Flight Dynamic problem
Printed From: Just Flight Forum
Category: Just Flight Products
Forum Name: VC10 Jetliner
Forum Description: Discussion area for VC10 Jetliner
URL: http://forum.justflight.com/forum_posts.asp?TID=31911
Printed Date: 16 Apr 2024 at 8:40pm
Topic: Flight Dynamic problem
Posted By: jimos87
Subject: Flight Dynamic problem
Date Posted: 30 Nov 2017 at 10:56am
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Is anyone else expeireinng issues with autopilot alt hold moving up /down by 2000 fpm when its supposed to be level flight. This is the 2nd time ive reinstalled now and the issue is still there on P3 V4. I had to give up on my inaugral flight today because of this issue. Also the AT does not engage when i turn on AT power. |
Replies:
Posted By: Martyn
Date Posted: 30 Nov 2017 at 11:31am
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Are you trimming out the aircraft before engaging altitude hold mode? In the real aircraft the altitude hold mode is designed to be engaged once the desired altitude has been reached and the aircraft trimmed out for level flight, however we've included a vertical speed mode for convenience. Have you engaged airspeed hold mode using the IAS switch after switching on the autothrottle power and selecting the desired airspeed? Thanks Martyn ------------- Martyn Just Flight Ltd |
Posted By: Delta558
Date Posted: 30 Nov 2017 at 12:07pm
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Further to Martyn's comment, initial rate of climb is under 2,000fpm for the standard so you should definitely be climbing at or below that rate before engaging the AP. Lightly loaded, it will climb faster - I have just flown a light and steep climb-out at a touch under 4,000fpm and set the Alt hold to 5,000ft. At that rate of climb, it did take a couple of cycles but captured the altitude. I then set it to a 2,000fpm climb and it captured 8,000ft perfectly. At higher altitudes, your RoC will be lower and there should be no issues capturing an altitude. Cheers, Paul. |
Posted By: jimos87
Date Posted: 30 Nov 2017 at 12:07pm
| Airspeed was engaged as per the tutorial flight, The Alt hold system set the V/S to 0 but the pitch trim automatically moves by itself. I tried to centre it manually and turn Alt hold back on but it just did the same thing. on the very first flight I did it was fine there was just the speed dial bug which I also reported. |
Posted By: jimos87
Date Posted: 30 Nov 2017 at 12:08pm
| My rate of climb is default at 1800 fpm thats set by the AC config |
Posted By: Delta558
Date Posted: 30 Nov 2017 at 12:13pm
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The pitch trim needle moving is a side-effect of the default FSX / P3D AP system, which uses trim rather than elevator to control pitch. With most aircraft it's not seen, but with the VC10 you have a great big instrument there to show you! Don't try fighting it, unfortunately it is doing what FS needs it to do. |
Posted By: jimos87
Date Posted: 30 Nov 2017 at 12:19pm
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Thats irelevent becuase it is literally doing what its showing me its doing which is not right |
Posted By: Martyn
Date Posted: 30 Nov 2017 at 12:25pm
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This is something which is probably best discussed directly with our support team as the autopilot/autothrottle is working fine here, so this will require some investigation. If you haven't done so already, please submit a support ticket via the website and our support team will look into this. Thanks Martyn ------------- Martyn Just Flight Ltd |
Posted By: jimos87
Date Posted: 30 Nov 2017 at 12:26pm
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https://www.dropbox.com/s/b2qdvj0t5jjv98y/Video%2030-11-2017%2010-17-56.avi?dl=0 Watch here you can see it going up and down. IDK why the sound is doing that i think i had the recorder on the wrong setting |
Posted By: jimos87
Date Posted: 30 Nov 2017 at 12:26pm
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I have they told me to come and read my own post. |
Posted By: Martyn
Date Posted: 30 Nov 2017 at 12:27pm
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OK. They will be in touch again shortly. Apologies for the confusion. Martyn
------------- Martyn Just Flight Ltd |
Posted By: jimos87
Date Posted: 30 Nov 2017 at 12:39pm
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I will record a video of the issue from start to finish to assist |
Posted By: Martyn
Date Posted: 30 Nov 2017 at 12:56pm
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Thanks. Please send that to Craig so he can continue his investigation. Martyn ------------- Martyn Just Flight Ltd |
Posted By: petesmiffy
Date Posted: 30 Nov 2017 at 7:41pm
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I have had no problem withe A/P in climb or altitude hold after the initial climb. However, if I change altitude and try to re-engage altitude hold the aircraft begins to wobble about 150 - 200 feet either side of the selected altitude. Enough to have the passenger reaching in the seat pocket for the paper bags. |
Posted By: Debowing
Date Posted: 30 Nov 2017 at 7:48pm
| I think that the AP needs a bit of getting used to, I had similar issues but I believe these are due to my poor VC 10 piloting skills. |
Posted By: Lord Nibbo
Date Posted: 01 Dec 2017 at 10:51am
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I think the flight model needs a lot of attention. Try flying at FL 10000 on auto pilot with auto throttle on doing
250 knots now do a 90deg turn and then tell me what happens to you? I suggest this should not happen. Try an ILS approach starting
at about 160 knots and about 30 deg off
the ILS feather. Slow aircraft before glide slope is attained to approximately 135/140
knots now try adding flaps ( suggest only 19
deg) I’ll bet your airplane is
nose down too high too fast and no way
will you land on your back wheels before the front wheels. |
Posted By: Delta558
Date Posted: 01 Dec 2017 at 11:58am
Some specifics - the flaps create large pitching moments which need to be trimmed out: from up to T/O creates a nose-up pitch initially, which you start to trim out but then (combined with the drag and speed reduction) towards the end of the movement it becomes nose down, so you have to reverse the trimming. That's over a time period of roughly 15 seconds. Moving from T/O to Approach or Land is similar to many other heavy jets and gives a strong nose-down pitch, again exacerbated by the deceleration, which you need to trim out. That is straight from a VC10 pilot who is on the testing team and is happy with the reaction of the aircraft. The problem you are seeing is not a flight model problem, but specifically an Autopilot problem: The AP (default FS) uses pitch trim to control pitch, rather than the elevator. Hopefully you can see the start of the problem - if the AP has taken over the pitch trim, how can you trim out the significant pitching motion caused by flap deployment? Then you move forwards to the speed of capture of certain elements - altitudes, glide slopes etc. Because the VC10 has an all-moving tailplane for trim and seperate elevators for pitch control, the trim in terms of degrees moved is less than you may expect. It is also slower in its reaction, hence the roughly 30 ft either side of selected altitude during the turn and then the overshoot by a couple of hundred feet on wings-level at the end of the turn. The 'simple' answer is to build a completely custom autopilot (that would be a few weeks' worth of work for whoever gets to code it!) which uses the elevator rather than trim to control pitch. Meantime, I'll keep plugging away to get more acceptable results from the default system which only really works with aircraft that run on rails and have no significant 'quirks'  I don't think full autoland is implimented in this version, either - if you set up to capture the glideslope correctly (from below, 'sensible' angle off) and are in the correct configuration already, it will fly you down the glideslope and put the mains on the ground first. A heavy landing as there is no flare, but it will put you there! Cheers, Paul. |
Lord Nibbo wrote:Posted By: Martyn
Date Posted: 01 Dec 2017 at 12:44pm
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Flare mode is partially simulated but not fully and it is largely reliant on the standard ILS approach mode. With FLARE selected on the autopilot mode selector, the aircraft will pitch up and the throttle will move to idle as you approach the runway. Thanks Martyn ------------- Martyn Just Flight Ltd |
Posted By: Lord Nibbo
Date Posted: 01 Dec 2017 at 2:43pm
edited..... Yes with the Flare mode selected it is much more realistic, thanks again Martyn
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Posted By: Hriches2
Date Posted: 01 Dec 2017 at 6:55pm
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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 |
Posted By: jimos87
Date 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. |
Posted By: ncooper
Date Posted: 04 Dec 2017 at 6:30pm
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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. |
Posted By: Delta558
Date Posted: 04 Dec 2017 at 9:27pm
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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. |
Posted By: ncooper
Date Posted: 04 Dec 2017 at 9:51pm
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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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Posted By: vanhelsing
Date Posted: 10 Dec 2017 at 2:03pm
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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 |
Posted By: jimos87
Date Posted: 10 Dec 2017 at 5:24pm
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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. |
Posted By: Delta558
Date Posted: 11 Dec 2017 at 1:26am
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. |
Posted By: Delta558
Date Posted: 11 Dec 2017 at 1:38am
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.
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. |
Posted By: Delta558
Date Posted: 11 Dec 2017 at 3:27pm
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. |
Posted By: kayjaydeee
Date Posted: 02 May 2018 at 4:12pm
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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? |
Posted By: Delta558
Date Posted: 02 May 2018 at 6:42pm
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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. |
Posted By: kayjaydeee
Date Posted: 03 May 2018 at 10:32am
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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. |
Posted By: Delta558
Date Posted: 03 May 2018 at 1:37pm
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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. |
Posted By: kayjaydeee
Date Posted: 03 May 2018 at 1:47pm
| Was that hand flown or autopilot flare? |
Posted By: Delta558
Date Posted: 03 May 2018 at 2:03pm
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Hand flown. |
Posted By: kayjaydeee
Date Posted: 03 May 2018 at 2:50pm
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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 |
Posted By: Omid
Date Posted: 02 Oct 2018 at 2:27pm
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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 |
Posted By: Lord Nibbo
Date 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. |
Posted By: Omid
Date Posted: 04 Oct 2018 at 12:35pm
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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 |
Posted By: Lord Nibbo
Date Posted: 04 Oct 2018 at 2:04pm
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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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Posted By: Omid
Date Posted: 04 Oct 2018 at 3:19pm
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Thanks buddy!!! ------------- Regards-Omid |
Posted By: Omid
Date Posted: 22 Oct 2018 at 2:48pm
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Just an update: As you may know there is an on-going issue with the aircraft bouncing up and down violently on the tarmac which is discussed here: http://forum.justflight.com/forum_posts.asp?TID=32235&PID=214327𴔷 The solution provided to this problem by user Willykurtz using the .CFG file from version 1.2 seems to have corrected both the bouncing issue and the problem currently discussed in this topic. This is after testing the aircraft with the provided .CFG file during several flights since my last post. I have not yet compared the text from this file with the current CFG file to see what's exactly different but simply replacing it has apparently fixed the problem. More feedback will be appreciated. ------------- Regards-Omid |
Posted By: Christoph4445
Date Posted: 30 Nov 2018 at 11:38pm
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I'm sorry about continuing with this thread so late, but I've just bought the vc10 about a week ago. This plane is a lot of fun. I love it. However, I find the transition from clean to flaps 1 very difficult. In fact, I've tried a Level flight at 3500 feet with flaps 1, 170 knots, 97000 gross weight. What I was surprised to see was a level flight with the nose down about 5 on the HSI. It's even worse with a higher speed (e.g. 190). Now I'm wondering if that is like the real thing. To my mind this looks really odd. What can I do about this? Thanks for your patience. Regards Chris |
Posted By: Christoph4445
Date Posted: 30 Nov 2018 at 11:46pm
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In this real video, the vc10 does a low pass along the runway. It is completely level at 0:38. I can't say how far the flaps have been deployed. I'll try this when I have the time. https://youtu.be/I5S_C3kKMi0 |
Posted By: Delta558
Date Posted: 01 Dec 2018 at 12:08am
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All I can say is that the VC10 pilot who tested for us was happy with it and told me not to alter anything about the pitching (which makes it particularly frustrating that a number seems to have disappeared from the start of the pitch MOI, but I digress). One area we spent a lot of time looking at was the pitching on the initial flap selection, as it causes an initial upwards pitch followed by a smaller downwards change. Apparently the RAF simulator never got this right - I've attempted to create something of the sort by using the timings of flap and slat extension (total of approximately 15 seconds), with the first 10 seconds (slat extension time) pitching up and then the final 5 seconds only the pitching downwards from the trailing edge flaps should be noticeable. The flaps are incredibly powerful and are set well aft, the effect is much more dramatic at higher speeds. If you watch some of the circuit work (such as the final landing at Bruntingthorpe) you'll see a lot of 'nose down' in fairly level flight! Cheers, Paul.
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Posted By: Delta558
Date Posted: 01 Dec 2018 at 12:11am
| Duplicate |
Posted By: Christoph4445
Date Posted: 01 Dec 2018 at 12:26am
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I've tried a low pass: 98000 gross weight, full flaps, 120 knots: works great, the aircraft is level. After that I climbed up to 3000 at 170 knots and flaps 1. When I levelled off, the HSI showed -5. So the problem zone is flaps 1
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Posted By: Christoph4445
Date Posted: 01 Dec 2018 at 12:38am
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Thank you for the fast reply. It is a great add-on and I can only thank you for your time and patience. Maybe your work with the super vc10 will bring a solution. Cheers Chris |
Posted By: THibben
Date Posted: 06 Jan 2019 at 11:07pm
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I have been having the same problem with the trim drifting. Lots of times I have just loaded the plane and nothing is turned on but the trim wheel starts to turn and will drive all the way to the end. I uninstalled the plane because it was not usable. I just installed it again to see if the problem is still there. I am using FSX and have a high end system. Tom
------------- Tom |