What i wish I knew about FCS when I started

[LastRifleRound]

This thread is dedicated to simmers just recent to the DCS sim (mostly folks who waited for the DVD version such as myself). I know there have been many threads dedicated to the autopilot already, but there are some things I learned from flying that I feel would be useful to new pilots and hopefully help them realize why they cannot fly with precision.

 

First, let's start with a scenario: You are flying along, trimmed well for level flight at about 130 km/h, and spot something to the left. You need to make a turn to that heading quickly. You pitch up, trim again and adjust collective to bleed off speed, no problem there. When speed is around 60 km/h or so you level off, trim again, then begin a nice, stable, turn toward the heading. You trim these settings. Looks good.

 

As you approach the desired heading, you apply right rudder and bank to stabilize the bird on the new heading, then hit trim again. You lock your target at about 2.8 km, call up rockets and prepare to engage. However, you notice that your side slipping. Slightly, but enough to prevent you from engaging. You try to fight the pipper down to the target, then re-trim when it's in the neighborhood, but when the AP goes to hold the settings, the bird lurches slightly off aimpoint. You fight to put it there again, no joy.

 

Distance is now 2.3 km. You know you're supposed to have engaged already, but the helo is becoming less and less responsive to your inputs. You are side slipping everywhere, and no matter how precisely you lay the pipper on target, when you trim then center the controls, the AP errors the manual told you about prevent you from keeping the target in your sights.

 

Distance is now 1.9 km, and corrections now cause you to be extremely off target. You decide to hold the trimmer button down, as you realize that fighting the autopilot is forcing you into oversteer situations, and even if you manage those, the accumulated errors will never allow you to hold pipper on target.

 

When you hold the trimmer down, the bird banks at an odd angle, begins yawing and side slipping, as well as pitches in a manner you weren't expecting. What happened? I thought I was supposed to trim after every input?

 

Well, here is your problem: Trim, trim, and trim again is only good advice if you actually know which control inputs match with the attitude you are at, when they are stabilized there, and when it is done every 30 sec. or so to allow AP errors not accumulate. Even then, if you are skilled enough to know the flight envelope to this degree, you probably don't need to read this thread.

 

The reason this is the case is that the trimmer button, when AP channels are active, does 2 things: 1.) It zeroes your control input (you probably know this) causing whatever control inputs you had to become constant and 2.) It commands the autopilot to hold the bank, heading, and pitch you were at when you release the trimmer.

 

Why is this a problem? Because if 1 and 2 don't match the bird will not do what you want it to.

 

Case in point using the example above, if you trimmed in the initial yaw, the yaw required to fight the autopilot onto the new heading (where you began arresting your yaw on the target heading) is in EXCESS of what you would ordinarily need by a factor of 20%. Therefore, when you trim in this new input, the helo tries to hold your excess right rudder while simultaneously holding the heading you were at. The only way it can do this is by sideslipping.

 

Adjunct: the same applies to bank. So when you try to arrest the bank, you are using more than actually needed for the flight profile you're trying to acheive. The amount of erroneous inputs you are banging into the FCS increases exponentially.

 

Holding the trimmer is a solution to this. There are many who don't do this, but I don't know how from what I've witnessed. There is a sticky in this forum that tells you not to do this, and the manual repeats it, as well as the book that comes with the DVD version, so it is likely drilled into your head that holding the trimmer down is a bad idea, and since you are a simmer, you want to do it "right." Know that "right" is whatever it takes to fly with precision, so ignore these 2 items and experiment.

 

However, when the trimmer button is released, you will still notice a "jump" as the AP attempts to hold the new settings. This is because, like I said, 1 must match 2, and it probably doesn't for you.

 

How do you fix that? Well, I'm still trying. I would imagine flying in FD mode will help you understand the helicopter's true flight envelope, which will help you to understand when your control input truly matches your flight profile. Once this is understood, you can begin turn off FD and fly the Shark the "right" way. That is the course I'm taking.

 

I apologize for the length of this thread, but this facet of the sim was and still is the most frustrating for me (but also enjoyable, much respect to the guys who actually fly these things), and I feel any input regarding how to truly understand how to fly a helo would be more useful to noobs than just "trim, trim, trim" Anybody who has flown Longbow 2 etc. is used to having flight maneuvers explained in exacting detail, and may feel a little lost in the 'shark as a result of this not being there.

 

Info such as, what speed should rudder be used up until to execute tight turns? What is the proper way to execute a high speed turn? What are the steps needed to stabilize a heli in level flight at a nose down attitude sufficient to attack with rockets or gunpods?

 

I hope this has helped you realize you are not alone if you are having these problems. Yes, the autopilot will be patched, but if I understand the patch correctly, the above problem will still exist, as it is not engaging turns that is difficult, it is arresting them with stability with 0 bank/sideslip AND 0 yaw.

Edited May 9, 2009 by LastRifleRound

[HitchHikingFlatlander]

I have a tough time fighting the shark as well using trim constantly and I'm struggling to learn how to keep control too. Standoff weapons are easy to engage but when I get to gunpods and rockets, it never works out like planned. Having only 10-15 hrs in the sim I know I have a lot to learn but would like to know WHAT I need to learn so I can get past these hurdles. Good post!

[WynnTTr]

 

Holding the trimmer is a solution to this. There are many who don't do this, but I don't know how from what I've witnessed. There is a sticky in this forum that tells you not to do this, and the manual repeats it, as well as the book that comes with the DVD version, so it is likely drilled into your head that holding the trimmer down is a bad idea, and since you are a simmer, you want to do it "right." Know that "right" is whatever it takes to fly with precision, so ignore these 2 items and experiment.

 

I was told to hold trimmer, make your maneuver then release. Every time you need to make an attitude change, hold trimmer release.

There was a big thread about this and posters that actually work with Russian helis and a black hawk pilot say that you hold the trimmer.

Check out his vid - it's clear that the pilot is holding the trimmer down when making extreme maneuvers.

http://www.patricksaviation.com/videos/Force_Feedback/485/

 

People kept telling me not to use the FD and keep the 3 APs on - like real pilots do irl. Holding down the trimmer enables you to fly this way... and I believe it's the correct way of flying.

[Feuerfalke]

I think there are 2 basic problems I found in your descriptions:

 

1. There should be a delay between trimming and the trimming actually being activated. In RL if you push the trim, the stick will stay in place, as far as I understood it.

If you do it in the sim though, it means that the current input will be added to your control-input. Now, while this exactly simulates the RL situation, as while your stick is centered, your last input is still added, giving it a virtual new center.

It is not real for the you trim, though, as your control input is still there, basically doubling your input if you don't understand you need to center your stick immediately.

Depending on the strength of the input, this can crash your blades easily.

 

IIRC the patch will hold a more common way to trim and you also have the option to increase the time until the trim actually hits you. (IIRC it's 0.2 seconds?)

 

2. This is even worse if you don't take physics into account. If you give an input to turn to some position and order the chopper to hold this, it's pretty obvious that won't work. That's like driving your car around a corner and as soon as you are aligned with the other road, "You say hold this input". But what you'd need to say is: "Hold this bearing.", because your wheels are not pointed forward, but still to the side, turning your car!

 

Additionally, the less friction the medium has you are moving on/in, the more you have to take masses and inputs into account. In a car, for example, the first thing that happens when turning is that your chasis will bend and the first result will move your car not to the sides, but rolls it on your suspension. You can see that pretty well in those nice oldfashioned carchases with US cars.

In a boat it's worse and in a plane even more. You basically turn and reposition the aircraft quite some time before you see the aircraft actually doing what you want it to. But it won't simply do what you want, but additionally it will respond to torque and innertias colliding with your inputs.

The result is, that you have to compensate and give excess control input to bring the aircraft into the actual turn. When ending the turn, you have to compensate for that excess input, for the changed flight-characteristics of your plane, the changed center of gravity, the torque and for the mass trying to keep turning.

 

Thus the order to "Hold this input" will result in quite a different effect than your intended "Hold this bearing" even (or especially) with all flight-assistance turned on.

 

Instead of trimming the plane when you reach the desired track, you should rather make the plane going where you want to go and THEN press trim to make it continue that way. The earlier after the maneuver trim however, the more likely you have to repeat trimming to compensate for the helos physics. Remember, even the helos speed change the characteristics dramatically. The flightassistance is usually not able to compensate for that completely, e.g. when going from a hover or slow turn to full cruising speed.

 

 

Well, my 2 cents before bedtime ;)

[LupinYonder]

I just wanted to add to this discussion, I have recently really started to get a feel for unguided rockets and gun pods in the shark and here's how i manage it.

 

I trim roughly for a heading old that overflies the target and might also trim some forward pitch too maintain airspeed. BUT for me trim is the starting point of my controls.

 

When trying to aim the pipper I just fly the aircraft i.e. hold the stick at the required angels and adgust accordingly to aim the pipper. No need to fine trim to hold the pipper on target, that kind of precision triming is very difficult and not nessasary imho.

 

When lining up a target constant adjustments are nessasary I find there is no need to trim these adjustments into the AP channels, just use the stick :-). I hope I am making myself understandable.

 

Also, dont fire till you see the whites of their eyes ;-) some one on these forums said "unguided rockets are like a shotgun" and to a certain exctent that is true.

[LastRifleRound]

points well taken here, but to #4, note that it is not that i don't understand how to manever the aircraft, it is just that the control input required to actually receive airframe response is DIFFERENT depending on whether or not you have FD active or the trim button held down. In other words, the stick position required to hold a certain bank angle is not the same when you have the trim button held down, as the AP is actively maneuvering against your input.

 

This took me a LONG time to understand, as it is not immediately apparent, and isn't explained any where, hence the title of this thread. I have since overcome this issues by holding trim down, which, according to the manual and the sticky on "trimiming" in this very forum are considered to be bad ideas. FOr me, I was simply informing new pilots that the method of holding trim, making sure your helo is ABSOLUTELY stable on the exact attitude you desire, then releasing trim, is the only sensible way i've been able to fly.