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 Post subject: Re: Trim Takeoff Setting
PostPosted: Tue Aug 16, 2016 6:06 am 
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Oliver Branaschky wrote:
Or maybe it's as simple as a mis-calibrated joystick/yoke? I definitely cannot reproduce the behavior either, Bob.


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Oliver Branaschky



I fly many other aircraft, all payware, and no issue with elevator or trim with any of them including the A2A Cherokee . In addition I have found numerous mentions of the trim issue on the C 172 on this forum and on Avsim forum on various threads, with the suggestion of setting trim as I mentioned above, at -35% or the bottom of the letter K in Takeoff.
viewtopic.php?f=64&t=38333

Anyway, I did some more reading on the topic and made a change last night which is not related to takeoff trim setting but to trim wheel movement speed. I had found a Youtube video on speeding up the trim movement on the C 172, when using FSUIPC, and I was having that issue with the trim just moving way to slowly to adjust the trim in any kind of normal manner. In FSUIPC I was using the trim up and down command. The video suggested using instead, a key stroke, the + and - on the num pad and having the joystick trim buttons trigger those letters, and then in FSX or P3D, have + and - set the trim up and down.. https://www.youtube.com/watch?v=RLicQD-jndY This produced a different response when adjusting the trim. When first pressing up or down, the trim wheel starts out slowly and then after a second or two, it speeds up. This produced a faster response of the trim wheel once the non linear movement of the trim wheel reached it's higher rate of turning, but made it difficult to judge how long to hold the trim button down to get the desired trim adjustment, and resulted in trim overshoots when trying to adjust, in other words, to nose up, and then too nose down. Never pass a checkride adjusting the trim like that. :wink:

Last night I read about assigning the trim movement in the C 172 using the built in A2A configurator, so I decided to give that a try. I deleted the C 172 trim assignment in FSUIPC for the C-172, and set the trim up and down joystick buttons on my joystick using the configurator. Now I had a totally different trim wheel response. The action is the faster movement of the trim wheel, which I wanted, but now the movement speed was linear. It did not start slowy for 1-2 seconds and then speed up, the speed was constant. Now the combination of setting the takeoff trim nose down at the bottom of the letter K or -35%, and the new linear response of the trim wheel speed using the A2A configurator, the result, trimming the C 172 is now ideal. Upon rotation I get a climb rate of about 7-800 FPM rather than more than 1600 fpm +, and to tweak it for the exact airspeed I want with trim adjustment, to around 80 knots, works perfectly.

Again, the question I ask to anyone that is interested in this take off trim setting topic, is to set your C 172 up for a 700 fpm climb rate after rotating, using the AP, and see what you trim setting settles down at, and post it on this thread. I think you will find that it will be pretty close to -35% or the bottom of the letter K.

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 Post subject: Re: Trim Takeoff Setting
PostPosted: Tue Aug 16, 2016 7:31 am 
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bobsk8 wrote:
Now the combination of setting the takeoff trim nose down at the bottom of the letter K or -35%, and the new linear response of the trim wheel speed using the A2A configurator, the result, trimming the C 172 is now ideal. Upon rotation I get a climb rate of about 7-800 FPM rather than more than 1600 fpm +, and to tweak it for the exact airspeed I want with trim adjustment, to around 80 knots, works perfectly.
Bob - as mentioned in my previous post, this is very different to the behaviour I see. You're not taking off with flaps at 10° are you by any chance? If so, this would certainly explain why more nose down trim would be required.

bobsk8 wrote:
Last night I read about assigning the trim movement in the C 172 using the built in A2A configurator, so I decided to give that a try. I deleted the C 172 trim assignment in FSUIPC for the C-172, and set the trim up and down joystick buttons on my joystick using the configurator. Now I had a totally different trim wheel response. The action is the faster movement of the trim wheel, which I wanted, but now the movement speed was linear. It did not start slowy for 1-2 seconds and then speed up, the speed was constant.
Yeah, I agree the constant speed trim response via the input configurator is much better than the default 'trim acceleration' feature. :wink:

bobsk8 wrote:
Again, the question I ask to anyone that is interested in this take off trim setting topic, is to set your C 172 up for a 700 fpm climb rate after rotating, using the AP, and see what you trim setting settles down at, and post it on this thread. I think you will find that it will be pretty close to -35% or the bottom of the letter K.
Not with flaps retracted it won't on my setup. I think it'll trim down to no more than -15% or so as the aircraft accelerates. As mentioned, if I pitch for VX, very little adjustment to the trim is needed initially. Pitching for VY requires a bit of nose down trim to relieve control pressure, but nowhere near -35%.

Nick

P.S. Remember that the A2A C172 in particular has gone through many updates and tweaks since release, so some of the comments/observations in old threads (such as this one) may no longer be entirely valid.


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 Post subject: Re: Trim Takeoff Setting
PostPosted: Tue Aug 16, 2016 7:45 am 
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Nick M wrote:
bobsk8 wrote:
Now the combination of setting the takeoff trim nose down at the bottom of the letter K or -35%, and the new linear response of the trim wheel speed using the A2A configurator, the result, trimming the C 172 is now ideal. Upon rotation I get a climb rate of about 7-800 FPM rather than more than 1600 fpm +, and to tweak it for the exact airspeed I want with trim adjustment, to around 80 knots, works perfectly.
Bob - as mentioned in my previous post, this is very different to the behaviour I see. You're not taking off with flaps at 10° are you by any chance? If so, this would certainly explain why more nose down trim would be required.

bobsk8 wrote:
Last night I read about assigning the trim movement in the C 172 using the built in A2A configurator, so I decided to give that a try. I deleted the C 172 trim assignment in FSUIPC for the C-172, and set the trim up and down joystick buttons on my joystick using the configurator. Now I had a totally different trim wheel response. The action is the faster movement of the trim wheel, which I wanted, but now the movement speed was linear. It did not start slowy for 1-2 seconds and then speed up, the speed was constant.
Yeah, I agree the constant speed trim response via the input configurator is much better than the default 'trim acceleration' feature. :wink:

bobsk8 wrote:
Again, the question I ask to anyone that is interested in this take off trim setting topic, is to set your C 172 up for a 700 fpm climb rate after rotating, using the AP, and see what you trim setting settles down at, and post it on this thread. I think you will find that it will be pretty close to -35% or the bottom of the letter K.
Not with flaps retracted it won't on my setup. I think it'll trim down to no more than -15% or so as the aircraft accelerates. As mentioned, if I pitch for VX, very little adjustment to the trim is needed initially. Pitching for VY requires a bit of nose down trim to relieve control pressure, but nowhere near -35%.

Nick

P.S. Remember that the A2A C172 in particular has gone through many updates and tweaks since release, so some of the comments/observations in old threads (such as this one) may no longer be entirely valid.


Zero flaps takeoff, as I would in a real C 172 on a normal runway. I am still asking what trim setting are you seeing in a 700 fpm minute steady climb rate with AP on? If you see around negative 35% than what I am seeing is what you have, if not, then maybe there is something wrong with my aircraft cfg. which I have never touched by the way. I don't want to try and fix something that isn't broken, so knowing what other people are seeing for trim at this normal climb rate will certainly tell me if there is something wrong with my 172 installation.

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 Post subject: Re: Trim Takeoff Setting
PostPosted: Tue Aug 16, 2016 7:52 am 
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bobsk8 wrote:
I am still asking what trim setting are you seeing in a 700 fpm minute steady climb rate with AP on?
Not able to check this right at the moment Bob, but I'll attempt to quantify the figure I see later. As mentioned, it's definitely not -35% though! Did you see my earlier suggestion about 'forcing' the update by deleting the client.wyc file?

Thanks,
Nick


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 Post subject: Re: Trim Takeoff Setting
PostPosted: Tue Aug 16, 2016 7:55 am 
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Nick M wrote:
bobsk8 wrote:
I am still asking what trim setting are you seeing in a 700 fpm minute steady climb rate with AP on?
Not able to check this right at the moment Bob, but I'll attempt to quantify the figure I see later. As mentioned, it's definitely not -35% though! Did you see my earlier suggestion about 'forcing' the update by deleting the client.wyc file?

Thanks,
Nick


No I missed that info on forcing update, will look for it..... Where is it located. I will give it a try?

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 Post subject: Re: Trim Takeoff Setting
PostPosted: Tue Aug 16, 2016 8:06 am 
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This post on the previous page: viewtopic.php?f=64&t=38333&start=30#p427100. :wink:

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 Post subject: Re: Trim Takeoff Setting
PostPosted: Tue Aug 16, 2016 9:26 am 
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Nick M wrote:
This post on the previous page: http://a2asimulations.com/forum/viewtop ... 30#p427100. :wink:

Nick



That fixed it :D :D :D I renamed that client .wyc file, and ran the update again. The down side is it put the aircraft. cfg file back to default, but I have everything on a backup drive, so I just copied the repaints in the cfg I had over to the new one, and I also had to re-edit the camera cfg file to get Ezdok outside view and inspection view to work together again, and that just took a few minutes.

The result after re downloading the update and running it again , is now I can take off with the trim set at the takeoff mark, and the pitch up is much more normal around Vx, and a quick down trim adjustment produces a nice Vy speed.... Thanks very much for your help, I would never have been able to figure this out....

BTW, assigning the trim in the A2A configurator is definetly a major improvement in trim adjust functionality.

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 Post subject: Re: Trim Takeoff Setting
PostPosted: Tue Aug 16, 2016 10:15 am 
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Hey - that's good news Bob. Glad we could help. :) As mentioned, there are quite a few fixes that have been added to the 172 since its release, so you'll likely see a few other enhancement in terms of handling and so on.

All the best,
Nick


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 Post subject: Re: Trim Takeoff Setting
PostPosted: Tue Aug 16, 2016 10:33 am 
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Nick M wrote:
Hey - that's good news Bob. Glad we could help. :) As mentioned, there are quite a few fixes that have been added to the 172 since its release, so you'll likely see a few other enhancement in terms of handling and so on.

All the best,
Nick


Yes, I had run the update a couple of times and as recently as a couple of weeks ago, but apparently it never "took". The proof of that is I had installed a few repaints almost a year ago, and when I ran the update this time, the cfg was changed and the repaints cfgs had to be reentered, which had never happened previously. I think I figured out how this all happened. When I bought the C 172 last year, I had P3D version 2, which I uninstalled when I got version 3. Once version 3 was installed, I took the original install file of the C 172 and ran it again, and apparently because of that client .wyc file itg thought it had already been updated, so the update never ran, until I deleted client .wyc file this morning. I just ran the Cherokee update again following the same procedure just to make sure it had really installed, since I got the Cherokee before P3D V 3.

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 Post subject: Re: Trim Takeoff Setting
PostPosted: Thu Oct 06, 2016 6:38 pm 
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Well I do not know about all that has been talked about here. This is what I do and it works very well for me. After run up I set trim to take off mark. drop flaps 10 release parking brake. roll out at 55 knts. then the first thing is I throttle back so the manifold pressure is at the top of the green. At 400 ft AGL I retract flaps to 0. Then I throttle back to cruse about 20 inches and decrease prop to 2.4 k or a little less. 500 ft below Cruse Alt I start to trim for level flight little by little. I have assigned elv trim through fsuipc4 to a rotatory on my throttle.
Works soothe every time. of course I compensate for cross wind and weather. maybe and I am not trying to be a wise guy here but it might more about knowing how to take off than all this trim wheel stuff.


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 Post subject: Re: Trim Takeoff Setting
PostPosted: Thu Oct 06, 2016 6:41 pm 
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Roland Ives wrote:
Well I do not know about all that has been talked about here. This is what I do and it works very well for me. After run up I set trim to take off mark. drop flaps 10 release parking brake. roll out at 55 knts. then the first thing is I throttle back so the manifold pressure is at the top of the green. At 400 ft AGL I retract flaps to 0. Then I throttle back to cruse about 20 inches and decrease prop to 2.4 k or a little less. 500 ft below Cruse Alt I start to trim for level flight little by little. I have assigned elv trim through fsuipc4 to a rotatory on my throttle.
Works soothe every time. of course I compensate for cross wind and weather. maybe and I am not trying to be a wise guy here but it might more about knowing how to take off than all this trim wheel stuff.

I don't think reducing manifold pressure is recommended by real pilots at such low altitudes.

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 Post subject: Re: Trim Takeoff Setting
PostPosted: Thu Oct 06, 2016 8:48 pm 
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Trim isn't set according to throttle position. It's set for a "Takeoff Position" and once airborne, it is used to relieve control pressures.

If no obstacle, flaps come up once above a safe retraction speed - Vx or better - but check the POH (edit: mis-read the power reference).

Years back when learning takeoffs in Complex / Multi- Aircraft, it was typical to bring the power back to 25/25 at 400'agl. I posted on this a while back - one reason why I no longer think this is a good idea.

The guys at Advanced Pilot Seminars say they have hard data that demonstrate reduced power settings cause more stress on the engine than full throttle / full rpm.

The goal of a takeoff is to gain airspeed and altitude - not to make things easy with respect to trim.

-Rob

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