Amount of elevator trim required for level flight?

[Yo-Yo]

12 minutes ago, Holbeach said:

Here is the view I use to set the trim. (No parallax).

Which one is 7.5 deg on the tab? The tab is still moving between the two.

 

Both of these settings will overcome elevator full aft stick.

 

..

If some some light added...
But actually it has no big sense as you must not be interested how much trim do you have, because it depends on many things that change.
The only case it can interest you is takeoff presetting.

 

[Holbeach]

That's true. I'm only using it as a reference for the point at which the aircraft becomes uncontrollable.

At 18000 lb it occurs forward of this point.

This is full aft stick point.

The trimmer shouldn't be able to overcome the power of the elevator, for obvious resons.

The Spitfire has got it right.

 

 

 

[Yo-Yo]

It's not Spitfire. It's a much bigger plane. I can not understand your point completely, but I can say they in RL improper trim can kill you at takeoff because of very high forces at the stick.

[Holbeach]

OK. Thanks for the reply.

 

..

[Art-J]

On 10/17/2021 at 5:21 PM, SMH said:

I find it very unlikely that they trim out in cruise to anywhere but very close to the center position. Why would you make the center not the center?

And, again, this strong nose-heavy trim is an indicator that we're tail heavy, which explains the extreme touchiness in the pitch axis that real Mosquito pilots don't report. Why would they make the aircraft like this when it's just a matter of balancing it correctly to make it far more stable?

It's clearly wrong, and so is the Spitfire. (I'd bet you money that they started with the Spitfire model for this one.)

 

Playing Devil's advocate, some manufacturers clearly did just that for whatever reason. Spitfire is the most obvious example - check any picture of a any version of Spit flying, restored or historical - you'll see they all fly with elevator slightly down (about +1 div nose-heavy was standard cruise setting) - it's almost a visual trademark of this plane and I'm glad that DCS , unlike Il-2GB, portrays it accurately on both flight model and animation level.

Same for all Bf-109 versions requiring more or less nose down trim to fly level.

For me, as this thread starter, these flight properties seem somewhat strange I admit, but if original manufacturer's drawings or flight test data (especially trim curves) show that's the way they were, then who am I to argue. We can only test fly in ISA conditions, trying to match the loadout configs from these charts and see if DCS model matches test results closely enough.

[Robi-wan]

In response to @Art-J in a different thread. I think he is correct that 2 units nose down in cruise flight is incorrect. My source? A reprint of the 1942/43 flight control rigging guidance used by Mosquito erks.

But here's the bottom line...

[grafspee]

So the problem does not lie how trim works in DCS but problem is that when we set neutral elevator trim, trim tab is perfectly aligned to elevator trailing edge, but according to the manual it should be deflected up when in cockpit indicator  shows half a notch.

It looks like that neutral trim is not exactly trim tab aligned with trailing edge.

Fix easy to implement i think. It is indicator pointer problem

Edited April 5, 2022 by grafspee

[Robi-wan]

5 hours ago, grafspee said:

It looks like that neutral trim is not exactly trim tab aligned with trailing edge.

That's what the first highlighted note states, and it could be either up or down.

5 hours ago, grafspee said:

It looks like that neutral trim is not exactly trim tab aligned with trailing edge.

Sorta, in some airplanes it will be exactly aligned, in some/many/most (take your pick of an undetermined number) the trim tab will be slightly out of neutral to achieve ZERO on the indicator at cruise. To say that in ALL cases it won't be aligned is inferring something NOT implied by the documents.

5 hours ago, grafspee said:

Fix easy to implement i think. It is indicator pointer problem

Finally we agree. I have to ask you, are you a pilot IRL? And what real airplanes have you flown that requires TWO UNITS of nose down trim in level flight AND in a climb? I've never flown an airplane with such an odd trim requirement, and in my very brief experience with the DCS Mosquito that just screams something was wrong with the trim model or trim indication.

A big thank you to @Art-J for pointing out the error back in Oct. As we'd say back in my Jurrassic Era fighter squadrons..."Good on ya!" Without his prompting I wouldn't have kept searching for the documentation.

[grafspee]

@Robi-wan I am not a pilot IRL.

Back to the elevator trim, what you showed on screens from manuals, it is obvious that mosquito supposed to be rigged so the level flight could be done with elevator trim indicator being between neutral and 1 notch.

I wasn't totally against you, plane behavior from manual which you showed show same behavior in DCS, when i deploy flaps mosquito pitches up, when i drop gear mosquito pitches down so those 2 deployed at the same time will more or less cancel so trim change isn't noticeable for me.

Edited April 5, 2022 by grafspee

[Robi-wan]

@grafspeeokay, it's all good. We're good mate.

[Art-J]

19 hours ago, Robi-wan said:

Finally we agree. I have to ask you, are you a pilot IRL? And what real airplanes have you flown that requires TWO UNITS of nose down trim in level flight AND in a climb? I've never flown an airplane with such an odd trim requirement, and in my very brief experience with the DCS Mosquito that just screams something was wrong with the trim model or trim indication.

Just to keep in mind various old plane design peculiarities, Spitfires and 109s for example required nose down trimming for level flight all the time (in the latter - full nose down for anything above econo-cruise speed actually), so I don't consider Mossie's case to be particularly strange in this regard. 

Granted, based on docs posted, trim indicator itself seems be simulated incorrectly here, but honestly the only time I use it in Mossie (or any other DCS warbird for that matter) is before takeoff, not really needing it through the rest of the flight. Knowing DCS development and bug-fixing pace all too well, I suspect the indicator won't ever be tweaked (not anytime soon at least). I'd rather have them prioritize more pressing issues first, like steaming port engine problem or bomb fuses implementation.

[Robi-wan]

7 hours ago, Art-J said:

Just to keep in mind various old plane design peculiarities, Spitfires and 109s for example required nose down trimming for level flight all the time (in the latter - full nose down for anything above econo-cruise speed actually), so I don't consider Mossie's case to be particularly strange in this regard. 

No disrespect intended, but you make that as a statement of fact based upon what exactly? Game experience or technical manual references? Being the skeptical assh*le by nature that I am, I would expect the Spitfire rigging manual (perhaps one in this book) Spitfire Mk V Manual would have steps similar to the Mosquito regarding installing the horizontal stab (flight testing that installation) and rigging the trim. Since I can't read German, it might be interesting to know what their rigging guidance says. If I think about it, requiring full nose down trim for high speed level flight would essentially eliminate diving after a target because you quickly lose elevator authority as your airspeed increases (resulting in what we called in the USAF as a bananna pass).  I read the Mosquito rigging guidance (neutral trim for level cruise) to be consistent with every other airplane I've flown, so forward trim for low AoA and aft trim for high AoA. YMMV.

7 hours ago, Art-J said:

Granted, based on docs posted, trim indicator itself seems be simulated incorrectly here, but honestly the only time I use it in Mossie (or any other DCS warbird for that matter) is before takeoff, not really needing it through the rest of the flight.

With almost 50 years of flying and trimming, I frequently glance at the trim settings in every game since trimming IRL is done by feel ("trim the pressure off") and that is something I find grossly lacking in the 1GCCFP experience. I even checked the trim settings frequently in RL.

Edited April 6, 2022 by Robi-wan

[Art-J]

No offense taken and I certainly respect real pilot's feedback.

About the Spit, take a look at any photo of the plane in level flight. Early mark, late mark, wartime, restored, doesn't matter. They all show light elevator down horns up, which is almost as visually "iconic" for Spits as their wing platform. Then there's controversial bit in DCS Spit manual stating that pointer two notches above level on the pitch trim indicator corresponds to "neutral" trim (whatever that means) - although, there's always a chance an indicator itself might have been modelled not quite correctly. Oh well, let's be happy there is an indicator at all, 'cause Brits didn't bother to put one for rudder trim at all throughout entire war.

About the 109, that's a can of worms and scorching hot topic that was discussed on this forum ad nauseam since 2014. I don't feel like messing with it again, prefer to fly the damn plane instead ;). If you're interested, though, I'll just point to Yo-Yo's explanation thread on the subject (with further data posted in the other thread that first one links to):

When talking about not needing an indicator in flight, what I meant was I just react to what the plane does after takeoff (by watching slip indicator and VVI) and to what I need to do to eliminate slip and "neutralize" my joystick in various power/flap/gear configurations. Then I trim accordingly - no need to check the indicators for that (the manuals usually don't mention them either anyway, but rather tell you to trim "as required").

Edited April 6, 2022 by Art-J

[Bozon]

49 minutes ago, Art-J said:

...

When talking about not needing an indicator in flight, what I meant was I just react to what the plane does after takeoff (by watching slip indicator and VVI) and to what I need to do to eliminate slip and "neutralize" my joystick in various power/flap/gear configurations. Then I trim accordingly - no need to check the indicators for that (the manuals usually don't mention them either anyway, but rather tell you to trim "as required").

 

The reason that trim indication matters IRL and why I was worried about the constant indicated nose-down trim was that this may be an indication that the center of gravity is too far back. The documents presented above suggest that in the case of the Mosquito FB.VI this is by design, for some reason. Otherwise, it's true that once trimmed, the indicated trim does not matter and trim changes are relative to the current trim state - whatever it happens to be.