircaft for landing without overdoing the trim. New to the trim situation and sorry for the begginers comment. Great if you could explain trimming the VC-10 in more detail for all starters.

Thanks


Hi,  sorry for the late reply but I missed this one!

Very basically, as mentioned above there are large pitching moments associated with the flaps - these will need to be trimmed out.

Looking at the plan view of the aircraft,  the fuel is contained in the wings so you will see the CG shifting forwards as you decrease the fuel load. Therefore, re less fuel and lower AUW the more nose-up trim you will need to use.

Take-off: trim should be within the white band on the trim gauge. Fully laden you should be looking at about 6 units. Take out some fuel and you could head up as high as 8 units,  conversely if you maintain fuel and remove passengers and payload you'll be heading back down towards 4 units.

As the aircraft climbs and speed builds, you should be trimming forwards until you are at roughly 0 units at cruise speed. A fast cruise may require a touch of nose-down trim, but very little.

Setting up for the initial approach, once you have dealt with the initial flap deployment you should be aiming for roughly 7 units of trim and about 82% on the engines.

Hope that is the sort of thing you were looking for,
Paul.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote kayjaydeee Quote  Post ReplyReply Direct Link To This Post Posted: 02 May 2018 at 4:12pm
Looking at the outside view with full flap, 130 kts and 600 fpm descent the body angle is about zero or slightly nose down. During my 7 years as VC10 flight crew I always felt the body angle to be nose up in that config. Is the model producing too much lift?
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Delta558 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Delta558 Quote  Post ReplyReply Direct Link To This Post Posted: 02 May 2018 at 6:42pm
I think you may be right in focusing on the lift there - lift from the flaps particularly is very high to meet the stall speeds from the ODM graphs, in fact I had to resort to multiple flap entries with different lift and drag figures for specific ranges because with just one flap entry (as is normally done in the sim), the correct lift amount at full flap to give the right stall speeds resulted in the take-off config causing the mains (and entire rear of the aircraft) to lift off first, sort of B52 style.

However, there are plenty of videos strewn across YouTube of VC10s approaching in either a level or nose-down attitude, a selection of 3 RAF and one BOAC below to illustrate:


https://www.youtube.com/watch?v=WWLxxX65MPA

https://www.youtube.com/watch?v=iF0M3Y1lJos

https://www.youtube.com/watch?v=O6cpdsuk5KI

https://youtu.be/fx8Ezjk6qqQ?t=1m3s

I found the majority of videos to show this sort of angle, but again in none of them do we know the actual speeds, rate of descent or payload / CG. I have built the fde primarily off the figures from the ODM, then watching endless videos and having conversations with a VC10 pilot who tested for us, but I'm not going to rigidly insist that it's right as it is - what I will do is look at it again when we come to the Pro / RAF / Super versions and anything which gets altered for that will (where relevant) be adjusted in this version.

Cheers,
Paul.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote kayjaydeee Quote  Post ReplyReply Direct Link To This Post Posted: 03 May 2018 at 10:32am
Thanks for that. Having played around with the numbers I have got it to land in a level attitude 120 Kts at 90,000 kgs. The flare appears to be non existent though.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Delta558 Quote  Post ReplyReply Direct Link To This Post Posted: 03 May 2018 at 1:37pm
You're spot on with the threshold speed there for 90,000, power off stall speed at that weight in the landing config is 92kts (power on slightly higher, but I've not got the graph for that one!). Provided you are correctly trimmed for the approach there should be plenty of elevator authority for a flare - I've just tried it and found myself floating off down the runway waiting for a little bit of sink when the speed had bled off, and most definitely landed with a nose-up attitude.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote kayjaydeee Quote  Post ReplyReply Direct Link To This Post Posted: 03 May 2018 at 1:47pm
Was that hand flown or autopilot flare?
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Delta558 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Delta558 Quote  Post ReplyReply Direct Link To This Post Posted: 03 May 2018 at 2:03pm
Hand flown.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote kayjaydeee Quote  Post ReplyReply Direct Link To This Post Posted: 03 May 2018 at 2:50pm
I had forgotten that Flare meant you had to land it yourself! OK now hopefully the Super will have Autoland although it wasn't very good on the real thing. Ken
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Omid Quote  Post ReplyReply Direct Link To This Post Posted: 02 Oct 2018 at 2:27pm
Hi there
Sorry for resurrecting the seemingly dead thread!
Now, I need to get back to the original post on this thread which is about maintaining altitude during cruise; I'm NOT talking any flap levels and yes the aircraft has been trimmed before engaging the autopilot but it goes through large swings of pitching up and down and gaining/losing altitude by THOUSANDS rather than hundreds or tens of feet and literally never settling into stead flight.
And during a turn.........OMG.
Disengaging the AP and hand trimming is of no help and in fact trimming the AC in this crazy phase is next to impossible.
I'm a newbie with this aircraft and I've only flown it a few times but in 3 out of 4 flights I've been unable to take my hands off the yoke/trim for a minute! Only in 1 flight did the AC behave completely normally in the air (bouncing on the ground remains an unsolved issue and I acknowledge it's mentioned in another thread which also appears to have reached a dead-end).
With all the explanations Paul provided here (with thanks!), I do not think this should be the normal behaviour of ANY aircraft and I've never seen it happen on any other freeware or payware for that matter.
Paul, Martyn and other gurus, have  you actually seen a footage of what we're talking about? I understand that so far you guys have not been able to reproduce the problem.
Has anybody provided videos of the problem?

Regards-Omid
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Lord Nibbo Quote  Post ReplyReply Direct Link To This Post Posted: 04 Oct 2018 at 10:19am
I have cured this with a huge edit of the aircraft.cfg if you would like a copy of my aircraft.cfg I fly using Prepar3Dv4 but I expect it should work in FSX my email is djbeckett at gmail.com   change the at for @ the same goes for anyone not satisfied with the flight model, email me and I'll post you a copy of my cfg.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Omid Quote  Post ReplyReply Direct Link To This Post Posted: 04 Oct 2018 at 12:35pm
Many thanks Lord Nibbo
Can you please forward it to dr_kah at yahoo dot com?
And may I ask what did you identify as the culprit? and what logic did you follow to make those modifications?
I'm sure the others including the developers would be interested in knowing how changing things have solved the problem for you as well as comment on the pros and cons.
Regards
Omid
Regards-Omid
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Lord Nibbo Quote  Post ReplyReply Direct Link To This Post Posted: 04 Oct 2018 at 2:04pm
I've altered too many things to put it down to one causing the problem, no doubt those pureists that want it to be an exact copy of how the real planes flies will cringe at what I've done. But I just want something that dont porpoise over 2000 ft in a turn and to keep quoting to trim the plane out.... well thats ok if you got more than twenty miles to trim it but making a tight turn into an ILS you aint going to manage it.  If I were to list the main thing I altered it would be this


[flight_tuning]
cruise_lift_scalar=1.0
pitch_stability=0.1 

But as I've already said these are just a couple of what I've changed I just can't remember all the others I've changed.
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