Is the TO Trim still bugged?

[pauldy]

Sorry in advance ..as I haven't really visited these forum boards that much for a sometime now...

 

Last time I read.. the F-15's TO trim doesn't work as it should or so..

 

So yeah, was it already addressed or not?

 

Thank you^

Edited August 27, 2016 by pauldy

[Xenovia]

people actually use that? i just put flaps down, and floor it, until i takeoff.

[pyromaniac4002]

Sorry in advance ..as I haven't really visited these forum boards that much for a sometime now...

 

Last time I read.. the F-15's TO trim doesn't work as it should or so..

 

So yeah, was it already addressed or not?

 

Thank you^

 

Would also appreciate an answer to that.. Now when you use it, it beeps at you and the horizontal stabilizers move for like 30 seconds, and when they stop it keeps beeping in exactly the same fashion. Definitely doesn't seem like this is how it should work.

[joey45]

Little bit of up trim and floor it....

[Chipwich]

I find that it's set pretty neutral for takeoff with flaps extended and a full load. But a couple of thumb strokes either way should help make it right for you.

[pr1malr8ge]

Would also appreciate an answer to that.. Now when you use it, it beeps at you and the horizontal stabilizers move for like 30 seconds, and when they stop it keeps beeping in exactly the same fashion. Definitely doesn't seem like this is how it should work.

 

The beeping you hear means that all control surfaces are neutral/zerod out and you can let go of the button. So yes it is exactly how it should be in that respect. How ever this does not mean the game actually zeros out the trim correctly. See below..

 

 

The point of T/O trim is to set all control surfaces to Neutral. it is not to set a trim bias to raise the nose. It has nothing to do with the actual "Take off". If the PIC wants to add up trim to bring the nose up with out touching the stick then he can do that him self via the trim button. I have yet to ever use the T/O button on an f15 I just jumped into from spectator. How ever I do use it when ever I land to reset any left/right trim that I placed. I then end up adjusting the trim nose down due to it having way to much nose up trim for take off.

 

 

So yes the T/O trim is still broken, NO you do not need to use it when jumping into a new plane as all control surfaces are neutral. It will work if you had used a lot of trimming during a flight and land. Just need to remove the excessive nose up trim after it "zeros" out.

[pauldy]

I see, thanks..^ hope it gets addressed eventually..

[Pocket Sized]

I need to do a bit more searching but the dash 1 and some pilot accounts imply the takeoff trim DOES set the stabilators above the center position. Most convincingly, the manual states a clean F-15 should raise it's nose at 160-180 knots without pilot input if I remember correctly.

[pr1malr8ge]

I need to do a bit more searching but the dash 1 and some pilot accounts imply the takeoff trim DOES set the stabilators above the center position. Most convincingly, the manual states a clean F-15 should raise it's nose at 160-180 knots without pilot input if I remember correctly.

 

With any plane for the most part will nose up when under acceleration and speeds that generate lift..

 

as far as the real bird and t/o trim I'm not for certain on that I can how ever ask my cousin about it.. It could very well put a a degree or 2 of nose up pitch.

 

My statement how ever holds true that T/O trim isn't really anything other then a "centering" button for trim to prevent some wild unknown trim settings from the previous flight.

[GGTharos]

Is the TO Trim still bugged?

 

T/O trim sets the stabs 5 deg down on the forward edge and biases the PTC to keep them that way. The stick moves 1deg aft of centre, which is not neutral. After T/O the pilot must trim out the bias in game.

 

The spec is from the CAS maintenance manual.

Edited September 9, 2016 by GGTharos

[NineLine]

The beeping you hear means that all control surfaces are neutral/zerod out and you can let go of the button. So yes it is exactly how it should be in that respect. How ever this does not mean the game actually zeros out the trim correctly. See below..

 

 

The point of T/O trim is to set all control surfaces to Neutral. it is not to set a trim bias to raise the nose. It has nothing to do with the actual "Take off". If the PIC wants to add up trim to bring the nose up with out touching the stick then he can do that him self via the trim button. I have yet to ever use the T/O button on an f15 I just jumped into from spectator. How ever I do use it when ever I land to reset any left/right trim that I placed. I then end up adjusting the trim nose down due to it having way to much nose up trim for take off.

 

 

So yes the T/O trim is still broken, NO you do not need to use it when jumping into a new plane as all control surfaces are neutral. It will work if you had used a lot of trimming during a flight and land. Just need to remove the excessive nose up trim after it "zeros" out.

 

Apparently ED's SME F-15 pilot disagrees. He has tested and feels it is dead on.

[mvsgas]

I guess a better question would be;

- How to properly use T/O trim?

- Is the aircraft suppose to take off without stick inputs?

- If the pilots has to pull the stick, at what speed?

- Does it depend on the weight?

- Do we go by units of AOA or pitch?

[SinusoidDelta]

IIRC a clean eagle will fly itself off the runway at 165 knots with TO trim. I'll have to dig up the Eagle Digest article I saw that in.

[pr1malr8ge]

I

NO aircraft takes off on its own. (at the correct CG and speed that is)

 

have to disagree

 

 

In a stable aircraft even with the correct CG that is under acceleration with no adjustment to trim will NOSE up and climb. This is more apparent in single engine prop or non center line trusted aircraft with out a t-tail due to increased prop/thrust wash hitting the stabs.

 

given a long enough runway any aircraft under acceleration[obviosly under t/o power] with no trim adjustment[at a centered-t/o setting] will "take off" on its own. You also have Ground affect & physics to thank for this as well.

[pr1malr8ge]

Apparently ED's SME F-15 pilot disagrees. He has tested and feels it is dead on.

 

Unless there was changes that I am not aware of I apologies if there has been.

 

in the past

Using T/O trim in the eagle with out re-adjustment resulted in an rapid onset of nose up pitch during take off requiring forward stick pressure to keep the nose down then I guess I will have to talk to my cousin and ask about this for sure.

 

I know that in the -1 it stated needing aft stick command at rotation speeds not forward?

 

how ever if no changes have been made?

Is this the supposed same SME that concluded the f15 was fine when it would hit 200* of uncommanded roll Per Second when at or above 38k ft while trying to make a turn? Because my SME clearly stated other wise, along with youtube proof showing it was wrong. Ohh and last I checked it was fixed in updates.

 

I am willing to say that I could be wrong about the current state of T/O trim in the eagle. I will say that I will have my own SME look at it when I get him over to my house. If he agrees its fine I will report. if he disagrees then I will report on that also.

Edited September 10, 2016 by pr1malr8ge

[pr1malr8ge]

If the F-15 needs at least 10deg pitch to lift off at an acceptable speed, it's doesn't seem possible that she will lift off on her own at a 165kts and 0° pitch attitude.

 

 

1.If the plane pitches up on it's own than there has been a serious mistrim condition. I once had a 767 pitching up on her own at a way too low speed due to wrong loading7 loadsheet.

2. That's why I said at the 'correct' speed. Of course if the speed is high enough (and you ignore the tire limits) anything takes off sooner or later.

3. If you need forward pressure than you are in really serious trouble!

 

1. No there isn't. Well actually if it drastically pitches up then yes.. How ever most plane will enter ground affect then slowly pitch up gaining altitude if trim is not adjusted. Again, this is not a "you should try this" idea. Regardless, its simple physics. an accelerating plane must constantly be trimmed to prevent a raise in pitch attitude. Along with the same on a decelerating plane requires re-trim to prevent decrease in pitch.

On a side note, this is also why a "stable" designed plane "should" self correct from a stall with no input from the pilot. Again subject to CG loading.

 

2. Never said it was inherent or safe to try.. How ever in Lighter aircraft or high lifting wing designs with high thrust the plane should enter ground affect before max tire speeds.

 

3. This what the point I was bringing up the last time I used T/O with out adjusting trim the f15c in dcs with flaps down pitched rapidly up requiring forward force to stop.

 

4. Just to reiterate, I am not saying you or anyone should go out and try to verify a plane wanting to fly it self off the run way.. How ever you're more then welcome to enter an equilibrium [i.e. constant speed] straight and level flight [at a safe altitude] trimmed out where no pressure is required on the flight controls to maintain. Then add power and tell me if the plane doesn't start to pitch up and climb[of course with out counter pressure].

[pr1malr8ge]

1.of course it does and that's one of the reasons why you need to set the correct take off trim, to avoid that this pitch increase happens prematurely during take off!

Especially in multiengined planes it would be desastrous if you would loose an engine below Vmcg and the plane would have started to pitch up on ist own already.

3.That has more to due with the area where flow separation starts and hence depends on wing sweep and washout. There are even stable conventional civil airliners that pitch up at the stall.

 

It should not be disatourus as the aircraft should be well above vr,v2min, and vmcg. What you keep misinterupting is that the trim is causing this pitch up. While it is to a degree as you could dial in nose down trim. Again this will not prevent ground affect from raising the aircraft. How ever the nose down trim will start a porpoise maneuver resulting in a prop strike or nose gear collapse.

 

So as you understand what I am getting at. The stabs,stabableator,elevator etc.. Is a reverse wing that generates lift or should I say rather down force to push the epenage down. With more speed results in more down force applied to the epenage thus pitching the nose up and increasing the aoa thus again creating more lift at the wing. As I said this will happen at speeds above vr with a correct t/o trim. so unless an idiot is at the controls it shouldn't happen "un commanded"

 

As far as wing sweep is a contributing factor. The thing is I did not say every aircraft I said stable aircraft. While I guess you could conclude that a swept wing aircraft is "stable" I don't consider it so. As a swept wing design with out a lifting body is much harder to control during a stall. It requires intervention other wise it will probably result in a flat spin.

 

Again coming from your experience with wide body airliners with considerable weight and requiring the use of slats and compounded flaps to increase lift at slower speeds you very well are probably right as the stabs probably won't be producing enough down force to command pitch up until well above vr and probably max tire speeds. Again it will still happen.

[SinusoidDelta]

Here is the link to the MCD Eagle Talk Product Support Digest

(Vol. 2 Pg. 16)

STICK BACK!

Another variable that can cause a change in nose wheel liftoff is the aircraft speed at aft stick initiation. A couple of profound statements can be regarding this matter. An F-4 in normal takeoff configuration would probably never rotate and fly off the runway without pilot-supplied aft stick. The F-15, on the other hand, flies off the runway at about 165 knots without any pilot action other than selecting takeoff trim before takeoff roll. The nose wheel liftoff speed will be increased as much as 12 knots by pulling the stick aft at 130 KCAS vs 100 KCAS in an F-15 at Mil power equipped with a full centerline tank.

 

So if you trust the source is accurate (I certainly do) the F-15 will fly itself off the runway at approx 165 knots when TO trim is selected. As GG pointed out this is because TO trim stick position is established as 0.4" aft of neutral. As I understand it, this serves the purpose of defeating the PTC in order to get full commanded stabilator without delay. See the excerpt below:

(Vol. 2 Pg 18 )

Take Off Trim

At this point in the meeting, a revelation occurred when one of the FSO's volunteered that some pilots take a couple clicks of nose down trim just before takeoff to avoid having to do it immediately after gear and up. Boy, what we have here is an example of the right hand (pilot) not knowing what the left hand (designer) is doing! Let's take a quick look at this part of the Eagle flight control system.

The pitch trim compensator (PTC) is part of the mechanization in the mechanical control system that minimizes trim changes in flight as the speeds up or slows down. It is an energetic device with 7.5° of stabilator authority. On the ground with the stick centered (trimmed for 1G) could either be adding 2° to the stabilator position commanded by the mechanical system or it could be subtracting 5.5° but it won't be neutral! The F-15 design compensates for this by establishing the takeoff trim position 0.4 inches aft of the centered stick position (ie, commanding slightly more than 1G). This causes the PTC to be in the full aircraft nose up position during takeoff. With takeoff trim selected and the stick at half of full aft stick travel, you would normally get 20° of stabilator leading edge down deflection on takeoff (full stabilator deflection is 26°). If you defeat the takeoff trim design feature by either trimming the stick forward or by holding a small amount of forward stick during the takeoff roll.you may drive the PTC to the full nose down position. In this case, you would initially get only 12.5 of stabilator for the same half stick take five seconds to get back to the full 20° deflection normally commanded by a 50% stick input. Five seconds at 150 knots would seem like an eternity and guarantee that if your PTC is full nose down when lead rotates, you'll have a difficult job compensating quickly enough to fly off anywhere near him.

Hopefully this clears things up a bit.

[pr1malr8ge]

1. That doesn't make sense. Trim is variable, the pitch up or down moment depends on its setting.

2. So we are back at square one. If trim is correct, the plane will pitch up well after reaching Vr on it's own. That's why I said no plane takes off on it's own at the correct speed and trim.

If trim is too much nose up, the plane will pitch up prematurely and uncommanded which is unacceptable dangerous if this happens below Vmcg.

3. I definitely wouldn't call e.g. a 747 'unstable'.

4. I did write already that this uncommanded pitch up happened to me in a 767 well below Vr.

 

it does make sense. You keep misinterpreting my statements with setting the trim directly to cause a nose up condition. I'm saying that a general t/o trim setting is considered roughly a 0 /neutral trim setting.

 

2. Defining correct speed was never mentioned in anything I said.

 

3. In overall terms it is stable. Well when comparing it to say an f16 or f117 where it can be flown with out a computer as the for mentioned can't. How ever it is not "stable" as it will not self correct during a stall it will only deepen the stall if no proactive action is rendered.

 

4. Your uncommanded pitch up was well an error on your part. I have not been talking about improper cg loading or ignorent/stupid pilots putting in clearly a wrong trim setting.

 

You need to toss out your engrained training on vspeeds and procedures and just think about the physics of aerodynamics.

[SinusoidDelta]

2.? Looks like you should re-read my first post and your reply. I wrote that a plane doesn't take off on its own at the correct speed and you replied that you disagree.

4. I have no idea why you think that this was an error on my part. The point I've tried to make is that the stabilizer has a lot of power than you think it has.

Enough to raise the nose even at a very low speed.

5. Thank you for that input but I think I've gathered enough knowledge about aerodynamics in the last few decades.

However IMO this discussion has strayed too far off topic already and it's not going to lead anywhere.

 

I'm not sure what you and pr1mal are arguing about.

 

If we are trying to understand how TO trim should work, read my post and look at the link. There's more than one article that touches on TO trim. I'm not asking anyone to take my word for it, the article was written by an MCD Lead Engineer.

[Sierra99]

T/O trim sets the stabs 5 deg down on the forward edge and biases the PTC to keep them that way. The stick moves 1deg aft of centre, which is not neutral. After T/O the pilot must trim out the bias in game.

 

The spec is from the CAS maintenance manual.

 

GGTharos Is this how it currently works in the game?

 

Sierra

[GGTharos]

That's how it is.