#4424220 - 06/02/18 07:40 PM
Re: EECH Test build - Hover Mods
[Re: XIII]
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Joined: Jan 2001
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Marc
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Awesome! X2 Marc..
HP-Compaq-8100-Elite-SFF-Intel-Core-i5-660-3-33GHz-8GB-250GB-Windows7, GTX1050 -X45+Rudder Pedals, Playseat Challenge
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#4424262 - 06/03/18 12:15 AM
Re: EECH Test build - Hover Mods
[Re: Javelin]
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Joined: Apr 2018
Posts: 300
Javelin
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Idaho Falls, Idaho USA
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I was interested in how the actual helicopters implement advanced control functions like these and found a paper detailing the testing done on the Comanche control system for the prototypes. I found that they implement Hover-Hold, Altitude-Hold, and one more, Velocity-Stabilization.
Hover-Hold was limited to horizontal and axial motion, no vertical control was implemented because it was intended to be used in conjunction with Altitude-Hold. Our Hover-Hold does all three axes.
The Comanche Altitude-Hold has two modes, below 300 ft it uses the radar altitude like ours currently does, above 300 ft it uses the barometric altitude. I might add the barometric part into ours. The professional system also doesn't concern itself with station keeping, heading keeping, or speed control, all it does is maintain altitude. The professional system also uses a manual control lever, which is used to perform the Bob-Up maneuver as described in the Enemy Engaged manual. We now have an automated version of that. You can also use the incremental hover height adjustments (Alt-J and Alt-K) similar to the lever control described in the paper.
Velocity-Stabilization from what I can tell was only for forward speeds, lateral control was not considered. I've implemented a form of Velocity-Stabilization when you select Altitude-Hold in our control system already. It attempts to keep your speed up to about 50 knots on the low end, and below about 110 knots on the high end. You can be anywhere in that range and it doesn't interfere, and you can over-ride it by simply moving the control stick. The paper didn't go into enough detail on how it functions, so I don't have any more changes in mind at this point. It's mostly for use as a long-distance cruise control, which isn't really too much of an issue with our sim anyway.
I suppose we could separate out each control function like they've done in the professional system, but I don't really see the advantage of that. I really like the controls the way they function now.
I just thought you guys might like knowing that our sim is on par now with the actual flight control systems of the more advanced helicopters.
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#4424409 - 06/03/18 10:34 PM
Re: EECH Test build - Hover Mods
[Re: Javelin]
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Joined: Apr 2018
Posts: 300
Javelin
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Idaho Falls, Idaho USA
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Thanks XIII ! It really does change the nature of the sim, doesn't it. Flying the helos is such a pleasure now.
Cohokum_Test7.exe is up on the server. Two major changes.
1. I altered Altitude-Hold to add the Barometric Altitude mode the real Comanche has. When you engage it over 200 meters (660 ft) your helo flys level at altitude, until you fly at a mountain. When your Radar Altitude drops to less than 100 meters (about 300 ft) it shifts into ground following mode so you don't hit the mountain. It's pretty seamless in operation. All of the Russian helicopters do just fine on this mode also.
In testing it I ran into an annoying problem, though. Why does the Comanche Altimeter quit at 500 ft? That's just stupid, someone should fix that. The Apache at least goes up to 1500 ft.
2. I fixed the nose-down problem with the AH-1's, so now the Viper, SeaCobra, and SuperCobra will fly correctly on Altitude-Hold. Before, over 100 knots the darn things would nose down and hit the ground. I don't really know why, but I fixed it anyway.
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#4424459 - 06/04/18 10:42 AM
Re: EECH Test build - Hover Mods
[Re: Javelin]
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Joined: Dec 2010
Posts: 1,883
messyhead
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Thanks XIII ! It really does change the nature of the sim, doesn't it. Flying the helos is such a pleasure now.
Cohokum_Test7.exe is up on the server. Two major changes.
1. I altered Altitude-Hold to add the Barometric Altitude mode the real Comanche has. When you engage it over 200 meters (660 ft) your helo flys level at altitude, until you fly at a mountain. When your Radar Altitude drops to less than 100 meters (about 300 ft) it shifts into ground following mode so you don't hit the mountain. It's pretty seamless in operation. All of the Russian helicopters do just fine on this mode also.
In testing it I ran into an annoying problem, though. Why does the Comanche Altimeter quit at 500 ft? That's just stupid, someone should fix that. The Apache at least goes up to 1500 ft.
2. I fixed the nose-down problem with the AH-1's, so now the Viper, SeaCobra, and SuperCobra will fly correctly on Altitude-Hold. Before, over 100 knots the darn things would nose down and hit the ground. I don't really know why, but I fixed it anyway. Brilliant work! As for the Comanche quitting at 500ft, I think I remember seeing somewhere that the radar alt stopped at 500ft, so that was how the gauge was built. I remember seeing something like that for my blackhawk project, but I've not looked at the code for quite a while now I can't really remember (makes mental note to pick up the blackhawk project again)
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#4424516 - 06/04/18 03:05 PM
Re: EECH Test build - Hover Mods
[Re: Javelin]
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Joined: Apr 2018
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Javelin
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In the research paper I found on the Comanche controls, it said the altimeter switches over to Barometric Altitude at about that height. It wasn't supposed to stop dead. It would be reasonable though, to simply extend it up to 1500 ft (or more) like the Apache. The Russian Helo altimeters switch over at 300 meters. https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19940008849.pdfOn page 424 it says the altimeter switches between radar altitude and barometric altitude at 300 ft. The HMD shown in the paper is also reversed to the EECH HMD, the altitude is on the left vs. the right on page 425. It could have changed when they built the prototypes, though. I also just read a description of the Ka-50 Blackshark control modes. It's just as capable as the Comanche, but far more complicated to operate than ours.
Last edited by Javelin; 06/04/18 04:18 PM.
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#4424535 - 06/04/18 04:36 PM
Re: EECH Test build - Hover Mods
[Re: Javelin]
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Joined: Apr 2018
Posts: 300
Javelin
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Idaho Falls, Idaho USA
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The Advanced Flight Model 2 isn't bad, there are only a couple of items that are not physics based. FM2 uses an artificial vertical restorative force rather than off-setting the center of gravity of the helo to use the weight to correctly bring it back to vertical. There is also an artificial heading restorative force which they used instead of modeling the rear vertical stabilizers. Everything else is correctly physics modeled, especially the main rotor. The body drag force should also be moved slightly if I move the center of gravity and the weight force. Other than that, it's actually a pretty good model.
The "G" key Auto-Pilot is another issue altogether, it's not physics based at all. It moves you around without any basis in physics. I'll look at that next, maybe in a few weeks when I get back from the next work trip. Enemy aircraft are probably controlled the same way, but you don't notice it as much since you aren't in the cockpit.
Thinking about it, there are two other forces/behaviors that could be added in. When you hover the helo will drift sideways because of the tail rotor side force. You need a little cyclic angle to counter it. In most helos the manufacturer off-sets the weight distribution to remove this tendency. There is also a gyroscopic force that could be modeled. Let me see if I can get this right... While you are in the act of turning to the right in a helo with a counter-clockwise main rotor, the nose will pitch slightly down during the turn. Turn left and it pitches up. That might be backwards, I'd have to get out my dynamics text to check. These behaviors are hardly noticable, so it isn't that big of a deal if they aren't in the sim. I can go through the code and put in the weight restorative force and the rear stabilizers and remove the artificial ones if you guys want me to. It's pretty close to accurate now, though.
Last edited by Javelin; 06/04/18 04:49 PM.
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#4425199 - 06/08/18 03:11 PM
Re: EECH Test build - Hover Mods
[Re: Javelin]
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Joined: Dec 2010
Posts: 1,883
messyhead
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I tried this out today in the Apache only, and it's great. The helo feels much more realistic in manoeuvring.
I was trying out the hover hold and pop-up. I hit the ground a few times, so I'll try and recreate it and see what happens.
Also, when I engage Hover or Stable-hover, it drops me to 20m and hovers there. Even if I was much higher when I engaged it. Again, I'll try it again and see if it happens every time.
Another thing I noticed. When I first engaged Pop up, it went up 20m. But then after I'd used alt-j/k to adjust my height, it went up a lot more.
It also dropped me into the ground when I switched pop-up off.
I think what I did was...
Engage pop-up, adjust height down using alt-J dis-engage pop-up - dropped to the ground.
I didn't have time to properly watch everything I was doing, so I'll try it step by step. I'll try it another time and let you know.
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#4425220 - 06/08/18 05:09 PM
Re: EECH Test build - Hover Mods
[Re: Javelin]
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Joined: Dec 2010
Posts: 1,883
messyhead
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Hi Messyhead, Stable-Hover sets the Hover height and maintains that height. Alt-J and Alt-K adjust the Hover height down/up respectively. Watch your altitude gauge as you press the keys, it jogs up or down 10 ft or 5 meters depending upon whether you are blue or red.
Pop-Up works Up and Down from the Hover height. Pop-Up toggles Up 20m on the first keypress, then Down 20m on the second keypress.
Does that clear up the functions?
Is blue feet, and red metres? In the Apache, it was going up and down by around 70 marks (whether that's feet or metres). But that was after I'd already used the height adjustment. I'll try it again, and keep track of what I'm doing. i was just playing around quickly with it. p.s. I'm a software tester, and the fact I think I've spotted an issue and not properly recreated it is bothering me. I'll do it justice next time I'm on
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Exodus
by RedOneAlpha. 04/18/24 05:46 PM
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