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Tail heaviness, stab trim, elevator and the Bf 109s in BoS...


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It's known from reports of rw Bf109 pilots that the 109s, specially the latest models, like the G2 or the K series, are considerably tail heavy, specially with fuel tanks considerably filled.

 

With a fuel tank considerably filled, guns loaded or even gun pods, considerable nose-heavy trim has to be used.

 

Usual setting is +1 for takeoff, but as gear and flaps are retracted and the aircraft gains speed, further nose heavy trim, sometimes up to +2 and still requiring forward stick input is required.

 

This was what a well known Messerschmitt Museum pilot recently confirmed to me, when flying the G10, or other models. As gear is retracted, flaps come up, further nose heavy trim will be required.

 

Now, I have posted at the FM section of this forums, at another thread not specifically on this matter that in BoS the 109s if trimmed at +1 during takeoff will require tail heavy trim settings as they get airborne, because otherwise we will have to pull the stick.

 

This is not the way it should be, I believe, but someone replied with an interesting observation in this post :

 

http://forum.il2sturmovik.com/topic/19480-whats-wobbling-thing/page-15#entry327851​

 

This raises a question regarding what, in the real aircraft, happens to the elevator, and control stick travel as stab trim is applied, because indeed and using a normal ( non FFB ) joystick, I can observe that when I set the trim to +1, the elevator can be observed deflected down, while in the cockpit the stick stays put. If I pull the stick, and align the elevator with the new position ( +1 ) of the "stabilator" then indeed the aircraft becomes tail heavy, and I am forced to apply further nose heavy ( towards +2 ) trim when becoming airborne and after retracting flaps and gear, specially if carrying more fuel.

 

Questions:

 

1) Users with FFB joysticks: Do you also observe this, I mean, when you apply +1 nose heavy trim, do you observe your elevator becomes unaligned with the stabilator, or does it's neutral position automatically adapt to the new stabilator incidence ? (This also implies that the total available positive and negative travel of the elevator varies as stab trim is applied)

 

2) How is it in the real aircraft ? When stab trim is applied, does the stick change it's position in the cockpit ? I thought that in the real Bf109s, as stab trim is applied the elevator moves aligned with it, and only total available travel will be affected ( positive or negative depending on the trim setting being + or - ) ?

 

Finally, if the behavior in il-2 BoS differs between users with FFB and conventional joysticks, I think this should be updated in future patches. If in the real aircraft, when stab trim is applied:

 

A) The elevator follows it and keeps aligned with it ( on ground, aircraft stopped );

B) The stick stays put in the cockpit

 

then the same should happen in the simulator, irrespective of what hardware is being used.

 

Looking forward for your comments :-)

Edited by jcomm
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I have little knowledge on the subject, but my common sense answer (which is not necessarilly the right one) would be, that stabilizer trim, unlike trim tabs fitted on the control surfaces, should not significantly alter the neutral position of the stick while in flight.

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When you adjust stabilizer (MSFFB2) physical joy is not moving. I have to check in game control column if it's moving. Btw when you adjust trim tabs for example in lagg 3 - you feel that physical joy is moving in hand. This is not in happening 109 or 190.

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The elevator trim tabs on all german fighters have been tweaked for level flight attitude at cruise speed and 0° stabilizer angle, hence why it may differ from historical/current pilot accounts.

 

If you know which setting at which speed should be required to keep the plane level you may PM Han about it. Maybe they can change it so that we have to use the historical trim settings with a centered physical stick position.

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I believe the only feasible solution will be to, as in real life, make the elevator keep aligned with the stabilator, and not as it's happening presently, where we can easily observe that when, on ground, aircraft stopped, we move the stab trim to, say, +1. we will be able to observe from an outside view that the elevator becomes actually deflected down thus causing a pitching down moment and requiring that after takeoff we have to trim tail heavy, which is not historial nor according to how pilots flying the presently available 109s report.

 

If we pull the stick and make the elevator align with the stabilator then, as is accurate, the aircraft will become tail heavy and require further stab trim down ( towards +2, or +3 in the F4 ) as speed builds up and gear and flaps are retracted...

Edited by jcomm
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I believe the only feasible solution will be to, as in real life, make the elevator keep aligned with the stabilator, and not as it's happening presently, where we can easily observe that when, on ground, aircraft stopped, we move the stab trim to, say, +1. we will be able to observe from an outside view that the elevator becomes actually deflected down thus causing a pitching down moment and requiring that after takeoff we have to trim tail heavy, which is not historial nor according to how pilots flying the presently available 109s report.

 

If we pull the stick and make the elevator align with the stabilator then, as is accurate, the aircraft will become tail heavy and require further stab trim down ( towards +2, or +3 in the F4 ) as speed builds up and gear and flaps are retracted...

 

I think that may be a control setup issue on your end.. I tested this with 109 on the ground..  and whenever I move the trim, the stabilizer fin and control surface both move and stay in their relative alignment..

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I think that may be a control setup issue on your end.. I tested this with 109 on the ground..  and whenever I move the trim, the stabilizer fin and control surface both move and stay in their relative alignment..

 

Zeebra, you really have to look close at it... From F2, try to zoom in, and you'll see the elevator deflected down relative to the adjustable stabilizer ( when set at +1 or +2 ).

 

 

See THIS POSTY BY PeterZVan...

Edited by jcomm
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Well.

 

I see Zeebra - I will have to re-check at home latter today.

 

I'll zero the curve for pitch ( it is presently at 40% ), and see that the "force feedback" is not ticked because my joystick is a T.16000.  Will also make sure there is no filter on.

 

Of one thing I am sure - in the calibration menu when it is centered the pointer is at "0"....

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Ok, I finally figured out what was causing my observation of the elevator deflection.

 

Zeebra's movie was taken from a parked Bf109 G2, probably with the engine stopped or running at low idle, but if we make the same observation with the engine running and propwash available over the tail, and specially if we brake the aircraft using the toe brakes and start applying power, the elevator will eventually move, deflecting down if the stabilizer trim is set to a positive value ( +1, +2, +3 in the F4 ). This happens because:

 

- In BoS, the elevator ground adjustable trim tab, which is set by default in the simulator for a given speed range, and is not adjustable, will move the elevator relative to the stabilizer when there is propwash.

 

If the engine is not running, and one sets, say, trim +1 (or any other value), the elevator will be perfectly aligned with the stabilizer.

 

When  the ebgine is running, as you increase thrust, brakes holding the aircraft in place, the propwash will be sufficient to move the elevator relative to the stabilizer. From within the cockpit, as power is applied the stick will move forward too ( for a stab trim setting greater than "0" ).

 

That explains why the 109s don't feel so tail heavy in BoS.. The moment power is applied, even on ground, the elevator deflects down for a stabilizer trim setting greater than "0"  ( +1, +2... +3 on the F4 ).

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On many aircraft with powered controls (like airliners) the elevator will typically move with the stab maintaining its neutral position with the stab.  The odd aircraft will move (creep) the neutral position in the direction of trim.  On unpowered control systems (Piper Cub, 109 ...) the elevator is typically going to go to (or stay at) aerodynamic neutral (basically, not move much), the stab incidence being the bulk of the trim force.  The "fixed trim tabs" on the 109's elevators may have been adjusted for a particular speed with a preset stab trim setting, but there doesn't seem to be any evidence (photos, existing aircraft/elevators) that supports that that I am aware of.  Their effect would have been next to nothing against the effect of the moving stab.  (Likewise, the fixed trim tabs on tall tail 109s don't appear to have ever been adjusted either, the boost tab being used for the adjustment.)

 

 

 

On the Airbus 320 (what I work on) the stick sometimes seems like it's mounted in a bowl of Jell-O with the control surfaces having a mind of their own - lol.

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It's known from reports of rw Bf109 pilots that the 109s, specially the latest models, like the G2 or the K series, are considerably tail heavy, specially with fuel tanks considerably filled.

 

With a fuel tank considerably filled, guns loaded or even gun pods, considerable nose-heavy trim has to be used.

 

Usual setting is +1 for takeoff, but as gear and flaps are retracted and the aircraft gains speed, further nose heavy trim, sometimes up to +2 and still requiring forward stick input is required.

 

This was what a well known Messerschmitt Museum pilot recently confirmed to me, when flying the G10, or other models. As gear is retracted, flaps come up, further nose heavy trim will be required.

Now, I have posted at the FM section of this forums, at another thread not specifically on this matter that in BoS the 109s if trimmed at +1 during takeoff will require tail heavy trim settings as they get airborne, because otherwise we will have to pull the stick.

Dear Jcomm:

 

1/  In the book "Messerschmitt Bf-109; Owners' Workshop Manual" of Haynes Publishing 2009.

There is some commentaries about trim settings of Bf-109 in operations and Bf-109G2/trop "Black-6", a original "Made in Germany" werk nummber: 10639, restored to airworthy condition.

 

In that book, Dave Southwood the RAF test pitot, who flew the Bf-109G2 "Black-6", He says.

In page 96:

"" In the pre -take-off check, I set 20º flaps and 1º nose up tailplane trim. The original data said 0º trim, but 1º nose up was added after the propeller ground strike on the first sortie. "

 

MovingUr.jpg

 

As far I know, and I was studied in many books, the behavior of the elevator trim in the Bf-109 G2 BoS, is a lot of more closer to reality than DCS K4, today.

Only the number of turns required from full nose-up, to full nose-down stop is worng in BoS. In the BoS G2, we have one turn only for full travel of elevator trim, and this is worng. The real airplane have rougly 4 wheel turns, from -6º to +2º, (rougly; 2 degrees of trim for a wheel turn )

 

2/ I don't know what you've asked to Klaus Plasa, but I am sure he answered the true, and his 109 G4 probably needs full nose-heavy trim, and a sightly stick forward, in level flying at full power... but surely not at cruise power. 

No forget, that the G4 of Klaus is a Buchon; without weapons, without armor plates, re-engined with a DB-605, and with a 30kg ballast (the 3 bricks) installed in the tail), and some Buchon´s have limited the VNE to 463 km/h IAS due to they are not capable to trim beyond this speed. The G2 "Black-6" is not limited in speed. 

 

By the way, I have checked the elevator trim marks that the G4 in flight in several pictures, of this aircraft and i can stated that the cruise flight trim position in the Bf-109G4 is ZERO. Acording with the checks marks that this airplane have painted in the port side of the tailfin (The marks were re-painted in 2015).

 

 

 

11214117_10208166420340516_8936406786165

 

12063770_10208166420100510_3352734638249

12417688_10208633015845112_1002413502961

 

 

 

 

 

 

 

Questions:

 

1) Users with FFB joysticks: Do you also observe this, I mean, when you apply +1 nose heavy trim, do you observe your elevator becomes unaligned with the stabilator, or does it's neutral position automatically adapt to the new stabilator incidence ? (This also implies that the total available positive and negative travel of the elevator varies as stab trim is applied)

 

2) How is it in the real aircraft ? When stab trim is applied, does the stick change it's position in the cockpit ? I thought that in the real Bf109s, as stab trim is applied the elevator moves aligned with it, and only total available travel will be affected ( positive or negative depending on the trim setting being + or - ) ?

 

Finally, if the behavior in il-2 BoS differs between users with FFB and conventional joysticks, I think this should be updated in future patches. If in the real aircraft, when stab trim is applied:

 

A) The elevator follows it and keeps aligned with it ( on ground, aircraft stopped );

B) The stick stays put in the cockpit

 

then the same should happen in the simulator, irrespective of what hardware is being used.

 

Looking forward for your comments :-)

 

Why you not asked this question to Klaus Plasa?  ;)

 

As you must know, the real Bf-109 have 15º30' forward stick control travel, and the same rearward. this travel NO change when you changes the horizontal stabilizer incidence, but the elevator control surface travel always change.

 

Taking as example the chart of angles of control surfaces  in Bf-109K4.

In the box marked with (2) refers to the elevator surface travel in degrees, with corresponding travels "pulling" and "pushing"..

With the same stick travel 15º30' pulling, and 15º 30' pushing, We Have:

For the position of the stabilizer, marked (4) in 0 ° (zero) position , you have 27º pulling and 24º pushing , with 51º of total travel.

For the stabilizer in position -6 degrees, you would 30º pulling and 21º pushing , and 51º of total travel..

 

This means that the control stick have always the same center and the same travel regardless the position of the angle of incedence of the horizontal stabilizer.  :joy: 

1782071_10207232594715459_53359033642874

Edited by III/JG52_Otto-I-
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Someone noticed the 109G2 most unstable in the new 1.107 version than previous version? or  Am I more psychotic than last month?  :wacko:  :biggrin:

 

Just the G-2 or other models as well? My understanding from the future dev plans is that the Bf109E-7 may be the one with the most accurate modelling and that the other models are being looked over.

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  • 1 month later...

Apologies for not reading all posts here as carefully as I should, but wanted to mention that, with FFB enabled (MSFF2), P-40 (and the few others I played with) can't be made to go nose heavy with maximum elevator trim in that direction. Nose only falls when nearing stall. Uncheck FFB, and trim works as expected. I've had one instance when re-enabling FFB (in mission) seemed to work better. I need to recheck, but I also think the displayed deflection percentage shifted (when I switched between FFB/no FFB, percent value went from 0 to full positive). I don't have the patience/flying skills to check more carefully, but there it is.... 

Edited by buster_dee
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