AFCS? DAFCS? DASH? LCT? Explained Below

[47_Driver]

Been wanting to cover this for a while to clear some things up. I am 47Driver on YouTube, some of you have been watching my videos on the DCS CH-47F, (I really appreciate that), and everybody wants to know about all these weird acronyms that I mention, along with many others.

First of all I want to point out something in regards to the flight model. I see a ton of complaints about how unrealistic it is, etc. Yes, the FM is very WIP and that is what it is. Tandem Rotor physics are straight up wizardry. This is far and away the most complex flight model that ED has ever tried to replicate, and I can say that confidently as an actual Pilot of this aircraft and someone who understands a fair bit about aerodynamics. Tandem rotor helicopters are very weird, and what I'm seeing in the flight model so far indicates that the devs have done their research on how these helicopters behave when none of the things that are built in to help you fly are working, which is true in the module's current state. Please keep that in mind as you fly this thing.

AFCS: Automated/Advanced Flight Control System. This alone is what makes the Chinook so easy to fly. Put your feet flat on the floor, don't touch the pedals, and fly all day long. Thanks Turn Coordination. She's very smooth, steady, coordinated, and controllable when this system is on. When the AFCS in DCS is fully fleshed out, it's gonna make a huge difference.

DAFCS: Digital Advanced Flight Control System. Super cool autopilot(ish) functionality. Basically allows us to capture current Inertial Altitude or Radar Altitude, maintain low speed over the ground via TRC or Translational Rate Command, or capture current position over the ground via P-Hold. P-Hold + Altitude mode = perfect hands off hovering. We also have a full 4 axis autopilot via Flight Director for cruise/instrument flight.

DASH: Differential Air Speed Hold. As you increase speed, the DASH, (a long tube in the flight controls with an actuator on each end) will decrease in length. You'll notice eventually when this is modeled that as you increase speed, you'll actually start moving cyclic backwards towards center and the aircraft will keep the speed. Pretty nice and allows us to fly with a more neutral cyclic position.

LCT: Longitudinal Cyclic Trim (Actuators). As speed increases, the LCTs will extend, this will increase forward tilt in both the fwd and aft heads. Allows a more level fuselage at cruise and reduces stress on rotor system. You'll be flying at 140kts and the fuselage will be completely level with the horizon. No more staring at the ground 10deg nose low anymore. When you land, the LCTs drive to the GND position, allowing easier ground taxi. When you hover, they drive to the RET position to facilitate a level hover attitude.

DCP: Differential Collective Pitch. This is mostly why the Thrust Lever is called the Thrust Lever and not a collective. DCP comes from longitudinal cyclic input. Forward cyclic increases collective pitch on the aft rotor system while decreasing collective pitch on the fwd, and vice versa. So basically, the cyclic is also a collective...

Hope this clears some things up and helps you folks understand why the flight model feels so weird right now. With most of these things not being implemented yet, because I'd imagine they're all very hard to simulate, the Chinook is gonna fly a little weird. I'm still having a great time with the module and I'm very excited for more systems depth to be added, so I can continue to share with you guys.

Thanks!

47Driver

Edited November 1 by 47_Driver
typo

[dahui]

Thanks for the Explanation

Question to the LCT:

Will it Tilt the whole Gearbox or just the swashplate (as in all other Helos)?

[47_Driver]

1 hour ago, dahui said:

Thanks for the Explanation

Question to the LCT:

Will it Tilt the whole Gearbox or just the swashplate (as in all other Helos)?

Just the swashplate. Gearboxes have some fwd tilt built in as well. 9deg in the fwd and 4deg in the aft.

[Rabies]

Excellent, thanks mate, love the yotube channel too. 

[Slippa]

Cheers for explaining these things. Good to get input from a pilot as always. Enjoying the vids etc. too, keep it up. 

[[DE] T-Bone]

Thank you very much for this great explanation! 

[DD_Friar]

@Brickle Many thanks for your time and effort you have put into your videos. I am subscriber and have found them very informative and well done.

I would urge anyone who is learning or wants to learn this bird check out his channel. 

Salute Sir and thanks again.

regards

DD_Friar

[Crash *]

vor 5 Stunden schrieb Brickle:

I'm still having a great time with the module and I'm very excited for more systems depth to be added, so I can continue to share with you guys.

 

Thank you for your comments and efforts.

I'm looking forward to seeing more of it. I really like what I've seen so far.

[Zentaos]

Great work! Keep the info coming!

[Watari]

Thank you very much. 

Great content. I hope they update that her soon. Love the heli as i loved the mi8 but sitting in that big VR and running down noe with 300kmh is just amazing.

 

 

[shagrat]

Thanks for investing your time into the community.

It's so incredibly helpful to get these infos first hand and "unfiltered" and have someone for questions, that come up.

[Fumes 1-3]

Thank you for the explanation, great to learn new stuff

Am 15.8.2024 um 08:05 schrieb Brickle:

DASH: Digital Air Speed Hold. As you increase speed, the DASH, (a long tube in the flight controls with an actuator on each end) will increase in length. You'll notice eventually when this is modeled that as you increase speed, you'll actually start moving cyclic backwards towards center and the aircraft will keep the speed. Pretty nice and allows us to fly with a more neutral cyclic position.

LCT: Longitudinal Cyclic Trim (Actuators). As speed increases, the LCTs will extend, this will increase forward tilt in both the fwd and aft heads. Allows a more level fuselage at cruise and reduces stress on rotor system. You'll be flying at 140kts and the fuselage will be completely level with the horizon. No more staring at the ground 10deg nose low anymore. When you land, the LCTs drive to the GND position, allowing easier ground taxi. When you hover, they drive to the RET position to facilitate a level hover attitude.

Q to DASH: Can I imagine this as a PP-tube with a worm gear/screw thread drive?

Q to LCT: So you are able to adjust the airframes horizontal plane in flight manually, correct?!

[Tjim62]

LCTs drive the swash plate so the aircraft maintains a mostly level attitude in fwd flight.  When doing HAAR, we put the LCTs in manual to ensure the tip path is a far away from the basket/hose as possible.  

DASH Yea thats a good wat to look at it.  It’s a link with 2 motors top and bottom.  If I recall correctly top is no 1 system and bottom is no 2 system. 

Edited August 24 by Tjim62
Correct swash plate spelling

[nachomaga]

Thanks for explanation, very comprehensive. And thanks too for the videos! Is nice to see tutorials from a pilot who flies the real thing.

Edited August 25 by nachomaga

[trev5150]

Lawler, Michael & Ivler, Christina & Tischler, Mark & Shtessel, Yuri. (2006). System Identification of the Longitudinal/Heave Dynamics for a Tandem-Rotor Helicopter Including Higher-Order Dynamics. 10.2514/6.2006-6147.

https://www.researchgate.net/figure/CH-47F-Chinook-DAFCS-test-aircraft_fig1_255575073

[Cobrajet]

Thank you for sharing your knowledge withs this amazing helicopter. It is very much appreciated. I also get excited with each new YouTube video that you post.

 

 

 

[Focha]

Amazing engineered flying machine!
 

I wonder... did the first CH-47 version had already those controls and augmentation systems?

Also, the Frog, CH-46, had similar systems? 

Thank you for the explanation.

[47_Driver]

On 8/27/2024 at 4:31 AM, Focha said:

Amazing engineered flying machine!
 

I wonder... did the first CH-47 version had already those controls and augmentation systems?

Also, the Frog, CH-46, had similar systems? 

Thank you for the explanation.

47 has always had at least a basic SAS or Stability Augmentation System. Just too difficult to fly without it. The 46 would have had to have had very similar systems, yes. All tandem rotors will, as these systems overcome the inherent lack of stability of a tandem rotor design.

[attackbee]

This is some great insight. Thank you for sharing! Like most EA modules I'm biding my time before getting too into flying it.

[dresoccer4]

great read. really helpful insight into what's making the wizardry happen behind the scenes.

do we know, which of the 5 augmentation modules listed above are currently in the EA release?

[Fuerte]

On 8/15/2024 at 9:05 AM, 47_Driver said:

DASH: Digital Air Speed Hold. As you increase speed, the DASH, (a long tube in the flight controls with an actuator on each end) will increase in length. You'll notice eventually when this is modeled that as you increase speed, you'll actually start moving cyclic backwards towards center and the aircraft will keep the speed. Pretty nice and allows us to fly with a more neutral cyclic position.

A question regarding the statement "you'll actually start moving cyclic backwards towards the center and the aircraft will keep the speed...".

Why would you want to move it backwards as you have reached desired airspeed? Instead of just keeping cyclic around new position, corresponding to that desired airspeed. Is it in order to keep heli from further pitch down attitude progression or further IAS gain?

Im missing the understanding of difference between DASH working in two scenarios:

• when you reach desired IAS and want to keep it
• when you want to change your airspeed through further longitudinal cyclic corrections 

If its possible to explain it to an enthusiast person with no aeronautical education - it would be very great.

Thank you for your time.

Edited October 31 by Fuerte

[DD_Friar]

Update on how the new controls work

 

[BIGNEWY]

Thank you for all the feedback @47_Driver we have the reported the inverted actions of the LTC AFT and FWD switches. 

 

[47_Driver]

10 hours ago, Fuerte said:

A question regarding the statement "you'll actually start moving cyclic backwards towards the center and the aircraft will keep the speed...".

Why would you want to move it backwards as you have reached desired airspeed? Instead of just keeping cyclic around new position, corresponding to that desired airspeed. Is it in order to keep heli from further pitch down attitude progression or further IAS gain?

Im missing the understanding of difference between DASH working in two scenarios:

• when you reach desired IAS and want to keep it
• when you want to change your airspeed through further longitudinal cyclic corrections 

If its possible to explain it to an enthusiast person with no aeronautical education - it would be very great.

Thank you for your time.

 

Because essentially the DASH programs to basically replace your FWD or AFT stick position. DASH authority is equivalent to around 2" of fwd cyclic and around 4" of aft cyclic. So as the DASH programs to maintain speed, not as much fwd cyclic as required to maintain that speed. 

[adrift_foolish1]

20 hours ago, Fuerte said:

Why would you want to move it backwards as you have reached desired airspeed? Instead of just keeping cyclic around new position, corresponding to that desired airspeed. Is it in order to keep heli from further pitch down attitude progression or further IAS gain?

Im missing the understanding of difference between DASH working in two scenarios:

• when you reach desired IAS and want to keep it
• when you want to change your airspeed through further longitudinal cyclic corrections 

If its possible to explain it to an enthusiast person with no aeronautical education - it would be very great.

Thank you for your time.

 

Just wanted to make an attempt to clear up a few things.

1. The Dash Acronym is Differential Airspeed Hold.

2. With a functioning DASH, airspeed is mostly a function of longitudinal stick position. The aircraft is rigged to fly at a steady 100 knots when the stick is at 1" forward. There is no forward/aft balancing act required to hold airspeed. Increasing forward stick always results in increasing forward airspeed, also known as positive stick gradient.

3. WITHOUT the dash, one of the things lost is that positive stick gradient. Now when you've accelerated to your desired airspeed, you have to move the cyclic aft to some position to maintain that airspeed, generally farther aft than the hovering stick position.

4. DAFCS is an entire system replacement for the older, analog AFCS. AFCS was not installed on any F model.

Edited November 1 by adrift_foolish1