Author Topic: realistic trim reponse  (Read 1345 times)

Offline Ack-Ack

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Re: realistic trim reponse
« Reply #30 on: December 18, 2009, 04:39:45 PM »
The AAF Manual 51-127-1 on the  P-38, under the section titled Compressibility Recovery Procedure, states: "Use only a few degrees of elevator trim tab". This is also listed under Normal Dive Recovery as well as being part of the procedure for recovering from compressibility in a dive.

That was only if they were on the onset of compressability.  If a P-38 was in a full compressability state, using elevator trim to come out of it wouldn't work.  Otherwise there would have been no need for the dive flaps that were introduced first in the P-38J-25-L0 and later L models.


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Offline Ack-Ack

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Re: realistic trim reponse
« Reply #31 on: December 18, 2009, 04:41:58 PM »
I need to confirm, but I believe that the boosted ailerons and dive flaps first appeared on the P-38J-25-LO. 

I believe you are correct.


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Offline catdaddy

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Re: realistic trim reponse
« Reply #32 on: December 18, 2009, 05:14:37 PM »
See Rule #4
« Last Edit: December 19, 2009, 07:21:56 AM by Skuzzy »

Offline Lusche

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Re: realistic trim reponse
« Reply #33 on: December 18, 2009, 05:19:08 PM »
See Rule #4

You seem to be pretty fascinated with consoles... you mention them in almost every post :)

I start to see some good PNG potential here ;)
« Last Edit: December 19, 2009, 07:22:13 AM by Skuzzy »
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Offline FLS

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Re: realistic trim reponse
« Reply #34 on: December 18, 2009, 05:26:31 PM »
That was only if they were on the onset of compressability.  If a P-38 was in a full compressability state, using elevator trim to come out of it wouldn't work.  Otherwise there would have been no need for the dive flaps that were introduced first in the P-38J-25-L0 and later L models.


ack-ack

It was also when recovering. According to the manual the denser lower air would slow you down enough after cutting power that your controls would become effective again. I never said trim eliminated compressibility.

In any case the trim effectiveness is already reduced in AH at compressibility.

Offline catdaddy

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Re: realistic trim reponse
« Reply #35 on: December 18, 2009, 06:00:09 PM »
I stand corrected, the 109's did trim through the horizontal stab, however after reading the flight test results it mentioned the actual performance of 109's at the various speeds. At 400 mph it takes FIVE (5) seconds to roll the acft to 45 degrees bank.

 Ailerons
At low speeds the aileron control is very good, there being a definite resistance to stick movement, while response is brisk. As speed is increased, the ailerons become heavier, but response remains excellent. They are at their best between 150 mph and 200 mph, one pilot describing them as an 'ideal control' over this range. Above 200 mph they start becoming unpleasantly heavy, and between 300 mph and 400 mph are termed 'solid' by the test pilots. A pilot exerting all his strength cannot apply more than one-fifth aileron at 400 mph. Measurements of stick-top force when the pilot applied about one-fifth aileron in half a second and then held the ailerons steady, together with the corresponding time to 45 degrees bank, were made at various speeds. The results at 400 mph are given below:
Max sideways force a pilot can apply conveniently to the Bf.109 stick 40 lbs.
Corresponding stick displacement 1/5th.
Time to 45-degree bank 4 seconds.
Deduced balance factor Kb2 - 0.145

Several points of interest emerge from these tests:
a. Owing to the cramped Bf.109 cockpit, a pilot can only apply about 40 lb sideway force on the stick, as against 60 lb or more possible if he had more room.
b. The designer has also penalized himself by the unusually small stick-top travel of four inches, giving a poor mechanical advantage between pilot and aileron.
c. The time to 45-degree bank of four seconds at 400 mph, which is quite excessive for a fighter, classes the airplane immediately as very unmanoeuvrable in roll at high speeds.

Elevator
This is an exceptionally good control at low air speeds, being fairly heavy and not over-sensitive. Above 250 mph, however, it becomes too heavy, so that manoeuvrability is seriously restricted. When diving at 400 mph a pilot, pulling very hard, cannot put on enough 'g' to black himself out; stick force -'g' probably exceeds 20 lb/g in the dive.

Rudder
The rudder is light, but rather sluggish at low speeds. At 200 mph the sluggishness has disappeared. Between 200 mph and 300 mph the rudder is the lightest of the three controls for movement, but at 300 mph and above, absence of a rudder trimmer is severely felt, the force to prevent sideslip at 400 mph being excessive.

Harmony
The controls are well harmonised between 150 mph and 250 mph. At lower speeds harmony is spoiled by the sluggishness of the rudder. At higher speeds elevator and ailerons are so heavy that the worn 'harmony' is inappropriate.

Offline Masherbrum

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Re: realistic trim reponse
« Reply #36 on: December 18, 2009, 06:03:27 PM »
You seem.......bitter.   
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Offline catdaddy

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Re: realistic trim reponse
« Reply #37 on: December 18, 2009, 06:08:49 PM »
and again I was wrong about the 190 (sigh) German technology it was even electric trim...just really slow.


              The controls are highly effective at most speeds and forces are moderate giving good control feel. However, at speeds over 400 MPH indicated airspeed, the elevator tends to become quite heavy and noticeable buffeting and vibration of the airplane occurs.

        F.    Trim and Stability

                Longitudinal trim of the airplane is accomplished by changing the incidence angle of the stabilizer rather than by trim tabs on the elevator. Ground adjustable tabs are only provided for rudder and aileron but are adequate since rudder and aileron trim changes for most flight conditions are very slight.

                The elevator trim control is electrically operated and is controlled by a toggle switch. This control arrangement operates too slowly for maneuvers, requiring a rapid change in elevator trim.

                Stability was satisfactory at this weight and C.G. location.

Offline Dream Child

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Re: realistic trim reponse
« Reply #38 on: December 18, 2009, 06:15:08 PM »
It was also when recovering. According to the manual the denser lower air would slow you down enough after cutting power that your controls would become effective again. I never said trim eliminated compressibility.

In any case the trim effectiveness is already reduced in AH at compressibility.

Actually, the trim was spring loaded, so when the aircraft's mach speed became slower in the denser air, it would move the elevators to enable the aircraft to pull out. If one didn't do that and just pulled back on the stick, it could suddenly unlock with the lower mach speed, with the sudden up elevator causing other issues, like blackouts and broken planes.

Offline Ack-Ack

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Re: realistic trim reponse
« Reply #39 on: December 18, 2009, 07:01:03 PM »
See Rule #4

The intent of the dive flaps in the P-38 were never meant to 'delay the onset of compressability', but rather to help the pilot pull out of a high speed dive in which they entered compressability.  The dive flaps didn't increase the mach threshold to stave off compressability.  The dive flaps didn't just work to a point, they worked very well and those P-38s outfitted with the dive flaps had no troubles following German planes as they tried to dive away.  Tony LeVier (Lockheed test pilot) used to do demonstrations where he would dive a P-38L at high speeds and recover easily using the dive flaps.  Also, a little known thing is that before the dive flaps, some P-38 pilots had no troubles following German planes as they tried to dive away.  P-38 pilots like Mosier, Olds and Lowell used to use their rudders to help slow them down in high speed dives, but they were amongst the small number of very experienced P-38 pilots in the ETO.


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« Last Edit: December 19, 2009, 07:23:26 AM by Skuzzy »
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Offline Motherland

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Re: realistic trim reponse
« Reply #40 on: December 18, 2009, 07:06:06 PM »
I stand corrected, the 109's did trim through the horizontal stab, however after reading the flight test results it mentioned the actual performance of 109's at the various speeds. At 400 mph it takes FIVE (5) seconds to roll the acft to 45 degrees bank.

 Ailerons
At low speeds the aileron control is very good, there being a definite resistance to stick movement, while response is brisk. As speed is increased, the ailerons become heavier, but response remains excellent. They are at their best between 150 mph and 200 mph, one pilot describing them as an 'ideal control' over this range. Above 200 mph they start becoming unpleasantly heavy, and between 300 mph and 400 mph are termed 'solid' by the test pilots. A pilot exerting all his strength cannot apply more than one-fifth aileron at 400 mph. Measurements of stick-top force when the pilot applied about one-fifth aileron in half a second and then held the ailerons steady, together with the corresponding time to 45 degrees bank, were made at various speeds. The results at 400 mph are given below:
Max sideways force a pilot can apply conveniently to the Bf.109 stick 40 lbs.
Corresponding stick displacement 1/5th.
Time to 45-degree bank 4 seconds.
Deduced balance factor Kb2 - 0.145

Several points of interest emerge from these tests:
a. Owing to the cramped Bf.109 cockpit, a pilot can only apply about 40 lb sideway force on the stick, as against 60 lb or more possible if he had more room.
b. The designer has also penalized himself by the unusually small stick-top travel of four inches, giving a poor mechanical advantage between pilot and aileron.
c. The time to 45-degree bank of four seconds at 400 mph, which is quite excessive for a fighter, classes the airplane immediately as very unmanoeuvrable in roll at high speeds.

Elevator
This is an exceptionally good control at low air speeds, being fairly heavy and not over-sensitive. Above 250 mph, however, it becomes too heavy, so that manoeuvrability is seriously restricted. When diving at 400 mph a pilot, pulling very hard, cannot put on enough 'g' to black himself out; stick force -'g' probably exceeds 20 lb/g in the dive.

Rudder
The rudder is light, but rather sluggish at low speeds. At 200 mph the sluggishness has disappeared. Between 200 mph and 300 mph the rudder is the lightest of the three controls for movement, but at 300 mph and above, absence of a rudder trimmer is severely felt, the force to prevent sideslip at 400 mph being excessive.

Harmony
The controls are well harmonised between 150 mph and 250 mph. At lower speeds harmony is spoiled by the sluggishness of the rudder. At higher speeds elevator and ailerons are so heavy that the worn 'harmony' is inappropriate.

That report is about the Bf 109E model, which had (and has in game) much worse high speed maneuverability in general to its later counterparts, in roll rate in particular. Take the Emil up in game and try to roll it at 400mph. If you're feeling extra daredevilish, try to roll it against the engine torque.
Not only that but you misquoted the roll time even in the report, which was four seconds, not 'FIVE (5)' seconds.

I just took up the Bf 109E offline, climbed to about 7k so I could actually reach 400mph in a dive, leveled at 400mph and guess what... it took about 4 seconds to roll 45% right with full stick deflection.

Quote
and again I was wrong about the 190 (sigh) German technology it was even electric trim...just really slow.
Just tested this offline as well, it takes a little under 5 seconds to go from neutral to full up on the elevator trim.
« Last Edit: December 18, 2009, 07:25:03 PM by Motherland »

Offline BnZs

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Re: realistic trim reponse
« Reply #41 on: December 18, 2009, 08:52:11 PM »
See Rule #4
« Last Edit: December 19, 2009, 07:25:28 AM by Skuzzy »
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Offline Templar

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Re: realistic trim reponse
« Reply #42 on: December 18, 2009, 09:06:39 PM »
BNZ....dang....sir, you are the man.....  :salute  :airplane:
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