Re: [Jsbsim-devel] Helicopter

[Bill G. <bil...@gm...>]

Simon, et.al. 

 

A little education, specially about the Sikorsky H60 line. Other helicopters are similar. Maybe some of this is known, maybe not.

 

The control system is fully irreversible. The cyclic and collective just over hydraulic valves which move actuators. The trim system provides a centering force when displaced from a set position through some centering springs. Without it, the cyclic and collective just move about willy-nilly (that’s a technical term). For our discussion, let’s assume that in a hover, the cyclic is centered, at 50% fore/aft throw, and at 100 knots, the cyclic has to move forward 10%, to about 40% throw (0% forward, 100% aft). So, Joe Pilot is in a hover. He will probably move the cyclic forward to 30-35% to get the aircraft accelerating forward (which drops the nose, and a bit of altitude can be lost). When Joe reaches 100 knots, he moved the stick a position where the aircraft neither accelerators or decelerates, about 40%. Now, when he establishes a new trim position, he can do this one of two ways: 

 

1.     Move the stick against the force springs, momentary press and release the trim release button. This establishes the new trim position where the stick is at when the trim release button is release. The force is instantly removed, and will remain where it is placed.

2.     Press the trim release button, and move the stick without the centering force. Once the desired position is reached, release the trim release button, and the new trim position is established when the button is release.

 

Now, let’s take this system onto the PC, with a conventional spring-centering joystick (centers at 50%). Hover, not a problem. Accelerate to 100 knots, you’ll have to hold a constant forward joystick. You might be able to implement a ‘trim position’ when you press a button on the joystick, and then move the joystick back to center within one second. When you pressed that button, it records the ‘trim’ position as 10%, and adds that to the stick position, maybe feeding it in over a second, or maybe it feeds it in as the stick is centered, regardless of how long it takes.

 

In your case, since you are using a mouse for a cyclic, that’s not really a problem.

 

I might suggest using a non-linear scaling on the stick, such as a squared-function. That makes the stick less touchy.

 

Good luck. Keep us informed how it is going. Hope everyone else enjoyed the read.

 

Bill

 

 

 

 

 

From: Simon Julie Morley via Jsbsim-devel [mailto:jsb...@li...] 
Sent: Sunday, October 25, 2020 2:37 PM
To: Development issues <Jsb...@li...>
Cc: Simon Julie Morley <sim...@go...>
Subject: Re: [Jsbsim-devel] Helicopter

 

Hi Bill,

 

Thanks for taking.

 

I'm currently using a mouse with a saitek throttle and so haven't ran into this issue.

 

I'll have to give it some thought to how to create a trim cyclic for joystick users, if the workload is considered onerous over a long flight.

 

I chose to use a turbine and prop combination, which I'm really happy with.

 

I'm happy with the flight characteristics after adapting it to have a stabilizing rotation around the lift point.

 

 

Regards

 

Simon.

 

 

 

On Sun, 25 Oct 2020, 18:08 Bill Galbraith, <bil...@gm... <mailto:bil...@gm...> > wrote:

Simon,

 

I had devoted some brain cells towards that idea a while ago, but never implemented it.

 

Imagine a point mass, with a point vertical force located above it. At 50% collective, vertical force equals weight. Cyclic tilts that vertical force fore/aft, left/right. Displacing the cyclic yields a slight loss (sine of angle) loss of lift, requiring slightly more collective.

 

The painful part comes when you try to fly it with a joystick. When you release the joystick, the cyclic returns back to neutral, the aircraft will slow to a hover. You basically need a joystick that has a trim lever, or allows you to reestablish the trim point.

 

Enough to get your brain cells excited?

 

Bill

 

From: Simon Julie Morley via Jsbsim-devel [mailto:jsb...@li... <mailto:jsb...@li...> ] 
Sent: Sunday, October 25, 2020 1:41 PM
To: Development issues <Jsb...@li... <mailto:Jsb...@li...> >
Cc: Simon Julie Morley <sim...@go... <mailto:sim...@go...> >
Subject: [Jsbsim-devel] Helicopter

 

Anyone here ever done one ?

 

Want to talk about it, share knowledge ?

 

Simon

 

 

 

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