Trimming the Bf 109 for level flight

[Jenisch]

Hello,

In the IL2 Cliifs of Dover sim, I was flying the Bf 109 E-3 and using the rudder to keep the ball centered. However, I noticed that when I realized the rudder, the RPM raised dramatically, a clear indicator the rudder deflected was creating a lot of drag.

I know the Bf 109 E at least didn't have a pilot adjustable rudder trim, but it did have ground adjustable rudder trim, which as far as I'm aware is a device that should be enough to stabilize the plane in a determined speed range (which I couldn't find).

I would like to know if in the real 109 it was necessary to keep the feet in the rudder all the time, and so if the adjustable tab was not enough to keep the acft stabilized.

 

[davebender]

Why would the rudder create more drag then a trim tab? Both would exert the same amount aerodynamic force to keep the aircraft flying straight.

 

[Milosh]

Why would the rudder create more drag then a trim tab? Both would exert the same amount aerodynamic force to keep the aircraft flying straight.

How much area of the rudder is exposed to the air stream? Ditto for the MUCH smaller trim tab.

 

[davebender]

Hence a trim tab must move further into the airstream to achieve the same effect as a tiny rudder movement.

 

[GregP]

The real Bf 109 had no rudder trim and was usually set so the rudder was in trim at about 180 - 200 mph with low cruise power set. Otherwise, the pilot needed to either apply rudder force or put up with flying out of yaw trim. Mostly, they allowed the out of trim condition to happen unless they were in combat or about to engage in combat, in which case rudder trim was essential for good aiming and good aircraft control. The other time when rudder was essential was takeoff and landing, but you knew that.

 

[tyrodtom]

The trim tab moves the rudder the opposite direction it is bent, or turned. So the rudder's got the same deflection, wheather it's from you foot or the trim tab.

 

[razor1uk]

As Greg said, (early/pre tall-tail) Bf109's didn't have a trimmable rudder tab, it was a fixed tab, plus in what 109 info I have (Messerschmitt Hurricane, Fighting Bf109, plus most of the 109 pdf manuals from this site), 300kmh/kph for a 'free' rudder with straight flight vector as Greg hinted at was the norm for final flight acceptance trials/test where the A/C was then ready to be released to the Luftwaffe.

Of course 'Waffe pilots could get their aircrew to adjust the fixed trim tab a touch with pliers, if there was enough reason, rank or privilage to get it done; but then he'd have to do a few test flights to see how and where the adjustment affected the rudder A/C, with usual landings for re-adjustments a more test flights.

I perhaps think as the war progressed, pilots and/or their brass, would've had less time, logged flight time to notice issues and eventually the lack of, or ristriction of fuel for such adjustment tests would lead to them not happening at all.

Now Tyrod Dave are true about the more common adjustable rudder trim...

 

[Milosh]

As Greg said, (early/pre tall-tail) Bf109's didn't have a trimmable rudder tab, it was a fixed tab, plus in what 109 info I have (Messerschmitt Hurricane, Fighting Bf109, plus most of the 109 pdf manuals from this site), 300kmh/kph for a 'free' rudder with straight flight vector as Greg hinted at was the norm for final flight acceptance trials/test where the A/C was then ready to be released to the Luftwaffe.

Of course 'Waffe pilots could get their aircrew to adjust the fixed trim tab a touch with pliers, if there was enough reason, rank or privilage to get it done; but then he'd have to do a few test flights to see how and where the adjustment affected the rudder A/C, with usual landings for re-adjustments a more test flights.

I perhaps think as the war progressed, pilots and/or their brass, would've had less time, logged flight time to notice issues and eventually the lack of, or ristriction of fuel for such adjustment tests would lead to them not happening at all.

Now Tyrod Dave are true about the more common adjustable rudder trim...

The 109 never got a pilot trimable rudder or rudder tab. Late production 109s got a Flettner tab but this was only to easy control inputs and was no way adjustable by the pilot in flight.

 

[razor1uk]

Ah... so the red area/band on the rear of the (aero-mechanical input assisting) Flettner tab was its own fixed tab?
That'd explain why the tall tails had the red fixed tabs on the rudder itself as well as the Flettner.

Incedently in a seperate but similar point, all 109's used similar fixed tabs for fine control adjusment (ground based + flight-test hops) on all control axis/surfaces - only the tailplane was flight trimmable for incedence via a leading edge screw-jack - the elevators didn't change angle along with the incedence of the tailplane, and they too had fixed tabs.

 

[cimmex]

The Bf109 had an asymmetrical tail fin.
cimmex

 

[Jenisch]

(Messerschmitt Hurricane, Fighting Bf109, plus most of the 109 pdf manuals from this site), 300kmh/kph for a 'free' rudder with straight flight vector

300 km/h is just the speed I'm having for "free rudder" in the sim. So, if it's like that, I can use the sim to do all the comparisons for discussion here, great!

ironic mode/off

 

[stona]

The Bf109 had an asymmetrical tail fin.
cimmex

I was wondering when someone would point that out! All the above still apply. Particularly when flying fast rudder input was needed to keep the aircraft flying straight. By all contemporary accounts this was both inconvenient and tiring.
Cheers
Steve

 

[razor1uk]

Asymmetrical aerodynamics were more researched, tolerated, understood and utilised during WWII by Germany.

Well highlighted their by Cimmex Stona

My opinion of the 109 rudders counter torque-yaw 'lift' is taken for granted by myself (apologies to all) as an assumed known fact by all 109 fans;
it's uses an wing like 'profile' as well as its IIRC angle of incedence to the longitudinal cetral axis being (yaw-ed) around 11 degrees offset to Port to counter torque roll at (the earlier noted) normal cruise speed the combined profile and incedence equated to a symmetrical fin+rudded being yaw-ed out to 14 deg.

If my frazzled memory is firing on 3 of its 12 cylinders, the tall tails were of a much different 'profile' and were yawed out to around 12-ish deg portwards to account for the much higher powered hence 'torquing' engines of the later 109 series standard, I have no initial recall of what the tall tails acclumative angle of its profile and incedence equals.

 

[tyrodtom]

I knew the Me109 had a airfoil or offset rudder, but probably set up for cruise flight. The trim tab is to compensate fot small inperfections that occur during airframe assembly. Not just in the Me109, but any aircraft. But a fixed tab, or just a offset or asymmetrical fin can only work in a certain speed range.

Didn't either the Czechs or Spanish put a opposite rotating engine in their manufactored Me109 clones and not change that asymmetrical fin ?