trim, trim trim (grrrrrrrr!)

[juzz]

Do a little experiment with trim, control surface deflections and the external view to see how it "works"....

[Gunthr]

Flying a zeke in warbirds, in a 90 deg banked turn you could feed in up elev trim and gain significant angle - sometimes just enough to get your solution.  I'm not sure how well this works in AH.

I do know you really have to be nimble with the trim to fight the 109-G10.

Time and time again elev trim has helped me to pull out of dives when nothing else works (except maybe better speed management  ) You have to be ready to feed in left aileron trim in the high speed dive too.

You can't really fly this plane well without attending to trim. After reading the pilot's report on Andy's link, the 109 sounds like it was not that easy to fly in RL either.

[Westy]

 Just to add to the conversation here is a post from Earl 'Dutch' Miller, from the 350th FG, on trimming the Jug (P-47-D-R25 flyer I beleive. the same group the Brazilian Jug pilots flew with in Italy)...

 "The P-47 had its rudder trim control toward the floor on the left side of the seat.  As Dan  (an AW guy) reported, the Me109 had no trim adjustable in flight.  Hugh Dow, who reconstructed one in Sardinia, said that it was tricky on takeoff because of this.  In fact, while Dow was on leave to the States, "Pee Wee" Page pranged it on takeoff because of this.
 In divebombing, it was important to have the needle and ball centered at the moment of bomb release or the bombs would impact left or right horizontally of the target. Unless the aircraft was retrimmed, it would be practically impossible to maintain the proper rudder pressure for this.  As I began my dive, I would reach down and give the knob three twists counterclockwise.  This would over trim the aircraft at that speed, but would be about right on at the bomb-release speed.  One had to retrim after the pullout. We had pilots with control cables severed by enemy fire who could maneuver the aircraft by the use of rudder and elevator trim and thus were able to return to the base.  Once there, the aircraft was headed out to sea and the pilot bailed out over the field...."

 -Westy  

[This message has been edited by Westy (edited 07-22-2000).]

[Andy Bush]

Gunthr

Trim certainly can help pull out of a dive...in AH and in real life.

The reason is that the pilot retains the ability to move the trim surface at high indicated speeds when he has otherwise lost the ability to move the ailerons or elevator due to air loads. The pilot report mentioned this and commented upon the poor mechanical leverage the Me-109 pilot had in roll control. The air loads on the elevator, aileron, and rudder can be too strong for a human to overpower.

To explain this, I think of someone trying to open a car door at 100mph. The force of the air flowing by the door makes it tough to open the door up...and the more the door opens, the harder it gets to move further.

So how does aircraft trim help in situations like this? Using trim would be like having someone on the outside helping you to pull the door open...it's added mechanical advantage, pure and simple.

Westy

Your A2G example is good. I used to teach the same thing in RL fighters. On the way to the gunnery range, I would accelerate to release airspeed and then trim out the aircraft. In my case, I was mostly trying to trim out the elevator, but I would always double check the rudder 'ball' also. Aileron trim was not a significant factor and even if it was off, this would not adversely affect weapons accuracy.

Andy

[Duckwing6]

Ahheemm guys a lot of the airplanes we are talking about are a little bit faster and have a little bit more power than your favourite Cessna/Piper but yet still have the same unpowered flight controls (push rods and or cables) ... this means some of these airplanes are NOT controllable when out of trim (under the worst conditions)!

I dare to say that any High power tail dragger pilot will tell you never EVER to attempt a takeoff with the trim not set for the takoff position (rudder, as well as all the other trims) if there is one.

In AH we are flying basically conventionally controlled aircraft with a "fly by wire" stick .. therfore to get optimum performance and even controllability in some phases of flight (high speed dive, and slow speed manouvers) you NEED to trim the aircraft properly. This is mainly because you we have no feedback as you would have in real world through your control stick.

(your aircaft is properly trimmed when it does what you input with your stick e.g. when the stick is centered it should not roll and or pitch up/down, yaw)

DW6
 

[Andy Bush]

DW6

>>... this means some of these airplanes are NOT controllable when out of trim (under the worst conditions)!<<

Nope. Not true. You misunderstand trim controls. Read Toad's post again...he explained it well. A pilot will retain control over his plane if the trim settings are at full deflection...he'll probably have a uncomfortable time muscling the stick and rudder in maintaining control,but he'll be able to do it. Aircraft designers simply don't design trim controls that are so effective they can over power the pilot.

Now, that's not to say that trim malfunctions are not serious...they are and in some aircraft are a full blown emergency...but they are controllable.

>>I dare to say that any High power tail dragger pilot will tell you never EVER to attempt a takeoff with the trim not set for the takoff position (rudder, as well as all the other trims) if there is one.<<

True on this. But, again, let's understand what's going on here. The engine power will cause the nose to swing on takeoff. In a tail-dragger, the pilot corrects for this with rudder.

He can do this two ways. He can push the rudder in and hold it in a deflected position during the takeoff...or he can set the rudder trim to offset the rudder the same amount and thereby save himself the work of having to do it himself.

The result is exactly the same...a rudder that is deflected to provide a yaw force to offset engine torque.

Andy

 

[Sorrow[S=A]]

I think leph hit it on the nail when it comes to WWII fighters- The aileron and elevator trim was used in RL to make it easier to control and line up a fine shot control. Rudder in RL I don't think was near as important as it is in AH- they just used the pedals and accepted the slight drag induced. While the pilot has complete control despite the trim conditions the extra deflection needed to overcome a badly trimmed surface made for more E loss and drag. However just as in RL when lining up a shot I usually have my trim so that my plane requires almost no input from the stick to keep my lift vector from straying, and usually is just slightly pulling me up or down- I find it easier to line up my target by adjusting the pressure than trying to add then compensate.

  In AH I usually use the level auto trim to center my controls then do all the rest by hand- the occasional angle trim during brief extensions to center my trim. In combat I do not usually adjust my trim during BFM unless the extra deflection is interfering with my control- ie. during a loop I might trim elevators near the top if it is making my stick move too far to keep the plane on the angle I want. However in firing solutions I quicly put the trim very close to allow me greater accuracy in my shot.

  My advice is to try flying the plane in many many BFM at different altitudes and speeds and trimming her by hand to see what she needs to stay in "perfect trim". Then in combat anytime you need it you will be able to do it without thought. In the La-5FN I can stay very very close to trim with my elevators and ailerons simply by knowing what I have to adjust during the manuevers by practice. This means I have very good accuracy with her guns- compared to the YAK where I am still learning and have much less control.

[Toad]

Anyone out there have a Pilot's Operating handbook for a P-51, a P-47 or an F-4U? Particularly would like to see the page/pages for the Taxi and Takeoff Checklists.

Thx.

[Duckwing6]

Funny thing that there are so many loss of control on takeoff accidents where the cause was improper trim setting ..

I don't know what we are arguing about here Andy ... he'll not be able to fly the sim in an overly complicated manner if he's not trimming.

Toad:

F4U POH:

Item 10. Standard Checks for all Flights (Before Takeoff)
Item 18-20
Rudder Tab - 6° Nose Right
Aileron Tab - 6° Right wing down
Elevator Tab - 1° Nose up

Sorry can't put the page up because i have no scanner..

This is a reprint available at Amazon ISBN 0-87994-026-9

[Toad]

Duck,

What's the total amount of trim available in those axis?

In other words, how many degrees of rudder trim are available Right and Left? Same for Aileron, Same for Elevator up and down?

Also, do they post any notes, cautions or warnings in the text concerning use of trim for T/O?

Thanks!

[This message has been edited by Toad (edited 07-23-2000).]

[Andy Bush]

DW6 and Toad

From the F4U Pilot's Manual, the next paragraph following the steps outlined in the post above:

 

DW6...please not the qualifying statements regarding the rudder trim position. The rudder rim setting is there to assist the pilot in holding the required rudder input to counter engine torque...it was not the lack of rudder trim that caused accidents, it was the pilot losing control as a result of failure to use the rudder in a correct and timely manner.

I am not trying to make an argument. These posts make clear that some do not understand trim, plain and simple. I'm not surprised. Trim is somewhat of a 'Johnny Come-Lately' in flight sims...it doesn't help simmers to understand how to use it if a sim models it incorrectly.

Andy

[Andy Bush]

Toad

The picture of the trim control shows a plus or minus '20' on the elevator and rudder trim gauge. I cannot make out the markings on the aileron gauge.

Andy

[This message has been edited by Andy Bush (edited 07-24-2000).]

[Toad]

Andy,

Thank you!

I see you have already grasped the point I was going to make.  

Yet another way to view it:

In the "new" scheme of things, WARNINGS are put in flight manuals when experience shows that you can hurt <well, usually "kill"   > somebody if you don't follow this advice. CAUTIONS give information that can avoid damaging your airplane. NOTES give advice that makes flying the plane a lot easier or more efficient.

What Andy posted above is an "old scheme" WW2 NOTE. "The rudder force required to maintain a straight run will be high unless the rudder tab has been set to approximately 6 degress Nose Right prior to the start."

It clearly doesn't say "Hey, there won't be enough rudder available to successfully takeoff and you'll crash and burn!" <WARNING>

It clearly doesn't say "Hey, you might run off the side into the grass unless you do this!" <CAUTION>

It's a NOTE that says, "Hey, make life easy on yourself...use a little trim."

If you don't use it at all, you'll simply need "high" rudder force. Not "impossible force" or "incredible force" just "high". That means they expect every pilot to be able to provide both "normal" and "high" levels of rudder force...and "low" as well.

Is there anyone here who really believes that an F4U could not successfully takeoff if the rudder trim tab was completely removed from the aircraft?

Trim is not a primary flight control.  

[Duckwing6]

for loss of control i wasn't refering to the F4U in particualr .. i was talking about many and many general aviation aircraft...

See my point is that pilot workload is a very important thing to consider .. i know that Trim isn't a primary flight control but sure as hell it is important enough for all of us to recheck it's position before departure for example.

My point is why add pilot workload when this mental and physical capacity is needed to fly and FIGHT (here ins the sim) with the airplane. This is especially true as there are no tactile imputs (apart from the centering spring of your stick..) that help you keeping your orientation.

(btw guys i'm a RL pilot as well, there are more of us here than you might think)

[Toad]

Duck,

I'm not sure of the point you are making.

I have no problem with the idea of trim in a sim.

Trimming for most RL pilots is such an ingrained procedure that they don't even consciously think about it. I'm sure you're that way in what you fly.

What I'm saying here is that trim is a little TOO important to the flight model. It was that way in WB too. And we don't have the tactile feedback through the stick prodding us to unconsciously trim as we do in an airplane. You sorta have to "just know" and that's probably pretty hard for new guys to develop a feel for. Heck, I sure don't have it completely yet.

Now that's all fine if you are adding "difficulty" to the sim because you want to simulate a heavier pilot workload. Like you can't put all the stuff a pilot would have to do, like managing rpm and manifold pressure, arming and charging the guns, switching fuel tanks manually, trimming, tightening laps straps, etc., etc.

But to me, peak aircraft performance here seems a little too dependent upon trim. You and I both know that you can get essentially all of your control authority in 98% of your flight situations even if you are pretty out of trim just by moving the stick till you get what you need. So, trim here in relation to RL is overemphasized.

That's all I'm saying. But I can accept that they made it that way if it's to add "complexity" or "difficulty".

Does that make any sense?