realistic trim reponse

[catdaddy]

ALL WW II acft had trim tabs, there was not one single WW II acft that was equipped with with an all flying tail (entire horizontal stabilizer moves to trim acft) and the ONLY fighter equipped with boosted controls (ailerons ONLY) was the P-38 J and subsequent  lightnings. As the onset of the sonic shock wave becomes apparent the control forces increase enormously. Another WW II design limitation was the cable and pulley control system incorporated into all the WW II acft, there was not a mechanical advantage designed into any of the control systems that I have seen to date.
 
 The point I'm trying to illustrate is this; Trim tabs could not conceivably overcome the several tons of force required to move a fabric covered control surface on ANY acft experiencing the effects of the sonic wave build up (compression) at high speed.
 In some cases the aircraft the compression effects are more pronounced at lower speed due to the wing planform and/or the control surface area, a good example is the A6M series, lightly built, large ailerons, thicker planform. These features allowed zeros to perform very well at low to medium speeds 250 mph and lower, above 250 mph testing revealed the inability to roll to the right and a limited ability to roll left assisted only via engine torque (only at 1/2 throttle and above). Many zeros were shot down by taking advantage of this controls issue.

ME-109s compressed earlier than P-47's or P51's and U.S. pilots took advantage of that as well, TRIM did not affect the onset of compression nor did it add any amount of effective control input during the effects of compression. In nearly all cases the trim tabs were MANUALLY adjusted via trim wheels in the cockpit.  MY wish....( insert drum roll here) ...is for the trim to be diminished at higher speed and eliminated during the effects of compression. keep it real   

[PFactorDave]

ALL

Not a good start to a thread...   

[Anaxogoras]

The 109 did not suffer from compression.  Quite the opposite; it suffered from heavy controls.  Many seem oblivious to the fact that compression and control stiffness are entirely different phenomena.  The former is caused when there is not enough airflow over the control surfaces, i.e. horizontal stabilizer.  The latter is caused by too much airflow over the control surfaces.

[saantana]

The 109 did not suffer from compression.  Quite the opposite; it suffered from heavy controls.  Many seem oblivious to the fact that compression and control stiffness are entirely different phenomena.  The former is caused when there is not enough airflow over the control surfaces, i.e. horizontal stabilizer.  The latter is caused by too much airflow over the control surfaces.

You'd think they would have thought of powered steering.

[BnZs]

EDIT: Nevermind. I just don't care.

[FLS]

Inconceivable as it may seem, pilots actually did use trim to counter compressibility.

If you want to criticize the flight model it's better to cite references so people don't think you just made stuff up.

[Anaxogoras]

Inconceivable as it may seem, pilots actually did use trim to counter compressibility.

I doubt that, otherwise the P-38 series would not have had dive flaps introduced.  I think you mean that trim could be used to counter control stiffness so that the aircraft would pitch up on its own.

[Anaxogoras]

This time wikipedia is very helpful:

Compressibility is an important factor in aerodynamics. At low speeds, the compressibility of air is not significant in relation to aircraft design, but as the airflow nears and exceeds the speed of sound, a host of new aerodynamic effects become important in the design of aircraft. These effects, often several of them at a time, made it very difficult for World War II era aircraft to reach speeds much beyond 800 km/h (500 mph).

Some of the minor effects include changes to the airflow that lead to problems in control. For instance, the P-38 Lightning with its thick high-lift wing had a particular problem in high-speed dives that led to a nose-down condition. Pilots would enter dives, and then find that they could no longer control the plane, which continued to nose over until it crashed. Adding a "dive flap" beneath the wing altered the center of pressure distribution so that the wing would not lose its lift. This fixed the problem.[4]

A similar problem affected some models of the Supermarine Spitfire. At high speeds the ailerons could apply more torque than the Spitfire's thin wings could handle, and the entire wing would twist in the opposite direction. This meant that the plane would roll in the direction opposite to that which the pilot intended, and led to a number of accidents. Earlier models weren't fast enough for this to be a problem, and so it wasn't noticed until later model Spitfires like the Mk.IX started to appear. This was mitigated by adding considerable torsional rigidity to the wings, and was wholly cured when the Mk.XIV was introduced.

The Messerschmitt Bf 109 and Mitsubishi Zero had the exact opposite problem in which the controls became ineffective. At higher speeds the pilot simply couldn't move the controls because there was too much airflow over the control surfaces. The planes would become difficult to maneuver, and at high enough speeds aircraft without this problem could out-turn them.

[FLS]

I doubt that, otherwise the P-38 series would not have had dive flaps introduced.  I think you mean that trim could be used to counter control stiffness so that the aircraft would pitch up on its own.

Nonsense.

[Mister Fork]

ME-109s compressed earlier than P-47's or P51's and U.S. pilots took advantage of that as well, TRIM did not affect the onset of compression nor did it add any amount of effective control input during the effects of compression. In nearly all cases the trim tabs were MANUALLY adjusted via trim wheels in the cockpit.  MY wish....( insert drum roll here) ...is for the trim to be diminished at higher speed and eliminated during the effects of compression. keep it real  

Ummm... what makes you think this doesn't happen now?  I remember a patch a couple of years ago that addressed this very issue.  The 109 could squeak out of a compression dive by using trim - actually any aircraft could PRIOR to the patch.  Now, trim barely moves the aircraft.  Trust me, it was a lot more obvious than before - for me.  

I do have a trick (I fly the Bf-109F4/G2 + Ki-84) - I trim all the way up and then engage combat trim.  When I'm dog fighting and I need the extra pull - I disengage combat trim and it pulls my nose up that much harder.  During compression however, I cannot trim out of a dive. Ever.

[Anaxogoras]

Nonsense.

Is that all you got?

[Soulyss]

EDIT: Nevermind. I just don't care.

 

[FLS]

The 109 did not suffer from compression.  Quite the opposite; it suffered from heavy controls.  Many seem oblivious to the fact that compression and control stiffness are entirely different phenomena.  The former is caused when there is not enough airflow over the control surfaces, i.e. horizontal stabilizer.  The latter is caused by too much airflow over the control surfaces.

Since you asked, this is also nonsense.

[Anaxogoras]

You still haven't made a substantive point in favor of your opinion.  All you're saying is "no."

Argument by appeal to no argument at all is way too popular at the AH forum.

[BnZs]

ALL WW II acft had trim tabs, there was not one single WW II acft that was equipped with with an all flying tail (entire horizontal stabilizer moves to trim acft)

The 109's whole stabilizer moved for trim. As did the 190's. Only a trivial amount of research would have been needed to discover this before posting.